scholarly journals Effect of Machine Entropy Production on the Optimal Performance of a Refrigerator

Entropy ◽  
2020 ◽  
Vol 22 (9) ◽  
pp. 913 ◽  
Author(s):  
Michel Feidt ◽  
Monica Costea
Keyword(s):  
Heat Transfer ◽  
Entropy Production ◽  
Optimal Allocation ◽  
Minimum Energy ◽  
Transfer Entropy ◽  
Coefficient Of Performance ◽  
Environmental Constraints ◽  
Minimum Energy Consumption ◽  
Control Command ◽  
Internal Irreversibility

The need for cooling is more and more important in current applications, as environmental constraints become more and more restrictive. Therefore, the optimization of reverse cycle machines is currently required. This optimization could be split in two parts, namely, (1) the design optimization, leading to an optimal dimensioning to fulfill the specific demand (static or nominal steady state optimization); and (2) the dynamic optimization, where the demand fluctuates, and the system must be continuously adapted. Thus, the variability of the system load (with or without storage) implies its careful control-command. The topic of this paper is concerned with part (1) and proposes a novel and more complete modeling of an irreversible Carnot refrigerator that involves the coupling between sink (source) and machine through a heat transfer constraint. Moreover, it induces the choice of a reference heat transfer entropy, which is the heat transfer entropy at the source of a Carnot irreversible refrigerator. The thermodynamic optimization of the refrigerator provides new results regarding the optimal allocation of heat transfer conductances and minimum energy consumption with associated coefficient of performance (COP) when various forms of entropy production owing to internal irreversibility are considered. The reported results and their consequences represent a new fundamental step forward regarding the performance upper bound of Carnot irreversible refrigerator.

scholarly journals OPTIMIZATION OF HEAT PROTECTION CHARACTERISTICS OF COUNTRY COTTAGE ENCLOSURES

2021 ◽  
Vol 11 (1) ◽  
pp. 39-45
Author(s):  
Yuri S. VYTCHIKOV ◽  
Mikhail E. SAPAREV ◽  
Vladislav A. GOLIKOV ◽  
Evgeniy G. SAFRONOV
Keyword(s):  
Heat Transfer ◽  
Energy Consumption ◽  
Thermal Protection ◽  
Minimum Energy ◽  
Thermal Conditions ◽  
Outer Wall ◽  
Wall Material ◽  
Transfer Resistance ◽  
Heating Systems ◽  
Minimum Energy Consumption

The article presents a method for determining the minimum permissible value of the heat transfer resistance of the outer wall, at which the minimum energy consumption is achieved during the operation of buildings with variable thermal conditions. A review of the sources devoted to this problem showed the presence of high costs of thermal energy during the heating of premises. On the basis of studies of all components of energy consumption in the operation of premises with intermitt ent heating systems, the authors of the article propose a method for determining the minimum permissible resistance to heat transfer, which provides minimum energy consumption. According to the described method, the calculation was made for external walls made of various materials. The analysis of the obtained results showed that a signifi cant infl uence on the minimum permissible value of the heat transfer resistance is exerted by a complex of thermophysical values cρλ. The presented graphical dependence R0 усл on the complex cρλ allows the designer to rationally choose a wall material that provides a minimum of energy consumption during the operation of the building. In the context of rising energy tariff s, such optimization of thermal protection characteristics is especially important for country cott ages operated in intermitt ent heating conditions.

scholarly journals Research on heat transfer characteristics of flow in tube of water-based nanofluids

2020 ◽  
pp. 301-301
Author(s):  
Pengfei Chen ◽  
Zhuangzhuang Jia ◽  
Zhumei Luo ◽  
Shan Qing ◽  
Xiaoyan Huang
Keyword(s):  
Heat Transfer ◽  
Entropy Production ◽  
Forced Convection ◽  
Volume Fraction ◽  
Convection Heat Transfer ◽  
Transfer Entropy ◽  
Hybrid Nanofluid ◽  
Convection Heat ◽  
Forced Convection Heat Transfer ◽  
Water Based

