Critical heat flux and pressure drop for tubes containing multiple short-length twisted-tape swirl promoters

This paper presents correlations developed for predicting critical heat flux (CHF) and pressure drop in tubes containing multiple short-length twisted tapes (MSLTT) at operating conditions applicable to pressurised water reactors (PWRs). The specific design application motivating these developments was the Inverted Pressurised Water Reactor (IPWR) for which MSLTTs were chosen for the tubular flow channels in order to reduce the excessive pressure drop caused by full-length twisted tapes (FLTTs). Available correlations were examined, but they either had applicability ranges that for some parameters did not cover the IPWR operating conditions, or did not exhibit acceptable accuracy. Accordingly, a new correlation was developed for MSLTTs that is accurate for IPWR conditions. The MSLTT correlation is bounded by the performance of a FLTT for fully developed swirl, and the empty tube value where the swirl intensity is negligible. The development of the thermal–hydraulic analysis methodology for the tubular flow channels was completed by modifying existing correlations for pressure drop with multiple short-length twisted tapes and the attendant swirl decay between the individually spaced tapes. The methodology described herein can be used for the overall design of an IPWR as well as any heat transfer apparatus using MSLTTs in circular tubes at the operating conditions specified in this paper.