UNIVERSITY OF BOLTON RAK ACADEMIC CENTRE ......Page 4 of 13 University of Bolton RAK Academic Centre BEng (Hons) Mechanical Engineering Semester 2 Examination 2017/2018 Thermofluids

OCD045

UNIVERSITY OF BOLTON

RAK ACADEMIC CENTRE

BENG (HONS) MECHANICAL ENGINEERING

SEMESTER TWO EXAMINATION 2017/2018

THERMOFLUIDS & CONTROL SYSTEM

MODULE NO: AME5003

Date: Wednesday 30 May 2018 Time: 2:00 – 4:00 INSTRUCTIONS TO CANDIDATES: There are 6 questions. Answer 4 questions. All questions carry equal marks. Attempt TWO questions from PART A

and TWO questions from PART B Marks for parts of questions are shown

in brackets. CANDIDATES REQUIRE : Take density of water = 1000 kg/m3

Formula sheets provided

Page 2 of 13 University of Bolton RAK Academic Centre BEng (Hons) Mechanical Engineering Semester 2 Examination 2017/2018 Thermofluids & Control System Module No. AME5003

PART A

Q1. a) Derive from Bernoulli’s theorem expressions for the theoretical velocity

and discharge through a venturimeter in a pipe of diameter d1 as shown

in Figure Q1a.

Figure Q1a. Venturimeter

(13 marks)

b) A pitot tube is inserted in a pipe of 300mm diameter. The static

pressure in pipe is 100mm of mercury(vacuum).The stagnation

pressure at the centre of the pipe recorded by the pitot tube is

0.981N/cm2.Determine the rate of flow of water through the pipe if

mean velocity of the flow is 0.85 times the central velocity. Given

Cv=0.98.

(7 marks)

c) An orifice meter with orifice diameter 15cm is inserted in a pipe of 30cm

diameter. Given the pressure difference measured by a mercury-oil

differential manometer on the two sides of the orifice meter as 50cm of

mercury. Find the rate of flow of oil of specific gravity 0.9 when the co-

efficient of discharge of the meter is 0.64.

(5 marks) Total 25 marks

Please turn the page


Q2. a) A pipe line carrying oil of specific gravity 0.87 changes in diameter from

200mm diameter at a position A to 500mm diameter at a position B

which is 4metres at a higher level as shown in Figure Q2a.If the

pressures at A and B are 9.81N/cm2 and 5.886N/cm2 and the discharge

is 200litres/s determine the following:

i. Loss of head (7marks)

ii. Direction of flow (8 marks)

Figure Q2a. Line diagram of the system

b) An air compressor takes in air having an enthalpy of 100kJ/kg.The air is

compressed to a final condition at which the enthalpy is 180kJ/kg.As

the air travels through the compressor, it losses 20kJ/kg of heat(Q) as

shown in FigureQ2b . Using the steady flow equations evaluate the

work of the compressor.

FigureQ2b.Air compressor (10marks)

Total 25 marks



Q3 a) A 300mm diameter pipe carries water under a head of 20metres with a

velocity of 3.5m/s as shown in Figure 3a.Let p1 ,p2 be the inlet and outlet

pressures and v1,v2 be the corresponding velocities of flow at inlet and

outlet . If the axis of the pipe turns through 450, determine the following:

i) Magnitude of the resultant force at the bend (6 marks)

ii) Direction of the resultant force at the bend. (7 marks)

Figure 3a.Diagrammatic representation of 45o bend

b) A piston and cylinder machine contains a fluid system which passes

through a complete cycle of four processes. During a cycle, the sum of

all heat transfers is -170kJ.The system completes 100 cycles per minute

.Complete the following Table Q3.b showing the method for each item,

and computes the net rate of work output in kW.

Table Q3.b Heat, Work and internal energy transfer for a cycle

(12 marks)

Total 25 marks



PART B

Q4 a) For the spring damper and mass system shown in Figure Q4. (a), where

M1 = 3 Kg, K1 = 1 N/m, B1 = 3 Ns/m M2 = 2 Kg, K2 = 2 N/m, B2 = 4 Ns/m F(t) = force applied

Figure Q4. (a) Spring damper mass system

(i) Develop differential equations for the system given in Q4.(a) (2 marks)

(ii) Determine the Laplace transforms of the differential equations

obtained from Q4( i) above. (2 marks)

(iii) Determine the transfer function G(s) = X1(s)/F(s), Assume that the

system is subjected to a unit step input and the initial conditions of the

system are zeros (i.e. at time = 0, x, x’, x’’ are all zeros).

