Reverse Osmosis

Reverse osmosis (RO) is a water purification method that uses a semipermeable membrane to remove ions, molecules, and sediments from water to make it drinkable. In reverse osmosis process, pressure applied with pump to overcome osmotic pressure. Reverse osmosis can remove many types of dissolved and suspended particles or species from water, including bacteria, sediments etc. and is used in both industrial processes and the production of potable water. The result is that the solute is retained on the pressurised side of the membrane and the pure solvent is allowed to pass to the other side of the membrane. To be selective, this membrane should not allow large molecules or ions through the pores or holes, but should allow smaller components of the solution such as solvent molecules to pass freely.

In the normal osmosis process, the solvent naturally moves from an area of low solute concentration or high water potential through a membrane, to an area of high solute concentration or low water potential. The driving force for the movement of the solvent is the reduction in the free energy of the system when the difference in solvent concentration on either side of a membrane is reduced, generating osmotic pressure due to the solvent moving into the more concentrated solution. Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications. However, key differences are found between reverse osmosis and filtration. Reverse osmosis also involves diffusion, making the process dependent on pressure, flow rate, and other conditions. Reverse osmosis is most commonly known for its use in drinking water purification from seawater, removing the salt and other effluent materials from the water molecules.

Steam Turbine

Steam Turbine

A Steam Turbine is a rotary mechanical device (turbo machine) that extracts energy from fluid flow and converts it into useful work. Turbine has a moving part called rotor assembly, which is a shaft or drum with blades attached on it. High velocity moving fluid acts on blades so that they impart rotational energy to the rotor. Turbines have a casing around the blades that contains and controls the working fluid.A working fluid contains potential energy (pressure head) and kinetic energy (velocity head). The fluid may be compressible or incompressible.

Steam turbines are used for the generation of electricity in thermal power plants, such as plants using coal, fuel oil or nuclear fuel.

Classification of Steam Turbine:

According to the working principle:

Impulse Turbine

Reaction Turbine

According to the number of Cylinder:

Single Cylinder Turbine

Double Cylinder Turbine

According to the method of Governing:

Throttle Governing Turbine

Nozzle Control Governing Turbine

Bypass Governing Turbine

According to Steam Pressure:

Low Pressure Turbine (1.2 to 2 kg/cm²)

Medium Pressure Turbine (up to 40 kg/cm²)

High Pressure Turbine (40 to 170 kg/cm²)

Very High Pressure Turbine (170 to kg/cm²or higher and temperature of 550 ºC)

Supercritical Turbine (225 kg/cm²)

According to shaft Arrangement:

Cross Compound Turbine

Tandem Compound Turbine

According to Direction of Flow:

Single Flow Turbine

Double flow Turbine

Reverse Flow Turbine

According to the Direction of Steam Flow:

Axial Turbine

Radial Turbine

Power Plant Engineering

Basic Definition of Power Plant Engineering

Load Curve: A consumer of electrical power will use the power as and when required, and hence the load always be changing with time.

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.

COOLING TOWER MATERIAL BALANCE

Quantitatively, the material balance around a wet, evaporative cooling tower system is governed by the operational variables of make-up flow rate, evaporation and windage losses, draw-off rate, and the concentration cycles.

Air Flow Generation Methods in Cooling Tower:

With respect to drawing air through cooling tower, there are three types of cooling towers:

1)      Natural Draft: Utilizes buoyancy via a tall chimney. Warm, moist air naturally rises due to the density differential compared to the dry, cooler outside air. Warm moist air is less dense than drier air at the same pressure. This moist air buoyancy produces an upwards current of air through the tower.

COOLING TOWER

A cooling tower is a heat rejection device which rejects waste heat of water to atmosphere through cooling of a water stream to a lower temperature. Cooling towers may either use evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or, in the case of closed circuit dry cooling towers, rely solely on air to cool the working fluid to near the dry-bulb air temperature.

BASICS OF AIR HANDLING UNIT AND ITS DESIGN

In this article we know the followings:

1)     Know the different types of AHUs, and their basic anatomy

2)     Understand the codes and standards that govern AHU specification

3)     Learn about how energy can be saved in HVAC systems that use AHUs.

A basic definition of an air handling unit (AHU) might be “a box with a fan, coils, and filters.” From there it gets considerably more complicated.

Air Handling Unit

Air Handling Unit

There are basically two types of Air Handling Unit that are in used and they are the "Draw-Through" or "Blow-Through". 

In Draw-Through type, the fan pulls the air through the mixing box, filters and cooling coil before discharging it from the fan outlet to the space to be conditioned or to the ducting network. The design can be vertical or horizontal. In this case, the section before the fan has negative pressure.

Fluid Mechanics

Fluid mechanics is categorises into three section

a)     Kinematics - Study of motion without taking help of force.

b)     Dynamics - Study of motion with taking help of force.

c)     Statics – Study of fluid mechanics in which fluid particles are at rest.

Fluid – A fluid is a substance which continuously deforms under the action of tangential / shears forces.