In this study, a copper plate measuring 9.8 mm x 9.8 mm x 0.5 mm was used as a fixed substrate for designs with single-layer-and-parallel or multi-nozzle microchannel heat sinks. Water was applied as the coolant. Channel lengths from 0.2 to 5.6 mm and five different channel shapes, including a circle, square, trapezium, two concave surfaces, and two convex surfaces, were numerically investigated in detail at a constant hydraulic diameter of 200 mu m with a Reynolds number in the range of 700-2200. A novel scheme for meshing was proposed. A structure for a multi-nozzle microchannel heat sink was presented. For all cases in this study, it was found that the best thermal performance was achieved with a circular channel shape which could dissipate a heat flux up to 1500 W/cm(2), and the maximum temperature was kept at less than 75 degrees C at a Reynolds number of 2200. Furthermore, novel equations were proposed to predict the temperature differences between inlet and outlet coolant temperatures depending on the channel length and Reynolds number, as well as to predict the maximum temperatures on the bottom walls of the circular channel shape depending on the Reynolds number and heat flux. (C) 2016 Elsevier Ltd. All rights reserved.