The Regenerative Criteria of an Irreversible Brayton Heat Engine and its General Optimum Performance Characteristics

2005 ◽  
Vol 128 (3) ◽  
pp. 216-222 ◽  
Author(s):  
Yue Zhang ◽  
Congjie Ou ◽  
Bihong Lin ◽  
Jincan Chen
Keyword(s):  
Heat Transfer ◽  
Power Output ◽  
Pressure Ratio ◽  
Heat Engine ◽  
Optimal Performance ◽  
Performance Characteristics ◽  
Heat Transfer Area ◽  
Total Heat Transfer ◽  
Heat Engines ◽  
Compression And Expansion

An irreversible cycle model of the Brayton heat engine is established, in which the irreversibilities resulting from the internal dissipation of the working substance in the adiabatic compression and expansion processes and the finite-rate heat transfer in the regenerative and constant-pressure processes are taken into account. The power output and efficiency of the cycle are expressed as functions of temperatures of the working substance and the heat sources, heat transfer coefficients, pressure ratio, regenerator effectiveness, and total heat transfer area including the heat transfer areas of the regenerator and other heat exchangers. The regenerative criteria are given. The power output is optimized for a given efficiency. The general optimal performance characteristics of the cycle are revealed. The optimal performance of the Brayton heat engines with and without regeneration is compared quantitatively. The advantages of using the regenerator are expounded. Some important parameters of an irreversible regenerative Brayton heat engine, such as the temperatures of the working substance at different states, pressure ratio, maximum value of the pressure ratio, regenerator effectiveness and ratios of the various heat transfer areas to the total heat transfer area of the cycle, are further optimized. The optimal relations between these parameters and the efficiency of the cycle are presented by a set of characteristic curves for some assumed compression and expansion efficiencies. The results obtained may be helpful to the comprehensive understanding of the optimal performance of the Brayton heat engines with and without regeneration and play a theoretical instructive role for the optimal design of a regenerative Brayton heat engine.

Power Performance of a Nonisentropic Brayton Cycle

1991 ◽  
Vol 113 (4) ◽  
pp. 501-504 ◽  
Author(s):  
C. Wu ◽  
R. L. Kiang
Keyword(s):  
Heat Transfer ◽  
Power Output ◽  
Finite Time ◽  
Heat Engine ◽  
Heat Transfer Analysis ◽  
Brayton Cycle ◽  
Power Performance ◽  
Engine Efficiency ◽  
Compression And Expansion ◽  
Cycle Efficiency

Work and power optimization of a Brayton cycle are analyzed with a finite-time heat transfer analysis. This work extends the recent flurry of publications in heat engine efficiency under the maximum power condition by incorporating nonisentropic compression and expansion. As expected, these nonisentropic processes lower the power output as well as the cycle efficiency when compared with an endoreversible Brayton cycle under the same conditions.

scholarly journals Modeling and Performance Optimization of an Irreversible Two-Stage Combined Thermal Brownian Heat Engine

Entropy ◽  
2021 ◽  
Vol 23 (4) ◽  
pp. 419
Author(s):  
Congzheng Qi ◽  
Zemin Ding ◽  
Lingen Chen ◽  
Yanlin Ge ◽  
Huijun Feng
Keyword(s):  
Power Output ◽  
Performance Optimization ◽  
External Load ◽  
Thermal Contact ◽  
Heat Engine ◽  
Design Parameters ◽  
Load Effect ◽  
Heat Engines ◽  
Heat Leakage ◽  
Steady Current

Based on finite time thermodynamics, an irreversible combined thermal Brownian heat engine model is established in this paper. The model consists of two thermal Brownian heat engines which are operating in tandem with thermal contact with three heat reservoirs. The rates of heat transfer are finite between the heat engine and the reservoir. Considering the heat leakage and the losses caused by kinetic energy change of particles, the formulas of steady current, power output and efficiency are derived. The power output and efficiency of combined heat engine are smaller than that of single heat engine operating between reservoirs with same temperatures. When the potential filed is free from external load, the effects of asymmetry of the potential, barrier height and heat leakage on the performance of the combined heat engine are analyzed. When the potential field is free from external load, the effects of basic design parameters on the performance of the combined heat engine are analyzed. The optimal power and efficiency are obtained by optimizing the barrier heights of two heat engines. The optimal working regions are obtained. There is optimal temperature ratio which maximize the overall power output or efficiency. When the potential filed is subjected to external load, effect of external load is analyzed. The steady current decreases versus external load; the power output and efficiency are monotonically increasing versus external load.

