4,263 research outputs found
Exploratory Research on MEMS Technology for Air-Conditioning and Heat-Pumps
This report details the efforts to exploit micro-electrical-mechanical-systems (MEMS)
and micro device technologies to improve control of multi-channel evaporators by
reducing maldistribution among channels, and increase capacity and efficiency of
current vapor-compression refrigeration chillers and heat-pumps. Besides
summarizing the market potential of MEMS technology for use in evaporators and
micro-heat-pumps, the report describes the accomplishments of an experimental
investigation of refrigerant-side maldistribution in multi-channel plate heat exchangers
(PHE's). A special test facility designed for the purpose of studying the
maldistribution of refrigerant in evaporators is described in the report. The facility
allows maldistribution caused by either normal superheat temperature control, or
induced by the user in controlled amounts, to be measured and quantified. Four
different techniques were used to detect the presence of liquid droplets in the stream of
superheated vapor at the evaporator exit, an indication of maldistributed flow. They
are: Helium-Neon laser, beaded thermocouple, static mixer and newly designed heated
MEMS sensor. Comparison of the four techniques shows that the MEMS sensor
designed and fabricated in this project has the highest potential for indicating
maldistribution, manifested by entrained liquid droplets, in multi-channel evaporators.
A complete set of test results in the time and frequency domain is show in graphical
form in the appendices. The design, fabrication, calibration, and testing of the MEMS
serpentine resistance sensor is also reported, along with a control scheme and strategy
for implementing the MEMS sensor in multi-channel evaporator systems
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Two-phase heat transfer in small passages and microfinned surfaces - Fundamentals and applications
Micro channels and internally finned tubes are increasingly being utilized in the evaporators and condensers of refrigeration systems. The adoption of such geometries in the development of micro-cooling systems is first discussed in this paper. Recent work on flow boiling heat transfer and condensation in small to micro passages as well as on microfinned surfaces is then presented. The complex effect of diameter size on flow boiling patterns and heat transfer and correlations currently available in literature are summarized. Condensation in microfinned tubes and microchannels is then discussed
Micro-evaporators for kinetic exploration of phase diagrams
We use pervaporation-based microfluidic devices to concentrate species in
aqueous solutions with spatial and temporal control of the process. Using
experiments and modelling, we quantitatively describe the advection-diffusion
behavior of the concentration field of various solutions (electrolytes,
colloids, etc) and demonstrate the potential of these devices as universal
tools for the kinetic exploration of the phases and textures that form upon
concentration
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On-chip micro-evaporation: Experimental evaluation of liquid pumping and vapor compression cooling systems
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Thermal designers of data centers and server manufacturers are showing a great concern regarding the cooling of new generation data centers, which are more compact and dissipate more power than is currently
possible to cool by conventional air conditioning systems. With very large data centers exceeding 100 000 servers,
some consume more than 50 MW [1] of electrical energy to operate, energy which is directly converted to heat and then simply wasted as it is dissipated into the atmosphere. A potentially significantly better solution would be to make use of on-chip two-phase cooling [2], which, besides improving the cooling performance at the chip level, also adds the capability to reuse the waste heat in a convenient manner, since higher evaporating and condensing
temperatures of the two-phase cooling system (from 60-95°C) are possible with such a new green cooling technology. In the present project, two such two-phase cooling cycles using micro-evaporation technology were
experimentally evaluated with specific attention being paid to energy consumption, overall exergetic efficiency and controllability. The main difference between the two cooling cycles is the driver, where both a mini-compressor and a gear pump were considered. The former has the advantage due to its appeal of energy recovery since its exergy potential is higher and the waste heat is exported at a higher temperature for reuse.This study is supported by: the Swiss Commission for Technology and Innovation (CTI) contract number 6862.2; the LTCM laboratory; IBM ZĂĽrich Research
Laboratory (Switzerland) and Embraco (Brazil)
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Microstructure devices for water evaporation
This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.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 falling-film 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
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Development of interconnected silicon micro-evaporators for the on-detector electronics cooling of the future ITS detector in the ALICE experiment at LHC
