compressor work input..

Raj,

In laymans terms....person A can dominate Person B if Person B possess less energy..........

here Person A( Work done by compression) can Dominate Person B (Gas to be Compressed) if it has less energy i,e. less temperature(Temperature of Gas in Compressor to be compressed)

Hence u require less energy for compression if temperature of Gas is less

but at constant volume if we reduce the temperature , pressure will reduce.then wat's the use of copmressing it?

When you compress a gas, the module requires more heat to compress, thus the suction side of the compress is cold and when the compress gas is released, the gas give off the heat that is took in when the molecule expands, so the discharge is hot.

When gas is compressed it heats up (and it cools when expanding). When hot compressed gas cools its pressure will come down, and so if you can cool it as it is being compressed you can pack much more air into a tank at a given pressure. If on the other hand you have a tank which is insulated so well that heat cannot leak away, there is no need to cool the air to achieve a pressure. Of course such a perfectly insulated tank is a fiction, and so it is a good plan to cool the air while compressing it.

plez want more explanation..i can't understand wat it is?" If on the other hand you have a tank which is insulated so well that heat cannot leak away, there is no need to cool the air to achieve a pressure. Of course such a perfectly insulated tank is a fiction, and so it is a good plan to cool the air while compressing it." 'heat cannot leak away'- 'good plan to cool'.....contradicting!!!

In most cases a compressor is used to pack as much mass of air as possible into a tank, and then it makes sense to cool it as it is being compressed. The cooler the air going into a tank, the more would be its mass. But if you just want pressure, then it makes sense to avoid the cooling because you do lose energy in the cooling. In a jet engine for example the hot air from the compressor goes directly into the combustion chambers, where as when you want to fill your tires you need high pressure at ambient temperature. If you fill a tire with hot compressed air you will find the pressue going down as the air cools. So there is no contradiction.

hello sir,sorry for my stupid doubts. you said ' if we just want pressure, then it makes sense to avoid the cooling because you do lose energy in the cooling'.then wat we want from the compressor,simply pressure or something else.

When compressed air is made to do work in a pneumatic motor, it will be better to start with hot air because it will cool as work is extracted from it. The work done is a function of the pressure and volume, not mass. But when you are trying to extract more power from an engine by packing more air into the cylinders (supercharging), then mass counts, as the energy of the chemical reaction of burning is greater as the mass of air (and fuel) goes up. So in this case cold compressed air is better. This is what I meant when I said it depends on what you want from the compressor.

sir ,thanks a lot ...

It the mass of the gas you need to watch. A hot tank has less mass.

The work is minimized on per mass basis not volumetric.