ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
Pipe Tee Fluid Flowmeter LEO GARWIN' AND SPENCER
H.
LANDES2
Oklahoma A. & M. College, Sfillwater, Okla.
0
F T H E differential head meters used for the measurement of
fluid flow in pipes, the most common is the orifice meter. An extensive discussion of this meter has appeared recently (10). The pitot tube finds its greatest application in the measurement of gases and in the obtaining of fluid velocity profiles. The patented flow tube ( 2 ) manufactured bv the Bethlehem Foundry and Machine Co., Bethlehem, Pa., is another example of a differential head meter. All these, when either properly installed or calibrated in place, provide an accurate measurement of fluid flow, but they also possess one or more disadvantages. They are relatively expensive, or require careful installation, or require careful positioning of the sensitive element, and, in some cases, thrv are not a permanent, integral part of the piping system. .4 ne\; meter, which measures mass instead of volume, regardless of flow conditions, and which depends on the Coriolis acceleration for its operation, has been developed (1). Several attempts have been made to use a component of the piping setup for the measurement of flow. One of these, the elbow flowmeter (5), requires precise tap location and generates only a small differential. The valve flowmeter (4) requires calibration for each make of valve and for each type of valve of a particular make. The use of a set of pipe tees as a flowmeter has been explored brieflv. Ford ( 7 ) has reported a fern experiments with a l/Rinch pipe tee flowmeter, using air ab the fluid. The pipe tee flowmeter measures the impact head of the fluid by allowing the fluid to flow into the run and out of the branch of one tee, using the other run end of the tee for the impact pressure tap. A second tee, located close to the first, is so installed that the fluid flows into and out of its run, the branch being used for a atatic pressure tap. Nord located the static tee upstream of the impart tee. In the work described in this paper, the static tee was located downstream of the impact tee. Such a scheme would be expected to possess the advantage of a greater meter differential because the loss rrsulting from the 90" change in direction of the fluid in the impact tee would be included, and all frictional losses would be added to the impact head instead of subtracted from it. The anticipated meter reading would then be as follows: 1 0 velocity head Impact pressure 08velocity head Friction loss in tee used as ell ( 3 ) Total 1 8 velocity heads plus the losses due to friction in the pipe connecting the teee. The objective of the present work was to evaluate thoroughly the performance of the tee flowmeter, and to obtain from its accuracy and reproducibility characteristics an indication of the potential usefulness of the meter as a fluid measuring device. Basic Parts of Meter Incorporate Simplicity Of Design and Sensitivity of Performance
Materials Used. Flowing fluid was laboratory tap water, ranging in temperature from 42" to 72" F. Manometer fluid was carbon tetrachloride, commercial grade. 1 2
Present address, Kerr-McGee Oil Industries, Inc., Oklahoma City, Okla. Present address, Brown and Root, Inc., Houston, Tex.
April 1954
Tees were screw-type, Schedule 40, sizes from to l 1 / 2 inches, black and galvanized, manufactured by the Crane Co., Chicago, Ill., Detroit Brass and LIalleable Iron Works, Detroit, Mich., Stockham Pipe Fittings Co., Birmingham, Ala., and Walworth C o , Xew York, N. Y. Other fittings were Schedule 40, and nipples were stock lengths, Schedule 40. Standard Meter. As the investigation progressed, and as the factors controlling the performance of the tee meter were evaluated one by one, there ultimately emerged a meter configuration which was adopted as standard. This meter is shown in Figure 1. The component parts of the meter were selected to impart the greatest simplicity of design, as well as reproducibility and sensitivity of performance, consistent, however, with the maintenance of stability. Thus, referring to Figure 1, it would have been simpler to have eliminated the nipple and coupling of section 3; these components were found necessary, however, in order to avoid erratic, fluctuating meter readings. Thr standard meter specifications for all sizes were as follows: Section 1. Calming section, longer than 10 pipe diameters; no straightening vanes Section 2. Impact tee, screwed Section 3. Impact tap, consisting of a short nipple, coupling, l/a-inch bushing and l/c-inch street elbow; nipple acrewed into section 2 five turns; nipple end in section 2 reamed to exact pipe diameter Section 4. Connecting nipple. 73/, inches long (stock length); screwed into section 2 five turns; screwed into section 5 five turns; nipple reamed a t both ends to exact pipe diameter Section 5. Static tee, screwed Section 6. Static tap, '/,-inch bushing Section 7 . Downstream nipple Each meter studied mas composed of pipe and fittings of one particular size; the effect of hvbridixation was not investigated. The manometer lines were 1/4-inch pipe. They were connected to a 30-inch clean-out type Meriam manometer. Procedure. Water from a constant head elevated tank flowed through an orifice meter well upstream of the test meter, through the test meter, and into a weigh drum resting on a platform scale. The level in the constant head tank was maintained by allowing excess water from the laboratory main to overflow from the tank to the sewer. The orifice meter was used to set the magnitude of the flow and to indicate its constancy. The actual flow was obtained by weighing the effluent discharging into the weigh drum. The temperature of the mater leaving the meter was measured with 5 thermometer. I t was found that manometer fluctuations were severe with certain test meter configurations. Moderate throttling by a valve in the impact manometer lead line eliminated this to a large extent. For each meter setup, a series of runs was made a t different water velocities. The range of Reynolds numbers studied was 5000 to 70,000. The frictional resistance of a fierewed tee has been found to be markedly affected by the degree of perfection of reaming of the pipes connected to it ( 3 ) . The following reaming procedure was employed for the preparation of pipe nipple components of the standard meter. The burr was reamed to approximately the inside pipe diameter with a regular pipe reamer. The ridge was smoothed with a round file and emerv cloth. Trueness of diam-
I N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY
665
ENGINEERING. DESIGN. AND PROCESS DEVELOPMENT
Table I.
