KR101170072B1 - Thermal diffusivity of nanofluid measurement equipment - Google Patents

Abstract

The present invention relates to a thermal diffusivity measuring apparatus for measuring the thermal diffusivity inside the nanofluid. According to the present invention, a heating wire for applying heat to the inside of the nanofluid is supplied with power, and a portion of the bridge is disposed so as to be spaced apart from the heating wire by a predetermined value based on a resistance value that changes in response to the heat diffused from the heating wire. And an amplifier configured to receive the voltage difference between the circuit and the bridge circuit and amplify and output the voltage difference. With such a configuration, the present invention can detect the heat diffused in the nanofluid by the voltage difference in the bridge circuit.

Nanofluid, Thermal Diffusion, Unsteady Heating, Sensor Module

Description

Thermal diffusivity of nanofluid measurement equipment

The present invention relates to a thermal diffusivity measuring apparatus, and more particularly, to a thermal diffusivity measuring apparatus of a nanofluid for measuring heat diffused inside a nanofluid using a voltage difference generated inside the bridge circuit.

In general, a fluid is a general term for a liquid or gas that is undetermined and easily deformable and can flow freely. Fluids are used in various fields such as air conditioning systems and chillers.

Nanofluids are mixed fluids that enhance the heat transfer and thermal diffusion performance of fluids by adding nanosized solid particles such as metals, oxides, ceramics or nonmetals with high thermal conductivity to liquids such as water, ethylene glycol and oils. Nanofluid is used as a heat exchange or heat transport device that exchanges heat from a high temperature to a low temperature in a heat transfer medium or a heat removal device because of its excellent heat transfer characteristics.

Therefore, since the performance of nanofluids is determined by thermal conductivity and thermal diffusion, the thermal conductivity and thermal diffusion of the fluid before the solid particles are inserted and the thermal conductivity and thermal diffusion of the nanofluids into which the solid particles are inserted are compared to determine the usefulness of the nanofluid. Verified.

In general, the method of measuring the thermal conductivity and thermal diffusion of the nanofluid has an abnormal heat wire method that can simultaneously measure the thermal conductivity and thermal diffusion of the nanofluid.

The unsteady hot wire method is inserted in the direction of gravity inside a fluid in which a thin hot wire sensor whose resistance value changes with temperature changes is measured. If the current flows momentarily to the heating sensor, the temperature of the heating sensor itself increases and the temperature of the fluid into which the heating sensor is inserted increases.

At this time, if the heat conduction effect of the fluid inserted into the heat sensor is good, most of the heat generated by the heat sensor is transferred to the fluid, so that the temperature rise of the heat sensor is small, so that the increase in the resistance value of the heat sensor is small and If the heat conduction effect is not good, most of the heat generated by the heat sensor is accumulated in the heat sensor, so that the temperature rise of the heat sensor is large, and the increase in the resistance value of the heat sensor is increased.

In other words, if the amount of increase in the resistance value of the heat sensor is measured, the heat conduction effect of the fluid is good. If the amount of increase in the resistance of the heat sensor is large, the effect of heat conductivity of the fluid is not good.

Using this method, the thermal diffusivity inside the fluid is measured by the abnormal hot wire method.

However, due to the difference in temperature inside the fluid, the heat generated from the heat sensor is moved from the high to the low temperature. The heat diffusion is an abnormal hot wire method in which heat is generated and one heat sensor is used to measure the temperature. When measured, there was a problem in that the difference between the thermal diffusion rate calculated from the result data and the actual thermal diffusion rate of the nanofluid.

The present invention can reduce the error of the thermal diffusivity of the nanofluid and the actual thermal diffusivity of the nanofluid, which is calculated by the experimental result data that can be generated by the unsteady heating method that measures the thermal diffusivity inside the nanofluid by using a single heat ray sensor. An object of the present invention is to provide an apparatus for measuring the thermal diffusivity of nanofluids.

The apparatus for measuring the thermal diffusivity of the nanofluid of the present invention comprises: a heating wire that receives heat and is inserted into the nanofluid to apply heat; A bridge circuit having a portion spaced apart from the heating wire by a predetermined distance and generating a voltage difference therein based on a resistance value changed corresponding to the heat diffused from the heating wire; And an amplifier receiving the voltage difference of the bridge circuit and amplifying and outputting the voltage difference.

