JP5639714B2 - Nanofluid thermal conductivity measurement system using unsteady hot wire method - Google Patents

Description

  The present invention relates to an apparatus for measuring the thermal conductivity of a nanofluid using the unsteady hot wire method. More specifically, the present invention relates to the thermal conductivity of a nanofluid by minimizing measurement errors in consideration of the tension and gradient of the hot wire. The present invention relates to an apparatus for measuring thermal conductivity of nanofluids using an unsteady hot wire method that can be accurately measured.

  The transient hot-wire method is the most widely used method for measuring the thermal conductivity of fluids, and uses the temperature rise of the hot wire over time after applying an electric current to a fine hot wire. And measuring the thermal conductivity.

  Such an unsteady hot wire method can effectively suppress the influence of natural convection occurring in the fluid as compared with the steady method which is another method for measuring the thermal conductivity of the fluid. Therefore, not only can the thermal conductivity of the fluid be accurately measured, but it does not take much time to measure the thermal conductivity of the fluid, which is effective.

  FIG. 7 is a schematic diagram showing a thermal conductivity measurement system using a conventional unsteady hot wire method, and FIG. 8 is a diagram showing a thermal conductivity measurement device using a conventional unsteady hot wire method. 9 is a graph showing the time of occurrence of natural convection due to a change in the gradient of heat rays.

  Referring to the drawings, a thermal conductivity measurement system using a general unsteady hot wire method includes a thermal conductivity measuring device 10, a Wheatstone bridge 20 composed of a standard precision resistor and a precision variable resistor, a power supply device 30, a heat The data collection device 40 collects data measured by the conductivity measuring device 10.

  Among them, the thermal conductivity measuring device 10 has a structure using one heat wire having a relatively long length (see FIG. 8A) and a structure using two heat wires having different lengths (FIG. 8). (See (b)).

  The previous device uses only one heat wire, so the structure is simple and the measurement is easy. However, heat loss due to conduction occurs at the junctions at both ends of the heat wire, and the measurement error due to such heat loss causes heat conduction. There is a problem that it is difficult to accurately measure the degree. On the other hand, the latter structure is relatively complicated compared to the former, but the amount of heat loss generated at the junctions at both ends of the two heat wires is offset by the processing of the circuit configuration and the material. Measurement error due to conduction loss does not occur, and thermal conductivity can be measured accurately.

  However, in the conventional thermal conductivity measuring device, a measurement error due to natural convection occurs when the reference point for the measurement time is not clarified at the time of measurement. Especially when the tension of the hot wire cannot reach an appropriate value or the hot wire is not arranged vertically, as shown in FIG. Can't get.

  In addition, since the conventional heat conduction measuring device has a structure in which the heat wire is fixed by soldering, there is a trouble that soldering must be performed every time the heat wire is replaced, and the replaced heat wire is arranged vertically. As described above, it is not easy to adjust the gradient.

  The present invention is to solve the above-mentioned problems of the prior art, and its purpose is to accurately measure the thermal conductivity of nanofluids by minimizing measurement errors in consideration of the tension and gradient of the hot wire. It is an object of the present invention to provide a nanofluid thermal conductivity measuring apparatus using a non-stationary hot wire method that can be measured in a continuous manner.

  Another object of the present invention is to provide a nanofluid thermal conductivity measuring device using the unsteady hot wire method, which is very easy to install and replace the hot wire.

  In order to achieve the above object, a nanofluid thermal conductivity measuring apparatus using the unsteady hot wire method according to the present invention includes the following configuration.

  An upper plate and a lower plate separated vertically, a cylinder installed between the upper plate and the lower plate, an operation plate installed in the cylinder and movable up and down, and coupled so as to penetrate the upper plate Both ends of the first fixing means, the second fixing means installed on the upper surface of the operating plate and located on the same vertical line as the first fixing means, and the first fixing means and the second fixing means. Each fixed heat ray.

  According to the apparatus of the present invention configured as described above, the tension of the hot wire can be adjusted by raising or lowering the first fixing means using the tension adjusting means. Moreover, since the 1st fixing means and 2nd fixing means to which a heat ray is fixed are located on a perpendicular line, the gradient of a heat ray can be maintained in parallel with a perpendicular line. Accordingly, since the error caused by the tension and gradient of the hot wire when measuring the thermal conductivity of the nanofluid can be minimized, the thermal conductivity can be accurately measured.

  At this time, it is preferable to further include a sensor that is installed in the tension adjusting means and measures the tension of the heat ray.

  The first fixing means and the second fixing means are formed in a rod-shaped main body, an inclined fixing tool, and an inner wall surface in an inclined shape corresponding to the fixing tool, and are screwed to the main body. Including a fixing nut. At this time, a fixing hole through which the heat ray penetrates is formed in the center of the fixing tool, and a cross-shaped groove centering on the fixing hole is formed on the upper surface or the lower surface of the fixing tool.

