Thermodynamic Performance Characteristics of a Brownian Microscopic Heat Engine Driven by Discrete and Periodic Temperature Field

A Brownian microscopic heat engine with a particle hopping on a one-dimensional lattice driven by adiscrete and periodic temperature field in a periodic sawtooth potential is investigated.In order to clarify the underlyingphysical pictures of the heat engine, the heat flow via the potential energy and the kinetic energy of the particles areconsidered simultaneously.Based on describing the jumps among the three states, the expressions of the efficiency andpower output of the heat engine are derived analytically.The general performance characteristic curves are plotted bynumerical calculation.It is found that the power output-efficiency curve is a loop-shaped one, which is similar to onefor a real irreversible heat engine.The influence of the ratio of the temperature of the hot and cold reservoirs and thesawtooth potential on the maximum efficiency and power output is analyzed for some given parameters.When the heatflows via the kinetic energy is neglected, the power output-efficiency curve is an open-shaped one, which is similar to onefor an endroeversible heat engine.

Thermodynamic Performance of Three-Terminal Hybrid Quantum Dot Thermoelectric Devices

We propose four different models of three-terminal quantum dot thermoelectric devices. From general thermodynamic laws, we examine the rew;rsible efficiencies of the four different models. Based on the master equation, the expressions for the efficiency and power output are derived and the corresponding working regions are determined. Moreover, we particularly analyze the performance of a three-terminal hybrid quantum dot refrigerator. The performance characteristic curves and the optimal performance parameters are obtained. Finally, we discuss the influence of the nonradiative effects on the optimal performance parameters in detail.

Thermodynamic Performance Assessment of IGCC Power Plants with Various Syngas Cleanup Processes

The present work explores how much IGCC can benefit from warm gas clean-up（WGCU）in comparison with conventional cold gas clean-up（CGCU） and what are the respective contributions of dry particulates removal and warm gas desulfurization （WGD） in a plant-wide point of view. Influences of key parameters of WGD on ther- modynamic performance of IGCC plant including desulfurization temperature, oxygen concentration in the re- generation stream, and H2S removal efficiency are discussed. It is obtained that the net efficiency of IGCC with full WGCU experiences an improvement of 1.77 percentage points compared with IGCC with full CGCU. Of which, dry particulates removal without water scrubber contributes about 1 percentage point. The influence of desulfurization temperature on thermodynamic performance of IGCC with WGD is weak especially when it is higher than about 350~C, which indicates that more focus should be put on investment cost, technical feasibility and sorbent stability for the selection of optimal operation temperature. Generally, 2%-3% of oxygen concentra- tion in the regeneration stream might be reasonable in a thermodynamic performance point of view. In addition, the improvement of 0.31 percentage points can be obtained by removal of H2S in the syngas from 27 ppm to 3 ppm.

Thermodynamic Performance Comparison and Optimization of sCO_(2)Brayton Cycle,tCO_(2)Brayton Cycle and tCO_(2)Rankine Cycle

In this paper,to further improve thermodynamic performance of supercritical carbon dioxide cycle,simple/recompression transcritical carbon dioxide Brayton cycle(STBC/RTBC)and simple/recompression transcritical carbon dioxide Rankine cycle(STRC/RTRC)are proposed.Thermal and exergy performance analysis and optimization for the above four transcritical CO_(2)cycles and simple/recompression supercritical cycle(SSBC/RSBC)are conducted.The effect of key thermodynamic parameters on those CO_(2)cycle performance is studied.Results indicate that the improvements of thermodynamic performance of CO_(2)cycle are obvious when transcritical Brayton and Rankine cycle are applied in it.Within the same range of optimization variables,the maximum thermal efficiency improvements of RTRC and RTBC are 4.98%and 3.6%,and maximum exergy efficiency improvements of RTRC and RTBC are 7.08%and 5.13%when compared with RSBC.Moreover,the thermodynamic performances of STBC and STRC are also outstanding than that of SSBC.This work provides a way to further improve the thermodynamic performance of CO_(2)power cycle.

