Decrease In Pressure Drop Research Articles

Filtering Characteristics of Porous SiC Filter with High Surface Area.

Filtering characteristics of porous silicon carbide candle filters with high surface area were investigated. Cogwheel type silicon carbide ceramic filters consisting of a highly porous support and a filtration layer were fabricated by extrusion forming. Tube typed ceramic candle filters were also fabricated for comparison. The cogwheel type filter showed much less pressure drops than the tube typed one according to an increase of flow rate or continuous mass loading. While the cogwheel shape did not greatly affect the separation efficiency, it clearly affected the cleaning efficiency. Additionally, the cogwheel type filter showed better cleaning characteristics. It is suggested that the cogwheel shape is beneficial to decrease pressure drop and thus improves the operating performance.

A numerical investigation of louvered fin-and-tube heat exchangers having circular and oval tube configurations

A numerical investigation of the airside performance for fin-and-tube heat exchanger having circular and oval configuration is presented in this study. The geometrical parameters of louver angle, louver pitch, and louver length are examined. For a fixed louver length (6.25 mm) and louver angle (14°), a 10% decrease of heat transfer performance is observed and a 41% decrease of pressure drop is seen for oval tube configuration. The calculated results indicate that the pressure drops always with increase in louver angle. However, an optimal value of heat transfer performance is observed due to the difference in the development of thermal boundary layer on the upper and lower louver surface. Both the heat transfer and friction performance increase with louver length. However, the rate of the increase of heat transfer performance is about the same as the increase of pressure drops.

Renal Replacement Therapy: Physical Properties of Hollow Fibers Influence Efficiency

Physical properties of filters for continous renal replacement therapy have a great impact on biocompatibility. According to Poiseuille's law, a filter with more and shorter hollow fibers should offer a decreased pressure drop and, therefore, lower transmembrane pressure (TMP). The aim of this study was to study the effect of a new filter configuration in terms of TMP and clotting compared with the standard configuration. In a prospective randomized cross-over study 2 polysulphone hollow fiber hemofilters, one handmade, which differed only in length and number of hollow fibers were compared. In each group 12 filters were investigated during continous venovenous hemofiltration in patients with acute renal failure due to septic shock. Pressures were measured every 3 hours and running time until filter clotting was documented. Mediators before and after the filter, at the end of treatment and in filtrate were assessed. The standard filter with longer hollow fibers had significantly lower TMPs (106 vs. 194 mmHg, p=0.02) and longer running times (1276 vs. 851 min, p=0.04). There were no differences in hematocrit, total protein, cellular and plasmatic coagulation or blood temperature. No significant elimination of mediators was shown. In contrast to our expectations, the filter with the longer hollow fibers had a better performance, as it ran longer and had lower TMP This may be due to slower blood flow leading to an increase in blood viscosity in a filter with a larger cross section.

Non-newtonian pressure drop and critical reynolds number through rectangular duct

Results of an experimental study on non-Newtonian flow in rectangular duct are presented. The critical Reynolds numbers were measured using a flow visualization technique for flow of distilled water and CMC solutions as the working fluids. Also axial static pressure measurements in the different locations of the duct were made for Newtonian and purely viscous non-Newtonian fluids. Results indicate that as the pseudoplasticity of the solution increases the critical Reynolds number increases while the dimensionless pressure drop decreases. The results of pressure drop obtained by the present investigation are in very good agreement with available correlations in the literature.

00/03386 Improving hot gas filtration behavior in PFBC power plants

According to a previous paper, a laboratory-scale cold flow model of the hot gas filtration system in Escatron PFBC power plant has been built. The main objectives were to establish the validity of the scaling laws for cyclone separator systems (cyclone and dipleg) and to perform detailed room temperature studies in a rapid and cost effective manner. In Escatron PFBC power plant, the hot gas filtration equipment is a two-stage process performed in nine streams between the fluidized bed and the gas turbine. Due to the unsteadiness in the dipleg and the suction nozzle, and the effect of sintered deposit, the cyclone performance is modified. The performances of cyclone separator system and suction nozzle diplegs are scarcely reported in the open literature. This paper presents the results of a detailed research in which some important conclusions of well known studies about cyclones are verified. Also remarkable is the increase in cyclone efficiency and decrease in pressure drop when the solid load to the cyclone is increased. The possibility to check the fouling by means of pressure drop has not been previously addressed. Finally, the influences of gas input velocity to the cyclone, the transport gas to the ash conveying lines,more » the solid load and the cyclone fouling have been analyzed. This study has allowed characterizing the performance of the full-scale ash removal system, establishing safe limits of operation and testing design improvements as the two suction nozzle dipleg, pointing out important conclusions for the filtration process in PFBC power plants.« less

