HEAT TRANSFER DESIGN LAB

ASSIGNMENT – 4

Submitted by

Susanta Sethi

Roll no.:- 110CH0109

Guided by,

Dr. B. Munshi

REFRIGERATION CYCLE DESIGN

AIM:-

To simulate the refrigeration cycle having isentropic efficiency of 0.9 of the compressor, using aspen plus.

OBJECTIVE:-

1- To design and simulate the refrigeration cycle system. 2- To calculate the lost work and the thermodynamic efficiency

for the refrigeration cycle. 3- Find the effect of change in mass flow rate on:-

a- Lost work. b- Thermodynamic efficiency. c- Q value of evapourator. d- Q value of condenser.

THEORY:-

REFRIGERATION:

Refrigeration is the cooling effect of the process of extracting heat from a lower temperature heat source, a substance or cooling medium, and transferring it to a higher temperature heat sink, probably atmospheric air and surface water, to maintain the temperature of the heat source below that of the surroundings.

A refrigeration system is a combination of components, equipment, and piping, connected in a sequential order to produce the refrigeration effect. Refrigeration systems that provide cooling for air conditioning are classified mainly into the following categories:

Vapor compression systems: In these systems, a compressor(s) compresses the refrigerant to a higher pressure and temperature from an evaporated vapor at low pressure and temperature. The compressed refrigerant is condensed into liquid form by releasing the latent heat of condensation to the condenser water. Liquid refrigerant is then throttled to a low-pressure, low-temperature vapor, producing the refrigeration effect during evaporation. Vapor compression is often called mechanical refrigeration, that is, refrigeration by mechanical compression.

Absorption systems: In an absorption system, the refrigeration effect is produced by means of thermal energy input. After liquid refrigerant produces refrigeration during evaporation at very low pressure, the vapor is absorbed by an aqueous absorbent. The solution is heated by a direct fired gas furnace or waste heat, and the refrigerant is again vaporized and then condensed into liquid form. The liquid refrigerant is throttled to a very low pressure and is ready to produce the refrigeration effect again.

Gas expansion systems: In an air or other gas expansion system, air or gas is compressed to a high pressure by compressors. It is then cooled by surface water or atmospheric air and expanded to

a low pressure. Because the temperature of air or gas decreases during expansion, a refrigeration effect is produced.

REFRIGERANTS, COOLING MEDIUMS AND ABSORBENTS:

A refrigerant is a primary working fluid used to produce refrigeration in a refrigeration system. All refrigerants extract heat at low temperature and low pressure during evaporation and reject heat at high temperature and pressure during condensation.

A cooling medium is a working fluid cooled by the refrigerant during evaporation to transport refrigeration from a central plant to remote cooling equipment and terminals. In a large, centralized air conditioning system, it is more economical to pump the

cooling medium to the remote locations where cooling is required. Chilled water and brine are cooling media. They are often called secondary refrigerants to distinguish them from the primary refrigerants.

A liquid absorbent is a working fluid used to absorb the vaporized refrigerant (water) after evaporation in an absorption refrigeration system. The solution that contains the absorbed vapor is then heated. There refrigerant vaporizes, and the solution is restored to its original concentration to absorb water vapor again.

REFRIGERATION CYCLES :

When a refrigerant undergoes a series of processes like

evaporation, compression, condensation, throttling and expansion, absorbing heat from a low-temperature source and rejecting it to a higher temperature sink, it is said to have undergone a refrigeration cycle. If its final state is equal to its initial state, it is a closed cycle; if the final state does not equal the initial state, it is an open cycle. Vapor compression refrigeration cycles can be classified as single stage, multistage, compound, and

cascade cycles

DATA GIVEN:-

Propane flow rate = 5400 kg/hr.(working fluid)

Specification:-

For Stream 3 inlet: a. Vapor fraction: 1 b. Pressure : 185 psi c. Total flow :5400 lb/hr

