Throat Tap Research Articles

Multiple tap sets to improve Venturi flowmeters performance characteristics with disturbed flow

Venturi flowmeters are commonly used to accurately measure fluid flows in piped systems. The performance of a Venturi flowmeter can be affected when the flowmeter is installed in close proximity to a flow disturbance such as a valve, elbow, or pipe fitting. The presence of an upstream flow disturbance causes a non‐uniform velocity profile to enter the flowmeter and may adversely influence the pressure differential measure at the meter's pressure taps. This study investigated how hydraulically averaging pressure measurements from multiple inlet and throat tap sets would improve or stabilize the Venturi performance. Laboratory experiments and computational fluid dynamics were tested with several flow disturbances and a wide range of sizes and flow rates. Multiple tap sets on 2‐in. and 12‐in. diameter Venturi flowmeters were tested. The results of the study showed that the variation in the flow measurement was significantly decreased when the number of pressure taps was increased.

Further Experiments and Investigations for Discharge Coefficient of PTC 6 Flow Nozzle in a Wide Range of Reynolds Number

The discharge coefficients of the flow nozzles based on ASME PTC 6 are measured in a wide range of Reynolds number from Red = 5.8 × 104 to Red = 1.4 × 107, and the equations of the discharge coefficients are developed for the laminar, the transitional, and the turbulent flow ranges. The equation of the discharge coefficient consists of a nominal discharge coefficient and the tap effect. The nominal discharge coefficient is the discharge coefficient without tap, which is experimentally determined from the discharge coefficients measured for different tap diameters. The tap effects are correctly obtained by subtracting the nominal discharge coefficient from the discharge coefficient measured. The deviation of the present experimental results from the equations developed is from −0.06% to 0.04% for 3.0 × 106 < Red < 1.4 × 107 and from −0.11% to 0.16% for overall Reynolds number range examined. The developed equations are expected to be capable of estimating the discharge coefficient of the throat tap nozzle defined in PTC 6 with a high accuracy and contribute for the high accurate evaluation of steam turbines in power plants.

F111 スロートタップ式フローノズルの流出係数特性式に関する考察(OS9 熱・流動(1))

The discharge coefficients of the flow nozzles based on ASME PTC 6 are measured in wide Reynolds number range from Re_d=5.8×10^4 to Re_d=1.4×10^7 and the equations of the discharge coefficients are developed for the laminar, the transitional and the turbulent flow ranges. The equation of the discharge coefficient consists of a nominal discharge coefficient and the tap effect. The nominal discharge coefficient is the discharge coefficient without tap, which is experimentally determined from the discharge coefficients measured for different tap diameters. The tap effects are correctly obtained by subtracting the nominal discharge coefficient from the discharge coefficient measured. The deviation of the present experimental results from the equations developed is from -0.06% to 0.04% for 3.0×10^6<Re_d<1.4×10^7 and from -0.11% to 0.16% for overall Reynolds number range examined.

New Discharge Coefficient of Throat Tap Nozzle Based on ASME Performance Test Code 6 for Reynolds Number From 2.4 × 105 to 1.4 × 107

The throat tap nozzle of the American Society of Mechanical Engineers performance test code (ASME PTC) 6 is widely used in engineering fields, and its discharge coefficient is normally estimated by an extrapolation in Reynolds number range higher than the order of 107. The purpose of this paper is to propose a new relation between the discharge coefficient of the throat tap nozzle and Reynolds number by a detailed analysis of the experimental data and the theoretical models, which can be applied to Reynolds numbers up to 1.5 × 107. The discharge coefficients are measured for several tap diameters in Reynolds numbers ranging from 2.4 × 105 to 1.4 × 107 using the high Reynolds number calibration rig of the National Metrology Institute of Japan (NMIJ). Experimental results show that the discharge coefficients depend on the tap diameter and the deviation between the experimental results and the reference curve of PTC 6 is 0.75% at maximum. New equations to estimate the discharge coefficient are developed based on the experimental results and the theoretical equations including the tap effects. The developed equations estimate the discharge coefficient of the present experimental data within 0.21%, and they are expected to estimate more accurately the discharge coefficient of the throat tap nozzle of PTC 6 than the reference curve of PTC 6.

