Flow and Heat Transfer Characteristics of Impinging Jet from Expansion Pipe Nozzle with Air Entrainment Holes

Abstract

Flow and heat transfer characteristics of impinging jet from expansion pipe were experimentally and numerically investigated. The expansion pipe nozzle was drilled on expansion wall for increasing an entrainment of ambient air into a jet flow. The diameter of round pipe nozzle was d=17.2 mm and the diameter of expansion pipe was fixed at D=68.8 mm (=4d). The number of air entrainment holes was varied at 4, 6 and 8 holes, and the expansion pipe length was examined at L= 2d, 4d and 6d. In this study, the expansion pipe exit-to-plate distance was fixed at H=2d and the Reynolds number of jet was studied at Re=20,000. Temperature distribution on the impinged surface was acquired by using an infrared camera. The numerical simulation was carried out to reveal the flow field. The results show that the ambient air enters through the holes and subsequently blocked the entrainment of ambient air into the jet flow. It causes to enhance the heat transfer particularly at stagnation point higher than the case of conventional pipe: 4.68% for 4 holes at L=2d, 6.4% and 6.28% for 4 holes and without holes at L=4d and 5.48% for 8 holes at L=6d.

Effect of Rotation Number on Heat Transfer Characteristics of a Row of Impinging Jets in Confined Channel

“…̇ and ̇ are the heat loss from radiation and convection from TLCs to the surrounding, respectively, is the Stefan-Boltzmann constant, is the emissivity coefficient for the TLC sheet which was 0.9, and are respective the inlet and outlet temperature of the air, is the room temperature, ℎ is the natural heat transfer coefficient that was arranged for a vertical plate [19,20]. Finally, the local Nusselt number (Nu) can determine from = ℎ k (9) where k is the thermal conductivity at the mean air temperature. The uncertainty values due to measurements of this experiment were less than 4.2% for the Reynolds number and 3.8% for the Nusselt number evaluated according to Moffat [21].…”

“…It gives a high cooling rate in the impingement region. Recently, a single modified jet has been investigated for heat transfer enhancement by Kaewchoothong et al, [9], and Nuntadusit et al, [10], who used the air augmented duct to increase the heat transfer rate on an impingement surface at a diameter of air augmented duct ratio (D/dj) of 2.0, 3.3, 4.0, and 6.0 where dj is an inner diameter of jet. They reported that the heat transfer rate for the case of D/dj = 6 gave the largest by getting 25.42% higher compared to a conventional impinging jet.…”

Effect of Pulsating Flame Jet on Flow and Heat Transfer Characteristics

“…Usually, the impinging flame jet has been used widely in the metal and glass industry that requires high temperatures such as melting metal, heating metal material in a preheat furnace before fabrication and also for the glass-forming process, etc. Flame impinging jet can reduce the heating time [1][2][3][4], reducing emissions from combustion [5,6] and saving energy compared to conventional methods of heating by the infrared gas burner [7][8][9].…”

Heat Transfer Characteristic for Premixed Flame Jet from Swirl Chamber

“…Impinging flame jets have been extensively used in several industrial applications for heating, grilling or drying process, for examples, annealing of glass, processing of heating and metal and glass including cutting and welding, drying of textiles film and paper [1][2][3][4], and drying or grilling of food products [5][6][7][8]. The impinging flame jets can produce high heat transfer rate on the impingement surface.…”