scholarly journals Determination of long-term permissible currents in wires of power supply systems of railways

2019 ◽  
Vol 78 (2) ◽  
pp. 90-95 ◽  
Author(s):  
E. P. FIGURNOV ◽  
Yu. I. ZHARKOV ◽  
V. I. KHARCHEVNIKOV
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Solar Radiation ◽  
Transfer Coefficient ◽  
Surface Area ◽  
Meteorological Conditions ◽  
The Body ◽  
Additional Heating ◽  
The Heat Transfer Coefficient

In the standard for contact wires made from copper and its alloys, the values of long-term permissible temperatures have significantly decreased. This requires recalculation of previously valid values of long-term permissible currents. Authors considered revised method for calculating the long-term permissible currents, based on a more rigorous consideration of the laws of heat transfer and experimental studies of the conditions of heating and cooling of shaped (contact) and stranded wires. Technique is based on heat balance conditions, using which the sources of greatest inaccuracies become such quantities as cooled surface area, influence of wind direction, meteorological conditions, laws of change in heat transfer coefficient, effect on additional heating of solar radiation. Deviations when these indicators are taken into account by existing methods can cause errors of 40 % or more. Formulas for calculating the actual outer surface of stranded and shaped wires are given. The inadmissibility of calculating the surface area of the wires by their reference diameter is noted. Updated law of the change in heat transfer coefficient for stranded and shaped wires, as well as the degree of its dependence on wind speed and cooled surface, is given based on a summary of extensive domestic and foreign research. It is shown that with the longitudinal direction of the wind, the reduction of this coefficient occurs to a lesser extent than has been assumed so far. Authors propose method for taking into account an increase in the heat transfer coefficient under meteorological conditions characteristic of ice formation. The heat transfer coefficient of shaped and stranded wires in no case can not be taken as for round pipes with smooth surface. Existing method of accounting for solar radiation, which influences the additional heating of wires, leads to an unjustified and repeated exaggeration of this effect, since previously only the radiation incident on the wire was taken into account in the calculations. According to the laws of heat transfer, the temperature of the irradiated body does not depend on the incident, but on the resulting radiation, defined as the difference between the radiations incident on the body and emitted by it in accordance with its temperature. A formula for accounting for such heat transfer is proposed. The above methodology and calculation formulas allow performing reasonable calculations to determine the long-term permissible currents of individual stranded and shaped wires, as well as the contact network as a whole.

scholarly journals Effect of measurement errors in determining the heat transfer coefficient of the enclosing structures of an isothermal car

2019 ◽  
Vol 78 (2) ◽  
pp. 100-104 ◽  
Author(s):  
A. A. GOLUBIN ◽  
N. V. BELOVA ◽  
S. N. NAUMENKO
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Measurement Errors ◽  
The Body ◽  
Random Errors ◽  
Labor Costs ◽  
Express Method ◽  
Thermal Tests ◽  
The Heat Transfer Coefficient

When conducting thermal tests, the purpose of which is to determine the heat transfer coefficient of the body of an isothermal car K, the study of measurement errors affecting the accuracy of the obtained value plays an important role. The results of such experiments may contain various measurement errors that can introduce significant deviations into the resulting values of the desired coefficient. Obtaining accurate results when conducting this kind of experiments is impossible without a preliminary study of the causes that affect the final result. The article presents the types of measurement errors that affect the accuracy of determining the heat transfer coefficient of the body  of an isothermal car when conducting thermal tests. It was noted that the magnitude of labor costs and energy losses during the further operation of this body significantly depends on the accuracy of the value of this coefficient. It was emphasized that one of the main types of random errors arising from measurements and compliance with the established procedure for conducting typical thermal tests is a voltage drop (“slump”) in the electrical network, leading to significant errors in the calculations of the heat transfer coefficient of the isothermal car body. The values of this coefficient are presented, which were obtained as a result of heat engineering tests performed using the equilibrium mode method and the express method. It is shown that the use of the express method to determine the heat transfer coefficient of the bodies of isothermal cars reduces the risk of random errors due to the minimum experiment duration (from 5.5 h), allows to obtain exact values of the desired coefficient (with an error not higher than 3 % of its value of long-term equilibrium method) and use this data for practical purposes.

