Working Principle of Water Heaters

 

Working Principle of Water Heaters

Almost everyone uses a water heater in day to day life. But how many of us have the exact idea of how it works and how the cold water is converted to hot water? What are the elements that are used for this process?

Introduction          

●      We use hot water for various purposes in daily life. For domestic purposes like cooking, bathing, etc. or for industrial purposes, we require hot water. Water heating is a thermodynamic process where a source of energy is used to heat water. The energy source may be natural gas, liquefied petroleum gas, propane, oil, or electricity. Now-a-days solar energy is also used for the water heating process.

Parts of an Electric Water Heater

●      For the process of heating water we need three main components. They are:

○      Dip Tube (Inlet tube): Cold water enters the tank through this tube.

○      Outlet Tube: Hot water goes out of the tank through this tube.

○      Heating element: This element helps in heating the cold water.

●      There are various other parts used in a water heater.

○      Steel tank: This unit holds the water. The steel tank has to be constructed in such a way that it should be able to withstand the pressure of water inside the tank.

○      Temperature and Pressure relief valve: These valves are specially placed for safety purposes. This valve prevents the heater from explosion during abnormal conditions like high pressure and temperature. It can be mounted either at the top of the tank or at the sides of the tank.

○      Drain Valve: The drain valve is used for cleaning and maintenance.

○      Thermostat: A thermostat is generally used to control or maintain the temperature within the tank.

○      Anticorrosion Anode Rod: This rod, also known as a sacrificial anode rod, aids in keeping the steel tank free from corrosion. This rod is made up of magnesium, which attracts corrosive elements and thus prevents the tank from corroding. This rod can be replaced when it becomes eroded.

●      Apart from this there is insulation provided that surrounds the steel tank of the heater.

●      The steel tank is internally coated with an epoxy or glass lining to prevent corrosion (in addition to anticorrosion rod).

How Electric Water Heaters Work

●      Generally electric water heaters have two heating elements each wired with a thermostat. Both the heating elements do not function simultaneously. First the top heating element functions until the upper tank is hot and then the function is transferred to the bottom heating element, which has its own thermostat. Usually the water in the upper tank is heated from 120-140 F before the control is transferred to the lower heating element.

●      But some heaters have only one heating element which makes maintenance easier. In case of heating element failure it can be detected and replaced easily when there is only one heating element.

●      When the hot water is consumed, once again cold water enters through the dip tube and the process is repeated.

Gas Water heater

●      The gas water heater is very similar in construction to the electric water heater. Here instead of electric supply, there is a gas supply. Instead of heating elements, there is a burner and burner control. The burner is used for heating the water in gas water heaters.

●      The working principle is based on law of convection. The cold water always remains at the bottom as it is denser than the hot water. As the water gets heated up it expands and moves to the top of the tank. If you look at the construction, we can see that the outlet tube is always smaller than the dip tube (inlet tube). This is to ensure that cold water is not supplied and only hot water is supplied through the tube. There is also a flue exhaust in gas type water heater which acts as heat exchanger as well as is used in exhausting the combustion gasses.

Projectile Motion What is a Projectile? What is Projectile Motion and what are different equations used in projectile motion?

Projectile Motion

What is a Projectile? What is Projectile Motion and what are different equations used in projectile motion?

A particle moving under the combined effect of vertical and horizontal forces, is called a projectile. The following terms are commonly used in projectiles:

1. Trajectory. It is the path traced by a projectile in the space.

2. Velocity of projection. It is the velocity with which a projectile is projected.

3. Angle of projection. It is the angle,with thehorizontal,at which the projectile is projected.

4. Time of flight. It is the total time taken by a projectile, to reach maximum height and to return back to the ground.

5. Range. It is the distance between the point of projection and the point where the projectile strikes the ground.

Types of Flat Belt Drives

Types of Flat Belt Drives

                                       

The power from one pulley to another may be transmitted by any of the following types of belt drives:

1. Open belt drive. The open belt drive, as shown in Fig. 11.3, is used with shaftsarranged parallel and rotating in the same direction. In this case, the driver A pulls the belt from one side (i.e. lower side RQ) and delivers it to the other side (i.e. upper side LM). Thus the tension in the lower side belt will be more than that in the upper side belt.The lower side belt (because of more tension) is known as tight side whereas the upper side belt (because of less tension) is known as slack side, as shown in Fig.

2. Crossed or twist belt drive. The crossed or twist belt drive, as shown in Fig. 11.4, isused with shafts arranged parallel and rotating in the opposite directions. In this case, the driver pulls the belt from one side (i.e. RQ) and delivers it to the other side (i.e. LM). Thus the tension in the belt RQ will be more than that in the belt LM. The belt RQ(because of more tension) is known as tight side, whereas the belt LM (because of less tension) is known as slack side, as shown in Fig.

A little consideration will show that at a point where the belt crosses, it rubs against each other and there will be excessive wear and tear. In order to avoid this, the shafts should be placed at a maximum distance of 20 b, where b is the width of belt and the speed of the belt should be less than 15 m/s.

3. Quarter turn belt drive. The quarter turn belt drive also known as right angle beltdrive, as shown in Fig. (a), is used with shafts arranged at right angles and rotating in one definite direction. In order to prevent the belt from leaving the pulley, the width of the face of the pulley should be greater or equal to 1.4 b, where b is the width of belt. In case the pulleys cannot be arranged, as shown in Fig. (a), or when the reversible is desired, then a quarter turn belt drive with guide pulley, as shown in Fig. (b), may be used.

