Search

The efficient heat dissipation of electronic equipment is very important, its heat dissipation performance directly determines the life of the equipment itself. A hand-held electronic communications equipment, when used in surface temperature is exorbitant, need to heat dissipation equipment efficiently, to ensure that the use of comfort in the handheld. In accordance with this requirement, this article presents a flexible composite material based on nano-efficient cooling methods that can keep the layout, through the improvement of internal thermal path, it can achieve the effective heat dissipation. The network thermal resistance method is used to analyze the heat transfer in the equipment, and the thermal analysis of the local thermal resistance is carried out. At the same time, through the modeling of electronic equipment and the analysis of finite elements, the temperature drop of the equipment after improvement is accurately judged. Finally, the device experimental performance comparison before and after the optimization of the standby mode and working mode is verified. The results show that the optimized equipment heat source temperature can be reduced by up to 8.5°C, the surface temperature of the equipment can be reduced by about 5°C~7°C, and the final control equipment in the steady standby state of the temperature of about 39±0.5°C, to ensure the comfort of use, and also improved the service life of the equipment. The efficient thermal design of electronic equipment based on flexible nanocomposites can provide a convenient and reliable cooling solution for high-heat flow density devices.

As the underground engineering proceeds to a greater depth, the thermal stresses resulted from high-temperature surrounding rock become a major challenge for the deep construction and safe operation. Understanding of the characteristics of heat and moisture transfer in a roadway is critically required to assist in predicting and improving the thermal environment in the underground. The present work developed a fully coupled model capable of simulating the non-isothermal flow inside the roadway and heat transfer in surrounding rock together with moisture transfer driven by water evaporation. And the proposed model has been validated with the field test data and reasonable agreement was achieved. Comparing the models with or without water evaporation, it is discovered that ignoring latent heat will cause a serious deviation in air temperature prediction. Examining the critical factors on the effect of heat and mass transfer in the roadway is found that dehumidifying the initial airflow or increasing ventilation speed can effectively promote the latent heat release and reduce the temperature of airflow and surrounding rock. And this effect is greater significant for the higher temperature roadway. The present study can provide a robust theoretical basis and foundation for heat hazard control in underground engineering.

A steady and proper thermal environment in deep underground is imperative to ensure worker health and production safety. Understanding the thermal performance in the roadway is the premise of temperature prediction, ventilation design, and improvement in cooling efficiency. A full coupled model incorporated with a moving mesh method was adopted, reflecting the dynamic condition of roadway construction. This study revealed the characteristics of the thermal performance and its evolution law in an excavating roadway. Several scenarios were performed to examine the designs of the auxiliary ventilation system on thermal performance in the roadway. The results show that there is a limitation in the cooling effect by continuously increasing the ventilation volume. Reducing the diameter of the air duct or distances between the duct outlet and the working face will aggravate the heat hazard in the roadway. The heat release from the roadway wall increases with the increase of the advance rate of the working face or roadway section size. Furthermore, an orthogonal experiment was conducted to investigate the effect of major factors on the average air temperature and local heat accumulation in the roadway

Recently, an increasing number of tunnels were constructed in high-geotemperature regions and threatened with heat hazards, leading to an urgent required to analyze heat exchange characteristics and manage underground environment in these tunnels. To obtain the actual airflow and temperature field of high-temperature tunnel, a full coupled three-dimensional model incorporated with buoyancy flow was established describing the dynamic heat transfer process. The influence of buoyancy flow on temperature field in the radial and longitudinal direction of tunnel has been investigated respectively. Accounting for the buoyant effect is crucial to heat conduction and convection within tunnel, and it cannot be ignored in predicting air temperature with a large temperature difference tunnel. Additionally, this study highlights the significant effect of the presence and magnitude of groundwater flow on temperature variations and heat transfer of tunnel. When the magnitude of groundwater flow is larger than 0.01 m/d, the groundwater condition will significantly influence the temperature distribution of surrounding rock and airflow. The groundwater flow increases the temperature difference of tunnel and induces a clearer buoyancy effect inside the tunnel. As the groundwater flow direction angle increases from 0° to 90°, the influence of groundwater on heat transfer of tunnel increases first and then stabilizes. The longer the length of the seepage region is, the larger the average temperature at tunnel exit is, and the slower the temperature decreases with time. Furthermore, an orthogonal test was performed to investigate the influence degree of major factors on heat exchange of tunnel through range analysis. This study supplements the existing numerical model and research, making it more accurate to predict the thermal environment of tunnel, and guides optimization of tunnel design.

