scholarly journals Bypass Flow Resistance in Prismatic Gas-Cooled Nuclear Reactors

2016 ◽  
Vol 3 (1) ◽  
Author(s):  
Donald M. McEligot ◽  
Richard W. Johnson
Keyword(s):  
Friction Factor ◽  
Flow Resistance ◽  
Quantitative Information ◽  
Bypass Flow ◽  
Flow Area ◽  
Entry Length ◽  
Gap Spacings ◽  
Network Codes ◽  
Loss Coefficients ◽  
Vertical Gap

Available computational fluid dynamics (CFD) predictions of pressure distributions in the vertical bypass flow between blocks in a prismatic gas-cooled reactor (GCR) have been analyzed to deduce apparent friction factors and loss coefficients for nuclear engineering systems and network codes. Calculations were performed for vertical gap spacings “s” of 2, 6, and 10 mm — representing 1, 3, and 5 mm in a GCR design, horizontal gaps between the blocks of 2 mm and two flow rates, giving a range of vertical gap Reynolds numbers ReDh of about 40–5300. The present focus is on the examination of the flow in the vertical gaps. Horizontal gaps are treated in CFD calculations but their flows are not examined. Laminar predictions of the fully developed friction factor ffd were about 3–10% lower than the classical infinitely wide channel. In the entry region, the local apparent friction factor was slightly higher than the classic idealized case, but the hydraulic entry length Lhy was approximately the same. The per cent reduction in flow resistance was greater than the per cent increase in flow area at the vertical corners of the blocks. The standard k–ϵ turbulence model was employed for flows expected to be turbulent. Its predictions of ffd and flow resistance were significantly higher than direct numerical simulations (DNS) for the classic case; the value of Lhy was about 30 gap spacings. Initial quantitative information for entry coefficients and loss coefficients for the expansion–contraction junctions between blocks is also presented. The present study demonstrates how CFD predictions can be employed to provide integral quantities needed in systems and network codes.

Flow Resistance Characteristics of a Specific Fuel RP-3 in Helical Tubes at Supercritical Pressure With Uniform Heat Flux

2017 ◽  
Author(s):  
Nan Zhang ◽  
Yanchen Fu ◽  
Haoran Huang ◽  
Jie Wen ◽  
Nigeer Te
Keyword(s):  
Heat Flux ◽  
Friction Factor ◽  
Mass Flux ◽  
Flow Resistance ◽  
Flow Characteristics ◽  
Supercritical Pressure ◽  
Uniform Heat Flux ◽  
Inlet Temperature ◽  
Uniform Heat ◽  
Helical Tubes

The flow resistance characteristics of aviation kerosene RP-3 in horizontal helical tubes at the supercritical pressure under heating condition are investigated. Both pressure drop and friction factor were examined under uniform heat flux of 50kW/m2−300kW/m2, mass flux from 786kg/m2s to 1375kg/m2s, and helical diameter from 20mm to 40mm. The influence of viscous factors on the resistance is analyzed to explore flow characteristics in a helical tube and provide a reference for the design of heat exchangers. Friction factor decreases with the increase of heat flux at low inlet temperatures 323K and 423K. It is explained that the viscosity changes more dramatically than the density. When the fluid inlet temperature is 523K and the fluid mean temperature Tb is close to pseudo-critical temperature, frictional flow resistance becomes significantly larger Tpc due to huge variations in thermal properties in the radical direction. The effect of centrifugal force makes the friction factor decline slowly. The friction factor goes up with the enlargement of mass flux when Tb>0.81Tpc. This phenomenon is caused by the larger radial velocity gradient under the large mass flux. Different helical diameters play the leading roles for the bending flow in the tubes.

scholarly journals Loss coefficients of ice slurry in sudden pipe contractions

2010 ◽  
Vol 31 (3) ◽  
pp. 73-86
Author(s):  
Łukasz Mika
Keyword(s):  
Mass Fraction ◽  
Flow Resistance ◽  
Volume Fraction ◽  
Experimental Studies ◽  
Solid Particles ◽  
Minimal Flow ◽  
Ice Slurry ◽  
Slurry Flow ◽  
Flow Through ◽  
Loss Coefficients

Loss coefficients of ice slurry in sudden pipe contractionsIn this paper, flow systems which are commonly used in fittings elements such as contractions in ice slurry pipelines, are experimentally investigated. In the study reported in this paper, the consideration was given to the specific features of the ice slurry flow in which the flow behaviour depends mainly on the volume fraction of solid particles. The results of the experimental studies on the flow resistance, presented herein, enabled to determine the loss coefficient during the ice slurry flow through the sudden pipe contraction. The mass fraction of solid particles in the slurry ranged from 5 to 30%. The experimental studies were conducted on a few variants of the most common contractions of copper pipes: 28/22 mm, 28/18 mm, 28/15 mm, 22/18 mm, 22/15 mm and 18/15 mm. The recommended (with respect to minimal flow resistance) range of the Reynolds number (Re about 3000-4000) for the ice slurry flow through sudden contractions was presented in this paper.

