Compressor

by: muhammad suhandi

Compressor is used to produce compressed air. This compressed air is used in many applications such as drilling, food processing, milling, tooling etc. Pressured air produced range from 25 psig (172 kPa) to 60,000 psig (413,790 kPa). Normally usage is in range 90 to 110 psig.

There are two designs for compressor, positive displacement and dynamic compressor. The positive displacement takes a constant volume of gas and compressed it. The dynamic compressor operates by transferring momentum from high speed rotor into the gas.

The efficiency of compressor is largely depends in many factors for instance the inlet gas temperature, leak in compression chamber and etc. The pressure ratio between inlet and outlet of compressor is limited by temperature rise and mechanical stress. To achieve higher pressure, compressor arranged in cascaded resulting multistage compressor.

As mention previously, there are two types of compressor. These two types are divided more,

1. Positive displacement
a. Reciprocating
· Single acting
· Double acting
· Diaphragm
b. Rotary
· Lobe
· Screw
· Scroll
· Vane
2. Dynamic
a. Centrifugal
b. Axial

Dynamic compressor relatively needed in applications that require high flow rates. The centrifugal type has impeller rotate inside housing and move the gas radial. The axial type has arrays of blade rotate in housing cause the gas to flow axially for instance in exhaust fan. The axial compressor used in gas turbine and in many applications in plants.

Positive displacement pump needed in applications require high pressure. It relatively has larger volumetric efficiency compare to dynamic compressor. The reciprocating pump consists of pistons moved by crankshaft that further turned by electric motor or internal combustion engine. This type of compressor ranging from small horse power 5 to 30 HP such as in automotive and as large as 1000 HP such as used in oil and gas industry. This type is said to be the most efficient compressor. Rotary screw compressor consists of two positive displacement screws in mesh that force the gas to flow into continuously space becoming smaller.

Because the increases of fuel price the manufactures around the world continuously strive to design the more efficient compressor. They compete not only in the more efficient but also more inexpensive price offered to customers.

Modern compressor is controlled by sophisticated electronic control. With multiple option of operation we can select the optimum state the way the compressor works.

Mechanical Bearing

by: muhammad suhandi

Bearing is the one of the most important and as basic element of machinery. The function of bearing is to reduce friction. Bearing is the one component to be sacrificed. Bearing also limits the motion of two parts. Material used to make bearings are weaker that the shaft or components where those bearings should be installed.

There many types of bearing but mainly in mechanical engineering, bearing is divided as sliding bearing means that shaft is sliding in inner face of bearing and antifriction bearing means that this bearing reduce large portion of friction than sliding bearing. Antifriction bearing further divided into two types, roller bearing and ball bearing. Antifriction bearing has three main parts, the inner race, outer race and balls or rollers. Balls or rollers slide and rotate between inner and outer race.

Sleeve bearing and sometime called bushing used in high speed application such as in connecting rod and crankshaft of internal combustion engine. Antifriction bearing has more rigid construction and used in low speed high load application such as transmission and differential.

Although bearings reduce large portion of friction, they still need lubrication. Bearing that running in unlubricated condition will instantly collapse. There is varying method of lubrication. From the simplest one which we could lubricate in scheduled time by putting enough lubrication manually until pressurized system that contains complex components to assure all the bearing get its lubrication.

Whit the advance in technology and the complexity, some bearing even do not need lubrication. Such bearing could be made using magnetic action or use pressurized air as bearing so there is no contact between metal. Also now the manufactures have produced bearing made of plastic and rubber.

Electric Motor

by: muhammad suhandi

Electric Motor is a device that converts electrical energy to mechanical energy. Principally there are two types of electric motor, DC motor and AC motor. AC motor is sometime named induction motor. It is used to make distinction between synchronous motor and asynchronous motor. All types of electrical motor have the same main construction. It is formed by two main parts. The rotor that rotates and stator that always in stationer.

Other terms we usually encountered in electrical motor is armature and field. Armature is the component that housing the winding or the conductor, which the electrical power comes. Field is winding provides the magnetic field to as an important factor to convert electrical energy into mechanical energy.

Every electrical motor has its armature and field. Now we explain the DC motor. DC motor is the motor supplied by DC voltage and current source. Its armature is in the rotor and the field in it’s a stator. DC motor usually used in industry because its rotation is easy to manipulate. But because our utility supplied AC sources, the need for a rectifier is rised. So it is rather expensive if we use this type of motor for large application. Now the DC motor is dominant in low power spectrum.

Because the nature of our utility industry is AC, the need for motor that supplied by this type of sources is rised. First is syncronous motor. This type of motor actually same as generator but work in reverse direction. Its contruction is all the same as generator. This motor has limited application because its dificulty to handle its speed. Syncronous motor is mainly used as synchronous capacitor.

