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Steam Velocity

John_63
John_63 Member Posts: 2
in THE MAIN WALL
In Jan. issue of Plumbing and Mechanical Dan's article states that low pressure steam travles faster than high pressure steam. What does he mean ?, velocity or heat transfer rate. It does not appear that heat transsfer rate is the issue, the btu,s are the same in the given time frame. Please help

Comments

  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928


    The higher the pressure of the steam, the higher its temperature and the greater the latent heat per pound.

    So, for a given number of BTUs moved, low pressure steam must move at a higher velocity (speed through the pipe) compared to steam at higher pressure.
  • Tony Conner_2
    Tony Conner_2 Member Posts: 443
    The Latent...

    ... heat actually drops away as the steam pressure increases. The temperature and the total heat increase along with the pressure.
  • John_63
    John_63 Member Posts: 2


    The velocity of steam tables indicate low pressure steam travles at approx 8,000 FPM however high pressure steam travles up to 15,000 FPM . This seems to differ with what Dan states.
  • Dave Meers
    Dave Meers Member Posts: 103
    steam velocity vs. btus

    Hi John,

    I don't mean to speak for Dan here since I haven't read the article you mention. However, reviewing his discussion of this issue in the Lost Art, lower pressure moves faster through the pipes than high pressure. I think you agree to the speed, but are confused on the amount of heat.

    If I may quote from the Lost Art, "If the load is the same in both cases, the low-pressure steam will move through the pipes much more quickly than high-pressure steam." The higher pressure compresses the steam into a smaller volume. "So to transfer the same load, the steam doesn't have to move as quickly through the pipes."

    Did this help or confuse you more?

    Best regards, Pat
  • JimGPE_3
    JimGPE_3 Member Posts: 240
    Velocity.

    The key is pounds per cubic foot.

    1. Heat output is proportional to the pounds of steam condensed.

    2. Velocity is cubic feet per minute divided by the free area of the pipe.

    3. The higher the pressure, the more pounds of steam per cubic foot, so you can get the same output with fewer cubic feet of steam.

    Therefore, for the same output (BTU/hr) and the same pipe size, the higher the pressure the lower the velocity. You are jamming more BTU's per cubic foot, so fewer cubic feet are required.

    The fact that at higher pressures there are fewer BTU's per pound is overcome by jamming more pounds per cubic foot.
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