6 research outputs found
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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
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Numerical investigation of laminar flow in micro-tubes with designed surface roughness
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.Recently, there has been a rapid growth in applications that deal with fluid flow at micro-scale where surface roughness is a real feature in these applications. Published literature shows conflicting
findings regarding the effect of surface roughness on the friction factor of laminar flow at micro-scale. The understanding of fluid flow behavior in micro-tubes is very important for effective design of micro-fluidic devices. This work presents a numerical investigation of the effect of various surface roughness geometries on friction factor in fluid flow in the laminar regime. Results indicate that surface roughness causes deviation of the frictional factor from conventional theory with various values depending on the height and shape of
the roughness used
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Natural convection heat transfer effects with micro finned structures
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.Micro-scale natural convection plays an important role in heat removal from microelectronic components and Micro-Electro-Mechanical Systems (MEMS) devices. Natural convection of macrofin arrays has been extensively studied by many researchers over the past several decades; however analysis of free convection around microfin arrays is less well researched. The objective of this work was to experimentally investigate the effects of micro fin height and spacing for a horizontally mounted heat sink on heat transfer coefficient when operating under steady state natural convection conditions. An array of micro finned copper heat sinks was fabricated using micro-electro discharge wire machining (ÎĽ-EDWM) with fin height ranging from 0.25 to 1.0mm and fin spacing from 0.5 to 1.0mm respectively. Results showed that values of the convective heat transfer coefficient increased with increased fin spacing and decreased as fin height increased.This study is funded by Advantage West Midlands (AWM)
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Numerical investigation of laminar flow heat transfer through helically coiled tubes using Al2O3 nanofluid
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.Nanofluids have been reported to enhance heat transfer performance in heat exchangers.
Additionally, the use of helical coils has shown to be another passive heat transfer enhancement technique. This work presents a CFD modeling study to investigate the laminar heat transfer through helical tubes with nanofluids. The developed CFD models were validated against published experimental results and empirical
correlations in the literature. The effects of particles concentration and Reynolds number on heat transfer coefficient were numerically investigated. Results have shown that Al2O3 dispersed in water increases the
heat transfer coefficient in helical coils by up to 4.5 times that of pure water in straight tubes at same Reynolds number. For concentrations larger than 2%, Al2O3 is more suitable for thermal systems of small thermal loads where the pumping power is not critical