Air-Cooled Heat-Exchanger Costs

Air-Cooled Heat-Exchanger Costs The cost data that appear in Table 11-18 are unchanged from those published in the 1963 edition of this Handbook. In 1969 Guthrie [Chem. Eng., 75, 114 (Mar. 24, 1969)] presented cost data for field-erected air-cooled... 

For air-cooled heat exchangers, recirculation is more difficult to define or relate to standard practices. Banks of air-coolers are installed in a variety of configurations so, for a particular proposed installation, a study by specialists may be required. This study of recirculation would probably be done later in the projeet even though the results impact costs. There is a practical limit to the number of front-end studies and this is one that can be deferred until geometry is better defined. 

Design an air-cooled heat exchanger to cool water under the following conditions. The design ambient air temperature is 35°C (95°F). The tubes to be used are steel tubes [thermal conductivity = 25 Btu/ (h)(ft2)(°F), or 43 W/(m)(K)] with aluminum fins. The steel tube is 1 in (0.0254 m) outside diameter and 0.834 in (0.0212 m) inside diameter. The inside heat-transfer coefficient and the fouling coefficient hs are each 1000 Btu/(h)(ft2)(°F) [5680 W/(m2)(K)]. Heat-exchanger purchase cost is 22 per square foot for four-tube-row units, 20 per square foot for five-tube-row units, and 18 per square foot for six-tube-row units. 

Typical face velocities (FVs) used for design are also tabulated in Table 7.6. These values result in air-cooled heat exchangers that approach an optimum cost, taking into account the purchase cost, the cost for installation, and the cost of power to drive the fans. Each designer may wish to establish his or her own values of typical design face velocities these should not vary greatly from those tabulated. 

Operating costs. Power requirements for air-cooled heat exchangers can be lower than at the summer design condition provided that an adequate means of air-flow control is used. The annual power requirement for an exchanger is a function of the means of airflow control, the exchanger service, the air-temperature rise, and the approach temperature. 

Air cooled heat exchanger Rectangular tube bundles mounted on frame, with air used as the cooling medium Economic where cost of cooling water is high. 

Air cooled heat exchangers have rectangular bundles containing several rows of tubes, horizontally aligned and vertically offset. Air flows vertically upward across the tube bank. The flow can be induced by fans above the bundle or forced by fans below the bundle. The heat transfer is countercurrent, because the hot fluid enters at the top of the bundle and flows downward through successive passes. The cost of an air cooler depends on the length of the tubes and the number of the tube rows. 

---