international journal of pure and applied mathematics ...design of vapour absorption refrigeration...

DESIGN OF VAPOUR ABSORPTION REFRIGERATION SYSTEM OF 1.5TR CAPACITY BY

WASTE HEAT RECOVERY PROCESS

Prakash.Matta1 ,SaiKiran

2,Khaja SK

3,Manoj A.V.K

4.

1k.l.university, Green Fields, Vaddeswaram, Guntur Dist. (pin-522502) Andhra Pradesh, India.

2 k.l.university, Green Fields, Vaddeswaram, Guntur Dist. (pin-522502) Andhra Pradesh, India

[email protected] mobile -9032533882.

Abstract: this project deals with the design of a

vapor absorption refrigeration system. The initial

conditions are considered and accordingly the

design modules are calculated. The effective area

of an evaporator is calculated for fixed cooling

rate and the effective area of heat transfer of

condenser is calculated. The capacity of a

generator and absorber are calculated. The above

obtained values are then verified to collaborate

this design to an automobile industry where

waste heat is recovered and provided as input to

the designed absorption system.

Keywords:.refrigeration system, evaporator,

absorber, condenser, generator.

1. Introduction

Refrigeration has become an essential part of the

way we live our life. Almost everyone has a

household refrigerator, but not many know of the

process required to produce the drop in

temperature that we know as refrigeration. Nature

works much like a heat engine, heat flows from

high-temperature elements to low-temperature

elements. As it does this, work is also done to its

environment.

Refrigeration is a process to keep a cool element or

to reduce the temperature of one element below

that of the other. The refrigeration process is, in

essence then, a reverse heat engine, where heat is

taken from a cold element to be transferred to a

warmer element, generally by adding work to the

system.

Figure1.1.basic absorption refrigeration cycle

Absorption systems have been extensively paid

attention in recent years due to the potential for

CFC and HCFC replacements in refrigeration,

heating and cooling applications. Furthermore,

thanks to the progressive reduction of both

installation and maintenance cost and energy

consumption, their employment may become more

and more diffuse. Most of industrial process uses

lots of thermal energy by burning fossil fuel to

produce steam or heat for the purpose. After the

process, heat is rejected to the surrounding as a

waste. This exhaust waste heat can be used as

refrigeration by using a heat based refrigeration

system, like vapor absorption refrigeration cycle.

Despite a lower coefficient of performance (COP)

as compared to the vapor compression cycle,

absorption refrigeration systems are promising for

using inexpensive waste energy from industrial

processes, geothermal energy, solar energy etc.

International Journal of Pure and Applied MathematicsVolume 115 No. 7 2017, 613-619ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

613

2. Cycle description

In such systems, low pressure refrigerant vapor

leaves the evaporator and enters the absorber. Here

the formation of “solution pair” takes place i.e.

combination of refrigerant and absorbent and the

formed solution is strong in nature. Now this

strong solution is then pumped to the generator

and here the pressure increases. In generator this

strong solution is heated by some external source

which in this case study is“wasteheat”.

Figure.1.2.basic absorption refrigeration cycle

After the heating process is accomplished strong

solution at high pressure moves to the condenser

leaving back the weak solution which is send back

to the absorber using an expansion valve. Now the

high pressure refrigerant moves from generator to

the condenser where the refrigerant vapor is

condensed to high pressure liquid refrigerant. This

liquid refrigerant is passed to the expansion valve

and where it is forwarded to the evaporator, where

the refrigeration effect is achieved and thus

completes the complete vapor absorption

3.Methodology The design of a vapour absorption system consists

of the following modules. Design of an evaporator.

Design of condenser. Design of generator. Design

of absorber. The pressure of evaporator and

absorber are maintained at 4.7 bar and the pressure

of generator and condenser are maintained at 10.7

bar. Temperature of evaporator, condenser,

generator and absorber are maintained at 2ºC,

54ºC, 52ºC &120ºC.

By constraining the cooling rate at 1.5TR. Specific

enthalpies of ammonia water absorbent solution

are obtained from the charts. For an overall heat

transfer coefficient of 1000w/m2

using the LMTD

procedure effective area of an evaporator is

obtained or calculated and the same procedure is

repeated for the further modules of condenser,

absorber and generator.

