scholarly journals Modelling of Ice Accretion on Wires (Abstract only)

1983 ◽  
Vol 4 ◽  
pp. 302
Author(s):  
Lasse Makkonen
Keyword(s):  
Growth Rate ◽  
Meteorological Parameters ◽  
Collection Efficiency ◽  
Ice Accretion ◽  
Atmospheric Conditions ◽  
Temperature Dependent ◽  
Simple Method ◽  
Ice Load ◽  
Ice Loads

A time-dependent numerical model of ice accretion is used to simúlate the growth of ice loads on wires. Both dry growth (rime) and wet growth (glaze) are modelled in order to examine the dependence of the growth rate of ice load on atmospheric conditions. The results show that during dry growth under constant atmospheric conditions the growth rate of an ice load slightly decreases. In conditions of wet growth, however, the growth rate increases until the process turns to dry growth after reaching the critical deposit diameter. The effect of air temperature on the growth rate in dry growth turns out to be rather small. However, the final ice load after long-term rime formation is temperature-dependent, because the limiting deposit diameter, at which the collection efficiency becomes practically zero, is reached at different ice masses depending on the ice density. The modelled relationships between the growth rate of ice load and the atmospheric variables are compared with observational data and with proposed formulae for the calculation of the intensity of wire icing. The possibilities of estimating the formation of ice loads for practical purposes with a simple method, using the routinely measured meteorological parameters only, are discussed.

scholarly journals Modelling of Ice Accretion on Wires (Abstract only)

1983 ◽  
Vol 4 ◽  
pp. 302-302
Author(s):  
Lasse Makkonen
Keyword(s):  
Growth Rate ◽  
Meteorological Parameters ◽  
Collection Efficiency ◽  
Ice Accretion ◽  
Atmospheric Conditions ◽  
Temperature Dependent ◽  
Simple Method ◽  
Ice Load ◽  
Ice Loads

A time-dependent numerical model of ice accretion is used to simúlate the growth of ice loads on wires. Both dry growth (rime) and wet growth (glaze) are modelled in order to examine the dependence of the growth rate of ice load on atmospheric conditions.The results show that during dry growth under constant atmospheric conditions the growth rate of an ice load slightly decreases. In conditions of wet growth, however, the growth rate increases until the process turns to dry growth after reaching the critical deposit diameter. The effect of air temperature on the growth rate in dry growth turns out to be rather small. However, the final ice load after long-term rime formation is temperature-dependent, because the limiting deposit diameter, at which the collection efficiency becomes practically zero, is reached at different ice masses depending on the ice density.The modelled relationships between the growth rate of ice load and the atmospheric variables are compared with observational data and with proposed formulae for the calculation of the intensity of wire icing. The possibilities of estimating the formation of ice loads for practical purposes with a simple method, using the routinely measured meteorological parameters only, are discussed.

A Study of Ice Accretion Shape on Cables Under Freezing Rain Conditions

2002 ◽  
Vol 124 (3) ◽  
pp. 162-168 ◽  
Author(s):  
Krzysztof Szilder ◽  
Edward P. Lozowski ◽  
Gerhard Reuter
Keyword(s):  
Heat Flux ◽  
Transmission Lines ◽  
Center Of Mass ◽  
Flux Ratio ◽  
Horizontal Cylinder ◽  
Ice Accretion ◽  
Atmospheric Conditions ◽  
Freezing Rain ◽  
Ice Load ◽  
Air Temperatures

The influence of atmospheric conditions (specifically precipitation rate and external heat flux) on the freezing rain ice accretion forming on a non-rotating, horizontal cylinder is studied, using an analytical model based on a simple form of the equations for conservation of mass and heat balance. In keeping with the freezing rain application, but in order to simplify this first step, we have assumed vertical incidence of precipitation (no wind) and no dripping from the accretion (hence light to moderate precipitation rates with relatively low air temperatures). The initial ice accretion shape and the location of its center of mass are examined as a function of the ratio of the precipitation mass flux to the total heat flux lost from the ice surface. An increase in the flux ratio leads to a quantifiable downward displacement of the accretion center of mass. We complement this analysis with numerical simulations, using an improved, two-dimensional version of the Szilder-Lozowski morphogenetic model that predicts the evolution of the accretion shape. For the first time, the freezing probability, which is the critical model parameter, is expressed as a function of location and atmospheric conditions for an accretion shape evolving with time. Using the morphogenetic model, we examine the influence of atmospheric conditions on the accretion shape and ice load. In particular, we address the question of what gives rise to extreme ice loads by identifying the range of atmospheric conditions that tends to maximize (or minimize) the ice load for a given amount of precipitation. The results of this research are applicable to predicting ice formation on overhead transmission lines.

