In order to realize heat transfer of graphite heat exchanger, heat exchange equipment undoubtedly plays a very important role. Based on the specific working conditions in refrigeration and cryogenic technology, the tube and tube type graphite heat exchanger is used in most cases, especially the heat exchanger with heat transfer elements as tubes, which is widely used in refrigeration and cryogenic devices and has a long history. This is because the round tube is simple to process, mature in technology, easily available in the market, and can work reliably in a wide range of pressure and temperature. Even if the working condition is unstable, the thermal stress impact and the fins are added on both sides of the mechanical heat transfer tube, as well as the required fin shape, to achieve enhanced heat transfer; The whole graphite heat exchanger has the advantages of high heat transfer efficiency, compact structure, small size, light weight and small flow resistance; Tubular graphite heat exchanger has various structural forms according to different requirements, but it can be divided into tube and tube type, coil type and vertical shell and tube type. For example, condenser and evaporator in refrigeration technology; Condensation evaporator used in air separation unit, etc. A variety of coiled graphite heat exchangers are widely used in refrigeration and cryogenic devices.
Low temperature graphite heat exchanger is exposed to quite a lot of phase change heat transfer and two-phase flow. On the one hand, the low temperature graphite heat exchanger requires high heat transfer efficiency and high heat flow density; On the other hand, it is very easy to produce phase transition in the process of generation, storage, transportation and heat exchange of cryogenic fluid. These phase change heat transfer processes not only include all boiling and condensation modes, but also are in a large number of conditions of two-phase forced convection heat transfer and near critical zone convection heat transfer with very complex heat transfer mechanism. However, the heat transfer of low-temperature graphite heat exchanger has its own characteristics after all, and its physical properties change dramatically at low temperatures. At low temperature, the physical properties of working medium will change obviously with temperature and pressure, so the fixed physical properties of convection energy equation given in general heat transfer cannot be used at will, and the application of logarithmic uniform temperature difference is also limited. In particular, the heat transfer of low-temperature graphite heat exchanger often stops in the area close to the thermodynamic critical state, and the physical properties in the near critical area change violently with temperature and pressure, so the common conventional variable physical properties relationship is not applicable. Low temperature heat conduction mainly touches on the heat conduction with variable thermal conductivity, as well as the multi-dimensional heat conduction problem of anisotropic crystal deposits that are easy to form at low temperatures. In addition, low temperature equipment and low temperature graphite heat exchanger mostly work under conditions far below the ambient temperature, so the thermal insulation of equipment, high vacuum insulation of support heat conduction, vacuum insulation of multi-layer insulation powder, powder, foam insulation, heat conduction of deformed variable cross-section long rod, etc. all touch the characteristic low temperature heat conduction problem. Graphite heat exchangers are more and more widely used in various areas of the national economy.
