Showing papers on "Pressure drop published in 1989"

Transport of gas bubbles in capillaries

Abstract: The pressure drop and wetting film thickness for isolated bubbles and bubble trains moving in circular and square capillaries are computed. An arclength‐angle formulation of a composite lubrication equation allows for the numerical matching of the lubrication solution of the transition region to the static profiles away from the channel wall. This technique is shown to extend the classical matched asymptotic analysis of Bretherton for circular capillaries to higher capillary numbers Ca. More importantly, it allows the study of finite bubbles, which are shown to resemble infinitely long bubbles in film thickness and pressure drop if their lengths exceed the channel width. The numerical study of bubble trains, verified by a matched asymptotic analysis, shows a surprising result that the pressure drop across one member bubble is identical to that of an isolated bubble at low capillary numbers. This analysis of square capillaries neglects azimuthal flow and is only valid for Ca>3.0×10−3. Nevertheless the film...

Low pressure high heat transfer fluid heat exchanger

Abstract: A fluid heat exchanger for cooling an electronic component having a housing for receiving heat from the electronic component in which the housing has a fluid inlet and an outlet at opposite ends of the housing. The cross-sectional area of the housing for conveying fluid from the inlet to the outlet decreases from the inlet to the outlet thereby reducing pressure drop without sacrificing thermal performance. The cross-sectional area may be decreased by tilting a top of the housing relative to a bottom, or providing a plurality of fins separated by channels in which the cross-sectional area of the channels decreases from the inlet to the outlet.

Finite Analytic Solution of Convective Heat Transfer for Tube Arrays in Crossflow: Part II—Heat Transfer Analysis

Abstract: The convective heat transfer and pressure drop in flow past two types of tube array are solved numerically by the Finite Analytic Method in this investigation. The tube arrays considered are an in-line tube array and a staggared tube array with longitudinal and transverse pitch of two. The flow field solution is obtained and analyzed in Part 1 of the study. In the present Part 2, the temperature field, heat transfer characteristics, and pressure drop are investigated. The fluid and tubes are considered to be at the same temperature, except for the array tube, which is heated or cooled. The solution domain covers three pitches of tube arrays in order to simulate accurately the non-periodic behavior of the temperature field downsream of the heated tube. In general, the heat transfer in a staggered array of tubes is found to be higher than that in an in-lined array of tubes. However, the pressure drop in a staggered array arrangement is also higher. Local heat transfer varies between in-line and staggered tube arrays and depends on Reynolds number and Prandtl number. At high Reynolds number, the local heat transfer tends to peak at the upstream surface of the heated tube but awaymore » from the stagnation point and becomes minimum at the separation point. Heat transfer in recirculation zones are, in general, small.« less

Modelling the internal flow structure of circulating fluidized beds

Abstract: summary, given the pressure distribution along the CFB riser, or equivalently the average voidage profile and the net solids circulation rate, G, the model equations can be solved sequentially to provide a steady-state characterization of the two-phase flow. The gas and solids velocities provided by the model represent average values over the cross sectional area of the core and annular regions. However, if information is avail- able from similar units, a radial velocity distribution can be readily incorporated into the model to provide a more realistic representation of the flow. Kefa et al. (1988), for example, have found that the gas velocity follows the power law with the exponent n = 1/7. Simulation Results and Discussion The validity of the proposed model was tested using recently obtained experimental data available in the litera- ture (Bader et al., 1988; Horio et al., 1988; Brereton, 1987; Hartge et al., 1988). The experimental data employed in the evaluation cover a wide range of reactor sizes and operating conditions and are listed in Table 1. Each simulation has been performed by utilizing experimental average voidage profiles or pressure drop dis- tributions, as provided by the various authors, and by solving the model equations described

The existence of steady flow in a collapsed tube

Abstract: Self-excited oscillations arise during flow through a pressurized segment of collapsible tube, for a range of values of the time-independent controlling pressures. They come about either because there is an (unstable) steady flow corresponding to these pressures, or because no steady flow exists. We investigate the existence of steady flow in a one-dimensional collapsible-tube model, which takes account of both longitudinal tension and jet energy loss E downstream of the narrowest point. For a given tube, the governing parameters are flow-rate Q, and transmural pressure P at the downstream end of the collapsible segment. If E = 0, there exists a range of (Q, P)-values for which no solutions exist; when E ≠ 0 a solution is always found. For the case E ≠ 0, predictions are made of pressure drop along the collapsible tube; these solutions are compared with experiment.

Performance Characteristics of a Concentric Annular Heat Pipe: Part I—Experimental Prediction and Analysis of the Capillary Limit

Abstract: This paper describes the design, testing, and theoretical capillary limit prediction of a new heat pipe configuration, which is the concentric annular heat pipe. The concentric annular vapor space. With this arrangement, capillary wicks can be placed on both the inside of the outer pipe and the outside of the inner pipe. This design heat pipes, since the cross-sectional area of the wick as well as the surface area for heating and cooling are increased. The heat pipe was tested for the temperature distribution in the three sections of the heat pipe under various tilt angles and heating loads through the inner and outer pipes in the evaporator section. A simple analysis for the prediction of the capillary limitation of the concentric annular heat pipe is presented.

