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In this paper, the performance of the evacuated tube solar collector is investigated theoretically by the TRNSYS program. The simulation is conducted during the winter of 14th February-2019 in Cairo – Egypt. In this simulation, water and Nanofluids areworking fluids. The types of Nanofluids are CeO2/water, WO3/water and AL2O3/water. The simulation is conducted at0.015%,0.025%, 0.035% and 0.045% (volume concentrations).The mass flux rate and tilt angle are 0.017 kg/s.m2and 45o; respectively.The results show that the collector has the highest performance using nanofluids at studied concentrations. At 12:00 PM, thehighest useful energy gain can be obtained from CeO2/water Nanofluid at 0.045% concentration, while thermal efficiency ishigher by 34.2% than water. The nanofluidWO3/water presents low performance than that of CeO2/water and AL2O3/water. The thermal efficiencies ofAL2O3/ water and WO3/ water Nanofluids are higher than water by 28.4% and 12.5%; respectively, atconcentration of 0.045% and 12:00PM

The present paper investigates experimentally the performance of the evacuated tube heat pipe solar collector in Cairo-Egypt climate conditions. The experimental work conducts by using an evacuated solar collector with nanofluid in indirect building heating. The investigation parameters are tilt angle, AL2O3 nanoparticles concentrations, mass flow rates, water temperature difference, useful heat gain, collector thermal efficiency, air temperature difference, thermal optical efficiency and energy loss coefficients. The results show that the tilt angle 45o gives best performance characteristics of the collector. At tilt angle of 45o, 90 kg/h flow rate, 0.2% of nanofluid concentration and at 1:30 PM the air temperature difference increases by 16.4% than the reference fluid. The collector thermal efficiency increases by high concentrations of nanofluid, which reaches to 49%, 44.8%, 42.9% and 39% at a nanofluid concentration of 0.2%, 0.15%, 0.1% and 0% at 1:30 PM and 90kg/h, respectively. Also at low mass flow rate the air temperature difference increases by 9oC at 0.2% of nanofluid concentration.

The performance characteristics of a triple conically tube heat exchanger (TCTHE) are experimentally and numerically conducted. The new design developed by addition a new fluid path to a double conically tube heat exchanger (DCTHE). The research aims to evaluate the TCTHE thermal characteristics at various operating and designing key parameters involve water Reynolds number, water inlet temperatures variation, flow arrangements, inclination angles, and pitch ratios (coil torsions). A numerical model in 3D Cartesian was developed using Ansys 14.5 software package to give a clear insight on TCTHE thermal performance on a level of details not always available in experiments. A finite volume discretization method was applied to solve the governing equations. The experiments were carried out at Dean number from 450 to 6200 corresponding to Reynolds number from 2750 to 35,050. The results revealed that the effectiveness of TCTHE presents higher value compared to that of DCTHE by 50% and 57% for both experimental and numerical results. Decreasing the water inlet temperature from 80 °C to 50 °C enhances the Nusselt number, Nu by 23.2%. The counter flow pattern records a higher Nu compared to parallel flow pattern by 21.5%. Also, decreasing the coil torsion from 0.0111 to 0.035 enhances Nu by 34.4%, on expense of increasing the friction factor by 9.4%. Another outcome, the higher thermo-hydraulic performance index occurred at lower coil torsion of 0.035 and at 90o inclination angles (vertical orientations). Finally, new correlations involve Nusselt number, friction factor, as well as effectiveness were presented.

In the current paper, the thermo fluid characteristics of a new design of curved tube called a triple spiral tube heat exchanger (TSTHE) was achieved with a brave comparative with a double spiral tube heat exchanger (DSTHE) as particular reference. A three-dimensional computational fluid dynamic model was developed using Ansys 14.5 software package. The Realize k–e model had been applied with enhanced wall treatment to simulate the thermo-fluid characteristics. The governing equations were solved by a finite volume discretization method. The new design was created by adding a third tube to a double concentric spiral tube heat exchanger. The study carried out under consideration of turbulent fluid to fluid heat transfer condition. The influence of different key design parameter such as; inlet hot fluid temperatures, flow arrangements, concentration of Alumina (Al2O3) nanoparticles, and Dean number were the main point of interest. The effect of Alumina-water nanofluid was considered in three different concentrations of 0.5%, 1% and 2% by volume. The results carried out at Dean number ranged from 1100 to 10,500 in the turbulent region corresponding to Reynolds number from 6400 to 57,400. The results presented that the Nusselt number obtained from a TSTHE was higher than that value of DSTHE at the same flow conditions. The results also presented that a significant effect of hot water inlet temperature on the Nusselt number while the increase in pressure drop can be approximately considered neglect. Also, the counter flow arrangement gives better effect on hot fluid Nusselt number compared with the three other flow arrangements. A notice augmentation of heat transfer enhancement occurs due to use Alumina–water nanofluid in TSTHE by 20.8 %. New correlations for inner annulus hot fluid Nusselt number, effectiveness, and friction factor of heat exchanger were presented.