Thermal properties and convective heat transfer of phase changing paraffin nanofluids

Abstract

THERMAL PROPERTIES AND CONVECTIVE HEAT TRANSFER PERFORMANCE OF SOLID-LIQUID PHASE CHANGING PARAFFIN NANOFLUIDSWe aim to combine these two concepts for the first time by studying fluids containing nano-sized phase changing particles. In this study, the convective heat transfer performance and the thermal properties of solidliquid phase changing paraffin nanofluids are experimentally examined. Three water-based paraffin nanofluids with particle mass fractions of 5-10% are prepared and measured with an annular tube heat exchanger. The heat transfer measurements cover both laminar and turbulent regimes with Reynolds numbers varying in the range of 700-11000. The measurements also include pressure losses in order to study the suitability of the fluids for practical forced convection applications. In addition, the fluids are characterized: latent heats, specific heats, viscosities, thermal conductivities, densities and particle size distributions are all determined experimentally. In agreement with previous studies, the nanofluids are found to exhibit Nusselt numbers clearly higher than water when compared on the basis of equal Reynolds numbers. However, the differences in Prandtl numbers are shown to explain these deviations in Nusselt numbers. Indeed, the well-known Gnielinski correlation is able to explain the results quite adequately and thus, significant anomalies in the convection heat transfer caused by neither the melting of the phase change material nor the presence of the nanoparticles are observed. However, the nanofluids have systematically slightly higher Nusselt numbers than the correlation would predict, but the deviations are within the accuracy of the correlation (10%). When compared by using equal pumping powers, the nanofluids exhibit heat transfer performance poorer than that of water. The positive impact of the latent heat is outweighed by the negative effects of the increased viscosity and decreased specific heat.

Dynamic Viscosity, Surface Tension and Wetting Behavior Studies of Paraffin–in–Water Nano–Emulsions

“…This is more appreciable in the case of RT21HC(10 wt.%)/water sample, for which indicated difference reached 39%. A similar behavior was reported by Mikkola et al [42] when the viscosity of studied paraffin-in-water emulsions using either a falling ball viscosimeter or a rotational rheometer. In that last investigation, authors reported µ/µ water ratios of 2.35 (at temperatures at which paraffin droplets were solid) and 1.95 (liquid paraffin droplets) for a dispersed phase concentration of 10 wt.%.…”

Influence of particle properties on convective heat transfer of nanofluids

“…The largest difference of 12.5-20.5% was obtained for the sample with the highest particle fraction: 1.81 vol-% SiO2 nanofluid. Similar behavior has been reported widely in the literature [6][7][8]16,[52][53][54][55]. However, this presentation method has been criticized in several recent publications [14][15][16][17]52,[56][57][58].…”

“…However, an ongoing debate about the magnitudes of these changes exists, since the results of different groups are often contradictory. In some publications, an anomalous behavior in convective heat transfer has not been observed at all [12][13][14][15][16][17]. In spite of the large body of research, no theory has been able to provide a solid and well-established explanation for the physical basis of the possible anomalous heat transfer enhancement of nanofluids.…”

Experimental Investigation on Performance Comparison of Solar Water Heating-Phase Change Material System and Solar Water Heating System

“…It is found that the convective heat transfer performances were greatly enhanced during the phase change process. Mikkola et al [19] measured the heat transfer performance of 5.0, 7.5, and 10.0 wt% paraffin with an annular-tube heat exchanger. The heat transfer coefficients of all the PCMEs were greater than that of water for both laminar and turbulent flow.…”