Compact heat exchangers are key components for the development of future aircraft devices. An enhancement of the heat transfer rate results in a decrease of the heat exchanger size and thus in lower weight and lower investment costs. An exact knowledge of the temperature distribution in the boundary layer is necessary for a specific augmentation of heat transfer. For this reason the holographic interferometry was applied as measuring method enabling a visualization of the temperature field without disturbing the flow pattern. The local Nusselt number was determined from the isotherms at the wall. A digital image processing system was used for the evaluation of interferograms. The measuring method is demonstrated for three different types of geometries for compact heat exchangers using air as test fluid: Plain fin arrangements of plate-fin heat exchangers, flow in a profile shaped duct for tubular matrices, and flow over circular segment shaped turbulence promotors. During the experiments the Reynolds number was varied between 500 and 3000, a range, where low pressure losses occurred. The test section was heated by hot water in order to obtain a constant wall temperature as thermal boundary condition.
Investigation of local heat transfer in compact heat exchangers by holographic interferometry
Die Untersuchung der lokalen Wärmeübertragung in kompakten Wärmetauschern mittels holographischer Interferometrie
1993
17 Seiten, 18 Bilder, 2 Tabellen, 7 Quellen
Aufsatz (Konferenz)
Englisch
Plattenwärmetauscher , Luftfahrttechnik , Innovation , Wärmeübertragung , Gewichtsminimierung , Investitionskosten , Bauweise , Raumdimension , Temperaturverteilung , Grenzschicht , holographische Interferometrie , Temperaturfeld , Nusselt-Zahl , Vergleich (System) , Rohrströmung , Vergleichsmessung , Reynolds-Zahl , Druckverlust , Wandtemperatur , Forschungsbericht
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