Continuously Varying Cell Constant

Conductivity cell with continuously varying cell constant... 

Wang et al. (1992) developed a new technique for the measurement of electrical conductivity of fiuoride melts, which employs the principle of a Continuously Varying Cell Constant (CVCC) through a moving platinum disc electrode in a relatively large diameter capillary tube-type conductivity cell. At the same time, the real component of the circuit impedance, R a, at a fixed high-frequency current is measured. Since the Rm versus the cell constant plot is linear, the electrical conductivity of the electrolyte is given by the relation... 

So far we only considered transport of particles by diffusion. As mentioned in 1 the continuous description was not strictly necessary, because diffusion can be described as jumps between cells and therefore incorporated in the multivariate master equation. Now consider particles that move freely and should therefore be described by their velocity v as well as by their position r. The cells A are six-dimensional cells in the one-particle phase space. As long as no reaction occurs v is constant but r changes continuously. As a result the probability distribution varies in a way which cannot be described as a succession of jumps but only in terms of a differential operator. Hence the continuous description is indispensable, but the method of compounding moments can again be used. 

A stirred cell equipped with a 0.22iuni membrane filter was charged with 30 mL of latex, the dispersion of microsphere. The specific surfrice area was adjusted to 0.19 m per ImL and the ionic strength was calibrated to 0.01. At the constant stirrer speed, buffer solution was introduced into the stirred ceil until steady state flux was attained. Protein solutions were introduced with step of pulse injection. The permeate flux was measured continuously with an electronic balance (Precision plus, Ohaus Co., USA) by a data acquisition system. The electronic balance was connected to a PC through a RS 232C interfece. The surface charge density of microspheres was varied as 0.45, S.94, 9.14 and 10.25, and the stirrer speed was varied as 300,400 and 600rpm. 

There are two different ways of operating a continuous stirred-tank fermentor, namely chemostat and turbidostat. In the chemostat, the flow rate of the feed medium and the liquid volume in the fermentor are kept constant. The rate of cell growth will then adjusts itself to the substrate concentration, which depends on the feed rate and substrate consumption by the growing cells. In the turbidostat the liquid volume in the fermentor and the liquid turbidity, which varies with the cell concentration, are kept constant by adjusting the liquid flow rate. Whereas, turbidostat operation requires a device to monitor the cell concentration (e.g., an optical sensor) and a control system for the flow rate, chemostat is much simpler to operate and hence is far more commonly used for continuous fermentation. The characteristics of the continuous stirred-tank fermentor (CSTF), when operated as a chemostat, is discussed in Chapter 12. 

Suppose that a well-mixed, stirred tank is being used as a fed-batch fermentor at a constant feed rate F (m3 h-1), substrate concentration in the feed Csi (kg m-3), and at a dilution rate D equal to the specific cell growth rate /i. The cell concentration Cx (kgm 3) and the substrate concentration Cs (kgm-3) in the fermentor do not vary with time. This is not a steady-state process, as aforementioned. Then, by switching the mode of operation, part of the broth in the tank is continuously... 

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