CN103033533A - Measurement method for specific heat capacity of liquid - Google Patents

Abstract

The invention relates to a measurement method for the specific heat capacity of liquid. The method comprises the following steps: measuring to obtain the initial temperature T1 and the final temperature T'1 of a first calorimeter, the heat Q1 released by a heating device, the initial temperature T1 and the final temperature T'1 of a second calorimeter and the heat Q2 released by the heating device in a period of time; obtaining a group of equation of a formula (a) about D1 and D2; respectively obtaining the heat Q1 and Q2 released by the heating device through an integrator; respectively changing m1 and m2, and then repeating the steps; obtaining another group of equation of the formula (a); according to the obtained two groups of equations of the formula (a), calculating to obtain D1 and D2; and brining the obtained D1 and D2 in the formula (a), and calculating to obtain the specific heat c of liquid to be measured. The measurement method for the specific heat capacity of liquid utilizes the integrator to calculate the heat, can eliminate the influence of the product of the specific heat capacity of copper materials of the calorimeter such as an internal cylinder, a stirrer and the like and the quality and can also accurately record the heat Q released by the heating device by changing the quality of the liquid to be measured, and greatly increases the degree of accuracy of the measurement for the specific heat capacity of liquid.

Description

A method for measuring the specific heat capacity of liquid

technical field

The invention belongs to the technical field of specific heat capacity detection, and in particular relates to a method for measuring liquid specific heat capacity.

Background technique

Specific heat capacity (specific heat capacity), also known as specific heat capacity, referred to as specific heat, is the internal energy absorbed or released when a unit mass object changes a unit temperature, that is, the heat capacity of a unit mass substance. The specific heat capacity of a liquid is an important index to measure the thermodynamic properties of a liquid.

The traditional methods for measuring the specific heat capacity of liquids are mainly electrothermal method and comparative method. The specific heat capacity of liquid is measured by electrothermal method, and a single calorimeter is usually used as a heating device. The electrothermal method is used to measure the specific heat capacity of the liquid. During the measurement process, due to the agitation of the stirrer, the current in the circuit is extremely unstable, which affects the accuracy of the measurement results to a certain extent. When using the comparison method to measure the specific heat capacity of a liquid, in order to eliminate the systematic error caused by the difference in resistance, it is necessary to perform exchange measurement, which makes the measurement process very complicated.

Aiming at the problems existing in the traditional method for measuring the specific heat capacity of liquids, a novel liquid specific heat capacity measuring device was disclosed in the magazine "Laboratory Research and Exploration" in the fourth issue of volume 30 in April 2011. The liquid specific heat capacity measurement device includes a double calorimeter bridge circuit device, as shown in Figure 1, the materials of the two calorimeters are exactly the same in the external environment, and the resistances of the internal resistance wires are extremely _R1 and _R2 respectively. . R ₃ , R ₄ , R ₅ and R′ ₃ , R′ ₄ , R′ ₅ represent the adjustable resistance box respectively, and R′ ₁ , R′ ₂ and R represent the sliding wire rheostat. Wherein, R ₃ , R ₄ , R ₅ are equivalent to R' ₃ , R' ₄ , R' ₅ . During the measurement process, the same substance with different masses is put into the two calorimeters for simultaneous measurement, and the operator needs to record the output voltage values of the two calorimeter systems at the initial moment and the final moment respectively. Then, according to the output voltage values U ₁ , U′ ₁ and U ₂ , U′ ₂ of the two calorimeter systems at two moments, the masses m1 and m2 of the two parts of the liquid to be measured, and the internal values of the two calorimeters The product D1 and D2 of the specific heat capacity and the mass of the copper material such as the cylinder and the stirrer are calculated to obtain the specific heat capacity of the liquid to be tested.

The disadvantages of the above technical solution are: first, the influence of voltage and current fluctuations during the experimental measurement process cannot be ruled out. Since the resistance value of the heating device changes with temperature and changes nonlinearly, the output voltage values of the two calorimeter systems cannot be guaranteed to change completely linearly. It is inaccurate to calculate the calorific value during the whole experimental measurement process by the voltage value: according to the UI-t (voltage-current product and time) curve shown in Figure 2, the area surrounded by the curve is the accurate value of the calorific value Q. However, the above technical solution only calculates the heat Q according to the output voltage values of the two calorimeter systems at the initial time and the end time (assuming that the current is constant), and the numerical error of the heat Q is shown by the oblique line in Figure 2 error area. Second, in the experimental measurement results, the influence of heat absorbed by copper materials such as the inner cylinder of the two calorimeters and the stirrer cannot be ruled out, which further increases the error of the experimental measurement results of the specific heat capacity of the liquid.