In this paper, the characteristics of forced convection heat transfer in water-based nanofluids are studied by means of experimental and theoretical analysis. Nusselt number of nanofluids were calculated by changing the volume fraction and the type of nanoparticles in the tube. The effects of Reynolds number and the volume fraction of nanoparticles on the forced convection heat transfer were studied. An exergy analytical model was established for the laminar heat transfer of nanofluid under the condition of constant heat flow. At the same Reynolds condition, the friction entropy production of the flow and heat transfer process in the tube increases with the addition of nanoparticles, and the heat transfer entropy production decreases at the same time. However, the magnitude of friction entropy production is only 10-6, which is negligible compared with the heat transfer entropy production. Therefore, in general, the loss of nanofluids is lower than that of pure water; for nanofluids, the exergy loss of hybrid nanofluid is lower than that of single nanofluid at the same volume fraction.

Optimal Allocation of Heat Transfer Surface of a Two-Stage Refrigeration System

Volume 4 ◽  
2004 ◽  
Author(s):  
M. J. Morales ◽  
S. A. Sherif
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
High Performance ◽  
Optimal Allocation ◽  
Low Cost ◽  
Coefficient Of Performance ◽  
Refrigeration System ◽  
Two Stage ◽  
Isentropic Compression ◽  
Inventory Allocation

The purpose of this study is to investigate how the heat exchanger inventory allocation plays a role in maximizing the thermal performance of a two-stage refrigeration system with two evaporators. First, the system is modeled as a Carnot refrigerator and a particular heat transfer parameter is kept constant as the heat exchanger allocation parameter is allowed to vary. The value of the heat exchanger allocation parameter corresponding to the maximum coefficient of performance (COP) is noted. The results are compared to those of a non-Carnot refrigerator with isentropic and non-isentropic compression. It is found that the Carnot refrigerator can be used to predict the value of the heat exchanger allocation parameter where the maximum COP occurs for a non-Carnot refrigerator. In order to improve the accuracy of that prediction, the predicted value of the heat exchanger allocation parameter has to be inputted into the set of equations used for the non-Carnot refrigerator. This study is useful in designing a low cost, high-performance refrigeration system.

scholarly journals Progress in Carnot and Chambadal Modeling of Thermomechanical Engine by Considering Entropy Production and Heat Transfer Entropy

Entropy ◽  
2019 ◽  
Vol 21 (12) ◽  
pp. 1232 ◽  
Author(s):  
Michel Feidt ◽  
Monica Costea
Keyword(s):  
Heat Transfer ◽  
Power Output ◽  
Industrial Revolution ◽  
Mechanical Energy ◽  
Optimization Procedure ◽  
Maximum Energy ◽  
Transfer Entropy ◽  
Coefficient Of Performance ◽  
Environmental Criteria

Nowadays the importance of thermomechanical engines is recognized worldwide. Since the industrial revolution, physicists and engineers have sought to maximize the efficiency of these machines, but also the mechanical energy or the power output of the engine, as we have recently found. The optimization procedure applied in many works in the literature focuses on considering new objective functions including economic and environmental criteria (i.e., ECOP ecological coefficient of performance). The debate here is oriented more towards fundamental aspects. It is known that the maximum of the power output is not obtained under the same conditions as the maximum of efficiency. This is shown, among other things, by the so-called nice radical that accounts for efficiency at maximum power, most often for the endoreversible configuration. We propose here to enrich the model and the debate by emphasizing the fundamental role of the heat transfer entropy together with the production of entropy, accounting for the external or internal irreversibilities of the converter. This original modeling to our knowledge, leads to new and more general results that are reported here. The main consequences of the approach are emphasized, and new limits of the efficiency at maximum energy or power output are obtained.

