Validation of CFD Models for Double-Pipe Heat Exchangers with Empirical Correlations

Heat exchangers are present in most industries as they allow the recovery of thermal energy, making processes more profitable and environmentally sustainable. The design of classical heat exchangers is performed based on well-established semi-empirical equations, e.g. Double Pipe Heat Exchangers (DPHE). Those semi-empirical equations are very susceptible to geometry changes, as well as flow conditions at the entrance of the heat exchangers. Semi-empirical correlations are based on simplifying assumptions such as constant fluid properties along the heat exchanger. A design solution to this issue is Computational Fluid Dynamics (CFD), which is widely used for the design of novel heat exchanger geometries saving experimentation time and cost. To the best of our knowledge, CFD results have not been tested against the classical semiempirical equations. Before facing future complex geometries, the proper CFD model options are identified and validated against classical equations. In this study, this analysis is performed for the case of a classical DPHE. Series of CFD simulation results are critically compared with classical for DPHE. Different turbulence models and wall treatments are tested, as well as fully developed velocity profiles at the entrance of the heat exchangers, obtained by iteration. Results show that CFD codes are able to predict and model the flow in DPHE reliably, with the same accuracy as classical correlations. CFD simulations are found to differ from semi-empirical correlations up to 0.87 % in the case of pressure drop and 7.1 % in the case of heat transfer. Consequently, CFD simulations with proper setup parameters are a good choice for assessing novel configurations. Reliable novel heat exchange configurations assessment is compulsory for heat exchange network revamping in restricted space industrial scenarios and opens novel opportunities for higher heating and cooling services savings