FACTORS AFFECTING THE STABILITY OF THE PERFORMANCE OF AMBIENT FINE-PARTICLE CONCENTRATORS

This article describes a systematic evaluation of factors affecting the stability of the performance of Harvard ambient fine-particle concentrators, an essential requirement for controlled animal and human exposure studies that utilize these technologies. Phenomenological problems during the operation of the concentrator, including pressure drop increase and decrease in concentration enrichment, were statistically correlated with ambient air parameters such as temperature, relative humidity, PM2.5 mass concentration, and mass median diameter. The normalized hourly pressure drop across the concentrator was strongly associated (R2 =. 81) with the product of ambient PM2.5 mass concentration and the difference between the vapor pressure downstream of the impactor nozzle and the saturation vapor pressure at the adiabatic expansion temperature (i.e., the temperature of the aerosol immediately downstream of the virtual impactors). From multiple regression analysis, the average enrichment factor was predicted reasonably well (R2 =. 67) by aerosol mass median diameter and the normalized hourly pressure drop. Based on these results, we can anticipate in any given day whether an exposure study can be conducted without a considerable increase in the concentrator pressure drop, which might lead to an abrupt or premature termination of the exposure. As particle mass concentration and ambient dewpoint are the two main parameters responsible for raising the pressure drop across the concentrator, efforts should be made to either desiccate the ambient aerosol at days of high dewpoints, or to dilute the ambient PM at days of high concentrations, prior to drawing the aerosol through the virtual impactors. The latter approach is recommended on days of severe ambient pollution conditions because it is simpler and also makes it possible to maintain the appropriate concentration level delivered to the exposure chamber.

45 deg Round-Corner Rib Heat Transfer Coefficient Measurements in a Square Channel

Cooling channels, roughened with repeated ribs, are commonly employed as a means of cooling turbine blades. The increased level of mixing induced by these ribs enhances the convective heat transfer in the blade cooling cavities. Many previous investigations have focused on the heat transfer coefficient on the surfaces between these ribs and only a few studies report the heat transfer coefficient on the rib surfaces themselves. The present study investigated the heat transfer coefficient on the surfaces of 45 deg, round-corner ribs. Three staggered rib geometries corresponding to blockage ratios of 0.133, 0.167, and 0.25 were tested in a square channel for pitch-to-height ratios of 5, 8.5, and 10, and for two distinct thermal boundary conditions of heated and unheated channel wall. Comparisons were made between the surface-averaged heat transfer coefficients and channel friction factors for sharp-and round-corner ribs and 45 versus 90 deg ribs, reported previously. Heat transfer coefficients of the furthest upstream rib and that of a typical rib located in the middle of the ribroughened region were also compared. It was concluded that: (a) For the geometries tested, the rib average heat transfer coefficient was much higher than that for the area between the ribs. (b) The general effect of rounding the rib corners was a decrease in both rib heat transfer coefficient and channel pressure drop. (c) For the highest blockage ratio ribs (e/Dh = 0.25), 90 deg ribs performed superior to 45 deg ribs. However, this trend reversed for smaller rib blockage ratios. (d) Heat transfer coefficients for the two smaller rib geometries (e/Dh = 0.133 and 0.167) did not vary significantly with the pitch-to-height ratio in the range tested. However, the heat transfer coefficient for the high blockage rib geometry increased significantly as the ribs were brought closer to each other. (e) Under otherwise identical conditions, ribs in the furthest upstream position produced lower heat transfer coefficients than those in the midstream position. (f) Rib thermal performance decreased with the rib blockage ratio. The smallest rib geometry (e/Dh = 0.133) at a pitch-to-height ratio of 10 and the largest rib geometry (e/Dh = 0.25) at a pitch-to-height ratio of 5, both in midstream position, produced the highest and the lowest thermal performances, respectively.

