Compact Heat Exchangers were developed to have very high efficiency in transfer of heat within a very small space or volume and are being used in the automotive, aircraft and space applications. In order to obtain much higher heat transfer, these Heat Exchangers uses closely packed fins, narrow or small diameter passages and turbulators or turbulence promoters. Though these arrangements result in much higher pressure drop for the fluids, this disadvantage is expected to be off-set with a larger increase in heat transfer capability. Generally it is known that turbulence enables better mixing of the fluid and results in enhancing the heat being transferred. However in practice it has been observed that there is a limit to this enhancement and the heat transfer does not improve beyond certain turbulence levels. The higher turbulence level probably results in carrying the heat away along with the fluid without transferring all the heat to the cooling medium. The presence of turbulence promoters was found to be beneficial at a lower fluid velocity level, where they conduct the heat away more by surface conduction than by convection in the fluid. Detailed experimental investigation and findings of this phenomenon using a compact heat exchanger for a military vehicle is described in this paper.

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