Variation Of Nusselt Number Research Articles

Heat storage unit for melting of paraffin considering hybrid nanomaterial and helical tubes

In current article, spiral pipe has been employed in heat storage unit. The spiral pipe which contain the hot hybrid nanomaterial insert in the square cylinder which is full of RT82. To augment the conductivity of current paraffin, Cu with volume fraction of 0.04 has been added. The buoyancy effect has been involved in momentum equations and final PDEs were solved. Contours of streamline, temperature and liquid fraction in three time steps for two level of Re have been reported in outcomes as well as variation of Nusselt number. In both initial and end time of melting, augment of Re has no sensible impact on rate of charging but in other range of time, heat storage capacity declines with rise of time. At t = 10 min, Lf for Re=100 is 0.81% greater than that of Re=500. At Lf=0.5 and 0.8, Nusselt number augments about 46% and 34.2% with augment of Re.

Heat transfer and flow velocity study of a row of jets emerging from a perforated pipe at a low Reynolds number

Aerodynamic and thermal experimental investigations were carried out on a row of circular low Reynolds jets emerging from a perforated pipe. Particle Image Velocimetry and Infrared Thermography were performed to determine flow velocity fields and local Nusselt number variations along the impinged plate. Jet Reynolds number (1500<Rej<5000), upstream crossflow in the pipe (1.5<VR<9.7), injection-to-plate distance (3<H/d<7) as well as center-to-center jet spacing (2.25<p/d<5.8) were all taken into account. Measurements were compared to those of a fully developed circular jet issuing from a long tube under the same conditions (3000<Rej<5000 and 3<H/d<7). Experimental results showed that jets tend to emerge with an effective cross-sectional area reduced to a crescent shape unlike that of axisymmetric fully developed jets; their specific structure was attributed to flow deflection from the pipe to the holes and resulted in heat transfer specificities differing from those of a fully developed jet. Heat transfer rates were found to be primarily dependent on injection Reynolds number, injection-to-plate distance and center-to-center spacing, and they were found to be relatively low compared to a fully developed jet.

Impact of aspect ratio and thermophysical properties on heat transfer behavior in spiral microchannel

The heat transfer characteristics in spiral microchannels are studied numerically in this present work. Impact of aspect ratios (α = 0.5–2) and Reynolds number (Re = 15–1200) on Poiseuille number (f.Re) and Nusselt number (Nu) is investigated with the help of local flow patterns. Three-dimensional numerical simulations are performed by varying the Reynolds number at the inlet of spiral microchannel supplied with constant heat flux boundary condition and considering thermo-physical property variation. It is observed that, in the Dean flow regime, the Poiseuille number and Nusselt number vary directly with Reynolds number whereas they vary inversely with aspect ratio. However, some non-monotonous variation of Nusselt number is reported in spiral microchannel having aspect ratio equal to unity. This behavior has been explained with the help of merging and splitting of vortices along the flow direction. Interestingly, all the aspect ratio microchannels exhibit comparatively same thermal performance factor but different temperature homogeneity. These findings have direct implication in the design of micro heat sinks and microreactors employing spiral microchannels.

Effect of Nanoparticle Shape and Volume Fraction on Nanofluid Flow in Serpentine Microtube

The nanofluid flow in serpentine microtube was numerically investigated in this study. The study has been carried out in three-dimensional laminar flow (750≤Re≤2000) condition. Al2O3 – water nanofluid with different nanoparticle volume fractions (1.0%, 2.0%, 3.0%) have been used as the working fluid in the numerical analyzes. In addition, studies were carried out for blade, platelet and cylindrical nanoparticle shapes. The average Nusselt numbers and the average Darcy friction factors have been used to estimate the flow and heat transfer performance of nanofluid flow in serpentine microtubes. Velocity and temperature distributions inside the microtube were also examined for different cases. Numerical results of the study have been presented as the variation of average Nusselt number and average Darcy friction factor with Reynolds number, nanoparticle shape and nanoparticle volume fraction. As a result, the highest convective heat transfer performance has been obtained for platelet nanoparticle shape of the Al2O3-water nanofluid with 3.0% nanoparticle volume fraction.

