Investigation of Heat Transfer Characteristics in a Rotating Convection System With Bi-Directional Thermal Gradients

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Ayan Kumar Banerjee ◽  
Amitabh Bhattacharya ◽  
Sridhar Balasubramanian
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Thermal Gradient ◽  
Outer Edge ◽  
Thermal Gradients ◽  
Heat Transfer Characteristics ◽  
Rotating Convection ◽  
Transfer Characteristics ◽  
Cylindrical Annulus ◽  
Inner Surface

Abstract A series of rotating convection experiments have been conducted in a novel configuration, which comprises a cylindrical annulus with spot heating on the bottom outer edge and uniform cooling on the inner surface. Such a system provides bi-directional thermal gradients in both radial and vertical directions, thereby reenacting the thermal gradient patterns encountered in the atmosphere. Bulk heat transfer characteristics are studied by quantifying the overall Nusselt number, Nu, for a range of Taylor number, Ta, heating rate, Q, and Rayleigh number, Ra. Temperature measurements are carried out at different locations with the help of thermocouples. The Nusselt number is found to be quite sensitive to the buoyancy and relatively insensitive to the rotation rate. The correlation for Nu as a function of Ra revealed different power law exponents for low and high Ta values. The varying exponent is attributed to the presence of baroclinic eddies at high Ta, which in turn is verified with the help of flow visualization. The heat transfer characteristics in this new configuration are significantly different compared to other conventional rotational convection systems, where thermal gradients are present in only one direction.

scholarly journals Uncertainties Analysis on the Prediction of Flow and Heat Transfer of Liquid Sodium with CFD Technology

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Zhanwei Liu ◽  
Xinyu Li ◽  
Tenglong Cong ◽  
Rui Zhang ◽  
Lingyun Zheng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Coefficient ◽  
Liquid Sodium ◽  
Heat Transfer Characteristics ◽  
Backward Facing Step ◽  
Heating Wall ◽  
Transfer Characteristics ◽  
Cfd Models ◽  
Flow And Heat Transfer

The prediction of flow and heat transfer characteristics of liquid sodium with CFD technology is of significant importance for the design and safety analysis of sodium-cooled fast reactor. The accuracies and uncertainties of the CFD models should be evaluated to improve the confidence of the numerical results. In this work, the uncertainties from the turbulent model, boundary conditions, and physical properties for the flow and heat transfer of liquid sodium were evaluated against the experimental data. The results of uncertainty quantization show that the maximum uncertainties of the Nusselt number and friction coefficient occurred in the transition zone from the inlet to the fully developed region in the circular tube, while they occurred near the reattachment point in the backward-facing step. Furthermore, in backward-facing step flow, the maximum uncertainty of temperature migrated from the heating wall to the geometric center of the channel, while the maximum uncertainty of velocity occurred near the vortex zone. The results of sensitivity analysis illustrate that the Nusselt number was negatively correlated with the thermal conductivity and turbulent Prandtl number, while the friction coefficient was positively correlated with the density and Von Karman constant. This work can be a reference to evaluate the accuracy of the standard k-ε model in predicting the flow and heat transfer characteristics of liquid sodium.

Heat transfer characteristics of nanofluids from a sinusoidal corrugated cylinder placed in a square cavity

2021 ◽  
pp. 095440622110272
Author(s):  
Salaika Parvin ◽  
Nepal Chandra Roy ◽  
Litan Kumar Saha ◽  
Sadia Siddiqa
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Average Nusselt Number ◽  
Numerical Study ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Transfer Characteristics ◽  
Wide Range

