Integral Solutions for Transient Temperature Profiles in Stably-Stratified Open Enclosures

2003 ◽  
Vol 125 (2) ◽  
pp. 273-281 ◽  
Author(s):  
K. O. Homan
Keyword(s):  
Growth Rates ◽  
Interfacial Layer ◽  
Molecular Diffusion ◽  
Transient Temperature ◽  
Published Data ◽  
Flow Rates ◽  
Rate Asymmetry ◽  
Key Characteristics ◽  
Two Parameters ◽  
Integral Solutions

The stably-stratified filling of an enclosure produces an interfacial layer, or thermocline, separating the hot and cold fluid volumes which is transported through the vessel with the bulk flow. The evolution of this interfacial layer is characterized by profile asymmetries and growth rates not explained by simple molecular diffusion. The present paper presents integral solutions to the horizontally-averaged energy equation with variable diffusivities exhibiting these same characteristics. The formulation requires only two parameters in addition to those of the uniform diffusivity case. The solutions are compared to published data to illustrate determination of the empirical constants and show that key characteristics of the model, specifically a constant fill-line temperature and symmetric growth rates, are satisfied for a range of moderate flow rates. At higher flow rates, the layers are seen to exhibit an increasingly higher degree of growth rate asymmetry.

Experimental and Theoretical Analysis of Transient Response of Plate Heat Exchangers in Presence of Nonuniform Flow Distribution

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
N. Srihari ◽  
Sarit K. Das
Keyword(s):  
Steady State ◽  
Heat Exchangers ◽  
Sudden Change ◽  
Temperature Response ◽  
Flow Distribution ◽  
Transient Temperature ◽  
Nonuniform Flow ◽  
Flow Rates ◽  
Plate Heat ◽  
Flow Maldistribution

Transient analysis helps us to predict the behavior of heat exchangers subjected to various operational disturbances due to sudden change in temperature or flow rates of the working fluids. The present experimental analysis deals with the effect of flow distribution on the transient temperature response for U-type and Z-type plate heat exchangers. The experiments have been carried out with uniform and nonuniform flow distributions for various flow rates. The temperature responses are analyzed for various transient characteristics, such as initial delay and time constant. It is also possible to observe the steady state characteristics after the responses reach asymptotic values. The experimental observations indicate that the Z-type flow configuration is more strongly affected by flow maldistribution compared to the U-type in both transient and steady state regimes. The comparison of the experimental results with numerical solution indicates that it is necessary to treat the flow maldistribution separately from axial thermal dispersion during modeling of plate heat exchanger dynamics.

An Experimental Study of Fluid Flow in Disk Cavities

1992 ◽  
Vol 114 (2) ◽  
pp. 454-461 ◽  
Author(s):  
S. H. Bhavnani ◽  
J. M. Khodadadi ◽  
J. S. Goodling ◽  
J. Waggott
Keyword(s):  
Experimental Study ◽  
Fluid Flow ◽  
Gas Turbine ◽  
Experimental Studies ◽  
Reynolds Numbers ◽  
Turbine Disk ◽  
Published Data ◽  
Disk System ◽  
Flow Rates ◽  
Pressure Distributions

Results are presented for an experimental study of fluid flow in models of gas turbine disk cavities. Experiments were performed on 70-cm-dia disks for rotational Reynolds numbers up to 2.29 × 106. Velocity and pressure distributions are presented and compared to previous theoretical and experimental studies for a free disk, and an unshrouded plane Rotor–Stator disk system. Minimum coolant flow rates for the prevention of ingress, determined for the case of a simple axial rim seal, compare well with previously published data.

