Applications of the Discrete Sub-heat Exchanger Method to J-type Shell and Tube Heat Exchanger

Abstract

Abstract Effectiveness number of the transfer units method (ε – NTU) have an important place in dimensionless thermal analysis of heat exchangers. However, ε – NTU can be applied assuming that the fluid properties in the heat exchanger are constant. If changes in the fluid properties are moderate, ε – NTU with an iterative procedure can be proposed by averaging the input and output values of the fluid properties. Otherwise, discrete numerical methods would be required for two-phase, transcritical regional flows or large temperatures differences. This research presents the Discrete Sub-Heat Exchanger Method (DSHE) with applications of J-type shell and tube heat exchangers. DSHE discretizes any heat exchanger into sub-heat exchangers having basic flows and applies the ε – NTU to the sub - heat exchangers in an iterative manner. Thus, changes in the fluid properties are included in the thermal analyzes. In addition, the effectiveness values of heat exchangers having any complex flow patterns can be calculated numerically and the temperature profiles, possible pinch point or temperature cross can also be observed by using DSHE. In this research, the results of ε – NTU and DSHE have been compared with three different study cases. In the first case, the relative error of the effectiveness values is below 2% in relatively low temperature differences in single-phase flows. Thus, the DSHE can be considered validated according to the result. In the second case having relatively large temperature differences, the relative error of the effectiveness values is over 16% despite single-phase flows. The last case, including the transcritical regional flow has a relative error close to 14%. The relative errors in the last two cases are significant because the changes in fluid properties have not been reflected in thermal analysis with ε – NTU despite using the iterative procedure. Consequently, it is recommended to use DSHE instead of ε – NTU for thermal analysis when changes in the fluid properties aren’t moderate.