DARSHAN INSTITUTE OF ENGG. & TECH. Transfe… · DARSHAN INSTITUTE OF ENGG. & TECH. ... Heat Transfer through Composite Wall ... Fig. 1.1 Line Diagram of Composite Wall Apparatus

DARSHAN INSTITUTE OF ENGG. & TECH.

Department of Mechanical Engineering

B.E. Semester – V

Heat Transfer (2151909)

List of Experiments

Sr.

No. Title

Date of

Performance

Date of

submission Sign Remark

1. Heat Transfer through Composite

Wall

2. Heat Transfer through Lagged Pipe

3. Heat Transfer from a Pin Fin under

Free Convection

4. Heat Transfer from a Pin Fin under

Forced Convection

5. Heat Transfer in Forced Convection

6. Stefan Boltzmann Apparatus

7. Emissivity Measurement Apparatus

8. Parallel Flow/Counter Flow Heat

Exchanger

9. Drop Wise & Film Wise

Condensation Apparatus

10. Thermal Conductivity of Insulating

Slab

COMPOSITE WALL



Darshan Institute of Engineering and Technology, Rajkot

1-1

1. HEAT TRANSFER THROUGH COMPOSITE WALL

1. Objective:

Study of conduction heat transfer in composite wall

2. Aim:

To determine total thermal resistance and thermal conductivity of composite wall

To calculate thermal conductivity of one material in composite wall

3. Nomenclature:

A = Area of heat transfer, m2

d = Diameter, m

I = Ammeter reading, amp

Keff = Thermal conductivity of composite wall, W/m oC

k1 = Thermal conductivity of cast iron, W/m oC

k2 = Thermal conductivity of Bakelite, W/m oC

k3 = Thermal conductivity of Press wood, W/m oC

Q = Amount of heat transfer, W

q = Heat flux, W/m2

Rth = Total thermal resistance of composite wall, oC m

2/W

∆T = Overall temperature difference, oC

T1 & T2 = Interface temperature of cast Iron and heater, oC

T3 & T4 = Interface temperature of cast Iron and bakelite, oC

T5 & T6 = Interface temperature of bakelite and press wood, oC

T7 & T8 = Top surface temperature of press wood, oC

V = Voltmeter reading, volts

W = Heat supplied by the heater, W

∆X = Total thickness of wall, m

X1 = Cast Iron thickness, m

X2 = Bakelite thickness, m

X3 = Press wood thickness, m

COMPOSITE WALL




1-2

4. Introduction:

When a temperature gradient exists in a body, there is an energy transfer from the

high temperature region to the low temperature region. Energy is transferred by

conduction and heat transfer rate per unit area is proportional to the normal

temperature gradient:

X

T

A

q

When the proportionality constant is inserted,

X

TkAq

Where q is the heat transfer rate and ΔT/ ΔX is the temperature gradient in the

direction of heat flow. The positive constant k is called thermal conductivity of the

material.

5. Block Diagram:

Fig. 1.1 Line Diagram of Composite Wall Apparatus

COMPOSITE WALL




1-3

Fig. 1.2 Composite Wall Apparatus

6. Theory:

A direct application of Fourier’s law is the plane wall. Fourier’s equation:

12 TTX

kAq

Where the thermal conductivity is considered constant. The wall thickness is X, and

T1 and T2 are surface temperatures. If more than one material is present, as in the

multiplayer wall, the analysis would proceed as follows:

The temperature gradients in the three materials (A, B, C), the heat flow may be

written

C

C

C

B

BB

A

AA

X

TAk

X

TAk

X

TAkq

7. Description:

The Apparatus consists of a heater sandwiched between two asbestos sheets. Three

slabs of different material are provided on both sides of heater, which forms a

composite structure. A small press- frame is provided to ensure the perfect contact

between the slabs. A Variac is provided for varying the input to the heater and

measurement of input power is carried out by a Digital Voltmeter & Digital Ammeter.

Temperatures Sensors are embedded between inter faces of the slab, to read the

temperature at the surface. The experiment can be conducted at various values of

power input and calculations can be made accordingly.

COMPOSITE WALL




1-4

8. Utilities Required:

1. Electricity Supply: Single Phase, 220 VAC, 50 Hz, 5-15Amp socket with earth

connection.

2. Bench Area Required: 1m x 1m.

9. Experimental Procedure:

Starting Procedure:

1. Ensure that Mains ON/OFF switch given on the panel is at OFF position &

dimmer stat is at zero position.

2. Connect electric supply to the set up.

3. Switch ON the Mains ON / OFF switch.

4. Set the heater input by the dimmer stat, voltmeter in the range 40 to 100 V.

5. After 1.5 hrs. note down the reading of voltmeter, ampere meter and temperature

sensors in the observation table after every 10 minutes interval till observing

change in consecutive readings of temperatures (± 0.2 oC).

Closing Procedure:

1. After experiment is over set the dimmer stat to zero position.

2. Switch OFF the Mains ON/OFF switch.

3. Switch OFF electric supply to the set up.

10. Observation & Calculations:

10.1 Data:

d = 0.25 m

X1 = 0.02 m

X2 = 0.015m

X3 = 0.012 m

k1 = 52 W /m oC

k2 = 1.4 W /m oC

k3 = 0.12 W /m oC

COMPOSITE WALL




1-5

10.2 Observation Table:

Sr.No. V

volts

I

amp

T1

oC

T2

oC

T3

oC

T4

oC

T5

oC

T6

oC

T7

oC

T8

oC

10.3 Calculations:

2

WQ , W = ----------- W

IVW , W = ----------- W

A

Qq , W/m

2 = -----------

W/m

2

2

4dA

, m

2 = ----------- m

2

2

)()( 8271 TTTTT

,

oC = -----------

oC

q

TRth

,

oC m

2/W = -----------

oC m

2/W

321 XXXX , m = ----------- m

X

TKq eff

T

XqKeff

, W/m

oC

= --------------- W/m oC

3

3

2

2

1

1

k

X

k

X

k

X

T

R

Tq

th

2

2

1

1

3

3

k

X

k

X

q

T

Xk , W/m

oC

= --------------- W/m oC

COMPOSITE WALL




1-6

11. Precautions & Maintenance Instructions:

1. Never run the apparatus if power supply is less than 180 volts and above than

230volts.

2. Never switch on mains power supply before ensuring that all the ON/OFF

switches given on the panel are at OFF position.

3. Operator selector switch OFF temperature indicator gently.

4. Always keep the apparatus free from dust.

12. Troubleshooting:

1. If electric panel is not showing the input on the mains light, check the main

supply.

2. If voltmeter showing the voltage given to heater but ampere meter does not, check

the connection of heater in control panel.

13. Conclusion:

14. References:

1. Holman, J.P., “Heat Transfer”, 9th

ed., McGraw Hill, ND, 2008, Page 23-24

2. Kern, D.Q., “Process Heat Transfer”, 16th

ed., McGraw Hill, ND, 2007, Page

14-15

THERMAL CONDUCTIVITY OF MATERIALS

1. A. Domkundwar, “A Course in Heat & Mass Transfer”, S.C Arora & S

Domkundwar, NY, 2003, Page A.4 – A.5.

LAGGED PIPE




2- 1

2. HEAT TRANSFER THROUGH LAGGED PIPE

1. Objective:

To study the heat transfer through the insulating medium

2. Aim:

To estimate the actual rate of heat transfer through the composite cylinders from the

measured interface temperature of the two insulating materials with known thermal

conductivities.