318 スロートタップ式ノズルの流出係数およびタップ効果(OS9 オーガナイズドセッション《熱・流体・エネルギー変換工学の進展》)

318 スロートタップ式ノズルの流出係数およびタップ効果(OS9 オーガナイズドセッション《熱・流体・エネルギー変換工学の進展》)

Experimental Investigation for Discharge Coefficient's Characteristic of Throat Tap Type Flow Nozzle and for Extrapolation to High Reynolds Number

Experimental Investigation for Discharge Coefficient's Characteristic of Throat Tap Type Flow Nozzle and for Extrapolation to High Reynolds Number

Comparison of Primary Flow Measurement Techniques Used During Combined Cycle Tests

One of the most significant contributors to the overall uncertainty of a performance test of a combined cycle steam turbine is the uncertainty of the primary flow measurement. ASME performance test codes provide many alternative methods for determining flow. In two actual combined cycle tests performed in 2005, the following three alternate methods were used to determine the high-pressure (HP) steam flow into the combined cycle steam turbines: (1) Derivation from measured HP feedwater flow using calibrated PTC 6 throat tap nozzles, (2) derivation from low-pressure (LP) condensate using calibrated PTC 6 throat tap nozzles, and (3) derivation from LP condensate using calibrated orifice metering sections. This paper describes the design, calibration, and installation of each flow meter involved, the methods used to calculate the HP steam flow, the estimated uncertainty of the HP steam flow derived using each method, and the actual test results using each method. A comparison of the methods showed that there are distinct advantages with one of the methods and that very low uncertainties in HP steam flow can be achieved if sufficient attention is applied to the design, calibration, and installation of all flow meters involved. Note that the information in this paper was originally published in ASME Paper PWR2006-88074 and presented at the 2006 ASME Power Conference in Atlanta, GA. For detailed diagrams, figures, and tabulations of data and analysis, please refer to the published proceedings from that conference.

Discussion: “Theoretical Basis for Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles” (Murdock, J. W., and Keyser, D. R., 1991, ASME J. Eng. Gas Turbines Power, 113, pp. 228–232) and “A Method for the Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles” (Murdock, J. W., and Keyser, D. R., 1991, ASME J. Eng. Gas Turbines Power,

Discussion: “Theoretical Basis for Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles” (Murdock, J. W., and Keyser, D. R., 1991, ASME J. Eng. Gas Turbines Power, 113, pp. 228–232) and “A Method for the Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles” (Murdock, J. W., and Keyser, D. R., 1991, ASME J. Eng. Gas Turbines Power,

Theoretical Basis for Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles

Equations for the extrapolation of calibration data for ASME/PTC 6 throat tap nozzles are derived from boundary layer theory. The results match published coefficients with a maximum difference of +0.03 percent. It is also shown that the effects of transition in the boundary layer extend to throat Reynolds numbers in excess of 10,000,000, far beyond the capacity of any known calibration laboratory. The present PTC 6 requirement that calibration data must be in the fully turbulent range cannot be met with current facilities.

A Method for the Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles

This paper describes a precise method for extrapolating the coefficient of discharge of PTC 6 throat tap nozzles using all or most of the calibration data. The theoretical basis for this method is described in a parallel paper [3]. Numerical examples are given using actual calibration data to describe this method. Because this method permits the use of all calibration data at or above Reynolds numbers of 1,000,000, it is a clear improvement over the PTC 6-1976 method, which permits only the highest single point.

Discussion: “Theoretical Basis for Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles” (Murdock, J. W., and Keyser, D. R., 1991, ASME J. Eng. Gas Turbines Power, 113, pp. 228–232) and “A Method for the Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles” (Murdock, J. W., and Keyser, D. R., 1991, ASME J. Eng. Gas Turbines Power,

Discussion: “Theoretical Basis for Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles” (Murdock, J. W., and Keyser, D. R., 1991, ASME J. Eng. Gas Turbines Power, 113, pp. 228–232) and “A Method for the Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles” (Murdock, J. W., and Keyser, D. R., 1991, ASME J. Eng. Gas Turbines Power,

Closure to “Discussion of ‘Theoretical Basis for Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles’ and ‘A Method for the Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles’” (1991, ASME J. Eng. Gas Turbines Power, 113, pp. 239–240)