4. Calculations

The literature values for the design of the Aqua

Ammonia vapor absorption system

Capacity of system = 1.5 TR=1.5 ×3.5= 5.25 kW

Concentration of NH3 in refrigerant, Xr = 0.98

Concentration of NH3 in Solution, Xs = 0.42

Concentration of NH3 in absorbent, Xw = 0.38

Temperature of the evaporator, TE = 2ºC

Generator or condenser pressure, PH = 10.7 bar

Evaporator pressure, PL = 4.7 bar

Temperature of the Condenser, TC = 54ºC

Temperature of the Absorber, TA = 52ºC

Temperature of the Generator, TG = 120ºC

Using the enthalpy-concentration diagram for aqua

ammonia, at various concentrations of

ammonia/water and corresponding saturation

pressure, the corresponding enthalpy (KJ/Kg) and

temperature (OC) can be calculated and on the

basis of this enthalpy and various mass flow rates

calculated, the heat transfer in the various

components of the vapors absorption system are

calculated. On the basis of this heat transfer the

various components are designed.

Table4.1: Values of mixture at various state point

State

Points

Pressure

in bars

Temperature

in ºC

Specific

Enthalpy

h in

KJ/Kg

1 10.7 54 1135

2 10.7 54 200

3 4.7 2 200

4 4.7 2 1220

5 4.7 52 90

6 10.7 52 180

7 10.7 120 255

8 4.7 120 255

The enthalpy-concentration diagram has liquid

saturation region. If the liquid is saturated at a

given pressure and temperature. The enthalpy can

be calculated by plotting a point corresponding to

International Journal of Pure and Applied Mathematics Special Issue

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the given concentration. The other regions are

saturated vapor and superheated vapor region.

Calculation Equations

Mass Flow Rate:

Consider State Point 2:- (saturated liquid) P2=10.7bar

X2 =0.98

Using the enthalpy concentration diagram for

Ammonia / Water

We get: T2 = 54ºC

h2 = 200KJ/Kg

State Point 3: (expansion of refrigerant through

expansion valve from high pressure to low pressure at constant enthalpy)

h2 = h3 = 200 KJ/Kg

T3 = 2ºC

P3 = 4.7 bar

State Point 4: (extraction of heat by low

pressure ammonia vapors in the evaporator)

Saturation Pressure in evaporator;

P4 = 4.7 bar

Evaporator temp;T4 = 2ºC

Using Enthalpy concentration diagram;

Considering the ammonia vapor as saturated. h4

= 1220 KJ/Kg

Heat Extracted by evaporator

QE = mr × (h4-h3)

mr = Mass flow rate of refrigerant

Given that QE = 5.25 KW=mr× (1220-200)

mr= 5.147 gm/sec

Using Mass Balance Equation:

Mass Of solution (ms)=Mass of

refrigerant(mr)+ Mass of absorbent(mw) ms = mw + mr

Using Mass Balance Equation for NH3; msXs = mr Xr + mw Xw

(mw + mr) Xs = mrXr+ mwXw

(mw +5.147) × 0.42 = 5.147 × 0.98 + mw (0.38)

mw = 72.05 gm/sec

ms = mw + mr = 72.05 + 5.147

ms = 77.205 gm/sec

Design of Evaporator

Evaporator is an equipment in which

refrigerant vaporizes to generate the desired

refrigeration. It is also known as chiller.

Considering the evaporator made of tubes and air

cooled.

Let air inlet temperature to evaporator

th1 = 30ºC

Air outlet temp; th2 = 5ºC

θ1= 30- 2 = 28ºC

θ2 =5-2 = 3ºC

Figure 4.2.Temperature changes in evaporator

[LMTD]= (θm) =��.��

[ LMTD]= (θm) = (28-3) / ln (28/3)

= 11.193º C

Assuming, Overall heat transfer coefficient

(U)=1000 W/m2

Assuming, correction factor (F) = 1

QE = FUA θm

10.548 ×1000 = 1×1000 × AE ×11.193

∴ Area of the evaporator

AE = 0.9423 m2

Considering the number of evaporator tubes (n) =

30

Length of each tube (L) = 70cm

Diameter of evaporator tube (D) = to be

calculated

The effective area of evaporator

(AE) = n × π × D × L

0.9423= 30 × π ×D × 0.7

D = 1.382cm

= 0.543 inches.