Effect of Non Uniform Flow Distribution on Single Phase Heat Transfer in Parallel Microchannels

2007 ◽  
Author(s):  
Akhilesh V. Bapat ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Single Phase ◽  
Flow Distribution ◽  
Uniform Flow ◽  
Hydrodynamic Performance ◽  
Flow Area ◽  
Cross Sectional ◽  
Uniform Flow Distribution ◽  
Parallel Microchannels

The continuum assumption has been widely accepted for single phase liquid flows in microchannels. There are however a number of publications which indicate considerable deviation in thermal and hydrodynamic performance during laminar flow in microchannels. In the present work, experiments have been performed on six parallel microchannels with varying cross-sectional dimensions. A careful assessment of friction factor and heat transfer in is carried out by properly accounting for flow area variations and the accompanying non-uniform flow distribution in individual channels. These factors seem to be responsible for the discrepancy in predicting friction factor and heat transfer using conventional theory.

scholarly journals Heat transfer performance and friction factor of various nanofluids in a double-tube counter flow heat exchanger

2020 ◽  
Vol 24 (6 Part A) ◽  
pp. 3601-3612
Author(s):  
Dan Zheng ◽  
Jin Wang ◽  
Yu Pang ◽  
Zhanxiu Chen ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchanger ◽  
Friction Factor ◽  
Flow Resistance ◽  
Heat Transfer Performance ◽  
Weight Fraction ◽  
Transfer Performance ◽  
Tube Heat Exchanger ◽  
High Heat Transfer

Experimental research was conducted to reveal the effects of nanofluids on heat transfer performance in a double-tube heat exchanger. With nanoparticle weight fraction of 0.5-2.0% and Reynolds number of 4500-14500, the flow resistance and heat transfer were analyzed by using six nanofluids, i.e., CuO-water, Al2O3-water, Fe3O4-water, ZnO-water, SiC-water, SiO2-water nanofluids. Results show that SiC-water nanofluid with a weight concentration of 1.5% provides the best improvement of heat transfer performance. 1.0% CuO-water and 0.5% SiO2-water nanofluids have lower friction factors in the range of Reynolds number from 4500-14500 compared to the other nanofluids. Based on test results of heat transfer performance and flow resistance, the 1.0% CuO-water nanofluid shows a great advantage due to a relatively high heat transfer performance and a low friction factor. Finally, empirical formulae of Nusselt numbers for various nanofluids were established based on experimental data tested in the double-tube heat exchanger.

Turbulent Friction Factor for a Rod Bundle in Consideration of a Subchannel Geometry

2002 ◽  
Author(s):  
Joo Hwan Park ◽  
Chang Joon Jeong ◽  
Myung Seung Yang ◽  
Dong Suk Oh
Keyword(s):  
Friction Factor ◽  
Measurement Data ◽  
Experimental Results ◽  
Flow Area ◽  
Theoretical Derivation ◽  
Turbulent Friction ◽  
Law Of The Wall ◽  
Rod Bundle ◽  
Two Parameters ◽  
Geometry Parameter

A generalized turbulent friction factor for a rod bundle was developed based on “Law of the Wall” for a tube. It was included two parameters which are one parameter of hydraulic diameter and flow area of a subchannel and rod bundle and another parameter (called geometry parameter hereinafter) of subchannel configuration and pitch-to-diameter ratio (P/D) for a single subchannel. The turbulent geometry parameter for a single subchannel has been used as a constant on the previous works but it was found to be dependent on subchannel shapes and P/D from the present work. Hence, it was modeled as a function of the subchannel shapes and P/D from 1.0 to 1.5. The turbulent geometry parameters for single subchannels were validated by the theoretical derivation of a triangular and square subchannel. Those are compared and agreed well with the previous measurement data for 4 kinds of subchannel types such as a triangular, a square, a wall and a corner subchannel. The present model of turbulent friction factor for a rod bundle included the turbulent geometry parameter has been compared with the various experimental results for circular tubes and hexagonal tubes with various rod numbers. The predicted turbulent friction factors for those rod bundles were agreed excellently with experimental results.

