USE OF ULTRASONIC TDR FOR REAL-TIME NONINVASIVE MEASUREMENT OF COMPRESSIVE STRAIN DURING MEMBRANE COMPACTION

A major limitation in previous compaction studies has been the inabili ty to obtain direct simultaneous measurements of permeate flux and mem brane thickness changes in real-time. In this paper we describe the de velopment and application of ultrasonic time-domain reflectometry (TDR ) for quantifying membrane compressive strain. The non-invasive nature of the technique allows standard performance data including permeate flux to be simultaneously measured under realistic conditions. Represe ntative data for commercial reverse osmosis membranes are presented to demonstrate the potential benefits of this more complete approach to compaction studies. Results are also described for ultrasonic TDR expe riments using cellulose acetate membranes which show the effect on mem brane compressive strain behavior of changes in overall porosity and u pstream pressure. Additional results show the variation in compressive strain during both the creep and recovery phases of a single pressuri zation cycle as well as over multiple cycles. Given these capabilities , the use of ultrasonic TDR should enable improved experimental and mo deling analyses regarding the effects of operational and structural pa rameters on membrane performance.