Performance Evaluation Criterion Value Research Articles

Numerical analysis of thermal-hydraulic influence of geometric flow baffles on multistage Tesla valves in printed circuit heat exchangers

The innovative structure and flexible functionality of Tesla valves have attracted significant attention across various industries. Unlike conventional check valves, which open in response to fluid movement and pressure and close to prevent backflow, Tesla valves utilize interconnected pathways to create a highly efficient and reliable method for regulating fluid flow. However, the thermal–hydraulic influence associated with the utilization of different geometric configurations of flow baffles in Tesla valves remain incompletely understood. This study employs numerical simulations to assess the effectiveness of a printed circuit heat exchanger (PCHE) incorporating three layers of multistage Tesla valves with geometric flow baffles. The simulations, based on solving the Navier-Stokes and energy equations, focus on analyzing the behavior of liquid water within a temperature range of 30 to 90 °C, pertinent to applications such as geothermal heating systems. The employed Tesla valve configuration demonstrates superior performance, exhibiting a notable enhancement in thermal effectiveness ranging from 13 % to 55 % compared to configurations utilizing zigzag, separate, and overlapping NACA 0020 airfoils under otherwise identical conditions. Three crucial geometric parameters are introduced to characterize the shape of flow baffles in multistage Tesla valves: the length from the baffle apex to the baffle half-front sphere, the radius of the baffle half-front sphere, and the distance from the baffle apex to the centerline of the entrance flow channel. Performance evaluation criteria (PEC) indicate that while the overlapping airfoil configuration performs better than both zigzag and separate configurations, the current Tesla valve design achieves approximately a 10–14 % higher PEC value than the overlapping airfoil configuration. The manipulation of geometric parameters for flow baffles is generally believed to be a critical step in the advancement of multistage Tesla valves, contributing to the enhancement of heat transfer and potentially broadening the applicability of these valves to various practical heat transfer systems.

Comprehensive numerical investigation of the effect of various baffle design and baffle spacing on a shell and tube heat exchanger

This article explores the significance of Shell and Tube Heat Exchangers (STHX), with a focus on various baffle types such as Segmental, Double segmental, Helical, Disc-and-Doughnut, Clamping anti-vibration, and Flower-B. In this study, the commercial software ANSYS FLUENT is used to simulate the problem. The study evaluates their impact on heat exchanger performance using parameters like overall heat transfer coefficient (OHT), pressure drop (PD), and Performance Evaluation Criteria (PEC). Clamping anti-vibration, Flower-B, Helical, and Double segmental baffles exhibit reductions in shell side PD by 14%-28%. Despite OHT reductions in these designs, Disc-and-Doughnut baffles demonstrate a higher OHT (21%-24%) compared to Segmental baffles. Based on PEC values, Disc-and-Doughnut baffles are identified as the most favorable. Further investigation into different numbers of Disc-and-Doughnut baffles reveals increased OHT (17%-29%), PD (58%-59%), and cold water temperature (0.5%-1%). The STHX with Disc-and-Doughnut 10 baffles displays the highest PEC value, establishing it as the most effective STHX in the simulation.

Experimental investigation of shell and helical coiled heat exchanger with Al2O3 nano-fluid with wide range of particle concentration

The purpose of this study is to experimentally enhance the heat exchange rate of the shell and helical coil tube heat exchanger by mixing water with aluminum oxide (Al2O3) nanoparticles, as well as to explore the effect of inlet thermal parameters on the performance of the heat exchanger. A test rig was constructed to investigate the influence of particle concentration, and inlet temperatures on the performance of nano-fluid. Parameters such as Nusselt number, pressure drop, performance evaluation criteria (PEC) are considered to rate the performance of the nano-particle with the heat exchanger. In this study a wider range of particle concentration is considered, which varies from 0.0%–0.75%. Experiments with and without nanoparticles are carried out under identical working conditions. By analyzing the experimental data, it was found that nanoparticles significantly improve the coefficient of heat transfer inside the helically coiled tube. From sensitivity analysis, it is obseerved that there is a slight decrease in Nusselt number of the nano-fluid with increase in inlet temperatures of the nano-fluid and the cooling water. Furthermore, it is concluded that an 8.5% increase in PEC value is observed with increase in particle concentration from 0.15% to 0.75%.

