Control Volume Technique Research Articles

Pultrusion of a vertical axis wind turbine blade part-I: 3D thermo-chemical process simulation

A novel three dimensional thermo-chemical simulation of the pultrusion process is presented. A simulation is performed for the pultrusion of a NACA0018 blade profile having a curved geometry, as a part of the DeepWind project. The finite element/nodal control volume (FE/NCV) technique is used. First, a pultrusion simulation of a U-shaped composite profile is performed to validate the model and it is found that the obtained cure degree profiles match with those given in the literature. Subsequently, the pultrusion process simulation of the NACA0018 profile is performed. The evolutions of the temperature and cure degree distributions are predicted inside the heating die and in the post-die region where convective cooling prevails. The effects of varying process conditions on the part quality are investigated for two different heater configurations and with three different pulling speeds. Larger through-thickness gradients are obtained for the temperature and degree of cure as the pulling speed increases. This will affect the process induced residual stresses and distortions during manufacturing.

Effects of High-Order Slip/Jump, Thermal Creep, and Variable Thermophysical Properties on Natural Convection in Microchannels With Constant Wall Heat Fluxes

Natural convection gaseous slip flows in open-ended vertical parallel-plate microchannels with symmetric wall heat fluxes are numerically investigated. A second-order model, including thermal creep effects, is considered for velocity slip and temperature jump boundary conditions with variable thermophysical properties. Simulations are performed for wide range of Rayleigh numbers from 5 × 10− 6 to 5 × 10− 3 in the continuum to slip flow regime. The developing and fully developed solutions are examined by solving the Navier–Stokes and energy equations using a control volume technique. It is found that the second-order effects reduce the temperature jump and the slip velocity, whereas thermal creep strongly increases the slip velocity in both developing and fully developed regions. Moreover, the rarefaction effects increase the flow and heat transfer rates considerably, while decreasing the maximum gas temperature and friction coefficient as compared to the continuum limit. It was also shown that the axial temperature variations of the gas layer adjacent to the wall in the modeling of the thermal creep are of paramount importance and neglecting these variations, which is common in literature, leads to unphysical velocity and temperature distributions.

Numerical study of non-uniform magnetic fields effects on subcooled nanofluid flow boiling

The main goal of the present work is to investigating the effect of non-uniform axial magnetic field with positive and negative gradients on subcooled nanofluid flow boiling. Also, for better understanding the existing phenomena, single-phase convection has been studied in the first part. Control volume technique for discretizing the governing equations, SIMPLEC algorithm for pressure-velocity coupling, and SST k-ω model for turbulent flow have been used in this research, respectively. In the second part, a three dimensional two-fluid model is used to subcooled flow boiling and the available R-113 boiling experimental data are used to validate the results. The obtained results indicate that single-phase convection as well as subcooled flow boiling characteristics change not only by using nanofluid as a working fluid, but also by applying the non-uniform axial magnetic field. For the case of magnetic field with negative gradient, single-phase convection heat transfer rate increases. Also for the subcooled boiling flow, negative magnetic field gradient will lead to increase critical heat flux (CHF), due to the decrease in evaporation rate in the wall surface which is eventually responsible for wall dryout. As a result, a more safe operation condition of the industrial equipments can be achieved.

Numerical Investigation of the Transient Hydrothermal Behavior of a Ferrofluid Flowing Through a Helical Duct in the Presence of Nonuniform Magnetic Field

This paper investigates numerically the time dependent hydrothermal behavior of a ferrofluid (water and 4 vol. % Fe3O4) flowing in a helical channel, which is exposed to a nonuniform transverse magnetic field and its walls are subjected to uniform heat flux. The two phase mixture model and control volume technique have been used to study the flow. The results show that applying the nonuniform transverse magnetic field considerably increases the velocity and flow rate in the vicinity of the channel walls while it significantly decreases the velocity at the center of the channel. Applying magnetic field also decreases considerably the temperature of the inner wall of the helical channel. Furthermore, the average Nusselt number is increased by applying the nonuniform transverse magnetic field and it is more enhanced by increasing the magnetic field intensity.