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The design of the future High Energy Physics (HEP) particle detectors for the upgrade of the LHC (Large Hadron Collider) experiments at CERN (European Organization for Nuclear Research) is pushing technological frontiers to the limit trying to reach unprecedented accuracy in particles identification and particle production dynamics in ultra-relativistic hadron collisions. The thermal management of the on-detector electronics and the development of low mass integrated cooling systems have become a crucial task in the design of silicon tracking detectors for HEP applications. In this paper, we present a novel concept of low mass interconnected silicon microchannel devices for the future Inner Tracking System of the ALICE (A Large Ion Collider Experiment) detector at LHC. This innovative design achieves the requirements of the detector while minimizing the total material budget
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Microstructure devices for process intensification: Influence of manufacturing tolerances and measurement uncertainties
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Process intensification by miniaturization is a common task for several fields of technology. Starting from manufacturing of electronic devices, miniaturization with the accompanying opportunities and problems gained also interest in chemistry and chemical process engineering. While the integration of enhanced functions, e.g. integrated sensors and actuators, is still under consideration, miniaturization itself has been realized in all material classes, namely metals, ceramics and polymers. First devices have been manufactured by scaling down macro-scale devices. However, manufacturing tolerances, material properties and design show much larger influence to the process than in macro scale. Many of the devices generated alike the macro ones work properly, but possibly could be optimized to a certain extend by adjusting the design and manufacturing tolerances to the special demands of miniaturization. Thus, some considerations on the design and production of devices for micro process engineering should be made to provide devices which show reproducible and controllable process behavior. This following publication gives some examples
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Unified Modeling Suite for Two-Phase Flow, Convective Boiling and Condensation in Macro-and Micro-Channels
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The present paper focuses on the unified modeling suite for annular flow that the authors have and continue
to develop. Annular flow is of fundamental importance to the thermal design and simulation of microevaporators
and micro-condensers for compact two-phase cooling systems of high heat flux components for
the thermal management of computer chips, power electronics, laser diodes and high energy physics particle
detectors. First, the unified suite of methods is presented, illustrating in particular the most recent updates.
Then, results for convective evaporation of refrigerants in non-circular multi-microchannel configurations
for microelectronics cooling are presented and discussed. The annular flow suite includes models to predict
the void fraction, the entrained liquid fraction, the wall shear stress and pressure gradient, and a turbulence
model for momentum and heat transport inside the annular liquid film. The turbulence model, in particular,
allows prediction of the local average liquid film thicknesses and the local heat transfer coefficients during
convective evaporation and condensation. The benefit of a unified modeling suite is that all the included
prediction methods are consistently formulated and are proven to work well together, and provide a platform
for continued advancement based on the other models in the suite
Workshop on Two-Phase Fluid Behavior in a Space Environment
The Workshop was successful in achieving its main objective of identifying a large number of technical issues relating to the design of two-phase systems for space applications. The principal concern expressed was the need for verified analytical tools that will allow an engineer to confidently design a system to a known degree of accuracy. New and improved materials, for such applications as thermal storage and as heat transfer fluids, were also identified as major needs. In addition to these research efforts, a number of specific hardware needs were identified which will require development. These include heat pumps, low weight radiators, advanced heat pipes, stability enhancement devices, high heat flux evaporators, and liquid/vapor separators. Also identified was the need for a centralized source of reliable, up-to-date information on two-phase flow in a space environment
Design of LTCC-based Ceramic Structure for Chemical Microreactor
The design of ceramic chemical microreactor for the production of hydrogen needed in portable polymer-electrolyte membrane (PEM) fuel cells is presented. The microreactor was developed for the steam reforming of liquid fuels with water into hydrogen. The complex three-dimensional ceramic structure of the microreactor includes evaporator(s), mixer(s), reformer and combustor. Low-temperature co-fired ceramic (LTCC) technology was used to fabricate the ceramic structures with buried cavities and channels, and thick-film technology was used to make electrical heaters, temperature sensors and pressure sensors. The final 3D ceramic structure consists of 45 LTCC tapes. The dimensions of the structure are 75 Ă— 41 Ă— 9 mm3 and the weight is about 73 g
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