Lower Heat Transfer Rate Research Articles

Chemical Reaction and Cross Diffusion Effects on Heat and Mass Transfer Characteristics of Viscoelastic Oil-Based Nanofluid Over a Porous Nonlinear Stretching Surface

The impact of chemical reaction and cross diffusion on heat and mass transport characteristics of viscoelastic flow of Al2O3 and CuO oil-based nanofluids past a porous nonlinear stretching surface has been examined. Similarity transformation was used to transform the governing partial differential equations into coupled nonlinear ordinary differential equations and solved numerically by employing the fourth order Runge-Kutta algorithm with a shooting method. Results for the entrenched parameters controlling the flow dynamics have been tabulated and illustrated graphically. The results foundCuO-oil based nanofluid to exhibit higher mass transfer rate and lower heat transfer rate and skin friction coefficient than Al2O3-oil based nanofluid under the same viscoelastic condition. This indicates that CuO-oil based nanofluid can be used as the working fluid in mechanical dampers.

A Multi-Sized Unit Cell Method for the Design of LPBF Lattice Support Structures Concerning Complex Geometries

Abstract Composed of individual unit cells strategically arranged to achieve a desired function, lattices are a promising solution for laser powder bed fusion support structure design in additive manufacturing. Despite their many advantages (e.g., multifunctionality and reduced material cost), prior work in lattice support structure design primarily focuses on horizontal support domains that are not translatable to support domains for complex geometries, thereby limiting their application. This work introduces a multi-sized unit cell design optimization (MSO) method to create lattice support structures (LSS) for parts with complex geometries. The proposed method utilizes voxelization to generate LSS using box-like unit cells of different sizes. It also allows for efficient, high-dimensional design optimization for the types and locations of user-specified unit cells through a modified simulated annealing-based optimization algorithm. The effectiveness and efficiency of the MSO method are demonstrated through the case study of an adapter pipe for a high-temperature heat exchanger. For this demonstration, LSS using multi-sized unit cells is designed to increase heat transfer rate while satisfying structural integrity and material cost constraints. The case study results indicate that the design of the LSS derived from the MSO method fulfills all constraints, including the design constraint of 50% material cost reduction, compared to the solid support structure. In contrast, the lattice support structure designs derived from equal-sized unit cell methods either cannot satisfy all design constraints or have a lower heat transfer rate than the design of the MSO method.

Heat transfer enhancement in magnetohydrodynamic hybrid nanofluids over a Bi-directional extending sheet with slip and convective conditions

The hybrid nanofluids can enhance cooling systems in microelectronics by enhancing heat dissipation from processes which makes them vital for maintaining optimal performance. They are also beneficial in solar systems where efficient heat transfer is essential for exploiting the energy detention. Thus, this study has studied the three-dimensional flow of a water-based hybrid nanofluid comprising of Fe3O4 and CuO nanoparticles on a bi-directional extending sheet. The bi-directional extending sheet is subjected to thermal convective and velocity slip conditions. In addition, the effects of heat source, magnetic field, thermal radiation, viscous dissipation, and Joule heating are employed. The partial differential equations (PDEs) that represent the mathematical model are subsequently converted to ordinary differential equations (ODEs) by applying the appropriate similarity variables. The shooting technique is incorporated to determine the computational solution of the converted ODEs. The effectiveness of the current study is confirmed by published results, which also validate the current outcomes. Based on the results, it is concluded that CuO and Fe3O4 solid nanoparticle volume fractions improved the thermal distribution while decreasing the velocity distributions along x and y-axes. The thermal distribution is improved by the thermal heat source, thermal radiation, thermal Biot number, and thermal Eckert numbers. CuO-water nanofluid has a higher velocity panel than CuO-Fe3O4/water hybrid nanofluid. Conversely, the CuO-Fe3O4/water hybrid nanofluid has a higher thermal profile than the CuO-water nanofluid. CuO-water nanofluid flow has higher surface drags than CuO-Fe3O4/water hybrid nanofluid flow. CuO-water nanofluid has a lower heat transfer rate than CuO-Fe3O4/water hybrid nanofluid.

