Cavitation

Cavitation is the formation of vapour cavities in liquid to form bubbles or voids that are consequence of forces acting upon the liquid.

Basic Effects of Fluid Properties

The effects of temperature and pressure on hydraulic system fluid properties and flow characteristics are listed below:

Density - Effects orifice and valve volume flow rates. As density increases, orifice and valve flow rates will decrease (see orifice flow equations).

a)     Increasing pressure increases density

b)     Increasing temperature decreases density

Kinematic Viscosity – Effects pipe (tube) volumetric flow rate. As viscosity increases, pipe flow rate will decrease (see orifice flow equations). Kinematic viscosity increases with increased pressure and decreasing temperature.

a)     Increasing pressure increases kinematic viscosity

b)     Increasing temperature decreases kinematic viscosity

Bulk Modulus - Effects compressibility of fluid and system response time (see pressure derivative equation). As bulk modulus decreases, the pressure derivative will decrease leading to slower response times. Compressibility will affect the performance of actuators, motors and pumps because the stiffness of the fluid is less as bulk modulus is reduced.

a)     Increasing pressure increases bulk modulus

b)     Increasing temperature decreases bulk modulus

HOW PUMPS WORK

HOW PUMPS WORK

In dynamic machines there is no closed volume, instead rotating blades supply or extract energy to or from the fluid. For pumps, these rotating blades are called impeller. For incompressible flow it is more common to use volume flow rate rather than mass flow rate. Volume flow rate is called capacity and is simply mass flow rate divided by fluid density.

PRINCIPLES OF SUPERCHARGING AND TURBOCHARGING

To better understand the technique of turbo charging, it is useful to be familiar with the internal combustion engine's principles of operation. Today, most passenger car and commercial diesel engines are four-stroke piston engines controlled by intake and exhaust valves. One operating cycle consists of four strokes during two complete revolutions of the crankshaft.

HOW TO PREPARE FOR GATE AND ENGINEERING SERVICES EXAMINATION

Dear friends if you want to get single digit rank in Gate or Engineering service examination then try to adopt following habits in your daily life:

a)   Make habits, go to bed around 11:30 pm night and try to get-up around 6 o-clock morning if possible else sleep 7 hours daily.

b)     Make a daily routine and follow it.

c)     Do half an hour physical exercise daily.

d)     Set your target for single digit rank, never thought negative in your mind.

e)      Do hard labour because hard labour beats talent when talent does not work hard.

f)      Read thoroughly 6-7 hours in a day there is no short-cut path for single digit rank. If your doubt is not clear with self study then take help from your friends or internet or your teacher.

g)     Try to take balance diet.

h)     Do not get nervous with time or syllabus.

i)       Always kept your mind cool and calm.

j)       Make own notes of all subjects for quick revision.

k)    Solve 20 years previous question papers of gate, engineering services and UPSC of Mechanical Engineering.

l)       Enjoy all the moments in your life and be happy always.

Basics Definitions of Rotating Equipment

Fan is a gas pump with relatively low pressure rise and high flow rate. Examples include ceiling fans, house fans, and propellers.

Blower is a gas pump with relatively moderate to high pressure rise and moderate to high flow rate. Examples include centrifugal blowers and squirrel cage blowers in automobile ventilation systems, furnaces, and leaf blowers.

Compressor is a gas pump designed to deliver a very high pressure rise, typically at low to moderate flow rates. Examples include air compressors that run pneumatic tools and inflate tires at automobile service stations, and refrigerant compressors used in heat pumps, refrigerators, and air conditioners.

Pump is a device which adds energy to a fluid, resulting in an increase in fluid pressure, not necessarily an increase of fluid speed across the pump.

Turbine is a device which extracts energy from a fluid, resulting in a decrease of fluid pressure, not necessarily a decrease of fluid speed across the turbine.