HEAT TRANSFER WITH VISCOUS DISSIPATION AND FLUID AXIAL HEAT CONDUCTION FOR FLOW THROUGH A CIRCULAR PIPE

Purpose: To investigate the effect of viscous dissipation and axial conduction on heat transfer for laminar forced convection flow through a circular pipe was studied. Constant wall temperature boundary condition was imposed on the circular pipe and the flow is assumed to be hydro dynamically developed and thermally developing. Methodology: Numerical solutions were obtained to observe the variations of non-dimensional bulk mean temperature, Nusselt number and wall heat from (or) to the fluid for Brinkman numbers   1.0, 0.5, 0.2,0.0 and Peclet numbers 10,50,100,300 and 500. Results: It was found that the heat generated by viscous dissipation was higher for higher Brinkman number and it delays the thermal entrance development of the fluid. Unique Contribution to Theory and Practice: Effect of axial conduction becomes negligible when the value of Peclet number crosses hundred

Slip Effects on MHD Boundary Layer Flow over a Flat Plate in Casson Ferrofluid

Present study investigated the slip effects on boundary layer flow and heat transfer on a horizontal flat surface immersed in blood-based Casson ferrofluid. The magnetite and cobalt ferrite ferroparticles suspended into Casson fluid represent by human blood to form Casson ferrofluid are numerically analysed. The study began with the transforming the governing equations which in dimensional partial differential equations to non-dimensional ordinary differential equations by using the similarity variable. Resulting similarity equations then solved by Runge-Kutta-Fehlberg (RKF45) method. The characteristics and effects of the slip parameter, the magnetic parameter and the ferroparticles volume fraction for magnetite and cobalt ferrite on the variation of Nusselt number and the skin friction coefficient are analyzed and discussed.

Effect of non-uniform heating on conjugate heat transfer performance for nanofluid flow in a converging duct by a two-phase Eulerian–Lagrangian method

In this paper, the effect of non-uniform heating on the conjugate thermal and hydraulic characteristics for Al2O3–water nanofluid flow through a converging duct is examined numerically. An Eulerian–Lagrangian model is employed to simulate the two-phase flow for the following range of parameters: Reynolds number (100 ≤ Re ≤ 800), nanoparticle volume fraction (0% ≤ ϕ ≤ 5%) and amplitude of the sinusoidal heat flux ( A = 0, 0.5 and 1). The results reveal a similar affinity between the applied heat flux and local Nusselt number variation qualitatively, mainly at the middle of the duct. The results also indicate that there is a considerable enhancement of Nusselt number with the increase in Reynolds number and the thermal conductivity of wall materials. In addition, increasing the particle loading contributes to an enhanced rate of heat transfer. The heat transfer rate is lower for non-uniform heating when compared with the constant heat flux and the same can be compensated by the application of volume fraction of nanoparticles

Effect of thermal radiation on MHD three dimensional natural convective Couette flow in presence of thermo-diffusion and chemical reaction

This paper analyzes the effect of thermal radiation on MHD three dimensional natural convective Couette flow of an incompressible, viscous and electrically conducting fluid with uniform magnetic field. The plates are taken vertically upward. The magnetic field is applied normal to the plates. The governing equations are solved using simple perturbation technique. The effect of various parameters like M , Pr , R , Re , Gr , Gm etc. are studied graphically on dimensionless velocity, temperature and concentration. Also the variations in shear stress ( τ ), Nusselt number ( Nu ) and Sherwood number ( Sh ) for different physical parameters are presented in tables.

