Temperature-dependent Fluid Properties Research Articles

Laminar flow with temperature-dependent fluid properties between two stretching rectangular surfaces

Abstract The Navier–Stokes equations and the energy equation are used to investigate a fluid flow between two stretching rectangular surfaces subjected to a temperature difference that affects the dynamic viscosity and thermal conductivity of the fluid. The wall stretching process enhances the momentum boundary layer thickness which slows the axial motion of the fluid away from the flow boundaries. When the stretching parameter γ is equal to 1, that is the case corresponding to symmetric stretching, the minimum of the axial velocity is located at the midplane of the channel y = 0.5 if the viscosity variational parameter α equals 0. This minimum moves towards the region 0.5 < y < 1 for α > 0, but migrates towards the region 0 < y < 0.5 for α < 0. Moreover, in the case of symmetric stretching corresponding to γ = 1, the growth in Reynolds number Re tends to increase the axial velocity around the middle of the channel for α ≥ 0 in the attempt to counteract the effects of enhancing the momentum boundary layer thickness leading to the flattening of axial velocity profiles for Re ≥ 100. While the conductivity variational parameter β does not influence enough the fluid dynamics and heat transfer, the Reynolds number Re and the Péclet number Pé can increase or decrease the temperature distribution inside the channel depending on the sign of the parameter α. Practical applications related to the present study include lubrification, food manufacturing, paint industries, extrusion processes in plastic and metal industries.

Numerical study of MHD flow over stretching cylinder with variable Prandtl number and viscous dissipation in ternary hybrid nanofluids with velocity and thermal slip conditions

Industrial applications in domains such as warm rolling, crystal development, thermal extrusion and optical fiber illustration are seeing a significant increase. These applications specifically focus on addressing the challenge of a cylinder in motion inside a fluid environment. Elevated temperatures may affect the viscosity and thermal conductivity of fluids. Understanding the relationship between temperature and the properties of fluids is crucial. In light of these presumptions, the primary goal of this study is to examine, under transverse magnetic field, shape factor, velocity, thermal slip conditions and viscous dissipation, how temperature-dependent fluid properties could enhance the heat transfer efficiency and performance evolution of ternary hybrid nanofluid. In order to study flow fluctuations, the impact of nanoparticle addition and improvements in heat transfer, a variable Prandtl number is also included. The use of similarity variables converts the controlling flow model from partial differential equations (PDEs) to ordinary differential equations (ODEs). Mathematica’s shooting strategy solves ODEs using the fourth-order Runge–Kutta (RK-IV) method. Numerical calculations were done after setting parameters to acquire the desired results. Analytical data are provided in tables and graphs for convenient usage. The results showed that the velocity profile increases as the values of [Formula: see text], Pr, M, Re and S grow, and decreases when the values of [Formula: see text] decrease. Re, Pr and S lower the temperature profile, whereas [Formula: see text], [Formula: see text] and Ec raise it. The skin friction profile steepens as [Formula: see text], S, Re and M increase relative to the stretched cylinder, and flattens as [Formula: see text] and [Formula: see text] decrease. The Nusselt number profile rises as [Formula: see text], Pr, S and Re decrease with [Formula: see text], Ec and [Formula: see text]. When the Prandtl number goes from 3.0 to 6.2 in a ternary hybrid nanofluid with brick-shaped nanoparticles, the Nusselt number goes up by around 55.7%.

Study of nanofluid flow in a stationary cone–disk system with temperature-dependent viscosity and thermal conductivity

The substantial temperature gradient experienced by systems operating at relatively high temperatures significantly impacts the transport characteristics of fluids. Hence, considering temperature-dependent fluid properties is critical for obtaining realistic prediction of fluid behavior and optimizing system performance. The current study focuses on the flow of nanofluids in a stationary cone–disk system (SCDS), taking into account temperature-dependent thermal conductivity and viscosity. The influence of Brownian motion, thermophoresis, and Rosseland radiative flux on the heat transport features are also examined. The Reynolds model for viscosity and Chiam's model for thermal conductivity are employed. The Navier–Stokes equation, the energy equation, the incompressibility condition, and the continuity equation for nanoparticles constitute the governing system. The Lie-group transformations lead the self-similar ordinary differential equations, which are then solved numerically. Multi-variate non-linear regression models for the rate of heat and mass transfers on the disk surface were developed. Our study reveals a notable decrease in the rate of heat and mass transfer when pre-swirl exists in the flow. The significant influence of nanofluid slip mechanisms on the effective temperature and nanofluid volume fraction (NVF) within the system is highlighted. Furthermore, the variable viscosity property enhances the temperature and NVF of the SCDS.

