CN117147011A - Heat dissipation rate detection unit - Google Patents

Heat dissipation rate detection unit Download PDF

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Publication number
CN117147011A
CN117147011A CN202210566830.5A CN202210566830A CN117147011A CN 117147011 A CN117147011 A CN 117147011A CN 202210566830 A CN202210566830 A CN 202210566830A CN 117147011 A CN117147011 A CN 117147011A
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CN
China
Prior art keywords
detector
axis
heat dissipation
detection unit
rate detection
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Pending
Application number
CN202210566830.5A
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Chinese (zh)
Inventor
何晓舟
鄢博
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Shenzhen Graduate School Harbin Institute of Technology
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Shenzhen Graduate School Harbin Institute of Technology
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Priority to CN202210566830.5A priority Critical patent/CN117147011A/en
Publication of CN117147011A publication Critical patent/CN117147011A/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K17/00—Measuring quantity of heat
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K17/00—Measuring quantity of heat
    • G01K17/06—Measuring quantity of heat conveyed by flowing media, e.g. in heating systems e.g. the quantity of heat in a transporting medium, delivered to or consumed in an expenditure device
    • G01K17/08—Measuring quantity of heat conveyed by flowing media, e.g. in heating systems e.g. the quantity of heat in a transporting medium, delivered to or consumed in an expenditure device based upon measurement of temperature difference or of a temperature

Abstract

A heat dissipation rate detection unit comprising: the original point detector is arranged at the original point position; the x-axis detector is arranged on the x-axis; the y-axis detector is arranged on the y-axis; the z-axis detector is arranged on the z-axis; wherein the spacing of the origin detector, x-axis detector, y-axis detector, and z-axis detector is set to be less than the thermal boundary layer thickness and the spacing is set to be large enough so as to reduce disturbances of the nearby temperature measurements by the detector tip. The heat dissipation detection unit provided by the embodiment of the invention has high precision and high resolution.

