Condensate flow issue
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I’m calculating the cooling water flow for a condenser using the formula G = ρ×π/4×d²×656. The pipe diameter is 14 millimeters, and there are 656 pipes in total; the calculated flow rate is 302 kg/s. Isn’t that impossible? I’ve seen that the flow rates in typical heat exchangers are around 2000 kg/h, which is equivalent to 0.9 kg/s. Why is there such a big difference? What’s the issue?
Where did this formula come from? The units don’t add up either; it’s nonsense. You can’t calculate it that way. If flow velocity is taken into account, then it’s more reasonable
The formula is incorrect; according to your formula, the units should be kg/m, and it’s also necessary to multiply by the flow velocity.
Your unit should be kg/h, right?
Oh, I made a mistake; it should be multiplied by the flow rate. I used 3 m/s as the flow rate value
How can it come out to be so large using this calculation? 0.3 tons of water per second need to go? Is it possible that there isn’t any?
I checked it, and the numbers are correct. But where did you get this flow rate from (don’t tell me you took it from a book as the reasonable flow rate)? This post was last edited by lucky1909 on 2009-4-20 16:39.]
The flow velocity inside the heat exchange tube is 3 m/s; generally, pipes cannot achieve such high velocities. How large is the pressure drop at such a high flow velocity? The amount of cooling water required isn’t calculated in that way; it needs to be determined based on heat balance. The appropriate type of heat exchanger structure is chosen based on the amount of cooling water needed, in order to ensure a reasonable flow rate within the heat exchange tubes. How is the flow rate determined then, using the cross-sectional area and flow rate of the tubes? If the flow rate isn’t known, how is it calculated then? Is it just an assumption?
A flow velocity of 3 m/s within the pipe is not impossible to achieve; brass pipes can support a maximum flow velocity of 3 m/s, although in practice a value of 2.8 m/s is chosen as the maximum. There are many other types of pipes available for use, and one can refer to the heat exchanger design manual; see my other post at http://bbs.hcbbs.com/thread-405577-1-1.html
Your formula seems to be incorrect; physically speaking, your formula should represent density multiplied by the flow area. This physical quantity hasn’t been defined yet – it’s neither flow rate nor mass flow rate. It’s recommended that you correct the formula. Last edited in this post by jy03018705 on 2009-4-21 09:01
OP, when comparing the flow rates of heat exchangers, it would be better not to compare their mass flow rates; instead, one should compare the flow rates in units of m/s, as this is more scientifically sound. Because that mass flow rate of yours still needs to be multiplied by density and flow area in order to convert it into a value representing flow velocity
The calculations are correct; it’s just that the flow rate was used incorrectly. Generally, the flow rate of water is 1.2–1.8 m/s, with an average of 1.5 m/s. The flow rate in the condenser you’re using is likely to be less than 1 m/s, and the actual water flow rate might be between 200–600 tons per hour, which is a fairly normal value for use in a condenser.
Why doesn’t it seem like there’s any velocity in the formula? Are the units used by the original poster correct?
I now know that it uses 656 pipes, as well as pipes of 19×2.5. I just want to get an approximate idea of the flow rate of the water; it’s not about doing a precise calculation. I know that the flow velocity should be calculated using that flow rate. I hope someone can help me with this