scholarly journals Study on Transport Packages Used for Food Freshness Preservation based on ANSYS Thermal Analysis

2016 ◽  
Vol 20 (2) ◽  
pp. 95-110
Author(s):  
Ying Yu
Keyword(s):  
Heat Transfer ◽  
Minimum Energy ◽  
Diesel Oil ◽  
Heat Transfer Process ◽  
Cold Chain ◽  
Cost Of Transport ◽  
Minimum Energy Consumption ◽  
Heat Transfer Theory ◽  
Seafood Products ◽  
The Cost

Abstract In recent years, as the Chinese consumption level increases, the consumption quantity of high-value fruits, vegetables and seafood products have been increasing year by year. As a consequence, the traffic volume of refrigerated products also increases yearly and the popularization degree of the cold-chain transportation enhances. A low-temperature environment should be guaranteed during transportation, thus there is about 40% of diesel oil should be consumed by the refrigerating system and the cold-chain transportation becomes very costly. This study aimed to explore a method that could reduce the cost of transport packages of refrigerated products. On the basis of the heat transfer theory and the fluid mechanics theory, the heat exchange through corrugated cases during the operation of refrigerating system was analyzed, the heat transfer process of corrugated cases and refrigerator van was theoretically analyzed and the heat balance equation of corrugated cases was constructed. Besides, this study simulated the temperature field of the corrugated box during transportation. The temperature of the goods was changed through different cooling temperature to calculate the minimum energy consumption, so as to achieve the best refrigeration transport packaging program.

THE INFLUENCE OF HEAT LEAKAGE AND INTERNAL IRREVERSIBILITY ON THE PERFORMANCE OF A QUANTUM SPIN REFRIGERATION CYCLE

2010 ◽  
Vol 24 (23) ◽  
pp. 4595-4610
Author(s):  
JI-ZHOU HE ◽  
JIAN-HUI WANG ◽  
XIN-FA DENG
Keyword(s):  
Entropy Production ◽  
Cooling Rate ◽  
Rate Coefficient ◽  
Power Input ◽  
Quantum Spin ◽  
Coefficient Of Performance ◽  
Quantum Master Equation ◽  
Refrigeration Cycle ◽  
Heat Leakage ◽  
Internal Irreversibility

The cycle model established here, for which the heat leakage and internal irreversibility are considered, consists of two irreversible non-isentropic adiabatic and two isomagnetic field processes. The working substance is composed of many non-interacting spin systems. Based on quantum master equation of an open system in the Heisenberg picture and semi-group approach, the general performance analysis of quantum refrigeration cycle is performed. Expressions for several important performance parameters, such as the cooling rate, coefficient of performance, rate of entropy production and power input, are derived. By using numerical calculations, the cooling rate as a natural optimization goal for a refrigerator is optimized with respect to external magnetic field. The characteristic curves of the cooling rate, rate of entropy production and power input subject to coefficient of performance are plotted. The optimal regions of the cooling rate, coefficient of the performance (COP) and temperatures of the working substance, are determined.

Optimal Allocation of Heat Transfer Area for a Heat Engine

2005 ◽  
Vol 21 (1) ◽  
pp. 1-4 ◽  
Author(s):  
Y. C. Hsieh ◽  
J. S. Chiou
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Optimal Allocation ◽  
Heat Engine ◽  
Thermal Conductance ◽  
Heat Transfer Area ◽  
Internal Irreversibility ◽  
Optimal Area ◽  
Special Case

AbstractFor an endoreversible heat engine operates steadily between two fixed temperatures, Bejan found the engine's best performance can be obtained if the total thermal conductance is evenly divided for hot-end and cold-end heat exchangers. In this study, a heat by-pass model is used to represent the losses due to internal irreversibilities, and the more general formulations are derived for both the optimal area allocation and the maximum thermal efficiency. The results calculated from the present formulations when there is no internal irreversibility(a special case) are consistant with that obtained by Bejan.

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