Dew point u. dew

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1. What is dew point?

What is the difference between dew point and pressure dew point?

 

The term "pressure dew point" is used when the

Dew point temperature of gases at pressures above the

Ambient pressure is measured. These are

So the dew point temperature of a pressurized

standing gas. This is of particular importance since

If the pressure changes, the dew point temperature of the

relevant gas changes.

 

 

What influence does the pressure have on the dew point?

 

With increasing gas pressure also increases

Dew point temperature. The following is an example

of air at ambient pressure of 1013.3 mbar and a

Dewpoint temperature of -10 ° C explained. Gemas

the above table is the water vapor partial pressure

(indicated by "e") 2.8 mbar. Compresses

now this air, doubling the total pressure to 2,026.6

mbar, doubles according to Dalton's law

also the partial pressure of water vapor (e) to a value of

5.6 mbar. This value of 5.6 mbar now corresponds to one

Dew point temperature of about -1 ° C. Thus increases with the

Air pressure also the dew point temperature of the air. Vice versa

decrease with expansion of a compressed gas

Ambient pressure the partial pressures of all gas components

including that of water vapor, so that the

Dew point temperature of the gas decreases. The relationship

between the total pressure to the water vapor partial pressure, e,

can be described as follows:

 

P1 / P2 = e1 / e2

 

After the conversion of the dew point temperature into

the corresponding saturation vapor pressure let itself

easily the influence of the change of the total pressure on

calculate the saturation vapor pressure. The calculated

Saturation vapor pressure can then return to the

corresponding dew point temperature to be converted.

These calculations can be done using tables

but they are also done through a series of programs.

 

 

 

Why is knowledge about the dew point of the compressed air important?

 

The meaning of the dew point temperature of the compressed air

depends on their respective purpose.

In many cases, the question about the dew point

disregarded (portable compressors for

Pneumatic tools, tire pressure systems at petrol stations, etc.).

In some cases, the dew point is only important because the lines,

through which the air flows, temperatures below freezing

are exposed, where too high a dew point

can lead to freezing and blocking of the lines.

 

Many modern industrial plants use compressed air for operation

various systems whose function in condensate formation

internal parts can be affected.

Some water sensitive processes using compressed air

Working (eg spray painting) can be very demanding

to the degree of drying. For medical and

pharmaceutical processes can be steam or other

Gases represent a "pollution", so very high

Purity levels are required.

 

 

 

Which dew point temperature range is typical for compressed air?

 

The dew point temperatures of compressed air range from ambient down to -80 ° C, in some cases even lower. Compressor systems without air drying tend to produce compressed air that is saturated at ambient temperature. Systems with refrigeration dryers direct the compressed air through a cooled heat exchanger, so that the moisture from the air flow condenses. Such systems typically produce compressed air with a dew point not lower than +3 ° C. With

Desiccant drying systems absorb the water vapor from the air stream, reaching dew points of -40 ° C tp and below.

What is the difference between dew point and pressure dew point?
 

The term "pressure dew point" is used when the

Dew point temperature of gases at pressures above the

Ambient pressure is measured. These are

So the dew point temperature of a pressurized

standing gas. This is of particular importance since

If the pressure changes, the dew point temperature of the

relevant gas changes.

 

 

What influence does the pressure have on the dew point?
 

With increasing gas pressure also increases

Dew point temperature. The following is an example

of air at ambient pressure of 1013.3 mbar and a

Dewpoint temperature of -10 ° C explained. Gemas

the above table is the water vapor partial pressure

(indicated by "e") 2.8 mbar. Compresses

now this air, doubling the total pressure to 2,026.6

mbar, doubles according to Dalton's law

also the partial pressure of water vapor (e) to a value of

5.6 mbar. This value of 5.6 mbar now corresponds to one

Dew point temperature of about -1 ° C. Thus increases with the

Air pressure also the dew point temperature of the air. Vice versa

decrease with expansion of a compressed gas

Ambient pressure the partial pressures of all gas components

including that of water vapor, so that the

Dew point temperature of the gas decreases. The relationship

between the total pressure to the water vapor partial pressure, e,

can be described as follows:

 

P1 / P2 = e1 / e2

 

After the conversion of the dew point temperature into

the corresponding saturation vapor pressure let itself

easily the influence of the change of the total pressure on

calculate the saturation vapor pressure. The calculated

Saturation vapor pressure can then return to the

corresponding dew point temperature to be converted.

These calculations can be done using tables

but they are also done through a series of programs.

 

 

 

Why is knowledge about the dew point of the compressed air important?
 

The meaning of the dew point temperature of the compressed air

depends on their respective purpose.

In many cases, the question about the dew point

disregarded (portable compressors for

Pneumatic tools, tire pressure systems at petrol stations, etc.).

