Baffle Height Research Articles

Calculation of turbulent flow and heat transfer in a porous-baffled channel

This study presents the numerical predictions on the turbulent fluid flow and heat transfer characteristics for rectangular channel with porous baffles which are arranged on the bottom and top channel walls in a periodically staggered way. The turbulent governing equations are solved by a control volume-based finite difference method with power-law scheme and the k– ε turbulence model associated with wall function to describe the turbulent structure. The velocity and pressure terms of momentum equations are solved by SIMPLE (semi-implicit method for pressure-linked equation) method. The parameters studied include the entrance Reynolds number Re (1×10 4–5×10 4), the baffle height ( h=10, 20 and 30 mm) and kind of baffles (solid and porous); whereas the baffle spacing S/ H are fixed at 1.0 and the working medium is air. The numerical calculations of the flow field indicate that the flow patterns around the porous- and solid-type baffles are entirely different due to different transport phenomena and it significantly influences the local heat transfer coefficient distributions. Relative to the solid-type baffle channel, the porous-type baffle channel has a lower friction factor due to less channel blockage. Concerning the heat transfer effect, both the solid-type and porous-type baffles walls enhanced the heat transfer relative to the smooth channel. It is further found that at the higher baffle height, the level of heat transfer augmentation is nearly the same for the porous-type baffle, the only difference being the Reynolds number dependence. As expected, the centerline-averaged Nusselt number ratio increases with increasing the baffle height because of the flow acceleration.

Mixed Convection From a Cylinder With Low Conductivity Baffles in Cross-Flow

The problem of laminar mixed convection from an isothermal cylinder with low conductivity baffles in cross flow was solved numerically. The average Nusselt number was calculated at different combinations of number of baffles, baffle height, Reynolds number, and buoyancy parameter. The reduction in the Nusselt number is as much as 75 percent. When using a small number of baffles at low values of buoyancy parameter, an odd number of baffles reduced the Nusselt number more than an even number of baffles, especially at high values of Reynolds number. This is not the case at high values of buoyancy parameter. There is an optimal baffle height, Reynolds number dependent, for maximum heat transfer reduction beyond which an increase in baffle height does not result in further decrease in heat transfer.

USE OF BAFFLES FOR HEAT TRANSFER REDUCTION FROM A CYLINDER IN CROSS FLOW

The problem of cross-flow forced heat transfer from a horizontal cylinder with multiple equally spaced low conductivity baffles on its outer surface was investigated numerically. The effect of several combinations of baffles and baffle heights on the average Nusselt number was studied over a wide range of Reynolds numbers. The results showed that there was an optimal number of baffles for a minimum Nusselt number for a given value of baffle height and Reynolds number. Short baffles slightly increased the Nusselt number at small Reynolds number values.

Method of calculation of new cyclone-type separator with swirling baffle and bottom take off of clean gas — part II: experimental verification

The results of tests and experimental verification of the derived model to predict collection efficiency and pressure drop of the Institute for Chemical Processing of Coal (IChPW) design of a cyclone-type separator with a swirling baffle are presented. The experimental work contains the testing of the effect of gas flow rate and rotational speed of the rotor on separation efficiency and pressure drop. The effect of sealing flow on dedusting efficiency was also tested. The separator with a swirling baffle is characterized by high efficiency and low pressure drop. Higher dedusting efficiency and lower pressure drop can be obtained by extension of the baffle height. The calculational method shows good agreement with the experiments.

Natural Convection in a Trapezoidal Enclosure with Offset Baffles

A numerical investigation has been made of natural convection heat transfer in a trapezoidal enclosure (representing attic spaces) with offset baffles. Two thermal boundary conditions representing summerlike conditions (upper surface heated) and winterlike conditions (upper surface cooled) and two baffle heights are studied. For each boundary condition and baffle height, two baffle positions are considered. In position I, the upper baffle is offset toward the heated vertical wall and the lower baffle is offset toward the symmetry plane of the enclosure, whereas in position II, the upper baffle is offset toward the symmetry plane and the lower baffle is offset toward the heated wall. Rayleigh number values range from 10 3 to 5 × 10 7 for summerlike conditions and from 10 3 to 10 6 for winterlike conditions. Predictions reveal a decrease in heat transfer in the presence of baffles. In winterlike conditions, convection starts to dominate at a Rayleigh number much lower than that in summerlike conditions. The maximum reduction in heat transfer is achieved with long baffles placed in position II for summerlike conditions and in position I for winterlike conditions. Average Nusselt number correlation for both boundary conditions are presented.

