Thermo-hydrodynamic model and parametric optimization of a novel miniature closed oscillating heat pipe with periodic expansion-constriction condensers

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In order to promote the thermo-hydrodynamic performance of a single miniature loop pulsating heat pipe (PHP), the oscillatory behaviors and thermal transport capability of PHPs should be comprehensively and accurately analyzed. A novel closed PHP with periodic expansion-constriction condenser was proposed, where phase change and thermal transport processes could be reproduced by a comprehensive computational fluid dynamics (CFD) technique together with volume of fluid (VOF) methodology. Moreover, available experimental data were utilized in the validation of the model for the average deviations within 10%. Subsequently, a full numerical modeling for oscillating flows under different operating conditions was sensitively tested, varying thermal power and filling ratio, respectively from 18 W to 86 W and from 40% to 60%. Complicated fluid dynamical phenomena such as nuclear boiling, formation of slug, coalescence of vapor plug and flow patterns transformation have been analyzed inside the PHPs; CFD visualizations were also presented excellent agreements with flow behaviors from previous experimental photographs. Additionally, the effects of periodic expansion-constriction condenser on the flow regimes, pressure difference and thermal performance have been comprehensively analyzed. Numerical results demonstrate that 45% sharply increase in the thermal efficiency of the expansion condenser, and oscillation frequency of liquid/vapor slugs has been directly promoted for the constriction condenser. Present investigations could contribute to enhance overall performance of PHP, particularly employed for electronic cooling or heat recovery units.