Method for measuring average velocity pressure and system thereof

• US 7,337,675 B2
• Filed: 07/05/2005
• Issued: 03/04/2008
• Est. Priority Date: 12/06/2004
• Status: Expired due to Fees

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Huang, Chien-Ping
• Primary Examiner(s): Lefkowitz; Edward
• Assistant Examiner(s): Kirkland, III; Freddie
• Application Number:
  US11/172,798
• Publication Number:
  US 20060117858A1
• Time in Patent Office: 973 Days
• Field of Search: 737/36, 73715-727, 737/54
• US Class Current: 73/736
• CPC Class Codes: G01F 1/36 the pressure or differential pressure being created by the use of flow constriction
• CPC Class Codes: G01F 1/46 Pitot tubes
• CPC Class Codes: G01P 5/14 by measuring differences of pressure in the fluid

Abstract

A method for measuring average velocity pressure of a stack comprises the following steps. First, a total pressure measuring device is provided. The total pressure measuring device then measures the total pressure at a first location in the stack. Next, physical parameters comprising a distance between the first location and an outlet of the stack, a diameter and shape thereof are obtained. A formula of a static pressure and the average velocity pressure between the outlet and the first location is obtained by comparing the physical parameters to known fluid mechanics data. Finally, the average velocity pressure is obtained from the formula and the total pressure.

Claims

1. A method for measuring an average velocity pressure of a pipe, comprising:

providing a total pressure measuring device;

obtaining a total pressure through the total pressure measuring device disposed at a first location in the pipe;

measuring at least one physical parameter between the first location and an outlet of the pipe;

obtaining a formula of a static pressure and the average velocity pressure between the outlet and the first location by comparing the physical parameter to known fluid mechanics data;

obtaining the average velocity pressure from the formula and the total pressure; and

wherein the said physical parameters comprise a diameter of the pipe and a shape of the pipe.

2. The method as claimed in claim 1, wherein the total pressure measuring device comprises a total pressure tube, a soft tube and a manometer, the total pressure tube is disposed at the first location, the soft tube is connected between the total pressure tube and the manometer, and the manometer obtains the total pressure by subtracting a measured pressure from an atmospheric pressure.

3. The method as claimed in claim 1, wherein when the pipe is a straight circular pipe, the physical parameters further comprise a distance between the first location and the outlet.

4. The method as claimed in claim 3, wherein the formula is equivalent to a first formula:

$\mathrm{\Delta <br><br>}<br><br><br><br>\mathrm{SP}\approx <br><br>C_1\times <br><br>\frac{L_1}{D^{C_2}}\times <br><br>\mathrm{VP}$

wherein, Δ

SP is a static pressure drop, VP is the average velocity pressure, L1 is a distance between the first location and the outlet, D is a diameter of the pipe, C1 and C2 are constants obtained by comparing the physical parameters to known fluid mechanics data, and the L1 and D are obtained by measurement.

5. The method as claimed in claim 4, wherein the average velocity pressure is obtained incorporating the first formula into a second formula:

VP=TP−

SP

wherein, TP is the total pressure, SP is the static pressure, and SP=Δ

SP.

6. The method as claimed in claim 1, wherein when the pipe is an L-shaped circular pipe comprising a first straight portion, an elbow portion and a second straight portion, the physical parameters further comprise a length of the first portion, a length of the second portion and a curvature radius of the elbow portion.

7. The method as claimed in claim 6, wherein the formula is equivalent to a third formula:

$\mathrm{\Delta <br><br>}<br><br><br><br>\mathrm{SP}\approx <br><br>K\times <br><br>\mathrm{VP}+C_1\times <br><br>\frac{L_1+L_2}{D^{C_2}}\times <br><br>\mathrm{VP}$

wherein, Δ

SP is a static pressure drop, VP is the average velocity pressure, L1 is a length of the first straight portion, L2 is a length of the second straight portion, D is a diameter of the pipe, C1, C2, and K are constants obtained by comparing the physical parameters to known fluid mechanics data, and the L1, L2, and D are obtained by measurement.

8. The method as claimed in claim 7, wherein the average velocity pressure is obtained incorporating the third formula into a second formula:

VP=TP−

SP

wherein, TP is the total pressure, SP is the static pressure, and SP=Δ

SP.

9. A method for measuring an average velocity pressure of a pipe, comprising:

providing a total pressure measuring device and a static pressure measuring device;

obtaining a total pressure through the total pressure measuring device disposed at a first location in the pipe;

obtaining an end static pressure through the static pressure measuring device disposed at a second location in the pipe;

measuring at least one physical parameter between the first location and the second location;

obtaining a formula of a static pressure drop and the average velocity pressure between the first location and the second location by comparing the physical parameter to known fluid mechanics data;

obtaining the average velocity pressure from the formula, the total pressure, the end static pressure and the static pressure drop; and

wherein the said physical parameters comprise a diameter of the pipe and a shape of the pipe.