In vitro assessment of the flow fields in a three‐dimensional pulmonary artery model with varying degrees of valvular stenosis

This study was conducted to assess the effects of varying degrees of valvular stenosis on the flow fields in a three‐dimensional pulmonary artery model. Porcine pulmonary arteries procured from a slaughterhouse were used as test models. To produce dilated main (MPA) and left (LPA) pulmonary arteries similar to those clinically observed in valvular pulmonic stenosis, an epoxy fixation technique was employed. A three‐dimensional echocardiographic reconstruction method for color Doppler flow mapping was used to examine the flow fields in the test models. Additionally, transvalvular pressure drops were measured by a side‐hole catheter and predicted by a Doppler‐derived Bernoulli equation. Changes in flow fields in the MPA were observed as the pulmonic valve became stenotic. A jet‐like flow was present distal to the stenotic valve. The change in geometry in the MPA, due to its dilatation, had a marked effect on the pulmonary artery hemodynamics. The jet‐like flow seen distal to the valve deflected away from the centerline and impinged on the roof of the MPA. The force impinging on the stenotic valve and the roof of the MPA increased with increasing degree of valvular stenosis. Clinically, this may impair the stenotic valve and make the dilatation of the MPA more profound. The Doppler‐predicted pressure drops correlated well with the catheter‐measured pressure drops. The measured transvalvular pressure drops increased with increasing degree of valvular stenosis. As a result of increasing pressure drop, the transvalvular energy loss increased as the valve became more stenotic. Some degree of pressure recovery, reflected by a decrease in transvalvular pressure drop with increasing distance from the valve, was observed for each stenotic valve. The extent of pressure recovery increased as the valve became more stenotic. The study demonstrates the necessity of considering complex biological flows from a three‐dimensional viewpoint.

Laboratory Tests and Field Implementation of Gas-Drag-Reduction Chemicals

SummaryDrag reduction in gas-transmission lines can be achieved by applying a thin chemical coating on the pipe inner surface to reduce friction between the flowing gas and pipe wall. Newly identified molecules used for gas-drag reduction can strongly bond to metal surfaces and form a smooth film to mitigate gas turbulence at the gas/solid interface. Effective gas-drag reducers have properties similar to corrosion inhibitors and lubricants or a combination of both. Fatty acids, oxylated fatty acid amines, and/or amides with carbon numbers between 18 and 54 can provide this type of behavior.1 The desired scenario is based on positively charged amine and amide functional groups providing strong binding to the metal surface and the long-chain hydrocarbon part serving as a compliant or lubricating surface to mitigate turbulence at the gas-phase boundary.2A field test using Nalco 945 corrosion inhibitor at High Island 24L [a 7.625-in. inside diameter (ID) and 6.25-mile-long gas line from an offshore platform to the inland facilities in Sabine Pass, Texas] demonstrated gas-throughput improvement up to 20% at its peak performance. The improvement can be defined either as a reduction in pressure drop at a constant flow or as a flow-rate increase at a constant pressure drop. In this case, the gas-drag reducer resulted in a decrease in pressure drop from 180 to 150 psi and an increase in flow rate from 50 to 52 MMscf/D, while maintaining discharge pressure at about 840 psi. Its effectiveness peaked at the third week after one injection treatment, and then gradually tapered off. Benefits lasted more than 2 months.

Thermal and flow analysis for the optimization of a parallel flow heat exchanger

The present paper examines the thermal and flow characteristics of a parallel flow heat exchanger and investigates the effects of the parameters on thermal performance by defining the flow nonuniformity. Thermal performance of a parallel flow heat exchanger is maximized by the optimization using Newton's searching method. The flow nonuniformity is chosen as an object function. The parameters such as the locations of separator, inlet, and outlet are expected to have a large influence on thermal performance of a parallel flow heat exchanger. The effect of these parameters are quantified by flow nonuniformity. The results show that the optimal locations of inlet and outlet are 19.73 mm and 10.9 mm, respectively. It is also shown that the heat transfer increases by 7.6% and the pressure drop decreases by 4.7%, compared to the reference model.

