A Convection Heat Transfer Correlation for a Binary Air-Helium Mixture at Low Reynolds Number

2007 ◽  
Vol 129 (11) ◽  
pp. 1494-1505 ◽  
Author(s):  
Arindam Banerjee ◽  
Malcolm J. Andrews
Keyword(s):  
Heat Transfer ◽  
Mixing Layer ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Gas Mixtures ◽  
Correlation Technique ◽  
Hot Wire ◽  
Nusselt Numbers ◽  
Low Reynolds ◽  
Constant Temperature Anemometer

The results of experiments investigating heat transfer from a hot wire in a binary mixture of air and helium are reported. The measurements were made with a constant temperature anemometer at low Reynolds numbers (0.25<Re<1.2) and correlated by treating the data in terms of a suitably defined Reynolds and Nusselt numbers based on the wire diameter. The correlation was obtained by taking into account the temperature dependency of gas properties, properties of binary gas mixtures, and the fluid slip at the probe surfaces as well as gas accommodation effects. The correlation has been used to measure velocity and velocity-density statistics across a buoyancy driven Rayleigh–Taylor mixing layer with a hot wire. The measured values obtained with the correlation agree well with measurements obtained with a more rigorous and extensive calibration technique (at two different overheat ratios). The reported correlation technique can be used as a faster and less expensive method for calibrating hot wires in binary gas mixtures.

Periodic Fluid Flow and Heat Transfer in a Square Cavity Due to an Insulated or Isothermal Rotating Cylinder

2009 ◽  
Vol 131 (11) ◽  
Author(s):  
Y.-C. Shih ◽  
J. M. Khodadadi ◽  
K.-H. Weng ◽  
A. Ahmed
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Rotating Cylinder ◽  
Flow Fields ◽  
Square Cavity ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Rotating Objects

The periodic state of laminar flow and heat transfer due to an insulated or isothermal rotating cylinder object in a square cavity is investigated computationally. A finite-volume-based computational methodology utilizing primitive variables is used. Various rotating objects (circle, square, and equilateral triangle) with different sizes are placed in the middle of a square cavity. A combination of a fixed computational grid and a sliding mesh was utilized for the square and triangle shapes. For the insulated and isothermal objects, the cavity is maintained as differentially heated and isothermal enclosures, respectively. Natural convection heat transfer is neglected. For a given shape of the object and a constant angular velocity, a range of rotating Reynolds numbers are covered for a Pr=5 fluid. The Reynolds numbers were selected so that the flow fields are not generally affected by the Taylor instabilities (Ta<1750). The periodic flow field, the interaction of the rotating objects with the recirculating vortices at the four corners, and the periodic channeling effect of the traversing vertices are clearly elucidated. The simulations of the dynamic flow fields were confirmed against experimental data obtained by particle image velocimetry. The corresponding thermal fields in relation to the evolving flow patterns and the skewness of the temperature contours in comparison to the conduction-only case were discussed. The skewness is observed to become more marked as the Reynolds number is lowered. Transient variations of the average Nusselt numbers of the respective systems show that for high Re numbers, a quasiperiodic behavior due to the onset of the Taylor instabilities is dominant, whereas for low Re numbers, periodicity of the system is clearly observed. Time-integrated average Nusselt numbers of the insulated and isothermal object systems were correlated with the rotational Reynolds number and shape of the object. For high Re numbers, the performance of the system is independent of the shape of the object. On the other hand, with lowering of the hydraulic diameter (i.e., bigger objects), the triangle and the circle exhibit the highest and lowest heat transfers, respectively. High intensity of the periodic channeling and not its frequency is identified as the cause of the observed enhancement.

A Heat Transfer Comparison Between a Synthetic Jet and a Steady Jet at Low Reynolds Numbers

2008 ◽  
Author(s):  
Rayhaan Farrelly ◽  
Alan McGuinn ◽  
Tim Persoons ◽  
Darina B. Murray
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Stroke Length ◽  
Low Reynolds Numbers ◽  
Nusselt Numbers ◽  
Significant Difference ◽  
Low Reynolds ◽  
Surrounding Fluid

A study has been carried out to compare steady jet and synthetic jet heat transfer distributions at low Reynolds numbers. Both jets issued from a 5mm diameter orifice plate with air for the steady jet being supplied by a compressor via a plenum chamber. Tests were conducted for Reynolds numbers ranging from 1000 to 4000, and for non-dimensional surface to jet exit spacings (H/D) from 1 to 6. Dimensionless stroke length (Lo/D) for the synthetic jet was held constant at 8. A significant difference was observed between the steady and synthetic jet Nusselt numbers at low Reynolds numbers and low H/D. In comparison to steady jets, the stronger entrainment of surrounding fluid and the vigorous mixing near the impingement surface are characteristics of synthetic jets that are beneficial to heat transfer. Nonetheless, the steady jet yields higher Nusselt numbers for all test conditions.

Transient Leading to Periodic Fluid Flow and Heat Transfer in a Cavity With Constant Temperature Walls Due to an Isothermal Rotating Object

2007 ◽  
Author(s):  
Y.-C. Shih ◽  
J. M. Khodadadi ◽  
K.-H. Weng
Keyword(s):  
Heat Transfer ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
High Heat ◽  
Sliding Mesh ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
High Heat Transfer ◽  
Transient Variations ◽  
Rotating Objects

Computational analysis of transient phenomenon followed by the periodic state of laminar flow and heat transfer due to a rotating object in a square cavity is investigated. A finite-volume-based computational methodology utilizing primitive variables is used. Various isothermal rotating objects (circle, square and equilateral triangle) with different sizes are placed in the middle of the cavity. A combination of a fixed computational grid with a sliding mesh was utilized for the square and triangle shapes. The motionless object is set in rotation at time t = 0 and its temperature is maintained constant but different from the temperature of the walls of the cavity. Natural convection heat transfer is neglected. For a given shape of the object and a constant angular velocity, a range of rotating Reynolds numbers are covered for a Pr = 5 fluid. The Reynolds numbers were selected so that the flow fields are not generally affected by the Taylor instabilities (Ta &lt; 1750). The evolving flow field and the interaction of the rotating objects with the recirculating vortices at the four corners are elucidated. Similarities and differences of the flow and thermal fields for various shapes is discussed. Transient variations of the average Nusselt numbers on the surface of the rotating object and cavity walls show that for high Re numbers, a quasi-periodic behavior due to the onset of Taylor instabilities is dominant, whereas for low Re numbers, periodicity of the system is clearly observed. Time-integrated average Nusselt number of the cavity is correlated to the rotational Reynolds number and shape of the object. The triangle object clearly gives rise to high heat transfer followed by the square and circle objects.

Heat transfer from a sphere at low Reynolds numbers

1973 ◽  
Vol 60 (2) ◽  
pp. 273-283 ◽  
Author(s):  
S. C. R. Dennis ◽  
J. D. A. Walker ◽  
J. D. Hudson
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Viscous Incompressible Fluid ◽  
Reynolds Numbers ◽  
Experimental Measurements ◽  
Low Reynolds Numbers ◽  
Nusselt Numbers ◽  
The Mean ◽  
Low Reynolds ◽  
Prandtl Numbers

The heat transfer due to forced convection from an isothermal sphere in a steady stream of viscous incompressible fluid is calculated for low values of the Reynolds number and Prandtl numbers ofO(1). The mean Nusselt number is compared with the results of experimental measurements. At very low Reynolds numbers, both the local and mean Nusselt numbers are compared with the results obtained from the theory of matched asymptotic expansions.

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