Study On The Performance Of Micro-Structure Heat Radiator For High Heat Flux Equipment

Micro-structure heat radiator has many advantages, such as compact microstructure, high heat density, low thermal resistance, flake design and batch production, therefore, it is considered as an effective way to solve the future cooling problem of laser and electronic equipments, which aim for the characteristics of small size, high integration, high-power, complex structure. However micro-structure heat radiator also has its disadvantages. On the time that the micro-channels achieve good capacity of heat dissipation, they encounter the larger pressure drop problem. This is the challenge for the fluid-driven pumps and integrated package of micro-structure heat radiator. In this paper, a large height/width ratio micro-structure heat radiator was proposed to solve the problem of larger pressure drop. Using deionized water as working fluid,the experimental and theoretical studies were conducted to reveal the pressure drop and heat transfer characters of different types of large height/width ratio micro-structure heat radiators.The effects of inlet/outlet arrangement on the fluid flow and heat transfer inside the heat sinks were numerical investigated. The microchannel heat sinks with 8 kinds of inlet/outlet arrangements are considered in this paper. All of the geometric dimensions of these heat sinks were the same except the inlet/outlet locations. The non-uniform coefficient of flux and temperature were proposed and used to assess quantify the inlet/outlet arrangement effect on mass flow distribution in micro channels, the best inlet/outlet arrangement for the heat radiator was achieved. On the basis of this conclusion, it is available for us to design high performance micro-structure radiators.The radiators with different large height/ width ratio mini-channels were designed for avoiding large pressure drop of micro-channel. The characters of single phase fluid flow and heat transfer for 3 types of large height/ width ratio mini-channels was experimental studied. The results showed that, the pressure drop in large height/ width ratio mini-channel was less than that in microchannel obviously. The pressure drop of per unit length was proportional to Reynolds Number, hydrodynamic diameter and 0.33 th power of height/width ratio. A general heat transfer empirical formula was proposed to evaluate cooling performance of the radiators with consideration of Nu number as a faction of Re number, height/width ratio, length/diameter ratio, and Pr number. For the purpose of maximum heat removal, the mini-channels radiators have the optimum channel height.After the analysis of the experimental data of large height/ width ratio mini-channels, it was found that the heat dissipation reduced once its height increased to the specific value. For heat transfer enhancement purpose, a mini-channel radiator with cylinder disturbed flow was proposed. The performance of heat transfer and pressure drop with/without disturbed flow was studied experimentally. It was found that the friction factor of mini-channel flow was larger than that of the macro-channel flow due to larger surface roughness and inlet/outlet effects. The pressure drop caused by cylinder disturbed flow was less than 5%, while heat transfer enlarged more than 10%. A general empirical formula was proposed to evaluate cooling performance of the radiators with consideration of Nu number as a faction of height/width ratio, length/diameter ratio, the dimensionless thermal entrance length. For the enhancement of fluid mixing performance in mini-structure heat radiator,the pin fin was considered to replace the mini-channel in designing the mini-structure heat radiator. The radiators with different large height/ width ratio mini-square fin were designed and processed. Experimental study on the characters of single phase fluid flow and heat transfer in two types'large height/ width ratio mini-square fin heat radiators is carried out. It is found that the pressure drop increased with the increase in channel Reynolds number. The transition phenomenon appeared when the Re number was higher than 300 in those two heat sinks. The heat dissipation of mini-square fin heat radiators was more excellent than mini-channel when their flow rate and surface temperature were equal. The average Nu number increases with the increase in fin Reynolds number. The heat transfer performance of present sink was over predicted by the previous correlations. Therefore, new correlations were proposed for the average Nu number prediction.To study the effect of surface roughness on laminar flow and heat transfer in mini-channels, the 3-D model and PML model which is based on the surface shape are developed. It is found that, there are the temperature and velocity sub layers in the rough mini-channel, where the temperatures and velocities are linearly with the distance to wall surface. The pressure drop of per unit length and Nu number are quadratic with the relatively surface relative roughness when the Re number is fixed. The per-unit pressure drop and Nu number increase linearly with the Re number when the surface relative roughness is fixed. In order to improve the heat transfer performance of traditional heat radiator, the tortuous heat radiator with open-cell copper foam heat radiator and the mini-channel heat radiator with insert fin were designed to meet the heat flux of 80W/cm2 and 50W/cm2. Experimental studies of the flow and heat transfer performance in those two heat radiator were performed. The results showed that the heat resistance of tortuous heat radiator was lower than that of micro channel and plate open-cell copper foam heat radiator. It is available to improve the heat transfer performance of mini-channel heat radiator though inserting the fin. The quantity of pressure drop in mini channel heat radiator with inserted fin was much lower than that in micro-channel.