This is a calculator for sizing a shell and tube heat exchanger with tubeside flow fixed. With shellside and tubeside inlet/outlet temperatures fixed, the required shellside flow is calculated corresponding to given tubeside flow. The log mean temperature difference (LMTD) is also reported. For known shellside and tubeside dimensions heat transfer areas and heat transfer coefficients on both sides are calculated. Finally the overall heat transfer coefficient is calculated and reported. If a different value of overall heat transfer coefficient is assumed or desired, then that value should be specified in the end section. The required heat transfer area corresponding to the assumed overall heat transfer coefficient is then reported.