Thermal Boundary Layer Research Articles

The physical mechanism of heat transfer enhancement for Al2O3-water nanofluid forced flow in a microchannel with two-phase lattice Boltzmann method

PurposeThe purpose of this paper is to analyze the mechanism of nanofluid enhanced heat transfer in microchannels and promote the application of nanofluids in industrial processes such as solar collectors, electronic cooling and automotive batteries.Design/methodology/approachThe two-phase lattice Boltzmann method was used to calculate the flow and heat transfer characteristics of Al2O3 nanofluids in a microchannel at Re = 50. By comparing the simulation results of pure water, nanofluids without calculated nanoparticle-fluid interaction forces and nanofluids with calculated nanoparticle-fluid interaction forces, the effects of physical properties improvement and interaction forces on flow and heat transfer are quantified.FindingsThe findings show that the nanofluid (φ = 3%, R = 10 nm) increases the average Nusselt number by 22.40% at Re = 50. In particular, 16.16% of the improvement relates to nanoparticles optimizing the thermophysical parameters of the base fluid. The remaining 6.24% relates to the disturbance of the thermal boundary layer caused by the interaction between nanoparticles and the base fluid. Moreover, the nanoparticle has a negligible effect on the average Fanning friction factor. Ultimately, we conclude that the nanofluid is an excellent heat transfer working medium based on its performance evaluation criterion, PEC = 1.225.Originality/valueTo the best of the authors' knowledge, this research quantifies for the first time the contribution of nanoparticle-liquid interactions and nanofluids physical properties to enhanced heat transfer, advancing the knowledge of the nanoparticle's behavior in liquid systems.

Enhancing the heat transfer in CuO-MWCNT oil hybrid nanofluid flow in a pipe

In this study, three-dimensional steady-state laminar flow simulations were conducted in a horizontal pipe using CuO and multi-walled carbon nanotubes (MWCNT) nanoparticles with engine oil as the base fluid. Various nanoparticle volume fractions were examined under a constant heat flux boundary condition applied to the pipe wall. The main goal was to assess and compare the effects of different nanoparticle volume concentrations, including CuO and MWCNT in ratios of 1:1 and 1:2, on convective heat transfer. A second-order discretisation method was employed for solving the equations, and the SIMPLE algorithm was used for pressure–velocity coupling in the CFD code. The study focused on the impact of nanoparticle volume fraction on the convective heat transfer coefficient and the Nusselt number at a Reynolds number of 750. The findings indicate that increasing the nanoparticle volume fraction enhances both the convective heat transfer coefficient and the Nusselt number, with MWCNT having a more pronounced effect compared to CuO. Specifically, adding 2% CuO increases the heat transfer coefficient by 65%, while a mixture of 1% CuO and 1% MWCNT boosts it by 75%. The thermal boundary layer thickness also grows with higher nanoparticle concentrations, with 1% CuO and 3% CuO increasing the thickness by 1.5% and 3.6%, respectively. A formula for the thermal boundary layer thickness in CuO-oil nanofluids is provided based on volume fraction, and a scale analysis of the average heat transfer coefficient confirms that the simulation results are consistent with this analysis.

Method for evaluating of the convective heat transfer of window for the non-uniform radiator heated environment

Understanding heat transfer mechanism of window is crucial to decreasing carbon emission and energy consumption. Distribution of indoor temperature in convective-heating room is uneven and determination of reference temperature in calculating convective heat transfer is still challenging. In addition, near-surface airflow is closely related to convective heat transfer due to the interaction of turbulent eddies and the surface of window. Theoretical and technical attempts on this issue are still insufficient. In this study, experimental measurements were conducted in a radiator heating chamber. Through comparing calculated convective heat transfer of window and actual values, the determinations of reference air temperature and surface temperature of window were suggested. Measurement results and root-mean-square error (RMSE) from different measurement schemes showed the utilization of the air temperature near the thermal boundary layer of window yielded better calculation results. In addition, it was found that center-point surface temperature of window was suggested in the experimental analysis. Through non-linear fitting, a simplified correlation, h=0.146ΔT1.630Vm2.261, was proposed for the convective heat transfer of window. Proposed correlation quantitatively related maximum air velocity near window and convective heat transfer of window. Findings in this study are conductive to further understanding the heat transfer mechanism of window and providing reference for evaluating heating loads of buildings. As one basic research, this study provides theoretical support for evaluating heating loads and multifaceted perspective on building energy efficiency and carbon reduction.

