scholarly journals Metamorphism and thermal properties of fresh snow (study in the Moscow region)

2016 ◽  
Vol 56 (2) ◽  
pp. 199-206 ◽  
Author(s):  
R. A. Chernov
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Temperature Gradient ◽  
Negative Temperature ◽  
Average Temperature ◽  
The North ◽  
Coefficient Of Thermal Conductivity ◽  
European Part Of Russia ◽  
Snow Conditions

As a result of laboratory tests were obtained values of the coefficient thermal conductivity (Keff) of new snow for different types of the solid precipitation: plates, needles, stellars, graupels. Snow samples were collected during a snowfall and placed in the freezer. For all types of sediment thermal conductivity of snow is equal to 0.03–0.04 W/m·°C. Transformation of new snow occurs within 10 days at average temperature −10 °C and the gradient temperature of 50–60 °C/m. Under these conditions, the metamorphism leads to an increase the density of snow, size of grains and rounded snow particles. At the beginning of the experiment, the thermal conductivity of snow is linearly increased in proportion to the density of the snow. However, after 3–5 days Keff stabilized at about 0.08–0.09 W/m·°C, although the density of the snow and size of grains continued to increase. This effect occurs with the appearance of faceted crystals and loosening of snow. In the future, while maintaining a negative temperature coefficient of thermal conductivity remained unchanged. Thus, the temperature gradient metamorphism affect to the thermal conductivity snow, which plays an important role in maintaining the thermal insulation properties of snow cover. The article describes the formula to calculate the thermal conductivity of the snow conditions in the temperature gradient metamorphism. Such conditions are characteristic of the vast expanses of the north and northeast of the European part of Russia. On the basis of long-term observations in Moscow shows the average minimum and maximum values for the density of the snow woods and fields on the basis of which can be calculated for the thermal properties of the snow.

Determination of the Thermal Properties of a PCB by Coupled Numerical and Experimental Approach

2020 ◽  
Author(s):  
Yener Usul ◽  
Mustafa Özçatalbaş
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Numerical Analysis ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Thermal Analyses ◽  
Analysis Model ◽  
Linear Temperature ◽  
Coefficient Of Thermal Conductivity

Abstract Increasing demand for usage of electronics intensely in narrow enclosures necessitates accurate thermal analyses to be performed. Conduction based FEM (Finite Element Method) is a common and practical way to examine the thermal behavior of an electronic system. First step to perform a numerical analysis for any system is to set up the correct analysis model. In this paper, a method for obtaining the coefficient of thermal conductivity and specific heat capacity of a PCB which has generally a complex composite layup structure composed of conductive layers, and dielectric layers. In the study, above mentioned properties are obtained performing a simple nondestructive experiment and a numerical analysis. In the method, a small portion of PCB is sandwiched from one side at certain pressure by jaws. A couple of linear temperature profiles are applied to the jaws successively. Unknown values are tuned in the analysis model until the results of FEM analysis and experiment match. The values for the coefficient of thermal conductivity and specific heat capacity which the experiment and numerical analysis results match can be said to be the actual values. From this point on, the PCB whose thermal properties are determined can be analyzed numerically for any desired geometry and boundary condition.

Effective heat conductivity of Honeycomb (porous) composite panel

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Cletus Matthew Magoda ◽  
Jasson Gryzagoridis ◽  
Kant Kanyarusoke
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Composite Material ◽  
Thermal Properties ◽  
Heat Conductivity ◽  
Composite Panel ◽  
Porous Composite ◽  
Content Type ◽  
One Dimensional ◽  
Coefficient Of Thermal Conductivity

