An Analysis of Heat Exchange Crisis in the Capillary Porous System for Cooling Parts of Heat and Power Units

2019 ◽  
pp. 21-35
Author(s):  
A.A. Genbach ◽  
D.Y. Bondartsev
Keyword(s):  
Heat Exchange ◽  
Heat Flow ◽  
Joint Action ◽  
Limit State ◽  
Bottom Layer ◽  
Heated Layer ◽  
Porous Coating ◽  
Porous System ◽  
Heat Flows ◽  
The Impact

A model of dynamics of the vapor bubbles that emerge on solid surfaces of porous structures and the steam generating wall (bottom layer) is presented in this work. The model was filmed and photographed by a high-speed camera SKS-1М. The discharge of high heat flows (up to 2·106 W/m2) was maintained by the joint action of capillary and mass forces with the help of intensifiers. An analytical model was developed based on the theory of thermoelasticity. The limit state of the porous coating with poor thermal conductivity and the metal bottom layer was determined. Heat flows were calculated from the spontaneous birth of the vapour nucleus (10–8) to the material destruction (102–103 s), thus the interval from the process of relaxation to the maximum process (destruction) was described. The size of the pullout particles determined in the model at the moment of porous coating destruction showed good congruence with the experimental data obtained at the optic stand. The destruction of coating under the compression forces occurs much earlier than the tension forces. It is probable that the destruction will happen under the impact of the compression and shear forces. The intervals of the heat flow when such destruction takes place are different for quartz and granite coating. Each thickness of the pullout particles under the impact of compression forces has its limit values of the heat flows, which are located within the mentioned intervals. As the specific heat flow in the heated layer increases and, therefore, the heating time decreases, the impact of the compression stresses increases as well. Despite the high resistance to compression, destruction from the compressive heat tension occurs in more favorable conditions immediately, and in diminutive volumes. Experimental testing units, test conditions, the outcome of the heat exchange crisis, the limit state of the surface and the calculation of critical heat flows are presented. The capillary porous system that works under the joint action of capillary and mass forces is studied. The system has advantages compared to pool boiling, thin-film evaporators and heat pipes.

scholarly journals Exergy of heat flows in exchanger consisting f gravity heat pipes

2012 ◽  
Vol 51 (No. 3) ◽  
pp. 73-78
Author(s):  
D. Adamovský ◽  
P. Neuberger ◽  
D. Herák ◽  
R. Adamovský
Keyword(s):  
Heat Flow ◽  
Air Temperature ◽  
Thermal Efficiency ◽  
Heat Pipes ◽  
Exergy Efficiency ◽  
Heat Flows ◽  
Heat Processes ◽  
The Impact

The paper deals with the analysis of the impact of inlet air temperature on the exergy efficiency and exergy of the losing heat flow and determination of the relation between the exergy and thermal efficiency in an exchanger consisting of gravity heat pipes. The assessment of heat processes quality and transformation of energy in the exchanger are also dealt with.

scholarly journals Analogy in the processes of heat exchange of capillary-porous coatings in energy installations

2019 ◽  
Vol 85 ◽  
pp. 05003
Author(s):  
Alexander Genbach ◽  
David Bondartsev ◽  
Iliya Iliev ◽  
Angel Terziev
Keyword(s):  
Heat Exchange ◽  
High Heat ◽  
Heat Fluxes ◽  
Porous Coating ◽  
Heat Conducting ◽  
Porous System ◽  
Experimental Conditions ◽  
Limiting State ◽  
Combined Action ◽  
System Operating

A model of the dynamics of steam bubbles generating on a solid surface in porous structures and a steam-generating wall (substrate) is developed. The model is based on the filming and photography with speed camera SKS-1M. The removal of high heat fluxes (up to 2х106 W/m2) is provided by the combined action of capillary and mass forces with application of intensifiers. An analytical model is developed based on the theory of thermoelasticity. The limiting state of a poorly heat-conducting porous coating and a metal substrate has been determined. The heat fluxes were calculated from the time of spontaneous appearance of the steam nucleation (10-8) up to the time of material destruction (102 ÷ 103 s). The destruction of the coating under the action of compression forces occurs in much earlier time than the tension forces. The intervals of the heat flux within which such destruction occurs are different for the quartz coating qmax ≈ 7х107 W/m2, qmin ≈ 8х104 W/m2 and for granite coating qmax ≈ 1х107 W/m2, qmin ≈ 21х104 W/m2. Experimental units, experimental conditions, the results of the heat exchange crisis and the limiting state of the surface are presented, and critical heat fluxes are calculated. The investigated capillary-porous system, operating under the combined action of capillary and mass forces, has the advantage over pool boiling, thin-film evaporators and heat pipes.