Quantitative analysis of heat and mass transfer in MoS2-Al2O3/EG hybrid flow between parallel surfaces with suction/injection by numerical modeling of HPM method

This description focuses on how the magnetic field affects mass and heat transfer in a hybrid nanofluid (Hnf) between two parallel, rotating plates. By dispersing aluminum oxide (Al2O3) and molybdenum disulfide (MoS2) nanoparticles (NPs) in ethylene glycol (EG), a hybrid nanofluid (Hnf) is created. This research aims to analyze the heat and mass transfer characteristics in the flow of a hybrid nanofluid (MoS2-Al2O3/EG) between two rotating parallel plates under the influence of a magnetic field. Furthermore, the statistical technique of response surface methodology (RSM) has been employed to optimize the parameters of velocity, temperature, and concentration of the nanofluid within the flow region bounded by the rotating plates. Dimensionless differential equations have been calculated and checked using the Homotopy perturbation method. This study introduces a novel approach by utilizing the RSM method to identify optimal points for velocity and temperature parameters of nanofluids between two stretching plates for the first time. Additionally, the article innovatively applies the exact HPM method to validate dimensionless linear and non-linear coupling equations. As the Reynolds number and the suction/injection coefficient of nanofluids flowing between two plates under tension increase, the results indicate a decrease in the velocity field. This decrease in velocity field can be attributed to the reduction in fluid diffusion as viscous forces diminish with varying Reynolds numbers. The ideal temperature distribution for nanofluids flowing between two parallel plates occurs when they are uniformly dispersed at the midpoint between them. As the distance from the initial point of nanofluid entry to the end of the plates increases, along with the vertical distance from the bottom plate, the temperature gradient diminishes, reducing the thickness of the thermal boundary layer. The velocity gradient and the rate of heat flux transfer between the nanofluid and plate rise by 34 % when the volume percentage is raised from 1 % to 5 %.

Study on the Flow and Heat Transfer Performance of Microchannel Heat Exchangers With Different Elliptical Concave Cavities

AbstractEllipticity has a significant impact on the flow and heat transfer performance of microchannel heat exchangers (MHEs) with elliptical concave cavities. In this study, five types of MHEs with different elliptical concave cavities (ellipticities of 0.4, 0.6, 0.8, 1.0, and 1.2) were designed. The influence of ellipticity on the flow and heat transfer performance of MHEs was numerically investigated using ANSYS Fluent 21.0 R1. Moreover, MHEs with corresponding elliptical concave cavities structures were processed and manufactured, and then an experimental platform was designed and built for experimental verification. The results showed that the fluid velocity distribution in MHEs with elliptical concave cavities was symmetrical, and the formation of secondary flow in the elliptical concave cavities led to the continuous destruction and reconstruction of the flow and thermal boundary layer in the microchannel, which is conducive to mass and heat transfer in the MHEs with elliptical concave cavities. The inlet and outlet pressure drop of MHEs with elliptical concave cavities increased as the inlet flow rate increased. At the same inlet flow rate, the inlet and outlet pressure drop of the MHE with elliptical concave cavities first increased and then decreased with increasing ellipticity. At an ellipticity of 1.0, the inlet and outlet of MHE exhibited the lowest pressure drop indicating that the MHE with an ellipticity of 1.0 featured the highest pressure drop performance. The cold‐water outlet temperature of the MHEs with elliptical concave cavities first decreased and then increased as the inlet flow rate increased. At the same inlet flow rate, the cold‐water outlet temperature of the MHEs with elliptical concave cavities first increased and then decreased with increasing ellipticity, while the hot‐water outlet temperature of the MHEs first decreased and then increased with increasing flow rate. This indicated that the MHE with an ellipticity of 1.0 exhibited excellent heat transfer performance.