Concentration polarization effects on the macromolecular transport in the presence of non-uniform magnetic field: A numerical study using a lumen-wall model

In this paper, the concentration polarization phenomena in a two dimensional tube under steady state conditions containing ferrofluid (blood and 4vol% Fe3O4) is reported in the presence of non-uniform magnetic field. Lumen-wall model has been used for solving the mass transport equation. Hemodynamics parameters such as flow rate, viscosity, wall shear stress (WSS) and the macromolecules surface concentration which accumulate on the blood vessel wall, influenced the formation and progression of atherosclerosis disease. Effective parameters on the low density lipoprotein (LDL) surface concentration (LSC) such as: the wall filtration velocity, inlet Reynolds number and WSS under applied non-uniform magnetic field have been examined.Numerical solution of governing equations of the flow field have been obtained by using the single-phase model and the control volume technique. Magnetic field is generated by an electric current going through a thin and straight wire oriented perpendicular to the tube. Results show WSS in the vicinity of magnetic field source increased and LSC decreased along the wall.

Numerical study of magnetic field effects on the mixed convection of a magnetic nanofluid in a curved tube

In this paper, effects of applying a linear magnetic field on a ferrofluid (water and 4 vol% Fe3O4) flow in horizontal straight and curved tubes have been investigated. The hydro-thermal behavior of the flow is investigated numerically using the two phase mixture model and control volume technique. The linear magnetic fields with various gradients in the perpendicular direction of the main flow have been examined. Based on the obtained results the heat transfer coefficient can be enhanced using the curved tube instead of straight tube, adding magnetic nanoparticles to the base fluid and applying external magnetic field. It is concluded that the heat transfer is enhanced due to the secondary flow augmentation (because of centrifugal force and Kelvin force) and thermal conductivity improvement (because of high thermal conductivity of magnetic nanoparticles relative to base fluid).

Euler‐Lagrangian Simulation of Magnetic Field Effects on the Mixed Convection of Ferrofluid

In this article, the hydro‐thermal behavior of a ferrofluid flow (kerosene and 4 vol% Fe3O4) in a vertical tube in the presence of different magnetic field gradients using a two‐phase Euler–Lagrange model and control volume technique has been reported. Two cases for the magnetic field gradients have been considered to affect the mixed convection of the ferrofluid: non‐uniform axial negative and positive field gradients. Unlike our previous studies instead of uniform nanoparticle distribution within the flow, it has been considered as non‐uniform (maximum concentration profile is at the flow centerline). Based on the obtained results in this case, the velocity profiles in the negative magnetic field gradients are more affected than our previous studies. Also the time variations of the Nusselt number and skin friction factor have been presented. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res 43(2): 148‐166, 2014; Published online 12 September 2013 in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21069

ENTRANCE EFFECTS OF THERMAL CREEP ON FLUID HEATING IN RECTANGULAR MICROCHANNELS

The effects of thermal creep on the development of gaseous fluid flow and heat transfer in rectangular microchannels with constant wall temperature are investigated in the slip-flow regime. Thermal creep arises from tangential temperature gradients, which may be significant in the entrance region of channels, and affects the velocity and temperature fields particularly in low Reynolds number flows. In the present work, the Navier–Stokes and energy equations coupled with velocity-slip and temperature-jump conditions applied at the channel walls are solved numerically using a control-volume technique. Despite the constant wall temperature, tangential temperature gradients form in the gas layer adjacent to the wall due to the temperature-jump condition. The effects of slip/jump and thermal creep on the flow patterns and parameters are studied in detail for a wide range of channel aspect ratios and, Knudsen and Reynolds numbers. Furthermore, the effects of variable properties on velocity-slip and, friction and heat transfer coefficients are also examined.

Hydrothermal Behavior of a Ferrofluid in a Corrugated Channel in the Presence of a Magnetic Field

In this paper, results of applying a non‐uniform magnetic field on a dilute ferrofluid (water and 3% vol. Fe3O4) flow in a corrugated channel under a constant heat flux boundary condition have been reported. The thermal behavior of the flow is investigated numerically using a two‐phase mixture model and control volume technique. It is concluded that using a magnetic field with a negative gradient on a nanofluid flow in corrugated channels can be proposed as a suitable method to achieve higher heat transfer performance and augment the heat transfer coefficient and also reduces the wall temperature. This method can lead to the design of more compact heat exchangers. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(1): 80–92, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21060

Eulerian simulation of subcooled boiling flow in straight and curved annuli

In this study, two types of water flow, turbulent single-phase flow and low-pressure subcooled boiling flow, in straight and curved horizontal annuli are investigated numerically. The control volume technique is used for discretizing governing equations, the SIMPLEC algorithm for pressure-velocity coupling, and the shear stress transport k-ω model for turbulent flow. A three-dimensional two-fluid model is used for the subcooled boiling flow, the results of which are compared with those of the single-phase flow. The available water boiling experiment results at low pressure are used to validate the numerical results and were found to have good agreement. The inner cylinder surface temperature of the curved annulus in almost all angles is less than that of the straight annulus in both single-phase and subcooled boiling flow. The maxmum and minimum temperatures in the curved annulus occur at defferent points compared to straight annulus ones due to effects of the centrifugal force.

