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N.e. Wijeysundera - One of the best experts on this subject based on the ideXlab platform.
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An irreversible-thermodynamic model for solar-powered absorption cooling systems
Solar Energy, 2000Co-Authors: N.e. WijeysunderaAbstract:The ideal three-Heat-Reservoir cycle with constant internal irreversibilities and external Heat transfer irreversibilities is used to model the absorption refrigeration machine of a solar operated absorption cooling system. Analytical expressions are obtained for the variation of the entropy transfer with storage tank temperature and the variation of the coefficient of performance (COP) with the cooling capacity of the plant. These expressions give the operating points for the maximum cooling capacity and the maximum COP. The results for ideal irreversible cycles are compared with those obtained by detailed simulation of the absorption cooling system. The effect of internal and external irreversibilities on the second-law efficiency of the plant is examined. The ideal cycles that include internal and external irreversibilities are found to give realistic limits and trends for the cooling capacity and the COP of solar powered absorption cooling systems.
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Simplified models for solar-powered absorption cooling systems
Renewable Energy, 1998Co-Authors: N.e. WijeysunderaAbstract:Ideal three-Heat-Reservoir cycles with constant internal irreversibilities and external Heat transfer irrevesibilities are used to obtain the performance limits of solar operated absorption cooling systems. Analytical expressions are obtained for the coefficient of performance (COP) and the cooling capacity of the plant. The results for ideal cycles are compared with those obtained by detailed simulation of the absorption machine. The ideal cycle models are found to give realistic upper limits for the cooling capacity and the COP of solar powered absorption cooling systems.
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Performance of three-Heat-Reservoir absorption cycles with external and internal irreversibilities
Applied Thermal Engineering, 1997Co-Authors: N.e. WijeysunderaAbstract:The ideal three-Heat-Reservoir (THR) model for absorption refrigeration cycles is extended to include external and internal ireversibilities. The operating point of the cycle is determined by equating the internal entropy generation to the net entropy transfer from the working fluid. The main features of the entropy transfer function are presented. Three empirical functions are used to model the internal entropy generation of the cycle. The parameters of the these functions are estimated by fitting data obtained by simulation to the predictions of the THR model. The THR model using a linear function or a logarithmic function for the internal entropy generation is able to reproduce performance data for single-stage and double-stage absorption systems with good accuracy. The THR model provides a convenient means for representing performance characteristics of absorption cooling systems over a wide range operating temperatures. It can be used in preliminary design studies and in larger simulation programmes in which the absorption machine is a sub-component.
Lingen Chen - One of the best experts on this subject based on the ideXlab platform.
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Entropy generation rate minimization for hydrocarbon synthesis reactor from carbon dioxide and hydrogen
International Journal of Heat and Mass Transfer, 2019Co-Authors: Lei Zhang, Shaojun Xia, Lingen Chen, Chao Wang, Huijun FengAbstract:Abstract The process of hydrocarbon synthesis from carbon dioxide and hydrogen in a fixed-bed reactor, a novel approach of converting renewable and distributed energy to high-energy-density liquid hydrocarbon fuels, is designed and optimized thermodynamically in the present study. With the minimum entropy generation rate (EGR) due to Heat transfer, frictional flow and chemical reactions as objective function, finite time thermodynamics (or entropy generation minimization) and optimal control theories are applied to find the minimum EGR along with the corresponding optimal paths of the carbon dioxide hydrogenation reactor. The results show that a reduction up to 26.29% can be achieved by optimizing the profile of the Heat Reservoir temperature outside the tube and inlet conditions, which is mainly due to a compromised decrease in the irreversibilities of chemical reactions and Heat transfer. The chemical driving forces of the FT (Fischer-Tropsch) reactions in the optimal reactors decrease considerably compared with those of the reference reactor under the operation of constant Heat Reservoir temperature. The results obtained in the present study can provide some theoretical guidelines for the optimal thermal design of the real-world reactor of hydrocarbon synthesis process from carbon dioxide and hydrogen.