Contents of the invention

In order to solve the technical problem that the liquid specific heat capacity measurement device in the prior art is inaccurate in calorific value measurement and cannot eliminate the influence of copper material absorption of calorific value, resulting in large measurement errors in liquid specific heat capacity, a new method is proposed that measures calorific value accurately and can exclude copper. The effect of the product of the specific heat capacity and mass of the material, the measurement method of the specific heat capacity of the liquid.

The technical solution adopted by the present invention to solve technical problems is as follows:

A method for measuring the specific heat capacity of a liquid, the applicable measuring device includes a first calorimeter and a second calorimeter connected in series; the first calorimeter and the second calorimeter are respectively provided with a heating device and a measuring device. temperature device; the first calorimeter and the second calorimeter are respectively equipped with mass m ₁ and m ₂ liquid to be measured;

The measuring device is also provided with a data collector and an integrator; a current collection point is provided on the main road, and a voltage collection point is respectively provided on the heating device on the first calorimeter and the second calorimeter; the data The collector can collect the data of the current collection point and the voltage collection point on the first calorimeter and the second calorimeter at the same time; The data, using the method of integral measurement to calculate heat;

The method specifically includes the following steps:

Step i: measure the initial temperature T ₁ and final temperature T' ₁ of the first calorimeter within a period of time, the heat Q ₁ released by the heating device; and the initial temperature T ₂ and final temperature T of the second calorimeter ' ₂ , the heat Q ₂ released by the heating device; the heat Q ₁ and Q ₂ released by the heating device are calculated by the integrator respectively;

Using Q ₁ =(cm ₁ +D ₁ )(T′ ₁ −T ₁ ), Q ₂ =(cm ₂ +D ₂ )(T′ ₂ −T ₂ ),

A set of equations for formula (a) is obtained:

$\frac{{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="cm"\; filenames="HDA00002599929200021.png"\; state="\{\{state\}\}">cm</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="T"\; filenames="HDA00002599929200021.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; cm</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; )</span>$

Wherein c is the specific heat of the liquid to be measured, and D _{and D} are respectively the product of the specific heat capacity and the mass of the first calorimeter and the second calorimeter itself;

Step ii: Repeat step i after changing m ₁ and m ₂ respectively to obtain another set of equations of formula (a);

Step iii: Calculate D ₁ and D ₂ according to the two sets of equations of formula (a) obtained in step i and step ii;

Step iv: Put D ₁ and D ₂ obtained in step iii into formula (a), and calculate the specific heat c of the liquid to be tested.

In the above technical solution, the data collector may also collect temperature signals of the temperature measuring devices on the first calorimeter and the second calorimeter.

The beneficial effects of the present invention are:

The method for measuring the specific heat capacity of a liquid of the present invention uses integral measurement to calculate heat, and by changing the quality of the liquid to be measured, the product of the specific heat capacity and the mass of copper materials such as the inner cylinder of the calorimeter itself and the stirrer can be eliminated. It can also accurately record the heat Q released by the heating device, which greatly improves the accuracy of the measurement of the specific heat capacity of the liquid.

The method for measuring the specific heat capacity of the liquid of the present invention uses an integrator to calculate the heat released by the heating device, thereby eliminating errors to the greatest extent and making the measurement result more accurate.

The measuring method of liquid specific heat capacity of the present invention, by arranging the data collector that can gather at five points simultaneously, the ammeter in the measuring device, the voltmeter on the first calorimeter and the second calorimeter, and the first calorimeter The readings of the temperature measuring device on the second calorimeter are collected at the same time, which well avoids human errors.

Description of drawings

Fig. 1 is the circuit schematic diagram of the liquid specific heat capacity measuring device of prior art;

Fig. 2 is the UI-t (voltage-current product and time) curve schematic diagram of the heat measurement error of the liquid specific heat capacity measuring device of the prior art;

Fig. 3 is the circuit schematic diagram of the measuring method of liquid specific heat capacity of the present invention;

Fig. 4 is the UI-t (voltage-current product and time) curve schematic diagram of the heat measurement error of the measuring method of liquid specific heat capacity of the present invention;

The reference signs in the figure represent:

1-data collector; 21-first temperature collection point; 22-second temperature collection point; 31-first voltage collection point; 32-second voltage collection point; 4-current collection point.

