Heat exchangers literally move heat from one substance to another. They are used to add or remove heat from processes. Heat exchangers come in many forms but most consist of a solid separating two fluid media. When the temperature difference between the two media is low, ever larger exchange surface areas are required for efficient heat exchange. However, large surfaces are often not feasible either economically or technically, or both. Employing novel nanomaterials, scientists working on the EU-funded project 'Low-temperature heat exchangers based on thermally-conducting polymer nanocomposites' (Thermonano) are solving this problem, which limits process efficiency. Exchange materials made from nanomaterial-filled polymers are being designed for effective heat conductivity (more conductivity per unit area means less area for the same conduction) and cost reduction compared to conventional metals. Additional expected benefits include design flexibility for volume exploitation, excellent corrosion resistance and highly effective drop condensation. Scientists developed and selected a number of polymer materials and nanofillers during the first year, including carbon nanotubes (CNTs) and metal-coated nanoparticles (NPs). Scientists experimented with modifying CNTs to determine the effects of certain parameters. Silver metallisation (build up of a blanket layer of metal) of substrates including glass flakes, nanofibres (wollastonite), polyamide flakes and cellulose fibres was also performed to produce metal-coated NPs for fillers. Selected conductive particles including both CNTs and metal-coated NPs were incorporated into thermoplastic polymers (those that can be remelted and reprocessed over and over again). Detailed characterisation studies led to a deeper understanding of the effects of metal NPs and their concentration within polymers. Contact resistance between adjacent NPs leading to a drop in temperature at every contact point was found to be the main factor impeding efficient thermal exchange. Thermonano has developed novel designs for polymer nanocomposite-based heat exchangers suited to low temperature difference-exchange. Commercial exploitation of Thermonano concepts may help increase the process efficiency of a number of relevant industrial applications. These include intercoolers for large diesel engines, heat recovery from combustion flue gases, and chemical processes with harsh chemicals or corrosive environments.
LOW-TEMPERATURE HEAT EXCHANGERS BASED ON THERMALLY-CONDUCTING POLYMER NANOCOMPOSITES
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29 June 2020