Heat Transfer In Channel Flow Research Articles

ENHANCING HEAT TRANSFER IN CHANNEL FLOW USING SYNTHETIC JETS

Synthetic jet's effectiveness in flow control, fluid mixing enhancement, and cooling has been established. The current study aims to examine the improvement of fluid blending and heat dissipation rate of two water inlets with varying temperatures in a channel that is disturbed by a synthetic jet at different excitation frequencies. The simulation analysis predicts the temperature distributions and the fully develop the velocity profile along symmetrical plane of the channel with interference of synthetic jet using establish CFD software. The RNG k- ε turbulence model was employed to compute the turbulent flow produced by the synthetic jet. A moving mesh approach was employed to replicate the movement of a synthetic jet diaphragm. The results indicate that the fluid flow behavior in the channel disrupted by the synthetic jet flow. Hence, indicating to an enhance in both the fluid flow velocity and the heat transfer rate. A higher frequency of the actuator enhances fluid mixing and reduces the channel distance required to achieve temperature equilibrium within the channel in comparison to a lower frequency of the actuator.

A Comprehensive Evaluation of Turbulence Models for Predicting Heat Transfer in Turbulent Channel Flow across Various Prandtl Number Regimes

Turbulent heat transfer in channel flows is an important area of research due to its simple geometry and diverse industrial applications. Reynolds-Averaged Navier–Stokes (RANS) models are the most-affordable simulation methodology and are often the only viable choice for investigating industrial flows. However, accurate modelling of wall-bounded flows is challenging in RANS, and the assessment of the performance of RANS models for heated turbulent channel flow has not been sufficiently investigated for a wide range of Reynolds and Prandtl numbers. In this study, five RANS models are assessed for their ability to predict heat transfer in channel flows across a wide range of Reynolds and Prandtl numbers (Pr) by comparing the RANS results with respect to the corresponding Direct Numerical Simulation data. The models include three Eddy Viscosity Models (EVMs): standard k−ϵ, low Reynolds number k−ϵLS, and k−ωSST, as well as two Reynolds Stress Models (RSMs): Launder–Reece–Rodi and Speziale–Sarkar–Gatski models. The study analyses the Reynolds number effects on turbulent heat transfer in a channel flow at a Pr of 0.71 for friction Reynolds number values of 180,395,640, and 1020. The results show that all models accurately predict velocity across all Reynolds numbers, but the accuracy of mean temperature prediction drops with increasing Reynolds number for all models, except for the k−ωSST model. The study also analyses the Pr effects on turbulent heat transfer in a channel flow with Pr values between 0.025 and 10.0. An error analysis is performed on the results obtained from different turbulence models, and it is shown that the k−ωSST model has the smallest error for the predictions of the mean temperature and Nusselt number for high-Prandtl-number flows, while the low Reynolds number k−ϵLS model shows the smallest errors for low-Prandtl-number flows at different Reynolds numbers. An analytical solution is utilised to identify Pr effects on forced convection in a channel flow into three different regimes: analytical region, transitional region, and turbulent diffusion-dominated region. These regimes are helpful to discuss the validity of the models in relation to the Pr. The findings of this paper provide insights into the performance of different RANS models for heat transfer predictions in a channel flow.

Effect of Vortex Generator Placement and Nanofluids on Channel Flow Heat Transfer

In this research, an attempt has been made to enhance the heat transfer for a plate-fin heat exchanger with the new arrangement of classic delta winglets used for vortex generators and compared the same with the existing literature. The computational domains are developed by dislocating delta winglets from their original position, so there is no additional pressure loss with flow geometry. All the flow domains are analyzed by computing the 3D Reynolds averaged Navier–Stokes equations using ANSYS Fluent. Two different working fluids are considered one is water and nanofluids (water with Aluminum oxide). Heat transfer characteristics are analyzed for different placements of winglets for both water and nanofluids. The plate-fin heat exchanger’s performance has been optimized with the optimum location of winglets and nanofluids from the analysis of numerical results. For the case of 0% nanofluids at 300 Reynolds number, Case 3 Nusselt number has been increased by 23.2% with a decrease in pressure drop of 17.7% with the dislocation of one winglet. It represents the enhancement of heat transfer.

