AnsweredAssumed Answered

Boundary Conditions for Spiral Heat Exchanger

Question asked by Will Invents on Dec 13, 2012



I'm inexperienced with SW Flow Simulation, but wish to model a small spiral heat exchanger. I have undertaken several simulations to date and had broadly been satisfied with the result. However, after querying further I am unsure if my boundary conditions are correct, specifically whether SW is properly simulating turbulent flow, if this flow condition is even present.


The simulation is set-up such that I have set two surface goals within the simulation for both hot (water) and cold (water) stream outlets. I know both goals have solved to 100% and I have set the HTC to outside (ambient) to zero.


The principal problem is that I am trying to increase the HTC and have added in small bars within the flow path to help to initiate turbulence. I am unsure if this is a flawed concept given that the channel is so thin (2.5mm and 5mm trialled). The Reynolds Number is 1,150 for 2.5mm gap - laminar flow (water).


Trialling different bar diameters and even using an insulating bar material, I find that whilst the heat exchanger efficiency increases with bars, the temperature difference (delta T) across the hot stream is sometimes different to the temperature difference across the cold stream. I would therefore suspect these results to be garbage, particularly since it did not occur without the bars.


Apologies if this problem is poorly explained - does anyone have any advice about what might be happening here?  I believe my mesh density is ok and have been specifying '7' for characteristic cells across narrow channel and '3' for narrow channel refinement.