Thermohydraulic analysis of nanofluid flow in tubular heat exchangers with multi-blade turbulators: The adverse effects

Based on the significance of heat transfer in tubular flows, various methods of heat transfer enhancement have been developed by scholars. The use of turbulator inserts like twisted tapes is widely discussed and suggested by researchers, and many studies have concentrated on the positive influence of these devices. However, the question is whether these devices always positively impact heat transfer and fluid flow. In this study, efforts were made to find possible adverse impacts of using twisted tapes on the average Nusselt number (Nu), friction factor (f), flow behavior, and performance evaluation criterion (PEC) of water-titania nanofluid. Three-dimensional (3D) numerical methods were used to assess a combination of three different configurations of 156 cases with/without turbulators with different numbers of blades and pitch ratios (PR). Results suggest that at Reynolds number (Re) = 4000, 6000, and 8000, only 25 %, 25 %, and 22.9 % of the examined cases led to PEC values over 1. Based on the results, while twisted tapes raised the Nu by up to 65.1 %, the f can be increased by up to more than six times. Furthermore, streamlines and velocity magnitude contours were employed to discuss the fluid flow behavior in the presence of the turbulators. According to the findings, while with the best turbulator, the PEC value was increased by only 6.3 %, some of the turbulators reduced this parameter by up to 11.8 %, which is more severe. The worst performance was observed with the Case C (three-bladed) turbulator at a PR value of 11, which reduced the PEC by 11.8 %.

Employing uniform and non-uniform inner twisted elliptical tubes in a double-pipe heat exchanger

Turbulent hydrothermal characteristics in a double-pipe heat exchanger with an internal twisted elliptical tube (TET) are investigated. The impacts of aspect ratio (AR = 1.4–2), uniform twist pitch (p = 100 mm-400 mm), and non-uniform twist pitch (five cases) on flow stream characteristics and heat transfer of parallel and counter-flows are investigated numerically. Utilizing a TET with a non-uniform twist pitch as an innovative approach yields noteworthy results, particularly in contrast to the traditional use of TETs with uniform twist pitch, owing to the longitudinal asymmetry. The outcomes depict that the pressure drop and heat transfer augment as the uniform twist pitch declines and the AR rises. The counter-flow has a more significant average Nusselt number than the parallel-flow by about 2–4 % without increasing the friction factor. Still, in some cases of non-uniform twist pitch, the average Nusselt number of the parallel flow is even 4 % higher than the counter-flow. The case with p = 100–200–400 mm (three parts with various twist pitches) and parallel-flow exhibits the most significant performance evaluation criterion (PEC) among the non-uniform twist pitch. As the aspect ratio increases from AR = 1.4 to AR = 2, the PEC factor in the counter-flow mode increases; however, there is an out-of-trend point at AR = 2 for the parallel-flow mode. The PEC factor augments about 8.47 % and 6.16 % for the counter-flow and the parallel-flow modes, respectively. The growth of TET twist pitch by 300 % reduces PEC by about 13.3 % in the counter-flow. The most significant PEC value is 1.166, which belongs to the case with the counter-flow condition and p = 100 mm.

Heat transfer and thermal–hydraulic evaluations of cross-circular grooved rectangular flow ducts depending on rectangular baffle design parameters

The cross-grooved rectangular flow ducts are largely used for plate heat exchangers. In this work, so as to better the heat transfer in cross-grooved rectangular ducts with circular grooves, rectangular baffles were located in the flow duct, and the influences of the rectangular baffle angles and heights on the features of heat transfer were numerically performed in detail. Equations of Navier–Stokes and energy were resolved by employing a program of Ansys-Fluent with k–ε turbulence model as steady and three-dimensional. Air employed as working fluid has a temperature of inlet 293 K while the circular groove’s wall temperature is 373 K. Rectangular baffles have various angles of 30°, 60°, and 90°, and heights of 0.25 H, 0.5 H, and 0.75 H. The mean Nusselt number (Num), temperature, turbulence kinetic energy (TKE), pressure, and PEC (Performance Evaluation Criterion) number of the flow duct with rectangular baffles were evaluated by comparing it with the cross-circular grooved channel non-baffle. Besides, the contours of velocity, turbulence kinetic energy, temperature, and velocity vector were exhibited for the cross-circular grooved rectangular channels with different baffle angles and height arrangements. Results were matched with experimental and numerical outcomes of the study found in the literature, and it was observed that they were fairly coherent. For Re = 6000, the number of Num increases by 180.48% in the duct with a 90° angle and 0.75 H baffle height compared to the duct non-baffle, and for 30° baffle angle, the PEC value at 0.25 H baffle height is 66.88% higher than that in the 0.5 H.Graphical Compared to the temperature contour distribution in the non-baffle state, the temperature gradient increases due to the turbulence intensity created by the inserting of baffles to the circular grooved ducts. When the baffle height is increased to 0.75 H, the increase in fluid temperatures toward the end of the ducts is the clearest evidence of this situation. Thus, while cooling increases in circular grooves, the temperature gradient in the duct above the circular grooved section gets better, especially in the case of 0.75 H height and 90° baffle angle. Temperature distribution contours of the ducts for non-baffle and with baffle of 90° angle and 0.75 H height for Re = 6000.

