WO2021189818A1

WO2021189818A1 - Temperature measurement device for flowing working medium in micro-channel and calculation method for thickness of thermal insulation layer

Info

Publication number: WO2021189818A1
Application number: PCT/CN2020/120947
Authority: WO
Inventors: 刘纳; 孟祥丰
Original assignee: 青岛理工大学
Priority date: 2020-03-26
Filing date: 2020-10-14
Publication date: 2021-09-30
Also published as: CN111272229A

Abstract

A temperature measurement device for a flowing working medium in a micro-channel, comprising a thermal insulation layer (2) provided at the outer side of a micro-channel measurement section (1); an outer protective layer (3) wrapping the outer side of the thermal insulation layer (2); a thermocouple (5) used for measuring the temperature of the micro-channel measurement section (1); and a temperature display terminal connected to the thermocouple (5), wherein the thermocouple (5) is provided between the thermal insulation layer (2) and a micro-channel, and is attached to the surface of the micro-channel temperature measurement section (1); the inner side of the thermal insulation layer (2) is tightly attached to the micro-channel, the thermocouple (5) is completely wrapped in the thermal insulation layer (2); and the outer diameter d2 of the thermal insulation layer (2) is greater than or equal to the length L of the micro-channel temperature measurement section (1). The problem that the existing methods for measuring the temperature in the micro-channel have defects can be solved. Further disclosed is a calculation method for the thickness of the thermal insulation layer (2).

Description

Temperature measuring device for flowing working fluid in microchannel and calculation method of insulation layer thickness

Technical field

The invention belongs to the field of physical measurement, and specifically relates to a temperature measuring device for a flowing working fluid in a microchannel and a method for calculating the thickness of an insulating layer.

Background technique

The statements here only provide background art related to the present invention, and do not necessarily constitute prior art.

Micro-channel heat exchanger refers to a heat exchanger with a channel equivalent diameter of 10-2000μm. As an emerging heat exchange technology, micro-channel heat exchangers have a broad range of applications in the fields of chip heat dissipation, aerospace, HVAC, fuel cells, natural gas liquefaction, etc. due to their high heat exchange efficiency, compact structure, and easy modularization. Application prospects.

However, there are still many problems in the development and application of microchannel heat exchangers, and a lot of basic research on microchannel flow and heat exchange is still needed. In basic experimental research, the accuracy of measuring the temperature parameters of the working fluid in the channel is the key to the success or failure of the experiment. Limited by the size of the channel, the traditional temperature measurement method cannot meet the measurement of the working fluid temperature in the microchannel, which is mainly reflected in the following points:

(1) The traditional temperature measurement method needs to extend the temperature measurement element into the fluid, which will disturb the flow state of the working fluid.

(2) Non-contact temperature measurement methods such as infrared temperature measurement, whose measurement accuracy cannot meet the requirements;

(3) For the microchannel test, limited by the diameter of the channel, it is difficult for the temperature measuring element to penetrate into the fluid.

Summary of the invention

In view of the shortcomings of the prior art, the purpose of the present invention is to provide a temperature measuring device for a flowing working fluid in a microchannel and a method for calculating the thickness of an insulating layer. problem.

In order to achieve the above objectives, the present invention is achieved through the following technical solutions:

In the first aspect, the technical solution of the present invention provides a temperature measuring device for flowing working fluid in a microchannel, including:

The thermal insulation layer arranged on the outer side of the microchannel measurement section;

The outer protective layer covering the outer side of the thermal insulation layer;

Thermocouple used to measure the temperature of the measurement section of the microchannel;

And, the temperature display terminal connected to the thermocouple;

Wherein, a thermocouple is arranged between the thermal insulation layer and the microchannel, and the thermocouple is attached to the surface of the temperature measurement section of the microchannel; the inner side of the thermal insulation layer is closely attached to the microchannel, and the thermocouple is completely wrapped in the thermal insulation Layer

The outer diameter d2 of the thermal insulation layer is greater than or equal to the length L of the temperature measuring section of the microchannel.

