Heat envelope

Figure 2-4 shows a low temperature (-300°F) applieation of a turboexpander in the separation of air in a simplified eyele. The air is eooled in a heat exehanger down to near its liquefaetion point, and then some further heat is removed by the turboexpander while a portion of the stream is eondensed. By visualizing a heat envelope around the proeess it ean be seen that virtually all the energy deerease... 

This is a striking anticipation of van t Hoff s gaseous theory of solution (see Vol. IV). It seems as if Dalton supposed that the particles of the gas retain their heat envelopes even whenithey are in solution. 

In the flame phase the water vapor forms an envelope around the flame, which tends to exclude air and dilute the flammable gases. The water vapor reacts endothermically with the flame radicals. The alumina residue becomes a conduit through which heat is conveyed away from the flame area, slowing down polymer decomposition. 

Although there are several limits which apply to heat pipe operation, these generally lend themselves to specific design solutions or occur at sufficiently high levels of performance to permit a wide latitude of practical appHcations. The envelope of these limits is shown generically in Figure 3. 

The constant-molar-overflow assumption represents several prior assumptions. The most important one is equal molar heats of vaporization for the two components. The other assumptions are adiabatic operation (no heat leaks) and no heat of mixing or sensible heat effects. These assumptions are most closely approximated for close-boiling isomers. The result of these assumptions on the calculation method can be illustrated with Fig. 13-28, vdiich shows two material-balance envelopes cutting through the top section (above the top feed stream or sidestream) of the column. If L + i is assumed to be identical to L 1 in rate, then 9 and the component material balance... 

Now for the snag of a soft bearing material - will it not fail to support the normal operating forces imposed on it by the crankshaft All bearing materials have a certain p - v envelope within which they function safely (Fig. 26.3). The maximum pressure, p, that the bearing can accept is determined by the hardness of the surface the maximum velocity, v, is determined by heating, and thus by the thermal conductivity... 

Outdoor air is generally less polluted than the system return air. However, problems with reentry of previously exhausted air occur as a result of improperly located exhaust and intake vents or periodic changes in wind conditions. Other outdoor contamination problems include contaminants from other industrial sources, power plants, motor vehicle exhaust, and dust, asphalt vapors, and solvents from construction or renovation. Also, heat gains and losses through the building envelope due to heat conduction through exterior walls, floor, and roof, and due to solar radiation and infiltration, can be attributed to effects from external sources. 

Heat losses and gains by heat conduction through the building envelope... 

The throw of downward-projected heated jets or upward-projected chilled jets can be derived from Eqs. (7.85) and (7.88) for K equal to some value, e.g., 0.1. Helander and Jakowatz, in their work on heated jets projected downward, have called attention to some of the differences between the actual conditions and those assumed for analysis. One of these is the radial escape of warm air in the terminal zone of a hot stteam projected downward. This escaping warm air then rises and causes a change in ambient conditions for the upper part of the jet. The terminal zone and the edges of the jet are zones of marked instability, with definite surges and fluctuations, so that the jet envelope is very difficult to define or to determine experimentally. In the closure to the paper presented by Knaak, Dr. Helander suggested that from the point of view of practical application, the distance to the beginning of the unstable, tet-minal zone of the jet is about 80% of the jet throw. 

The hunnidity ratio oJ a rotjm at any given time is given by a Jatent heat balance equation including the water vapor flows due to infiltration to ventilation to moisture transport through envelope elements... 

A fictive sky temperature, dependent on ambient temperature, emissivity, and cloudiness, is introduced to account for the long-wave radiative heat exchange between the building envelope and the sky. 

Dampf-heizrohr, n. steam (heating) pipe, -heizung, /. steam heating, -holzschliff, m. steamed mechanical wood pulp, -hiillet /. steam jacket vaporous envelope. 

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