Narrow Results

Research Problem: The importance of improving the temperature properties of commonly used fluids in industrial processes is being addressed in this research. Nanofluids, which are composed of extremely small particles dispersed in common liquids such as water or petrol, are the main subject of this area of study. Using a vertically stretchable surface subjected to thermal radiation, the study examines the heat transfer behavior and efficiency of nanofluids.

Methodology: Nanofluids that convey heat are studied by applying the fundamental rules of fluid physics to the variables that control their motion. To measure the amount of energy transferred, a nanofluid model is used. Similarity transformations are used to convert the system’s differential equations into ordinary differential equations (ODEs). The subsequent set of nonlinear ODEs is solved using numerical methods. Utilizing graphical analysis, patterns of velocity and temperature may be seen, and their responses to changes in other parameters can be investigated.

Implications: This research has important implications for our knowledge of how nanofluids act in heat transfer applications, especially when exposed to thermal radiation and working with vertically stretchy surfaces. The effects of flow direction and thermal conductivity on distributions of velocity and temperature were elucidated, among other important results. More effective heating and cooling systems may be possible as a result of these findings, which have consequences for improving heat transfer processes in industrial environments.

Future Work: To better understand how nanofluids behave in heat transfer applications, future studies might investigate more complicated situations and boundary circumstances. It may be possible to optimize nanofluid formulations by studying the impact of various nanoparticle kinds and concentrations on heat transfer efficiency. Research could be more applicable to real-world industrial processes if the numerical results were experimentally validated.

In this paper, fluid flows with enhanced heat transfer in porous channels are investigated through a stable finite volume (FV) formulation of the thermal lattice Boltzmann method (LBM). Temperature field is tracked through a double distribution function (DDF) model, while the porous media is modeled using Brinkman–Forchheimer assumptions. The method is tested against flows in channels partially filled with porous media and parametric studies are conducted to evaluate the effects of various parameters, highlighting their influence on the thermo-hydrodynamic behavior.

The characteristics of heat transfer from a hot wall surface for the oblique impingement of a free turbulent slot jet have been investigated numerically. Different turbulent models — the $k$-$ϵ$, $k$-$\omega$, SST $k$-$\omega$, cubic $k$-$ϵ$ and quadratic $k$-$ϵ$ models — are used for the prediction of heat transfer and their results were compared with experimental results reported in the literature. The comparison shows that the $k$-$ϵ$, quadratic $k$-$ϵ$ and SST $k$-$\omega$ models give more unsatisfactory results for the investigated configuration, while the cubic $k$-$ϵ$ model is capable of predicting the local Nusselt number in wall-jet region only. The $k$-$\omega$ model exhibits the best agreement with the experimental results in both stagnation and wall-jet regions. Further, the $k$-$\omega$ model is applied to analyze the obliquely impinging jet heat transfer problem. The parametric effects of the jet inclination ($\varphi =50^{\circ }$, $70^{\circ }$ and $90^{\circ }$), jet-to-surface distance ($\frac{d}{L}=4$, 6 and 8), Reynolds number ($\mathrm{\text{Re}}=12000$, 15000 and 20000), and turbulent intensity ($I=5\%$, $7.5\%$ and $10\%$) have been presented. The heat transfer on the upward direction is seen to decrease, while that on the downward direction it rises for the increasing angle. It is to be noted that as the value of $\varphi$ decreases, the point of maximum Nusselt number (${\mathrm{\text{Nu}}}_{max}$) displaces toward the upward direction from the geometric center point as well as its value reduces. The shifting of the ${\mathrm{\text{Nu}}}_{max}$ is found to be independent of Re and $\frac{d}{L}$ within the range considered for the study.

