Book Description

Heat transfer enhancement studies were conducted on two main research areas in heat transfer. Those areas are fluid jet impingement and the use of porous mediums. Fluid jet impingement is a common heat transfer application in industry and is widely studied in research due to the high heat and mass transfer they provide. Porous mediums are another common engineering application that is typically found in heat exchangers and heat pipes due to the high heat transfer coefficient they produce. However, not much research stems from the combination of the two applications. By combining these two heat transfer applications, experiments were broken into two categories, non-boiling and boiling. Here, an apparatus was fabricated that allowed for both categories to be studied while allowing an inclination toward experimental plausibility. For the non-boiling experiment, flow rates were chosen that ranged from 4,000 ≤ Rew ≤ 11,000 under both free surface and submerged impinging jets. The goal was to determine the Nusselt number and compare the forced convection effect to the plain surface and porous mediums, i.e., monolayer wick and columnar post wick. Also, the variation in the Nusselt number was determined during lateral nozzle movement. The problems faced in pool boiling are the limited critical heat flux (CHF) and heat transfer coefficient (HTC) caused by the phase change over the heated surface. By employing the monolayer wick and columnar post wick, a decrease in the hydrodynamic instability (Rayleigh-Taylor) wavelength can occur, which provides heat transfer enhancements. To see if further heat transfer enhancements can be obtained, an impinging jet was added to the boiling apparatus with working flow rates of 800 ≤ Rew ≤ 1,700. Results for the non-boiling experiment show that the plain surface outperforms both monolayer wick and columnar post wick. This is due to the flow resistance present in both porous mediums. The rough surface of the monolayer wick saw a drop in the convection effect which was influenced by this flow resistance. The columnar post wick saw a further reduction in the convection effect due to the post's tight pitch distance, lp=1 mm. This was present in both free surface and submerged impinging jets. The boiling results showed a significant increase in CHF enhancements when the monolayer wick and columnar post wick were employed in the pool boiling setup. This is due to the reduced hydrodynamic instability wavelength, which reduced the vapor generation and delayed surface dry-out. CHF enhancements were further increased by employing an impinging jet. With the combination of the reduced hydrodynamic instability wavelength and impinging jet at the highest flow rate, the plain surface, monolayer wick, and columnar post wick saw an increase of 323.1%, 244.3%, and 266.6%, respectively, in CHF measurements when compared to the basic pool-boiling experiment.