Propane Tank Vaporization Capacity

Which is the number that fails long before the tank runs out of gas. A tank is a boiler: liquid absorbs heat through the wetted wall and boils, so capacity goes with WETTED SURFACE AREA and with the temperature difference driving heat through the shell. The wetted area is computed here from the tank's geometry at the entered level; the capacity itself is SCALED FROM THE MANUFACTURER'S PUBLISHED TABLE rather than derived, because the real rate also depends on wind, on whether the tank is buried, on insulation and paint colour and on how long the draw lasts, and no closed form covers those. BOTH TERMS MOVE THE WRONG WAY AT THE SAME TIME, which is the point. In a cold snap the driving temperature difference shrinks, and a tank that has been drawn down has less wetted surface -- so a tank at half the area and half the drive has a QUARTER of the capacity it was commissioned with. That is why the failure is a January morning on a tank at 30%, and never the full tank in November when the system was signed off. FROST ON THE SHELL IS THE DIAGNOSIS. It means liquid is boiling fast enough to chill the wall below the dew point, so the tank is at or past its capacity, and the frost layer then insulates the shell and makes it worse. The consequences follow in order: the tank frosts, the vapour pressure falls, the regulator can no longer hold outlet pressure, and the appliances lose flame. THE FIX IS NOT A BIGGER REGULATOR. It is more wetted area -- a larger tank or a second one manifolded in -- or a vaporizer that adds heat deliberately. Manifolding two tanks adds wetted area, which is why a bank of cylinders on a high-demand appliance is a vaporization decision rather than a run-time one. This scales an entered table reading by computed geometry. It does not compute vaporization from first principles, model wind, burial, insulation, paint colour or the duration of the draw, distinguish continuous from intermittent draw capacity (they differ, and the table gives both), size regulators or piping, determine tank placement, or select a vaporizer, which carries its own requirements. NFPA 58, the adopted fuel gas code, the tank and appliance manufacturers, and the AHJ govern.

wetted surface of a horizontal cylinder at the entered fill -- the shell arc 2R*acos((R-h)/R)*L plus both head segments -- with the manufacturer's table capacity scaled by the wetted-area ratio and by the temperature-difference ratio.

Vaporization capacity from the tank manufacturer's published table, scaled by computed geometry. The rate is NOT derived: it also depends on wind, burial, insulation, paint colour and the duration of the draw.

Circular-segment geometry and two ratios on an entered table reading.

Estimate. AHJ and licensed professional govern.

Field names used by the API: tank_diameter_ft, tank_length_ft, percent_full, ambient_f, liquid_temperature_f, reference_capacity_btuh, reference_percent_full, reference_ambient_f, connected_load_btuh, wetted_area_ft2, reference_wetted_area_ft2, area_ratio, temperature_ratio, capacity_btuh, margin_btuh, limit_percent_full, tanks_required

• The table reading is the input wind, burial, insulation and paint colour are not modelledthe tank manufacturer's vaporization table
• Horizontal cylinder with flat heads a dished or hemispherical head changes the wetted areathe container drawing
• Continuous draw assumed intermittent capacity is higher and the table gives boththe tank manufacturer