Solved Problems - Chapter 13

Learning Resources

		If the variance is changed for the asymmetric RTD in Example 13-1, how is the conversion affected?


		Solution Below are three similar RTDs, with the same mean residence time but with different variances. The variances are listed below. Note: E_1.1(t) is the same as curve (1) in Example CDE13-2.1.

		for the original RTD E_1.1(t) is 0.157. for the second RTD E_1.2(t) is 0.302. for the third RTD E_1.3(t) is 0.0834.

		A comparison of the RTDs is shown in Figure CDE13-2.1. Figure CDE13-2.1. E(t) for different variations The only equations that need to be changed in the POLYMATH examples above are those for the E(t) curves. They are changed to:



		The conversions are given below.



		Comparing the conversion and variance of the RTD curves, one can deduce that as the variance increases, the conversion decreases. This result can be explained by analyzing the RTD. With the higher variance curves, more reactants are able to leave the reactor at an earlier time, not allowing the reaction time to occur, thus decreasing the conversion.