Pump Calculations Chapter

This appendix contains the calculations required to specify the pump for delivery of 60% wt. red nitric acid from the absorption column to 

Partial pressure of nitric acid Partial pressure of water 

This value is compared with the result achieved by applying the economic pipe diameter formula for stainless steel from Ref. P1 (P-161)  

Accept the larger value as a conservative estimate. This suggests that a standard pipe of nominal pipe size 1.5, schedule number 80S, is suitable (Ref. P2 Table 6.6). This piping is 48 mm (1.9 in.) o.d. and 38 mm (1.5 in.) i.d. 

Normal fluid velocity (u) = Volumetric flowrate/Area 

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The volume of iron-free groundwater that can be pumped per volume of injected, aerated water defines the efficiency of the process. The efficiency is determined by the ratio of the retardations of oxygen during injection and of iron during pumping. This chapter shows how these retardations can be calculated forgiven water qualities and aquifer compositions. 

The Hvp, vapor head, is calculated by ob.serving the fluid temperature, and then consulting the water properties graph in this chapter. Let s say we re pumping water at 50° F (10° C). The Hvp is 0.411 feet. If the water is 212° F (100° C) then the Hvp is 35.35 feet. The vapor head is subtracted because it robs energy from the fluid in the suction pipe. Remember that as the temperature rises, more energy is being robbed from the fluid. Next, we mu.st subtract the Hf... 

This operating window is quantified or rated by the term Suction Specific Speed, Nss . The Nss is calculated with three parameters, the speed, the flow rate, and the NPSHr. These numbers come from the pump s performance curve, discussed in Chapter 7. The formula is the following ... 

The reader should refer to the chapter on pumps for more detailed calculation methods and for a description of common pumping equipment and pumping applications. The simple relationships provided here are useful in obtaining initial design specifications information in sizing a pump for an application. 

Mechanical vibration of pipe is handled in the same manner as for reciprocating pumps (Volume 1, Chapter 12). Normally, if the pipe support spacing is kept short, the pipe is securely tied down, the support spans are not unifoiTn in length, and fluid pulsations have been adequately dampened, mechanical pipe vibrations will not be a problem. It is good practice to ensure that the natural frequency of all pipe spans is higher than the calculated pulsation frequency. The pulsation frequency is given by ... 

A different set of forms, in extensive use for failure rate calculation, are used to illustrate the remaining sections of this chapter. Beginning with Figure 6.3, the forms present a worked pump example for the conversion of actual plant raw data to plant-specific failure rate data. 

The system of Figure 2-27 consists of 125 feet of unknown size schedule 40 steel pipe on the discharge side of a centrifugal pump. The flow rate is 500 gallons per minute at 7o°F. Although the tank is located above the pump, note that this elevation difference does not enter into the pipe size-friction drop calculations. How ever it will become a part of selection of the pump for the serrice (see Chapter 3). For quick estimate follow these steps ... 

Centrifugal pumps, 181 Discharge systems, 187 Example calculation, 186 Flow friction losses, 185. 186 Friction losses, pipe, see Chapter 2 Friction, 188 Pressure head, 184—186 Static head, 184-186 Suction head, 184, 185 Suction lift, 184, 185 Suction systems, 186 Hvdroclones, 265—267 Application system, 267 Ignition, flammable mixtures, 493 Impellers, centrifugal, reducing diameter, 203 Impellers,... 

Methods for the calculation of pressure drop through pipes and fittings are given in Section 5.4.2 and Volume 1, Chapter 3. It is important that a proper analysis is made of the system and the use of a calculation form (work sheet) to standardize pump-head calculations is recommended. A standard calculation form ensures that a systematic method of calculation is used, and provides a check list to ensure that all the usual factors have been considered. It is also a permanent record of the calculation. Example 5.8 has been set out to illustrate the use of a typical calculation form. The calculation should include a check on the net positive suction head (NPSH) available see section 5.4.3. 

Other pieces may have to be elevated to enable the system to operate. A steam jet ejector with an intercondenser that is used to produce a vacuum must be located above a 34 ft (10 m) barometric leg. Condensate receivers and holding tanks frequently must be located high enough to provide an adequate net positive suction head (NPSH) for the pump below. For many pumps an NPSH of at least 14 ft (4.2 m) H2O is desirable. Others can operate when the NPSH is only 6 ft (2 m) H2O. See Chapter 8 for a method of calculating NPSH. 

Experiments were run on a laboratory screw pump to evaluate the fluid temperature increase of an enclosed fluid as a function of element rotation time. For this case, the device was similar to that shown in Fig. 7.4, and the discharge was blocked using a valve. The blocked flow caused the rate to be zero and = 0 p. Both the device and the fluid were at room temperature at the start of each experiment. The task at hand is to use the information below and the equations presented in Chapter 7 to calculate the temperature increase for the fluid for a total time of 30 seconds in three-second increments. The dimensions of the single-flighted extrusion device are provided in Table 7.5. 

The screw pump was operated at a screw speed of 85 rpm (N = 1.417 revolu-tions/s). The calculated results are shown in Table 7.6, which was generated using the method found earlier in this chapter and in Appendix A7. 

The simplest way of cutting costs is to standardize extraction plants. In batch processes with solid feed materials it is advisable to standardize the plants by using the payload volume of feed-material and calculating the capacity corresponding to the given bulk density and the elaborated cycle time. To justify these efforts a certain market size for the materials in question must be given, and the number of plants of the selected size that can be sold. The individual sizes depend on the availability of individual plant components, such as pumps, compressors, piping and armatures. For standardized pressures see Chapter 7.3.1. 