To determine the effective thermal conductivity of the composite cylinders

To compare the theoretical temperature profile within the composite cylinders, with that

of observed profile

3. Nomenclature:

A = Heat transfer area, m2

keff = Effective thermal conductivity of lagged pipe, W/m oC

k1 = Thermal conductivity of Asbestos, W/m oC

k2 = Thermal conductivity of Sawdust, W/m oC

L = Length of the pipe, m

Q = Heat input, W

R1 = Radius of the inner most pipe, m

R2 = Radius of the middle pipe, m

R3 = Radius of the outer most pipe, m

Ti = Inside temperature of the pipe, oC

To = Outside temperature of the pipe, oC

Tm = Mean temperature of the pipe, oC

T1,T2 = Surface temperature of the inner most pipe, oC

T3,T4 = Surface temperature of the middle pipe, oC

T5,T6 = Surface temperature of the outermost pipe, oC

T = Temperature profile, oC

LAGGED PIPE




2-2

4. Bock Diagram:

Fig. 2.1 Line Diagram of Lagged Pipe Apparatus

Fig. 2.2 Lagged Pipe Apparatus

5. Introduction:

When a temperature gradient exists in a body, there is an energy transfer from the high

temperature region to the low temperature region. Energy is transferred by conduction

and heat transfer rate per unit area is proportional to the normal temperature gradient:

X

T

A

q


X

TkAq

Where q is the heat transfer rate and ΔT/ ΔX is the temperature gradient in the direction

of heat flow. The positive constant k is called thermal conductivity of the material.

6. Theory:

Consider a long composite cylinder of inside radius ri, outside radius ro and length L. We

expose this cylinder to a temperature differential Ti - To and see what the heat flow will

LAGGED PIPE




2- 3

be. For a cylinder with length very large compared to diameter, it may be assumed that

the heat flow in a radial direction, so that the only space coordinate needed to specify the

system is „r‟. In cylindrical system the Fourier‟s law is written.

dr

dTkAq r

rLAr 2

dr

dTkrLq 2

With the boundary conditions

T = Ti at r = ri

T = To at r = ro

The solution to equation is

io

oi

rr

TTLkq

ln

2

And the isothermal resistance in this case is

Lk

rrR io

th

2

ln

The thermal resistance concept may be used for multiple – layer cylindrical walls just as

it was used for plane walls. For the two-layer system the solution is

BA

oi

krrkrr

TTLq

2312 lnln

2

7. Description:

The apparatus consist of three concentric pipe mounted on suitable stands. The inside

pipe consists of the heater. Between first two cylinders the insulating material with which

lagging is to be done is asbestos and in second and third pipe is wooden dust.

Temperature Sensors are attached to the surface of cylinders appropriately to measure the

temperatures. The input to the heater is varied through a dimmer stat and measured by

Digital Voltmeter and Digital ammeter.

LAGGED PIPE




2-4


1. Electricity Supply: Single Phase, 220 VAC, 50Hz, 5-15Amp socket with earth

connection.

2. Bench Area Required: 1.5 m x 1m


9.1 Starting Procedure:






5. After 1.5 hrs note down the reading of voltmeter, ampere meter and temperature



9.2 Closing Procedure:


2. Switch OFF the Main ON/OFF switch.


10. Observations & Calculations:

10.1 Data:

R1 = 0.025 m

R2 = 0.05 m

R3 = 0.075 m

L = 1 m

k1 = 0.26 W/m oC

k2 = 0.069 W/m oC

LAGGED PIPE




2- 5

10.2 Observation table:

Sr.

No

V,

volts I, amp T1,

oC T2,

oC T3,

oC T4,

oC T5,

oC T6,

oC

10.3 Calculations:

IVQ , W = ------------------- W

2

21 TTTi

,

oC = ------------------------

oC

2

43 TTTm

,

oC = ---------------------

oC

2

65 TTTo

,

oC = -----------------------

oC

)(2

)/ln( 13

oi

effTTL

RRQk

, W/m

oC = -------------------- W/m

oC

At any radius R, Temperature is given by,

eff

ikL

RRQTT

2

)/ln( 1,oC = ------------------------

oC


1. Never run the apparatus if power supply is less than 180volts and above than

230volts.

2. Never switch on mains power supply before ensuring that all the ON/OFF switches

given on the panel are at OFF position.

3. Operate selector switch off temperature indicator gently.



1. If electric panel is not showing the input on the mains light, check the main supply.

LAGGED PIPE




2-6



13. Conclusion:

14. References:


ed., McGraw Hill, NY, 2008, Page 25-27.

2. McCabe, Smith, J.C., Harriott, P., “Unit Operations of Chemical Engineering”, 7th

ed. McGraw Hill, NY, 2005, Page 306-307.

Thermal Conductivity of Materials

1. A. Domkundwar, “A Course in Heat & Mass Transfer”, S.C Arora & S.

Domkundwar, NY, 2003, Page A.4 – A.5.

PIN FIN UNDER FREE CONVECTION




3-1

3. HEAT TRANSFER FROM A PIN FIN UNDER FREE

CONVECTION

1. Objective:

To study the heat transfer in a pin fin under free convection.

2. Aim:

To calculate the heat transfer coefficient experimentally & theoretically for free

convection.

Compare the theoretical temperature distribution with experimentally obtained

distribution.

3. Nomenclature:

Nom Column Heading Units Type

A Cross sectional area of fin m2 Calculated

AS Surface heat transfer area m2 Calculated

C Perimeter m Calculated

D Fin diameter m Given

g Acceleration due to gravity m/sec2 Given

Gr Grashoff’s number * Calculated

H Parameter m Calculated

hEx Experimental heat transfer coefficient W/m2 oC Calculated

hTh Theoretical heat transfer coefficient W/m2 oC Calculated

k Thermal conductivity of air at temperature Tmf W/m oC Calculated

kf Thermal conductivity of fin material W/m oC Given

L Fin length m Given

m Fin parameter m Calculated

Nu Nusselt number * Calculated

Pr Prandtl number * Calculated

Q Amount of heat transfer W Calculated

T1- T5 Temperatures of the pin fin test section surface oC Measured





3-2

T6- T7 Temperature at center of pin fin at Xo distance oC Measured

T8 Temperature of the suction duct surface oC Measured

Tb Fin base temperature oC Calculated

TEx Experimental temperature within the fin oC Calculated

TEx1 Experimental temperature at the first sensor oC Calculated

TEx2 Experimental temperature at the second sensor oC Calculated

TEx3 Experimental temperature at the third sensor oC Calculated

TEx4 Experimental temperature at the fourth sensor oC Calculated

TEx5 Experimental temperature at the fifth sensor oC Calculated

Tf Fin temperature at any point oC Calculated

Tm Fin mean temperature oC Calculated

Tmf Fluid mean temp oC Calculated

TTh Theoretical temperature within the fin oC Calculated

TTh1 Theoretical temperature at the first sensor oC Calculated

TTh2 Theoretical temperature at the second sensor oC Calculated

TTh3 Theoretical temperature at the third sensor oC Calculated

TTh4 Theoretical temperature at the fourth sensor oC Calculated

TTh5 Theoretical temperature at the fifth sensor oC Calculated

V1 Velocity of air at temperature Tmf m/sec Calculated

X Distance of the sensors from one end of the fin m Given

X1

Distance of first temperature sensors (T1) from the one

end point m Given

X2 Distance of second temperature sensors (T2) from the one

end point m Given

X3 Distance of third temperature sensors (T3) from the one

end point m Given

X4 Distance of fourth temperature sensors (T4) from the one

end point m Given

X5 Distance of fifth temperature sensors (T5) from the one

end point m Given

Xo Distance between temperature sensors (T6) and

temperature sensors (T7) m Given

a Density of air kg/m3 Given

a1 Density of air at temperature (Tmf) kg/m3 Calculated





3-3

Coefficient of thermal expansion of fluid K-1 Calculated

Fin effectiveness * Calculated

Dynamic viscosity of air kg/m-sec Calculated

Kinematic viscosity of air m2/sec Calculated

ΔT Temperature difference on fin surface oC Calculated

ΔT1 Temperature difference on fin surface K Calculated

* Symbols represent unit less quantity

4. Bock Diagram:

Fig. 3.1 Line Diagram of Pin Fin Apparatus

5. Introduction:

Extended surfaces or fins are used to increase the heat transfer rate from a surface to a

fluid wherever it is not possible to increase the value of the surface heat transfer

coefficient or the temperature difference between the surface and the fluid. The use of this

is very common and they are fabricated in a variety of shapes circumferential fins around

the cylinder of a motorcycle engine and fins attached to condenser tubes of a refrigerator

are few familiar examples.





