Simulation of Double Effect Absorption Refrigeration System

Abstract

In this study the Double effect Absorption Refrigeration system (DAR) is developed and its thermodynamic analysis is performed using different working fluid pairs. The DAR consists of a high and low temperature generator, high and low temperature absorbers, condenser, evaporator, expansion valves, mixture and refrigerant heat exchangers and pumps and it is made up of two cycles.

In the DAR system, NH₃/H₂O is used as refrigerant/absorbent working pair at high temperature cycle and NH₃/LiNO₃ is used a refrigerant/absorbent working pair at low temperature cycle. This system is called as System I. In order to be able to compare the effects of using different fluid pairs in these two cycles, a new system is formed. In this new system, fluid pair at the high temperature cycle remained same as before (NH₃/H₂O), but NH₃/NaSCN is used at low temperature cycle and this new system is called as System II. While the selected results of calculations of both systems were presented in the figures, only the results of analysis of system II are tabulated in the study.

The analysis of the system is performed at various operation conditions and the coefficient of performance (COP) and the high temperature circulation ratios (f_H) were calculated and given graphically. Low temperature circulation ratios (f_L) were also calculated but not shown in the study. A computer program is developed in FORTRAN for the simulation of the DAR and results are given graphically. The results show that the performance of the NH₃/LiNO₃ working fluid pair has slightly better performance than NH₃/NaSCN, at low temperature cycle for the same working conditions. It is also observed that COP of the double effect system is greater than the COP of single effect system.

In this study, energy and exergy analyses of a two-stage heat pump-drying system are conducted, and the performance of the overall system is evaluated. The system has two cycles: a heat pump and a drying cycle. The working fluid of the heat pump and the drying cycles are R-134A and air, respectively.

Nomenclature

C:

Heat capacity per unit time (kW/K)

C:

The heat capacity ratio

C_P :

Specific heat at constant pressure (kJ/kmol K)

D:

The values

f_H :

The circulation ratio of the high temperature cycle

f_L :

The circulation ratio of the low temperature cycle

h:

The specific enthalpy (kJ/kg)

h_I :

The specific enthalpy of the saturated liquid ammonia (kJ/kg)

h_S :

The specific enthalpy of superheated ammonia vapour (kJ/kg)

h_V :

The specific enthalpy of saturated ammonia vapour (kJ/kg)

g:

The specific Gibbs free energy function (kJ/kmol)

m:

Mass (kg)

$\dot{m}$ :

Mass flow rate (kg/s)

P:

Pressure (kPa bar)

p_L :

Low pressure (kPa bar)

p_H :

High pressure (kPa bar)

T:

Temperature (°C)

T_E :

Evaporator temperature (°C)

T_C :

Condenser temperature (°C)

q:

Heat load (kW)

q_E :

Heat load at evaporator (kW)

q_C :

Heat load at condenser (kW)

W_P :

Pump energy supplied (kW)

X:

Mole fraction

x:

Mass concentration

COP:

Coefficient of performance

DAR:

Double effect absorption refrigeration system

HTA:

High temperature absorber

HTG:

High temperature generator

LTA:

Low temperature absorber

LTG:

Low temperature generator

HE:

Heat exchanger

EV:

Expansion valve

C:

Condenser

E:

Evaporator

P:

Pump