PROJECT REPORT ON

REFRIGERATION WITH HOT BOX

1

OUR PROJECT

1. We are converting domestic refrigerator into twin

type Hot and Cooled Refrigerator.

2. Changing CFC system into HC system so that the

system becomes ecofriendly.

2

ACKNOWLEDGEMENT

We would like to thank sincerly to our guide

whose able guidance gave us the direction of study and was eager

enough to quench or instable thirst of answering to the smallest

queries. We shall cherish his help and guidance for a long time to

come.

3

PREFACE

In vapour compression cycle the condenser rejects heat to the

atmosphere. This heat is a waste heat we install a plate type heat

exchanger as used in the refrigerator evaporator in the discharge

line of the system and then insulate with glass wool. Now this

heat exchanger will act as an auxiliary condenser and the

refrigerator rejects its heat in the cabinet, which can be utilized

to keep the cooked food warm.

Our project also includes changing over the refrigerating

system from chlorofluorocarbon to hydrocarbon. As we know

R-12 is phased out in our country in this year so we switch over

our refrigerator to its substitute refrigerant that is HC blend (by

mass 50% Propane + 50% Isobutene) which posses an ozone

depletion potential (ODP) of value zero and negligible global

warming potential (GWP). Therefore, system becomes

completely eco friendly.

Also by providing an extra condenser with the main one will

leads to the sub cooling of the liquid refrigerant in the latter part

of the condenser resulting in a better-increased refrigerating

effect or increase a net COP...

4

It can be used in domestic applications to keep the cooked food

hot. It can also be used to make curd faster in the winter season

and so on.

.

5

INTRODUCTION

In domestic refrigerator, the circulation of a refrigerant

achieves constant cooling in a closed system. The refrigerant is

compressed by means of compressor to a pressure at which

temperature obtained at the end of compression will be more than

atmosphere and will then be condensed. This condensed refrigerant

is then allowed to pass through a capillary so that the pressure and

temperature are lowered. Capillary device acts as a throttling

device. The pressure of the refrigerant when it leaves the capillary

maintained above atmosphere where as the temperature of

refrigerant will corresponds to the saturation temperature to be

maintained in the cabinet of the refrigerator, so that when this

vapour flows through the evaporator (placed in the cabinet of the

refrigerator), it will absorb heat. Due to heat absorption, refrigerant

evaporate and when it leaves the evaporator, it will be either dry or

saturated or super heated which compressor then sucks and the

cycle is repeated.

From the above discussion we have studied the working of

the domestic refrigerator. Now to switch over the normal domestic

refrigerator to a twin type hot and cool refrigerator, we have

proceeded as follows.

6

Firstly, make a small box of sheet metal with a door in the

front and place that sheet metal box on the top of the refrigerator.

Now place a heat exchanger, which can be same as that of the

evaporator used in the domestic refrigerator, inside the sheet metal

box. Make sure the sheet metal box is such that there should be a

space of around 2” according to design between the heat exchanger

(auxiliary condenser) and sheet metal box for providing insulation.

Now insulate the auxiliary condenser with glass wool. Connect the

heat exchanger with normal refrigeration cycle after to the

compressor and before the existing the condenser. It should be in

series with the pre-existing condenser. Now that heat exchanger

will also act as a condenser, and heat rejected by high pressure,

high temperature refrigerant can be utilized as a useful heat.

7

SPECIFICATION OF THE

REFRIGERATION SYSTEM

In this section, we dealt with the basic review of domestic

refrigerator cycle. The basic refrigeration cycle is as follows -

Compression system employs four elements in the

refrigeration cycle: compressor, condenser, expansion valve and

evaporator. In the evaporator, the refrigerant is vaporized and heat

8

is absorbed from the space being cooled and its contents. The

vapour is next drawn into a motor driven compressor and raised to

a high-pressure gas is than condensed to liquid in an air or water-

cooled condenser. From the condenser the liquid flows through an

expansion valve in which its pressure and temperature are reduced

to the conditions that are maintained in the evaporator.

9

REFRIGERATION COMPONENTS

1. The Evaporator

2. The Compressor

3. The Condenser

4. The Expansion valve

5. The Receiver

6. The Filter drier

3.1 The Evaporator: The evaporator absorbs heat into the

system. When the refrigerant is boiled at a lower temperature than

that of the substance to be cooled, it absorbs heat from the

substance. The evaporator in a refrigerating system is responsible

for absorbing heat into system from whatever medium is to be

cooled. This heat absorbing process is accomplished by

maintaining the evaporator coil at a lower temperature than the

medium to be cooled. To summarize the three main function of the

evaporator are to:

10

a) Absorb heat.

b) Allow the heat to boil off the liquid refrigerant to a vapour in

its tubing bundle.

c) Allow the heat to superheat the remaining refrained vapour in

it tumbling bundle.

3.2 The Compressor: The compressor is the heart of the

refrigeration system. It pumps heat through the system in the form

of heat. A compressor can be considered as vapour pump. It

reduces the pressure on the low-pressure side of the system, which

includes the evaporator and increases the pressure in the high-

pressure side of the system. The compressor actually increases the

pressure from suction pressure level to the discharge pressure

level. This creates refrigerant flow from low-pressure side to high-

pressure side. All compressors in refrigeration system perform this

function by compressing the vapour refrigerating.

