Hot or cold spots

Sensors are distributed equally in various areas of the stability chamber no less than 2 inches from any wall. A set of sensors should be placed near or at the temperature and/or humidity controller of the chamber, as the controller will maintain the set-point temperature and/or humidity within the chamber during normal use. For a typical walk-in chamber, a minimum of 24 thermocouples and six resistance-transmitting devices are recommended for use in the mapping study. For a benchtop or reach-in chamber, a reduced number of sensors may be used. It is important to note that regardless of the size of the chamber, the placement pattern of the sensors should be such that any potential hot or cold spots are mapped, particularly those areas near the door and comers of the chamber. Typical sensor placement patterns for a reach-in and walk-in chamber are shown in Figures 16.1 and 16.2, respectively. In these examples, the extremities of the chamber (i.e., top and bottom) have a larger number of sensors than the middle of the chamber, since these areas would have a greater probability of either hot or cold spots, due to the airflow pattern within the stability chamber. 

What do you do if the acceptance criteria for successful qualification are not met specifically, the limits for temperature and/or humidity Reasons for the failure to meet the acceptance criteria must be determined. There may be mechanical problems associated with the chamber that disrupt the airflow uniformity throughout the chamber. This will increase the likelihood of hot or cold spots developing in the chamber. This issue must be addressed before another qualification is attempted. If the problem cannot be resolved, a wider tolerance limit for normal... 

Microwave heating for 20 min is the same as Method 1 except that the heating is employed four times for 5 min each. Total time required is 35 min. Improved immunostaining of many types of antigens can be achieved by extending the heating time. The procedure requires attention for 20 min to check the fluid level, and occurrence of hot or cold spots may complicate the procedure. 

In most spray towers, the air flow rate and the temperature are adjusted at the inlet ports to maintain balanced air/temperature patterns. When the atomized slurry is sprayed into the drying chamber, the air flow pattern is disturbed and becomes very turbulent. This effect can cause localized temperature gradients (hot or cold spots) and affect the particle drying characteristics. It is possible to have... 

Thermal testing Voids or disbands in both metallic and nonmetallic materials, location of hot or cold spots in thermally active assemblies Laminated structures, honeycomb, and electronic circuit boards Produces a thermal image that is easily interpreted Difficult to control surface emissivity poor discrimination... 

For systems requiring more uniform temperature, to minimize local hot or cold spots for systems that tend to foul for systems that operate close to the freezing points for systems vith materials that thermally degrade easily. Example, batch polymerizers condensers for fatty acids or alcohols or for maleic anhydride. 

Disadvantages to the use of a separate transfer line and separate FTIR inclnde the need for a separate heater for the transfer line, hot or cold spots in an improperly heated line, leading to the possibility of contamination due to buildup of condensable gases in the transfer line. In addition, more linear bench space is required for side-by-side instruments. New instruments are now available with no separate transfer line between the thermal analysis system and the FTIR spectrometer. In the Netzsch Perseus TGA-DSC-FTIR system, a Bruker Optics ALPHA FTIR spectrometer is connected directly to the thermal analyzer in a vertical arrangement (Figure 16.29b). The built-in heated gas cell of the spectrometer is directly connected to the gas outlet of the furnace. No separate heating controller is needed. The low volume of the short gas path results in rapid response and is especially useful where condensable evolved gases are present. 

The die is attached either directly to the end of the extruder or with a transfer pipe or adapter that connects the die to the extruder. Polymer melt temperature in the adapter must be maintained. Transfer pipes like extruder barrels should have healer bands covering as much surface area as possible to minimize the possibility of hot or cold spots. Remember two of the extruder objectives are to provide uniform melt temperature and the proper melt temperature. Transfer pipes normally have smaller diameters than the extruder barrel with a converging hole as material... 

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