The bridge circuit may include a first loop in which a resistance value is changed in response to heat spread from the heating wire, a first loop in which a first fixed resistor is connected in series, and a second loop in which a second fixed resistor and a variable resistor are connected in series. And a first loop and a second loop are connected in parallel.

In addition, the heat sensing unit is characterized in that the insertion in the interior of the nano-fluid corresponding to the heating wire.

Here, the heat sensing unit is characterized in that the resistance value is increased in proportion to the heat diffused from the heating wire.

The voltage difference between the first loop and the second loop is increased in proportion to the resistance of the heat sensing unit.

According to the thermal diffusion measuring apparatus of the present invention, it is possible to precisely spread heat inside the nanofluid by using a heating circuit that applies heat to the nanofluid and a bridge circuit that measures the internal temperature of the nanofluid at a portion away from the heat generator. It is possible to reduce the error between the thermal diffusion rate of the nanofluid and the actual thermal diffusion rate of the nanofluid, which is calculated by the experimental data.

Hereinafter, an apparatus for measuring heat diffusion of a fluid according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic diagram showing an apparatus 100 for measuring the thermal diffusion rate of a nanofluid according to an embodiment of the present invention.

Referring to FIG. 1, the apparatus 100 for measuring heat diffusion rate of a nanofluid according to an exemplary embodiment of the present invention includes a heating wire 110, a temperature detector 120, and an amplifier 130.

The heating wire 110 is for applying heat to the interior of the nanofluid 11 accommodated in the experiment container 10. The heating wire 110 is inserted into the nanofluid 11 and the electrical energy supplied from the first power supply 111 is converted into thermal energy. To generate heat.

In addition, the heating wire 110 is preferably made of a platinum wire or tungsten wire with good thermal conductivity.

The first power supply 111 is for supplying power to the heating wire 110 and is connected to the heating wire 110.

In addition, the measuring device 100 indirectly calculates the amount of heat generated from the switch 112 and the heating wire 110 inserted into the nanofluid 11 to selectively cut off the power applied to the heating wire 110. In order to heat the heating line 110 may further include a calorimetric resistor 113 is connected in series.

The bridge circuit 120 detects heat diffused inside the fluid 11, and includes a first loop 121 and a second loop 124, and includes a first loop 121 and a second loop 124. Are connected in parallel.

In the first loop 121, the heat sensing unit 122 and the first fixed resistor 123 are connected in series.

The heat detection unit 122 has a resistance value corresponding to the heat diffused from the heating wire 110, and is inserted into the nanofluid 11 in parallel with the heating wire 110 so that the heating wire 110 is inside the nanofluid 11. The resistance value is increased in proportion to the heat diffused from.

In addition, the heat detection unit 122 preferably has a shape that matches the heating wire 110 in order to effectively receive the heat generated from the heating wire 110, and preferably made of a platinum wire or tungsten wire having good thermal conductivity.

In the second loop 124, the second fixed resistor 125 and the variable resistor 126 are connected in series.

The variable resistor 126 may have a voltage value corresponding to a resistance value changed by the basic temperature of the nanofluid 11 when the heat sensing unit 122 is inserted into the nanofluid 11 so that the first loop 121 is changed. Voltage applied to the first node 121a between the heat sensing unit 122 and the first fixed resistor 123 of the first and second resistors 125 and the variable resistor 126 of the second loop 124. The voltage applied to the two nodes 124a is equalized to prevent current from flowing through the amplifier 128.

The voltage applied to the first node 121a and the voltage applied to the second node 124a are in equilibrium when the temperature of the nanofluid 11 is not changed, and the temperature of the nanofluid 11 is caused by the heating wire 110. When the change occurs, a difference occurs between the voltage applied to the first node 121a and the voltage applied to the second node 124a, so that current flows to the amplifier 130.

That is, when the resistance of the heat detector 122 increases in proportion to the internal temperature of the nanofluid 11, the voltage applied to the first node 121a is increased, and the voltage applied to the first node 121a and the second voltage are increased. The difference in voltage across node 124a is increased.

The amplification unit 130 is for amplifying a voltage difference generated in the bridge circuit 120. One side of the amplifier 130 is connected to the bridge circuit 120 to compare the voltage applied to the first node 126 and the second node 127. The inverting terminal and the inverting terminal are received and amplified, and the other side is connected to a separate display member, that is, a data recorder 12 or an oscilloscope, and outputs a temperature value.