3.3 The Condenser: The condenser rejects both sensible

(measurable) and latent (hidden) heat from the refrigeration

system. This heat can come from what the evaporator has absorbed

any heat of compression or mechanical friction generated in the

compression stroke, motor binding heat, and any heat absorbed by

super heating the suction line before entering the compressor. The

11

condenser receives hot gas after it leaves the compressor through

the short pipe (short pipe between the compressor and the

condenser called the hot gas line). The hot gas is forced into the

top of the condenser coil by the compressor, the gas is being

pushed along at high speed, and hot gas temperature is system and

application dependent. The condenser is a heat exchange device

similar to the evaporator; it rejects the heat from the system

absorbed by the evaporator. This heat is rejected from a hot super

heated vapour in the first passes of the condenser. The middle of

the condenser rejects vapour, which is in the process of the phase

changing to a saturated liquid. The last passes of the condenser

rejects heat from sub-cooled liquid. This further sub cooled the

liquid to below its condensing temperature.

In fact, the three function of a normal condenser is to de-

superheat, condense and to subcool the refrigerant. When the heat

was being absorbed in to the system, we pointed out that it is at the

point of change of state (liquid to vapour) of the refrigerant where

the greatest amount of heat is rejected.

The condenser is operated at a higher pressure and

temperature than the evaporator and is often located outside. The

same principle is applied to heat exchange in the condenser as in

12

the evaporator. The materials a condenser is made of the medium

used to transfer the heat make a difference in the efficiency of the

heat exchange.

3.4 The Expansion Devices: The expansion device, often

called the metering device, is the fourth component necessary for

the compression refrigeration cycle to function. The expansion

device is not as visible as the evaporator, the condenser, or the

compressor. Generally, the device is concealed inside the

evaporator cabinet and so obvious to the casual observer. It can

either be a valve or a fixed-bore device.

The expansion device is a division line between the high

side of the system and the low side of the system. The expansion

device is responsible for metering the correct amount of refrigerant

to the evaporator.

The evaporator performs best when it is as full of liquid

refrigerants as possible without leaving any in the suction line.

Any liquid refrigerant that enters the suction line may reach the

compressor because only a small amount of heat should be added

to the refrigerant in the suction line.

13

The expansion devices are normally installed in the liquid

line between the evaporator and the condenser. The liquid line may

be warm to touch on a hot day and can be followed quite easily to

the expansion device where there is a pressure drop and an

accompanying temperature drop. For example, on a hot day the

liquid line entering the expansion device may be 110oF. If this is a

low temperature cooler using R-12, the low side pressure on the

evaporator side may be 3 psig at a temperature of –15oF. This is a

dramatic temperature drop and can be easily detected when found.

The device may be warm on one side and frosted on the other side.

Because some expansion devices are valves and some are fixed

bore devices, this change can occur in a very short space less than

an inch on a valve, or a more gradual change on some fixed bore

devices.

Expansion devices come in the following different types:

a) high side float

b) low side float

c) thermostatic expansion valve

d) automatic expansion valve

e) fixed bore such as the capillary tube.

14

However, only three are currently being furnished with

refrigeration equipment. The high side float and the low side float

are not currently being used on typical refrigeration equipment and

should not be encountered in this field.

3.5 The Receiver: The condensed liquid refrigerant from the

condenser is stored in a vessel known as receiver from where it is

supplied to the evaporator through the expansion valve or the

refrigerant control valve.

3.6 The Filter Drier: Filter drier is used to remove the acid,

moisture and carbon sludge.

15

BASIC VAPOUR COMPRESSION

DOMESTIC REFRIGERATION

SYSTEM

4.1.Working of refrigeration system

A refrigeration system does not cool products; they remove

product heat, causing temperatures to be lowered. All systems have

an area, which collects heat from inside an insulated cabinet,

dispersing it outside. This collection and disposal of heat continues

until the refrigerator cuts out, usually by thermostat when the

required product temperature has been achieved. Therefore a

refrigeration system is heat pump, collecting heat from one area

and disposing of it elsewhere with the consequence that the area

which heat is being removed from will be lowered in temperature.

Refrigeration system have three major components, each

connected in recycling circuit. The evaporator is the heat collector

located inside the cabinet. The condenser disperses the collected

heat elsewhere. The compressor pumps a refrigerants gas around

the circuit. (Other minor components also service these).

16

Refrigerant gas is the vehicle used to transport heat from the

evaporator to the condenser.

17

Refrigerant gas is pumped around the circuit above, (similar to

water circulating around a cars cooling system), performing

different duties in each of the components. The compressor sucks

the heat laden gas vapour from the evaporator, pumping it at a high

pressure into the condenser. The condenser disposes heat from this

compressed hot gas, causing it to condense into high-pressure

liquid. This liquid returns to the evaporator via a restriction device

(set to cause the correct pressure build up). As this liquid is

released by the restriction into the low-pressure evaporator pipes, it

expands into a vapour, again absorbing heat. These activities are

simultaneous whenever the compressor is running.

COPHP = QH WNET IN

Qh Qh=desired output

Wnet,in=required input

Wnet,in=required input

OPR = QL

WNET IN

QL =desired output QL

18

R

COLDrefrigerated

space

HP

WARMenvironmen

t

WARMhouse

(A) Refrigerator (B) Heat pump

Fig: 4.2 Cooling Vs Heating

4.2.Domestic Refrigerators:

Most domestic refrigerators are of two types – either a

single door fresh food refrigerator or two- door refrigerator-freezer

combination, with the freezer compartment on the top portion of

the cabinet, or a vertically split cabinet (side by side), with the

freezer compartment on the left side of the cabinet. They are

completely self-contained units and are easy to install.

