Experimental and numerical investigation of heat transfer and fluid flow were conducted for classic heat exchanger elements (flat plate with f'm-tubes in-line, staggered and with vortex generators) and corrugated-undulated ducts under transitional and weakly turbulent conditions.The dependence of average heat transfer and pressure drop on Reynolds number and geometrical parameters was investigated. Distributions of local heat transfer coefficient were obtained by using liquid crystal thermography and surface-averaged values were computed. Three-dimensional numerical simulations were conducted by a finite-volume method using a low-Reynolds number k-e model under the assumption of fully developed flow. Computed flow fields provided otherwise inaccessible information on the flow patterns and the mechanisms of heat transfer enhancement.

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A visualisation technique is used to measure the heat transfer to a plane surface with obstacles. Liquid crystal coated on a mylar sheet is used to locate isotherms on a cooled plate. The isotherms on the plate surface are recorded by JVC-camera and true-colour image processing system. Experimental procedure cover full-field flow pauerns in heat exchanger element (flat plate with discs in-line, staggered and with vortex generators) describing local heat transfer coefficient and Nusselt number on the surface.

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