scholarly journals Actual problems of the thermal hydraulic reliability ensuring of prospective nuclear reactors with supercritical parameters

2021 ◽  
Vol 20 ◽  
pp. 27-38
Author(s):  
I. G. Sharayevsky ◽  
◽  
N. M. Fialko ◽  
A. V. Nosovskyi ◽  
L. B. Zimin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermodynamic Parameters ◽  
Experimental Studies ◽  
Heat Removal ◽  
Heat Transfer Process ◽  
Critical Area ◽  
Water Coolant ◽  
Operational Parameters ◽  
Reliable Determination ◽  
Light Water

There is a significant lack of reliable information on the physical characteristics of thermohydraulic processes in emergency heat transfer modes when cooling the surface of fuel rods with light water coolant with supercritical thermodynamic parameters, in particular, on the physics of heat transfer processes and hydromechanics in the critical area. It is shown that in these conditions there is physical uncertainty about the causes of deteriorating heat transfer, which limits the possibility of creating effective calculation techniques for reliable determination of the upper limit of safe forcing of the heat transfer process in the core. At present, the vast majority of theoretical and experimental studies of thermohydraulic processes in the near-critical area have been performed only for the socalled “normal” heat transfer, which corresponds to the heat removal conditions with mixed turbulent convection of superheated to “gas” state of light water coolant in its inertial mode. Attention is paid to the possible appearance of macromolecular ensembles on this surface in the form of pseudo-vapor formations, which are capable of causing an emergency mode of pseudo-film boiling. On the basis of the given experimental data of various authors existence of rather deep physical analogy between processes of heat exchange in supercritical thermodynamic system and unheated boiling at subcritical parameters of the heat carrier is proved. Existence of the pseudo-boiling process in the conditions of supercritical thermodynamic parameters makes it impossible to use in the thermohydraulic calculation the empirical dependences for “hot” gas for the range of active zones operational parameters.

scholarly journals Heat transfer investigations in a liquid that is mixed by means of a multi-ribbon mixer

2021 ◽  
Vol 23 (2) ◽  
pp. 66-72
Author(s):  
Tomasz Borowski ◽  
Dawid Sołoducha ◽  
Daniel Musik ◽  
Krzysztof Wójcik ◽  
Mariusz Chyla ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Transfer Process ◽  
Heat Transfer Process ◽  
Operational Parameters ◽  
Empirical Correlations ◽  
Transfer Coefficients ◽  
Flowing Liquid ◽  
The Heat Transfer Coefficient

Abstract The objective of this paper is to present the investigations of the heat transfer process carried out by means of the multi-ribbon mixer. It is shown that the heat transfer process for the synergic effect of the mixing process and the flowing liquid through the mixer has significantly higher values of the heat transfer coefficients than the mixer with motionless impellers. The empirical correlations between the heat transfer coefficient and the operational parameters obtained in this work can provide guidance for the design and operation of an apparatus equipped with the multi-ribbon impeller. These empirical correlations can be used to predict the heat transfer coefficient for the multi-ribbon mixer.

scholarly journals Experimental Investigation on Condensation of Vapor in the Presence of Non-Condensable Gas on a Vertical Tube

2018 ◽  
Author(s):  
Shengjun Zhang ◽  
Feng Shen ◽  
Xu Cheng ◽  
Xianke Meng ◽  
Dandan He
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Total Pressure ◽  
Mass Fraction ◽  
Heat Removal ◽  
Heat Transfer Process ◽  
Transfer Model ◽  
Operation Conditions ◽  
The Heat Transfer Coefficient

