Mist/Steam Cooling in a 180-Degree Tube Bend

Abstract

An experimental study on mist/steam cooling in a highly heated, horizontal 180-deg tube bend has been performed. The mist/steam mixture is obtained by blending fine water droplets (3∼15 microns) with the saturated steam at 1.5 bar. The test section consists of a thin wall (∼0.9 mm), welded, circular, stainless steel 180-deg tube (20-mm inside diameter) with a straight section downstream of the curved section, and is heated directly by a DC power supply. The experiment was conducted with steam Reynolds numbers ranging from 10,000 to 35,000, wall superheat up to 300°C, and droplet to steam mass ratio at about 1∼2 percent. The results show that the heat transfer performance of steam can be significantly improved by adding mist into the main flow. The highest enhancement occurs at a location about 45-deg downstream of the inlet of the test section. Generally, only a small number of droplets can survive the 180-deg turn and be present in the downstream straight section, as observed by a phase Doppler particle analyzer (PDPA) system. The overall cooling enhancement of the mist/steam flow ranges from 40 percent to 300 percent. It increases as the main steam flow increases, but decreases as the wall heat flux increases. [S0022-1481(00)02003-X]

Simulation of Film Cooling Enhancement With Mist Injection

“…The highest local heat transfer enhancement of 200% was achieved with 1~5% (weight) mist, and the average enhancement was 100%. Guo et al [12] also conduced mist/steam cooling study in a 180 o tube bend. The overall cooling enhancement ranged from 40% to 300% with the maximum local cooling enhancement being over 800%, which occurred at about 45 o downstream of the inlet of the test section.…”

Computational Analysis of Droplet Mass and Size Effect on Mist/Air Impingement Cooling Performance

“…A promising technology is to enhance film cooling with mist (small water droplets) injection. Based on the aforementioned heat transfer mechanisms, mist can be used in gas turbine systems in different ways, including gas turbine inlet air fog cooling [10], overspray cooling through wet compression in the compressor [11], and airfoils (vanes and blades) internal cooling [12][13][14][15][16]. Recently, Li and Wang [17] conducted the first numerical simulations of air/mist film cooling.…”

“…The main objective of this thesis is to elucidate how the mass and dimension of the droplet affect the mist impingement cooling performance over a curved surface with a hole of double chamber model, calculated by CFD. Earlier studies discussed the mist film performance on the blade and combustor of gas turbine [10][11][12][13][14][15]. The model created in the paper looks like a flat with two double chambers, simulating the structure of transition piece.…”

Computational Analysis of Surface Curvature Effect on Mist Film Cooling Performance

“…Nirmalan et al [24] conducted an experimental study of turbine vane heat transfer with water-air mist cooling. The authors' research group has conducted a series of mist/steam cooling experimental studies by injecting fine droplets into steam flow [25][26][27][28] for application in the H-type gas turbine using a closed-loop steam cooling scheme. The highest local heat transfer enhancement of 200% was achieved with 1~5% (weight) mist in a straight pipe flow [25], and the average enhancement was 100%.…”