NATURAL CONVECTION IN TRAPEZOIDAL CAVITIES WITH BAFFLES MOUNTED ON THE UPPER INCLINED SURFACES

A numerical investigation has been undertaken to study the effects of mounting baffles to the upper inclined planes of trapezoidal cavities (representing a building or attic space). Two thermal boundary conditions are considered: (a) the vertical and upper surfaces are heated while the lower surface is cooled (summerlike conditions); (b) the lower surface is heated while the other surfaces are cooled (winterlike conditions). For each boundary condition, computations are performed for two baffle heights and two baffle locations. Rayleigh number (Ra) values range from 103 to 5 x 107 for summerlike conditions and from 103 to 106 for winterlike conditions. For both boundary conditions, results obtained with air as the working fluid reveal a decrease in heat transfer in the presence of baffles. In winterlike conditions, convection starts to dominate at an Ra much lower than that in summerlike conditions. The decrease in heat transfer becomes increasingly more significant as the baffle gets closer to the heated vertical wall for the bottom-cooled situation and as the baffle gets closer to the symmetry line for the bottom-heated case. In general, this decrease in heat transfer is higher with taller baffles. Average Nusselt number (Nu) correlations for both boundary conditions are presented.

Natural Convection Heat Transfer and Entropy Generation From a Horizontal Cylinder With Baffles

The problem of laminar natural convection heat transfer from a horizontal cylinder with multiple, equally spaced, low conductivity baffles on its outer surface was investigated numerically. The effect of several combinations of number of baffles and baffle height on the average Nusselt number was studied over a wide range of Rayleigh numbers. The computed velocity and temperature fields were also used to calculate the local and global entropy generation for different cylinder diameters. The results showed that there was an optimal combination of a number of baffles and baffle height for minimum Nusselt number for a given value of the Rayleigh number. Short baffles slightly increased the Nusselt number at small values of the Rayleigh number. The global entropy generation increased monotonically with increasing Rayleigh number and decreased with increasing cylinder diameter, baffle height, and number of baffles. [S0022-1481(00)01203-2]

Hydrodynamics of a Circulating Fluidized Bed with a Bubbling Bed Section Separated by an Inner Rim Baffle.

The hydrodynamics of a circulating fluidized bed with a bubbling bed section separated by an inner rim baffle are examined both by experiment and mathematical analysis. To maintain sufficient solids holdup in the upper section, the inner rim baffle was set up in the middle of the riser. It is found that the solids holdup in the section above the baffle is greatly increased. Investigation into the baffle dimensions shows that the variation of the baffle clearance has little effect on the solids holdup in the upper section when the clearance is greater than a certain value, whereas the variation of the baffle height has a significant effect on the solids holdup in the upper section, i.e. the lower the baffle height, the higher solids holdup. A hydrodynamic model is developed based on the mass balance and the pressure balance of the solids circulation loop. With respect to gas-solids flow behavior in the upper section, the clustering suspension and the core-annulus flow are taken into account; for the lower section, a bubbling fluidized bed model is included. By comparing the calculated results with the experimental ones, the model is found to predict fairly well the gas-solids flow behavior of the compact bubbling-circulating fluidized bed.

BUOYANCY-INDUCED HEAT TRANSFER IN PARTIALLY DIVIDED TRAPEZOIDAL CAVITIES

Numerical results are reported for natural convection heat transfer in partially divided trapezoidal cavities representing attic spaces. Two boundary conditions are considered. In the first, corresponding to summer-like conditions, the vertical and upper surfaces are heated while the lower surface is cooled. In the second, corresponding to winter-like conditions, the lower surface is heated while the other surfaces are cooled. The effects of Rayleigh number, baffle height, and baffle location on the heat transfer are investigated. Results are displayed in terms of streamlines, isotherms, velocity and temperature profiles, and local and average Nusselt number values. In winter-like conditions, convection starts to dominate at a Rayleigh number much lower than that in summer-like conditions. For both boundary conditions, the presence of baffles decreases heat transfer. For the bottom-cooled case this decrease is greater with a taller baffle, placed closer to the heated walls. For the bottom-heated case the decrease in heat transfer due to the baffles is greater with increasing distance from the vertical wall. Average Nusselt number correlations for both boundary conditions are presented.

