Regarding plate heat exchangers, I need an answer
Thread Content
Everyone, our company has a plate heat exchanger. The steam inlet pressure is 0.4 Mpa, while the outlet pressure is at atmospheric pressure. The steam inlet temperature is 143°C, and the outlet temperature is 99°C. The heat exchanger is made of 304 material, with a heat exchange area of 25 square meters. There is also a hot water tank nearby; a pump with a capacity of 50 T/h is used to circulate water and raise its temperature to 98°C. The capacity of the hot water tank is 3 T. I would like to know how long it will take to heat up those 3 T of water Is there any way to calculate this? I’ve never been able to figure it out; the time I calculate is quite different from the actual heating time. It actually takes around 40 minutes to heat it up
There is a gap between theoretical calculations and reality, such as the thermal conductivity of heat exchangers, scale formation, as well as the calculation methods, required conditions, and instrument accuracy. For reference.
What is the flow rate of the steam? What is the water inlet temperature as well?
Calculate the power of the heat exchanger – just divide by the heat required for 3 tons of water, and you’ll have the answer
The last edit to this post was made by Heat exchanger or Plate heat exchanger on 2021-12-14 at 14:29. OP, it’s impossible for it to take 40 minutes; unless your steam supply is insufficient. Heating a 3-ton water tank with steam, with such a high flow rate for circulation heating, and the plate heat exchanger having such a large heat exchange area – it’s impossible. :I don’t know what specific purpose this application scenario of yours serves, but this configuration is quite strange indeed.
40 minutes is too long; if there’s enough steam, it should take about 10 minutes to heat up
This post was last edited by lupg on 2021-12-16 21:52. 1. Since the problem posed by the friend in post 1 lacks data, the problem has no solution, or there are infinitely many solutions. Here, a hypothesis is first made regarding the lack of data; based on this, a set of solutions is provided for reference. 2. Assuming the temperature of the cold water is 50°C, it is determined that the cold water needs to be raised by 48 degrees℃ ； The dirt coefficient, thermal conductivity, etc. use commonly available data for heat exchangers ； Regarding the properties of steam, the conditions provided by the colleague on the first floor are all saturation temperatures, with a heat exchanger pressure drop of 0.3 MPa. If a condition without phase change is specified, then the load on the heat exchanger is very low. For now, it is assumed to be in a phase-change condition, that is, the incoming steam is discharged as condensed water. 3. Under hypothetical conditions. The heat load for a heat exchange area of 25 square meters is 558 KW, which is sufficient to raise the temperature of 10 tons of water from 50°C to 98°C. 4. Since it is assumed that the heat exchanger can handle a load of 558 KW, it is calculated that it takes 18 minutes to heat 3 tons of water from 50°C to 98°C. That is, the method mentioned by the friend on the 4th floor. 5. However, the result of 18 minutes is a theoretical value; it takes into account only the heat balance, using an imaginary full-load steam volume to heat water at a low load. In fact, due to the lower flow rate on the low-temperature side, the heat transfer coefficient changes, which reduces the efficiency of heat transfer; as a result, the time required is slightly higher than the value calculated theoretically. If it is assumed that both the inlet and outlet fluids are steam, then a heat exchange area of 25 square meters will only be sufficient to achieve the assumed temperature rise of 48°C for 2 tons of water. 7. Once again, it should be noted that the above figures are not the only possible results; they are estimates based on various assumptions.