Absorption heat pump attracts increasing attention due to itsadvantages in low grade thermal energy utilization. It can be appliedfor waste heat reuse to save energy consumption, reduce environmentpollution, and bring considerable economic benefit. In this paper,three important aspects for absorption heat pump for waste heat reuseare reviewed. In the first part, different absorption heat pump cyclesare classified and introduced. Absorption heat pumps for heat amplificationand absorption heat transformer for temperature upgrading are included.Both basic single effect cycles and advanced cycles for better performanceare introduced. In the second part, different working pairs, includingthe water based working pairs, ammonia based working pairs, alcoholbased working pairs, and halogenated hydrocarbon based working pairs,for absorption heat pump are classified based on the refrigerant.In the third part, the applications of the absorption heat pump andabsorption heat transformer for waste heat reuse in different industriesare introduced. Based on the reviews in the three aspects, essentialsummary and future perspective are presented at last.

Solar fuel is one of the ideal energy sources in the future.The synergy of photo and thermal effects leads to a new approach tohigher solar fuel production under relatively mild conditions. Thispaper reviews different approaches for solar fuel production fromspectrum-selective photo-thermal synergetic catalysis. The reviewbegins with the meaning of synergetic effects, and the mechanismsof spectrum-selectivity and photo-thermal catalysis. Then, from atechnical perspective, a number of experimental or theoretical worksare sorted by the chemical reactions and the sacrificial reagentsapplied. In addition, these works are summarized and tabulated basedon the operating conditions, spectrum-selectivity, materials, andproductivity. A discussion is finally presented concerning futuredevelopment of photo-thermal catalytic reactions with spectrum-selectivity.

Research on applying a supercritical carbon dioxide power cycle(S-CO₂) to concentrating solar power (CSP)instead of a steam Rankine cycle or an air Brayton cycle has beenrecently conducted. An S-CO₂ system is suitablefor CSP owing to its compactness, higher efficiency, and dry-coolingcapability. At the Korea Institute of Energy Research (KIER), to implementan S-CO₂ system, a 10 kWe class test loop witha turbine-alternator-compressor (TAC) using gas foil bearings wasdeveloped. A basic sub-kWe class test loop with a high-speed radialtype turbo-generator and a test loop with a capability of tens ofkWe with an axial type turbo-generator were then developed. To solvethe technical bottleneck of S-CO₂ turbomachinery,a partial admission nozzle and oil-lubrication bearings were usedin the turbo-generators. To experience the closed-power cycle anddevelop an operational strategy of S-CO₂ operatedat high pressure, an organic Rankine cycle (ORC) operating test usinga refrigerant as the working fluid was conducted owing to its operationalcapability at relatively low-pressure conditions of approximately30 to 40 bar. By operating the sub-kWe class test loop using R134aas the working fluid instead of CO₂, an averageturbine power of 400 W was obtained.

Solar multiple (SM) and thermal storage capacity are two keydesign parameters for revealing the performance of direct steam generation(DSG) solar power tower plant. In the case of settled land area, SMand thermal storage capacity can be optimized to obtain the minimumlevelized cost of electricity (LCOE) by adjusting the power generationoutput. Taking the dual-receiver DSG solar power tower plant witha given size of solar field equivalent electricity of 100 MW_e in Sevilla as a reference case, the minimum LCOE is21.77 ￠/kWh_e with an SM of 1.7 and a thermalstorage capacity of 3 h. Besides Sevilla, two other sites are alsointroduced to discuss the influence of annual DNI. When compared withthe case of Sevilla, the minimum LCOE and optimal SM of the San Josesite change just slightly, while the minimum LCOE of the Bishop sitedecreases by 32.8% and the optimal SM is reduced to 1.3. The influenceof the size of solar field equivalent electricity is studied as well.The minimum LCOE decreases with the size of solar field, while theoptimal SM and thermal storage capacity still remain unchanged. Inaddition, the sensitivity of different investment in sub-system isinvestigated. In terms of optimal SM and thermal storage capacity,they can decrease with the cost of thermal storage system but increasewith the cost of power generation unit.

This paper presents an experimental evaluation of a speciallydesigned falling particle receiver. A quartz tube was used in thedesign, with which the particles would not be blown away by wind.Concentrated solar radiation was absorbed and converted into thermalenergy by the solid particles flowed inside the quartz tube. Severalexperiments were conducted to test the dynamic thermal performanceof the receiver on solar furnace system. During the experiments, themaximum particle temperature rise is 212°C, with an efficiencyof 61.2%, which shows a good thermal performance with a falling distanceof 0.2 m in a small scale particle receiver. The average outlet particletemperature is affected by direct normal irradiance (DNI) and otherfactors such as wind speed. The solid particles obtain a larger viscositywith a higher temperature while smaller solid particles are easierto get stuck in the helix quartz tube. The heat capacity of the siliconcarbide gets larger with the rise of particle temperature, becauseas the temperature of solid particles increases, the temperature riseof the silicon carbide decreases.