For Cond1 heater: a. Pressure:185 psi

S1

S2

S3S4

C1

V1

EVAP1

COND1

b. Vapor fraction:0 For Evap1 heater:

a. Vapor fraction:1 b. Pressure: 38.37 psi

For C1 compressor: a. Pressure: 187 psi b. Efficiency: 0.9

For V1 valve: a. Pressure out:40 psi

RESULTS :-

1.Q (evaporator) = 176.26 kW

2. Lost work= Work(input) +[ 1- { T(cond) / T(evap) } *Q(evap) ] LW = 70 kW + [1- 537/470]* 176.26 kW = 70 – 25.126 kW =

44.874 kW Thermodynamic efficiency (ɳ) = main goal / (main goal - LW) ɳ = (-25.126) / {(-25.126) – 44.874 } = 0.3589 3. EFFEECT:- Effect of mass flow rate on different parameters is given below:-

Mass flow rate (lb/hr)

Lost work (kW)

Thermodynamic efficiency

Q (evaporator) (kW)

Q (condenser) (kW)

1000 65.35 0.066 32.64 -44.407

1500 63.02 0.099 48.963 -66.611

2000 60.69 0.133 65.28 -88.815

2500 58.367 0.166 81.604 -111.019

3000 56.04 0.199 97.925 -133.22

3500 53.71 0.232 114.245 -155.43

4000 51.39 0.266 130.57 -177.63

4500 49.06 0.299 146.89 -199.83

5000 46.73 0.332 163.21 -222.04

5500 44.407 0.3656 179.53 -244.24

6000 42.081 0.3988 195.85 -266.44

6500 39.75 0.432 212.17 -288.65

7000 37.43 0.465 228.49 -310.85

7500 35.1 0.498 244.81 -333.06

8000 32.77 0.532 261.13 -355.26

8500 30.45 0.565 277.45 -377.46

9000 28.122 0.598 293.77 -399.67

9500 25.795 0.6315 310.09 -421.87

10000 23.47 0.665 326.41 -444.07

PLOTS:-

1-Lost work vs mass flow rate:

2- thermodynamic efficiency vs mass flow rate:

0

10

20

30

40

50

60

70

0 2000 4000 6000 8000 10000 12000

Lost

Wo

rk (

kW)

mass flow rate (lb/hr)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 2000 4000 6000 8000 10000 12000

The

rmo

dyn

amic

eff

icie

ncy

mass flow rate (lb/hr)

3- Q (evaporator) vs mass flow rate:

4- Q (condenser)vs mass flow rate:

0

50

100

150

200

250

300

350

0 2000 4000 6000 8000 10000 12000

Q (

eva

po

rato

r)

mass flow rate (lb/hr)

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

0

0 2000 4000 6000 8000 10000 12000

Q (

con

de

nse

r)

mass flow rate (lb/hr)

APPLICATION:-

Probably the most widely used current applications of refrigeration are for air conditioning of private homes and public buildings, and refrigerating foodstuffs in homes, restaurants and large storage warehouses. The use of refrigerators in kitchens for storing fruits and vegetables has allowed adding fresh salads to the modern diet year round, and storing fish and meats safely for long periods.

In commerce and manufacturing, there are many uses for refrigeration. Refrigeration is used to liquify gases - oxygen, nitrogen, propane and methane, for example. In compressed air purification, it is used to condense water vapor from compressed air to reduce its moisture content. In oil refineries, chemical plants, and petrochemical plants, refrigeration is used to maintain certain processes at their needed low temperatures (for example, in alkylation of butenes and butane to produce a high octane gasoline component). Metal workers use refrigeration to temper steel and cutlery. In transporting temperature-sensitive foodstuffs and other materials by trucks, trains, airplanes and seagoing vessels, refrigeration is a necessity.

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REPORTS:- COMPRESSOR:-

BLOCK: C1 MODEL: COMPR

-----------------------------

INLET STREAM: S1

OUTLET STREAM: S2

PROPERTY OPTION SET: RK-SOAVE STANDARD RKS EQUATION OF STATE

*** MASS AND ENERGY BALANCE ***

IN OUT RELATIVE DIFF.

