Analysis of steam and hydronic compartment heating systems aboard U.S. Coast Guard 140 foot WTGB class cutters

Abstract

The compartment heating system on the U.S. Coast Guard's Icebreaking Tug (WTGB) class cutter was studied to determine heat transfer performance characteristics of existing heat exchangers when used with circulating hot water vice steam. Characterizations such as Reynolds number vs. Colburn j factor plots, convection coefficients, overall coefficients, and Effectiveness-NTU relations were generated. Initial analysis with acknowledged conservative definitions of air side convection coefficients determined that the hydronic system provided on average seventy percent of the heat transfer capabilities available with the steam system. Improvements to the hydronic system were shown to increase heat exchanger performance parameters by an average of ten percent. It was notable that the added heat transfer available from steam is not due to a property of steam itself such as latent phase change effects, but is due solely to the increase in entering tube side temperature. Judging by heat transfer capabilities alone, with the described conservative assumptions on which these results are based, use of currently installed heat exchangers in a hydronic system is a viable option.