scholarly journals Transient cooling of two circular cylinders arranged in Tandem an bounded by an adiabatic wall

2021 ◽  
Vol 15 (4) ◽  
pp. 8580-8591
Author(s):  
Nawaf Hazim Saeid ◽  
N. Hasan ◽  
Seri Rahayu Ya'akob ◽  
S. Shuib
Keyword(s):  
Reynolds Number ◽  
Heat Dissipation ◽  
Cross Flow ◽  
Thermal Inertia ◽  
Separation Distance ◽  
Carbon Steels ◽  
Cooling Time ◽  
Circular Cylinders ◽  
Adiabatic Wall ◽  
The Difference

Parametric study is carried out on the transient cooling process of two circular cylinders in tandem arrangement for a specified period of time. Transient analysis of conjugate (conduction and convection) heat dissipation from two identical cylinders is considered with various parameters. The two cylinders of same size and properties are bounded by an adiabatic flat wall from below and the cooling air is flowing normal to their axis (cross flow). The following parameters are investigated in the present study: Reynolds number, cylinders thermal properties, separation distance between the two cylinders and the cooling time. The laminar flow is considered with Reynolds number values from 50 to 500. The simulations are carried out for cooling the two cylinders made of carbon steels, plastics plexiglass and plywood. The local and average Nusselt number for both steady and transient cooling of the two cylinders are presented. The effects of the parameters are investigated and the results are presented to understand the process. It is found that increasing either the separation distance and/or the Reynolds number will increase the heat dissipation and reduce the cooling time. The results show that carbon steels cylinders need longer time of cooling compare with the plywood cylinders due to the difference in their thermal inertia.

scholarly journals Energy and Exergy Analyses of Tube Banks in Waste Heat Recovery Applications

Energies ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 2094 ◽  
Author(s):  
Mustafa Erguvan ◽  
David MacPhee
Keyword(s):  
Energy Efficiency ◽  
Reynolds Number ◽  
Heat Recovery ◽  
Waste Heat ◽  
Cross Flow ◽  
Exergy Efficiency ◽  
Circular Cylinders ◽  
Published Data ◽  
Energy And Exergy ◽  
Exergy Analyses

In this study, energy and exergy analyses have been investigated numerically for unsteady cross-flow over heated circular cylinders. Numerous simulations were conducted varying the number of inline tubes, inlet velocity, dimensionless pitch ratios and Reynolds number. Heat leakage into the domain is modeled as a source term. Numerical results compare favorably to published data in terms of Nusselt number and pressure drop. It was found that the energy efficiency varies between 72% and 98% for all cases, and viscous dissipation has a very low effect on the energy efficiency for low Reynolds number cases. The exergy efficiency ranges from 40–64%, and the entropy generation due to heat transfer was found to have a significant effect on exergy efficiency. The results suggest that exergy efficiency can be maximized by choosing specific pitch ratios for various Reynolds numbers. The results could be useful in designing more efficient heat recovery systems, especially for low temperature applications.

Strouhal Number for VIV Excitation of Long Slender Structures

2018 ◽  
Author(s):  
Andrew E. Potts ◽  
Douglas A. Potts ◽  
Hayden Marcollo ◽  
Kanishka Jayasinghe
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Degrees Of Freedom ◽  
Measurement Techniques ◽  
Cross Flow ◽  
Degree Of Freedom ◽  
Circular Cylinders ◽  
Two Degrees Of Freedom ◽  
Shedding Frequency ◽  
Eddy Shedding