Effect of Utilizing Staggered Semi-Porous Fins on Channel Flow Heat Transfer Enhancement

A comprehensive numerical investigation of fluid stream and laminar forced convection were conducted to simulate the effects of the semi-porous fins, which are a new combination of porous and solid parts, inside a partially heated channel with a staggered arrangement. The present numerical approach is based on the Navier-Stocks and Darcy-Brinkman-Forchheimer equations in the fluid and semi-porous regions, respectively. The effects of various parameters such as Reynolds number, Darcy number, fin height, and aspect ratio of the porous region’s height to total fin height were studied. Also, the effects of these parameters are illustrated further as a variation of dimensionless pressure penalty and heat transfer enhancement ratio in the flow domain. The results demonstrate that using a new type of fin with both solid and porous parts in a single fin, enhances the heat transfer up to 6% compared to the porous fin and decreases the pressure penalty up to 23% compared to the solid fin at Darcy number of 10−4 when the percentage of aspect ratio is equal to 20%. Furthermore, it was found that the Darcy number of 10−5 is a critical value for the optimum utilization of semi-porous fins.

Heat Transfer-Friction Factor and Correlations for Wavy Porous Screens as Inserts in Channel Thermal Performance

Abstract Structural inserts are employed to enhance the heat transfer in channel flow with the expense of thermal performance. The present investigation employs the wavy porous screens as inserts in an air channel and measures the pressure drop and heat transfer along the channel. The wave vectors are parallel to the flow and in point contact at the tips with the channel walls. The pores in the insert generate turbulence to enhance the heat transfer from the channel walls with a moderate pressure penalty because of the low blockage ratio. The objectives are to investigate the effects of wavelength (λ), porosity (ξ), and height (H) of the sinusoidal wave of the insert as well as the Reynolds number (Re) on the friction factors (f) and Nusselt numbers (Nu). Twelve inserts are formed from the flat metal mesh screens for testing between the Reynolds number (Re) of 400 and 35,000. The results of (f, Nu) and smooth channel-based enhancements (f/f0, Nu/Nu0) are affected the most by Re followed by λ and then ξ. The values of both (f/f0, Nu/Nu0) increase significantly as the Reynolds number increases in Re < 3000. However, both the (f/f0, Nu/Nu0) decrease little as both the (λ, ξ) increase at all Re. The performance factor index, (Nu/Nu0)/(f/f0)(1/3) > 1.0 irrespective of (λ, ξ, H) only when Re is about 3000. The correlations developed for the f, Nu, and performance factor provide reasonable predictions of the experimental results.

A New Idea of Fractal-fractional Derivative with Power Law Kernel for Free Convection Heat Transfer in a Channel Flow between Two Static Upright Parallel Plates

Nowadays some new ideas of fractional derivatives have been used successfully in the present research community to study different types of mathematical models. Amongst them, the significant models of fluids and heat or mass transfer are on priority. Most recently a new idea of fractal-fractional derivative is introduced; however, it is not used for heat transfer in channel flow. In this article, we have studied this new idea of fractal fractional operators with power-law kernel for heat transfer in a fluid flow problem. More exactly, we have considered the free convection heat transfer for a Newtonian fluid. The flow is bounded between two parallel static plates. One of the plates is heated constantly. The proposed problem is modeled with a fractal fractional derivative operator with a power-law kernel and solved via the Laplace transform method to find out the exact solution. The results are graphically analyzed via MathCad-15 software to study the behavior of fractal parameters and fractional parameter. For the influence of temperature and velocity profile, it is observed that the fractional parameter raised the velocity and temperature as compared to the fractal operator. Therefore, a combined approach of fractal fractional explains the memory of the function better than fractional only.

Effect of Aspect Ratio and Installation Direction on Channel Flow Heat Transfer Performance under a Wide Range of Reynolds Number

In recent years, in the cooling technology for high-power electronic devices such as power transistors used for drive motor control of electric vehicles and hybrid vehicles, a method of flowing a cooling fluid to a cooling substrate having a fin structure has become the main technology. The structure of the cooling fluid flow path is a channel flow through multiple narrow plate gaps to secure a heat transfer area. In this study, the heat transfer characteristics when the aspect ratio of the channel having a flat rectangular cross-section was changed were investigated in detail by experiments. Moreover, the difference in the heat transfer characteristic at the time of making a rectangular flow path into vertical installation and horizontal installation was also investigated.

