Design of Compact Plate Fine Heat Exchanger

Abstract

Plate fin heat exchangers, because of their compactness, low weight and high effectiveness are widely used in aerospace and cryogenic applications. This device is made of a stack of corrugated fins alternating with nearly equal number of flat separators known as parting sheets, bonded together to form a monolithic block. Appropriate headers are welded to provide the necessary interface with the inlet and the exit streams. While aluminum is the most commonly used material, stainless steel construction is employed in high pressure and high temperature applications.

The performance of a plate fin heat exchanger is determined, among other things, by the geometry of the fins. The most common fin configurations are - (1) plain (straight and uninterrupted) rectangular or trapezoidal fins (2) uninterrupted wavy fins and (3) interrupted fins such as offset strip, louver and perforated fins. The interrupted surfaces provide greater heat transfer at the cost of higher flow impedance.
Here I have designed rectangular offset plate fin heat exchanger. I have assumed some data and based on them I have designed heat exchanger . The flowing fluid in heat exchanger is liquid nitrogen and material of heat exchanger is Al. After designing the heat exchanger, rating is also necessary .
The heat transfer and flow friction characteristics of plate fin surfaces are presented in terms of the Colburn factor j and the Fanning friction factor f vs. Reynolds number Re, the relationships being different for different surfaces.
The laminar flow model under predicts j and f values at high Reynolds number, while the 2-Layer k-e turbulence model over predicts the data throughout the range of interest. Because most industrial heat exchangers operate with Re less than 3000, and because the j and f data predicted by the laminar and the 2-layer k-e turbulence model differ little from each other at low Reynolds numbers, we have used the laminar flow model up to Reynolds number of 10,000, which is considered to be the limit for plate fin heat exchangers operating with gases. Velocity, pressure and temperature fields have been computed and j and f factors determined over appropriate range of Reynolds number and geometric dimensions.