3-4

6. Theory:

Natural convection phenomenon is due to the temperature difference between the surface

and the fluid and is not created by any external agency. The experimental heat transfer

coefficient is given for both the free and forced convection by,

TA

Qh

S

aEx

Theoretical heat transfer coefficient for free and forced convection, can be calculated by

following formulae:

D

kNh

u

Th

Where hEx, hTh are experimental and theoretical heat transfer coefficient respectively.

Qa is amount of heat transfer, SA is heat transfer area and T is temperature

difference. Nu is nusselt no., k is thermal conductivity and D is diameter.

It is obvious that a fin surface stick out from primary heat transfer surface. The

temperature difference with surrounding fluid will steadily diminish as one moves out

along the fin. The design of the fins therefore requires knowledge of the temperature

distribution in the fin. The main object of this experimental set up is to study the

temperature distribution in a simple pin fin.

Fin parameter

Ak

hCm

b

Fin effectiveness

mL

mLtanh

The temperature profile within a pin fin is given by:

mLHmL

xLmHxLm

TT

TT

Fb

f

o sinhcosh

)(sinh)(cosh

Where Tf is the free stream temperature of air; Tb is the temperature of fin at its base;

T is the temperature within the fin at any x; L is the length of the fin and D is the fin

diameter, m is the fin parameter, o

is temperature distribution profile.





3-5

7. Description:

It consists of pin type fin fitted in a duct. A heater is provided to heats one end of fin and

heat flows to another end. Heat input to the heater is given through variac. Digital

voltmeter and digital ammeter are provided for heat measurement. Digital temperature

indicator measures temperature distribution along the fin.



connection.



9.1 STARTING PROCEDURE:

1. Ensure that mains ON/OFF switch given on the panel is at OFF position &



3. Switch ON the mains ON / OFF switch.

4. Set the heater input by the dimmer stat, voltmeter in the range 40 to 100V.


sensors at every 10 minutes interval (till observing change in consecutive readings

of temperatures ± 0.2 oC).

9.2 CLOSING PROCEDURE:

1. When experiment is over set the dimmer stat to zero position.

2. Switch OFF the mains ON/OFF switch.



10.1 DATA:

Thermal conductivity of fin material kf = 204.2 W/moC

Density of air a = 1.15 kg/m3





3-6

Acceleration due to gravity g = 9.81 m/sec2

Diameter of fin D = 0.020 m

Length of fin L = 0.145 m

Distance of first temperature sensors (T1) from the one end point X1 = 0.045 m

Distance of second temperature sensors (T2) from the one end point X2 = 0.07m

Distance of third temperature sensors (T3) from the one end point X3 = 0.095 m

Distance of fourth temperature sensors (T4) from the one end point X4 = 0.12 m

Distance of fifth temperature sensors (T5) from the one end point X5 = 0.145 m

Distance between temperature sensors (T6) and temperature sensors (T7) Xo = 0.0140m

10.2 OBSERVATION TABLE:

Sr.No. T1 (oC) T2 (

oC) T3 (

oC) T4 (

oC) T5 (

oC) T6 (

oC) T7 (

oC) T8 (

oC)

10.3 CALCULATIONS:

Free Convection: Experimentally

5

54321 TTTTTTm

(

oC)

8TT f (oC)

fm TTT (oC)

2

4DA

(m

2)

o

f

X

TTAkQ

)( 76 (W)

LDAS (m2)

TA

Qh

S

Ex

(W/m2 oC)





3-7

Free Convection: Theoretically

5

54321 TTTTTTm

(

oC)

8TT f (oC)

15.27315.2731 fm TTT (K)

2

)15.273()15.273( fm

mf

TTT (K)

Find the properties of air ( , k , , Pr) at temperature mfT from data book.

)(K 1 1-

mfT

_____k (W/moC)

_____ (m2 /sec)

_____rP

2

1

3

TDgGr

4/1)(53.0 rru PGN

D

kNh

u

Th (W/m2 oC)

DC (m)

2

4DA

(m

2)

Ak

Chm

f

Th (m)

mL

mLtanh

mk

hH

f

Th (m)

1TTb (oC)





3-8

ffbTh TTTmLHmL

XLmHXLmT

sinhcosh

)(sinh)(cosh 111 (

oC) (X = X1)

ffbTh TTTmLHmL

XLmHXLmT

sinhcosh

)(sinh)(cosh 222 (

oC) (X = X2)

ffbTh TTTmLHmL

XLmHXLmT

sinhcosh

)(sinh)(cosh 333 (

oC) (X = X3)

ffbTh TTTmLHmL

XLmHXLmT

sinhcosh

)(sinh)(cosh 444 (

oC) (X = X4)

ffbTh TTTmLHmL

XLmHXLmT

sinhcosh

)(sinh)(cosh 555 (

oC) (X = X5)

11 TTEx (oC)

22 TTEx (oC)

33 TTEx (oC)

44 TTEx (oC)

55 TTEx (oC)

CALCULATION TABLE:

S.No. X (m) TTh (oC) TEx (

oC)


1. Never run the apparatus if power supply is less than 200 volts and more than 230

volts.








3-9






13. Conclusion:

14. References:


ed., McGraw Hill, ND, 2008, Page 39-46.

2. D.S Kumar, “Heat & Mass Transfer”, 7th

ed, S.K Kataria & Sons, ND, 2008, Page

233-239, 253-256, 260-262.

PIN FIN UNDER FORCED CONVECTION




4-1

4. HEAT TRANSFER FROM A PIN FIN UNDER FORCED

CONVECTION

1. Objective:

To study the heat transfer in a pin fin under forced convection.

2. Aim:

To calculate the heat transfer coefficient experimentally & theoretically for forced

convection.

Compare the theoretical temperature distribution with experimentally obtained

distribution.

3. Nomenclature:

Nom Column Heading Units Type

A Cross sectional area of fin m2 Calculated

AS Surface heat transfer area m2 Calculated

C Perimeter m Calculated

D Fin diameter m Given

g Acceleration due to gravity m/sec2 Given

Re Reynolds number * Calculated

H Parameter m Calculated

hEx Experimental heat transfer coefficient W/m2 oC Calculated

hTh Theoretical heat transfer coefficient W/m2 oC Calculated

k Thermal conductivity of air at temperature Tmf W/m oC Calculated

kf Thermal conductivity of fin material W/m oC Given

L Fin length m Given

m Fin parameter m Calculated

Nu Nusselt number * Calculated

Pr Prandtl number * Calculated

Q Amount of heat transfer W Calculated

T1- T5 Temperatures of the pin fin test section surface oC Measured





4-2

T6- T7 Temperature at center of pin fin at Xo distance oC Measured

T8 Temperature of the suction duct surface oC Measured

Tb Fin base temperature oC Calculated

TEx Experimental temperature within the fin oC Calculated

TEx1 Experimental temperature at the first sensor oC Calculated

TEx2 Experimental temperature at the second sensor oC Calculated

TEx3 Experimental temperature at the third sensor oC Calculated

TEx4 Experimental temperature at the fourth sensor oC Calculated

TEx5 Experimental temperature at the fifth sensor oC Calculated

Tf Fin temperature at any point oC Calculated

Tm Fin mean temperature oC Calculated

Tmf Fluid mean temp oC Calculated

TTh Theoretical temperature within the fin oC Calculated

TTh1 Theoretical temperature at the first sensor oC Calculated

TTh2 Theoretical temperature at the second sensor oC Calculated

TTh3 Theoretical temperature at the third sensor oC Calculated

TTh4 Theoretical temperature at the fourth sensor oC Calculated

TTh5 Theoretical temperature at the fifth sensor oC Calculated

Vo Velocity of air m/sec Calculated

V1 Velocity of air at temperature Tmf m/sec Calculated

X Distance of the sensors from one end of the fin m Given

X1

Distance of first temperature sensors (T1) from the one

end point m Given

X2 Distance of second temperature sensors (T2) from the one

end point m Given

X3 Distance of third temperature sensors (T3) from the one

end point m Given

X4 Distance of fourth temperature sensors (T4) from the one

end point m Given

X5 Distance of fifth temperature sensors (T5) from the one

end point m Given

Xo Distance between temperature sensors (T6) and

temperature sensors (T7) m Given

a Density of air kg/m3 Given





4-3

a1 Density of air at temperature (Tmf) kg/m3 Calculated

Fin effectiveness * Calculated

Dynamic viscosity of air kg/m-sec Calculated

Kinematic viscosity of air m2/sec Calculated

ΔT Temperature difference on fin surface oC Calculated

ΔT1 Temperature difference on fin surface K Calculated

* Symbols represent unit less quantity

4. Bock Diagram:

Fig. 4.1 Line Diagram of Pin Fin Apparatus

5. Introduction:

Extended surfaces or fins are used to increase the heat transfer rate from a surface to a

fluid wherever it is not possible to increase the value of the surface heat transfer

coefficient or the temperature difference between the surface and the fluid. The use of this

is very common and they are fabricated in a variety of shapes circumferential fins around

the cylinder of a motorcycle engine and fins attached to condenser tubes of a refrigerator

are few familiar examples.





