• Energy Research

Abstract The environment temperature has great effects on temperature field of cold storage refrigerator car and melting process of cold storage materials. NaCl aqueous solution was used as the cold storage material, Solidworks was used to establish physical model of the cold storage refrigerator car, Gambit for meshing and Ansys was used to make simulation calculation. The simulation results indicate that: with the rise of temperature, the melting process of storage plate will be fast, the time of latent heat discharge will be shorter. The temperature field of car can stabilize in a high temperature and the time is short. When environment temperature is 303K, cold storage material needs 70.2h to be melted into salt solution. The temperature field of car can stabilize in 293K for 73.6h. At this moment, environment and the temperature of cold plate existed large difference in, heat exchange is large and the heat flux is 2.75W/h.

Abstract The environment temperature has great effects on temperature field of cold storage refrigerator car and melting process of cold storage materials. NaCl aqueous solution was used as the cold storage material, Solidworks was used to establish physical model of the cold storage refrigerator car, Gambit for meshing and Ansys was used to make simulation calculation. The simulation results indicate that: with the rise of temperature, the melting process of storage plate will be fast, the time of latent heat discharge will be shorter. The temperature field of car can stabilize in a high temperature and the time is short. When environment temperature is 303K, cold storage material needs 70.2h to be melted into salt solution. The temperature field of car can stabilize in 293K for 73.6h. At this moment, environment and the temperature of cold plate existed large difference in, heat exchange is large and the heat flux is 2.75W/h.

Gasification of biomass waste has a significant potential to reduce environmental impact and promote sustainability by producing syngas, which is considered as renewable energy. This work investigated the gasification of macadamia nutshells in air-preheated, batch-fed fluidized bed gasifier. The study conducted a parametric analysis to assess the effect of equivalence ratio (ER) and air temperature on the gasifier temperature profile and its performance based on gas composition, higher heating value (HHV), and gas yield. The research was conducted within the range of 0.15–0.35 for the ER and 25–825 °C for the air temperature. Multi-objective numerical optimization was conducted using response surface methodology (RSM). From the parametric study, a distinct temperature profile was observed along the gasifier height, with the peak temperature near the top of the fluidized bed section and the lowest temperature at the top of the gasifier. Air preheating mostly favored gasification temperature at the lower part of the gasifier and showed rare significance at the top. No improvement in gasifier performance was observed beyond an air temperature of 620 °C, which was identified as the ideal air-preheating temperature. Analysis of variance (ANOVA) revealed that the ER was the most influential parameter in the production of combustible gasses, syngas HHV and gas yield. Air preheating did not have a significant effect on methane production and gas yield. The most optimal values for ER and air temperature were obtained as 0.195 °C and 620 °C, respectively, producing optimal values of 9.54, 14.65%, 2.03, 4.02 MJ·Nm−3, and 1.82 Nm3·kg−1 for hydrogen, carbon monoxide, methane, HHV, and gas yield, respectively.

Gasification of biomass waste has a significant potential to reduce environmental impact and promote sustainability by producing syngas, which is considered as renewable energy. This work investigated the gasification of macadamia nutshells in air-preheated, batch-fed fluidized bed gasifier. The study conducted a parametric analysis to assess the effect of equivalence ratio (ER) and air temperature on the gasifier temperature profile and its performance based on gas composition, higher heating value (HHV), and gas yield. The research was conducted within the range of 0.15–0.35 for the ER and 25–825 °C for the air temperature. Multi-objective numerical optimization was conducted using response surface methodology (RSM). From the parametric study, a distinct temperature profile was observed along the gasifier height, with the peak temperature near the top of the fluidized bed section and the lowest temperature at the top of the gasifier. Air preheating mostly favored gasification temperature at the lower part of the gasifier and showed rare significance at the top. No improvement in gasifier performance was observed beyond an air temperature of 620 °C, which was identified as the ideal air-preheating temperature. Analysis of variance (ANOVA) revealed that the ER was the most influential parameter in the production of combustible gasses, syngas HHV and gas yield. Air preheating did not have a significant effect on methane production and gas yield. The most optimal values for ER and air temperature were obtained as 0.195 °C and 620 °C, respectively, producing optimal values of 9.54, 14.65%, 2.03, 4.02 MJ·Nm−3, and 1.82 Nm3·kg−1 for hydrogen, carbon monoxide, methane, HHV, and gas yield, respectively.

Abstract Sodium thiosulfate pentahydrate (Na2S2O3·5(H2O)) has poor cycling stability, experiences phase separation and low crystallization due to large supercooling. In order to improve these properties, the influences of nucleating agent and thickening agent on the supercooling degree, phase separation and exothermic performance of Na2S2O3·5(H2O) were investigated by using the fusion-curing cycle and step-cooling curve system. Observation of the structure and testing of its thermophysical properties by scanning electron microscope, thermostatic bath and differential scanning calorimeter were carried out. The results show that, the addition of sodium pyrophosphate (TSPP) with a mass fraction of 0.08% had a significant improvement effect, and the thickener sodium acrylate (PASS) had the best results. A phase change composite material (CPCM) with a mass fraction of 0.08% TSPP and 2% PAAS had a phase transition temperature of 47.3 °C; the degree of subcooling was 3.6 °C; the phase transition enthalpy was 206.8J/g; the discharge time was 106 min. There was no phase separation during the storage/discharge process. After 100 high and low temperature cycles, the phase transition temperature of the composite was 42.5 °C; the phase transition enthalpy was 202.1J/g, and the cycle stability was good. The improved energy storage material can be used in building heat storage system.

