Baffled Duct Research Articles

Effects of Baffle Height and Baffle Location on Heat Transfer and Flow Profiles in a Baffled Duct: A CFD Analysis

CFD analysis of flow and heat transfer characteristics in a baffled duct is reported. The baffle locations ( s = 0.05 H – 0.40 H ), flow paths (V-apex directing Downstream or VD and V-apex directing Upstream or VU), and baffle heights ( b = 0.05 H – 0.30 H ) are investigated in the laminar flow regime with the Reynolds number based on the entry conditions between 100 and 2,000. Solutions of the present work are obtained by the finite volume method (a commercial code). Key mechanisms such as fluid streams, impinging streams, and disturbed thermal boundary layer in the baffled duct are observed. The baffle locations have high impact on flow and heat transfer behavior. The best heat transfer rate of the baffled duct is 15.55 times higher than that of the general duct with no baffle, while the optimum TEF is 4.06.

Heat and Fluid Flow Characteristics of Nanofluid in A Channel Baffled Opposite to The Heated Wall

In this paper, a nanofluid-based solar collector duct equipped with baffles is examined numerically. Baffles are located on the back plate to guide nanofluid flow toward absorber plate for heat transfer enhancement purposes. Cu-water nanofluid with fixed flow rate and concentration in the baffled duct are investigated for thermohydraulic mechanisms. Baffles with different inclination angles, heights and pitches are considered in this study. Numerical simulations are performed using Ansys fluent software with verified results compared to those of an experiment in the literature. The results show that the baffle angle 60° causes the lowest thermohydraulic performance. Because in the angle range of 30 to 60° the heat transfer is less variable while the pressure loss increases sharply. At the baffle pitch of 40 mm, there is no reattachment point at the non-heated surface. At the angle of 90°, three eddies are formed around a baffle. The slope linear regression analysis yields that baffle height has the strongest effects on thermohydraulic performance followed by baffle pitch and baffle angle. Nanofluid pressure loss respectively increases with baffle height and baffle angle at the rate of 0.463675 and 0.0049607 while absorber plate temperature respectively decreases with the baffle height and baffle angle at the rate of -0.176746 and -0.001377. Flow patterns and isotherms of all the cases examined are presented and analyzed in this study.

Hydrodynamic Behavior in Solar Oil Heat Exchanger Ducts Fitted with Staggered Baffles and Fins

The attachment of turbulators, such as baffles, fins, ribs, bars, and blocks, inside the thermal solar receiver ducts, is among the most effective mechanisms for important thermal exchange by creating the turbulence, extending the trajectory of the flow, increasing the surface of heat exchange, forcing recycling cells, and hence a high thermal exchange. The solar finned and baffled heat exchangers are employed in a wide application interval, and it is important to examine the design of a duct for this configuration of the flow field and its effect on the heat transport phenomenon. In This study, dynamic field simulations are reported in horizontal rectangular form ducts, using three obstacles with oil HTF (heat transfer fluid). Two various finned and baffled duct configurations are treated, i.e., case (A) with one fin and two baffles, and case (B) with two fins and one baffle. Different hydrodynamic fields, i.e., X-velocity and Y-speed, as well as various X-velocity profiles in many flow stations, related to Re value, are analyzed. A computational approach is applied in order to simulate the oil flow, using finite volume (FV) integration method, SIMPLE discretization algorithm, QUICK interpolation scheme, Standard k-epsilon turbulence model, and ANSYS FLUENT 12.0 software. Simulation results reported an unstable flow structure, with powerful recycling cells, on the backsides of each fin and baffle, as a result of fluid detachment at their upper front sharp edges, in both studied models (A and B). As expected, the first duct model, i.e., Case A, has better X- and Y-velocity values, due to its large recirculation regions. In This paper, many physical phenomena, such as the turbulence, instability, flow separation, and the appearance of reverse secondary currents, are reported. As its data confirmed by many previous numerical and experimental results, the suggested new models of finned and baffled heat exchangers filled with high thermal conductivity oil, allow an improvement in the dynamic thermal-energy behavior of many thermal devices such as flat plate solar collectors.

