阅读说明：本技术 一种简易测量液体导热系数的实验装置 (Experimental device for simply measure liquid coefficient of heat conductivity ) 是由 焦冬生 于 2021-08-16 设计创作，主要内容包括：本发明涉及一种简易测量液体导热系数的实验装置,该装置包括两根上下分布的金属圆柱,其中上端圆柱作为热源,下端圆柱作冷源,上端圆柱的下圆柱端面和下端圆柱的上圆柱端面相对设置,在所述下圆柱端面和所述上圆柱端面上分别以圆柱中心为圆心设置一个圆形槽道用于放置O形圈,放置该O形圈后,热源和冷源之间构成测液腔,在上端圆柱和下端圆柱相对的圆柱端部且靠近待测液体附近沿圆周方向分别开设多个测试孔,该测试孔内放置温度传感器用于测试冷源和热源温度。将本装置测量并进一步计算得到的参数带入导热系数计算公式即可得到液体导热系数。本发明实验原理明确,结构简单,易于测试,设备成本低,有利于推广。(The invention relates to an experimental device for simply measuring the heat conductivity coefficient of liquid, which comprises two metal cylinders which are distributed up and down, wherein the upper end cylinder is used as a heat source, the lower end cylinder is used as a cold source, the lower cylinder end surface of the upper end cylinder and the upper cylinder end surface of the lower end cylinder are oppositely arranged, a circular channel which takes the cylinder center as the circle center is respectively arranged on the lower cylinder end surface and the upper cylinder end surface and is used for placing an O-shaped ring, after the O-shaped ring is placed, a liquid measuring cavity is formed between the heat source and the cold source, a plurality of test holes are respectively arranged at the opposite cylinder end parts of the upper end cylinder and the lower end cylinder and close to the liquid to be measured along the circumferential direction, and temperature sensors are arranged in the test holes and are used for testing the temperatures of the cold source and the heat source. Parameters obtained by measurement and further calculation of the device are substituted into a heat conductivity coefficient calculation formula The liquid thermal conductivity can be obtained. The invention has the advantages of clear experimental principle, simple structure, easy test, low equipment cost andis beneficial to popularization.)

1. The utility model provides a simple and easy experimental apparatus who measures liquid coefficient of heat conductivity which characterized in that:

the device comprises two metal cylinders which are distributed up and down, wherein the upper end cylinder is used as a heat source (5), an electric heater (11) is arranged in the metal cylinders, the electric heater (11) is connected with a direct current power supply, the temperature of the heat source is controlled by adjusting voltage, the lower end cylinder is used as a cold source (7), a water-cooling radiator (12) is arranged in the metal cylinders, and the water-cooling radiator (12) is connected with a constant-temperature water bath to maintain the constant temperature of the cold source;

the liquid measuring device comprises a lower cylindrical end face of an upper end cylinder and an upper cylindrical end face of a lower end cylinder, wherein the lower cylindrical end face of an upper end cylinder and the upper cylindrical end face of a lower end cylinder are oppositely arranged, a circular channel (10) is respectively arranged on the lower cylindrical end face and the upper cylindrical end face by taking the center of a cylinder as the center of a circle, the section of the circular channel (10) is a circular part, the circular channel (10) is used for placing an O-shaped ring (6), after the O-shaped ring (6) is placed, a liquid measuring cavity (1) is formed between a heat source (5) and a cold source (7), and the heat of the heat source (5) is transferred to the cold source (7) through liquid to be measured and the O-shaped ring (6);

a plurality of test holes (13) are respectively formed in the cylindrical end parts, opposite to the upper end cylinder and the lower end cylinder, of the upper end cylinder and the lower end cylinder and close to the liquid to be tested along the circumferential direction, and temperature sensors are placed in the test holes and used for testing the temperatures of the cold source and the heat source.

2. The experimental device for simply measuring the heat conductivity coefficient of liquid according to claim 1, wherein:

the diameter of the circular channel (10) is equal to the nominal diameter D of the O-shaped ring, the depth h of the circular channel is less than 1/2 of the section diameter D of the O-shaped ring, and the area A of the liquid to be measured passes through a formulaObtaining the design thickness of the liquid to be measured through a formula delta₀Obtained as d-2 h.