Thermodynamic Performances of[mmim]DMP/Methanol Absorption Refrigeration

In order to study the theoretical cycle characteristic of [mmim]DMP （1-methyl-3-methylimidazolium dimethyl- phosphate）/methanol absorption refrigeration, the modified UNIFAC group contribution model and the Wilson model are established through correlating the experimental vapor pressure data of [mmim]DMP/methanol at T= 280~370 K and methanol mole fraction x= 0.529-0.965. Thermodynamic performances of absorption refrigera- tion utilizing [mmim]DMP/methanol, LiBr/H20 and H20/NH3 are investigated and compared with each other under the same operating conditions. From the results, some conclusions are obtained as follows： 1） the circula- tion ratio of the [mmim]DMP/methanol absorption refrigeration is higher than that of the LiBr/H2O absorption refrigeration, but still can be acceptable and tolerable. 2） The COP of the [mmim]DMP/methanol absorption refrigeration is smaller than that of the LiBr/H2O absorption refrigeration, while it is higher than that of the H2O/NH3 absorption refrigeration under most operating conditions. 3） The [mmim]DMP/methanol absorption refrigeration are still available with high COP when the heat source temperature is too high to drive LiBr/H2O absorption refrigeration.

Analysis of the thermodynamic performance limits of the organic Rankine cycle in low and medium temperature heat source applications

In this paper,an exploration of the practical thermodynamic performance limits of the organic Rankine cycle(ORC)under working fluid and cycle parameter restrictions is presented.These performance limits are more realistic benchmarks for the thermodynamic cycle than the efficiency of the Carnot cycle.Subcritical ORC configuration with four typical case studies that are related to temperature ranging from 373.15 to 673.15 K is taken into account.The ORC is defined by its cycle parameters and working fluid characteristic properties.The cycle parameters involve evaporation temperature(T_(eva)),condensation temperature(T_(con))and superheat degree(ΔT_(sup)),while the working fluids are represented by the characteristic properties including critical temperature(T_(c)),critical pressure(p_(c)),acentric factor(ω),and molar ideal gas isobaric heat capacity based on the principle of corresponding states.Subsequently,Pareto optimum solutions for obtained hypothetical working fluids and cycle parameters are achieved using multi-objective optimization method with the consideration of both thermal efficiency(η_(th))and volumetric power output(VPO).Finally,sensitivity analysis of the working fluid characteristic properties is conducted,and the second law of thermodynamics analysis,especially the applicability of entropy generation minimization,is performed.The results show that the current commonly used working fluids are widely scattered below the Pareto front that represents the tradeoff betweenη_(th) and VPO for obtained hypothetical fluids.T_(eva) and T_(con) are the most dominant cycle parameters,while T_(c) and ωtend to be the most dominant characteristic property parameters.The entropy generation minimization does not give the same optimal results.

Thermodynamic and Techno-economic Analysis of a Triple-pressure Organic Rankine Cycle: Comparison with Dual-pressure and Single-pressure ORCs

Investigation of a triple-pressure organic Rankine cycle(TPORC) using geothermal energy for power generation with the net power output of the TPORC analyzed by varying the evaporation pressures, pinch temperature differences(tpp) and degrees of superheat(tsup) aimed to find the optimum operation conditions of the system. The thermodynamic performance of the TPORC was compared with a dual-pressure organic Rankine cycle(DPORC) and a single-pressure ORC(SPORC) for geofluid temperatures ranging from 100°C to 200°C, with particular reference to the utilization of a hot dry rock(HDR) geothermal resource. Thermodynamic performances of the TPORC system using eight different organic working fluids have also been investigated in terms of the net power outputs. Results show that a higher geofluid mass flow rate can make a considerable contribution to shortening the payback period(PBP) as well as to decreasing the levelized electricity cost(LEC), especially when the geofluid temperature is low. For the temperature range investigated, the order from high to low based on thermodynamic and techno-economic performances is found to be TPORC > DPORC > SPORC. In terms of using geothermal resources within the given temperatures range(100°C–200°C), the TPORC system can be a better choice for geothermal power generation so long as the wellhead geofluid temperature is between 140°C and 180°C.