Intermittent Flow Control Schemes for Heat Stress Mitigation in Lactating Sows on a Floor Cooling Pad

The Purdue hog cooling pad has previously been demonstrated to mitigate heat stress in lactating sows by conductively transferring heat from a sow to cool water running through an integral heat exchanger. Coolant effectiveness, which describes how much heat is removed per volume of water flushed through the cooling pad, is used to compare the operation under varying conditions. Past studies have indicated that the intermittent flow of cooling water achieves a greater coolant effectiveness than continuous flow operational schemes. An electronic control system was implemented with the current cooling pad design to allow for the automated control of a solenoid valve to create the intermittent flow conditions. All testing was performed using 18 ± 1 °C inlet water. Potential control schemes were categorized into two groups, temporal and temperature threshold. The temporal schemes opened the solenoid for 30 s, enough time to flush the entire contents of the cooling coils, before closing for 3, 6, or 9 min. The temperature threshold control schemes utilized feedback from thermal probes embedded beneath the surface of the cooling pad to open the solenoid for 30 s, when a maximum surface temperature was detected. Trigger temperatures of 28.0, 29.5, or 31.0 °C were used. The temperature threshold control schemes achieved greater heat transfer rates (348, 383, 268 W) compared to the temporal control schemes (324, 128, 84 W). The cooling effectiveness for all control schemes ranged from 46.6 to 64.7 kJ/L. The tested intermittent flow control schemes in this study achieved greater cooling effectiveness than continuous flow systems from previous studies (time: 51 kJ/L; temperature: 61 kJ/L; steady: 5.8 kJ/L), although the temporal control schemes exhibited lower heat transfer rates (time: 180 W; temperature: 330 W; steady: 305 W).

A Novel Liquid–Solid Fluidized Bed of Large-Scale Phase-Changing Sphere for Thermal Energy Storage

The storage of thermal energy has been hindered by the low heat-transfer rate of the solid phase of the phase-changing materiel. With water being the heat-transfer fluid as well as the liquid phase in the liquid–solid two-phase system, a novel type of fluidized bed is designed in this study. Numerous hollow spheres are fabricated with phase-changing materiel encapsulated. Adding the solid–liquid phase-change material capsules to the flowing fluid, the capsules are dispersed suspended in the carrier. The large spheres, 25 mm in present experiment, possess the merits of guaranteeing energy-storage density and tolerating internal interface chaotic motion. Both the fluidization status and phase-changing process are recorded by photography combined with image-processing technology. It is found that the large spheres, with density less than water, can be fluidized by the downward flowing fluid. As the flow rate increases, the expansion ratio of the solid phase increases and the regimes of incipient fluidization and bubbling fluidization can be observed. In comparison to the fixed bed, the oscillation of pressure drop across a fluidized bed is more severe, but the averaged value is less than the fixed bed. The melting and solidifying can be accelerated by 22.6% and 50%, respectively, thus proving the superiority of the fluidized bed in improving the heat-transfer rate while charging/discharging the thermal energy. Three types of basic movement of the spheres are shown to contribute to the enhanced phase-changing rate, which are shifting, colliding and rotating.

Investigation of the impact of transient pressure gradients on turbulent channel flow dynamics

AbstractThe effect of transient pressure gradients, or transient pumping in turbulent channel flow configuration, is investigated. Employing a cost‐efficient reduced‐order stochastic method known as one‐dimensional turbulence (ODT) modeling, simulations explore different signal shapes for the modulation of the prescribed pressure gradient forcing, including sinusoidal modulation, step‐like modulation, and piecewise sinusoidal beating. Various cycle periods and active pumping times are investigated. The simulations are conducted at a frictional Reynolds number of and a molecular Prandtl number of . The study adopts a passive scalar formulation to investigate heat transfer properties. The study quantifies the effects of transient pressure gradients on heat transfer rate, drag, and pumping power. Preliminary ODT predictions suggest that all transient cases exhibit lower heat transfer rates and a higher pumping power requirement than the constant pressure gradient case, with the step‐like modulation yields superior skin‐friction drag and heat transfer rate reductions relative to other signals.