Experimental Study of Entrance Effects on Laminar Gas Flow Through Silicon Orifices

2005 ◽  
Author(s):  
Aaron J. Knobloch ◽  
Joell R. Hibshman ◽  
George Wu ◽  
Rich Saia
Keyword(s):  
Flow Rate ◽  
Gas Flow ◽  
Flow Area ◽  
Fully Developed Flow ◽  
Flow Rates ◽  
Flow Models ◽  
Entry Length ◽  
Orifice Flow ◽  
Measured Flow ◽  
Flow Through

This study summarizes a fundamental investigation of flow through an array of silicon micromachined rectangular slots. The purpose of the study is to evaluate the effect of entrance pressure, flow area, orifice thickness, slot length, and slot width of the orifice on flow rate. These orifices were fabricated using a simple frontside through wafer DRIE process on a 385 μm thick wafer and wafer bonding to create thicker orifices. The dies were then packaged as part of a TO8 can and flow tested. To complement the results of this experimental work, two simple flow models were developed to predict the effect of geometrical and entrance conditions on the flow rate. These models were based on macroscale assumptions that were not necessarily true in the case of thin orifices. One relationship was based on Pouiselle flow which assumes fully developed flow conditions. Calculation of the entry length required for fully developed flow indicate that in the low Reynolds Number regime (32-550) evaluated, the entry flow development requires 2-8 times the thickness of the thickest orifices used for this study. Therefore, calculations of orifice flow based on a Pouiselle model are an overestimate of the actual measured flow rates. Another model examined typical orifice relationships using head loss at the entrance and exit of the slots did not accurately capture the particular flow rates since it overestimated the expansion or constriction losses. A series of experiments where the pressure was varied between 75 and 1000 Pa were performed. A comparison of the Pouiselle flow solution with experimental results was made which showed that the Pouiselle flow model overpredicts the flow rates and more specifically, the effect of width on the flow rates. The results of these tests were used to develop a transfer function which describes the dependence of flow rate on orifice width, thickness, length, and inlet pressure.

The Production of Duct Velocity Profiles Having High Ratios of Maximum to Mean Velocity

1956 ◽  
Vol 60 (546) ◽  
pp. 415-417 ◽  
Author(s):  
J. L. Livesey ◽  
E. Parker ◽  
P. K. Jones
Keyword(s):  
Reynolds Number ◽  
Incompressible Flow ◽  
Pressure Loss ◽  
Velocity Ratio ◽  
Velocity Profiles ◽  
Mean Velocity ◽  
Entry Length ◽  
Loss Coefficients

The results are presented of an investigation of a particular type of baffle for the production of symmetrical velocity profiles having high ratios of maximum to mean velocity in ducted incompressible flow. Two similar families of profiles are obtained depending on whether a short (12 diameters) or a long (48 diameters) entry length is used before the baffle. The highest value of the maximum to mean velocity ratio obtained is 1·42 and the pressure loss coefficients associated with the use of the baffle are given together with an indication of the effect of Reynolds number.

Two Phase Flow: Accounting for the Presence of Liquids in Gas Pipeline Design

2004 ◽  
Author(s):  
Ben Asante
Keyword(s):  
Multiphase Flow ◽  
Liquid Film ◽  
Friction Factor ◽  
Experimental Studies ◽  
Small Diameter ◽  
Gas Pipeline ◽  
Experimental Investigations ◽  
Two Phase ◽  
Flow Area ◽  
Operating Data

Multiphase flow of gas and low loads of liquids occurs frequently in natural gas gathering and transmission pipelines for both onshore and offshore operations. Literature and experimental investigations indicate that dispersed droplet and stratified flow patterns are obtained when gas and small quantities of liquids flow concurrently in a pipe. Very few correlations exist for the prediction of holdup and pressure drop for these systems and fewer still give satisfactory results. Experimental studies for air-oil and airwater systems flowing through small diameter plastic and steel horizontal pipes ranging in size from 1-inch to 3-inches were performed. The experiments were carried out at the multiphase flow laboratories of Imperial College in London and the University of Calgary in Canada. Data from actual operating gas pipeline systems transporting small amounts of hydrocarbon liquids were also evaluated. Based on the experimental results and the operating data, two approaches for modeling these systems are proposed: 1) A homogeneous approach for very low liquid loads (holdups up to 0.005), typical in gas transmission systems. A friction factor correlation based on the holdup has been developed for this flow regime. 2) A mechanistic stratified two-phase approach for higher liquid loads (holdups greater than 0.005) usually found in gas gathering systems with consideration given to: a) The reduction in the available flow area and extent of wetting of the pipe perimeter by the liquid film. The gas/liquid interface was observed to be either flat or curved. b) The interfacial friction factor between the liquid film and the gas. A new correlation based on the liquid and gas Reynolds numbers as well as the film thickens and hold up has been developed. This correlation has been successfully tested against both experimental and actual pipeline operating data.

scholarly journals Effects of Biochar Addition on Rill Flow Resistance

Water ◽  
2021 ◽  
Vol 13 (21) ◽  
pp. 3036
Author(s):  
Alessio Nicosia ◽  
Vincenzo Pampalone ◽  
Vito Ferro
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Flow Resistance ◽  
Accurate Estimate ◽  
Power Equation ◽  
Flow Turbulence ◽  
Bed Slope ◽  
The Relationship ◽  
Resistance Equation ◽  
Rill Flow

