scholarly journals EXPERIMENTAL STUDIES OF THE DEPENDENCE OF THE CRITICAL SURFACE DENSITY OF HEAT FLUX FROM WIND INFLUENCE

2020 ◽  
Vol 1 (1) ◽  
pp. 107-115
Author(s):  
А Borysova ◽  
V Nignyk ◽  
D Sereda
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Surface Heat Flux ◽  
Surface Density ◽  
Heat Flux Density ◽  
Experimental Studies ◽  
Surface Heat ◽  
Critical Surface ◽  
Wind Influence ◽  
The Individual

The article presents the results of an experimental study to determine the dependence of the critical surface density of heat flux from wind influence.  The convergence of the obtained experimental data in each of the individual experiments was investigated.  The dependence of the critical surface heat flux density on wind influence is established and the regression is defined, which describes such dependence with the corresponding coefficients.

scholarly journals METHOD OF EXPERIMENTAL RESEARCH OF THE DEPENDENCE OF THE CRITICAL SURFACE DENSITY OF THE HEAT FLOW FROM THE WIND INFLUENCE

2020 ◽  
Vol 3 (156) ◽  
pp. 200-203
Author(s):  
A. Borysova ◽  
V. Nizhnyk
Keyword(s):  
Heat Flux ◽  
Flux Density ◽  
Experimental Research ◽  
Surface Heat Flux ◽  
Surface Density ◽  
Heat Flux Density ◽  
Experimental Studies ◽  
Surface Heat ◽  
Critical Surface ◽  
Wind Influence

According to the results of the analysis of methods for determining the critical value of the surface heat flux density for substances and materials, it is established that there is no single approach to determining the critical surface heat flux density for substances and materials today. The development of the method of experimental research of the dependence of the critical surface density of the heat flow from the wind influence as a basis for substantiation of the regularity of change of density of a heat stream from wind influence is an actual scientific task. The article analyzes the current state of the study of the critical surface heat flux density. A method has been developed and experimental studies of the values of the surface heat flux density from wind exposure for substances and materials have been carried out. At the time of experimental research, the regularities of the change in the heat flux density depending on the influence of the amount of airflow introduced into the study space were determined. The purpose of the study is to identify the pattern of changes in the heat flux density of substances and materials depending on the influence of the amount of airflow introduced into the study space. To achieve this goal it is necessary to justify the type and quantity of required test and measuring equipment, as well as the number, shape, and design of sample fragments, justify the methodology of experimental studies of samples under the influence of airflow of different speeds, justify the range of wind speed. The article briefly presents the procedure for conducting experimental research. The obtained data will be used for further research of the flammability of substances and materials. Keywords: critical surface heat flux density, heat flux, heat transfer, radiation heat transfer

Сurrent situation on determination of critical value of heat flow density

2020 ◽  
pp. 99-106
Author(s):  
V.V. Nizhnyk ◽  
◽  
A.S. Borysova ◽  
Keyword(s):  
Heat Flux ◽  
Flux Density ◽  
Environmental Conditions ◽  
Surface Heat Flux ◽  
Heat Flux Density ◽  
Continuous Process ◽  
Critical Value ◽  
Surface Heat ◽  
Process Equipment ◽  
Critical Surface