3. The experimental device for simply measuring the heat conductivity coefficient of liquid according to claim 2, wherein:

the heat conduction area of the O-shaped ring (6) is less than 5-10% of the heat conduction area of the liquid to be measured, and the size of the O-shaped ring meets the requirement

4. The experimental device for simply measuring the heat conductivity coefficient of liquid according to claim 3, wherein:

a small hole is respectively arranged on the end surface of the lower cylinder and the end surface of the upper cylinder to be used as a liquid discharge hole (2) and a liquid charging hole (9), the liquid charging hole (9) and the liquid discharge hole (2) are oppositely arranged along the diameter direction of the end surface of the cylinder, a cavity communicated with the liquid discharge hole (2) is arranged on the upper end cylinder positioned at the upper end of the liquid discharge hole, and the cavity is used as a liquid storage cavity (3); a rubber plug (8) with a slightly larger outer diameter can be inserted into the outer end of the liquid filling port (9) for injecting the liquid to be measured into the syringe and sealing.

5. The experimental device for simply measuring the heat conductivity coefficient of liquid according to claim 4, wherein:

three channels (14) with the depth and the width of 5mm are respectively milled in the circumferential direction of the upper end cylinder and the lower end cylinder and are used for indirectly measuring the actual thickness delta of the liquid to be measured, and the thickness value of the liquid is measured by three points in the circumferential direction so as to ensure the uniform thickness of the liquid to be measured.

6. The experimental device for simply measuring the heat conductivity coefficient of liquid according to claim 5, wherein:

four testing holes (13) are respectively formed in the cylindrical end parts, opposite to the upper end cylinder and the lower end cylinder, close to the liquid to be tested and along the circumferential direction, the cold source temperature is obtained based on four temperature values measured by the four testing holes in the lower end cylinder, and the heat source temperature is obtained based on four temperature values measured by the four testing holes in the upper end cylinder.

7. The experimental device for simply measuring the heat conductivity coefficient of liquid according to claim 1, wherein:

and cylindrical heat-insulating covers (4) are arranged outside the upper end cylinder and the lower end cylinder.

Technical Field

The invention belongs to the field of heat transfer science and heat transfer experiment teaching, and particularly relates to an experimental device for simply measuring a liquid heat conductivity coefficient.

Background

In the heat transfer experiment, the experiment theory of measuring the liquid heat conductivity coefficient based on the flat plate method is a one-dimensional flat plate heat conduction equation derived according to the Fourier law, namely:

transforming the formula (1) to obtain a formula for calculating the heat conductivity coefficient:

the heat conductivity coefficient k (Wm) of the liquid can be calculated by measuring the related parameters on the right side of the above formula^-1K^-1) The value is obtained. In the above formula, A (m)²) The thermal power Q (W) vertically penetrates through the area of the liquid to be measured; t is_h(K),T_c(K) The temperatures of the hot side and the cold side of the liquid to be measured are respectively; δ (m) is the thickness of the test liquid.

In order to suppress the natural convection of the liquid due to the temperature difference and influence the measurement of the thermal conductivity, a top heating measure is usually adopted. Typically, the heat Q is provided by an electric heater or a heat exchanger connected to a thermostatic water bath. The power of the electric heater is easier to measure by the following formula (3) and the measuring precision is high,

Q＝IU (3)

in the above formula, I (A) is current, U (V) is voltage.

The heat supplied by the constant temperature water bath is calculated by the following formula

(4) In the formula (I), the compound is shown in the specification,to mass flow rate, C_p(Jkg^-1K^-1) The specific heat at constant pressure and the temperature difference between the front and the back are delta T (K), the measured parameters of the formula are more, and the introduced system error is large. Therefore, formula (3) is often used for heat measurement and calculation.

