Maximum allowable tube

All x-ray tubes have a maximum power rating which cannot be exceeded without injury to the tube. This limit is fixed by the amount of heat that can be dissipated by the target and is usually stated by the manufacturer in terms of the maximum allowable tube current (in mA) for a given tube voltage (in kV). 

Where A max. is the coke thickness which coincides with the maximum allowable tube metal temperature or the maximum allowable pressure drop. 

If we use this rule of thumb, we here obtain a value for Ar ax of 40 K, which also confirms that a diameter of 4.6 cm is small enough to avoid a runaway as we then have a value of ATted.max of only 26 K (Figure 6.11.21). An alternative, although very rough estimation of the maximum allowable tube diameter to avoid a temperature... 

The maximum allowable tube stress will need to be calculated in order to calculate the actual reformer tube life. This is accomplished by using the Mean Diameter Formula given below. 

The maximum allowable dispersion will include contributions from all the different dispersion sources. Furthermore, the analyst may frequently be required to place a large volume of sample on the column to accommodate the specific nature of the sample. The peak spreading resulting from the use of the maximum possible sample volume is likely to reach the permissible dispersion limit. It follows that the dispersion that takes place in the connecting tubes, sensor volume and other parts of the detector must be reduced to the absolute minimum and, if possible, kept to less than 10% of that permissible (i.c.,1 % of the column variance) to allow large sample volumes to be used when necessary. 

For exchangers with fixed tube-plates the longitudinal stresses in the tubes and shell must be checked to ensure that the maximum allowable design stresses for the materials are not exceeded. Methods for calculating these stresses are given in the standards. 

Maximum allowable pressure drops (shell or tube side)... 

Vapor tube diameter 150mm from reactor to condenser Gas tube diameter following the condenser 80 mm Set pressure of bursting disk 1 bar g Maximum allowed working pressure 3.2 bar g Test pressure 6 bar g... 

The constraints changed from one trial configuration of the reaction system to the next, but typically included things like the minimum coolant temperature to permit efficient utilization of the heat of reaction as process steam, the maximum allowable aldehyde concentration in the condensed crude product to avoid refining and product specification problems, and a prescribed reactor pressure drop to insure adequate flow distribution among the reactor tubes at a minimum energy cost. All of these are implicit constraints — they establish the maximum or minimum levels for certain response variables. Explicit constraints comprise the ranges for search variables. 

Tm)c s maximum allowable skintemperature on a coked tube, (Tm)p s skin temperature on a clean tube,... 

Therefore, the heat transfer coefficients given in this table are only for very rou estimating purposes and assume the use of plain or low-Tinned tubes without special nucleation enhancement. th maximum allowable temperature difference between... 

Estimate the heat transfer area, using the maximum allowable heat flux. Take as 39,700 W/m for vertical and 47,300 W/m for horizontal reboilers. Choose the tube diameters and length. Calculate the number of tubes required. Estimate the recirculation ratio, not less than 3. 

The maximum allowable stress values for ASME BPV Code Sec. VIII D. 1 are given in ASME BPV Code Sec. II Part D Table lA for ferrous metals and Table IB for nonferrous metals. Maximum allowable stress values for Sec. VIII 0.2 are given in Sec. II Part D Table 2A for ferrous metals and Table 2B for nonferrous metals. Different values are given for plates, tubes, castings, forgings, bars, pipes, and small sections, as well as for different grades of each metal. 

The maximum allowed stress value in the tubes is strongly influenced by the maximum tube wall temperature and by the maximum heat flux. Even a slight increase in the maximum tube wall temperature may result in a serious decline of the expected tube life. 

Each time the tube count or number of tube passes is changed, the velocity is checked to make sure it is not too high. The maximum allowable velocity is calculated from equation 23. If the fluid is clean, the value to be used in the numerator will depend on the tube material used. A value of approximately 3,500 can be used for admiralty tubes. 

The machine starts with maximum baffle pitch and maximum percent cut. The maximum allowable baffle pitch is that specified in TEMA and will vary with tube OD. For most designs, the maximum cut is approximately 45%. The machine starts with this baffling arrangement and calculates the pressure drop. 

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