Reboiler Tutorial Answers PDF

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Reboiler Answers
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Reboiler Tutorial Answers

1. Forced Circulation Reboilers are good for viscous and/or heavily-fouling fluids. They are also used for low vacuum operations. The main disadvantages with this type of reboiler are the running cost of the pump, reliability of pump, leakage from pump seals. Thermosyphon Reboilers are the most economical but not suitable for viscous fluids or high-vacuum operations. The disadvantage with this design is that the column must be elevated to provide the hydrostatic head necessary for the thermosyphon effect. Kettle Reboilers are suitable for vacuum operation and high evaporation rates. The reboiler can be built in to the column. The disadvantages with this design are the low heat transfer coefficient due to lack of circulation. They are not suitable for fouling materials. They generally have a high capital cost.

2. Pool or nucleate boiling consists of mostly liquid with bubbles of vapour. The liquid is in good contact with the heating surface. The excess temperature – the temperature difference between the heating element and the boiling liquid – is considerably less than 75°C. In film boiling the liquid detaches itself from the heating element and forms a film. The excess temperature is greater than 75°C. This buffer layer of vapour between the boiling liquid and the heating element leads to a considerable reduction in heat transfer coefficient. This is why film boiling is generally avoided in reboilers.

3. Mostinski equation: hnb = 0.104(Pc)0.69(q)0.7[1.8(P/Pc)0.17 + 4(P/Pc)1.2 + 10(P/Pc)10] = (0.104)(45)(300)0.7[1.8(10/45)0.17 + 4(10/45)1.2 + 10(10/45)10] hnb = 520.5W/m2K

4. Bromley equation: hf = 0.62[kv 3(ρL – ρv)ρvgλ/µvd0(Tw – Ts)]0.25 = (0.62)[0.153(880-1.2)(1.2)(9.81)(390 x 103)/(0.0002)(0.0254)(200-105]0.25

= 254W/m2K

5. The Lockhart-Martinelli equation gives X as: 1/X = [x/(1-x)]0.9[ρL/ρv]0.5[µv/µL]0.1 1/X = [0.2/(0.8)]0.9[760/1.3]0.5[0.0005/0.008]0.1 1/X = 5.26 From first of two charts, fc = 7 approximately....