Contact heat exchange in conjunction with metal surfaces which have deviations in form or waviness

In the design of thermally stressed units in the sectors of mechanical engineering, aviation, aerospace, energetics it is often necessary to have information about the formation of the contact thermal resistance resulting from the discrete nature of parts metal surfaces contacting. While passing through the section zones of heat flows the temperature gradient increases, thus reducing the heat transfer capability of the contact junction and leads to thermal expansion of the constituent elements of the systems, relative shifts and warpages. The process of heat transfer through the zone of contact between metal surfaces having deviation of shapes in the form of nonflatness or waviness under conditions suitable to small mechanical loads is considered. The model of formation of the contact thermal resistance (CTR), in case of double contraction of the heat flow of channel and contact mаcrospots, caused by nonflatness or waviness, and then to microspots caused by roughness. Subject to the provisions of the theory of mechanical contacting of solids theoretical curves is derived describing the contact thermal resistance for compounds with surfaces having microdeviation or waviness operating in the regime of small mechanical loads. The results of physical experiments give satisfactory agreement with the calculated data. It was established that the presence of nonflatness or waviness on the contact surfaces increases CTR significantly as compared with rough surfaces. Increase of CTR is explained by the increase of wave height or equivalent nonflatness

An Engineering Method for Asphalt Foaming Modeling Integrating Gas-Liquid Phase Change Process

The asphalt foaming is a nonlinear kinetics process under high temperature and high pressure with multi-phase medium and multi-field condition. It includes stages like transient contact, heat exchange, phase change and bubble generating process. In order to quantitatively describe the relationship between the asphalt foamability and the asphalt foaming equipment physical parameters, the engineering method for asphalt foaming modeling integrating gas-liquid phase change process is created. Meanwhile, the asphalt foaming dynamic model for design parameters and coupled field distribution, which can express multiphase contact, heat exchange and further phase change, is built. Compared to the old non-phase change model, the new model has a stronger correlation to the asphalt foaming experimental results. Therefore, the study is significant for the redesign of the asphalt foaming equipment.