2,3,3,3-Tetrafluoroprop-1-ene (HFO-1234yf) is considered as the promising alternative low-global warming potential refrigerant to replace HFC-134a. In this study, the gaseous pvT properties of HFO-1234yf were measured at temperatures from 252 to 345 K and pressures up to 1.91 MPa using a single-sinker densimeter. The density range is from 3.732 to 112.152 kg/m3. The standard uncertainties of the experimental data are estimated as 6 mK and 0.7 kPa for the temperature and pressure, respectively. The relative uncertainty in density is 0.014–0.034% in this study. The average absolute deviation and relative deviation of density from reported equations of state are 0.024 kg/m3 and 0.157%, respectively. A virial equation of state was developed for HFO-1234yf. The calculated results show good agreement with the experimental data.

Helical-coil is a common structure of heat exchanger unit in phase change heat accumulator and usually has the equal coil pitch between adjacent coils. Its thermal performances could be improved by improving the uniformity of the phase change material (PCM) temperature distribution. Thus, a novel non-equidistant helical-coil structure was proposed in this study. Its coil pitch decreased along the flow direction of heat transfer fluid, which made the heat exchange area in unit volume increase to match the decreasing temperature difference between the heat transfer fluid and PCM. The structure was optimized using numerical simulation. An experimental system was developed and the experiment results indicated that the proposed non-equidistant helical-coil heat accumulator was more effective than equidistant helical-coil for latent heat storage. The uniformity of the temperature distribution was also confirmed by simulation results.

•Solid-solid PCM XLPE was obtained through irradiating HDPE by 60Co source irradiation.•Phase change temperature of XLPE is 115°C and latent heat is 147.79 Jg−1.•Structures of XLPE and HDPE were analyzed.Crosslinked high density polyethylene (XLPE) is kind of a solid–solid phase change material with high latent heat. In this study, melt flow indexer prove that such phase change material can be obtained through irradiating high density polyethylene by a 60Co source irradiation. DSC was used to distinguish the phase change temperature and latent heat of the prepared sample, and the specific heat was determined. Also, the structure of the crosslinked polyethylene and uncrosslinked one were analyzed using FTIR, XRD and SEM. Thermogravimetry analysis illustrated the samples׳ stability.

•2D thermal model for parabolic solar trough collector.•Radiation loss of side plate of the tube receiver.•Coupled 2D thermal and 3D optical model for parabolic solar trough collector.•High precision and quick algorithm of the model.A 2D thermal model for tube receiver in parabolic trough solar collector is proposed, and a fast numerical algorithm is developed. Comparing to the previous models, we consider the radiation loss from the side plate of the tube receiver and direct transmission of the absorber radiation to the air to construct a physical model and mathematical equations. We also reduce the calculation by simplifying them to algebraic equations for numerical solution without needing iteration after ignoring the axial heat transfer. It is further coupled to the three-dimensional optical model to predict the performance of parabolic trough solar collector. The performances of the overall model and thermal model are tested against experimental measurements from Sandia National Laboratories. In all cases, the simulation results show a good agreement with the experimental results. The models developed in this paper can predict performance of parabolic trough solar collector with parabolic trough reflector and tube receiver accurately and quickly based on the structure and material properties of the system.

•Experimental VLE data for HHFC-134a + HFO-1234yf + HC-600a were reported.•Parameters in PR-vdW model and PR-WS-NRTL model were determined on the basis of VLE data of binary mixtures.•The predicted values of PR-vdW model and PR-WS-NRTL model agree well with the experimental data.Vapor–liquid equilibrium data for the ternary mixture of 1,1,1,2-tetrafluoroethane (HFC-134a) + 2,3,3,3-tetrafluoroprop-1-ene (HFO-1234yf) + isobutane (HC-600a) were measured at temperatures from 283.15 K to 323.15 K using a recirculation apparatus. The uncertainties of the experimental data are estimated within 5 mK, 0.5 kPa, and 0.003 for the temperature, pressure, and the equilibrium liquid and vapor mole fractions, respectively. The experimental data were compared with the predicted data by the Peng Robinson equation of state with the vdW mixing rule and the Wong Sandler mixing rule, respectively. The binary interaction parameters of each binary mixture were determined from the experimental data in literature. The results show that the predicted data agree well with the experimental data. It indicates that the PR equation can be used to predict VLE data of ternary mixture of HFC-134a + HFO-1234yf + HC-600a. The proposed ternary mixture has potential to be refrigerant with low GWP and excellent thermodynamic performance.

