New approach for transient simulation of closed batch evaporation in a plate heat exchanger

This paper proposes a new concept for the simulation of transient heat transfer processes in a batch evaporator. It has been shown that the batch evaporation can offer advantages in terms of overall efficiency in power cycles. The main challenge with the simulation of a closed, isochoric evaporation is the combination of the dynamic pool boiling on the cold side, the transient heat conduction in the wall and the 1-D forced flow on the hot side of the evaporator. The pool boiling causes a gradually rising pressure and boiling temperature as well as a shifting liquid level. As the heat transfer coefficients change with a high gradient around the moving liquid level, the entire wall of the plate heat exchanger has to be discretized in fine steps. By combining a build-in MATLAB solver with a finite differencing method, a dynamic step-size can be accomplished for the discretization in space. Thereby, only a narrow zone of refined steps moves along with the liquid. With this approach, the number of cells of a reference case can be remarkably reduced compared to commonly used models.