Abstarct: The heat and temperature control systems for high heat flux in industries such as electronics, aerospace, military, automotive, fuel cells, solar cells, and so has a great importance. In most cases, improving heat transfer systems by increasing their surface, which is always increases the volume and size of these devices. Two important phenomena occurring in the heat exchanger. The fluid in the flow channel between the fluid and wall heat transfer takes place. So to improve First, because the rate of heat transfer surface area to volume ratio will depend on the channels with smaller dimensions make better thermal conductivity. The use of fluids with improved properties can increase the efficiency of the heat exchanger. So one of the effective ways to ward off the heat generated by the use of micro-channel. In the present study we investigate heat transfer in microchannels that the deionized water displacement happens there. The micro-channel heat sink with 80 parallel channels with a rectangular cross section with width of 100μm, height 100 μm, and the length is 20 mm. The channels made of silicone with a specific orientation <110>, which was created by wet etch. In this paper, we study the heat transfer coefficient of a constant heat flux (41.378 kW / m ^ 2) with three different mass flow rate.