Simulation study of flow and heat transfer in wavy microchannel heat sink with manifolds and secondary channels composite

With the continuous increase in power density of electronic devices, traditional cooling methods have gradually shown their limitations. Microchannel heat sinks (MCHSs) have enormous potential in thermal management for electronic devices due to their excellent heat dissipation performance. To improve the flow and heat transfer performance of MCHSs, a numerical study was conducted on 56 types of wavy microchannel heat sinks with manifolds and secondary channels composite (WMCHS-MSCs). The results indicate that compared to the original manifold wavy microchannel heat sink (MWMCHS), the optimal WMCHS-MSC increases the thermal enhancement factor by 45.1 % when the inlet volume flow rate Q = 1.0 × 10−6 m³/s. At the same time, the overall thermal resistance, the maximum temperature difference on the bottom wall, and the pressure drop of the optimal WMCHS-MSC are reduced by 7.6 %, 21.9 %, and 10.6 %, respectively. Compared to the original MWMCHS, the increase in Q for WMCHS-MSCs results in an overall trend of increased thermal performance, decreased temperature non-uniformity and hydraulic performance, and initially increased and then decreased overall performance. The flow field distribution of the secondary channels of WMCHS-MSCs intuitively demonstrates the improved hydraulic and thermal performance brought about by disrupting the thermal boundary layer and mixing the flow. The study presents a novel approach for the design of wavy MCHSs, potentially paving the way for enhanced thermal management solutions in electronic devices.

Impact of Navier’s Slip and MHD on a Hybrid Nanofluid Flow over a Porous Stretching/Shrinking Sheet with Heat Transfer

The main objective of this study is to explore the inventive conception of the magnetohydrodynamic flow of a hybrid nanofluid over-porous stretching/shrinking sheet with the effect of radiation and mass suction/injection. The hybrid nanofluid advances both the manufactured nanofluid of the current region and the base fluid. For the current investigation, hybrid nanofluids comprising two different kinds of nanoparticles, aluminium oxide and ferrofluid, contained in water as a base fluid, are considered. A collection of highly nonlinear partial differential equations is used to model the whole physical problem. These equations are then transformed into highly nonlinear ordinary differential equations using an appropriate similarity technique. The transformed differential equations are nonlinear, and thus it is difficult to analytically solve considering temperature increases. Then, the outcome is described in incomplete gamma function form. The considered physical parameters namely, magnetic field, Inverse Darcy number, velocity slip, suction/injection, temperature jump effects on velocity, temperature, skin friction and Nusselt number profiles are reviewed using plots. The results reveal that magnetic field, and Inverse Darcy number values increase as the momentum boundary layer decreases. Moreover, higher values of heat sources and thermal radiation enhance the thermal boundary layer. The present problem has various applications in manufacturing and technological devices such as cooling systems, condensers, microelectronics, digital cooling, car radiators, nuclear power stations, nano-drag shipments, automobile production, and tumour treatments.

Multi-cycle Direct Numerical Simulations of a Laboratory Scale Engine: Evolution of Boundary Layers and Wall Heat Flux

AbstractMulti-cycle direct numerical simulations (DNS) of a laboratory-scale engine at technically relevant engine speeds (1500 and 2500 rpm) are performed to investigate the transient velocity and thermal boundary layers (BL) as well as the wall heat flux during the compression stroke under motored operation. The time-varying wall-bounded flow is characterized by a large-scale tumble vortex, which generates vortical structures as the flow rolls off the cylinder wall. The bulk flow is found to strongly affect the development of the BL profiles, especially at higher engine speeds. As a result, the large-scale flow structures lead to alternating pressure gradients near the wall, invalidating the flow equilibrium assumptions used in typical wall modeling approaches. The thickness of the velocity BL and of the viscous sublayer was found to scale inversely with engine speed and crank angle. The thermal BL thickness also scales inversely with engine speed but increases with in-cylinder temperature. In contrast, thermal displacement thickness, which is sometimes used as a proxy for thermal BL thickness, was found to decrease with increasing temperature in the bulk. Examination of the heat flux distribution revealed areas of increased heat flux, particularly at places characterized by strong flow directed towards the wall. In addition, significant cyclic variations in the surface-averaged wall heat flux were observed for both engine speeds. An analysis of the cyclic tumble ratio revealed that the cycles with lower tumble ratio values near top dead center (TDC), indicative of an earlier tumble breakdown, also exhibit higher surface averaged wall heat fluxes. These findings extend previous numerical and experimental results for the evolution of BL structure during the compression stroke and serve as an important step for future engine simulations under realistic operating conditions.