A numerical study is performed to investigate nanofluids' flow field and heat transfer characteristics between the domain bounded by a square and a wavy cylinder. The left and right walls of the cavity are at constant low temperature while its other adjacent walls are insulated. The convective phenomena take place due to the higher temperature of the inner corrugated surface. Super elliptic functions are used to transform the governing equations of the classical rectangular enclosure into a system of equations valid for concentric cylinders. The resulting equations are solved iteratively with the implicit finite difference method. Parametric results are presented in terms of streamlines, isotherms, local and average Nusselt numbers for a wide range of scaled parameters such as nanoparticles concentration, Rayleigh number, and aspect ratio. Several correlations have been deduced at the inner and outer surface of the cylinders for the average Nusselt number, which gives a good agreement when compared against the numerical results. The strength of the streamlines increases significantly due to an increase in the aspect ratio of the inner cylinder and the Rayleigh number. As the concentration of nanoparticles increases, the average Nusselt number at the internal and external cylinders becomes stronger. In addition, the average Nusselt number for the entire Rayleigh number range gets enhanced when plotted against the volume fraction of the nanofluid.

Heat Transfer Characteristics of the Phase Change Material Microcapsule Slurry in Solid Phase State

2011 ◽  
Vol 71-78 ◽  
pp. 1187-1190
Author(s):  
Yan Lai Zhang ◽  
Zhong Hao Rao ◽  
Shuang Feng Wang ◽  
Hong Zhang ◽  
Li Jun Li ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Phase State ◽  
Solid Phase ◽  
Heat Transfer Characteristics ◽  
Rectangular Enclosure ◽  
Transfer Characteristics ◽  
Change Material

This experiment is performed to investigate heat transfer characteristics with the PCM microcapsule slurry in a solid phase state at a horizontal rectangular enclosure heating from below and cooling from top. Some important parameters are taken into account such as the mass concentration of the PCM, the temperature difference between heating plate and cooling plate, Nusselt number Nu, Rayleigh number Ra and the aspect ratio (width/height) of the horizontal rectangular enclosure. Experiment is done under the thermal steady condition in the PCM microcapsule slurry. Heat transfer coefficient is measured under various temperature differences in PCM mass concentrations of 10% and 20%. And relationship with Nusselt number Nu and Rayleigh number Ra is summarized to various heights H or the aspect ratio (width/height) Ar of enclosure.

scholarly journals Effect of Prandtl number on heat transfer characteristics in an axisymmetric sudden expansion: A numerical study

2007 ◽  
Vol 11 (4) ◽  
pp. 171-178
Author(s):  
Khalid Alammar
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Prandtl Number ◽  
Turbulent Flow ◽  
Turbulence Model ◽  
Numerical Study ◽  
Sudden Expansion ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Simulated Effect

Using the standard k-e turbulence model, an incompressible, axisymmetric turbulent flow with a sudden expansion was simulated. Effect of Prandtl number on heat transfer characteristics downstream of the expansion was investigated. The simulation revealed circulation downstream of the expansion. A secondary circulation (corner eddy) was also predicted. Reattachment was predicted at approximately 10 step heights. Corresponding to Prandtl number of 7.0, a peak Nusselt number 13 times the fully-developed value was predicted. The ratio of peak to fully-developed Nusselt number was shown to decrease with decreasing Prandtl number. Location of maximum Nusselt number was insensitive to Prandtl number.

Boiling heat transfer characteristics of binary magnetic fluid flow in a vertical circular pipe with a partly heated region

2004 ◽  
Vol 218 (2) ◽  
pp. 223-232 ◽  
Author(s):  
S Shuchi ◽  
K Sakatani ◽  
H Yamaguchi
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Boiling Heat Transfer ◽  
Transfer Rate ◽  
Heated Region ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
The Magnetic Field

An investigation was conducted for heat transfer characteristics of binary magnetic fluid flow in a partly heated circular pipe experimentally. The boiling heat transfer characteristics on the effects of the relative position of the magnetic field to the heated region were particularly considered in the present study. From the experimental verification, the Nusselt number, representing boiling heat transfer characteristics, was obtained for various flow and magnetic conditions which were represented by the non-dimensional parameters of the Reynolds number and the magnetic pressure number. Additionally, the rate of change of the Nusselt number found by applying the magnetic field was also estimated and the optimal position of the field to the partly heated region was discussed. The results indicated that the effect of the magnetic field to the heat transfer rate from the heated wall was mainly subjected to the effect of the vortices induced in the magnetic field region and the possibility of controlling the heat transfer rate by applying an outer magnetic field to utilize the effect.