In order to ensure that the heat of the electric heater vertically penetrates through the liquid to reach the cold surface as much as possible, a heat insulation layer made of a material with low heat conductivity coefficient is arranged around the test system, so that the heat loss is reduced, the external interference is reduced, and the stability of the test environment is ensured.

Disclosure of Invention

In order to achieve the effects of clear experimental principle, simple structure, easy test and convenience for students to install, debug and practice and operate, the invention provides the experimental device for simply measuring the heat conductivity coefficient of the liquid, so as to improve the teaching quality, and the device has low cost and is beneficial to popularization.

In order to solve the technical problems, the technical scheme provided by the invention is as follows:

an experimental device for simply measuring the heat conductivity coefficient of liquid comprises two metal cylinders which are distributed up and down, wherein the upper end cylinder is used as a heat source, an electric heater is arranged in the metal cylinders, the electric heater is connected with a direct current power supply, the temperature of the heat source is controlled by adjusting voltage, the lower end cylinder is used as a cold source, a water-cooling radiator is arranged in the metal cylinders, and the water-cooling radiator is connected with a constant-temperature water bath to maintain the constant temperature of the cold source;

the lower cylindrical end surface of the upper end cylinder and the upper cylindrical end surface of the lower end cylinder are oppositely arranged, a circular channel is respectively arranged on the lower cylindrical end surface and the upper cylindrical end surface by taking the center of the cylinder as the center of a circle, the section of the circular channel is a part of a circle, the circular channel is used for placing an O-shaped ring, after the O-shaped ring is placed, a liquid measuring cavity is formed between a heat source and a cold source, and the heat of the heat source is transferred to the cold source through liquid to be measured and the O-shaped ring; and milling the cylindrical end surface in contact with the test liquid by using a numerical control machine.

A plurality of test holes are respectively formed in the cylindrical end parts, opposite to the upper end cylinder and the lower end cylinder, close to the liquid to be tested in the circumferential direction, and temperature sensors are placed in the test holes and used for testing the temperatures of the cold source and the heat source.

The diameter of the circular channel is equal to the nominal diameter D of the O-shaped ring, the depth h of the circular channel is smaller than 1/2 of the section diameter D of the O-shaped ring, and the area A of the liquid to be measured passes through a formulaObtaining the design thickness of the liquid to be measured through a formula delta₀Obtained as d-2 h.

Wherein the heat conduction area of the O-shaped ring is less than 5-10% of the heat conduction area of the liquid to be measured, and the size of the O-shaped ring meets the requirement

The upper end cylinder is positioned at the upper end of the liquid discharge hole, a cavity communicated with the liquid discharge hole is arranged on the upper end cylinder, and the cavity is used as a liquid storage cavity. A rubber plug with a slightly larger outer diameter can be inserted at the outer end of the liquid filling port for injecting liquid to be measured and sealing the syringe.

Under the action of gravity of the heat source metal block, the O-shaped ring is pressed and deformed, so that the actual thickness delta of the liquid is smaller than the designed thickness delta₀And the small thickness and narrow gap are difficult to directly measure by a caliper. In order to measure the actual thickness delta conveniently, three channels with the depth and the width of 5mm are respectively milled in the circumferential direction of the upper end cylinder and the lower end cylinder and used for indirectly measuring the actual thickness delta of the liquid to be measured, and the upper measuring surface and the lower measuring surface are ensured to be parallel through three-point measurement. Wherein, the distance x between the channel of the heat source and the lower cylindrical end surface is measured firstly₁The distance x from the channel of the cold source to the upper cylindrical end surface₂Measuring the distance x of the cold and heat source channel after the installation is finished to obtain the actual liquid thickness delta which is x-x₁-x₂. The thickness value of the liquid is measured by three circumferential points to ensure that the thickness of the liquid to be measured is uniform.

The four testing holes are respectively formed in the cylindrical end parts, opposite to the upper end cylinder and the lower end cylinder, of the upper end cylinder and close to the position close to the liquid to be tested along the circumferential direction, the cold source temperature is obtained based on four temperature values measured by the four testing holes in the lower end cylinder, and the heat source temperature is obtained based on four temperature values measured by the four testing holes in the upper end cylinder. Wherein the temperature of the cold source is determined by the formulaObtaining the temperature of the heat source through a formulaThus obtaining the product.

