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Session: Session 1B: Working fluids
Session starts: Monday 09 September, 10:30
Presentation starts: 11:50
Room: Attica

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Giovanna Cavazzini (University of Padova)
Serena Bari (University of Padova)
Vittoria Benedetti (University of Bolzano)
Peter McGrail (PNNL)
Giorgio Pavesi (University of Padova)
Guido Ardizzon (University of Padova)

Abstract:
In the industrial sector, medium, low and ultra-low temperature waste heat represents a significant source of energy loss as well as constitutes a harmful environmental effect, which must be avoided. Nonetheless, waste heat could represent a free and vast potential when a technology to recover effectively energy at low temperatures is utilized. In this context, the Organic Rankine Cycle (ORC) technology is a proven solution because, being the working fluid an organic substance with low boiling temperature, it is more suitable than water when low grade heat needs to be recovered. However, the recovery process presents several challenges when dealing with low and ultra-low temperature heat sources (<150°C) and one of the most significant is the proper choice of the working fluid. In such a context, numerous studies have been already carried out to identify in each particular application the working fluid that overperformed the others, but at low grade heat source temperatures organic working fluids showed similar decaying performances with thermal efficiencies typically ranging from 8 to 10%. So, the identification of a working fluid, performing significantly better than the others, is still far from being achieved, due to difficulty in the maximization of the heat transfer from low grade heat sources. To achieve higher heat transfer efficiencies, unconventional working fluids with enhanced thermal properties should also be investigated. Regarding this topic, nanofluids, suspensions of nanoparticles in a base fluid, synthesized intentionally to have enhanced thermal properties, might have the potential to increase ORCs efficiency. This paper presents a more in-depth investigation of the applications of this particular type of nanofluids in the ORC field, developing a numerical model for assessing the nanofluid gain in terms of net power production. In particular, the possible combination of the base fluid R245fa with the nanoparticle MIL101, a robust Metal Organic Heat Carrier, is considered. Thermo-physical models have been used to predict the nanofluids behaviour in different operative conditions of the ORC plant. Therefore, in order to limit the influence of the model uncertainties on the results of the numerical analysis preliminary experimental analyses are carried out to assess the adsorption behaviour of MIL101 in R245fa. The resulting performance of the MIL101/R245fa is then compared with those of pure organic fluids, whose cycle is optimized in order to maximize the power output.