4-4

6. Theory:

Forced convection phenomenon is due to the temperature difference between the surface and

the fluid and is created by any external agency, such as blower, pump etc. The experimental

heat transfer coefficient is given for both the free and forced convection by,

TA

Qh

S

aEx

Theoretical heat transfer coefficient for free and forced convection, can be calculated by

following formulae:

D

kNh

u

Th

Where hEx, hTh are experimental and theoretical heat transfer coefficient respectively.

Qa is amount of heat transfer, SA is heat transfer area and T is temperature

difference. Nu is nusselt no., k is thermal conductivity and D is diameter.

It is obvious that a fin surface stick out from primary heat transfer surface. The

temperature difference with surrounding fluid will steadily diminish as one moves out

along the fin. The design of the fins therefore requires knowledge of the temperature

distribution in the fin. The main object of this experimental set up is to study the

temperature distribution in a simple pin fin.

Fin parameter

Ak

hCm

b

Fin effectiveness

mL

mLtanh

The temperature profile within a pin fin is given by:

mLHmL

xLmHxLm

TT

TT

Fb

f

o sinhcosh

)(sinh)(cosh

Where Tf is the free stream temperature of air; Tb is the temperature of fin at its base;

T is the temperature within the fin at any x; L is the length of the fin and D is the fin

diameter, m is the fin parameter, o

is temperature distribution profile.





4-5

7. Description:

It consists of pin type fin fitted in a duct. A blower is provided on one side of duct. Air flow

rates can be varied by given flow control valve. A heater is provided to heats one end of fin

and heat flows to another end. Heat input to the heater is given through variac. Digital

voltmeter and digital ammeter are provided for heat measurement. Digital temperature

indicator measures temperature distribution along the fin. Airflow is measured with the help

of velocity meter.



connection.



9.1 STARTING PROCEDURE:

1. Ensure that mains ON/OFF switch given on the panel is at OFF position &



3. Switch ON the mains ON / OFF switch.

4. Set the heater input by the dimmer stat, voltmeter in the range 40 to 100V.

5. Switch ON the blower.

6. Set the flow of air by operating the valve V1.

7. After 0.5 hrs. note down the reading of voltmeter, ampere meter, velocity sensor

and temperature sensors at every 10 minutes interval (till observing change in

consecutive readings of temperatures ± 0.2 oC).

9.2 CLOSING PROCEDURE:

1. When experiment is over set the dimmer stat to zero position.

2. Switch OFF the blower.

3. Switch OFF the mains ON/OFF switch.







4-6


10.1 DATA:

Thermal conductivity of fin material kf = 204.2 W/moC

Density of air a = 1.15 kg/m3

Acceleration due to gravity g = 9.81 m/sec2

Diameter of fin D = 0.020 m

Length of fin L = 0.145 m

Distance of first temperature sensors (T1) from the one end point X1 = 0.045 m

Distance of second temperature sensors (T2) from the one end point X2 = 0.07m

Distance of third temperature sensors (T3) from the one end point X3 = 0.095 m

Distance of fourth temperature sensors (T4) from the one end point X4 = 0.12 m

Distance of fifth temperature sensors (T5) from the one end point X5 = 0.145 m

Distance between temperature sensors (T6) and temperature sensors (T7) Xo = 0.0140m

10.2 OBSERVATION TABLE:

Sr. No. T1 (oC) T2 (

oC) T3(

oC) T4(

oC) T5(

oC) T6(

oC) T7(

oC) T8(

oC) Vo m/sec

10.3 CALCULATIONS:

Forced Convection: Experimentally

5

54321 TTTTTTm

(oC)

8TT f (oC)

fm TTT (oC)

2

4DA

(m2)

o

f

X

TTAkQ

)( 76 (W)





4-7

LDAS (m2)

TA

Qh

S

Ex

(W/m2 oC)

Forced Convection: Theoretically

5

54321 TTTTTTm

(oC)

8TT f (oC)

2

)15.273()15.273( fm

mf

TTT (K)

Find the properties of air ( 1a , k, ) at temperature mfT from data book.

_____k (W/moC)

_____ (kg/m-sec)

_____1 a (kg/m3)

15.2731

f

mfo

T

TVV (m/sec)

11 ae

DVR

466.0)(615.0 eu RN

D

kNh u

Th (W/m2 oC)

2

4DA

(m2)

DC (m)

Ak

Chm

f

Th (m)

mL

mLtanh

mk

hH

f

Th (m)





4-8

1TTb

ffbTh TTTmLHmL

XLmHXLmT

sinhcosh

)(sinh)(cosh 111 (oC) (X = X1)

ffbTh TTTmLHmL

XLmHXLmT

sinhcosh


ffbTh TTTmLHmL

XLmHXLmT

sinhcosh


ffbTh TTTmLHmL

XLmHXLmT

sinhcosh


ffbTh TTTmLHmL

XLmHXLmT

sinhcosh


11 TTEx (oC)

22 TTEx (oC)

33 TTEx (oC)

44 TTEx (oC)

55 TTEx (oC)

CALCULATION TABLE:

S.No. X (m) TTh (oC) TEx (

oC)


1. Never run the apparatus if power supply is less than 200 volts and more than 230

volts.





4-9

2. Never switch on mains power supply before ensuring that all the ON/OFF switches








13. Conclusion:

14. References:



2. D.S Kumar, “Heat & Mass Transfer”, 7th

ed, S.K Kataria & Sons, ND, 2008, Page

233-239, 253-256, 260-262.

FORCED CONVECTION




5- 1

5. HEAT TRANSFER IN FORCED CONVECTION

1. Objective:

Study of convection heat transfer in forced convection.

2. Aim:

Comparison of heat transfer coefficient for different air flow rates and heat flow rates.

To find surface heat transfer coefficient for a pipe losing heat by forced convection.

3. Nomenclature:

A = Heat transfer area, m2

Cp = Specific heat of air, kJ/kg oC

Co = Coefficient of discharge

Di = Inner diameter of test section, m

Do = Outer diameter of test section, m

dp = Diameter of pipe, m

do = Diameter of orifice, m

∆H = Head loss, m of air

I = Ammeter reading, amp

L = Length of test section, m

m = Mass flow rate of air, kg/s

Qa = Heat taken by air, W

Q = Flow rate of air, m3/s

h1,h2 = Manometer readings, cm

T1 = Air inlet temperature, oC

T2,T3,T4,T5 = Surface temperature of test section, oC

T6 = Air outlet temperature, oC

Ts = Average surface temp, oC

Ta = Average temperature of air, oC

Tmf = Mean film temperature, o

C

U = Heat transfer coefficient, Watt/m²C

V = Voltmeter reading, volts

FORCED CONVECTION




5-2

w = Density of water, kg/m3

a = Density of air, kg/m3

4. Introduction:

Convection is defined as process of heat transfer by combined action of heat

conduction and mixing motion. Convection heat transfer is further classified as

Natural Convection and Forced Convection. If the mixing motion takes place due to

density difference caused by temperature gradient, then Natural or Free Convection

knows the process of heat transfer as heat transfer. If the mixing motion is induced by

Forced Convection knows some external means such as a pump or blower then the

process as heat transfer.

