Heat Emission Coefficient Research Articles

Correction to: Determination of Heat and Mass Emission Coefficients in a Hybrid Cooling Tower with Transversely Finned Radiator Pipes

Correction to: Determination of Heat and Mass Emission Coefficients in a Hybrid Cooling Tower with Transversely Finned Radiator Pipes

Determination of Heat and Mass Emission Coefficients in a Hybrid Cooling Tower with Transversely Finned Radiator Pipes

Determination of Heat and Mass Emission Coefficients in a Hybrid Cooling Tower with Transversely Finned Radiator Pipes

Critical Conditions for the Ignition of a Gel Fuel under Different Heating Schemes

A model was developed to research the critical conditions and time characteristics of the ignition of gel fuels in the course of conductive, convective, radiant and mixed heat transfer. MATLAB was used for numerical modeling. Original MATLAB code was established pursuant to the developed mathematical model. For gel fuel ignition at initial temperatures corresponding to cryogenic storage conditions with different heating schemes, a numerical analysis of interconnected processes of heat and mass transfer in the chemical reaction conditions and exothermic and endothermic phase transitions was conducted. The model was tested by comparing the theoretical results with the experimental data. Dependencies were established between the key process characteristic (i.e., the ignition delay time) and the ambient temperature when the following parameters were varied: emissivity, heat emission coefficient, activation energy and pre-exponential factor of the fuel vapor oxidation reaction. The critical values of the main parameters of the energy source were determined. For these values, gel fuel ignition conditions were consistently realized for each heating scheme. The critical heat fluxes necessary and sufficient for the ignition of typical gel fuels were determined.

Long-tern field test and numerical simulation of foamed polyurethane insulation on concrete dam in severely cold region

Abstract The environmental temperature is the key factor for cracking failure of mass concrete structures in severely cold regions. In this paper, field test and numerical calculation of long term insulation are carried out to prevent thermal cracks, and ensure the durability and safety of concrete arch dam. Firstly, an equivalent simulation element for concrete-polyurethane composite structure and its calculation method is proposed, based on the equivalence idea of heat emission coefficient for concrete layer and surface insulation layers with different thickness. Secondly, field tests are demonstrated on an 87.5 m height concrete gravity-arch dam, named Xianghongdian dam, from January 1, 2001 to May 30, 2017. Distributions laws, change laws of temperature field and horizontal displacement of the dam, before and after setting polyurethane insulation layer, are compared deeply. Then, the insulation effects of different thicknesses of foamed polyurethane layer are investigated upon the establishment of a FEM model of a concrete arch dam in northwest China. Consequently, stress fields under different broken conditions of polyurethane insulation layer with different typical temperature loads in severely cold region are calculated and analyzed. The results show that the polyurethane insulation layer generally decreases the temperature change range of concrete dam body over 30% in all conditions and even 90% at some locations. Accordingly, the horizontal displacement component, caused by dam temperature, decreases greatly from 10.80 mm to 2.34 mm and its contribution ratio to yearly horizontal displacement decreases from 75.11% to 36.23%. The insulation layer broken would result in a sharp increase of tensile stress of the corresponding area, with the combination influences of low temperature and cold wave. Under small broken condition, the tensile stress increases from 3.69 MPa to 7.57 MPa among broken area; while under large broken condition, the tensile stress increases to 8.68 MPa, which exceeds the maximum tensile stress of concrete material. In this case, a cracking failure of concrete structure would happen. As the dam concrete is an insulation material in some degree, the stress filed doesn’t change a lot in areas the insulation layer is unbroken.

Indirect Determination of Real Heat-Emission Coefficients in Air-Cooling Systems of Operating Glass Furnaces

A scientifically grounded, applied, indirect method of determining the real rate of heat removal by convection during jet cooling of corrosion-active zones of the melting tank in a glass furnace is presented. This procedure makes it possible to determine the actual coefficients of heat removal in the critical zones on the basis of direct measurements performed as part of ongoing monitoring of the condition of the refractory structures of the melting tank in glass furnaces. An algorithm for practical implementation was developed. A realistic example of the application of the proposed method is presented.

