The issue of nozzle size in plate heat exchangers
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The nozzle sizes on the hot side and cold side of the plate heat exchanger in our current units are the same. May I ask whether we should design it using the same size, with a diameter reduction at the inlet to make adjustments? To be more specific: I need to choose a plate heat exchanger. On the hot side, there is hot water with a flow rate of 20 te/hr, which needs to be cooled from 100°C to 40°C. On the cold side, based on calculations, there is circulating water with a flow rate of 120 te/hr, which needs to be heated from 30°C to 40°C. Based on these flow rates, it seems that the pipe sizes for the hot and cold sides shouldn’t be the same. Should I consider using 2” pipes for the hot side and 6” pipes for the cold side, or should I use 6” pipes for both sides, with diameter changes at the inlet and outlet on the hot side? Questions from non-design professionals – please feel free to give your guidance. Thank you
When designing a heat exchanger, the flow velocity of the fluid within the channels is already determined; the size of the pipe openings should be based on the largest possible value. The flow rate of the cooling water is generally 1.5–2 meters per second; you can determine it based on your own requirements and agree on it with the manufacturer.
Generally, the interface sizes of plate heat exchangers are the same, as the corner holes in the plates are identical. Steam condensation is a special case: the interface on the steam side is larger, while that on the cold water side is smaller. For a scenario like yours, a reducing fitting will suffice, or a blind flange can be used; the inner diameter of the flange is then machined according to the actual size of the pipe connection. It is likely that a better alignment is needed on the hot side.