5. Block Diagram:

Fig. 5.1 Line Diagram of Forced Convection Apparatus

FORCED CONVECTION




5- 3

Fig. 5.2 Forced Convection Apparatus

6. Theory:

Air flowing into the heated pipe with very high flow rate the heat transfer rate

increases. The temperature taken by the cold air from the bulk temperature and rises

its temperature. Thus, for the tube the total energy added can be expressed in terms of

a bulk-temperature difference by

)( 12

.

bbP TTCmq

Bulk temperature difference in terms of heat transfer coefficient

12 bb TThAq

7. Description:

The apparatus consists of blower unit fitted with the test pipe. The test section is

surrounding by nichrome heater. Four Temperature Sensors are embedded on the test

section and two temperature sensors are placed in the air stream at the entrance and

exit of the test section. Test Pipe is connected to the delivery side of the blower along

with the Orifice. Input to the heater is given through a dimmerstat and measured by

volt meter & Ampere meter. Digital temperature indicator is provided to measure

temperature. Airflow is measured with the help of Orifice meter and the water

manometer fitted on the board.

FORCED CONVECTION




5-4



connection.

2. Floor Area Required: 1.5 m x 0.5 m






3. Fill water in manometer up to half of the scale, by opening PU pipe connection

from the air flow pipe and connect the pipe back to its position after doing so.



6. Switch ON the blower and Set the flow of air by operating the valve.

7. After 0.5 hrs. note down the reading of voltmeter, ampere meter, manometer and

temperature sensors in the observation table after every 10 minutes interval till

observing change in consecutive readings of temperatures (± 0.2 oC).



2. Switch OFF the blower.



10. Observation:

10.1 Data:

Di = 0.028 m

Do = 0.038 m

L = 0.4 m

do = 0.014 m

dp = 0.028 m

w = 1000 kg/m3

Co = 0.64

FORCED CONVECTION




5- 5


Sr.

No.

V

volts

I

amp

T1

oC

T2

oC

T3

oC

T4

oC

T5

oC

T6

oC

h1

cm

h2

cm

11. Calculations:

4

5432 TTTTTs

,

oC =

oC

2

61 TTTa

,

oC =

oC

2

as

mf

TTT

,

oC =

oC

Cp = ___________ J/kg-K (Take value from data book at Tmf )

a = ___________ kg/m3 (Take value from data book at Tmf )

LDA i , m2 = m

2

1

100

21

a

whhH

, m = m

22

2

op

opo

aa

HgaaCQ

, m

3/s = m

3/s

aQm , kg/s = kg/s

)( 16 TTCmQ Pa , W = W

)( as

a

TTA

QU

, W/m

2 C = W/m

2 C

12. Result Table

Sr. No. m, kg/s , Watt U, W/m2 C

FORCED CONVECTION




5-6


1. Never run the apparatus if power supply is less than 180 volts and above than 230

volts.

2. Never switch ON mains power supply before ensuring that all the ON/OFF


3. Operate selector switch of temperature indicator gently.




supply.

2. Voltmeter showing the voltage given to heater but ampere meter does not, check


15. Conclusions

16. References:

1. McCabe, W.L., Smith, J.C., Harriott, P., “Unit Operations of Chemical

Engineering”, 7th

ed., McGraw Hill, NY, 2005, Page 296.

2. Y.A.Cengel, “Heat & Mass Transfer”, McGraw Hill, ND, 2008, Page 25-26.

STEFAN BOLTZMANN




6-1

6. STEFAN BOLTZMANN APPARATUS

1. Objective:

Study of Radiation heat transfer by black body and study the effect of hemisphere

temperature on it.

2. Aim:

To find out the Stefan Boltzmann constant

3. Nomenclature:

AD = Area of disc, m2

D = Diameter of disc, m

m = Mass of disc, kg

s = Specific heat of the disc material, kJ/kg oC

T = Temperature of disc at time t, K

T1 = Temperature of enclosure, oC

T2 = Temperature of disc at time t, oC

T2i = Initial temperature of the disc, oC

TE = Temperature of enclosure, K

TD = Initial temperature of the disc, K

t = Time, sec

σ = Stefan Boltzmann constant, Watt/m2

K4

4. Introduction:

All substances at all temperature emit thermal radiation. Thermal radiation is an

electromagnetic wave and does not require any material medium for propagation. All

bodies can emit radiation and have also the capacity to absorb all of a part of the

radiation coming from the surrounding towards it.

STEFAN BOLTZMANN




6-2

5. Block Diagram:

Fig. 6.1 Line Diagram of Stefan Boltzmann Apparatus – Front and Top View

Fig. 6.2 Stefan Boltzmann Apparatus

STEFAN BOLTZMANN




6-3

6. Theory:

The most commonly used law of thermal radiation is the Stefan Boltzmann law which

states that thermal radiation heat flux or emissive power of a black surface is

proportional to the fourth power of absolute temperature of the surface and is given by

4TEA

Qb W/m

2 K

4

The constant of proportionally is called the Stefan Boltzmann constant and has the

value of 5.67 X 10-8

W/m² K4

. The Stefan Boltzmann law can be derived by

integrating the Planck’s law over the entire spectrum of wavelength from 0 to ∞. The

objective of this experimental set up is to measure the value of this constant fairly

closely, by an easy arrangement.

7. Description:

The apparatus consists of a hemisphere fixed to a Bakelite Plate, the outer surface of

which forms the jacket to heat it. Hot water to heat the hemisphere is obtained form a

hot water tank, which is fixed above the hemisphere. The copper test disc is

introduced at the center of hemisphere. The temperatures of hemispheres and test disc

are measured with the help of temperature sensors.



Connection.

2. Water supply: Initial fill.

3. Drain Required.

4. Bench Area Required: 1m x 1m.


Starting Procedure:

1. Close all the valves.

2. Fill heater tank 3/4th

with water by removing the lid of the tank and put the lid

back to its position after doing so.

3. Ensure that switches given on the panel are at OFF position.


STEFAN BOLTZMANN




6-4


6. Set the desired water temperature in the DTC by operating the increment or

decrement and set button of DTC.

7. Switch ON the heater and wait till desired temperature achieves.

8. Remove the disc from the bottom of test chamber by removing the support

provided to hold it.

9. Switch OFF the heater.

10. Fill test chamber with hot water of heater tank by opening the valve provided at

top of the chamber, till observing the overflow of water through chamber outlet

and then close the valve.

11. Note the reading of water temperature (T1) and initial temperature of the disc

(T2i).

12. Insert the disc to the bottom of the chamber and note the reading of temperature

T2 after 5-10 sec interval.

Closing Procedure:

1. After experiment is over switch OFF the Mains ON/OFF switch.


3. Drain the water from chamber and heater tank by the drain valve provided.

10. Observation & Calculation:

10.1 Data:

D = 0.02 m

m = 0.0051 kg

s = 383 J/kg-K

10.2 Observation:

T1 = ----------- oC

T2i = ----------- oC

t, sec T2, ºC t, sec T2, ºC t, sec T2, ºC

0 20 40

5 25 45

10 30 50

15 35 55

STEFAN BOLTZMANN




6-5

10.3 Calculations:

2

4DAD

, m

2 = -------------------- m

2

15.2731TTE K = -------------------- K

15.2732 iD TT K = -------------------- K

t, sec 15.2732TT K t, sec 15.2732TT K

0 30

5 35

10 40

15 45

20 50

25 55

Plot the graph of T vs t and obtain the slop dT/dt.

Emissive power of Black body is given by,

44

DEDb TTAE

Energy stored in the copper plate (black body) = dtdTsm

According to first law of thermodynamics,

Energy transferred by radiation = energy stored in the black body

44

DED TTA

dtdTsm

W/m

2 K

4

= ------------------------- W/m

2 K

4



230 volts.



3. Operator selector switch off temperature indicator gently.

STEFAN BOLTZMANN




6-6




supply.

13. Conclusion

14. References:


ed., McGraw Hill, ND, 2008, Page 372.

2. Y.A.Cengel, “Heat & Mass Transfer”, McGraw Hill, ND, 2008, Page 28, 667-

671.

