Industrial Microchannel Devices: Where Are We Today?

Abstract

Heatric has been involved in the commercial design and manufacturing of “micro/milli” scale heat exchanger core matrices called Printed Circuit Heat Exchangers (PCHEs) since 1985. These core matrices are formed by diffusion bonding together plates into which fluid flow microchannels have (usually) been formed by photo-chemical machining. Complex fluid circuitry is readily implemented with this technique. Diffusion bonding is a ‘solid-state joining’ process creating a bond of parent metal strength and ductility. The complete microchannel heat exchangers are highly compact, typically comprising about one-fifth the size and weight of conventional heat exchangers for the same thermal duty and pressure drops. PCHEs can be constructed out of a range of materials, including austenitic stainless steels suitable for design temperatures up to 800°C, and nickel alloys such as Incoloy 800HT suitable for design temperatures more than 900°C. Single units ranging from a few grams up to 100 tonnes have been manufactured. Currently there are thousands of tons of such microchannel matrix in hundreds of services — many of them arduous duties on offshore oil and gas platforms where the size and weight advantages of microchannel heat exchangers are of obvious benefit. Whilst these matrices are predominantly involved in thermally simple two-fluid heat exchange, albeit at pressures up to 500 bar, PCHEs have also been used for many multi-stream counter-flow heat exchangers. However the field of applications is very varied, including specialised chemicals processing, and PCHEs are even to be found orbiting the Earth in the International Space Station! Due to the inherent flexibility of the etching process, the basic construction may readily be applied to both a wider range, and more complex integration of process unit operations. Chemical reaction, rectification, stripping, mixing, and absorption, as well as boiling and condensation, can be incorporated into compact integrated process modules. Crucially, the resulting degree of compactness has led printed circuit technology to be the enabling technology in certain duties. Techniques for chemical coating onto the surfaces of channels continue to evolve, with applicability both to protective coatings and catalytically active coatings. We will describe a selection of innovative printed circuit technology examples. Alongside the more esoteric, Heatric is actively extending printed circuit technology to adapt to new market opportunities such as nuclear power generation plant and fuel cell systems. These applications perhaps represent two extremes of the both size and process integration, and thus aptly serve to demonstrate the range of industrial use of microchannel devices.