Flow Behavior and Heat Transfer Characteristics Between Outer and Slotted Inner Cylinders

2021 ◽  
Author(s):  
Tomohisa Yuasa ◽  
Akiko Kaneko ◽  
Yutaka Abe
Keyword(s):  
Heat Transfer ◽  
Flow Behavior ◽  
Side Wall ◽  
Separated Flow ◽  
Back Side ◽  
Front Side ◽  
Heat Transfer Characteristics ◽  
Coaxial Cylinders ◽  
Transfer Characteristics ◽  
Nusselt Numbers

Abstract The performance of air-cooled generators can be improved only if they have efficient system designs for heat removal. An air-cooled generator is composed of a pair of coaxial cylinders, namely, a fixed outer cylinder (stator) and a rotating inner cylinder (rotor); the rotor has axial slits. In this study, we experimentally and numerically clarified the flow behavior and the heat transfer characteristics of rotating coaxial cylinders by simulating a salient-pole rotor in an air-cooled generator. The flow behavior in the slit between the salient poles was observed by using a high-speed video camera. We measured the temperature on the slit walls to investigate the heat transfer. The velocity fields and the heat transfer coefficient between the rotor and the stator were obtained via a numerical simulation. From the results, we experimentally and numerically observed the vortex structure in the slit. The local Nusselt numbers on the front-side wall of the slits near the impinging flow were higher than those on the back-side wall near the separated flow. The local Nusselt numbers on the front-side wall were high because the gap flow between the cylinders impinged on the front-side wall and promoted heat transfer. By contrast, the local Nusselt numbers on the back-side wall were low because a separated flow appeared near the back-side wall, where the hot fluid was retained, thereby causing the separated flow to disturb the heat transfer on the back-side wall.

Effect of Participating Medium Radiation and Nano-Fluidic Behaviour of Atmospheric Aerosol on Natural Convection of Industrial Dusty Air

2013 ◽  
Author(s):  
Sofen K. Jena ◽  
Swarup K. Mahapatra
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Behavior ◽  
Carbon Black Particle ◽  
Laboratory Model ◽  
Heat Transfer Characteristics ◽  
Participating Media ◽  
Transfer Characteristics ◽  
Flow Circulation ◽  
Marker And Cell Method

The current study is focused on thermal radiation interaction with the natural convection of atmospheric brown cloud (ABC). The current study puts emphasis on ultra fine carbon-black particle suspension of several nano meter range along with some pollutant gas mixture with atmospheric air. The numerical simulation of double diffusive thermo-gravitational convection of ABC is done with Hide and Mason laboratory model for atmosphere. The effect of flow circulation is simulated by setting different value of buoyancy ratios. The effect of participating media radiation has been investigated for various values of optical depth. The governing equations, describing circulation of ABC are solved using modified Marker and Cell method. Gradient dependent consistent hybrid upwind scheme of second order is used for discretization of the convective terms. Discrete ordinate method, with S8 approximation is used to solve radiative transport equation. Comprehensive studies on controlling parameters that affect the flow and heat transfer characteristics have been addressed. The results are provided in graphical and tabular form to delineate the flow behavior and heat transfer characteristics.

Comparison of Heat Transfer Characteristics of Radial Jet Reattachment Nozzle to In-Line Impinging Jet Nozzle

1998 ◽  
Vol 120 (2) ◽  
pp. 335-341 ◽  
Author(s):  
J. Seyed-Yagoobi ◽  
V. Narayanan ◽  
R. H. Page
Keyword(s):  
Heat Transfer ◽  
Peak Pressure ◽  
Exit Angle ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Nusselt Numbers ◽  
Zero Degree ◽  
Jet Nozzle ◽  
Flow Power ◽  
Impingement Surface

The heat transfer characteristics of three submerged radial jet reattachment (RJR) nozzles with exit angles of +45, 0, and −10 deg are compared to the heat transfer characteristics of a conventional submerged in-line jet (ILJ) nozzle. The nozzles are compared at their favorable spacing from the impingement surface. The comparisons are based on two criteria: (1) identical fluid flow power, and (2) identical peak pressure exerted on the impingement surface. The local and area-averaged Nusselt numbers are presented. Experiments were conducted for two different flow power conditions. Comparison under identical flow power indicates that significant enhancements in local and comparable enhancements in area-averaged Nusselt numbers can be achieved with the RJR nozzles over the conventional ILJ nozzle while being able to control the net force exerted on the impingement surface. The comparison between the ILJ and RJR nozzles on the basis of the same peak pressure exerted on the impingement surface indicates that the zero degree exit angle RJR nozzle heat transfer characteristics are superior to the ILJ nozzle.

Experimental Investigation of the Air Flow Behavior and Heat Transfer Characteristics in Microchannels With Different Channel Lengths

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Zhi Tao ◽  
Zhibing Zhu ◽  
Haiwang Li
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Friction Factor ◽  
Critical Reynolds Number ◽  
Flow Behavior ◽  
Channel Length ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Poiseuille Number ◽  
Channel Lengths

This paper attempts to experimentally investigate the influence of channel length on the flow behavior and heat transfer characteristics in circular microchannels. The diameters of the channels were 0.4 mm and the length of them were 5 mm, 10 mm, 15 mm, and 20 mm, respectively. All experiments were performed with air and completed with Reynolds number in the range of 300–2700. Results of the experiments show that the length of microchannels has remarkable effects on the performance of flow behavior and heat transfer characteristics. Both the friction factor and Poiseuille number drop with the increase of channel length, and the experimental values are higher than the theoretical ones. Moreover, the channel length does not influence the value of critical Reynolds number. Nusselt number decrease as the increase of channel length. Larger Nusselt numbers are obtained in shorter channels. The results also indicate that in all cases, the friction factor decreases and the Poiseuille number increases with the increase of the Reynolds number. It is also observed that the value of critical Reynolds number is between 1500 and 1700 in this paper, which is lower than the value of theoretical critical Reynolds number of 2300.

