Endoreversible Carnot Heat Pump Research Articles

Performance optimization of non-isothermal endoreversible chemical pump via Lewis analogy

By considering heat and mass transfer (HMT) coupling, an endoreversible non-isothermal chemical pump cycle model is established and the optimal performance is studied herein. Assuming that the HMT follows Lewis analogy (heat transfer (HT) process obeys Newton's HT law and mass transfer (MT) process obeys diffusion MT law), rate of energy-pumping (Σ) and its corresponding vector coefficient of performance (χT and χμ, which are defined herein) are deduced analytically. Based on the general optimization results, the special examples of endoreversible Carnot heat pump with Newton's HT law and the endoreversible isothermal chemical pump with diffusion MT law are further deduced. The effects of heat flux rate (q1) and mass flux rate (g1) on the optimization results are analyzed. The Σ increases with the increases of q1 and g1. The surface of Σ to [χT,χμ] is a monotonically decreasing plane, and the Σ decreases with the increases of χT and χμ. The special cases of endoreversible Carnot heat pump with Newton's HT law and endoreversible isothermal chemical pump with diffusion MT law are further obtained. The Σ and χμ obtained by endoreversible non-isothermal chemical pump are larger than those obtained by endoreversible isothermal chemical pump. Coupling effect of HMT increases Σ and χμ, but correspondingly decreases χT.

Effect of heat transfer on the performance of thermal Brownian heat pump

<p indent="0mm">A finite-time thermodynamic model of the thermal Brownian heat pump is established in this paper. The heat transfer between a reservoir and viscous medium is assumed to obey Newton’s law. The expressions for the heating load and coefficient of performance (COP) are derived. The effects of heat transfer on thermal Brownian heat pump performance are analyzed, and the valid working region of a thermal Brownian heat pump is obtained. The performance characteristics of the Brownian heat pump are compared with those of the macro endoreversible Carnot heat pump. For a fixed total heat-exchanger inventory, the distribution of heat-exchanger inventory is optimized for maximizing the heating load. The results indicate that the new model with thermal resistance delivers less heating load than the nonequilibrium thermodynamic model, and the new performance characteristics are closer to reality. The system performance can be improved by enhancing the heat transfer between the reservoir and the heat pump. An optimal heat-exchanger inventory ratio exists for maximizing the heating load, and the COP is irrelevant to the heat-exchanger inventory. When the total heat-exchanger inventory is infinite, the model becomes a nonequilibrium thermodynamic one. The heating load can be improved by reducing the reservoir temperature difference, and the COP is not affected by the reservoir temperatures.

Effects of unequal finite piston speeds on the optimal performances of endoreversible Carnot refrigeration and heat pump cycles

The performances of endoreversible Carnot refrigeration and heat pump cycles with loss of heat resistance and finite piston speeds are analysed and optimized by using the combination of finite time thermodynamics, finite speed thermodynamics and direct method. The unequal finite piston speed model on four branches is adopted. Expressions of cooling load of endoreversible Carnot refrigeration cycle and of heating load of endoreversible Carnot heat pump cycle are derived with a fixed cycle period and unequal finite piston speeds on the four branches. Numerical examples show that there exist optimal expansion ratios, which lead to maximum cooling load and maximum heating load for the fixed coefficient of performance (COP), respectively. The maximum cooling load, maximum heating load, optimal ratios of finite piston speeds and optimal hot- and cold-side working fluid temperatures versus COP characteristics for the endoreversible Carnot refrigeration and heat pump cycles are obtained. Moreover, the effects of design parameters on the performances of the two cycles are discussed.

Exergoeconomic performance of an endoreversible Carnot heat pump with complex heat transfer law

The finite-time exergoeconomic performance of an endoreversible Carnot heat pump with a complex heat transfer law, including generalized convective heat transfer law and generalized radiative heat transfer law q∝ (Δ T n ) m , is investigated in this paper. The focus of this paper is to obtain the compromised optimization between economics (profit) and the energy utilization factor (coefficient of performance, COP) for the endoreversible Carnot heat pump, by searching the optimum COP at maximum profit, which is termed as the finite-time exergoeconomic performance bound. The obtained results include those obtained in much of the literature and can provide some theoretical guidance for the design of practical heat pumps.

