Longitudinal eddy diffusivities of liquid on sieve plates have been determined experimentally with fiber optic technique. The experiments were carried out in a rectangular simulator with air-water system. Two sieve plates were used: one with 5mm diameter holes and 7% free area of tray

the other 10mm and 9%. The weir heights were ranged from 10 to 50mm

as conventionally used nowadays. The stimulus-response technique used was first proposed by Aris and later corrected by Bischoff. In the experimental work the tracer

here aqueous rhoda-mine-B solution being used

was not injected upstream inside the boundary of the active plate area

but upstream outside the boundary of that

i. e. injected into the liquid in the upstream downcomer

and the tracer concentrations were measured at two sections along the flow path. Consequently

the problem of a perfect delta function of tracer into the flowing system and the difficulty of uniformly distributing tracer along the section of injection were thus avoided. Since the measuring probes were quite small in size(about 2mm in diameter) and the tracer was not injected into the liquid on the plate

the flow pattern on plate would not be disturbed and the results should be more reliable than those reported previously in the literature. The data have been correlated as follows: ( 1 ) For Sieve plate with 5mm holesD0.5e= 0.0339 - 6.27 × 10-4/hw+ 0.0165FT + 2.57 × 10-3L ( 2 ) For Sieve plate with 10mm holes D0.5e=0.0243 - 6.40 × 10-4hw+ 0.0121FT+ 3.77× 10-3L And a generalized correlation for hole diameters from 5 to 10mm is: D0.5e = 0.0155 -6.31 × 10-4hw + 0.0275FT + 3.13 × 10-3L where De= Eddy diffusivity

m2/s FT=Vapor flow parameter based on total column sectional area

(m/s)(kg/m3)1/2 hw - Height of weir above plate floor

mm. L = Liquid flow rate

m3/hr per m length of weir. By using the eddy diffusion model and the eddy diffusivity found by the above correlations

the predicted Murphree efficiency agrees well with the actually determined one of a well known precise experiment of Foss et al.