EMISSIVITY MEASUREMENT




7-1

7. EMISSIVITY MEASUREMENT APPARATUS

1. Objective:

Study of Radiation heat transfer by black plate and test plate

2. Aim:

To find out the emissivity of test plate

3. Nomenclature:

A = Heat transfer area of disc, m2

εs = Emissivity of test plate

εb = Emissivity of black plate

IB = Ammeter reading of black plate, amp

IS = Ammeter reading of test plate, amp

QB = Heat input to black plate, W

QS = Heat input to test plate, W

DS = Diameter of test body, m

DB = Diameter of black body, m

T1 = Surface temperature of black plate, oC.

T2 = Surface temperature of test plate, oC.

T3 = Ambient temperature of enclosure, oC.

TS = Surface temperature of Discs, K

TD = Ambient temperature of enclosure, K

VB = Voltmeter reading of black plate, volts

VS = Voltmeter reading of test plate, volts

= Stefan Boltzmann Constant, W/m2

K

4. Introduction:

All substances at all temperature emit thermal radiation. Thermal radiation is an

electromagnetic wave and does not require any material medium for propagation. All

bodies can emit radiation and have also the capacity to absorb all of a part of the

radiation coming from the surrounding towards it.





7-2

5. Block Diagram:

Fig. 7.1 Line Diagram of Emissivity Measurement Apparatus

Fig. 7.2 Emissivity Measurement Apparatus

6. Theory:

An idealized black surface is one, which absorbs all the incident radiation with

reflectivity and transmissivity equal to zero. The radiant energy per unit time per unit

area from the surface of the body is called as the emissive power and is usually

denoted by E. The emissivity of the surface is the ratio of the emissive power of the

surface to the emissive power of a black surface at the same temperature. It is denoted

by ε.





7-3

BE

E

For black body absorptivity = 1 and by the knowledge of Kirchoff's Law of

emissivity of the black body becomes unity. Emissivity being a property of the

surface depends on the nature of the surface and temperature. The present

experimental set up is designed and fabricated to measure the property of emissivity

of the test plate surface at various temperatures.

7. Description:

The experimental set up consists of two plates; the test plate comprises of a mica

heater sandwiched between two circular plates. Black plate is identical with test plate,

but its surface is blackened. As all the physical properties, dimension and temperature

are equal; heat losses from both plates will be same except radiation loss. Hence the

input difference will be due to difference in emissivity. Both plates are supported on

individual brackets in a wooden enclosure with one side glass to ensure steady

atmospheric conditions. Temperature Sensors are provided to measure the

temperature of each plate and surrounding. Supply is given to heaters through

separate variacs so that temperatures of both can be kept equal and is measured with

Digital Voltmeter and Digital Ammeter.



connection.

2. Bench Area Required: 1m x 1m


Starting Procedure:





4. Set the test plate heater input by the dimmer stat, voltmeter in the range 40 to

100V.





7-4

5. Set black plate heater input by dimmer state, voltmeter, 2 V above than test plate

heater.

6. After 0.5 hrs. observe the difference in surface temperature of black plate (T1)

and test plate (T2) and adjust the heater input of black plate to make both the

sensor reading same.

7. Wait for 5 minutes every time after changing the black plate heater input and then

again change the input if required.

8. At same surface temperature note down the reading of voltmeter, ampere meter

and temperature sensors in the observation table.

Closing Procedure:





10.1 Data:

DS = 0.16 m

DB = 0.16 m

σ = 5.67 x 10-8

W/m2 K

εb = 1


Black Plate:

Sr.No.

VB

volts

IB

amp

T1

oC





7-5

Test plate:

Sr.No. VS

volts

IS

amp

T2

oC

T3

oC

10.3 Calculations: (At T1=T2)

BBB IVQ , W = ----------------W

SSS IVQ , W = --------------- W

2

4SDA

, m

2 = --------------- m

2

15.2731 TTS K

15.2733 TTD K

Emissive power of black plate,

)(44

DSbB TTAE

Emissive power of test plate,

)(44

DSsS TTAE

But,

Difference in radiation heat transfer = Difference in input electric energy

SbSB EEQQ

)()(4444

DSsDSbSB TTATTAQQ

)(44

DS

SBbs

TTA

QQ

= --------------------



230volts.





7-6







supply.



13. Conclusion:

14. References:



2. Y.A.Cengel, “Heat & Mass Transfer”, McGraw Hill, ND, 2008, Page 27-29.

TUBE IN TUBE HEAT EXCHANGER




8-1

8. PARALLEL FLOW/COUNTER FLOW HEAT EXCHANGER

1. Objective:

To study the heat transfer phenomena in Parallel / Counter flow arrangements

2. Aim:

To calculate rate of heat transfer, LMTD and overall heat transfer coefficient for both

type of heat exchanger

To compare the performance of Parallel and Counter flow heat exchanger

3. Nomenclature:

Ai = Inside heat transfer area, m2

Ao = Outside heat transfer area, m2

Cph = Specific heat of hot fluid at mean temperature, kJ/kg oC

Cpc = Specific heat of cold fluid at mean temperature, kJ/kg oC

Do = Outer diameter of tube, m

Di = Inner diameter of tube, m

Fh = Flow rate of hot water, LPH

Fc = Flow rate of cold water, LPH

L = Length of tube, m

Mh = Mass flow rate of the hot water, kg/s

Mc = Mass flow rate of the cold water, kg/s

Q = Average heat transfer from the system, W

Qc = Heat gained by the cold water, W

Qh = Heat loss by the hot water, W

Th = Mean temperature of hot water, oC

Tc = Mean temperature of cold water, oC

T1 = Inlet temperature of the hot water, oC

T2 = Outlet temperature of the hot water, oC

T3 = Inlet temperature of the cold water, oC

T4 = Outlet temperature of the cold water for parallel flow, oC

T5 = Outlet temperature of the cold water for counter flow, oC





8-2

ΔTm= Log mean temperature difference, oC

Ui = Inside overall heat transfer coefficient, W/ m2 o

C

Uo = Outside overall heat transfer coefficient, W/ m2 o

C

c = Density of cold water at mean temp, kg/m3

h = Density of hot water at mean temp, kg/m3

4. Blok Diagram:

Fig. 8.1 Line Diagram of Parallel/Counter Flow Heat Exchanger Apparatus





8-3

Fig. 8.2 Parallel/Counter Flow Heat Exchanger Apparatus

5. Introduction

Heat Exchanger is a device in which heat is transferred from one fluid to another. The

necessity for doing this arises in a multitude of industrial applications. Common examples

of heat exchangers are the radiator of a car, the condenser at the back of a domestic

refrigerator and the steam boiler of a thermal power plant.

Heat Exchangers are classified in three categories:

1) Transfer Type 2) Storage Type & 3) Direct Contact Type.

6. Theory:

A transfer type of heat exchanger is one on which both fluids pass simultaneously through

the device and heat is transferred through separating walls. In practice most of the heat

exchangers used are transfer type ones.

The transfer type exchangers are further classified according to flow arrangement as -

1. Parallel flow in which fluids flow in the same direction.

2. Counter flow in which they flow in opposite direction and

3. Cross flow in which they flow at right angles to each other.

A simple example of transfer type of heat exchanger in the form of a tube type

arrangement in which one of the fluids is flowing through the inner tube and the other





8-4

through the annulus surroundings it. The heat transfer takes place across the walls of the

inner tube.

7. Description:

The apparatus consists of a tube in tube type concentric tube heat exchanger. The hot

fluid is hot water which is obtained from an insulated water bath using a magnetic drive

pump and it flow through the inner tube while the cold fluid is cold water flowing through

the annuals. The hot water flows always in one direction and the flow rate of which is

controlled by means of a valve. The cold water can be admitted at one of the end enabling

the heat exchanger to run as a parallel flow apparatus or a counter flow apparatus. This is

done by valve operations. For flow measurement Rotameters are provided at inlet of cold

water and outlet of hot water line. A magnetic drive pump is used to circulate the hot

water from a recycled type water tank, which is fitted with heaters and Digital

Temperature Controller.



connection.

2. Water Supply: Continuous @ 5 LPM at 1 Bar.

3. Drain Required.

4. Bench Area Required: 1.75 m x 0.5 m



1. Close all the valves provided on the set up.

2. Open the lid of hot water tank, fill the tank with water and put the lid back to its

position.

