Valve expansion, electronic

The electronic expansion valve has been fitted for some years onto factory-built packages but is nowavailable for field installations, and its use will become more general. The extent of its future... 

Electronic expansion valves are nowwidelyused on small automatic systems, mainly as the refrigerant flow control de vice (evaporating or condensing) in an integrated control circuit. 

An integrated control circuit with an electronic expansion valve can he arranged to permit the condensing pressure to fall, providing the valve can pass the refrigerant flow required to meet the load. This gives lower compressor energy costs. 

Thermostatic expansion valves or electronic expansion valves for most dry expansion circuits. 

Low condensing pressure operation should present no problem with float or electronic expansion valves, since these can open to pass the flow of liquid if correctly sized. 

Improved condenser pressure control. If the expansion valve is too tightlyrated to accept lower condenser pressure, change the expansion valve, possibly for the electronic type. 

Halocarbon systems are almost invariably controlled by mechanical or electronic thermostatic expansion valves, requiring a superheat signal to operate the control. The superheating of the suction gas into the compressor will cause it to expand, resulting in a lower mass flow for a given swept volume. Reduction of the superheat setting of the expansion valve will therefore result in better use of the compressor. The limit will be reached when there is insufficient signal to work the expansion valve. 

The LDPE production with tubular reactors (see Section 5.1) requires some sophisticated control valves [45]. The let-down valve (Fig. 4.2-6 B) controls the polymerization reaction via the pressure and temperature by a high-speed hydraulic actuator (9) together with an electronic hydraulic transducer. The position of the valve relative to the stem is determined by a high-resolution electronic positioner (7). The cone-shaped end of the valve stem (2), as well as the shrunk valve seat (3) are made from wear-resistant materials (e.g., sintered tungsten carbide) in order to tolerate the high differential pressure of around 3000 bar during the expansion of the polymer at that location. 

I- 1 REMPI of S( P2,i,o> D2)IC H S. The experimental setup and procedures used to measure the electronic S( P2.i,o, 2) state distribution formed in the 193-nm photodissociation of organosulfur species have been described in Section II.A [58-60]. In this experiment, a pulsed molecular beam of neat thiophene is produced by supersonic expansion through a pulsed valve (nozzle diameter = 0.5 mm, temperature 298 K, stagnation pressure = 90 Torr). 

A pulsed beam of OH radicals is produced by photodissociation of HNO3 molecules that are co-expanded with a rare gas through a room-temperature pulsed solenoid valve. In most experiments, either Kr or Xe is used as a carrier gas, producing a beam with a mean velocity of 450 m/s or 360 m/s, respectively. In the supersonic expansion, the beam is rotationally and vibrationally cooled, and after the expansion most of the OH radicals reside in the lowest rotational (J = 3/2) and vibrational level of the electronic... 

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