Thermal Performance Analysis of Porous Foam-Assisted Flat-Plate Solar Collectors with Nanofluids

This study proposed a model of a porous media-assisted flat-plate solar collector (FPSC) using nanofluid flow. The heightened thermal efficiency of FPSC undergoes numerical scrutiny, incorporating various factors for analysis, including aspects like the configuration of the porous block introduced, Darcy number (Da = 10−5~10−2), types of nanoparticles, volume fraction (φ), and mixing ratio (φc). The numerical findings indicate that the dominant factor in the channel is the global Nusselt number (Nug). As the Darcy number rises, there is an improvement in the heat transfer performance within the channel. Simultaneously, for the case of Re = 234, φ = 3%, and φc = 100%, the Nug in the channel reaches a maximum value of 6.80, and the thermal efficiency can be increased to 70.5% with the insertion of rectangular porous blocks of Da = 10−2. Finally, the performance evaluation criteria (PEC) are employed for a comprehensive assessment of the thermal performance of FPSC. This analysis considers both the improved heat transfer and the pressure drop in the collector channel. The FPSC registered a maximum PEC value of 1.8 when rectangular porous blocks were inserted under conditions of Da = 10−2 and Re = 234 and the nanofluid concentrations of φ = 3% and φc = 100%. The findings can be provided to technically support the future commercial applications of FPSC. The findings may serve as a technical foundation for FPSC in upcoming porous media and support commercial applications.

CFD Analysis for Comparative Evaluation of Different Hybrid Nanofluids Flowing Through PTSC

This research paper focuses on CFD analysis for comparative evaluation of different hybrid nanofluids (NFs): MWCNT-Al2O3/H2O, MWCNT-MgO/H2O, Al2O3-CuO/H2O performance as working fluid (WF) inside parabolic trough solar collector (PTSC). The performance of the collector is evaluated using different performance indicators, including Nusselt number (Nu), friction factor (f), and Performance Evaluation Criterion (PEC) for different Reynolds number (Re) (10000-50000). Among the investigated hybrid nanoparticles (NPs), MWCNT-Al2O3 emerges as the most promising choice for significantly enhancing the system’s thermal performance with the highest PEC value of 1.9. This outcome signifies the superior efficiency of MWCNT-Al₂O₃/H₂O hybrid NF in enhancing convective heat transfer, thus underlining the paramount significance of adopting them in thermal systems operating within the specified Re range.

Optimization Study of Cooling Channel for the Oil Cooling Air Gap Armature in a High-Temperature Superconducting Motor

With the continuous advancement of science and technology, the application of high-temperature superconductivity has developed rapidly. The high-temperature superconducting (HTS) motor replacing the copper coil in the traditional motor with HTS winding is increasingly used in power equipment, and the effective thermal management of HTS winding is vital in ensuring the life and effective operation of the HTS motor. In this study, five enhancement structures of indirect oil cooling channels were designed to improve the heat dissipation capacity of the HTS motor winding, and the enhancement effects of the different structures were comprehensively evaluated through numerical simulation using Fluent software 2022R1. The best enhancement structure was selected through structural optimization. The results showed that the Nusselt number of the gap-type enhanced structure was higher than that of the V- and staggered-type structures at the same flow velocity and 68% higher than that of the bare pipe. At the same inlet flow velocity and with a pressure drop limit of 30 kPa, the performance evaluation criterion value of the gap-type structure was 39% and 63% higher than that of the staggered- and V-type structures, respectively. The gap type is the optimal enhancement structure and can effectively improve the heat dissipation of the HTS winding coil.