Heat transfer and pressure drop during evaporation and condensation of R22 in horizontal micro-fin tubes☆

Abstract: The heat transfer and pressure drop performance of three tubes with many small innerfins, called micro-fin tubes, having 9.5 mm outside diameter and 8.9 mm maximum inside diameter were obtained using R22 as the working fluid. The test apparatus had a straight, horizontal test section with a length of 3.67 m and was heated or cooled by water circulated in a surrounding annulus. Nominal evaporation conditions were 0 to 5°C (0.5 to 0.6 MPa) with inlet and outlet qualities of 10% and 90%, respectively. Condensation conditions were 39 to 42°C (1.5 to 1.6 MPa) with inlet and outlet qualities of 90% and 10%, respectively. Mass flux was varied from 150 to 500 kg m−2 s−1. The micro-fin tubes were generally found to have an enhancement of heat transfer ranging from 50 to 100% when compared to an equivalent smooth tube. The maximum increase in pressure drop was only 40%.

Phenomena of a liquid drop falling to a liquid surface

Abstract: Two kinds of phenomenon have been observed when a liquid drop falls to a surface of the same liquid. The first, which can nearly always be observed, involves splash and some degree of penetration and “cleavage” and the conditions for this occurrence are identified. The experimental observations are compared with previous computational results. The second kind of colliding phenomena can be observed only by chance in an ordinary falling drop experiment and appears to be random. It includes the two phenomena investigated in this paper: the floating drop and the rolling drop.

Effect of frost growth on the performance of louvered finned tube heat exchangers.

Abstract: An experimental investigation of the effects of frost growth on the performance of heat exchangers with louvered fins has been conducted. Frost accumulation, pressure drop across the heat exchanger and an energy transfer coefficient based on a logarithmic mean enthalpy difference (LMED) were quantified under frosting conditions as functions of the air humidity, air face velocity and fin spacing. Higher air humidity, air face velocities and smaller fin spacing all led to increased frost growth, higher pressure drops and higher energy transfer coefficients. As frost accumulated on the heat exchanger, the overall energy transfer coefficient eventually dropped. These trends are consistent with those reported in the literature.

Performance Characteristics of a Concentric Annular Heat Pipe: Part II—Vapor Flow Analysis

Abstract: The solutions of the equations of fluid motion for compressible and incompressible flow in a concentric annular heat pipe have been analyzed In addition, a similarity solution is presented that can predict the pressure losses in all the segments of the concentric annular heat pipe as well as conventional heat pipes A theoretical analysis to predict the sonic limit for this new pipe is also presented

Liquid flow in molds with prelocated fiber mats

Abstract: The mechanism associated with mold filling in the manufacture of structural RIM (SRIM) and resin transfer molding (RTM) composites is studied by means of flow visualization and pressure drop measurements. To facilitate this study, an acrylic mold with a variable cavity was constructed and the flow patterns of nonreactive fluid flowing through various layers, types, and combinations of preplaced glass fiber reinforcement mats were photographed for both evacuated and nonevacuated molds. The pressure drops in the flow through a single type of reinforcement (e.g., a continuous strand random fiber mat) and also a combination of reinforcement types (e.g., a stitched bidirectional mat in combination with a random fiber mat) were recorded at various flow rates to simulate high-speed feeding processes (e.g., SRIM) and low-speed feeding processes (e.g., RTM). By changing the amount of reinforcement placed into the mold, the permeabilities of the different types and combinations of glass fiber mats were obtained as a function of porosity. It is shown that partially evacuating the mold cavity decreases the size of bubbles or voids in the liquid, but ultimately increases the maximum pressure during filling. The results also show that glass fiber mats exhibit anisotropic permeabilities with the thickness permeability, Kz, being extremely important and often the determining factor in the pressure generated in the mold during filling.

Pressure Drop and Mass Transfer in Two-Pass Ribbed Channels

Abstract: The combined effects of the sharp 180-deg turn and of the rib configuration on the pressure drop and mass transfer characteristics in a two-pass square channel with a pair of opposite rib-roughened walls (to simulate turbine airfoil cooling passages) were determined for a Reynolds number range of 10,000-60,000. Heat transfer enhancements were compared for the first pass and for the two-pass channel with the sharp 180-deg turn. Correlations for the fully-developed friction factors and loss coefficients were obtained.

Particulate filter trap load regeneration system

Abstract: A particulate filter trap regeneration system and control mechanism is disclosed including a downstream vent tube section across which a pressure signal is derived as an analog of the exhaust gas stream velocity flowing through the particulate trap. A novel particulate loading parameter formula is disclosed by which the maximum acceptable pressure drop across a loaded particulate trap may be calculated and related to exhaust gas flow through the trap in order to determine when particulate trap regeneration should commence. In one embodiment, a vent tube equipped with a venturi throat for increasing the accuracy of the pressure signal indicative of exhaust gas stream velocity is disclosed along with representative dimensional parameters.

