3.2.1. Simulation in HTRI Xchanger Suite

Compared to a full-scale CFD simulation of the boiler, which would rarely be done in the case of equipment of such size, the actual computational time required by HTRI Xchanger Suite was negligible (units of seconds). Unlike CFD, however, the software generally focuses on the thermal side of the apparatus design, i.e., its primary goal is to provide as accurate stream temperatures as possible while the flows in both the tube and shell sides are assumed to be uniformly distributed (unless the user specifies the distribution explicitly). Moreover, one cannot directly set tube inner and outer surface roughnesses, which may significantly influence the predicted pressure drops.

Results obtained using the discussed software package are listed in Table 4 together with the data provided by the operator of the heat recovery hot water boiler. The table also mentions the absolute and relative errors. From these, one can see that the predictions of both the outlet temperatures and the tube-side pressure drop were quite accurate. The predicted shell-side pressure drop, however, was markedly lower than the measured value. It also was a notable disadvantage that no detailed information was given by HTRI Xchanger Suite regarding the actual flow distributions in the bundles and the shell.


**Table 4.** Results obtained using HTRI Xchanger Suite and the corresponding errors compared to the data from the operator of the boiler. It is apparent that the temperatures and the tube-side pressure drop were predicted quite accurately, but the shell-side pressure drop was markedly below the measured value.