Lamprophyres from the Chhota Udaipur alkaline–carbonatite sub-province, Deccan Large Igneous Province, India: implication for petrogenesis and crustal structure

This paper discusses the petrogenesis of lamprophyre dykes occurring in the Chhota Udaipur Alkaline–Carbonatite Sub-province (CUACS). Both calc-alkaline as well as alkaline varieties occur in the area. The major and trace elements geochemistry of the CUACS lamprophyres display good correlation with each other and other Deccan-related lamprophyres. Trace element ratios reveal a minor role of crustal contamination and support their derivation from partial melting of a lithospheric mantle source that is significantly modified by interaction with asthenosphere-derived melts emanating from an impinging mantle plume. The restricted initial 87 Sr/ 86 Sr (0.70599–0.70658) and 143 Nd/ 144 Nd (0.512501–0.512513) ratios of the CUACS lamprophyres further attest to their derivation from an ocean island basalts (OIB)-type parental melt. Their negative εNdi values (−1 to −6) are comparable with other lamprophyres of the Deccan Large Igneous Province (LIP). The lamprophyres from the present study share similar geochemical characteristics to Mt Girnar lamprophyres, which are derived from the spinel–garnet transition zone at a depth of ∼85 km, distinct from the previously considered depth (∼100 km) of the post-Deccan lithosphere–asthenosphere boundary (LAB) beneath NW India. Such geochemical characteristics of the Chhota Udaipur lamprophyres indicate a vital role of plume–lithosphere interaction at the thermal boundary layer at about ∼66 Ma.

Incompressible boundary layer flow past a hump with temperature-dependent viscosity

The problem of boundary layer flow past a hump placed on a flat surface, where viscosity is coupled with temperature, is investigated using triple-deck theory. The incompressible Navier–Stokes equations supplemented by the heat and viscosity equations are considered in the limit that the Reynolds number is large. The triple-deck scalings are adopted, and asymptotic expansions are used to obtain some novel triple-deck equations coupled with the thermal boundary layer. We have used the same viscosity–temperature dependence as in Jasmine and Gajjar [Int. J. Heat Mass Transfer 48, 1022–1037 (2005)], in which viscosity varies inversely proportional to the temperature. The linear analysis is performed, and the nonlinear equations are solved numerically. Our results show that increasing the characteristic constant of the viscosity leads to enhanced peaks and troughs in the pressure and in the skin friction over the hump, as compared to the constant viscosity case. This suggests that temperature-dependent viscosity is more likely to provoke separation.

Electromagnetic mixed convective flow of dusty hyperbolic tangent hybrid nanofluid over a stretching surface: A quadratic regression analysis using RSM

This article investigates the flow dynamics of electrically conducting dusty hyperbolic tangent fluid over a stretching sheet with thermal radiation and heat source effects. Moreover, the suspension of Aluminium oxide (Al2O3) and Tantalum nanoparticles in engine oil as base fluid at 300 K is considered. The flow and thermal dynamics are analysed using Xue and Hamilton Crosser's thermal conductivity models. Moreover, using various ranges, the effect of the Richardson number on forced, mixed and natural convection is examined. The governing partial differential equations of the flow model are converted into ordinary differential equations and then solved numerically using the boundary value problem solver BVP4C along with the shooting technique in MATLAB. The Xue model enhances the heat transfer rate by 3.55% compared to the Hamilton Crosser model ϕ1 = 0.03, ϕ2 = 0.01, R = 0.1, Q = 0.6, βt = 0.2, βv = 0.07. A moderate adjustment to the Richardson number can reduce skin friction by 0.889% in the case of forced convection. The absence of dust particles enhances the thermal and momentum boundary layer thickness. Tantalum nanoparticles outperform Al2O3 in terms of temperature and velocity. It is possible to regulate the temperature and velocity of the backflow by changing the heat source parameter and the nanoparticle volume percentage. The maximum achievable heat transfer rate in the fourth experimental run is 0.2609 when R = 2.5 and Q = 1.5 as determined by the quadratic regression analysis.