The hydrodynamics and thermal characteristics due to mixed convection in a vertical two-sided lid-driven differentially square cavity containing four hot cylinders in a diamond array are investigated by the lattice Boltzmann equation model. The moving walls of the cavity are cold while the others are adiabatic. The flow in the cavity is driven by both the temperature difference and the moving vertical walls. The influence of different flow governing parameters, including the direction of the moving walls (the left wall moves up and the right wall moves down (Case I), both the left and right walls are moving upward (Case II), both the left and right walls are moving downwards (Case III)), the distance between neighboring cylinders $\delta$ ($0.3L\le \delta \le 0.5L$), and the Richardson number $\text{Ri}$ ($0.1\le \mathrm{\text{Ri}}\le 10$) on the fluid flow and heat transfer are investigated with the Reynolds number in the range of $375\le \mathrm{\text{Re}}\le 3752$, the Grashof number of $1.4\times 10^6$ and the Prandtl number of $\mathrm{\text{Pr}}=0.71$. Flow and thermal performances in the cavity are analyzed in detail by considering the streamlines and isotherms profiles, the average Nusselt number, as well as the total Nusselt number. It is found that the heat transfer efficiency is highest when $\mathrm{\text{Ri}}=1.0$ for the cases of the walls moving in the opposite direction. When the walls move in the same directions, the heat transfer efficiency obtained by $\mathrm{\text{Ri}}=0.1$ is maximum among the considered values of $\text{Ri}$. On the other hand, compared with the cases of $\mathrm{\text{Ri}}=1.0$ and $\mathrm{\text{Ri}}=10$, the cylinder positions corresponding to the largest and the smallest Nusselt numbers are very sensitive to the moving direction of the walls for $\mathrm{\text{Ri}}=0.1$. Moreover, the results also show that in terms of the value of Nusselt number and the stability the case of both walls moving downwards works well. Besides, the effect of the distance between neighboring cylinders is also discussed, it is found that increasing or decreasing the spacing between cylinders could enhance heat transfer to different degrees for the range of $\text{Ri}$ number considered. Finally, the empirical relationships among ${\mathrm{\text{Nu}}}_{\mathrm{\text{ave}}}$, $\text{Ri}$, and the spacing between the cylinders ($\delta$) are given, and predictive results match with the computed values very well.

To evaluate the heat transfer performance (HTP) of hybrid nanofluids, numerical simulations are carried out in an industrial length single pass shell and tube heat exchanger. In shell, ISO VG 68 oil enters with $75^{\circ }$C and with $30^{\circ }$C, the coolant passes into the tube. CNT-${\mathrm{\text{TiO}}}_2$/water and CNT-${\mathrm{\text{TiO}}}_2$/sodium alginate (SA) are used as Newtonian and non-Newtonian hybrid nanofluid, respectively. The influence of base fluid and nanoparticles on thermal performance of heat exchanger is studied. The chosen nanoparticles are reliable to the industrial deployment. The current numerical procedure is validated with the earlier experimental results. Volume fraction of nanoparticles is optimized for an effective HTP of the heat exchanger. About 60% increment in heat transfer coefficient is observed when hybrid nanofluid is employed. By using Newtonian hybrid nanofluid, 50% improvement in Nusselt number is marked out. Effectiveness and heat transfer rate of heat exchanger are higher with the employment of Newtonian hybrid nanofluid. Results indicated that, even though Newtonian hybrid nanofluid shows higher thermal performance, non-Newtonian hybrid nanofluid is preferable for energy consumption point of view.

Natural convection takes up the attention of researchers due to its expansive industrial and engineering utilizations i.e., heat exchangers and electronic cooling. In this work, free convection of Cu-H₂O nanoliquid flow and heat transfer (HT) in porous circular wavy domain under the internal heat generation has been perused by finite element method (FEM). The shape factor of nanomaterials is also considered. The influences of active factors like Rayleigh number Ra, nanofluid concentration, wavy wall’s contraction ratio A, number of undulations D, and shape factor of nanomaterials m are explored on flow and HT specifications. Moreover, the correlations for average Nusselt number Nu_ave have been attained with regard to impressive parameters of current study. Findings show that Nu_ave soars with soaring nanofluid concentration and nanoparticles’ shape factor. Further, the outcomes characterize that Nu_ave may lessen up to 15.11% and 9.95% by detracting A from 0.1 to 0.3 and by mounting D from 4 to 12, respectively.

The paper’s primary goal is to investigate mass and heat transfer processes in reactive nanofluid particles. Within Buongiorno’s model, three chemical reactions are discussed. The main subject is on the nanoparticle fractions at the boundary. The characteristics of $Nt$ and $Nb$ with regard to the nanoparticle fraction have been found to be passively rather than actively controlled at the boundary. To put it another way, these qualities naturally develop and are controlled by the circumstances at the boundary or interface where the nanoparticles interact with the surrounding medium. They are not the result of active manipulation or outside forces. The system of partial differential equations was converted into ordinary differential equations using similarity transformations. To solve the system of ODEs, they combined the shooting method with a numerical technique known as RK-Fehlberg. The study examines various physical parameters and their effects using graphs. The paper also contains a table showing how different parameters affect the regional Nusselt and Sherwood numbers. This enables a deeper comprehension of the impact that these variables have on the heat and mass transfer within the reactive nanofluid particles. Core findings: Examining three chemical reactions involving nanofluids has led to the study’s key discoveries. Additionally, it looks into how specific physical variables may affect the Nusselt and Sherwood numbers.

