In industry, fired heaters are used to heat process fluids and to generate steam. The efficiency of these devices is increased with air preheating. Gnerally, the flow through the air preheaters is driven by a centrifugal fan, via forced draft. Through a widening transition duct (large angle diffuser), air flows from the fan towards the air preheater. In terms of fluid mechanics, the geometry of such a duct is often unfavorable. This research is aimed at improving the flow in large angle diffusers. A test platform was built with which the flow in diffusers of various geometries can be studied.

Flat plate heat exchangers are widely used in industrial and domestic applications. Industrial plate type heat exchangers generally operate in the turbulent flow regime. Although, increase in flow speeds leads to higher transport of heat, it also causes a rise in the pressure loss which is undesirable. Therefore, to combat the problem of high pressure drop, this thesis explores the use of a passive enhancement technique to improve heat transfer. The aim of this thesis is to experimentally investigate the effect of dimple-protrusion surfaces in a counter flow type heat exchanger. The flow behavior is studied using Laser Doppler Anemometry and the local heat transfer characteristics are investigated with the help of Infrared thermography. The average Nusselt number and friction factor data is compared with those of a flat plate and it is found that the use of dimple-protrusion surfaces provide maximum improvement in the performance of the heat exchanger by 21% in the laminar-to-turbulent transition regime, at Reynolds number of approximately 2900.