Microstructure, hydrogen storage thermodynamics and kinetics of La_5Mg_(95-x)Ni_x(x=5, 10, 15) alloys

The microstructure, hydrogen storage thermodynamics and kinetics of La5Mg95-xNix (x=5, 10, 15) ternary alloys with different Ni contents were investigated. The evolutions of the microstructure and phase of experimental alloys were characterized by X-ray diffractometry and scanning electron microscopy. The hydrogen storage kinetics and thermodynamics, and P-C-I curves were tested using a Sievert apparatus. It is found that increasing Ni content remarkably improves hydrogen storage kinetics but reduces the hydrogen storage capacity of alloys. The highest hydrogen absorption/desorption rate is observed in the La5Mg80Ni15 alloy, with the lowest hydrogen desorption activation value being 57.7 kJ/mol. By means of P-C-I curves and the van’t Hoff equation, it is determined that the thermodynamic performance of the alloy is initially improved and then degraded with increasing Ni content. The La5Mg85Ni10 alloy has the best thermodynamics properties with a hydrogenation enthalpy of -72.1 kJ/mol and hydrogenation entropy of -123.2 J/(mol·K).

不同工况和应用场景下CAES-CFP三联产系统特性分析

To meet the goal of worldwide decarbonization,the transformation process toward clean and green energy structures has accelerated.In this context,coal-fired power plant(CFPP)and large-scale energy storage represented by compressed air energy storage(CAES)technology,are tasked with increasing renewable resource accommodation and maintaining the power system security.To achieve this,this paper proposes the concept of a CFPP-CAES combined cycle and a trigenerative system based on that.Considering the working conditions of the CFPP,thermal characteristics of three typical operation modes were studied and some general regularities were identified.The results of various potential integration schemes discussion indicated that extracting water from low-temperature points in the feedwater system to cool pressurized air and simultaneously increase the backwater temperature is beneficial for improving performance.In addition,preheating the pressurized air before the air expanders via lowgrade water in the feedwater system as much as possible and reducing extracted steam contribute to increasing the efficiency.With the optimal integration scheme,2.85 tonnes of coal can be saved per cycle and the round-trip efficiency can be increased by 2.24%.Through the cogeneration of heat and power,the system efficiency can reach 77.5%.In addition,the contribution degree of the three compression heat utilization methods to the performance improvement ranked from high to low,is preheating the feedwater before the boiler,supplying heat,and flowing into the CFPP feedwater system.In the cooling energy generation mode,the system efficiency can be increased to over 69%.Regardless of the operation mode,the benefit produced by integration is further enhanced when the CFPP operates at higher operating conditions because the coupling points parameters are changed.In addition,the dynamic payback period can be shortened by 11.33 years and the internal rate of return increases by 5.20%under a typical application scenario.Regarding the effect of different application scenarios in terms of economics,investing in the proposed system is more appropriate in regions with multiple energy demands,especially heating demand.These results demonstrate the technical advantages of the proposed system and provide guiding principles for its design,operation,and project investment.

Efficiency analysis of trilateral-cycle power systems for waste heat recovery-to-power generation

Numerous innovative heat recovery-to-power technologies have been resourcefully and technologically exploited to bridge the growing gap between energy needs and its sustainable and affordable supply.Among them,the proposed trilateral-cycle(TLC) power system exhibits high thermodynamic efficiency during heat recovery-to-power from low-to-medium temperature heat sources.The TLCs are proposed and analysed using n-pentane as working fluid for waste heat recovery-to-power generation from low-grade heat source to evaluate the thermodynamic efficiency of the cycles.Four different single stage TLC configurations with distinct working principles are modelled thermodynamically using engineering equation solver.Based on the thermodynamic framework,thermodynamic performance simulation and efficiency analysis of the cycles as well as the exergy efficiencies of the heating and condensing processes are carried out and compared in their efficiency.The results show that the simple TLC,recuperated TLC,reheat TLC and regenerative TLC operating at subcritical conditions with cycle high temperature of 473 K can attain thermal efficiencies of 21.97%,23.91%,22.07% and 22.9%,respectively.The recuperated TLC attains the highest thermodynamic efficiency at the cycle high temperature because of its lowest exergy destruction rates in the heat exchanger and condenser.The efficiency analysis carried out would assist in guiding thermodynamic process development and thermal integration of the proposed cycles.

