Impact of Jet Reynolds Number and Feed Channel Geometry on Heat Transfer in a Channel with Inclined Target Surface Cooled by Single Array of Centered Impinging Jets with Outflow in Both Directions
An experimental investigation has been carried out to study the heat transfer characteristics in a channel with heated target plate inclined at an angle cooled by single array of equally spaced centered impinging jets for three different jet Reynolds numbers (Re=9300, 14400 and 18800). Air ejected from an array of orifices impinges on the heated target surface The target plate forms the leading edge of a gas turbine blade cooled by jet impingement technique. The work includes the effect of jet Re and feed channel aspect ratios (H/d = 5, 7, 9 where H=2.5, 3.5, 4.5 cm and d=0.5 cm) on the heat transfer characteristics for a given orifice jet plate configuration with outflow exiting in both directions (with inclined heated target surface). In general, It has been observed that, H/d=9 gives the maximum heat transfer over the entire length of the target surface as compared to all feed channel aspect ratios. H/d=9 gives 3% more heat transfer from the target surface as compared to H/d=5 (for Re=14400). Also, it has been observed that the magnitude of the averaged local Nusselt number increases with an increase in the jet Re for all the feed channel aspect ratios studied.
The effect of volumetric quality on heat transfer and fluid flow characteristics of air-assistant jet impingement
Abstract Heat transfer characteristics of air-assistant water jet impingement was experimentally investigated under a fixed water flow rate condition. Water and air were used as the test fluids. The effects of volumetric quality (β = 0–0.9) on the Nusselt number and pressure were considered. The results showed that the stagnation Nusselt number increased with volumetric quality, attained a maximum value at around 0.8 of the volumetric quality, and then decreased. The stagnation Nusselt number of the air-assistant water jet impingement is governed by the stagnation pressure. Based on the experimental results, a new correlation for the normalized stagnation Nusselt number is developed as a function of the normalized stagnation pressure alone. In addition, the lateral variation of Nusselt number is governed by hydraulic jump radius.
Augmented heat transfer in triangular ducts with full and partial ribbed walls
Fully developed heat transfer coefficients and friction factors in triangular ducts with full and partial ribbed walls were experimentally obtained for Reynolds numbers between 10-10. The vertex corners of the triangular ducts were 90, 55, and 35 deg. Five rib configurations were tested: full and partial 90-deg transverse ribs, full and partial 45-deg crossed ribs on three-wall, and partial 45-deg crossed ribs on two-wall of the triangular duct. The results show that heat transfer coefficients were higher on the ribbed walls and the 90-deg vertex corner of the triangular duct than on the 55-deg vertex corner, and subsequently higher than those on the 35-deg vertex corner. The heat transfer coefficients and friction factors in triangular ducts with partial ribbed walls (90or 45-deg ribs) were 10% higher than those with full ribbed walls. The results also show that heat transfer coefficients and friction factors were higher in triangular ducts with 90-deg transverse ribs (full or partial) than those with 45-deg crossed ribs. The semi-empirical friction and heat transfer correlations in ribbed triangular ducts were obtained.