The physical properties of incompressible fluids used in heat exchangers, such as viscosity and thermal conductivity, change considerably with temperature during their normal operating conditions. This study investigates the heat transfer characteristics of microchannel flows by taking these variations into account. Our results demonstrate that the temperature effects are significant and must be taken into account if accurate predictions are to be obtained.

An experimental study on the heat transfer characteristics of the steam bubbles generated by steam injection was performed. The bubble Nusselt number and Reynolds number were calculated based on the visual observation. The steam bubble Reynolds number and water subcooling were 600–360,000 and 15–60 K, respectively. In the large range of steam bubble Reynolds number, it was found that the heat transfer correlation in previous literatures cannot accurately predict the heat transfer coefficient of steam bubble. Based on the experimental results, the steam bubble Reynolds range was divided into three sections, namely 600–3000, 3000–22,000 and 22,000–360,000, to analyze the bubble heat transfer coefficient. Three experimental correlation formulas were obtained to calculate the steam bubble interfacial heat transfer coefficient, with deviations within ±30%. By comparing these three correlations, it was found that with the increase of Re${}_b$, the exponential coefficient of Re${}_b$ term in the correlation of Nu${}_c$ increased, and the absolute value of Ja term exponential coefficient decreased. The results indicated that with the increase of Re${}_b$, the influence of Re${}_b$ on bubble heat transfer increased, and the influence of water subcooling on bubble heat transfer decreased.

In this article, Magnetohydrodynamic (MHD) squeezing flow between two parallel disks is considered. The upper disk is taken to be solid and the lower one is permeable. Soret and Dufour effects are measured to explore the thermal-diffusion and diffusion-thermo effects. Governing PDEs are converted into system of ODEs with the support of suitable similarity transforms. Homotopy analysis method (HAM) has been employed to obtain the expressions for velocity, temperature and concentration profiles. Effects of different emerging parameters such as squeezing number $S$, Hartman number $M$, Prandtl number Pr, Eckert number Ec, dimensionless length $\delta$ and Schmidt number Sc on the flow are also discussed with the help of graphs for velocity, temperature and concentration. The local Nusselt and Sherwood numbers along with convergence of the series solutions are presented with the help of graphs. From the results obtained, we observed that the physical quantities like skin friction coefficient increases with increasing value of Hartmann number $M$ in the blowing case $(A<0)$ whereas a fall is observed in the suction case $(A>0)$. However, the rate of heat transfer at upper wall increases with increasing values of Dufour number Du and Soret number Sr for both the suction $(A>0)$ and blowing flow $(A<0)$, whereas, for the larger values of Dufour number Du and smaller values of Soret number Sr, a rapid fall is observed in Sherwood number Sh for both the suction $(A>0)$ and blowing $(A<0)$ cases. A numerical solution is obtained by employing Runge–Kutta method of order four (RK-4) to check the validity and reliability of the developed algorithm. A well agreement is found between both the solutions.

The present investigation deals with a mathematical model representing the response of heat transfer to blood streaming through the arteries under stenotic condition. The flowing blood is represented as the suspension of all erythrocytes assumed to be Casson fluid and the arterial wall is considered to be rigid having differently shaped stenoses in its lumen arising from various types of abnormal growth or plaque formation. The governing equations of motion accompanied by the appropriate choice of the boundary conditions are solved numerically by Marker and Cell (MAC) method. The necessary checking for numerical stability has been incorporated into the algorithm for better precision of the results computed. The quantitative analysis carried out finally includes the respective profiles of the flow-field and the temperature along with their individual distributions over the entire arterial segment as well. The key factors like the pressure drop, wall shear stress, flow separation, Nusselt number and streamlines are examined for qualitative insight into the blood flow and heat transport phenomena through arterial stenosis. In conformity with other several existing findings the present simulation predicts that the pressure drop and Nusselt number diminishes with increasing yield stress values, and significant enhancement in values of Nusselt number is observed with increasing severity of the stenosis. However, the effect of the shapes of the stenoses on flow separation cannot be ruled out from the present investigation.

