Abstract: The heat transfer characteristics of gas slip flowing in the rectangular microchannels heated unsymmetrically with constant axial heat flux are analyzed theoretically for the slip flow regime. The energy equation with temperature jump bou-ndary conditions in slip flow regime is solved by a computation-oriented method of the orthonormal function analysis. The dim-ensionless temperature profiles and the average Nusselt numbers for various thermal boundary conditions are obtained and com- pared with those in macrochannel under the same conditions. The effects of Knudsen number, aspect ratio, and thermal boundary conditions on the heat transfer characteristics in slip flow regime are discussed, respectively. The calculated results show that the average Nusselt numbers in rectangular microch- annels is lower for slip flow than for no-slip flow under any heating condition, and decreases with increasing Knudsen number. The smaller the aspect ratio is, the more the decrease of the average Nusselt number is. The decrease of the average Nusselt number in rectangular microchannel compared with the macrochannel for the condition of only one wall heated is the smallest at the same Knudsen number and aspect ratio compared with others heating conditions.

Key words: Heat transfer characteristics, Rectangular microchannel, Slip flow regime, Unsymmetrical thermal boundary