Temperatures in the test rig, as reported henceforward, are taken to be the temperatures above ambient. The inlet temperature is also taken as ambient temperature. It is further assumed that the width of the channel, 92.5 cm, is sufficient that edge effects are largely eliminated at the centre. This width is similar to large-scale test rigs used by other investigators [31,32,38], and most small-scale investigations had similar height-to-width ratios. Therefore, the conditions measured at the centre line of the test rig are taken to be representative of the conditions in an infinitely wide channel. However, this assumption may be tested in future experiments.