Compressed air basic theory - power and specific power

The basic theory of compressed air ( 3 )

     Power and specific power

( Energy consumption ratio , volume ratio can )

1 , compressor efficiency

Volumetric efficiency of the compressor and the theoretical volume of the actual gas volume ratio , expressed as a percentage .

A given amount of compression efficiency is a compressed gas is actually required power and the ratio of theoretical power . Theoretical power can be isothermal or adiabatic conditions working conditions to calculate . Corresponding compression efficiency can be determined and expressed as a percentage . On the steam -driven or internal combustion engine driven compressors , compressor mechanical efficiency is the indicated work of the shaft brake horsepower and fractional horsepower ratio . The motor-driven compressor , the mechanical efficiency is the compression in the cylinder axis indicates power and the power ratio of the compressor . Expressed as a percentage .

2, the overall efficiency

Overall efficiency of the compression efficiency of the compressor and the total mechanical efficiency .

Compressor shaft power ( braking power ) include: gas compression work - indicates power , friction power

Ni

Mechanical efficiency ηm =

Nad

Rough calculation : Nad = 1.634PjVm (k/k-1) [ε (k-1 / k) -1] Kw

N = N motor shaft / η biography , η Chuan ( belt: 0.92 to 0.98 gear : 0.97 to 0.99 )

Screw compressor, air compressor fan motor shaft power to add power .

3, the volume ratio can

Volume ratio of energy per unit time is sucked into the compressor unit of the power consumption of gas , usually Kw/M3/min that in the same volume ratio in the exhaust pressure can be smaller . Ie, less power consumption . The compressor efficiency is the true measure of efficiency compressor .

Specific power : required conditions : Pj = 1bar (A), tj = 20 ℃, ψ = 0, t = 15 ℃ water

Pc = 7bar ( table ) , water ≤ 2.5L/M3

Power is work done per unit of time , such as horsepower ( kW ) was set at 76Kg-m / h

Power is the energy conversion of measurable indicators .

To get the cost of power , we must also include time, for example : it costs money than kWh kWh.

Take and convert the horsepower into consuming user cost , we use the following equation:

Motor brake horsepower × 0.746 ( converted to kW ) × annual operating hours × power cost

Annual cost = -

Motor efficiency

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Noise and sound assessment

Is considered to be objectionable noise or interference sound .

User sits perfectly willing disco night , while smoking while enjoying up to 95 decibels disco music, but inconceivable that he had not tolerate the next morning 65 db noise copier . Users like disco noise not like the noise of the copier . A typical cocktail party noise is 90 decibels, the noise rock band is between 100-138 db .

So what is the decibel it ?

Db definition can be interpreted as the ratio of the two energy logarithm ( base 10 ) multiplied by 10.

W2

dB = 10log -

W1

An increase of 10 decibels increased energy 10:1 , an increase of 20 decibels increased energy 100:1 , increasing 30 db increased 1000:1.

For our application , we are discussing the sound power level - set W1 reference value 10-12 , the formula becomes:

PWL (dB) = 10log W/10-12

For example , if we have a sound source , issuing a 10-5 watt power level , that sound power is :

10-5

PWL = 10log - = 70dB

10-12

When the ear back to the noise, it was found that the ear is automatically " hear " low-frequency noise , very similar to the following "A" class networks.

Therefore, selection of industrial noise measurement standards are class "A" noise level, and use dBA terminology.

The noise due to reflection can be easily captured by the test probe , so setting another criterion . The standard requires that all noise measurements in the " open field conditions " under .

Measuring gas device sounds ANSIS51 rule states that : noise from the machine should be one meter , one five meters height measurements.

So here we have identified the location and measurement of test probe locations and with "A" class network measurement noise.

All manufacturers use these same basic provisions measurement noise .

If two same noise level of the machine run side by side , the results of the noise level will increase the 3dBA ( twice )

For example: In our original formula :

10-5

PWL = 10log - = 70dB

10-12

If we double our sound power level to 2 × 10-5

2 × 10-5

PWL = 10log - = 73 dB

10-12

A compressor manufacturer declares : +3 dBA noise level guarantees is its noise level is the noise level of their declaration double or half .