The thermal diffusion measuring apparatus 100 may further include a second power supply unit 140 for supplying power to the bridge circuit 120 and the amplifier 130.

In addition, the thermal diffusion measuring apparatus 100 may further include a protective case (not shown) for fixing the positions of the heating wire 110 and the heat sensing unit 122 inserted into the nanofluid 11 and protecting other devices. .

The protective case is preferably a hollow rectangular parallelepiped shape.

The protective case is exposed to the heating wire 110 and the heat detection unit 122 in the hollow portion of the protective case can fix the position of the heating wire 110 and the heat detection unit 122 and the heating wire 110 and the heat detection unit 122 Other connected device parts can be inserted inside the protective case to prevent other device parts from being exposed to the nanofluid.

Comparing the measured value and the theoretical value obtained by the thermal diffusion measuring apparatus 100 of the present invention described above is as follows.

The temperature rise inside the nanofluid 11 at a distance r from the heating wire 110 is expressed as follows.

(1)

(One)

Where α is the thermal diffusion rate, k is the thermal conductivity, and q is the amount of heat generated per unit length. In this equation, the function E ₁ can be found using mathematical software:

(2)

(2)

Here, r is approximately 3 mm in the interval between the heating wire 110 and the heat sensing unit 122 and the thermal diffusion rate of the engine oil is 0.859 * 10 ^−7, so that the variable r ² / 4αt over time is represented as follows.

(4)

(4)

At this time, since 15 seconds after the buoyancy flow is generated in the nanofluid 11 it is impossible to measure the thermal diffusivity, the measured value measured using this device is used only up to approximately 15 seconds of data.

The heat sensing unit 122 is approximately 12.963Ω in the fluid 11 and the first fixed resistor 123 is 2kΩ. The second fixed resistor 125 is 10 kΩ and the variable resistor 126 is adjusted in the range of 1 kΩ.

The resistance of the variable resistor 126 in the balanced state of the bridge circuit 120 before heat is generated in the heating wire 110 is 64.815Ω. The characteristic of the bridge circuit 120 is that the resistance value of the first fixed resistor 123 is much larger than the resistance value of the heat sensing unit 122. The change of the resistance value according to the temperature rise is expressed as follows.

(5)

(5)

Where R _t is the resistance value of the heat sensing unit 122 and R _t0 is the original resistance value of the heat sensing unit 122. At this time, the temperature that changes for 15 seconds even in the engine oil that the temperature rise is great change about 1 ℃. As described above, the resistance value of the heat sensing unit 122 that changes according to the temperature rise of 1 ° C. of the internal temperature of the nanofluid 11 is 0.047Ω (= 12.023 * 0.0039092 * 1). The total resistance of the first loop 121 including the heat sensing unit 122 is 2012.963Ω (= 2000Ω + 12.963Ω) when the temperature of the nanofluid 11 is 21 ° C., and the temperature of the nanofluid 11 is 1. It is 2013.01Ω (= 2000Ω + 13.963Ω + 0.047Ω) at 22 ° C. Accordingly, when 15 V is applied to the bridge circuit 120, when the temperature of the nanofluid 11 is 21 ° C., the current flowing in the first loop 121 including the heat sensing unit 122 is 7.4517 mA and the nanofluid 11 When the temperature of 1 ° C. increases to 22 ° C., the current flowing in the first loop 121 including the heat sensing unit 122 becomes 7.4515 mA. Therefore, when the magnitude of the resistance value changes small, since a substantially constant current flows in the bridge circuit 121 and the current is constant, when the resistance value of the heat sensing unit 122 increases, the voltage applied to the first node 121 is increased. The voltage difference between the first loop 121 and the second loop 124 increases. The amount of change in voltage and the amount of change in temperature between the first loop 121 and the second loop 124 are expressed as follows.

(6)

(6)

Since the amount of change in voltage and the amount of change in temperature increase in proportion, the equation (4) above is taken into account the constants such as the mass and thermal diffusion rate of the nanofluid 11 and the spacing between the heating wire 110 and the heat sensing unit 122. It is displayed as follows.

(7)

(7)

If (7) is modified, it is displayed as follows.