Turbulent Heat Transfer and Fluid Flow in a Porous-Baffled Channel

Experiments were conducted to examine the effect of porous-type baffles on heat transfer and friction in a baffled channel. The porous-type baffles are arranged on the bottom and top channel walls in a staggered manner. Flowfield, pressure loss, isotherm pattern, and channel centerline heat transfer coefficients are obtained inside the periodic cell formed between the segmented baffles. Results of the conventional solid-type-baffled channel are also obtained for comparison. The void fraction ν o of porous-type baffle and the baffle spacing S/H are fixed at 0.42, and 1.0, respectively; whereas the baffle height ratio h/H varies from 0.25 to 0.75 and the flow Reynolds number Re ranges from 1 x 10 4 to 5 x 10 4 , respectively. It is disclosed that the flow patterns around the porous- and solid-type baffles are entirely different. These different transport phenomena, in conjunction with the change in baffle effectiveness significantly influence the local heat transfer coefficient distributions but negligibly influence the average heat transfer coefficients. Relative to the solid-type-baffled channel, the porous-type-baffled channel has a lower friction loss.

The Design of Acoustic Radar Baffles

Abstract Compact acoustic antenna arrays, commonly used for profiling urban atmospheres, usually require acoustic baffles to minimize reflections from hard objects and to limit the impact of the 2–6-kHz signals on inhabitants. To facilitate optimum compact design, the authors show how to find the velocity potential or intensity for a wide range of baffle illuminations and baffle shapes immersed in a homogeneous atmosphere. Results are presented for baffle configurations in terms of wavenumber k = 2π/λ. Baffle height needs to be about 40k−1, and baffle sides should not be so close to the speaker array as to cut the main beam. This is particularly important for steered beams, when sloping baffle sides are recommended. Square plan baffles are advantageous for arrays of regular columns and rows of speakers. A triangular fringe baffle top edge (thnadner) will also reduce sidelobes by about 18 dB if their width is about a wavelength and their height more than 10k−1. The basic baffles design criteria suggested a...

Effects of wall conduction, internal heat sources and an internal baffle on natural convection heat transfer in a rectangular enclosure

Conjugate natural convection heat transfer in a two-dimensional, air-filled enclosure containing discrete internal heat sources and an internal baffle is examined. The enclosure formed of finite conductive walls is designed to simulate the behavior of an experimental window calorimeter in order to correct for losses from the calorimeter. The equations are solved using a finite-volume method for a wide range of Rayleigh numbers, internal-extemal heat source ratios, solid-fluid conductivity ratios and baffle heights. The influences on the heat transfer and the flow characteristics resulting from the internal heat sources as well as the conductive baffle are discussed. Measurements of temperature distributions in the window calorimeter are also reported. The comparison between numerical predictions and experimental measurements shows that it is inappropriate to specify simple boundary conditions on the window surface of the calorimeter and to neglect the conduction through the baffle, window, and walls. A modified procedure for calculating the temperature distributions on the window surface improves the predicted results and yields good agreement with the measured data.

THREE-DIMENSIONAL HEAT TRANSFER IN A CHANNEL WITH A BAFFLE IN THE ENTRANCE REGION

A numerical investigation of laminar forced convection was performed in a three-dimensional channel with a baffle in the entrance region. The top and bottom watts were subjected to a uniform heat flux heating condition, while the side watts were insulated. The numerical study was conducted using a finite volume approach, and the grid independence was established. Parametric runs were made for Reynolds numbers (Re) of 100-500; Prandtl numbers of 0.7 and 7.0; baffle heights (Bk /Dh) of 0.25, 0.50, and 0.75; and thermal conductivity ratios (K) of 10,100, and 1000. Three-dimensional effects in the flow field were confined to the neighborhood of the baffle, but three-dimensional effects in the temperature field were present in the entire channel In general, separation length upstream of the baffle and recirculation length downstream of the baffle increased with an increase in the flow Reynolds number and baffle height The spanwise averaged Nussett number increased with an increase in the thermal conductivity of the wall

Performance of Baffle-Sluice Modules with Changed Module Dimensions

An irrigation module delivers nearly constant discharge irrespective of water-level fluctuations in the supply channel. Low discharge baffle-sluice modules have been designed for the field outlets considering the desirable features of a good module. The flow-regulating characteristics of three baffle-sluice modules with the option of reduced module width and baffle heights are discussed in detail. The modules are found to deliver discharges within ±5 of the design value in a modular range of 10 cm. Thus the concept of baffle-sluice modules already conceived and designed can contribute to the modernization of water management systems in supplying the requisite amounts of irrigation water depending on crop requirements.

THE EFFECT OF VORTICES INDUCED BY BAFFLES ON CONCENTRATION POLARIZATION

A numerical analysis was performed to investigate the effect of recirculations formed by rectangular or triangular baffles on depolarization of concentration in a flat sheet membrane module. The k- ϵ turbulent model was used to predict the flow field in the flat channel. Control-volume-based finite difference methods were employed to solve for the two-dimensional fluid velocity and solute concentration distributions. We examined rigorously the effect of various parameters including the velocity, diffusivity, permeate flux, baffle size, baffle shape, and interbaffle spacing in an effort to find optimum operating conditions which may provide enhanced mass transfer. The vortices induced by the baffles on the membrane are found to be extremely effective in depolarizing the retained solutes at the membrane surface. The predictions show that baffle configurations and flow conditions have a great influence on depolarization of concentration. To achieve effective concentration depolarization, the baffle height sh...

