The first and second law analysis on an organic Rankine cycle with ejector

In consideration of the low efficiency of the organic Rankine cycle (ORC) with low-grade heat source (LGHS), an organic Rankine cycle with ejector (EORC) and a double organic Rankine cycle (DORC) based on the ORC is introduced in this paper. The thermodynamic first law and second law analysis and comparison on the ORC, EORC and DORC cycles are conducted on the cycle’s power output, thermal efficiency, exergy loss and exergy efficiency. Water is chosen as the LGHS fluid, and the same temperature and mass flow rate of the water is the standard condition for the comparative analysis on the cycles. The emphasis is on the thermodynamic performance at the maximum net power output of the cycles. The results show the power output is higher in the EORC and DORC compared to the ORC. And the cycle’s exergy efficiency could be ranked from high to low: DORC > EORC > ORC.     

First and second law investigations of a new solar‐assisted thermodynamic cycle for triple effect refrigeration

This investigation is persuaded for the first and second law analyses of a new solar‐driven triple‐effect refrigeration cycle using Duratherm 600 oil (Duratherm Extended Life Fluid, NY, USA) as the heat transfer fluid is performed. The proposed cycle is an integration of ejector, absorption, and cascaded refrigeration cycles that could produce refrigeration output of different magnitude at different temperature simultaneously. Both exergy destruction and losses in each component and hence in the overall system are determined to identify the causes and locations of the thermodynamic imperfection. The effects of some influenced parameters such as hot oil outlet temperature, refrigerant turbine inlet pressure, and the evaporator temperature of ejector and cascaded refrigeration cycle have been observed on the first and second law performances. It is found that maximum irreversibility occurs in central receiver as 52.5% and the second largest irreversibility of 25% occurs in heliostat field. The second law efficiency of the solar driven triple effect refrigeration cycle is 2%, which is much lower than its first law efficiency of 11.5%. Analysis clearly shows that performance evaluation based on the first law analysis is inadequate and hence, more meaningful evaluation must be included in the second law analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermochemical H2 production via solar driven hybrid SrO/SrSO4 water splitting cycle

This article reports the thermodynamic efficiency analysis of the strontium oxide – strontium sulfate (SrO-SrS) water splitting cycle by applying the principles of the second law of thermodynamics and by utilizing the commercially available HSC Chemistry software. Initially, the thermodynamic equilibrium compositions allied with a) the thermal reduction of SrSO₄, b) H₂ production via water splitting reaction (through SrO re-oxidation) are recognized. Moreover, the temperatures desirable for performing the thermal reduction and the water splitting steps are determined. The consequence of the molar flow rate of Ar on the thermal reduction of SrSO₄ is also examined in detail. The effect of the thermal reduction and water splitting temperatures on the total solar energy input mandatory to run the cycle, re-radiation shortfalls from the cycle, heat energy emitted by the coolers and the water splitting reactor, and the cycle and the solar-to-fuel energy conversion efficiency (with heat recuperation) is scrutinized in detail. The attained outcomes specify that the cycle and the solar-to-fuel energy conversion efficiency up to 18.9 and 22.8% can be accomplished if the thermal reduction and the water splitting steps are conducted at 2380 and 1400 K (with 30% heat recuperation).     

Analysis of a combined power and refrigeration cycle by the exergy method

The exergy analysis method was applied in order to evaluate the new combined cycle proposed by Goswami [Solar thermal technology: present status and ideas for the future. Energy Sources 1998;20:137–45], using Hasan–Goswami–Vijayaraghavan parameters. This new combined cycle was proposed to produce both power and cooling simultaneously with only one heat source and using ammonia–water mixture as the working fluid. The simulation of the cycle was carried out in the process simulator ASPEN Plus. The Redlich–Kwong–Soave equation of state was used to calculate the thermodynamic properties. The cycle was simulated as a reversible as well as an irreversible process to clearly show the effect of the irreversibilities in each component of the cycle. At the irreversible process two cases were considered, changing the environmental temperature. However, in order to know the performance of the new cycle at different conditions of operation, the second irreversible case was analyzed varying the rectification temperatures, the isentropic efficiency of the turbine and the return temperature of the chilled water. Exergy effectiveness values of 53% and 51% were obtained for the irreversible cycles; with heat input requirements at temperatures of 125 and 150 °C. Solar collectors or waste heat are suggested as heat sources to operate the cycle.     