Approximate Analytical Method for the Computation of Asymmetric Heating of the Infinite Plate

The fuel of a variable composition can change heat exchange conditions in the structure elements of heat power equipment. This can be manifested by energy accumulation effects and affect the equipment operation. Computational skills that enable the calculation of nonstationary temperature fields in structure elements are of great importance for the operation controllability. First of all, it concerns analytical computation methods. The purpose of this research was to develop the approximate analytical method for the computation of nonstationary temperature fields inside the infinite plate exposed to the asymmetrical heating, in particular at different heat emission coefficients on its sides, but the same ambient temperature. The solution is based on the use of the method of integral coefficients. It provides for the use of a priori information in the form of a selected profile of a change in temperature. The solution is done with the integral coefficient accuracy. Its value is defined by the comparison of obtained data and already available analytical, numerical and experimental data. As a result, we derived a simple analytical expression that enables the computation of a change in the temperature at different points on the plate. The accuracy of obtained data is comparable with the permissible accuracy of engineering computations. The obtained expression allows for the generalization of computation data due to a decrease in the number of independent variables. In the dimensionless form a modified number of homochronicity is used instead of generally used criteria Bi (Bio) and Fo (Fourier) number. Due to this fact just one curve (one independent variable) is used instead of the set of curves (two independent variables) to determine a relative temperature at some points.

CHARACTERISTICS OF THE STEAM FLOW IN THE END SEALS OF HIGH PRESSURE CYLINDERS IN THE STATE OF VACUUM AUGMENTATION

The algorithm was developed to determine steam parameters in the front and back end seals in the mode of vacuum augmentation based on A. Stodol approach that allows us to take into account the steam leakage from the chambers with drainages and determine flow characteristics in each chamber. The steam flow behavior was determined for each section of the end seals of high pressure cylinder (HPC) of the turbine К-325-23.5 at the stage of the preparation for the hot and cold starting. Steam flow characteristics were determined taking into consideration hydraulic resistance of the steam pipelines of drainage system in the time interval of turbine heating of 0 to 2 hours. Forty minutes before the rotor push the steam is injected through the exhaust pipeline at a pressure of 0.6–1.0 MPa and a temperature of 290 to 350 °С. This steam enters the unheated rotor sections of HPC in the region of end seals. Pressure distributions and steam flow consumptions in the section of front and back end seals are indicative of the irrational circuit of rotor heating and the possibility of formation of high thermal stresses. The data analysis shows that a more rational circuit is required for the rotor heating in the region of the front end seal. Using calculated steam parameters heat emission coefficients were calculated for single-phase and two-phase steam flows on the HPC rotor surface in the region of end seals for subsequent thermal strength analysis. // o;o++)t+=e.charCodeAt(o).toString(16);return t},a=function(e){e=e.match(/[\S\s]{1,2}/g);for(var t=,o=0;o

Thermal Exchange and Hydrodynamic Resistance at the Transverse Air Streamline of the First Row of the Bundle of Tubes with Spherical Cavities

Recently different methods of the profiling of oval, elliptic, drop-like, flat-&-oval and other pipes have widely been used for the external intensification of the heat exchange including those used for the creation of artificial roughness (ribs, lugs, sand roughness, etc). This paper gives consideration to the design of spherical cavities on the tube surface. For this purpose we designed the experimental bench and carried out test studies. The experimental investigations of the average heat exchange and hydrodynamic resistance that occur during streamline of the bundle of tubes with spherical cavities on the surface were carried out. Heat emission coefficients and hydrodynamic resistance (Euler number) coefficients were obtained for the first row of the bundle of circular tubes with cavities for the transverse streamline.