Performance Optimization and Parametric Analysis of a Class of Solar-Driven Heat Engines

2010 ◽  
Author(s):  
Houcheng Zhang ◽  
Lanmei Wu ◽  
Guoxing Lin
Keyword(s):  
Heat Transfer ◽  
Heat Loss ◽  
Performance Optimization ◽  
Solar Collector ◽  
Heat Engine ◽  
Working Fluid ◽  
Convection Heat ◽  
Combined System ◽  
Heat Engines ◽  
Internal Irreversibility

A class of solar-driven heat engines is modeled as a combined system consisting of a solar collector and a unified heat engine, in which muti-irreversibilities including not only the finite rate heat transfer and the internal irreversibility, but also radiation-convection heat loss from the solar collector to the ambience are taken into account. The maximum overall efficiency of the system, the optimal operating temperature of the solar collector, the optimal temperatures of the working fluid and the optimal ratio of heat transfer areas are calculated by using numerical calculation method. The influences of radiation-convection heat loss of the collector and internal irreversibility on the cyclic performances of the solar-driven heat engine system are revealed. The results obtained in the present paper are more general than those in literature and the performance characteristics of several solar-driven heat engines such as Carnot, Brayton, Braysson and so on can be directly derived from them.

Heat Transfer in Liquid-Coupled Indirect Heat Exchanger Systems

1975 ◽  
Vol 97 (4) ◽  
pp. 499-503 ◽  
Author(s):  
R. B. Holmberg
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Flow Rate ◽  
Liquid Flow ◽  
Rate Ratio ◽  
Liquid Flow Rate ◽  
Coupled System ◽  
Heat Transfer Area ◽  
Cold Side ◽  
Total Heat Transfer

The theory of liquid-coupled indirect heat exchanger systems has been studied to ascertain optimum criteria with respect to the coupling-liquid flow rate and the distribution of total heat transfer area between the hot-side and cold-side exchanger units in the case of counterflow arrangement. The optimum coupling-liquid capacity rate is derived and given as a function of the over-all capacity rate ratio and the Ntu ratio between the two exchanger units. For this optimum liquid capacity rate together with the proposed over-all number of transfer units, it is shown that the over-all heat transfer effectiveness of the liquid-coupled system can be expressed in the ordinary form for individual exchanger units in true counterflow.

Thermo-Mechanical Modeling of a Shape Memory Alloy Heat Engine

2011 ◽  
Author(s):  
Christopher B. Churchill ◽  
John Shaw
Keyword(s):  
Heat Transfer ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Heat Engine ◽  
The United States ◽  
Thermodynamic Efficiency ◽  
Low Grade ◽  
Heat Engines ◽  
Deformation Mechanics ◽  
Sma Spring

Two thirds of the energy generated in the United States is currently lost as waste heat, representing a potentially vast source of green energy. Low Carnot efficiency is an inherent limitation of extracting energy from low-grade thermal sources (temperature gradients near or below 100C), and SMA heat engines could be useful for those applications where low weight and packaging are overriding considerations. Although many shape memory alloy (SMA) heat engines have been proposed to harvest this energy, and a few have been built and demonstrated in past decades, they have not been commercially successful. Some of the barriers to commercialization include their perceived low thermodynamic efficiency, high material cost, low material durability, complexities when using fluid baths, and the lack of robust constitutive models and design tools. Recent advances, however, in SMA longevity, reductions in materials costs (as production volumes have increased), and a better understanding of SMA behavior have stimulated new research on SMA heat engines. The Lightweight Thermal Energy Recovery System (LighTERS) is an ongoing ARPA-E funded collaboration between General Motors, HRL Laboratories, Dynalloy, Inc., and the University of Michigan. In the LighTERS engine (a refinement of the Dr. Johnson engine), a closed loop SMA spring element generates mechanical power by pulling itself between alternating hot and cold air regions. The first known thermo-mechanical model for this type of heat engine was developed in three stages. First, the constitutive and heat transfer relationships of an SMA spring form were characterized experimentally. Second, those relationships were used as inputs in a steady-state model of the heat engine, including both convective heat transfer and large-deformation mechanics. Finally, the model was validated successfully against measurements of a experimental heat engine built at HRL Labs.

