Download ASME PTC 30-1991 Air Cooled Heat Exchangers_Part1 PDF

TitleASME PTC 30-1991 Air Cooled Heat Exchangers_Part1
TagsHeat Transfer Heat Exchanger Heat Transport Phenomena Mechanical Fan
File Size964.1 KB
Total Pages25
Document Text Contents
Page 1

Air Cooled
Heat Exchangers

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PTC 30-1 991

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Page 2

T H E

A S I E PTC*30 7 1 O757670 0883227 T m

Air Cooled
Heat. Exchangers

ASME PTC 30-1991

PERFORMANCE
TEST
CODES

AN AMERICAN NATIONAL STANDARD

A M E R I C A N S O C I E T Y OF M E C H A N I C A L E N G I N E E R S

Engineering Center 345 East 47th Street New York, N .Y. 1 O01 7






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Page 12

ASME P T C * 3 0 71 m 0757670 0083235 7 m

AIR COOLED HEAT EXCHANGERS ASME PTC 30-1991

SECTION 1 OBJECT AND SCOPE

1.1 OBJECT
The object of this Code is to provide uniform meth-

ods and procedures for testing the thermodynamic
and fluid mechanical performance of air cooled heat
exchangers, and for calculating adjustments to the
test results to design conditions for comparison with
the guarantee as defined in para. 5.9.4.

Excluded from the scope of this Code are evapo-
rative type coolers (wet cooling towers), and any
cooling equipment which combines evaporative and
convective air cooling (wet/dry type).

This Code does apply to wet/dry type heat exchan-
gers when, by mutual agreement, the heat exchanger
can be operated and tested as a dry type unit.

1.2 SCOPE

The scope of this Code covers, but is not limited
to, the testing of mechanical draft heat exchangers,
of both the forced draft and induced draft types; nat-
ural draft heat exchangers; and fan assisted natural
draft heat exchangers.

From a heat transfer surface standpoint, this Code
covers all tube bundle orientations, including: verti-
cal, horizontal, and slanted conduit heat exchangers.

Both bare surfaces and finned surfaces are included
as conduit type heat exchanger components. While
conventional round tubes with circular fins are as-
sumed in this Code, the procedures can be modified
by mutual agreement to apply to other surface con-
figurations.

While the cooling fluid is restricted to atmospheric
air, the tube-side fluid can be any chemical element,
compound or mixture, in single-phase flow, liquid or
gas, or in two-phase flow.

This Code is written under the assumption that the
Air Cooled Heat Exchanger (ACHE) may be tested as
having a discrete process stream or that only one
process fluid stream is being investigated. In other
cases, modifications must be made to the procedures

presented. Such modifications shall be agreed by the
parties to the test.

The scope of this Code also includes, directly or
by reference, recommended methods for obtaining
data, measurements, observations, and samples to
determine the following:

(a) Physical Dimensions
(b) Air Flow Rate
(c) Air-Side Pressure Differential
(d) Fan Driver Power
(e) Sound Level
(0 Atmospheric Pressure
@ Environmental Effects
(h) Wind Velocity
(i) Air Temperatures
0) Entering Air Temperature
(k) Exit Air Temperature
(I) Process Fluid Temperatures
(m) Process Fluid Pressures
(n) Process Fluid Flow Rate
(o) Composition of Process Fluid
(o) Percent Capability
(9) Process Fluid Pressure Drop

1.3 UNCERTAINTY

In keeping with the philosophy of the Code, the
best .available technical information has been used in
developing the recommended instrumentation and
procedures to provide the highest level of testing ac-
curacy. Every measurement has some uncertainty;
therefore, so do the test results. Any departure from
Code recommendations could introduce additional'
uncertainty in the measurements beyond that consid-
ered acceptable to meet the objectives of a Code test.
The expected uncertainty level(s) of tests run in ac-
cordance with this Code, based on estimates of pre-
cision and bias errors of the specified instrumentation
and procedures, is f two to five percent.

Users of the Code shall determine the quality of a
Code test for the specified equipment being tested

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Page 13

ASME PTC 30-1991

ASME PTC830 91 m 0759670 0083236 O m

AIR COOLED HEAT EXCHANGERS

by performing pre-test and post-test uncertainty anal-
yses. If either of these indicates uncertainty exceeding
& five percent, the test shall not be deemed a Code
test.

An example of the magnitude of the uncertainty in
individual measurements and the manner in which
individual uncertainties are combined to obtain over-
all test uncertainty of final results is included in Ap-
pendix C for a typical jacket-water cooler.

Test results shall be reported as calculated from
test observations, with only such corrections as are
provided in this Code. Uncertainties are not to be
used to alter test results.

The Supplement on Measurement Uncertainty
(PTC 19.1) provides additional information on com-
bining types of errors into an overall test uncertainty.

