Momentum transfer in a fixed-bed reactor described by the surface renewal model

This paper presents experimental measurements and theoretical predictions of the velocity gradient in a fixed-bed reactor with single phase liquid flow. The local measurements are carried out by means of microelectrodes embedded in the packing of the bed, whereas the corresponding predictions are based on the surface renewal model. The fluid elements age distributions, needed in the surface renewal model, were determined using the variable-interval time-averaging (VITA) method. The parameters of VITA method, i.e. local interval time-averaging length a and threshold level k, were optimally selected and are equal to 3T_C (T_C is the integral time deduced from auto-correlation functions) and 0.9, respectively. It was shown that the surface renewal model is appropriate for predictions at high liquid flow rates, corresponding to a flow that behaves like a turbulent flow. Moreover, it was shown that with only one velocity gradient signal measurement, both experimental and theoretical values are obtained for a specified flow rate. The average value of the signal provides the experimental measurement, whereas its fluctuating part yields the corresponding theoretical prediction.