Heat Transfer Velocity. The basic equation for the rate of convection heat transfer is known as newtons law of cooling. Typical values of α are shown in table 1 from which it can be seen that increases in velocity generally result in increases in heat transfer coefficient so that α is smallest in natural convection and increases to 100 and more on flat surfaces with air velocities greater than around 50 ms.
Often less understood is the effect of velocity on the thermal transfer characteristics of the heat exchanger. The heat transfer rate from heat sink base to air is given by equation 3 below. The results showed that the overall averaged heat transfer coefficient was generally proportional to the inlet velocity.
The left hand side of the equation represents convective heat transfer that is heat transfered by the fluids motion.
Water is a great heat transfer fluid. In the world of hydronic heating fluid mechanics at lower velocities the reymolds number re remains high enough and the prandtl number pr remains low enough that low velocity is not an issue. From here the heat sinks thermal resistance is calculated using equation 4. Often less understood is the effect of velocity on the thermal transfer characteristics of the heat exchanger.