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Go to Editorial ManagerAn experiment was conducted on two types of microchannels (zigzag and symmetrical circular) using water as the working fluid under normal boiling conditions. Heat fluxes ranging from 180 to 780 kW/m² were used, the Reynolds number varied from 58 to 107, and the water flow was streamlined. Temperatures were measured at ten ports (inlet, outlet, and walls). The results showed that for the zigzag channel at a heat flux of 580 kW/m², the average wall temperature decreased from 112°C to 87°C as the Reynolds number increased to 107. Both the Nusselt number (from 42 to 86) and the Reynolds number (from 58 to 107) also increased. The zigzag channel exhibited an improvement in heat transfer coefficient with a 30% decrease in the average temperature. The temperature of the circular cavity channel decreased from 126°C to 96°C, while the flow remained constant. Flow patterns were captured using a high-resolution camera for study during boiling.
In this paper the conjugate heat transfer in rectangular channel is numerically investigated, where the effect of both axial heat conduction and entrance region on the internal forced convection in rectangular channels are studied. With decreasing the dimensions of channels the thickness of walls become large and in order of the channels dimensions as in microchannels. As a results the heat conduction in the walls especially in the axial direction can not be ignored, since it lead to decrease in the efficiency of heat transfer process. Also the effect of entrance region is taken into consideration where the flow is assumed developing hydro dynamically and thermally. A finite volume method is used to numerically solve the conjugate heat transfer in both the fluid and wall simultaneously. The results obtained shows that the existing of axial heat conduction lead to reduction in the heat transfer and it's effect increased with increasing the thickness of walls and Reynolds number. In this paper a correlation has been developed to calculate the value of axial heat conduction in channel's walls based on most of the affecting parameters. This correlation can be used accurately to compute the value of axial conduction in rectangular channels.