Modeling and Simulations of Deteriorated Turbulent Heat Transfer in Wall-Heated Cylindrical Tube

2019 ◽  
Vol 4 (3) ◽  
Author(s):  
Prasad Vegendla ◽  
Rui Hu
Keyword(s):  
Heat Transfer ◽  
Nuclear Power ◽  
Three Dimensional ◽  
Cylindrical Tube ◽  
Fluid Flows ◽  
Turbulent Heat Transfer ◽  
Wall Region ◽  
Turbulent Heat ◽  
Modeling And Simulations ◽  
Computational Fluid Dynamics Cfd

Abstract This paper discusses the modeling and simulations of deteriorated turbulent heat transfer (DTHT) for a wall-heated fluid flows, which can be observed in gas-cooled nuclear power reactors during pressurized conduction cooldown (PCC) event due to loss of force circulation flow. The DTHT regime is defined as the deterioration of normal turbulent heat transport due to increase of acceleration and buoyancy forces. The computational fluid dynamics (CFD) tools such as Nek5000 and STAR-CCM+ can help to analyze the DTHT phenomena in reactors for efficient thermal-fluid designs. Three-dimensional (3D) CFD nonisothermal modeling and simulations were performed in a wall-heated circular tube. The simulation results were validated with two different CFD tools, Nek5000 and STAR-CCM+, and validated with an experimental data. The predicted bulk temperatures were identical in both CFD tools, as expected. Good agreement between simulated results and measured data were obtained for wall temperatures along the tube axis using Nek5000. In STAR-CCM+, the under-predicted wall temperatures were mainly due to higher turbulence in the wall region. In STAR-CCM+, the predicted DTHT was over 48% at outlet when compared to inlet heat transfer values.

scholarly journals Modeling and Simulations of Deteriorated Turbulent Heat Transfer in Wall Heated Cylindrical Tube

2019 ◽  
Author(s):  
Prasad Vegendla ◽  
Rui Hu
Keyword(s):  
Heat Transfer ◽  
Nuclear Power ◽  
Cylindrical Tube ◽  
Fluid Flows ◽  
Turbulent Heat Transfer ◽  
Wall Region ◽  
Turbulent Heat ◽  
Modeling And Simulations ◽  
Computational Fluid Dynamics Cfd ◽  
Good Agreement

Abstract The paper discusses the modeling and simulations of Deteriorated Turbulent Heat Transfer (DTHT) for a wall-heated fluid flows, which can be observed in gas-cooled nuclear power reactors during Pressurized Conduction Cooldown (PCC) event due to loss of force circulation flow. The DTHT regime is defined as the deterioration of normal turbulent heat transport due to increase of acceleration and buoyancy forces. The Computational Fluid Dynamics (CFD) tools such as Nek5000 and STAR-CCM+ can help to analyze the DTHT phenomena in reactors for efficient thermal-fluid designs. 3D CFD non-isothermal modeling and simulations were performed in a wall-heated circular tube. The simulation results were verified with two different CFD tools, Nek5000 and STAR-CCM+, and validated with an experimental data. The predicted bulk temperatures were identical in both CFD tools, as expected. Good agreement between simulated results and measured data were obtained for wall temperatures along the tube axis using Nek5000. In STAR-CCM+, the under-predicted wall temperatures were mainly due to higher turbulence in the wall region. In STAR-CCM+, the predicted DTHT was over 48% at outlet when compared to inlet heat transfer values.

Theoretical Model of Wall Heat Transfer in Turbulent Flow

2011 ◽  
Vol 201-203 ◽  
pp. 171-175
Author(s):  
Wei Zheng Zhang ◽  
Xiao Liu ◽  
Chang Hu Xiang
Keyword(s):  
Heat Transfer ◽  
Theoretical Model ◽  
Turbulent Flow ◽  
Local Heat ◽  
Turbulent Heat Transfer ◽  
Wall Region ◽  
Turbulent Heat ◽  
Wall Heat Transfer ◽  
Local Heat Flux ◽  
Turbulent Wall

The turbulent flow in the near-wall region affects the wall heat transfer dominantly. The farther it is from the wall, the less effect it has. So a two-step mechanism of the turbulent wall heat transfer is released: first, the energy is transferred to the outside of the viscous sub-layer by the rolling of the micro-eddy; secondly, the energy gets to the wall by conduction. Then, a theoretical model of wall heat transfer is developed with this concept. The constant in the model is confirmed by experiment and simulation of the transient turbulent heat transfer in pipe flow. Finally, the model is used to predict the local heat flux under different conditions, and the results agree well with the experimental results as well as the simulation results.

