What level of heat loss in warm water pipes is considered acceptable?
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This post was last edited by yehudie on 2016-5-3 at 19:45. The factory’s production process requires warm water at 40°C to cool the MDI gas; the freezing point of this material is around 38°C. The water supply pipe has a diameter of DN300, and it is insulated with 50mm thick aluminum silicate insulation. The temperature gauge at the outlet of the plate-type heat exchanger using warm water shows 40.5°C. After passing through 40–50 meters of piping, the fluid reaches the heat exchanger (where the inlet pipe diameter changes to DN200). The inlet flow rate is 203 t/h, and the temperature of the warm water at the inlet is 39.8°C, with the ambient temperature being 28°C. The boss asked us if this temperature is considered acceptable, and why I’ve never thought about this before. I’d like to ask: after a certain period of time, what temperature should the warm water pipeline still have to be considered acceptable? How is this calculated? Please help, experts on this forum!!
Whether the cooling water temperature is acceptable depends on whether it can meet the cooling requirements. Based on the conditions you provided, it seems that these requirements can be satisfied; the inlet water temperature of the plate heat exchanger is 39.8, and the outlet temperature is 40.5. It’s clear that it’s not possible to reduce the temperature of the material below 38, and since the temperature remains between 39.8 and 40.5, the process objectives are met as long as the material does not solidify and the temperature remains appropriate. Furthermore, the thickness of the insulation layer is already more than sufficient; for our low-pressure steam pipes with angles of 180 degrees or more, we use 50 mm thick aluminum silicate insulation. If there are doubts regarding the insulation effectiveness, it is sufficient to measure the temperature on the outside of the insulation using an infrared thermometer – theoretical calculations are not necessary at all. Finally, if the temperature difference between the inlet and outlet of the heat exchange plate is too small, it is possible to reduce the flow rate of the cooling water as well as the temperature at the inlet of this water stream; this ensures that the temperature at the outlet of the material remains above 38 degrees, while also maximizing energy savings.