The use of cooling garments is emerging as an effective, convenient, and energy-efficient way to maintain thermal comfort, which is crucial for conserving physical and psychological health and for avoiding potentially life-threatening situations. Current cooling garments are generally bulky and have short operating periods, uncontrollable cooling capacity, and low effectiveness. Here, a novel man-portable cooling garment based on thermoelectric refrigeration was designed, and the heat generated by body is absorbed by capillary tube and dissipated in semiconductor refrigeration system. The coolant is circulated in the pipeline to recover residual cold energy and improve the thermal stability of the system. Several performance tests were conducted in a simulated hot environment to evaluate and to optimize refrigeration efficiency and cooling effectiveness. The results indicated that the system was capable of providing a water temperature of 15.7 °C and cooling power of 340.4 W, with a coefficient of performance of 3.40 at 100 W of electrical power and a climatic chamber at 30 °C. Additionally, the operating environment of the system significantly influenced the cooling capacity of the garment; and the cooling power of the system was significantly improved by increasing the heat dissipation capacity. The increase in electrical power was limited by constant heat dissipation capacity restrictions. The wearing trial confirmed the effectiveness of the thermoelectric cooling garment. Furthermore, our study improved the understanding of performance characteristics for the thermoelectric cooling garment, and a road map for the further development of thermoelectric cooling garments was suggested.

Heat hazard is major challenge for the safe and efficient exploitation of deep resources. Understanding the heat transfer behaviors in roadway is the premise of temperature prediction and ventilation design. A fully coupled model incorporated with a moving mesh method was developed, which considers the convective heat transfer between surrounding rock and airflow, unsteady-state heat transfer in rock, and non-isothermal flow in roadway. The characteristics of thermal performance and its evolution law in an excavating roadway were obtained. The numerical model was validated against previous experimental data with a deviation of less than 3%. Analysis of the airflow and temperature field revealed the characteristic of convection heat transfer in the wall and local heat accumulation in roadway. The air temperature in roadway is associated with the airflow characteristics, and a local high temperature zone is presented in the vortex zone. By comparing the heat flux of the surrounding rock and excavation condition, it is found that the heat released from the working face poses a crucial effect on the airflow temperature in roadway. The present study provided a robust theoretical basis for improving cooling efficiency and thermal comfort in roadway construction.

In recent years, the spontaneous combustion of coal has led to numerous gas explosions in mines that have resulted in hundreds of fatalities and very substantial damage to facilities. The present work developed a fully coupled model capable of simulating spontaneous coal combustion and carbon monoxide (CO) release together with methane (CH4) desorption rates, concentration distributions and migration. The aim was to evaluate the combined hazard posed by spontaneous coal combustion and CH4 build-up in mine as a result of the heat release generated by coal oxidation. The results show that the zone representing the highest degree of compound hazard is in the shape of an inclined strip located between 75 and 115 m from the working face on the inlet airway side but closer to the working face on the return airway side. Increases in the CH4 concentration in the return corner decrease as the ventilation flux increases, while the potential danger zone moves deeper into the gob. A greater initial CH4 release rate from the coal increases the size of the danger zone and moves this zone closer to the working face. The danger zone also moves away from the working face with decreases in the residual coal thickness and in the coal oxidation rate. Multivariate functions were developed to predict the positions of the gas explosive zone and the oxidation zone in the gob, and a model for assessing the risk of the compound hazard was established based on evaluating the index gas concentrations in the return corner.