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Helical coil tubes are essential in a variety of engineering applications due to their improved heat transfer and compact shape. The current study presents an experimental and numerical investigation of geometrical optimization for helical coil elliptic tubes. Four distinct coil pitch values are examined with a constant perimeter for all geometries and three aspect ratio values (1, 0.75, 0.5) utilizing water as the working fluid across varying the volume flow rates. The helical coil has the same surface area as the tube for each coil. The numerical simulation is conducted using the ANSYS FLUENT CFD software (Version 19.2). The experimental and numerical results indicate that the increase in heat transfer due to an increase in mass flow rate is significantly greater than the improvement gained by changing the aspect ratios. Increasing the volume flow rate to 3 L/min significantly improves the average heat transfer coefficient, with a 66.6 % increase found at a maximum coil pitch of 0.08 m and an aspect ratio of 0.5. Furthermore, a helical coil with an aspect ratio of one (circular cross-section) exhibits the best compromise between pressure drop penalty and heat transfer enhancement, resulting in the greatest hydraulic thermal performance parameter.

This research investigates the impact of vortex generators integrated with a corrugated absorber plate of solar air heater on the enhancement of heat transfer and thermal-hydraulic performance utilizing a 3D numerical model for Reynolds numbers varying from 7,000 to 25,000. Three different types of vortex generators (rectangular, trapezoidal, and delta) are investigated separately. Vortex generators in two pairs with various angles of attack of 15º, 30º, 45º, and 60º are mounted on the entrance section's upper wall of the domain of computation. The current numerical models are validated by comparisons with experimentally published data. The velocity vectors, turbulent kinetic energy, friction factor, Nusselt number, and thermal-hydraulic performance parameters are examined for the considered current cases considered. The numerical results demonstrate a significant impact of vortex generators on friction loss and transmission of heat. The values of thermal-hydraulic performance for utilizing a corrugated absorber plate integrated with vortex generators are found to be considerably higher than those for using a corrugated absorber plate alone. The highest value of the thermal-hydraulic performance parameter is 0.91 in the case of rectangular vortex generators at Re of 7000 and an angle of attack of 30º.

Thermal energy storage is critically necessary for most solar energy applications. The phase change energy storage systems are the most promising; however, the poor thermal conductivity of the material is a major disadvantage. This work aims to simulate the melting process and investigate the optimum design parameters for a stable and high melting rate of phase-change energy storage systems. A 2-D axisymmetric numerical model has been developed using ANSYS 17. The model was validated by published experimental data. A new elliptical design of the inner tube was investigated; and the main parameters considered were eccentricity (0, 0.1, 0.2, 0.3, 0.4, and 0.5), aspect ratio (1, 0.9, 0.8, 0.7, 0.6, and angle of 0.5), and inclination (0°, 30°, 60°, and 90°) of the inner tube. The outcome of this investigation revealed that the maximum enhancement of the average melting rate was 19.14%, 42.65%, 71.3%, 105.51%, and 150.1%, for eccentricity of 0.1,0.2,0.3,0.4, and 0.5, respectively, for an aspect ratio of 1. The maximum and minimum average melting rate were 0.00516 and 0.00417 kg/min for the vertical inner elliptical tube (θ = 90°) and the horizontal inner elliptic (θ = 0°) respectively for an aspect ratio of 0.5.

Shell and tube latent heat thermal energy storage systems are compact and effective among other types of energy storage systems. The present numerical study deals with geometry optimization of a modified design of shell and tube latent heat thermal energy storage system over melting and solidification cycles. The modified design was produced by splitting the single inner tube into three smaller inner tubes arranged in a line array with different orientations. The numerical model covered four different line array orientations: 0°, 30°, 60°, and 90°, along with a storage model consisting of a single inner tube. The surface temperature, perimeter of inner tubes, and mass of PCM in all numerical cases were assumed to be identical. The numerical model has been validated by comparing the melting fraction contours and the PCM temperature with the experimental published data. It has been found that the line array of 0° orientation has the minimum full cyclic duration with an improvement of 44.4% compared to the base case. Conversely, the line array of 90° orientation has the maximum full cyclic time; 15.83% longer compared to the base case of a single inner tube. Lastly, the orientation of the line array is more significant for melting compared to the solidification.