Performance analyses and improvement guidelines for organic Rankine cycles using R600a/R601a mixtures driven by heat sources of 100°C to 200°C

R600a/R601a mixtures are promising to be widely used in organic Rankine cycle (ORC) systems and also can promote the popularization of ORC technology. While, most of existing studies on ORC systems using R600a/R601a mixtures are based on certain heat source temperatures (generally below 150°C) and saturated vapor at the evaporator outlet. Variations in the optimal mixture composition and superheat degree of R600a/R601a mixtures with increasing heat source temperature remain indeterminate thus far, especially for heat sources above 150°C. Suitable approaches to further improve the system thermodynamic performance are also unclear. This study carried out a systematized analysis for subcritical ORC systems using R600a/R601a mixtures driven by heat sources of 100°C to 200°C, based on the first and second law analysis methods. Guidelines for selections of optimal mixture composition and cycle parameters were provided. Characteristics of exergy loss distribution were revealed to point out the crucial process to further improve the system thermodynamic performance. Results show that the effects of critical parameters on the selections of optimal mixture composition and evaporation pressure become remarkable for heat sources above approximately 160°C. A minimum superheat degree is optimal for heat sources below 170°C, whereas the optimal superheat degree may increase with increasing heat source temperature and R600a mass fraction for heat sources above 170°C. Moreover, reducing the exergy losses in the heat absorption process, turbine, and condenser is vital to further increase the heat‐work conversion efficiency for heat sources of approximately 100°C to 160°C, 170°C to 190°C, and 200°C, respectively.     

Parametric analysis and optimization for a combined power and refrigeration cycle

A combined power and refrigeration cycle is proposed, which combines the Rankine cycle and the absorption refrigeration cycle. This combined cycle uses a binary ammonia–water mixture as the working fluid and produces both power output and refrigeration output simultaneously with only one heat source. A parametric analysis is conducted to evaluate the effects of thermodynamic parameters on the performance of the combined cycle. It is shown that heat source temperature, environment temperature, refrigeration temperature, turbine inlet pressure, turbine inlet temperature, and basic solution ammonia concentration have significant effects on the net power output, refrigeration output and exergy efficiency of the combined cycle. A parameter optimization is achieved by means of genetic algorithm to reach the maximum exergy efficiency. The optimized exergy efficiency is 43.06% under the given condition.     

An analytical formula for the estimation of a rankine-cycle heat engine efficiency at maximum power

The authors develop an analytical formula for estimating the Rankine power cycle efficiency at maximum power, which can be extracted from the given mass flow rates of heating and cooling fluids. This formula does not need any detailed thermodynamic data. The accuracy of the procedure is shown by comparisons between analytical values and those calculated using detailed thermodynamic data. The results indicate that the thermal efficiency at maximum power depends primarily on the initial temperatures of the heating and cooling fluids and pinch-temperature differences between the working fluid and the heating and cooling fluids. The efficiency at maximum power provides a measure of the power available in a Rankine heat engine.     

Hot water cooled electronics: Exergy analysis and waste heat reuse feasibility

We report an experimental study on exergetically efficient electronics cooling using hot water as coolant. It is shown that water temperatures as high as 60 °C are sufficient to cool microprocessors with over 90% first law (energy based) efficiency. The chip used in our experiment is kept at temperatures of 80 °C or below so as not to exceed any allowable industrial specifications for maximum microprocessor chip temperature. The use of hot water as coolant will eliminate the requirement for chillers typically used in air-cooled data centers and, therefore, significantly reduce the power consumption. An exergy analysis shows that a six fold rise in second law (exergy based) efficiency is achieved by switching the water inlet temperature from 30 °C to 60 °C. The resulting high exergy at the heat sink outlet is a measure of the potential usefulness of the waste heat of data centers, thereby helping to design data centers with minimal carbon footprint. A new metric for the economic value of the recovered heat, based on costs for electricity and fossil fuels, heat recovery efficiency and an application specific utility function, is introduced to underscore the benefits of hot water cooling. This new concept shows that the economic value of the heat recovered from data centers can be much higher than its thermodynamic value.     