Forced Convective Flow of Bingham Plastic Fluids in a Branching Channel With the Effect of T-Channel Branching Angle

2021 ◽  
Vol 143 (5) ◽  
Author(s):  
Anamika Maurya ◽  
Naveen Tiwari ◽  
R. P. Chhabra
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Length Variation ◽  
Heat Transfer Characteristics ◽  
Local Pressure ◽  
Bingham Plastic ◽  
Transfer Characteristics ◽  
Wide Range ◽  
Branching Angle ◽  
Plastic Fluids

Abstract This work aims to explore the T-channel momentum and heat transfer characteristics with the combined effect of Bingham plastic fluids (0.01 ≤ Bn ≤ 20) behavior and geometrical variation in terms of branching angle (30 deg ≤ α ≤ 90 deg). The problem has been solved over a wide range of Reynolds number (50 ≤ Re ≤ 300) and Prandtl number (10 ≤ Pr ≤ 50). For the momentum flow, qualitative and quantitative features are analyzed in terms of streamlines, structure of yielded/unyielded regions, shear rate contours, plug width and length variation, and local pressure coefficient. These features have been represented in terms of isotherm patterns, temperature profile, Nusselt number, and its asymptotic value for heat transfer characteristics. The recirculating flows have been presented here in the vicinity of T-junction, which promote mixing and heat transfer. Broadly, the size of this zone bears a positive dependence on Re and α. However, fluid yield stress tends to suppress it. The critical Reynolds and Bingham numbers were found to be strong functions of the pertinent parameters like α. The inclination angle exerts only a weak effect on the yielded/unyielded regions and on the recirculation length of main branch. Results show a strong relationship of the plug width and length with key parameters and branches. The Nusselt number exhibits a positive relationship with α, Bn, and Re but for lower Pr in the T-junction vicinity for both branches. Such length indicates the required optimum channel length for thermal mixing.

Heat Transfer and Flow Structure in a Latticework Duct With Different Sidewalls

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Wei Du ◽  
Lei Luo ◽  
Songtao Wang ◽  
Jian Liu ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Flow Structure ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Pressure Side ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Abstract Heat transfer characteristics in a latticework duct with various sidewalls are numerically investigated. The crossing angle is 90 deg and the number of subchannels is eleven on both the pressure side and suction side for each latticework duct. The thickness of the ribs is 8 mm and the distance between adjacent ribs is 24 mm. The investigation is conducted for various Reynolds numbers (11,000 to 55,000) and six different sidewalls. Flow structure, pressure drop, and heat transfer characteristics are analyzed. Results revealed that the sidewall has significant effects on heat transfer and flow structure. The triangle-shaped sidewall provides the highest Nusselt number accompanied by the highest friction factor. The sidewall with a slot shows the lowest friction factor and Nusselt number. An increased slot width decreased the Nusselt number and friction factor simultaneously.

Numerical Study of Flow and Heat Transfer Characteristics of Impinging Jets

2010 ◽  
Author(s):  
Tarek M. Abdel-Salam
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Numerical Study ◽  
Three Dimensional ◽  
Impinging Jets ◽  
Two Dimensional ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

This study presents results for flow and heat transfer characteristics of two-dimensional rectangular impinging jets and three-dimensional circular impinging jets. Flow geometries under consideration are single and multiple impinging jets issued from a plane wall. Both confined and unconfined configurations are simulated. Effects of Reynolds number and the distance between the jets are investigated. Results are obtained with a finite volume computational fluid dynamics (CFD) code. Structured grids are used in all cases of the present study. Turbulence is treated with a two equation k-ε model. Different jet velocities have been examined corresponding to Reynolds numbers of 5,000 to 20,000. Results of the three-dimensional cases show that Reynolds number has no effect on the velocity distribution of the center jet. Results of both two-dimensional and three-dimensional cases show that Reynolds number highly affects the heat transfer and values of the Nusselt number. The maximum Nusselt number was always found at the stagnation point of the center jet.

