الفهرس 
EXPERMENTAL APPARATUS AND TEST PROCEDUREOnly 14 pages are availabe for public view
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Abstract
The condenser in a refrigeration system is a heat exchanger that
generally rejects all the heat from the system. This heat consists of heat
absorbed by the evaporator plus the heat from the energy input to the
compressor. The compressor discharges hot, high-pressure refrigerant gas into
the condenser, which rejects heat from the gas to some cooling medium. Thus,
the refrigerant condenses back to the liquid state and drains from the condenser
to continue in the refrigeration cycle. The common forms of condensers may be
classified on the basis of the cooling medium as (1) water-cooled, (2) aircooled,
and (3) evaporative (air- and water-cooled) condensers.
Evaporative condenser is the subject of this research. As with watercooled
and air-cooled condensers, evaporative condensers reject heat from a
condensing vapor into the environment. In an evaporative condenser, hot, highpressure
vapor from the compressor discharge circulates through a condensing
coil that is continuously wetted on the outside by a recirculating water system.
Air is simultaneously directed over the coil, causing a small portion of the
recirculated water to evaporate. This evaporation removes heat from the coil,
thus cooling and condensing the vapor.
Evaporative condensers reduce the water pumping and chemical
treatment requirements associated with cooling tower/refrigerant condenser
systems. In comparison with an air-cooled condenser, an evaporative
condenser requires less coil surface and less airflow to reject the same heat, or
alternatively, greater operating efficiencies can be achieved by operating at a
lower condensing temperature.
The evaporative condenser can operate at a lower condensing
temperature than an air-cooled condenser because the ambient dry-bulb
temperature limits the air-cooled condenser. In the evaporative condenser, the
ambient wet-bulb temperature limits heat rejection, which normally is 8 to 14
°C lower than the ambient dry bulb. Also, evaporative condensers typically
provide lower condensing temperature than the cooling tower/water-cooled
condensers because the heat and mass transfer steps (between the refrigerant
and the cooling water and between the water and ambient air) are more
efficiently combined in a single piece of equipment, allowing minimum
sensible heating of the cooling water. Evaporative condensers are, therefore,
the most compact for a given capacity.In this research an experimental investigation is conducted on the
condensation of R11 refrigerant in an evaporative condenser under saturated
condition. This investigation is to study the different factors affecting the
evaporative condenser performance. A test rig is designed, constructed and
installed in the refrigeration laboratory, for the purpose of investigating these
factors. Many test runs are carried out by changing the refrigerant vapor
pressure, the air face velocity (or the air flowrate) and the water flowrate. The
air inlet conditions are kept constant at 33.5 °C and 45% RH.
In an evaporative condenser, heat flows from the condensing refrigerant
vapor inside the tubes, through the tube wall, to the water film outside the
tubes, and then from the water film to the air. The driving potential in the first
step of heat transfer is the temperature difference between the condensing
refrigerant and the surface of water film, whereas the driving potential in the
second step is a combination of temperature and water vapor enthalpy
difference between the water surface and the air. Sensible heat transfer
between the water stream and the air-stream at the water-air interface occurs
because of the temperature gradient, while mass transfer (evaporation) of water
vapor from the water-air interface to the air-stream occurs because of the
enthalpy gradient.
The experimental data were represented in curves. The results obtained
indicate that the rate of heat transfer is increased very much with respect to the
dry operation. However, the overall heat transfer coefficient is not necessarily
increased. The increase in pressure DROP due to the reverse flow direction of
the sprayed water leads to an increase in the energy consumption of the blower
circulating the air. This energy increase is incomparable to the reduction in the
energy consumed by the refrigeration cycle.