Multi-objective evolutionary optimization and thermodynamics performance assessment of a novel time-dependent solar Li-Br absorption refrigeration cycle

This research paper aims to perform dynamics analysis,3E assessment including energy,exergy,exergoeconomic,and the multiobjective evolutionary optimization on a novel solar Li-Br absorption refrigeration cycle.The research is time-dependent,owing to solar radiation variability during different timelines.Theoretically,all the necessary thermodynamic,energy,and exergy equations are applied initially.This is followed by the thermoeconomic analysis,which takes place after defining the designing variables during the thermoeconomic optimization process and is presented together with the economic relations of the system and its thermoeconomic characteristics.Furthermore,the sensitivity analysis is undertaken,the source of system inefficiency is determined,the multi-objective evolutionary optimization of the whole system is carried out,and the optimal values are compared with the primary stage.Engineering Equation Solver(EES)software has been used to accomplish comprehensive analyses.As part of the validation process,the results of the research are compared with those published previously and are found to be relatively consistent.

Power Generation Enhancement in a Solar Energy and Biomass-Based Distributed Energy System using H_(2)O/CO_(2)Hybrid Gasification

A new solar energy and biomass-based distributed energy system using H_(2)O/CO_(2)hybrid gasification is proposed,and their complementarity to enhance the system's energy efficiency is investigated and shown.In the system,concentrated solar energy is used to provide heat for biomass gasification;two gasifying agents(H_(2)O and CO_(2))are adopted to enhance syngas yields,and the produced solar fuel is further burned for power production in a combined cycle plant.Results show that CO share in gasification products is remarkably increased with the increment of CO_(2)/H_(2)O mole ratio caused by the boudouard reaction with the consumption of fixed carbon,while the H_(2)share is decreased;the optimal solar-to-fuel efficiency,27.88%,is achieved when the temperature and CO_(2)/H_(2)O mole ratio are 1050℃and 0.45,respectively.The emission reduction rate of CO_(2)in the system under design conditions is reduced by 2.31%compared with that using only H_(2)O agent.The annual power production of the system is increased by 1.39%,and the thermodynamic and environmental performances are significantly improved.Moreover,an economic assessment is conducted to forecast the technical feasibility of the hybrid gasification technology.This work provides a promising route to improving the thermochemical utilization efficiency of solar energy and solid fuel.

Integration of a thermochemical energy system driven by solar energy and biomass for natural gas and power production

Energy systems with multi-energy product outputs driven by renewable energy sources are becoming increasingly popular.To satisfy the diversification of energy use forms in China,this study proposes a new thermochemical energy system driven by solar energy and biomass for natural gas and power production.In this system,syngas from solar-driven biomass gasification is used to synthesize natural gas,whereas the unreacted syngas is burned directly in a combined cycle for power generation.To adjust the production capacity of the system,a shift reaction was used to change the H_(2)/CO ratio in the syngas.The biomass gasification model was experimentally verified,and the thermodynamic performance of the system was studied numerically.The results showed that the production rate of natural gas,with a heat value of 714.88 k J/mol,was approximately 0.306 m^(3)-SNG/kg-bio,and the primary energy efficiency was 47%.The new system showed a good energy-saving potential of 15.29%.Parametric analysis indicated that an increase in the gasification temperature led to a reduction in the natural gas production and an increase in the power output of the system,with a maximum energy efficiency of 66.72%at gasification temperature of 1050°C.With an increase in the syngas share entering the transfer reactor,the natural gas production rate and energy efficiency of the system were improved with an optimum share of approximately 0.55,thereby facilitating the development and optimization of operation strategies.This study provides a promising way to increase the share of renewable energy instead of fossil fuels.