Assessment of performance of subgrid stress models for a LES technique for predicting suppression of turbulence and heat transfer in channel flows under the influence of body forces

The main purpose of this work was to assess the performance of subgrid stress models for large eddy simulation (LES) of the flow and heat transfer of a conductive liquid simulating a molten salt (Pr = 4.1) in a square duct under the influence of a transverse magnetic field and an upward flow of air in a vertical heated pipe under a strong influence of buoyancy. An analysis of these problems is important when choosing the most appropriate subgrid-scale LES model for calculating the flows of an electrically conductive liquid under the combined influence of a magnetic field and buoyancy forces. Four subgrid-scale (SGS) models were verified: the Smagorinsky model with damping function (SMP), a coherent structure model (CSM), a WALE model and a hybrid model based on the equation for turbulent kinetic energy (KDES). For magnetohydrodynamic (MHD) flow in the duct, computations were performed in a domain with periodic inlet-exit boundaries and in a domain corresponding to the entrance region of a duct with a transverse magnetic field. Mixed convection of the air in the vertical heated pipe was simulated only in the domain with periodic boundaries. The results are compared with available data of direct numerical simulations (DNS).For MHD flow in the duct, the best predictions of DNS data for the average and fluctuating velocity components at Ha=21.2 and Re=5602 were obtained with the CSM and WALE models. The skin-friction and heat transfer coefficients are well known to have a minimum as Ha increases due to turbulence suppression by the magnetic field. The SMP and KDES models predict a minimum at Hadip≈22, whereas the CSM and WALE models predict a minimum at Hadip≈30 for Re=5602. The DNS data marked these values as the lower and upper boundaries of the complete turbulence suppression region for the same Reynolds number.For mixed convection of the air upward flows in a circular heated pipe at Re=5300, the CSM and WALE models showed weaker suppression of turbulence due to buoyancy forces when compared to the DNS results. The results of calculations of skin-friction and heat transfer coefficients performed with the help of the SMP and KDES models are much more coincident with the DNS data.

Analysis of convective heat transfer in channel flow with arbitrary rough surface

AbstractWe consider forced convective heat transfer in a channel flow with a rough boundary. The roughness of the domain is expressed as the product of length scale ε and arbitrary smooth function h. The boundaries of the channel are assumed as hot (top) and cold (bottom) walls. We derive an effective model reflecting the rough boundary effects, and analyze the average Nusselt number and wall laws (effective boundary conditions). Consequently, we provide the criterion for the shape of the rough boundary to enhance the heat transfer. We further confirm that the Robin–type effective boundary condition is sufficient to describe the effect of the rough layer on the heat transfer.

Optimal Patterned Wettability for Microchannel Flow Boiling Using the Lattice Boltzmann Method

Microchannel flow boiling is a cooling method studied in microscale heat-cooling, which has become an important field of research with the development of high-density integrated circuits. The change in microchannel surface characteristics affects thermal fluid behavior, and existing studies have optimized heat transfer by changing surf ace wettability characteristics. However, a surface with heterogeneous wettability also has the potential to improve heat transfer. In this case, heat transfer would be optimized by applying the optimal heterogeneous wettability surface to channel flow boiling. In this study, a change in cooling efficiency was observed, by setting a hydrophobic and hydrophilic wettability pattern on the channel surface under the microchannel flow boiling condition, using a lattice Boltzmann method simulation. In the rectangular microchannel structure, the hydrophobic-hydrophilic patterned wettability was oriented perpendicular to the flow direction. The bubble nucleation and the heat transfer coefficient were observed in each case by varying the length of the pattern and the ratio of the hydrophobic-hydrophilic area. It was found that the minimum pattern length in which individual bubbles can occur, and the wettability pattern in which the bubble nucleation-departure cycle is maintained, are advantageous for increasing the efficiency of heat transfer in channel flow boiling.