As a further technical solution, the thermal insulation layer is made of nano-silica aerogel; the thermal insulation layer is cylindrical.

As a further technical solution, the thermocouple is welded to the microchannel temperature measuring section; the thermocouple is directly in contact with the thermal insulation layer.

As a further technical solution, the thermocouple is fixed to the temperature measurement section of the microchannel through a thermocouple patch; the outer layer of the thermocouple is covered with a thermocouple patch; the outside of the thermocouple patch is covered with an insulation layer .

In the second aspect, the technical solution of the present invention also provides a method for calculating the thickness of the insulation layer, which includes the following steps:

Through calculation, determine the heat dissipation per unit length of the microchannel temperature measurement section;

Determine the temperature of the outer surface of the microchannel through measurement;

Determine the inner surface temperature of the microchannel through calculation;

The thickness of the thermal insulation layer is determined according to the difference between the temperature of the fluid in the microchannel and the temperature of the outer surface of the microchannel.

As a further technical solution, when determining the heat dissipation per unit length of the microchannel temperature measurement section, the heat dissipation per unit length is composed of the sum of the convective heat exchange and the radiative heat exchange between the outer surface of the outer protective layer and the environment.

As a further technical solution, the difference Δt between the temperature of the fluid in the microchannel and the temperature of the outer surface of the microchannel is calculated to be less than 0.5°C.

As a further technical solution, the outer surface of the microchannel is also the outer surface of the thermal insulation layer.

The beneficial effects of the above-mentioned embodiments of the present invention are as follows:

1) In the technical solution provided by the present invention, an insulating layer is used to compensate for the temperature loss caused by the heat dissipation of the microchannel, and the temperature of the flowing working fluid in the microchannel can be indirectly measured by measuring the outside of the microchannel, which solves the problem of the traditional temperature measurement method. The problem that the temperature measuring element cannot extend into the microchannel.

2) In the technical solution provided by the present invention, a thermocouple with high measurement accuracy is used. Compared with non-contact temperature measurement methods such as infrared temperature measurement, the temperature measurement accuracy is high, and the requirement for temperature measurement accuracy in the microchannel heat exchange test is solved. .

3) In the technical scheme provided by the present invention, the adopted temperature measurement method has no requirement on the material of the microchannel, has a wide application range, has a simple overall structure, low cost, and reliable performance.

Description of the drawings

The drawings of the specification forming a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention, and do not constitute an improper limitation of the present invention.

Figure 1 is a perspective view of the present invention according to one or more embodiments,

Figure 2 is a radial cross-sectional view of the present invention according to one or more embodiments,

Figure 3 is an axial cross-sectional view of the present invention according to one or more embodiments,

Fig. 4 is a graph of operating conditions according to one or more embodiments of the present invention,

Fig. 5 is an error diagram under an 85mm thick insulation layer according to one or more embodiments of the present invention.

In the picture: 1-microchannel temperature measurement section, 2- insulation layer, 3- outer protective layer, 4-thermocouple patch, 5-thermocouple.

In order to show the position of each part, the distance or size between each other is exaggerated, and the schematic diagram is only for illustration.

Detailed ways

It should be noted that the following detailed descriptions are all illustrative and are intended to provide further descriptions of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

It should be noted that the terms used here are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the present invention clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should also be understood that when the terms "comprising" and/or "including" are used in this specification, they Indicate the existence of features, steps, operations, devices, components, and/or combinations thereof;

For the convenience of description, if the words "up", "down", "left" and "right" appear in the present invention, they only indicate that they are consistent with the up, down, left, and right directions of the drawings themselves, and do not limit the structure, but only It is for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

Term explanation part: The terms "installed", "connected", "connected", "fixed" and other terms in the present invention should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or a whole; It can be a mechanical connection, an electrical connection, a direct connection, or an indirect connection through an intermediate medium, an internal connection between two components, or an interaction relationship between two components. For those of ordinary skill in the art The specific meaning of the above terms in the present invention can be understood according to the specific situation.