  According to the 1st fixing means and the 2nd fixing means of such a structure, if the fixing nut is tightened in a state where the heat ray is inserted into the fixture, the fixing operation of the heat ray is completed. Therefore, not only is the installation and replacement of the heat ray easy, but the first fixing means and the second fixing means are located on the vertical line, so that the work of adjusting the gradient of the heat ray is not necessary.

  The present invention configured as described above is based on the tension and gradient of the hot wire when measuring the thermal conductivity of the nanofluid using the tension adjusting means and the sensor, and the first fixing means and the second fixing means located on the vertical line. Since the generated error can be minimized, the thermal conductivity can be accurately measured.

  In addition, fixing the heat wire through screw fastening that is not a soldering method is not only easy to install and replace, but also because the first fixing device and the second fixing device are located on the vertical line, There is an effect that the work of adjusting the gradient is unnecessary.

It is sectional drawing which shows the heat conductivity measuring apparatus using the unsteady hot wire method which concerns on one Embodiment of this invention. It is a disassembled perspective view which shows a 1st fixing means among the thermal conductivity measuring apparatuses using the unsteady hot-wire method which concerns on embodiment of FIG. It is sectional drawing which shows a 1st fixing means among the thermal conductivity measuring apparatuses using the unsteady hot-wire method which concerns on embodiment of FIG. It is the figure which expanded a part among thermal conductivity measuring apparatuses using the unsteady hot-wire method which concerns on embodiment of FIG. It is a flowchart which shows the measuring method using the thermal conductivity measuring apparatus using the unsteady hot wire method which concerns on embodiment of FIG. It is a graph which shows the measurement result of the thermal conductivity of water using the thermal conductivity measuring apparatus using the unsteady heat ray method which concerns on embodiment of FIG. It is the schematic which shows the thermal conductivity measuring system using the conventional unsteady hot-wire method. It is a figure which shows the thermal conductivity measuring apparatus using the conventional unsteady hot-wire method. It is a graph which shows the generation | occurrence | production time of the natural convection by the gradient change of a heat ray.

  Embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, embodiments according to the present invention are described, and reference numerals are given to components in each drawing, and even if the same components are shown in other drawings, as much as possible. The same reference numerals are given.

  As shown in FIG. 1, a nanofluid thermal conductivity measuring device (100, hereinafter referred to as a measuring device) using the unsteady hot wire method according to the present embodiment includes an upper plate 110 and a lower plate 120 that are separated vertically. A cylinder 130 installed between the upper plate 110 and the lower plate 120, an operation plate 140 installed at the inner lower portion of the cylinder 130, and a first fixing means 150 coupled to penetrate the upper plate 110, The second fixing means 160 installed on the upper surface of the working plate 140, the heat wire W fixed at both ends to the first fixing means 150 and the second fixing means 160, and the tension adjusting means installed on the upper surface of the upper plate 110. 170 and a sensor 180 installed on the tension adjusting means 170.

  The upper plate 110 has a disk shape with a predetermined thickness. A coupling hole 112 to which the first fixing means 150 is coupled is formed at the center, and a screw for coupling with a through-hole 114 through which a rod 192 described later passes and a cylinder 130 is formed around the coupling hole 112. A fastening hole 116 to be S-fastened is formed. In addition, a cover 118 in which the upper part of the first fixing means 150, the tension adjusting means 170, and the lower part of the sensor 180 are provided is formed at the center of the upper surface of the upper plate 110.

  The lower plate 120 has a disk shape in which a groove 122 is formed on the lower surface, and a fastening hole 124 in which a screw for coupling with the cylinder 130 is fastened is formed in the groove 122. The reason why the groove 122 is formed on the lower surface of the lower plate 120 in this way is to prevent the screw S from protruding and maintain the level when the measuring apparatus 100 is installed.

  The cylinder 130 is a portion filled with a thermal conductivity measurement fluid (hereinafter referred to as nanofluid). The flange 132 is formed in a cylindrical shape having an upper end and a lower end, and the flange 132 is formed with a fastening hole 134 in which screws for coupling with the upper plate 110 and the lower plate 120 are S-fastened.

  The cylinder 130 having the above-described shape must have a sealed structure so that the nanofluid filled therein does not leak. For this purpose, an airtight holding O-ring 194 is provided between the cylinder 130 and the upper plate 110, between the cylinder 130 and the lower plate 120, and between the upper plate 110 and the first fixing means 150. .

