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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 thermofluid characteristics of Al2O3–water nanofluid in the annulus of double-helical coiled tubes were experimentally and numerically carried out. The purpose was to investigate the effect of combined enhancement techniques of nanofluid and helicoid tube shape on the performance of a double tube heat exchanger. The effects of concentration of nanoparticles, Reynolds number, coil curvature ratio, and flow arrangement through the annulus of double-helical coiled tube were the main points of interest. Three coiled tube heat exchangers were manufactured and experimentally tested to study the design parameters on the performance of such a heat exchanger. A three-dimensional numerical computational fluid dynamic (CFD) model was developed to get additional insights on the thermal performance of double helically coiled tubes with nanofluid on a level of details not always available in experiments. It was found that the Al2O3–water nanofluid achieved an enhancement by 32% on the overall heat transfer coefficient. The heat exchanger effectiveness, heat transfer per unit pumping power, and the Nusselt number were also presented for different design parameters.

In this study, the thermofluid characteristics of double spirally coiled tube heat exchanger (DSCTHE) were investigated numerically. A three-dimensional (3D) computational fluid dynamic (CFD) model was developed using ansys 14.5 software package. To investigate the heat transfer and pressure drop characteristics of DSCTHE, the Realize k–ε turbulence viscous model had been applied with enhanced wall treatment for simulating the turbulent thermofluid characteristics. The governing equations were solved by a finite volume discretization method. The effect of coil curvature ratio on DSCTHE was investigated with three various curvature ratios of 0.023–0.031 and 0.045 for inner tube side and 0.024–0.032–0.047 for annular side. The effects of addition of Al2O3 nanoparticle on water flows inside inner tube side or annular side with different volume concentrations of 0.5%, 1%, and 2% were also presented. The numerical results were carried out for Reynolds number with a range from 3500 to 21,500 for inner tube side and from 5000 to 24,000 for annular side, respectively. The obtained results showed that with increasing coil curvature ratio, a significant effect was discovered on enhancing heat transfer in DSCTHE at the expense of increasing pressure drop. The results also showed that the heat transfer enhancement was increased with increasing Al2O3 nanofluid concentration, and the penalty of pressure drop was approximately negligible.

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 present article, the thermal and hydrodynamic characteristics of a new design heat exchanger called a triple spirally coiled tube heat exchanger (TSCTHE) are experimentally conducted and compared with a double spirally coiled tube heat exchanger (DSCTHE) as a particular reference. The new design was created by adding a third tube to a DSCTHE. The study carried out under consideration of turbulent fluid to fluid heat transfer condition. The research aims to present the TSCTHE thermo-hydraulic characteristics with different operating and design parameters. The experiments were carried out at four water inlet temperatures from 50°C to 80°C, four flow arrangements include parallel, counter, counter-parallel, and parallel-counter flow patterns with three coil inclination angles from 0° to 90°. The experimental runs applied at Dean number ranged from 500 to 6,500 corresponding to Reynolds number from 3000 to 37,000. The results obtained that the TSCTHE presents a significant enhancement of the Nusselt number compared to DSCTHE by 94.8% and 82.8% for both counter and parallel flow patterns, respectively. Also, the Nusselt number enhancement occurs with decreasing the hot water inlet temperature from 80°C to 50°C by 40%, while the increment in pumping power is approximately neglected. Moreover, the highest values of Nusselt number occurred at counter flow patterns compared to other flow arrangements. In addition, the higher performance index was recorded at higher coil inclination angle of 90°. New correlations to predict the Nusselt number of hot water, friction factor, effectiveness, and performance index 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.

Heat transfer and pressure drop characteristics in the annulus of concentric helical coils heat exchangers were experimentally investigated. The effects of coil curvature ratio, flow configuration, number of turns and addition of surfactant were investigated. Five test coils were designed and manufactured to study the effect of different parameters on heat transfer and pressure drop. The liquids used in the present study were water and oleyl-dihydroxy-etheyl-amine-oxide (ODEAO, C22H45NO3 = 371) non-ionic aqua surfactant solution flowing through the annulus side. The inner side Reynolds number range 11,000–27,000 and the annulus side range 5,000–19,000. The results showed that the annulus Nusselt number decreases as annulus curvature ratio increases and increases when number of turns decrease. Moreover, the friction factor increases with the curvature ratio and also increases as number of turns decreases. Both Nusselt number and friction factor decrease when ODEAO concentration increases.