DYNAMIC AND THERMAL INTERFERENCE EFFECTS ON TWO NEIGHBOURING BUILDING MODELS

2019 ◽  
Vol 21 (5) ◽  
pp. 138-150
Author(s):  
S. V. Korobkov ◽  
A. I. Gnyrya ◽  
V. I. Terekhov
Keyword(s):  
Heat Exchange ◽  
Mutual Effect ◽  
Convective Heat Exchange ◽  
Physical Models ◽  
Interference Effects ◽  
Total Contribution ◽  
Heat Flows ◽  
Building Models ◽  
Number Of Factors ◽  
Thermal Interference

The paper considers the dynamic and thermal interference effects on two neighbouring building models in the form of square prisms arranged at a short distance from each other. It is shown how relative positions of the models affect the specific phenomena caused by the airflow interactions.The aim of this paper is to experimentally study the dynamic and thermal interference of a tandem of two building models in the form of square prisms depending on their relative position.The phenomenon of wind loads on buildings and structures has always attracted great interest among engineers and researchers. With the accumulation of knowledge and technical capabilities, the potential for likely ways to study wind flows and their impact on different objects increased. In recent years, the world science has accumulated an extensive knowledge base on wind impacts on objects of various shapes, such as prisms, pyramids, cylinders, etc. Studies are carried out for their mutual impact of several objects on changes in both the wind load and heat exchange. Their mutual effect on the air motion and turbulence is considered.There are two main areas in the field of the wind impact. The first impact is the force load on building, the second is the wind as a source of convective heat exchange. The object of this study is the interference parameters allowing to assess the influence on the field of pressure and heat recoil of disturbances evoked in front of the barriers.At the first stage, physical models help to study the pressure field on different facets and ratios of the local and medium heat exchange under the forced convection conditions. The next step is to jointly consider the wind (dynamic) load and heat flows, attempting to detect the total contribution to changes depending on the reciprocal model arrangement. All experiments are performed in the aerodynamic tube, at the TSUAB department. It is shown that the dynamic and thermal interference ratios vary greatly in two building models. At the same time, the thermal interference is very conservative compared to the dynamic. Using the interference parameters, it is easy to analyze the extreme pressure and the heat flow on the model surface depending on a large number of factors, including their arrangement.

The Impact of Heat Flow Variations in Shale Gas Evaluation: A Haynesville Shale Case Study

2013 ◽  
Author(s):  
Aimen Amer ◽  
Rolando di Primio ◽  
Robert Ondrak ◽  
Vikram Unnithan
Keyword(s):  
Heat Flow ◽  
Shale Gas ◽  
The Impact ◽  
Heat Flow Variations

scholarly journals The Impact of Microstructure Geometry on the Mass Transport in Artificial Pores: A Numerical Approach

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Matthias Galinsky ◽  
Ulf Sénéchal ◽  
Cornelia Breitkopf
Keyword(s):  
Mass Transport ◽  
Porous Materials ◽  
Effective Diffusion ◽  
Direct Simulation Monte Carlo ◽  
Numerical Approach ◽  
Porous System ◽  
Length Scales ◽  
General Evaluation ◽  
Pulse Experiment ◽  
The Impact

The microstructure of porous materials used in heterogeneous catalysis determines the mass transport inside networks, which may vary over many length scales. The theoretical prediction of mass transport phenomena in porous materials, however, is incomplete and is still not completely understood. Therefore, experimental data for every specific porous system is needed. One possible experimental technique for characterizing the mass transport in such pore networks is pulse experiments. The general evaluation of experimental outcomes of these techniques follows the solution of Fick’s second law where an integral and effective diffusion coefficient is recognized. However, a detailed local understanding of diffusion and sorption processes remains a challenge. As there is lack of proved models covering different length scales, existing classical concepts need to be evaluated with respect to their ability to reflect local geometries on the nanometer level. In this study, DSMC (Direct Simulation Monte Carlo) models were used to investigate the impact of pore microstructures on the diffusion behaviour of gases. It can be understood as a virtual pulse experiment within a single pore or a combination of different pore geometries.

