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Project C02: Multiscale Investigations of Boiling of Complex Fluids on Complex Surfaces

In the nearer future microelectronics will get smaller and at the same time more powerful. Thus, cooling of those components becomes more important. The heat removal via heat pipe is a desirable solution. The phase change phenomena like boiling and condensation are the dominant heat transfer mechanisms inside a heat pipe. During boiling several boiling regimes can be differentiated. Nucleate boiling is the most desirable regime. It combines high heat fluxes with moderate wall superheats.

The aim of this project is to investigate the interactions between evaporation, hydrodynamics and dynamic wetting properties. This project is a first step to develop a physically accurate model to predict the heat transfer in the nucleate boiling regime for various surfaces and fluids.

A test setup was built to enable nucleate boiling experiments in a wide temperature and pressure range and with different fluids and surfaces. To explore and study the relevant parameters for the boiling process on different length scales two heaters are used. One of them is made of copper, which is heated via a ceramic heater. This heater is used to study multiple bubbles and very high heat fluxes. The second heater is made of an infrared transparent material sputtered with a metallic layer. This layer is used as a resistance heater. Using a high speed infrared camera the local heat flux on the back of the metallic layer can be measured. This allows experiments with single or few bubbles at low or medium heat fluxes.

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