Heat pipes are passive two-phase heat transfer devices that used in various heat transport applications because of their high thermal conductance capacities with low temperature differences. One of these applications is aerospace avionics that heat pipes are exposed to transient heat loads. Although heat pipes have been one of the heat removal alternatives for compact electronic devices, they have some restrictions during the usage in such high heat flux areas.  In order to use heat pipes as effective heat removal devices, operating heat load range should not be exceeded during the operation of avionics or electronic devices. Out of these operating range, heat pipes no longer perform as effective heat removal devices because of phenomena called dry-out. In addition, varying heat loads have important effects on heat pipe’s thermal performance.  In this study, a novel Finite Element (FE) Analysis Method was developed to model transient heat transfer behaviour in heat pipes including dry-out phenomenon. Transient heat transfer analysis using Finite Element Method (FEM) was conducted to investigate heat pipe thermal performance considering heat flux dependent thermal conductivity under randomly varying heat inputs, which were assumed as heat dissipation of an electronic device. Validation of the FE model was done by using the results given in the literature. Heat pipe was made of Al with a length of L~HP~=200 mm. Heat flux was applied to simulate heat input. At the condenser, convective heat transfer boundary condition with T~ambient~=25 °C was used for cooling purposes. Effective thermal conductivity of heat pipe, *k~eff~*, was calculated by using the heat input depended thermal resistance, *R~th~*, values given in literature. Under transient heat loads, heat flux dependent effective thermal conductivity was defined using user defined subroutines to simulate the dry-out. The transient heat transfer analysis was conducted using ABAQUS commercially available software and outputs of the analysis were compared with the results given in literature. Temperature differences between evaporator and condenser sections, ∆T=Te-Tc, are calculated during the analysis and compared with the results that provided in literature for different heat input values. The maximum temperature difference was occurred as ∆T=5.3°C when Q~in~= 50 W. In addition the temperature differences compression, thermal resistance, R~th~, values were calculated and compared with the literature. The maximum difference in thermal resistances seen with 10.0% error when Q~in~=15 W. As a result of this study, a finite element analysis method was developed and validated with the literature studies. FE results showed that they are in good agreement with the test data given in literature. The developed method can be used to obtain accurate results in the transient analysis of heat pipes under time dependent heat loads.


Modeling Transient Heat Transfer and Dry-Out Phenomena in Heat Pipes Using Finite Element Analysis

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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