What is Ambient Pressure?
What is atmospheric pressure?
What is ambient pressure: Ambient pressure refers to the atmospheric pressure, or liquid pressure, acting on an object at a specific location. For objects on land, ambient pressure generally refers to the atmospheric pressure at their location.
What is atmospheric pressure: From the perspective of molecular motion, atmospheric pressure is the result of the combined effect of the irregular motion of air molecules and the earth gravity.
The greater the density of air molecules, the more collisions of air molecules an object receives per unit area, and the greater the atmospheric pressure it receives.
And because of the earth’s gravity, the density of air at sea level (when the altitude is 0) is the highest, so the atmospheric pressure at sea level is the maximum.
The standard atmospheric pressure at sea level is approximately 101.325 kPa. As the altitude increases, the atmospheric pressure gradually decreases. At an altitude of 2,000 meters, the atmospheric pressure will drop significantly. For every 100 meters of altitude increase, atmospheric pressure decreases by approximately 0.12 kPa.
How is atmospheric pressure measured
The famous Magdeburg hemisphere experiment proved the existence of atmospheric pressure. In 1640, Italian scientist Evangelista Torricelli realized that the pressure exerted by the air in the atmosphere on the mercury in the basin was equal to the weight of the mercury pressed into the glass tube by it.
So people calculated the atmospheric pressure based on the density of mercury and the height of the mercury column in the glass tube, and invented the initial instrument for meteorological research: the barometer.
The calculation formula is: P = ρgh 【wherein: ρ = mercury density, g = 9.8 m/s², h = height of the mercury column】
Therefore, later in meteorology, people generally use millimeters of mercury column (mmHg) or kilopascals (kPa) as the unit of atmospheric pressure.
And it is stipulated that the atmospheric pressure at sea level with a temperature of 0℃ and a latitude of 45 degrees is a standard atmospheric pressure, which is approximately equal to the weight of a mercury column 760 mm high, which is equivalent to an atmospheric pressure of 1.0336 kg on an area of 1 square centimeter.
Different places have different atmospheric pressures. The most obvious example is that air pressure varies not only with altitude, but also with temperature. Changes in air pressure at the same location are closely related to weather changes.
What is absolute pressure and gauge pressure?
Absolute pressure and gauge pressure (relative pressure) are two different ways of measuring pressure, which differ in definition and application. When a barometer is used to measure the local ambient pressure, the gauge pressure is obtained.
Absolute pressure: Absolute pressure is the pressure calculated from absolute vacuum. It represents all pressures in the space where the medium is located.
It is often used in situations where the true pressure of the medium needs to be accurately measured, such as vacuum and negative pressure fields.
Gauge pressure: Gauge pressure is the pressure calculated from the atmospheric pressure at that time and place. When the measured system pressure is higher than the atmospheric pressure, the gauge pressure is positive, vice versa.
In our daily life, we usually use gauge pressure to calculate air pressure. such as water pressure gauges, barometers, pressure gauges on air compressor tanks, etc., because it reflects the change of pressure in the container relative to the atmospheric pressure.
Absolute pressure and gauge pressure can be converted into each other through atmospheric pressure: Absolute pressure = gauge pressure + 1 atm pressure. Gauge pressure = absolute pressure – 1 atm pressure. It is gauge pressure that we usually use to calculate air pressure in daily life.
The Impact of Ambient Pressure on Air Compressors
How ambient pressure affects air compressor
According to the principle of atmospheric pressure generation, when the ambient pressure at a specific location decreases, the density of the air will also decrease, and the air compressor can obtain less air mass each time it inhales.
This causes the compression ratio of the air compressor (the ratio of exhaust pressure to ambient pressure) to increase. Studies have shown that for every 0.01MPa decrease in ambient pressure, the compression ratio of the air compressor will increase by 6% to 8%.
Why ambient pressure is important to air compressor?
The increase in compression ratio means that the air compressor needs to consume more energy to compress the same volume of air. Therefore, the higher the altitude of the use area, the lower the atmospheric pressure, and the greater the energy consumption of the air compressor.
In addition, changes in ambient pressure will also affect the performance of the lubricating oil in oil-lubricated air compressors. A drop in ambient pressure will reduce the affinity between oil molecules, causing the oil viscosity to drop and the air compressor performance to decline.
When using an air compressor on a plateau or in a high-altitude area, it is necessary to select an air compressor model with larger rated power. The speed of the compressor can also be appropriately reduced to compensate for the impact of ambient pressure changes, but the speed adjustment range is limited.
In summary, the decrease in ambient pressure will directly lead to an increase in the compression energy consumption of the air compressor, and a decrease in the compression quality and working stability of the air compressor, so attention must be paid to the ambient pressure adaptability of the air compressor when selecting it.
How to Adjust Ambient Pressure for Air Compressors?