According to the operation conditions of time unlimited passive containment heat removal system (TUPAC), a separate effect experiment facility was established to investigate the heat transfer performance of steam condensation in presence of non-condensable gas. The effect of wall subcooling temperature, total pressure and mass fraction of the air on heat transfer process was analyzed. The heat transfer model was also developed. The results showed that the heat transfer coefficient decreased with the rising of subcooling temperature, the decreasing of the total pressure and air mass fraction. It was revealed that Dehbi’s correlation predicted the heat transfer coefficient conservatively, especially in the low pressure and low temperature region. The novel correlation was fitted by the data obtained in the following range: 0.20~0.45 MPa in pressure, 20% ~ 80% in mass fraction, 15°C ~ 45°C in temperature. The discrepancy of the correlation and experiment data was with ±20%.

scholarly journals Heat load of bimetallic ribbed tube

2021 ◽  
Vol 33 (5) ◽  
pp. 271-282
Author(s):  
Elena Sergeevna Baimetova ◽  
Albina Firdavesovna Gizzatullina ◽  
Maria Ravilevna Koroleva ◽  
Olga Vladimirovna Mishchenkova ◽  
Fyodor Nikolaevich Pushkarev ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Conjugate Heat Transfer ◽  
Heat Removal ◽  
Cylindrical Tube ◽  
Longitudinal Section ◽  
Heat Transfer Process ◽  
Finned Tube ◽  
Qualitative Comparison ◽  
Bimetallic Finned Tube ◽  
Metal Metal

This study is devoted to the problem of numerical modeling of the conjugate heat transfer in a closed-type power installation. The working elements of that are ribbed bimetallic tubes using the openFoam toolbox. The heat transfer process modeling in bimetallic tubes is associated with solving the problem of determining the value of the contact thermal resistance at the metal / metal interface. Considered design of a bimetallic tube involves crimping copper washers on the surface of an aluminum cylindrical tube. Hence, the contact surface of the tube is not isotropic in its properties. A mathematical model of conjugate heat transfer for air / bimetal / coolant medium is proposed. The features of the organization of thermophysical processes at the metal contact interface and at the metal / air and metal / coolant medium are shown. A qualitative comparison of the obtained results with the famous experimental data is carried out. Generalized temperature profiles in the rib longitudinal section are obtained by mathematical modeling. The given distributions of temperature and heat flux make it possible to estimate the contribution of each individual rib to the investigated heat removal process from the air environment. The efficiency of the considered technology of manufacturing a bimetallic finned tube is shown.

Numerical Modeling of Water Impingement and Heat Transfer With Solid Slabs During Secondary Cooling in a Continuous Caster

2018 ◽  
Author(s):  
Haibo Ma ◽  
Kaile Tang ◽  
Rui Liu ◽  
Michael Lowry ◽  
Armin Silaen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Continuous Caster ◽  
Cooling Water ◽  
Heat Removal ◽  
Heat Transfer Process ◽  
Standoff Distance ◽  
Slab Surface ◽  
Secondary Cooling ◽  
Cooling Effects

In the steel continuous casting process, cooling water is directly injected through multiple rows of nozzles to remove heat from the slab to allow the slab to solidify in secondary cooling. Effective heat removal from the slab without causing slab cracking and deformation is desired. The present study focuses on developing a reliable numerical model which can accurately predict the impingement and heat transfer between water droplet and solid slab. The flat fan atomizer is chosen as a representative nozzle to be simulated. The spray pattern on the slab surface, as well as the impingement behaviors of water droplets, are obtained through an Eulerian-Lagrangian approach. The wall jet model coupled with modified evaporation rate depending on the droplet Weber number has been applied in the numerical model. A series of parametric studies have been performed to investigate the effects of spray direction, standoff distance, and distance between adjacent nozzles on the impingement heat transfer process. Simulation results reveal that intense cooling effects can be found in the center of the spray, where the concentration of droplets is the highest regardless of the spray direction. Double the standoff distance can reduce the heat transfer coefficient on slab surface by 10%. Finally, the distance between two adjacent nozzles should be adjusted to be smaller than the standoff distance in order to avoid the “fountain” effect induced by the collision of the two neighboring wall jets.

