Lithium carbonate (Li2CO3; density 2.11 kg/L, solubility in water13 kg/m3) is used as a medication for...

 

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Lithium carbonate (Li2CO3; density 2.11 kg/L, solubility in water13 kg/m3) is used as a medication for bipolar disorder. To prepare for a conference presentation next week, a student needs to estimate its diffusion constant in water. The student decides to use a spinning disc to measure the diffusion constant. A layer of lithium carbonate is placed on one side of a 5 cm diameter disc and placed in 1 L of water at 25 C and the disc is rotated. Salt dissolves from the rotating disc surface to the well-mixed solution in the chamber. Solution flows out of the chamber with the same concentration as the bulk at 1 mL/min and is replaced by pure water at the same flow rate, so that the amount of fluid in the chamber remains constant. Unfortunately, the meter used to measure the disc's rotational speed is broken, so that a correlation between rotation rate and mass transfer cannot be used. The student's advisor insists that the diffusion constant can still be measured and threatens to delay his graduation date if the diffusion constant is not obtained before the conference. During an experiment, the student finds that after 12 hours of steady state operation, the thickness of the lithium carbonate has decreased by 0.5 mm. A/ Calculate the steady-state concentration of lithium carbonate exiting the chamber in kg/m3. The student tries a second experiment in which an electric heater is used to maintain the bare disc (containing no salt) at 30C, and the flow into and out of the reactor is stopped. He finds that after 30 minutes, the bulk temperature has increased from 25C to 26.5C. B/ Calculate the average heat transfer coefficient from the spinning disc. C/ Calculate the diffusion coefficient of lithium carbonate in water. Lithium carbonate (Li2CO3; density 2.11 kg/L, solubility in water13 kg/m3) is used as a medication for bipolar disorder. To prepare for a conference presentation next week, a student needs to estimate its diffusion constant in water. The student decides to use a spinning disc to measure the diffusion constant. A layer of lithium carbonate is placed on one side of a 5 cm diameter disc and placed in 1 L of water at 25 C and the disc is rotated. Salt dissolves from the rotating disc surface to the well-mixed solution in the chamber. Solution flows out of the chamber with the same concentration as the bulk at 1 mL/min and is replaced by pure water at the same flow rate, so that the amount of fluid in the chamber remains constant. Unfortunately, the meter used to measure the disc's rotational speed is broken, so that a correlation between rotation rate and mass transfer cannot be used. The student's advisor insists that the diffusion constant can still be measured and threatens to delay his graduation date if the diffusion constant is not obtained before the conference. During an experiment, the student finds that after 12 hours of steady state operation, the thickness of the lithium carbonate has decreased by 0.5 mm. A/ Calculate the steady-state concentration of lithium carbonate exiting the chamber in kg/m3. The student tries a second experiment in which an electric heater is used to maintain the bare disc (containing no salt) at 30C, and the flow into and out of the reactor is stopped. He finds that after 30 minutes, the bulk temperature has increased from 25C to 26.5C. B/ Calculate the average heat transfer coefficient from the spinning disc. C/ Calculate the diffusion coefficient of lithium carbonate in water.

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