scholarly journals Stability of graphene-based heterojunction solar cells

RSC Advances ◽  
2015 ◽  
Vol 5 (90) ◽  
pp. 73575-73600 ◽  
Author(s):  
Eric Singh ◽  
Hari Singh Nalwa
Keyword(s):  
Solar Cells ◽  
Environmental Stability ◽  
Light Illumination ◽  
Atmospheric Conditions ◽  
Air Humidity ◽  
Heterojunction Solar Cells ◽  
Commercial Applications

The long-term environmental stability and degradation of graphene-based heterojunction solar cells under different atmospheric conditions such as air, humidity, temperature, and light illumination for commercial applications are discussed.

ON THE CONSUMPTION/DISTRIBUTION THEOREM UNDER THE LONG-RUN GROWTH CRITERION SUBJECT TO A DRAWDOWN CONSTRAINT

2010 ◽  
Vol 13 (06) ◽  
pp. 931-957 ◽  
Author(s):  
MICHAEL J. KLASS ◽  
KRZYSZTOF NOWICKI
Keyword(s):  
Growth Rate ◽  
Short Term ◽  
Long Run ◽  
Time Period ◽  
Total Capital ◽  
Growth Criterion ◽  
Drawdown Constraint ◽  
Riskless Asset ◽  
Distribution Theorem

Consider any discrete time sequence of investment fortunes Fn which has a finite long-run growth rate [Formula: see text] when subject to the present value capital drawdown constraint Fne-rn ≥ λ* max 0≤k≤nFke-rk, where 0 ≤ λ* < 1, in the presence of a riskless asset affording a return of er dollars per time period per dollar invested. We show that money can be withdrawn for consumption from the invested capital without either reducing the long-run growth rate of such capital or violating the drawdown constraint for our capital sequence, while simultaneously increasing the amount of capital withdrawn for consumption at the identical long-term rate of V(r, λ*). We extend this result to an exponentially increasing number of consumption categories and discuss how additional yearly contributions can temporarily augment the total capital under management. In addition, we assess the short-term practicality of creating such an endowment/consumption/distribution program.

The Effects of Reduced Salinity on the Shell Growth of Small Mytilus Edulis

1984 ◽  
Vol 64 (1) ◽  
pp. 171-182 ◽  
Author(s):  
Patricia C. Almada-Villela
Keyword(s):  
Growth Rate ◽  
Mytilus Edulis ◽  
High Salinity ◽  
Shell Growth ◽  
Experimental Period ◽  
Gradual Decline ◽  
Poor Growth ◽  
Term Response ◽  
Better Than

The shell growth of small coastal Mytilus edulis L. was measured at three different constant low salinities over short periods of time. Growth was significantly depressed in 6·4 and 16‰ S but not in 22·4‰ S. Fluctuating salinities between 0 and 32‰ S depressed growth whether the fluctuations were of sinusoidal or abrupt form. After 1 week of preconditioning to constant 32‰ S the growth of coastal (Bangor) mussels was better than estuarine (Conwy) mussels. However, after two weeks’ preconditioning to 32‰ S the estuarine mussels displayed the best growth. In the fluctuating regime, both coastal and estuarine mussels exhibited poor growth rates. The long-term response of the shell growth of coastal M. edulis was followed over a period of 44 days. Salinities in the range 1·8–9·6‰ S were lethal to the mussels within 10 days. In 12·8 and 16‰ S growth was initially delayed but recovered eventually. There was a gradual decline in the growth rate of the mussels exposed to the higher salinities (19·2–32‰) and an improvement in the growth of the mussels living in lower salinities (12·8 and 16‰) to levels nearly matching that of the high salinity animals by day 37. This suggests that acclimation of the shell growth of M. edulis to salinities in the 12·8–28·8‰ S range was achieved by the mussels during the experimental period.