A Novel Hydraulic Heat Engine Based on Ferrofluid Displacer With Applications in Solar Power Generation

2017 ◽  
Author(s):  
Mohsen Saadat ◽  
Mehdi Mirzakhanloo ◽  
Pieter Gagnon ◽  
Mohammad-Reza Alam
Keyword(s):  
Heat Transfer ◽  
Power Density ◽  
Heat Engine ◽  
Closed Cycle ◽  
Dynamic Simulations ◽  
Solar Power Generation ◽  
Heat Engines ◽  
Stirling Engines ◽  
Transfer Capability ◽  
Order Of Magnitude

Conventional closed cycle heat engines — such as Stirling engines — have many advantages, such as high theoretical efficiency and the ability to produce useful work out of any heat source. However, they suffer from low power density due to poor heat transfer capability between the working gas and its surrounding walls. In this work, we proposed a new architecture where the solid displacer of a Stirling engine is replaced with a ferrofluid liquid displacer. In this approach, the relative displacer location with respects to the engine chamber is controlled (and stabilized) through a strong magnetic field generated by a permanent magnet. The liquid nature of the displacer allows the hot and cold chambers of the engine to be filled with porous material, improving the heat transfer by an order of magnitude. Additionally, this engine architecture mitigates sealing issues, can operate at higher pressures, and has naturally lubricating surfaces. A relatively simple configuration of this idea is modeled in this work. Exploratory dynamic simulations of this unoptimized architecture show a thermal efficiency of 21% and a power density of approximately 700W/lit.

scholarly journals Optimal temperatures and maximum power output of a complex system with linear phenomenological heat transfer law

2009 ◽  
Vol 13 (4) ◽  
pp. 33-40 ◽  
Author(s):  
Lingen Chen ◽  
Jun Li ◽  
Fengrui Sun
Keyword(s):  
Complex System ◽  
Heat Transfer ◽  
Power Output ◽  
Finite Time ◽  
Heat Engine ◽  
Thermal Capacity ◽  
Maximum Power ◽  
Finite Time Thermodynamics ◽  
Maximum Power Output ◽  
Different Temperatures

A complex system including several heat reservoirs, finite thermal capacity subsystems with different temperatures and a transformer (heat engine or refrigerator) with linear phenomenological heat transfer law [q ? ?(T -1)] is studied by using finite time thermodynamics. The optimal temperatures of the subsystems and the transformer and the maximum power output (or the minimum power needed) of the system are obtained.

HEAT TRANSFER ENHANCEMENT IN A RECTANGULAR COOLING CHANNEL WITH AIRFOIL SHAPED FINS

2020 ◽  
pp. 1-29
Author(s):  
Lesley Wright ◽  
Andrew F. Chen ◽  
Hao-Wei Wu ◽  
Je-Chin Han ◽  
Ching-pang Lee ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Surface Area ◽  
Total Heat ◽  
Cooling Channel ◽  
Heat Transfer Area ◽  
Transfer Enhancement ◽  
Total Heat Transfer ◽  
Cooling Passage

Abstract This paper experimentally investigates heat transfer in a cooling passage with airfoil shaped fins for channel Reynolds numbers 10,000 to 40,000. This study uses airfoil shaped fins, instead of circular or oblong-shaped pins, for heat transfer augmentation. The airfoil shaped fins have more surface area than traditional pins. Assuming they both provide similar internal surface heat transfer coefficients, airfoil shaped fins will perform better than circular or oblong fins due to increased surface area. There is a need to obtain the heat transfer enhancement and pressure drop penalty in this cooling passage with airfoil shaped fins. Results are compared to the same rectangular cooling channel with smooth surfaces. The heat transfer can be enhanced 6 to 8 times while pressure drop is increased 70 to 90 times, as compared with the same channel with a smooth surface. With the fins significantly increasing the heat transfer area, three different methods are proposed for analyzing the heat transfer enhancement: (a) using the smooth channel area with the endwall temperature, (b) combining the total heat transfer area with the endwall temperature, and (c) coupling the total heat transfer area with the area weighted, average temperature including both the endwall and fin temperatures. Finally, compared directly to round pins, the airfoil shaped fins incur similar pressure penalties while providing slightly less heat transfer. The airfoil shaped fins benefit from a significant increase in the heat transfer area, a characteristic similar to more narrow strip fins.

Introduction to the Comprex

1950 ◽  
Vol 17 (1) ◽  
pp. 47-53
Author(s):  
F. W. Barry
Keyword(s):  
Gas Turbine ◽  
Gas Flow ◽  
Pressure Ratio ◽  
Performance Characteristics ◽  
Simple Analysis ◽  
Compression And Expansion ◽  
Gas Turbine Cycle

Abstract This paper describes the construction and operation of a comprex, or pressure exchanger, together with its application to a gas-turbine cycle. A simple analysis is also developed, which is intended to indicate the performance characteristics of a comprex. This analysis shows that the pressure ratio, relative gas flow, and the ratio of the temperature of the leaving gas to that of the entering air are all functions of scavenging velocity and of the nature of the compression and expansion processes (as is shown graphically). Some irreversibility is found to be essential to the useful operation of a comprex. Finally, formulas for the major dimensions of a comprex are presented.

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