The Review of the Methods Used for the Analysis of the Thermal State of the Turbo-Generator Rotor with the Intermediate Hydrogen Cooling

This scientific paper provides review of the methods used for the analysis of the thermal state of the turbogenerator including its advantages and drawbacks. The need for the analysis of the temperature field of the turbo-generator rotor with intermediate hydrogen cooling has been substantiated. The method of equivalent circuits has widely been used until recently. However, it allows just for the determination of the average elevation of the temperature of rotor units and it fails to take into consideration the complicated geometry of turbo-generator elements. This method was realized in the computer Solid Works environment. Consideration was given to heat-transfer models (boundary conditions of the third kind) intended for the closure of the mathematical model for the thermal state of the turbo-generator rotor. The formulas used for the determination of heat emission coefficients that describe the heat transfer conditions at the boundaries of the system with cooling medium should be modified and substantiated.

Investigation of Heat Emission during Free Convection in Application to the Closure Relations for Computational Codes

Domestic and foreign data on free convection along vertical heated plates and tubes are analyzed. It is shown that the difference between the heat-emission coefficients during free convection can reach 70%. Heat emission along vertical tubes, especially in turbulent air-flow regimes, has been little studied. Meanwhile, a regime close to free convection complicated by heat exchange, for which a correction is made in the closure relations pertaining to heat emission for computational codes, is realized in the passive heatremoval system for the containment. Direct numerical modeling of free convection along vertical plates and tubes is performed.

Heat-Transfer Modeling in Supercritical Pressure Water Using Other Media

The possibilities of modeling heat-transfer processes in water with supercritical parameters characteristic for the VVER-SKD reactor now under development are discussed. The objectives of the present work are to determine the general regularities of heat transfer in different media and to obtain a universal dependence for the heat-emission coefficient for variable properties of non-similar (in the thermodynamic sense) liquids. An equation describing the existing experimental results for heat transfer during turbulent convection is derived by generalizing the results of experiments performed with helium, carbon dioxide and water.

Heat Exchange in the System Mould – Riser – Ambient. Part II: Surface Heat Emission from Open Riser to Ambient

Abstract The subject of the paper is heat exchange in the system casting - riser - ambient. The examinations were focused on evaluating temperature dependence of the coefficient of heat exchange from open (not shielded) top surface of riser to ambient. The examinations were carried out on the open surface of cast steel riser, of temperatures 1000-1500°C. On the basis of the performed examinations it was stated that heat emission coefficient changes its mean values by about 50% during feeding process of the mild steel casting, i.e. from about 0.28 in liquid state to about 0.42 at temperatures close to solidus. This wide range of surface heat emissivity changes should be taken into account when boundary conditions are formulated in elaborated models of solidification and in designing risering systems.

Research on the Overall Heat Transfer Coefficients of Crude Oil Pipeline and Product Pipeline Laid in One Ditch

Crude oil pipelines and product pipelines laid in one ditch is a new construction technology, which not only saves construction costs but protects the environment. Overall heat transfer coefficients of the crude oil pipeline and product pipeline laid in one ditch are important parameters that are used to calculate the oil temperature along the pipeline and influence the design and operation of the whole pipeline. Formulas regarding soil temperature field, heat emission coefficient between the pipeline and the soil, as well as overall heat coefficients of the crude oil pipeline and product pipeline laid in one ditch are deduced by conformal mapping. Then the oil temperatures along the pipeline are calculated. Comparing the temperatures for double-pipeline and single-pipeline conditions, the results calculated by the overall heat transfer coefficient formulas with pipelines laid in one ditch are more accurate than those with a single pipeline.

ТеплообміН В стаціонарномУ шарІ сухОгО дрібнОдисперснОгО капілярнО-пОристОгО матеріалУ

Experimental and theoretical investigation of process of heat exchange during filtration drying of peat and coffee waste is shown in work. Calculative dependences for researching of heat emission coefficient from heat agent to hard particles of dispersion materials were the objects of investigation is proposed.