Most refrigerators use R-12 refrigerant, normally

maintaining temperatures of 0oF in the freezer compartment and

about 35oF to 45oF in the refrigerator compartment. The technician

must be able to perform various duties in the maintenance and

repair of domestic refrigerators, water coolers, and ice machines;

this section provides information to aid you in handling some of

19

COLDenvironmen

t

the more common types of troubles. But let us remind you that the

information given here is intended as a general guide and should,

therefore, be used with the manufacture’s detailed instructions.

4.3.Vapour Compression Refrigeration Cycle

Introduction:

The challenge in refrigeration (and air conditioning, etc.) is

to remove heat from a low temperature source and dump it at a

higher temperature sink. Compression refrigeration cycles in

general take advantage of the idea that highly compressed fluids at

one temperature will tend to get colder when they are allowed to

expand. If the pressure change is high enough, then the compressed

gas will be hotter than our source of cooling (outside air, for

instance) and the expanded gas will be cooler than our desired cold

temperature. In this case, we can use it to cool at a low temperature

and reject the heat to a high temperature.

20

Vapour-compression refrigeration cycles specifically have

two additional advantages. First, they exploit the large thermal

energy required to change a liquid to a vapour so we can remove

lots of heat out of our air-conditioned space. Second, the

isothermal nature of the vaporizations allows extraction of heat

without raising the temperature of the working fluid to the

temperature of whatever is being cooled. This is a benefit because

the closer the working fluid temperature approaches that of the

surroundings, the lower the rate of heat transfers. The isothermal

process allows the fastest rate of heat transfer.

Some Other Parameter

An ideal refrigeration cycle looks much like a reversed

Carnot heat Engine or a reversed Rankine cycle heat engine. The

primary distinction being that refrigeration cycles lack a turbine,

using a throttle instead to expand the working fluid. (of course, a

turbine could be incorporated into a refrigeration cycle if one could

be designed to deal with liquids, but the useful work output is

usually too small to justify the cost of the device).

The cycle operates at two pressures, Phigh and Plow, and the

state points are determined by cooling requirements and the

21

properties working fluid. Most coolants are designed so that they

have relatively high pressures at typical application temperature to

avoid the need to maintain a significant vacuum in the refrigeration

cycle. The T-S diagram for a vapour compression refrigeration

cycle is shown below.

1

2 cooler P high

T high

throttle compressor

T Plow

T low

3 heater 4

S

Fig: 4.4 Vapour compression refrigeration cycle

T-S diagram

22

Cooling Requirements

For purpose of illustration, we will assume that a refrigeration

system used to cool air for an office environment. It must be able

to cool the air to 15.5oC (about 60oF) and reject heat to outside air

at 32oC (90oF).

The Working Fluid

We have working fluids available for use in refrigeration

cycles. Four of the most common working fluids are available in

cycle pad: R-12, R-134, ammonia. (Nitrogen is also available for

very low temperature refrigeration cycles). We will choose R-12

for this example.

23

Description of Cycle Stages

We will examine each state point and component in the

refrigeration cycle where design assumptions must be made,

detailing each assumption. As we can see from the example design

constraints, very few members need be specified to describe a

vapour-compression refrigeration cycle. The rest of the

assumptions are determined by applying reasoning and background

knowledge about the cycle. The two principle numerical design

decisions are determining Phigh and Tlow at the cooler outlet and the

compressor inlet.

Cooler (Condenser) Inlet (S1)

Thi

s state does not involve any design decisions, but it may be

important to come back here after the cycle has been solved and

check that T2, which is the high temperature of the cycle, does not

violate any design or safety constraints. In addition, this is as good

a place as any to specify the working fluid.

Cooler (Condenser): Heat rejection (CLRI)

24

The cooler (also known as the condenser) rejects heat to

the surroundings. Initially, the compressed gas (at SI) enters the

condenser where it loses heat to the surroundings. During this

constant pressure process, the coolant goes from a gas to a

saturated liquid-vapour mix, and then continues condensing until it

is saturated liquid, but there is little gain in doing so because we

have already removed so much energy during the phase transition

from vapour to liquid.

Cooler (Condenser) Outlet (S2)

We cool the working fluid until it is a saturated liquid, for reasons

stated above. An important design question arises at this state: how

high should the high pressure of the cycle be?

We choose Phigh so that we can reject heat to the

environment. Phigh is the same as P2 and P2 determines the

temperature at state S2, T2 (T2 is just the saturation temperature at

Phigh). This temperature must at least be higher than that of the

cooling source otherwise no cooling can occur.

25

However, if T2 is too high (that is, higher than the critical

temperature Tc for the working fluid), then we will be beyond the

top of the saturation dome and we will loose the benefits of the

large energy the fluid can reject while it is being cooled.

Furthermore, it is often impractical and unsafe to have very high

pressure in our fluids in our system and the higher P2 we choose,

the higher T1 must be, leading to additional safety concerns. For

reference, Tc for our four working fluids is given below.

Critical Temperature of some refrigerants

Substance TC (OC)

R-12 (CCL2F2) 111.85

R-22 (CHCLF2) 96.15

R-134a (CF3CH2F) 101.05

Ammonia (NH3) 132.35

HC-blend 113.0

Table: 4.1

For example using R-12, we must be able to reject heat to air that

is 32oC. We can choose if T2 to be anywhere between that number

and the 96oC Tc. We will choose it to be 40oC for now.

