Hello Hans,

I think Modelica would be perfectly suited for the task. You can model a slice/layer of your heat storage as a component (class) and test it separately. Then you can instantiate and interconnect an array of N layers to simulate the distributed effect with the spatial resolution necessary for your studies.

In my work with disctrict heating systems I often use a model of of a thermal heat storage tank modelled in a similar way. It lets me take into account the stratification of water in the tank. The tank model is based on model in the freely available Modelica Buildings Library (Buildings.Fluid.Storage.Stratified.mo). I would advise you to take a look at that library and its excellent documentation and use the mentioned tank model as inspiration.

Best regards
Rene Just Nielsen

justnielsen wrote:

You can model a slice/layer of your heat storage as a component (class) and test it separately. Then you can instantiate and interconnect an array of N layers to simulate the distributed effect with the spatial resolution necessary for your studies.

Hi Rene,
Thank you for replying so quick.

You mention "instantiate and interconnect an array of layers". Can this be implemented in OpenModelica as freely as that without defining explicit connections between the layers?

Just to be clear that my understanding is correct. The problem can be formulated as PDFs in time and position and the dt is handled by modelica whereas I need to take care of the dx resolution in the way I build the model?

With e.g. Matlab this can be done by adjusting the number of elements in the vectors representing a given tank size and I can then reference layers by indexes in the vector. Is a similar technic available in modelica?

I am not sure stratified water can correctly mimic the behaviour of solid/gas properties but I will locate the building library and have a look.

/Hans

Yes, you can declare a vector of N layer models and subsequently use a 'for' loop to connect the outlet of layer[n-1] with inlet of layer[n]. See, for example, https://mbe.modelica.university/compone … _transfer/
Modelica currently hasn't go any language constructs for PDEs, so you will have to make the spatial discretization yourself.

You are right, stratified water is not the solution for you — that was just an example to point you in the direction of what is possible. You probably want each of your layers to be the combination of a flow resistance (air through pebble bed) and the convective heat transfer to the bed mass. For a start that can be constructed with a Modelica.Fluid.Pipes.DynamicPipe connected to a Modelica.Thermal.HeatTransfer.Components.HeatCapacitor via the heat port. The dynamic pipe model has a lot of features that you may want to disable. For instance, you could use a simple pressure drop model (NominalTurbulentFlow) and disable the dynamic mass, energy and momentum balance.


BR. Rene

PS. It's a great question. If you (re)post it on Stack Exchange (https://stackoverflow.com/questions/tagged/modelica) with tags 'modelica' and 'openmodelica' you may get many more replies and comments.