OHAM analysis of Newtonian heating in mixed convective flow of CNTs over a stretched cylinder

This work reports mathematical modeling and analysis of mixed convection flow of nanofluids with stagnation point by a stretching cylinder. Carbon nanotubes are dispersed as nanomaterial in the baseliquid of water. Heat transfer characteristics are explored through Newtonian heating. Transformation method is employed in order to obtain ODEs. Furthermore series solutions are developed. Variations in flow, temperature, skin friction and local Nusselt number under influential variables have been plotted. It is elaborated that fluid velocity intensifies with rise in curvature parameter, conjugate parameter, mixed convection parameter, nanoparticle volume fraction and velocity ratio parameter. Similarly decay in temperature of the fluid is analyzed for higher velocity ratio parameter while it enhances with increment in nanoparticle volume fraction, mixed convection parameter, conjugate parameter and curvature parameter. Skin friction can be minimized via higher estimations of mixed convection parameter, velocity ratio parameter and nanoparticle volume fraction. Heat transfer rate or cooling process (Nusselt number) is regulated through higher conjugate and curvature parameters. During comparative analysis of SWCNTs with MWCNTs, better performance is shown by SWCNTs. Skin friction coefficient in limiting sense is also compared with previously published articles.

Analytical Thermal Boundary Condition for Quasi-Transient Simulation of Internal Flow Experiments

Transient thermochromic liquid crystal (TLC) experiments can provide high-fidelity spatially resolved heat transfer data for complex geometries, particularly where infrared techniques cannot be applied. One challenge when applying transient methods to internal geometries is the local definition of the driving gas temperature. The transient nature of the streamwise driving gas temperature profile has led to comparisons with steady-state computational fluid dynamics being questioned. This paper explores simulating the temporal behavior of transient TLC experiments directly. A novel technique is developed to account for differences in the gas and solid time scales, where surface temperature is calculated at each spatial location analytically from the surface heat flux, using an impulse response method assuming one dimensional, semi-infinite conduction. Postprocessing of the simulated surface temperature history is performed using the same method as experimentally, allowing for direct comparison. This analytical thermal boundary condition (ATBC) is applied to simulate a transient TLC experiment of a stationary superscaled rib turbulated internal cooling passage in a gas turbine engine. Traditional steady-state simulations were also performed with constant temporal and spatial temperature boundary conditions. Results show that calculations using the new ATBC and traditional steady-state method give very similar Nusselt number distributions and mean values in relation to the experimental data, suggesting the larger discrepancy between simulations and the experiments is not the definition of the driving gas temperature. Analysis of transient variation of Nusselt number indicated brief highly localized maximum variations up to 40%, although this was not found to significantly affect the mean values, and passage-averaged values converged to within 0.5% of the final value within 0.2 s.

Local & Average Heat Transfer and Friction Factor Characteristics of a Flow through a Helical Wire Coil for Turbulent Flow Conditions

Heat transfer augmentation is essential for numerous industrial applications. The flow through a helical coil is one of the most efficient and effective techniques of heat transfer enhancement due to the provision of a large surface area. The present study is focused on the thermo-hydraulic performance of turbulent flow through a helical coil, made up of copper with a curvature ratio of 0.0519 (d/D) and pitch equal to 50 mm using water as a test fluid. The objective of the present study is to reveal the influence of secondary flow, centrifugal force, and Reynolds number (Re) on local velocity, local heat transfer coefficient in a helical coil. The values of average heat transfer and friction factor at different Re for a flow through a helical coil are compared with corresponding values for a flow through a smooth tube. The numerical results are presented for the Re number range at inlet conditions of the helical coil from 5000 to 20000 in the increment of 2500 under constant heat flux conditions. Numerical results indicate that there is a circumferential variation of local velocity and local Nusselt number (Nu) values concerningthe inner and outer sides of the helical coil. The values of average heat transfer are observed to be 150 to 200% more than the smooth tube values with increased pressure drop.