Detailed ways

The inventive idea of the present invention is: the method for measuring the specific heat capacity of a liquid of the present invention overcomes the influence of voltage fluctuations in the measurement process by using the integral measurement method; The influence of specific heat capacity D on the measurement of liquid specific heat capacity; five points of data are collected at the same time to eliminate errors to the greatest extent.

Similar to the process of calculating the area under a certain curve by integral in mathematics, such as the rectangle method: it is to divide the curved trapezoid into several narrow curved trapezoids, and then use narrow rectangles to approximate the narrow curved trapezoids, so as to obtain the definite integral approximation. The method for measuring liquid specific heat capacity of the present invention utilizes the principle of integral measurement of heat as follows: using a circuit capable of performing integral operations, the output signal is the integral of the input signal, and similarly, the input signal is the differential of the output signal.

Specifically, the UI-t (voltage-current product versus time) curve shown in Figure 4, the area surrounded by the curve is the exact value of heat Q. When calculating heat Q, the present invention adopts an integral method to divide the entire UI-t curve into multiple rectangles, the height of each rectangle is the product of voltage and current at this moment, and the width is the time interval. When the time interval is set to a small period of time, such as one hundredth of a second, the difference between the area of this rectangle and the area under the curve within one hundredth of a second is the approximately triangular oblique shadow above the rectangle The area of the part, the area of the part is very small. Therefore, it can be considered that the sum of the areas of multiple rectangles is the size of the area under the UI-t curve, and the size of the area is the size of the heat.

On the other hand, when measuring the specific heat capacity of a liquid, it is necessary to heat the liquid to be measured. During the heating process, due to the constant temperature change, the resistance value of the heating device such as the resistance wire is constantly changing. Therefore, when the same voltage or current is applied to the heating device, the current or voltage also changes continuously. Therefore, the measurement method of liquid specific heat capacity in the prior art assumes that the current does not change during the heating process, which is inappropriate. The measuring method of liquid specific heat capacity of the present invention, utilizes integrator to measure the heat that heating device emits, when the frequency of voltage and electric current collection is very high, when for example exceeding 100 times or even more than 100,000 times per second, the resistance of heating device It can be considered as constant between two acquisition intervals. The heat released by the heating device measured in the liquid specific heat capacity measuring method of the present invention is more accurate.

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Figures 3 and 4 show a specific embodiment of the method for measuring the specific heat capacity of a liquid according to the present invention. As shown in Figure 3, the measuring device applicable to this method includes a first calorimeter and a second calorimeter connected in series, and a current collection point 4 is arranged on the main road; on the first calorimeter and the second calorimeter The heating device resistance wire for heating, the first voltage collection point 31 and the second voltage collection point 32 for measuring and collecting the voltage value of the heating device, and the first temperature collection point for collecting and measuring the temperature of the liquid to be measured are respectively provided. Point 21 and second temperature collection point 22. The first temperature collection point 21 and the second temperature collection point 22 are two digital thermometers respectively. The measuring device is provided with a data collector that can collect the current collection point 4, the first voltage collection point 31, the second voltage collection point 32, the first temperature collection point 21 and the second temperature collection point 22 at the same time. 1. The first calorimeter and the second calorimeter are respectively filled with mass m ₁ and m ₂ of the liquid to be measured. The heating device is provided with an integrator that can calculate heat according to the data of the current collection point 4 and the first voltage collection point 31 and the second voltage collection point 32 .

The measuring method of liquid specific heat capacity of the present invention specifically comprises the following steps:

Step i: measure the initial temperature T ₁ and final temperature T' ₁ of the first calorimeter within a period of time, the heat Q ₁ released by the heating device; and the initial temperature T ₂ and final temperature T of the second calorimeter ′ ₂ , the heat Q ₂ released by the heating device;

Using Q ₁ =(cm ₁ +D ₁ )(T′ ₁ −T ₁ ), Q ₂ =(cm ₂ +D ₂ )(T′ ₂ −T ₂ ),

A set of equations for formula (a) is obtained:

$\frac{{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="cm"\; filenames="HDA00002599929200021.png"\; state="\{\{state\}\}">cm</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="T"\; filenames="HDA00002599929200021.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; cm</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; )</span>$

Where c is the specific heat of the liquid to be measured, and _D1 and _D2 are the products of the specific heat capacity and mass of the first calorimeter and the second calorimeter themselves, respectively.

