[Mahk]

Hello everyone,

I am trying to model the pressurization of a 50-liter air tank, initially at atmospheric pressure, and raised to a pressure of 12.5 bar by a compressor, with an injection pressure of 12.5 bar into the tank. The objective is to determine the time required to reach 12.5 bar in the tank, as well as to capture the mass flow rate and the fluid velocity at the injection point.

On paper, my model is quite simple. It consists of a 50-liter cylindrical tank. A pressure inlet (Gauge: 1,148,675 Pa) with a passage area of 12 mm. The air density follows the ideal gas law, with a temperature of 303.15 K, and the rest of the properties are constant. The energy equation is activated. Turbulence model: k-w SST. Pressure-based resolution.

The calculation converges; however, the pressure evolution in the tank seems inconsistent to me. It follows a linear behavior and only approaches an asymptote near the injection pressure. If we look at the flow rate, it remains constant and only drops to zero when the pressure reaches its asymptote.
Physically, the pressure increase in the tank should slow down as the pressure rises. Similarly, the flow rate should decrease in response to the rising pressure.

Do you have an explanation for this result? And how can it be corrected?

Thank you for your responses,

Mahk