Condenser operation

Let s say we have a centrifugal refrigeration compressor, driven by a motor. The motor is tripping off because of high amperage. Should we open or close the suction throttle valve shown in Fig. 22.2 Answer— close it. Of course, both the evaporator vapor outlet temperature and the process fluid outlet temperature will increase. But that is the price we pay for having too small a motor driver on the compressor. Does this mean that when our home air conditioner gets low on freon, our electric bill drops Correct. But the price we pay is a hot home. 

How about the compressor discharge pressure What is this controlled by Answer—the condenser. The compressor discharge pressure has nothing whatsoever to do with the compressor. And this statement is true regardless of whether the compressor is a reciprocating or centrifugal machine, or fixed- or variable-speed. It is the condenser temperature that determines the compressor discharge pressure. 

Lowering the compressor discharge pressure can be achieved by changing to cooler water to the refrigerant condenser. But how does this affect the horsepower load or electrical power demand on the compressor s driver Well, it depends. It depends on how much the refrigerant vapor flow increases, as the compressor discharge pressure is reduced. 

For instance, suppose we are working with a reciprocating compressor. This particular machine has a very small volumetric clearance and a very high volumetric efficiency (these mysterious terms are fully explained in Chap. 29, Reciprocating Compressors ). With this compressor, a significant decrease in discharge pressure will result in only a tiny increase in vapor flow. Therefore, the load on the driver will decrease. 

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Distillation is a method of separation that is based on the difference in composition between a Hquid mixture and the vapor formed from it. This composition difference arises from the dissimilar effective vapor pressures, or volatihties, of the components of the Hquid mixture. When such dissimilarity does not exist, as at an a2eotropic point, separation by simple distillation is not possible. Distillation as normally practiced involves condensation of the vaporized material, usually in multiple vaporization/condensation operations, and thus differs from evaporation (qv), which is usually appHed to separation of a Hquid from a soHd but which can be appHed to simple Hquid concentration operations. 

Condensers may be of one or two general types depending on the specific application. Contact condensers operate with the coolant, vapors, and condensate intimately mixed. In surface condensers, the coolant does not come in contact with either the vapors or the condensate. The usual shell-and-tube condenser is of the surface type. Figure 29-14 illustrates a contact condenser which might be used to clean or preclean a hot corrosive gas. 

Condenser operation for fouling. 1. Fouling on refrigerant side (lube... 

Although condensers likely warrant a separate chapter, conventional equipment often used alongside with heat exchanger are described here. In surface and contact condensers, the vapors can be condensed either by increasing pressure or extracting heat. In practice, condensers operate through removal of heat from the vapor. Condensers differ principally in the means of cooling. In surface... 

Some general facts about condenser operations should be noted ... 

The condenser operating pressure should be so selected as to give a reasonable temperature difference between the condensing temperature and the water temperature. The quantity of water required should not be penalized by requiring a small temperature rise in the water. 

As an example of the effects of a scale deposit, assume a copper-alloy tubed condenser operating at 70 °F inlet temperature, 2 in Hg back-pressure and in a clean condition ... 

For desorption the vapor desorbed from the silica gel has to be condensed. For this reason a low temperature heat sink is required. The hydraulics of the plant provides two heat sinks a 10 m3 rain water cistern and the thermal solar plant. With these heat sinks two desorption modes could be carried out a desorption with simultaneous condensation of the vapor an a second mode in which the desorption and condensation were not done simultaneously. If desorption and condensation of the vapour occur at the same time, then the condensation heat is rejected via the rain water cistern. The condensation heat can also be removed by the solar plant when the desorption and condensation operation are discontinuous. In this case the solar plant heats up the adsorber during daytime but no condensation is done. The condensation take place through the solar system during the night given correspondingly low outside temperatures. 

The major consumption of water in coke plants is for cooling purposes in a variety of cooling and condensing operations. For the coke quenching operation alone, about 120 to 900 gal of water are required per ton of coke.1 The various sources of process wastewater include the following ... 