When calculating the heat _Q1 and _Q2 emitted by the heating device in step i, the heat _Q1 and _Q2 emitted by the heating device are respectively collected by the integrator according to the current collection point 4 and the first voltage collected by the data collector The data of the collection point 31 and the second voltage collection point 32 are obtained, thereby eliminating errors to the greatest extent and making the measurement result more accurate.

Step ii: Repeat step i after changing m ₁ and m ₂ respectively to obtain another set of equations of formula (a).

Step iii: Calculate D ₁ and D ₂ according to the two sets of equations of formula (a) obtained in step i and step ii. The principle of calculating D ₁ and D ₂ in step iii is that since the unknowns in the two sets of equations (a) are only D ₁ and D ₂ , these two unknowns can be obtained through two equations.

Step iv: Put D ₁ and D ₂ obtained in step iii into formula (a), and calculate the specific heat c of the liquid to be tested.

The method for measuring liquid specific heat capacity of the present invention eliminates the influence of the product of specific heat capacity and mass of copper materials such as the inner cylinder of the calorimeter itself and the stirrer by changing the quality of the liquid to be measured, and greatly improves the measurement of liquid specific heat capacity. degree of accuracy.

The measuring method of liquid specific heat capacity of the present invention, by arranging the data collector that can gather at five points simultaneously, the ammeter in the measuring device, the voltmeter on the first calorimeter and the second calorimeter, and the first calorimeter The readings of the temperature measuring device on the second calorimeter are collected at the same time, which well avoids human errors.

Apparently, the above-mentioned embodiments are only examples for clear description, rather than limiting the implementation. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. And the obvious changes or changes derived therefrom are still within the scope of protection of the present invention.

Claims (2)

1. the measuring method of a specific heat of liquid, the applicable measurement mechanism of the method comprises the first calorimeter and second calorimeter of mutual series connection; Be respectively equipped with heating arrangement and temperature measuring equipment on this first calorimeter and the second calorimeter; It is m that quality is housed respectively in this first calorimeter and the second calorimeter ₁And m ₂Testing liquid;

It is characterized in that, also be provided with the data acquisition unit sum-product intergrator in the described measurement mechanism; Be provided with the current acquisition point on the main line, be respectively equipped with the voltage acquisition point on the heating arrangement on the first calorimeter and the second calorimeter; Described data acquisition unit can gather the current acquisition point simultaneously, and the data of the voltage acquisition point on the first calorimeter and the second calorimeter; The current acquisition point that described integrator can collect according to described data acquisition unit and the data of voltage acquisition point utilize the method for integral measurement to calculate heat;

The method specifically may further comprise the steps:

Step I: the initial temperature T that measures the first calorimeter in a period of time scope ₁With end temperature T ' ₁, heating arrangement liberated heat Q ₁And the initial temperature T of the second calorimeter ₂With end temperature T ' ₂, heating arrangement liberated heat Q ₂Heating arrangement liberated heat Q ₁And Q ₂Calculated by described integrator respectively;

Utilize Q ₁=(cm ₁+ D ₁) (T ' ₁-T ₁), Q ₂=(cm ₂+ D ₂) (T ' ₂-T ₂),

Obtain one group of equation of formula (a):

$\frac{Q_1}{Q_2}=\frac{({\mathrm{cm}}_1+D_1)(T_1^{\&prime;}-T_1)}{({\mathrm{cm}}_2+D_2)(T_2^{\&prime;}-T_2)}---\left(a\right)$

Wherein c is the specific heat of testing liquid, D ₁And D ₂Be respectively the specific heat capacity of the first calorimeter and the second calorimeter itself and the product of quality;

Step I i: change respectively m ₁And m ₁Rear repeating step i obtains other one group of equation of formula (a);

Step I ii: two groups of equatioies according to the formula (a) that obtains among step I and the step I i calculate D ₁And D ₂

Step I v: will obtain D among the step I ii ₁, D ₂Bring formula (a) into, calculate the specific heat c of testing liquid.

2. the measuring method of specific heat of liquid as claimed in claim 1 is characterized in that, described data acquisition unit can also gather the temperature signal of the temperature measuring equipment on the first calorimeter and the second calorimeter.

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