Designing heat exchangers with the aid of computer simulation
By means of numerical computer models (CFD = Computational Fluid Dynamics) the thermal design of heat exchangers can be optimized with respect to the length or the size of the heat transferring surfaces resulting in less material costs. Additionally the flow parameters can be optimized, e.g. minimal volume fluxes of fluid B needed as well as minimal temperatures, resulting in minimal energy consumption and reduces operating costs. In the numerical simulation the
fluids and the solids are modelled, respectively.
Additionally the surrounding conditions can be taken into account, e.g. free convection. Together with the flow field (velocities and pressure) the temperature distribution in the model is solved for. The physical models which can be taken into account include heat conduction through solids and fluids, energy transport through free or forced convection and radiation effects.
The results include not only the temperature distribution but also the flow field. As the heat transfer coefficient depends
mainly on the fluid velocity distribution close to the surface the design of the heat exchanger can be optimized for example by influencing the flow field in a way that the heat transfer coefficient is maximized.
EXAMPLE
The two examples shown here are an extraction of the results of a “dummy” model of the MHE33 and the MHP23 double tube heat exchanger just to show the possibilities of a CFD simulation. The colours indicate the resulting temperature distributions (red means high temperature, blue stand for a low temperature). The environment was assumed to be air with free convection. The results show e.g. that only 2% of the total heat flux are lost to the environmental air.
The increase in temperature of fluid A is about ΔT = 3K. But the enthalpy of the heating fluid B is only reduced by 0,3%, hence a lot of energy could be saved by an optimization.
PICTURES