If you are an air compressor user in high altitude areas, in order to improve the performance and output compressed air quality of air compressors in high altitude or low ambient pressure areas, you can take the following measures:
Choose air compressor that designed for low ambient pressure: These air compressors usually have higher suction efficiency and better sealing performance, and can better adapt to the atmospheric pressure in high altitude areas.
Optimize the cooling system: Select powerful air compressor aftercooler that can maintain a stable operating temperature for air compressor even at high ambient temperatures, thereby improving air compressor efficiency and service life.
(Kotech diesel air compressor with external high-efficiency aftercooler)
Choose lubricants suitable for high altitude or low ambient pressure: High-quality compressor oil can reduce wear and friction losses of mechanical parts, thereby improving the efficiency of the air compressor.
Regular inspection and maintenance: Regularly check the sealing system, compressor oil and cooling system of the air compressor to detect and solve potential problems in a timely manner to ensure that the air compressor maintains the best operating condition under high altitude or low atmospheric pressure.
The impact of other ambient factors on air compressors
How ambient temperature affects air compressors
High ambient temp causes high power loss
The increase in ambient temperature will cause the air density to decrease, thereby reducing the air volume of the air compressor and increasing its shaft power.
Studies have shown that for every 3°C increase in ambient temperature, the shaft power of the air compressor increases by about 1%.
High ambient temp causes more energy consumption
Another reason why the ambient temperature increase leads to an increase in power is that the heat capacity of hot air is greater than that of cold air, and the air compressor needs to consume more energy for compression.
It can be seen that under high ambient temperature conditions in summer, the power consumption of the air compressor is significantly higher than that in winter.
High ambient temp causes less cooling effect
In addition, the increase in ambient temperature will also increase the exhaust temperature of the air compressor, increasing the heat dissipation and cooling loss.
In order to maintain a stable outlet temperature, the air compressor needs a higher cooling capacity to balance the loss, which will eventually lead to a greater operating power consumption of the air compressor.
How to adjust ambient temperature for air compressor
If the air compressor aftercooler power is insufficient, the internal operating temperature of the air compressor cannot be maintained at an ideal level, the efficiency of the air compressor will be greatly reduced, the wear will also increase significantly.
Therefore, it is worth considering to pay attention to ventilation and cooling in the compressor station, and even add an auxiliary air refrigerator to offset adverse effects of rising ambient temperature.
(Kotech KAD Series Refrigerated air dryer)
Effects of ambient humidity on air compressor
The higher the air humidity in the environment, the more water vapor is contained in the air. The air compressor needs to consume higher shaft power to compress the water vapor, so the energy consumption of operation will increase.
At the same time, the heat capacity of humid air is also greater than that of dry air, and the shaft power consumption is also greater when compressing humid air. During the compression process, some moisture will condense inside the air compressor, causing erosion and pollution to various air paths and components.
The effective exhaust volume of air compressors used in a humid environment will be reduced, which will not only affect the air supply effect but also make the subsequent operation of pneumatic equipment and system maintenance more difficult.
Therefore, the selection and use of air compressors need to consider the influence of ambient humidity, and pre treatment air dryer can be added for dehumidification when necessary. It is also necessary to keep the machine room dry to reduce the failure and loss of air compressors caused by ambient humidity.
(KTAD II Series Heatless Purge Desiccant Compress Air Dryer)
Impact of the cleanliness of ambient air
If the dust, sulfide or other hydrocarbons in the ambient air exceed the normal standard, it will not only affect ambient pressure of air compressor, but also have a great negative impact on the long-term operation of the air compressor.
The presence of these pollutants will greatly shorten the service life of the air compressor, increase maintenance and repair costs, and also cause the performance of the air compressor to decline.
Particulate matter in the air will also wear the negative pressure components of the air compressor, causing mechanical failure. In addition, the participation of dusty and sulfur-containing air in compression will reduce the heat exchange efficiency of the air compressor.
Overall, air pollution will not only impact the ambient pressure, but also reduce the overall performance of the air compressor. Therefore, it is necessary to control the cleanliness of the air environment and the working effect of the air compressor filters to ensure the high-efficient operation of the air compressor.
Conclusion
As the main body of the compressed air system, the operating status and performance of the air compressor are closely related to its working environment, such as ambient pressure, ambient temperature, air humidity, etc.
Changes in these factors may lead to negative effects such as decreased air flow, increased energy consumption, reduced operation efficiency, and shortened service life of the air compressor. Therefore, when selecting and using the air compressor, its environmental adaptability must be fully considered.
Take necessary measures such as dehumidification, installing additional air filters, and optimizing ventilation and cooling systems to optimize ambient pressure, temperature, etc., regular maintenance should be implemented as well.
Only when the air compressor is in a place with appropriate ambient pressure and ambient temperature can the unnecessary energy loss and maintenance cost be effectively reduced, and the good operation and performance of the air compressor can be ensured.
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