Ecological Performance of a Generalized Radiative System Light-Driven Engine (LDE) With [A] ⇌ [B] Reacting System Improved by Controlling Piston Motion

2018 ◽  
Author(s):  
Huijun Feng ◽  
Kang Ma ◽  
Lingen Chen ◽  
Shaojun Xia
Keyword(s):  
Heat Transfer ◽  
Working Fluid ◽  
Minimum Entropy ◽  
System A ◽  
Ecological Performance ◽  
Maximum Work ◽  
Far From Equilibrium ◽  
Minimum Entropy Generation ◽  
Configuration Problem ◽  
Maximum Work Output

This paper introduces the ecological criterion (EC) into the optimal configuration problem of an irreversible light-driven engine (LDE) under the assumption that heat transfer (HT) between the working fluid (WF) and the surroundings is presumed to abide by the generalized radiative heat transfer law (HTL) [q ∝ Δ(Tn) ]. The WF is made up of the reacting system [A] ⇌ [B] , and the primary irreversibilities corresponding to the practical engine are the piston friction and heat conduction with the WF operating at a nonzero rate and far from equilibrium. Meantime, in order to obtain the optimal paths (OPs) for maximum ecological performance (EP) of the engine, the optimal control theory (OCT) is utilized in this paper. Numerical calculations of the OPs at maximum EP with linear phenomenological (n = −1), Newton’s (n = 1) and radiative (n = 4) HTLs are performed. The results derived by maximum EP are compared with those derived by maximum work output (WO) and minimum entropy generation (EG) as well as different HTLs. The results obtained in this paper indicate that utilizing the maximum EC as the design objective could effectively accomplish the EG reduction with a little decrease in the WO. Moreover, the OPs for maximum EP with different HTLs are quite different.

scholarly journals Maximum work output of multistage continuous Carnot heat engine system with finite reservoirs of thermal capacity and radiation between heat source and working fluid

2010 ◽  
Vol 14 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Jun Li ◽  
Lingen Chen ◽  
Fengrui Sun
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Heat Sink ◽  
Heat Engine ◽  
Thermal Capacity ◽  
Working Fluid ◽  
Work Output ◽  
Maximum Work ◽  
Engine System ◽  
Maximum Work Output

Optimal temperature profile for maximum work output of multistage continuous Carnot heat engine system with two reservoirs of finite thermal capacity is determined. The heat transfer between heat source and the working fluid obeys radiation law and the heat transfer between heat sink and the working fluid obeys linear law. The solution is obtained by using optimal control theory and pseudo-Newtonian heat transfer model. It is shown that the temperature of driven fluid monotonically decreases with respect to flow velocity and process duration. The maximum work is obtained. The obtained results are compared with those obtained with infinite low temperature heat sink.

Effect of Absorptive Coating of the Hot Fluid Passage of a Heat Exchanger Employing Exergy-Optimized Pin Fins in High Temperature Applications

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
Nwosu P. Nwachukwu ◽  
Samuel O. Onyegegbu
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Simple Relation ◽  
Base Temperature ◽  
Minimum Entropy ◽  
Pin Fin ◽  
Temperature Heat ◽  
Pin Fins ◽  
Minimum Entropy Generation ◽  
Fluid Parameters

An expression for the optimum pin fin dimension is derived on exergy basis for a high temperature exchanger employing pin fins. The present result differs from that obtained by Poulikakos and Bejan (1982, “Fin Geometry for Minimum Entropy Generation in Forced Convection,” ASME J. Heat Transfer, 104, pp. 616–623) for a low temperature heat recovery application. Also, a simple relation is established between the amounts the base temperature of the optimized pin fin is raised for a range of absorptive coating values. Employing this relation, if the absorptivity of the coating, the plate emissivity, the number of protruding fins, and some area and fluid parameters are known, the corresponding value for the base temperature of the fin is immediately obtained. The analysis shows that the thermal performance of the exchanger improves substantially with a high absorptivity coating hence can be seen as a heat transfer enhancement feature of the exchanger operating with radiation dominance.

scholarly journals Optimal Configuration of a Gas Expansion Process in a Piston-Type Cylinder with Generalized Convective Heat Transfer Law

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3229 ◽  
Author(s):  
Lingen Chen ◽  
Kang Ma ◽  
Huijun Feng ◽  
Yanlin Ge
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Bath ◽  
Working Fluid ◽  
Expansion Process ◽  
Work Production ◽  
Maximum Work ◽  
Gas Expansion ◽  
Optimal Configurations

Optimal configurations for the working fluid expansion process in a piston-type cylinder with maximum work production are studied by applying finite time thermodynamics. The problem is solved by utilizing the modified Lagrangian. The initial and final volumes, initial internal energy and total time are fixed, and the heat transfer between the working fluid and the external heat bath obeys the generalized convective heat transfer law, which can be transformed into Newton’s heat transfer law, the Dulong–Petit heat transfer law and the square convective heat transfer law. The optimal configurations of the expansion process under three different conditions of heat transfer law are provided and compared, respectively. The results show that the heat transfer law has both quantitative and qualitative influences on the optimal configurations of the expansion process.

