Abstract
This study investigates the effect of curvature ratio on the liquid-gas mixing in an air humidification process by choosing the optimum positioning of nozzles matrix fixed prior to a bent duct. The present study is considered as a simulation of the gas turbine compressor inlet air cooling by the fogging technique. The experiments were conducted using a wind tunnel with an average air velocity of (5 m/s) through a 50 cm square cross sectional duct. The study employs three curvature ratios of 0.25, 0.5 and 0.75. Also three nozzles tilt angles were tested at – 45°, 0° and 45° with respect to the axial air flow direction. The design and the configuration of the nozzles matrix is decided according to the flow structure extracted from numerical simulation using CFD analysis with RNG-k-ε turbulent model. The results indicate that a curvature ratio of 0.75 gives the best performance of the humidification system when the nozzles matrix installed as far as possible prior to the bent duct giving enough residence time for the injected droplets to evaporate. At nozzles tilt angle of 0°, the relative humidity increased about 53.63% and the corresponding reduction in air temperature was 17%. Therefore, the optimum position of the nozzles has been shown in this study is at 1.5 m prior to the curve and a tilt angle of 0° when using the largest curvature ratio of 0.75 due to the shrink in the separation zone accompany the weakening of centrifugal forces. This effect would widen the mixing area for the two streams to react and producing better cooling and humidification of the air.
Highlights
Fluid flow in a bent duct or pipe bend is very common in engineering applications and has a significant importance for the designers of industrial equipment
Most of the adiabatic processes are realized by evaporation from an atomizing water spray, a wetted medium, but in the isothermal mode, the heat energy of evaporation water is supplied from a source other than the heat of the air as used in air steam injection causing increase humidity ratio and the temperature of the air is kept unchanged, as mentioned by Morton, (2015)
If the spray is tilted towered the inner wall of the duct, i.e. with angle – 45o, the improvement is nearly the same because at this direction the droplets are drifted to the center of the flow due to the centrifugal forces created by the secondary flow within the bent duct
Summary
Fluid flow in a bent duct or pipe bend is very common in engineering applications and has a significant importance for the designers of industrial equipment Such equipment are heat exchangers, turbomachinery, aircraft intakes, fittings, HVAC appliances, turbine and blade passages, cooling and heating applications, and several other equipment. Most of the adiabatic processes are realized by evaporation from an atomizing water spray, a wetted medium, but in the isothermal mode (no cooling), the heat energy of evaporation water is supplied from a source other than the heat of the air as used in air steam injection causing increase humidity ratio and the temperature of the air is kept unchanged, as mentioned by Morton, (2015)
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