Flow field and heat transfer of ferromagnetic nanofluid in presence of magnetic field inside a corrugated tube

The present study investigates the effects of using a magnetic field on the flow field and heat transfer of ferromagnetic Fe3O4/H2O nanofluid considering two-phase model for nanofluid in heat exchanger equipped with helical ribs. Three methods are employed to enhance the thermal efficiency of heat exchanger, as employing of corrugations, utilizing nanofluid as heat transfer fluid, and employing the magnetic field. The performance evaluation criteria index (PEC) is employed to analyze the thermal-hydraulic characteristics of the heat exchanger. The main aim is to achieve an optimum model with the highest performance evaluation criteria value. Usaging of corrugated heat exchanger or nanofluid can increase the average Nusselt number and friction factor in the tube sharply. Also, it is understood that the presence of a magnetic field has a significant effect on the heat transfer enhancement inside the heat ex-changer. The model with magnetic field of 600 G has the highest Nusselt number ratio among all studied models, which is followed with 400 G, 200 G, and 0 magnetic fields, respectively. Furthermore the effects of different corrugation heights, widths, and pitches have been stud-ied. Finally, usage of the novel corrugated heat exchanger with 14 mm corrugation heights, 9 mm rib width, and 12.5 mm blade pitches filled with nanofluid, and under a magnetic field of 600 G it suggested as the most efficient configuration. Also, at the Reynolds number of 4,000, the highest performance evaluation criteria values are achieved.

Turbulent forced convection flow of water-based nanofluids with temperature-dependent properties over backward-facing step channel with upwardly deflected downstream wall

The heat transfer performances of various water-based nanofluids (NFs) relative to the base fluid in turbulent forced convection flow within a 2-D backward-facing step (BFS) channel with an upwardly deflected downstream wall with a uniform heat flux are analyzed using the package OpenFOAM. The k-ω shear stress transport (SST) model based on the Euler-Euler single-phase framework is used. The performance evaluation criterion (PEC) is defined to assess the relative importance of the enhanced heat transfer and intensified resistance (pressure drop) caused by Cu/water NFs and MWCNT-Fe3O4/water hybrid NFs (low concentration NFs), Fe3O4/water NFs, and Cu-MWCNT/water hybrid NFs (high concentration NFs). At Re = 30215, the maximum enhancement of the average Nusselt number (ANN) is 7% when the copper NPs are added to the water. In addition, the increment of the deflection angle from 0.0 to 1.27 enhances the ANN values by 44 ∼ 45% concerning low-concentration NFs. At Re = 7940, the friction factor increases by 24.3% and 32.1% when copper and MWCNT-Fe3O4 hybrid NPs are dispersed in the base fluid, respectively. The highest PEC value (1.07) is achieved when the copper NPs with ϕ = 0.003 are used in configuration BFS1 at Re = 7940. Using MWCNT-Fe3O4 hybrid NPs is only proposed at lower Re numbers when the downstream wall is deflected and ϕ = 0.001. At Re = 30215, due to the addition of magnetic NPs, the ANN value abates by 28.5% and 30.7%, respectively, in the canonical case and configuration BFS2. Among the high-concentration NFs, the highest PEC (1.05) is obtained using Cu-MWCNT hybrid NPs with ϕ = 0.01 at Re = 30215 when the downstream wall is deflected upwardly. As Mouromtseff (Mo) number-based figure-of-merit (FOM) verifies, the worst scenario (PEC < 1.0) is substituting the base fluid with Fe3O4/water NFs. Cu-MWCNT/water hybrid NFs with ϕ = 0.02 become an effective coolant (PEC > 1.0) when the deflection angle and Re number increase simultaneously.