Drop oscillations in liquid-liquid systems

Abstract: When the ratio of the drop radius to the distance separating any two drops and the relative importance of gravitational to surface forces are both small, the small amplitude oscillations of a drop of one viscous fluid immersed in another fluid are governed by the nonlinear dispersion relation derived by Miller and Scriven. The dispersion relation has been solved numerically to determine the character of oscillations for arbitrary values of drop size, physical properties of the two fluids, and interfacial tension. The new theoretical results determine the range of validity of the low-viscosity approximation, and are also shown to be essential for proper interpretation of many previously reported experimental results. New experimental measurements of natural frequencies of oscillation of water drops falling in 2-ethyl-1-hexanol, a system having properties characteristic of many others in solvent extraction, agree well with the theoretical predictions when drop radius is smaller than a critical size.

Impingement/Effusion Cooling: The Influence of the Number of Impingement Holes and Pressure Loss on the Heat Transfer Coefficient

Abstract: Measurements of the overall heat transfer coefficient within an impingement/effusion cooled wall are presented. The FLUENT CFD computer code has been applied to the internal aerodynamics to demonstrate the importance of internal recirculation in the impingement gap. This generates a convective heat transfer to the impingement jet. Measurements of this heat transfer plate coefficient are presented that show it to be approximately half of the impingement/effusion heat transfer coefficient. The influence of the relative pressure loss or X/D between the impingement and effusion walls was investigated, for an effusion X/D of 4.67 and a Z of 8 mm, and shown to be only significant at high G where a reduction in h of 20 percent occurred. Increasing the number of holes N in the impingement/effusion array at a constant Z of 8 mm reduced h by 20 percent, mainly due to the higher Z/D for the smaller holes at high N. Reduced numbers of impingement holes relative to the effusion holes, in a ratio of 1 to 4, were shown to have a small influence on h with a maximum reduction in h of 20 percent at high G and a negligible effect at low G.

The Effect of Variations in Stream-Wise Spacing and Length on Convection From Surface Mounted Rectangular Components

Abstract: The effect of variations in stream-wise spacing and component length on convection from rectangular, surface mounted components in a channel flow are reported. Component dimensions are the same order of magnitude as the channel wall-to-wall spacing. The channel Reynolds number, with air as the coolant, ranged from 670 to 3000. Flow visualization showed that under the above conditions the channel flow is transitional. The effect of variations in component stream-wise spacing on the level of turbulence in the channel and on the interaction between the core of the channel flow and the recirculating flow in cavities between components is discussed. Pressure drop measurements show that the dominant loss mechanism is due to form drag caused by the components. Local heat transfer measurements are made using an interferometer. Analysis of the results shows that the overall heat transfer is properly correlated in terms of a flow Reynolds number based on the component length. At small component Reynolds number, the overall conductance tends towards the laminar smooth wall value. An overall correlation is proposed which includes the effect of component Reynolds number, channel wall-to-wall spacing, and component stream-wise spacing.

Two-phase pressure drop reduction bwr assembly design

Abstract: In a boiling water reactor having discrete bundles of fuel rods confined within channel enclosed fuel assemblies, an improved fuel design of bundles of fuel rods interior of the channels is disclosed. Specifically, partial length rods are utilized which extend from the bottom of the channel only part way to the top of the channel. These partial length rods are shortened with respect to the remaining rods and are symmetrically distributed throughout the fuel bundle with the preferred disposition being in the second row of the bundle of fuel rods from the channel wall. The symmetrical distribution of the partial length rods is at spaced apart locations one from another. The partial length rods extend from the bottom of the fuel bundle and terminate within the boiling region. during shutdown of the reactor, an improved cold shutdown margin is produced at the top of the fuel assembly due to the improved moderator-to-fuel ratio and reduction in plutonium formation at the upper portion of the bundle. Shutdown control rod worth is improved due to greater moderator-to-fuel ratio and a longer thermal neutron diffusion length. During power reator operation, the partial length fuel rods improve flow distribution above the ends of the partial length rods by channeling steam in the open interstitial area between rods above the ends of the partial length rods. This enables a high slip ratio of steam with respect to water and increases the density of the moderating water about the remaining rods in the upper region of the bundle at power operation. The total pressure drop is reduced, permitting more fuel rods in the design or a larger fuel rod diameter. The ratio of two-phase pressure drop to single phase pressure drop also is reduced, tending to increase the threshold for thermal hydraulic instability or coupled nucler-thermal-hydraulic instability. Rod spacers and bundle tie plates are provided with larger apertures overlying the partial length rods for further channeling of the steam and reduction of two-phase pressure drop. Most importantly and during full reactor power output, the pressure drop in the two-phase region of the bundle is reduced without substantial corresponding degradation of the fuel assemblies thermal limits. These features permit designs with larger fuel rod diameter than are possible without part length rods and results in a net increase in fuel assembly uranium weight with the larger fuel rod diameter more than compensating for the weight removed by shortening some of the fuel rods.