Purpose The purpose of this paper is to validate an assumption of what to use as an effective (steady state) heat transfer coefficient of thermal conductivity for the honeycomb core sandwiched by Fiberglass face sheets composite. A one-dimensional model based on Fourier law is developed. The results are validated experimentally. Design/methodology/approach The results were obtained from the one-dimensional mathematical model of an overall or effective heat conductivity of the Honeycomb composite panel. These results were validated experimentally by applying heat flux on the specimen under controlled environment. The surface temperatures at different voltages were recorded and analysed. The skin of the sandwich composite material used in the investigation was Fiberglass sheet with a thickness of 0.5 mm at the bottom and 1.0 mm at the top surface. Both skins have a stacking sequence of zero degrees. Due to the presence of air cells in the core (Honeycomb), the model considers the conduction, convection and radiation heat transfer, across the thickness of the panel, combined as an effective conduction mode, whose value may be predicted by using the coefficient of thermal conductivity of the air based on the average temperature difference between the two skins. The experimental results for the heat transfer through the thickness of the panel provide validation of this assumption/prediction. Both infrared thermography and conventional temperature measurement techniques (thermocouples) were used to collect the data. Findings The heat transfer experiment and mathematical modeling were conducted. The data obtained were analyzed, and it was found that the effective thermal conductivity was temperature-dependent as expected. The effective thermal conductivity of the honeycomb panel was close to that of air, and its value could be predicted if the panel surface temperatures were known. It was also found that as temperature raised the variation between experimental and predicted effective air conduction raised up. This is because there was an increase in molecular diffusion and vibration. Therefore, the convection heat transfer increased at high temperatures and the air became an insulator. Originality/value Honeycomb composite panels have excellent physical and thermal properties that influence their performance. This study provides an appropriate method in determining thermal conductivity, which is one of the critical thermal properties of porous composite material. This paper also gives useful and practical data to industries that use or manufacture honeycomb composite panels.

Temperature Gradient of Concrete Pavement Slab Overlaid with Asphalt Surface Course

2000 ◽  
Vol 1730 (1) ◽  
pp. 25-33 ◽  
Author(s):  
Tatsuo Nishizawa ◽  
Shigeru Shimeno ◽  
Akinori Komatsubara ◽  
Masashi Koyanagawa
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Thermal Stress ◽  
Temperature Gradient ◽  
Numerical Simulations ◽  
Structural Design ◽  
Concrete Slab ◽  
Concrete Pavement ◽  
Reduction Effect ◽  
The Relationship

In the structural design of composite pavement with a concrete pavement slab overlaid with an asphalt surface course, it is very important to estimate the temperature gradient in the concrete slab. An asphalt surface course reduces the temperature gradient in an underlaid concrete slab, resulting in the reduction of thermal stress of the concrete slab. This effect was investigated by temperature measurement in model pavements and by thermal conductivity analysis. Thermal properties were estimated by a backanalysis by using measured temperatures over 1 year. From the numerical simulations varying the thickness of asphalt surface and concrete slab, the relationship between the reduction effect and the asphalt thickness was derived as a function of the thickness of asphalt surface course, which can be used in the structural design of the composite pavement.

scholarly journals Climate change in Victoria: trends, predictions and impacts

2013 ◽  
Vol 125 (1) ◽  
pp. 5 ◽  
Author(s):  
Lesley Hughes ◽  
Will Steffen
Keyword(s):  
Global Trends ◽  
Sea Levels ◽  
North West ◽  
Average Temperature ◽  
The Past ◽  
The North ◽  
Hot Days ◽  
National Trends ◽  
Do So

Australia’s climate is changing, consistent with global trends. Continental average temperatures have increased nearly 1°C since the early 20th century, with warming accelerating since the 1950s. The number of extreme hot days is increasing, whereas the number of cold days and frosts is decreasing. With an average temperature over 1.0°C above the long-term mean, 2005 was Australia’s warmest year on record; 2009 was the second warmest year on record. The decade 2000–2009 was Australia’s warmest. Rainfall has been decreasing in the south-west and south-east of Australia, but increasing in the north-west. The ocean is warming and sea levels are rising, consistent with global averages. Consistent with global and national trends, Victoria’s climate is already changing and will continue to do so, posing significant risks to the State. Over the past few decades Victoria has become hotter and drier, and these trends are likely to continue, together with an increasing intensity and/or frequency of extreme events, such as heatwaves, droughts, bushfires and floods, posing significant risks to the State’s infrastructure, coasts, ecosystems, agriculture and health.