Fourier series-based modelling of the effects of thermal coupling on the transient dynamics of component loops in a coupled natural circulation loop

Energy efficiency in process industry and passive safety systems in nuclear power plants necessitate the use of buoyancy driven heat exchangers. The current study presents a 1-D numerical model of the buoyancy driven fluid system in a Coupled Natural Circulation Loop (CNCL) comprising water as the working fluid. In this study water at different temperatures is considered as the operating fluid in each of the loops. The study employs a 1-D model derived using a semi-analytical Fourier series. A validation study was carried out using the relevant literature to verify the mathematical model. A detailed parametric study on individual NCLs and their coupled system was conducted by varying the cross-sectional area keeping the other parameters constant to gain insights into the effect of thermal coupling on the long-term transient dynamics of each of the individual loops of the CNCL system, for stable, unstable – periodic, and unstable – chaotic conditions. The dynamics were analysed using the difference between transient buoyancy and viscous forces, and it was found that the overall heat transfer coefficient influences the coupling behaviour and the dynamics of the component loops in a CNCL. At lower values of the overall heat transfer coefficient, the component loops in the CNCL nearly retain their independent behaviour, i.e., the component loops hardly influence each other. It was also found that the temperature dependent fluid properties influence the stability of the CNCL system in some cases.

Study of hybrid nanofluid flow in a stationary cone-disk system with temperature-dependent fluid properties

Cone-disk systems find frequent use such as conical diffusers, medical devices, various rheometric, and viscosimetry applications. In this study, we investigate the three-dimensional flow of a water-based Ag-MgO hybrid nanofluid in a static cone-disk system while considering temperature-dependent fluid properties. How the variable fluid properties affect the dynamics and heat transfer features is studied by Reynolds’s linearized model for variable viscosity and Chiam’s model for variable thermal conductivity. The single-phase nanofluid model is utilized to describe convective heat transfer in hybrid nanofluids, incorporating the experimental data. This model is developed as a coupled system of convective-diffusion equations, encompassing the conservation of momentum and the conservation of thermal energy, in conjunction with an incompressibility condition. A self-similar model is developed by the Lie-group scaling transformations, and the subsequent self-similar equations are then solved numerically. The influence of variable fluid parameters on both swirling and non-swirling flow cases is analyzed. Additionally, the Nusselt number for the disk surface is calculated. It is found that an increase in the temperature-dependent viscosity parameter enhances heat transfer characteristics in the static cone-disk system, while the thermal conductivity parameter has the opposite effect.

Unveiling impacts of heat flux distribution on forced convection in horizontal evacuated tubes

Integration of evacuated tubes with solar thermal desalination can significantly enhance thermal efficiency and water production. To provide optimization strategies for such desalination systems, 3D numerical simulations were performed to analyze the influence of the heat flux distribution on forced convection in horizontal evacuated tubes in terms of pressure drop, secondary flow, temperature distribution, and Nu. The improved method considered multi-layer wall heat transfer, fluid–solid coupling heat transfer, and temperature dependent fluid properties. Non-uniform heat fluxes significantly affected the friction pressure drop in the laminar regime, but were less pronounced in the transition and turbulent regimes. At low Re, the backward non-uniform heat flux strengthened the secondary flow while the forward non-uniform heat flux suppressed it. The rapid warming of the wall temperature occurred over a short distance due to the difference in thermal conductivity between the fluid and solid domains. The non-uniformity of heat flux distribution moderately affected average fluid temperature. The influence of heat flux distribution on secondary flow and average temperature weakened as Re increased. Furthermore, a correction factor was introduced to quantify the impact of heat flux distribution on Nu. For forward and backward non-uniform heat fluxes, it assumes values of 0.94 and 0.86 respectively.