CVD Filling of Narrow Deep 4H-SiC Trenches in a Quasi-Selective Epitaxial Growth Mode

2018 ◽  
Vol 924 ◽  
pp. 116-119 ◽  
Author(s):  
Shi Yang Ji ◽  
Ryoji Kosugi ◽  
Kazutoshi Kojima ◽  
Kazuhiro Mochizuki ◽  
Yasuyuki Kawada ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Epitaxial Growth ◽  
Growth Rates ◽  
Low Risk ◽  
Growth Mode ◽  
Flow Rates ◽  
Defect Generation ◽  
Selective Epitaxial Growth ◽  
Dependent Growth

By mapping the source and HCl flow rates dependent growth rates, the evolving trend of a quasi-selective epitaxial growth (quasi-SEG) that growing very thin epilayer on mesa top and ensuring an extremely low risk of voids defect generation was firstly figured out on a 5-μm 4H-SiC trench. Then, basing on the acquired knowledge, a 25-μm 4H-SiC trench with an aspect ratio up to ~10 was completely filled in the quasi-SEG mode.

scholarly journals Lateral vegetation growth rates exert control on coastal foredune hummockiness and coalescing time

2017 ◽  
Vol 5 (3) ◽  
pp. 417-427 ◽  
Author(s):  
Evan B. Goldstein ◽  
Laura J. Moore ◽  
Orencio Durán Vinent
Keyword(s):  
Growth Rates ◽  
Coastal Dunes ◽  
High Water ◽  
Lateral Direction ◽  
Plant Dispersal ◽  
Vegetation Growth ◽  
The Us ◽  
Two Parameters ◽  
Coastal Foredunes ◽  
Conceptual Work

Abstract. Coastal foredunes form along sandy, low-sloped coastlines and range in shape from continuous dune ridges to hummocky features, which are characterized by alongshore-variable dune crest elevations. Initially scattered dune-building plants and species that grow slowly in the lateral direction have been implicated as a cause of foredune hummockiness. Our goal in this work is to explore how the initial configuration of vegetation and vegetation growth characteristics control the development of hummocky coastal dunes including the maximum hummockiness of a given dune field. We find that given sufficient time and absent external forcing, hummocky foredunes coalesce to form continuous dune ridges. Model results yield a predictive rule for the timescale of coalescing and the height of the coalesced dune that depends on initial plant dispersal and two parameters that control the lateral and vertical growth of vegetation, respectively. Our findings agree with previous observational and conceptual work – whether or not hummockiness will be maintained depends on the timescale of coalescing relative to the recurrence interval of high-water events that reset dune building in low areas between hummocks. Additionally, our model reproduces the observed tendency for foredunes to be hummocky along the southeast coast of the US where lateral vegetation growth rates are slower and thus coalescing times are likely longer.

Prediction of Ingestion Through Turbine Rim Seals—Part II: Externally Induced and Combined Ingress

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
J. Michael Owen
Keyword(s):  
Experimental Data ◽  
Flow Rate ◽  
Gas Turbines ◽  
Swirling Flows ◽  
Published Data ◽  
Flow Rates ◽  
Hot Gas ◽  
Predicted Values ◽  
Good Agreement

Ingress of hot gas through the rim seals of gas turbines can be modeled theoretically using the so-called orifice equations. In Part I of this two-part paper, the orifice equations were derived for compressible and incompressible swirling flows, and the incompressible equations were solved for axisymmetric rotationally induced (RI) ingress. In Part II, the incompressible equations are solved for nonaxisymmetric externally induced (EI) ingress and for combined EI and RI ingress. The solutions show how the nondimensional ingress and egress flow rates vary with Θ0, the ratio of the flow rate of sealing air to the flow rate necessary to prevent ingress. For EI ingress, a “saw-tooth model” is used for the circumferential variation of pressure in the external annulus, and it is shown that ε, the sealing effectiveness, depends principally on Θ0; the theoretical variation of ε with Θ0 is similar to that found in Part I for RI ingress. For combined ingress, the solution of the orifice equations shows the transition from RI to EI ingress as the amplitude of the circumferential variation of pressure increases. The predicted values of ε for EI ingress are in good agreement with the available experimental data, but there are insufficient published data to validate the theory for combined ingress.

