Advancing thermohydraulic performance of micro-grooved flat heat pipes through a combined numerical-experimental approach

• A combined numerical-experimental model for flat heat pipes is developed. • A systematic method for calibrating the heat pipe model is introduced. • A new method to assess heat transfer in the liquid block region is proposed. • Converging microchannels are introduced to enhance heat pipe performance. A combined numerical-experimental model has been developed to predict the thermohydraulic characteristics of micro-grooved flat heat pipes (FHPs). This model uses a limited number of experimental data for calibration with two parameters, β exp,1 and β exp,2 , which account for uncertainties in the accommodation coefficients used to determine evaporation and condensation mass fluxes. This calibration, which is a key feature of the developed model, addresses the uncertainties and challenges in determining these coefficients. Moreover, the model incorporates the effects of interfacial shear stress, axial wall conduction, heat transfer in the liquid block region, and the contact angle of the liquid–vapor interface. Furthermore, the evaporation mass flux from the curved liquid–vapor interface is calculated using a separate multiscale approach developed in two recent works for analyzing evaporation from the extended meniscus in microchannels, considering thin-film evaporation. The model demonstrates high accuracy in predicting the maximum heat transport capacity (Q max ) and wall temperature distribution across various input heat powers, with a maximum error of less than 0.5 % in wall temperature predictions, as validated against experimental data. The validated model is then used to explore a new micro-grooved wick structure featuring converging/diverging microchannels. In this structure, the channel width is constant and equal to W f2 in the first half of the heat pipe, from the condenser end to the midpoint, and then it decreases or increases to W f1 by the end of the evaporator section. Results indicate that a flat heat pipe with a converging micro-grooved wick structure (W f1 = 200 µm and W f2 = 160 µm) can enhance Q max from 53 to 70 W, 70.8 to 91.8 W, and 91.2 to 116.5 W at working temperatures of 60 °C, 70 °C, and 80 °C, respectively. This means the new converging micro-grooved wick structure can boost flat heat pipe performance by more than 25 % compared to a flat heat pipe with a straight micro-grooved wick (W f1 = W f2 = 200 µm) without increasing the occupied space.