الفهرس يوجد فقط 14 صفحة متاحة للعرض العام
 |  | from | 178 |  |  |
| | | from | 178 | | |
المستخلص
Energy conservation is a major concern in the vapor
compression refrigeration cycle especially in areas of hot
weather (such as in the middle east countries, where the
temperature may exceed 50°C) where air conditioning systems
are used for long periods causing high energy consumption. In
such a weather condition, the performance of the air-cooled
condensers decreases sharply and the electrical power
consumption increases excessively. Such a problem led to many
research programs in order to improve the performance of these
condensers by making some modifications aiming in enhancing
the heat transfer from them. The common forms of condensers
may be classified on the basis of the cooling medium into (1)
air-cooled condensers, (2) water-cooled condensers, and
(3) evaporative condensers.The evaporative condenser will be the subject of this
research. The evaporative condensers-as air cooled and water
cooled ones- reject heat from the condensing vapor into the
cooling medium. In the evaporative condenser, superheated
high pressure vapor, coming from the compressor discharge,
flows through a banks of tubes. The external surface of the
tubes is continually kept wet by a water distribution system. On
the other hand, air is drawn around the condenser tubes.
Absorbing heat from the refrigerant, some of the water on the
tubes evaporates in the air. Consequently, the refrigerant vapor
gives up its heat and condenses.Evaporative condensers have an advantage over the water
cooled condensers which is the reduction of water pumping and
chemical treatment requirements associated with the cooling
tower/refrigerant condenser systems. They also have an
advantage over the air cooled condensers which is the lower
iv
coil surface area and air flow requirements to reject the same
amount of heat, hence greater operating efficiencies may be
obtained by operating at lower condensing temperature.The evaporative condenser operates at a lower condensing
temperature than the air cooled condenser which is limited by
the ambient dry bulb temperature, while the evaporative
condenser is limited by the ambient wet bulb temperature and it
is well known that the ambient wet bulb temperature is usually
lower than the ambient dry bulb temperature by 8-14 °C, which
makes the evaporative condenser operate at a lower condensing
temperature. Therefore, these systems are usually energy
efficient compared to those using an air cooled condenser.
Furthermore, the initial cost of the evaporative condenser is
lower than that of the water cooled condenser due to reduced
space and number of components.In this research, a theoretical analysis is adopted to calculate
the amount of heat transfer to both water and air flows using the
enthalpy potential difference. In this method, the control surface
was taken as the condenser plus the two sections before and
after it.An experimental investigation is also conducted using hot
water flowing under a high flow rate in an evaporative
condenser. This investigation aims to determine and study the
factors affecting the performance of the evaporative condenser.
For this purpose, a test rig was designed, constructed and
installed in the refrigeration laboratory. Many experiments were
conducted by varying the hot water temperature, the air flow
rate and the injection water flow.