Magnetohydrodynamic hybrid nanofluid flow through moving thin needle considering variable viscosity and thermal conductivity

In modern science and technology, industrial applications that deal with the problem of continuously moving thin needle, surrounded with fluid in sectors like hot rolling, crystal growing, heat extrusion, glass fiber drawing, etc., are rapidly increasing. Such processes involve high temperatures which may affect the fluid properties that is, viscosity and thermal conductivity. So, it’s crucial to understand temperature-dependent fluid properties. Focused on these assumptions, the main objective of the current research work is to investigate how temperature-dependent fluid properties might improve the heat transfer efficiency and performance evolution of hybrid nanofluid in the presence of transverse magnetic field over a moving thin needle. Variable Prandtl number is also introduced to observe flow fluctuation, the effect of adding nanoparticles, and enhancement in heat transmission. The results are obtained for different needle thicknesses, temperature-dependent viscosity, temperature-dependent thermal conductivity, and heat generation. Moreover, Fe3O4/Graphene nanoparticles are considered to be dispersed in water. The governing partial differential equations of flow and heat transfer are transformed into a system of coupled nonlinear ordinary differential equations using analysis of similarity conversion. Subsequently, the numerical solution of the problem is attained by employing the MAPLE software. The fourth-fifth-order Runge-Kutta-Fehlberg (RFK45) approach is used by default in this MAPLE program to address the numerical problem of boundary value. The velocity and temperature field are pictured for different values of the parameters as well as physical quantities of interest such as skin friction coefficient and rate of heat transfer are visually depicted in graphs and tables. It is found that fluid motion and energy transport are highly regulated by the variation of magnetic field strength. As the volume fraction of Fe3O4 is increased, the heat generation, and thermal conductivity parameter vehemently enhance the temperature profile which leads to a rise in thermal boundary layer. A strong augmentation in the heat transfer rate has been found with the increment in the variable Prandtl number.

Variable fluid properties and concentration species analysis of a chemically reactive flow of micropolar fluid between two plates in a rotating frame with cross diffusion theory

The importance of this study is that the physical properties no longer to be consider as a constant, therefore dynamics of the mechanism of temperature dependent fluid properties and species concentration variation on the magnetized flow of a micropolar fluid in a rotating frame is studied in this article. The flow is considered between two porous plates with slip boundary conditions on the lower plate. The cross-diffusion theory on the thermal and solutal transportation investigation is presented by the help of non-uniflorm source / sink and nonlinear chemical reaction. The equations of motion and energy are reduced into the set of couple nonlinear ordinary differential equations by the usage of appropriative transformation. These couple nonlinear equations are tackled numerically with the utilization of BVP4C function on MATLAB. The graphical and numerical outcomes are obtained with physical discussion for various parameter. The study concludes that as the material parameter approaches to zero, the flow of micropolar fluids approaches to the Newtonian fluids. It is worth mentioning that the variable viscosity reduces the fluid velocity near the lower plate due to domination of viscous forces, while fluid temperature shows rising trend by the improvement of variable thermal conductivity because of the more heat production. Further, it is noticed that the Soret and Dufour impacts precludes the solutal deposition and coolant the bounding at surface, as a result fluid temperature and concentration enhances.

Similarity solutions of a Blasius flow with variable fluid properties and viscous dissipation

AbstractAn analytical model of the Blasius flow is studied including temperature-dependent fluid properties and viscous dissipation. The friction coefficient and Nusselt number at the wall are calculated from the resulting dimensionless velocity and temperature fields. The variable properties model is compared to a constant properties model to verify if and under which conditions this simplification is valid. Air, water and oil are analyzed as fluids over a representative operating regime, respectively. For air, the variable properties do not influence the friction coefficient and the Nusselt number. For water, the influence of the variable properties is present for both parameters but limited since no large temperature difference can occur in water without a phase change. New correlations for the friction coefficient and Nusselt number were derived for water and oil over a large range of operating conditions. Viscous dissipation does not significantly affect these parameters for air and water because of their relatively low Prandtl numbers. The high Prandtl number of oil in combination with a viscosity that is strongly decreasing with increasing temperature, leads to a more complex behavior. The friction coefficient as well as the Nusselt number are strongly dependent on the fluid properties. Dissipation effects cannot be neglected above an Eckert number of around 0.01. The superposition principle to evaluate wall heat flux in experiments is based on the assumption of constant fluid properties. It can be used without restrictions for air but should be thoroughly checked for all other fluids, especially liquids, using the presented methodology.