長期呼吸補助用人工肺の開発

This paper describes a membrane oxygenator for long term lung assist. A Membrane Oxygenator has been used for extracorporeal circulation as ECMO. However, the major oxygenators which have microporous membrane cause plasma leakage that deteriorates the performances for long term circulation. The authors developed a fine silicone hollow fiber which is twice the mechanical strength, low diameter and thin wall thickness. The fine silicone hollow fiber has almost the same transfer performance as microporous hollow fiber when it used in extracapillary flow type. However, extracapillary flow type which causes partial and accumulate flow easily has possibility of causing thrumbus and reduction of gas transfer performance. On the other hand, an intracapillary flow type oxygenator can make laminar flow in the hollow fibers. It is able to keep gas transfer performance stably for long term circulation without thrumbus. One of the disadvantages of intracapillary flow type is large pressure drop. Therefore, using softness of the silicone material, the authors designed and manufactured an oxygenator which has expanded inlet for decreasing pressure drop. This intracapillary oxygenator consists of25000silicone hollow fibers with a length of8cm inserted in the housing. The surface area of the membrane is3.0m 2. The priming volume is390mL. Gas transfer performance of the oxygenator was evaluated by in vitro experiments. Oxygen and carbon dioxide transfer rate were 52mL/min and95mL/miri, and pressure drop was30mmHg at a blood flow rate1L/min. The oxygenator developed in this study can be used for extended duration in such application as extracorporeal membrane oxygenator.

The effects of temperature-dependent viscosity on flow in a cooled channel with application to basaltic fissure eruptions

A theoretical description is given of pressure-driven viscous flow of an initially hot fluid through a planar channel with cold walls. The viscosity of the fluid is assumed to be a function only of its temperature. If the viscosity variations caused by the cooling of the fluid are sufficiently large then the relationship between the pressure drop and the flow rate is non-monotonic and there can be more than one steady flow for a given pressure drop. The linear stability of steady flows to two-dimensional and three-dimensional disturbances is calculated. The region of instability to two-dimensional disturbances corresponds exactly to those flows in which an increase in flow rate leads to a decrease in pressure drop. At higher viscosity contrasts some flows are most unstable to three-dimensional (fingering) instabilities analogous, but not identical, to Saffman-Taylor fingering. A cross-channel-averaged model is derived and used to investigate the finite-amplitude evolution.

Normal-phase high-performance liquid chromatography using enhanced-fluidity liquid mobile phases

The application of an enhanced-fluidity liquid mixture ( n-hexane-CO 2) as a mobile phase in normal-phase HPLC using a 3-cyanopropyl polysiloxane stationary phase was evaluated. Decreased pressure drop across the chromatographic column was observed with increasing proportions of added CO 2 to the mixtures. For selected mixture conditions, increased efficiency and decreased peak asymmetry were obtained in comparison to that for separations with 100% n-hexane. A limiting amount of CO 2 that could be added to hexane was found. If more CO 2 was added past that limit, serious peak asymmetry lowered the measured column efficiency.

Numerical Study of Forced Convection in a Partially Porous Channel With Discrete Heat Sources

A numerical study was performed to analyze steady laminar forced convection in a channel partially filled with a fluid-saturated porous medium and containing discrete heat sources on the bottom wall. Hydrodynamic and heat transfer results are reported for the configuration in which the porous layers are located above the heat sources while the rest of the channel is nonporous. The flow in the porous medium was modeled using the Brinkman-Forchheimer extended Darcy model. Parametric studies were conducted to evaluate the effects of variable heat source spacing and heat source width on heat transfer enhancement and pressure drop in the channel. The results indicate that when the heat source spacing was increased within the range considered, there was a negligible change in heat transfer enhancement while the pressure drop decreased significantly. When the heat source width was decreased, there was a moderate increase in heat transfer enhancement and a significant decrease in pressure drop.

A Multi-Kilowatt Immersion-Cooled Standard Electronic Clamshell Module for Future Aircraft Avionics

A new type of immersion cooled module, the BTPFL-C2, was developed for thermal management of future high flux avionics while conforming to the geometrical constraints of existing military modules and avionic enclosures. The BTPFL-C2 houses two circuit boards separated by a flow distribution plate and employs two sleeveless quick connection coolant couplers. The flow distribution plate supplies the coolant inside the module into parallel narrow channels formed between the distribution plate and the surfaces of the chips. Theoretical predictions of the thermal performance of the BTPFL-C2 were substantiated by experimental data using a test module populated with ten chips. Increasing the coolant subcooling at the module inlet was found to decrease pressure drop across the module, decrease the coolant flow rate requirements, and extend the upper cooling limit of the BTPFL-C2. These results reveal the BTPFL-C2 is capable of dissipating an order of magnitude more heat than today’s most advanced avionic module. At an inlet subcooling of 40.3°C, the BTPFL-C2 could dissipate over 3000 W using only about 0.051 kg/s (0.50 gpm) of Fluorinert FC-72 and a pressure drop of only 2.8 kPa (0.41 psi).