HEAT TRANSFER IN A THREE-DIMENSIONAL CHANNEL WITH BAFFLES

A numerical investigation of laminar forced convective heat transfer was performed in a three-dimensional channel with baffles in which a uniform heat flux was applied to the top and bottom walls, and the sidewalk were considered adiabatic. The trade-off between heat transfer enhancement and pressure drop produced by the baffles was studied for periodically fully developed flow (PDF). The numerical analysis was performed using a finite volume approach. The computer code was validated against the experimental results of Goldstein and Kreid [1] and Beavers et al. [2] for a three-dimensional channel without baffles. Parametric runs were made for Reynolds numbers of 150, 250, 350, and 450 for baffle height to channel width ratios (H/Dy) of 0.5, 0.6, 0.7, and 0.8. Heat transfer behavior was studied for Prandtl numbers of 0.7 and 7.0, and for wall thermal conductivity to fluid thermal conductivity ratios (K) of 1, 10, 100, and 1000.

Experimental Investigation of Heat Transfer and Flow Over Baffles of Different Heights

The phenomenon of flow separation in ducts with segmented baffles has many engineering applications, for example, shell-and-tube heat exchangers with segmented baffles, labyrinth shaft seals, laser curtain seals, air-cooled solar collectors, and internally cooled turbine blades. In the present work, an experimental investigation has been done to study the characteristics of the turbulent flow and heat transfer inside the periodic cell formed between segmented baffles staggered in a rectangular duct. In particular, flow field, pressure loss, and local and average heat transfer coefficients were obtained. The experimental runs were carried out for different values of Reynolds numbers and baffle heights (window cuts) at uniform wall heat flux condition along the top and bottom walls. The results indicate that the pressure loss increases as the baffle height does, for a given flow rate. Also, the local and average heat transfer parameters increase with increasing Reynolds number and baffle height. However, the associated increase in the pressure loss was found to be much higher than the increase in the heat transfer coefficient.

MULTIGRID COMPUTATION OF NATURAL CONVECTION IN ENCLOSURES WITH A CONDUCTIVE BAFFLE

Conjugate heat transfer has been investigated in a two-dimensional square enclosure with a conducting vertical baffle of finite thickness and varying height. The horizontal end walls are assumed to be adiabatic, and the vertical watts are at constant but different temperatures. Calculations are made by a staggered, finite volume multigrid procedure. The performance of the multigrid method in accelerating the convergence rate is remarkable by comparison with the usual iterative method. The influence of inserting a baffle into the buoyancy-driven square cavity on the heat transfer, as well as on the temperature distribution and velocity field, has been obtained for various Rayleigh numbers Ra, solid /fluid conductivity ratio k∗ dimensionless baffle height H, and baffle location L. Predicted flow patterns and isotherms indicate that the effect of inserting baffles of varying height upon the overall heat transfer and local temperature profiles in the cavity is limited, except when the height of baffle is large (H > 0.5). The effect of conductivity is also found to be marginal. However, both the height and the conductivity become very important when the baffle is located very near the hot wall or cold walls.

Radial flow stilling basins with baffle blocks

A total of 120 tests of forced radial flow hydraulic jumps have been analyzed in order to develop curves and equations for the design of radial stilling basins. The jump depth, the water surface profile, wave amplitudes, the allowable flare angle, and the jump length are defined in terms of entrance conditions, the baffle position, and the baffle height. An example design is given and compared with a USBR (U.S. Bureau of Reclamation) Type III stilling basin. Key words: forced hydraulic jump, radial flow, design, stilling basins, baffles, radial hydraulic jump, circular hydraulic jump.

Hydraulics of culvert fishways II: slotted-weir culvert fishways

This paper presents the results of an experimental study on the hydraulics of culvert fishways with a slotted-weir baffle system. Six designs with two baffle heights and three spacings were tested. A flow equation has been developed to predict the flow depth for any given discharge, diameter, and slope. The barrier velocity that would exist at the slot in the baffles has also been predicted in a general manner. This relatively simple slotted-weir baffle system has been found to match the performance of the more complicated but frequently used offset baffle system of similar dimensions. Key words: culverts, fishways, baffles, hydraulics, turbulent flow, open-channel flow.