Investigation of the effect of cylindrical insert devices on laminar convective heat transfer in channel flow by applying the Field Synergy Principle

The Field Synergy Principle is widely applied to the evaluation of the convective heat transfer mechanism. In fact, as highlighted in literature, the evaluation of the synergy between the velocity and the temperature gradient vectors could provide a better insight on the local convective heat transfer mechanism. In this paper, the field synergy approach is adopted to numerically investigate the fluid dynamic and thermal behaviour of a fully developed flow between parallel plates with asymmetric heating, when cylindrical inserts are present. To better evaluate the influence of the inserts on the convective heat transfer mechanism, different values of the insert diameter are considered, for a given pitch value. The numerical results in terms of Nusselt number point out that the convective heat transfer coefficient decreases as the insert diameter increases. The Field Synergy Principle allows to explain the cause of the convective heat transfer reduction identifying the regions in which the heat transfer mechanism is ineffective: the extent of these areas increases as the insert diameter increases.

Eulerian–Eulerian Modeling of Convective Heat Transfer Enhancement in Upward Vertical Channel Flows by Gas Injection

Two-phase bubbly flows by gas injection had been shown to enhance convective heat transfer in channel flows as compared with that of single-phase flows. The present work explores the effect of gas phase distribution such as inlet air volume fraction and bubble size on the convective heat transfer in upward vertical channel flows numerically. A two-dimensional (2D) channel flow of 10 cm wide × 100 cm high at 0.2 and 1.0 m/s inlet water and air superficial velocities in churn-turbulent flow regime, respectively, is simulated. Numerical simulations are performed using the commercial computational fluid dynamics (CFD) code ANSYS fluent. The bubble size is characterized by the Eötvös number. The inlet air volume fraction is fixed at 10%, whereas the Eötvös number is maintained at 1.0 to perform parametric studies, respectively, in order to investigate the effect of gas phase distribution on average Nusselt number of the two-phase flows. All simulations are compared with a single-phase flow condition. To enhance heat transfer, it is determined that the optimum Eötvös number for the channel with a 10% inlet air volume fraction has an Eötvös number of 0.2, which is equivalent to a bubble diameter of 1.219 mm. Likewise, it is determined that the optimum volume fraction peaks at 30% inlet air volume fraction using an Eötvös number of 1.0.

Modeling of MHD turbulent heat transfer in channel flows imposed wall-normal magnetic fields under the various Prandtl number fluids

Zero-equation heat transfer models based on the constant turbulent Prandtl number are evaluated using direct numerical simulation (DNS) data for fully developed channel flows imposed on a uniform wall-normal magnetic field. Quasi-theoretical turbulent Prandtl numbers are estimated by DNS data of various molecular Prandtl number fluids. From the viewpoint of highly-accurate magneto-hydrodynamic (MHD) heat transfer prediction, the parameters of the turbulent eddy viscosity of the k–ɛ model are optimized under the magnetic fields. Consequently, we use the zero-equation model based on a constant turbulent Prandtl number to demonstrate MHD heat transfer, and show the applicability of using this model to predict the heat transfer.

DNS of Turbulent Heat Transfer in Channel Flow under Supercritical Pressure Conditions

DNS of Turbulent Heat Transfer in Channel Flow under Supercritical Pressure Conditions

Two-Dimensional Numerical Simulation of the Combined Heat Transfer in Channel Flow

A numerical investigation was conducted to analyze the flow field and heat transfer characteristics in a vertical channel with radiation and blowing from the wall. Hydrodynamic behaviour and heat transfer results are obtained by the solution of the complete Navier–Stokes and energy equations using a control volume finite element method. Turbulent flow with Low Reynolds Spalart-Allmaras Turbulence Model and radiation with Discrete Transfer Radiation Method had been modeled. In order to have a complete survey, this article has a wide range of study in different domains including velocity profiles at different locations, turbulent viscosity, shear stress, suctioned mass flow rate in different magnitude of the input Rayleigh number, blowing Reynolds number, radiation parameter, Prandtl number, the ratio of length to width and also ratio of opening thickness to width of the channel. In addition, effects of variation in any of the above non-dimensional numbers on parameters of the flow are clearly illustrated. At the end resultants had been compared with experimental data which demonstrated that in the present study, results have a great accuracy, relative errors are very small and the curve portraits are in a great agreement with real experiments.

