Question

e. Consider a system which contains saturated liquid-vapor mixture of water at 50°C. The system is located in a place where the local atmospheric pressure is 98 kPa. What is the absolute (actual) pressure inside this system? If we want to express the pressure of the system as gage pressure or vacuum pressure, determine which one is more suitable for this case and calculate it.

Answer 1

At temperature 50°C , and liquid vapour mixture stauration phase, from steam table actual absolute pressure inside system is equal to 12.3513 KPa. So it is less than atmospheric pressure , so vaccum pressure is best to express when the pressure is less than atmospheric pressure as vaccum pressure is also known as negative gauge pressure.

So its value is Pvaccum = Patm - Pabs = 98-12.3513 = 85.6487 KPa . Also vaccum pressure is always with negative sign . So Vaccum pressure inside the system is - 85.6487 KPa.