Effect of droplet characteristics and rotation speed on the flow and heat transfer characteristics of mist/air cooling in a rotating ribbed two-pass rectangular channel

2016 ◽  
Vol 231 (2) ◽  
pp. 119-132 ◽  
Author(s):  
Xinjun Wang ◽  
Feng Zhang ◽  
Daren Zheng ◽  
Jun Li
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Performance ◽  
Rotation Speed ◽  
Rectangular Channel ◽  
Air Cooling ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

The flow and heat transfer characteristics of mist/air cooling in the rotating ribbed two-pass rectangular channel are numerically investigated using the CFD software ANSYS-CFX. In this article, a comparison in heat transfer performance between the mist/air cooling and the air-only cooling is performed. Additionally, the effect of the initial mist diameter, temperature, velocity and the channel rotation speed on the mist/air cooling performance is analysed. The results show that the droplet flow distance and Nusselt number of the mist/air cooling increase as the initial mist temperature decreases. In addition, as the initial mist diameter decreases, the diameter of mist on the whole channel decreases, resulting in the higher heat transfer, whilst the mist concentration also decreases, leading to the lower heat transfer. Therefore, there is an optimal initial mist diameter which makes the heat transfer performance best. Nevertheless, the droplet movement and heat transfer performance of mist/air cooling are nearly insensitive to the initial mist velocity. It is also noted that the Coriolis force increases with the channel rotation speed, causing the flow deflection becomes more obvious. Consequently, as the channel rotation speed increases, in the first passage the averaged Nusselt number on the trailing wall increases, and that on the leading wall decreases, while the trend in the second passage is reversed.

scholarly journals Numerical study on the flow and heat transfer of water-based Al2O3 forced pulsating nanofluids based on self-excited oscillation chamber structure

2021 ◽  
pp. 167-167
Author(s):  
Hong Yuan ◽  
Zhao Wang ◽  
Quan Gao ◽  
Ting Fu
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Performance Index ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Excited Oscillation

In this study, the flow and heat transfer characteristics of the forced pulsating Al2O3/water nanofluid were numerically studied. The pulsating excitation of the nanofluid is provided by the Helmhertz self-excited oscillating cavity. The large eddy simulation method is used to solve the equation, and the local Nusselt number and heat transfer performance index are used to analyze the heat transfer characteristics of the nanofluid in the self-excited oscillation heat exchange tube. In addition, the effect of different downstream tube diameters on heat transfer enhancement is discussed. The research results show that the existence of the countercurrent vortex can increase the disturbance of the near-wall fluid, thereby improving the mixing degree of the near-wall fluid and the central mainstream. As the countercurrent vortex migrates downstream, pulse enhanced heat transfer is realized. Furthermore, it was also found that when the downstream tube diameter d2=1.8d1, the periodic effect of the local Nusselt number of the wall is the best and the heat transfer performance index has the most stable pulsation effect within a pulsation cycle. But when d2=2.0d1, the change curve of heat transfer performance index in a pulsating period is the highest, the maximum value is 3.95.

scholarly journals Numerical Simulation of Flow and Heat Transfer in Structured Packed Beds with Smooth or Dimpled Spheres at Low Channel to Particle Diameter Ratio

Energies ◽  
2018 ◽  
Vol 11 (4) ◽  
pp. 937 ◽  
Author(s):  
Shiyang Li ◽  
Lang Zhou ◽  
Jian Yang ◽  
Qiuwang Wang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Heat Transfer Performance ◽  
Particle Diameter ◽  
Packed Bed ◽  
Packed Beds ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer

Packed beds are widely used in catalytic reactors or nuclear reactors. Reducing the pressure drop and improving the heat transfer performance of a packed bed is a common research aim. The dimpled structure has a complex influence on the flow and heat transfer characteristics. In the present study, the flow and heat transfer characteristics in structured packed beds with smooth or dimpled spheres are numerically investigated, where two different low channel to particle diameter ratios (N = 1.00 and N = 1.15) are considered. The pressure drop and the Nusselt number are obtained. The results show that, for N = 1.00, compared with the structured packed bed with smooth spheres, the structured packed bed with dimpled spheres has a lower pressure drop and little higher Nusselt number at 1500 < ReH < 14,000, exhibiting an improved overall heat transfer performance. However, for N = 1.15, the structured packed bed with dimpled spheres shows a much higher pressure drop, which dominantly affects the overall heat transfer performance, causing it to be weaker. Comparing the different channel to particle diameter ratios, we find that different configurations can result in: (i) completely different drag reduction effect; and (ii) relatively less influence on heat transfer enhancement.