Fundamental optimal relation of a generalized irreversible Carnot heat pump with complex heat transfer law

The fundamental optimal relation between heating load and coefficient of performance (COP) of a generalized irreversible Carnot heat pump is derived based on a new generalized heat transfer law, which includes the generalized convective heat transfer law and generalized radiative heat transfer law, q ∝ (ΔT n ) m . The generalized irreversible Carnot heat pump model incorporates several internal and external irreversibilities, such as heat resistance, bypass heat leakage, friction, turbulence and other undesirable irreversibility factors. The added irreversibilities besides heat resistance are characterized by a constant parameter and a constant coefficient. The effects of heat transfer laws and various loss terms are analysed. The heating load vs. COP characteristic of a generalized irreversible Carnot heat pump is a parabolic-like curve, which is consistent with the experimental result of thermoelectric heat pump. The obtained results include those obtained in many literatures and indicated that the analysis results of the generalized irreversible Carnot heat pump were more suitable for engineering practice than those of the endoreversible Carnot heat pump.

Effect of a complex generalised heat transfer law on the ecological performance of an endoreversible Carnot heat pump

SYNOPSIS The effect of a complex generalised heat transfer law q ∝ (ΔTn)m on the ecological performance of an endoreversible Carnot heat pump is derived by taking as the objective function an ecological optimisation criterion representing the best compromise between the exergy output rate and exergy loss rate (entropy production rate) of the heat pump. The results obtained include the optimal ecological performance of an endoreversible heat pump with various heat transfer laws, as obtained in existing literature.

Heating load vs. COP characteristic of an endoreversible Carnot heat-pump subjected to the heat-transfer law q ∝ (Δ Tn) m

The relation between heating load and coefficient of performance (COP) of an endoreversible Carnot heat-pump is derived based on a new generalized convective heat-transfer law and generalized radiative heat-transfer law, q ∝ (Δ T n ) m . Our results include those obtained in many literature studies and can provide some theoretical guidance for the designs of real heat pumps.

The Optimal Performance of a Carnot Heat Pump under the Condition of Mixed Heat Resistance

The optimal performance of an endoreversible Carnot heat pump under the condition of mixed heat resistance is investigated. The relationship between the optimal coefficient of performance (COP) and the heating load is derived.

Optimum Performance of a Generalized Irreversible Carnot Heat Pump with a Generalized Heat Transfer Law

The sole irreversibility considered in an endoreversible Carnot heat pump model is the loss of heat resistance between the heat pump and its surrounding heat reservoirs. This paper presents a generalized irreversible Carnot heat pump model by taking into account several additional internal irreversibilities of the heat pump, such as heat leakage, friction, turbulence and other undesirable irreversibility factors. This is done by means of a constant parameter and a constant coefficient, together with the loss of heat resistance. The relation between optimal heating load and coefficient of performance (COP) is derived based on a generalized heat transfer law Q = K (ΔT)m. The effect of heat leakage, internal irreversibility, and heat transfer law on the optimal performance of the generalized irreversible Carnot heat pump is investigated.

Optimum performance parameters for a quantum Carnot heat pump with spin-1/2

The purpose of this paper is to study the optimal performance for an endoreversible Carnot heat pump with a working fluid system consisting of many spin-1/2 fermi. The relationship between the optimal heating load and the coefficient of performance (COP) for the quantum Carnot heat pump is derived. The optimum parameters are obtained at a maximum heating load point and at a maximum ecological function point, respectively.