Numerical investigation of mixed convection through an infrared-suppression (IRS) device

The flow through an infrared-suppression (IRS) device, installed on a warship, is often subject to various thermal regimes, including forced, natural, and mixed convection. When the ship becomes stationary/idle in the middle of a sea or in a port, mixed convection flow through the IRS device becomes noteworthy. In this paper, we numerically investigate the thermo-fluid characteristics through a cylindrical IRS device in mixed convection regime. Computations are performed for turbulent flow mixed convection with Richardson number in the range 0.1 ≤ Ri ≤ 10 to analyze the entrainment ratio (ER), flow field, and temperature variations in the IRS device. For a parametric study, dimensionless parameters such as nozzle-exit temperature, diameter ratio, nozzle protrusion, and funnel overlap are varied over the range of 1.91 ≤ T* ≤ 2.577, 1.05 ≤ DR ≤ 1.25, −1.5 ≤ NP ≤ 1.5, and − 22% ≤ OL ≤ 22% respectively. Temperature-dependent fluid properties are considered to obtain accurate results at higher temperature scales. The computed ER fairly agrees with the benchmark experimental results. With increase in Ri, the ER rises, whereas the actual mass suction diminishes. The centerline plume temperature at the exit of the IRS device is around 0.53 times the nozzle-exit temperature for Ri = 10, whereas it is almost identical at Ri = 0.1. The optimal Ri (=0.75) is obtained based on the maximum cooling efficiency. Finally, an empirical correlation for the ER is developed as a function of the above pertinent parameters.

An isothermal constant surface area horizontal helical coil under natural convection and radiative heat loss: A CFD study

This paper presents a numerical analysis of a horizontally oriented constant surface area isothermal helical coil under natural convection heat transfer and surface radiation. Numerical computationsare carried out in the laminar regime of Rayleigh number (104 ≤ Ra ≤ 108), surface emissivity (0 ≤ ε ≤ 1), and geometrical parameters of the helical-coil, like diameter of the coil (8 ≤ D/d ≤ 24), pitch (3 ≤ p/d ≤ 7.5), and coil height (40 ≤ H/d ≤ 60) to study the heat transfer characteristics. This study is used for effectively designing the helical coils, which are typically manufactured at an extremely high temperature. The numerical computation has been validated by comparing the average Nusselt number (Nu) with the previous experimental results. Temperature-dependent fluid properties are incorporated to achieve precise results over a wide range of temperatures. The effect of the geometrical parameters on the heat transfer characteristics has been depicted graphically in terms of average Nu, relative convection and radiation heat transfer rate, and the temperature profile. It is found that the relative contribution of radiative heat transfer is 87.8% at an emissivity of 0.9 and Ra of 10(Ali, 19944), whereas, for an emissivity of 0.1 and Ra of 10(Moawed, 20058), the relative contribution of radiation heat transfer is only 6.4%. Lastly, a correlation has been developed for the average Nu based on all the pertinent parameters which can be beneficial to the engineers in the industry and also academic researchers. The developed correlation has been used to predict the cooling curve of the helical coil in certain situations.