Throttling (THR1)

26

The high pressure, saturated liquids are throttled down to a lower

pressure from state S2 to state S3. This process is irreversible and

there is some inefficiency in the cycle due to this process, which is

why we note an increase in entropy from state S2 to stateS3, even

there is no heat transfer in the throttling process. In theory, we can

use a turbine to lower the pressure of the working fluid and thereby

can extract any potential work from the high-pressure fluid (and

use it to offset the work needed to drive the compressor). This is

the model for the Carnot refrigeration cycle. In practice, turbines

cannot deal with the most liquid fluids at the cooler outlet and,

even if they could, the added efficiency of extracting this work

seldom justifies the cost of the turbine.

Heater (Evaporator): Heat Absorption (HTR1)

The working fluid absorbs heat from surroundings, which we

intend to cool. Since this process involves a change of phase from

liquid to vapour, this device is often called the evaporator. This is

where the useful “function” of the refrigeration cycle takes place,

because it is during this part of the cycle that we absorb heat from

27

the area we are trying to cool. For an efficient air conditioner, we

want this quantity to be large compared to the power needed to run

the cycle.

The usual design assumption for an ideal heater in a

refrigeration cycle is that it is isobaric (no pressure loss is incurred

from forcing the coolant through the coils where heat transfer takes

place). Since the heating process typically takes place entirely with

in the saturation region, the isobaric assumption also ensures that

the process is isothermal.

Compressor Inlet (S4)

Typically, we want state S4 to be right at the saturated vapour side

of the saturation dome. This allows us to absorb as much energy

from the surroundings as possible before leaving the saturation

dome where the temperature of the working fluids starts to rise and

the (now non-isothermal) heat transfer becomes less efficient.

Of course, we would get the same isothermal behaviour if

we were to start the compression before the fluid was completely

saturated. Further, there would seem to be a benefit in that state

28

point S1 would be closer to the saturation dome on the Phigh isobar,

allowing the heat rejection to be closer to isothermal and,

therefore, more like the Carnot cycle.

It turns out that, for increased efficiency, we can choose S4

such that S1 is on the saturation dome, instead of outside of it in

the superheat region. Following figure shows the T-S diagrams for

two refrigeration cycles, one where S4 is saturated vapour and the

other where S4 has been moved further into the saturation dome to

allow S1 to be a saturated vapour.

The advantages in the second case are that we have

reduced the compressor work. We have also reduced the heat

transfer somewhat; but the reduced compressor work has a greater

effect on the cycle’s coefficient of performance. Fig shows the

cycle’s COP Vs the Quality of S4. We note that the change in COP

is noticeable, but not terribly impressive.

Temperature (o C)

100

50 Compressor

29

0

-50

-100

-0.25 0.25 0.75 1.25

Entropy (kj/kg K)

Fig: 4.6 T-S diagram for different compressor conditions

Compressor (COMP1)

Ideal compressor is like ideal pumps like adiabatic and isentropic.

We also note that compressor is the only device in the system that

does work to the fluid. For an efficient air conditioner, we want

this quantity to be small.

4.4.Some Definitions:

1) Cooling Capacity: Maximum rate of heat removal from the

refrigerated space by refrigerator.

2) Heating Capacity: Maximum rate of heat addition to heated

space by heat pump.

3) 1 Ton of Refrigeration: Capacity of a refrigerator that can

freeze 1 ton of water in 24 hours (12000BTU/hr, 211Kj/min).

30

OR

1 tonne of refrigeration is defined as the refrigeration effect (RE)

produced by the melting of 1 tonne of ice from and at 0oC in 24

hours since the latent heat of fusion of ice is 336 Kj/Kg.

1 tonne of refrigeration =336 * 1000/24 = 14000 Kj/hr.

4) COP: It is defined as the ratio of heat absorbed by the

refrigerant by passing through the evaporator to the work input

required to compress the refrigerant in the compressor, in short it is

the ratio between heat extracted and work done.

COP = Net refrigerating Effect/ work expanded in by the machine

during the same time interval.

31

CHANGED VAPOUR COMPRESSION

DOMESTIC REFRIGERATION

SYSTEM

(Project Work)

In changed vapour compression system an auxiliary

condenser (hot cabinet) is used in the vapour compression cycle.

The auxiliary condenser is placed after the compressor outlet and

before the main condenser inlet. So due to this arrangement some

heat is rejected in auxiliary condenser and some heat is rejected in

32

the main condenser. Therefore, heat rejection by two condensers

results some sub-cooling of liquid refrigerant. Remaining cycle is

same as simple vapour compression cycle.

5.1.Working of changed system

A flow diagram of a changed vapour compression system

is shown in figure. The principle parts of the system are an

evaporator, whose function is to provide heat transfer surface

through which heat can pass from the refrigerated space or product

in to the vaporizing; a suction line, which conveys the low pressure

vapour from the evaporator to the suction inlet of the compressor;

a vapour compressor, whose function is to remove the vapour from

the evaporator and raise the temperature and pressure of the vapor

to a point such that the vapour can be condensed with normally

available condensing medium; a hot gas or discharge line which

delivers the high pressure, high temperature vapour from the

discharge or the compressor to the auxiliary condenser; an

auxiliary condenser whose purpose is to serve as a hot space by

utilizing the waste heat rejected in condenser; a main condenser,

whose purpose is to provide a heat transfer surface through which

heat passes from the hot refrigerant vapour to the condensing

33

media; a refrigerant flow control, whose function is to meter the

proper amount of refrigerant to the evaporator and to reduce the

pressure of the liquid entering the evaporator so that the liquid will

vaporize in the evaporator at the desired low temperature.

