Analysis of the topography of microchannels with different sizes

The influence of different rough and structured surfaces of microchannels on the heat transfer from the heating surface to the boiling liquid have been investigated by a joint research project of Brunel and Hannover (now Kassel) Universities with refrigerants boiling in single microchannels of different inner diameter. The microchannels are capillary tubes and they are manufactured by industrial processes. The samples of the microchannels have to be prepared by special methods, because the surfaces inside the microchannels cannot be measured in the same way as is used for the heat transfer measurements. The microstructure of the surfaces of three microchannels (D = 0.4, 0.5 and 0.8 mm) is measured by a contact stylus instrument. The paper focuses on the detailed analysis of the profiles and the topographies of the samples. The roughness parameters in accordance with standard practice are calculated for ca. 1000 runs (profiles). The roughness parameters of the smaller microchannels are twofold higher than those of the largest microchannel investigated. The scattering of the roughness of the largest microchannel (D = 0.8 mm) is less and the cavities are smaller than those of the other ones (D = 0.4 and 0.5 mm). All surfaces investigated demonstrate a deterministic microstructure as for emery ground surfaces on smooth tubes in the literature.