RTD from Experimental Tracer Curves

Previously, the RTD funetions for flow systems were deseribed. In praetiee, the RTD is determined experimentally by injeeting a traeer at the inlet of the system and monitoring the response at the outlet information about the system is derived from these results. In a tubular reaetor, the RTD measurements are used to determine how elosely the plug flow assumption is obeyed. 

The methods used in determining the RTD are an impulse signal and a step-ehange or a periodie input of the traeer. The following reviews these methods of injeeting a traeer to analyze the RTD in flow systems. 

Suppose that a quantity m of traeer is injeeted at the inlet of a system during a period of time, whieh is very short eompared to the mean residenee time, f. The eoneentration of this traeer material is measured in the outlet stream as a funetion of time. Assume the following eonditions  

Closed system input and output by bulk flow only (i.e., no diffusion takes plaee aeross the system boundaries). 

Linearity with respect to the tracer analysis, that is, the magnitude of the response at the outlet is directly proportional to the amount of tracer injected. 

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