Influence of Human Error on Structural Reliability

2017 ◽  
Author(s):  
Eric Brehm ◽  
Robert Hertle ◽  
Markus Wetzel
Keyword(s):  
Human Error ◽  
Structural Reliability ◽  
Failure Modes ◽  
Structural Model ◽  
Limit State ◽  
Design Procedure ◽  
Material Strength ◽  
Limit States ◽  
The Impact

In common structural design, random variables, such as material strength or loads, are represented by fixed numbers defined in design codes. This is also referred to as deterministic design. Addressing the random character of these variables directly, the probabilistic design procedure allows the determination of the probability of exceeding a defined limit state. This probability is referred to as failure probability. From there, the structural reliability, representing the survival probability, can be determined. Structural reliability thus is a property of a structure or structural member, depending on the relevant limit states, failure modes and basic variables. This is the basis for the determination of partial safety factors which are, for sake of a simpler design, applied within deterministic design procedures. In addition to the basic variables in terms of material and loads, further basic variables representing the structural model have to be considered. These depend strongly on the experience of the design engineer and the level of detailing of the model. However, in the clear majority of cases [1] failure does not occur due to unexpectedly high or low values of loads or material strength. The most common reasons for failure are human errors in design and execution. This paper will provide practical examples of original designs affected by human error and will assess the impact on structural reliability.

The Influence of Lubricant Supply Conditions and Bearing Configuration on the Performance of (Semi) Floating Ring Bearing Systems for Turbochargers

2017 ◽  
Author(s):  
Luis San Andrés ◽  
Feng Yu ◽  
Kostandin Gjika
Keyword(s):  
Heat Flow ◽  
Thermal Energy ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Engine Oil ◽  
Large Temperature ◽  
Oil Viscosity ◽  
Supply Pressure ◽  
The Impact ◽  
Bearing System

Engine oil lubricated (semi) floating ring bearing (S)FRB systems in passenger vehicle turbochargers (TC) operate at temperatures well above ambient and must withstand large temperature gradients that can lead to severe thermo-mechanical induced stresses. Physical modeling of the thermal energy flow paths and an effective thermal management strategy are paramount to determine safe operating conditions ensuring the TC component mechanical integrity and the robustness of its bearing system. On occasion, the selection of one particular bearing parameter to improve a certain performance characteristic could be detrimental to other performance characteristics of a TC system. The paper details a thermohydrodynamic model to predict the hydrodynamic pressure and temperature fields and the distribution of thermal energy flows in the bearing system. The impact of the lubricant supply conditions (pressure and temperature), bearing film clearances, oil supply grooves on the ring ID surface are quantified. Lubricating a (S)FRB with either a low oil temperature or a high supply pressure increases (shear induced) heat flow. A lube high supply pressure or a large clearance allow for more flow through the inner film working towards drawing more heat flow from the hot journal, yet raises the shear drag power as the oil viscosity remains high. Nonetheless, the peak temperature of the inner film is not influenced much by the changes on the way the oil is supplied into the film as the thermal energy displaced from the hot shaft into the film is overwhelming. Adding axial grooves on the inner side of the (S)FRB improves its dynamic stability, albeit increasing the drawn oil flow as well as the drag power and heat flow from the shaft. The predictive model allows to identify a compromise between different parameters of groove designs thus enabling a bearing system with a low power consumption.

Design capacities of joints with laterally loaded nails

2001 ◽  
Vol 28 (2) ◽  
pp. 282-290 ◽  
Author(s):  
Ian Smith ◽  
Steven T Craft ◽  
Pierre Quenneville
Keyword(s):  
Limit State ◽  
Ultimate Limit State ◽  
Joint Models ◽  
Yield Model ◽  
Rigid Plastic ◽  
Double Shear ◽  
Modelling Assumptions ◽  
Ultimate Limit State Design ◽  
Laterally Loaded ◽  
The Impact

