A miniature heat sink heat exchanger is constructed with circular cross section channels, each of which has a diameter of 3.0 mm, drilled through a rectangular block. Cooling water at 20°C flows at the rate of 0.5 kg/h through each circular pipe, which has a constant surface temperature of 80°C. Assuming fully developed velocity and temperature distribution conditions, determine the length of the drilled pipe if the outlet water temperature is 60°C. Also, based on your calculations, verify the fully developed condition assumption.