Potential energy effects

An inventor claims to have devised a CO. compressor that requires no shaft work. The device operates at steady state by transferring heat from a feed stream of 2 lb,/s of CO. at 150 psia and 100°F. The CO is compressed to a final pressure of 500 psia and a temperature of 40°F. Kinetic and potential energy effects are negligible. A cold source at -140°F drives the device at a heat transfer rate of 60 Btu/sec. Check the validity of the inventor s claim. 

In most circumstances of interest to the designer of chemical reactors, the kinetic and potential energy effects are negligible as is the shaft work term. Under these circumstances,... 

If one again takes note of the fact that work effects and kinetic and potential energy effects are usually negligible in chemical reactors, equation 10.1.6 simplifies to... 

For liquids stored at their saturation vapor pressure, P = Ps, and Equation 4-91 is no longer valid. A much more detailed approach is required. Consider a fluid that is initially quiescent and is accelerated through the leak. Assume that kinetic energy is dominant and that potential energy effects are negligible. Then, from a mechanical energy balance (Equation 4-1), and realizing that the specific volume (with units of volume/mass) v = 1/p, we can write... 

Two computer programs for determination of i, vn, and ( ) are listed in Appendices II and III of reference [9]. The former accounts for adsorption potential energy effects. The latter neglects these contributions. 

A general thrust of the chapter will be SIMPLICITY. Differences in terminology have been eliminated wherever possible. In this analysis Availability, Available Energy, Exergy, and Work will be used as equivalent. This means that kinetic and potential energy effects and the potential work to be derived from the diffusion of chemical species into equilibrium with the environment have been ignored. This simplification may introduce significant inaccuracies in some studies, but is not important here. The intent is to demonstrate that simplified - perhaps even approximate - analysis can have valuable practical applications. 

Solution Choose the tank as the control volume. As in Example 7.1, there is no shaft work, and again we assume negligible kinetic- and potential-energy effects. Equation (7.7) therefore is written... 

The kinetic and potential energy effects can be neglected ( = 0). There is no exchange of heat with the surroundings (Q = 0). The general energy balance reduces to AH = W Note that the value of W is positive (work done on the system). ... 

Assume that there are no work interactions, the potential energy effects are negligible, and the nozzle operates at steady state. 

Assume that kinetic and potential energy effects are negligible... 

Disregarding the kinetic and potential energy effects, the energy balance over the control volume for a steady-state operation is... 

Assume that heat transfer effects between the turbine and surroundings are negligible. Also, kinetic and potential energy effects are disregarded. 

Consider the heat of reaction of a substance obtained in a bomb calorimeter, sucti as in a bomb in which the volume is constant but not the pressure. For such a process (the system is the material in the bomb), the general energy balance, Eq. (4.2 a), reduces to (with no work, mass flow, nor kinetic or potential energy effects)... 

We assume that we have a solid plane adsorbent of density p (molecules per cubic centimeter) in the semi-infinite space 2 < 0, and an adsorbed film in the form of a slab with parallel walls in the region 0 < s < h. The adsorbed film is assumed to have the bulk liquid density uniformly, pr, = T/h. We consider only potential energy effects, as explained above. 

This work W differs from the W of Eq. (2,7-1), which also includes kinetic- and potential-energy effects. Writing the first law of thermodynamics for this case, where A becomes AC/,... 

The potential energy effect is neglected because of the magnitude of the other effects ... 

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