Prediction of Ingestion Through Turbine Rim Seals—Part 2: Externally-Induced and Combined Ingress

2009 ◽  
Author(s):  
J. Michael Owen
Keyword(s):  
Experimental Data ◽  
Flow Rate ◽  
Gas Turbines ◽  
Swirling Flow ◽  
Published Data ◽  
Flow Rates ◽  
Hot Gas ◽  
Predicted Values ◽  
Good Agreement

Ingress of hot gas through the rim seals of gas turbines can be modelled theoretically using the so-called orifice equations. In Part 1 (ASME GT 2009-59121) of this two-part paper, the orifice equations were derived for compressible and incompressible swirling flow, and the incompressible equations were solved for axisymmetric rotationally-induced (RI) ingress. In Part 2, the incompressible equations are solved for non-axisymmetric externally-induced (EI) ingress and for combined EI and RI ingress. The solutions show how the nondimensional ingress and egress flow rates vary with Θ0, the ratio of the flow rate of sealing air to the flow rate necessary to prevent ingress. For EI ingress, a ‘saw-tooth model’ is used for the circumferential variation of pressure in the external annulus, and it is shown that ε, the sealing effectiveness, depends principally on Θ0; the theoretical variation of ε with Θ0 is similar to that found in Part 1 for RI ingress. For combined ingress, the solution of the orifice equations shows the transition from RI to EI ingress as the amplitude of the circumferential variation of pressure increases. The predicted values of ε for EI ingress are in good agreement with available experimental data, but there are insufficient published data to validate the theory for combined ingress.

Heat Transfer and Pressure Drop Correlations for Twisted-Tape Inserts in Isothermal Tubes: Part I—Laminar Flows

1993 ◽  
Vol 115 (4) ◽  
pp. 881-889 ◽  
Author(s):  
R. M. Manglik ◽  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Swirl Flow ◽  
Laminar Flows ◽  
Low Flow ◽  
Published Data ◽  
Twisted Tape ◽  
Flow Rates ◽  
Uniform Wall Temperature ◽  
Uniform Wall

Laminar flow correlations for f and Num are developed based on experimental data for water and ethylene glycol, with tape inserts of three different twist ratios. The uniform wall temperature condition is considered, which typifies practical heat exchangers in the chemical and process industry. These and other available data are analyzed to devise flow regime maps that characterize twisted-tape effects in terms of the dominant enhancement mechanisms. Depending upon flow rates and tape geometry, the enhancement in heat transfer is due to the tube partitioning and flow blockage, longer flow path, and secondary fluid circulation; fin effects are found to be negligible in snug- to loose-fitting tapes. The onset of swirl flow and its intensity is determined by a swirl parameter, Sw=Resw/y, that defines the interaction between viscous, convective inertia, and centrifugal forces. Buoyancy-driven free convection that comes into play at low flow rates with large y and ΔTw is shown to scale as Gr/Sw2≫ 1. These parameters, along with numerical baseline solutions for laminar flows with y = ∞, are incorporated into correlations for f and Num by matching the appropriate asymptotic behavior. The correlations describe the experimental data within ±10 to 15 percent, and their generalized applicability is verified by the comparison of predictions with previously published data.

Quantitative In Situ Growth Measurements of Chlorine-Activated Homoepitaxial Diamond Cvd

1994 ◽  
Vol 349 ◽  
Author(s):  
Chenyu Pan ◽  
John L. Margrave ◽  
Robert H. Hauge
Keyword(s):  
Growth Rate ◽  
Substrate Temperature ◽  
Growth Rates ◽  
Diamond Growth ◽  
Flow Rates ◽  
Temperature Range ◽  
Quantitative Studies ◽  
Growth Activation ◽  
Lower Temperature

ABSTRACTIn situ quantitative studies of the effects of substrate temperature, methane and chlorine flow rates on homoepitaxial diamond growth rates on (110) surfaces in a chlorine-activated diamond CVD reactor have been carried out using a Fizeau interferometer. The temperature dependence of diamond growth rates was found to display three distinct growth activation energies, ranging from 9±2 kcal/mol in the substrate temperature of 750-950°C, to 3.2±0.2 kcal/mol in the temperature range of 300-650°C, followed by 1.2±0.2 kcal/mol in the temperature range of 102-250°C. Atomic hydrogen is believed to be the dominant activating species in the highest temperature range, and atomic chlorine is believed to be the dominant species in the lower temperature regions. Studies of the methane flow effect on diamond growth rates revealed a linearity, indicating that the diamond growth rate was of the first order in methane flows. Diamond growth rates were also found to increase linearly with the chlorine flow. At high chlorine flow rates, however, an accelerated diamond growth rate was observed. Discussion is given to explain the observed results.

