Second-Law Analysis of Vapor Compression Heat Pumps With Solution Circuit

1994 ◽  
Vol 116 (3) ◽  
pp. 453-461
Author(s):  
K. Amrane ◽  
R. Radermacher
Keyword(s):  
Heat Pump ◽  
Heat Pumps ◽  
Single Stage ◽  
Heat Transfer Fluid ◽  
Second Law ◽  
Fluid Temperature ◽  
Ammonia Vapor ◽  
Vapor Compression ◽  
Second Law Analysis ◽  
Work Input

A second-law analysis is conducted on both the single-stage vapor compression heat pump with solution circuit (VCHSC) and its modified version, the cycle with a preheater and additional desorber. The results are compared to a conventional heat pump cycle operating with pure ammonia. The location and magnitude of the irreversibilities of the individual components constituting the cycles are determined. The entropic average temperature is used in computing the irreversibilities. The total work input to the heat pumps is then conveniently decomposed into two parts: the minimum work input or the work of a reversible cycle operating between the desorber and absorber entropic average temperatures, plus an additional input of work caused by the irreversibilities of the different processes of the cycles. The analysis reveals that the compressor is the most inefficient component of the heat pumps with losses accounting for about one fourth of the work input. The irreversibilities in the desorber and absorber are found to be minimum when there is a good match in both the solution and heat transfer fluid temperature glides. By adding a preheater and an additional desorber, the irreversibilities in the single-stage VCHSC are considerably reduced. However, it is shown that it is the preheater and not the additional desorber that has by far the most significant impact on the heat pump’s efficiency improvements. Compared to a conventional ammonia vapor compression cycle, the modified VCHSC, which has twice as many sources of irreversibility, shows nevertheless a maximum improvement of 56.1 percent in second-law efficiency.

Performance Curves for Single-Stage Vapor Compression Cycles With Solution Circuit

1991 ◽  
Vol 113 (2) ◽  
pp. 221-227 ◽  
Author(s):  
K. Amrane ◽  
M. V. Rane ◽  
R. Radermacher
Keyword(s):  
Weak Solution ◽  
High Temperature ◽  
Heat Pump ◽  
Solution Concentration ◽  
Operating Conditions ◽  
Single Stage ◽  
Solution Temperature ◽  
Ammonia Vapor ◽  
Vapor Compression ◽  
Performance Curves

The performance curves for a single-stage vapor compression heat pump with solution circuit (VCHSC) and for its modified version, the cycle using a subcooler and a preheater, are obtained and are compared for the same total UA value including all heat exchangers. The two cycles are simulated at low and high temperature lifts. The weak solution concentration and flow rate are varied. The parameters studied are the cooling COP, the solution heat exchanger (SHX) effectiveness, the pressure ratio, the solution temperature glides in the absorber and the desorber, the desorber load, and the distribution of the UA value. Changing the weak solution concentration from 20 to 90 wt% ammonia increased the desorber load ten times. The cooling COP improved by as much as 20 percent by incorporating the preheater and the subcooler, for both the low and the high temperature lifts. Compared to the conventional ammonia vapor compression cycle, the modified VCHSC showed a maximum improvement in cooling COP of 88 and 35 percent for the low and high temperature lifts, respectively. The results indicate that VCHSC is a very versatile heat pump and/or refrigeration system suitable for a wide range of applications and changing operating conditions.

scholarly journals Second-Law Analysis of a Double-Effect Evaporator with Thermal Vapor Compression

2021 ◽  
Vol 8 ◽  
pp. 50-61
Author(s):  
Ali Snoussi ◽  
Maha BenHamad
Keyword(s):  
Theoretical Work ◽  
Double Effect ◽  
Performance Criterion ◽  
Second Law ◽  
Vapor Compression ◽  
Future Design ◽  
Second Law Analysis ◽  
Work Input ◽  
Energy Balances