An experimental study on heat transfer using electrohydrodynamics (EHD) over a heated vertical plate.

The Corona effect offers significant potential for improving heat transfer efficiency in air. This study thoroughly examined how a single corona discharge affects heat transfer on a heated vertical flat plate. Key parameters tested included corona voltage, the aspect ratio of the vertical plate (y/L), and the inter-electrode discharge gap ratio (x/d). The findings revealed that increasing the corona voltage and decreasing the discharge gap enhanced heat transfer efficiency along the vertical surface. A predictive formula for the local Nusselt number was developed to characterize heat transfer on the plate. Additionally, Particle Image Velocimetry (PIV) was used to analyze the corona wind generated by the discharge. The study observed that the corona wind formed a vortex in the upstream region, which resulted in lower heat transfer rates upstream compared to the downstream region.

Multi-grooved channel design in continuous casting mold for enhancing heat transfer efficiency considering pressure drop and flow rate loss

An efficient, speedy, multi-grooved (ESMG) mold was designed and manufactured for optimization to address issues such as low heat transfer rate, slow casting speed, and quality defects in traditional continuous casting molds. The flow resistance mechanism of multi-grooved channels with varying parameters was investigated by considering the ESMG geometric model, the convective heat transfer characteristic variation trends were revealed with different channel designs. Considering constraints of the dimensional chain and supply pressure, variation trends and mechanisms of the pressure drop, flow rate loss, and convective heat transfer coefficient of the ESMG mold were explored using multiple channel variables. Based on the numerical model of the ESMG channel, temperature variation trends in the copper mold were verified by comparison with relevant literature data, supporting the convective-heat-transfer model and variation trends of the ESMG mold. A high-efficiency heat-transfer ESMG assembly that casts U71Mn high-carbon large rectangular billets was fabricated, achieving a closed-loop dimensional chain and replacing traditional molds. Experimental validation on the continuous casting machine (CCM) proved directly that redesigning the ESMG mold cooling channel improved heat transfer efficiency and reduced CO2 emissions. After 504 h on the CCM, the ESMG mold casting speed increased from 1.1 to 1.6 m/min, the heat transfer efficiency was 17.6% higher than that of traditional molds and CO2 emissions were estimated to decrease by 31.2%. The billets produced by the ESMG mold had no quality defects in shape or surface with the original casting conditions, which provided enhanced support for accelerating continuous casting lines.

Experimental analysis of the synergistic impact of fan and nocturnal thermal insulation on enhancing the thermal performance of latent-energy-storage solar air collectors

Solar air collectors equipped with energy storage functionality are widely utilized to address the mismatch between heat demand and supply periods during winter, effectively facilitating heating needs. However, phase change energy storage flat plate solar air collectors are hindered by inefficiencies, primarily due to the low rate of convective heat transfer and substantial nocturnal energy losses, which considerably undermine the overall energy efficiency of these collectors. In response to these challenges, a forced convection approach utilizing a fan was adopted to augment the convective heat transfer rate, and insulation was applied to glass panes overnight to curb energy wastage. Two solar air collector systems were constructed and examined: a natural convection-based energy storage solar air collector (NCSAC-PCM) and another solar air collector incorporating forced convection with nocturnal thermal insulation (FCSAC-PCM-NTI). Comparative experiments revealed that the combination of forced convection with nighttime insulation in the latter design led to an elevation in the mean indoor temperature by 1.4 °C, alongside a decrease in the temperature gradient variation within the space during the test period. Furthermore, this integration significantly enhanced the energy efficiency by 53.71 % and the exergy efficiency by 11.45 %.