PaScaL_TCS: A versatile solver for large-scale turbulent convective heat transfer problems with temperature-dependent fluid properties

PaScaL_TCS is an efficient and scalable solver for large-scale direct numerical simulations of natural convective flow that considers temperature-dependent fluid properties. For increased scalability on a massive-scale distributed memory system, the solver decomposes the computational domain into a cubic sub-domain. The numerical procedure is based on the monolithic projection method with staggered time discretization [1], which is an implicit and non-iterative solver for wall-bounded domains. The PaScaL_TDMA library is used to solve batched tridiagonal systems, which are partitioned according to domain decomposition. For parallel fast Fourier transform in a Fourier Poisson solver for pressure, two transpose schemes with different communicator sizes are proposed and compared according to the number of cores. An explicit intermediate aggregation scheme for MPI-IO is suggested to reduce the number of processes that simultaneously take part in parallel IO. The overall implementation was evaluated using the Nurion cluster system of the Korea Institute of Science and Technology Information with detailed performance profiling. With the efficient communication, the results showed good strong and weak scalability up to 131,072 cores. The file IO performance improved with the suggested MPI-IO scheme using explicit aggregation, especially when many processes are involved in parallel IO. The solver was verified by conducting large-scale differentially heated vertical convection flow simulations under the Oberbeck–Boussinesq (OB) approximation. The capability of the solver to capture and quantitatively describe the non-OB effect was demonstrated via glycerol Rayleigh–Bénard convection flow simulations. Program summaryProgram Title: PaScaL_TCSCPC Library link to program files:https://doi.org/10.17632/3b2bysrcxm.1Developer's repository link:https://github.com/MPMC-LabLicensing provisions: MITProgramming language: Fortran90Nature of problem: Solving the incompressible Navier-Stokes equations for natural convective flow considering the non-Oberbeck–Boussinesq effect, which considers the temperature dependence of fluids properties, in three-dimensional channel domain.Solution method: PaScaL_TCS uses the monolithic projection-based method with staggered time discretization (MPM-STD) [1]. It employs the Crank-Nicolson scheme along with staggered time which evaluates scalar and vector variables at the (n+1/2) and (n+1) time level, respectively. PaScaL_TDMA [2] is used to solve multiple tridiagonal matrix systems for decoupled energy and momentum equations in a distributed memory system. The Poisson equation solver for the pressure-correction scheme is based on Fourier diagonalization. MPI_Alltoallw is used for parallel FFT. PaScaL_TCS supports a single-file-based parallel IO for efficient data generation in large-scale computing.

Investigation of field synergy principle for convective heat transfer with temperature-dependent fluid properties

The field synergy principle is widely used in the analyses and optimizations of convective heat transfer, but its original derivations are based on fluids with constant thermal properties. The applicability of the principle for fluids with temperature-dependent properties needs clarification. A theoretical analysis of the problem is conducted. It is found that a synergy principle of mass flux vector and specific enthalpy gradient is more fundamental. Because temperature gradients are parallel to specific enthalpy gradients, the original field synergy principle of velocity and temperature fields is still valid. Heat transfer of supercritical CO2 and molten salt in different finned channels is numerically studied, and different mean synergy angles are compared. It is found that the domain integration mean synergy angles calculated with specific enthalpy gradient or temperature gradient have the same trends. For the volume-weighted mean angles, the absolute value of dot product of velocity and temperature gradient should be used in calculating the local synergy angles. Otherwise, the trend of the volume-weighted mean angles can be contrary to the field synergy principle. Meanwhile, the accuracy of the mesh and the temperature gradient near the heat transfer surfaces is important for the numerical applications of the field synergy principle.

Effect of thermal radiation on convective heat transfer in MHD boundary layer Carreau fluid with chemical reaction

The temperature dependent thermophysical fluid properties have numerous aspects in different industries and engineering processes in which heat transmission is based on fluid flow. For such heat transmission processes, heat transmission system is highly fluctuated with variation of viscosity. Thus, the aim of this study is to investigate the transfer of heat in magnetized Carreau fluid with chemical reaction and under influence of thermal radiation over nonlinear stretching/shrinking surface. Additionally, we have incorporated variable heat dependent thermophysical properties to analyze the heat transfer in magnetized Carreau fluid. Set of flow governing non linear PDE’s are obtained using Carreau fluid tensor and boundary layer approximation (BLA) theory. Dimensionless set of ODE’s are obtained using suitable similarity transforms. Shooting method in conjunction with Newton's method have been utilized to solve the problem. It is noted that when stretching Bge 0 is significant with strictly increasing mass suction S shear stress rate increase with minor levels and sharp increase has been observed in Nusselt number, whereas in shrinking case B<0 shear stress and heat transfer coefficient values are improved raising the value of S mass suction. Further, raising the values of power law index n produce reduced skin friction over stretching surface Bge 0 while skin friction dramatically enhance in shrinking case B<0. It is observed that raising the non-linearity m values for stretching or shrinking, skin friction and Nusselt number considerably improved. Moreover, computational outcomes of the study are validated with already published previous results and the results obtained in this study are found in good agreement.