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Modelling, Analyses and Optimization for Exergy Performance of an Irreversible Intercooled Regenerated Brayton CHP Plant: Part 1 — Thermodynamic Modelling and Parametric Analyses
Volume 6: Energy, 2017Co-Authors: Lingen Chen, Huijun Feng, Bo Yang, Zemin DingAbstract:A variable-temperature Heat Reservoir irreversible intercooling regenerated Brayton combined Heat and power (CHP) plant model is set up in this paper. The model considers the Heat transfer losses in all the Heat exchangers, the working substance pressure drop loss in the piping, and the expansion and compression losses in turbine and compressor. Exergy output rate and exergy efficiency are considered as the research targets, and their analytical formulae are obtained. The optimal performances are gotten by optimizing the intercooled pressure ratio and total pressure ratio. The influences of some important parameters on the performances are studied in detail. Besides, the relation of exergy output rate versus exergy efficiency is investigated, and the curve is loop-shaped one. The results indicate that optimum Heat capacity rate matching between the Heat Reservoir and working substance, and optimum Heat consumer required temperature exist respectively, which generate double-maximal exergy output rate and double-maximal exergy efficiency, respectively. The Heat conductance allocation optimization of all the Heat exchangers will be carried out in Part 2 of this paper.
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finite time thermodynamic studies on absorption thermodynamic cycles a state of the art review
Arabian Journal for Science and Engineering, 2013Co-Authors: Xiaoyong Qin, Lingen Chen, Fengrui SunAbstract:The state-of-the-art on the thermodynamic optimization of absorption thermodynamic cycles is presented in this paper. The review covers the endoreversible and irreversible three-Heat-Reservoir cycle models, four-Heat-Reservoir cycle models, four-temperature-level cycle models and other related cycles and methods on absorption refrigeration cycles, absorption Heat pump cycles and absorption Heat transformer cycles coupled to finite and infinite Heat capacity Reservoirs.
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Ecological, exergetic efficiency and Heating load optimizations for irreversible variable-temperature Heat Reservoir simple air Heat pump cycles
Indian Journal of Pure & Applied Physics, 2009Co-Authors: Yuehong Bi, Lingen ChenAbstract:Thermodynamic optimization of an irreversible air Heat pump with variable-temperature Heat Reservoirs and hot- and cold-side counter-flow Heat exchangers has been studied. The expressions of the Heating load, the exergetic efficiency and the ecological function of the Heat pump cycle are derived. Performance comparisons among exergetic efficiency optimization, ecological optimization and traditional Heating load optimization objectives are done. The effect of the pressure ratio of the compressor, the allocation of Heat exchanger inventory and the Heat capacity rate matching between the working fluid and the Heat Reservoirs on the optimal performance of the cycle has been investigated by detailed numerical examples. When the performance optimization of the cycle is carried out by selecting the pressure ratio, three optimization objectives give simultaneously attention to the coefficient of performance (COP). The pressure ratio should be the one that is little bigger than the optimum pressure ratio corresponding to maximum COP, however, the results of three optimization objectives are consistent by optimizing the allocation of Heat exchanger inventory and optimizing the Heat capacity rate matching between the working fluid and the Heat Reservoirs. The optimum allocations of Heat conductance are close to each other, and they are all less than 0.5. The results may provide guidelines for the design and optimization of practical air Heat pump plants.
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Ecological, exergetic efficiency and Heating load optimizations for endoreversible variable-temperature Heat Reservoir simple air Heat pump cycles
International Journal of Low-carbon Technologies, 2009Co-Authors: Yuehong Bi, Lingen ChenAbstract:This paper presents thermodynamic optimization of an endoreversible air Heat pump with variable-temperature Heat Reservoirs and hot- and cold-side counter-flow Heat exchangers. The expressions of the Heating load, the exergetic efficiency and the ecological function of the Heat pump cycle are derived. Performance comparisons among exergetic efficiency optimization objective, ecological optimization objective and traditional Heating load optimization objective are performed. The influences of the pressure ratio of the compressor, the allocation of Heat exchanger inventory and the Heat capacity rate matching between the working fluid and the Heat Reservoirs on the optimal performance of the cycle are investigated by detailed numerical examples. When the performance optimization of the cycle is carried out by selecting the pressure ratio, three optimization objectives give different results; however, the results of three optimization objectives are consistent by optimizing the allocation of Heat exchanger inventory and optimizing the Heat capacity rate matching between the working fluid and the Heat Reservoirs. The results may provide guidelines for the design and optimization of practical air Heat pump plants. Copyright The Author 2009. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org, Oxford University Press.
Fengrui Sun - One of the best experts on this subject based on the ideXlab platform.
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finite time thermodynamic studies on absorption thermodynamic cycles a state of the art review
Arabian Journal for Science and Engineering, 2013Co-Authors: Xiaoyong Qin, Lingen Chen, Fengrui SunAbstract:The state-of-the-art on the thermodynamic optimization of absorption thermodynamic cycles is presented in this paper. The review covers the endoreversible and irreversible three-Heat-Reservoir cycle models, four-Heat-Reservoir cycle models, four-temperature-level cycle models and other related cycles and methods on absorption refrigeration cycles, absorption Heat pump cycles and absorption Heat transformer cycles coupled to finite and infinite Heat capacity Reservoirs.
