Thermal conductivity of metal (A1, Cr, and Ni) and semiconductor (ZnS and CdS) nanofluids determined by a transient hot wire method

In heat transfer application, the challenge in development of the nanofluids is in understanding on how the interactions between the particles and fluid affect thermal properties of the fluids. The main objective of this work is to determining the thermal conductivity of the metallic and semiconductor nanofluids. The specific objectives are to study the effect of volume fraction concentration, metal nanoparticles, base fluid, pH valueof Al, Ni, and Cr nanofluids and radiation doseof ZnS and CdSnanofluidson the enhancement of the thermal conductivity. The metallic nanofluidssamples were prepared at various volume fraction concentrations ranging from 0.01- 0.30 vol.% using a single step technique. For semiconductor nanofluids, the samples were prepared at different radiation dose range from 10-60 KGy. The thermal conductivity of the samples was measured using KD2 Pro Thermal Analyzer which employed transient hot wire (THW) method at the room temperature. The thermal conductivity of pure base fluids measured are 0.254, 0.614, and 0.168 W/m·K, for ethanol, distilled water and ethylene glycol and 0.551W/m·K for pure polyvinyl alcohol (PVA). The result shows that the thermal conductivity of all nanofluids samples was increased proportionally with the increment of volume fraction. The enhancement of thermal conductivity of Al nanoparticles in ethanol, distilled water, and ethylene glycol are increased up to 26.19, 16.48, and 5.62% at 0.02 vol.%. The enhancement of the thermal conductivity of Cr nanoparticles in ethanol, distilled water, and ethylene is 21.42, 17.42, and 15.66% at 0.20 vol.%and for thermal conductivity of Ni nanoparticles in ethanol, distilled water, and ethylene glycol increased up to 21.42, 13.52, and 9.64% at 0.03 vol.%.In measuring effect of pH concentration on the thermal conductivity of Al nanofluids theresults show that there exists an optimal pH value for the highest thermal conductivity. The optimal pH value the nanofluids containing a small amount of Al nanoparticles have noticeably higher thermal conductivity than that of the base fluid without nanoparticles. In this work, the optimal pH value were observed at pH 10 for 0.03, 0.05, and 0.10 vol.% with the percentage of enhancement are 8.63, 11.25, and 20.58%. . Interpretation from the results of the effect of radiation dose shows thatthe thermal conductivity of CdS and ZnS are decreased by increasing the dose of the radiation exposure on the sample. Thermal conductivity of CdSis 0.558 W/m·K and 0.561 W/m·K for ZnSrespectively, after been expose to the radiation at 20 KGy. While the thermal conductivity values is 0.0554 W/m·Kfor CdSand 0.555 W/m·Kfor ZnSrespectively, after been expose to the radiation at 50 KGy.

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