Questions about steam ejectors
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Does anyone know how the temperature of the fluid inside a steam ejector changes? For example, by how much can the temperature of the power steam drop after passing through the nozzle? Why are some ejectors equipped with a jacketed steam supply in the mixing section? Is it because of the large temperature difference between the steam on the inlet and outlet sides that such ejectors have jackets, in order to prevent the temperature from dropping too low?
I don’t have time to read it; I just want to know right away why some injectors have jackets while others don’t
After the steam is ejected from the power nozzle, it is in a mixing chamber where the temperature is generally low. As for the exact temperature, it depends on the pressure conditions behind the nozzle and within the mixing chamber, as well as the initial temperature of the power steam. When the pressure in the mixing chamber drops below the melting point of the gas to be evacuated or of the driving gas, it is necessary to heat the mixing chamber, primarily to prevent the components in the gas from condensing into a liquid state or freezing! If condensation or freezing occurs, the vacuum level will fluctuate, going up and down!
If we assume isentropic expansion of the steam within the nozzle, then 150°C saturated steam will, after passing through the nozzle, reach a pressure of 0.005 MPa. According to the enthalpy-entropy diagram of water vapor, the temperature can drop to around 33 degrees, and it will still be wet saturated steam. Is this correct?
If the suction pressure is 0.005 MPa, which is roughly at room temperature, you can feel this temperature with your hand when using the ejector. In this operating condition, no heating jacket is needed! Unless there are organic compounds with a very high molecular weight in the inhalation medium.
From a practical perspective, it shouldn’t be correct, as no condensation occurs； It is generally superheated, rather than saturated. It should not be a completely stationary process.
With all other conditions unchanged, if the amount of steam injected decreases, will the temperature at the throat decrease accordingly? .
Is there any way to determine the temperature of the mixed fluid at the throat? I’ve looked through lots of materials, but nothing mentions it
The charts of water’s enthalpy and entropy that are provided after thermodynamics or caloristics – you’ve seen that table as well. With empirical correction, there’s nothing that can be done; perhaps well-known injector manufacturers abroad have experimental data, but domestic manufacturers likely don’t have such data.
What do you need this data for? For research? It is generally not required in engineering.