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We present optical measurements of an LED module consisting of 98 UV LEDs with an emission wavelength of 395 nm soldered onto a ceramic substrate within an area of 211 mm 2 . The module is mounted to a high performance microstructured water cooler. This cooler enables a maximum optical power density of 45.9 W/cm 2 at a forward current of 1350 mA and 447.9 W electrical input power.Further we describe the development of an LED module based on an aluminum substrate with thick film printed insulator and conductor layers and embedded, meander shaped water cooling channels. Numerical and experimental studies with different channel cross-sections are shown. Finally experimental results for this kind of UV LED module with 98 LED chips are presented and compared to the ceramic based module.

We present an improved cooling for a high power density UV LED module for a wavelength of 395 nm. The module consists of 98 LED chips soldered on a thick film printed alumina substrate on an area of 2.11 cm 2 . We investigated cooling by a commercial water cooler as well as by a surface micro cooler developed by our own.Further we describe a technology to replace alumina by aluminum as substrate material. A module consisting of 25 UV LEDs was optically characterized without and with liquid encapsulation.Finally we conducted numerical studies to develop an easily producible, sufficiently powerful, and robust water cooler. Based on the results we present a water cooler design with cooling channels embedded in the aluminum substrate of an LED module, removing the interface between LED substrate and heat sink. IntroductionMany industrial applications today use UV light. It is used to cure paints, lacquers, coatings, and adhesives with low emissions and timesaving. Waste water treatment with UV light offers an important ecological advantage compared to chemical treatment. Currently these applications use high power gas discharge lamps. But high power UV LED sources are gaining increased attention. LED technology promises easier operation, faster switching, lower power consumption, variable light output, and longer lifetime than gas discharge lamps. UV LED chips for the near UV spectral range at wavelengths between 400 nm and 365 nm are currently available with several hundred milliwatt of optical output power. These LEDs enable powerful UV LED light sources.Applications needing just a small spectral band benefit from lower power and cooling demands, because in contrast to gas discharge lamps LEDs emit only in the required spectral band and no light has to be filtered out. Additional power can be saved through an efficient control in non-continuous processes due to the instantaneous light output after switching on the LEDs.As lifetime, efficiency, and reliability of LED systems is closely associated with the junction temperature of every single LED, the thermal properties of the packaging and the cooling system are crucial issues.We present substantial improvements in the cooling of an LED cluster built on a ceramic substrate using a high performance microstructured water cooler. Additionally we show a novel LED cluster built on a thick aluminum substrate with thick film printed dielectrics and silver traces. The LEDs are

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, providing relatively limited performance, or by other systems like fallingfilm evaporators. Due to the advantages of microstructure devices especially in chemical process engineering the interest in microstructure evaporators and steam generators have been increased through the last decade. In this publication different microstructure devices used for evaporation and generation of steam will be described. Starting with simple liquid-heated devices, different types of electrically powered devices containing micro channels as well as non-channel microstructures will be shown. 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. Thus, a new design was proposed to obtain complete evaporation and superheating of the generated steam.

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...