Comparative study of two-phase flow approaches for modeling conjugate heat transfer in a three-dimensional wavy microchannel-heat sink with CuO-water nanofluid

This study aims to numerically investigate the conjugate heat transfer (CHT) and the changes in the hydraulic and thermal terms of laminar flow (300 ≤ Re ≤ 800) in a 3-D wavy microchannel heat sink (MCHS). The obtained results from different nanofluid flow simulated models will be compared. The numerical simulation approaches used include single-phase, mixture, Eulerian, DPM, and DDPM. The effect of adding 1%, 3%, and 6% concentration of CuO nanoparticles (100 nm) in deionized water as the base fluid is examined on various parameters such as local and axial temperature, heat transfer convective coefficient, friction factor, Nusselt number (Nu), velocity distribution, and thermal and hydraulic boundary layer parameters. The substrate surface, due to its larger area surface and the amplitude of the sinusoidal wave, has a greater impact on the nanofluid flow as a channel bottom conjugate surface compared to others. The results obtained from the different models show close agreement with each other for various cases. For example, at Re = 304, the average Nu and friction factor for pure water are approximately 10.43 and 0.0260, respectively. For water with 0.01 concentration of CuO nanoparticles, Nu is found to be in the range of 10.43–10.78, and the friction factor ranges from 0.260 to 0.290, depending on the approach used for simulation. This shows a 2% increase in Nusselt number compared to a 0.05% increase in the friction factor. Moreover, these values increase by approximately 5.7% and 11.3% on average with an increase in CuO nanoparticle concentration to 0.06. Additionally, the DPM and DDPM models show a 15% difference in the scattering of CuO nanoparticles compared to the Eulerian-Eulerian models. The single-phase model presented in this study yields similar results to the multiphase approaches. Furthermore, the PEC parameter increases by about 1.9% with the addition of CuO nanoparticles at a concentration of 0.06.

Enhancement of cooling process of hot blocks mounted inside a horizontal channel using flexible baffles — Alternative arrangement

In this paper, two heated blocks and three flexible baffles that are alternately placed on the upper and bottom sides of a rectangular channel are used to replicate the transient heat and air movement. The novelty of this research is the use of flexible baffles to destruct the thermal boundary layer with maintaining little pressure drop, and thus reducing the required pumping capacity. The finite thickness blocks are subject to a constant heat flux, while the baffles are very thin and deforms depending on the strength of the flow of coolant (air). Finite element method with arbitrary Lagrangian–Eulerian approach is used for solving such deforming domain problem. The problem is inspected transiently by varying the dimensionless time (τ=0.0 to 10) and two salient parameters which are Reynolds number Re=10−500, and baffle elasticity parameter E=105−108. Results show that the flexibility feature of the baffles contributes not only in directing the coolant towards the hot blocks, but also contributes in reducing the skin friction and pressure drop through the channel. At Re=150, the skin friction and pressure drop of the flexible baffles are 13.2% and 16.5%, respectively lesser than the rigid baffles. The improvement of Nusselt number with flexibility parameter is marginal and within a limited low Reynolds number, where the maximal improvement is about 3.4% at Re=150.

Multi-objective optimization of a non-uniform sinusoidal mini-channel heat sink by coupling genetic algorithm and CFD model

Wavy mini-channel heat sinks (MCHS) can disrupt the development of the thermal boundary layer, resulting in superior performance compared to straight MCHS. For complete utilization of the coolant, this study proposed and optimized a non-uniform sinusoidal MCHS with varying wavelength or varying amplitude along the flow direction. The optimization for five design variables was accomplished through a multi-objective genetic algorithm, where the thermal resistance θ or the pressure drop Δp were defined as two objectives. The computational fluid dynamics (CFD) software was employed to solve all direct problems encountered during the evolutionary process. Compared to the straight MCHS with different channel widths, the optimal designs achieved reductions of 27.74 % in θ or 59.51 % in Δp. Simultaneously, all the optimal values of the wavelength ratio and amplitude ratio indicate that enhancing the heat transfer performance downstream is more efficient. It was observed that among the five design variables, the number of wave cycles is the most relevant parameter with a Spearman’s correlation up to 0.983. Subsequently, a multiple-criteria decision-making approach was employed to ascertain the best compromise solution to balance the two objectives. Although the θ of the best compromise solution could be higher by 38.57 % than that of the lowest θ solution, the Δp presents a more substantial reduction of 92.45 % after the trade-off. Compared to the straight MCHS with the same Δp, the best compromise solution with varying wavelength reduces the θ and the standard temperature deviation by 26.20 % and 76.98 % respectively, while lowering the average base temperature by 3.07 K. Therefore, the optimal non-uniform wavy MCHS, along with the optimization approach presented, is meaningful for practical applications.

