Absorption System Operating Equipment Evaporator

Absorption System Operating Equipment Evaporator Points : Absorption System Operating Equipment Evaporator, Absorber, Purgers, Concentartor, Condenser, Heat Exchanger, Water returns from n air condition system at about 55° F, is cooled to about 45°F, in the evaporator, and is then pumped to the air conditioning units where it picks up heat from the conditioned space. The chilled water pump is external to the refrigeration machine. Liquid refrigerant in the bottom of the evaporator lows by gravity into a sump mounted on the side of the shell. The evaporator pump takes refrigerant from this sump and delivers it to spray tank in. the evaporator. The spray provides a higher rate of heat transfer between the water in the tubes and the refrigerant on the outside of the tubes than simply immersed in the refrigerant. The high rate of heat transfer is, of course describe since the purpose of the evaporator is to remove heat from the water used for air conditioning and thereby boil the refrigerant. Absorber The refrigerant vapor produced in the evaporator flows to the absorber because of the low pressure in this area. This low pressure exists because that concentrated absorbent solution (Lithium bromide) exerts a strong attractive force of the molecules of refrigerant (water) vapor. The molecules of the refrigerant vapor condense into a liquid as they come in contact with the molecules of the absorbent solution.

The absorbent solution is sprayed into absorber, to at exposes the greatest area of the solution to the molecules of the refrigerant vapor, and thus speed the condensing process. In the absorber, three quantities of heat are released. The heat of condensation from vapor condensing into the absorbent, the heat of dilution as the vapor goes into solution with the absorbent and sensible heat. In order to remove this heat and maintain a constant temperature in the absorber the absorbent solution falls over a cooling coil after being sprayed into the absorbent cooling water is supplied to this coil remove the three quantities of heat from absorber. In this heat were not remove the temperature and pressure in the absorber would rise, and flow from the evaporator would stop.

After falling over the cooling coil, solution of refrigerant and absorbent drain into the bottom of the absorber shell. Purgers All units include a purge unit which used to remove non-condensable gases. Non-condensable gases present in small quantities can raise the total pressure the absorber sufficiently to significant change the evaporator pressure very small pressure increases causes appreciable change in the refrigerant evaporating temperature. Concentartor In concentrator a steam coils supply to boil away the refrigerant from the solution, the concentrated absorbent in the bottom of the concentrator. The boiling away of the refrigerant from the solution while the absorbent remains in the concentrator is possible because the refrigerant and absorbent are carefully selected with the refrigerant having a lower boiling temperature than the absorbent. The concentrator is never at a temperature high enough for the absorbent to boil. As the refrigerant vapor boil away from the solutions the absorbent left in the bottom of the unit has a higher percentage of absorbent than it does refrigerant. The solution is said to be “concentrated” hence, the name concentrator for this component of the machine. Hot water can also be used in the concentrator as a source of heat from the cycle. Condenser The refrigerant vapor boiling from the solution in the concentrator flows to the condenser. Here it comes into contact with coil tube surface filled with condenser water. The condenser piping should c9ntain a bypass for control purposes. This will permit adjusting the water flow rate through the condenser to give the optimum condenser temperature for the most efficient operation The refrigerant vapor condenses and drops to the bottom of the condenser from which it flows to the evaporator through a regulating orifice. This competes the operating cycle. Heat Exchanger The efficiency of the cycle is substantially improved by the used of a heat exchanger external to the shell. Note that the concentrator for a certain operation condition has a temperature of 210°F, whereas the temperature of the absorber is about 15.0°F. The heat exchange is used to transfer heat from. the hot, solution leaving the concentrator to the lower temperature solution going to the ‘concentrator. After passing through the heat exchanger, the concentrated solution enters the flash chamber. Here a small part of the water in the, concentrated solution flashes,’ or evaporates due to the low pressure. This flashing cools the remaining solution. The hash vapors then move into the absorber, while the remaining solution flows to mix with the solution being pumped to the absorber spray tree.

The use of a heat exchanger’ results in a two fold again, lower steam consumption for the same amount of refrigerant evaporated from the concentrator, and less heat to be removed from the absorber by the cooling water.