Wherein, the outside of upper end cylinder and lower extreme cylinder sets up cylindrical heat preservation cover.

Further, the heat conductivity coefficient k of the liquid to be measured can be obtained by using the aforementioned formula (2) and formula (3) related to the heat transfer principle and combining the area a of the liquid to be measured, the actual thickness δ of the liquid to be measured, the heat source temperature and the heat source temperature obtained by the experimental device of the present invention.

The invention has the following beneficial effects: the invention has the advantages of clear experimental principle, simple structure and convenient installation, debugging and practical operation; the invention has smooth and flat surface, good sealing performance and small system error through the processing precision of an advanced numerical control machine tool; wherein, a standard industrial product O-shaped ring is used, the whole equipment has low cost and is convenient to popularize.

Drawings

FIG. 1 is a schematic diagram of an experimental apparatus for measuring the thermal conductivity of a liquid according to the present invention;

FIG. 2 is a schematic view of an O-ring structure;

FIG. 3 is a schematic view of a heat source configuration;

FIG. 4 is a schematic view of a cooling source structure;

fig. 5 is a schematic structural view of the heat-insulating cover.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

FIG. 1 is a schematic diagram of an experimental apparatus for simply measuring the thermal conductivity of liquid according to the present invention, and FIGS. 2-5 are schematic diagrams of the structure of the apparatus components, in which two metal cylinders are used as cold and heat sources for measuring the thermal conductivity of liquid, a cylinder at the upper end is used as a heat source 5, an electric heater 11 is built in, the electric heater 11 is connected to a DC power supply, and the temperature of the heat source is controlled by adjusting the voltage; the lower end cylinder is used as a cold source 7, a water-cooling radiator 12 is arranged in the lower end cylinder, and the water-cooling radiator 12 is connected with a constant temperature water bath to maintain the constant temperature of the cold source. The surface of the cylindrical end head in contact with the test liquid is milled flat by a numerical control machine, and a circular channel 10 is milled on the surface by taking the center of the cylinder as the center of the circle, the section of the channel 10 is a part of a circle, the circular channel is used for placing the O-shaped ring 6, the diameter of the circular channel 10 is equal to the nominal diameter D of the O-shaped ring, and the depth h of the circular channel 10 is less than 1/2 of the section diameter D of the O-shaped ring. The liquid measuring cavity 1 is formed by the O-shaped ring 6, the heat source 5 and the cold source 7 up and down, the numerical control machine tool is high in machining precision, and good sealing effect can be achieved by the aid of the self weight of metal and the elasticity of the O-shaped ring.

Wherein the area of the liquid to be measured is calculated by the formulaThus obtaining the product.

Wherein the liquid to be measured has a design thickness delta₀＝d-2h。

The heat of the heat source 5 is transferred to the cold source 7 through the liquid to be measured, the O-shaped ring 6 and the edge interlayer air ring. Because of the low air heat conductivity coefficient, the air ring of the edge interlayer can be ignored. In order to reduce the system error caused by the heat conduction of the O-shaped ring 6, the heat conduction area of the O-shaped ring 6 is less than 5-10% of the heat conduction area of the liquid, and the experiment is selected to meet the requirementThe O-ring of (1). The emissivity of the metal polished surface is low, and the heat loss caused by heat transfer from the hot surface to the cold surface through radiation is low.

Specifically, fig. 2 is a schematic view of an O-ring structure, fig. 1 is a schematic view of an apparatus, fig. 3 is a schematic view of a heat source structure, and fig. 4 is a schematic view of a cold source structure.