The physical process of energy transfer in the form of a certain amount of heat from a body with a higher temperature to a body with a lower temperature until the onset of thermodynamic equilibrium is a continuous process and is present in many areas of human activity. Determining the surface heat flux density makes it possible to measure and control the thermal processes of almost any object made of different materials, as well as substances in order to assess their condition. Based on a theoretical review, the article analyzes the current state to determine the critical value of the surface heat flux density depending on environmental conditions. Based on statistics and arrays of fire cards, it was concluded that every fourth fire in Ukraine can spread to adjacent buildings and structures, process equipment and natural ecosystems by spreading thermal energy with subsequent ignition. The authors consider the concept of heat flux and the concept of heat flux density, as well as define the essence of the concept of critical surface heat flux density as characteristics of heat flux. Scientists conducted a detailed analysis of literature sources, regulations and other sources of information related to this topic. Based on the research, the authors analyzed and found that the value of the surface heat flux density significantly depends on environmental conditions, namely the introduction of finely divided water into the space where the heat process and wind exposure. The authors found that to assess the value of the critical surface heat flux density, it is advisable to use the sign of flame combustion of substances and materials for the criterion base. However, to date there is no statistical base of critical values of surface heat flux density for various substances and materials, in particular those that can be used in the decoration of buildings and technological installations. The article analyzes modern approaches to determining the parameters of heat flux, as well as identifies some differences in these approaches, which allowed to formulate the purpose and relevance of further research, and identifies the main tasks to be achieved to achieve this goal.

Analysis of significant measures for thermal conductivity

2020 ◽  
pp. 35-42
Author(s):  
Yuri P. Zarichnyak ◽  
Vyacheslav P. Khodunkov
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Surface Heat Flux ◽  
Heat Flux Density ◽  
Measurement Method ◽  
Conductivity Measurement ◽  
Surface Heat ◽  
Measuring Instrument ◽  
New Class ◽  
Achievable Accuracy

The analysis of a new class of measuring instrument for heat quantities based on the use of multi-valued measures of heat conductivity of solids. For example, measuring thermal conductivity of solids shown the fallacy of the proposed approach and the illegality of the use of the principle of ambiguity to intensive thermal quantities. As a proof of the error of the approach, the relations for the thermal conductivities of the component elements of a heat pump that implements a multi-valued measure of thermal conductivity are given, and the limiting cases are considered. In two ways, it is established that the thermal conductivity of the specified measure does not depend on the value of the supplied heat flow. It is shown that the declared accuracy of the thermal conductivity measurement method does not correspond to the actual achievable accuracy values and the standard for the unit of surface heat flux density GET 172-2016. The estimation of the currently achievable accuracy of measuring the thermal conductivity of solids is given. The directions of further research and possible solutions to the problem are given.

Stress-Blended Eddy Simulation/Flamelet Generated Manifold Simulation of Film-Cooled Surface Heat Transfer and Near-Wall Reaction

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Yu Xia ◽  
Patrick Sharkey ◽  
Stefano Orsino ◽  
Mike Kuron ◽  
Florian Menter ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Surface Heat Transfer ◽  
Eddy Simulation ◽  
Flamelet Generated Manifold ◽  
Aero Engine ◽  
Cooling Hole

Abstract Accurate numerical prediction of surface heat transfer in the presence of film cooling within aero-engine sub-components, such as blade effusion holes and combustor liners, has long been a goal of the aero-engine industry. It requires accurate simulation of the turbulent mixing and reaction processes between freestream and the cooling flow. In this study, the stress-blended eddy simulation (SBES) turbulence model is used together with the flamelet generated manifold (FGM) combustion model to calculate the surface heat flux upstream and downstream of an effusion cooling hole. The SBES model employs a blending function to automatically switch between Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) based on the local flow features, and thus significantly reduces the computational cost compared to a full LES simulation. All simulations are run using ansys fluent®, a commercial finite-volume computational fluid dynamics (CFD) solver. The test case corresponds to an experimental rig run at Massachusetts Institute of Technology (MIT), which is essentially a flat plate brushed by a uniform freestream of argon with ethylene seeded inside, and is cooled by either a reacting air or a non-reacting nitrogen jet inclined at 35 deg to the freestream. Calculations are performed for both reacting and non-reacting jet cooling cases across a range of jet-to-stream blowing ratios and compared with the experimental data. The effects of mesh resolution are also investigated. Calculations are also performed across a range of Damköhler number (i.e., flow to chemical time ratio) from zero to 30, with unity blowing ratio, and the differences in the maximum surface heat flux magnitude in the reacting and non-reacting cases at a specific location downstream of the hole are investigated. Results from these analyses show good correlation with the experimental heat flux data upstream and downstream of the cooling hole, including the heat flux augmentation due to local reaction. Results from the Damköhler number sweep also show a good match with the experimental data across the range investigated.