Double criterion optimisation of transparent façades based on solar thermalprocesses

This work aimed to find the best possible solution for transparent façades. The evaluation was formulated to assure the highest user comfort criteria corresponding to energy efficiency—two criterion optimisation. The analyses were based on BESTEST, south-oriented zone geometry. Computer model was designed using Finite Control Volume Techniques with assumptions for applied materials and specified boundary conditions, plus reference year for energy calculation (WYEC2). The natural ventilation façade system was designed to determine airflow network inside the façade. The adjustable size of openings (inlets and outlets) was selected at the level of 80% for the cold season and totally closed during the hot season. Environmental parameters for thermal comfort evaluation were: zone resultant temperature and solar radiation in zone space. Energy efficiency was assessed based on heat flux between the zone with controlled temperature and external environment. Results showed that well selected design of buffer zone section could improve energy efficiency of adjacent zones for both winter and summer periods. The most profitable Double Skin Façade solution is DGC (double glazing with low-e coating) combined with single glazing with internal blinds (SGB) or coloured glazing.

Two-phase simulation of non-uniform magnetic field effects on biofluid (blood) with magnetic nanoparticles through a collapsible tube

In this paper, the behavior of a two-dimensional tube with an elastic segment containing ferrofluid (blood and 3vol% Fe3O4), in presence of non-uniform magnetic field is reported. Two cases of magnetic field including constant gradient (both positive and negative) and field of a wire, carrying electric current were examined. Surface tension of the membrane is considered to be fixed and constant along the elastic wall. Numerical solution of governing equations of the flow field has been obtained using the two-phase mixture model and control volume technique. Also, the membrane equation has been used to iterate and access the membrane position. Based on the obtained results, applying positive gradient magnetic field makes the tube narrower, but the negative one and magnetic field of electric wire opens the tube up.

EFFECTS OF THERMAL CREEP ON COOLING OF MICROFLOWS IN SHORT MICROCHANNELS WITH CONSTANT WALL TEMPERATURE

Fluid flow and heat transfer in the entrance region of rectangular microchannels of various aspect ratios are numerically investigated in the slip-flow regime with particular attention to thermal creep effects. Uniform inlet velocity and temperature profiles are prescribed in microchannels with constant wall temperature. An adiabatic section is also employed at the inlet of the channel in order to prevent unrealistically large axial temperature gradients due to the prescribed uniform inlet temperature as well as upstream diffusion associated with low Reynolds number flows. A control-volume technique is used to solve the Navier–Stokes and energy equations which are accompanied with appropriate velocity slip and temperature jump boundary conditions at the walls. Despite the constant wall temperature, axial and peripheral temperature gradients form in the gas layer adjacent to the wall due to temperature jump. The simultaneous effects of velocity slip, temperature jump and thermal creep on the flow and thermal patterns along with the key flow parameters are examined in detail for a wide range of cross-sectional aspect ratios, and Knudsen and Reynolds numbers. Present results indicate that thermal creep effects influence the flow field and the temperature distribution significantly in the early section of the channel.

ADI method based on [formula omitted]-continuous two-node integrated-RBF elements for viscous flows

We propose a C2-continuous alternating direction implicit (ADI) method for the solution of the streamfunction–vorticity equations governing steady 2D incompressible viscous fluid flows. Discretisation is simply achieved with Cartesian grids. Local two-node integrated radial basis function elements (IRBFEs) [D.-A. An-Vo, N. Mai-Duy, T. Tran-Cong, A C2-continuous control-volume technique based on Cartesian grids and two-node integrated-RBF elements for second-order elliptic problems, CMES: Comput. Model. Eng. Sci. 72 (2011) 299–334] are used for the discretisation of the diffusion terms, and then the convection terms are incorporated into system matrices by treating nodal derivatives as unknowns. ADI procedure is applied for the time integration. Following ADI factorisation, the two-dimensional problem becomes a sequence of one-dimensional problems. The solution strategy consists of multiple use of a one-dimensional sparse matrix algorithm that helps saving the computational cost. High levels of accuracy and efficiency of the present methods are demonstrated with solutions of several benchmark problems defined on rectangular and non-rectangular domains.

