A frequency response method is examined as a possible experimental method for the simultaneous determination of liquid mixing, plate efficiency, vapor-liquid equilibrium, and liquid holdup on a single bubble tray. The method depends upon the introduction of sinusoidal fluctuations in the concentration of a species in the liquid and vapor fed to the plate and the measurement of the induced concentration variations of the same species in the effluent liquid. It is applicable to multi-component systems.
The analytical results used to interpret the measurements are based on a linearized model. Despite this idealization, systems exhibiting marked curvature of the liquid-vapor equilibrium relation are adequately represented. Systems showing very significant enthalpy effects are treated quantitatively when the liquid on the plate is perfectly mixed. This is done with the aid of the “signal flow graph” technique.
With incompletely mixed plate liquid, mathematical difficulties have so far prevented the quantitative interpretation of measurements of the frequency response when enthalpy effects are large. At present it appears that the frequency response technique is limited to perfectly mixed plates, i.e., to small laboratory sized plates, or to incompletely mixed systems in which the heat effects are small, i.e., gas absorption plates and distillation systems in which the volatilities and latent heats of all components are of comparable magnitude.