Heat conservation problem in heat exchangers
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Conditions: Heat the water using steam at 14 barg in a cyclic process; the initial temperature of the water is 30 degrees, and it needs to be heated to 180 degrees at a pressure of 18 barg. Steam: 3200 kg/h, water: 227 m3/h. I used PROII for simulation in the initial condition; the first time, the water temperature increased from 30 degrees to 38 degrees. I then calculated the final temperature – after trying several times, with a water temperature of 168 degrees, the final temperature was 180 degrees. However, according to the law of conservation of energy, W_heat·Cp·T1 = W_cold·Cp·T2; steam at 14 bar and 3200 kg/h can raise the temperature of water at 227 m3/h by at most 6 to 8 degrees. I don’t understand how a temperature increase of 12 degrees is possible. The thermodynamic equation I’m using is NRT01. Could everyone please help me figure out where I made the mistake?
I’m not sure what conditions you set; I didn’t encounter this problem with my setup. $ Generated by PRO/II Keyword Generation System $ Generated on: Sat Mar 14 19:31:02 2009 TITLE DIMENSION METRIC SEQUENCE SIMSCI COMPONENT DATA LIBID 1,H2O, BANK=SIMSCI,PROCESS ASSAY CONVERSION=API94, CURVEFIT=IMPROVED, KVRECONCILE=TAILS THERMODYNAMIC DATA METHOD SYSTEM=NRTL, SET=NRTL01, DEFAULT STREAM DATA PROPERTY STREAM=H2O, TEMPERATURE=160, PRESSURE=19.388, PHASE=M, & RATE(LV)=227, COMPOSITION(M)=1,1 PROPERTY STREAM=S3, PRESSURE=15.309, PHASE=V, RATE(WT)=3200, & COMPOSITION(M)=1,1 UNIT OPERATIONS HX UID=E1 HOT FEED=S3, M=S4 COLD FEED=H2O, M=S2 CONFIGURE COUNTER OPER TMIN=10 END Additionally, your energy conservation law W_hot*Cp*T1=W_cold*Cp*T2 applies under conditions without phase changes; if there is a phase change, the latent heat of the material must also be taken into account.
Because the sensible heat released when steam turns into condensed water, as its temperature drops, is much smaller than the latent heat involved in the phase change, I overlooked this factor; considering only the latent heat, cold water can only rise by 6 degrees.
I think it’s because there’s an issue with your pressure units; BARG and bar are not the same.