Heat single-phase

Most chemical processes involve two important operations (reaction and separalion) that are typically carried out in different sections of the plant and use different equipment. The reaction section of the process can use several types of reactors [continuous stirred-tank reactor (CSTR), tubular, or batch] and operate under a wide variety of conditions (catalyzed, adiabatic, cooled or heated, single phase, multiple phases, etc.). The separation section can have several types of operations (distillation, extraction, crystallization, adsorption, etc.), with distillation being by far the most commonly used method. Recycle streams between the two sections of these conventional multiunit flowsheets are often incorporated in the process for a variety of reasons to improve conversion and yield, to minimize the production of undesirable byproducts, to improve energy efficiency, and to improve dynamic controllability. 

The first direct-arc furnace in the United States was a single-phase two-electrode rectangular furnace of 4-t capacity at the Halcomb Steel Company (Syracuse, New York), which made its first heat in 1906. A similar but smaller furnace was installed two years later at the Firth-Sterling Steel Company in McKeesport, Pennsylvania. In 1909, a 15-t three-phase furnace was installed in the South Works of the Illinois Steel Company, in Chicago, Illinois, which was, at that time, the largest electric steelmaking furnace in the world. It was the first round instead of rectangular furnace and operated on 25-cycle power at 2200 V. 

Thermal Design for Single-Phase Heat Transfer. 11-5... 

THERMAL DESIGN FOR SINGLE-PHASE HEAT TRANSFER... 

If the vapor is superheated at the inlet, the vapor may first be desuperheated by sensible heat transfer from the vapor. This occurs if the surface temperature is above the saturation temperature, and a single-phase heat-transfer correlation is used. If the surface is below the saturation temperature, condensation will occur directly from the superheated vapor, and the effective coefficient is determined from the appropriate condensation correlation, using the saturation temperature in the LMTD. To determine whether or not condensation will occur directly from the superheated vapor, calculate the surface temperature by assuming single-phase heat transfer. 

Adequate single-phase protection is provided on low-voltage ac motor starters by three overload relays, which are now standard. Rotor heating is not particularly a problem on smaller motors which have more thermal capacity, but it is important to protect the stator windings of these machines against burnout. 

Voltage unbalance (negative phase sequenceJ This causes negative sequence components and results in excessive heating of the motor windings. An unbalanced voltage may occur due to unevenly distributed single-phase loads. 

In the event of single phasing, in star-connected windings, one of the phases of each positive and negative sequence components will counter-balance each other, to produce zero current in the open phase (Figure 12.8(a)). The magnitude of these components in the two healthy phases are equal, i.e. I, = 1, and the maximum heat of the stator as in equation (12.4)... 

At room temperature, diffusion is so slow that the alloy just stays like this, frozen as a single phase. But if you heat it up just a little - to 160°C, for example - and hold it there ("ageing"), the copper starts to diffuse together to form an enormous number of very tiny (nm) plate-like particles, of composition roughly CuAlj. On recooling to room temperature, this new structure is again frozen in. 

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