Ulrich Schygulla

Microstructure Heat Exchanger Applications in Laboratory and Industry

In this article, heat transfer in microstructure devices and its application in laboratory and industry will be described. Basic principles of microstructure heat exchangers made of metal, ceramics, and polymers will be presented. A variety of laboratory prototype applications will be shown, as well as some examples for industrial use of not only microstructure heat exchangers, but also microstructure devices as chemical reactors. A brief outlook will describe possible future application fields.

Comparison of Crossflow Micro Heat Exchangers With Different Microstructure Designs

Microstructure heat exchanger are well known for their superior heat transfer capabilities and the good temperature management for applications. Most microstructure heat exchangers presented so far consisted of a number of microchannels in a defined arrangement to provide the transfer of thermal power from one fluid to another, mostly in laminar flow regime. In this publication, several crossflow microstructure heat exchangers are presented. The devices design ranges from simple linear microchannels of different dimensions and shape, complex micro column arrangements up to three dimensional flow structures like crossed sinusoidally shaped microchannels, a kind of split-and-recombine structure. By comparing experimental results of the most interesting devices, microstructure devices with good performance can be chosen.Copyright

Microstructure devices for efficient heat transfer

Microstructure devices provide unique properties with regard to heat and mass transfer. Due to the tremendously high surface-to-volume ratio they are very well suited for many thermal and chemical processes in which large amount of heat has to be transferred. Metal microstructure devices also provide very high stability against high pressure, combined with an adjustable mass flow range of up to several thousand kg of liquid per hour and per passage, depending on the size and number of the integrated microstructures. Aside of fluid driven metallic microstructure devices like the famous Karlsruhe Cube, electrically powered devices have been developed and applied for temperature ranges where thermoliquids reach their limits or the use of gases may be disadvantageous due to their high viscosity and the arising pressure drop. In this publication several microstructure devices for heating and evaporation of fluids as well as for chemical reactions are presented in overview style. Details on manufacturing and device properties are given. Some process examples and experimental data for different types of microstructure devices are shown. Fouling problems are discussed briefly by an example.

Micro Heat Changers and Surface-Micro-Coolers for High Heat Flux

This publication describes the development of a new microstructure to transfer high heat fluxes. With a simple mathematical model based on heat conduction theory for the heat transfer in a micro channel at laminar flow conditions it was deduced that for the transmission of high heat fluxes only the initial part at the beginning of the micro channels is of importance, i.e. the micro channels should be short. Based on this principle a micro structure was designed with a large number of short micro channels taken in parallel. With this newly developed microstructure a prototype of a micro heat exchanger and a surface micro cooler was manufactured and tested. Using the prototype of the micro heat exchanger, manufactured of plastic, heat fluxes up to 500 W/cm2 were achieved at a pressure loss of 0.16 MPa and a mass flow of the water of 200 kg/h per passage. Due to the use of materials with a higher temperature resistance and higher stability like aluminum or ceramic, higher water throughputs and higher flow velocities could be realized in the micro channels. Thus it was possible to increase the heat flux up to approx. 800 W/cm2 at a pressure loss of approx. 0.35 MPa and a mass flow of 350 kg/h per passage. The important focus of investigation of the surface micro cooler was set on the examination of the surface temperatures for different heat fluxes and different velocities of the water in the micro channels. The experimental results of these surface micro coolers are summarized to characteristic maps. With this characteristic maps it is possible to determine whether a micro surface cooler can be used for a specific application.Copyright