This paper investigated radiation heat transfer and temperaturedistributions of solar thermochemical reactor for syngas productionusing the finite volume discrete ordinate method (fvDOM) and P1 approximationfor radiation heat transfer. Different parameters including absorptivity,emissivity, reflection based radiation scattering, and carrier gasflow inlet velocity that would greatly affect the reactor thermalperformance were sufficiently investigated. The fvDOM approximationwas used to obtain the radiation intensity distribution along thereactor. The drop in the temperature resulted from the radiation scatteringwas further investigated using the P1 approximation. The results indicatedthat the reactor temperature difference between the P1 approximationand the fvDOM radiation model was very close under different operatingconditions. However, a big temperature difference which increasedwith an increase in the radiation emissivity due to the thermal non-equilibriumwas observed in the radiation inlet region. It was found that theincident radiation flux distribution had a strong impact on the temperaturedistribution throughout the reactor. This paper revealed that thetemperature drop caused by the boundary radiation heat loss shouldnot be neglected for the thermal performance analysis of solar thermochemicalreactor.

In this paper, the simulation approach and exergy analysis ofmulti-stage compression high temperature heat pump (HTHP) systemswith R1234ze(Z) working fluid are conducted. Both the single-stageand multi-stage compression cycles are analyzed to compare the systemperformance with 120°C pressurized hot water supply based uponwaste heat recovery. The exergy destruction ratios of each componentfor different stage compression systems are compared. The resultsshow that the exergy loss ratios of the compressor are bigger thanthat of the evaporator and the condenser for the single-stage compressionsystem. The multi-stage compression system has better energy and exergyefficiencies with the increase of compression stage number. Comparedwith the single-stage compression system, the coefficient of performance(COP) improvements of the two-stage and three-stage compression systemare 9.1% and 14.6%, respectively. When the waste heat source temperatureis 60°C, the exergy efficiencies increase about 6.9% and 11.8%for the two-stage and three-stage compression system respectively.

The present paper aims at exploring a hybrid absorption-compressionheat pump (HAC-HP) to upgrade and recover the industrial waste heatin the temperature range of 60°C–120°C. The new HAC-HPsystem proposed has a condenser, an evaporator, and one more solutionpump, compared to the conventional HAC-HP system, to allow flexibleutilization of energy sources of electricity and waste heat. In thesystem proposed, the pressure of ammonia-water vapor desorbed in thegenerator can be elevated by two routes; one is via the compressionof compressor while the other is via the condenser, the solution pump,and the evaporator. The results show that more ammonia-water vaporflowing through the compressor leads to a substantial higher energyefficiency due to the higher quality of electricity, however, onlya slight change on the system exergy efficiency is noticed. The temperaturelift increases with the increasing system recirculation flow ratio,however, the system energy and exergy efficiencies drop towards zero.The suitable operation ranges of HAC-HP are recommended for the wasteheat at 60°C, 80°C, 100°C, and 120°C. The recirculationflow ratio should be lower than 9, 6, 5, and 4 respectively for thesewaste heat, while the temperature lifts are in the range of 9.8°C–27.7°C, 14.9°C–44.1 °C, 24.4°C–64.1°C,and 40.7°C–85.7°C, respectively, and the system energyefficiency are 0.35–0.93, 0.32–0.90, 0.25–0.85,and 0.14–0.76.

Exergy loss analysis was conducted to identify the irreversibilityin each component of the isopropanol-acetone-hydrogen chemical heatpump (IAH-CHP). The results indicate that the highest irreversibilityon a system basis occurs in the distillation column. Moreover, theeffect of operating parameters on thermodynamic performances of theIAH-CHP was studied and the optimal conditions were obtained. Finally,the potential methods to reduce the irreversibility of the IAH-CHPsystem were investigated. It is found that reactive distillation isapromising alternative. The enthalpy and exergy efficiency of theIAH-CHP with reactive distillation increases by 24.1% and 23.2%, respectively.

A solid sorption combined cooling and power system driven byexhaust waste heat is proposed, which consists of a MnCl₂ sorption bed, a CaCl₂ sorptionbed, an evaporator, a condenser, an expansion valve, and a scrollexpander, and ammonia is chosen as the working fluid. First, the theoreticalmodel of the system is established, and the partitioning calculationmethod is proposed for sorption beds. Next, the experimental systemis established, and experimental results show that the refrigeratingcapacity at the refrigerating temperature of –10°C and theresorption time of 30 min is 1.95 kW, and the shaft power is 109.2W. The system can provide approximately 60% of the power for the evaporatorfan and the condenser fan. Finally, the performance of the systemis compared with that of the solid sorption refrigeration system.The refrigerating capacity of two systems is almost the same at thesame operational condition. Therefore, the power generation processdoes not influence the refrigeration process. The exergy efficiencyof the two systems is 0.076 and 0.047, respectively. The feasibilityof the system is determined, which proves that this system is especiallysuitable for the exhaust waste heat recovery.