Hydrogen enrichment effects on the second law analysis of a lean burn natural gas engine

This paper presents a computational work aimed at investigating the effects of hydrogen addition on the exergy (or availability) balance in a lean burn natural gas spark ignition (SI) engine. A thermodynamic engine cycle simulation was extended to perform the exergy analysis. A zero dimensional, two-zone computational model of the engine operation was used for the closed part of the cycle. The results of the model were compared with experimental data to demonstrate the validation of the model. Exergetic terms, such as exergy transfer with heat, exergy transfer with work, irreversibilities, fuel chemical exergy, and total exergy, were computed based on principles of the second law. The exergetic (the second law) efficiency was also calculated. The results of exergy analysis show that increasing hydrogen content and lean burn have considerably affected the exergy transfers, irreversibilities and second law efficiency. With increasing hydrogen content, the irreversibility produced during combustion decreases, and the second-law efficiency sharply increases at near the lean limit.     

Hydrogen production through the sulfur–iodine cycle using a steam boiler heat source for risk and techno-socio-economic cost (RSTEC) reduction

A modified sulfur-iodine cycle with a non-nuclear heat source is proposed to enhance the economics and reduce risk and damage to society in terms of cost. A modified sulfur cycle employs a steam boiler as a heat source. The modified sulfur iodine cycle is composed of fewer reactions than the original. Thermodynamic feasibility analysis, economic evaluation, risk assessment, and socio-economic analysis are carried out on both the sulfur-iodine cycle and modified sulfur-iodine cycle, and the results are compared. 50.9 kJ/mol of steam was required for the minimum entropy range without the violation of the second law. The results show that the modified process is thermodynamically feasible with a positive entropy region at operating temperatures. The capital cost and operating cost are reduced by 40% and 29% for 1 kmol/h hydrogen production, respectively. The failure rate in the modified process is reduced by 64% compared to that of the original. The social health cost in the modified cycle is reduced by 41% compared to that of the original.     

Theoretical analysis of a thermodynamic cycle for power and heat production using supercritical carbon dioxide

A numerical study of a thermodynamic cycle is described: solar energy powered Rankine cycle using supercritical carbon dioxide as the working fluid for combined power and heat production. A model is developed to predict the cycle performance. Experimental data is used to verify the numerical formulation. Of interest in the present study is the thermodynamic cycle of 0.3–1.0 kW power generation and 1.0–3.0 kW heat output. The effects of the governing parameters on the performance are investigated numerically. The results show that the cycle has a power generation efficiency of somewhat above 20.0% and heat recovery efficiency of 68.0%, respectively. It is seen that the cycle performance is strongly dependent on the governing parameters and they can be optimized to provide maximum power, maximum heat recovery or a combination of both. The power generation and heat recovery are found to be increased with solar collector efficient area. The power generation is also increased with water temperature of the heat recovery system, but decreased with heat exchanging area. It is also seen that the effect of the water flow rate in the heat recovery system on the cycle performance is negligible.     

低温余热双循环发电系统的设计与优化

采用螺杆膨胀机双循环系统回收低温余热用于发电,拟合有机工质R245fa的热物性参数进行热力设计计算,并提出2种确定蒸发温度的方法,对单位质量的热源,分别以系统净功率、系统效率为优化目标,结合热力学第一定律与第二定律评价2种方法的优劣性.结果表明：随着蒸发温度的升高,存在最佳蒸发温度使得系统净功率最大,而系统热效率逐渐提高;系统净功率最大时,系统对余热能量回收较大,且回收量最大,故选择以系统净功率为目标作为蒸发温度的优化方法;基于蒸发压力恒定不变,证明了余热回收热量、系统净功率和系统效率随着过热度的增加而减少,应尽量采用饱和状态蒸气动力循环.     