In early twentieth century, Tesla an electrical engineer came with idea to design the motor that supplied by AC sources. Its construction is actually same as a transformer except it has an air gap to make it rotates. The induction motor has two types that depend on its rotor construction, squirrel-cage rotor and wound rotor. The analysis of induction motor is the same for transformer except we should introduce the speed parameter.

Induction motor is mainly used to drive large load in industry. These motors supplied by three phase AC source. For home appliances because our utility outlet is single phase in nature we used single phase induction motor.

The isueses of global warming, increase oil price has force the engineers to install electrical motors in our cars. The type of motor could be DC or even induction motor. There is hybrid car that moved by two sources, the internal combustion engine and electrical motor supplied by batteries. For pure electrical cars, no engine installed. All wheels moved by electrical motor supplied by batteries that could be charged from our utility outlet. That is the future.

Gas Turbine

by: muhammad suhandi

Gas turbine is a energy conversation that covert thermal energy from burning fuel into mechanical energy. Gas turbine is second popular from internal combustion engine like diesel engine and gasoline engine.

Gas turbine is installed in air plane, power plant, large ship and even vehicle.

How the turbine gas works?. Gas turbine is constructed from three main parts, a compressor, combustion chamber and turbine. This arrangement depends on for what application the gas turbine installed. The simplest arrangement is for air plane. In this type the compressor and turbine are in one shaft.
Compressor is used to compress air for combustion. The fuel for gas turbine is a form of gasoline but lighter. This fuel is very easy to flash. In power plant, the fuel is natural gas. The burning fuel results very high temperature and pressure. This pressure is then used to rotate the turbine. In here the energy conversion is take place.

The principal of turbine gas is from Brayton cycle. The efficiency of turbine gas can achieves as high as 50%.

Base on its application, in aviation, the turbine section is made short because the function of turbine is just for rotates the compressor. Actually the turbine gas for aviation is used to make a trust from burning gas. In power plant, the turbine section connected directly to generator. It is relatively long because almost all the power resulting from burning is used to rotate generator.

Turbine gas in power plant also has modification. Its exhaust gas is usually reused by recycling it to rotate the turbine once more or to rotate another turbine. From this mechanism, the efficiency of turbine gas is increase.

Wood Gas - The Future Biomass-Derived Fuel

by: Krzysztof Lis

Let's assume, that you own a farm. You produce grain and have a lot of straw. You'd like to make your energy on site from the biomass you have available. You might plant your fields with rapeseed or canola and produce biodiesel. But you'd need to get methanol and lye first, since both of them can't be made there! And you can use your biodiesel only in compression ignition (diesel) engines. And what if you have an old genset powered by spark-ignition (gasoline / petrol) engine? I think I might have a solution for you...

You'll make use of a technology that's more than 200 years old. It's greatest development took place during World War II in 1940s in Europe. At that time most of petroleum-derived fuels were used by military and there was no fuel left for civilians. So they made their own fuel, the wood gas from wood or charcoal. In some countries 95% of civilian transport (trucks, buses, even fishermen's boats) were fueled with this gas.

What is this wood gas? From chemical point of view it's a mixture of combustible carbon monoxide (CO), hydrogen (H2) and methane (CH4), dilluted with some water vapor, carbon dioxide (CO2) and nitrogen (N2). This gas can be easily used for almost every internal combustion engine. Well... except for the most modern ones, they'd require to have their electronics to be modified.

How wood gas is made? When you heat wood it is pyrolysed, i.e. all the tars vaporize. When you add some oxygen, the carbon bound within the wood cells is burnt to carbon dioxide. The vapors burn too. When those burnt gasses pass through a layer of very hot char, they are reduced to carbon monoxide and hydrogen. A small amount of methane is also produced. When the gas is cooled and cleaned of any tars and particles, it can be used in internal combustion engine, boiler or any other device!

What do you need to produce your own wood gas? You'd need a device that's called gasifier. It consists of fuel hopper, gasifying chamber and a set of filters. It's very easy to build, the people during WWII made it out of old water heaters and stuff like that.

Is wood gas safe? Well, if you don't inhale it, you'll be OK. Carbon monoxide is very toxic and poisonous, so caution is required when using wood gas. From the engine point of view, if it's clean, it's safe. The tars might condense inside the engine, for example on valves, which might cause the engine to fail. The particles would probably destroy the contact surfaces on pistons and cylinders. If the gas is too hot the engine will not work (hot gas is diluted and has small energy content per unit volume), but it will not harm it.

Any drawbacks? One that's worth mentioning. Petrol engines will suffer 1/3 power loss -- the wood gas does have small heating value. Diesel engines will not suffer such power loss, since they work on stratified mixtures and because of that you can introduce more wood gas to recover the power loss. You'd need to leave some small amount of diesel to be injected to the cylinders to ignite the wood gas.

Interested? One liter of petrol / gasoline can be replaced with 2.5 - 4 kg (5.5 - 9 lbs) of wood. How cool is that!