3. Ensure that switches given on the panel are at OFF position.


5. Set the desired water temperature in the DTC by operating the increment or

decrement and set button of DTC.

6. Open by pass valve and Switch ON the pump.

7. Switch ON the heater and wait till desired temperature achieves.





8-5

8. Connect cooling water supply to the set up.

9. Connect both the outlet (parallel / counter) of cooling water to drain.

10. Open the inlet & outlet valve for cold water as per desired mode (parallel/counter

flow).

11. Allow cold water to flow through heat exchanger and adjust the flow rate by

Rotameter and control valve.

12. Allow hot water to flow through heat exchanger and adjust the flow rate by

Rotameter, control valve and by pass valve.

13. At steady state (constant temperature) record the temperatures & flow rate of hot and

cold water.

14. Repeat the experiment for different flow rate of hot & cold water.

15. Repeat the experiment for different bath temperature.

16. Repeat the experiment for other mode (counter/parallel flow).


1. When experiment is over switch OFF heaters.

2. Switch OFF pump.

3. Switch OFF Power Supply to Panel.

4. Stop cooling water supply.

5. Drain hot water tank by the drain valve provided.


10.1 Data:

Di = 0.0095 m

Do = 0.0127 m

L = 1.6 m


S. No. Mode

Parallel / Counter Fh LPH T1

oC T2

oC Fc

LPH T3

oC T4 / T5

oC

1.

2.





8-6

10.3 Calculations:

Find the properties of water (Cph, ρh) at 2

21 TTTh

and (Cpc, ρc) at

22

5343 TTor

TTTc

(as per mode selected) from data book.

Cph = ----------- J/kg oC

Cpc = ----------- J/kg oC

ρh = ----------- kg/m3

ρc = ----------- kg/m3

10003600

hh

h

FM

, kg/sec = ---------------- kg/sec

21 TTCMQ phhh , W = ---------------- W

10003600

cc

c

FM

, kg/s = ---------------- kg/s

34 TTCMQ pccc , W (for parallel flow) = ---------------- W

35 TTCMQ pccc , W (for counter flow) = ---------------- W

2

QQQ ch , W = ------------------------- W

311 TTT , oC (for parallel flow) = -----------------

oC

511 TTT , oC (for counter flow) = -----------------

oC

422 TTT , oC (for parallel flow) = -----------------

oC

322 TTT , oC (for counter flow) = -----------------

oC

2

1

21

lnT

T

TTTm

,

oC = -------------------

oC

LDA ii , m2 = --------------------- m

2

LDA oo , m2 = --------------------- m

2

mi

iTA

QU

, W/m

2 oC = ------------ W/m

2 oC

mo

oTA

QU

, W/m

2 oC = ------------------- W/m

2 oC





8-7


1. Never run the apparatus if power supply is less than 180volts and above than

230volts.

2. Never switch ON mains power supply before ensuring that all the ON/OFF switches






supply.

13. Conclusion:

14. References:


ed., McGraw Hill, NY, 2008, Page 525-526,

528-531.

2. McCabe, Smith, J.C., Harriott, P., “Unit Operations of Chemical Engineering”,

7th

ed. McGraw Hill, NY, 2005, Page 327-329, 331-333.

Properties Of Water

1. Arora.Domkundwar, “A Course in Heat & Mass Transfer”, 6th

ed., Dhanpat Rai

& CO.(P) LTD.,NY, 2003, Page A.6

DROPWISE & FILMWISE CONDENSATION




9-1

9. DROPWISE & FILMWISE CONDENSATION APPARATUS

1. Objective:

To study of heat transfer in the process of condensation

2. Aim:

To find the overall heat transfer coefficient for Dropwise condensation and Filmwise

condensation process theoretically as well as experimentally

3. Nomenclature:

Ai = Inside heat transfer area, m2

Ao = Outside heat transfer area, m2

Di = Inner dia. of condenser, m

Do = Outer dia. of condenser, m

FW = Flow rate of cooling water, LPH

hi = Inside Heat Transfer Coefficient, W/m2 C

ho = Outside Heat Transfer Coefficient, W/m2 o

C

MS = Rate of steam condensation, Kg/s

MW = Cold Water Flow rate, Kg/s

Nu1 = Nusselt number.

Pr = Prandtl number.

Q = Average heat transfer, W

QS = Heat losses from steam, W

QW = Heat taken by cold water, W

Red = Reynolds number.

TS = Temperature of steam, oC.

TW = Temperature of condenser wall, C.

T1 = Surface Temperature of Plated Condenser,C.

T2 = Surface Temperature of Plain Condenser,C.

T3 = Temperature of steam in column,C.

T4 = Water inlet temperature,C.

T5 = Water outlet temperature,C.





9-2

∆T1 = Temperature difference of steam and surface of condenser, oC

∆T2 = Temperature difference of water circulating through condenser, oC

∆Tm = Log mean temp. difference, oC

t = Time taken to collect V ml of condensed steam, sec

UEX = Experimental overall heat transfer coefficient, W/m2 o

C

UTH = Theoretical overall heat transfer coefficient, W/m2 o

C

V = Volume of condensed steam collected in measuring cylinder, ml.

Cp = Specific heat of water, KJ/kg K

L = Length of condenser, m

W = Density of water, kg/m3

= Kinematic Viscosity, m2 /sec.

k = Thermal conductivity, W/m oC

λ = Latent heat of steam, J/ kg

4. Block Diagram:

Fig. 9.1 Line Diagram of Dropwise & Filmwise Condensation Apparatus – Front View





9-3

Fig. 9.2 Line Diagram of Dropwise & Filmwise Condensation Apparatus – Back View

Fig. 9.3 Filmwise & Dropwise Condensation Apparatus – Front View

5. Introduction:

In all applications, the steam must be condensed as it transfer heat to a cooling

medium, e.g. cold water in the condenser of a generating station, hot water in a

heating calorimeter, sugar refinery, etc. During condensation very high heat fluxes





9-4

are possible & provided the heat can be quickly transferred from the condensing

surface to the cooling medium, heat exchangers using steam can be compact &

effective.

6. Theory:

Steam may condense on to a surface in two distinct modes, known as “Film wise” &

“Drop wise”. For the same temperature difference between the steam & the surface,

drop wise condensation is much more effective than film wise & for this reason the

former is desirable although in practical plants it rarely occurs for prolonged periods.

Filmwise Condensation:

Unless specially treated, most materials are wettable & as condensation occur a film

condensate spreads over the surface. The thickness of the film depends upon a

numbers of factors, e.g. the rate of condensation, the viscosity of the condensate and

whether the surface is vertical or horizontal, etc.

Fresh vapor condenses on to the outside of the film & heat is transferred by

conduction through the film to the metal surface beneath. As the film thickness it

flows downward & drips from the low points leaving the film intact & at an

equilibrium thickness.

The film of liquid is a barrier to the transfer of heat and its resistance accounts for

most of the difference between the effectiveness of film wise and drops wise

condensation.

Dropwise Condensation:

By specially treating the condensing surface the contact angle can be changed and the

surface becomes „non-wettable‟. As the steam condenses, a large number of generally

spherical beads cover the surface. As condensation proceeds, the beads become larger,

coalesce, and then strike downwards over the surface. The moving bead gathers all

the static beads along its downward in its trail. The „bare‟ surface offers very little

resistance to the transfer of heat and very high heat fluxes are therefore possible.

Unfortunately, due to the nature of the material used in the construction of condensing

heat exchangers, film wise condensation is normal.





9-5

7. Description:

The apparatus consists of a vertical frame. Condensation tubes are fitted inside

compact glass cylinder. Steam generator is fitted at the backside of the cylinder.

Steam comes directly from generator to cylinder. Two valves are fitted to control flow

rate of water in individual tubes. Digital Temperature Indicator monitors

temperatures. Pressure gauge and Rotameter can observe steam pressure and cold

water flow rates respectively. A digital Temperature Controller is provided for

controlling the temperature of steam. Water level indicator is provided to safe guard

the heater. Condensate is measured by measuring cylinder.


1. Electricity Supply: Single Phase, 220 VAC, 50 Hz, 5-15 amp socket with earth

connection.