Thermal conductivity enhancement of polyethylene glycol/NF composite as stabilized phase change materials for thermal energy storage

Polyethylene glycol (PEG) has the advantages of large latent heat of phase transition, a wide range of phase transition, and cheap price, but the application of PEG in the latent thermal energy storage (TES) systems is hindered due to its lower heat transfer rate and leakage. Porous metal foam has excellent thermal conductivity and high strength, which can effectively improve the problems of PEG. In this study, PEG/nickel foam (NF) composite phase change materials (PCM) were prepared by vacuum molten impregnation method using NF as substrate. It was found that PEG had good compatibility with NF, and the highest impregnation rate of PEG6000/NF reached 85.73 %. The thermal conductivity of PEG2000/NF can be increased to 1.58 1.58 W·m−1 K−1, nearly 4 times larger than that of pure PEG. The phase change temperature range of the composite PCM is 51–63 °C, and the phase change enthalpy is 67.8–126.3 J·g−1. Furthermore, the PEG/NF composite demonstrated outstanding photothermal conversion properties and high thermal stability, which can be widely used in the field of building temperature control and device heat dissipation.

Correlations of mixed convection in a double lid‐driven shallow rectangular cavity: The case of non‐Newtonian power‐law fluids

AbstractThis work provides an analytical and numerical assessment, complete with correlations, of mixed convection in a double lid‐driven shallow rectangular enclosure, which confines non‐Newtonian fluids of the Ostwald–de Waele type and which a uniform thermal flux heats. The finite volume method with the SIMPLER algorithm is the numerical method used to solve the governing partial differential equations along with the boundary conditions, where the parallel flow concept is the analytical approach. In the limits of the explored values of the governing parameters of this study, which are the Rayleigh number, the Peclet number, and the behavior index, the results obtained by these approaches appear to be in good harmony. On the basis of the results obtained by these approaches, we established helpful correlating relations between the governing parameters to realize the contribution of mixed convection to heat transfer. This leads to the finding that the ratio Ra/Pe2+n is the mixed convection parameter, which is the key to distinguishing the three convective flow modes. On the basis of this parameter, which allows the transition from one regime to another, it is possible to identify the zones that designate the predominance of natural, forced, and mixed convection. The limits of these latter depend on the behavior index, n, which is diversified from 0.6 to 1.4 to account for shear thinning (0 < n < 1, low apparent viscosity, high fluid flow, and high heat transfer rate), Newtonian (n = 1), and shear thickening (n > 1, high apparent viscosity, slow fluid flow, and low heat transfer rate) fluids. On the other hand, the study presents and interprets the influences of the steering factors on heat transfer and fluid flow.

Designing an absorber for solar photovoltaic thermal systems: a heat pipe approach and comparative evaluation

Abstract Renewable energy power generation is extensively promoting for the global objective of mitigating greenhouse gas emissions. Solar energy leads all renewables due to its ubiquitous nature which can be harvested by solar thermal and solar photovoltaic devices. Solar PV is used widely because of its flexibility in working with both direct and diffuse radiation. However, PV systems experience efficiency loss for every degree rise of solar cell temperature above room temperature. Solar photovoltaic-thermal (PVT) collectors are proposed for co-generation of electrical and thermal energy by utilizing excess heat generated in the PV layer. The low heat transfer rate, energy-intensive nature, and freezing of working fluid in colder regions are some problems that persist in water- and air-based PV/Ts, leading us to consider alternatives. Thus, the present study addresses the current opportunities by utilizing heat pipes as PV/T absorbers. Heat pipe PVT is a passive system which operates in phase transition facilitating a tremendous amount of heat transfer enhancement. To enhance the efficiency of PV/T systems, the integration of advanced technologies, like heat pipe thermal absorbers, becomes imperative. Incorporating cutting-edge solutions, such as heat pipe thermal absorbers, is essential to optimize the performance of PV/T systems. Hence, the current study provides insight into heat pipe design through a case study on the application of heat pipes as thermal absorbers for photovoltaic systems. The existing absorbers with fluid flow configurations like Raster, Spiral or Rectangular spiral, etc. used in PV/T are considered as reference. Copper as tube material and water as working fluid are found to be compatible with each other for the proposed heat pipe. The maximum heat input of 0.55kW is computed by the inadequacy of the mentioned existing PVTs to extract the maximum available heat from the PV surface. Additionally, an analytical approach used to define the optimum size of the system and calculation of minimum requirement of tubes. The optimized design of copper heat pipes was found to be ½ inch in diameter and at least ten heat pipes were required to transfer a computed heat flux of 466kW/m 2 per pipe to outperform the existing PV/Ts.