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Page 24

ASME PTC*30 91 0759670 0083249 9

AIR COOLED HEAT EXCHANGERS ASME PTC 30-1991

SECTION 4 - INSTRUMENTS AND METHODS OF
MEASUREMENT

4.1 GENERAL

This Section describes choice of instruments, re-
quired sensitivity or precision of instruments, and cal-
ibration corrections to readings and measurements.
Included are instructions as to methods of measure-
ment, location of measuring systems, and precau-
tions to be taken including critical timing of
measurements to minimize error due to changing
conditions. The Supplements on Instruments and Ap-
paratus (PTC 19 Series) describe methods of mea-
surement, insfruhent types, limits, sources of error, 0 corrections, and calibrations. When appropriate, and
to avoid repetition, this Code refers to and makes
mandatory the applicatibn of the Supplements on In-
struments and Apparatus (PTC 19 Series). All re-
quired instruments that are not covered by
Supplements on Instruments and Apparatus have the
rules and precautions described completely in this
Section.

For any of the measurements necessary under this
Code, instrumentatiqn systems or methods other
than those prescribed herein may be used provided
they are at least as accurate as those specified herein.
Other methods may be employed if mutually agreed.
Any departure from prescribed methods shall be de-
scribed in the test report.

4.2 MEASUREMENT OF PHYSICAL DIMENSIONS
The physical data shall be obtained for usa in per-

formance testingand evaluation. Most details for the
tube bundle prqcess side are'defined in the ACHE
data sheet. Othqr data may include:

(a ) face area;
(b) ratio of free flow area to face area;
(c) the total cross-sectional area for fluid flow in

each pass.

4.3 FAN MEASUREMENTS
The fan speed shall be measured in accordance

with the provisions of PTC 19.1 3, "Measurement of
Rotary Speed." The fan ring diameter shall be mea-
sured along two perpendicular diameters a-c and
b-d (see Fig. 4.1).

The following measurements may be taken for di-
agnostic purposes.
O Fan blade minimum tip clearance should be deter-
mined by rotating the fan 360 deg. and locating the
minimum clearance of the longest blade.
O Fan blade maximum tip clearance should be deter-
mined by rotating the fan 360 deg. and locating the
maximum clearance of the shortest blade.
i Blade track should be determined by moving each
blade past a common vertical line on the fan ring
inner wall. Results should be shown as vertical de-
viation from a selected horizontal datum plane.
O Fan blade angle should be measured (e.g., by
means of a protractor equipped with a scale and
level). The measurement should be made at the po-
sition on the blade specified by the fan manufacturer.
O Clearances and tracking of the blade tips should be
measured at the equivalent dynamic position.

4.4 MEASUREMENT OF AIR FLOW
4.4.1 This measurement requires a traverse of air ve-
locities over a selected area: Suitable instruments for
the traverse include the propeller anemometer or a
rotating vane anemometer. Pitot tubes may also be
used for fan ring traverses, as described in PTC 11 -
1984. Instructions provided with the instrument must
be followed so as to limit the overall test uncertainty
to +.5 percent. A minimum timed interval of 30 sec
for individual readings is recommended. Since the
direction of the air flow is not necessarily normal to

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Page 25

ASME PTC*30 91 W 0759670 0083250 5 W :

ASME PTC 30-1991 HEAT EXCHANGERS

FIG* 4.1 LOWTlON OF AIR VELOCITY AND TEMPERATURE MEASUREMENT POINTS
ACROSS FAN RING

the plane of the area surveyed, it may be necessary
to'correct the readings for yaw. The anemometer shall
be held parallel to the traverse plane, and the actual
direction of air flow during the timed interval esti-
mated. If the angle between the observed direction
of air flow and the anemometer-axis is 5 deg. or more,
the reading shall be correcte!. Specific corrections

,for yaw shall be determined by calibration prior to
the test.

4.4.2 The selection of the most'suitable area for the
anemometer traverse shall be guided by the general,
physical arrangement, accessibility, obstructions,
wind conditions, and air temperatùre rise. Because
of the decreased effect of ambient wind, accuracy i.s
usually better when the traverse is made in a high
velocity stream. In the case where these constraints
require that a velocity traverse be done at the inlet,
a velocity traverse is also required at the exit in order
to allow weighting the exit temperatures.

4.4.3 For induced draft units, air flow should be de-
termined by traversing the streams emitting from the
fans. The'recommended minimum number of mea-
surement points and the locations of these points are
given in Table 4.1. Measurements along additional
diameters may be necessary to avoid error due to the
effects of structural members. For additional infor-
mation on traversing methods, instrumentation, and
evaluation of data, refer to PTC 18 and PTC 19.5.

To illustrate, a 20-point traverse (five measurement
points per quadrant) is made as follows.

The plane bounded by the inner periphery at the
top of the fan ring is divided into ten equal concentric
areas numbered consecutively from 1 to I O as shown
in Fig. 4.1.

The ring is also divided into four quadrants as
shown. The air velocity is then measured at each
point of intersecfion of the radii a, b, c, and d with
the inner peripheries of areas, 1, 3, 5, 7, and 9, at
the center. The average velocities in comb¡-ned areas
1 + 2,3 + 4,5-+ 6, 7 + 8, and 9 + 1 O are then obtained

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