Hdispersed Hcollected

Fig 3.1 changed vapour compression cycle

T

sub cooling

∆TS 2

T cond 3

TH

34

HOT BOX

EXPANSION DEVICEFILTER

CONDENSER(outside cabinet)

EVAPORATOR(inside cabinet)

COMPRESSOR(heat pump)

T evap TL superheat

4 ∆TS

S

Fig 5.2: T-S diagram of changed system

5.2.Practical Data’s

Hot Box Specification:

Table 5.1

S. No. Parameter Size

1. Width 14.5”

2. Height 6.5”

3. Breadth 11.5”

4. Glass Wool Insulation 2”

5. Sheet Metal 22Gage

Hot Cabinet Air Temperature:

35

S. No. Mode of Thermostat Air Temp. of Hot

Cabinet

1. Minimum 50oC

2. Normal 55oC

3. Maximum 60oC

Table 5.2

Evaluation of Temperature in Hot Box:

S . No. Substance Quantity Time

Duration

T1oC T2oC

1. Water 200ml. 30 min. 25 45

2. Milk 200ml. 30 min. 12 44

3. Tea 200ml. 30 min. 60 56

4. Daal 200gm. 30 min. 55 52

Table 5.3

T1 – Temperature of substance before putting into hot case.

T2 – Temperature of substance after putting into hot case.

36

5.3.Benefits of Changed System

1. An extra facility (hot cabinet) is obtained with small change

in price of the system.

2 Power consumption is same as in basic vapour compression

system (without hot cabinet).

3 Increment of room temperature is reduced.

4 Due to sub cooling C.O.P of system is increased.

5 Due to conversion of CFC to HC system becomes eco-

friendly

5.4.Applications of Hot Changed System

37

1. To keep the cooked food hot.

2. It can also be used to make curd faster in the winter season

and so on.

3. To keep the fast food in hot condition.

CONVERSION OF CFC TO HC

SYSTEM

In changed system CFC (R-12) refrigerant is changed into HC

(blend of propane and isobutane) refrigerant due to some benefit.

So comparison of R-12 and HC mixture is given below.

6.1.Refrigerant R-12

Refrigerant R-12 probably has been the most widely used

of all the refrigerants. It is a safe refrigerant in that it is non-toxic,

non-inflammable, and non-explosive. Furthermore, it is a highly

stable compound that is difficult o break down even under extreme

operating conditions. However, if brought in contact with an open

38

flame or with an electrical heating element. R-12 will decompose

into highly toxic products.

Along with its safe properties the fact that R-12 condenses

at moderate pressure under normal atmospheric conditions and has

a boiling point of -21.6oF (-29.8oC) at atmospheric pressure makes

it a suitable refrigerant for use in high, medium and low

temperature application and with all three types of compressors.

When employed in conjunction with multistage centrifugal type

compressor, R-12 has been used to cool brine to temperature as

low as -80deg.C.

The fact that R-12 is oil miscible under all operating

condition not only simplifies the problem of oil return, but also

tends to increase the efficiency and the capacity of the system in

that the solvent action of the refrigerant maintain the evaporator

and the condenser tube relatively free of oils films, which

otherwise would tends to reduce the heat transfer capacity of these

two units.

Although the refrigerating effect per pound for R-12 is

relatively small compared with those of some of the other popular

39

refrigerants, this is not necessarily a serious disadvantage. Infact in

small systems, the greater weight of R-12 that must be circulated is

a decided advantage in that it permits closer control of the liquid.

In large systems, the disadvantage of the low latent heat value is

offset somewhat by a high vapour density so that the compressor

displacement required per Ton of refrigeration is not much greater

than that required for the other popular refrigerants. The power

required per ton of capacity also compares favorably with that

required for other commonly used refrigerants.

Some of the more common application for R-12 include

automotive air conditioning, home freezers and refrigerators, liquid

chillers, dehumidifiers, ice makers, water fountains and transport

refrigeration. Unfortunately, like R-11, R-12 has unusually high

ozone depletion potential and is being replaced by other

refrigerants. One frequent replacement refrigerant is R-134a and

HC.

40

6.2.Refrigerant R-134a

It is one of the leading candidates to replace R-12 in many of the

applications employing this refrigerant. It is an HFC and has a zero

ozone depletion potential and low green house effect. It is non-

inflammable and non-explosive and preliminary data indicate a

favorable toxicology as well as chemical stability within the

refrigerating system although it does have a relatively high affinity

for moisture.

The physical and thermodynamic properties of R-134a approach

those of R-12 closely enough to provide similar levels of

performance in system with evaporator temperature of -7 Deg. C

and above. For example, both the isentropic discharge temperature

and the horsepower required per ton of refrigeration nearly the

same for both refrigerants. Also with the saturation temperature of

-15.08 Deg. F at standard barometric pressure, evaporator

temperature of 0 Deg. F and below is practical without maintaining

a vacuum pressure on the low-pressure side of the system.

Also NBP of R-134a (-26.15) Deg. C is quite close to R-12’s NBP

(-29.8 Deg. C). Heat transfer coefficient is significantly higher for

R-134a than R-12. Depending on the temperature, the single-phase

41

increase varies from 27% to 37% for the liquid and 37% to 45%

for the vapor.

The two phase’s increases range from 28% to 34% in the

evaporator and from 35% to 41% in the condenser.

However there are still many unresolved issues related to its

compatibility. It should be noted that R-134a has relatively high

GWP. The use of oil in R-134a system requires a very stringent

quality control. It is not soluble in mineral oil.

The polyester based synthetic oil that is used with it should be

totally dry. This would be difficult considering the fact that

synthetic ester oils are 100 times more hygroscopic then mineral

oils.

Retrofitting an R-12 system with R-134a requires the following

changes:

Compressor is changed in most of the cases.

Capillary is changed.

Filter drier is changed.