10. The method as claimed in claim 9, wherein the total pressure measuring device comprises a total pressure tube, a soft tube and a manometer, the total pressure tube is disposed at the first location, the soft tube is connected between the total pressure tube and the manometer, and the manometer obtains the total pressure by subtracting a measured pressure from an atmospheric pressure.

11. The method as claimed in claim 9, wherein when the pipe is a straight circular pipe, the physical parameters further comprise a distance between the first location and the second location.

12. The method as claimed in claim 11, wherein the formula is equivalent to a first formula:

$\mathrm{\Delta <br><br>}<br><br><br><br>\mathrm{SP}\approx <br><br>C_1\times <br><br>\frac{L_1}{D^{C_2}}\times <br><br>\mathrm{VP}$

wherein, Δ

SP is a static pressure drop, VP is the average velocity pressure, L1 is a distance between the first location and the second location, D is a diameter of the pipe, C1 and C2 are constants obtained by comparing the physical parameters to known fluid mechanics data, and the L1 and D are obtained by measurement.

13. The method as claimed in claim 12, wherein the average velocity pressure is obtained incorporating the first formula into a second formula:

VP=TP−

SP

wherein, TP is the total pressure, SP is the static pressure, and the static pressure drop Δ

SP adds the end static pressure equal to the static pressure SP.

14. The method as claimed in claim 9, wherein when the pipe is an L-shaped circular pipe comprising a first straight portion, an elbow portion and a second straight portion, the physical parameters further comprise a length of the first portion, a length of the second portion and a curvature radius of the elbow portion.

15. The method as claimed in claim 14, wherein the formula is equivalent to a third formula:

$\mathrm{\Delta <br><br>}<br><br><br><br>\mathrm{SP}\approx <br><br>K\times <br><br>\mathrm{VP}+C_1\times <br><br>\frac{L_1+L_2}{D^{C_2}}\times <br><br>\mathrm{VP}$

wherein, Δ

SP is a static pressure drop, VP is the average velocity pressure, L1 is a length of the first straight portion, L2 is a length of the second straight portion, D is a diameter of the pipe, C1, C2, and K are constants obtained by comparing the physical parameters to known fluid mechanics data, and the L1, L2, and D are obtained by measurement.

16. The method as claimed in claim 15, wherein the average velocity pressure is obtained incorporating the third formula into a second formula:

VP=TP−

SP

wherein, TP is the total pressure, SP is the static pressure, and the static pressure drop Δ

SP adds the end static pressure equal to the static pressure SP.

17. A pressure measuring system for measuring an average velocity pressure between a first location and an outlet of a pipe, comprising:

a total pressure measuring device, disposed at the first location in the pipe obtaining a total pressure;

a processor, coupled to the total pressure measuring device and obtaining the average velocity pressure according to the total pressure and at least one physical parameter between the first location and the outlet;

an output device, coupled to the processor and outputting the average velocity pressure; and

wherein the said physical parameters comprise a diameter of the pipe and a shape of the pipe.

18. The pressure measuring system as claimed in claim 17, wherein the total pressure measuring device comprises a total pressure tube, a soft tube and a manometer, the total pressure tube is disposed at the first location, the soft tube is connected between the total pressure tube and the manometer, and the manometer obtains the total pressure by subtracting a measured pressure from an atmospheric pressure.

19. A method for measuring an average velocity pressure of a pipe, comprising:

providing a total pressure measuring device;

obtaining a total pressure through the total pressure measuring device disposed at a first location in the pipe;

measuring at least one physical parameter between the first location and an outlet of the pipe;

obtaining a formula of the total pressure and the average velocity pressure between the outlet and the first location by comparing the physical parameter to known fluid mechanics data;

obtaining the average velocity pressure from the formula; and

wherein the said physical parameters comprise a diameter of the pipe and a shape of the pipe.

20. The method as claimed in claim 19, wherein when the pipe is a straight circular pipe, the formula is equivalent to a fourth formula:

$\mathrm{VP}\approx <br><br>\left[\frac{1}{1+C_1\times <br><br>L_1/D^{C_2}}\right]\times <br><br>\mathrm{TP}$

wherein, TP is the total pressure, VP is the average velocity pressure, L1 is a distance between the first location and the outlet, D is a diameter of the pipe, C1 and C2 are constants obtained by comparing the L1 and D to known fluid mechanics data, and the L1 and D are obtained by measurement.

21. The method as claimed in claim 19, wherein when the pipe is an L-shaped circular pipe comprising a first straight portion, an elbow portion and a second straight portion, the formula is equivalent to a fifth formula:

$\mathrm{VP}\approx <br><br>\left[\frac{1}{1+K+C_1⨯<br><br>\left(L_1+L_2\right)/D^{C_2}}\right]⨯<br><br>\mathrm{TP}$

wherein, TP is the total pressure, VP is the average velocity pressure, L1 is a length of the first straight portion, L2 is a length of the second straight portion, D is a diameter of the pipe, C1, C2, and K are constants obtained by comparing the L1, L2, D, and a curvature radius of the elbow portion to known fluid mechanics data, and the L1, L2, D, and curvature radius of the elbow portion are obtained by measurement.