(8)

(8)

Here, assigning a new variable to Equation (8) above will display:

(9)

(9)

According to Equation (9), time data (hereinafter, referred to as 'experimental data') of the internal voltage rise of the bridge circuit 120 may be curved into a linear function equation through an appropriate conversion process. In Equation (7) above, C ₂ has thermal diffusivity information, and in Equation (9) above, which is transformed into a linear function, A represents C ₂ . The process of obtaining the coefficient C ₂ using the measured experimental data first takes a log of the voltage signal, then obtains the reciprocal of the time, adds a negative number to the reciprocal of the obtained time, and measures the thermal diffusion rate of the nanofluid shown in FIG. The slope of the straight line is obtained by displaying the test data obtained by 100) in a straight line through the curve fitting.

In applying the conversion process to the voltage change data for the engine oil and glycerin, C ₂ is as follows.

(10)

10

Therefore, the thermal diffusivity α is expressed as follows.

(11)

(11)

3 mm, the interval between the heating wire 110 and the heat sensing unit 122, is substituted in r, and the slope of the straight line 33.26 of the graph in which the engine oil test result shown in FIG. 3 is changed into a straight line through curve fitting is expressed by Equation (11) above The thermal diffusivity is calculated by substituting for.

If we compare 0.859 * 10 ^-7 , the thermal diffusivity of the engine oil, and the measured values measured through the experiment, we can see that it has an error of 0.6% (= (0.854-0.859) * 100 / 0.859).

The slope of the straight line 30.862 of the graph changed into a straight line through curve fitting is substituted into Equation (11), and the thermal diffusivity is calculated as follows.

Comparing the measured thermal diffusivity of 0.935 * 10 ^-7 with the measured value of the experiment, it can be seen that the error is 1.6% (= (0.920-0.935) * 100 / 0.935).

That is, it can be seen that there is almost no error in the thermal diffusivity measured through the experiment and the thermal diffusivity according to the theory of the nanofluid 11.

As mentioned above, although the apparatus for measuring heat diffusion of the fluid of the present invention has been described with reference to the preferred embodiment of the present invention, it will be apparent to those skilled in the art that modifications, changes, and various modifications can be made without departing from the spirit of the present invention.

1 is a schematic view showing an apparatus for measuring the thermal diffusivity of nanofluids according to an embodiment of the present invention;

Figure 2 is the voltage change data of the engine oil and glycerin obtained by the device for measuring the thermal diffusivity of the nanofluid;

3 is a graph of a straight line in which the experimental result of the engine oil is changed into a straight line through curve fitting; And

4 is a graph of a straight line in which the experimental result of glycerin is changed into a straight line through curve fitting;

<Description of the symbols for the main parts of the drawings>

10: Experimental container 11: Nanofluid

12: data recorder 100: thermal diffusivity measuring device

110: heating wire 111: first power supply unit

112: switch 113: calorimetric resistance

120: bridge circuit 121: first loop

121a: first node 122: thermal sensing unit

123: first fixed resistor 124: second loop

124a: second node 125: second fixed resistor

126: variable resistance 130: amplifier

140: second power supply unit

Claims (5)

A heating wire that receives power and is inserted into the nanofluid contained in the test container to apply heat; A first loop and a second fixed resistor in which the resistance is changed in response to the heat diffused into the nanofluid so as to be spaced apart from the heating wire by a predetermined distance, and the first fixed resistor is connected in series; And a second loop having a variable resistor connected in series, wherein the first loop and the second loop are connected in parallel to generate a voltage difference therein based on the resistance value; And And an amplifier configured to receive the voltage difference of the bridge circuit and amplify and output the voltage difference. The thermal diffusion coefficient ( ₁ ) is calculated using the thermal diffusion coefficient C ₂ , which is a slope of a straight line calculated by converting the voltage difference change amount of the bridge circuit, and the interval r of the heating wire and the heat sensing unit.

A device for measuring the thermal diffusivity of a nanofluid to calculate). [Equation 1]

(C ₂ is the thermal diffusion coefficient, r is the distance between the heating wire and the heat sensing unit) delete The method according to claim 1, The heat detection unit is a thermal diffusion rate measuring device of the nanofluid, characterized in that inserted into the interior of the nanofluid corresponding to the heating wire. The method according to claim 1, The heat detection unit is a thermal diffusion rate measuring device of the nanofluid, characterized in that the resistance value is increased in proportion to the heat diffused from the heating wire. The method of claim 4, And the voltage difference between the first loop and the second loop is increased in proportion to the resistance of the heat sensing unit.

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