exh-dg-1826

Chevron Data Sheet Guide EXH-DG-1826

INSTRUCTIONS FOR EXTENDED SURFACE AIR COOLED HEAT EXCHANGER

DESIGN DATA SHEET EXH-DS-1826

December 1989 Page 1 of 5

INSTRUCTIONS FOR EXTENDED SURFACE

AIR COOLED HEAT EXCHANGER





Page 2 of 5 December 1989

CONTENTS

1.0 PURPOSE ............................................................................................................................3

2.0 SCOPE .................................................................................................................................3

3.0 RESPONSIBILITY FOR THE DATA SHEET ....................................................................3

4.0 DESCRIPTION OF ITEMS.................................................................................................3

4.1 Performance Data ...................................................................................................................3

4.2 Construction Data...................................................................................................................4

4.3 Materials of Construction ........................................................................................................5

4.4 Notes.....................................................................................................................................5

4.5 Order Data .............................................................................................................................5





1.0 PURPOSE

This guide provides instruction on how to complete the Extended Surface Air Cooled Heat

Exchanger Data Sheet EXH-DS-1826. It does not provide rules for the design of air coolers.

Section 600, Model Specification EXH-MS-1826 and API STANDARD 661 have more detailed

information and illustrations of air coolers. Unless otherwise specified, the sections referred to in

this guide refer to sections in the Heat Exchanger and Cooling Tower Manual.

2.0 SCOPE

Data Sheet EXH-DS-1826 summarizes important parameters of performance, construction and

materials. This guide explains terms on the Data Sheet. The section headings in Section 4.0 of this

guide correspond to the section headings on the Data Sheet. This guide does not define every term

on the Data Sheet, only those which need some interpretation.

3.0 RESPONSIBILITY FOR THE DATA SHEET

A Data Sheet should be completely filled out for each air cooler purchased. Air coolers are

usually vendor designed items. Consequently, the engineer normally only completes the parts of

the Data Sheet needed to define the design basis. Items normally filled out by the engineer are

indicated by an asterisk in Figure DG-1826-1. The Vendor completes the rest of the Data Sheet.

4.0 DESCRIPTION OF ITEMS

4.1 Performance Data

4.1.1 Duty is the rate of energy transfer between the process fluid and the ambient air.

4.1.2 Effective mean temperature difference is the area weighted temperature difference

between the cooling process fluid and the heating air.

4.1.3 Overall Transfer Coefficient (Service and Clean) - The value for clean includes

resistances for film coefficients of the process fluid and air, the tube wall, the fin

bond, and the effect of fin efficiency (variable fin temperature). The value for

service includes the expected fouling resistance and/or an allowance to provide

operating flexibility.

4.1.4 Not all fluid property information applies in every case. For example,

condensation/vaporization curve number, latent heat of vaporization and "L/V"

(L=liquid & V=vapor) are not needed for single phase service. The engineer should

cross out or indicate N/A (not applicable) for such items.




Page 4 of 5 December 1989

4.1.5 Enter tube side fouling allowance where experience indicates the need and the value.

Where tube side fouling is not expected (the usual situation), indicate the desired

degree of excess surface area in a note (i.e., "provide 125% of calculated clean

surface area.").

4.1.6 Design dry bulb air temperature is the highest ambient air temperature at which the

design duty can be achieved. Section 610 gives the normal basis for picking this

temperature.

4.2 Construction Data

4.2.1 Number of bays - A bay is one or more tube bundles serviced by one or two fans

with a common plenum chamber. See API STANDARD 661 for illustrations.

4.2.2 Effective surface all bays (finned and bare tube) - Finned surface is the actual

external surface area including the fins. Bare tube surface is the outside surface area

of the tubes without fins.

4.2.3 Louvers, air recirculation and steam coils are used for winterization. See API

Recommended Practice 632 for guidance.

4.2.4 Mounting refers to where the air cooler will be installed. Specify pipe-rack and its

width and elevation for air coolers to be mounted over pipe ways. The vendor

usually decides overall length and width for grade mounted units.

4.2.5 Header type is almost always the plug type. See API STANDARD 661 for

illustrations.

4.2.6 Minimum design pressure is the highest pressure the unit will see in service and is

specified by the engineer. The as-built design pressure is determined by the vendor

and should be equal to or greater than the specified minimum.

4.2.7 Nozzle size, facing and rating should match the piping classification and is specified

by the engineer.

4.2.8 Standard air cooler tubes are 1" OD. Tube wall thickness, or Birmingham Wire Gage

(BWG), is usually minimum wall (min) for carbon steel and average wall (ave) for

alloys. The difference between average and minimum wall is approximately one

BWG point. Specified tube thickness is based on design pressure and corrosion

considerations.

4.2.9 Tube layout should be specified as triangular in all cases. In-line layouts result in

channelling and poor heat transfer.





4.2.10 Fin type is selected by the vendor subject to limitations in Specification EXH-MS-

1826.

4.2.11 The engineer should specify forced draft if the process inlet temperature or steam

out temperature is high enough to damage the fan or automatic fan pitch control hub.

When in doubt, let the vendor select draft.

4.2.12 50 % auto-variable pitch fans is usually justified to save fan power consumption

and/or control process temperature. The remaining fans have manually adjustable

pitch.

4.2.13 Specify the steam out temperature if the unit will be steamed out during shut downs.

This may affect selection of fan material or type of draft.

4.2.14 Electric motors are used for most air coolers.

4.2.15 High torque drive (HTD) belts are used for most air coolers.

4.3 Materials of Construction

Materials of construction and minimum pressurizing temperature are usually specified by

a materials specialist or project engineer. Material for the tube sheet, plug sheet, pass

partitions, stiffeners, end plates and top/bottom plates should be the same.

4.4 Notes

4.4.1 The blanks in Note 2 should be filled in to tell the vendor how to balance fan power

cost against the cost of heat transfer surface, and how we intend to evaluate the

vendors bid.

4.4.2 Additional notes should be added to the Data Sheet to describe any design features

not addressed by the pre-printed items on the Data Sheet.

4.5 Order Data

The manufacturer, manufacturers shop order number and the Company order number

should be listed here. This reference information may be needed to get additional information

from the vendor in the future.

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