For vacuum pipes, what is an appropriate flow rate for the secondary steam?
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In multi-effect evaporation, the last effect is usually evacuated. Regarding the flow velocity of the secondary steam in the pipes for this last effect, various opinions can be found in forums and manuals; for example: (1) Regardless of the degree of vacuum, the flow velocity of the secondary steam must not exceed 10 m/s； (3) The secondary steam flow rate is 20–30 m/s; the vacuum level is low, resulting in a slow flow rate ； High vacuum level, fast flow rate ； (2) At low vacuum levels, it is 30 m/s; at -0.08 MPa, it is 60 m/s, and at -0.095 MPa, it is 90 m/s ； Dear experts, which statement is the most reliable?
That is just a reference value; the actual speed has to be calculated based on the acceptable pressure drop
Recommended value in the Process Piping Installation Design Manual: 50-100 kPa, 40 m/s； 20-50kpa,60m/s;5-20kpa,75m/s
The formula is too complex; I don’t want to lose, haha. For example, in a multi-effect evaporator, the secondary steam from one effect is used as heating steam in the next effect. If the maximum temperature loss I’m willing to accept (equivalent to pressure drop) is 1 degree, then I can use this value to determine the maximum gas velocity I can tolerate. I’m not sure if this explanation is clear enough
Is the pressure here gauge pressure or absolute pressure?
Oh, now I understand after you explain it like that.
50~100KPa(A), flow rate of 40m/s； 0.1~50KPa(A), flow rate of 60m/s ； 0.01~0.1KPa(A), with a flow velocity of 80m/s. This has been proven through practice; there’s no problem with it. These are the empirical values obtained by vacuum equipment manufacturers in China and abroad.