JPH01239436A - Detection of generation position of in-pipe cavitation - Google Patents

Abstract

PURPOSE:To easily and surely detect the generation position of cavitation from a temp. change on an IR image by heating or cooling a pipe in which liquid flows from the outside surface to apply a temp. change thereto and photographing the outside surface by an IR camera. CONSTITUTION:The point to detect the cavitation of the pipe 1 is heated by a heater 5 consisting of a reflecting plate 3 and an IR heater 4. The heat capacity of the part where the cavitation arises decreases and the quantity of the heat deprived of the pipe wall decreases and, therefore, the temp. of the pipe wall in said part rises, thus generating a temp. difference from the pipe wall of the part where the cavitation does not arise. The outside surface of the pipe wall is, thereupon, photographed by the camera and the generation of the cavitation is detected from the temp. change on the IR image. This effect is obtd. as well by cooling the pipe wall. The generation position of the cavitation is thereby easily and surely detected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for detecting the position of occurrence of cavitation in a pipe.

[Prior Art] Where the cross-sectional area of a pipe is narrowed, the fluid flowing inside the pipe is accelerated and the pressure is reduced, so air and gas absorbed in the fluid are dissipated, creating air bubbles (cavities) in the fluid. cavitation occurs. When the cross-sectional area of the tube expands and flow resumes, the fluid is decelerated and the pressure increases, causing the cavity to collapse. At that time, severe vibrations and noise are generated.

Conventionally, there has been technology to artificially generate and detect cavitation in pipes at the laboratory level, but there is no suitable method for detecting cavitation actually occurring in pipes in equipment. There wasn't.

Recently, a method has been published to detect the characteristic noise generated by cavitation (Manri Hirotsu, "Water Current Engineering", Jitsugaku Publishing, pp. 364 and below), and according to this method, it is possible to detect cavitation occurring in pipes in equipment. becomes possible.

The above method has been reported as a research result at the laboratory level, in which a stirrer is rotated at high speed by a motor in a water tank to generate cavitation, and the ultrasonic waves generated when the bubbles collapse are transmitted into the water. The ultrasonic wave is captured by a horn, received by a variable frequency receiver controlled by a signal generator, and the sound pressure level of the received ultrasonic wave is measured by a voltmeter. According to this, it becomes possible to detect cavitation actually occurring by applying it to pipes in equipment.

[Problem to be solved by the invention]

However, the above method has the following problems.

(1) The detection device is complicated and the results are difficult to judge.

(2) Although it is possible to determine whether cavitation has occurred and its approximate location, the distribution shape of cavitation cannot be determined.

(3) When cavitation occurs at two or more locations in a pipe, it is difficult to detect the locations where cavitation occurs, and a large number of underwater horns are required, making the equipment more complex and making it difficult to judge the results. .

(4) It is necessary to install an underwater horn inside the pipe, which may obstruct the flow and cause secondary problems.

Therefore, in view of the above-mentioned current situation, the purpose of this invention is to investigate the location of not only cavitation that is artificially generated in pipes at the laboratory level, but also cavitation that actually occurs in pipes in equipment. An object of the present invention is to provide a method for detecting the position of occurrence of cavitation in a pipe, which can be easily and reliably detected from the outside of the pipe.

[Means for Solving the Problems] The detection method of the present invention applies a temperature change to a tube through which a liquid is flowing by heating or cooling it from its outer surface, and photographs the outer surface with an infrared camera. The present invention is characterized in that the position of cavitation occurring within the tube is detected as a temperature change position on the infrared image of the outer surface.

The detection method of the present invention will be described in detail below.

FIG. 1 is an explanatory diagram showing one embodiment of the detection method of the present invention.

In FIG. 1, reference numeral 1 denotes a tube whose position of occurrence of intra-tube cavitation is to be detected, and the tube 1 has a cross-sectional shape similar to, for example, a Pentieri tube. The liquid flows inside the tube 1 from the left to the right as shown by the arrow.

In this invention, first, the area of the tube 1 where cavitation is to be detected, for example, around the throat of the narrow cross section, is detected.
Heat from the outside to give it a temperature rise.

Note that it is only necessary to apply a temperature change to the location to be detected, and the temperature may be lowered by cooling the location from the outside. It is preferable to make these temperature changes rapidly, and from this point of view, it is effective to heat the pipe 1 when it is a low-temperature pipe, and to cool it when the pipe 1 is a high-temperature pipe.

