Liquid metals, such as alloys of bismuth, gallium and indium, potentially offer both low interfacial resistance and high conductivity. Several alloys of gallium with very low melting points have also been identified as potential liquid metal interface materials. Thermal performance of such an interface would be more than one order of magnitude greater than many adhesives typically in use.LMA alloys as a thermal interface material offer superior thermal performance due to their high thermal conductivities and low contact resistance, resulting from excellent surface wetting. Reworkability, ease of handling, and a lack of cure make this attractive in a high volume setting. The various failure mechanisms which have plagued the past and present LMA products will be mitigated by applying a multidisciplinary approach to the challenge. Liquid metals flow quite well. The solid structures or phases proposed for incorporation within the thermal interface address the basic problem of getting an LMA to stay put when in service. These structures increase the surface contact area with the LMA in the thermal interface. As long as the total solid-liquid interface energy is less than the interface energy of the liquid-gas and solid-gas interfaces it replaces, the LMA will minimize its surface energy by wetting the surfaces within the interface. The LMA may still wet the surface adjacent to the thermal interface if it is the same wettable surface used under the die, particularly when acted upon by an additional force. Additional forces will arise from shock, vibration, and CTE mismatches between the LMA and other components. Once the LMA has wet the surface adjacent to, but outside the thermal interface, it is doubtful surface tension alone will retain it within the interface when acted upon by external forces. Others have proposed to address this difficulty with gaskets to contain the LMA and fillers or non-eutectic (slushy) compositions to increase its viscosity. We have found that simply modifying the surface around the thermal interface so that the LMA will not wet it is sufficient to contain the LMA within the interface during shock, vibration, and temp cycling. It is conceivable that if excess LMA were incorporated during assembly, this excess could end up airborne from shock or vibration. Therefore, LMA TIM should be deployed in closed cavities where no opportunities for shorts or adverse reactions with other metals exist.
Liquid metals have a very large thermal conductivity, which allows them to achieve large heat transfer coefficients and achieve efficient energy exchange at low temperatures. Since this memory condition relies on efficient molecular energy transfer, large single-phase results can be obtained within simple geometries. In other words, a large increase in the heat transfer coefficient of liquid metal (3 to 20 times) is possible. The old one that significantly increased the heat transfer coefficient should allow higher heat flux during work, while maintaining a constant temperature This is a major limitation of the design of the former molten salt receiver. Therefore, in the receiver area, the liquid metal can also reduce the overall capital investment; in addition, higher receiving efficiency can be achieved by improving the heat transfer performance. Usually in a thermal power station, the ideal result is to have a higher temperature to achieve greater thermodynamic efficiency. The solar photovoltaic efficiency as a whole should also consider the impact of optical aspects and receiver performance. The state-of-the-art central receiving system is a subcritical steam Rankine cycle operated by nitrate. In general, when operating to a high steam temperature of 630 ° C, the overall photoelectric efficiency of wet and dry condensers increases by 8-12%. However, the higher temperatures required to implement this advanced power cycle cannot be achieved with molten salts at all, as their temperature is limited to 560 ° C. Direct application of solar thermochemical processes at high operating temperatures is feasible. The development of industrial processes in chemical reactors at high temperatures is necessary, and molten metal can stably perform the function of a thermal fluid.Application of high temperature liquid metal in heat engine cycle700 ° C ultra-supercritical steam turbine cycle: With the development of solar modules (receivers, storage systems, and solar modules) compared to other high-temperature concepts, the relatively low development demand for future 700 ° C ultra-supercritical steam power modules can be achieved through liquid Heat transfer provided. An outlet temperature of 700 ° C is necessary for such receivers, and nickel-based alloys can help overcome physical issues. In the temperature range corresponding to the receiving system and storage system, it is necessary to develop a steam cycle temperature exceeding 700 ° C. It can be seen that the main risks related to the feasibility of this concept are nickel welding problems and transient strains, as well as corrosion problems.Open gas turbine cycle: the lowest 600 ℃ gas in the combined cycle. The steam power module has been commercialized and can be improved on the basis of the advanced technology of current coal-fired and gas-fired power plants. Adopted-solar-gas turbines have significant advantages over other conventional Taigangneng power plants. Although there is no commercial scale, the concept of using compressed air as the heat sink receiver has been extensively studied.Closed Gas Turbine Cycle: In a closed cycle, it can be used to replace air with an optional inert gas, resulting in more efficient power conversion. Similarly, the high-temperature heat energy collected in an open cycle must be transferred by a heat exchanger or indirect or direct contact type. Direct contact heat exchangers are attractive from a cost reduction point of view, but practical issues involving pressure seals and Rankine-Steam delivery to steam turbines need to be addressed. Similar to the open gas turbine cycle, the closed cycle needs additional development. The main method to reduce costs is related to the partial load in the closed Brayton cycle.
Metal thermal pad as one of the important techniques to enhance heat transfer, is widely used to improve the heat transfer rate of solid wall. Such as aircraft, air conditioning, electronic components, motor vehicle thermal conductivity, Marine thermal conductivity and so on. The research on the heat transfer enhancement of thermal conductive pad has attracted the attention of many researchers at home and abroad, such as the research on the natural convection of thermal conductive sheet and the research on the forced convection of thermal conductive sheet.Heat conduction pad is mainly used to strengthen the heat conduction of the heating surface to the air, so we take the heat conduction sheet in contact with the air as the research object.Due to the low surface temperature (generally no more than 250 ℃) of the thermal conductive pad, the radiative heat transfer ratio of the thermal conductive pad group to the air is less than 3% of the total thermal conductivity. Therefore, the heat conduction between the surface and the surrounding environment is mainly convection heat transfer. Influence of height on the heat conduction of heat conducting pad: increasing the height of heat conducting pad H can increase the heat exchange area A, thus achieving the purpose of strengthening heat transfer. However, increasing the height will reduce the local heat transfer coefficient on the top of the heat conducting sheet and lead to the decrease of the average heat transfer coefficient. In addition, the height also affects the temperature drop from the base surface of the heat conducting sheet to the end. The higher the height, the greater the temperature drop, resulting in a decrease in the average temperature difference between the surface and the surrounding atmosphere, which is not conducive to heat conduction.In fact, the height of the heat conductor will also be limited by the overall size of the machine. Influence of thickness on the heat conduction of heat conducting sheet: the thinner the heat conducting sheet is, the more heat conducting sheet can be loaded per unit length, thus increasing the heat conducting area and strengthening the heat conducting pad; Along with the rising of the slice thickness of thermal conductivity, thermal conductivity and surface atmosphere around the average heat transfer temperature difference Δ T decreases, which is harmful for thermal conductivity. In practical applications, thickness is often limited by the technological level. Generally, the thickness of the casting heat conducting sheet shall be no less than 2 mm, and the thickness of the machined heat conducting sheet shall be no less than 1 mm.