Average Meter Velocity Head Coefficients ( R e = 40,000)
Size, Inches
Tee Manufacturer
Standaid meter
Ra Adjusted for section 4 friction
1 . 9 5 i0.08 1.40 k 0.08 Detroit 1 . 7 2 i 0 . 0 4 1 . 3 1 j: 0 . 0 4 Stockham, Detroit 1 . 7 8 1 0 . 0 3 1 . 4 6 % 0.03 Stockham 1 . 6 2 3~ 0.02 1 . 3 0 zt 0.02 Crane 1.50 i0.06 1.26 = 0.OG Stockham Crane 1 . 6 8 i 0 . 0 6 1.49 = O . O G Crane, De'troit Stockham. TYalworth, 1 . 3 1 i 0 . 1 3 1.19 k O . 1 3 Crane Standard deviation is used t o express precision.
s o . of 3Ietrr Conibinations Tested 5
6 4
1 6
16 G
It should be noted that, because C is directly proportional to the flow rate while K is inversely proportional to the square of the flow rate, a given percentage error in K is only one half as serious in its effect on the accuracy of f l o measurement ~ as the same percentage error in C. The measure of precision employed in the expression of results is the standard deviation. Results. The nieter differential data are reported as K , the number of velocity heads, a t a Reynolds number of 40,000, The efect of Reynolds number on the coefficient of several meters (some standard, ot'hers not standard) is shown in Figure 2. The lines are straight and essentially parallel on log-log coordinat,es; the average slope of the lines on this plot' is -0.07. The value of the slope can be used t'o calculate the K a t any Reynolds number from t,he one reported a t 50,000. 11 this is done a t several values of the Reynolds number, a complete calibration curve can be developed. The variation in Reynolds number in each series of runs shown in Figure 2 reflects variations in velocity only, since, in this study, water was the only fluid employed and its temperature did not w r y greatly during any particular series of runs. Changes in density were negligible and changes in viscosity were modemte. The velocity head coefficients for the standard meter are summarized in Table 1. Table I1 presents the velocity head coefficient of each of the various standard meter combinations studied. Since t n o tees are used in each meter, these were reversed in place and interchanged v i t h one anot,her to determine symmetry eharact,eristics and differences betn-een t'ees from one manufacturer, as ire11 as differences between tees made by different manufacturers. It \vas found that the tees were generally symmetrical, that variations within a brand were small, and t'hat variations from brand to brand yere also not significant, except for the case of 1I2-inch Stockham and Crane tees. The average coefficients for thesc are presented scpamtely in Table I.
1
3t-
I/+"DETROIT
-'-----0-*-
eter and the existence of ridges not apparent to the eye Irere checked Tvith an inside caliper. Differential Coefficients, Expressed as Velocity Heads, Are Determined for Standard Meter
The meter reading, in inches of carbon tetrachloride minus Tvater, was converted to the number of velocity heads of fluid floring, designated by coefficient K ,and expressed as folloixs:
it
I 1
I
I
I
I
I
2
a
4
5
REYNOLDS
where
R
(1.5S4
AH=12--=
-
1.000)
o.0487
Figure 2.
1.000
The linear velocity of the fluid flosing was calculated from the handbook (9) value for the inside diameter of Schedule 40 pipe. Differences between the actual and handbook pipe diameters iJ ere small, ordinarily no more than around 2%. The nieter differential may also be expressed in ternis of the faniiliar orifice coefficient, C, defined by 21
= cd2TpI
By comparing Equations 1 and 3,
666
(3)
NUMBER
l
I 0
7
l
l
6
3
l
Y
Variation of Meter Coefficient with Reynolds Number
Figure 3 is a log-log plot of K vcrs11s nominal nirtt can be seen from Figure 3 that there is a progrcssir-r dwrcasc in K with increasing mewr size, except for the 1-inch mctcr, which has an unusually high value, comparable to that for the I / 2 - and inch meters. The reason for this is not cleur, 3inc:t: the tees studied s1iomc:d a regular progression of dirnensions with size (aa shoivn in Table 111). I n this connection. asymmetrical friction effects have bccn noted with tees which showed no observthle differences in the physical chamcteristics of the t x o sides (3).
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 4
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT ~~
Table II. Effect of Tee Reversal and Interchange on Velocity Head Coefficient of Standard Meter :Re = 40,000) Tee in Srction 5
Tee in Section 2
K
ll/?-Inch Tees Stockham Stockham Stockham Walworth Crane 1 Stockham
2 1 2 1 2
Stockham Stockham Walworth Stockham Stockham Crane 1
1 2 1 2 2
1.30 1.27 1.51 1.24 1.12 1.43 1 . 3 1 (Mean)
I
01
1 . 6 8 (Mean) B/i-Inch Tees Stockham Stockham Stockham Stockham Crane 1 Crane 2 Crane 1 Crane 3
1 2
1 3
Stockham Stockham Stockham Stockhain Crane 2 Crane 1 Crane 3 Crane 2
2 1 3 2
1.50 1.46 1.62 1.55 1.42 1.53 1.43 1.51
1 . 5 0 (Mean)
l/n-Inch Tees Stockham Stockham Stockham Stockham
1 1
1
2
Stockhani Stockham Stockhain Stockham
2 2 2 1
1.75 1.75 1.80 1.83 1 78 ( l l e a n )
Crane Crane Crane Crane
Crane Crane Crane Ciane
1 1 1 2
1.61 1.62 1 58 1 65
2
2 2 1
S/s-Inch Tees Stockliam Stockham Stockham Stockham Detroit 1 Detroit 2
1 2 1 3
Stockham Stockhani Stockham Stockham Detroit 2 Detroit 1
2 1
3 2
]/