Study of Heat Transfer Characteristics of a Single Jet Impinging on a Conical Surface

2020 ◽  
Author(s):  
Bo Su ◽  
Wei-jiang Xu ◽  
Zhi-ping Li ◽  
Tian-liang Zhou ◽  
Fei Lu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Stagnation Point ◽  
Target Surface ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Maximum Value ◽  
Conical Target ◽  
Single Jet

Abstract In this paper, the heat transfer performance of single jet impinging conical surface is investigated based on transient liquid crystal experiments. Because of different target surface structures, impingement heat transfer will have different heat transfer characteristics. In order to better understand the heat transfer mechanism of the impinging conical target surface, this paper studies the three jet Reynolds number (Re) ranged from 25000 to 70000, three the dimensionless nozzle-to-surface distance (H/D) from 0.75 to 6 on heat transfer characteristics. The liquid crystal thermal imaging technology is used in the experiment to obtain the heat transfer efficiency of jet heat transfer on the conical target surface. The research in this paper shows that the larger the jet Reynolds number, the larger the Nusselt number at the stagnation point. It is worth noting that the maximum Nusselt number is not necessarily obtained at the stagnation point. When Re = 70000 and H/D = 0.75, the maximum value of the Nusselt number is 1.24 times the stagnation point. The larger the Reynolds number, the smaller the impingement distance, and the more obvious the secondary maxima. At the same impingement distance, when the Reynolds number is larger, the position of the secondary maxima appears earlier. When Re = 25000, H/D = 3.5, 6 and Re = 45000, H/D = 6, the local Nusselt number monotonously decreases from the maximum value at the stagnation point along the flow, and it appears secondary maxima in other experimental conditions. Within the scope of this study, the overall heat transfer performance is better when the dimensionless distance between the jet hole and the target surface is 3.5.

Experimental Investigation on Heat Transfer and Friction Factor in Open Matrix Sub-Channels

2021 ◽  
Author(s):  
Anjana Narottambhai Prajapati ◽  
Andallib Tariq
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Nusselt Number ◽  
Friction Factor ◽  
Elevated Temperatures ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Aspect Ratios ◽  
Factor Ratio ◽  
The Matrix

Abstract Matrix cooling has opened new possibilities for enhancing the convective heat transfer coefficients without compromising upon the structural rigidity and the life of the gas turbine blade at elevated temperatures. However, the dense structure of the matrix significantly increases the flow resistance, and imposes the limitation to its usage. Recently, a matrix with a gap on the sidewalls called open matrix has been proposed by few researchers to reduce the associated pressure penalties. This detailed experimental investigation aims to study the open matrix channel flow, and presents the effects of varying sidewall gaps on heat transfer characteristics and friction factor in the open matrixes having rib angle 45o for three different sub-channel aspect ratios 1.2, 0.8, and 0.4. Liquid crystal thermography has been utilized to discern the detailed heat transfer characteristics. Results have been evaluated in terms of augmentation Nusselt number, friction factor ratio, and overall thermal performance factor over the Reynolds numbers 5800 -14000. The closed matrixes provided the highest augmentation in Nusselt number, and the gaps on the sidewall have shown an overall reduction in augmentation Nusselt number in most cases. However, the suitable sidewall gap showed the effective reduction in pressure penalties for the smaller sub-channel aspect ratios. The highest augmentation Nusselt number amongst the open matrixes has been found as 3.83 with a reduced friction factor ratio for the matrix with a 4 mm gap in sub-channel aspect ratio = 0.8 (i.e. 4 sub-channels) at Re = 8100.

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