Applying isovolumic steam capsule as new thermal energy storage unit

In order to make up the inefficiencies of liquid–solid phase change material (PCM) such as low latent heat and low heat transfer rate, the possibility of adopting water steam as the phase change material is explored. Although great volume change occurs during the gas–liquid phase-changing, the specific latent heat is at least one order of magnitude larger than that of liquid–solid phase-changing. To minimize the adverse effect of the great volume change during vaporization or condensation, the steam can be accommodated inside sealed vessel with sturdy shell. In this study, an isovolumic steam capsule (ISC) was made by filling a cylinder with a small amount of liquid water and then heated and boiled to extinguish the non-condensable gas (NCG) before sealing it. Thermodynamic analysis shows the thermal energy contained in the isovolumic steam capsule per unit volume increases in approximately an exponential manner with the increase of temperature due to the evaporation of liquid, and can reach several times that of liquid–solid phase change material, demonstrating great potential as energy storage material. The heat transfer experiments show that the energy charging and discharging rates increase with the temperature difference. There exists thermodynamic non-equilibrium during heat transfer and the deviation from saturation enlarges with increasing temperature difference and non-condensable gas concentration. For both charging (vaporization) and discharging (condensation), a higher non-condensable gas concentration in the steam exhibits larger heat transfer rate in the beginning, but smaller heat transfer rate in the later stage. The mechanism of vaporization and condensation in the isovolumic steam capsule awaits to be further clarified.

Energy and exergy experimental analysis for innovative finned plate solar air heater

In this current experimental study, a flat absorber plate of a solar air heater (SAH) with innovative straight interrupted fins arranged in a V-shaped pattern is analyzed using energy and exergy approaches, as the literature clearly shows that the low rate of heat transfer of flat plate SAH remains a source of concern for energy experts. The aluminum finned absorption plate was designed, manufactured, and tested during the summer in Saudi Arabia, examining the effect of changing the SAH tilt angle of θ = 0°, θ = 10°, θ = 20°, and θ = 30°. The study found that tilting the SAH at θ = 10°, θ = 20°, and θ = 30° increases the hot air exit temperature by 7.5 %, 15.7 %, and 12.5 %, respectively, compared to the horizontal position at θ = 0°. Tilting the SAH to θ = 20° increased absorbed solar radiation and air draft, resulting in 38.2 % SAH energy efficiency, 26.4 % exergy efficiency, and a 1.36 sustainability index that increased by 5.5 %, 12.8 % and 3.8 % compared to the horizontal position θ = 0°.

