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Air-cooled condensers

The simplest air-cooled condenser consists of a plain tube containing a refrigerant, placed in the still air, and, relying on the natural circulation of air. For example, a domestic refrigerator condenser, which can also have some secondary surface in the form of support and wiring.

Above this size, the air flow through the condenser surface by forced convection, i.e. fans. High thermal stability of a boundary layer on the air side of the heat exchanger allows the use of all but a very small capacitors in the surface. This takes the form of lamellas with attached refrigerant tubes in most commercial structures. The balance of external and internal surface will be from 5 : 1 to 10 : 1.

Consumption of liquefied refrigerant help of gravity, so the input will be in the upper part of the vessel, and exit at the bottom. The growth of the tubes should be avoided in the design, and you should exercise caution when installing to get the pipes level.

The air flow can be vertically or horizontally, and configuration of the capacitor will follow from this (see Fig.
6.2). Small cylindrical matrices are used air flowing radially inward and outward through the fan at the top.

Forced convection of a large volume of air at low resistance leads to the General use of the screw or single-stage axial fans. Where one of the fans will be too big, somewhat less than the fans give advantages to the lower limit of speed and noise, and flexibility of operation in the winter period (see Section 6.12). Residential areas with a lower fan speed can be specified to reduce the noise level. Lower air flow derate condenser, and producers can to give ratings to 'standard' and 'quiet' products.

Low calorie and high specific volume of air implies a large amount remove the condenser heat. If the mass flow decreases, temperature increase should grow, increasing the temperature and condensing pressure to give lower plant efficiency. In practice, the increase of air temperature remains between 9 and 12 K. the mass flow, assuming the growth 10.5 K, then 1/(10.5*1.02)=0.093 kg/s kW), where 1.02-specific heat capacity of air.

As an example of these large air flows required, condenser air, installation of air conditioning systems for office buildings cooling capacity of 350 kW and rejecting 430 kW to 40.85 kg/sec or about 36m3 from the air. This cooling air must be cold soon as possible so capacitor should be mounted where such a flow of fresh atmospheric air without recirculation. In large air flows necessary, the power to move them, and as a result of noise, are the factors that restrict the use of air-cooled condensers.

As the capacitor increases the load on the temperature difference of inlet air (dew point temperature will rise to reject heat faster with the same surface. He with a constant flow of air. Capacitor nominal, kW/K, where capacitor load in kW and K is the temperature difference can be considered as constant, as a first approximation.....

 
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