Search

In this article, a combined experimental and numerical study has been performed to investigate the thermal performance of a mine refuge chamber (MRC) under natural convection. In the current study, a 20-hour heating experiment is carried out in a fifty-person MRC laboratory and the heat lamps are utilized to simulate the human heat loss. A new analytical model is proposed to predict the air temperature and validated against the experimental data. Sensitivity analysis is performed to further investigate the effects of the thermal parameters of the rock. Results indicated that: (1) two different air temperature increase stages, rapid and slow increase stages, are observed in the MRC; (2) A new analytical method for predicting the air temperature in MRC under natural convection is proposed, it shows that the air temperature increasing trend becomes slow with the increase of the thermal conductivity, density and specific heat capacity of the rock; (3) the surface heat transfer coefficient on the vertical walls reaches the largest and it increases linearly with air temperature.

Efficient latent heat thermal energy storage (LHTES) systems can be potentially employed to improve the energy saving capability and thermal performance of buildings. In this paper, a new coupled cooling method with phase-change chairs (PCC) and phase-change plates (PCPs) is firstly proposed to solve the cooling problem in isolated environments, such as mine refuge chamber with high temperature. A mathematical model of the new coupled cooling system is developed, validated, and applied to evaluate the heat transfer, temperature control effect, and operation optimization. The results show that when the number of PCPs is increased from 180 to 260, the proposed system helps decrease room temperature by 0.3 °C. For every 1 °C increase in melting temperature or for 1 °C decrease in cold storage temperature, the room temperature increases by 0.5 °C. Compared to the coupled cooling method with PCP alone, the proposed system leads to a temperature reduction of 1.4 °C in the first 50 h, while the volume occupied by the cooling system is reduced by 31.4%. Therefore, the technical proposal of combining PCC and PCP is recommended to further improve the indoor thermal comfort and reduce the occupied space without significant utilization of the phase-change materials (PCM).

Electro-to-heat energy conversion/storage provides a new direction for the development of phase change materials (PCMs). However, conversion rate and energy storage density of the existing PCMs are limited by their low intrinsic electrical and thermal conductivities and poor compressive strength. In this work, a novel form-stable phase change material (FSPCM) has been prepared via ligand replacement followed by the embedment of acetylene black conductive network. The addition of 20 wt% acetylene black reduces the resistivity of the polyethylene glycol-based PCM from 107−1012 Ω·m to 0.3 Ω·m, while its thermal conductivity is increased by 300%. The resulting conductive composite possesses the ability to store heat at voltage as low as 1.8 V and high electro-to-heat conversion efficiency. The composite compressive strength reaches 105 Pa at an ambient temperature of 110 °C, while the temperature is 60 °C more than that of phase transition temperature of PCM. Further, the magnitude of the temperature change in the electrothermal conversion curves recorded after 50 solid-liquid phase transition cycles does not exceed 2.0%. The excellent electrical and thermal conductivities as well as good mechanical properties of the synthesized composite suggest a promising route for manufacturing novel materials with high power capacity for thermal storage applications.

A study of an underground building ventilated by a long vertical earth-air heat exchanger (EAHE) system is especially of interest because it shows a mechanism to alter the thermal characteristics in the building. However, studies on this thermal configuration are rare. In this paper, based on the free-falling equation of water film and the heat and mass transfer equations of airflow, a coupled numerical solution method is proposed to predict the thermo-hygrometric performance of the system. The Heat Index (HI) is chosen as the thermal evaluation index. According to the numerical results, the long vertical EAHE system can significantly reduce the indoor air temperature in summer while it only has a lag effect on the air humidity ratio, causing a high relative humidity and making it the main reason for the indoor thermal discomfort. The indoor HI decreases by approximately 1 °C for every 6 m3/(h·p) (“p” is short for “per person”) increase of the ventilation volume, but the reduced rate gradually slows down; the diameter of ventilation pipe less than 0.25 m is not conducive for the thermal control; the EAHE system is more suitable for application with a buried depth less than 200 m.

Air curtain systems for mine refuge chambers prevent harmful gases in the tunnel from entering the chambers, but their barrier efficiency is affected by their structural parameters, installation location and air flow angle as well as the size of the chamber door. Previous studies focused on air curtain systems installed on the top of the door frames of the mine rescue capsule, but no studies have investigated air curtain systems installed on two or three sides of the door frames. To improve the barrier efficiency of air curtain systems for refuge chambers, this study conducted an experimental investigation of the effects of the structural parameters, installation location, and air flow angle on the barrier efficiency for a constant size of the door frame. The results demonstrate that air curtain systems with air curtains installed on two sides of the door frame behind the door wall that ejected air parallel to the door frame provided a relatively good barrier effect; an air curtain system that used pipeline air curtains with a nozzle diameter of 1 mm and a nozzle distance of 15 mm exhibited a relatively good barrier effect and a barrier efficiency of 55–60%. In air curtain systems that use air knives, the air knife gap should be 0.1–0.2 mm wide. Under reasonable parameters and installation conditions, there was no significant difference between the barrier effects against CO2 of air curtain systems that use pipeline air curtains and those that use air knives.

This paper investigated the dynamic coupling heat transfer characteristics of rock and air in a Mine Refuge Chamber (MRC) under ventilation. In the current work, a comprehensive fifty-person MRC model combining human-body heat sources and ventilation is established, the proposed model is validated against available experimental data with deviation less than 4%. Furthermore, sensitivity analysis is performed to investigate the influence of several control parameters such as heating rate, ventilation and wall area in a MRC through using numerical simulation. Results indicated that: (i) the heat transfer process in a MRC will reach a stage of air temperature slow increase (ATSI) in less than 0.5 h. The air temperature rises linearly with the square root of time during the ATSI stage; (ii) for a MRC built in a sandstone seam with an initial rock temperature of less than 27 °C, the average air temperature will not exceed 35 °C in 96 h when the ventilation volume rate is 0.3 m3/min per person; (iii) the rate of temperature rise in MRC is proportional to the rate of heat generation, but it is inversely proportional to the thermal conductivity, density and thermal capacity of the rock, as well as the ventilation volume rate and the wall area; (iv) an empirical correlation for the MRC average air temperature is developed while the supply air temperature equals to the initial rock temperature.