Thermo-hydrodynamics analysis of vapor–liquid two-phase flow in the flat-plate pulsating heat pipe

A three-dimensional unsteady model of vapor–liquid two-phase flow and heat transfer in a flat-plate pulsating heat pipe (FP-PHP) is developed and numerically analyzed to study the thermal-hydrodynamic characteristics in two different configurations of FP-PHPs. The thermo-hydrodynamics characteristics under steady unidirectional circulation condition of the studied FP-PHPs are numerically investigated and discussed. The results indicate that the bubbly flow, slug flow and semi-annular/annular flow occur in the FP-PHP under the condition of steady unidirectional circulation, when the adjacent tubes of the FP-PHP become ‘upheaders’ and ‘downcomers’ of working fluid. The periodical oscillations of fluid temperature and vapor volume fraction are observed to be synchronous, while the temperature oscillation amplitude at adiabatic section is larger than that at condenser section but less than that at evaporator section. The increases in the heat load lead to the high temperature level and small integral equivalent thermal resistance of the FP-PHP. Additionally, compared with the traditional FP-PHP with uniform channels, the FP-PHP with micro grooves incorporated in the evaporator section is effective for the heat transfer enhancement and possesses a smaller thermal resistance at high heat loads.