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Optimisation between cooling load and entropy-generation rate of an endoreversible four-Heat-Reservoir absorption refrigerator
International Journal of Ambient Energy, 2009Co-Authors: Guisheng Tao, Lingen Chen, Fengrui SunAbstract:SYNOPSIS An ecological criterion is introduced into the performance analysis and optimisation of an endoreversible four-Heat-Reservoir absorption refrigerator cycle with Newtonian Heat transfer law. The ecological optimisation criterion is set up based on the viewpoint of energy analysis. The optimal relationship between the ecological criterion and the (COP) coefficient of performance, the optimal relationship between the entropy generation rate and the COP, and the maximum ecological criterion and the corresponding COP, cooling load and entropy generation rate are derived by using finite-time thermodynamics. Moreover, the ecological criterion is compared with the cooling load criterion by numerical example. The results show that the ecological criterion is a significant one for the optimal design of absorption refrigerators.
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power optimization of an endoreversible closed intercooled regenerated brayton cycle coupled to variable temperature Heat Reservoirs
Applied Energy, 2005Co-Authors: Wenhua Wang, Lingen Chen, Fengrui SunAbstract:In this paper, in the viewpoint of finite-time thermodynamics and entropy-generation minimization are employed. The analytical formulae relating the power and pressure-ratio are derived assuming Heat-resistance losses in the four Heat-exchangers (hot- and cold-side Heat exchangers, the intercooler and the regenerator), and the effect of the finite thermal-capacity rate of the Heat Reservoirs. The power optimization is performed by searching the optimum Heat-conductance distributions among the four Heat-exchangers for a fixed total Heat-exchanger inventory, and by searching for the optimum intercooling pressure-ratio. When the optimization is performed with respect to the total pressure-ratio of the cycle, the maximum power is maximized twice and a [`]double-maximum' power is obtained. When the optimization is performed with respect to the thermal capacitance rate ratio between the working fluid and the Heat Reservoir, the double-maximum power is maximized again and a thrice-maximum power is obtained. The effects of the Heat Reservoir's inlet-temperature ratio and the total Heat-exchanger inventory on the optimal performance of the cycle are analyzed by numerical examples.
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Thermo-economic optimization of an endoreversible four-Heat-Reservoir absorption-refrigerator
Applied Energy, 2005Co-Authors: Xiaoyong Qin, Lingen Chen, Fengrui SunAbstract:Based on an endoreversible four-Heat-Reservoir absorption-refrigeration-cycle model, the optimal thermo-economic performance of an absorption-refrigerator is analyzed and optimized assuming a linear (Newtonian) Heat-transfer law applies. The optimal relation between the thermo-economic criterion and the coefficient of performance (COP), the maximum thermo-economic criterion, and the COP and specific cooling load for the maximum thermo-economic criterion of the cycle are derived using finite-time thermodynamics. Moreover, the effects of the cycle parameters on the thermo-economic performance of the cycle are studied by numerical examples.
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performance analysis for an irreversible variable temperature Heat Reservoir closed intercooled regenerated brayton cycle
Energy Conversion and Management, 2003Co-Authors: Wenhua Wang, Lingen Chen, Fengrui SunAbstract:In this paper, the theory of finite time thermodynamics is used in the performance analysis of an irreversible closed intercooled regenerated Brayton cycle coupled to variable temperature Heat Reservoirs. The analytical formulae for dimensionless power and efficiency, as functions of the total pressure ratio, the intercooling pressure ratio, the component (regenerator, intercooler, hot and cold side Heat exchangers) effectivenesses, the compressor and turbine efficiencies and the thermal capacity rates of the working fluid and the Heat Reservoirs, the pressure recovery coefficients, the Heat Reservoir inlet temperature ratio, and the cooling fluid in the intercooler and the cold side Heat Reservoir inlet temperature ratio, are derived. The intercooling pressure ratio is optimized for optimal power and optimal efficiency, respectively. The effects of component (regenerator, intercooler and hot and cold side Heat exchangers) effectivenesses, the compressor and turbine efficiencies, the pressure recovery coefficients, the Heat Reservoir inlet temperature ratio and the cooling fluid in the intercooler and the cold side Heat Reservoir inlet temperature ratio on optimal power and its corresponding intercooling pressure ratio, as well as optimal efficiency and its corresponding intercooling pressure ratio are analyzed by detailed numerical examples. When the Heat transfers between the working fluid and the Heat Reservoirs are executed ideally, the pressure drop losses are small enough to be neglected and the thermal capacity rates of the Heat Reservoirs are infinite, the results of this paper replicate those obtained in recent literature.