scholarly journals The surface heat flux density of a bare soil

1983 ◽  
Vol 21 (4) ◽  
pp. 431-443 ◽  
Author(s):  
M.D. Novak ◽  
T.A. Black
Keyword(s):  
Heat Flux ◽  
Flux Density ◽  
Surface Heat Flux ◽  
Heat Flux Density ◽  
Bare Soil ◽  
Surface Heat

Surface heat transfer coefficient measurement by immersed temperature sensor and inverse modelling

2016 ◽  
Vol 83 (11) ◽  
Author(s):  
Mirko Javurek ◽  
Andreas Mittermair
Keyword(s):  
Heat Flux ◽  
Inverse Problem ◽  
Flux Density ◽  
Temperature Sensor ◽  
Surface Heat Flux ◽  
Heat Flux Density ◽  
Surface Heat ◽  
Problem Solution ◽  
Inverse Problem Solution

AbstractA transient surface heating or cooling process of a solid is considered. A procedure for the determination of surface temperature and surface heat flux density during such a process is presented using a submersed temperature sensor in the solid. From this measured temperature the surface temperature and surface heat flux density are calculated by inverse process modelling. This method is prone to errors since measurement errors are amplified in the inverse process modelling and can thus easily become unacceptably large. The LSQR regularisation algorithm is optimised for fast performance as well as less memory requirement and applied to the inverse problem solution. The proposed method allows to simulate an experimental setup and to determine the accuracy of the results gained from the simulated experiment. This is essential for the determination of the accuracy of a planned or existing test facility. The influence of process parameters like sensor depth, sensor noise level, sampling rate, heat flux density amplitude and cooling/heating process duration is investigated. In most cases it is very important to carefully adjust the process parameters in order to obtain reliable and accurate results. Additionally the proper selection of the regularisation parameter required for the inverse problem solution is analysed.

The Probability Distribution Modeling of Surface Heat Flux Density on Metal Material

2013 ◽  
Vol 738 ◽  
pp. 42-45
Author(s):  
Cheng Zhi Yang ◽  
Li Zhou
Keyword(s):  
Heat Flux ◽  
Energy Consumption ◽  
Flux Density ◽  
Surface Heat Flux ◽  
Heat Flux Density ◽  
New Technology ◽  
Surface Heat ◽  
Heating Process ◽  
Metal Material ◽  
Flux Density Distribution

In order to get the energy consumption relationship in the heating process of metal material, the probability and statistics law between the temperature distribution and surface heat flux density of heating metal material is established in this paper. Moreover the surface heat flux density distribution of heating metal material is used to associate with its energy consumption. And it builds a new technology method for saving energy control decisions.

scholarly journals Ocular surface heat flux density in healthy subjects

2021 ◽  
Vol 99 (S265) ◽  
Author(s):  
Lukyan Anatychuk ◽  
Nataliya Pasyechnikova ◽  
Volodimir Naumenko ◽  
Roman Kobylianskyi ◽  
Oleg Zadorozhnyy
Keyword(s):  
Heat Flux ◽  
Flux Density ◽  
Ocular Surface ◽  
Surface Heat Flux ◽  
Healthy Subjects ◽  
Heat Flux Density ◽  
Surface Heat

Mathematical Model of the Cooling of a Plastic, Thermoformed Part

2010 ◽  
Author(s):  
Thomas M. Aidich ◽  
Tien-Chien Jen ◽  
Yi-Hsin Yen
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Boundary Condition ◽  
Heat Flux ◽  
Boundary Conditions ◽  
Surface Temperature ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Cooling Cycle ◽  
Transient Conduction