Description

Heat dissipation rate detection unit
Technical Field
The invention relates to the field of condensation state, in particular to a heat dissipation rate detection unit.
Background
In classical theory, the transfer of heat in a turbulent versus flow field is generally considered to be a stepwise transfer of energy, with turbulent thermal energy being transferred from large-sized vortices to small-sized vortices until the turbulent thermal energy is eventually completely dissipated when the size of the vortices is comparable to the temperature dissipation length. In this process, the heat dissipation rate describes how fast the thermal energy dissipates.
The theory of Grossmann and Lohse explains the relationship between overall heat transfer efficiency and system control parameters by breaking the dissipative field into two parts, please refer to four papers, s.grossmann and d.lohse, as follows: j.fluid mech.407,27 (2000), phys.rev.lett.86,3316 (2001), phys.rev.e 66,016305 (2002), phys.fluids 16,4462 (2004), in its theoretical assumption, different heat dissipation rate spatial distributions derive the same overall heat transfer amount. Therefore, theory does not give what spatial distribution of heat dissipation rates corresponds to the actual heat transfer process, so experimental measurement data is required to provide this important information.
Disclosure of Invention
The problem to be solved by the present invention is to provide a heat dissipation rate detection unit with high accuracy and high resolution.
In order to solve the above-described problems, the present invention provides a heat dissipation rate detection unit including: the original point detector is arranged at the original point position; the x-axis detector is arranged on the x-axis; the y-axis detector is arranged on the y-axis; the z-axis detector is arranged on the z-axis; wherein the spacing of the origin detector, x-axis detector, y-axis detector, and z-axis detector is set to be less than the thermal boundary layer thickness and the spacing is set to be large enough so as to reduce disturbances of the nearby temperature measurements by the detector tip.
Optionally, the origin detector is a thermistor.
Optionally, the x-axis detector is a thermistor.
Optionally, the y-axis detector is a thermistor.
Optionally, the z-axis detector is a thermistor.
Optionally, the origin detector, the x-axis detector, the y-axis detector, and the z-axis detector have tip diameters.
Optionally, the spacing is set to 2-3 times the tip diameter.
Optionally, the tip diameter is 80 microns.
Optionally, the pitch is set to 250 microns.
Alternatively, each of the origin detector, x-axis detector, y-axis detector, and z-axis detector is connected as a resistive arm to an ac transformer bridge, and the other resistive arm is connected to a variable resistor to balance the bridge, which is driven by a lock-in amplifier.
Compared with the prior art, the technical scheme of the invention has the following advantages: the embodiment provided by the invention can measure the heat dissipation rate with high resolution, high response and high precision, and can effectively measure the Rayleigh-B\enard heat convection experiment platform heat dissipation, the heat dissipation experiment in a wind tunnel, the heat dissipation of a heat pipe in engineering and the heat dissipation measurement experiment in sea, atmosphere and lakes.
Drawings
FIG. 1 is a schematic diagram of a heat dissipation rate detection unit according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a heat dissipation rate detection unit according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a measurement circuit of a heat dissipation rate detection unit according to an embodiment of the present invention;
fig. 4 is a temperature fourier spectrum calculated from signals measured by four temperature detectors of a heat dissipation rate detection unit according to an embodiment of the present invention.
Detailed Description
In classical theory, the transfer of heat in a turbulent versus flow field is generally considered to be a stepwise transfer of energy, with turbulent thermal energy being transferred from large-sized vortices to small-sized vortices until the turbulent thermal energy is eventually completely dissipated when the size of the vortices is comparable to the temperature dissipation length. In this process, the heat dissipation rate describes how fast the thermal energy dissipates.
However, unlike solid media, the dissipation ratio in the flow field (especially turbulent flow fields) is spatially unevenly distributed and fluctuates drastically over time at the same location, resulting in a large deviation between theoretical calculations and actual values. Therefore, the heat dissipation rate is directly subjected to high resolution and high response, and the accurate spatial distribution of the heat transmission rate and important time statistical information can be obtained by high-precision measurement, and important experimental data is provided for continuously iterating and improving the prediction parameters of the theoretical model.
There have been several attempts to measure the heat dissipation rate directly experimentally, such as measuring the temperature gradient with a plurality of cold wire anemometers (probes for measuring the air temperature in wind tunnels) in wind tunnel experiments to calculate the heat dissipation rate. The probe designed in the way can be used for wind tunnel experiments mostly, and has limited measurement scenes; the cold wire anemometer is used for measuring, so that excessive electric signal analysis and conversion exist, the cold wire anemometer is more sensitive to environmental noise signals, and the measuring precision is low; more, compared with a common thermistor probe, the cold wire anemometer has insufficient structural strength and long-time measurement stability.
Based on the analysis, the invention provides the heat consumption rate detection unit which has wider measurement scene, more stable long-time measurement performance, high resolution, high response and high accuracy, and is used for heat dissipation measurement of a heat flow experiment and detection of geographical temperature dissipation. The method can effectively measure the heat dissipation of Rayleigh-B\enard heat convection experiment platforms, the heat dissipation experiment in wind tunnels, the heat dissipation of heat pipe flows in engineering and the heat dissipation measurement experiment in sea, atmosphere and lakes.
An embodiment of the present invention provides a heat dissipation rate detection unit, please refer to fig. 1 and 2, including: an origin detector 101 provided at an origin position; an x-axis detector 102 disposed on the x-axis; a y-axis detector 103 disposed on the y-axis; a z-axis detector 104 disposed in the z-axis; wherein the spacing of the origin detector, x-axis detector, y-axis detector, and z-axis detector is set to be less than the thermal boundary layer thickness, and the spacing is set to be large enough so as to reduce disturbances of the nearby temperature measurements by the detector tip.
The heat dissipation rate describes the rate at which thermal energy is dissipated at a certain location (x, y, z) in the temperature field, at a certain time t, expressed mathematically as:
where κ is the thermal diffusivity of the medium,is a function of temperature gradient with spatial position and time.
Because convection theory considers that the temperature is linearly distributed within the thickness of the temperature boundary layer, the distance between detectors is only smaller than the thickness of the temperature boundary layer, and the temperature gradient is obtained by dividing the measured temperature difference by the distance. Based on the above analysis, the inventors have found that the spacing of the detectors should be kept above a minimum length to ensure that fluid flow through the detectors is not compromised and that no interference between two or more detectors occurs, primarily from the effects of spontaneous heating of the detectors on the temperature of the fluid being measured and from the interference of alternating signals in the detector circuit.