scholarly journals Development of an algorithm for determining the heat transfer coefficient of the body of an isothermal vehicle based on the results of analysis of the heat exchange processes occurring in it

2017 ◽  
Vol 76 (5) ◽  
pp. 306-311 ◽  
Author(s):  
A. A. Golubin ◽  
S. N. Naumenko
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchange ◽  
Transfer Coefficient ◽  
Thermal Imaging ◽  
The Body ◽  
Internal Heating ◽  
Heating Method ◽  
Exchange Processes ◽  
The Heat Transfer Coefficient

The article analyzes the heat exchange processes the thermal imaging method using a thermal imaging device. An occurring in the body of an isothermal vehicle when determining algorithm for determining the heat transfer coefficient is proposed, the heat transfer coefficient K by the internal heating method. which makes it possible to calculate its value with an accuracy not The differences are shown in the values of the heat transfer coef-exceeding 5 %, which is regulated by a number of international ficients obtained by the equilibrium internal heating method and normative documents, while reducing the duration of the experiment by at least 6 times. The study gives comparative experimental data and results of calculating the unknown values of K for bodies of isothermal vehicles obtained by the equilibrium method and an express method based on the algorithm described in the article. It is shown that the use of the algorithm for calculating the heat transfer coefficient of the body of an isothermal vehicle will not only increase the productivity of testing stations, but will also lead to the organization of an electronic passport for the thermotechnical state for each body of an isothermal vehicle, the control of which will enable timely diagnosing the thermo-technical condition of the bodies of isothermal vehicles, providing energy-optimal operating modes of energy equipment and, hence, increasing its resource.

Evaluating Quasi-Clothing Heat Transfer: A Comparison of the Vertical Hot Plate and the Thermal Manikin

1997 ◽  
Vol 67 (7) ◽  
pp. 503-510 ◽  
Author(s):  
Yayoi Satsumoto ◽  
Kinzo Ishikawa ◽  
Masaaki Takeuchi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
The Body ◽  
Human Model ◽  
Thermal Manikin ◽  
Physical Factors ◽  
Hot Plate ◽  
Air Space ◽  
The Heat Transfer Coefficient

In earlier work, we used a vertical hot plate as a simple model of the human body, and it was important to determine whether or not our experimental results from the hot plate could really be applied to the body. Recently, thermal manikins have emerged as substitutes for the body, and this work tests whether or not the vertical hot plate can still be used as the substitute. Experiments are done with the abdominal segment of the thermal manikin and the vertical hot plate to investigate the effect of clothing construction factors like the size of air spaces and opening designs, open or closed, on quasi-clothing heat transfer. Results from the two methods agree with each other only when the size of the air space is 20 mm, and it is difficult to reproduce a setup with a precisely sized air space for the thermal manikin. The manikin has more experimental errors than the vertical hot plate, as clarified by results of the vertical hot plate model and the theoretical analysis that follows. The heat transfer coefficient of the open garment case is larger than that for the closed garment case, with proximity to the opening. In addition, the difference in the heat transfer coefficient is largest when the size of the air space is 10 mm. We have verified that the results of the vertical hot plate are helpful in understanding the results of the thermal manikin. Moreover, if the investigation of the effect of certain physical factors on heat transfer of quasi-clothing is performed analytically, it is not absolutely necessary to use a human model of actual dimensions, like a thermal manikin.

scholarly journals Delineation of dew formation zones in Iran using long-term model simulations and cluster analysis

2021 ◽  
Vol 25 (9) ◽  
pp. 4719-4740
Author(s):  
Nahid Atashi ◽  
Dariush Rahimi ◽  
Victoria A. Sinclair ◽  
Martha A. Zaidan ◽  
Anton Rusanen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Cluster Analysis ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Negative Trend ◽  
Balance Model ◽  
Formation Potential ◽  
Dew Formation ◽  
The Heat Transfer Coefficient