Review on convection heat transfer in channel flow with discrete heater arrays for electronic cooling

A review on three convection modes, forced, natural or free and mixed, is made related to laminar and turbulent direct air and liquid cooling channel flow, for application to cooling of electronic systems, and with emphasis on useful correlations. The scope covers single-phase flow over plain heaters, protruded heaters and wall heating. For forced convection, the review continues from the previous review, and describes work from 1995 onward. It is observed that protruded heater distorts the flow in the channel, causing a substantial increase in heat transfer. In natural convection, the methods of cooling and channel aspect ratio strongly affect the heat transfer. In the mixed regime, the location of the heater is less important, and at low Reynolds number, heat transfer is mainly controlled by the Grashof number. However, there are still inconsistent findings among reported results. Keywords : Forced, Natural and Mixed Convection Heat Transfer, Discrete Heat Sources, Electronics Cooling, Channel Flow.

Effect of cylinder proximity to the wall on channel flow heat transfer enhancement

Heat-transfer enhancement in a uniformly heated slot mini-channel due to vortices shed from an adiabatic circular cylinder is numerically investigated. The effects of gap spacing between the cylinder and bottom wall on wall heat transfer and pressure drop are systemically studied. Numerical simulations are performed at Re=100, 0.1⩽Pr⩽10 and a blockage ratio of D/H=1/3. Results within the thermally developing flow region show heat transfer augmentation compared to the plane channel. It was found that when the obstacle is placed in the middle of the duct, maximum heat transfer enhancement from channel walls is achieved. Displacement of circular cylinder towards the bottom wall leads to the suppression of the vortex shedding, the establishment of a steady flow and a reduction of both wall heat transfer and pressure drop. Performance analysis indicates that the proposed heat transfer enhancement mechanism is beneficial for low-Prandtl-number fluids.

Piezoelectric translational agitation for enhancing forced-convection channel-flow heat transfer

Piezoelectric translational agitator (PTA) is proposed and its heat transfer performance is demonstrated by experiments in a narrow channel. For the present study, this channel simulates a portion of an air-cooled heat sink. An oval loop shell structure successfully generates millimeter-range translational displacement to a blade attached to the shell. A PTA operating at 961Hz as its second resonance mode with a 1.4mm displacement under 60Liters Per Minute (LPM) of cross flow achieved about 55% improvement in heat transfer coefficient compared to the non-agitated state. Pressure drop in the test section and the corresponding power required to drive the flow through the channel against the oscillating blade were measured. In addition, the PTAs were tested in the open channel without through-flow to examine the sole effect of agitation and to investigate the possibility of using it as a stand-alone cooling device. A total Reynolds number was defined to characterize the combined effects of cross flow and agitation. The Stanton number developed from the relationship between the total Reynolds number and heat transfer coefficients enables predicting operating performance.

Numerical investigation of transient heat transfer to hydromagnetic channel flow with radiative heat and convective cooling

This present study consists of a numerical investigation of transient heat transfer in channel flow of an electrically conducting variable viscosity Boussinesq fluid in the presence of a magnetic field and thermal radiation. The temperature dependent nature of viscosity is assumed to follow an exponentially model and the system exchanges heat with the ambient following Newton’s law of cooling. The governing nonlinear equations of momentum and energy transport are solved numerically using a semi-implicit finite difference method. Solutions are presented in graphical form and given in terms of fluid velocity, fluid temperature, skin friction and heat transfer rate for various parametric values. Our results reveal that combined effect of thermal radiation, magnetic field, viscosity variation and convective cooling have significant impact in controlling the rate of heat transfer in the boundary layer region.

DNS of heat transfer in turbulent and transitional channel flow obstructed by rectangular prisms

Direct numerical simulation (DNS) of heat transfer in a channel flow obstructed by rectangular prisms has been performed for Re τ = 80–20, where Re τ is based on the friction velocity, the channel half width and the kinematic viscosity. The molecular Prandtl number is set to be 0.71. The flow remains unsteady down to Re τ = 40 owing to the disturbance induced by the prism. For Re τ = 30 and 20, the flow results in a steady laminar flow. In the vicinity of the prism, the three-dimensional complex vortices are generated and heat transfer is enhanced. The Reynolds number effect on the time-averaged vortex structure and the local Nusselt number are investigated. The mechanism of the heat transfer enhancement is discussed. In addition, the mean flow parameters such as the friction factor and the Nusselt number are examined in comparison with existing DNS and experimental data.