Assessment of the Thermal Performance of Alternate Firing Schemes in Oxygen-Fired Glass Melting Furnaces

2003 ◽  
Author(s):  
Kris L. Jorgensen ◽  
Satish Ramadhyani ◽  
Raymond Viskanta
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Computer Model ◽  
Thermal Performance ◽  
Glass Melting ◽  
Side Wall ◽  
Shear Stresses ◽  
Heat Transfer Characteristics ◽  
Unstable Flow ◽  
Transfer Characteristics

Three firing schemes for an industrial oxygen-fired glass melting furnace were examined to determine the thermal performance and relative merits of each scheme. A comprehensive computer model was used to investigate the effects of each scheme on the combustion and heat transfer in the furnace. The three-dimensional computer model, suitable for predicting and analyzing fluid flow, combustion and heat transfer has been used to simulate the combustion space of the furnace. The turbulent flow field is obtained by solving the Favre averaged Navier-Stokes equations and using the k-ε model to calculate the turbulent shear stresses and close the equation set. The combustion model consists of a single step, irreversible, infinitely fast reaction. A mixture fraction is used to track the mixing of fuel and oxidant and thus reaction progress in this mixing limited model. An assumed shape PDF method is utilized to account for turbulent fluctuations. Radiative heat transfer in the combustion gases and between surfaces is modeled using the discrete ordinates method coupled with the weighted-sum-of-gray-gases model. The model furnace for all three firing schemes was the same size and shape, was charged from the rear end wall and was pulled from the front wall. The three schemes investigated were: 1) non-interlaced side-wall fired, 2) interlaced side-wall fired, and 3) end fired. The results show that all three arrangements provide similar thermal performance and heat transfer characteristics. However, the flow field for the non-interlaced arrangement is very complex in the region where jets from opposing walls meet at the furnace center line. This type of jet interference can lead to unstable flow, particularly at the centerline of the furnace. Unstable flow conditions can affect the heat transfer characteristics of the furnace and make the furnace difficult to operate. Conversely, the interlaced and end-fired schemes do not exhibit the jet interference seen in the non-interlaced arrangement. While the results indicate that the thermal performance of all three arrangements were similar, the possibility of jet interference suggests that an interlaced or end-fired arrangement is preferable.

Flow and Heat Transfer Enhancement Characteristics of Impinging Jets in Transitional Time Periodic Flow Regimes

2010 ◽  
Author(s):  
Julian P. Gutierrez ◽  
Alfonso Ortega ◽  
Amador M. Guzman
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Temporal Evolution ◽  
Flow Regimes ◽  
Periodic Flow ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Time Average

The flow and heat transfer characteristics of an impinging jet on a perpendicular flat surface are obtained by two dimensional numerical simulations of laminar and transitional flow regimes for the Reynolds number of Re = 300, 350, and 400 for a Prandtl number of Pr = 0.7. A fixed jet to plate spacing of H/W = 5 and a given heat flux on the plate surface are considered. Temporal evolution of velocity and temperature fields, Fourier spectra of the velocity temporal evolution and time average local and global Nusselt numbers are obtained for increasing Reynolds numbers for determining the time depending behavior and its effect on the heat transfer characteristics. Numerical simulation results demonstrate that self-sustained transitional periodic flow regimes arise from a laminar regime, when the Reynolds number is further increased to Re = 400 and that these regimes spread out to the whole domain with similar time dependent characteristics due to the flow incompressibility. Evaluations of time average local and global Nusselt numbers demonstrate the asymmetric Gaussian-type spatial distribution and the increase of both parameters when the flow evolves through the transitional periodic regime, with reasonable increases on the pumping power requirements.

scholarly journals Numerical study on heat transfer characteristics of nanofluid based natural circulation loop

2018 ◽  
Vol 22 (2) ◽  
pp. 885-897 ◽  
Author(s):  
Ramesh Bejjam ◽  
Kiran Kumar
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Natural Circulation ◽  
Flow Behavior ◽  
Circulation Loop ◽  
Heat Transfer Characteristics ◽  
Step Size ◽  
Particle Volume ◽  
Transfer Characteristics ◽  
Natural Circulation Loop

In this paper the steady-state analysis has been carried out on single phase natural circulation loop with water and water based Al2O3 (Al2O3-water) nanofluid at 1%, 3%, 5%, and 6% particle volume concentrations. For this study, a 3-D geometry of natural circulation loop is developed and simulated by using the software, ANSYS (FLUENT) 14.5. Based on the Stokes number, mixture model is adopted to simulate the nanofluid based natural circulation loop. For the simulations, the imposed thermal boundary conditions are: constant heat input over the range of 200-1000 W with step size of 200 W at the heat source and isothermal wall temperature of 293 K at the heat sink. Adiabatic boundary condition is imposed to the riser and down-comer. The heat transfer characteristics and fluid-flow behavior of the loop fluid in natural circulation loop for different heat inputs and particle concentrations are presented. The result shows that the mass-flow rate of loop fluid in natural circulation loop is enhanced by 26% and effectiveness of the natural circulation loop is improved by 15% with Al2O3-water nanofluid when compared with water. All the simulation results are validated with the open literature in terms of Reynolds number and modified Grashof number. These comparisons confidently say that the present 3-D numerical model could be useful to estimate the performance of natural circulation loop.

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