Heat and mass transfer of oils in baffled and finned ducts

This analysis intends to simulate the forced-convection and oil flow characteristics in the turbulent regime (Re = 5000-25000) through rectangular-shaped ducts with staggered, transverse, solid, and flat baffle plates. The study is achieved by using a calculation software based on the finite volume method (FLUENT) with selected SIMPLE, Quick, and k-? model. Two various models of baffled ducts are simulated in this analysis under steady flow conditions. In the first model (Case A), a duct with one upper fin and two lower baffles is examined. However and in the second model (Case B), a duct with two upper fins and one lower baffle is treated. The con?tour plots of stream-function, number of Nusselt, and coefficient of skin friction are addressed. As expected, the heat transfer rates raised in the second case (Case B), due to the presence of the lower second obstacle that directs the entire oil current towards the hot upper part of the second duct at very high velocities, resulting thus in enhanced heat transfer rates, especially in the case of high Reynolds number values.

Heat and mass transfer of oils in baffled and finned ducts

This analysis intends to simulate the forced-convection and oil flow characteristics in the turbulent regime (Re = 5000-25000) through rectangular-shaped ducts with staggered, transverse, solid, and flat baffle plates. The study is achieved by using a calculation software based on the finite volume method (FLUENT) with selected SIMPLE, Quick, and k-? model. Two various models of baffled ducts are simulated in this analysis under steady flow conditions. In the first model (Case A), a duct with one upper fin and two lower baffles is examined. However and in the second model (Case B), a duct with two upper fins and one lower baffle is treated. The con?tour plots of stream-function, number of Nusselt, and coefficient of skin friction are addressed. As expected, the heat transfer rates raised in the second case (Case B), due to the presence of the lower second obstacle that directs the entire oil current towards the hot upper part of the second duct at very high velocities, resulting thus in enhanced heat transfer rates, especially in the case of high Reynolds number values.

Suppression of Ag deposition by Ar gas in mtorr range and its implication to mitigation of impurity deposition on first mirrors

We observe that Ar gas confined in a tube maintained at a pressure higher than 10 mtorr by a baffled duct is very effective in minimizing the deposition of incoming Ag particles onto the surface of quartz crystal microbalance (QCM) in the tube. Ar gas is introduced into the tube and the gas flow to the main chamber is minimized by a baffled duct. In this way, the tube pressure of 10 mTorr or higher is achieved. The pressure is found to be enough to suppress the deposition of nearly 97% Ag particles onto the QCM in the tube. The suppression of the Ag deposition is successfully explained by reduced mean-free path at the high pressure in the tube. We propose that the present approach can be very promising in the mitigation of impurity particles on first mirrors in thermonuclear reactors.

The application of inverse methods to spatially-distributed acoustic sources

Acoustic inverse methods, based on the output of an array of microphones, can be readily applied to the characterisation of acoustic sources that can be adequately modelled as a number of discrete monopoles. However, there are many situations, particularly in the fields of vibroacoustics and aeroacoustics, where the sources are distributed continuously in space over a finite area (or volume). This paper is concerned with the practical problem of applying inverse methods to such distributed source regions via the process of spatial sampling. The problem is first tackled using computer simulations of the errors associated with the application of spatial sampling to a wide range of source distributions. It is found that the spatial sampling criterion for minimising the errors in the radiated far-field reconstructed from the discretised source distributions is strongly dependent on acoustic wavelength but is only weakly dependent on the details of the source field itself. The results of the computer simulations are verified experimentally through the application of the inverse method to the sound field radiated by a ducted fan. The un-baffled fan source with the associated flow field is modelled as a set of equivalent monopole sources positioned on the baffled duct exit along with a matrix of complimentary non-flow Green functions. Successful application of the spatial sampling criterion involves careful frequency-dependent selection of source spacing, and results in the accurate reconstruction of the radiated sound field. Discussions of the conditioning of the Green function matrix which is inverted are included and it is shown that the spatial sampling criterion may be relaxed if conditioning techniques, such as regularisation, are applied to this matrix prior to inversion.

