This is a step-by-step, illustrative walkthrough of sizing a vertical ammonia suction accumulator for a representative liquid overfeed system, from refrigeration duty to a vessel selection. Every number below is a plausible, rounded placeholder value, marked [ELI-REVIEW], for the site owner to check or replace before this page is published — it is not a validated engineering calculation and must not be used for an actual project. To run the same calculation on your own system data, use the Vessel Sizer directly.
1. Starting duty and assumptions
| Parameter | Assumed value |
|---|---|
| Refrigerant | Ammonia (R-717) |
| Saturated suction temperature (SST) | [ELI-REVIEW: −20°F] |
| Refrigeration load (TR) | [ELI-REVIEW: 100 tons] |
| Liquid overfeed ratio | [ELI-REVIEW: 3:1] |
| Orientation | Vertical |
| Mist eliminator | None |
| Ammonia liquid density at SST | [ELI-REVIEW: approximately 42 lb/ft³] |
| Ammonia vapor density at SST | [ELI-REVIEW: approximately 0.65 lb/ft³] |
| Ammonia latent heat at SST | [ELI-REVIEW: approximately 560 Btu/lb] |
2. Compressor vapor mass flow
Converting refrigeration load to a heat-rejection rate and dividing by latent heat gives the vapor mass flow the compressor pulls from the accumulator at design load: [ELI-REVIEW: 100 TR × 12,000 Btu/hr per TR = 1,200,000 Btu/hr; divided by 560 Btu/lb latent heat ≈ 2,140 lb/hr, or about 35.7 lb/min].
3. Circulated liquid flow at the overfeed ratio
Multiplying the compressor mass flow from the previous step by the overfeed ratio gives the total liquid mass flow the pump circulates through the system: [ELI-REVIEW: 35.7 lb/min × 3 ≈ 107 lb/min. At a liquid density of about 42 lb/ft³ (5.6 lb/gal), that is roughly 19 gpm circulated].
4. Allowable vapor velocity (Souders-Brown)
Using a Souders-Brown check with an illustrative vertical, no-mist-eliminator K-factor: [ELI-REVIEW: K ≈ 0.1 ft/s; v = K × the square root of ((42 − 0.65) ÷ 0.65) ≈ 0.1 × 7.97 ≈ 0.80 ft/s, or about 48 ft/min].
5. Required vapor-space diameter
Vapor volumetric flow divided by allowable velocity gives the minimum vapor-space cross-sectional area, which sets a minimum diameter: [ELI-REVIEW: 35.7 lb/min ÷ 0.65 lb/ft³ ≈ 55 ft³/min (0.92 ft³/s) of vapor; divided by 0.80 ft/s allowable velocity ≈ 1.15 ft² required area, or about 14.5 in. minimum diameter]. That raw minimum is rounded up to a practical standard shell size in the next step.
6. Liquid holdup check and vessel selection
Rounding up to a standard shell size and checking liquid holdup against a [ELI-REVIEW: 30-second minimum hold time for a pumped recirculator]: at 19 gpm circulated, the required usable liquid volume is [ELI-REVIEW: about 9.6 gal at design flow (roughly 14.3 gal at 1.5× overload)]. A [ELI-REVIEW: 16 in. inside-diameter shell, 48 in. tangent-to-tangent, with 2:1 ellipsoidal heads] holding liquid to about [ELI-REVIEW: 25% of shell height] provides roughly [ELI-REVIEW: 10.4 gal of usable liquid volume], which clears the 30-second hold-time requirement with a small margin, and the vessel’s [ELI-REVIEW: length-to-diameter ratio of about 3] falls inside the conventional range described in vessel L/D ratio.
7. Shell wall thickness and MAWP back-check
With a [ELI-REVIEW: 250 psig design pressure, SA-516-70 carbon steel (S ≈ 20,000 psi), 0.85 longitudinal joint efficiency (spot radiography), and 1/8 in. corrosion allowance], the [ELI-REVIEW: UG-27] shell calculation described in the [ELI-REVIEW: UG-27] shell thickness formula gives a required thickness of [ELI-REVIEW: about 0.245 in., rounding up to a 1/4 in. (0.25 in.) stock plate]. Back-calculating MAWP on the corroded thickness gives [ELI-REVIEW: approximately 263 psig], which is at or above the 250 psig design pressure, as required — see MAWP vs. design pressure.
Result
| Item | Value |
|---|---|
| Orientation | Vertical |
| Shell inside diameter | [ELI-REVIEW: 16 in.] |
| Tangent-to-tangent length | [ELI-REVIEW: 48 in.] |
| Head type | [ELI-REVIEW: 2:1 ellipsoidal] |
| Nominal shell thickness | [ELI-REVIEW: 0.25 in.] |
| MAWP | [ELI-REVIEW: ≈263 psig] |
| Separation-velocity result | Governed the raw minimum diameter |
| Liquid holdup result | Satisfied at the selected geometry, small margin |
Run it
Run this exact sizing sequence against your own refrigeration duty in ColdCalcs' Vessel Sizer and see every check's safety factor on screen, free.
Open the Vessel Sizer →FAQ
Is this worked example a validated design?
No. Every value on this page is a plausible, rounded placeholder for illustration, marked for the site owner's review, and none of it has been checked against a real project's data or the current code edition. It must never be used for an actual vessel selection.
Why did the raw separation-velocity diameter get rounded up?
Vessels are built from standard shell sizes, not an arbitrary calculated diameter, and rounding up also builds in a small margin. The example checks that the rounded-up size still satisfies liquid holdup and L/D, not just the raw minimum from the velocity check.
Why is the calculated MAWP higher than the design pressure?
Because required thickness gets rounded up to the next available stock plate gauge, the as-built vessel typically has more capacity than the design pressure alone required. See MAWP vs. design pressure for why that's expected, not an error.
Where can I see a real thickness calculation walked through?
See the companion PRELIM shell thickness walk-through worked example for a closer look at the [ELI-REVIEW: ASME VIII-1] thickness step specifically.