3. Drain Required.



Starting procedure:

1. Ensure that ON/OFF switches given on the panel are at OFF position.

2. Close all the drain valves.

3. Open the funnel valve and air vent valve provided at the top of steam generator.

4. Fill water in the steam generator up to 3/4th

of its capacity by observing the level

of water in the level indicator.

5. Switch ON the main supply.

6. Set the temperature of required steam with the help of DTC (100-120 oC).

7. Switch ON the heater and wait until steam temperature reaches to required value.

8. Ensure that wet steam vent valve and niddle valve provided at front are closed.

9. Allow steam to pass through the pipe and slowly open wet steam vent valve to

release wet steam from the pipe.

10. Close the vent valve.

11. Connect cooling water supply.





9-6

12. Open the valve to allow cooling water to flow through desired condenser (Ensure

that during experiment, water is flowing only through the condenser under test

and second valve is closed).

13. Set the flow rate of cooling water by the Rota meter.

14. Open the niddle valve to allow steam to enter in the test section and start the stop

watch to measure mass of steam condensed.

15. Observe Steam gets condensed on the tubes, and falls down in the glass cylinder

(Depending upon type of condenser under test Dropwise or Filmwise

condensation can be visualized.)

16. After steady state record the temperature, flow rate of cooling water, pressure.

17. Close the niddle valve.

18. Stop the Stopwatch and open the drain valve of the glass chamber to measure the

condensate at particular time.

Closing procedure:

1. After experiment is over switch OFF the heater.

2. Partially open air vent valve at steam generator to release the steam.

3. Stop cooling water supply to the condenser.

4. Switch OFF main supply.


10.1 Data:

Do = 0.019 m

Di = 0.016 m

L = 0.175 m

CP = 4.186 kJ/kg K

W = 1000 kg/m3

= at 40 oC (0.657 m

2 /sec)

= at 100 oC (0.2932 m

2 /sec)

μ = at 100 oC (0.2822 * 10

3 kg/m-s)

= at 35 oC (0.7196 * 10

3 kg m/s)

k = at 40 oC

(0.628 W /m

oC)

= at 100 oC

(0.6775 W /m

oC)

λ = 2257.2 x 103 J/kg





9-7

Pr = 1.75


S.NO. FW, LPH V, ml T, sec T1,

oC

T2,

oC

T3,

oC

T4,

oC

T5,

oC

10.3 Calculation:

SSt

VM

610

60, kg/s = ------------------ kg/s

3103600

WW

W

FM

, kg/s = ------------------ kg/s

SS MQ , W = ------------------ W

)( 45 TTCMQ PWW , W= ------------------ W

2

WS QQQ

, W = -------------------- W

131 TTT , oC (For Plain condenser) = --------------------

oC

231 TTT , oC (For Plated condenser),

oC = --------------------

oC

452 TTT , oC = --------------------

oC

1

2

12

lnT

T

TTTm ,

oC = --------------------

oC

mi

iTA

Qh

, W/m

2 oC = -------------------- W/m

2 oC

mo

oTA

Qh

, W/m

2 oC = -------------------- W/m

2 oC

oo

i

iEX hx

D

D

hU

111, W/m

2 oC = -------------------- W/m

2 oC

11

4

i

wed

D

mR = --------------------

4.08.0

1 PR023.0 reduN = --------------------

L

KNuhi

1 , W/m2 o

C = -------------------- W/m2 o

C





9-8

25.03

2

2

2

)(943.0

LTT

gkh

WS

o

, W/m

2 oC = -------------------- W/m

2 oC

oo

i

iTH hx

D

D

hU

111, W/m

2 oC = -------------------- W/m

2 oC



230volts.






1. If electric panel is not showing the input on the mains light. Check the main

supply.

13. Conclusion:

14. References:


ed., McGraw Hill, ND, 2008, Page 484-489,

491-492.

2. Y.A.Cengel, “Heat & Mass Transfer”, McGraw Hill, ND, 2008, Page 578-583,

591-592.

Properties Of Water

1. A. Domkundwar, “A Course in Heat & Mass Transfer”, S.C Arora & S

Domkundwar,NY, 2003, page A.6.

INSULATING SLAB




10-1

10. THERMAL CONDUCTIVITY OF INSULATING SLAB

1. Objective:

Study of heat transfer through insulating slab

Study of variation of thermal conductivity of the material with temperature

2. Aim:

To find out the thermal conductivity of insulating material in the form of slab.

3. Nomenclature:

A = Area of the specimen, m2

d = Diameter of specimen, m

IC = Central Heater current, amp

IG = Guarded heater current, amp

k = Thermal conductivity of slab, W/m oC

Q = Heat flow rate in the specimen, W

Th = Hot plate temperature, oC

Tc = Cold plate temperature, oC

T1,T2 = Temperature of the upper heater slab, oC

T3,T4 = Temperature of the side guarded heater, oC

T5,T6 = Surface temperature of the cooling plate, oC

Vc = Central Heater voltage, volts

VG = Guarded Heater voltage, volts

x = Thickness of specimen, m

4. Introduction:

When a temperature gradient exists in a body, there is an energy transfer from the

high temperature region to the low temperature region. Energy is transferred by

conduction and heat transfer rate per unit area is proportional to the normal

temperature gradient:

X

T

A

q

INSULATING SLAB




10-2


X

TkAq

Where q is the heat transfer rate and ΔT/ ΔX is the temperature gradient in the

direction of heat flow. The positive constant k is called thermal conductivity of the

material.

5. Block Diagram:

Fig 10.1 Line Diagram of Insulating Slab Apparatus

Fig.10.2 Insulating Slab Apparatus

INSULATING SLAB




10-3

6. Theory:

For the measurement of thermal conductivity (k) what is required is to have a one

dimensional heat flow through the flat specimen, an arrangement for maintaining its

faces at constant temperature and some metering method to measure heat flow

through a known area. To eliminate the distortion caused by edge losses in

unidirectional heat flow, the central plate is surrounded by a guard ring, which is

separately heated. Temperatures are measured by calibrated temperature sensors

either attached to the plates or to the specimens at the hot and cold faces. Two

specimens are used to ensure that all the heat comes out through the specimen only.

Knowing the heat input to the central plate heater, the temperature difference across

the specimen, its thickness & the metering area, one can calculate K of the specimen

by the following formula:

K W/m,2

ch TT

L

A

qK

7. Description:

The apparatus consists of main central heater and ring guard heater, sandwiched

between the specimens. Cooling plates are provided on the either side of the

specimen. Two identical specimens are clamped between heater ensures

unidirectional heat flow through specimen. The whole assembly is kept in chamber

and insulated by ceramic wool insulation around the set-up.



connection.


3. Drain.



Starting Procedure:

1. Connect continuous water supply to the inlet of water chamber.

INSULATING SLAB




10-4

2. Connect outlet of chamber to drain.





6. Set the central heater input by the dimmer stat, voltmeter in the range 40 to 100 V.

7. Set guarded heater input by dimmer state, voltmeter, 5 V above than central

heater.




Closing Procedure:




4. Stop flow of water by closing the valve provided.


10.1 Data:

d = 0.18 m

x = 0.012 m


Sr.

No.

Central Heater Guarded Heater Cooling Plate

VC IC T1 T2 VG IG T3 T4 T5 T6

1.

2.

3.

10.3 Calculations:

CC IVQ , W = --------- W

INSULATING SLAB




10-5

2

4dA

, m

2 = --------- m

2

2

)( 21 TTTh

,

oC = ---------

oC

2

)( 65 TTTc

,

oC = ---------

oC

)(2 ch TTA

xQk

, W/m

oC = --------- W/m

oC


1. Never run the apparatus if power supply is less than 180 volts and above than 230

volts.







supply.

2. Voltmeter showing the voltage given to heater but ampere meter does not, check


13. Conclusion:

14. References:


ed., McGraw Hill, ND, 2008 Page, 34

2. Kern, D.Q., “Process Heat Transfer”, 16th

ed., McGraw Hill, ND, 2007, Page 7

3. Dr. D.S, Kumar, “Heat & Mass Transfer”, 7th

ed., S.K Kataria & Sons, ND,

2007, Page 156-158.

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