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Chen X.,University of Nottingham | Su Y.,University of Nottingham | Reay D.,David Reay and Associates | Riffat S.,University of Nottingham
Renewable and Sustainable Energy Reviews

Due to their low cost, light weight and corrosive resistant features, polymer heat exchangers have been intensively studied by researchers with the aim to replace metallic heat exchangers in a wide range of applications. This paper reviews the development of polymer heat exchangers in the last decade, including cutting edge materials characteristics, heat transfer enhancement methods of polymer materials and a wide range of polymer heat exchanger applications. Theoretical modelling and experimental testing results have been reviewed and compared with literature. A recent development, the polymer micro-hollow fibre heat exchanger, is introduced and described. It is shown that polymer materials do hold promise for use in the construction of heat exchangers in many applications, but that a considerable amount of research is still required into material properties, thermal performance and life-time behaviour. © 2016 Elsevier Ltd. Source

Law R.,Northumbria University | Harvey A.,Northumbria University | Reay D.,David Reay and Associates
Applied Thermal Engineering

Energy efficiency in the process industry is becoming an increasingly important issue due to the rising costs of both electricity and fossil fuel resources, as well as the tough targets for the reduction in greenhouse gas emissions outlined in the Climate Change Act 2008. Utilisation of waste heat sources is key to improving industrial energy efficiency, with an estimated 11.4 TWh of recoverable heat being wasted each year, a quarter of which is from the food and drinks processing sector. This paper examines the low-grade waste heat sources common to the food and drinks processing sector and the various opportunities for the use of this heat. A review of the best available technologies for recovery of waste heat is provided, ranging from heat transfer between source and sink, to novel technologies for the generation of electricity and refrigeration. Generally, the most economic option for waste heat recovery is heat exchange between nearby/same process source and sink, with a number of well-developed heat exchangers widely available for purchase. More novel options, such as the use of organic Rankine cycles for electricity generation prove to be less economical due to high capital outlays. However, with additional funding provision for demonstration of such projects and development of modular units, such technologies would become more common. © 2012 Elsevier Ltd. All rights reserved. Source

MacGregor R.W.,AECOM Technology Corporation | Kew P.A.,Heriot - Watt University Dubai | Reay D.A.,David Reay and Associates
Applied Thermal Engineering

Two-phase thermosyphons are devices offering very high thermal conductance. The study reported here examined two-phase thermosyphons of length 2200 mm and external diameter 15.9 mm. Potential applications include air to air heat exchangers with operating temperature ranges of -10-50 °C for the ambient (cold) side and 60-80 °C for the hot side. The work is prompted by the fact that R134a, used in similar units, will be subject to a ban in the future as it has a high Global Warming Potential. A shortlist of potential replacement fluids was drawn up, and considering the environmental, operating and storage conditions, and cost, five were selected for tests in representative thermosyphons. The results of the experimental work showed a water-5% ethylene glycol mixture was a suitable replacement fluid, although under certain conditions its performance was less than that of R134a. The tests also showed water alone can give the highest heat transfer, although it is not suited to the target temperature range, and methanol did not perform as well as R134a for most of the experimental range. A predictive model based on the equations published by ESDU International was developed. It was found to give good results for water, workable results for water-5% ethylene glycol, be of limited use for methanol and be unsuitable for R134a. © 2012 Elsevier Ltd. All rights reserved. Source

Reay D.A.,David Reay and Associates
International Journal of Low-Carbon Technologies

Heat-powered cycles (HPCs) are well established in many areas of life. The heat pump (vapour compression cycle) is becoming an essential feature of houses in many countries, and mechanical vapour recompression systems are popular in the food and drink sector of the process industries. However, historically, earlier energy crises have spurred many advances in the use of HPCs in industry-the coal crisis in the 1940s and the oil crises in the 1970s being noteworthy examples. More recently, in spite of technological advances inmaterials and manufacturing technologies, in particular in furthering intensification andminiaturisation, the benefits these have brought to HPCs seem to have neglected uses inthe process industries. This needs remedying, if competitiveness, coupled with carbon emission reductions, are to retain and strengthen their important position in industry. In conjunction with the examination of some early examples of HPCs where size and cost may have inhibited investment, this paper presents some heat transfer and manufacturing technologies that might help to break perceived cost barriers to further progress the use of HPCs. © The Author 2013. Published by Oxford University Press. All rights reserved. Source

Ferhati A.,Brunel University | Karayiannis T.G.,Brunel University | Lewis J.S.,Brunel University | McGlen R.J.,Thermacore | Reay D.A.,David Reay and Associates
Heat Transfer Engineering

An experimental investigation of the thermal-hydraulic characteristics for single-phase flow through three electron beam enhanced structures was conducted with water at mass flow rates from 0.005 kg/s to 0.045 kg/s. The structures featured copper heat transfer surfaces, approximately 28 mm wide and 32 mm long in the flow direction, with complex three-dimensional (3D) electron beam manufactured pyramid-like structures. The channel height varied depending on the height of the protrusions and the tip clearance was maintained at 0.1-0.3 mm. The average protrusion densities for the three samples S1, S2, and S3 were 13, 11, and 25 per cm2 with protrusion heights of 2.5, 2.8, and 1.6 mm, respectively. The data gathered were compared to those for a smooth channel surface operating under similar conditions. The results show an increase up to approximately three times for the average Nusselt number compared with the smooth surface. This is attributed to the surface irregularities of the enhanced surfaces, which not only increase the heat transfer area but also improve mixing, disturb the thermal and velocity boundary layers, and reduce thermal resistance. The increase in heat transfer with the enhanced surfaces was accompanied by an increase of pressure drop, which has to be considered in design. Copyright © Taylor and Francis Group, LLC 2015. Source

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