A detailed experimental investigation of a perforated heat transfer surface applied to gas turbine recuperators

An effort is made to explain and improve the understanding of the mechanisms behind the thermo-hydraulic performance of perforated extended surfaces used in compact heat exchangers in the laminar flow regime (Re D = 400-2500). A transient liquid crystal technique, which uses Helium as operating fluid, together with digital image photographic processing have been used to provide measurements of local heat transfer coefficients for this geometry. This work has found that through the use of perforated surfaces there exists a local heat transfer enhancement benefit. It has also been found that although perforations cause a partial restart of the thermal boundary layer, a significant overall surface heat transfer enhancement may not be achieved over plain surfaces. It was also found that the distance between the fin's leading edge and the point of last significant enhancement resulting from a perforation, linearly depends on Reynolds number. Local heat transfer coefficient measurements were validated by single blow experimentation of similar geometries. The transient single blow technique used the curve-matching method to compare predicted and experimental temperatures