Holding section

A homogenizer or rotary positive pump may be used as a timing or metering pump to provide a positive, fixed flow through the pasteurization system (Fig. 6). The pump is placed ahead of the heater and the holding section. Various control drives assure that the pasteurized side of the heat exchanger is at a higher (7 kPa (1 psi)) pressure than the opposite side. 

In the holding section of a continuous sterilizer, correct exposure time and temperature must be maintained. Because of the distribution of residence times, the actual reduction of microbial contaminants in the holding section is significantly lower than that predicted from plug flow assumption. The difference between actual and predicted reduction in viable microorganisms can be several orders of magnitude therefore, a design based on ideal flow conditions may fail. 

If the flow of the medium in the holding section were an ideal plug flow, the degree of sterilization could be estimated from the average residence time in the holding section by Equation 10.6 ... 

Figure 10.4 [1] shows the results for theoretical calculations [4] for the ratio n, the number of viable cells leaving the holding section of a continuous sterilizer, to Hq, the number of viable cells entering the section, as a function of the Peclet number (Pe), as defined by Equation 10.7, and the dimensionless Damkohler number (Da), as defined by Equation 10.8 ... 

Calculate the required length of the holding section of the sterilizer... 

From Figure 10.4, the value of n/rig is about 3 X 10 ° and almost equal to that required in this problem. Thus, the length of the holding section should be 36 m. 

A medium, which flows through an 80 mm i.d. stainless tube at a flow rate of 1.0 m h , is to be continuously sterilized by indirect heating with steam. The temperature ofthe holding section is maintained at 120 °C. The number of bacterial spores of 10 rn in the entering medium must be reduced to 0.01 m . The specific death rate of the bacterial spores in the medium, medium density, and medium viscosity at 120 °C are 180 h , 950 kgm , and 1.0kgm h , respectively. 

Therefore, the holding section should be 26.8 m, which is 2.7 m longer than the result from the assumption of ideal plug flow. 

H enthalpy of steam relative to raw medium temperature, J/kg n flux of microorganisms due to axial dispersion, m 2s 1 k Boltzmann s constant, 1.3805 x 10 23 J/K or 1.3805 x l-16 erg/K kd specific death rate, s or kg/m s L length of holding section, m M initial mass of medium in batch sterilizer, kg Mw molecular weight of gas molecules, kg/kmol ms steam mass flow rate, kg/s mc coolant mass flow rate, kg/s... 

Later, after section 271 of 35 U.S. Code (53) on contributory infringement became the law, the Appellate Court (12) refused to hold contributory infringement, holding section 271 (c) on a staple article was dominant over the rest of the section, presumably 271 (b), and refused to reopen the case. Later a new attempt to retry was unsuccessful (13). Hence, on the point of contributory infringement, the patent was in essence valid, but ineffective. 

Determine the required holding time,. Since the temperature of the holding section is constant, Eq. (17.20) simplifies to... 

Roig, S. M., Vitali, A. A., Ortega Rodriguez, E. and Rao, M. A. 1976. Residence time distribution in the holding section of a plate heat exchanger. Journal Lebensmittel Wissenschaft und Technologie, 9 255-256. 

Mount sections on microscope slides for processing with antibodies. Cryostat sections can be collected on microscope slides SUPERFROST PLUS slides hold sections well. Alternatively, glass microscope slides can be coated with a 0.1 mg/ml poly-L-lysine (Sigma PI399) solution in water. Loss of sections during processing is a frequent problem. 

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