Wall Panels with Improved Thermal Properties on KBR's Porous Fillers

2018 ◽  
Vol 931 ◽  
pp. 243-246 ◽  
Author(s):  
Valery K. Khuranov ◽  
Aues S. Tsipinov ◽  
Muzarib I. Bjakhov
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Thermal Characteristics ◽  
Engineering Calculation ◽  
Wall Panel ◽  
Structural Concrete ◽  
External Wall ◽  
Constructive Solution ◽  
Coefficient Of Thermal Conductivity ◽  
Wall Panels

The article describes the design of buildings for multi-apartment houses 139 series, designed for construction in the conditions of the Kabardino-Balkaria Republic (KBR). An analysis of existing wall panel variants based on their thermal characteristics was carried out and a new constructive solution was proposed using porous fillers of KBR. The coefficient of thermal conductivity of the proposed structural concrete is determined analytically and the heat engineering calculation of the external wall panel is presented.

Comparison of Conductivity of Al2O3 Nanofluids between Experiments and Maxwell Model

2013 ◽  
Vol 668 ◽  
pp. 571-574
Author(s):  
Jin Ze Yu ◽  
Bin Liu ◽  
Zhen Liang Li
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Mass Fraction ◽  
Base Fluid ◽  
Volume Fraction ◽  
Critical Role ◽  
Maxwell Model ◽  
Nano Particle ◽  
Coefficient Of Thermal Conductivity ◽  
Nano Fluids

The thermal properties of nano-fluids are affected by many factors. The effect of the diameter, mass fraction and volume fraction of Al2O3 in water on the thermal conductivity was measured by the method of hotwire. The diameter of nano-particle of Al2O3 was 10nm, 20nm, 50nm, 100nm and 500nm respectively. The mass fraction of Al2O3 in water was 10%, 12%, 15% and 20%. The results show that the diameter of the particle plays a critical role on thermal properties of the base fluid. And for the mass fraction, it will increase the thermal conductivity of the base fluid. When the size is more than 100nm, the coefficient of thermal conductivity is increased rapidly. Compared with the results calculated by the Maxwell model, the conductivity of the nanofulid with a diameter less than 10nm is consistent with the model’s result. And with the increasing of the diameter o f the nanoparticle, the deviation of the conductivity will also increase compared with the model’s results.

scholarly journals Results of the 10-Year Monitoring of Bat (Chiroptera, Vespertilionidae) Winter Aggregation from the North-Eastern Ukraine (Liptsy Mines, Kharkiv Region)

2018 ◽  
Vol 52 (5) ◽  
pp. 395-416 ◽  
Author(s):  
A. Vlaschenko ◽  
A. Naglov
Keyword(s):  
Relative Abundance ◽  
Population Monitoring ◽  
Population Estimates ◽  
Average Temperature ◽  
The North ◽  
Diffi Cult ◽  
Yearly Average ◽  
North Eastern ◽  
The Mean

Abstract Monitoring of bats in hibernacula is a key element for the estimation of long-term population trends in Northern hemisphere bats. However, there is currently limited winter bat monitoring data from Ukraine, making long-term population estimates diffi cult. We present data on bat population monitoring in the largest bat hibernacula in North-Eastern Ukraine (Liptsy mines). Between 1999-2010 we conducted 115 censuses inside the three mines and counted 1150 specimens of M. daubentonii, M. dasycneme and P. auritus. 385 individuals of the same species were captured by mist-nets (39 nights). Th e yearly average temperature in the Liptsy 1 mine is close to the mean of annual temperature in the Kharkiv Region (about +7 .C); the humidity ranged from 85-100 %. Th e mean number of bats counted in a visit ranged from 1.4 to 4.9 bats, and 28 in one case. Great fl uctuations in bat number were noted in Liptsy 1 and Liptsy 3-4 mines. Th ere were high bat numbers (up to one hundred individuals on average) in the winters 2000- 2001 and 2007-2008, and low bat number in winters 2002-2003 and 2003-2004. Th e species relative abundance for M. daubentoniiwas - 75-90 %, P. auritus - 7-20 %, M. dasycneme - 1-10 % respectively.

scholarly journals Silvicultural Production as a Basis for Continuity of Forest Management

2021 ◽  
pp. 80-96
Author(s):  
Boris Mochalov ◽  
◽  
Svetlana Bobushkina ◽  
Keyword(s):  
Sustainable Use ◽  
European Part ◽  
Stem Volume ◽  
Planting Stock ◽  
The North ◽  
Information Gap ◽  
Pine Trees ◽  
European Part Of Russia ◽  
The Difference