As described in the background art, in view of the shortcomings of the prior art, the purpose of the present invention is to provide a temperature measuring device for the flowing working fluid in the microchannel and a method for calculating the thickness of the insulation layer, which can solve the current problems in the channel. The temperature measurement method has insufficient problems, which will be described below in conjunction with the embodiments and the drawings of the specification.

Example 1

In a typical implementation of the present invention, as shown in FIG. 1, a temperature measuring device for a flowing working fluid in a microchannel includes a thermocouple 5, an insulation layer 2 and an outer protective layer 3. The thermocouple 5 is used for pasting Attached to the surface of the microchannel temperature measuring section 1, the thermal insulation layer 2 is wrapped on the outside of the microchannel temperature measurement section and the thermocouple 5, and the outer sheath 3 is wound on the outside of the thermal insulation layer 2; wherein, the outer diameter d2 of the thermal insulation layer 2 is greater than or equal to The length L of the temperature measuring section 1 of the microchannel.

The temperature measurement device of this embodiment is applied to measure the temperature of the flowing medium in the microchannel. By setting the thermal insulation layer 2 on the microchannel measurement section, the heat is forcibly blocked in the thermal insulation layer 2 of the microchannel measurement section for indirect measurement. The temperature of the flowing working fluid in the microchannel; due to the physical properties of the microchannel, it can conduct heat quickly, so the pipe wall of the microchannel can be used as a heat-conducting element to guide the heat of the flowing working fluid inside the microchannel to the outside of the microchannel for measurement. The temperature obtained in this way is less likely to destroy the flow state of the internal flowing working fluid than in the prior art, and the temperature measurement of the thermocouple 5 is more accurate than the infrared temperature measurement. In addition, the temperature measurement system of the present invention does not require any personnel to participate. The temperature can be obtained and output by the temperature measuring device in real time, which improves the timeliness of temperature detection.

In the specific use of this embodiment, when the microchannel starts to measure the temperature, multiple devices described in this embodiment can be set on the microchannel to detect the temperature at different locations and record these temperatures; After the fluid working fluid inside is replaced, the temperature at each detection point can be continuously detected, and these temperatures can be compared with the above-mentioned temperatures. The use method can be performed through the server without manual judgment.

Figures 1 to 3 show the positional relationship between the thermal insulation layer 2, the thermocouple 5 and the thermocouple 5 patch 4. In order to facilitate thermal insulation, the position of the thermocouple 5 is fixed. In addition, the thermal insulation in this embodiment Layer 2 is cylindrical. In order to ensure that the thermal insulation layer 2 can closely fit the microchannel, the central axis of the thermal insulation layer 2 coincides with the central axis of the microchannel; when a section of microchannel is equipped with multiple temperature measuring devices, multiple temperature measuring devices They are independent of each other to comply with the principle of rapid heat exchange in microchannels.

For example, in order to judge the difference in temperature at different positions on the same microchannel, detection points a and b can be set at two different positions of the microchannel, and the distance between detection points a and b is greater than L, so that the liquid working medium is For heat loss after a certain distance, the parameters of the temperature measuring devices set at detection points a and b are exactly the same, and the measured temperatures are recorded separately.

For example, in order to judge the temperature difference of different working fluids in the same microchannel, the detection points a and b can be set at two different positions of the microchannel, and the distance between the detection points a and b is greater than L, so that the liquid After a certain distance, the temperature measurement device parameters set at detection points a and b are exactly the same. After using the A mobile working fluid for testing, record the measured temperatures at points a and b respectively; Then replace the B flowing working fluid to perform a yes test, and record the measured temperatures at points a and b respectively.

In more detail, the thermal insulation layer 2 in this embodiment is made of nano-silica aerogel and nano-silica aerogel. Those skilled in the art can understand that the composition of nano-silica aerogel is Similar to glass, it begins to melt above 1200 degrees Celsius. The thermal conductivity and refractive index are also very low, so the silica aerogel material used in this embodiment can ensure the heat preservation effect.