scholarly journals Modeling of the heat transfer process in an air heat pump fanless evaporator

2018 ◽  
Vol 240 ◽  
pp. 05012
Author(s):  
Piotr Kopeć ◽  
Beata Niezgoda-Żelasko
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Mixed Convection ◽  
Heat Pump ◽  
Transfer Process ◽  
Experimental Studies ◽  
Heat Transfer Process ◽  
Cfd Modeling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

This paper analyses the mixed convection process in a fanless evaporator of an air heat pump. The text of the paper shows the authors’ experimental studies results of the temperature distribution and the local values of heat transfer coefficients on the outer surface of vertical tubes with longitudinal fins for the case of mixed convection and fins of a specific shape of their cross-section (prismatic, wavy fins). The experimental studies include the air velocities wa=2,3 m/s and the temperature differences between air and the refrigerant inside the heat exchanger tubes which is ΔT=24-40K. The results obtained were used for verification of CFD modeling of the heat transfer process for the discussed case of heat transfer and the geometry of the finned surface. The numerical analysis was performed for: the temperature distribution along the fin height, the tube perimeter and height, the distribution of local heat transfer coefficients on the finned tube perimeter and along its height. The simulated calculations were used to verify the method of determination of fin efficiency.

Numerical Analysis of Convection Heat Transfer From an Array of Circular Perforated Fins due to Variable Perforation Size

2012 ◽  
Author(s):  
A. H. Dastbelaraki ◽  
M. Yaghoubi
Keyword(s):  
Heat Transfer ◽  
Numerical Analysis ◽  
Stokes Equations ◽  
Experimental Studies ◽  
Convection Heat Transfer ◽  
Heat Removal ◽  
Industrial Applications ◽  
Working Fluid ◽  
Manufacturing Cost ◽  
Convection Heat

Among rapid advances of electrical systems electronic circuit boards have become more compact and heat production rate from their components increased considerably. Such developments raised more attention and tendency in tackling their cooling problems. A wide variety of cooling systems are developed such as various fins for decreasing the circuit board temperature. Extended surfaces or fins are good heat transfer equipments that are used for various industrial applications. The wide industrial applications of fins to enhance heat transfer rate highlighted the need for further research of optimization of fins to increase their thermal performances. Among various fin types, rectangular fins are commonly used due to their simplicity of manufacturing. Fin configurations affect the cooling rate significantly, hence a comprehensive parametric study on the fin geometries may be improve their performance. Rectangular fins show a good performance of increasing heat removal rate, while reducing the manufacturing cost. Moreover the inspiration of putting holes along the flow through the fins may be very helpful in increasing the heat removal and reduction of the needed material. The present study investigates a numerical analysis of three dimensional, turbulent convection heat transfer from an array of rectangular perforated fins with increasing the perforation size from bottom to top. The perforations considered are like circular channels along the length of fins and the number of perforations is 3. For investigation, incompressible air as working fluid is modeled using Navier–Stokes equations. RNG based k-ε turbulent model is used to predict turbulent flow parameters. Temperature field inside the fins is obtained by solving Fourier’s conduction equation. The conjugate differential equations for both solid and gas phase are solved simultaneously by finite volume procedure using SIMPLE algorithm. Flow and heat transfer characteristics are presented for Reynolds numbers from 2 × 104 to 4 × 104 based on the fin length and Prandtl number of Pr = 0.71. Numerical model is first validated with previous experimental studies and good agreements were observed. Based on the valid simulation model, numerical solution is made to find flow field and temperature distribution for various perforation size. Results show that for a specific type of perforated fins the fin effectiveness is higher than other types and drag coefficient decreases with increasing the perforation size.

