Maximum pressure drop

The term essentially a drag coefficient for the dust cake particles, should be a function of the median particle size and particle size distribution, the particle shape, and the packing density. Experimental data are the only reflable source for predicting cake resistance to flow. Bag filters are often selected for some desired maximum pressure drop (500—1750 Pa = 3.75-13 mm Hg) and the cleaning interval is then set to limit pressure drop to a chosen maximum value. 

The diameter of the air core varies with the feed volumetric flow rate. If the rate is too low, there is no air core and all of the pulp leaves the cyclone as underflow if the rate is too high, the air core expands, closing off the apex and forcing all of the pulp to leave the cyclone as overflow. Consequently there is a minimum and maximum volumetric feed rate. Because the pressure drop is proportional to the square of the volumetric feed rate, the minimum and maximum rates can be monitored by the pressure drop. The ratio of the maximum pressure drop to the minimum pressure drop should be less than 4, meaning the maximum to minimum volumetric feed rate should be less than 2. 

Ttbles 9.20 and 9.21 present recommendations for maximum pressure drops of components in the supply and extract air systems in order to achieve a certain target level for power consumption in the whole system. In category Low," this target level is 1500 in Normal, 2500 and in High 4000 W/(mVs),... 

TABLE 9.20 Recommended Maximum Pressure Drops for Specific Components in Supply Air Systems... 

Air filter resistance, final The maximum pressure drop allowed across a filter to ensure that the design airflow rate is achieved. 

Description Particie size (/im) Minimum theoreticai piates/30 cm Exclusion limit (poiystyrene moiecuiar weight) Standard flow rate (ml/min) Maximum flow rate (ml/min) Maximum pressure drop/30 cm (bar)... 

H type columns must be used at a flow rate and pressure drop below maximum values listed in Tables 4.12-4.16. Standard flow rates are also listed in these tables. They are flow rate range recommendable for long-term usage in tetrahydrofuran at 25°C and vary with temperature. H type columns can be operated at a higher flow rate at elevated temperatures. They also vary with solvent depending on the viscosity. They are approximately inversely proportional to the solvent viscosity. The maximum pressure drop listed in the tables is for one column. When some columns are used in series, the total maximum pressure drop is a summation of values of all columns. 

Check maximum pressure drop through wet caps ... 

Since /q VLdx < [(1 + Vl,s)/2]4 and < 1. the following estimate of the maximum pressure drop in the liquid domain is valid ... 

The maximum number of theoretical plates that can be achieved for a particular column depends on the pressure drop per theoretical plate and the maximum pressure drop allowed over the column, (ising the same reduced parameters given earlier, the maximum number of theoretical plates obtained for an open tubular... 

A 6 in. sch 40 pipeline is designed to carry SAE 30 lube oil at 80°F (SG = 0.87) at a maximum velocity of 10 ft/s. You must install an orifice meter in the line to measure the oil flow rate. If the maximum pressure drop to be permitted across the orifice is 40 in. H20, what size orifice should be used If a venturi meter is used instead of an orifice, everything else being the same, how large should the throat be ... 

Other practical features that must be taken into account are the fixed and integer lengths of tubes (8, 12, 16, and 20 feet), and the maximum pressure drops allowed. 

HEP A filter operating conditions (separate analysis under way) —Minimum and maximum pressure drop... 

An inlet pressure about 10 times greater than the maximum pressure drop across the column was required. By going to inlet pressures of 100 atm, the flow should be controllable to 0.2%. The main problem with this technique is that if the column or any part of the system should plug, the pressure of the system prior to that point rises until it reaches the primary pressure. This can result in dangerously excessive pressures. 

THE VENDOR SHALL GUARANTEETHE MECHANICAL OPERATION OF THE EGUPMENT AND SYSTEM PROVIDED FOR A MINIMUM OF ONE YEAR AFTER START-UP. HLR EXPECTS PROCESS GUARANTEES ON THE SPECIFIED DISTILLATION RATES. CONDENSER PmFORMANCE.AM> MAXIMUM PRESSURE DROPS. ENTRAINMENT, AIR LEAKAGE RATES AND UTILITY CONSUMPTIONS SHALL BE SPECIFIED. ALLPROOUCT AND PROCESS SPECIFICATIONS WHICH THE VENDOR CANNOT GUARANTEE SHALL BE ENUMERATED. 

What is the maximum pressure drop that can be sustained without danger... 

The pressure drop across the length of the packing was extremely small and was beyond the detectable limit of the available pressure gauges. The full scale of the available transducer (validyne differential transducer) was 200 units, which correspond to a pressure drop of 1 cm of water. In our study, it was observed that the maximum pressure drop within the gas and liquid flow rates studied was about 1 mm of water (20 calibration units). A trend was seen wherein the pressure drop increases with increasing gas and liquid velocities. 

American Petroleum Institute (API) recommends a maximum pressure drop of 3%. This should be taken into account when sizing valves higher pressure drops not only cause reduced flow but also cause quick damage to the valve due to chatter, especially when the blowdown is set below the effective pressure drop. Therefore, always try to obtain short and simple inlet piping. Complex inlet piping is only effective if the piping is at least one or two pipe sizes larger than the SRV inlet and its size is reduced just before the SRV inlet. 

There are, however, specially designed switch-over systems on the market that respect the API recommendation of a maximum pressure drop of 3% and that are designed to have a smooth flow path. This needs careful checking with the manufacturer, as the 3% is considered over the valve only and does not take into account any additional pipe riser runs (Figure 6.9). 

Next to the traditional changeover valves, some suppliers offer selector valves which comply with the API requirements and only have a maximum pressure drop of 3%. This low-pressure drop is obtained by means of their special... 

Maintaining the downcomer or a standpipe under a moving bed condition allows a large pressure buildup along the downcomer. For a given quantity of particles in the downcomer, the pressure at the bottom of the downcomer is closely associated with the relative velocity between the gas and particles. The pressure drop rises with the relative velocity as the particles are in a moving packed state. The maximum pressure drop in the downcomer is established when particles are fluidized, a state which can be expressed in terms of the pressure drop under the minimum fluidization condition as... 

Figure 2.63 illustrates the effect of the distortion coefficient (Dc) on the characteristics of a linear and an equal-percentage valve. As the ratio of the minimum to maximum pressure drop increases, the Dc drops and the equal-percentage characteristics of the valve shift toward linear and the linear characteristics shift toward QO. In addition, as the Dc drops, the controllable minimum flow increases, and therefore, the rangeability (the flow range within which the valve characteristic remains as specified) of the valve also drops. 

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