GT4603 metal specific heat capacity tester manual
Cooling method to measure the specific heat capacity of metal
The determination of the specific heat capacity of a metal or liquid by the cooling method according to Newton's law of cooling is one of the commonly used methods in calorimetry. If the specific heat capacity of a standard sample at different temperatures is known, the specific heat capacity of various metals at different temperatures can be measured by using a cooling curve. In this experiment, the copper sample is used as the standard sample, and the specific heat capacity of the iron and aluminum samples at 100 ° C is determined. The relationship between the cooling rate of the metal and its temperature difference with the environment and the experimental conditions for the measurement are obtained through experiments. Thermocouple numbers The display temperature measurement technology is a commonly used test method in current production practice. It has a wider measurement range than the general thermometer temperature measurement method, and has high evaluation accuracy, which can automatically compensate for the nonlinear factors of the thermocouple; secondly, its electric quantity is digitized. It can also directly monitor the temperature in industrial production automation.
[Experimental principle]
The mass of a unit mass, the temperature required to increase the temperature by 1K (or 1 ° C) is called the specific heat capacity of the substance, and its value varies with temperature. After heating the metal sample of mass M1, it is placed in a lower temperature medium. (for example, room temperature air), the sample will gradually cool. The heat loss per unit time (ΔQ / Δt) is proportional to the rate of temperature drop, so the following relationship is obtained:
(1)
(1) where C1 is the specific heat capacity of the metal sample at temperature θ1,
For the temperature drop rate of the metal sample at θ1, according to the cooling law:
(2)
(2) where α1 is the heat exchange coefficient, S1 is the area of ​​the outer surface of the sample, m is a constant, θ1 is the temperature of the metal sample, and θ0 is the temperature of the surrounding medium. From equations (1) and (2),
(3)
Similarly, for another metal sample with a mass of M2 and a specific heat capacity of C2, the same expression can be used:
(4)
Available from equations (3) and (4)
and so
It is assumed that the shapes and sizes of the two samples are the same (for example, a small cylinder), that is, S1=S2; the surface conditions of the two samples are also the same (such as coating, color, etc.), and the properties of the surrounding medium (air) are of course unchanged. Then there is α1=α2. Then when the temperature of the surrounding medium is constant (that is, the room temperature θ0 is constant), and the two samples are at the same temperature θ1=θ2=θ, the above formula can be simplified as:
(5)
Table 1
If the specific heat capacity C1, mass M1 of the standard metal sample, the mass M2 of the sample to be tested, and the cooling rate of the two samples at the temperature θ are known, the specific heat capacity of the metal material to be tested can be determined. C2. Specific heat capacity of several metal materials See Table 1:
Specific heat capacity
temperature
CFe(cal/g°C)
CA1(cal/g°C)
Ccu(cal/g°C)
100 ° C
0.110
0.230
0.0940
ã€laboratory apparatus】
Figure 1 GT4603 type cooling method metal specific heat capacity measuring instrument
The experimental device is composed of a heating device and a tester. The heating device of the heating device can be freely raised and lowered by adjusting the hand wheel. The sample to be tested is placed on a base of a large-capacity windproof cylinder, that is, a sample chamber, and the thermocouple is placed on the temperature measuring thermocouple. In the small hole in the sample to be tested. When the heating device moves down to the bottom, the sample to be tested is heated; when the sample needs to be cooled, the heating device is moved up. The instrument is equipped with an automatic temperature limiting device to prevent long-term failure. Turn off the heating power supply and cause the temperature to rise continuously.
The temperature of the sample is measured by a commonly used thermocouple made of copper-constantan (thermal potential is about 0.024 mV/°C), and the cold end of the thermocouple is placed in an ice-water mixture, and the end with the measuring flat fork is connected. The “input†side of the tester. The secondary instrument with thermoelectric potential difference is composed of a highly sensitive, high-precision, low-drift amplifier plus a three-and-a-half-digit digital voltmeter with a full-scale of 20mV. When the cold end is frozen, The mV number table displayed by the digital voltmeter can be converted into the corresponding temperature value to be measured.
[Experimental content]
Connect the heater and tester before starting the machine. There are two sets of wires for heating the four core wire and the thermocouple wire.
1. Select three metal samples (copper, iron, aluminum) with the same length, diameter and surface finish as possible to balance their mass M0 with a physical balance or an electronic balance. Then according to the characteristics of MCu>MFe>MA1, The difference is open.
2. Connect the copper wire of the thermocouple end to the positive terminal of the digital meter; the cold end copper wire is connected to the negative terminal of the digital meter. When the sample is heated to 150 ° C (the thermoelectric potential shows about 6.7 mV),
Turn off the power and remove the heating source. The sample is placed in a plexiglass cylinder that is basically isolated from the outside. It is naturally cooled (the lid must be covered), and the cooling rate of the sample is recorded.
.
The specific method is to record the time Δt required for the value on the digital voltmeter to decrease from E1=4.36mV to E2=4.20mV (because the value on the digital voltmeter shows that the number is leaping, so E1
E2 can only take nearby values)
.
According to the order of iron, copper and aluminum, the temperature drop rate is measured separately. Each sample should be measured 6 times repeatedly because of the thermocouple.
The relationship between the thermoelectromotive force and the temperature can be regarded as a linear relationship within the same small temperature difference range, that is,
,
Equation (5) can be simplified as:
3. The heating indicator of the instrument is on, indicating that it is heating; if the connection line is not connected or the heating temperature is too high (more than 200 °C), the indicator light will not light. When the temperature is raised to the specified temperature, the heating power should be cut off.
4. Note: When measuring the cooling time, press the “Timer†or “Pause†button should be fast and accurate to reduce the artificial timing error.
5. When the heating device moves downward, the action should be slow. It should be noted that the sample to be tested should be placed vertically so that the heating device can completely fit into the sample to be tested.
[Data Processing and Analysis]
Sample quality: Mcu = g; MFe = g; MA1 = g.
Thermocouple cold junction temperature: °C
Time required for the sample to fall from 4.36mV to 4.20mV (in S) Table 2
frequency
sample
1
2
3
4
5
6
Average value Δt
Fe
Cu
A1
Based on copper: C1=Ccu=0.0940 cal/g K
iron:
Cal/(g K)
aluminum:
Cal/(g K)
The following is a set of measured data to illustrate the processing and analysis of data.
Sample quality: Mcu = 9.549 g; MFe = 8.53 g; MA1 = 3.03 g.
Time required for the sample to fall from 4.36mV to 4.20mV (in S) Table 3
frequency
sample
1
2
3
4
5
Average value Δt
Cu(S)
17.33
17.70
17.42
17.76
17.57
17.56
Fe(S)
19.40
19.54
19.52
19.35
19.44
19.45
A1(S)
13.89
13.82
13.82
13.83
13.80
13.83
Based on copper: C1=Ccu=0.0940 cal/(gK)
iron:
aluminum:
* The above data is for reference only.
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