Heat transfer enhancement through pitch ratio optimization of butterfly inserts in minichannel heat sinks

Thermohydraulic characteristics of square minichannel heat sinks (MHS) with butterfly inserts are computationally studied for Reynolds numbers between 200–900 for two hydraulic diameters (Dh) of 2mm and 2.6mm and varied pitch distances (P). The present investigation examines the effect of pitch ratio (P∗=P/Dh) of butterfly inserts on overall thermal performance of MHS to discern its optimal value for the best possible overall performance. Since inserts result in a concurrent rise in both pressure drop and heat transfer rate, this overall thermohydraulic performance is measured using Performance Evaluation Criteria (PEC), which incorporates the simultaneous effects of change in hydraulic and thermal performance. In the present study, PEC values for all analyzed configurations are found to be above unity, which indicates the adequacy and efficacy of the employed butterfly inserts. The study also corroborates the literature-reported finding that the pitch ratio of butterfly inserts significantly alters the thermohydraulics of MHS. Heat transfer performance is found to improve drastically when pitch ratio is reduced from 5 to 1.5, showing a Nusselt number enhancement of 29.57% to 78.47% for Dh=2mm and 27.73% to 63.47% for Dh=2.6mm for the tested range of Reynolds numbers. However, further reduction in pitch ratio is found to deteriorate the thermohydraulic performance of these inserts. The highest PEC value is obtained for P∗=1.5 for both the studied hydraulic diameters, leading to the conclusion that P∗=1.5 is the optimal pitch ratio of butterfly inserts when employed within rectangular MHS.

Computational investigation of cross flow heat exchanger: A study for performance enhancement using spherical dimples on fin surface

Performance improvement of a heat exchanger is a vast topic for research work right now. This paper presents a numerical analysis of cross flow heat exchanger using CFD software package ANSYS FLUENT. To improve the performance of a traditional smooth fined heat exchanger, dimples are used on the fin surfaces. A cross flow heat exchanger with spherical dimples on the surfaces of the fins was modelled and effect of dimples on the performance of the heat exchanger was numerically investigated. Numerical investigations were carried out for different dimple depths such as 3 mm, 4 mm, 5 mm, 5.5 mm dimples on different positions such as on one side, on both side; and different number of dimples such as 32, 26, 20. Boundary conditions were considered as constant tube outer surface temperature, Reynolds number of 3553, inlet air temperature Ti = 299.45 K. Considering balance between heat transfer enhancement and pressure drop, performance evaluation criterion (PEC) was estimated to observe the optimal result. PEC value greater than 1 means there is better performance in consideration of both heat transfer rate and frictional loss. The case of 26 dimples on both sides of fin with 5.5 mm dimple depth provides highest 7.33 % increases of Nusselt number compared to smooth fin. The maximum PEC value 1.034 was found for the case of 32 dimples on both side of fin with 3 mm dimple depth. From the PEC analysis, it was observed that the case of 32 dimples on both sides of the fin with 3 mm dimple depth is the optimum case among all other cases with 5.71 % higher Nu and 6.75 % higher friction factor than smooth fin. To compare the heat exchanger performance, temperature effectiveness has also been evaluated. The case of 32 dimples and 26 dimples on both side of fin with 5.5 mm dimple depth have same and highest value of temperature effectiveness which is 11.45 %, where that value for smooth fin is 10.16 %. Furthermore, the results have been analyzed with the variation of Reynolds numbers.

Experimental Study on Indirect Liquid Cooling Performance of Metal 3D-Printed Cold Plates for Battery Thermal Management

Two new cold plates manufactured via metal 3D printing were experimentally investigated for thermal performance analysis in indirect liquid cooling operations; then they were compared to the traditional cold plates. Experiments were performed with different coolant inlet temperatures (15.7 °C and 24.5 °C) and ambient air velocities (0.5 m/s and 3 m/s) at tropical conditions; hereby, the impact of high dew point temperatures at tropics was also investigated. Body-centered cubic (BCC) and pillar elements were applied in the cooling cavity of the cold plates. The results showed that the target surface temperature in both BCC- and pillar-filled plate designs was maintained below the limits at the lower inlet temperature. However, at the higher inlet temperature, the temperature was only maintained below the limit when the ambient air velocity was 3 m/s. The convective heat transfer coefficient at the inlet temperature of 15.7 °C was found 1.5 and 2.5 times higher than the convective heat transfer coefficient value at the inlet temperature of 24.5 °C for the pillar- and BCC-filled plates, respectively. The performance evaluation criterion values were found in the range of 1.2 − 2.4, which depended on the operating conditions and were already higher than the referenced studies in the literature.