(8 marks) b) With the aid of a block diagram explain how an RFID system works.

(8 marks)


Q4 continued over the page…

B1

K1

X1

K2

M2

M1

X2

F(t)

B2


Q4 continued…

c) Derive the mathematical model for the heat transfer system shown in Figure Q4.c.

Figure Q4.c Thermal Water Heating System

Given:

Thermal resistance of the insulation: R (oC/joule/sec)

Thermal capacity: C (joule/oC)

Heat input to the system: q (joule/sec)

Assume that the Specific thermal insulation is negligible and tank is

thoroughly mixed so that uniformity of temperature is maintained.

(5 marks)

Total 25 marks

Q5 a) Block diagram for a closed loop control system for a thermostatically

controlled air-conditioning system for an automobile is shown in Figure

Q5.(a).The system is to have a damping ratio of 0.7.Determine the value

of K to satisfy this condition and calculate the settling time, peak time and

maximum overshoot for the value of K thus determined.


Water

Output Water

Temperature ɵo

Thermal Insulation

Input Water

Temperature ɵi

Electric Heating



Q5 continued…

Figure Q5. (a) Thermostatically controlled air-conditioning system

(11 marks)

(b) The transfer function of a unity feedback control system for a pick and

place robotic arm is given by

Obtain an expression for unit step response of the system. (3 marks)

(c) A robotic arm has an open loop transfer function for its angular position of

The input of the system is a ramp input changing at the rate 10 degrees

and K has the values 1, 10,100.

i) What will be the steady state errors for different K values when it is

an open loop system.

(5 marks)

ii) What will be the steady state errors for different K values when it is

an closed loop system.

(5 marks)


iii) Comment on the significance of increasing the value of K.

(1 marks)

Total 25 marks

Please turn the page Q6 (a) Analyse the stability of a control system for speed control of a DC motor

given in Figure Q6. (a) Based on location of poles and zeros in S

plane for the following conditions.

i) Open loop stability (4 marks)

ii) Closed loop stability K=10 (3 marks)

iii) Closed loop stability K=200 (3 marks)

Figure Q6. (a) Block diagram for an air traffic control systems

(b) Large welding robots are widely used in automobile assembly lines.

The welding head is moved to different positions on the automobile

bode, and rapid, accurate response is required. The characteristic

equation for the welding system is

s5 +1.5 s4 + 2s3 + 4s2 + 5s + 10 = 0

Using Routh-Hurwitz stability criterion determine the stability of the

system.

(4 marks)

(c) Reduce the following block diagram for an air traffic control systems shown

in Figure Q6. (c) and determine the system transfer function.




Q6 continued…

Figure Q6. (c) Block diagram for an air traffic control systems

(6 marks)

(d) Discuss the various types of sensors that can be employed in water boiler

automation system for continuous monitoring of temperature, pressure and

water level.

(5 marks)

Total 25 marks

END OF QUESTIONS


Please turn the page for the Formula Sheet

FORMULA SHEET

R= 287 J/ Kg K P = F/A ρ = m/V m. = ρAV P = ρgh Bernoulli’s Equations

Q= A v Q=V/t

Flow meter Equation

Fluid Force Calculation at the bend

.ΔMΔt

ΔMF

Fx = ρQ( v1x –v2x) + (p1A1)x + (p2A2)x

Fy = ρQ( v1y –v2y) + (p1A1)y + (p2A2)y

FR = Thermodynamics


Q = W+ΔU + ΔPE + ΔKE Q=mC ΔT PV=mRT Cp – Cv =R

Control Systems Laplace Transforms A unit impulse function 1

A unit step function s

1

A unit ramp function 2

1

s

Block Diagram Reduction Blocks with feedback loop


G(s) = )()(1

)(

sHsGo

sGo

(for a negative feedback)

G(s) = )()(1

)(

sHsGo

sGo

(for a positive feedback)

Blocks G1(S) & G2(s) in series G(s) = G1(S) *G2(s) Blocks G1(S) & G2(s) in parallel G(s) = G1(S) +G2(s) Steady-State Error

)]()(1

1[lim

0s

sGse i

os

ss

(For the closed-loop system with a unity feedback)

Time Response for second-order systems

d = n (21( )

ᶲ = tan-1(

)1( 2)

tr = ( - ᶲ)/d

tp = /d

n

4= ts

%100))1(

(exp = Mp.2


End of Paper

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UNIVERSITY OF BOLTON RAK ACADEMIC CENTRE ......Page 4 of 13 University of Bolton RAK Academic Centre BEng (Hons) Mechanical Engineering Semester 2 Examination 2017/2018 Thermofluids