Saturated pressure and temperature

For a pump, one should consider the inlet pressure and outlet pressure. If the inlet pressure of the pump is higher than the saturated vapor pressure of the liquid, then the liquid is in a liquid state. If the net positive suction head available (NPSHa) of the system is greater than the required net positive suction head (NPSHr) of the pump, then the pump can operate. Otherwise, it will vaporize upon entering the pump, causing cavitation.

There is no relationship whatsoever between the saturated vapor pressure and the pressure applied by the pump to the liquid.

The increase in water pressure caused by pumping is intended to give the water the momentum needed to flow to its target location. You might wonder what pressure is required; it depends on the flow rate of the water, the number of devices it passes through (including manual/control valves), as well as the number of pipes involved, etc. The key factor is the vertical height difference over which the water is pumped from a lower point to a higher one...

First, let’s look at the definition of saturated vapor pressure; then we’ll study the ideal gas law. After that, considering what you mentioned about using a pump, we’ll see that a state of equilibrium is ultimately reached, but this state won’t last long. When the pressure at the pump outlet is higher than the pressure in the tank, the liquid level in the tank rises and the volume of the gas phase decreases. When the pressure at the pump outlet equals the pressure in the tank, the flow stops, and the pump is prone to cavitation.

This seems a bit… I’ve heard that it can be used to create water with a relatively low temperature; it depends on how you look at it. If the water is poured into the tank at the end, when equilibrium is reached, the pressure applied must be higher than that of the water, otherwise it won’t be able to enter. The senior colleagues upstairs also said that if you only focus on the pressure after pumping, it will definitely have an impact! The saturated vapor pressure is inherently related to temperature and pressure

Let’s clarify the concepts: 1. A certain saturation temperature of a water medium corresponds to a specific saturation pressure. 2. When the temperature remains constant, pressure is applied to the water; this is assumed to be done through adiabatic compression using a pump. Although the temperature remains unchanged (ignoring the slight temperature rise during flow through the pump channels), at another pressure, the water is no longer saturated. 3. If water is to be at its saturation temperature at a new pressure, external energy must be absorbed to raise its temperature to the saturation point at that other pressure

It is necessary to clarify the concept first: there is a saturation temperature for each pressure, and inversely, there is a saturation pressure for each temperature. However, the pressure corresponding to a specific operating temperature is not necessarily the saturation pressure. When the operating pressure is lower than the saturation pressure, water is in a vapor state; when the operating pressure is higher than the saturation pressure, water is in a liquid state. Therefore, pressurizing water with a pump has no direct relation to the saturation pressure.

If we only consider water or steam, different fluids have different saturation pressures； The saturation pressure is only related to the “temperature” of water or steam ； It has nothing to do with the pressure of water or gas supplied by pumps, compressors, or other machines ； At what temperature does water or steam have a corresponding saturated pressure? ； At this temperature, if the water’s pressure is below the saturation pressure, it will vaporize partially until it is completely vaporized ； At a certain temperature, if saturated water is pressurized by a pump, its saturation pressure remains unchanged if the temperature stays the same. In fact, the temperature will rise, so the water remains saturated. Since the temperature increases, the corresponding saturated pressure also changes (it rises) ； At a certain temperature, when the vapor pressure is below the saturation pressure, part of the water vapor condenses into water ； When heated, the temperature rises and the water vapor turns into superheated vapor, no longer being saturated vapor. I’ll talk about humidity issues related to moist air another time.

The saturation pressure depends only on the temperature of the medium and does not change due to other factors.