Abstract. Dew is a non-conventional source of water that has been gaining interest over the last two decades, especially in arid and semi-arid regions. In this study, we performed a long-term (1979–2018) energy balance model simulation to estimate dew formation potential in Iran aiming to identify dew formation zones and to investigate the impacts of long-term variation in meteorological parameters on dew formation. The annual average of dew occurrence in Iran was ∼102 d, with the lowest number of dewy days in summer (∼7 d) and the highest in winter (∼45 d). The average daily dew yield was in the range of 0.03–0.14 L m−2 and the maximum was in the range of 0.29–0.52 L m−2. Six dew formation zones were identified based on cluster analysis of the time series of the simulated dew yield. The distribution of dew formation zones in Iran was closely aligned with topography and sources of moisture. Therefore, the coastal zones in the north and south of Iran (i.e., Caspian Sea and Oman Sea), showed the highest dew formation potential, with 53 and 34 L m−2 yr−1, whereas the dry interior regions (i.e., central Iran and the Lut Desert), with the average of 12–18 L m−2 yr−1, had the lowest potential for dew formation. Dew yield estimation is very sensitive to the choice of the heat transfer coefficient. The uncertainty analysis of the heat transfer coefficient using eight different parameterizations revealed that the parameterization used in this study – the Richards (2004) formulation – gives estimates that are similar to the average of all methods and are neither much lower nor much higher than the majority of other parameterizations and the largest differences occur for the very low values of daily dew yield. Trend analysis results revealed a significant (p<0.05) negative trend in the yearly dew yield in most parts of Iran during the last 4 decades (1979–2018). Such a negative trend in dew formation is likely due to an increase in air temperature and a decrease in relative humidity and cloudiness over the 40 years.

scholarly journals FEATURES OF CALCULATION OF THE TEMPERATURE STATE OF THE BUS SALON

2020 ◽  
Vol 22 ◽  
pp. 78-84
Author(s):  
S. Niemyі
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Thermal Resistance ◽  
Transfer Coefficient ◽  
Unit Area ◽  
Heat Losses ◽  
The Body ◽  
City Bus ◽  
The Heat Transfer Coefficient ◽  
Air Exchange

The safety of passenger transportation is not only to prevent accidents but also to ensure the conditions of health and efficiency of passengers and driver and the comfort of moving, which is guaranteed by the microclimate in the bus and the driver's workplace. One of the principal indicators of the microclimate is the air temperature in the cabin. The purpose of the work is to develop and substantiate the method of calculating the temperature of the bus interior.Unorganized air exchange due to body leaks (infiltration) influence on the thermal regime of the bus interior. Air exchange due to body leaks depends linearly on the speed of the bus. Heat loss through the structural elements of the body linearly depends on the outside air temperature.The calculation of the thermal state of the bus interior, in principle, is reduced to the estimation of the calorific value of the liquid heater, taking into account all heat losses in the cabin. The method of calculation developed on two indicators: experimentally defined coefficient of heat transfer of a body of the city bus and its inverse size, the calculated value of thermal resistance of unit of the area of salon of the bus. The thermal regime of the interior of a city bus in the conditions of winter operation is significantly influenced by heat exchange through the openings of open doors at short-term service stops. As for long-distance coaches, open the passenger door is much less. Therefore at the operation of buses of the specified class, it is necessary to give in salon-fresh air which needs to be heated.Since there are statistics on heat transfer of the body of city buses, the temperature of their cabins proposes to be calculated by the heat transfer coefficient of the bus body.In this method, the calculation depends on the heat transfer coefficient of the body. The supply and heating of air for ventilation are not taken into account, as the passenger door carries out air exchange in the cabin during bus stops.As calculations have shown, heat losses primarily depend on the temperature difference between the outside air and in the cabin. However, statistics on heat transfer of intercity (tourist) bus bodies are not currently available in the available publications. The temperature condition of intercity buses must correspond to the following calculations, inverse to the heat transfer coefficient of the body - thermal resistance per unit area of the bus.The method of calculating the temperature of the bus interior is substantiated. For city buses should be based on the calculation of heat transfer coefficients body. The temperature condition of intercity buses must be calculated from the thermal resistance per unit area of the bus interior. We proved that heat losses in the cabin of intercity buses, compared to city buses, are much lower due to the absence of heat losses at service stops at the exit and entry of passengers, which account for more than half of all heat losses. To reduce heat loss, the use of double-glazed windows instead of single panes has a particularly significant effect.

