10 Years of Past Exam Questions 40
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As shown in the figure: the flow rate of the vapor at the top of a distillation column (V) is 2400 kg/h, with a temperature of 80 ℃. The temperature after complete condensation in the condenser at the column top is 25 ℃. The output from the column top (D) is 600 kg/h, and the reflux ratio is 3. It is given that the average heat of fusion of the material is 4.0 kJ/(kg·K), while the latent heat of vaporization of the material at 80 ℃ is 2500 kJ/(kg·K). What is the cooling heat load (kJ/h) of the tower top condenser, and which of the following values is it closest to? A. 6.786×10^6 KJ/h B. 6.528×10^6 KJ/h C. 6.639×10^6 KJ/h D. 6.549×10^6 KJ/h. In the textbooks used at Tianjin University, the heat load on the condenser is given by Q=(R+1)D(Ivd-Ild). The values provided in the question are specific heats and latent heats of vaporization; so can’t we simply use 2400*2500? Please, fellow sailors, feel free to point out any mistakes
You have only calculated the load for changing the gas from 80°C to a liquid at 80°C; you also need to add the load for cooling the liquid from 80°C to 25°C.
=2400*2500+2400*4*80-2400*4*25=6.528*10^6