Second Law Efficiency Analysis of Heat Exchangers

Analytical analysis of unbalanced heat exchangers is carried out to study the second law thermodynamic performance parameter through second law efficiency by varying length‐to‐diameter ratio for counter flow and parallel flow configurations. In a single closed form expression, three important irreversibilities occurring in the heat exchangers—namely, due to heat transfer, pressure drop, and imbalance between the mass flow streams—are considered, which is not possible in first law thermodynamic analysis. The study is carried out by giving special influence to geometric characteristics like tube length‐to‐diameter dimensions; working conditions like changing heat capacity ratio, changing the value of maximum heat capacity rate on the hot stream and cold stream separately and fluid flow type, i.e., laminar and turbulent flows for a fully developed condition. Further, second law efficiency analysis is carried out for condenser and evaporator heat exchangers by varying the effectiveness and number of heat transfer units for different values of inlet temperature to reference the temperature ratio by considering heat transfer irreversibility. Optimum heat exchanger geometrical dimensions, namely length‐to‐diameter ratio can be obtained from the second law analysis corresponding to lower total entropy generation and higher second law efficiency. Second law analysis incorporates all the heat exchanger irreversibilities. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21109     

On the recovery of LNG physical exergy by means of a simple cycle or a complex system

The maximum and minimum temperatures available limit the usable fraction (or Carnot efficiency) of a power cycle. The construction of LNG terminals and the need to vaporize LNG offers a thermal sink at a very much lower temperature than seawater. By using this thermal sink in a combined plant, it is possible to recover power from the vaporization of LNG.To this purpose, in this paper combined systems using LNG vaporization as low-temperature thermal sink are considered and their pros and cons are presented. A system utilizing waste energy as heat source and with a single working fluid is analyzed in detail. However, the use of a single fluid is not the best solution from a thermodynamic point of view. Thus, a series of cascading cycles is also outlined. In these systems, both the thermal source and the thermal sink are exploited as exergy sources.     

Performance improvement of a butane/octane absorption chiller

To improve the coefficient of performance (COP) of an absorption chiller working with the n-butane as refrigerant and the n-octane as absorbent, a thermodynamic analysis based on the first and the second law of thermodynamic is required. A simulation model is established to calculate the different thermodynamic properties of each point of the cycle such as compositions, flow rates, and temperatures. Heat transfer rates and some performance parameters are calculated using the first law analysis. Compared to an ideal machine, the performances are degraded because of the irreversibilities occurring in the different components of the machine. The second law analysis provides the entropy generation in each element and its contribution at the degradation of the COP as well as the total entropy generation of the system. We have proposed a modification of the initial configuration of the machine to reduce the energy losses occurring in the components of high entropy generation and to improve the performance. This recuperation increases the COP from 0.36 to 0.59 and the efficiency from 0.24 to 0.39.     

利用地热能的双压有机朗肯循环性能分析

根据地热利用系统回灌的要求,对热源在系统出口处的温度进行限制,研究了双压有机朗肯循环（DPORC）中的热量分配以及随运行时间的系统性能变化,针对5种不同的有机工质进行了计算分析。研究表明：系统热力学性能的最大值和有机工质流量的最小值在同样的k值（热源提供给高压循环的热量与热源为DPORC提供的热量比）处获得。而采用R600和R245fa系统的净输出功率较大;相比R601,采用R245fa可以将系统的净输出功率提高168.06 kW（5.55%）,热效率和效率分别可提高0.70%和2.86%。相比于单压有机朗肯循环（SPORC）,DPORC可以有效减小系统随运行时间净输出功率降低的幅度。经过40 a的运行,采用R601的系统净输出功率降低幅度最低（428.11 kW, 14.14%）,而采用R600系统的净输出功率降低幅度最大（526.75 kW, 16.55%）。     

Thermodynamic analysis and optimization of various power cycles for a geothermal resource

In this study, geothermal resources in Kutahya-Simav region having geothermal water at a temperature suitable for power generation is considered. The study is aimed to yield the method of the most effective use of the geothermal resource and a rational thermodynamic comparison of various cycles for a given resource. Maximum first law efficiencies vary between 6.9 to 10.6% while the second law efficiencies vary between 38.5 to 59.3% depending on the cycle considered. The maximum power output, the first law, and the second law efficiencies are obtained for Kalina cycle followed by combined cycle and binary cycle.     