Chih Wu - One of the best experts on this subject based on the ideXlab platform.
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optimum distribution of Heat exchanger inventory and optimum thermal capacitance rate matching for power optimisation of a regenerated closed brayton cycle
International Journal of Energy Technology and Policy, 2007Co-Authors: Lingen Chen, Chih WuAbstract:The power output of the cycle is taken as objective for performance analysis and optimisation of an irreversible regenerated closed Brayton cycle coupled to variable-temperature Heat Reservoirs. The analytical formulae about the relations between power output and pressure ratio are derived with the Heat resistance losses in three Heat exchangers, the irreversible losses in the compressor and turbine, the pressure drop losses in the piping and system, and the effect of the finite thermal capacity rate of the Heat Reservoirs. The power output optimisation is performed by searching the optimum Heat conductance distribution among the three Heat exchangers for the fixed total Heat exchanger inventory, and by searching the optimum thermal capacitance rate matching between the working fluid and the Heat Reservoir.
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Cooling load and coefficient of performance optimizations for real air-refrigerators
Applied Energy, 2006Co-Authors: Youming Tu, Lingen Chen, Chih WuAbstract:Based on a simple irreversible variable-temperature Heat Reservoir air (Brayton) refrigeration cycle model, a performance analysis and optimization of a real air refrigerator is carried out using finite-time thermodynamics. To maximize the cooling load and the coefficient of performance (COP) of the cycle, the allocation of a fixed total Heat-exchanger inventory and thermal-capacity rate matching between the working fluid and Heat Reservoirs are optimized, respectively. The influences of pressure ratio, the total Heat-exchanger inventory, the efficiencies of the compressor and expander, the thermal capacity rate of the working fluid and the ratio of the thermal-capacity rates of the Heat Reservoirs on the performance of the cycle are shown by numerical examples. The results obtained provide guidances for the design of practical air-refrigeration plants.
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Performance of a four-Heat- Reservoir absorption refrigerator with Heat resistance and Heat leak
International journal of ambient energy, 2003Co-Authors: Tong Zheng, Fengrui Sun, Lingen Chen, Chih WuAbstract:SYNOPSIS On the basis of an endoreversible absorption refrigeration cycle model with Newton's Heat transfer law, an irreversible four-Heat-Reservoir cycle model is built by taking account of the Heat leak and Heat resistance losses. The fundamental optimal relation between the coefficient of performance (COP) and the cooling load, the maximum COP and the corresponding cooling load, as well as the maximum cooling load and the corresponding COP of the cycle coupled to constant-temperature Heat Reservoirs are derived by using finite-time thermodynamics. The optimal distribution relation of the Heat-transfer surface areas is also obtained. Moreover, the effects of the cycle parameters on the COP and the cooling load of the cycle are studied by detailed numerical examples. The results obtained herein are of importance to the optimal design and performance improvement of a four-Heat-Reservoir absorption refrigeration cycle.
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Optimal coefficient of performance and Heating load relationship of a three-Heat-Reservoir endoreversible Heat pump
Energy Conversion and Management, 1997Co-Authors: Lingen Chen, Chih WuAbstract:The relationship between optimal COP (coefficient of performance) and Heating load of a three-Heat-Reservoir endoreversible Heat pump (including both temperature amplifier and Heat amplifier cycles) with non-linear Heat transfer (phenomenological law in irreversible thermodynamics) is derived. The results presented in this paper are different from those obtained with a linear Heat transfer law. The relationships provide a theoretical basis for developing and utilizing a variety of three-Heat-Reservoir Heat pumps.
Fangming Jiang - One of the best experts on this subject based on the ideXlab platform.
