Pore scale thermal response and transient energy evolution in a porous wick evaporator during pre-dryout

Microscale heat pipes have been widely used for the thermal management of high heat flux electronic devices, such as electronic chips, owing to their efficient passive heat transfer capability. However, when a high heat flux load is imposed within a short period, the evaporator may readily enter the pre-dryout stage. During this stage, local liquid is continuously depleted, and the heat flux distribution, energy partition, and temperature field inside the evaporator are significantly altered. To address this issue and provide a more general description of the underlying mechanism, the residual liquid in the porous wick during the pre-dryout stage was represented by a droplet unit attached to the solid skeleton surface, and a pore scale transient heat transfer and evaporation model was established. Under the coupled effects of substrate conduction, air side heat transfer, and radiative energy input, a numerical framework was developed in which droplet phase change, temperature field evolution, and radiative transport were solved simultaneously. The peak heat flux near the three phase contact line, the temperature inhomogeneity along the wick skeleton surface, and the energy partition mechanisms at different evaporation stages during the pre-dryout process were identified. On this basis, the effects of substrate material, heating boundary condition, substrate heat flux, air temperature, and radiation intensity on the local heat flux distribution, transient energy variation, and evaporation behavior were systematically investigated. A more detailed physical basis was thereby provided for heat transfer enhancement and structural optimization of microscale heat pipe evaporators. Direct support was also offered for hotspot suppression, critical operating state identification, and device safety assessment.