One of the key factors in designing an affinity membrane contactor is the flow pattern in the device. This paper presents a study carried out on the residence time distribution (RTD) of a tracer in a cross-flow tubular affinity module. For simplicity, no membrane was incorporated in the system. A tubular conduit with a total length of 0.7 m was designed and to improve the RTD of the tracer, various screw-threaded inserts were tested. The experimental tests for the RTDs in a channel with no inserts, a channel with a plain rod and a channel with helical inserts were performed and compared with the corresponding theoretical models. Two different methods of analyzing the data were adopted. The first method was based on the evaluation of the variance of the E-curves, and the second was based on the use of Fourier transform analysis. The experimental data showed that appropriate combination of pulsation frequency, piston stroke length, and geometry resulted in an optimum value for the Peclet number. This provides an explanation of why the capturing efficiency of the target species in membrane affinity separations is enhanced significantly by oscillatory flow.