The prediction of Vortex-Induced Vibration (VIV) of cylinders under fluid flow conditions depends upon the eddy shedding frequency, conventionally described by the Strouhal Number. The most commonly cited relationship between Strouhal Number and Reynolds Number for circular cylinders was developed by Lienhard [1], whereby the Strouhal Number exhibits a consistent narrow band of about 0.2 (conventional across the sub-critical Re range), with a pronounced hump peaking at about 0.5 within the critical flow regime. The source data underlying this relationship is re-examined, wherein it was found to be predominantly associated with eddy shedding frequency about fixed or stationary cylinders. The pronounced hump appears to be an artefact of the measurement techniques employed by various investigators to detect eddy-shedding frequency in the wake of the cylinder. A variety of contemporary test data for elastically mounted cylinders, with freedom to oscillate under one degree of freedom (i.e. cross flow) and two degrees of freedom (i.e. cross flow and in-line) were evaluated and compared against the conventional Strouhal Number relationship. It is well established for VIV that the eddy shedding frequency will synchronise with the near resonant motions of a dynamically oscillating cylinder, such that the resultant bandwidth of lock-in exhibits a wider range of effective Strouhal Numbers than that reflected in the narrow-banded relationship about a mean of 0.2. However, whilst cylinders oscillating under one degree of freedom exhibit a mean Strouhal Number of 0.2 consistent with fixed/stationary cylinders, cylinders with two degrees of freedom exhibit a much lower mean Strouhal Number of around 0.14–0.15. Data supports the relationship that Strouhal Number does slightly diminish with increasing Reynolds Number. For oscillating cylinders, the bandwidth about the mean Strouhal Number value appears to remain largely consistent. For many practical structures in the marine environment subject to VIV excitation, such as long span, slender risers, mooring lines, pipeline spans, towed array sonar strings, and alike, the long flexible cylinders will respond in two degrees of freedom, where the identified difference in Strouhal Number is a significant aspect to be accounted for in the modelling of its dynamic behaviour.

VIV Response and Drag Measurements of Circular Cylinders Fitted With Permeable Meshes

2015 ◽  
Author(s):  
Murilo M. Cicolin ◽  
Gustavo R. S. Assi
Keyword(s):  
Reynolds Number ◽  
Long Range ◽  
Flow Direction ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Peak Response ◽  
Vortex Induced Vibrations ◽  
Different Types ◽  
Cylindrical Tubes ◽  
Low Mass

Experiments have been carried out on models of rigid circular cylinders fitted with three different types of permeable meshes to investigate their effectiveness in the suppression of vortex-induced vibrations (VIV). Measurements of amplitude of vibration and drag force are presented for models with low mass and damping which are free to respond in the cross-flow direction. Results for two meshes made of ropes and cylindrical tubes are compared with the VIV response of a bare cylinder and that of a known suppressor called the “ventilated trousers” (VT). All three meshes achieved an average 50% reduction of the peak response when compared with that of the bare cylinder. The sparse mesh configuration presented a similar behaviour to the VT, while the dense mesh produced considerable VIV response for an indefinitely long range of reduced velocity. All the three meshes have increased drag when compared with that of the bare cylinder. Reynolds number ranged from 5,000 to 25,000 and reduced velocity was varied between 2 and 15.

Experiment on smooth, circular cylinders in cross-flow in the critical Reynolds number regime

2011 ◽  
Vol 51 (4) ◽  
pp. 949-967 ◽  
Author(s):  
J. J. Miau ◽  
H. W. Tsai ◽  
Y. J. Lin ◽  
J. K. Tu ◽  
C. H. Fang ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Cross Flow ◽  
Circular Cylinders

VORTEX INTERFERENCE IN THE WAKE OF TWO TANDEM CIRCULAR CYLINDERS IN A CROSS FLOW

2005 ◽  
Vol 19 (28n29) ◽  
pp. 1595-1598 ◽  
Author(s):  
KAZUO OHMI ◽  
SUXIA LI ◽  
SEUNGHEE JEON ◽  
LINGYUN CHEN
Keyword(s):  
Reynolds Number ◽  
Image Analysis ◽  
Cross Correlation ◽  
Laser Sheet ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Water Tank ◽  
Cylinder Wake ◽  
Flow Reynolds Number ◽  
Spacing Ratio

