The second law efficiency of a heat pump system

Akau, Ronald L.; Schoenhals, R. J.

doi:10.1016/0360-5442(80)90101-2

Cited by 17 publications

(10 citation statements)

References 2 publications

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“…(3), we can define the efficiency as η II = 1 − exergy destruction total flow exergy entering (12) Wepfer et al [6] defined the second-law efficiency in terms of product and supply exergy. This was also calculated to make a comparison between the two definitions.…”

Section: Analytical Frameworkmentioning

confidence: 99%

“…Krakow [10] and Kestin [11] used the actual and ideal cycle values to estimate how well the actual cycle approaches a thermodynamic perfection. Akau and Schoenhals [12] described various methods for calculating the second-law efficiency for a heat pump system using water as a heat source and a heat sink. The second-law efficiency was defined as the ratio of the required minimum energy input for an ideal system to the actual energy input of a real system when achieving the desired task, which, in effect, was essentially the same definition used by Krakow [10] and Kestin [11].…”

Section: Introductionmentioning

confidence: 99%

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Second-law-based performance evaluation of cooling towers and evaporative heat exchangers

Qureshi

Zubair

2007

International Journal of Thermal Sciences

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Section: Analytical Frameworkmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Second-law-based performance evaluation of cooling towers and evaporative heat exchangers

Qureshi

Zubair

2007

International Journal of Thermal Sciences

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“…Kestin (1980) and Krakow (1994) used the actual and ideal cycle values to estimate how well the actual cycle approaches a thermodynamic perfection. Akau and Schoenhals (1980) described various methods for calculating the secondlaw efficiency for a heat pump system using water as a heat source and a heat sink. The secondlaw efficiency was defined as the ratio of the required minimum energy input for an ideal system to the actual energy input of a real system when achieving the desired task, which, in effect was essentially the same definition used by Krakow (1994) and Kestin (1980).…”

Section: Introductionmentioning

confidence: 99%

Application of exergy analysis to various psychrometric processes

Qureshi

Zubair

2003

Int. J. Energy Res.

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SUMMARYThe relation between work and changes in entropy generation arises from the simultaneous treatment of the first and second laws referred to as exergy (or available energy) analysis. In this paper, we discuss thermodynamic analysis of various psychrometric processes using the concept of exergy. A parametric study of each of the processes is carried out to determine the variation of second-law efficiency as a function of mass flow rate, relative humidity and temperature. Other trends such as variation of temperature with relative humidity are also shown where applicable. Irreversible losses are calculated by applying an exergy balance on each system. In this regard, an engineering equation solver (EES) programme is used, which is unique because it has built-in functions for most thermodynamic and transport properties; removing the need for approximate equations. The concept of total exergy as the sum of thermomechanical and chemical parts is employed in calculating the flow exergies for air and water vapor mixtures. It is shown for some processes investigated that an increase in the relative humidity of the incoming air stream increases second-law efficiency. We notice that a decrease in mass flow rate of fresh air (second incoming stream) in the case of adiabatic mixing decreases the second-law efficiency of the process. Also, it is shown that the mass flow rate (of both water and steam) has almost a linear relationship with relative humidity in the range investigated.

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“…For instance, at a specified T H Inlet, T C Inlet , and T C outlet, the condenser leaving water temperature (T H outlet ) of a reverse Carnot cycle [2] can be obtained as:…”

Section: Carnot Cop and Carnot Powermentioning

confidence: 99%

“…In contrast to ideal vapor compression cycle that operates isothermally and isentropically, actual vapor compression chiller suffers from several irreversibilities that are mainly governed by fluid friction (pressure drop), finite rate heat transfer and heat leaks to and from the surroundings [1][2][3][4][5][6][7][8]. Pressure drops at the condenser and the evaporator as well as nonisentropic compression and expansion by the compressor and the expansion valve contribute to entropy generation in a VC system.…”

Section: Introductionmentioning

confidence: 99%