Q1-1 IST Incrementation Technique

H. S. Carter

IST (Incremental Shell and Tube), HTRI’s next-generation heat transfer software, will be released in August 1996. This program is designed to rate shell-and-tube heat exchangers for a wide selection of baffle types and shell styles, with a maximum of 16 tubepasses. The new calculation engine in IST eliminates the convergence failures sometimes exhibited by CST for cases with temperature crosses or large desuperheating or subcooling regions. The key to this success is the new incrementation technique applied over a three-dimensional grid that more accurately calculates the heat transfer coefficient, pressure drop, and other variables for the given process conditions. This article describes how the incrementation logic in IST differs from CST and presents a simple example for a TEMA E shell with segmental baffles.