- How to define the cross sectional area of the heat pipe system (in this case, rectangular) in order to calculate the heat transfer coefficient, h (W/(m²K) of the system which can then be used to calculate the value of heat dissipation, Q (W or J/s) for the total system.
- Which values to be chosen for calculating the different pressure drops across the heat pipe wick (due to gravity, vapour and liquid) including vapour viscosity, μvap (kg/s·m) which can be found in heat transfer tables varies little with pressure, and the latent heat of vaporisation, hfg (kJ/kg) which is very much dependent on pressure changes (values found in thermodynamic tables).
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| Circular channels with over hanging section |
Most importantly, he clarified how I should define the effective pore radius! Previously I had been looking at the lizard wick as an open surface with hexagonal micro posts. I was simplifying the design to make it easier but in doing so, complicated the problem. I failed to recognise that due to the overhanging part of the post, the wick could be viewed as an almost closed section covering the circular channels. So the effective pore radius can be taken has half the channel width.
It was also noted again that the cross sectional area of the channel is very important in calculating the maximum capillary action achievable. By decreasing the size of the channels, the capillary action will increase.
In future iterations of the design, varying the cross sectional area of the channels across the wick could take into account the different stages of wetting of the working fluid (in this case deionized water). At the evaporator end where fluid is heated, the channels will be more tightly packed to take into account that wetting will be less than at the condenser end. However, I need to have a concept first before thinking these details. Thanks Masoud.
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