Experimental study of heat transfer enhancement in a helical tube heat exchanger by alumina nanofluid as current flow
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In the present study, the heat transfer rate through a shell and helical tube heat exchanger with alumina nanofluid as current flow was investigated and the obtained results were compared to those of the distilled water. Effects of alumina concentration in the nanofluid (0–0.5 vol.%) and the temperature of hot fluid (40–70 °C) were evaluated at different flow rates (2–3.5 L/min). Heat transfer coefficients were determined using Wilson method. The overall heat transfer rate decreased with Dean number at low Dean numbers and increased after passing through a minimum at higher dean numbers due to simultaneous and competitive effects of convective heat transfer coefficient and temperature difference on heat transfer rate. At low Dean numbers, the effect of temperature difference dominated the effect of convective heat transfer coefficient and at high Dean numbers, the convective heat transfer coefficient effect was more determining. Higher temperature of the hot fluid led to higher convective heat transfer coefficient due to increased thermal conductivity of the fluid at higher temperatures. Compared to the distilled water, higher convective heat transfer coefficient was obtained for nanofluid as the current flow at low volume fractions of the nanofluid. The maximum heat transfer rate (9505.6 W) was obtained at a volume fraction of 0.016, flow rate of 3.5 L/min, and temperature of 70 °C.
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