Showing papers by "S.V. Prabhu published in 2011"

Review on vortex flowmeter—Designer perspective

Abstract: This paper highlights various aspects of design of a vortex flowmeter. Vortex shedding and vortex flowmeters are known from decades. However, the vortex shedding phenomenon is not understood clearly as applicable to vortex flowmeter. In the recent past large body of literature is reported on the performance of vortex flowmeter. This report comprehensively summarizes all the improvements which help the designer to build a vortex flowmeter. The paper systematically explains various aspects related to development of a vortex flowmeter with peculiarities associated with its design.

Local heat transfer distribution between smooth flat surface and impinging air jet from a circular nozzle at low Reynolds numbers

Abstract: An experimental investigation is performed to study the effect of jet to plate spacing and low Reynolds number on the local heat transfer distribution to normally impinging submerged circular air jet on a smooth and flat surface. A single jet from a straight circular nozzle of length-to-diameter ratio (l/d) of 83 is tested. Reynolds number based on nozzle exit condition is varied between 500 and 8,000 and jet-to-plate spacing between 0.5 and 8 nozzle diameters. The local heat transfer characteristics are obtained using thermal images from infrared thermal imaging technique. It was observed that at lower Reynolds numbers, the effect of jet to plate distances covered during the study on the stagnation point Nusselt numbers is minimal. At all jet to plate distances, the stagnation point Nusselt numbers decrease monotonically with the maximum occurring at a z/d of 0.5 as opposed to the stagnation point Nusselt numbers at high Reynolds numbers which occur around a z/d of 6.

Experimental Investigations on Two and Three Stage Modified Savonius Rotor

Abstract: Single stage modified Savonius rotor (without shaft) is having higher coefficient of power (0.21) compared to single stage conventional Savonius rotor (0.17). Coefficient of static torque is negative for a 1/6th of a cycle from rotor angle 135° to 165° and from 315° to 345°. There is a large variation in the coefficient of static torque in a cycle of 180° from a peak of 0.44 at 30° to a lowest value of -0.21 at 165°. Multi-staging provides positive coefficient of static torque at all rotor angles and reduces large variations in a cycle. Wind tunnel tests were conducted to assess the aerodynamic performance of two and three stage modified Savonius rotors without shaft in between the end plates at different rotor aspect ratios and stage aspect ratios. The coefficient of static torque variations decrease with the increase in the number of stages. However, the coefficient of power decreases with the increase in the number of stages. The effect of intermediate plates on the performance of rotors is also studie...

Local Heat Transfer Distribution in a Rectangular Pin Channel With and Without Vortex Generators

Abstract: Short pin fins are used to enhance heat transfer rates by increasing the level of turbulence in the trailing edge of gas turbine blades. Experiments are conducted to investigate the local Nusselt number distributions in a staggered pin-fin array using the infrared thermal imaging technique. The pin fins are arranged in a rectangular channel with an aspect ratio of 9. The pins have streamwise pitch-to-diameter (XS/D) and spanwise pitch-to-diameter (XT/D) ratios of 2 with a pin height-to-diameter (H/D) ratio of 2. Ejection holes of 5-mm diameter with a pitch of 12.7 mm are used to study the effects of lateral ejection. Both one-wall and two-wall heating situations are studied for straight-flow and lateral-ejection cases. It is found that the local Nusselt numbers are highest below the horseshoe vortices just upstream of the individual pin fins. For the straight-flow case, the Nusselt numbers for the two-wall heating case are observed to be 15–20% higher than those of the one-wall heating case. Lateral eject...

Blowoff Stability of Methane-Air Premixed Flame on Tube Burners

Abstract: Stability of premixed flames is important in applications involving industrial and domestic impingement heat transfer processes, gas turbine combustion chamber and others. Blowoff limits of premixed methane-air flames stabilised on an uncooled Bunsen type burner is considered in the present experimental work. The effect of burner material, wall thickness and burner exit shape on the blowoff limits is presented. Burner materials covered in this study are stainless steel, brass and pyrex. Wall thicknesses considered are 1 mm, 2 mm and 3 mm for pyrex tubes of 10 mm inside diameter. The burner exit shapes covered in this study are circle, triangle, square and hexagon. The operating mixture Reynolds number range is 800 - 4000. It is found that the burners with low thermal conductivity, larger wall thickness and minimal sided polygon shapes provide better lean blowoff stability. Critical velocity gradient parameter defined on the basis of hydraulic diameter collapses the blowoff limits for all shapes covered in...