Two different speeds of the unit , may have the same noise level, but a completely different sounds . A more strident than another . This is because the noise is all according to the frequency spectrum is derived by adding a number to form dBA.

For measuring the noise level , the measured noise with each scale , with "A" anti- phase to assess and compare the derived number A (dBA).

All of these means:

1 , this means that we will not be due to reflection of a compressor is placed in the room, and expect to have in the open field conditions and the same noise level.

2 , we can not alone two different units ( at different speeds , different drivers , different components and different case ) the noise level can be wise to make a guess. The only way to measure the noise with a sound measuring device .

How do we overcome the significant difference in the noise level ?

1, through the accurate measurement of the noise level

2 , the noise level is by knowing how to rationally constituted specified frequency differences and harsh elements .

3 , knowing two have the same noise level , however, the frequency characteristics of different unit noise on the ear damage is the same, even if one does "sounds " Some lighter .

How can we further reduce noise ?

1 , ensure that all the body joint is safe forklift hole is closed , the unit on the ground substrate is a solid sealed .

2 , through the pipeline inlet and exhaust .

3, to reduce reflection noise .

Sound and noise measurement is at best just a very inexact science . For a discussion of this topic hoping to avoid the problem field , field correction substantial costs and user dissatisfaction .

1, all the noise levels measured using ANSLS51 standards. This is an industry standard . We should pass this standard used in reference to the reference noise level. In short, this standard requires the open field measurements ( non-reflective walls and roof ) , the unit around the multi-point measurement , and the measured values were averaged. Should be one meter away from the unit , the ground and on the basis of the level measured at 1.5 meters . Any single point measurements can be played referenced A noise level. As long as the average reading level to meet or below the reference . Moreover, the measurements are used to measure the average value of the noise should be wideband . When asked or given frequency band should be analyzed , some readings in the band can and often does mean higher than the noise measurement . Again noted that this is the standard accepted .

2 , the structure has not given in the standard and the applicable tolerances

3 , there is no real place in the wild, the unit should be written on the " open field " placement. In fact, the noise level in place rules always higher, because from nearby walls and roofs as well as nearby facilities or the distribution of reflection .

4 , the noise level may be submitted when the measured data should be used when a specific compressor actual measurements obtained in a same type compressor repeated under the same conditions can be interpreted as a typical operation of the noise level.

Note that

For any multi-point measurement or repeated compressor measurement, there is a certain error contact . These errors indicate the noise level to guarantee a particular compressor , it should be measured by the total value dBA plus three decibels. When given to a user when the noise level guarantees , obedience above requirements are absolutely necessary.

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Empirical formula

A compressor station 0.7MPa of gas per horsepower produced 0.1416M3

Pressure ｄｒｏｐ equal to 0.5% per 0.007MPa power

Air compressor heat load = HP × 2545BTU / time (1BTU = 1.055KJ)

Water-cooled compressor GPM ( liters of water per minute )

HP × 2545

500 × △ T water

Or, if △ T water = 11.1 ℃ ( closed loop ) for HP / 4

If △ T water = 22.2 ℃ ( urban water supply systems ) for the HP / 8

By 65% after the after cooler condensate has been removed

After the freeze- dryer 96% of the condensed water has been removed

Exhaust temperature is increased by 11 ℃, moisture will be doubled

Each 0.028M3 = 7.48 gallon = 28.31 liters = 1 cubic foot

Each compressor intake air to be equipped with M3 cylinder gas storage capacity of 133.5 liters

Deduced from the ideal gas law pump gas formula

Volume ( cubic meters ) × pressure rise (MPa)

Time ( minutes ) = ---------------

Volume ( cubic meters ) × 0.1013 (MPa)

Motor pulley size ( inches ) × compressor speed (RPM)

Motor pulley size ( inches ) = motor speed (RPM)