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 January 2007, April 2007,  July 2007, October 2007

Issue 3, Volume 2, July 2007
Print ISSN: 1790-5087
E-ISSN: 2224-347X







Title of the Paper: Characteristics of Air Bubble Rising in Low Concentration Polymer Solutions


Authors: Hassan, N. M. S., Khan, M. M. K. and Rasul, M. G.

Abstract: The bubble rise phenomena in different low concentration polymer solutions for higher Reynolds number are presented in this paper. The main characteristics, namely, the bubble velocity, the bubble trajectory and the drag relationship are investigated. The experiments were conducted in two different cylindrical columns at various liquid heights by introducing different bubble volumes (from 0.1mL to 20.0mL) corresponding to each height. The bubble rise velocity, bubble size and bubble trajectory were measured using a combination of non-intrusive-high speed photographic method and digital image processing. The parameters that significantly affect the rise of air bubble are identified. The bubble rise velocity of different volumes and the effect of liquid heights on the bubble rise velocity are analysed and discussed. The results show that the average bubble rise velocity increases with the increase in bubble volume for different low concentration polymer solutions and the bubble velocity is not dependant on the size of the test rig. The results of bubble trajectory for various bubbles are compared and discussed. In trajectory analysis, it is seen that the smaller bubbles show helical or zigzag motion and larger bubbles follow spiral motion. A new set of data of the drag coefficient for air bubble for higher Reynolds number are reported and compared with the results of other analytical and experimental studies available in the literature. The bubble rise characteristics, i.e., bubble velocity, trajectory and drag coefficient produced acceptable and consistent results.

Keywords: Bubble rise velocity, bubble trajectory, bubble volume, drag co-efficient, Reynolds number, polymer solution, non-intrusive method

Title of the Paper: A Numerical Study of Natural Convection in a Tilted Cavity with Two Baffles Attached to its Isothermal Walls


Authors: M. Ghass Emi, M. Pirmohammadi, Gh. A. Sheikhzadeh

Abstract: The purpose of this study is to investigate the effect of inclination angle on flow field and heat transfer in a differentially heated square cavity with two insulated baffles attached to its isothermal walls. The isothermal walls are at different temperatures. The walls that make an angle φ with the horizontal are adiabatic. In our formulation of governing differential equations, mass, momentum and the energy equations are applied to the cavity and the baffles. To solve the governing differential equations a finite volume code based on Pantenkar's simpler method is utilized. The results are presented for various Rayleigh number in form of streamlines, isotherms as well as Nusselt number. It is observed that for all baffle lengths and baffle positions when ϕ = 90o the Nusselt number is almost minimum. In addition the Nusselt number decreases as baffle length increases, generally. Finally it is shown that Nusselt number changes with baffles position.

Keywords: Natural Convection, inclined cavity, baffles, Nusselt Number

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