Thermal Radiation and Magnetohydrodynamics Effect on Unsteady Squeezing Non-Newtonian Nanofluids with Heat and Mass Transfer

The research article primarily deals with non-Newtonian squeezing nanofluid flow between parallel plates by taking into account different phenomena in the modeled problem. The thermal radiation and magneto hydrodynamics impact in fluid flow model is mainly focused in this analysis. The proposed nanofluid model also encompasses thermophoresis and the Brownian movement effects. The basic equations of nanofluids model such as velocity, heat and concentration equations are transformed into ordinary differential equations with the help of appropriate similarity transformations. As a tool, the semi numerical scheme is used for solving the proposed problem with the greatest possible accuracy for the purpose of illustration and analysis. The basic physical parameters involved in velocity, heat and concentration profiles in the nanofluids flow are discussed in detail. The variation of skin friction, Nusselt number and Sherwood number along with their impacts on the velocity, heat and concentration are determined. It is also focused to show the influence of different physical parameters graphically as well as in tabulated form. Excellent agreement between the results of semi analytical method and already published work is obtained, indicating the validity of the semi analytical approach. The study presented herein fills the gap in the literature, and will have a broad impact in industrial and biomedical fields.

Effect of an internal thermal-conductive cylinder on the conjugate conduction-convection in an enclosure

We numerically studied the conjugate conduction-convection in an enclosure with a circular cylinder placed at the center. The enclosure is differentially heated on its lateral sidewalls but keeps adiabatic for the top and bottom sidewalls. The internal cylinder is assumed thermally conductive which is determined by the ratio of thermal conductivity coefficient between solid and fluid medium. The influence of the cylinder is conducted through two mechanisms: the conduction in the cylinder which alters the temperature distribution in the enclosure and thus the buoyancy acting on the fluid, and the confinement on the fluid circulation especially in the region close to the walls of the enclosure. We aim to explore the effects of cylinder diameter and thermal conductivity ratio on the conjugate conduction-convection under two Rayleigh numbers, i.e., Ra = 104 and 106, to consider both weak convection and convection dominant conditions. The effects of the two parameters are analyzed by the thermal and flow distributions, wall heat transfer and the flow behaviors around the cylinder. Numerical results reveal smooth circulation of fluid within the enclosure at Ra = 104 without the formation of local vortices. Since convection is relatively weak at this Rayleigh number, the thermal and flow distributions are roughly skew-symmetric about the center of the geometry, and the variation of thermal characteristics with the cylinder diameter and thermal conductivity ratio is significant for the top-left and bottom-right regions of the enclosure because of strong local heat transfer. However, two local circulating vortices are generated beside the cylinder and move upward with increasing thermal conductivity ratio and are deformed at Ra = 106. The spatial variations of temperature and Nusselt number on the solid walls are relatively small in magnitude compared with the Ra = 104 case, while the variation tendency with respect to the two governing parameters is generally monotonic.

Experimental investigation on triple concentric tube heat exchanger

The main objective of this research paper is to evaluate the performance of triple concentric tube heat exchangers experimentally under steady-state conditions. Water is considered as the working fluid and is circulated through the inner tube, inner annulus, and outer annulus at different temperatures. For this purpose hot water, normal water, and intermediate temperature water are considered. The experiment has been performed in the laboratory of the Mechanical Engineering Department at BIT Sindri Dhanbad in India. The arrangement of a triple concentric tube is installed by using three tubes of different materials. Aluminium, Copper, and galvanized iron (G.I) are used to make an inner tube, inner annulus, and outer annulus respectively. The variation of fluid temperature along the length of the heat exchanger has been measured. Also, the variation of friction factor and Nusselt number with Reynolds number has been studied for different conditions. The best result of this experimental study has been found in counter-current arrangement (A2) and the value of the overall coefficient is 0.42.