Mixed convective heat transfer and pressure drop penalty of nanofluids flow in an isothermal horizontal tube are numerically examined in developed flow region. The study examines three types of nanofluids, simple nanofluids ([Water]/ Al2O3, TiO2, and Cu), Hybrid nanofluids ([Water]/ Al2O3 + Cu), and Ionic nanofluids ([C4mim] [NTf2]/ Al2O3). Richardson number is varied from 0.016 to 2, and Reynolds number is varied from 500 to 2000. The governing equations are solved numerically via the finite volume method by using the SIMPLER algorithm computer code. The computer code is validated by comparing the average Nusselt number with the experimental published data, a good agreement was observed. Performance evaluation criterion (λ) is introduced to evaluate the heat transfer enhancement gain of nanofluid usage to pressure drop penalty at different concentrations of nanoparticles. Results for nanofluids show that the maximum enhancement of the average Nusselt number is 15.5 % for Al2O3 with a concentration of 2% at Richardson number of 0.016. However, for hybrid nanofluids, no enhancement is noticed. Ionic nanofluid results are promising, as the Nusselt number increases significantly (by 37%) with a concentration of 2.5%. Finally, findings of various types of nanofluids investigated in the same numerical conditions are reported and compared.

Thermal and hydraulic performance for laminar flow over a fin and flat tube heat exchanger with various aspect ratios studied numerically. The parameters studied were inlet air velocity and flat-tube aspect ratio. The inlet air velocity was changed within the range of 0.5–3.5 m/s, and the aspect ratio of the flat-tubes has been changed in the range of 0.33–1. To do this study, a three-dimensional numerical model was implemented to investigate the airside performance using the commercial CFD software ANSYS FLUENT 17.2. The numerical model consists of 4 tubes in a staggered arrangement, to simulate a dry cooling process in a heat exchanger. The numerical model has been validated by comparing the pressure drop and the heat transfer coefficient with the experimental published data. A good agreement was observed between the present and experimental published data. In the current study, pressure drop (ΔP), heat transfer coefficient (h), area goodness factor (j/f), and heat transfer per unit fan power (Q/Pf) were determined and illustrated graphically. The results indicated that the flat-tube aspect ratio has a significant effect on the pressure drop and the heat transfer per unit fan power. Decreasing the flat tube aspect ratio from 1 (circular tube) to 0.33 the pressure drop reduced by 33.7% and 57.3% with an air inlet velocity of 0.5 and 3.5 m/s respectively. Also, decreasing the flat tube aspect ratio from 1 to 0.33, the Q/Pf is enhanced by 52.9% and 111.5% with an air inlet velocity of 0.5 and 3.5 m/s respectively. Finally, it is concluded that the flat-tube with the lowest aspect ratio has the highest overall performance of the heat exchanger, and thus it is recommended to reduce the energy consumption.

The latent heat energy utilized phase-change material stores enormous amounts of energy in relatively small spaces. The poor thermal conductivity of the phase change material has a significant drawback. Several techniques have been developed to solve this drawback, a geometrical modification was applied to predict the impact on the charging rate and time of the phase change material. A numerical analysis is presented to optimize the angular orientation of the inner flat tube in a double tube latent heat storage system. ANSYS 17.2 was used to execute a two-dimensional unsteady numerical model. The numerical model was validated via experimental published work. Twenty numerical cases of inner flat-tube aspect ratios of 0.5, 0.6, 0.7, 0.8, and 0.9 with angular orientations of 0°, 30°, 60°, and 90° were analyzed. The findings showed that; as the aspect ratio decreases, the average charging rate improvement is increased. For aspect ratios of 0.9 and 0.5, the improvement in entire charging time for the greatest orientation (θ = 90°) relative to the horizontal flat-tube case (θ = 0°) was 11.19% and 49.46%, respectively. The inner tube with an aspect ratio of 0.5 and angular orientation of 90° had the highest average charging rate.

The latent heat thermal energy storage systems are widely used in several applications like solar energy systems to correct the mismatch between the available energy and demand. This paper introduces a numerical study to optimize the eccentricity of the inner flat-tube placed in a double pipe storage unit. A 2-D transient numerical model was simulated using ANSYS 17.2. The model was validated by experimental data and the results indicated a good agreement with published work. The study investigated the effects of the inner flat-tube eccentricity of a double pipe storage unit on the melting characteristics of the PCM. Twenty-four cases of various aspect ratios of the inner flat-tube (1, 0.9, 0.8, 0.7, 0.6, and 0.5) and different eccentricities (0, 0.25, 0.5, and 0.75) were simulated. The results revealed that; the higher melting rate enhancement is achieved for the circular inner tube which is 41%, 110.7%, and 218.5% for inner tube eccentricity of 0.25, 0.5, and 0.75, respectively, compared with the concentric case. Among all applied cases, the best melting performance was achieved for the circular tube with the least eccentricity.