![]() How Inlet Air Temperature Impacts Different Types of Compressors Volumetric Efficiency: This is the inlet volume flow (icfm) divided by the ideal flow with no slip or “displacement.” Isothermal efficiency is the ideal isothermal power divided by the actual power. This is closer to how an oil-injected screw compressor works, particularly a multi-stage unit or a centrifugal with many stages and inter-cooling between stages. Interestingly, it is quite “efficient” to compress this way. Isothermal Compression: This is an ideal model of compression when all the heat is transferred out of the compressor, and temperature is constant through compression. Adiabatic efficiency is the ideal adiabatic power divided by the actual power. ![]() Two-stage, oil-free compressors with inter-cooling have good efficiency, but they behave like “adiabatic” compressors as far as the inlet temperature is concerned. This is closer to the way a single-stage, oil-free screw compressor works. Interestingly, it is not particularly “efficient” to compress this way. Isentropic (or Adiabatic) Compression: This is an ideal model of compression when no heat is transferred out of the compressor, as if the walls of the compression chamber are insulated, and temperature goes way up. This is what you would measure with a mass flow meter at the discharge of a compressor that compensates the measurement with pressure and temperature. ![]() It is essentially mass flow divided by a constant. Standard cubic feet per minute (scfm): This is the delivered airflow in volume, converted to a standard reference point that doesn’t exist in the actual compressed air system. This is what you could measure at the inlet of a compressor using a velocity measurement like a pitot tube. It is at actual conditions, uncorrected for density. Inlet cubic feet per minute (icfm): This is the airflow rate in actual volume per time units at the intake of a compressor. This article will discuss the following two factors that impact efficiency: (1) The Type of Compressor, and (2) The Compressor Controls.īefore I launch into the article, let’s define several key terms: In summary, inlet air temperature has a modest impact on compressor efficiency, depending on the situation. The goal of this article is to debunk a few misconceptions, and show how inlet air temperature actually affects compressor efficiency in three kinds of systems. But, what if non-compressed air could be seen as “free?” Is there something we can get for free from nature to reduce the cost of our compressed air? What if lower temperature intake air was nature’s gift? What if all we need is a bit of tin to duct air from a different source? Pressure loss in pneumatic tubes - sizes ranging 5 - 36 mm.There is a partly true idea floating around some plant maintenance circles that “compressed air is free.” Readers of this journal know that isn’t true. Pressure drop in compressed air pipe lines.Ĭompressed air is used for power tools, instrumentation, processing, breathing and medical purposes.Ĭalculate horsepower required by air compressors.Ĭylinder volume and compression ratios in piston engines. ![]() Pressure loss in compressed air pipe lines.Ĭalculate the storage volume of compressed air or other gases.Ĭapacities of compressed air pipelines - pressure ranging 5 - 250 psi (0.5 - 17 bar).Ĭompressed Air Pipe Lines - Pressure Loss vs. Q C = compressed air flow (m 3/s, cfm) Example - Converting Compressed Air Volume Flow to Free Air Volume FlowĪ compressed air volume flow of 10 acfm (actual cfm) at 100 psig must be multiplied with Compression Ratio approximately 8 to estimate the volume of free air at atmospheric pressure.Įxample - Converting Free Air Volume Flow to Compressed Air Volume FlowĪ free air volume flow of 1 m 3/s is compressed to 10 bar (gauge) and must be divided with Compression Ratio approximately 11 to estimate the volume of compressed air.Īir, LNG, LPG and other common gas properties, pipeline capacities, sizing of relief valves.Ĭompressed Air - Pipe Line Pressure Drop DiagramĬalculate pressure drop in compressed air pipe lines with a nomograph diagram.Ĭompressed Air - Pipe Line Pressure Loss - Online Calculator with Metric and Imperial UnitsĬalculate pressure drop in compressed air pipe lines - metric and imperial units.Ĭompressed Air - Pressure Drop Diagrams, Metric Units The compression ratio of free air - to compressed air, is indicated in the diagram below.Ĭonverting Compressed Air Volume Flow to Free Air Volume FlowĪ compressed air volume flow can be converted to a free air volume flow by using the equation P s = suction absolute pressure (bar abs, psia) P d = discharge absolute pressure (bar abs, psia) Free air is air at ambient conditions at a specific location whereĬompression Ratio is based on the Ideal Gas Law and is the ratio between Discharge Pressure Absolute and Suction Pressure Absolute.
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