Study On The Heat Transfer Performance Of Thermosyphon Loop With Minichannel Evaporator

With the rapid devlopment of global informatization, more and more data centers have been set up for information storage and transfer. The normal operation of the data center needs to consume a large amount of electric energy, especially the room temperature control. Almost 50% of the power has been used by air conditioner to keep the center at a specified temperature. Heat pipe technology is applied to cool data center in order to reduce power consumption by using outdoor cold source. Thermosyphon loop is similar to heat pipe, but with simpler structure. Liquid refrigerant is brought back to evaporator by gravity. When the temperature difference between indoor and outdoor reaches a certain value, thermosyphon loop will start up spontaneously. On the other hand, thermsyphon loop can transmit heat over a long distance, which meets the requirement of date center cooling. According to the literature, the heat transfer performance of thermosyphon loop is affected by its structure, liquid filling ratio, height difference between evaporator and condenser, the cooling condition. However, in the existing literature, experimental and theoretical studies on thermosyphon loop with minichannel evaporator are few. In this paper, theory calculation and experiment work were carried out as follows:(1) The present research progress of two-phase thermosyphon loop at home and abroad has been reviewed. These work defined the significance and future research direction of the thesis.(2) Thermosyphon loop with minichannel evaporator were build to cool air with water. The start-up process, the influence of different parameter such as height difference between evaporator and condenser, inlet temperature difference between water and air, water flow rate, refrigerant charge ratio on the heat transfer performance were investigated. At last, the thermal resistances in those processes were analyzed.(3)Traditional filling rate models were used to calculate the minimal filling amount of refrigerant. In order to know the liquid level in the downcomer, the conservation of mass, homogeneous flow pressure drop model, energy conservation equation were used. After that, a vertical tube falling film model was used to calculate the refrigeration quantity of falling liquid film section. Then the new theoretical filling rate model for thermosyphon loop was established.(4) Thermodynamic calculation was conducted at minichannel evaporator. Chang&Wang heat transfer model was used to calculate the air side heat transfer coefficient. Cooper pool boiling model was used to calculate the refrigerant side heat transfer coefficient. Calculation results were compared with experiment results.