This paper presents research into the mechanism involved in the cooling of a plastic thermoformed part after it is formed onto a mold. The intent of this research is to develop a simple and practical mathematical model useful to small thermoforming companies without a large engineering staff that describes the transient heat conduction of the cooling process. The model should also be able to predict the temperature distribution within the thickness of the part during the cooling. This mathematical model, which began with simplified boundary conditions, was then compared to experimental cooling data and modified accordingly to properly fit that data and the actual boundary conditions of the cooling part. The research began by examining the cooling of a series of high molecular weight polyethylene thermoformed side panels for plastic, portable restrooms. These parts where chosen for this preliminary research because of their very simple, flat geometric shape that lends them to being modeled as simple plane walls in transient conduction. The shape of the parts also leads to near constant thickness over the vast majority of the part. Using the model of a plane wall in transient conduction, the governing partial differential equation was solved for two possible boundary conditions on the mold side of the part: constant imposed surface temperature and constant imposed surface heat flux. These two solutions were then compared to experimental data gathered on the temperature profile of the free surface of the part during a production environment. After the experimental data and simple mathematical models were compared the necessary changes to the assumed mold side boundary condition was made to adjust the mathematical model to the experimental data. The research found that the use of simple boundary conditions at the mold side of the part is incorrect. Neither the constant imposed surface temperature nor the imposed surface heat flux boundary conditions fit the data. Initial analysis of the experimental data showed that a time of 30 seconds into the cooling cycle an apparent change in that boundary condition occurs for the part and mold used to gather the data. Further analysis showed that the boundary condition begins as a constant surface heat flux and then changes to an imposed surface temperature that decays exponentially to the initial mold surface temperature. Using this boundary condition, a revised mathematical was developed that match the experimental data very well. The error of the new model compared to the experimental was less than 1.5% for all times during the cooling cycle.

scholarly journals A Revised Equation for Heat Flux Reduction in Film Cooling Studies and Discussion of Its Applications

2011 ◽  
Author(s):  
Ting Wang ◽  
Lei Zhao
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Wall Temperature ◽  
Film Cooling ◽  
Surface Heat Flux ◽  
Experimental Studies ◽  
Flux Ratio ◽  
Surface Heat ◽  
Implicit Assumption ◽  
Film Cooling Effectiveness

In film cooling experimental studies, due to the difficulty in measuring the surface heat flux variation, a Heat Flux Ratio (HFR) equation originally derived by Mick and Mayle [1], has been widely employed to calculate the surface heat flux distribution using the measured adiabatic film effectiveness and surface temperature. A close examination of the derivation process and applications of the HFR equation reveals two issues of concern. First, an implicit assumption was introduced by letting the wall surface temperature of the system without-film be the same as that which would occur with a film-cooled condition. A revised equation is then derived by removing this implicit assumption and incorporating the wall temperature change due to film cooling Secondly, a uniform value of the non-dimensional metal temperature φ (or film cooling effectiveness) has been used in all the previous applications of the HFR equation. This practice implicitly implies that a uniform wall temperature is distributed throughout the entire surface under film cooling, which is usually not the case in real conditions. A series of computational experiments are conducted to verify the revised HFR equation under different conditions as well as examine the validity of using a constant surface temperature in the HFR equation. Results reveal that using a constant value of φ (0.5 ∼ 0.7) to calculate surface heat flux may result in a negative HFR in some simulated cases showing the commonly adopted value φ = 0.5∼0.7. This could induce errors and give false HFR. The error is reduced in 3D cases because the streamwise wall temperature becomes more uniform than 2D cases. The difference between the old and new equations can reach about 20%. A conjugate wall cooling simulation shows negative HFR is possible in the region close to the film hole due to the heat conduction from the downstream hotter region into the cooler region near the film hole. Using the actual wall temperature as the φ-value, the newly revised HFR equation produces the exact heat flux as calculated by CFD including the correct calculation of negative heat flux caused by the conjugate wall.

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