Experimental Investigation of Micro Cooling Units on Impingement Jet Array Flow Pressure Loss and Heat Transfer Characteristics

With the development in additive manufacturing, the use of surface treatments for gas turbine design applications has greatly expanded. An experimental investigation of the pressure loss and heat transfer characteristics within impingement jet arrays with arrays of target surface micro cooling units is presented. The discharge coefficient and Nusselt number are measured and determined for an evaluation of the pressure loss of the flow system and heat transfer level, respectively. Considered are effects of impingement jet Reynolds number ranging from 1000 to 15,000 and micro cooling units (square pin fin) height (h) with associated values of 0.01, 0.02, 0.05, 0.2, and 0.4 D, where D is the impingement hole diameter. Presented are variations of Nusselt number, and Nusselt number ratio, discharge coefficient, discharge coefficient ratio, discharge coefficient correlation. Depending upon the micro cooling unit height, discharge coefficient ratios slightly decrease with height, and the ratio values generally remain unit value (1.0). When Rej = 1000 and 2500 for several cooling units height values, discharge coefficient ratios show the pressure loss decreases about 2–18% and 3–6%, respectively, when compared to the data of a baseline smooth target surface plate. The observed phenomenon is due to the effects of flow blockage of micro cooing units, local flow separation, and near-wall viscous sublayer reattachment. Results also show that heat transfer levels increase 20–300% for some of the tested toughened target surface plates when compared to smooth target surface plates. The heat transfer level enhancement is because of an increase in thermal transport and near-wall mixing, as well as the increased wetted area. In addition, micro cooling units elements break the viscous sublayer and cause greater turbulence intensity when compared to the smooth target surface. Overall, results demonstrate that the target surface micro cooling units do not result in a visible increment in pressure loss and reduce pressure loss of the flow system for some of the tested patterns. Moreover, results show the significant ability of micro cooling units to enhance the surface heat transfer capability of impingement cooling relative to smooth target surfaces.

Numerical modeling on hybrid nanofluid (Fe3O4+MWCNT/H2O) migration considering MHD effect over a porous cylinder.

The free convective hybrid nanofluid (Fe3O4+MWCNT/H2O) magnetized non-Darcy flow over a porous cylinder is examined by considering the effects constant heat source and uniform ambient magnetic field. The developed coupled PDEs (partial differential equations) are numerically solved using the innovative computational technique of control volume finite element method (CVFEM). The impact of increasing strength of medium porousness and Lorentz forces on the hybrid nanofluid flow are presented through contour plots. The variation of the average Nusselt number (Nuave) with the growing medium porosity, buoyancy forces, radiation parameter, and the magnetic field strength is presented through 3-D plots. It is concluded that the enhancing medium porosity, buoyancy forces and radiation parameter augmented the free convective thermal energy flow. The rising magnetic field rises the temperature of the inner wall more drastically at a smaller Darcy number. An analytical expression for Nusselt number (Nuave) is obtained which shows its functional dependence on the pertinent physical parameters. The augmenting Lorentz forces due to the higher estimations of Hartmann retard the hybrid nanoliquid flow and hence enhance the conduction.

Studying the Internal Heat Transfer By Natural Convection Through an Inclined and a Modified Square Enclosure with a Triangular Top Wall.

A numerical analysis used to simulate laminar natural convective heat transfer in a two-dimensional inclined and a modified square enclosure having a triangular top wall has been performed. The model is applied to analyze natural convection in this enclosure where the left side wall is subjected to a constant heat flux while the other opposite wall is kept at isothermal cold temperature. The other enclosure walls are considered adiabatic. The enclosure under study is filled with air with Prandtl number is taken as 0.71. The two-dimensional flow is solved numerically by using the Finite Volume Method (FVM).The computations are carried out at different heights of triangular top wall. The Rayleigh numbers considered ranging from 103 to 106. The effect of inclination angle of the enclosure on the resulting convection process is investigated for inclination angles ranging from 0o to 60o. The results of the present investigation show that the convective phenomenon is greatly influenced by the inclined top wall height and the dominance of the convective currents with the increase of Rayleigh number and inclination angle. The streamline and isotherm plots and the variation of the average Nusselt number at the hot left side wall are also presented. The results showed a good agreement with another published results.