Convective Heat Transfer Enhancement in Solar Receivers Using Minimum Entropy Generation Optimization

2011 ◽  
Author(s):  
Qi Li ◽  
Xigang Yuan ◽  
Pierre Neveu ◽  
Gilles Flamant
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Convective Heat ◽  
Entropy Generation ◽  
Minimum Entropy ◽  
Transfer Enhancement ◽  
Optimal Velocity ◽  
Minimum Entropy Generation ◽  
Convective Heat Transfer Enhancement

Convective heat transfer enhancement can significantly improve the thermal efficiency in the conversion, utilization, recovery and storage of energy (in particular solar thermal). Modifying velocity field is the most direct approach to enhance convective heat transfer. However, in most cases the optimal velocity field is unknown and difficult to find even for an experienced researcher. In this paper, a predictive optimization methodology in convective heat transfer enhancement based on minimum entropy generation (MEG) principle was developed. A set of Euler’s equations were derived by the variation calculus to the Lagrange function established by governing equations, specific constraints and objective functional—total entropy generation rate. The solution of these equations resulted in the optimal velocity fields, leading to the minimum entropy generation. To validate and demonstrate the future application of this methodology to solar absorbers used to convert concentrated solar energy, the steady laminar convection heat transfer process in a two-dimensional channel with fixed heat flux boundaries was optimized for given total viscous dissipations. The numerical simulation results showed that lower value of maximum wall temperature was obtained by MEG optimization, which means cheaper and safer materials. The present work indicated that the new methodology could be a good guide in convective heat transfer enhancement design work, especially in CSP receivers.

Optimal Paths for a Light-Driven Engine with [A]=[B] Reacting System and Generalized Radiative Heat Transfer Law

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Lingen Chen ◽  
Kang Ma ◽  
Fengrui Sun
Keyword(s):  
Heat Transfer ◽  
Radiative Heat Transfer ◽  
Optimal Control Theory ◽  
Radiative Heat ◽  
Working Fluid ◽  
Rate Dependent ◽  
System A ◽  
Optimal Paths ◽  
Heat Leakage ◽  
Optimal Configurations

Abstract A generalized radiative heat transfer law is introduced into an irreversible light-driven engine with a working fluid composed of the bimolecular reacting system [A]=[B], and the effects of heat transfer laws on the optimal paths of the engine are investigated in this paper. Piston paths for maximizing work output and minimizing entropy generation are determined for such an engine with rate-dependent loss mechanisms of friction and heat leakage by applying the optimal control theory. Numerical examples for the optimal configurations with three special heat transfer laws ( n=-1, n=1 and n=4 ) are provided, and the obtained results are compared with each other. The research on the optimal paths of a light-driven engine from Newton’s heat transfer law to the generalized radiative heat transfer law enriches the finite time thermodynamics. The results presented herein can provide some guidelines for optimal design and operation of real light-driven engines.

Flow and heat transfer in a closed loop thermosyphon Part II – experimental simulation

2007 ◽  
Vol 18 (4) ◽  
pp. 41-48 ◽  
Author(s):  
J.C. Ruppersberg ◽  
R.T. Dobson
Keyword(s):  
Heat Transfer ◽  
Closed Loop ◽  
Cooling System ◽  
Operating Conditions ◽  
Experimental Simulation ◽  
Theoretical Modelling ◽  
Working Fluid ◽  
Small Scale ◽  
System A ◽  
Test Loop

A closed loop thermosyphon is an energy transfer device that employs thermally induced density gra-dients to induce circulation of the working fluid thereby obviating the need for any mechanical moving parts such as pumps and pump controls. This increases the reliability and safety of the cool-ing system and reduces installation, operation and maintenance costs. These characteristics make it a particularly attractive option for the cavity cooling system of the Pebble Bed Modular Reactor (PBMR). Loop thermosyphons are however, known to become unstable under certain initial and operating conditions. It is therefore necessary to conduct an experimental and theoretical study of the start-up and transient behaviour of such a system. A small scale test loop was built representing a section of a concept cooling system. A number of representative yet typical experimental temperature and flow rate curves for a range of initial and boundary condi-tions were generated, plotted and are given as a function of time. These curves show that oscillatory temperature and flow occurred that was dependent on the differing design and operating conditions. A number of theoretical modelling and actual cooling system design problem areas were identified. These problem areas need to be addressed if more accu-racy is required to capture the erratic and ostensibly chaotic heat transfer behaviour of the loop.

“Entransy,” and Its Lack of Content in Physics

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Adrian Bejan
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Entropy Generation ◽  
Solid Body ◽  
Thermodynamic Temperature ◽  
Entransy Dissipation ◽  
Minimum Entropy ◽  
Constructal Law ◽  
Minimum Entropy Generation ◽  
False Claim

Here, I show that “entransy” has no meaning in physics, because, at bottom, it rests on the false claim that in order to transfer heat to a solid body of thermodynamic temperature T, the heat transfer must be proportional to T. Entransy “dissipation” is a number proportional to well known measures of irreversibility such as entropy generation and lost exergy (destroyed available work). Furthermore, the “principle of entransy dissipation minimization” adds nothing to existing work based on minimum entropy generation, minimum thermal resistance, and constructal law. The broader trend illustrated by the entransy hoax is that it is becoming easy to take an existing idea, change the keywords, and publish it as new.

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