M Wierzbowski, M Ciofalo, and J Stasiek
Liquid crystal thermography combined with image processing techniques used for experimental work at the Department of Heat Technology are described.
The experimental procedure covers full-field flow patterns in classic heat exchanger elements (flat plate with fine-tubes in-line, staggered, and with vortex generators) describing local heat-transfer coefficient and Nusselt numbers on the surfaces. Also the dependence of average heat-transfer and pressure drop on Reynolds number and geometrical parameters was investigated.
The main features of performance required of a heater are high heat-transfer rates, low-pressure losses and low sensitivity to fouling. These depend crucially on the geometrical design of the heat-transfer elements. However, despite the importance of the problem, the various classic and compact designs have been developed, mainly on an empirical basis. Although both operating and laboratory data are available, they do not cover the full range of shapes, sizes, and operating conditions (in particular Reynolds number) that would be required for an optimization study. Moreover, data are generally available in the form of overall performance (average heat-transfer coefficient) and the phenomena that determine these, including flow patterns and transition to turbulence, are not fully understood.
Authors at Technical ...