The development of engine waste heat recovery technologies attractsever increasing interests due to the rising strict policy requirementsand environmental concerns. This paper presented the study of enginecoolant and exhaust heat recovery using organic Rankine cycle (ORC).Eight working fluids were selected to evaluate and compare the performanceof the integrated waste heat recovery system. Rather than the conventionalengine ORC system mainly focusing on the utilization of exhaust energy,this work proposed to fully use the engine coolant energy by changingthe designed parameters of the ORC system. The case study selecteda small engine as the heat source to drive the ORC system using ascroll expander for power production. The evaluation results suggestthat under the engine rated condition, the solution to fully recoverthe engine coolant energy can achieve a higher power generation performancethan that of the conventional engine ORC system. The results suggestthat adding a recuperator to the ORC system can potentially improvethe system performance when the working fluids are dry and the overalldumped heat demand of the system can be reduced by 12% under optimalconditions. When the ORC evaporating and condensing temperature arerespectively set at 85°C and 30°C, the integrated engine wasteheat recovery system can improve the overall system efficiency by9.3% with R600, R600a or n-Pentaneas the working fluid.

Surface tension plays a core role in dominating various surface and interface phenomena. For liquid metals with high melting temperature, a profound understanding of the behaviors of surface tension is crucial in industrial processes such as casting, welding, and solidification, etc. Recently, the room temperature liquid metal (RTLM) mainly composed of gallium-based alloys has caused widespread concerns due to its increasingly realized unique virtues. The surface properties of such materials are rather vital in nearly all applications involved from chip cooling, thermal energy harvesting, hydrogen generation, shape changeable soft machines, printed electronics to 3D fabrication, etc. owing to its pretty large surface tension of approximately 700 mN/m. In order to promote the research of surface tension of RTLM, this paper is dedicated to present an overview on the roles and mechanisms of surface tension of liquid metal and summarize the latest progresses on the understanding of the basic knowledge, theories, influencing factors and experimental measurement methods clarified so far. As a practical technique to regulate the surface tension of RTLM, the fundamental principles and applications of electrowetting are also interpreted. Moreover, the unique phenomena of RTLM surface tension issues such as surface tension driven self-actuation, modified wettability on various substrates and the functions of oxides are discussed to give an insight into the acting mechanism of surface tension. Furthermore, future directions worthy of pursuing are pointed out.

The rapid depletion of fossil fuel and growing demand necessitatesresearchers to find alternative fuels which are clean and sustainable.The need for finding renewable, low cost and environmentally friendlyfuel resources can never be understated. An efficient method of generationand storage of hydrogen will enable automotive manufacturers to introducehydrogen fuelled engine in the market. In this paper, a conventionalDI diesel engine was modified to operate as gas engine. The intakemanifold of the engine was supplied with hydrogen along with recirculatedexhaust gas and air. The injection rates of hydrogen were maintainedat three levels with 2 L/min, 4 L/min, 6 L/min and 8 L/min and 10L/min with an injection pressure of 2 bar. Many of the combustionparameters like heat release rate (HRR), ignition delay, combustionduration, rate of pressure rise (ROPR), cumulative heat release rate(CHR), and cyclic pressure fluctuations were measured. The HRR peakpressure decreased with the increase in EGR rate, while combustionduration increased with the EGR rate. The cyclic pressure variationalso increased with the increase in EGR rate.

In this paper, the influence of different external wall insulation materials on the energy consumption of a newly built apartment in Germany is investigated. Three types of insulation materials commonly used in Germany including mineral fiber, polyurethane, and vacuum insulation panel are chosen for the case studies. An energy analysis model is established to clarify the primary energy use for production of the insulation materials and for building space heating. The calculation results show that the energy consumption for insulation material production increases with the insulation thickness, whereas the energy use for space heating decreases with the insulation thickness. Thus, there exists an optimum thickness to get the lowest total energy consumption for each kind of insulation material. The ascending order of the total energy consumption of the three materials is mineral fiber, polyurethane, and vacuum insulation panel. However, the optimum insulation thicknesses for the three insulation materials show a verse order at a certain heat transfer coefficient of the base envelope. The energy payback time (EPT) is proposed to calculate the payback time of the primary energy use for insulation material production. Mineral fiber has the shortest time, followed by polyurethane and vacuum insulation panel. The EPTS is 10, 19 and 21 years, respectively when the heat transfer coefficient of the base envelope is 0.2 W/(m²·K). In addition, the simulated results show that the theoretical value and the simulated value are basically identical.