The wake of two circular cylinders in tandem arrangement is investigated by flow visualization and PIV experiments in a towing water tank. The two cylinders are spaced at L/d (spacing ratio) = 2.0 to 15.0 and the cross flow Reynolds number ranges from 60 to 120. The flow is seeded with fine Rilsan particles and illuminated by a 2 mm thick laser sheet. The PIV image analysis is done by a standard cross correlation scheme with a powerful validation algorithm followed by multi-pass adaptive cross correlation iterations. The main objective of the study is to investigate the characteristics of the downstream cylinder wake changing considerably with the spacing ratio of the two cylinders.

scholarly journals Transient Cooling Of A Cylinder In Cross Flow Bounded By An Adiabatic Wall

2018 ◽  
Vol 17 (2) ◽  
pp. 17
Author(s):  
Nawaf H Saeid ◽  
Bashir S. Abusahmin
Keyword(s):  
Thermal Properties ◽  
Cross Flow ◽  
Thermal Inertia ◽  
Cooling Process ◽  
Adiabatic Wall ◽  
Cold Air ◽  
Cooling Period ◽  
Air Stream ◽  
Storage Area ◽  
High Thermal Inertia

The present study investigates the parameters controlling the cooling process of acylindrical food in the storage area for a period of time. Transient analysis of theconduction and convection (conjugate) heat transfer from a cylindrical food, or acylindrical can filled with food is selected for numerical simulations. The cylinder isbounded by an adiabatic wall and the cold air is flowing normal to the cylinder axis (crossflow). The parameters investigated are: Reynolds number, food thermal properties(density, specific heat and thermal conductivity) and the cooling period. The range of theReynolds number is selected from 50 to 500 to be in laminar flow conditions. Threedifferent materials were selected according their thermal properties. The results arepresented to show the cooling process starting from blowing cold air stream on thecylinder for a period of 4 hours. The results show that the food with low thermal inertia iscooled faster than that of high thermal inertia. The present results show also that thecooling process can be shortened by increasing the air velocity and lower its temperature.

Effect of Pulsed Film Cooling on Leading Edge Film Effectiveness

2010 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Richard B. Rivir
Keyword(s):  
Film Cooling ◽  
Cross Flow ◽  
Thermal Inertia ◽  
Leading Edge ◽  
Continuous Film ◽  
Adiabatic Wall ◽  
Blowing Ratio ◽  
Velocity Waveform ◽  
Edge Surface ◽  
Cross Flow Velocity

Detailed film effectiveness measurements have been made on a cylindrical leading edge surface for steady and pulsating flow. The film hole is off-centered by 21.5° from the centerline and angled 20° to the surface and 90° from the stream wise direction. Two jet-to-cross-flow velocity ratios have been considered: VR = 1 and 2 which correspond to blowing ratio of 1 and 2, respectively. The pulsating frequency is 10 Hz and the duty cycle is 50%. Comparisons between film effectiveness with a pulsating film and a continuous film show that for the same blowing ratio, the effectiveness of the film drops by a factor of 2 when the flow is pulsed. Hotwire measurements are made to characterize the pulsating velocity waveform at the exit of the film exit and verify the integrity of the pulse. The variation in the measured surface adiabatic wall temperature over the pulsing duration is very small suggesting a large thermal inertia that keeps the wall surface largely unaffected by the time scale of the pulsations; this holds true for both blowing ratios tested.

scholarly journals Statistical and Simulation Analysis on Dimple Configurations Performance of Heat Dissipation

2021 ◽  
Vol 86 (2) ◽  
pp. 74-90
Author(s):  
Mohd Shahir Kasim ◽  
Nur Husnina Najeah Husshini ◽  
Raja Izamshah ◽  
Hema Nanthini Ganesan ◽  
Muhamad Ammar Farhan Maula Mohd Azam ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Structure ◽  
Heat Dissipation ◽  
Simulation Analysis ◽  
Air Flow ◽  
Orientation Angle ◽  
Cooling Time ◽  
Cooling Effect ◽  
Staggered Arrangement

