Experimental study of the heat transfer and of pressure losses with gaseous hydrogen in turbulent flow in a tube and in an annular space

Three different dispositions were used: a tube (diameter 4 mm, length 320 mm) and two annular spaces (3 x 8.8 and 5 x 8.8 mm, length 260 mm). The tubes are of stainless steel and are heated by a 50 cycle alternating current. The Reynolds number varied from 4000 to 120000, the wall temperature up to 700 deg. C, and the exit-temperature up to 500 deg. C. Heat flows of up to 170 W/cm2 were observed. All the experimental results can be summed up by a correlation expression of the Colburn type Nu = 0,020 Re0.8 Pr0.4, as long as the physical properties of the gas are expressed at the film temperature t0.3 = tm + 0.3 (tp - tm). For each particular disposition, a more exact correlation has however been obtained. A variation of the film temperature index with the ratio of the heated to the wetted perimeters has been observed. The pressure loss coefficients measured are lightly higher than those calculated using von Karman formula for smooth tubes. (author)