Simulation of the global flow and heat transfer over tube banks heat exchangers using a momentum and energy sources formulation

A numerical model is developed for the simulation of the global fluid flow and heat transfer in cross-flow tube bank heat exchangers using a momentum and energy sources formulation. The incompressible Reynolds-averaged Navier-Stokes equations are discretized using a cell-centered finite-volume algorithm. The discretized equations are iteratively solved using a Multigrid-SIMPLEC algorithm with a modified strongly implicit (MSI) smoother. Turbulence closure is obtained by means of the standard κ - ε turbulence model. It is assumed that the resistance to the flow created by the tube banks can be modeled as a drag force, that is, introduced into the discretized momentum equations as a source term. Similarly, the heat flux over the tubes is introduced into the energy equation as a source term. The strength of the momentum sources is estimated by using empirical relations to obtain appropriate values of pressure drop. The intensity of the energy sources is calibrated using empirical relations to obtain the convective and radiative heat transfer coefficients, and adjusted to achieve overall energy conservation. The results presented here include calibration curves and validations over a three-dimensional boiler geometry, as well as simulation over two different types of boilers.