I.e. during the measurement, it is most critical that the following two conditions are fulfilled: a) The measurement probe needs to be small enough to meet the spatial resolution required for measuring the temperature gradient; b) The measurement accuracy is high enough that when the probe spacing is too small, mutual interference can occur between them, severely affecting the measurement accuracy (because the square term in the definition results in white noise not being cancelled, but superimposed into the signal).
To this end, the inventors assembled a temperature gradient probe: four identical thermistors were used as origin detectors, an x-axis detector, a y-axis detector and a z-axis detector, for measuring three components of the local temperature gradient. The thermistor was model BB05JA243N manufactured by GE thermo metrics. One of the thermistors is placed at the origin, called T0, and the other three thermistors are aligned along the x, y and z axes, respectively. The assembly process uses a three-axis precision moving platform, and the spatial resolution reaches 10 micrometers. By measuring four temperature signals simultaneously, we obtain three temperature gradient components δT i Delta/delta l, wherein delta T i ＝T i -T 0 (i=x, y, z) is the temperature difference between the two thermistors.
Each of them has a semiconductor head with a diameter of 80 microns and two metal wires with a length of 1 cm with a diameter of 10 microns. Each metal wire was bonded to an extension wire having a diameter of 100 microns with silver paste. The thermistor assembly is then coated with a thin waterproof paint to prevent shorting.
The main material of the probe is a semiconductor, the resistance of which changes with temperature, and the common use method is to firstly measure the resistance of the probe and then calculate the temperature value according to the parameters provided in the specification of the product. This is also the method employed by most users. This approach has two problems: 1. the current in the measurement circuit will heat the probe itself and raise the temperature in the vicinity of the probe (heating power w=i2r, where I is the current and R is the probe resistance, which is about 100kΩ at room temperature when two or more probes are very close, this additional temperature rise effect will become more severe, resulting in distortion of the measured data.2, each probe is connected with a metal wire of 1 meter length and 100 micrometers diameter, when two or more semiconductor probes are closely spaced, an LC equivalent circuit will be formed and will change with changes in ambient temperature (since the resistance value of each probe will change with temperature.) at this point, errors will occur if the temperature is calculated still according to the parameters provided in the specification.
In order to improve the measurement accuracy, the inventor designs and develops a new set of measurement circuits. As shown in fig. 3, each thermistor (thermistor) is connected as a resistor arm to the ac transformer bridge, and the other resistor arm is connected to a variable resistor to balance the bridge. The bridge is driven by a lock-in amplifier (model Standford Research, 830) with an operating frequency of 1000Hz. Four identical bridges and lock-in amplifiers are used, each amplifier uses a different operating frequency (each amplifier differs from each other by 100 Hz), because each lock-in amplifier only amplifies signals at the respective operating frequency and does not amplify signals at other frequencies, four circuits operating at different operating frequencies can effectively avoid measurement errors caused by erroneously amplifying alternating current signals in other circuits. The method can effectively avoid the cross interference of adjacent circuits. The output signals are simultaneously digitized by the multi-channel analog-to-digital I/O boards (BNC 2110, NI), and finally the data is transmitted and stored to a computer. The temperature accuracy of the alloy can reach +/-0.005K.
And as mentioned above, the resistance of the probe is measured first, and then the temperature value is calculated according to the parameters provided in the product specification, so that the influence of signal interference on the temperature value is strong. This is determined by the technological path of measuring resistance-calculating temperature, and is difficult to raise on this basis. To this end the inventors devised a new approach to break through this limitation. Taking an original point detector as an example for exemplary illustration, an alternating current Wheatstone bridge is specially designed for the thermistor, the thermistor and the other high-precision high-stability resistor box are used as two arms of the bridge, and the bridge is adjusted to be in a balanced state near the temperature of a reference point, namely, the output voltage is 0. When the temperature changes, the output voltage also changes correspondingly, so that the output voltage can be converted into a temperature signal by recording the output voltage. During measurement, the input voltage source of the bridge is set to be sine voltage with the amplitude of 1 micro volt (10-6 volts) and the frequency of 1000Hz, and the output voltage signal of the bridge is amplified by a phase-locked amplifier. The phase-locked amplifier only amplifies the signal with the frequency of the input signal (namely, the signal with the frequency of 1000 Hz) and does not amplify noise with other frequencies, and the signal-to-noise ratio can be greatly improved by the method. The technical scheme ensures higher measurement accuracy and stronger anti-interference capability in principle. The circuit designed and manufactured according to the technical scheme ensures that the temperature measurement precision of the circuit reaches +/-0.005K, which is an order of magnitude higher than the precision of the prior other technologies.
Scientific determination of reasonable spacing between thermistors: for measuring local gradients of temperature fieldsIt is desirable to keep the distance between the thermistors as small as possible. This spacing should be less than the thermal boundary layer thickness, which is the minimum dissipation length in turbulent thermal convection. On the other hand, the probe spacing should be large enough to minimize disturbances to nearby temperature measurements by the thermistor tip and interference between electrical signals. In the experiment, we set the pitch of the thermistor to 250 microns. The spacing is 2-3 times larger than the tip diameter of the thermistor to ensure that fluid can pass smoothly through each probe without being blocked, and at the same time, each probe can independently measure the fourier spectrum of the temperature data T (T), please refer to fig. 4, which is a temperature fourier spectrum calculated from the signals measured by the four temperature probes. The measurement data shows that the four sets of fourier spectrum data are completely coincident, confirming that no significant mutual interference is generated between the detectors. As described above, since the interval is 1-3 times smaller than the thickness of the temperature boundary layer and is in a linear temperature distribution region, the temperature can be accurately measuredGradient.
As shown in fig. 4, the measurement found that the standard deviation of the temperature difference was kept constant with the change rate of the pitch for a pitch within 4 mm, and it was found by mathematical derivation that: e-shaped article 2 ≈κ(σ 2 /l) 2 . Therefore, the measured value of the heat dissipation rate component can be kept unchanged by selecting the pitch in the linear range of 4 mm. The inventors set the spacing (250 microns) between the two temperature probes in this linear region in the experiment.
Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention, and the scope of the invention should be assessed accordingly to that of the appended claims.

