Experimental Research On Contact Heat Transfer Coefficient Based On Transient Method

Contact heat transfer coefficient as the key parameter to estimate the ability of heat transfer across the interface has been broadly applied in many fields, such as cryonics engineering, microelectronics, metal hot forming and the manufacture of equipments. Many theoretical and steady experimental studies were developed, and researchers consistently agreed that the constriction of heat flow at the rough contact surface causes thermal contact resistance. In fact, some thermal contacts occur in a very short time dynamically with high temperature samples. The contact between blank and die in metal hot forming process is a typical example. It is necessary to research the thermal contact in transient state deeply due to the paucity of the related data. In this work, surface profile model, contact deformation model and contact heat transfer model were introduced based on many related literatures. The analytical model and theoretical correlation were also described according to the model established by Cooper, Mikic and Yovanovich. A new experimental apparatus with the data acquisition system was developed using the inverse method. Contact heat transfer coefficient of several typical metals was investigated at different contact pressure and initial temperature. It can be concluded from the experimental results as follows:1. The temperature field inner samples redistributes immediately after contact occurs. The variation of temperature at the interface reaches maximum in 5 seconds. Calculated and measured temperature at the verification position agrees well, which indicates that the experimental method is reliable.2. Contact heat transfer coefficient increases rapidly to a level at the beginning of contact, and then a much slower increase may occur with the increasing time because of the deformation of contact surface and calculated error.3. Contact pressure and initial temperature are both significant factors for contact heat transfer coefficient. Contact heat transfer coefficient increases with the increasing contact pressure generally. The study of temperature on low temperature sample provides some references for preheating of the die material in practice.4. The principles are different between steady and transient experiments. However, the experimental results between aluminum alloy and die steel show that there exists some relationship on contact heat transfer coefficient obtained from the two methods.