A forward-feed double-effect evaporator, having 10 m2 of heating surface in each effect, is used to concentrate 0.4 kg/s of caustic soda solution from 10 to 50 per cent by mass. During a particular run, when the feed is at 328 K, the pressures in the two calandrias are 375 and 180 kN/m2 respectively, and the condenser operates at 15 kN/m2. For these conditions, calculate ... 

A triple-effect backward-feed evaporator concentrates 5 kg/s of liquor from 10 per cent to 50 per cent solids. Steam is available at 375 kN/m2 and the condenser operates at 13.5 kN/m2. What is the area required in each effect, assumed identical, and the economy of the unit ... 

A double-effect forward-feed evaporator is required to give a product which contains 50 per cent by mass of solids. Each effect has 10 m2 of heating surface and the heat transfer coefficients are 2.8 and 1.7 kW/m2 K in the first and second effects respectively. Dry and saturated steam is available at 375 kN/m2 and the condenser operates at 13.5 kN/m2. The concentrated solution exhibits a boiling-point rise of 3 deg K. What is the maximum permissible feed rate if the feed contains 10 per cent solids and is at 310 K The latent heat is 2330 kJ/kg and the specific heat capacity is 4.18 kJ/kg under all the above conditions. 

The results show that, at temperatures below 60 °C and an air feed stoichiometry below three, the cathode exhaust is fully saturated (nearly fully saturated at 60 °C) with water vapor and the exhaust remains saturated after passing through a condenser at a lower temperature. In order to maintain water balance, all of the liquid water and part of the water vapor in the cathode exhaust have to be recovered and returned to the anode side before the cathode exhaust is released to the atmosphere. Because of the low efficiency of a condenser operated with a small temperature gradient between the stack and the environment, a DMFC stack for portable power applications is preferably operated at a low air feed stoichiometry in order to maximize the efficiency of the balance of plant and thus the energy conversion efficiency for the complete DMFC power system. Thermal balance under given operating conditions was calculated here based on the demonstrated stack performance, mass balance and the amount of waste heat to be rejected. 

A single jet, which discharges to the atmosphere, or to a condenser operating at atmospheric pressure, is called a hogging jet. Let s... 

Two problems arose with the use of the barometric condenser. First, if the condenser operated at subatmospheric pressure, how can the water be drained out of the condenser That is easy. Set the condenser on a hill 34 ft high. Then drain the water down, through a barometric leg, to a seal pot. The pressure which a column of water 34 ft high exerts is equal to one atmosphere, or one bar. Hence the term, barometric leg. ... 

The curve in Fig. 18.4 also represents the best possible vacuum that can be obtained in any surface condenser. The majority of surface condensers I have seen do operate right on the curve. Condensers operating below the curve are typically suffering from air in-leakage through the turbine shaft seals. 

Sublimation temperatures are in the range of —10 to —40°C and corresponding vapor pressures of water are 2.6-0.13 mbar. Cabinet tray dryers are the most commonly used type. The trays are lifted out of contact with hot surfaces so the heat transfer is entirely by radiation. Loading of 2.5 lb/sqft is usual for foodstuffs. Drying capacity of shelf-type freeze dryers is 0.1-1.0kg/(hr)(m2 exposed surface). Another estimate is 0.5-1.61b/(hr)(sqft). The ice surface has been found to recede at the rate of 1 mm/hr. Freeze drying also is carried out to a limited extent in vacuum pans, vibrating conveyors, and fluidized beds. Condensers operate as low as —70°C. 

Experience at ORC has shown that a condenser operating temperature of 0 C is too low when processing residue-containing feedstocks. The product recovery is reduced by 5% or more due to retention of heavy ends in the condenser. A temperature of 38 C is sufficiently high to avoid this problem. In order to ensure that, in spite of this, light liquids are condensed and not... 

In this system, steam, cooling water, and steam condensate operate and sustain the three subsystems. The state variables of each flow, that is, temperature, pressure, and composition are shown in Table I together with the flow rate. 

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