Analysis of SINR for Unitary and Non-Unitary Precoded MIMO Systems

2011 ◽  
Vol 460-461 ◽  
pp. 414-419
Author(s):  
Xin Lu ◽  
Xiong Xu ◽  
Jian Hu Wang
Keyword(s):  
Computational Complexity ◽  
Mimo Systems ◽  
Original Method ◽  
Coding System ◽  
Simple Method ◽  
Method Of Calculation ◽  
Term Evolution ◽  
3Gpp Long Term Evolution ◽  
Output Sinr

Pre-coding type can be grouped into two approaches, unitary or non-unitary for 3GPP Long Term Evolution(LTE). Output SINR of unitary Pre-coding for MU-MIMO is investigated in this paper. A more simple method of calculation for SINR is presented, which Leads to the computational complexity down to 18% compared with original method, while calculating MIMO Pre-coding system with 4 matrices (i.e. 8 vectors). In addition, we also analyzed the loss of SINR when using unitary or non-unitary Pre-coding. Corresponding simulations show that output SINR of non-unitary pre-coding system is inferior to the unitary pre-coding case and such losses can been described using statistical linear approximation.

Walleye (Stizostedion vitreum vitreum) and Yellow Perch (Perca flavescens) Populations and Fisheries of the Red Lakes, Minnesota, 1930–75

1977 ◽  
Vol 34 (10) ◽  
pp. 1774-1783 ◽  
Author(s):  
Lloyd L. Smith Jr.
Keyword(s):  
Growth Rate ◽  
Yellow Perch ◽  
Climatic Factors ◽  
Perca Flavescens ◽  
Growing Season ◽  
Commercial Fishery ◽  
Class Strength ◽  
Parent Stock ◽  
Catch Statistics

In an investigation of the commercial fishery of Red Lakes, Minnesota, for the 46-yr period 1930–75, catch statistics were analyzed, and the dynamics of the perch and walleye populations were examined. Mean annual yields of walleye for two statistical periods, 1930–53 and 1954–75, were 309,900 and 245,100 kg, respectively for walleyes, and 96,400 and 109,500 kg for perch. Annual abundance (CPE based on average catches per day per 5-net units of gill nets) varied from 3.8 to 64.6 kg for walleye, and from 2.5 to 34.4 kg for perch. Causes of fluctuations in harvestable stock were directly related to strength of year-classes and to growth rate during the season of capture. Year-class strength was not related to the abundance of parent stock or of potential predators. The respective strengths of year-classes of perch and walleye in the same year were positively correlated (r = 0.859, P < 0.01), and are directly related to climatic factors. Growth rate of walleye in different calendar years varied from +30.7 to −42.2% of mean growth, and that of perch from +13.4 to −8.6% (1941–56). Growing season began in mid-June and was almost over by September 1. Walleye yield could be enhanced by starting harvest July 1 instead of early June. Perch yield could be improved by harvesting small perch. Key words: Percidae, Perca, population dynamics, Stizostedion, long-term yield

Temperature dependency of the long-term thermal conductivity of spray polyurethane foam

2021 ◽  
pp. 174425912110454
Author(s):  
Neal Holcroft
Keyword(s):  
Thermal Conductivity ◽  
Polyurethane Foam ◽  
Cellular Structure ◽  
Gas Diffusion ◽  
Temperature Dependent ◽  
Blowing Agent ◽  
Closed Cell ◽  
Wall Assembly ◽  
Cell Foam

The thermal properties of closed-cell foam insulation display a more complex behaviour than other construction materials due to the properties of the blowing agent captured in their cellular structure. Over time, blowing agent diffuses out from and air into the cellular structure resulting in an increase in thermal conductivity, a process that is temperature dependent. Some blowing agents also condense at temperatures within the in-service range of the insulation, resulting in non-linear temperature dependent relationships. Moreover, diffusion of moisture into the cellular structure increases thermal conductivity. Standards exist to quantify the effect of gas diffusion on thermal conductivity, however only at standard laboratory conditions. In this paper a new test procedure is described that includes calculation methods to determine Temperature Dependent Long-Term Thermal Conductivity (LTTC(T)) functions for closed-cell foam insulation using as a test material, a Medium-Density Spray Polyurethane Foam (MDSPF). Tests results are provided to show the validity of the method and to investigate the effects of both conditioning and mean test temperature on change in thermal conductivity. In addition, testing was conducted to produce a moisture dependent thermal conductivity function. The resulting functions were used in hygrothermal simulations to assess the effect of foam aging, in-service temperature and moisture content on the performance of a typical wall assembly incorporating MDSPF located in four Canadian climate zones. Results show that after 1 year, mean thermal conductivity increased 15%–16% and after 5 years 23%–24%, depending on climate zone. Furthermore, the use of the LTTC(T) function to calculate the wall assembly U-value improved accuracy between 3% and 5%.

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