On the rotary concentrated solar collector containing twisted ribs and MgO-Ag-water nanofluid

BackgroundIncreasing the solar collectors' performance is of importance to produce higher clean energy. Twisted ribs, having a lengthy background, are beneficial fitted elements to improve mixing between the hot fluid sticking to the absorber with cold fluid flow. MethodThe combination of twisted rib and rotary wall of the tubular solar collector is seeking in the current numerical work. Further, the solar absorber is considered to be filled with a hybrid nanofluid made by water and MgO-Ag nanoparticles. The variations of the average Nusselt number, friction factor, and performance evaluation criteria for all cases are drawn. The power demand of the system to assess the current cost of the new configuration is also calculated. FindingsThe geometry with one twisted rib shows better heat transfer. Adding nanoparticles to the base fluid can improve Nusselt number 18 percent, on average. The increment in the Reynolds number causes 60 to 65 percent higher Nusselt number. The wall rotation has remained either a little aiding or an inverse effect on the heat transfer. However, this makes a lower pressure drop along the solar absorber by demanding low power, as the main advantage.

Implication of corrugation profile on thermo-hydraulic characteristics of Cu-water nanofluid flow through partially filled porous channel

We study numerically the thermo-hydraulic characteristics for forced convective flow of Cu-water nanofluid within a corrugated channel of different corrugated profiles namely triangular, sinusoidal and trapezoidal incorporated with single-layer aluminium porous foam at the core. The results are elaborated in terms of the streamline and isotherm distribution and variation of averaged Nusselt number, enhancement ratio and performance factor, for a range of Reynolds number (5–500) and nanofluid volume fraction (0–5%) at Darcy number = 10−6. Results indicate that the mixing capability between the hot and cold fluid enhanced and hence the heat transfer rate increases upon the introduction of the corrugated wall in a partially filled porous channel. Moreover, trapezoidal corrugated channel shows better heat transfer augmentation as compared to its counterparts namely sinusoidal and triangular ones. The combined effect of enhancement in heat transfer and pressure drop penalty of the corrugated channel is presented by performance factor, which is strongly dependent upon the Reynolds number and the profile of the corrugated channel. In nutshell, trapezoidal corrugated channel found to be the best irrespective of Reynolds number and nano-fluid volume fraction.

Numerical Investigation of Thermal Performance of Key Components of Electric Vehicles Using Nucleate Boiling

Abstract An efficient thermal management system is desirable for improving the performance of key components of electric vehicle (EV), such as battery packs and insulated-gate bipolar transistors (IGBTs). This paper investigates the application of single bubble nucleate boiling heat transfer in battery and IGBT component cooling pack. A semi-mechanistic flow boiling model, which combines four main submodels i.e., phase change model, micro-region model, Marangoni model, and contact angle model, is developed to get the insight of various subprocesses like bubble inception, growth, departure, scavenging effect while the bubble departs, and condensation. For model validation, simulations are carried out for single bubble flow boiling in a vertical rectangular channel and compared against the experimental data available in the literature. Thereafter, simulations are carried out for the battery and IGBT cooling pack to understand the physical phenomena associated with nucleate boiling in such systems. The choice of a single vapor bubble vis-à-vis multiple bubbles has been based on the objective of validating the developed numerical model. An enhancement of ∼30% in heat transfer is achieved for both battery and IGBT components when the system is subjected to a nucleate boiling cooling regime as compared to a conventional single-phase convection cooling system. Nusselt number variation due to the single bubble movement along the coolant path is studied in detail for both serpentine-shaped cooling path in a battery and straight flow path in an IGBT. Moreover, the influence of Reynolds number over bubble dynamics is analyzed.