In this study, isothermal vapor–liquid equilibrium (VLE) data were measured for the binary system of fluoroethane (HFC-161) + 2,3,3,3-tetrafluoroprop-1-ene (HFO-1234yf) over the whole composition range in the temperature range from 283.15 to 323.15 K at 10 K intervals. The experimental VLE data were correlated with the Peng–Robinson equation of state. The van der Waals (vdW) one-fluid mixing rule and the Wong–Sandler (WS) mixing rule with the non-random two-liquid (NRTL) activity coefficient model were both used. The correlation results show good agreement with the experimental data.

•Nano-AlN was proposed as the nucleating agent for solid–solid phase change material Pentaerythritol (PE).•PE/3 wt% nano-AlN composite was prepared.•The composite PCM has a higher crystallization rate and negligible supercooling.•Solid–solid phase change temperature and latent heat are 182.4 °C and 222.5 J/g for the composite.Pentaerythritol (PE) is a kind of solid–solid phase change materials with high latent heat. To improve its performances of crystallization and phase change, nano-AlN particles were physically mixed into PE as nucleating agent. The PE/3 wt% nano-AlN composite and pure PE were characterized using FT-IR and SEM analysis technique. Thermal properties and non-isothermal crystallization kinetics of the composite PCM were determined by DSC analysis. The solid–solid phase change processes of PE/3 wt% nano-AlN composite and pure PE were experimental investigated. The results showed that the addition of nano-AlN can accelerate the crystallization rate and reduce the supercooling degree of PE during cooling process.

•A novel CPV/T hybrid system employing beam splitter and sloped linear Fresnel reflector concentrator was proposed.•Structural parameters of the system components were calculated and optimized.•Concentrated radiation distribution on the PV device surface shows a good uniformity.•The system performance was analyzed on the basis of the experimental data of components and showed a high efficiency.Spectral splitting technology that separates solar spectrum into several parts and enables different energy conversions such as photovoltaic (PV) conversion and photo-thermal conversion aims to utilize the full spectrum solar energy efficiently. A novel concentrating PV/Thermal (CPV/T) hybrid system with beam splitter and fully tracked linear Fresnel reflector concentrator utilizing sloped panels was proposed in this study. The relations between the structural parameters and the optical performances of the system were investigated. The concentrated radiation distribution on the PV device surface was simulated by taking into account the main optical errors and shows a good uniformity. Based on the experimental data of the components, thermodynamic analysis on the CPV/T hybrid system was carried out and the results reveal that the overall energy conversion efficiencies of the proposed CPV/T hybrid system is higher than that of the CPV system under the same conditions.

•Experimental VLE data for HFO-1234yf + HFC-152a were reported.•The mixture exhibits azeotropic and near azeotropic behaviors.•Temperature glide is less than 0.4 K within the complete range of composition.Isothermal vapor–liquid equilibrium (VLE) data for the binary mixture of 2,3,3,3-tetrafluoroprop-1-ene (HFO-1234yf) + 1,1-difluoroethane (HFC-152a) were measured at temperatures from 283.15 K to 323.15 K using a recirculation apparatus. The experimental data were correlated by using PR EoS with vdW mixing rule, the comparison between the correlation results and experimental data showed a good agreement. HFO-1234yf (1) + HFC-152a (2) system shows not only azeotropic behavior but also near azeotropic behavior with a very small temperature glide of less than 0.4 K within the complete range of composition and of temperature.

•Experimental VLE data for HFO-1234yf + HFC-227ea were reported.•The mixture exhibits non-azeotropic behaviors.•PR-vdW model was employed to correlate the phase equilibrium data.Isothermal vapor–liquid equilibrium data for the binary system of 2,3,3,3-tetrafluoroprop-1-ene (HFO-1234yf) + 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) were measured at 10 K intervals from 283.15 K to 323.15 K over the whole composition range. The uncertainties of the experimental data are estimated at ±5 mK, ±3.5 kPa, and ±0.003 for the temperature, pressure, and the equilibrium liquid and vapor mole fractions, respectively. The experimental data were correlated with the Peng–Robinson equation of state using the van der Waals mixing rule, and the binary interaction parameter was optimized to fit the experimental data. The comparison between the experimental data and the correlated results shows a good agreement.

