Stabilized hot water tank simulation – please ask an expert to take a look
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The model is shown in Figure 1. Stream 1 is hot water, with a temperature of 195°C, a pressure of 1.99 MPa, and a flow rate of 25 kg/s. The valve pressure drop is set at 10 kPa for all. The tank volume is set at 800 m3, and it is insulated. During the water filling process, VLV-100 is turned on while VLV-102 is turned off; the controller controls the opening degree of VLV-101, which functions as a breathing valve to maintain the pressure in the storage tank at 1.98 MPa. For the property methods, I tried NRTL and PR-Twu, and the results were similar. . . The initial settings of the storage tank are shown in Figure 2: the liquid level is at 0 m, the tank is filled with nitrogen, the temperature is 25°C, and the pressure is 1.98 MPa. The simulation results are shown in Figure 3. The tank pressure (blue line) remains essentially constant, while the temperature (red line) stops rising around 190°C. This temperature is a bit abstract – my inlet temperature is 195°C, so does the temperature drop even after it’s filled? I wonder if there are any experts who can help take a look.
This situation in the simulation results may be due to some issues with the model settings or the selection of material properties. During the water filling process, if the pressure inside the storage tank remains constant, it indicates that the controller and the breather valve are functioning properly, and nitrogen should be being discharged from the tank. However, if the temperature of the incoming water is 195°C, the temperature inside the storage tank should theoretically not decrease, as the water inside the tank is insulated and there is no heat loss. This situation may arise due to errors in some of the assumptions or calculation methods used in the simulation, such as incorrect calculation of heat loss or inaccurate property data. It is recommended to check the following aspects: 1. Whether heat loss has been taken into account, and whether the storage tank is truly completely insulated. 2. Check the physical property parameters to ensure that the models and parameters used can accurately describe the behavior of water and nitrogen under high temperature and pressure. 3. Check whether the boundary conditions and initial condition settings are correct. 4. Verify whether the algorithms and iteration processes of the simulation software are stable, and whether numerical instability during computation may lead to inaccurate results.