Influence of Different Rib Height on Heat Transfer Augmentation in Rectangular Convergent / Divergent Channels With Continuous Ribs on Bottom Surface

2013 ◽  
Author(s):  
K. Sivakumar ◽  
E. Natarajan ◽  
N. Kulasekharan
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Heat Transfer Performance ◽  
Rectangular Channel ◽  
Bottom Surface ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Smooth Channel ◽  
Mean Diameter

The work reported in this paper is a systematic experimental study of friction and heat transfer characteristics of divergent /convergent rectangular ducts with an inclination angle of 1° in the y-direction. Measurements were taken for a convergent / divergent rectangular channel of aspect ratio, AR = 1.25 to 1.35 with three uniform rib heights, e = 3, 6 and 9 mm the ratio between rib height (e) to hydraulic mean diameter (Dm) are 0.0348, 0.0697 and 0.1046, a constant rib pitch distance, P = 60 mm. The flow rate in terms of average Reynolds numbers based on the hydraulic mean diameter (Dm) of the channel was in a range of 20000 to 50,000 is 0.085 m. A ceramic strip of 10 mm thickness is used as a heating coil has been attached on top and bottom surfaces for the test sections. The heat transfer characteristics degraded with increase in the rib height in 90° attached ribs over smooth channel. The heat transfer performance of the divergent/convergent ducts for 3, 6 and 9 mm ribs was conducted under identical mass flow rate based on the Reynolds number. In convergent duct having three test sections each having three different size ribs 3, 6, and 9mm. Similarly, divergent section is also three different rib heights duct. So, in our experiments has totally 6 different ducts were used. In addition, the acceleration / deceleration caused by the cross section area, the divergent duct generally shows enhanced heat transfer behavior for three different rib sizes, while the convergent duct has an appreciable reduction in heat transfer performance.

Research on External Flow and Heat Transfer Characteristics of H-Type Fin Tube Based on Longitudinal Vortex

2014 ◽  
Vol 614 ◽  
pp. 133-137 ◽  
Author(s):  
Bo Jiang ◽  
Wei Dong Hao ◽  
Zhi Hong Hu ◽  
Fu Guo Liu
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Heat Transfer Performance ◽  
External Flow ◽  
Longitudinal Vortex ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Fin Tube

An H-type fin tube based on longitudinal vortex for boiler economizer is put forward in this paper, in order to solve the problem of too high temperature for denitration catalyst reaction for flue gas leaving the econonmizer. CFD method is adopted to study the external flow and heat transfer characteristics of the H-type fin tube based on longitudinal vortex, obtaining the flow field and temperature field distribution in the near wall region outside the fin tube. The results show that vortex flow in different degrees occurs in the rear flow field of the H-type fin tube based on longitudinal vortex, which introduces velocity component normal to main stream direction to the fluid of main flow zone, improves the synergy of temperature gradient field with velocity field and significantly enhances heat transfer performance of the fin tube. Within the parameter range studied in this paper, the 30° attack angle makes the best PEC value and correspondingly best comprehensive heat transfer performance.

scholarly journals On Heat Transfer Performance of Cooling Systems Using Nanofluid for Electric Motor Applications

Entropy ◽  
2020 ◽  
Vol 22 (1) ◽  
pp. 99 ◽  
Author(s):  
Ali Deriszadeh ◽  
Filippo de Monte
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Base Fluid ◽  
Heat Transfer Performance ◽  
Volume Fraction ◽  
Cooling System ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

This paper studies the fluid flow and heat transfer characteristics of nanofluids as advance coolants for the cooling system of electric motors. Investigations are carried out using numerical analysis for a cooling system with spiral channels. To solve the governing equations, computational fluid dynamics and 3D fluid motion analysis are used. The base fluid is water with a laminar flow. The fluid Reynolds number and turn-number of spiral channels are evaluation parameters. The effect of nanoparticles volume fraction in the base fluid on the heat transfer performance of the cooling system is studied. Increasing the volume fraction of nanoparticles leads to improving the heat transfer performance of the cooling system. On the other hand, a high-volume fraction of the nanofluid increases the pressure drop of the coolant fluid and increases the required pumping power. This paper aims at finding a trade-off between effective parameters by studying both fluid flow and heat transfer characteristics of the nanofluid.

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.

Numerical Investigation of Impingement Heat Transfer on Concave- and Convex-Dimpled Plate With Different Dimple Arrangements

2016 ◽  
Author(s):  
Feng Zhang ◽  
Xinjun Wang ◽  
Jun Li ◽  
Rui Tan ◽  
Dongliang Wei
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Pressure Loss ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Impingement Cooling ◽  
Transfer Characteristics

The present numerical study is conducted to investigate the flow and heat transfer characteristics for impingement cooling on concave or convex dimpled plate with four different dimple arrangements. The investigation of the impingement cooling on the flat plate is also conducted to serve as a contrast and these results are compared with experimental measurements to verify the computational method. Dimples studied here are placed, relative to impingement holes, in either spanwise shifted, in staggered, in in-line, or in streamwise shifted arrangements. The flow structure, pressure loss and heat transfer characteristics of the concave and convex dimpled plate of four different dimple arrangements have been obtained and compared with flat plate for the Reynolds number range of 15000 to 35000. The results show that compared with flat plate, the added concave or convex dimples only causes a negligible increase in the pressure loss, and the pressure loss is insensitive to concave or convex dimple arrangement patterns. In addition, compared with flat plate, both spanwise shifted and staggered concave dimple arrangements show better heat transfer performance, while in-line concave dimple arrangement show worse results. Besides that, the heat transfer performance for streamwise shifted concave dimple arrangement is the worst. Furthermore, compared with flat plate, all convex dimple arrangements studied here show better heat transfer performance.

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