Claims (10)

1. A heat dissipation rate detection unit, characterized by comprising:
the original point detector is arranged at the original point position;
the x-axis detector is arranged on the x-axis;
the y-axis detector is arranged on the y-axis;
the z-axis detector is arranged on the z-axis; wherein the spacing of the origin detector, x-axis detector, y-axis detector, and z-axis detector is set to be less than the thermal boundary layer thickness and the spacing is set to be large enough so as to reduce disturbances of the nearby temperature measurements by the detector tip.
2. The heat dissipation rate detection unit of claim 1, wherein the origin detector is a thermistor.
3. The heat dissipation rate detection unit of claim 1, wherein the x-axis detector is a thermistor.
4. The heat dissipation rate detection unit of claim 1, wherein the y-axis detector is a thermistor.
5. The heat dissipation rate detection unit of claim 1, wherein the z-axis detector is a thermistor.
6. The heat dissipation rate detection unit of claim 1, wherein the origin detector, x-axis detector, y-axis detector, and z-axis detector have tip diameters.
7. The heat dissipation rate detection unit as recited in claim 6, wherein the pitch is set to 2-3 times the tip diameter.
8. The heat dissipation rate detection unit of claim 7, wherein the tip diameter is 80 microns.
9. The heat dissipation rate detection unit of claim 1, wherein the pitch is set to 250 microns.
10. The heat dissipation ratio detection unit of claim 1, wherein each of the origin detector, the x-axis detector, the y-axis detector, and the z-axis detector is connected as a resistive arm to an ac transformer bridge, and the other resistive arm is connected to a variable resistor to balance the bridge, which is driven by a lock-in amplifier.
CN202210566830.5A 2022-05-23 2022-05-23 Heat dissipation rate detection unit Pending CN117147011A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202210566830.5A CN117147011A (en) 2022-05-23 2022-05-23 Heat dissipation rate detection unit

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202210566830.5A CN117147011A (en) 2022-05-23 2022-05-23 Heat dissipation rate detection unit

Publications (1)

Publication Number Publication Date
CN117147011A true CN117147011A (en) 2023-12-01

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Family Applications (1)

Application Number Title Priority Date Filing Date
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Country Status (1)

Country Link
CN (1) CN117147011A (en)

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