In this paper, we present a steady-state analysis of a double-effect evaporator with thermal vapor compression (MED-TVC) installed in the Tunisian Chemical Group (GCT) factory. A thermodynamic model including mass and energy balances of the system is developed and integrated in a Matlab program. The model resolution yields to the determination of the operating parameters of the plant and the Gain Output Rate (GOR) was found to be roughly equal to 5. In a second step, the simulation results served to conduct a second law analysis of the unit. The performance criterion used in this analysis is the second law efficiency, i.e., the ratio of the least theoretical work of separation to the actual work input to the plant. The second law efficiency was found to be 2.4%. The distribution of the irreversibility between the different components of the plant was, in addition, assessed. As a conclusion, it was established that the most irreversibility occurs in the thermo-compressor which contributes with more than 50% to the global imperfection and which presents an exergy efficiency of less than 77%. The remaining irreversibility comes from the three exchangers (the two evaporators and the condenser) with an average contribution of 16%. As it is very difficult to introduce modifications into an existing unit, we assume that the importance of the results is not limited to the studied unit. They serve, rather, as an aid to the future design of a MED-TVC plant.

Second-law analysis of solar-assisted heat pumps

Energy ◽  
1991 ◽  
Vol 16 (6) ◽  
pp. 941-949 ◽  
Author(s):  
Sushil K. Chaturvedi ◽  
Taj O. Mohieldin ◽  
D.T. Chen
Keyword(s):  
Heat Pumps ◽  
Second Law ◽  
Second Law Analysis

scholarly journals Performance of Heat Pumps at Elevated Evaporating Temperatures—With Application to Solar Input

1980 ◽  
Vol 102 (3) ◽  
pp. 203-210 ◽  
Author(s):  
E. A. Kush
Keyword(s):  
Heat Pump ◽  
Heat Pumps ◽  
Difficult Problem ◽  
Vapor Compression ◽  
Competitive System ◽  
Temperature Heat ◽  
Theoretical Predictions ◽  
High Temperature Heat Pump ◽  
Pump Component ◽  
Current Heat

As part of the study of Solar Assisted Heat Pump (SAHP) systems, the performance of the heat pump component itself under conditions attendant to series solar input is being investigated. Notably the effect of high source temperatures, for which current heat pumps are not designed, and the associated thermodynamic potential to raise performance are of interest. This paper presents theoretical predictions, results of systematic experiments run on a special heat pump simulator, and interpretation/analysis of how high Coefficients of Performance (COP) heat pumps can be used in installed SAHP systems. The latter aspect is vital for—although results have shown that substantial increase in COP can be achieved even using off-the-shelf heat pump components—the more difficult problem is supplying sufficient solar energy to the heat pump with a practical, cost-competitive system. The approach taken to the high temperature heat pump study makes the results generally applicable to any vapor compression heat pump with related evaporating temperatures.

scholarly journals Exergy Evaluation of a Heat Supply System with Vapor Compression Heat Pumps

Energies ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 1028 ◽  
Author(s):  
Agata Rijs ◽  
Tomasz Mróz
Keyword(s):  
Heat Pump ◽  
Heat Supply ◽  
Heat Supply System ◽  
Heat Pumps ◽  
Supply System ◽  
Exergy Efficiency ◽  
Vapor Compression ◽  
Outdoor Temperature ◽  
Pump System ◽  
Heat Pump System

The vapor compression heat pumps are very popular solutions regarding heat supply systems of modern, low energy buildings. It is partly due to the fact that they are treated as a sustainable heat supply. The question arises: Can a vapor compression heat pump be treated as a sustainable heat supply? To answer this question; the exergy model of a heat pump system operation has been proposed. The proposed model has been employed for evaluation of exergy efficiency of an existing heat supply system equipped with two heat pumps installed in an educational building located on the campus of Poznan University of Technology, Poznan, Poland. The analysis shows that the system exergy efficiency decreases with an increase in outdoor temperature and its values are in the range of 10.9% to 42.0%. The primary exergy efficiency, which considers the conversion of fossil fuel into electricity, is on average 3.2 times lower than the system exergy efficiency for the outdoor temperature range of −9 °C to 11 °C. The performed analysis allowed for the identification of a set of solutions that may increase the exergy and primary exergy efficiency of the system. The first solution is to cover a part of the electricity demand by a renewable energy source. The second proposition is to apply a low-temperature emission system for heating. The third idea is to apply a district heating network as the heat supply instead of the heat pump. The conclusion is that the exergy performance of systems with heat pumps is rather poor because they generate low-quality heat from high-quality electricity. The best way to improve the primary exergy efficiency of a heat pump system is to power the system by electricity generated from a renewable energy source.

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