Experimental Analysis And Parameter Optimization On The Interface Thermal Contact Resistance

Airborne computers are used in the aviation field for providing the aircraft systems with high-performance computer hardware resources and rich communication interfaces.It is usually regarded as the ‘brain' of the aircraft.Obviously,the reliability of airborne computers is extremely important for the aircraft.Researches have shown that the reliability of electronic devices can be significantly influenced by the temperature and 70% device faults are related with temperature rising.While the temperature increase by 10 ?,the probability of device faults would increase by 50%.Therefore,effectively increasing the heat dissipation efficiency of the airborne computer is a key to ensure its well operational stability and high reliability.However,in order to meet the requirement of the three proof-design,the airborne computer usually adopts a reinforced chassis.Therefore the heat produced by the chip can only be transferred through the interface between the cold plate and the chassis guide rail and,the heat transfer efficiency of the interface plays an important role in the heat dissipation of the airborne computer.Unfortunately,the solid surfaces are usually non-smooth on micro-scale,i.e.,the real contact between the two solid surfaces only occurs at discrete points and small areas.This would lead to the contraction of heat flow at the contact interface.In other words,there exists thermal contact resistance on the interface,which is usually called as interface thermal resistance or thermal contact resistance.The thermal contact resistance can significantly decrease the heat dissipation efficiency of the airborne computer.If the heat produced by the chip cannot be effectively dissipated through the interface,the chip temperature would be considerably increased and the operation performance and reliability of the airborne computer would be lowered.Therefore,it is very important to study the effects of some typical factors on the thermal contact resistance of airborne computer.According to the specific thermal dissipation structure and material characteristics of some typical airborne computers,this thesis carried out some experiments and numerical analysis to study the thermal contact resistance of two airborne computers.(1)Design and establish a set of thermal contact resistance test system.It is proven that system can be successfully used to measure the thermal contact resistance by a steady-state measurement method.(2)By using the above test system,45# steel and 6061-T6 aluminum alloy,which are often used as heat transfer structures materials in airborne computer.The effects of the material properties,interface roughness,interface pressure and interface temperature on thermal contact resistance were experimentally studied.It was shown that the surface roughness of the 45# steel sample with higher hardness has a greater influence on the thermal contact resistance than 6061-T6 aluminum alloy.With the increase of the interface pressure,the thermal contact resistance decrease significantly,but the influence of interface temperature on the thermal contact resistance is relatively small.It should be point out that with the increase of interface pressure,the influence of surface roughness and interface temperature on thermal contact resistance would be weakened.(3)Based on the above data,the least square method was used for data fitting,and the fitting formula between the interface pressure and the thermal contact resistance under different roughness was obtained.At the same time,the finite element method was used for the mechanical analysis of the JA locking device and JB locking device,which are two typical cooling structures used on the airborne computer.The corresponding relation between the contact pressure distribution and the bolt torque of the locking bolt of the cooling structure is obtained.Then,on the basis of the above fitting formula between interface pressure and thermal contact resistance,a calculation program of the thermal contact resistance distribution and the average thermal contact resistance was written by the Matlab software.Using this program,the distribution of the interfacial thermal resistance and average thermal contact resistance under different bolt torque are calculated,which can be directly used to guide the preload setting and thermal contact resistance estimation of the heat dissipation device.(4)In order to reduce the thermal contact resistance of the bottom surface of the chassis cooling structure,this thesis carried out a parameter optimization design for the chassis guide rail of JA and JB structures.The finite element results show that the thermal contact resistance between the chassis guide rail and the end plate of JA and JB structures can be effectively reduced by improving the rigidity of the chassis guide rail,i.e.,reducing the size of the internal groove.These findings are beneficial to increase the heat dissipation efficiency of the airborne computer.