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A novel flow-resistor network model for characterizing enhanced geothermal system Heat Reservoir
Frontiers in Energy, 2019Co-Authors: Jian Guo, Wenjiong Cao, Yiwei Wang, Fangming JiangAbstract:The fracture characteristics of a Heat Reservoir are of critical importance to enhanced geothermal systems, which can be investigated by theoretical modeling. This paper presents the development of a novel flow-resistor network model to describe the hydraulic processes in Heat Reservoirs. The fractures in the Reservoir are simplified by using flow resistors and the typically complicated fracture network of the Heat Reservoir is converted into a flow-resistor network with a reasonably simple pattern. For Heat Reservoirs with various fracture configurations, the corresponding flow-resistor networks are identical in terms of framework though the networks may have different section numbers and the flow resistors may have different values. In this paper, numerous cases of different section numbers and resistor values are calculated and the results indicate that the total number of flow resistances between the injection and production wells is primarily determined by the number of fractures in the Reservoir. It is also observed that a linear dependence of the total flow resistance on the number of fractures and the relation is obtained by the best fit of the calculation results. Besides, it performs a case study dealing with the Soultz enhanced geothermal system (EGS). In addition, the fracture numbers underneath specific well systems are derived. The results provide insight on the tortuosity of the flow path between different wells.
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an analytical method to determine the fluid rock Heat transfer rate in two equation thermal model for egs Heat Reservoir
International Journal of Heat and Mass Transfer, 2017Co-Authors: Wenbo Huang, Wenjiong Cao, Jian Guo, Fangming JiangAbstract:Abstract The two-equation thermal model could be an effective method for the simulation of thermal-hydrodynamic process in industry-scale EGS Heat Reservoirs. The conventional way of computing the Heat transfer rate between rock and fluid in the two-equation model is using Newton’s law of cooling with a constant equivalent solid-fluid Heat transfer coefficient. However, the present work reveals that this method is unable to precisely simulate EGS Heat extraction, in which the thermal resistance of solid plays an important role and the temperature of fluid is in rapid changing. Instead, we propose an analytical method to determine the Heat transfer rate between rock and fluid, in which variations of fluid and rock temperatures are adequately considered. Simulation cases with different meshes or using different thermal models corroborate that the proposed method improves the prediction accuracy of the two-equation model and makes the model to be more applicable for industrial-scale EGS simulations as a larger mesh size is allowed to be used in the simulation.
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a numerical study of egs Heat extraction process based on a thermal non equilibrium model for Heat transfer in subsurface porous Heat Reservoir
Heat and Mass Transfer, 2016Co-Authors: Jiliang Chen, Fangming JiangAbstract:With a previously developed numerical model, we perform a detailed study of the Heat extraction process in enhanced or engineered geothermal system (EGS). This model takes the EGS subsurface Heat Reservoir as an equivalent porous medium while it considers local thermal non-equilibrium between the rock matrix and the fluid flowing in the fractured rock mass. The application of local thermal non-equilibrium model highlights the temperature-difference Heat exchange process occurring in EGS Reservoirs, enabling a better understanding of the involved Heat extraction process. The simulation results unravel the mechanism of preferential flow or short-circuit flow forming in homogeneously fractured Reservoirs of different permeability values. EGS performance, e.g. production temperature and lifetime, is found to be tightly related to the flow pattern in the Reservoir. Thermal compensation from rocks surrounding the Reservoir contributes little Heat to the Heat transmission fluid if the operation time of an EGS is shorter than 15 years. We find as well the local thermal equilibrium model generally overestimates EGS performance and for an EGS with better Heat exchange conditions in the Heat Reservoir, the Heat extraction process acts more like the local thermal equilibrium process.
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a novel three dimensional transient model for subsurface Heat exchange in enhanced geothermal systems
International Communications in Heat and Mass Transfer, 2013Co-Authors: Fangming Jiang, Liang Luo, Jiliang ChenAbstract:Abstract Understanding the subsurface Heat exchange process in enhanced geothermal systems (EGS) is crucial to the efficiency of Heat extraction and the sustainable utilization of geothermal Reservoir. In the present work we develop a novel three-dimensional transient model for the study of the subsurface Heat exchange process in EGS. The novelty of this model is embodied by a couple of salient features. First, the geometry of interest physically consists of multiple domains: open channels for injection and production wells, the artificial Heat Reservoir, and the rock enclosing the Heat Reservoir, while computationally we treat it as a single-domain of multiple sub-regions associated with different sets of characteristic properties (porosity and permeability etc.). This circumvents typical difficulties about matching boundary conditions between sub-domains in traditional multi-domain approaches and facilitates numerical implementation and simulation of the complete subsurface Heat exchange process. Second, the Heat Reservoir is treated as an equivalent porous medium of a single porosity, while we consider thermal non-equilibrium between solid and fluid components and introduce two sets of Heat transfer equations to describe the Heat advection and conduction for fluid in rock apertures and the Heat conduction in rock matrix, respectively, thus enabling the simulation and analysis of convective Heat exchange between rock matrix and fluid flowing in the apertures. Case study with respect to an imaginary EGS demonstrates the validity and capability of the developed model.