Experimental Analysis on Non-Dimensional Parameters of Closed-Loop Pulsating Heat Pipes

2013 ◽  
Vol 732-733 ◽  
pp. 230-233
Author(s):  
Xun Wang ◽  
Xiao Wen Zhang ◽  
Cheng Si Yang
Keyword(s):  
Heat Transfer ◽  
Closed Loop ◽  
Heat Transfer Performance ◽  
Experimental Studies ◽  
Heat Pipes ◽  
Operational Parameters ◽  
Characteristic Parameters ◽  
Experimental Conditions ◽  
Operation Stage ◽  
Dimensional Parameters

Based on experimental studies, this paper discusses the variation tendencies of three non-dimensional parameters including Ja, Bo and Pr which consist of various operational parameters and characteristic parameters, and then analyses their effects on heat transfer performance of closed-loop pulsating heat pipes (PHPs) at startup stage and steady operation stage. Results indicate that at startup stage, the values of Ja and Bo increase over time as a whole, while the values of Pr decrease; at steady operation stage, the values of three parameters all fluctuate within a narrow range. The results also show that heat transfer is due mainly to the exchange of latent heat under the experimental conditions.

scholarly journals Computational Fluid Dynamics of Heat Transfer in Stirred Tank Reactors

2021 ◽  
Author(s):  
Chaitanya Moholkar ◽  
Punit Gharat ◽  
Vivek Vitankar ◽  
Channamallikarjun Mathpati ◽  
Jyeshtharaj Joshi
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Reynolds Number ◽  
Heat Removal ◽  
Design Parameters ◽  
Operational Parameters ◽  
Power Requirement ◽  
Maximum Heat ◽  
Maximum Heat Transfer

In the present work, computational fluid dynamics study of stirred tanks of three sizes (20L, 400L and 5000L) provided with helical coils has been carried out. Various design parameters (impeller diameter, type and clearance) and operational parameters (Reynolds Number and Power per unit volume) have been varied and their effect on process side heat transfer coefficient has been studied. CFD model is validated with experimental work of Cummings and West[9] and in house experimentation. Design settings of D/T=0.5, C/T=0.33 for PBTD450 resulted in maximum heat transfer (5440 W/m2K for P/V=1000 W/m3). For constant RPM and constant D/T (Constant Reynolds Number), Increasing the power number of impeller increased process side HTC at the cost of increased power requirement (decreasing efficiency). In such cases, proper selection of impeller system needs to be made based on the requirements of heat removal and optimizing parameters such as product yield, product quality etc.

scholarly journals Computational Fluid Dynamics and Experimental Studies of a New Mixing Element in a Static Mixer as a Heat Exchanger

2015 ◽  
Vol 36 (1) ◽  
pp. 59-72 ◽  
Author(s):  
Maciej Konopacki ◽  
Marian Kordas ◽  
Karol Fijałkowski ◽  
Rafał Rakoczy
Keyword(s):  
Heat Transfer ◽  
Experimental Studies ◽  
Heat Transfer Process ◽  
Transformer Oil ◽  
Static Mixer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Heat Transfer Efficiency ◽  
Water Glycerol

Abstract The main aim of this work is to study the thermal efficiency of a new type of a static mixer and to analyse the flow and temperature patterns and heat transfer efficiency. The measurements were carried out for the static mixer equipped with a new mixing insert. The heat transfer enhancement was determined by measuring the temperature profiles on each side of the heating pipe as well as the temperature field inside the static mixer. All experiments were carried out with varying operating parameters for four liquids: water, glycerol, transformer oil and an aqueous solution of molasses. Numerical CFD simulations were carried out using the two-equation turbulence k-ω model, provided by ANSYS Workbench 14.5 software. The proposed CFD model was validated by comparing the predicted numerical results against experimental thermal database obtained from the investigations. Local and global convective heat transfer coefficients and Nusselt numbers were detrmined. The relationship between heat transfer process and hydrodynamics in the static mixer was also presented. Moreover, a comparison of the thermal performance between the tested static mixer and a conventional empty tube was carried out. The relative enhancement of heat transfer was characterised by the rate of relative heat transfer intensification.

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