In this paper, we present a numerical study of the radiation-natural convection interactions in a differentially heated enclosure, within which a centered, squared, heat-conducting body generates heat. A specifically developed numerical model based on the finite-volume method and the SIMPLER algorithm is used for the solution of the governing equations. The working fluid (air) is perfectly transparent to the radiation. The Rayleigh number Ra and the temperature-difference ratio ΔT* were varied parametrically. For Pr = 0.71, the results obtained show that: (i) The isotherms and streamlines are strongly affected by the radiation exchange at high Rayleigh numbers (Ra ≥ 10⁶), (ii) the temperature of the inner body decreases under the radiation exchange effect, (iii) for a constant Ra, the average Nusselt number at the hot and cold walls (Nu_h and Nu_c) vary linearly with increasing ΔT*: Nu_h decreases with ΔT* while Nu_c increases with ΔT*. Furthermore, the radiation exchange increases both average Nusselt numbers Nu_h and Nu_c, especially at Ra ≥ 10⁵, and consequently, increases.

Unsteady simulations were performed to investigate time dependent behaviors of the leakage flow structures and heat transfer on the rotor blade tip and casing in a single stage gas turbine engine. This paper mainly illustrates the unsteady nature of the leakage flow and heat transfer, particularly, that caused by the stator–rotor interactions. In order to obtain time-accurate results, the effects of varying the number of time steps, sub iterations, and the number of vane passing periods was firstly examined. The effect of tip clearance height and rotor speeds was also examined. The results showed periodic patterns of the tip leakage flow and heat transfer rate distribution for each vane passing. The relative position of the vane and vane trailing edge shock with respect to time alters the flow conditions in the rotor domain, and results in significant variations in the tip leakage flow structures and heat transfer rate distributions. It is observed that the trailing edge shock phenomenon results in a critical heat transfer region on the blade tip and casing. Consequently, the turbine blade tip and casing are subjected to large fluctuations of Nusselt number (about Nu = 2000 to 6000 and about Nu = 1000 to 10000, respectively) at a high frequency (coinciding with the rotor speed).

The present work considered fluid circulation in an annular region between two cylinders with the inner cylinder heated and rotating. The Prandtl number (Pr) considered here varies from 0.01 to 1.0 and Rayleigh number (Ra) is of the order of 10⁵. Reynolds number Re in the range of 0 to 1120 was considered. Mono-thermal plume above the stationary inner was observed for higher Prandtl number fluids (Pr≫0.1) while bi-thermal plume above the stationary inner cylinder was observed for lower Prandtl number fluids (Pr≪0.1). However, when the inner cylinder is made to rotate, the thermal plume for higher and lower Prandtl number fluids were observed to move in different directions. The mechanism of the mono- and bi-thermal plumes movements were investigated through numerical flow simulations.

Bioconvection has shown significant promise for environmentally friendly, sustainable “green” fuel cell technologies. The improved design of such systems requires continuous refinements in biomathematical modeling in conjunction with laboratory and field testing. Motivated by exploring deeper the near-wall transport phenomena involved in bio-inspired fuel cells, in the present paper, we examine analytically and numerically the combined free-forced convective steady boundary layer flow from a solid vertical flat plate embedded in a Darcian porous medium containing gyrotactic microorganisms. Gyrotaxis is one of the many taxes exhibited in biological microscale transport, and other examples include magneto-taxis, photo-taxis, chemotaxis and geo-taxis (reflecting the response of microorganisms to magnetic field, light, chemical concentration or gravity, respectively). The bioconvection fuel cell also contains diffusing oxygen species which mimics the cathodic behavior in a proton exchange membrane (PEM) system. The vertical wall is maintained at iso-solutal (constant oxygen volume fraction and motile microorganism density) and iso-thermal conditions. Wall values of these quantities are sustained at higher values than the ambient temperature and concentration of oxygen and biological microorganism species. Similarity transformations are applied to render the governing partial differential equations for mass, momentum, energy, oxygen species and microorganism species density into a system of ordinary differential equations. The emerging eight order nonlinear coupled, ordinary differential boundary value problem features several important dimensionless control parameters, namely Lewis number (Le), buoyancy ratio parameter i.e. ratio of oxygen species buoyancy force to thermal buoyancy force (Nr), bioconvection Rayleigh number (Rb), bioconvection Lewis number (Lb), bioconvection Péclet number (Pe) and the mixed convection parameter ($𝜀)$ spanning the entire range of free and forced convection. The transformed nonlinear system of equations with boundary conditions is solved numerically by a finite difference method with central differencing, tridiagonal matrix manipulation and an iterative procedure. Computations are validated with the symbolic Maple 14.0 software. The influence of buoyancy and bioconvection parameters on the dimensionless temperature, velocity, oxygen concentration and motile microorganism density distribution, Nusselt, Sherwood and gradient of motile microorganism density are studied. The work clearly shows the benefit of utilizing biological organisms in fuel cell design and presents a logical biomathematical modeling framework for simulating such systems. In particular, the deployment of gyrotactic microorganisms is shown to stimulate improved transport characteristics in heat and momentum at the fuel cell wall.