Comparative study of models for packed bed molten salt storage systems

To date various models for packed bed single tank molten salt storage systems have been developed. The question arises in how far certain modelling assumptions can affect the outcome of these models. This can also depend on the applied use case, for example a short validation simulation versus an annual simulation. Thus, a comparative study is performed, considering four one-dimensional models for packed beds: the Schumann model, the continuous-solid-phase model, the single-phase model and a recently developed bidisperse model. Additionally, the impact of heat losses and variable fluid properties are considered as well. The comparison is performed for different use cases and covers the single blow operation, cyclic operation and annual simulations. Common boundary conditions are derived from a 100 MWel concentrating solar thermal power plant with molten salt as heat transfer fluid. A large and a small storage volume, each with a small and a large particle packing are designed to cover a range of practical storage configurations. The aim of this work is to provide guidelines for the selection of a reasonable level of modelling detail depending on the desired accuracy and computational effort. Results indicate that the outcome can significantly differ between the use cases. Effective conductivity has visible impact in stand-by periods and small sized packings with strong thermal gradients. The single-phase model has low computing effort but is applicable only with packings in the range of millimeters. The bidisperse model has significantly improved accuracy when applied to packings with smaller particles in combination with larger particles. Heat losses showed little impact for the considered storage volumes. Temperature dependent fluid properties have an impact within short periods but average out in cyclic and annual simulations, which justifies neglecting them.

Importance of Temperature-Dependent Non-Newtonian Fluid in Conventional Thermal Processing

Abstract Computational fluid dynamics (CFD) simulation provides full-field variables, enabling a better understanding of flow physics and associated heat transfer. However, assumptions involved in CFD simulation should not affect flow and temperature fields and their correspondence to practical situations. Therefore, the present study analyzed the importance of temperature-dependent fluid properties in a sealed container during thermal treatment. We compared the thermal behavior trends of temperature-dependent fluid properties with those obtained from constant properties for two carboxyl methyl cellulose (CMC) solution concentrations. The results show that natural convection occurs earlier in the temperature-dependent fluid properties, which leads to attaining a desired level of sterility within a shorter time than the constant properties of the fluid. The variations in the viscosity with the shear rate and temperature played essential roles in affecting thermal behavior. So, results indicate that temperature-dependent non-Newtonian fluid must be considered to avoid miscalculating heating time in conventional thermal treatment. Besides, the thermal trends of both cases approach pure conduction when CMC solutions’ apparent viscosity increases.

Natural Convection and Radiative Heat Transfer From Constant Surface Area Vertical Helical Coils: Effect of Pitch and Height

Abstract In this work, numerical simulations are carried out to delineate the natural convection and surface radiation heat transfer characteristics of vertically oriented isothermal helical coils having a constant surface area. Numerical computations using the finite-volume method are carried out in the laminar regime for the following non-dimensional parameter ranges: Rayleigh number (104 ≤ Ra ≤ 108), surface emissivity of the coil (0 ≤ ɛ ≤ 1), pitch to the rod-diameter of the coil (3 ≤ p/d ≤ 7.5), and coil-height to the rod-diameter (40 ≤ H/d ≤ 60). Temperature-dependent fluid properties have been implemented to obtain accurate results. The impact of Ra and ɛ on both convective and radiative heat losses is discussed in detail. At a high Ra of 108, when H/d varies from 40 to 60, the mass flowrate inducted through the coil reduces from 40.6% at p/d = 3 to 11.4% at p/d = 7.5. As a result, the relative strength of convection heat loss declines with a rise in H/d. For a higher emissivity of the coil surface of 0.9 and a lower Ra of 104, heat transfer by convection contributes only 12.66% of the total heat transfer. In contrast, the contribution of radiative heat transfer is only 7.46% for a lower emissivity of the coil surface of 0.1 and a higher Ra of 108.