Performance analysis and optimization of a new two-stage ejector-expansion transcritical CO2 refrigeration cycle

In this paper, a new two-stage configuration of ejector-expansion transcritical CO₂ (TRCC) refrigeration cycle is presented, which uses an internal heat exchanger and intercooler to enhance the performance of the new cycle. The theoretical analysis on the performance characteristics was carried out for the new cycle based on the first and second laws of thermodynamics. Based on the simulation results, it is found that, compared with the conventional two-stage transcritical CO₂ cycle, the COP and second law efficiency of the new two-stage cycle are about 12.5–21% higher than that of conventional two-stage cycle. It is also concluded that, the performance of the new two-stage transcritical CO₂ refrigeration can be significantly improved based on the presented new two-stage cycle. Hence the new two-stage refrigeration cycle is a promising refrigeration cycle from the thermodynamically and technical point of views. A regression analysis in terms of evaporator and gas cooler exit temperatures has been used, in order to develop mathematical expressions for maximum COP, optimum discharge and inter-stage pressures and entrainment ratio.     

Performance investigation in modified and improved augmented power generation Kalina cycle using Python

In the generation of electricity and cogeneration, Kalina cycle is considered as one of the competitors to organic Rankine cycle. With the simplicity and identical components of the binary mixture, Kalina system makes it more prominent to get developed and implemented as well with its environmental friendly associate. This work proposes a new improved Kalina cycle system to convert the natural source from sun to useful work. The proposed system utilizes heat source suitable to medium temperature heat applications. The proposed cycle have 2 units of solar collector, favoring an additional heat recovery and higher performance. Solar hot source temperature and pressure are 190°C and 45 bar with additional flow to the turbine of 1.15 kg/s. Energy and second law analysis have considered in evaluating the performance of the proposed plant. The energy analysis shows minimum value of net power, energy efficiency and plant efficiency as 241 kW, 15.5% and 5.7. The exergy analysis defines that, to the proposed cycle, the exergy efficiency initializes at 77% with more exergy destruction at turbine with 31%. With the parametric analysis, the system is amended to have the maximum values of energy and exergy performances as 18.5%, 7.1% and 85%. The parametric study identifies the optimum value of the inlet temperature and pressure of the pump and turbine.     

Theoretical and experimental investigation of an ammonia–water power and refrigeration thermodynamic cycle

A combined thermal power and cooling cycle proposed by Goswami is under intensive investigation, both theoretically and experimentally. The proposed cycle combines the Rankine and absorption refrigeration cycles, using a binary ammonia–water mixture as the working fluid. This cycle can be used as a bottoming cycle using waste heat from a conventional power cycle or an independent cycle using low temperature sources such as geothermal and solar energy. Initial parametric studies of the cycle showed the potential for the cycle to be optimized for first or second law efficiency, as well as work or cooling output. For a solar heat source, optimization of the second law efficiency is most appropriate, since the spent heat source fluid is recycled through the solar collectors. The optimization results verified that the cycle could be optimized using the generalized reduced gradient method. Theoretical results were extended to include realistic irreversibilities in the cycle, in preparation for the experimental study. An experimental system was constructed to demonstrate the feasibility of the cycle and to compare the experimental results with the theoretical simulation. Results showed that the vapor generation and absorption condensation processes work experimentally. The potential for combined turbine work and refrigeration output was evidenced in operating the system. Analysis of losses showed where improvements could be made, in preparation for further testing over a broader range of operating parameters.