Closure to “Discussion of ‘Theoretical Basis for Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles’ and ‘A Method for the Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles’” (1991, ASME J. Eng. Gas Turbines Power, 113, pp. 239–240)

Discharge Coefficient for Venturi Flowmeter With Short Laying Length

This paper presents a method for predicting the discharge coeffcient for a venturi flowmeter with a short laying length where the static pressure is not uniform at the throat due to streamline curvature. The discharge coefficient is determined by combining potential flow calculations and one-dimensional viscous flow considerations. For the potential flow, an accurate computational technique proposed by the author is used to calculate the pressure at the throat tap by assuming that the total pressure is equal to the average one at the throat. The average total pressure is related to the inlet pressure by use of a generalized empirical equation based on one-dimensional considerations. Validity of the method is verified by comparison with published experimental data for short venturi flowmeters.

Statistical Improvement in Differential Producer Type Flowmeters

First steps have been taken to demonstrate the feasibility of reducing uncertainties in the use of differential producers. Given a suitable flow conditioner, discharge coefficients are shown to be a highly reproducible function of approach length L/D. In the case of venturis and throat-tap flow nozzles, large effects of excessively small pressure tap diameter ratio δ/d are demonstrated and correlated, and much of the scatter and the premature roll-off of the coefficient with decreasing Reynolds number are thus accounted for. Some influence of throat length ratio x/d upstream of a throat tap is shown.

Closure to “Discussions of ‘Comparisons Between Throat and Pipe Wall Tap Nozzles’” (1975, ASME J. Eng. Power, 97, pp. 573–574)

Closure to “Discussions of ‘Comparisons Between Throat and Pipe Wall Tap Nozzles’” (1975, ASME J. Eng. Power, 97, pp. 573–574)

Comparisons Between Throat and Pipe Wall Tap Nozzles

The history of pipe wall tap nozzles and throat tap nozzles, as to performance characteristics, is briefly reviewed. A series of tests was conducted on pipe wall tap and throat tap nozzle installations at three independent calibration laboratories. These results are presented, analyzed, and compared with existing rational, empirical, and nominal performance characteristics in the form of discharge coefficient versus the throat Reynolds number. On the basis of these results, a recommendation is made that both pipe wall tap and throat tap nozzle installations be considered as equally accurate for use in precision fluid metering work.

“C” Evaluation—Differences Between “Mathematical” and “Physical” Possibilities

A review of the pertaining ASME literature shows that so far all ASME efforts to assign “uncalibrated” tolerances to ASME devices (orifice plates, ASME nozzles, PTC-6 throat tap nozzles) failed when tested against a newer set of calibration data. The paper shows that the cause of failure may have been the use of statistical methods and/or mathematical generalizations without physical scrutinization of the calibration data and the device under investigation. The purpose of the paper, therefore, is to help to map out the “physical road” to reliable “C” evaluation work. Another purpose of the paper is to uncover some hidden obstacles that have retarded progress in this area and would assure failure for future investigators, unless recognized and handled properly.

A Generalized Discharge Coefficient for Differential Pressure Type Fluid Meters

A generalized rational equation is derived for the discharge coefficient of differential pressure-type fluid meters. Its factors are particularized for throat tap meters, pipe wall tap nozzles, and for orifice-type flow meters. Comparisons are made with available theories and with current Fluid Meter practices, and these support the new formulation. Because of its rational basis, the generalized equation may be useful for extrapolations to Reynolds numbers which lie beyond the capabilities of calibration laboratories.

Closure to “Discussions of ‘Throat Tap Nozzles Used for Accurate Flow Measurements’” (1960, ASME J. Eng. Power, 82, pp. 253–261)

Closure to “Discussions of ‘Throat Tap Nozzles Used for Accurate Flow Measurements’” (1960, ASME J. Eng. Power, 82, pp. 253–261)

Discussion: “Throat Tap Nozzles Used for Accurate Flow Measurements” (Cotton, K. C., and Westcott, J. C., 1960, ASME J. Eng. Power, 82, pp. 247–253)

Discussion: “Throat Tap Nozzles Used for Accurate Flow Measurements” (Cotton, K. C., and Westcott, J. C., 1960, ASME J. Eng. Power, 82, pp. 247–253)