Development on evacuated tube solar collectors: A review of the last decade results of using nanofluids

In the present study, the effect of inserting an innovative curved turbulator and utilizing two types of hybrid nanofluids on thermal performance in a helical double-pipe heat exchanger is evaluated numerically. The considered hybrid nanofluids include silver (Ag) and graphene (HEG) nanoparticles/water and multi-wall carbon nanotubes–iron oxide nanoparticles/water (MWCNT-Fe3O4/water). The considered innovative turbulator has 12 blades to create secondary flows. Also, a hole is considered at the end of the turbulator. The present study has two sections: In the first one, the results of utilizing hybrid nanofluids are compared with pure water (φ = 0.3%). In the second section, the hybrid nanofluid based on the first section was selected and utilized. The effect of the volume concentration of the selected hybrid nanofluid was investigated. Results show that utilizing the present innovative turbulator leads to higher heat transfer rate. As a result, the Ag-HEG/water hybrid nanofluid has better thermal performance at low mass flow rate. Also, the thermal efficiency of the considered helical heat exchanger is lowest at φ = 0.1%. In the case of highest volume concentration (φ = 0.7%), the thermal performance is maximum at low mass flow rate.

Laminar heat transfer and fluid flow of two various hybrid nanofluids in a helical double-pipe heat exchanger equipped with an innovative curved conical turbulator

Melting and solidification processes of phase change material in evacuated tube solar collector with U-shaped spirally corrugated tube

In the present work, hybrid nanofluids flow and heat transfer in a pipe equipped with vortex generator are evaluated numerically. At the first part, the impact of the type of working fluid (two various hybrid nanofluids in comparison with pure water at φ = 3%) and at the second part, impact of the volume concentration of selected hybrid nanofluid (based on section one) on the turbulence thermal performance of the pipe with innovative vortex generator are evaluated numerically. All the simulations were performed for the Reynolds number range between 4125 and 5363. The considered hybrid nanofluids include silver (Ag) and graphene (HEG) nanoparticles/water and MWCNT–Fe3O4/water. The proposed vortex generator has 18 blades to create secondary flows. Also, five output ports are considered at the conical part of vortex generator (four side outputs and one axial one). Results indicated that using both two techniques of heat transfer enhancement in a pipe including proposed vortex generator and hybrid nanofluids leads to higher heat transfer rate. As a result, the MWCNT–Fe3O4/water hybrid nanofluid has better thermal performance in all studied Reynolds number. At low Reynolds number (Re = 4125), the maximum thermal performance was achieved at φ = 1% by 11.3% growth in thermal performance. Also, case with φ = 5% has a minimum improvement, 10.5%. Furthermore, at high Reynolds number (Re = 5363), the highest and lowest growths belong to cases φ = 3% and φ = 7% by 9.9 and 7% improvement in thermal performance, respectively.

Numerical evaluation of turbulence heat transfer and fluid flow of hybrid nanofluids in a pipe with innovative vortex generator

Analysis of thermal performance of an improved shell and helically coiled heat exchanger

In this study, the effect of using twisted tapes with various geometries in both tubes of a double-pipe heat exchanger is numerically investigated. The twisted tapes are inserted in both sides of double-pipe heat exchanger to improve the heat transfer where the fluid is water in both sides. The influence of geometrical parameters including the number of twisted tape and creating hollow on twisted tape with different aspect ratios is investigated numerically. The obtained results are analyzed by calculating the outlet temperature of both sides, pressure drop, Nusselt number, and coefficient of performance. Numerical simulations are performed by a commercial CFD code, ANSYS FLUENT 18.2. The results indicate that increasing the number of twisted tape from one-fin to four-fin leads to an increase in the Nusselt number 3.1%, pressure drop 64%, and coefficient of performance 63.9%. Eventually, based on outcomes, four-fin twisted tapes provided better coefficient of performance. In the second part of the study, the effect of creating hollow on the four-fin twisted tape with different aspect ratios (AR = W/H) is studied. Three different aspect ratios including 2.25, 1, and 0.44 are considered. The results show that creating the hollows with AR = 1 on the twisted tape leads to better coefficient of performance.

Numerical evaluation of the effect of using twisted tapes as turbulator with various geometries in both sides of a double-pipe heat exchanger

Heating and cooling of a system by heat exchanger Plays an important role in various industries. Improvement of heat transfer in heat exchangers resulted in reducing the size of heat exchanger, and utilizing more compressed heat exchangers with higher efficiency. Using helical/spiral tube is a passive method for improving the performance of heat exchangers due to its low geometry and high heat transfer coefficient. Also, in heat exchangers, one of the most important methods is additives such nanoparticles for liquids and classified as a passive method which does not need any external power like in active methods. The objective of this study is to investigate efficient operational and geometrical parameters. The considered geometrical parameters include helix pitch, coil diameter, and helix height. Also, the effect of using Al2O3, CuO, SiO2 nanofluids on thermal performance of the heat exchanger is investigated numerically. The results show that the geometric parameters of the coil have a significant effect on the heat exchangers of the shell and coil.

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Effects of geometrical and operational parameters on heat transfer and fluid flow of three various water based nanofluids in a shell and coil tube heat exchanger

In this paper, heat transfer enhancement in a double pipe heat exchanger with a twisted tape as a swirl generator in both sides is investigated numerically. The three-dimensional numerical simulations have been done by finite volume method using a commercial CFD code. The spatial discretization of mass, momentum, turbulence dissipation rate, and turbulence kinetic energy equations has been achieved by a second-order upwind scheme. A SIMPLE algorithm has been used for velocity–pressure coupling. To calculate gradients, Green–Gauss cell-based method has been utilized. The swirl generator is considered in both channels of the heat exchanger (hot and cold streams). Three types of nanofluids containing Al2O3, CuO, and SiO2 are considered as heat transfer fluid in the inner channel (hot fluid flow). Results showed that the maximum thermal performance belongs to CuO/water nanofluid at Re = 5492 by 7% enhancement in thermal performance in comparison with net water. Also, the SiO2/water nanofluid at Re = 3343 has the minimum enhancement in thermal performance by 2.5% in comparison with the net water. In a lower Reynolds number (Re = 3343), the greatest thermal performance is obtained for a case with ϕ = 4% by 1% improvement in thermal performance compared to pure water. However, the case with ϕ = 5% presents a lower thermal performance by 3.7% compared to pure water. However, in higher Reynolds number (Re = 5492), the highest thermal performance is achieved for the case with ϕ = 4% by 6.4% improvement in thermal performance compared to pure water and the lowest improvement belongs to the case with ϕ = 3% by 1.3% enhancement in thermal performance compared to pure water.

Mehdi Noorbakhsh

Papers

Numerical evaluation of the effect of using twisted tapes as turbulator with various geometries in both sides of a double-pipe heat exchanger

Effects of geometrical and operational parameters on heat transfer and fluid flow of three various water based nanofluids in a shell and coil tube heat exchanger

Thermal analysis of nanofluids flow in a double pipe heat exchanger with twisted tapes insert in both sides

Numerical evaluation and the effects of geometrical and operational parameters on thermal performance of the shell and double coil tube heat exchanger