Flow analysis of water conveying nanomaterials over a rotating surface with thermal radiation

PurposeThe present findings aim to investigate the thermal behavior of water-based nanofluid flow over a rotating surface, focusing on understanding the effects of different types of nanoparticles on thermal efficiency, considering thermal radiation and variable viscosity effects. By considering four distinct nanoparticles – silicon dioxide titanium dioxide, aluminum oxide and molybdenum disulfide – the study aims to provide insights into how nanoparticle addition influences heat production, thermal boundary layer thickness and overall thermal performance.Design/methodology/approachThe study employs computational methods, utilizing the BVP mid-rich algorithm for the solution procedure. The computational approach allows for a detailed investigation of the thermal behavior of nanofluid flows across a rotating surface under varying conditions.FindingsThe study concludes that adding nanoparticles in the base liquid increases heat production in the system, resulting in enhanced thermal boundary layer thickness. The comparative analysis shows that different nanoparticle types exhibit varying effects on thermal efficiency, suggesting that careful selection of nanoparticles can optimize heat transport and thermal management processes. Moreover, there's a noteworthy uptrend in the radial velocity profile concerning the stretching parameter, whereas a converse trend is observed in the thermal profile.Originality/valueThis study contributes original insights by comprehensively investigating the thermal behavior of water-based hybrid nanofluid flow over a rotating surface.

Linear stability analysis of micropolar nanofluid flow across the accelerated surface with inclined magnetic field

PurposeThe purpose of this paper is to study the two-dimensional micropolar fluid flow with conjugate heat transfer and mass transpiration. The considered nanofluid has graphene nanoparticles.Design/methodology/approachGoverning nonlinear partial differential equations are converted to nonlinear ordinary differential equations by similarity transformation. Then, to analyze the flow, the authors derive the dual solutions to the flow problem. Biot number and radiation effect are included in the energy equation. The momentum equation was solved by using boundary conditions, and the temperature equation solved by using hypergeometric series solutions. Nusselt numbers and skin friction coefficients are calculated as functions of the Reynolds number. Further, the problem is governed by other parameters, namely, the magnetic parameter, radiation parameter, Prandtl number and mass transpiration. Graphene nanofluids have shown promising thermal conductivity enhancements due to the high thermal conductivity of graphene and have a wide range of applications affecting the thermal boundary layer and serve as coolants and thermal management systems in electronics or as heat transfer fluids in various industrial processes.FindingsResults show that increasing the magnetic field decreases the momentum and increases thermal radiation. The heat source/sink parameter increases the thermal boundary layer. Increasing the volume fraction decreases the velocity profile and increases the temperature. Increasing the Eringen parameter increases the momentum of the fluid flow. Applications are found in the extrusion of polymer sheets, films and sheets, the manufacturing of plastic wires, the fabrication of fibers and the growth of crystals, among others. Heat sources/sinks are commonly used in electronic devices to transfer the heat generated by high-power semiconductor devices such as power transistors and optoelectronics such as lasers and light-emitting diodes to a fluid medium, thermal radiation on the fluid flow used in spectroscopy to study the properties of materials and also used in thermal imaging to capture and display the infrared radiation emitted by objects.Originality/valueMicropolar fluid flow across stretching/shrinking surfaces is examined. Biot number and radiation effects are included in the energy equation. An increase in the volume fraction decreases the momentum boundary layer thickness. Nusselt numbers and skin friction coefficients are presented versus Reynolds numbers. A dual solution is obtained for a shrinking surface.

Enhancing the heat transfer efficiency of an engine heat exchanger through the utilization of an innovative conical braided wire turbulator

This study introduces innovative turbulators with unique geometries, namely the Conical Simple Wire Turbulator (CSWT) and Conical Braided Wire Turbulator (CBWT), designed to enhance heat transfer in a constant temperature tube. These turbulators resemble a conical shape in appearance but are constructed by interconnecting multiple wires, enabling fluid flow to pass through. The distinct geometry of these turbulators not only disrupts the thermal boundary layer for improved heat transfer and Thermal Enhancement Factor (TEF), and results in a favorable pressure drop. The study explored various geometrical parameters of the turbulator, including wire diameters (a) ranging from 0.5 to 1.5 mm and turbulator gaps (TG) ranging from −10 to 30 mm. Using the RNG k–ε model, the finite-volume scheme is utilized to discretize the turbulence flow equations. A numerical investigation was conducted across Reynolds numbers ranging from 5500 to 12375. The results show that increasing the wire diameter and reducing the turbulator gaps simultaneously enhanced heat transfer, pressure drop, and TEF. The highest heat transfer and TEF were achieved with the CBWT featuring a 1.5 mm wire diameter and a −10 mm TG. In this configuration, Nusselt was 2.84 times greater than a plain tube, with a maximum TEF recorded at 1.4.

