Effect of plenum length and diameter on turbulent heat transfer in a downstream tube and on plenum-related pressure loss

The heat transfer experiments were supplemented by pressure drop and flow visualization experiments. Air was the working fluid for the heat transfer and pressure drop tests, whereas water was used for the flow visualizations. The heat transfer apparatus was specially designed to defend against extraneous conduction heat losses by guard heating/cooling of the electrical power leads and by thermally isolating the heated test section from the plenum and the surroundings. Three parameters were varied throughout the experiments. One of these, the ratio L/d of the plenum length to the test section diameter ranged from one to ten. A second parameter, the ratio D/d of the plenum to tube parameter, took on values of three and six. The third parameter was the Reynolds number, which varied between 5,000 and 60,000. There is substantial enhancement of the local heat transfer coefficients in the tube due to processes which take place in the plenum.