Automatic icemakers are integrated into refrigerators to ensure a consistent ice supply and improve energy efficiency. Despite these advantages, a thorough investigation of the automatic icemaking process in domestic refrigerator-freezers is lacking in the literature. This study aims at assessing the performance of automatic icemaking process in a domestic freezer through detailed theoretical, numerical and experimental analyses. A simplistic zero-dimensional transient energy balance model is developed to investigate the heat transfer during different stages of the water solidification process. The convective heat transfer coefficient calculated from the theoretical analysis is used to inform the numerical model. A three-dimensional transient model is proposed to predict the temperature and density variation inside the ice cube modelled as a pyramid. The free surface flow is modelled using volume of fluid method, while enthalpy-porosity method is employed for the water freezing process. The results show a non-uniform temperature distribution throughout the solidification process and that the temperature of the outer frozen layers keeps decreasing with the solidification time. Experiments are conducted to measure the temperature variation of the ice cube. It is shown that the icemaking process is accelerated by around 18 % when the ice-removal temperature is set at −8°C instead of −12 °C, which is a conventional set temperature for ice remover in current domestic freezers.

It is indicated that the solder joint of the metal fibrous materials is a critical factor impacting the heat conduction. To reveal the mechanism by which solder joint sizes, solder joint skips, solder flux materials, and filling media affect the thermal conductivity of fibres, pore-scale numerical simulation is employed to study the thermal transport in two-directional (2-D) random fibres. Satisfactory agreement with existing data validates the numerical model. The dimensionless effective thermal conductivity (ETC) of the porous fibres increases with the solder joint sizes. As the solder joint size (i.e., solder joint ratio) increases by 3.06%, the in-plane (k_e-in) and out-of-plane (k_e-out) dimensionless ETC increase by 9.0% and 437.2%, respectively. However, the solder joint skips will weaken the thermal conductivity of the fibres. For the same fibre, the ETC of the fibre increases as the thermal conductivity of solders increases. Further, when the dissimilarity in thermal conductivity between the filling medium and the fibre is reduced, the fibre is less affected by the solder joint skips. Finally, it should be supplemented that the in-plane and out-of-plane ETC (k_e-in and k_e-out) of the fibre without any solder joint are reduced by an average of 14.3% and 98.8%, respectively.

NO_x emission reduction from gas boilers has become a key issue in improving air quality. Combustion air humidification technology is gradually being used to reduce NO_x emissions. However, the NO_x emission reduction effect of gas boilers at a higher combustion air humidity has been studied less. A flue gas with low NO_x emissions and a waste heat recovery system using combustion air humidification technology are proposed in this study. In the ultra-low NO_x mode, the effect of high combustion air humidity on NO_x emission reduction and efficiency of the gas boiler were studied experimentally. In the waste heat recovery mode, the effects of the heat network backwater temperature on the NO_x emission reduction and system efficiency were studied experimentally. Results showed that an increase in air humidity can significantly reduce the NO_x concentration formed by combustion. The ultra-low NO_x mode reduces NO_x emissions from 130 mg/m³ to 23.3 mg/m³ and affects the boiler efficiency slightly. In the waste heat recovery mode, NO_x emissions can be reduced to 39.9 mg/m³ when the backwater temperature of the heat network is 55 °C. This condition improves the efficiency to 93.8%. The analysis results provide suggestions for the selection of the operation modes.

Foodstuff has to be transported from where it is produced or packaged to the market. It is important to control the temperature and humidity of the delivered food to minimize the waste and ensure customer satisfaction. At the same time, unfortunately, the transport sector is among the polluting sectors. Therefore, innovative solutions have been proposed such as the adoption of Latent Thermal Energy Storage (LTES) systems based on Phase Change Materials (PCMs) to control the food temperature. Such systems minimize the fuel consumption and thereby reduce the emission. LTES systems rely on the phase change process to absorb and store heat in a more sustainable way while ensuring a nearly constant temperature for the foodstuff while being transported. Hence, we first present a general overview of the application of PCMs at low temperatures. Then, the literature on the adoption of PCMs in the refrigerated transport sector is critically surveyed. Different proposals offered in the literature are recovered, compared, and critically assessed based on their merits. Despite the differences between the proposed technologies, significant advantages in terms of temperature uniformity in the refrigerated space, product thermal stress reduction, product quality, energy consumption, and pollutant emissions reduction are reported in the literature as surveyed in this paper.

