I am trying to model this rig in 2-D to validate my experiments. I would like to determine the heat transfer behaviour of the storage and determine the temperature of HTF and PCM at certain positions on the rig. Any information or link would be really useful.
See attached image of the rig.
The easiest way without involving too much knowledge of heat trasnfer and fluid flow is to run CFD simulation. Pick the one you are familar with.
CFD would work, but a lumped element model would be simpler and get results for a variety of scenarios much more quickly. Discretize into a series of cylinders corresponding to each horizontal tube run. Calculate convective resistance from the fluid flow rate and fluid properties. The tube wall resistance is likely to be low in comparison to the PCM and fluid and can ignored.
there are multiple approaches you can take to model that heat, depending on the level of fidelity you want. since you say you want both fluid and PCM temperatures throughout the component, you'll need to solve, or at least approximate, both fluid flow and heat transfer problems. Also, although you can calculate steady state operating points, thermal energy storage is by its nature a transient problem. so expect other complexity there. I expect you'll either be implementing a custom numerical solution, or using a FEA or CFD solver.
David's approach would probably be the simplest, set up each tube as an individual flow model, use an analytical equation or correlation to get heat transfer coefficient as a fn. of flow rate. then, you can solve the heat transfer to the PCM using that HTC as a boundary condition at the tube. However. between tubes isn't really symmetry plane since its a multi-pass tube. likely you'd need to solve the heat transfer between pairs of tubes to avoid any approximation.
next, how to solve the heat transfer problem: phase change is inherently non-linear. there are very few analytical solutions, and those only under certain ideal conditions. the simplest, and maybe sufficient for your case, you can approximate phase change as an effective heat capacity, changing the solution process to one of temperature dependent material properties. look up 'effective capacity method' 'apparent capacity method' and 'enthalpy method' for examples. the advantage of this method is that it can often be implemented in standard FEA/CFD solvers, but you have to be careful of how you implement the material property. poor choices in enthalpy profile can introduce severe discontinuities and prevent numerical convergence.
- Badges
- Science topic
- Similar topics
- Engineering
- Thermal Engineering
- Thermofluid
- Heat Transfer