  The operation plate 140 is installed at the inner lower part of the cylinder 130 and is installed so as to be movable up and down so that the length of the heat ray W can be adjusted. More specifically, the operation plate 140 is installed below a rod 192 whose upper end is fixed to the upper plate 110, and is fixed by nuts N on the upper and lower surfaces of the operation plate 140. That is, when the nut N is loosened and the operating plate 140 is moved up and down, the installation height can be adjusted.

  At this time, the upper plate 110 and the operation plate 140 are preferably made of a Teflon (registered trademark) material. In addition, the rod 192 that supports the operating plate 140 is preferably made of stainless steel or copper material having excellent thermal conductivity so as not to affect the measurement of the thermal conductivity of the nanofluid.

  The first fixing means 150 and the second fixing means 160 are means for fixing the heat ray W. The first fixing means 150 is installed in the coupling hole 112 formed in the center of the upper plate 110, and the second fixing means 160 is installed in the center of the upper surface of the operation plate 140.

  The reason why the first fixing means 150 and the second fixing means 160 are positioned on the same vertical line is that the gradient of the heat ray W has an influence on the measurement of the thermal conductivity of the nanofluid. . That is, by positioning the first fixing means 150 and the second fixing means 160 on the same vertical line, the occurrence of natural convection is delayed and the measurement error of thermal conductivity is minimized.

  Meanwhile, the structure of the first fixing means 150 and the second fixing means 160 will be described in detail with reference to FIGS. Here, since the second fixing means 160 has the same structure and shape as the first fixing means 150, the first fixing means 150 will be described as a representative.

  The first fixing means 150 includes a main body 150a, a fixing tool 150b positioned at the lower part of the main body 150a, and a fixing nut 150c that covers the fixing tool 150b and is screwed to the lower part of the main body 150a.

  The main body 150a has a rod shape, and a male screw (151 in FIG. 4) for coupling with the tension adjusting means 170 is formed in the intermediate portion. Further, a screw thread 152 for coupling with the fixing nut 150c is formed at the lower end of the main body 150a, and an insertion groove 153 into which the heat ray W is inserted is formed on the lower surface (see FIG. 3).

  In FIG. 3, the fixture 150b is an elastic body formed in an inclined shape whose diameter increases toward the top. A fixed hole 154 through which the heat ray W passes is formed in the center, and a cross-shaped groove 155 centering on the fixed hole 154 is formed in the lower surface. The cross-shaped groove 155 is a space for expanding the fixing hole 154 when the heat wire W is coupled and for crimping the fixing tool 150b to the heat wire W when the fixing nut 150c is coupled.

  In FIG. 2, such a cross-shaped groove 155 is formed at a certain depth on the upper surface of the fixture 150b. The fixing nut 150c is a fastening means that is screwed to the main body 150a and presses the fixing tool 150b to the heat ray W. As shown in FIG. 3, a lower portion 156 of the inner wall surface of the fixing nut 150c is formed in an inclined shape corresponding to the fixing tool 150b, and a screw thread 157 corresponding to the screw thread 152 of the main body 150a is formed on the upper portion of the inner wall surface. Is formed.

  In the first fixing means 150 having the above-described structure, the fixing nut 150c is screwed to the main body 150a, so that the heat wire W can be easily installed and replaced. That is, after the fixing tool 150b is positioned between the main body 150a and the fixing nut 150c with the heat ray W inserted into the fixing hole 154, the installation is completed when the fixing nut 150c is coupled.

  At this time, the lower part 156 of the inner wall surface of the fixing nut 150c presses the fixing tool 150b in the process of screwing the fixing nut 150c to the main body 150a, and the heat ray W is fixed if the fixing tool 150b is crimped. On the other hand, if the fixing nut 150c is loosened, the crimping state of the fixing tool 150b that has pressurized the fixing tool 150b is released, and the heat ray W can be easily separated.

  Referring to FIG. 4, a linear motion bearing 196 is installed in the coupling hole 112 of the upper plate 110, and a first fixing unit 150 is installed inside the linear motion bearing 196. Further, a tension adjusting unit 170 is installed in the middle of the first fixing unit 150, and a sensor for measuring the tension of the hot wire W is installed at the upper end of the first fixing unit 150.

  At this time, the first fixing unit 150 and the tension adjusting unit 170 are coupled to each other through a male screw 151 formed in the middle of the first fixing unit 150 and a female screw 172 formed inside the tension adjusting unit 170.

  According to such a structure, when the tension adjusting means 170 is rotated in the direction of the arrow A in the drawing, the first fixing means 150 moves upward by moving the male screw 151 and the female screw 172 in mesh with each other, and the heat wire W is moved. Tension. On the other hand, if the tension adjusting means 170 is rotated in the direction opposite to the arrow A, the first fixing means 150 moves downward while relaxing the heat ray W.