Simulation of Circular Tubes Fitted with V Cut and Square Cut Rotors

2013 ◽  
Vol 561 ◽  
pp. 547-552
Author(s):  
Peng Jiang ◽  
Hua Yan ◽  
Zhen Zhang ◽  
Yu Mei Ding ◽  
Wei Min Yang
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Turbulent Heat Transfer ◽  
Cfd Modeling ◽  
Turbulent Heat ◽  
Circular Tubes ◽  
Performance Factor ◽  
Thermal Performance Factor ◽  
Computational Fluid Dynamics Cfd ◽  
Good Agreement

This work presents the effect of V cut and square cut rotors in circular tubes for turbulent heat transfer using computational fluid dynamics (CFD) modeling. The computational results are in good agreement with experimental data. The obtained results reveal that the use of square cut rotors leads to higher Nusselt number than use of V cut rotors. The results also show that the heat transfer rate, friction factor and thermal performance factor of rotors with square cut increase with the increase of width (a) and depth (b) of rotors’ cut. Square cut rotors with a=b=3 yields higher mean thermal performance factor than those with other width and depth, a=b=1, 2 and the highest thermal performance factor of square cut rotors at a=b=1, 2, 3 are found to be 2.08, 2.11 and 2.13.

scholarly journals Numerical Simulation of Turbulent Heat Transfer and Flow in a Rotating Multiple-Pass Square Channel

1997 ◽  
Author(s):  
Jenn-Jiang Hwang ◽  
Wei-Jyh Wang ◽  
Dong-Yuo Lai
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Straight Channel ◽  
Turbulent Fluid Flow ◽  
Square Channel

Three-dimensional turbulent fluid flow and heat transfer characteristics are analyzed numerically for fluids flowing through a rotating periodical two-pass square channel. The two-pass channel is characterized by three parts: (1) a radial-inward straight channel, (2) 180-deg sharp turns, and (3) a radial-outward straight channel. The smooth walls of the two-pass channel are subject to a constant heat flux. A two-equation k-ε turbulence model with modified terms for Coriolis and rotational buoyancy is employed to resolve this elliptic problem. The effects of rotational buoyancy are examined and discussed. It is found that adjacent the 180-deg turn, the rotational buoyancy effect on the local heat transfer is nearly negligible due to the relatively strong entrance effect of 180-deg turns. Downstream the entrance length, the changes in local heat transfer due to the rotational buoyancy in the radially outward flow are more significant than those in the radially inward flow. However, the channel averaged heat transfer is affected slightly by the rotational buoyancy. Whenever the buoyancy effects are sufficiently strong, the flow reversal appears over the leading face of the radial outward flow channel. A comparison of the present numerical results with the available experimental data by taking buoyancy into consideration is also presented.

scholarly journals A study of turbulent heat transfer in convergent-divergent shaped microchannel with ribs and cavities using CFD

2020 ◽  
Vol 14 (1) ◽  
pp. 6344-6361
Author(s):  
Pankaj Srivastava ◽  
Anupam Dewan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Thermal Resistance ◽  
Average Nusselt Number ◽  
Three Dimensional ◽  
Fluid Mixing ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Rectangular Microchannel ◽  
Better Than

This paper presents the effects of microchannel shape with ribs and cavities on turbulent heat transfer. Three-dimensional conjugate heat transfer using the SST k-ω turbulence model has been investigated for four different microchannels, namely, rectangular, rectangular with ribs and cavities, convergent-divergent (CD) and convergent-divergent with Ribs and Cavities (CD-RC). The flow field, pressure and temperature distributions and friction factor are analyzed, and thermal resistance and average Nusselt number are compared. The thermal performance of the CD-RC microchannel is found to be better than that of other microchannels considered in terms of an average Nusselt number increased from 16% to 40%. Heat transfer increases due to a strong fluid mixing and periodic interruption of boundary-layer. It is observed that with an increase in Reynolds number (Re), the thermal resitance drops rapidly. The thermal resistance of the CD-RC microchannel is decreased by 30% than that of the rectangular microchannel for Re ranging from 2500 to 7000. However, such design of microchannel loses its heat transfer effectiveness due to a high pumping power at high values of Re.

scholarly journals Radiation Effects on Turbulent Heat Transfer Characteristics in Vertical Channel

2020 ◽  
Vol 9 (1) ◽  
pp. 2783-2787
Keyword(s):  
Heat Transfer ◽  
Radiation Effects ◽  
Vertical Channel ◽  
Turbulent Heat Transfer ◽  
Discrete Ordinates ◽  
Turbulent Heat ◽  
Governing Equations ◽  
Heat Transfer Characteristics ◽  
Discrete Ordinates Method ◽  
Computational Fluid Dynamics Cfd

In this study we concentrated on the radiative turbulent air to enter into the convective vertical channel. The vertical channel is having two openings at top and the bottom. The radiation is modelled with discrete ordinates method and turbulence is modelled with computational fluid dynamics (CFD) approach using Lambremhorst turbulence model. The governing equations are solved and discretized by using Finite Difference Method (FDM). The parametric study is performed on Assisting and opposing cases by comparing both the cases with the radiation and without radiation in the channel and found that temperature and velocity characteristics have much impact when the channel is involved with radiation

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