Currently, the principle of sustainable use of forests is a fundamental direction in the management of natural resources. Solving the problems of sustainable development of forestry in the European North involves ensuring the quality reproduction of forest resources. The main parts of silvicultural production are procurement and preparation of seeds; growing planting stock, creation of new stands and agricultural tending of them. The goal of the federal project “Forest Conservation” is to ensure the balance of forest felling and reproduction in the ratio of 100 % by 2024. The emphasis is on the use of ball-rooted planting stock for artificial reforestation. Information gap on the long-term prospects of its use, as well as the lack of data on the results of long-term observations of growth and condition of forest crops created by seedlings with a lump of substrate, and comparison of such seedlings with traditional planting stock, especially in northern conditions, update the topic of research. The research purpose is to identify conditions for obtaining high-quality planting stock, as well as to assess the possibility of successful restoration of pine on felling sites in the north of the European part of Russia by creating forest crops using regional intensive technologies, based on the results of long-term technologies. The main objects of observations are nurseries of the region, the procedures used in them and the experimental planting of pine trees in the Kargopol and Arkhangelsk forestries in 2000–2001. Preservation, diameter, height, and volume were determined in dynamics in the areas of crops created from various types of planting stock (seedlings, plantlet, ball-rooted planting stock). The counts were carried out with several repetitions and dividing plants into healthy, weak and dry. Wood flaws of pine trunks were also noted and natural regeneration was recorded. Based on the research materials, the possibility of successful restoration of pine trees on felling sites in the north of the European part of Russia is shown using regional intensive technologies for the production of various planting stock and the creation of forest crops. This will reduce the period of transfer of young trees to natural conditions and increase the productivity of plantations. Comparison of average diameters and heights for all accounting periods indicates the influence of the type of planting stock and density of planting on the growth and development of trees. During the observation period, plantlets lead in all respects. Their height and diameter is 20–44 % higher than that of yearling seedlings, and in terms of stem volume the difference with other types of planting stock reaches 1.9–2.9 times.

The Steel Slag Fly Ash Foamed Concrete Thermal Properties

2016 ◽  
Vol 852 ◽  
pp. 1398-1403
Author(s):  
Shui Jun Yu ◽  
Bin Li ◽  
Xiao Li Chen
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Fly Ash ◽  
Specific Heat ◽  
General Model ◽  
Steel Slag ◽  
Industrial Emissions ◽  
Foam Concrete ◽  
Coefficient Of Thermal Conductivity ◽  
Foamed Concrete

Industrial emissions used as admixture in foam concrete not only save resources, but also improve the properties of foam concrete. In this paper the thermal properties of steel slag fly ash foamed concrete was studied through experiments, and the results were analyzed. This paper included several of them and validated them using test dates, compared the results with other researchers. The result is the general model can predict the thermal conductivity of foam concrete better. Maxwell-Eucken model can regard as the boundaries’ formula to predict the coefficient of thermal conductivity of foam concrete and determine the limits. For the same density with the increasing of the steel slag thermal conductivity increases, specific heat decreases. The porosity is linear to the density of foam concrete.

scholarly journals THERMAL CONDUCTIVITY AND FROST RESISTANCE OF FOAMED CONCRETE WITH POROUS AGGREGATE

2017 ◽  
Vol 3 ◽  
pp. 222 ◽  
Author(s):  
Eva Namsone ◽  
Genadijs Sahmenko ◽  
Elvija Namsone ◽  
Aleksandrs Korjakins
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Optical Microscopy ◽  
Frost Resistance ◽  
Mechanical And Thermal Properties ◽  
Coefficient Of Thermal Conductivity ◽  
Foamed Concrete

The paper reports a study, which was carried out to examine thermal and frost resistance properties of foamed concrete (FC) with porous aggregate (expanded glass (EG) granules and cenospheres). By adding lightweight and porous aggregate to the FC mixture, it is possible to improve important physical, mechanical, and thermal properties of the prepared FC specimens. In the framework of this study the coefficient of thermal conductivity and frost resistance of hardened FC samples were determined. The structure of FC matrix and used aggregates were characterised by using a method of optical microscopy.

Sign in / Sign up

Export Citation Format

Share Document