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Abstract

This report contains the development and testing of a component model which is compatible with a large computer program for the simulation of solar energy systems, the so-called TRNSYS transient simulation program. The component model holds the numerical description of two different short term heat storage vessels. In both vessels the energy is stored in the latent heat of phase change materials. In one tank the phase change material is packed in cylinders and the heat transfer fluid flows parallel to it. In the other tank, pipes containing the fluid are embedded in the phase change material. Both configurations can be described in a cylindrical way, resulting in a two-dimensional mathematical model. The basis of the model is the enthalpy method in which the transition range of the phase change material is introduced. Furthermore, special attention is paid to the modelling of the cylinder and pipe wall, the energy transport between the heat transfer fluid and these walls, the energy loss into the environment and the special requirements of the TRNSYS program. The resulting set of equations is solved by means of the Gauss-Seidel iteration process. The model is validated on the basis of a comparison between the numerical results of a simple problem and its analytical solution. The agreement is the best in the case of a linear grid in the radial direction of the phase change material cylinder. An optimum between the accuracy and the calculation time of the component model is derived from tests. Calculations using 5 grid points in the radial direction in the phase change material, approach the real thermal behaviour of the storage vessels for common situations within some 5 or 6 %. However, in this case large calculation times do appear. For normal flows the number of calculation grid points in the axial direction of the phase change material cylinder is 10. By very large flows this number can be reduced. Finally, a simple TRNSYS simulation of a solar water heating system, containing the phase change material storage vessel, is carried out. This example shows the correct communication between the component model and TRNSYS.

Additional information

Authors: VISSER H DELFT UNIVERSITY OF TECHNOLOGY (THE NETHERLANDS), DELFT UNIVERSITY OF TECHNOLOGY (THE NETHERLANDS)
Bibliographic Reference: EUR 10836 EN (1986) MF, 166 P., BFR 300, BLOW-UP COPY BFR 825, EUROFFICE, LUXEMBOURG, POB 1003
Availability: Can be ordered online
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