Because the O-shaped ring 6 has elasticity, the metal cylinder placed on the O-shaped ring has certain weight, the O-shaped ring 6 is deformed under pressure, and the actually measured thickness is less than the designed thickness delta₀. Three channels 14 with the depth and the width of 5mm are milled in the circumferential direction of the cylinder, so that the actual thickness delta of the liquid to be measured can be measured indirectly, and the parallelism of two surfaces can be ensured through three-point measurement. Wherein the distance x of the channel 14 of the heat source 5 from the lower cylindrical end surface is measured first₁And the distance x between the channel 14 of the cold source 7 and the upper cylindrical end surface₂Measuring the distance x of the cold and heat source channel 14 after the installation is finished to obtain the actual liquid thickness delta which is x-x₁-x₂。

Two ends of the diameter direction of the cylindrical end surface are provided with a small hole, the cold source end is used as a liquid filling hole 9, the hot source end is used as a liquid discharging hole 2, and the cavity at the upper end of the liquid discharging hole is a liquid storage cavity 3. From up filling the liquid that awaits measuring down, do benefit to the elimination bubble, liquid thermal expansion in the test process, liquid volume inflation gets into stock solution chamber 3, reduces the thermal stress in the test chamber 1. A rubber plug 8 with a slightly larger outer diameter can be inserted at the outer end of the liquid filling port 9 for injecting the liquid to be measured and sealing the syringe.

Four test holes 13 are circumferentially formed near the cylindrical test end near the liquid for placing temperature sensors, such as thermocouples or thermal resistors, for testing the temperatures of the heat source and the heat sink.

Cold end constant temperature passing formulaThus obtaining the product.

Temperature of heat source by formulaThus obtaining the product.

In order to reduce heat loss, the testing system is separated from the outside by using a cylindrical heat-insulating cover 4 shown in fig. 5, the heat of the electric heater is ensured to be transmitted to a cold source through liquid as far as possible, and finally, parameters obtained by measurement and further calculation of the device are substituted into a heat conductivity coefficient calculation formula (2) to obtain the heat conductivity coefficient of the liquid.

This is further illustrated by a specific example.

Two copper cylinders with the diameter of 270mm are used as cold and heat sources for measuring the heat conductivity coefficient of the liquid, the upper end cylinder is used as a heat source, an electric heater is arranged in the copper cylinders, the electric heater is connected with a 60V direct current power supply, the electric power is 1000W, and the temperature of the heat source is controlled by adjusting the voltage.

The lower end cylinder is used as a cold source, a water-cooling radiator is arranged in the lower end cylinder, and the water-cooling radiator is connected with a constant-temperature water bath with the power of 1500W.

The O-shaped ring specification inner diameter D is 250mm, and the wire diameter D is 5.3 mm.

The diameter of the section of the circular channel is 5.3mm, and the depth of the circular channel is 0.8 mm.

The emissivity of the metal polished surface is low, and the radiant heat loss is low.

Three channels with the depth and the width of 5mm are milled in the circumferential direction of the cylinder and are used for measuring the thickness of liquid, and the two surfaces are ensured to be parallel.

The two ends in the diameter direction are provided with a small hole, the cold source end is used as a liquid filling hole, the hot source end is used as a liquid discharging hole, and the upper end of the liquid discharging hole is provided with a liquid storage tank. And air bubbles are removed from the bottom to the top through liquid filling, liquid expands when heated in the test process, and the liquid expands in volume to enter the liquid storage tank, so that the thermal stress in the test cavity is reduced.

Four test holes are formed near the cylindrical test end close to the liquid along the circumferential direction, and a K-type thermocouple is placed in each test hole and used for testing the temperatures of the heat source and the cold source.

Two stainless steel cylinders with one closed end are filled with 30mm glass wool, and then the stainless steel cylinders are sealed by stainless steel ring pieces to serve as heat preservation covers, so that heat of the electric heater is guaranteed to be transmitted to a cold source through liquid as far as possible.

Parameters obtained by measurement and further calculation of the device are substituted into a heat conductivity coefficient calculation formula (2) to obtain the liquid heat conductivity coefficient.

The above description is only for the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto, and these examples are only for illustrative purpose and are not intended to limit the scope of the present invention. The scope of the invention is defined by the appended claims and equivalents thereof. Various alternatives and modifications can be devised by those skilled in the art without departing from the scope of the invention, and these alternatives and modifications are intended to fall within the scope of the invention.