An Experimental Study On The Heat Transfer Characteristics Of Micro-encapsulated Phase Change Material Suspension In Mini-channels

With the development of the micro-electronic mechanical system,the tendency of the electronic equipment developing towards high power and miniaturization is speeding up, just as Moore`s law dictates that: the number of transistors on a computer chip will double every 18 months, the more transistors, the faster operating speed, the circuit on a chip will be more complex, resulting in the consumption of the energy and the heat generated increasing by the run-time, the heat dissipation demand increase.In the existing new cooling technique, the micro-structure cooling with the strengths of high fluid mixing speed, high heat transfer coefficient, high heat transfer and easily encapsulated is widely recognized by researchers. The micro-structure cooling fluid adding in micro-encapsulated Phase Change Material(MEPCM)particle can enhance the heat transfer because of the latent heat resulting to high temperature difference, which is expected to achieve better cooling effect. So, this paper attempts to add the MEPCM particle in the micro-structure cooling fluid to study the heat transfer characteristics of the MEPCM suspension in micro-structure. The main work is as follows:Firstly, the heat transfer characteristics of MEPCM suspension in the diameter of 1mm tube was experimentally studied. The results show that, under the constant heat flux condition, the cooling effect of MEPCM suspension to the tube wall increase with the concentration of the suspension, the maximum of wall temperature reduction rate is up to 27.1%. The MEPCM suspension local heat transfer enhancement ratio is smaller and smaller with the change of the flow length, and appear the negative value, so there is an optimum heat transfer length.Based on the experimental results, this paper summarizes the formula of the mean Nusselt number changing with the Reynolds number,length diameter ratio, Prandtl number and suspension concentration,and taking into account the influence of the thermal entrance, this paper summarizes the formula of the local Nusselt number.Secondly, the heat transfer characteristics of MEPCM suspension in the diameter of 1.6mm rectangle mini-channel was experimentally studied. The results show that, under the constant heat flux condition,the maximum of wall temperature reduction rate is up to 35.6%. The MEPCM suspension local heat transfer enhancement ratio is smaller and smaller with the change of the flow length. The mean Nusselt number increases with Reynolds number and suspension concentration increasing, its corresponding mean heat transfer enhancement ratio increases with the Reynolds number decreasing and increases with the suspension concentration increasing, under the experimental condition, the mean heat transfer enhancement ratio is up to 33.9%.Taking into account the influence of the thermal entrance, this paper summarizes the formula of the local Nusselt number changing with the Reynolds number, length diameter ratio, Prandtl number, suspension concentration and the inlet and outlet heat loss, the formula is well fit to the experimental results.Thirdly, the heat transfer characteristics of the microencapsulated phase change material suspension in micro-tube and rectangle minichannel is compared. The results show that, the wall temperature reduction rate in the two channels increases with the suspension concentration increasing, but the wall temperature reduction rate in micro-tube is none of business with Reynolds number, while it in the rectangle mini-channel decreases with the Reynolds number increasing.There is two different heat transfer characteristics regions along the tube wall and existing obvious turning point for the two regions while there is not in rectangle mini-channel. Due to the influence of the fluid thermal resistance the mean heat transfer enhancement ratio in microtube is less than zero at low Reynolds number, and due to the influence of the latent heat the mean heat transfer enhancement ration is greater than zero, while the mean heat transfer enhancement inrectangle mini-channel is greater than zero among the range of Reynolds number.