Maintaining constant temperature

Isothermal Gas Flow in Pipes and Channels Isothermal compressible flow is often encountered in long transport lines, where there is sufficient heat transfer to maintain constant temperature. Velocities and Mach numbers are usually small, yet compressibihty effects are important when the total pressure drop is a large fraction of the absolute pressure. For an ideal gas with p = pM. JKT, integration of the differential form of the momentum or mechanical energy balance equations, assuming a constant fric tion factor/over a length L of a channel of constant cross section and hydraulic diameter D, yields,... 

If the temperature rise over the temperature range is very high, then to operate at constant temperature requires internal cooling coils in the column, or other means of heat remo al to maintain constant temperature operation. Usually this condition will require considerably less transfer imits for the same conditions when compared to the adiabatic operation. 

FIGURE 6.16 (a) On the reversible path, the work done in Example 6.5 is relatively large (w = -2.12 kj) because the change in internal energy is zero, heal flows in to maintain constant temperature and constant internal energy. Therefore, q =... 

Heating, ventilation, and air conditioning (HVAC) is a very expensive utility. However, it is essential and serves a variety of purposes. Not only is it important to maintain constant temperature and humidity, it is also important to balance the pressure in the processing areas to minimize cross-contamination opportunities. Dust collection, as mentioned earlier, is very important when handling powders. The dust generated during some processes may be toxic and may pose an explosion hazard. This system is typically very closely associated with the HVAC system. 

It may be necessary to transfer a quantity of heat, dQ, from the reservoir into the system in order to maintain constant temperature in the system the total entropy change of the system plus reservoir, dS, will then be... 

Isothermal Gas Flow in Pipes and Channels Isothermal compressible flow is often encountered in long transport lines, where there is sufficient heat transfer to maintain constant temperature. Velocities and Mach numbers are usually small, yet compressibility... 

In some hybrid systems, the generated vapor in a vented reaction is high enough to remove sufficient latent heat to moderate or temper the runaway (i.e., to maintain constant temperature). This subsequently gives a smaller vent size. 

The latent heat of pressure change hTt, which is usually negative, is the amount of heat that must be removed from the system for unit increase in pressure to maintain constant temperature when the system is compressed at constant composition. For an ideal gas in which pV = nRT and (dUldp)T S = 0, the second term on the right hand side of Eq. 2.10 gives us hT s = (dUldp)T + p dVldp)T %. We then obtain the latent heat of pressure change as shown in Eq. 2.17 ... 

The correct answer is (D). This process varies the pressure while maintaining constant temperature. This causes a change from a gas to a liquid, otherwise known as condensation. 

An experimental mixing process for a binary system is represented schen cally in Fig. 13.4. The two pure species, both at T and P, are initially sepa by a partition, withdrawal of which allows mixing. As mixing occurs, expans or contraction of the system is accompanied by movement of the piston so i the pressure is constant. In addition, heat is added or extracted to maintain constant temperature. When mixing is complete, the total volume change of system (as indicated by piston displacement d) is... 

As we have seen already, najms is dependent on the equilibrium pressure, p, and the adsorbent temperature, T. The usual practice is to maintain constant temperature... 

The heat flows passing the two metals are TJS. a and 7.7sb and are not equal, since the Peltier heat must be absorbed at the junction to maintain constant temperature. Therefore,... 

Description Air is heated and loaded with evaporated (1) o-xylene and/ or naphthalene. The hydrocarbon/air mixture enters a multitubular reactor (2) containing catalyst. An agitated salt melt removes the heat of reaction and maintains constant temperature conditions. Reaction heat generates high-pressure steam. 

In special cases, cationic surfactants are used as dye-leveling agents (63, 64). Cationic dyes with temperature-sensitive diffusion coefficients often yield non-uni-form shades, because of the difficulty of maintaining constant temperatures in large... 

All that is necessary to maintain constant temperature in a system is to place it in a thermostat. In essence a thermostat is a system which can absorb or give out indefinite amounts of heat without changing in temperature. Thus a mixture of ice and... 

Cells with built-in water jackets are available for maintaining constant temperature for kinetic studies. Flow-through cells for flow injection and HPLC applications typically have cell volumes between 0.5 and 2 pi, with a path length of approximately 1cm. For limited samples, typically with a cross-sectional area of 2 X 2.5 mm, holding at least 60 pi of sample is available. With special ultramicrocells, samples volume as low as 5 pi can be used. 

---