Numerical investigation of thermocapillary and buoyancy driven convection of nanofluids in a floating zone

In this paper, the results of adding nanoparticles (spherical shape Al2O3 with a diameter of 20nm) to silicone oil (Prf=16.08) as a base fluid in a floating zone with aspect ratio equal to unity have been reported. In the absence of gravity the thermocapillary convection, driven by surface tension gradient, is dominant in the floating zone. In the range of Marangoni number considered here, the flow is steady and axisymmetric. Numerical study was conducted on the effect of the increase in the volume fraction of nanoparticles on various thermo–hydrodynamic parameters of the flow, with the use of two phase mixture model and control volume technique. It has been concluded that adding nanoparticles and increasing their volume fraction deteriorate thermocapillary convective characteristics. The effect of gravity (by taking the buoyancy driven convection into account) has also been studied.

Heat transfer element for modeling the thermal response of non-uniformly heated plates

This paper presents a novel heat transfer element for modeling the 3D thermal response in plates and shells exposed to non-uniform heating. The formulation uses a combination of finite element and control volume techniques to discretize the governing equations into a series of 2D layers that are linked by a finite difference calculation. While a combination of techniques are used in the element formulation, the governing element equations are in a form that can readily be implemented into a commercial finite element code. The nine-node quadratic element considered here is implemented in ABAQUS as a user-defined element. Two- and three-dimensional verification cases are presented to demonstrate the capabilities of the element. Comparisons between the proposed shell heat transfer element and traditional continuum elements demonstrate that the proposed model exhibits a high level of accuracy and requires minimal computational power. The layered formulation offers the additional advantage of simplifying the transfer of temperature data from a thermal analysis to a structural analysis because both models can have the same mesh.

Numerical study of the ferrofluid flow and heat transfer through a rectangular duct in the presence of a non-uniform transverse magnetic field

This paper investigates numerically the hydro-thermal characteristics of a ferrofluid (water and 4vol% Fe3O4) in a vertical rectangular duct which is exposed to a non-uniform transverse magnetic field generated by an electric current going through a wire located parallelly under the duct. The two phase mixture model and the control volume technique have been used to study the flow.The results show that applying the aforementioned magnetic field increases the Nusselt number and friction factor and also creates a pair of vortices that enhances heat transfer and prevents sedimentation of nano-particles. Furthermore, unlike the axial non-uniform magnetic field, the increase of the Nusselt number for the transverse magnetic field is considerable in all length along the duct and it is also concluded that with increasing the Reynolds number, the effect of the transverse non-uniform magnetic field on the Nusselt number is more than that of the axial non-uniform magnetic field.

Slip flow over micron-sized spherical particles at intermediate Reynolds numbers

A numerical investigation has been performed to identify the rarefaction effects on the flow structure of an isolated micron-sized spherical particle. An isothermal sphere in the slip flow regime 10−3 ≤ Kn ≤ 10−1 at intermediate Reynolds numbers (1 ≤ Re ≤ 50) is considered. The Navier-Stokes equations are solved by a control volume technique in conjunction with the velocity slip boundary condition. It was found that the wake region can shrink considerably as the Knudsen number increases. Furthermore, the skin friction and pressure drag coefficients decrease as the Knudsen number increases due to the reduction in normal velocity gradients and shrinkage of the wake region, respectively. Engineering correlations for predicting the total drag coefficient in the slip flow regime are presented.

Numerical simulation of nucleate pool boiling on the horizontal surface for nano-fluid using wall heat flux partitioning method

In this paper, for the first time nucleate pool boiling heat transfer of nanofluids; has been investigated numerically. Two-phase and three-phase mixture model and control volume technique have been used to predict boiling curve of silica/water. Numerical results are in very good agreement with experimental data. In the next step, this method has been used to study nanofluids with alumina nanoparticles. The obtained results are more accurate than silica nanofluid compared to experimental data.

Numerical study of ferrofluid flow and heat transfer in the presence of a non‐uniform magnetic field in rectangular microchannels

AbstractThis paper presents a numerical investigation of the hydro‐thermal behavior of a ferrofluid in rectangular minichannels in the presence of a non‐uniform magnetic field using a two‐phase mixture model and control volume technique. Effects of increasing the diameter of nanoparticles, and channel aspect ratio have also been studied. It is concluded that the magnetic field with a negative gradient increases the Nusselt number and the rate of this increment depends on the channel aspect ratio. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21004