All the seniors, please take a look at the board-type heat exchanger cooling issue (urgent)?
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A plate heat exchanger for central air conditioning cooling, but its cooling performance is poor; this heat exchanger was not designed or selected based on proper calculations. It was removed from another heat exchange system. Plate heat exchanger model: BR03B. Number of plates: 172. Heat exchange area: 50 square meters. Single-pass design. Operating conditions: Inlet temperature of cooling water is 7 degrees Celsius; outlet temperature of cooling water is 11 degrees Celsius. Flow rate: 40 tons/h (the outlet temperature of cooling water can be increased). This is because the cold water at 7 degrees Celsius is drawn from underground, exchanged heat through the plate heat exchanger, and then discarded – it’s not utilized. For the air-conditioning system’s internal circulation cooling mode, the inlet water temperature is 19 degrees, while the outlet water temperature is only 17 degrees. The flow rate is 80 tons per hour; the flow velocity inside the plate heat exchanger is unknown. A temperature of 17 degrees at the outlet is not sufficient – it should be at least 15 degrees. The cooling water inflow and outflow rate is 40 tons/h, while the heat exchange water inflow and outflow rate is 80 tons/h – these values cannot be changed. Please help me, experienced colleagues; what methods can be used to reduce the outlet water temperature to below 15 degrees? Should we increase the plate heat exchangers, change the process, or are there other methods? Replacing it with a new one is too costly. I would like to thank all the seniors here first. This post was last edited by bodian on 2009-2-28 at 12:31.]
I have examined your operating conditions. From that perspective, the temperature rise and drop are correct; however, for an area of 50 square meters, these values are not reasonable. If it is a single-pass configuration with 172 plates, the flow velocity between the plates is too low. A two-pass configuration could be used to increase the flow velocity, and in that case the temperature drop would be acceptable.
By using counterflow operation to raise the cooling water outlet temperature to 15°C, the requirements should be met. Because the calculated heat transfer coefficient K value is around 1110, which is not too high. Note: Since well water is used, scaling tends to occur, so it should be cleaned regularly to prevent excessive thermal resistance due to dirt, which could prevent proper operation. It would be best to increase the cooling water flow rate to 80 T/H as well, as that would yield much better results.
The theoretical calculated heat transfer rate is 190 KW; using a counterflow configuration with a value of K of 500 W/m2·K should be sufficient. The heat exchange in plate heat exchangers should work fine as well. But isn’t scaling a problem in floor-mounted plate heat exchangers? Or is it not counterflow that is being used?
Counterflow heat exchange should be used; if the flow rate is low, a two-stream system can be adopted to increase the flow rate. Additionally, regular cleaning is necessary to prevent blockages. It should be able to meet the requirements.
I checked and it uses counterflow; the plate exchanger has also been cleaned, with no scaling and it’s very clean. It’s just that the plate is thicker, at 0.7 millimeters. Can using a dual-flow system lower the water temperature? :o :o Last edited by bodian on 2009-3-3 13:12 ]