Effect ZOF heat transfer law on finite-time exergoeconomic performance of carnot heat pump

The operation of a Carnot heat pump is viewed as a production process with exergy as its output. The short-run economic optimization of the endoreversible heat pump is performed in this paper. The profit of the heat pump is taken as the optimization objective function. Using the method of finite-time exergoeconomic analysis, which emphasizes the compromise optimization between economics (profit) and the utilization factor of energy (Coefficient of Performance, COP) for finite-time (endoreversible) thermodynamic cycles, this paper derives the relation between optimal profit and COP of an endoreversible Carnot heat pump based on a relatively general heat transfer law: q∞ Δ( T n ). The COP bound at the maximum profit is also obtained. The results obtained involve those for three common heat transfer laws: Newton's Law ( n = 1), the linear phenomenological law in irreversible thermodynamics ( n = − 1), and the radiative heat law ( n = 4).

Optimization of specific rate of heat pumping in combined heat pump cycles

The optimization problem of a combined heat pump cycle made of two endoreversible Carnot heat pump cycles in series without intermediate reservoirs is investigated using finite-time thermodynamics. The fundamental relation between heating quantity and coefficient of performance (COP) of the combined cycle is derived. Relations are also derived between the SRHP (specific rate of heat pumping), the average rate of heat pumping per unit of total heat-transfer surface area and the COP for reciprocating and stable flow models of combined cycles. The results obtained from this paper may be extended to an endoreversible, combined heat pump cycle formed by more than two endoreversible Carnot heat pump cycles.

Optimal performance of an endoreversible Carnot heat pump

The optimal performance of an endoreversible Carnot heat pump under the condition of non-linear heat transfer with its surroundings is investigated. The relationship between the coefficient of performance (COP) and the heating load of the heat pump is derived. The result provides additional criteria for use in the study and performance evaluation of heat pumps.

Equivalent combined cycle of an endoreversible absorption heat transformer and optimal analysis of primary performance parameters

With the help of a combined cycle model having an endoreversible Carnot heat pump driven by an endoreversible Carnot heat engine, the optimal performance of an absorption heat transformer affected by the irreversibility of finite-rate heat transfer is investigated. The maximum specific heating load of the heat transformer and the corresponding coefficient of performance are derived. It is proven that the state of the maximum specific heating load of the endoreversible heat transformer corresponds to that of the maximum specific power output of the endoreversible Carnot heat engine in the combined cycle model. A detailed analysis of the optimal distribution of heat exchanger areas is given. Other problems concerning the optimal design of absorption heat transformers are also discussed.

96/06754 Experimental study of turbulent flow in the near wakes of single and tandem prisms

With the help of a combined cycle model having an endoreversible Carnot heat pump driven by an endoreversible Carnot heat engine, the optimal performance of an absorption heat transformer affected by the irreversibility of finite-rate heat transfer is investigated. The maximum specific heating load of the heat transformer and the corresponding coefficient of performance are derived. It is proven that the state of the maximum specific heating load of the endoreversible heat transformer corresponds to that of the maximum specific power output of the endoreversible Carnot heat engine in the combined cycle model. A detailed analysis of the optimal distribution of heat exchanger areas is given. Other problems concerning the optimal design of absorption heat transformers are also discussed.

Equivalent combined systems of three-heat-source heat pumps

In this paper, the equivalent combined systems of three-heat-source heat pumps are studied. It is pointed out that there may be three combined ways for us to conceive a reversible three-heat-source heat pump as a combined system having a reversible Carnot heat pump driven by a reversible Carnot engine. Whereas for an endoreversible three-heat-source heat pump affected by the heat resistances, there is only one combined way for us to conceive it as a combined system having an endoreversible Carnot heat pump driven by an endoreversible Carnot engine. Then, the fundamental optimum formula of a three-heat-source heat pump is derived simply and directly by using those of two-heat-source cycles. The optimal peformance of an endoreversible three-heat-source heat pump is thus discussed. The inherent relation between the two- and the three-heat-source cycles as well as the fundamental distinction between the reversible and the endoreversible three-heat-source cycles is also revealed. These results may enrich the theory of finite time thermodynamics, and provide some new theoretical bases for the exploitation and application of three-heat-source apparatus such as chemical heat pumps, absorption heat pumps, and so on.