Details

Autor(en) / Beteiligte

• Trabold, Thomas Aquinas

Titel

Impingement evaporation and heat transfer from complex surface geometries

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

1990

Link zum Volltext

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• An experimental investigation of impingement evaporation from free water surfaces and heat transfer from impermeable, smooth surfaces was made using single and multiple circular air jets. Also, the influence of surface roughness on impingement heat transfer under multiple jets was investigated. For multiple jet impingement on a smooth surface, the best heat transfer performance, in terms of magnitude and uniformity, is obtained with minimum crossflow, the scheme whereby the spent air flows freely from the target surface. Constraining the spent air to leave the test plate through two opposite sides (intermediate crossflow) or one side (maximum crossflow) results in degradation of heat transfer in the downstream direction, the magnitude of which is more pronounced with the maximum than with the intermediate scheme and, for either exhaust configuration, depends on nozzle open area and standoff spacing. The presence of rectangular ribs, situated transversely to the direction of crossflow, can have profound effect on the local heat transfer coefficient; notably, in the presence of maximum crossflow for which the general trend is one of small upstream degradation and significant downstream enhancement. For impingement of a single jet on a free water surface, average mass transfer coefficient varies as $Re\sp m$, where $Re$ is the jet Reynolds number and $m$ is a function of the surface-to-jet diameter ratio, $D/d$. For multiple jets impinging on a liquid surface in the presence of minimum crossflow, Reynolds number exponent is as high as 0.981, and definite benefits can be realized by maintaining a greater number of jets over the target surface. This is attributed to the extremely rough nature of the air-water interface. The present results validate the predictive method which involves calculation of evaporation rates from heat transfer data via the heat-mass transfer analogy for the case of single impinging jets. There are also indications that the same may be true for multiple impinging jets.