Abstract Sodium thiosulfate pentahydrate (Na2S2O3·5(H2O)) has poor cycling stability, experiences phase separation and low crystallization due to large supercooling. In order to improve these properties, the influences of nucleating agent and thickening agent on the supercooling degree, phase separation and exothermic performance of Na2S2O3·5(H2O) were investigated by using the fusion-curing cycle and step-cooling curve system. Observation of the structure and testing of its thermophysical properties by scanning electron microscope, thermostatic bath and differential scanning calorimeter were carried out. The results show that, the addition of sodium pyrophosphate (TSPP) with a mass fraction of 0.08% had a significant improvement effect, and the thickener sodium acrylate (PASS) had the best results. A phase change composite material (CPCM) with a mass fraction of 0.08% TSPP and 2% PAAS had a phase transition temperature of 47.3 °C; the degree of subcooling was 3.6 °C; the phase transition enthalpy was 206.8J/g; the discharge time was 106 min. There was no phase separation during the storage/discharge process. After 100 high and low temperature cycles, the phase transition temperature of the composite was 42.5 °C; the phase transition enthalpy was 202.1J/g, and the cycle stability was good. The improved energy storage material can be used in building heat storage system.

Abstract With increasing concerns over global warming, there is compelling need to apply energy technologies to improve energy efficiencies. One of the new technologies is the use of phase change materials (PCMs) to store energy and release it on demand. However, most of these materials undergo supercooling, aggregation and have low thermal conductivity that inhibits effective heat transfer. In this paper supercooling, stability, energy storage,thermal conductivity and latent heat of fusion of water based nanofluid of barium chloride dehydrate (BaCl2·2H2O) were experimentally studied by adding a mass fraction of 0.2 w.t%–1 wt.% magnesium oxide (MgO) and 0.2 wt.%–1 wt.% multi-walled carbon nanotubes (MWCNTs). Results show that by adding separately mass fraction of 1.% of MgO and MWCNTs reduce the supercooling degree of barium chloride dehydrate by 85% and 92% respectively. At the same mass fraction, thermal conductivity also improves by 6% on addition of MWCNTs and 17% on addition of MgO. However, the enthalpies reduce by 7% at 1 wt.% MgO and by 12.3% at 1 wt% MWCNTs. It was found that MgO exhibited relatively higher thermal conductivity and a lower reduction in latent heats at a mass fraction of 1 wt.%. Surfactant was also found to prevent aggregation at low temperatures.

Abstract With increasing concerns over global warming, there is compelling need to apply energy technologies to improve energy efficiencies. One of the new technologies is the use of phase change materials (PCMs) to store energy and release it on demand. However, most of these materials undergo supercooling, aggregation and have low thermal conductivity that inhibits effective heat transfer. In this paper supercooling, stability, energy storage,thermal conductivity and latent heat of fusion of water based nanofluid of barium chloride dehydrate (BaCl2·2H2O) were experimentally studied by adding a mass fraction of 0.2 w.t%–1 wt.% magnesium oxide (MgO) and 0.2 wt.%–1 wt.% multi-walled carbon nanotubes (MWCNTs). Results show that by adding separately mass fraction of 1.% of MgO and MWCNTs reduce the supercooling degree of barium chloride dehydrate by 85% and 92% respectively. At the same mass fraction, thermal conductivity also improves by 6% on addition of MWCNTs and 17% on addition of MgO. However, the enthalpies reduce by 7% at 1 wt.% MgO and by 12.3% at 1 wt% MWCNTs. It was found that MgO exhibited relatively higher thermal conductivity and a lower reduction in latent heats at a mass fraction of 1 wt.%. Surfactant was also found to prevent aggregation at low temperatures.

Abstract Despite the fact that Nanofluids and nanofluid based phase change materials (PCMs) have been identified as potential candidate for various heat transfer and energy storage applications, they are still facing various challenges such as stability, pressure drop and high pumping power. Nanoparticle size plays a bigger role in hindering nanofluid applications, yet effect of nanoparticles size does not receive the attention it deserves. The inconsistence and contradiction of information gives an impression that the area is not well understood therefore more information need to be made available in the literature. In this paper, the effect of nanoparticle size on thermophysical properties of nanofuid and nanofluid PCMs is reviewed. The work involves discussing the effect of nanoparticle size on thermo-physical properties of nanofluid and nanofluid PCMs through systematic analysis of past experimental and theoretical work. The results show that, thermal conductivity generally increase as nanoparticle size decreases while surface tension increases as nanoparticle size increases. Latent heat of fusion reduces as nanoparticle diameter decreases. Although, nanoparticles increase viscosity, the effect of particle size diameter is not yet clear. More research is therefore needed in this area of nanoparticle size effect on nanofluid and nanofluid PCMs so that optimum size can be established for each application.