The development of rills on a hillslope whose soil is amended by biochar remains a topic to be developed. A theoretical rill flow resistance equation, obtained by the integration of a power velocity distribution, was assessed using available measurements at plot scale with a biochar added soil. The biochar was incorporated and mixed with the arable soil using a biochar content BC of 6 and 12 kg m−2. The developed analysis demonstrated that an accurate estimate of the velocity profile parameter Гv can be obtained by the proposed power equation using an exponent e of the Reynolds number which decreases for increasing BC values. This result pointed out that the increase of biochar content dumps flow turbulence. The agreement between the measured friction factor values and those calculated by the proposed flow resistance equation, with Гv values estimated by the power equation calibrated on the available measurements, is characterized by errors which are always less than or equal to ±10% and less than or equal to ±3% for 75.0% of cases. In conclusion, the available measurements and the developed analysis allowed for (i) the calibration of the relationship between Гv, the bed slope, the flow Froude number, and the Reynolds number, (ii) the assessment of the influence of biochar content on flow resistance and, (iii) stating that the theoretical flow resistance equation gives an accurate estimate of the Darcy–Weisbach friction factor for rill flows on biochar added soils.

Slope threshold in rill flow resistance

2021 ◽  
Author(s):  
Alessio Nicosia ◽  
Vito Ferro
Keyword(s):  
Friction Factor ◽  
Flow Resistance ◽  
Sediment Load ◽  
Steep Slope ◽  
Limiting Factor ◽  
Rill Erosion ◽  
Hydraulic Characteristics ◽  
Transport Capacity ◽  
Steep Slopes ◽  
Rill Flow

<p>Rills are small, steep sloping and ephemeral channels, shaped in soils, in which shallow flows move. Rill erosion strictly depends on hydraulic characteristics of the rill flow and for this reason flow discharge <em>Q</em>, rill width <em>w</em>, water depth <em>h</em>, mean flow velocity <em>V</em>, and friction factor are required to model the rill erosion process.</p><p>Erosive phenomena strictly depend on the attitude of the soil particles to be detached (<em>detachability</em>) and to be transported (<em>transportability</em>). These properties are affected by soil texture and influence the sediment load <em>G</em> to be transported by flow. The actual sediment load depends on the transport capacity <em>T<sub>c</sub></em> of the flow, which is the maximum amount of sediment, with given sizes and specific weight, that can be transported by a flow of known hydraulic characteristics.</p><p>According to Jiang et al. (2018) the hydraulic mechanisms of soil erosion for steep slopes are different from those for gentle slopes. Recent research on <em>T<sub>c </sub></em>equations exploring slopes steeper than 18% (Ali et al., 2013; Zhang et al., 2009; Wu et al., 2016) established that <em>T<sub>c</sub></em> relationships designed for gentle slopes (<18%) are unsuitable to be applied to steep slopes (17–47%). Also Peng et al. (2015) noticed that <<<em>there has been little research concerning rill flow on steep slopes (e.g. slope gradients higher than 10°)</em>>>. In other words, the slope of 18% could be used to distinguish between the “gentle slope” and the “steep slope” case for the recognized difference in hydraulic and sediment transport variables.</p><p>The applicability of a theoretical rill flow resistance equation, based on the integration of a power velocity distribution (Barenblatt, 1979; 1987), was tested using measurements carried out in mobile rills shaped on plots having different slopes (9, 14, 15, 18, 22, 24, 25 and 26%) and soil textures (clay fractions ranging from 32.7% to 73% and silt of 19.9% – 30.9%), and measurements available in literature (Jiang et al. (2018), Huang et al. (2020) and Yang et al. (2020)).</p><p>The Darcy-Weisbach friction factor resulted dependent on slope, Froude number, Reynolds number and <em>CLAY</em> and <em>SILT</em> percentages, which represent soil transportability and detachability, respectively. This theoretical approach was applied to two different databases distinguished by the slope threshold of 18%. The results showed that, for gentle slopes (< 18%), the Darcy-Weisbach friction factor increases with slope, <em>CLAY</em> and <em>SILT</em> content. Taking into account that for gentle slopes the hydraulic characteristics limit the transport capacity, for this condition <em>T<sub>c</sub></em> and the sediment load <em>G</em> are both limiting factors.</p><p>For steep slopes (> 18%), the flow resistance increases with slope and the ratio between <em>SILT</em> and <em>CLAY</em> percentage. Steep slopes determine high values of the transport capacity, which is consequently not a limiting factor. Thus, in this condition the actual sediment load is determined exclusively by the ratio between <em>SILT</em> and <em>CLAY</em> percentage. In other words, the only limiting factor for a steep slope condition is the sediment which can be transported (i.e. the sediment load <em>G</em>), affected by its soil detachability and transportability.</p>

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