A Composite Superhydrophobic, Photothermal Coating by Modified Carbon Nanotubes and the Study of Its Anti‐Icing/Deicing Behavior

Linearly structured carbon nanotubes (CNTs) are intertwined to form complex micro‐ and nanoscale structural undulations, and the structural undulations of the coating are further enhanced using large‐size nano‐SiO2. It can be prepared by the composite superhydrophobic coating (S‐C coating) with contact angle of 165.3° and sliding angle of 1°. Small‐size nano‐SiO2 can doped into the 3D‐network structure formed by the CNTs and act as anchor points to fix the structure. This enhances the stability of the coating as well as the abrasion resistance. The coating exhibits good long‐term durability and the ability to face harsh service environments. Due to the presence of the air layer with low heat transfer rate on the coating surface, the S‐C coating demonstrates good anti‐icing properties compared to the uncoated tinplate. By the lower surface free energy and contact area with the ice layer of the coating, the coating also exhibits good deicing performance. The ice adhesion strength of the coating is only 11.5 kPa. The photothermal properties of CNTs and the ability of the micro‐ and nanostructure to reflect light enable the coating to exhibit excellent photothermal properties. This also accelerates the melting and shedding of the ice layer on the coating.

Limitations of the enthalpy-porosity method for numerical simulation of close-contact melting on inclined surfaces

One of the main challenges for latent thermal energy storage (LTES) systems is low heat transfer rates due to the low thermal conductivity of most phase change materials (PCM). Close-contact melting (CCM) can accelerate melting times in LTES systems but the current numerical techniques for solid liquid phase change have difficulties with accurately predicting this process. In this study, close-contact melting of PCM on an inclined surface is simulated using the enthalpy-porosity method in ANSYS Fluent. All PCM properties, including density, are temperature-dependent. In this way, phenomena such as natural convection, volume change and buoyancy between the solid and liquid are taken into account. The volume change is compensated by a gaseous expansion volume. Both 2D and 3D simulations are used to show discrepancy between state-of-the-art enthalpy porosity modelling and experimentally observed phenomena in the case of CCM. The mushy zone constant, which is set to 105 to allow motion of the solid bulk, causes the solid phase to deform as a highly viscous fluid instead of moving as a rigid body. The velocity differences inside the solid are more than 50 % of its sinking velocity. As a result, the movement of the solid resembles creep behaviour and the obtained CCM patterns are not physically accurate. Furthermore, the density difference between the solid and liquid phases causes an avalanching effect in the mushy zone, which artificially strengthens convection. In conclusion, the enthalpy porosity method exhibits significant limitations in accurately capturing close-contact melting phenomena.

Anti-icing polyurethane coating on glass fiber-reinforced plastics induced by femtosecond laser texturing

Polyurethane coating has been commonly used in aerospace and construction, and enhancing anti-icing capabilities in low temperatures is crucial for preventing mechanical failures and reducing energy consumption. Utilizing a superhydrophobic surface was considered an important option to improve anti-icing performance. In this study, femtosecond laser treatment has applied to polyurethane coating on glass fiber-reinforced plastic (GFRP) to transform from hydrophilic to superhydrophobic. Results have indicated that laser treatment significantly reduced the solid–liquid contact area compared to the original surface. The non-polar groups on the surface contributed greatly to the enhancement of hydrophobicity. In comparison to the original surface, the freezing temperature of droplets on the superhydrophobic surface with improved anti-icing performance was reduced from −4.5 °C to −9.2 °C, while the freezing time was extended from 65 s to 269 s. This improvement was attributed to the reduction of solid–liquid contact area, resulting in a low heat transfer rate and a low heterogeneous nucleation rate. Additionally, the laser-treated surface exhibited excellent self-cleaning effects, along with mechanical and chemical stability.

Numerical investigation on assessing the influence of diverse-shaped hybrid nanofluids on thermal performance of triple tube heat exchanger

