In the current paper, a theoretical study of the effect of the viscosity variation on the squeeze film performance of a short bearing operating with couple stress fluids is presented. The modified Reynolds equation accounting for the couple stresses and viscosity variation is mathematically derived. To obtain a closed form solution, the short bearing approximation under constant load is considered. The modified Reynolds equation is solved for the fluid film pressure and then the bearing characteristics, such as the load carrying capacity and the squeeze time for the fluid film are obtained. According to the results evaluated, the couple stress fluid as a lubricant improves the squeeze film characteristics and results in a longer bearing life. Whereas the viscosity variation factor decreases the load carrying capacity and squeeze film time. The results are compared with the Newtonian fluid.

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Experiments were conducted on a solar parabolic trough collector (PTC) with graphene oxide (GO) nanofluid and Titanium oxide (TiO2) nanofluid as the working fluids, circulated forcibly with the aid of a pump. The PTC had a collector area of 2.3 m 2 , a concentric tube heat exchanger (CTHX) and a storage tank. The GO and TiO2 nanofluids was prepared by ultrasonication of the GO nanoparticles and TiO2 nanoparticles with de-ionized (DI) water as the base fluid, without adding any surfactant. Homogeneous and stable GO and TiO2 nanofluids for five different mass concentrations, (ϕ) = 0.05, 0.1, 0.2, 0.3 and 0.5, were prepared. The nanofluids were found to be stable for 60 days without any sedimentation issues. The thermo-physical properties of the GO and TiO2 nanofluids, such as the thermal conductivity, viscosity, density and specific heat, were estimated. For the flow supplied by the pump, the maximum value of the PTC inlet pipe and fluid property-based Reynolds number was found to be 4400. The PTC's overall heat transfer co-efficient (h), friction factor and collector efficiency were investigated for GO and TiO2 nanofluids under laminar conditions. It was observed that for GO nanofluid with ϕ = 0.5 and a flow rate of 0.05 kg/s, the enhancement in the collector efficiency was 16.3% over that of the TiO2 nanofluid and base fluid (DI water) . The collector efficiency was found to increase with increasing "ϕ" and flow rate. The increment in heat transfer co-efficient (h) for the GO nanofluid with ϕ = 0.1, 0.2 and 0.3 were 7.03%, 8.93% and 11.5%, respectively and for TiO2 nanofluid with ϕ =0.

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