# Subcooled Flow Boiling Heat Flux Enhancement Using High Porosity Sintered Fiber
## 1 Introduction
(I) Due to the space between the micro holes or the interconnected fibers, the wetted area and the nucleation sites increase; (II) the lower density and the reduction on the material used on the fabrication, the production cost is reduced; (III) the variety on the fabrication processes make easier to create nano/microstructures [17; 18]. [PERSON] et al. [19] conducted a flow boiling heat transfer experiment using deionized water as a working fluid. The flow pattern of the silicon micro gap with three different roughness was analyzed. Results showed that the boiling incipience and bubble formation density increases directly inverse to the roughness. The heat flux on the subcooled flow boiling process is directly related to the inlet subcooling temperature, the flow rate, the system pressure, the physical properties of the working fluid, and the surface conditions. This last parameter has been investigated by several researchers. They studied the bubble behavior and the flow pattern on the porous media and compared with the bare surfaces, recording and analyzing the bubble formation and departure with a high-speed camera [20; 21; 22; 23]. In the last decade, researchers have used copper foam materials to improve heat transfer performance and avoid burning out on heating surfaces. Experimental research using a deep microchannel copper on water flow boiling was performed by [PERSON] et al. [24]. Their results show the influence of the surface characteristics on the amount of heat transfer. The roughness, oxidation, and wettability have a direct relation with the nucleation site density. The wall superheat increased drastically, and the heat flux was reduced on the freshly machined surface. [PERSON] et al. [25] manufactured an interconnected microchannel net with square pores made by copper and tested its flow boiling performance, concluding that the amount of heat transfer in the two-phases region and the pressure drop changes depend on the channel width. In 2020 [PERSON] et al. [26] performed experimental research using an open-cell copper metal foam with three different thicknesses (3, 2, and 1 mm) on a pool boiling system with HFE-7100 as working fluid. They found that there was not a constant value for the optimum porous thickness, and the enhancement of the porous materials also changed on the low heat flux and high heat flux regions. However, the heat flux performance of the three different porous thicknesses was better in comparison with the plain (bare) surface. They also reported that the bubbles grow and coalescence easily on the high thicknessesporous body, and as a result, the mean bubble diameter increases, covering the heating area. Due to this effect, the heat transfer coefficient decreases. On the other hand, the bubbles on the low porous thickness are concentrated on the top, and they depart easily from the surface, thus the fluid supply keeps constant. In general terms, they found an increment on the heat transfer coefficient of 145% using the porous copper materials in comparison with the bare surface. The present research describes the experimental investigation on the horizontal subcooled flow boiling using porous media attached to the surface, extending the research and experiments performed by [PERSON] et al. [27]. The influence of the bubble formation and the flow pattern on the heat flux enhancement is discussed. The goal of the present research is to increase the heat flux using the porous media as a passive method in comparison with the bare surface. Besides, the influence of the mass flux and the inlet subcooling temperature is also discussed.