  After all, by adjusting the tension of the hot wire W to an appropriate value, the measurement error can be minimized in consideration of the tension of the hot wire W. Therefore, the thermal conductivity of the nanofluid can be accurately measured.

  A method for measuring the thermal conductivity of the nanofluid using the above-described measuring apparatus 100 will be described in detail with reference to FIG.

  First, the hot wire W is installed in the measuring apparatus 100 (S10). Referring to FIG. 3, the fixing nut 150c is separated from the main body 150a, and the heat ray W is passed through the fixing hole 154 of the fixing tool 150b. Thereafter, the fixing nut 150c is screwed to the main body 150a so that the fixing tool 150b is crimped to fix the heat ray W.

  When the installation of the heat ray W is completed, as shown in FIG. 4, the tension of the heat ray W is set to a desired value by raising or lowering the first fixing means 150 using the tension adjusting means 170 (S20). .

  Next, after water is injected into the cylinder 130, power is supplied to the heat wire W to measure the thermal conductivity of the water (S30). That is, when the tension of the hot wire W is adjusted using the tension adjusting means 170 and the sensor 180 and the thermal conductivity of water is measured, the tension of the hot wire W with the smallest measurement error can be grasped.

  The tension of the hot wire is adjusted according to the tension value measured in the above step (S40).

  Finally, the water injected into the cylinder 130 is discharged, and after the nanofluid for measuring the thermal conductivity is injected, the thermal conductivity of the nanofluid is measured (S50, S60).

  As described above, when the thermal conductivity of the nanofluid is measured using the measuring apparatus 100 according to the present embodiment, an appropriate tension is applied to the hot wire W. Moreover, the heat ray W is arranged in the vertical direction. Therefore, measurement errors caused by the tension and gradient of the hot wire W can be minimized, and the thermal conductivity can be accurately measured.

  Further, since the fixing means 150 and 160 fix the heat ray W through screw fastening which is not soldered, the installation and replacement are easy, and the first fixing means 150 and the second fixing means 160 are located on the vertical line. Measurement is easy because no gradient adjustment work is required.

  On the other hand, it will be as follows if the experimental result of the thermal conductivity of the fluid using the measuring apparatus 100 and measuring method which concerns on this embodiment is investigated in detail.

  As a result of measuring the thermal conductivity using water, as shown in FIG. 6, it can be confirmed that the measurement error range of the thermal conductivity is within 1.5%, and the linearity of the result showing the reliability of the experimental result It was found that the property was 0.9999 or more.

  The present invention has been described above through the preferred embodiments. However, the above-described embodiments are merely illustrative of the technical idea of the present invention, and various modifications can be made without departing from the technical idea of the present invention. It should be understood by those having ordinary knowledge in the field that such changes are possible. Therefore, the protection scope of the present invention should be construed based on the matters described in the claims, not the specific embodiments, and all technical ideas within the scope equivalent thereto also apply to the rights of the present invention. It should be construed as included in the scope.

100 measuring device 110 upper plate 120 lower plate 130 cylinder 140 operation plate 150 first fixing means 160 second fixing means 170 tension adjusting means 180 sensor

Claims (5)

An upper plate and a lower plate spaced apart from each other;
A cylinder installed between the upper plate and the lower plate;
An operating plate installed in the cylinder and capable of moving up and down;
First fixing means coupled to penetrate the upper plate;
Second fixing means installed on the upper surface of the operating plate and located on the same vertical line as the first fixing means;
A heat wire having both ends fixed to the first fixing means and the second fixing means ;
Tension adjusting means installed on the upper surface of the upper plate and moving the first fixing means up and down;
An apparatus for measuring the thermal conductivity of a fluid using an unsteady hot wire method, comprising: a sensor for measuring the tension of the hot wire . A male screw is formed in the middle of the first fixing means, a female screw is formed inside the tension adjusting means, and the first fixing means is raised or lowered when the tension adjusting means is rotated. An apparatus for measuring thermal conductivity of a fluid using the unsteady hot wire method according to Item 1. The first fixing means or the second fixing means is
The body,
A fixing hole of an elastic body in which a fixing hole through which the heat ray penetrates is formed, and a cross-shaped groove is formed on the lower surface around the fixing hole;
The apparatus for measuring thermal conductivity of fluid using the unsteady hot wire method according to claim 1, further comprising: a fixing nut screwed to a lower portion of the main body to fasten the fixture. The apparatus for measuring thermal conductivity of fluid using the unsteady hot wire method according to claim 3 , wherein the fixing tool has an inclined shape whose diameter increases toward the top. Unsteady heat rays according to claim 1, wherein the operating plate is connected further comprising a rod for guiding the vertical movement of the operation plate, wherein the upper plate and稼kinematic plate is Teflon material Measuring device for thermal conductivity of fluids using the method.

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