Injection work

Suppose we have as our system the tank shown in Fig. 4.1. We now bring into the tank a mass dmj from the inlet line nothing flows out, there is no heat transfer, and there is no work due to moving the volume-changing piston or turning the shaft. What will be the energy balance for this operation This is easiest to see when we do it by a two-step process see Fig. 4.2. 

In the first step we let the mass dm flow in and simultaneously move the volume-changing piston out. We move the piston at a rate such that the fluid originally in the tank is not compressed. This means that all the fluid pushed aside by the fluid coming in is pushed into the space vacated by the volumechanging piston. Thus, no net work is done on the system because, for all the fluid involved, there is no volume change. Therefore, the compression work P dV is zero. Thus, the energy balance for step 1 is 

to get to the desired final state, we must move the volume-changing piston back to its original position. It must move back by a volume exactly equal to the volume of the fluid which moved in, which is Uj dm- then the work to move it back is dW —Pv dm-. The minus sign indicates that dV— dm-. The energy balance for this second step is 

After step 2 Piston moves back to its original position 

The energy balance for the entire injection process, which is the equivalent of the two steps given above, must be the sum of the energy balances for the two separate steps  

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The variables involved in the reaction step, if there is one, and the detection step, are those typical of flow-injection work (viz. the composition of the carrier and reagent streams, and their flow-rates). 

Warfarin tablets take several days to begin to work LMWH or fondaparinux injections work right away, so at first, LMWH or fondaparinux injections and warfarin tablets are used together. 

Another recent advancement involving chemists and design is the development of diesel emissions fluid (DEF) systems. Diesel emissions fluid is a 35% urea and 65% water mixture injected into the exhaust stream of a diesel vehicle to improve or reduce the NOx emissions. The urea injection works by decomposition of urea into ammonia when injected into the exhaust stream ... 

What does this (Pu) term represent We call it injection work, because it is exactly the work that was needed to inject the mass dm across the system boundaries. It is also sometimes called intrusion wclrk, flow work, and flow energy. ... 

Obviously, we could repeat the calculation for fluid flowing out the outlet line. How, then, will we reconcile this injection work idea with Eq. 4.18 Equation 4.18 is correct as it stands for the process described above, the (Pu) dm, term is included in the dW term. HowevCT, we now break up the dW term as follows ... 

We now make this substitution in Eq. 4.18 and factor the injection work terms as shown in Eq. 4.30 ... 

The enthalpy is also called total heat, inherent heat, and several other names in older thermodynamics texts. Obviously, it is the combination of the internal energy per unit mass and the injection work per unit mass. You will soon appreciate its convenience in solving practical problems. Substituting Eq, 4.33 in Eq. 4.32, we find its exact equivalent ... 

We introduced the idea of injection work, split up the work term in Eq. 

In this statement the subscript all others on the work term is unnecessary, since there can be no injection work or out of a closed system. Thus, this term is usually written simply dW. 

In this system there is no work done except the injection work, which we have excluded from dW /, therefore, dW =0. When we make these substitutions in Eq. 4.34, we find... 

This increase in pressure which accompanies the decrease in velocity is often called pressure recovery. In such a device, kinetic energy is converted partly to injection work (shown by an increase in pressure) and partly to friction heating. 

The work terms in this chapter are all exclusive of injection work and would have the symbol g in Chaps. 4, 5, and 6. Here we drop the subscript because it causes no confusion to do so. 

This equation indicates that the section of the pump from the tip of the rotor blades to the outlet pipe converts the kinetic energy of the fluid to increased pressure (i.e., to injection work). This whole section is called the diffuser. Thus, the centrifugal pump may be considered a two-stage device ... 

Axial-flow compressors pass the gas between numerous (for example, 20) rows of blades arranged in an annulus see Fig. 9.10. The gas is successively accelerated by a [moving row of rotor blades and then slowed by a stator blade, which converts the kinetic energy imparted by the rotor blades to pressure (i.e., injection Work). The advantages of the axial-flow compressor over centrifugal compressors are the small cross-sectional area perpendicular to the... 

Comparing the simple impulse turbine in Fig. 9.12 with the simple reaction turbine in Fig. 9.13, we see that the former is more efficient. Either may be considered to consist of a nozzle which converts internal energy and injection work (AP/p) to kinetic energy and a device which uses this kinetic energy to produce work. In either case the kinetic energy of the fluid leaving the system is wasted. As shown in Sec. 7.4, we can, in principle, build an impulse turbine for which the outlet velocity (based on fixed coordinates) is zero. However, for a reaction turbine like that in Fig. 9.14, the maximum efficiency corresponds to = so the outlet kinetic energy will be... 

Centrifugal pumps work by giving the fluid kinetic energy and then converting this to injection work. They are generally high-flow-rate, low-pressure-rise devices. 

Thus, at this flow rate the conversion of injection work to internal energy by friction heating is 93 percent as large as the conversion of injection work to potential energy by increasing the elevation of the fluid. Finally, from Eqs. 14.2 and 14.3... 

The turbulent kinetic energy is fed into the flow by some kind of external work, generally a pressure gradient (i.e., injection work) in a pipe or a fan or a blower in a wind tunnel or the sun-driven work of thermal convection currents in the lower atmosphere. This work may first cause an increase in kinetic energy in the flow direction or merely a gradient in the velocity which will lead... 

The flow injection system used was a Control Equipment Corp. model MCA-103. The potentiostat used in conjunction with the flow injection work was either a PARC model 174 or an IBM 225. HPLC was performed on Waters Chromatography equipment consisting of model 510 pumps, model 680 gradient controller, model 460 electrocheptiical detector and U6K injector. 

Guide for Injection Works under Tunnel Construction in Complex Engineering Conditions, Ministry for Transport Construction, AU-Union Transport Construction Research Institute, Moscow (1983). 

Injection. For quantitative analysis, direct injection on the column, in our view, gives the best result. For such injections, unless one has the analytes efficiently focused on the column head, the flow rate of the mobile phase should not be too low. It is our experience that the direct injection works well on packed columns having an i.d. of 0.7 mm and larger. 

The retardation factor can also be used to explain how on-column injections work. When B is injected on-column, 90% of it sorbs into the stationary phase and only 10% goes into the vapor state. These numbers show that it is not necessary to evaporate all of the injected material in fact, most of the solute goes directly into the stationary phase. Similarly, in Chapter 9, R will aid in our understanding of programmed temperature GC. 

In pneumatic nebulization for ICP-OES, continuous sample feeding requires a sample aspiration time of about 30 s so as to attain a stationary signal, a measurement time of around 5-10 s, and a rinsing time again of 30 s at minimum. However, discrete sampling is also possible with injection systems known from flame AAS [140, 141] and by flow injection. Work with sample aliquots of down to 10 xL then becomes possible, which is particularly useful, for example, in work with microsamples [156] or for the analysis of solutions containing high salt contents [443]. 

Equation 2.9 would be a perfectly satisfactory form, except for a complication in the work term. When some amount of mass dm crosses the system boundary, it requires an amount of work of Pv- dm- to force it across the system boundary. This is called the injection work, flow work, injection energy, and some other names. If we divide the work term into this injection work, and all other types of work, we can rearrange Eq. 2.9 into... 

We normally see this equation with the excluding injection work deleted, because it is assumed that the reader knows that. Two special cases of Eq. 2.10 are widely used. If there is no flow of matter in or out, which means that we are considering some closed system containing a fixed mass of matter, then Eq. 2.10 becomes... 

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