Effects of surface roughness in microchannel with passive heat transfer enhancement structures

•A simple Fourier series method is used to establish surface roughness up to 2% in flat channel, wavy channel and dimpled channel.•In general, roughness could increase the flow resistance and average Nusselt number under laminar flow.•The local influence of roughness is highly depended on the local flow field. This phenomenon is more pronounced in channels with secondary flow.•Roughness could be either beneficial or adverse to overall performance of microchannel heat sink.