Using the solution to the reverse problem of heat conduction in the calculation of the heat transfer coefficient from temperature readings inside the body

1972 ◽  
Vol 23 (5) ◽  
pp. 1431-1434 ◽  
Author(s):  
V. L. Pokhoriler
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Conduction ◽  
Transfer Coefficient ◽  
The Body ◽  
Reverse Problem ◽  
The Heat Transfer Coefficient

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 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 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.

Influence of the Finite Element Model on the Inverse Determination of the Heat Transfer Coefficient Distribution over the Hot Plate Cooled by the Laminar Water Jets / Wpływ Modelu Metody Elementów Skonczonych Na Współczynnika Wymiany Ciepła Wyznaczany Z Rozwiazania Odwrotnego Procesu Laminarnego Chłodzenia Płyty Metalowej

2013 ◽  
Vol 58 (1) ◽  
pp. 105-112 ◽  
Author(s):  
B. Hadała ◽  
Z. Malinowski ◽  
T. Telejko ◽  
A. Szajding
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Transfer Coefficient ◽  
Heat Conduction ◽  
Transfer Coefficient ◽  
Shape Functions ◽  
Strip Surface ◽  
Coefficient Distribution ◽  
Laminar Jets ◽  
The Heat Transfer Coefficient

The industrial hot rolling mills are equipped with systems for controlled cooling of hot steel products. In the case of strip rolling mills the main cooling system is situated at run-out table to ensure the required strip temperature before coiling. One of the most important system is laminar jets cooling. In this system water is falling down on the upper strip surface. The proper cooling rate affects the final mechanical properties of steel which strongly dependent on microstructure evolution processes. Numerical simulations can be used to determine the water flux which should be applied in order to control strip temperature. The heat transfer boundary condition in case of laminar jets cooling is defined by the heat transfer coefficient, cooling water temperature and strip surface temperature. Due to the complex nature of the cooling process the existing heat transfer models are not accurate enough. The heat transfer coefficient cannot be measured directly and the boundary inverse heat conduction problem should be formulated in order to determine the heat transfer coefficient as a function of cooling parameters and strip surface temperature. In inverse algorithm various heat conduction models and boundary condition models can be implemented. In the present study two three dimensional finite element models based on linear and non-linear shape functions have been tested in the inverse algorithm. Further, two heat transfer boundary condition models have been employed in order to determine the heat transfer coefficient distribution at the hot plate cooled by laminar jets. In the first model heat transfer coefficient distribution over the cooled surface has been approximated by the witch of Agnesi type function with the expansion in time of the approximation parameters. In the second model heat transfer coefficient distribution over the cooled plate surface has been approximated by the surface elements serendipity family with parabolic shape functions. The heat transfer coefficient values at surface element nodes have been expanded in time by the cubic-spline functions. The numerical tests have shown that in the case of heat conduction model based on linear shape functions inverse solution differs significantly from the searched boundary condition. The dedicated finite element heat conduction model based on non-linear shape functions has been developed to ensure inverse determination of heat transfer coefficient distribution over the cooled surface in the time of cooling. The heat transfer coefficient model based on surface elements serendipity family is not limited to a particular form of the heat flux distribution. The solution has been achieved for measured temperatures of the steel plate cooled by 9 laminar jets.

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 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 Evaluation of localized heat transfer coefficient for induction heating apparatus by thermal fluid analysis based on the HSMAC method

Open Physics ◽  
2020 ◽  
Vol 18 (1) ◽  
pp. 504-511
Author(s):  
Satoshi Namiki ◽  
Tomoya Iino ◽  
Yoshifumi Okamoto
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Conduction ◽  
Transfer Coefficient ◽  
Induction Heating ◽  
Thermal Design ◽  
Electrical Machines ◽  
Fluid Analysis ◽  
Thermal Fluid Analysis ◽  
The Heat Transfer Coefficient

AbstractWith the development of electrical machines for achieving higher performance and smaller size, heat generation in electrical machines has also increased. Consequently, the temperature rise in electrical machines causes unexpected heating of components and makes it difficult to operate properly. Therefore, in the development of electrical machines, the accurate evaluation of temperature increase is important. In the thermal design of electrical machines, heat-conduction analysis using the heat-transfer boundary set on the surface of a heated target has been frequently performed. However, because the heat-transfer coefficient is dependent on various factors, it is often determined based on experimental or numerical simulation results. Therefore, setting the heat-transfer coefficient to a constant value for the surface of the heated target degrades the analysis accuracy because the actual phenomenon cannot be modeled. To enhance the accuracy of the heat-transfer coefficient, the coupled electromagnetic field with heat-conduction analysis finite element method (FEM), thermal-fluid analysis using FEM, and the highly simplified marker and cell method is applied to the estimation of the distribution of the heat-transfer coefficient. Moreover, to accurately calculate the localized heat-transfer coefficient, the temperature distribution and flow velocity distribution around the heated target are analyzed in the induction-heating apparatus.

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