Furthermore, when the aerogel material is used for heat preservation, it is necessary to customize the shape of the silica aerogel to be cylindrical. Those skilled in the art can understand that when silica aerogel is used as a thermal insulation material, it essentially relies on its internal nano-grid-like cavities to prevent thermal insulation, so it maintains its original state and can ensure the physical properties of the internal voids. Shape to avoid affecting its thermal insulation performance.

According to the different materials of the microchannel, the thermocouple 5 is welded or adhered to the surface of the temperature measuring section 1 of the microchannel. In this embodiment, the microchannel is made of non-metallic material. In the embodiment, the metal microchannel is attached by spot welding; regardless of the attachment method, in order to achieve measurement accuracy, it is required that the thermoelectrode must be firmly attached to the outer surface of the microchannel.

Furthermore, the thermocouple 5 converts the temperature signal into a thermoelectromotive force signal, which is converted into the temperature of the measured medium through an electrical instrument (secondary instrument) or a server, so the thermocouple 5 in this embodiment is also connected to an electrical instrument or server , To visually display and record the temperature.

It is understandable that the thermocouple 5 in this embodiment needs to be close to the surface of the microchannel, so it uses a fixtureless thermocouple 5 to be close to the surface of the microchannel. The thermocouple 5 is connected to an electrical instrument or server through a lead wire.

Because the thermocouple 5 is located between the insulation layer 2 and the microchannel. Therefore, the lead wires need to be led out from the end of the insulation layer 2 or pass through the insulation layer 2.

The outer protective layer 3 adopts aluminum foil tape, which can reflect the heat radiated by the thermal insulation layer 2.

The thermocouple 5 adopts one or more of S, B, E, K, R, J, and T models.

Example 2

This embodiment discloses a method for calculating the thickness of the thermal insulation layer 2, which includes the following steps:

Through calculation, determine the heat dissipation per unit length of the microchannel temperature measurement section 1;

The thickness of the thermal insulation layer 2 is determined according to the difference between the temperature of the fluid in the microchannel and the temperature of the outer surface of the microchannel.

When determining the heat dissipation per unit length of the microchannel temperature measuring section 1, the heat dissipation per unit length is composed of the sum of the convective heat exchange and radiation heat exchange between the outer surface of the outer protective layer 3 and the environment.

The difference Δt between the temperature of the fluid in the microchannel and the temperature of the outer surface of the microchannel is calculated to be less than 0.5°C.

The outer surface of the microchannel is also the outer surface of the thermal insulation layer 2.

The following is a specific calculation process to illustrate the above calculation process:

(1) For the cylindrical structure shown in Fig. 1, the heat dissipation per unit length is composed of the sum of the convective heat exchange and radiation heat exchange between the outer surface of the outer protective layer 3 and the environment.

In the formula, Q is the heat exchanged between the solid surface and the fluid per unit area in a unit time, called the heat flux density, in W/m ² ;

t _w and t _fa are the temperature of solid surface and fluid, respectively, in K;

πd ₃ is the wall surface area per unit length, in m ² ;

Q is the heat transfer amount on area A per unit time, unit W;

h _{0 is} called the surface convective heat transfer coefficient, the unit is W/(m ² ·K).

C ₀ is the mass specific heat of the flowing medium in the barrel;

ε is the emissivity;

(2) For the cylindrical structure in Example 1, the heat transfer amount can be calculated by the following formula.

d ₁ is the outer diameter of the microchannel, d ₂ is the outer diameter of the insulation layer 2, d ₃ is the outer diameter of the outer sheath 3, h _i is the convective heat transfer coefficient between the fluid in the microchannel and the wall, and d _i is the inner diameter of the microchannel , Λ is the thermal conductivity of each layer of material.

(3) The outer surface temperature t _{w1 of the} microchannel can be calculated by the following formula.

