# Enhancement of Subcooled Flow Boiling Heat Transfer with High Porosity Sintered Fiber Metal
## 1 Introduction  
The heat transfer process has been investigated due to the high heat flux dissipation demand of modern cooling systems. In recent years, energy consumption has increased exponentially in components such as electronic devices, nuclear power reactors, the cooling of rocket nozzles, etc. Thermal management is divided into single-phase and two-phase heat transfer where the two-phases have higher heat transfer efficiency in comparison with the single-phase heat transfer; however, this is a more complicated process that involves bubble formation, condensation, the vapor quality, flow boiling geometry, liquid subcooling temperature, etc. [1, 2]. Recently, new technologies such as surface modifications, decreasing the flow area dimensions, nanofluids, porous media structures, etc., have been proposed to increase the heat flux and the critical heat flux (CHF) for many researchers. In particular, a porous surface is defined as a porous matrix attached to a surface, and the porous material can be either the same as the base or a different material. The fabrication process also classified the porous surface into five main categories (sintering [3, 4, 5, 6, 7], spray coating [8, 9], electrochemical deposition [10, 11, 12], chemical vapor deposition [13], and additive machining [14]). The porous surface has three main advantages: (I) to increase the wetted area and the nucleation time due to the interconnected pores; (II) to reduce the cost of materials in their production in comparison with the bare solid surface; (III) micro/nanostructures are easier to make on porous surfaces. On the other hand, the manufacturing precision is lower than the bare solid surface and its modeling is much more difficult due to the random porous structure. In addition, oil fouling inside and outside the porous body have been reported, and, for this reason, the working fluid is limited to fluids that are clean and free of impurities [15, 16, 17]. In 2000 [PERSON] and [PERSON] [18] conducted an experimental and numerical study of single-phase forced convection in high-porosity aluminum metal foams, concluding a good agreement for the simulation and the experimental results. [PERSON] and [PERSON] [19] proposed a honeycomb porous media on pool boiling and their results showed an enhancement in the critical heat flux (CHF) of approximately 2.5 times in comparison with the plain surface. They attributed the CHF performance to the capillary suction, permeability, pore radius, wall thickness, height of the porous media, and vapor scope channels. [PERSON] and [PERSON] [20] and [PERSON] et al. [21] evaluated the bubble dynamics and the heat transfer performance on micro channeled copper surfaces; they attributed the heat flux enhancement to the bubble diameter, contact angle, and the distance from the bottom of the channel to the bubble, porosity, and pore diameter average. However, the case of high-porosity and large average particle diameter produced a local thermal effect with no equilibrium between the working fluid and the surface heating area. On the other hand, heat transfer enhancement tends to diminish at high and moderate mass fluxes. Due to the high fluxes, the liquid cannot replace and remove the vapor-liquid and this promotes the vapor blankets and dry out. [PERSON] and [PERSON] [22] studied CHF enhancement using a modulated porous layer on pool boiling. The heat transfer had a direct relation with the porous coating structure and the liquid and vapor flow paths. The deep porous-layer coating presented the worst performance and the artery evaporator system with completely separated liquid and the vapor flow paths presented a higher performance. [PERSON] et al. [23] investigated the effects on the CHF using deformable structures on pool boiling using ethanol, FC-72, and water as the working fluids, significantly reducing the superheat wall temperature at the same heat flux. [PERSON] et al.