scholarly journals Optimization of Fin Spacing of Vertical Plate Fin Heat Sink in Natural Convection

2019 ◽  
Vol 9 (1) ◽  
pp. 1020-1024
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Surface Area ◽  
Heat Sink ◽  
Vertical Plate ◽  
Heat Sinks ◽  
Geometrical Parameters ◽  
Fin Spacing ◽  
The Heat Transfer Coefficient

Heat sinks are frequently used in the cooling of electrical and electronics devices If the heat sink have very close fin spacing, it increases the surface area but reduces the heat transfer coefficient. On the other hand, if heat sink has wide fin spacing, it reduces the surface area but increases the heat transfer coefficient. Therefore, there is need to optimize the fin spacing that enhanced the heat transfer from the heat sink. A properly selected heat sink may reduced the operating temperature and reduce the risk of failure of components. A steady state natural convective heat transfer from aluminum plate fin heat sink was examined experimentally. The length and thickness of fin was kept constant while height were varied from 5mm to 25mm and spacing varied between 5.5mm to 17mm.After experimentation, it was observed that fin spacing plays important role than any other geometrical parameters. Response surface methodology is used for optimization of fin spacing. It is observed that optimum fin spacing of heat sink is 8.28mm.The error analysis is done with the help of ANN and flow visualization were done using CFD

Triple or Quadruple Glazing?

2016 ◽  
Vol 820 ◽  
pp. 242-247 ◽  
Author(s):  
Ivan Chmúrny
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Solar Radiation ◽  
Transfer Coefficient ◽  
Thermal Insulation ◽  
Strengthened Glass ◽  
Basic Properties ◽  
Low Emission ◽  
The Heat Transfer Coefficient

Comparison of basic thermal insulation properties of triple glazing and quadruple glazing. It also compares the heat transfer coefficient of glazing, transmittance of solar radiation, the weight of glass and other basic properties of glazing. It deals with the effect of number and position of low-emission coating the quadruple glazing on the heat transfer coefficient. Reducing weight of quadruple glazing using thin heat-strengthened glass and dimensional constraints.

Evaporation of lignin-lean black liquor

TAPPI Journal ◽  
2015 ◽  
Vol 14 (7) ◽  
pp. 441-450
Author(s):  
HENRIK WALLMO, ◽  
ULF ANDERSSON ◽  
MATHIAS GOURDON ◽  
MARTIN WIMBY
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Black Liquor ◽  
Salt Content ◽  
Solubility Limit ◽  
Lignin Removal ◽  
Kraft Black Liquor ◽  
Black Liquors ◽  
The Heat Transfer Coefficient

Many of the pulp mill biorefinery concepts recently presented include removal of lignin from black liquor. In this work, the aim was to study how the change in liquor chemistry affected the evaporation of kraft black liquor when lignin was removed using the LignoBoost process. Lignin was removed from a softwood kraft black liquor and four different black liquors were studied: one reference black liquor (with no lignin extracted); two ligninlean black liquors with a lignin removal rate of 5.5% and 21%, respectively; and one liquor with maximum lignin removal of 60%. Evaporation tests were carried out at the research evaporator in Chalmers University of Technology. Studied parameters were liquor viscosity, boiling point rise, heat transfer coefficient, scaling propensity, changes in liquor chemical composition, and tube incrustation. It was found that the solubility limit for incrustation changed towards lower dry solids for the lignin-lean black liquors due to an increased salt content. The scaling obtained on the tubes was easily cleaned with thin liquor at 105°C. It was also shown that the liquor viscosity decreased exponentially with increased lignin outtake and hence, the heat transfer coefficient increased with increased lignin outtake. Long term tests, operated about 6 percentage dry solids units above the solubility limit for incrustation for all liquors, showed that the heat transfer coefficient increased from 650 W/m2K for the reference liquor to 1500 W/m2K for the liquor with highest lignin separation degree, 60%.

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