(4) Combining the above equations (1), (2), (3), the difference between the temperature of the fluid in the microchannel and the temperature of the outer surface of the microchannel can be calculated:

Δt=t _fi -t _w1

(5) For a certain embodiment, the size of Δt is mainly determined by the thickness of the insulation layer 2 δ2, and the thickness of the insulation layer 2 is calculated as follows:

By adjusting the thickness of the thermal insulation layer 2, Δt can be reduced to an acceptable range. For conventional test equipment, the measurement error of the thermocouple 5 for temperature measurement is 0.5 ℃, so reducing Δt to below 0.5 ℃ can meet the accuracy requirements .

In this embodiment, a micro-channel aluminum tube with an inner diameter of 0.5 mm is taken as an example, and the measurement errors of several typical working conditions as shown in Fig. 4 are calculated as a function of the insulation thickness, and under the insulation thickness of 85 mm, the different fluids shown in Fig. 5 Temperature measurement error. It can be seen that the temperature measurement method of the present invention can have higher measurement accuracy in a larger temperature measurement range.

The above descriptions are only preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

A temperature measuring device for flowing working fluid in a microchannel, which is characterized in that it comprises:

The thermal insulation layer arranged on the outer side of the microchannel measurement section;

The outer protective layer covering the outer side of the thermal insulation layer;

Thermocouple used to measure the temperature of the measurement section of the microchannel;

And, the temperature display terminal connected to the thermocouple;

Wherein, the thermocouple is arranged between the thermal insulation layer and the microchannel, and the thermocouple is attached to the surface of the temperature measurement section of the microchannel; the inner side of the thermal insulation layer is closely attached to the microchannel, and the thermocouple is completely wrapped in the thermal insulation Layer

The outer diameter d2 of the thermal insulation layer is greater than or equal to the length L of the temperature measuring section of the microchannel.
The temperature measuring device for the flowing working fluid in the microchannel according to claim 1, wherein the thermal insulation layer is made of nano-silica aerogel; the thermal insulation layer is cylindrical.
The temperature measuring device for the flowing working fluid in the microchannel according to claim 1, wherein the thermocouple is welded to the temperature measuring section of the microchannel; the thermocouple is directly in contact with the thermal insulation layer.
The temperature measuring device for the flowing working fluid in the microchannel according to claim 1, wherein the thermocouple is fixed to the temperature measuring section of the microchannel through a thermocouple patch; The thermocouple patch is covered on the outside, and the thermocouple patch is covered with an insulation layer.
The temperature measuring device for a flowing working fluid in a microchannel according to claim 1, wherein the thermocouple comprises a plurality of thermocouples distributed on the surface of the temperature measuring section of the microchannel.
A temperature measuring device for a flowing working fluid in a microchannel according to claim 5, wherein the heat preservation layer comprises a plurality of heat preservation layers, and the outer side of each thermocouple is covered with a heat preservation layer.
The temperature measuring device for the flowing working fluid in the microchannel according to claim 1, wherein the outer protective layer is made of aluminum foil tape.
A method for calculating the thickness of an insulation layer is characterized in that it comprises the following steps:

Through calculation, determine the heat dissipation per unit length of the microchannel temperature measurement section;

Determine the temperature of the outer surface of the microchannel through measurement;

Determine the inner surface temperature of the microchannel through calculation;

The thickness of the insulation layer is determined according to the difference between the temperature of the outer surface of the insulation layer and the temperature of the outer surface of the microchannel.
The method for calculating the thickness of the thermal insulation layer according to claim 8, wherein when determining the heat dissipation per unit length of the microchannel temperature measuring section, the heat dissipation per unit length is determined by the convective heat transfer between the outer surface of the outer protective layer and the environment. The sum of radiation heat transfer.
The method for calculating the thickness of an insulation layer according to claim 8, wherein the difference Δt between the temperature of the outer surface of the insulation layer and the temperature of the outer surface of the microchannel is less than 0.5°C.