If a centrifugal compressor operates with a suction pressure of 3 psig and a discharge pressure of 10 psig, with an atmospheric pressure of 14.7 psia, what is the ratio closest to?

To determine the pressure ratio of a centrifugal compressor, it's essential to understand the formula used for calculating the pressure ratio, which is defined as the ratio of discharge pressure to suction pressure.

In this scenario, we must first convert the given pressures into absolute pressures, as the formula requires absolute values. The suction pressure is given as 3 psig (pounds per square inch gauge), which means it's relative to atmospheric pressure. To find the absolute suction pressure, we add atmospheric pressure:

Suction Pressure (absolute) = Suction Pressure (gauge) + Atmospheric Pressure = 3 psig + 14.7 psia = 17.7 psia.

Next, we convert the discharge pressure from gauge to absolute pressure in a similar manner:

Discharge Pressure (absolute) = Discharge Pressure (gauge) + Atmospheric Pressure = 10 psig + 14.7 psia = 24.7 psia.

Now, we can compute the pressure ratio using the absolute pressures:

Pressure Ratio = Discharge Pressure (absolute) / Suction Pressure (absolute) = 24.7 psia / 17.7 psia.

Calculating this gives:

Pressure Ratio ≈ 1.39.

This value indicates that under