Condenser size is increased.

42

Flushing of mineral oil from the system is a difficult job and

takes time.

6.3.HC Refrigerant

These are designed to replace ozone depleting global-warming

refrigerant, HC Refrigerant Products are made of natural, organic

compounds – not a blend of pre-existing, chemically based

synthetic refrigerants, making them.

Highly efficient

Non-ozone depleting

Non-corrosive

Non-toxic

Non-global warming

Safe to use

In fact, HC Refrigerant Products can actually enhance the life and

performance of air-conditioning and refrigeration equipment.

Thanks to an anti-friction additive and their excellent thermal and

chemical stability, HC Refrigerant Products can help to improve

the performance and extend the service life of air conditioning and

refrigeration systems and components. This reduces energy

requirements and prevents system leakage. After more than 12

43

years of extensive testing, it’s clear that HC Refrigerant Products

provide more efficient performance than the man-made, synthetic

refrigerants they replace. HC Refrigerants Products are designed to

replace many environmentally harmful refrigerants currently in

use.

But because of their widely different N.B.P.s, neither R-290

(Propane) nor R-600a (Isobutane) can be used as drop-in

substitutes in place of R-12. However by mass a 50% R-290 +

50% R-600a mixture has exactly the same pressure as R-12. Its

volume refrigerating capacity is also the same. Hence, this mixture

is favored as a drop-in substitute.

In our system we are using HC blend (by mass a 50% R-290 +

50% R-600a mixture), which is a perfect refrigerant to replace R-

12 as it works as good as R-12 does. HC Refrigerants also

consume less power. These refrigerants do not react with materials

and works properly with mineral oils uses now days.

Properties of Propane/Isobutane blend (like care 30, ECFC-12,

Hichill-12, and EcoolPIB) are very much similar to R-12

refrigerant.

44

HC Refrigerants have low density so they are used 40% by mass of

R-12 in comparison to R-12; HC Refrigerants also absorb more

heat during evaporation.

Mass of HC blend = 0.4 * mass of R-12

Mass of HC blend = 0.45 * mass of R-134a

Suction pressure of HC is same as that of R-12 but discharge is

less by 1-2 bars.

Compressors, evaporator, condenser, refrigerant control devices

and pipe size selection using hydrocarbon tend to be virtually the

same design and same size as those used for conventional fluoro

carbon refrigerants that operate at similar pressure.

45

to knock while pumping down the low side, it should be stopped

for short time to allow the oil to settle down after which the

operation can be continue.

The refrigeration system should never be opened while

under vacuum, because air, dirt and moisture would quickly be

forced into the system by outside pressure. It is always advisable to

break the vacuum with refrigerant vapour.

8.4. Testing for Leakage:

After charging the system, it is necessary to test the entire

joint to make sure that they are leak proof. Test is necessary

because even a minute leak will cause a complete loss of the

refrigerant in a relatively short period.

46

There are two methods using for leakage testing in domestic

refrigerator.

1 Soap bubble test.

2 Halide torch test.

In soap bubble test the dry nitrogen gas or atm. Air are filled in the

piping and soap water are lapped on piping. At the place of leakage

the bubbles are formed.

In second method the intake tube of the halide (alcohol)

torch is brought near the leakage joint. Then the leakage gas will

enter into intake tube of the torch and gives a green hue, which is a

sure indication of refrigerant leak.

47

SUMMARY

Bacterial growth that causes food spoilage shows at low

temperature.

Product temperatures above 45oF and below room

temperature are considered high temperature refrigeration.

Product temperatures between 35oF and 45o F are considered

medium- temperature refrigeration.

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Product temperatures between 0oF to 10oF are considered

low-temperature refrigeration.

Refrigeration is the process of removing heat from a place

where it is not wanted and transferring it to a place where it

makes little or no difference.

One ton of refrigeration is the amount of heat necessary to

melt 1 ton of ice in 24 hr period or takes 288,000BTU in 1

min.

The relationship of the vapour pressure and the boiling point

temperature is called the pressure/temperature relationship.

A compressor can be considered a vapour pump. It lowers the

pressure in the evaporator to the desired temperature and

increase the pressure in the condenser to a level where the

vapour may be condensed to a liquid.

The liquid refrigeration moves from the condenser to the

metering device where it again enters the evaporator.

Refrigerants have a definite chemical makeup and are usually

designated with an “R” and a number for field identification.

49

A refrigerant must be safe, must be detectable, must be

environment friendly, must have a low boiling point, and

must have good pumping characteristics.

Refrigerant cylinders are colour coded to indicate the type of

refrigerant they contain.

Refrigerants should be covered or stored while a refrigeration

system is being serviced, then recycled, if appropriate, or sent

to a manufacture to be reclaimed.

PRECAUTIONS

1. Refrigerants should be stored in pressurized containers and

handled with care.

2. Do not apply pressure more then the prescribed value.

3. Goggles and gloves should be worm while transferring the

refrigerants from the container to the system and while doing

brazing.

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4. Do not touch the compressor discharge line because you can

burn your finger.

5. All leakages must be properly checked.

6. Always work under an instructor or a supervisor.

DRAWBACK

The major drawback of the system is that heating depends on

cooling. The temperature in the hot box depends on the cooling of

the refrigerator. More the value of cooling more the heat is

obtained in the hot box.

This hot box is very much successful where the cooling is

required for long period or where heavy cooling is required.

51

CONCLUSION

In this project an extra facility is obtained in domestic refrigerator.