Analysis of bubble dynamics and thermal destratification induced by gas bubbles in cylindrical liquid storage tanks

• OpenFOAM code is modified to incorporate temperature-dependent transport properties. • A new parameter to estimate the extent of the destratification is introduced. • The destratification index increased by 25.29% as the diameter ratio is increased. • Bubble in square pitch with p/d =4 gives higher effectiveness for thermal destratification. • The destratification index increased by 44.65% as the gravity ratio is increased. Thermal stratification is of great concern for liquid propellant storage tanks of space vehicles. The present study's primary objective is to better understand the bubble dynamics on thermal destratification, quantify the extent of destratification and propose a scheme for destratification. This study investigates the effect of different geometric parameters on the destratification of thermally stratified layers of liquid using the volume of fluid and interface compression method of OpenFOAM CFD code. The OpenFOAM code is modified to incorporate temperature-dependent fluid properties. Different values of bubble diameter, spacing between the bubbles, and arrangement of bubbles in triangular and square fashion with different pitches are considered. The effect of gravitational forces on thermal destratification is also reported. For all these cases, the effectiveness of thermal destratification is quantified in terms of the destratification index ( I d ). The average destratification index ( I davg ) value increased by 25.29% as the ratio of bubble diameter to tank diameter ( d/D ) increased from 0.10 to 0.16. When the pitch to bubble diameter ratio ( p/d ) of triangular and square arrangements is reduced from 8 to 4, the I davg increases by 14.59% and 22.97%, respectively. The average destratification index increased by 44.65% when the g/g e ratio changed from 0.3 to 3. These studies give an overall idea of the sparger design for getting the correct gas flow rate for thermal destratification within the liquid propellant storage tanks.

Magneto-radiative gas near an unsmooth boundary with variable temperature

PurposeThis paper aims to study the magneto-radiative gas (water vapor) on an unsmooth boundary.Design/methodology/approachThis paper provided a numerical treatment via the implicit Chebyshev pseudo-spectral method to investigate unsteady compressible magneto-radiative gas (water vapor Pr = 1) flow near a heated vertical wavy wall through porous medium in the presence of inclined magnetic field. The impacts of viscous dissipation, temperature-dependent fluid properties, thermal conductivity and viscosity in the presence of nonlinear thermal radiation are studied. The sinusoidal surface is transformed into a flat one using a suitable transformation. The comparison figures of published data with the present outcomes illustrate a good match. The present steady-state outcomes are presented for the temperature, velocity, Nusselt number and the shearing stress through figures for several interested physical parameters, namely, compressibility, magnetic, radiation, viscosity–temperature variation, thermal conductivity–temperature variation, surface sinusoidal waveform and porous parameters.FindingsThe present numerical outcomes confirm the importance of applying nonlinear thermal radiation cases in all studies that investigate heat transfer under the influence of thermal radiation.Originality/valueA mathematical model is established for a wavy boundary, and Chebyshev pseudo-spectral method is adopted for the numerical study.

Effect of large temperature difference on drag coefficient and Nusselt number of an ellipsoidal particle in compressible viscous flow

Particle-resolved simulation which fully considers the temperature-dependence of fluid properties is performed to study the momentum and heat transfer between a high-temperature ellipsoidal particle and the fluid. A non-Boussinesq regime is first identified with the Richardson number larger than unity. The drag coefficient CD and Nusselt number Nu increase significantly with particle temperature. The increased pressure difference and the increased friction drag play the dominant role in the increase of CD at small and large incident angles, respectively. The increase of Nusselt number is mainly due to the increase of the thermal conductivity. The relationship between CD and the incident angle φ satisfies sin2φ, while Nu evolves as sinmφ, where m is a function of Reynolds number and aspect ratio. The values of CD and Nu at φ = 0° and φ = 90° are fitted from simulation results and values at any incident angle can be predicted based on functions of sin2φ and sinmφ.