In some cases, the dew point is only important because the lines,

through which the air flows, temperatures below freezing

are exposed, where too high a dew point

can lead to freezing and blocking of the lines.

 

Many modern industrial plants use compressed air for operation

various systems whose function in condensate formation

internal parts can be affected.

Some water sensitive processes using compressed air

Working (eg spray painting) can be very demanding

to the degree of drying. For medical and

pharmaceutical processes can be steam or other

Gases represent a "pollution", so very high

Purity levels are required.

Which dew point temperature range is typical for compressed air?
 
The dew point temperatures of compressed air range from ambient down to -80 ° C, in some cases even lower. Compressor systems without air drying tend to produce compressed air that is saturated at ambient temperature. Systems with refrigeration dryers direct the compressed air through a cooled heat exchanger, so that the moisture from the air flow condenses. Such systems typically produce compressed air with a dew point not lower than +3 ° C. With

Desiccant drying systems absorb the water vapor from the air stream, reaching dew points of -40 ° C tp and below.

How is the dew point reliably measured in compressed air?

 

Certain principles of dew point measurement apply

regardless of the manufacturer for all types of measuring instruments:

 

• Select a device with the correct measuring range:

 

Some meters are only suitable for measuring high

Dew point temperatures, and vice versa there are devices

with which very low dew point temperatures were measured

can not, but at high dew points not

work properly.

 

• Consider the pressure sensitivity of the dew point meter:

 

Some gauges are not for use below

Process pressure suitable. They can be mounted

to measure the compressed air after it has been released to ambient pressure.

However, if the pressure dew point to be measured, the

measured dew point value can be corrected later.

 

• Correct sensor mounting:

 

Follow the recommendations

of the manufacturer. The installation of dew point sensors should

not at the end of nozzles or other pipe ends

take place where the air can not circulate.

 

 

TPS manufactures meters that are ideal for measuring the dew point temperature in compressed air.

The TPS sensor technology enables fast

Dew point measurements with an accuracy of ?? +/- 2 ° C over

a measuring range that is at ambient temperature

begins and reaches up to a dew point of -80 ° C.

 

In addition to the above principles, you should

also the following aspects in the choice and the installation

of a TPS dew point meter take into account:

 

A. In the best case, the dew point sensor is used by the

Built-in compressed air line isolated. This is done by the

Mounting the sensor in a sampling cell,

in turn via a T-piece with the compressed air line

connected at the measuring point. So is always a small

Quantity of compressed air passed the sensor. The cell

should be made of stainless steel and piping

(1/4 "or 6 mm) can be connected to the tee.

It is recommended to install a shut-off valve

between cell and compressed air line. This will be the installation and removal

greatly eased the sensor.

 

B. The use of a flow restrictor makes sense

to control the flow of air through the sensor

can. The necessary volume flow is only

1 l / min. For flow limitation, both a

Drain plug and a valve can be provided.

To measure the pressure dew point, the

Flow restriction arranged after the sensor,

so that after opening the shut-off valve, the sensor

is exposed to the process pressure. To measure the

Dew point at ambient pressure should be the

Flow limitation before the dew point sensor

are located.

 

C. The recommended volume flow must not be exceeded

become. When measuring the pressure dew point leads a

increased volume flow to a local pressure drop at

Sensor. Since the dew point temperature is pressure-dependent,

this leads to a measurement error.

 

D. The optimal material for the pipeline is

stainless steel. Non-metallic pipes can

Desorb and desorb water vapor and cause

thus a delay in the measurement results.

Are no stainless steel tubes available, offer

PTFE or other materials that are not water

absorb. Transparent plastic pipes or yellow

Rubber tubes should not be used.

 

E. Through an installation directly into a compressed air line

can be used with permanently installed dew point measuring devices

Achieve cost savings during assembly. In these

Cases you should be careful that you are looking for the sensor

find a place with sufficient airflow and

the temperature of the compressed air near or equal to the

Ambient temperature is.

 

 

 

What are the signs of the failure of a dew point sensor?

 

• The meter shows on the display or analogue output

unchanged, the same measured value.

 

• The meter always displays the lowest possible value.

 

• The meter is unstable and shows over a wide area

Value range quickly changing or random values.

 

• The meter shows silly high or low

Dew point values ​​on.

 

 

How often should a dew point sensor be tested or calibrated?

 

Always follow the manufacturer's recommendations.

Depending on the instrument, TPS recommends a calibration interval of one or two years. Sometimes a simple on-site test with a calibrated one is enough

portable meter to check the proper operation of other meters.

 

Detailed calibration information can be found in the user manual,

that comes with every device. If in doubt about the correct

Operation of a dew point measuring device, should first the

Calibration state to be checked.

 

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