At large-scale production, very few amount of production cost is

increased (10% approx.) in comparison of extra facility. Due to

extra facility demand of the system will become double. This

system has cold as well as hot cabinet, so in both conditions (hot as

well as cold) this system can be used.

52

In this system the power consumption is same as in

domestic refrigerator (without hot cabinet). So extra facility of hot

cabinet is obtained without any power consumption, so operating

cost remains same as in domestic refrigerator. In this system heat

rejection in room is reduced so increment in room temperature

becomes less.

This system also involves conversion of CFC to HC. So

due to this system becomes eco-friendly. So it becomes more

suitable for the atmosphere because CGFC has the value of ODP

equal to one and high value of GWP but HC have the value of

ODP equal to zero and negligible value of GWP.

In this system some sub cooling of liquid refrigerant is also

existed. So when sub cooling is occurred the refrigerating effect is

increased and due to which COP of system is increased. In this

system practically small amount of compressor work is increased

due to increase in discharged line so due to which COP of the

system is decreased. So all of the above discussion results that in

future this system will become popular due to both facilities (hot

53

and cold cabinet) with very small amount of increase in

production cost of the system at large scale.

FURTHER IMPROVEMENTS

Wide range of further improvements can be done on this project to

improve its working and efficiency. Some of the suggestions are as

follows:

Insulation of the hot box can be further improved.

Electronic temperature controller could be used to control

the temperature in the hot box.

54

The pipe carrying the gas from the compressor to the hot

box could be insulated and the rate of transfer of heat from

the outlet pipe could be increased that will lead to increase

in temperature in the heat box.

An additional fan can be used to cool the gas at the outlet.

PROPERTIES OF CFC, HFC AND HC

REFRIGERANTS

Property, metric unit, weight basis

CFC-12

HFC-134A

R-600A

HC blend

Ozone Depleting Potential (ODP)

1 0 0 0

Global Warming Potential (GWP)

8500 1300 3 3

Boiling point at 1 atm.oC -29.8 -26.1 -11.8 -31.5Specific heat of liquid at 30.oC, kj/kgK

0.99 1.45 2.49 2.54

Specific heat of vapour at constant pressure at

0.62 0.86 1.86 1.7

55

30oC,Mj/kgKRatio of specific heat (Cp/Cv) at 1 atm ,30oC

1.136 1.118 1.10 1.16

Density of liquid at 30oC,kg/m3

1292 1187 545 517

Density of saturated vapour at boiling point,kg/m3

6.3 5.3 2.81 2.6

Latent heat of vaporization at boiling point, kj/kg

165 217 362 405

Thermal conductivity of liquid at 20oC,W/moC

0.07 0.08 0.098 0.1

Thermal conductivity of vapour at30oC,1 atm, W/moC

0.010 0.015 0.017 0.018

Surface tension at 25oC,mn/m 8.5 8.4 9.55 8.6Viscosity of liquid at 30oC,centipoise

0.19 0.20 0.14 0.11

Critical temperature, oC 112.04 101.06 135 113Critical pressure (bar) 41.15 40.56 36.45 39.89

V1 V5 V6

E V2 C V O A N P D O E R COMPRESSOR N A S

T OO RR

V3

56

P1

P2

V4EV RECEIVER

Flexible tube

Spring balance

Refrigerant cylinder

57

Fig: 8.1 Changing of refrigeration system

TECHNICAL DATA

1. Compressor : 1/6HP,2850 RPM, Single phase,

1.1amp, 220 V, 50 hz.

2. Capillary : 0.82 mm(dia.)

3. Normal refrigerator charge : 60 gm

4. Refrigerant used : hydrocarbon mixture

5. Power consumption : 2 to 3 Kwh for 165 litre

6. Refrigerator capacity : 165 litre

7. Minimum evaporator temp : (-17± 2) 0C

8. Temperature in hill tray : 0 oC or below

9. Suction pressure : 4.5 psig

10. Discharged pressure : 180 psig

58

11. Insulation : glass wool

Temp. Density Thermaldiffusivity

Thermalconductivity

Specificheat

Thermalconductivity

Specific Heat

ToC Kg/m3 α x 103

m2/hr.K x 103 Kcal/m-hr.oC

CpKcal/kgoC

K x 103

W/mkCp kj/kgk

20 200 1.00 32 0.16 37.2 0.67

59

INSTALLATION, CHARGING,

EVACUTION AND TESTING OF

DOMESTIC REFRIGERATOR

8.1. Installation

In installing the refrigeration system for commercial and

industrial purposes, the following few point must be noted.

The troubles in the refrigeration unit after installation come

under various heading such as no refrigeration, no continuous

running, a higher electric bill, poor refrigeration temp, frosted

suction line and so many.

The location of the condensing unit should be close to

various cabinets as possible in the multiple installation system. It is

always advisable to put it where it will be exposed to very low

60

temperatures. The location of considering unit is also governed by

the source of electric supply, water drainage.

Cooling coils should be carefully mounted and firmly

fastened. The cooling coils are usually fastened to the ceiling of the

cabinet. In few installations horizontal steel piping fastened to the

walls of the cabinet is used as supports for the coils.

The tubing of the installation in all cases should run

horizontally and vertically with neat bends as perfect radius as

possible. The tubing should not run near the sources of heat

because such sources of heat will cause poor refrigeration and low

efficiency of operation.

Tubing should not be placed in such a position, which will

come in the way of handling the articles. The compressor should

be placed in such a place that the noise of the compressor would

not disturb the occupants. It should as near to the suction line as

possible to avoid the superheat of the refrigerant along the tubing.

61

The position of the device should be as near to the cooling coils as

possible to avoid the cooling loss.