Refrigeration cycles "absorb" heat leaked in at a temperature level below that of the environment and "pump" it back to that environment. The minimum amount of work per Joule of heat absorbed, W, is given by the equation in the footnote of this chapter. Calculate W for the following temperatures 6°C, -18°C (freezer), -111°C (liquefied natural gas), and -253°C (liquid hydrogen). Assume that the temperature of the environment, To, is 20°C. What are the qualitative implications for the flow rate of heat leaked in and the power required to pump it back to the environment ... 

Industrial process streams are frequently treated as being single phase fluids, having simple properties of viscosity and density for calculations involving pumping, mass transfer, etc. In fact most industrial process streams occur as dispersions of two or more phases as discussed in earlier chapters. Dispersed phases introduce complications such that, in many cases, the viscosity is not expressed by a single number at constant temperature and pressure, but also depends upon whether the material is flowing, and even its recent history ... 

Ultrafast radiationless transitions are often observed through ultrashort pump-probe time-resolved measurements. In this section, a theoretical formula of the pump-probe time-resolved stimulated emission spectra is briefly introduced and the relationship between the dynamics calculation and the pump-probe spectra are presented. For this purpose, the dynamics of a simple model system with vibrationally non-equilibrated is discussed. For a real application of the theoretical treatment given in this chapter, ultrafast charge transfer taking place in photosynthetic RCs is studied. 

When the equilibrium constants are known, the partial pressures of the individual gases can be calculated under certain restrictive conditions, e.g., closed system, pressures of some gases are fixed, etc. For example, if one starts with a closed system that is initially pumped out and the salt allowed to decompose so that pressure builds until equilibrium is reached, it is possible to calculate the partial pressures of the gases in the system. Thus, for carbonates, the pressure of C02 equals the equilibrium constant. For other classes of salts the calculations can be much more complicated. Appropriate methods are discussed in the individual chapters. 

Chapter 2 begins by defining essential terms in vacuum technology - gas flow rate, pumping speed, conductance, etc. It also emphasises a basic assumption for calculation - that continuity is established in a system (what enters must eventually leave). Simple equations are stated and their use demonstrated. 

In this chapter, those pumps that are frequently encountered throughout the range of vacuum pressures are dealt with (see Table 3.1). Where necessary, to support the calculations, the operating principles and pump characteristics are reviewed. With gas-transfer pumps operating in the HV/UHV range (typically diffusion or turbomolecular pumps), continuous operation of backing (forevacuum) pumps is required for efficient performance. In such cases, the combination is considered. 

This chapter examines some areas in which vacuum technology is applied to the chemical sciences. Firstly, unit operations such as drying and distillation, of importance in chemical technology, are discussed. The use of condensers in association with vacuum pumps is introduced and typical calculations demonstrated. 

In Chapter 2, essential terms in vacuum technology (e.g. pV-throughput, pumping speed, conductance, etc.) were defined. These are required for the quantification of gas loads in vacuum systems. Calculations based on relevant relationships were demonstrated (Examples... 

Chapter 3 summarised initially the various types of vacuum pump available and the pressure ranges in which they normally operate. Subsequent sections dealt specifically with types of pump and, in some cases, to support calculations, reviewed the operating principles and characteristics. For example, aspects of oil-sealed rotary pump operation were discussed (Examples 3.1-3.5) and Roots pumps, widely used in applications where large gas loads at pressures in the rough-medium range have to be handled, were examined (Examples 3.7-3.9). 

Chapter 3 also considered those entrapment pumps that remove gas particles by sorption effects such as gettering and implantation. The operating principles of sputter ion pumps were explained (Example 3.26) and some typical calculations performed (Examples 3.27-3.29). Aspects of the use of titanium sublimation pumps were dealt with (Examples 3.30-3.33). 

Chapter 2 acknowledges the fact that in the design of vacuum systems, pump sets and pipework of an appropriate size must be used and that it is vital that the flow of gases into and out of the system be quantified. Terms widely used in vacuum technology are defined and the calculation of flow and related quantities under the three major types of gas flow is discussed. 

A linear relationship not only applies for the pressure characteristic but also for the power characteristic, see Fig. 6.11. For example, the pumping efficiency, Section 6.5.2, can be directly calculated using the dependencies shown. Examples can be found in Chapter 7. The plate-plate model therefore gives a maximum pumping efficiency of 1/3, see Fig. 6.10. 

Internal energy (through the enthalpy, defined in Sec. 2.5) is useful for the calculation of heat and work quantities for such equipment as heat exchangers, evaporators, distillation columns, pumps, compressors, turbines, engines, etc., because it is a state function. The tabulation of all possible Q s and W s for all possible processes is impossible. But the intensive state functions, such as specific volume and specific internal energy, are properties of matter, and they can be measured and their values tabulated as functions of temperature and pressure for a particular substance for future use in the calculation of Q or W for any process involving that substance. The measurement, correlation, and use of these state functions is treated in detail in later chapters. 

Chapter 5 considered pump types and their evaluation and selection. After selecting a pump type, the next step is to size the pump. This requires calculating the flow rate and the pressure rise across the pump or the pump head. The net positive suction head (NPSH), is also important, particularly for centrifugal pumps. NPSH is the difference between the total pressure and the vapor pressure of the fluid at the pump inlet. NPSH will be discussed later. 

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