Solar energy, as a kind of renewable energy, offers a large reserve to be harvested at a reasonably low cost for engineering applications. To decouple the temporal and spatial relevance of the continuous energy supply of solar energy, latent heat thermal energy storage can deal with this problem at different temperatures. Aiming to improve energy efficiency, a novel hybrid metal foam-pin fin structure is designed and assessed. Upon conducting measurements on a well-designed experimental bench, the phase change processes of paraffin that is filled in fins, metal foam, and a combination of both (hybrid structure) are evaluated. During the experiments, the transient melting interface is snapshotted and temperature development is documented under five different heat source temperatures of 61 °C, 63 °C, 65 °C, 68 °C, and 70 °C. In the foreground of the novel hybrid structure, each segment of the hybrid is also justified and discussed. Results indicate that the hybrid structure augments marked heat transfer. Compared to pure PCM, complete melting time decreases by 63.4% and simultaneously the temperature response rate increases by 143.9% as implementing the hybrid. Attempts to design hybrid structure find a solution to assess and operate thermal storage applications for solar engineering.

The use of metallic periodic structures was considered for melting rate enhancement of a phase change material (PCM) contained in a rectangular enclosure isothermally heated from the side. The critical (optimized) cell size, or pore size, of a periodic structure with fixed porosity, realising the shortest melting time by maximizing the convection and conduction heat transfer rate into the PCM, was studied. Furthermore, the effects of material properties (copper, aluminium, nickel, and stainless steel), enclosure length, wall-melting temperature difference and porosity were numerically investigated. It was observed that increasing porosity and/or reducing thermal conductivity enlarged the critical cell size (i.e. the optimal cell size that minimizes the melting time). The critical PPIs (pores per inch) of copper and aluminium periodic structures for all studied porosities were 10; for nickel, the critical values were 10 PPIs for porosity values of 0.75, 0.8 and 0.85 while it reduces to 5 PPI for the highest porosity considered here being 0.95. Interestingly, showing a different trend, the critical PPI of stainless-steel structures was 5 for the lowest porosity (0.75) and reduced to 3 for higher porosities. The results clearly demonstrated localised melting which was observed in all periodic structures except for the 10 PPI stainless-steel case. Scattered melting islands are observed as opposed to a moving interface when ϕ=(d_p/L)α_ligament/α_PCM>1. For such cases, localized melting occurs and the PCM is melted at the ligaments away from the heated wall before the melt front reaches those ligaments.

The rising energy demand for buildings has enhanced public awareness of sustainable energy sources and technologies. In particular, natural ventilation systems such as wind-catchers have attracted considerable new attention. A new wind-catcher design with single-stage direct-air evaporative cooling was proposed for indoor air conditioning. An Eulerian-Lagrangian approach employing the Realizable k-ε model was utilized to conduct the CFD simulations. Furthermore, the effects of inclining the bottom surface of the wind-catcher and installing a baffle across the flow path on the air temperature drop, water mass fraction, and air velocity distribution were studied. The inclined bottom surface led to more flow uniformity in the room compared to the conventional geometry. The baffled wind-catcher with β = 0, 30, 45, and 60° and unbaffled wind-catcher showed different flow patterns and thermal comforts. A methodology for evaluating the thermal comfort performance of evaporative cooling systems integrated into natural or passive cooling devices was also proposed based on the generated CFD results. The baffled wind-catcher with β = 60° combined with an evaporative cooling system significantly reduced the air temperature inside the building up to 17.4 °C and improved the occupants’ thermal comfort. The most suitable design for thermal comfort was also determined.