推廣 熱搜:
圖片報道
 Air Cooled Heat Exchangers are normally used where a process system generates heat which must be removed, for which there is no local use.

They are a “green” solution as compared to cooling towers and shell and tube heat exchangers because they do not require an auxiliary water supply (water lost due to drift and evaporation, plus no water treatment chemicals are required). Where there is a no utility such as water available as a cooling medium

They are usually used when the outlet temperature is more than about 20 deg. F above the maximum expected ambient air temperature. They can be used with closer approach temperatures, but often become expensive compared to a combination of a cooling tower and a water-cooled exchanger. Fig. 1 shows the operating principle of a typical Air Cooled Heat exchanger.

Operating-principle-of-Air-Cooled-Heat-Exchangers

Fig. 1: Operating principle of Air Cooled Heat Exchanger

How are they constructed (Refer Fig. 2 and Fig. 3)?

Construction-of-Air-Cooled-Heat-Exchangers
Fig. 2: Construction of Air Cooled Heat Exchangers
Construction-of-Air-Fin-Fan-Cooler.
Fig. 3: Construction of Air Fin Fan Cooler.
 

Bay Arrangement in Air Cooler:

one or more tube bundles, serviced by two or more fans, including the structure, plenum and other attendant equipment is called a bay. Refer Fig. 4 for bay arrangements.

Bay-arrangements-in-Air-Coolers

Fig. 4: Bay arrangements in Air Coolers

What standards are used for air cooled exchangers?

SHELL DEP special requirement for air cooled exchangers:

Air Cooler Tubes:

 

Wall thickness for tubes with an OD of 1 inch (25.4 mm) to 11/2 (38.1 mm) shall not be less than specified in table below: (Fig. 5)

Minimum-wall-thickness-requirements-for-Tube-Material
Fig. 5: Minimum wall thickness requirements for Tube Material

What kind of finned tubes are used?

 

Fin Types (Fig. 6):

Figure-showing-various-types-of-fins

Fig. 6: Figure showing various types of fins

Fin Selection (Fig. 7):

 

Refer fig. 7 for limiting temperatures of various types of fins.

Limiting-temperatures-for-various-types-of-Fins.

Fig. 7: Limiting temperatures for various types of Fins.

Fin Material

What are Headers?

Figure-showing-a-typical-header-for-air-fin-fan-cooler

Fig. 8: Figure showing a typical header for air fin fan cooler

  • The bonnet header design shall permit removal of the bonnet with the minimum dismantling of header piping connections. FigureÊ3 shows typical construction of tube bundles with removable bonnet headers.
  • Threaded plug holes shall be provided opposite the ends of each tube for access. Holes shall be threaded to the full depth of the plug sheet or 50 mm (2inch), whichever is less.

Why some coolers are forced draft & some induced draft (Fig. 9) and which one is better?

  • Mostly air cooled heat exchangers are of forced draft construction. Forced draft units are easier to manufacture and to maintain. Tube bundle is mounted on top of the plenum, so it can be easily removed & replaced. The fan shaft is short since it does not have to extend from the drive unit through the tube bundle and plenum to the fan as in an induced draft design. Forced draft units require slightly less horse power.
  • Since the fan is moving a lower volume of air at the inlet than they would at the outlet. If the process fluid is very hot, the cooling air is hot at the outlet, this could cause problems with some fans or fan actuators. If the fan is exposed to very hot exhaust air, since forced draft coolers do not have the fans exposed to hot exhaust air.
Types-of-Air-Fin-Fan-Cooler

Fig. 9: Types of Air Fin Fan Cooler

What kinds of controls are used?

As one might expect the best kind of control scheme depends on the application. Does the process require a very tight control on the process outlet temperature or is it better to allow the process temperature to go down with the ambient air temp. Following is a list of some of the commonly used control devices for air coolers, but in no particular order.

  • Manually operated louvers
  • Pneumatically activated automatic variable pitch fans.
  • Variable frequency fan drive (VFD).
 

VFD if used shall suit the motor name plate rating and similarly for the Belt Pulley transmission it shall suit the motor name plate rating.

Original URL:http://www.whatispiping.com/air-cooled-heat-exchangers



網站首頁  |  關於我們  |  聯繫我們  |  使用協議  |  隱私權政策  |  網站地圖  |  排名推廣  |  廣告服務  |  網站留言  |  RSS訂閱  |  違規舉報
Powered By DESTOON