The present study explored the effects of hybrid nanofluids, composed of water-based nanoparticles in various shapes (MWCNT-cylindrical, Al2O3-blade, Graphene-platelet, and Fe3O4-brick), within a triple concentric tube heat exchanger (TCTHX). Theoretical and computational modeling was conducted for the flow of hot water and hybrid nanofluids at varying inner annulus mass flow rates (0.1 kg/s to 0.5 kg/s and at a fixed temperature of 70 °C) in the TCTHX; their influence was analyzed by the energetic and exergetic performance and revealing the findings to enhance the heat transfer efficiency.The key finding of the work is that the thermal performance factor (TPF) of the brick-blade hybrid nanofluid in the TCTHX is 4.26, which is the maximum as compared to brick-platelet, brick-cylindrical, blade-platelet, blade-cylindrical, and platelet-cylindrical hybrid nanofluids for all mass flow rates. The brick-blade hybrid nanofluid is the most economical in the TCTHX system, followed by the brick-cylindrical hybrid nanofluid. Overall, the combination of brick-blade hybrid nanofluid performs best in the TCTHX system in terms of performance index, TPF, and CBR. Brick-platelet hybrid nanofluid is 7.20% less efficient than water at a mass flow rate of 0.1 kg/s. Platelet-cylindrical hybrid nanofluid exhibits 12.71% and 5.09% lower heat transfer rate and performance index than delaminated (DI) water at the lowest mass flow rate in the TCTHX system. Brick-platelet hybrid nanofluids show a reduced Nusselt number ratio for the tested mass flow rates. Entropy generation in blade-platelet hybrid nanofluid is 19.49% lower than in (DI) water.

Turbulent flow-thermal-thermodynamic characteristics of a solar air heater with spiral fins

This work proposes a strategy by employing multiple spiral fins (SFs) for enhancing the low heat transfer rate of traditional smooth solar air heaters (SAHs). A numerical study involving the effects of the pitch ratio (P/Dh), quantity (N), and arrangement of SFs on fluid flow, heat transfer, and thermodynamic characteristics of the SAHs was conducted. The research findings indicated that the flow field was homogenized and the thermal boundary layer was weakened by inserting multiple SFs into the smooth SAH. This could increase the heat transfer rate by 30.63–137.51 % and decrease the overall entropy generation by 9.64–57.05 %, causing a 25.01–99.18 % improvement in thermodynamic efficiency. Reducing P/Dh and increasing N could improve the heat transfer rate, increase flow viscous entropy generation, reduce thermal entropy generation, and augment thermodynamic efficiency (ηⅡ). In addition, changing the rotation arrangement of the SFs from the counterclockwise to the counter-swirl improved the thermal-hydraulic performance parameter (THPP). Within the scope of this study, the SAH with P/Dh = 1.5 and N = 5 in a counter-swirl layout achieved the highest THPP of 1.04, and the SAH with P/Dh = 0.6 and N = 5 in an anticlockwise arrangement yielded the lowest entropy generation ratio of 0.43 and the maximum ηⅡ of 18.16 %.

NUMERICAL INVESTIGATION OF HEAT TRANSFER AND TURBULENT FLUID FLOW FOR TRANSVERSE VORTEX GENERATORS WITH NANOPARTICLES

This paper proposes a simple design and easy-to-install vortex generator (VG) for heat exchangers to enhance heat transfer rates. The aim is to maintain low pressure drops and high heat transfer rates. The effects of the VG's geometrical parameters on thermal performance and pressure drop are investigated in this paper for divergent and convergent schemes using commercial software Comsol Multiphysics version 6. The effects of Reynolds number, VG angle, and the quantity of VGs on the response (i.e., Nusselt number and pressure drop) are investigated based on variance analysis. The nanoparticle concentration varies from 1 to 6%. The results indicate that the quantity of VGs is the most significant factor affecting pressure drop. The critical factor for heat transfer enhancement of divergent and convergent VGs are the Reynolds number and the quantity of VGs, respectively. Finally, the optimal conditions are predicted by the response surface methodology (RSM). The optimal requirements for using VG type A are β = 0°, the quantity is two, and the Reynolds number should be 9160. Furthermore, the optimal conditions for VG type B are β = 0°, Reynolds number is 10,000, and the number of VGs is two. The VG proposed in this study has a simple structure that can be efficiently designed and installed on heat exchangers. It is more efficient and applicable than the designs suggested in the literature.