A New Microstructure Device for Efficient Evaporation of Liquids

Abstract

Evaporation of liquids is of major interest for many topics in process engineering. One of these is chemical process engineering, where evaporation of liquids and generation of superheated steam is mandatory for numerous processes. Generally, this is performed by use of classical pool boiling and evaporation process equipment. Another possibility is creating mixtures of gases and liquids, combined with a heating of this haze. Both methods provide relatively limited performance. Due to the advantages of microstructure devices especially in chemical process engineering [1] the interest in microstructure evaporators and steam generators have been increased through the last decade. In this publication several microstructure devices used for evaporation and generation of steam as well as superheating will be described. Here, normally electrically powered devices containing micro channels as well as non-channel microstructures are used due to better controllability of the temperature level. Micro channel heat exchangers have been designed, manufactured and tested at the Institute for Micro Process Engineering of the Karlsruhe Institute of Technology for more than 15 years. Starting with the famous Karlsruhe Cube, a cross-flow micro channel heat exchanger of various dimensions, not only conventional heat transfer between liquids or gases have been theoretically and experimentally examined but also phase transition from liquids to gases (evaporation) and condensation of liquids. However, the results obtained with sealed microstructure devices have often been unsatisfying. Thus, to learn more onto the evaporation process itself, an electrically powered device for optical inspection of the microstructures and the processes inside has been designed and manufactured [2]. This was further optimized and improved for better controllability and reliable experiments [3]. Exchangeable metallic micro channel array foils as well as an optical inspection of the evaporation process by high-speed videography have been integrated into the experimental setup. Fundamental research onto the influences of the geometry and dimensions of the integrated micro channels, the inlet flow distribution system geometry as well as the surface quality and surface coatings of the micro channels have been performed. While evaporation of liquids in crossflow and counterflow or co-current flow micro channel devices is possible, it is, in many cases, not possible to obtain superheated steam due to certain boundary conditions [4]. In most cases, the residence time is not sufficiently long, or the evaporation process itself cannot be stabilized and controlled precisely enough. Thus, a new design was proposed to obtain complete evaporation and steam superheating. This microstructure evaporator consists of a concentric arrangement of semi-circular walls or semi-elliptic walls providing at least two nozzles to release the generated steam.*Received 15 Dec., 2011 (No. 11-0773) [DOI: 10.1299 Copyright © 2012 by JSME Vol. 7, No. 3, 2012 Journal of Ther...

In-Situ Measurements in Microscale Gas Flows—Conventional Sensors or Something Else?

“…Additional analytical methods like gas chromatography (GC) [99,100], infrared (IR) spectrometry [101], ultraviolet (UV) spectrometry [102], the above mentioned Raman spectrometry [103], mass spectrometry (MS) [104,105] or Nuclear Magnetic Resonance spectroscopy (NMR) [106,107,108,109,110] are used to determine the components of the mixture, depending on the applicability of the respective method to the gas. Visualization of flow processes can be obtained by, for example, high speed videography [111,112,113]. An example of a microstructure used for high speed videography is given in Figure 3.…”

“…A step between the single incoming channel and the two outgoing channels is clearly visible, which is due to manufacturing. Reproduced with permission from [111], published by J-STAGE, 2012.…”