Power required

In the case of a liquid recycle, the cost of this pressure increase is usually small. Pumps usually have low capital and operating costs relative to other plant items. On the other hand, to increase the pressure of material in the vapor phase for recycle requires a compressor. Compressors tend to have a high capital cost and large power requirements giving higher operating costs. 

The cost of power required to run a refrigeration system can be estimated approximately as a multiple of the power required for an ideal system. Thus, for an ideal system,... 

The configuration interaction calculation with all possible excitations is called a full Cl. The full Cl calculation using an infinitely large basis set will give an exact quantum mechanical result. However, full Cl calculations are very rarely done due to the immense amount of computer power required. 

Fan Rating. Axial fans have the capabiUty to do work, ie, static pressure capabiUty, based on their diameter, tip speed, number of blades, and width of blades. A typical fan used in the petrochemical industry has four blades, operates neat 61 m/s tip speed, and can operate against 248.8 Pa (1 in. H2O). A typical performance curve is shown in Figure 11 where both total pressure and velocity pressure are shown, but not static pressure. However, total pressure minus velocity pressure equals static pressure. Velocity pressure is the work done just to collect the air in front of the fan inlet and propel it into the fan throat. No useflil work is done but work is expended. This is called a parasitic loss and must be accounted for when determining power requirements. Some manufacturers fan curves only show pressure capabiUty in terms of static pressure vs flow rate, ignoring the velocity pressure requirement. This can lead to grossly underestimating power requirements. 

Flow meters have traditionally been classified as either electrical or mechanical depending on the nature of the output signal, power requirements, or both. However, improvement in electrical transducer technology has blurred the distinction between these categories. Many flow meters previously classified as mechanical are now used with electrical transducers. Some common examples are the electrical shaft encoders on positive displacement meters, the electrical (strain) sensing of differential pressure, and the ultrasonic sensing of weir or flume levels. 

Differential-Temperature Thermal Flow Meters. Meters of this type inject heat into the fluid and measure the resulting temperature rise or, alternatively, the amount of power required to maintain a constant temperature differential. The power required to raise the temperature of a flowing stream by an amount AT is given by the relation ... 

Reciprocating Compressors. Prior to 1895, when Linde developed his air Hquefaction apparatus, none of the chemical processes used industrially required pressures much in excess of I MPa (145 psi) and the need for a continuous supply of air at 20 MPa provided the impetus for the development of reciprocating compressors. The introduction of ammonia, methanol, and urea processes in the early part of the twentieth century, and the need to take advantage of the economy of scale in ammonia plants, led to a threefold increase in the power required for compression from 1920 to 1940. The development of reciprocating compressors was not easy Htfle was known about the effects of cycles of fluctuating pressure on the behavior of the... 

This electrolytic process technology is no longer used because of the extensive and continuous electrolyte purification needs, the high capital and power requirements, and economic inabiHty to compete with large-scale anthrahydroquinone autoxidation processes. 

Machining. Magnesium is the easiest of all stmctural metals to machine (120). Because of this machinabiUty, it is sometimes used in apphcations where a large number of machining operations are required. The machinability of magnesium alloys relative to that of other metals based on the lowest power required to remove 16 cm of metal and when magnesium is assigned a value of unity, is (120) ... 

The unit power consumption, P, or power required to cut a given quantity of a particular material, can be deterrnined by... 

A homogenize is a high pressure positive pump with three, five, or seven pistons, that is driven by a motor and equipped with an adjustable homogenizing valve. Smoother flow and greater capacity are obtained with more pistons, which force the product iato a chamber that feeds the valve. In design and operation, it is desirable to minimize the power requirements for obtaining an acceptable level of homogenization. At 17.2 MPa (2500 psi) and a volume of 0.91 t/h (2000 lb/h), a 56-kW (75-hp) motor is required. 

The decay constant is the key to the mixing rate number defined for Re > lO" by N/ D/TY = 0.5 for a disk flat blade turbine (DFBT), and N/ (D/TY = 0.9 for the propeUer. Therefore, power required to achieve any degree of uniformity in a fixed time is proportional to D and D for DFBT and propeUer, respectively. 

---