Performance Study of Solar Air Heater Having Absorber Plate with Half-Perforated Baffles

The paper presents a detailed mathematical model for performance prediction of a smooth duct solar air heater validated against the experimental results. Experimental study on a solar air heater having absorber plate with half-perforated baffles on the air flow side shows thermal efficiency enhancement of 28%–45% over that of the smooth duct solar air heater, which is attributed to the heat transfer enhancement (of the order of 180%–235%) due to the perforated baffles attached to the absorber plate and reduction in the mean temperature of the absorber plate by 20°C–25°C as compared to the temperature of absorber plate of smooth duct air heater. Using the mathematical model, the performance plot for the baffled duct air heater has been presented, and the effect of the variation of ambient parameters on the predicted thermal efficiency has been studied.

Aircraft Skin-Cooling Airflow Distribution

A skin-cooling system has been developed to reject heat from high-power electronic equipment onboard a CL-600 Challenger aircraft. This concept calls for baffled ducts at the aircraft skin to cool the air in the aft cabin, where the equipment is located. The hot air from the rack with the equipment that dissipates the most heat is exhausted Into a ceiling plenum, from which it is distributed by fans Into the baffled ducts. These ducts, which are bounded by the cold skin on one side, are used as a heat exchanger to reject the heat. The cooled air is then recirculated into the aft cabin. This paper describes a series of tests that were performed to evaluate the feasibility of providing a common inhale/exhale opening in the ceiling plenum. This opening is to prevent the ceiling fans from starving when some of the equipment is off (inhale), and to avoid excessive pressurization of the system when some or all of the ceiling fans are off (exhale). The tests were performed using a representative plenum configuration. We also describe a simulation model of the plenum flow distribution system

Performance Prediction and Control-System Design of an Aircraft Skin-Cooling Technique

We describe the steady state and transient thermal response of the aft cabin of an aircraft that is retrofitted with high-power electronic equipment and cooled by heat rejection through the skin. In this skin-cooling design, the outer surface of the fuselage is treated as a heat exchanger. Hot air from an equipment exhaust plenum is drawn into a series of baffled ducts within the fuselage support structure, where heat is rejected and then recirculated into the cabin. The cooler air from the cabin is then drawn into the electronic equipment. The aircraft air-conditioning unit is also modeled to provide chilled air directly Into the cabin. In addition, this paper presents an algorithm and a control-system concept to maintain the temperature of the aft cabin within acceptable limits. Results establish a control-system design, which is being implemented in a CL-600 Challenger aircraft

THE ACOUSTIC RADIATION OF BAFFLED FINITE DUCTS WITH VIBRATING WALLS

A mathematical model for the radiation of baffled finite ducts is presented. This model was developed to be used for the design process of Magnetic Resonance Imaging (MRI) scanners. The added value of utilizing this model over using general purpose acoustics software is the increased insight into the acoustic phenomena in the baffled finite duct and the increased efficiency. The problem domain of the scanner was characterized as a finite duct with infinite flanges, acoustically excited by wall vibration. A mathematical model for this problem domain was developed, based on a model description of the acoustic field. The model was constructed by using a Fourier transformation technique for the Helmholtz equation and the velocity boundary conditions at the duct's wall. The diffraction of sound at the flanges was described with reflection coefficients. Two simultaneous matrix equations were found describing the acoustic field in the wall-driven baffled finite duct. Special attention was paid to the efficient implementation of the model. The physical and computational characteristics of the model were determined by parameter study and by comparison with Fourier Boundary Element Method (BEM) models of the MRI scanner. A good agreement was found between the results obtained with the baffled duct and the Fourier BEM models. Because of the direct relationship between design parameters and acoustic response, and because of the better numerical efficiency of the baffled duct model as opposed to the Fourier BEM models, the application of the baffled duct model in the design process is viable.