4. Belt drive with idler pulleys. A belt drive with an idler pulley, as shown in Fig. (a), isused with shafts arranged parallel and when an open belt drive cannot be used due to small angle of contact on the smaller pulley. This type of drive is provided to obtain high velocity ratio and when the required belt tension cannot be obtained by other means.

When it is desired to transmit motion from one shaft to several shafts, all arranged in parallel, a belt drive with many idler pulleys, as shown in Fig. (b), may be employed.

5. Compound belt drive. A compound belt drive, as shown in Fig., is used when power is transmitted from one shaft to another through a number of pulleys.

6. Stepped or cone pulley drive. A stepped or cone pulley drive, as shown in Fig, is usedfor changing the speed of the driven shaft while the main or driving shaft runs at constant speed. This is accomplished by shifting the belt from one part of the steps to the other.

7. Fast and loose pulley drive. A fast and loose pulley drive, as shown in Fig., is usedwhen the driven or machine shaft is to be started or stopped when ever desired without interfering with the driving shaft. A pulley which is keyed to the machine shaft is called fast pulley and runs at the same speed as that of machine shaft. A loose pulley runs freely over the machine shaft and is incapable of transmitting any power. When the driven shaft is required to be stopped, the belt is pushed on to the loose pulley by means of sliding bar having belt forks.

Governing of IC Engines

The process of providing any arrangement, which will keep the engine speed constant (according to the changing load conditions) is known as governing of I.C. engines. Though there are many methods for the governing of I.C. engines, yet the following are important :

1. Hit and miss governing. In this system of governing, whenever the engine starts running at higher speed (due to decreased load), some explosions are omitted or missed. This is done with the help of a centrifugal governor. This method of governing is widely used for I. C. engines of smaller capacity or gas engines.

2. Qualitative governing. In this system of governing, a control valve is fitted in the fuel delivery pipe, which controls the quantity of fuel to be mixed in the charge. The movement of control valve is regulated by the centrifugal governor through rack and pinion arrangement.

3. Quantitative governing. In this system ofgoverliing, the quality of charge (i.e. air-fuel ratio of the mixture) is kept constant. But the quantity of mixture supplied to the engine cylinder is varied by means of a throttle valve which is regulated by the centrifugal governor through rack and pinion arrangement.

4. Combination system of governing. In this system of governing, the qualitative and quantitative methods of governing are combined together.

Jigs vs Fixtures

                                                          

The terms “jig" and “fixture" are many times referred as the synonyms of each other, sometimes both the terms are used together as “jig fixture." Although, both jig and fixture are used in mass production process, functionally the two are different tools.

What is a Jig?

In simple terms, the jig is a tool that guides the cutting (or machining) tool. The most common type of jig is the drill jig, which guides the drill bit for creating holes at desired locations. Using drill jigs increases production rate drastically by eliminating the time spent using a square scriber, height gauge, centre punch, etc. The picture below shows the functionality of a simple drill jig:

Like drill jigs, welding jigs and woodworking jigs are also used in industry quite extensively. Woodworking jigs are useful for creating intricate wooden profiles.

What is a Fixture?

The fixture is a tool which holds the workpiece with the machine bed precisely at the desired location. The fixture also reduces the nonproductive loading, unloading, and fixing time of the workpiece. For example, you need to use a milling machine for giving a chamfer at the corner of rectangular work pieces. You can use a vice to hold it in the desired position, but in that case every new work piece will take lots of time for fixing it. On the other hand if you can make a milling fixture like the one shown below and bolt the fixture to the milling machine bed, then you need not waste much time for fixing the work pieces every time:

You just place the workpiece and it will automatically aligned to the required angle, and straight away you run the machining operation, no need to measure the angle, and no need to be worried about the accuracy.

Conclusion

Both the jigs and the fixtures are used to reduce the nonproductive time of any mass production process. The principle of location or the 3-2-1 principle, CAD tools (like ProE), and FEA tools (like ANSYS) are used for the design of the jigs as well the fixtures. The jig is used for guiding the cutting tool (like a drill bit), and for doing so, jigs have components like a bush, which comes in contact with the cutting tool. On the other hand, a fixture never comes in direct contact with the cutting tool. Fixtures assure the position and alignment of the work pieces for getting the required machining operation done.

What Is Thermal Equilibrium

What Is Thermal Equilibrium

When there are variations in temperature from point to point of an isolated system. the temperature at every point first changes with time. This rate of change decreases and eventually stops. When no further changes are observed, the system is said to be in thermal equilibrium.

Hydraulic Turbines

Hydraulic Turbines

A hydraulic turbine is a machine which converts the hydraulic energy into mechanical energy. The hydraulic turbines are also known as water turbines. Following two types of hydraulic turbines are important.

1.     Impulse turbine

2.     Reaction turbine

In an impulse turbine, the total energy at the inlet of a turbine is only kinetic energy. The pressure of water both at entering and leaving the vanes is atmospheric. It is used for high head of water. A Pelton wheel is a tangential flow impulse turbine.

In a reaction turbine, the total energy at the inlet of a turbine is kinetic energy as well as pressure energy. It is used for low head of water. The Francis and Kaplan turbines are inward flow and axial flow reaction turbines respectively.