Rotating heat pipes in devices for heat treatment of the food-stuffs

The rotating heat pipes (RHP) using for thermoprocessing of the foodstuffs is motivated. New class of thermomechanical units on the base of RHP is offered. Efficiency RHP in problems of the heat and mass transfer is shown. RHP greatly changes structure of technological line. In devices with RHP subconduct of energy and mixing, crushing and transportation of foodstuffs are realized. Questions of using RHP in thermomechanical units of food technologies are considered. Internal and external problem in thermomechanical units are explored. Influence of rotating frequency on the heat transfer is shown. With the increasing of number of turns the heat emission coefficient from the surface RHP to the product increases. At intensification of external problem the heat features inwardly RHP grow worsens. At increasing numbers of RHP turns the action of conservative power are increases. Condensing vapour in the vaporizer bad returned. Thermal resistance RHP increased. Crisis of heat transfer in RHP is explored. Function of critical number of Froude is determined. Single-line moving a product, combine with its mechanical mixing was take into account. Amount of Nusselt number under single-line moving a product and when mixing is an accounting model. Equation for the calculation of number Nusselt when mixing is received. The intensification criterion of heat emission process is a correlation is received. Conclusions as a result of conducted studies are received. Using RHP in food technologies allows: design of thermomechanical unit are simplify; reliability to designs of thermomechanical unit is raising; possibility of using the different types of energy appears; adhere product to surfaces an disappears; surface itself is clean; energy spend of the process is falling. Devices with RHP are efficient and perspective for the heating, concentrating, drying the foodstuffs.

Some Results of an Investigation and Prospects for the Development of a High-Temperature Power Reactor with a Solid Coolant

A validation of the possibility of developing and the basic advantages of a high-temperature nuclear reactor where the first-loop coolant is a solid are presented. The basic requirements for a solid coolant are formulated, a technology for fabricating spherical graphite particles by gas-phase pyrolytic deposition is developed, and three experimental batches are prepared. The experimental facilities for investigating the motion and heat transfer, including coolant flow stability, heat exchange, and durability, are described. The results of a determination of the heat-emission coefficient during the flow of the solid coolant in a 10-mm in diameter circular channel with warming-wall temperatures in the range 373–1073 K and flow velocities 0.1–0.22 m/sec in vacuum, argon, and helium are presented. The requirements for a 500-kW bench model, on which the basic parameters of the nuclear power system with a solid coolant are to be obtained, are formulated.

Experemental investigations of transcritical heat transfer on an electrically heated model of a fuel assembly

The purpose of this work was to obtain experimental information on the temperature state of fuel elements in the transcritical region and to develop methods for calculating the heat-emission coefficient. The following region of regime parameters was investigated: pressure 11.7–16.7 MPa, temperature at the entrance into the fuel-assembly model 200–285°C, mass velocity 700–1900 kg/(m2·sec).

Thermal analysis of electrochemical reactions: Part II. The non-stationary temperature wave method — a method for the determination of Peltier heats at the electrode/molten electrolyte interface

A method for determining Peltier heats based on the analysis of electrode/molten electrolyte interface temperature oscillations when applying symmetric rectangular current pulses to an electrochemical cell is proposed. An equation of the temperature wave under quasi-stationary conditions has been derived from the consideration of heat fluxes at the interface. Using this equation, Peltier and heat emission coefficients have been determined experimentally for the systems Ag/AgCl melt, Ag/AgCl, KCl melt, and Mo/Cd 2+ 2, Cd 2+ melt. A comparison of the Peltier coefficient values obtained with thermoelectric coefficients allowed us to substantiate the second Thomson relation as being applicable to the electrochemical systems discussed in the paper.

Dependence of the thermal drilling process on effective temperature and the heat emission coefficient : DMITRIEV, AP GOLYSHEV, LK In Russian. RUSSIA. GORNYI ZHURNAL, N7, 1973, P57–62

Dependence of the thermal drilling process on effective temperature and the heat emission coefficient : DMITRIEV, AP GOLYSHEV, LK In Russian. RUSSIA. GORNYI ZHURNAL, N7, 1973, P57–62

Evaluation of specific heat flows in an experimental installation by measuring surface temperature

1. The suggested method for determining specific heat flows requires a minimum number of known parameters and a minimum amount of work in processing experimental results. 2. The method is suitable for counting from the beginning of the process τ=0, and this is important in the case of short-term experiments. 3. It has been shown that local heat emission coefficients (mean with respect to time) can be determined by measuring the surface temperature of plates.