Any heating method or cooling method is possible. In this example, an infrared heater 4 is placed inside the reflector 3 whose cross section is shaped like the character "<".
The tube 1 is heated using a heater 5 containing a.

At this time, if cavitation 2 occurs in the tube 1, the liquid in the part where it occurs is mixed with air bubbles, so it is worse than the liquid itself without air bubbles.
It has a small heat capacity, and the amount of heat absorbed from the tube wall during heating is smaller than from the liquid itself. Therefore, when a temperature increase is applied by heating, the portion of the tube wall that comes into contact with the liquid where cavitation 2 has occurred is lower than the portion of the tube wall that comes into contact with the liquid where cavitation 2 has not occurred. The degree of temperature rise is large, and the outer surface of the former tube wall section exhibits a higher temperature than the outer surface of the latter tube wall section, creating a temperature difference.On the other hand, if a temperature drop is applied by cooling, cavitation 2 The outer surface of the tube wall that comes into contact with the liquid in the area where cavitation 2 is occurring exhibits a lower temperature than the outer surface of the tube wall that comes into contact with the liquid in the area where cavitation 2 does not occur, and the temperature is similar although the height is reversed. There is a temperature difference. Therefore, if the outer surface of the tube 1 is photographed with the infrared camera 6 under these conditions, an infrared image of the outer surface showing the position where cavitation 2 has occurred can be obtained.

Therefore, after heating the tube 1 from the outside to give it a temperature rise, the outside surface is photographed by an infrared camera 6 while the heating is stopped or continued as it is, and an infrared image of the outside surface is displayed on a monitor, television 7, etc. get.

An example of an infrared image obtained at this time is schematically shown in FIG. In FIG. 2, 8 is a monitor screen, and 9 is an infrared image of the outer surface of the tube 1. The image portion 9b is displayed in the color of the display temperature L2, and the outside portion 1. When the display temperature is <12, the image portion 9c is displayed in the color 1. <1. The remaining image portion 9 displayed in the color of the lowest display temperature L0
It consists of d.

From this, it can be seen that cavitation 2 occurs in a range of positions ranging from image portions 9a to 9c, and the degree of occurrence is strongest at the position of image portion 9a, and becomes weaker as it goes outside of the image portion 9c. It can be seen that it is the weakest at the position.

In addition, the height difference Cts and L of the display temperature shown in the above-mentioned image 9
o) and its indicated temperature range (t.

The number of increments of the displayed temperature within ~ti) (in this example, t
O + tl + L t + ' 3) etc. are determined by the heating time of the tube 1, the heating method, the specifications of the tube 1, the occurrence of cavitation 2, the performance of the infrared camera 6 and how to determine the temperature setting, etc. .

When the tube 1 is cooled from the outside, an infrared image similar to the infrared image shown in FIG. 2 with the displayed temperature reversed is obtained.

Note that the tube 1 can be efficiently cooled by spraying a liquefied low-temperature gas such as LNG, fluorocarbon gas, alcohol, acetone, or the like onto the outer surface of the tube 1.

〔Effect of the invention〕

Since the detection method of the present invention is configured as described above, it has the following excellent effects.

(1) The position of cavitation occurring inside the pipe can be easily and reliably detected from outside the pipe without contact.

(2) Since the detection results are displayed as two-dimensional information of the temperature change position on the infrared image, the results are easy to understand.

(3) Even the distribution shape of cavitation can be seen.

(4) Even if cavitation occurs at two or more locations in the pipe, the locations where cavitation occurs can be easily detected.

(5) Since it is detected from outside the pipe, it does not obstruct the flow inside the pipe and there is no risk of secondary damage.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the detection method of the present invention, and FIG. 2 is a diagram schematically showing an example of an infrared image in which cavitation occurrence positions are detected by the detection method of FIG. 1. . In the drawings, 1... pipe, 2
... Cavitation, 5... Heater, 6
...Infrared camera, 7...Monitor TV, 8...
・Monitor screen, 9... Infrared image of tube outer surface, 9a, 9b, 9c, 9d=image part.

Claims (1)

[Claims] A temperature change is applied to the tube through which the liquid is flowing by heating or cooling from its outer surface, and the outer surface is photographed with an infrared camera, and the position of cavitation that has occurred inside the tube is thus detected on the infrared image of the outer surface. A method for detecting the position of occurrence of cavitation in a pipe, characterized by detecting the position of temperature change.