8.2. Charging

Charging a system refers to the adding of refrigerant to the

refrigeration system. The correct charge must be added for a

refrigeration system to operate as it was designed to and this is not

always easy to do. Each component in the system must have to be

added to the system in the vapour or liquid state by weighing,

measuring or using operating system charts.

Steps of charging refrigerant:

Use dry nitrogen for pressure testing, test for leaks using

soap solution on each joint. The pressure of dry nitrogen

is between 150 to250pisg.

62

Evacuate system using two stage vacuum pump to

vacuum of 500 to 1500 micron or lower of Hg (1000

micron = 1mm Hg)

Always charge with correct amount of refrigeration by

weight.

(In our case weight of refrigerant = 60 gm.).

The systematic line diagram for charging in a domestic

refrigerator is shown in fig. It is necessary to remove the air

from the refrigeration unit before charging. First the valve

V2 is closed and pressure gauge P2 and vacuum V are fitted

as shown in fig. The valve V5 is also closed, valves V1 and

V3 are opened, the motor is started. Thus the air from the

condenser, receiver and evaporator is sucked through the

valve V1 and it is discharged into atmosphere through the

valve V6 after compressing into the compressor the vaccum

gauge V indicates sufficiently low vaccum when most of

the air is removed from the system. After removing the air,

the compressor stopped and the valves V1 and V6 are

closed and valve V5, V2and valve V7 of the refrigerant

cylinder are opened and then the compressor started.

Whenever the sufficient quantity of refrigerant is taken into

63

system, which will be noted on the spring balance as shown

in the figure, compressor is stopped. The valve V7 and V5

are closed and the valve V1 is opened. The refrigerant

cylinder is disconnected from the system. The pressure

gauge is used to note the pressure during charging the

system. The valve V1, V2, V5 and V6 are the integral parts

of the compressor.

8.3 SYSTEM EVACUATION:

Refrigeration systems are designed to operate with only

refrigerant and oil circulation inside them. When system are

assembled or serviced, air enters the system. Air contains

oxygen, nitrogen and water vapour, all for which are

detrimental to the system. Removing air and/or other non-

condensable gases from a system with a vaccum pump is

called degassing a system. Removing water vapour from a

system is known as dehydration. In the HVAC industry, the

process of removing both air and water vapour is referred to

as evacuation.

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Degassing + Dehydration = Evacuation

These gases cause two problems. The nitrogen is called

a non-condensable gas. It will not condense in the

condenser and move through like the liquid instead, it will

occupy condenser space that would normally be used for

condensing refrigerants. This will cause a rise in head

pressure, resulting in an increase in discharge temperature

and compression ratios, which cause unwanted

inefficiencies.

Air contains about 20% oxygen. Because

noncondensables in a system head pressures and discharge

temperatures to rise, this oxygen in the air will react with

refrigeration oil to form organic solids.

Purging:

Many times during the operation of the system, the air

leaks inside the system. It is necessary to remove the air

for maintaining the efficiency of the system. Owing to the

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presence of air in the system, the high side pressure of the

condenser is increased. When this increase is 10% above

normal, it is necessary to remove the air from the system,

which is known as purging. During purging, the

compressor discharge valve V6 is intermittently opened

for few second at a time. Air and few grams of refrigerant

vapour escape under high-pressure side. A noticeable

pressure and temperature drop in the system occurs and

normal operating pressures are established. The refrigerant

is added from outside if excessive purging is occurred.

Pump Down of Refrigeration System:

If the refrigeration system is to be repaired or some

part of the system is not to be repared, then the refrigerants

must be pumped in to the receiver for the temporary

storage to do this, the liquid line shut off valve V4 and

compressor is started. The compressor pumps the entire

refrigerant into the receiver. The suction pressure reads

closed to zero the receiver inlet valve V2 is now closed

and the compressor stopped. The serviceman can open the

refrigerant system safely for repairs, as the refrigerant is

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safely stored in the receiver. During the pumping down

process, the rapid decrease in the crankcase pressure

causes the refrigerant in the oil to vaporize. This causes

foaming, which will often result in the slugging of oil

through the valves of the compressor. This causes

knocking and if allowed to continue may damage the

compressor. If the compressor is heard to knock while

pumping the low side, it should be stopped for short time

to allow the oil to settle down after which the operation

can be continue.

The refrigeration system should never be opened while

under vacuum, because air, dirt and moisture would

quickly be forced into the system by outside pressure. It is

always advisable to break the vacuum with refrigerant

vapour.

8.4. Testing for Leakage:

After charging the system, it is necessary to test the

entire joint to make sure that they are leak proof. Test is

67

necessary because even a minute leak will cause a

complete loss of the refrigerant in a relatively short period.

There are two methods using for leakage testing in

domestic refrigerator.

2 Soap bubble test.

2 Halide torch test.

In soap bubble test the dry nitrogen gas or atm air is filled

in the piping and soap water is lapped on piping. At the

place of leakage the bubbles are formed.

In second method the intake tube of the halide (alcohol)

torch is brought near the leakage joint. Then the leakage

gas will enter into intake tube of the torch and gives a

green hue, which is a sure indication of refrigerant leak.

68

BIBLIOGRAPHY

1.“Arora & Domkundwar” a text book of refrigeration and air

conditioning fourth edition year 2002.

2.“ Dossat R.J.” a textbook of refrigeration and air

conditioning year first reprint edition 2003.

3.“Khurmi & Gupta” a textbook of refrigeration and air

conditioning second edition year 2003.

4.Website: www.dupoint.com

5.Website: www.hcrefrigerant.com

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