TOTAL BALANCE

MOLE(LBMOL/HR) 122.459 122.459 0.000000E+00

MASS(LB/HR ) 5400.00 5400.00 0.000000E+00

ENTHALPY(BTU/HR ) -0.568672E+07 -0.546992E+07 -0.381229E-01

*** INPUT DATA ***

ISENTROPIC CENTRIFUGAL COMPRESSOR

PRESSURE CHANGE PSI 187.000

ISENTROPIC EFFICIENCY 0.90000

MECHANICAL EFFICIENCY 1.00000

*** RESULTS ***

INDICATED HORSEPOWER REQUIREMENT HP 85.2033

BRAKE HORSEPOWER REQUIREMENT HP 85.2033

NET WORK REQUIRED HP 85.2033

POWER LOSSES HP 0.0

ISENTROPIC HORSEPOWER REQUIREMENT HP 76.6830

CALCULATED OUTLET PRES PSI 225.370

CALCULATED OUTLET TEMP F 136.314

ISENTROPIC TEMPERATURE F 128.410

EFFICIENCY (POLYTR/ISENTR) USED 0.90000

OUTLET VAPOR FRACTION 1.00000

HEAD DEVELOPED, FT-LBF/LB 28,117.1

MECHANICAL EFFICIENCY USED 1.00000

INLET HEAT CAPACITY RATIO 1.14081

INLET VOLUMETRIC FLOW RATE , CUFT/HR 14,708.6

OUTLET VOLUMETRIC FLOW RATE, CUFT/HR 2,754.97

INLET COMPRESSIBILITY FACTOR 0.93399

OUTLET COMPRESSIBILITY FACTOR 0.79274

AV. ISENT. VOL. EXPONENT 1.03983

AV. ISENT. TEMP EXPONENT 1.16141

AV. ACTUAL VOL. EXPONENT 1.05698

AV. ACTUAL TEMP EXPONENT 1.17168

CONDENSER BLOCK: COND1 MODEL: HEATER

------------------------------

INLET STREAM: S2

OUTLET STREAM: S3

PROPERTY OPTION SET: RK-SOAVE STANDARD RKS EQUATION OF STATE

*** MASS AND ENERGY BALANCE ***

IN OUT RELATIVE DIFF.

TOTAL BALANCE

MOLE(LBMOL/HR) 122.459 122.459 0.000000E+00

MASS(LB/HR ) 5400.00 5400.00 0.000000E+00

ENTHALPY(BTU/HR ) -0.546992E+07 -0.628815E+07 0.130121

*** INPUT DATA ***

TWO PHASE PV FLASH

SPECIFIED PRESSURE PSI 185.000

VAPOR FRACTION 0.0

MAXIMUM NO. ITERATIONS 30

CONVERGENCE TOLERANCE 0.000100000

*** RESULTS ***

OUTLET TEMPERATURE F 97.327

OUTLET PRESSURE PSI 185.00

HEAT DUTY BTU/HR -0.87324E+06

OUTLET VAPOR FRACTION 0.00000E+00

PRESSURE-DROP CORRELATION PARAMETER 0.35415E+08

V-L PHASE EQUILIBRIUM :

COMP F(I) X(I) Y(I) K(I)

PROPA-01 1.0000 1.0000 1.0000 1.0000

EVAPOURATOR:-

BLOCK: EVAP1 MODEL: HEATER

------------------------------

INLET STREAM: S4

OUTLET STREAM: S1

PROPERTY OPTION SET: RK-SOAVE STANDARD RKS EQUATION OF STATE

*** MASS AND ENERGY BALANCE ***

IN OUT RELATIVE DIFF.

TOTAL BALANCE

MOLE(LBMOL/HR) 122.459 122.459 0.000000E+00

MASS(LB/HR ) 5400.00 5400.00 0.000000E+00

ENTHALPY(BTU/HR ) -0.628815E+07 -0.568672E+07 -0.956448E-01

*** INPUT DATA ***

TWO PHASE PV FLASH

SPECIFIED PRESSURE PSI 38.3700

VAPOR FRACTION 1.00000

MAXIMUM NO. ITERATIONS 30

CONVERGENCE TOLERANCE 0.000100000

*** RESULTS ***

OUTLET TEMPERATURE F 0.13127

OUTLET PRESSURE PSI 38.370

HEAT DUTY BTU/HR 0.64233E+06

OUTLET VAPOR FRACTION 1.0000

PRESSURE-DROP CORRELATION PARAMETER 0.20978E+06

V-L PHASE EQUILIBRIUM :

COMP F(I) X(I) Y(I) K(I)

PROPA-01 1.0000 1.0000 1.0000 1.0000

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