Design of Condenser

The function of the condenser is to remove the

heat of the hot vapor refrigerant.

State point 1 Ammonia Vapor Entering the

condenser shell as a Saturated Vapor P1 = 10.7 bar

Xr = 0.98

Using h-x Diagram for Ammonia/Water

T1 = 54ºC

h1 = 1135 KJ/Kg


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Heat rejected by condenser

QC = mr × (h1-h2)

QC =5.147 × 10-3 × (1135-200)

QC = 4.81 KW

The cooling medium used is air.

Inlet temperature of air is (tc1) = 30ºC

Exit temperature of cooling air (tc2) = 45ºC

θ1 = 54- 30 = 24ºC

θ2 = 54 – 45 = 9ºC

Figure 4.3Temperature changes in condenser

LMTDθm= (θ1 - θ2)/ ln (θ1/θ2)

LMTD (θm) = (24-9) / ln (24/9)

= 15.23ºC

Assuming, Overall heat transfer coefficient

(U) =1000 W/m2

Assuming, correction factor (F) = 1

QC= FUA θm

9.66 ×1000 = 1×1000 × A C ×15.23

Area of the Condenser AC = 0.315

m2

Considering the number of Condenser tubes (n) =

30

Length of each tube (L) = 70 cm

Diameter of Condenser tube (D) = to be

calculated

The effective area of Condenser

(AC) =n × π × D × L

0.315 = 30 × π ×D × 0.70

D = 0.478 cm

= 0.19 inches.

Design of Generator

State Point 5: strong solution entering the pump as

saturated liquid P5 = 4.7 bar

Xs = 0.42

Using enthalpy-concentration diagram;

T5 = 5ºC

h5 = 179.5 KJ/Kg

State Point 6: high pressure saturated strong

solution entering the generator P6 = 10.7 bar

Xs = 0.42

h6 = 180 KJ/Kg

State point 7: weak solution leaves the generator at

saturation temperature of generator P7 =10.7 bar

Xw = 0.38

Using h-x diagram

h7 = 255 KJ/Kg

T7 = 120ºC

Using energy balance for generator QG = Heat added

to generator

QG = mrh1+mwh7-msh6

= (5.147× 1335) + (72.05×255) – (72.05 ×180)

=12.27 KW

Design of Absorber

Heat rejected in the absorber

QA = mwh8 + mrh4 - msh5

QA = (72.05 × 255) + (5.147 × 1220) – (72x179) = =

11.75 Kw

Considering the absorber to be direct contact heat

exchanger in which the weak solution from the

generator mixes with the ammonia gas from the

evaporator and due to the direct mixing the heat is

rejected. Air is used as cooling medium.

COP of System Now, COP = QE/QG (Neglecting pump work

Wp)