This paper presents an investigation on cooling effect and flow structure of the spherical dimple configuration during air flow on the Aluminium surface. It is prominently known that applying dimples profile causes an enhancement in heat transfer over a plain surface. A three level of Box-Behnken response surface methodology was performed to find the correlation between the input and output variables. A total of 17 different combinations of these inputs were performed throughout the experiment. The variable inputs to be investigated namely: dimple diameter of 10 - 14 mm, dimple orientation angle of 60°- 90°, and airflow velocity of 16 - 18 m/s to observe the response on the cooling time. The Aluminium block was heated to 60°C and cooled down by air flow at room temperature. The ANOVA was used to identify the significant effect of each parameter. CFD software was used as a simulation tool to analyze the flow structure and Reynolds number that associate with the heat transfer rate to support the statistical findings. Based on the result, all the input parameters are found to be significantly dominated by air flow velocity. Staggered arrangement dimple profile surface improves cooling effect by 63% over the plain flat surface. The increment in Reynolds number will increase the heat transfer which then shortening the cooling time.

Suppression of the Vortex-Induced Vibration of a Circular Cylinder With Permeable Meshes

2014 ◽  
Author(s):  
Murilo M. Cicolin ◽  
Cesar M. Freire ◽  
Gustavo R. S. Assi
Keyword(s):  
Reynolds Number ◽  
Flow Direction ◽  
Vortex Formation ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Vortex Induced Vibrations ◽  
Image Velocimetry ◽  
Different Types ◽  
Cylindrical Tubes ◽  
Low Mass

Experiments have been carried out on models of rigid circular cylinders fitted with three different types of permeable meshes to investigate their effectiveness in the suppression of vortex-induced vibrations (VIV). Measurements of the dynamic response are presented for models with low mass and damping which are free to respond in the cross-flow direction. Reynolds number ranged from 1,000 to 10,000 and reduced velocity was varied between 2 and 13. Also presented are measurements of the wake of static models with Particle Image Velocimetry (PIV) at Reynolds number equal to 4000. Results for two meshes made of ropes and cylindrical tubes are compared with the VIV response of a bare cylinder and that of a known suppressor called the “ventilated trousers” (VT). All three meshes achieved an average 50% reduction of the response when compared with that of the bare cylinder. The sparse mesh configuration presented a similar behaviour to the VT, while the dense mesh produced considerable VIV response for an indefinitely long range of reduced velocity. Visualisation of the flow by PIV around static cylinders revealed that all suppressors disrupt the vortex shedding and increase the formation length when compared to the bare cylinder. The VT mesh, which presented the best suppression, also presented the largest vortex formation length.

Vorticity Shedding and Acoustic Resonance Excitation of Two Tandem Spirally Finned Cylinders in Cross-Flow

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Mohammed Alziadeh ◽  
Atef Mohany
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Root Diameter ◽  
Circular Cylinders ◽  
Resonance Excitation ◽  
Equivalent Diameter ◽  
Spacing Ratio

Abstract The aeroacoustic response of two tandem spirally finned cylinders is experimentally investigated. Three different pairs of finned cylinders are studied with fin pitch-to-root diameter ratios (p/Dr) ranging between 0.37≤p/Dr≤0.74. The spiral fins are crimped similar to those used in industrial heat exchangers. The results of the finned cylinders are compared with bare, circular cylinders with a modified equivalent diameter (Deq). The spacing ratio (L/Deq) between the cylinders are kept constant at L/Deq=2.00. The Strouhal number (StDeq) of the tandem finned cylinders is found to be higher compared to the tandem bare cylinders, resulting in an earlier onset of coincidence resonance. Moreover, unlike the tandem bare cylinders, the Strouhal number of the finned cylinders did not depend on the Reynolds number, suggesting that the flow characteristics around the finned cylinders are unaffected by Reynolds number. Only the tandem finned cylinders with the lowest fin pitch-to-root diameter ratio (p/Dr=0.37) were capable of exciting precoincidence acoustic resonance. The precoincidence resonance mechanism is similar to that observed in in-line tube bundles.

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