II B.Tech I Semester Supplimentary Examinations, February 2008
FLUID MECHANICS AND HYDRAULIC MACHINERY
(Electrical & Electronic Engineering)
1. (a) Define surface tension . Prove that the relationship between surface tension and pressure inside a droplet of liquid in excess of outside pressure is given by p = 4?/d
(b) A cubical block weighing 200 kN and having a 200 mm edge is allowed to slide down on an inclined plane making an angle of 300with the horizontal on which there is a thin film of a liquid having a viscosity of 2.1x 10?3N ?s/m2. What terminal velocity will be attained if the film thickness is estimated to be 0.025 mm.
2. In a circular pipe the velocity varies as V = Vm(1?r/R)2 where v is the velocity at a radial distance r from the axis of the pipe and Vm is the maximum flow at the axis. Find the ratio of average velocity in the pipe to maximum velocity.
3. (a) Derive an equation for discharge of a venturimeter.
(b) Explain why Cd of a venturimeter is more than that of orifice meter.
(c) A horizontal venturimeter with inlet and throat diameters 300mm and mm respectively is used to measure the flow of water. The pressure intensity at inlet is 130KN/m2. While the vaccum pressure head at the throat is 350mm of mercury. Assuming that 3% of head is lost in between inlet and throat, find Cdof venturimeter and rate of flow.
4. (a) Derive the expressions for force and work done per second by the jet when it strikes a curved plate moving in the direction of the jet.
(b) A jet of water 20cm in diameter and moving with a velocity of 20m/sec impinges normally on a series of flat vanes mounted on the periphery of a wheel. If the velocity of the vanes is 8m/sec, determine
i. the force exerted by the jet on the wheel
ii. work done by the jet on the wheel per second and
iii. hydraulic efficiency.
5. (a) What are the components of a mass curve? What are its properties? Explain how it is constructed from a hydrograph.
(b) Draw a neat sketch of a hydro power plant and show clearly the various elements. Explain about the elements clearly and elaborately.
6. (a) Explain why a Pelton wheel turbine is called an Impulse turbine with a neat sketch. Define draft tube and what are its functions.
(b) A Pelton wheel turbine develops 9000 Kw under a head of 300m. The turbine speed is 550 rpm and ratio of jet dia to wheel dia is 1/10. The hydraulic, volumetric and mechanical efficiencies are 0.98, 0.95 and 0.92 respectively. The speed ratio is 0.46 and coefficient of velocity is 0.98. Calculate the no of jets to be provided.
7. (a) What is necessity of governing a hydraulic turbine ? Explain how the Pelton wheel turbine can be governed.
(b) A turbine is working under varying conditions and the head drops down from 150m to 100m. How will the speed , discharge and power change under constant efficiency and homologous conditions.
8. (a) List all hydraulic losses, Mechanical losses and Leakage losses of a centrifugal pump. Explain when can centrifugal pumps arranged in series and in parallel.
(b) How can you find the power required to drive a reciprocating pump ? Define slip of a reciprocating pump.