An air receiver stores compressed air and can reject heat through its wall when the air is hotter than the surroundings. Cooling can condense some water vapor, which must be separated and drained; it does not automatically make the outlet air dry. This diagram illustrates those functions. The calculator compares an entered volume-per-flow factor and temperature difference, rather than predicting heat transfer or a required receiver size.
Air-cooling Receiver Interactive Calculator
Compare volume from an entered gallons-per-CFM factor, two fixed comparison factors and an entered temperature difference. Cooling performance and required receiver size are not solved.
Equation Used
The volume result is compressor flow multiplied by an entered factor in gallons per CFM. The other volume cards use fixed factors of 4 and 6 for comparison. These factors are not verified design limits or a FIRGELLI equipment specification. Receiver selection requires the actual demand profile, pressure range, control requirements and equipment data.
- Applies to shop compressed-air receivers used as passive aftercoolers.
- The 4 and 6 gal/CFM cards are arithmetic comparison cases, not a recommended band.
- An assumed factor of 4.8 gal/CFM at 25 CFM gives 120 gallons; this is not a calculated minimum.
- Temperature difference is entered inlet minus entered outlet, clamped at zero. The outlet temperature is not predicted.
Storage, heat loss and condensate
A receiver provides gas volume between compressor supply and downstream demand. Its larger flow area can reduce bulk velocity, while the vessel wall exchanges heat with the surroundings. Heat transfer, rather than slowing the gas by itself, determines cooling.
When compressed air cools below its pressure dew point, some vapor condenses. Collected liquid must be drained. Water vapor remains in the gas, and droplets can still be carried downstream, so a receiver alone does not guarantee dry air.
Main components
- Rated vessel: contains the compressed air.
- Inlet and outlet connections: connect the vessel to the system.
- Drain: removes collected liquid at the appropriate low point.
- Pressure indication and protective equipment: support operation within the equipment’s requirements.
Vessel wall thickness, support, port arrangement, relief capacity and settings require the applicable design and installation rules. They cannot be chosen from this volume multiplier. A generic percentage above compressor cut-out is not a complete relief-valve specification.
Where a receiver fits
Receivers can buffer demand peaks, reduce pressure fluctuations and provide storage appropriate to compressor controls. Their position relative to aftercoolers, filters and dryers affects how the complete air-treatment system behaves.
A wet receiver and a dry receiver serve different positions in that system; there is no universal volume split that makes two tanks better than one. Cooling and moisture removal depend on inlet conditions, ambient conditions, heat-transfer area, flow distribution and the downstream requirement.
Use this calculator to compare an assumed ratio of volume to compressor flow. It does not select treatment equipment or establish air quality for a process.
The comparison calculation
Let Q be entered compressor flow in CFM and F an entered factor in gal/CFM. Comparison volume is V = QF in gallons. The additional volume cards calculate 4Q and 6Q. Those are fixed examples, not engineering minimum and maximum sizes.
The temperature card calculates max(0, Tin − Tout) in degrees Fahrenheit. Both temperatures are inputs. If the entered outlet is hotter than the inlet, the card reports zero rather than a negative drop; that does not demonstrate cooling.
Actual storage sizing needs an allowable pressure range and the time and magnitude of supply-demand imbalance. A volume-per-CFM multiplier alone does not include them. The calculator also has no operating pressure, humidity, ambient temperature, heat-transfer coefficient or vessel surface-area input, so it cannot predict residence time, condensation, dew point or outlet temperature.
A nominal throughflow residence time would involve vessel volume divided by actual volumetric flow at vessel conditions. It is not an arbitrary shortened fraction of stored-air inventory. At zero throughflow, a finite throughflow residence time is not defined. Even a valid residence-time estimate would not by itself establish an outlet temperature.
Worked example: assumed factor and temperatures
Enter Q = 25 CFM and F = 4.8 gal/CFM. The selected comparison volume is 25 × 4.8 = 120 gallons. The fixed 4x and 6x cards give 100 and 150 gallons.
If the inlet temperature is entered as 250°F and outlet as 110°F, the temperature difference is 140°F. This is subtraction of two supplied values, not a prediction that a 120-gallon receiver will cool air to 110°F.
Doubling flow to 50 CFM at the same factor doubles the comparison volume to 240 gallons, but does not prove equivalent cooling or suitable control behavior. If the entered outlet temperature exceeds the inlet, the temperature card is clamped to zero.
Different compressed-air functions
| Component | Principal function | What it does not establish alone |
|---|---|---|
| Receiver | Stores compressed air; may reject heat and collect condensate. | A specified dry-air quality or adequate continuous supply. |
| Aftercooler and separator | Reject heat and remove collected liquid. | All downstream moisture or contamination limits. |
| Dryer | Reduces water content to its rated conditions. | Storage volume or unrestricted tolerance of hot, wet inlet air. |
These devices can complement one another. Compare their rated inlet conditions, flows, pressure losses and output requirements rather than treating one as a universal substitute for another.
Receiver calculation questions
No. It is flow multiplied by an entered factor. The fixed 4x and 6x cards are comparisons, not validated sizing limits.
No. The outlet temperature is entered directly. The difference card subtracts it from inlet temperature and clamps the result to zero.
No. Water vapor can remain after liquid separation. Required pressure dew point and downstream conditions determine whether further drying is needed.
No. Heat-transfer area, ambient conditions, inlet conditions, flow distribution and moisture behavior matter. They are not represented by this multiplier.
It can supply stored air temporarily over an allowed pressure range. It cannot sustain average consumption greater than compressor supply indefinitely.
No universal orientation follows from this calculator. Use the vessel’s designed supports, installation orientation and drainage arrangement.
No. Protective equipment and alterations must follow the applicable vessel, manufacturer and jurisdictional requirements. This comparison tool does not authorize welding, new ports or changed protection settings.
No. Drainage must prevent excessive liquid accumulation under the actual conditions and applicable instructions. The calculator does not determine condensate production or a maintenance schedule.
References and further reading
U.S. Department of Energy: Improving Compressed Air System Performance explains receiver storage and air-system assessment. OSHA 1910.169: Air Receivers addresses drainage, indication and protective equipment within its stated scope. These sources do not validate a universal 4–6 gal/CFM sizing requirement.
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