Pulsatile flow in circular tubes of varying cross-section with suction/injection

AbstractWe consider here pulsatile flow in circular tubes of varying cross-section with permeable walls. The fluid exchange across the wall is accounted for by prescribing the normal velocity of the fluid at the wall. A perturbation analysis has been carried out for low Reynolds number flows and for small amplitudes of oscillation. It has been observed that the magnitude of the wall shear stress and the pressure drop decrease as the suction velocity increases. Further, as the Reynolds number is increased, the magnitude of wall shear stress increases in the convergent portion and decreases in the divergent portion of a constricted tube.

Entry-flow calculations for the Oldroyd-B and FENE equations

Entry-flow calculations are presented for the Oldroyd-B and FENE equations in the limit of high contraction ratio in both planar and axisym- metric geometries. In addition to abrupt entry flow a cone-shaped entry flow of half-angle π/4 is also considered. A decoupled finite-difference scheme is used with time stepping to converge to the solution of the non-linear equations. For the solution of the stress equation a streamline integration technique is developed. For the FENE equation it is found that a reordering of the elliptic operator for the stream function enables larger time steps to be taken at high We when the polymers are near full extension. These calculations show that the FENE equation can predict much larger vortices than the Oldroyd-B equation when in the non-linear regime of the FENE spring. No vortices are observed for the Oldroyd-B equation in planar flow and only weak vortices when the flow is axisymmetric. For the cone entry flow, larger vortices are again predicted for the FENE equation but they remain localised near the entry, in a manner similar to lip vortices. Pressure drops are also considered and it is argued that at high We the non-dimensional decrease in pressure drop compared with the Newtonian pressure drop should be linear in We for the Oldroyd-B equation. An estimate of this pressure drop is made in the high We, but low concentration, limits.

FORCED CONVECTION IN CONVERGENT AND DIVERGENT DUCTS OF RECTANGULAR CROSS SECTION

Abstract This paper describes the simulation of forced convection in convergent and divergent ducts of rectangular cross section. The flow is modeled as being three-dimensional and parabolic, with constant wall temperature. The results show that the pressure drop decreases, while Nusselt number increases, with increasing Reynolds number or increasing aspect ratio. For convergent flows, both pressure drop and Nusselt number increase with convergent angle. For divergent flows, pressure drop may decrease with increasing divergent angle due to the recovery of the static pressure from dynamic pressure, but the variation of local Nusselt number is not so great as that of the convergent duct except in the entrance region.

Heat transfer from smooth and rough in-line tube banks at high Reynolds number

Pressure drop and heat transfer from smooth and rough in-line tube banks in cross-flow have been measured in the Reynolds number range 5 × 10 4 $ ̌ Re $ ̌ 6 × 10 6 . The coolant is pressurized air up to 40 bar. The roughness parameter is varied from k/ d = 0 to 9 × 10 −3 The results from the local heat transfer measurements contribute to the understanding of the complicated flow around the tubes. Also for in-line arrangements a critical Reynolds number exists beyond which the heat transfer is improved while the pressure drop decreases. Finally, the entrance effect on heat transfer is considered.

Liquid metal fusion reactor systems

Abstract The main conceptual designs of liquid metal blanket, methods of pressure drop decrease in the strong magnetic field of the fusion reactor are being discussed. Special features of the flows of electrically conductive fluids in the strong magnetic fields (N≫ M≫ 1) are examined. The approximate limits of the transition to the linear (Stokes) flow in the characteristic elements of the blanket, based on experimental data, are presented. It is noted, that the most promising ways of diminishing pressure losses are: laminated walls and ducts with high aspect ratio. Methods of heat transfer enhancement in the blanket, which make it possibie to decrease thermomechanical stresses and liquid metal flow rate, are discussed. Possibilities of free surface liquid metal flow application for erosion prevention of contact devices and main schemes of flow organization are briefly discussed.