Heat transfer

PAPERS 142-157

B. N. Furber, National Nuclear Corporation Ltd, Risley

Would Dr Wilkie comment on the possibility of matching the roughened surface to the axial duty and the difficulty of specifying surface emiss-ivity without knowledge of material history and surface condition (roughness)?

D. Wilkie, Taper 142

An answer to this is given in paragraph 14 of Paper 147. Because of various operating and fault conditions, the peak can and fuel temperatures can occur in the lower half of the channel. Ribs can be removed completely from the bottom two elements but thereafter a graduation in roughness is needed. Transverse ribs are not the best in this respect because reducing the rib heights leads to manufacturing, deposition and oxidation problems as well as reducing pitch for a given ratio of pitch to height. Increasing pitch to increase the ratio of pitch to height results in higher inter-rib hotspots. A good solution is to adopt multi-start ribs which, because of the extra degree of freedom given by the lead angle, can avoid these problems.