The Effect of Angled Fins in Generating Swirling Flows with Vortices That Augment Heat Transfer Performance in an Annular Conduit

This paper examined the usage of thermally conductive angled fins within an annular conduit through numerical simulation. Despite the thermally conductive nature of the fins increasing heat transfer surface area, this investigation found that using an optimal fin angle can promote the generation of vortical structures which aid heat transfer. Using ANSYS-Fluent with the SIMPLEC algorithm and the SST κ − ω turbulence model, this research found that heat transfer performance improved considerably when the generated vortices were sufficiently large and robust. However, the type of generated vortex had a profound impact when optimising for higher performance evaluation criterion (PEC) values. Longitudinal vortices improved heat transfer performance with a low impact on pressure drop increase, unlike transverse vortices, which increased pressure drop significantly. The fin angles of 50° and 60° yielded high heat transfer performance without much increase in pressure drop, thus resulting in higher PEC values. Additionally, using fin heights that correlate to 20% to 60% of the gap between the concentric walls was ideal when designing heat exchangers to achieve higher PEC values. The results of this numerical investigation have been validated both theoretically and experimentally to ensure accurate reporting of the findings.

Numerical Investigation of the Effect of Ethylene Glycol with SnFe2O3 Hybrid Nanofluid on Heat Transfer in Flat, Face Step, and Radial Corrugated Microchannels

Nanofluid technology is one of the latest technics aims to enhance the heat exchangers working systems. The nanofluid is used because it has better thermal performance properties than common fluids like water. Tin Oxide (SnO2) and Ferric Oxide (Fe2O3) has used due to their availability and low cost for manufacturing. Flat, face step and radial corrugated microchannels have been studied at the Reynolds number range (4000-7000 Re). In this study, a hybrid nanofluid combined Ferric Oxide and Tin Oxide SnFe2O3 at (0, 5, 15%) of Tin Oxide concentration. The volume concentration of the nanoparticles was from (1-5)% suspended in ethylene glycol as base fluid due to its high thermal performance compared with water. The performance evaluation criteria (PEC) are studied and the results were validated with experimental and numerical results from previous studies. Performance evaluation criteria (PEC) studied the heat transfer in all study steps and found that the 15Sn85Fe2O3 hybrid nanofluid in ethylene glycol at 5% volume concentration in radial corrugated microchannel increased 104% compared with base fluid ethylene glycol in the flat microchannel. The performance evaluation criteria value has increased by 82% from flat microchannel to radial microchannel at 5% of volume concentration of 15Sn85Fe2O3 hybrid nanofluid

Numerical Assessment of Nanofluids in Corrugated Minichannels: Flow Phenomenon and Advanced Thermo-hydrodynamic Analysis

The current study addresses the influence of the amplitude of distinct corrugation patterns on heat transfer and the performance of nanofluids as a coolant. A novel combined approach has been presented here to optimize the heat transfer, incorporating both geometry modification and coolant optimization. The computational model evolved for single-phase, and turbulent flow conditions in three-dimensional corrugated minichannels (i.e. rectangular, sine-shaped, and V-shaped) with Reynolds number varying from 10,000 to 30,000. Considering a uniform heat flux of 10,000 W/m2, the investigation evaluates the thermal-hydraulic performance of single nanofluids (CuO/water, Al2O3/water, TiO2/water) and hybrid nanofluids (Al2O3CuO/water, Al2O3-TiO2/water), with volume fractions ranging from 1% to 3%. Various nanoparticle compositions exhibited a 25–30% increased heat transfer coefficient in the corrugated minichannel relative to the smooth one. An enhanced Nusselt number is evident due to the sophisticated corrugated arrangement dependent on the amplitude and patterns of the corrugations. The obtained energy ratio quantifies the effectiveness of a heat exchanger, whereas the Bejan number signifies the heat transfer being characterized by higher irreversibility, leading to a notable dissipation of energy. To account for the PEC (performance evaluation criterion) value above one, the corrugated geometries can outperform smooth channels. With an optimal thermal performance improvement of 22.19%, the 3% Al2O3CuO/water has been found to be the most effective nanofluid in the rectangular corrugated minichannel with the amplitude-to-wavelength ratio of 0.12.