COP=5.25/12.27=0.427

5. Further scope

The final measurements of plant are finalized. It is

observed this plant is not much large in size the

absorption plant is coupled with an automobile

where heat rejection is available of 12KW. The

low grade thermal energy is used to run the

absorption plant. Heat rejected in an automotive

plant can be used todrive the absorption plant. The

typical layout of an AC components are mentioned

in below diagram for an idea


616

Figure 5.1. isometric view of air conditioned

automobile

Figure5.2 front view of bus condenser is placed in

radiator compartment

Figure 5.3 backside view of bus generator is kept

at heat rejection Chamber

isometric view of air conditioned

front view of bus condenser is placed in

backside view of bus generator is kept

Figure 5.4 top view of bus evaporator chamber is

placed

The AC compartment is modelled in Ansys to

check whether the designed air conditioner is

capable of cooling the space. It is simulat

CFD FLOW criteria fixing boundary to the air

conditioner and still compartment. The

temperature contours of air flowing in

compartment is observed to check cooling is

attained. The boundary contains are inlet velocity

of 3m/s at inlet of evaporator. Convective

coefficient of still air 5(W/m2

The evaporator interface at 290k and still air at

300k

Figure5.5 model of compartment with air

conditioner at top

top view of bus evaporator chamber is

The AC compartment is modelled in Ansys to

check whether the designed air conditioner is

capable of cooling the space. It is simulated in

CFD FLOW criteria fixing boundary to the air

conditioner and still compartment. The

temperature contours of air flowing in

compartment is observed to check cooling is

boundary contains are inlet velocity

of 3m/s at inlet of evaporator. Convective 2).

The evaporator interface at 290k and still air at

model of compartment with air

conditioner at top\


617

Figure 5.6 loading model in ANSYS CFD

FLUENT

6. Results

COP = QE/QG (Neglecting pump work W

COP=5.25/12.27=0.427

Capacity of generator=12.27 KW

Heat rejection at absorber=11.75

Heat exchange at condensor QC = 4.81 KW

Effective areas of heat exchange

Evaporator AE = 0.9423 m2

Condenser AC = 0.315 m2

Figure 6.7 temperature contour of compartment

7. Conclusion

It is evident that the compartment highest

temperature is 297k which is sufficient to keep

cool the surrounding. This particular size of plant

is compatible to couple with an heavy automobile

of (50-100) KW BP capacity as luxury travel

CFD

(Neglecting pump work Wp)

= 4.81 KW

temperature contour of compartment

It is evident that the compartment highest

temperature is 297k which is sufficient to keep

cool the surrounding. This particular size of plant

is compatible to couple with an heavy automobile

100) KW BP capacity as luxury travel

busses. As the plant require the generator as heat

input. So heat rejected from the automobile is

diverted as input to the generator compartment

which is beside it. The rest of cycle continues to

heat exchanger from there to evaporator to

absorber to generator again. So thi

are pollution n free uses low grade thermal energy

so they are economical to use.

8. References

[1] Absorption Refrigeration System as an

Integrated Condenser Cooling Unit in a

Geothermal Power Plant(Geothermal

Training Programme Report

Grensásvegur 9, IS-108 Reykjavík,

Iceland)

[2] Mohamed Arif.N, Y.udhayakumar and

Inbarasan.G, “Design of high frequency

earthingsystemUsed for gas insulated

substation”, International Innovative

Research Journal of Engineering and

Technology, Vol.2, No.1

[3] Design of Solar Powered Vapor Absorption

System (Proceedings of the World

Congress on Engineering 2012 Vol III

WCE 2012, July 4 - 6, 2012, London, U.K)

[4] Wikipedia

[5] PREDICTION METHODOLOGY FOR

THE HEAT REJECTION FROM

TURBOCHARGED OR NATURALL

ASPIRED AUTOMOBILE ENGINES by

OVERTON L. PARISH IV. B.S.M.E.,

M.S.M.E

nt require the generator as heat

input. So heat rejected from the automobile is

diverted as input to the generator compartment

which is beside it. The rest of cycle continues to

heat exchanger from there to evaporator to

absorber to generator again. So this type of plant

are pollution n free uses low grade thermal energy

References

Absorption Refrigeration System as an

Integrated Condenser Cooling Unit in a

Geothermal Power Plant(Geothermal

Training Programme Report Orkustofnun,

108 Reykjavík,

Mohamed Arif.N, Y.udhayakumar and

Design of high frequency

earthingsystemUsed for gas insulated

substation”, International Innovative

Research Journal of Engineering and

2, No.1, Sep 2016.

Design of Solar Powered Vapor Absorption

System (Proceedings of the World

Congress on Engineering 2012 Vol III

6, 2012, London, U.K)

PREDICTION METHODOLOGY FOR

THE HEAT REJECTION FROM

TURBOCHARGED OR NATURALLY

ASPIRED AUTOMOBILE ENGINES by

OVERTON L. PARISH IV. B.S.M.E.,


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