Allometric Models of Simuliid Growth Rates and Their Use for Estimation of Production

1988 ◽  
Vol 45 (2) ◽  
pp. 315-324 ◽  
Author(s):  
Antoine Morin ◽  
Michel Constantin ◽  
Robert Henry Peters
Keyword(s):  
Water Temperature ◽  
Significant Influence ◽  
Growth Rates ◽  
Dry Mass ◽  
Published Data ◽  
Power Relationship ◽  
Square Root ◽  
Allometric Model ◽  
Simulium Vittatum ◽  
Individual Mass

Growth rates of Prosimulium mixtum/fuscum, Stegopterna mutata, and Simulium vittatum are described in relation to individual mass, water temperature, and seston quality in the outlet of Lake Orford (southern Quebec) in the winter of 1985–86. Growth rates in mass (G, per day) of the three species were similar and inversely related to dry mass (DM, micrograms) following the power relationship G = 0.11 DM−0.28; neither water temperature nor seston abundance and quality varied sufficiently during the study period to have a significant influence on growth rates. The allometric model was used to estimate production of the three species, and the resulting estimates are compared with cohort methods and size–frequency estimates. Large larvae were responsible for most of the production, and most of the production occurred before the spring rise in water temperature. Measured growth rates in winter are significantly lower than those reported for simuliids in warmer waters. A reanalysis of published data shows that growth rates of simuliids increase as the square root of water temperature (T, degrees Celsius) (G = 0.08 DM−0.21 T0.48).

scholarly journals The demographics and morphometries of biogenic reefs: important considerations in conservation management

2017 ◽  
Vol 98 (6) ◽  
pp. 1231-1240 ◽  
Author(s):  
Jenna M. Brash ◽  
Robert L. Cook ◽  
Clara L. Mackenzie ◽  
William G. Sanderson
Keyword(s):  
Population Structure ◽  
Growth Rates ◽  
Conservation Management ◽  
Tidal Flow ◽  
Growth Curves ◽  
Shell Morphology ◽  
Published Data ◽  
Marine Habitat ◽  
Juvenile Abundance ◽  
Horse Mussel

Modiolus modiolus L. (horse mussel) reefs are a priority marine habitat of high conservation value that is currently listed as endangered and/or threatened across its European distribution. Population structure, density or shell morphology may influence the biodiversity of a reef, either directly or indirectly. Thus, such metrics are important considerations for successful conservation management of these biodiversity hotspots. Population structure, shell morphology and growth rates were examined in M. modiolus reefs across the UK range of the habitat to examine differences between key populations, including those near the Lleyn Peninsula in Wales (southern range), off Port Appin in Western Scotland (mid-range) and in Scapa Flow in the Orkney Isles, Scotland (northern range). Additionally, the influence of physical conditions (temperature and tidal flow) to growth rate and predicted maximum shell length for each population was examined. Growth rates were determined using acetate peels of sectioned shells. Lower juvenile abundance was observed in Scapa Flow. Small, narrow-shaped shells were found to be characteristic of North Lleyn mussels, and larger, globular-shaped shells were characteristic of mussels in Scapa Flow and off Port Appin. Mussels in Scapa Flow were slower growing, yet reached a longer asymptotic length (L∞) than mussels of Port Appin and North Lleyn. Growth curves from sites within this study were analysed with other published data. A trend of higher L∞ at higher latitudes and at lower flow rates was observed. Variations in growth and age are discussed in relation to flow regimes, connectivity to other reefs, density and latitude.

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