An effective thermodynamic transformation analysis method was proposed in this study. According to the phenomenon of exergy consumption always coupling with heat transfer process, the effective thermodynamic temperatures were defined, then the actual power cycle or refrigeration/heat pump cycle was transformed into the equivalent reversible Carnot or reverse Carnot cycles for thermodynamic analysis. The derived effective thermodynamic temperature of the hot reservoir of the equivalent reverse Carnot cycle is the basis of the proposed method. The combined diagram of TR-h and TR-q was adopted for the analysis of the system performance and the exergy consumption, which takes advantage of the visual expression of the heat/work exchange and the enthalpy change, and is convenient for the calculation of the coefficient of performance and exergy consumptions. Take a heat pump water heater with refrigerant of R22 for example, the proposed method was systematically introduced, and the fitting formulas of the effective thermodynamic temperatures were given as demonstration. The results show that the proposed method has advantage and well application foreground in the performance simulation and estimation under the variable working conditions.

A novel hybrid solar concentrating Photovoltaic/Thermal (CPV/T) system with beam splitting technique is presented. In this system, a beam splitter is used to separate the concentrated solar radiation into two parts: one for the PV power generation and the other for thermal utility. The solar concentrator is a flat Fresnel-type concentrator with glass mirror reflectors. It can concentrate solar radiation onto solar cells with high uniformity, which is beneficial to improving the efficiency of solar cells. The thermal receiver is separated to the solar cells, and therefore, the thermal fluid can be heated to a relatively high temperature and does not affect the performance of solar cells. A dimensionless model was developed for the performance analysis of the concentrating system. The effects of the main parameters on the performance of the concentrator were analyzed. The beam splitter with coating materials Nb2O3/SiO2 was designed by using the needle optimization technique, which can reflect about 71% of the undesired radiation for silicon cell(1.1 μm < λ ⩽ 3 μm) to the thermal receiver for thermal utility. The performance of this CPV/T system was also theoretically analyzed.

A new air-water dual source heat pump water heater with heat recovery is proposed. The heat pump system can heat water by using a single air source, a single water source, or air-water dual sources. The water is first pre-heated by waste hot water, then heated by the heat pump. Waste heat is recovered by first preheating the cold water and as water source of the heat pump. According to the correlated formulas of the coefficient of performance of air-source heat pump and water-source heat pump, and the gain coefficient of heat recovery-preheater, the formulas for the coefficient of performance of heat pump in six operating modes are obtained by using the dimensionless correspondence analysis method. The system characteristics of heat absorption and release associated with the heat recovery-preheater are analyzed at different working conditions. The developed approaches can provide reference for the optimization of the operating modes and parameters. The results of analysis and experiments show that the coefficient of performance of the device can reach 4–5.5 in winter, twice as much as air source heat pump water heater. The utilization of waste heat in the proposed system is higher than that in the system which only uses waste water to preheating or as heat source. Thus, the effect of energy saving of the new system is obvious. On the other hand, the dimensionless correspondence analysis method is introduced to performance analysis of the heat pump, which also has theoretical significance and practical value.

Taking nonequilibrium radiative heat transfer between two surfaces as an example, the nonequilibrium thermodynamics of radiation is studied and discussed. The formulas of entropy flow, entropy generation, exergy flux, and optimal temperature of absorbing surface for maximum exergy output are derived. The result is a contribution to the thermodynamic analysis and optimization of solar energy utilization and can be applied in more complex radiative heat transfer cases.

New corresponding temperature and corresponding enthalpy of refrigerant mixtures were defined. The relationship between saturated liquid corresponding enthalpy and corresponding temperature of refrigerant mixtures accorded with that of pure components. The characteristic parameters of saturated liquid enthalpy difference of refrigerant mixtures were calculated by three methods according to the different application conditions. The generalized equation of saturated liquid enthalpy of refrigerant mixtures was presented. The calculated values were compared with the values in literature for five ternary and binary refrigerant mixtures, namely R404A, R407A, R407B, R32/R134a, and R410A. The overall average absolute deviation was less than 1.0%.