Heat transfer using air jet impingement technique is one of the conspicuous tasks in the looming world of electronic packaging system. Here, the material selection of heat sink becomes one of the prior and important assignments to construct a heat sink with desired characteristic cooling rate. In order to study the material effect of heat sink over the cooling characteristic, the present work takes an initiative in plotting the Nusselt magnitude over the radial distance for different material of heat sink. This is done by computing the flow regime and heat transfer characteristic of a 2D axis symmetric geometry in commercial simulating software, ANSYS CFX. The computation of cooling characteristic in form of Nusselt profile is done using SST + Gamma–theta turbulence model. Since the prediction of heat interaction due to the intermediacy and transition in the flow regime is a unique issue of this problem. The results for Nusselt curve signifies a tangible elevation in local Nusselt value (nonuniformity) with decrease in thermal diffusivity of target surface. Also the nonuniformity is observed to vanish above a critical range (66.76mm²/s) of thermal diffusivity. This happens due to presences of abnormal turbulence of heat flow which occurs inside the target surface. Since the variation in thermal diffusivity causes some imbalance competition between the heat storage and dissipation capabilities. Above all the target surface carrying thermal diffusivity less than 66.76mm²/s possesses a dominating heat storage capability, on behalf of which some heat transfer occurring in near jet and far jet regions are being restricted. These are transferred towards stagnation region in radial direction.

In this paper, the assumptions implicited in Leveque’s approximation are re-examined, and the variation of the temperature and the thickness of the boundary layer were illustrated using the developed solution. By defining a similarity variable, the governing equations are reduced to a dimensionless equation with an analytic solution in the entrance region. This report gives justification for the similarity variable via scaling analysis, details the process of converting to a similarity form, and presents a similarity solution. The analytical solutions are then checked against numerical solution programming by FORTRAN code obtained via using Runge–Kutta fourth order (RK4) method. Finally, other important thermal results obtained from this analysis, such as; approximate Nusselt number in the thermal entrance region was discussed in detail. A comparison with the previous study available in literature has been done and found an excellent agreement with the published data.

This paper aims to study the convective heat transfer behavior of aqueous suspensions of nanoparticles flowing through a horizontal tube heated under constant heat flux condition. Consideration is given to the effects of particle concentration and Reynolds number on heat transfer enhancement and the possibility of nanofluids as the working fluid in various heat exchangers. It is found that (i) significant enhancement of heat transfer performance due to suspension of nanoparticles in the circular tube flow is observed in comparison with pure water as the working fluid, (ii) enhancement is intensified with an increase in the Reynolds number and the nanoparticles concentration, and (iii) substantial amplification of heat transfer performance is not attributed purely to the enhancement of thermal conductivity due to suspension of nanoparticles.

In this paper, the swirling nanofluid flow which is driven by a rotating bottom disk of a cylindrical container under magnetic field effect and temperature gradient is considered. Effects of electrical conductivity of cylindrical walls on heat transfer enhancement are numerically analyzed. The governing equations that describe the combined problem (magnetohydrodynamics and mixed convection) under the adoptive assumptions are solved numerically by the finite volume technique. Calculations were made for fixed Reynolds number (Re$=$1000), Richardson number (0$\le$Ri$\le$2), aspect ratio ($H/R=2$), Hartmann number (0$\le$Ha$\le$60), and solid nanoparticle (copper) with volume fraction ($\varphi =0.1$). Five cases are considered in this study: (EI-Walls), (EC-Walls), (EC-Bottom), (EC-Top), and (EC-Sidewall). A decrease in the mean Nusselt number was found with the increase of the Richardson number due to stratification layers. These latter limits the heat transfers between the hot and cold zones of the cylinder. The results indicate that the Nusselt number gets bigger within a certain range of Hartmann numbers, and especially when the rotating lid is electrically conducting. Indeed, average Nusselt number decreases while the Hartmann number increase after it exceeds a critical value. Finally, the electrical conductivity of the rotating lid plays an important role in heat transfer enhancement in nanofluid swirling flow.