Membrane fouling analysis of air-gap membrane distillation (AGMD) for recovery of water and removal of antibiotics from a model wastewater containing antibiotics and humic acid

The study investigates the efficiency of air-gap membrane distillation (AGMD) in water recovery and antibiotics removal from wastewater, focusing on high-concentration scenarios. Experimental findings reveal enhanced membrane performance with increasing the feed temperature, resulting in vapor permeate fluxes of up to 5 kg/m2.h at higher temperatures. Despite experiencing flux reduction caused by fouling from humic acid (HA) in the feed antibiotics solution, the antibiotics consistently maintain near-complete rejection rates (>99%) over 48 h. The foulant on the membrane surface was illustrated by SEM imaging. To know the temperature polarization and the fouling resistance, mathematical modeling was used, and it validates experimental results, elucidating temperature polarization effects and mass transfer coefficients. An increase in feed flow rates reduced thermal boundary layers, enhancing heat flux. Higher temperatures reduced HA fouling resistance. Therefore, AGMD proves effective in water recovery and antibiotics removal, with mathematical models aiding fouling understanding for future research and detailed computational fluid dynamics (CFD) models.

Bio-Convective Flow of Micropolar Nanofluids over an Inclined Permeable Stretching Surface with Radiative Activation Energy

The focal concern of this study is to examine the behaviour of bio-convective flow featuring micropolar nanofluids over an inclined permeable stretching surface while considering the influence of radiative activation energy. This investigation addresses the complex interplay of factors such as biological activity, convective heat and mass transfer, unique attributes of micropolar fluids, the dynamics of nanofluids, and radiative effects. This analysis employed Buongiorno’s model, considering thermal radiation and activation energy on the bioconvective flow of micropolar nanofluids over an inclined stretching surface. Some suitable similarity variables were used to obtain a set of non-linear differential equations from the initial partial differential equations which were then solved numerically using the Runge-Kutta Fehberg method along with shooting technique. The effects of some physical parameters were examined on the velocity, temperature, concentration, and microorganism density profiles of the flow. The result revealed that each increase in the heat source/sink, thermal radiation, thermophoresis, and Brownian motion lead to a corresponding increase in the thermal boundary layer; activation energy increased the concentration while Peclet number and bioconvective Lewis number declined the microorganism density profile. Insights gleaned from this study can find applications in biomedical fields. Understanding the behavior of bio-convective nanofluids has implications for controlled heat transfer in medical applications like hyperthermia treatments or targeted drug delivery, thereby impacting patient care.

Numerical investigation of the sensible heat storage in novel electrostatic precipitators with liquid-filled collection electrodes

Heat recovery from flue gas holds significant potential for energy conservation. A strategy is proposed for recovering and storing heat in electrostatic precipitators by utilizing liquid-filled collection electrodes. In the prototype, the hollow collection electrode is connected to the heat storage tank. Convective heat transfer occurs between the gas stream and the liquid contained in the collection electrode. The heat storage mechanism is revealed by numerical simulation of corona discharge, flow and heat transfer processes in a simplified electrostatic precipitator. The results indicate that both the gas-side and liquid-side heat transfer coefficients reach steady values within approximately 100 s. The buoyancy-driven liquid flow results in a heat transfer coefficient that is 28 times higher than that for gas-side forced convection. Increasing the gas inlet temperature leads to a greater buoyancy force and, consequently, a higher heat transfer coefficient on the liquid side. Both ionic wind and inlet velocity affect the gas-side heat transfer. The ionic wind disturbs the thermal boundary layer, leading to a 27.9 % increase in the gas-side heat transfer coefficient at an inlet velocity of 0.5 m/s. Furthermore, this enhancement becomes more pronounced as the inlet velocity decreases. The flow pattern of liquid in the collection electrode and heat storage tank is crucial to the heat storage process. Additionally, installing the heat storage tank above the electrostatic precipitator provides added benefits. During the process of heat storage, the largest heat resistance is found on the gas side.