Capacities of joints with laterally loaded nails may be predicted using "European yield" type models (EYMs) with various levels of complexity. EYMs presume that a nail and the wood on which it bears exhibit a rigid–plastic stress–strain response. Consideration is given in this paper to the "original" model published by K.W. Johansen in 1949, an empirical approximation proposed by L.R.J. Whale and coworkers in 1987, and a curtailed and "simplified" model proposed by H.J. Blass and coworkers in 1999. Predictions from the various EYMs are compared with experimentally determined ultimate capacities of single and double shear joints. Experiments covered a range of combinations of member thicknesses and two nail sizes. The impact of modelling assumptions is illustrated in the context of the Canadian timber design code. Suggestions are made regarding the necessary level of complexity for nailed joint models used in design.Key words: timber, joints, nails, yield model, ultimate limit state, design.

Experimental assessment of the influence of radiant heat transfer on the transition of a crown fire to settlements

2021 ◽  
pp. 19-26
Author(s):  
Николай Петрович Копылов ◽  
Елена Юрьевна Сушкина ◽  
Александр Евгеньевич Кузнецов ◽  
Виктория Ивановна Новикова
Keyword(s):  
Heat Flow ◽  
Forest Fire ◽  
Fire Resistance ◽  
Fire Protection ◽  
Forest Fires ◽  
Radiant Heat ◽  
Radiant Heat Transfer ◽  
Crown Fire ◽  
Fire Front ◽  
The Impact

Проведены экспериментальные исследования влияния лучистого теплообмена на переход верхового лесного пожара на постройки IV и V степеней огнестойкости. Лесной верховой пожар моделировался горением штабеля древесины с интенсивностью тепловыделения, близкой к интенсивности при реальных пожарах. Получена зависимость изменения плотности теплового потока от расстояния до кромки горения. Экспериментально определены температура воздуха с подветренной стороны пожара и плотность выпадения искр в зависимости от расстояния. Проверена эффективность защиты растворами ретардантов деревянных строений от возгорания при лучистом теплообмене между факелом пламени пожара и объектом защиты. Crown fires are the main threat of the combustion transfer from the forest to objects located in it. Fire services dealing with forest fires face the problem how to protect these objects from forest fires. It is proposed to treat the object with retardant solutions before a forest fire approaches. To assess the effectiveness of such tactics for fire protection of objects when exposed to a heat flow from the combustion front there were carried out experiments on large-scale crown fire models. A crown fire is simulated with a pile of wood with a heat release rate of ≈ 13 MW m. The wind is generated by fans, its speed is close to the speed at which a forest fire occurs. Measurements of the heat flux density, medium temperature, and the density of sparks falling downwind of the fire front at different distances and heights were carried out. Calculations were carried out to assess the impact of heat flow on buildings of IV-V degrees of fire resistance. The results obtained are compared with experimental data and they are in good agreement. There have been determined the distances from the fire front at which the fire protection with retardant solutions is effective for structures of IV-V fire resistance degrees at radiant heat exchange.

scholarly journals Estimating thermal transmittance of the aluminium window profiles in practice

2020 ◽  
Vol 172 ◽  
pp. 24003
Author(s):  
Arkadiusz Witek ◽  
Barbara Pietruszka
Keyword(s):  
Heat Exchange ◽  
Accurate Method ◽  
Radiative Heat Exchange ◽  
Conductivity Method ◽  
Equivalent Thermal Conductivity ◽  
Thermal Transmittance ◽  
Radiation Exchange ◽  
First Case ◽  
Air Cavities ◽  
The Impact

Calculation of the heat flow through the air cavities in the EN ISO 10077-2:2017 standard for the determination of the thermal transmittance of window profiles uses models based on the equivalent thermal conductivity method. The method takes into account the radiative heat exchange in a simplified or accurate manner. In the first case, the heat exchange depends on the average temperature in cavity, in the second case - it is determined accurately by the ray tracing method. It is also of importance to differentiate emissivity of surfaces due to aging or painting what influences calculation time. In this work, the impact of the calculation method and the impact of simplifications in modelling of the untreated surfaces on the value of the thermal transmittance of aluminium profiles was analysed on the example of a real series of products. Comparing the simplified and accurate method of determining the radiation exchange in cavities, the differences in the thermal transmittances of window profiles were up to 22%. The differences between the most simplified and the most accurate modelling of the surfaces emissivity reached 23%.

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