Investigation into the effect of multiple line dipoles magnetic field through LS-3 parabolic trough solar system

This paper simulates the LS-3 parabolic trough solar collector with Monte Carlo Ray Tracing and computational fluid dynamics methods. The heat flux is non-uniform around the absorber tube. Therefore, multiple line dipoles magnetic field location can effect on solar collector performance. There is no article that has investigated the effect of this parameter in the parabolic trough solar collector. Also, this collector is simulated for the first time for June 21 and December 21, and the heat flux distribution for it is provided by the Monte Carlo Ray Tracing method. The multiple line dipoles magnetic field leads to a decrease in the maximum temperature of the absorber tube wall by 2.3 %. The magnetic field intensity also affects the solar collector's performance. If the magnetic flux density is equal to 100 G, 75 G and 50 G, then the value of Performance Evaluation Criteria is equal to 1.47, 1.43 and 1.39, respectively. Finally, the magnetic field location affects the Nusselt number but does not affect the Darcy friction factor. For example, if the multiple dipoles magnetic field are placed at angles of 0, 30, 60, and 90°, then the Nusselt number ratio is 1.50, 1.42, 1.44, and 1.65, respectively.

Numerical assessment of hydraulic behavior and thermal efficiency of multiphase hybrid nanofluid in a shell-and-tube heat exchanger with inclined baffles

Improving the thermo-hydraulic performance of shell-and-tube heat exchangers (STHE) has always been the focus of researchers due to their wide applications in recent decades. This numerical study investigates the hydraulic behavior and thermal efficiency of turbulent multiphase flow of Fe3O4−MWCNT/water hybrid nanofluid (HN) in a shell-and-tube heat exchangers (STHE). The Reynolds number (Re) is 5000, 7500, 10000, and 12500 and the volume fraction of nanoparticles (φ) is 0, 2, and 4%. Numerical simulations are conducted using the k-ε turbulence model, two-phase mixture model, finite volume method (FVM), and PISO algorithm. The maximum value of the friction coefficient (FC) is 1.45, which corresponds to a baffle angle of 180º, φ = 4%, and Re = 5000. As the baffle angle is enhanced, the value of the average Nusselt number (Nuave) is intensified for all cases. The maximum value of the performance evaluation criteria (PEC) is about 1.55, which is related to a baffle angle of 180º and Re = 7500. For all the examined situations, the value of PEC is greater than one, indicating the effectiveness of the application of nanofluid and baffles at different angles. Hence, it is recommended to utilize baffles. The maximum value of thermal efficiency is about 37%, which occurs when the baffle angle is180º, φ = 4%, and Re = 5000.

Numerical simulation of dual-tube heat exchanger equipped with an innovative turbulator containing two-phase hybrid nanofluid: Hydrodynamic and exergy analysis

Due to the energy requirements of industries and the limitations of energy resources in the world, energy storage and prevention of energy loss are of particular importance. Therefore, energy loss and energy storage are among the most important new concerns of human beings. Heat exchangers (HE) are one of the most widely used heat transfer (HT) equipment that transfer heat from one fluid to another. For the simulation of water/silicon oxide-iron oxide hybrid nanofluid (HN), the mixed two-phase model has been used. The flow is turbulent and the turbulence model is RNG k-ε. The inlet Reynolds number (Re) and the volume fraction (φ) of SiO2 and Fe3O4 nanoparticles changes from 30,000 to 45,000 and 2% to 5%, respectively. Four different geometries of the novel turbulator with different values of pitch ratio (λ=0.15, 0.35, 0.55, 0.75) are modeled inside the HE and its effects on the average Nusselt number (Nuave), pressure drop (Δp), performance evaluation criterion (PEC), and exergy efficiency are examined. The results demonstrate that the use of water in the HE system leads to lower thermal performance compared to water/silicon oxide-iron oxide HN for all cases. Also, as λ and φ are enhanced, the values ​​of Nuave, Δp, and PEC are increased. In a dual-tube heat exchanger (DTHE) equipped with an innovative turbulator with maximum amounts of λ, using a HN with φ = 5% results in an enhancement in Nuave by 105.59% when Re changes from 30,000 to 45,000. Also, according to the values of the PEC, although the use of the turbulator leads to an increment in Δp, the enhancement of the thermal performance is higher. According to the exergy analysis, increasing the inlet velocity of the inner tube of the double-tube heat exchanger enhances the exergy efficiency. For all geometries, the maximum exergy efficiency corresponds to Re = 45,000.