Comprehensive chemical experiment report
Title: Assembly and performance test of thermostatic bath
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I. Research Background (Preface)
Temperature is an extremely special physical quantity. It often appears in thermodynamics and is ubiquitous in daily life. The data measured in physical and chemical experiments, such as viscosity, density, vapor pressure, surface tension, refractive index, conductivity and reaction rate constant, are all related to temperature. Therefore, many physical and chemical experiments must be carried out at constant temperature. An incubator is usually used to control and maintain the temperature. The thermostatic bath can keep a constant temperature.
The thermal balance of thermostatic bath is mainly controlled by thermostatic controller.
Principle of incubator: The constant temperature water bath discussed in this experiment is a common temperature control device, which achieves the purpose of constant temperature through the cooperation of relay, temperature regulator (mercury contact thermometer) and heater. Its simple constant temperature principle circuit is shown in Figure 2- 1- 1. When the water tank temperature is lower than the set value, I line is the channel, and the heater works to raise the water tank temperature; When the temperature of the water tank rises to the set value, the thermostat is turned on, and at this time, line II is the channel, the spring piece D is sucked down due to electromagnetic action, line I is turned off, and the heater stops heating; When the temperature of the water tank is lower than the set value, the thermostat is closed and the line II is disconnected. At this time, the electromagnet loses its magnetism, and the spring piece returns to its original position, making the I line become a channel again. Repeat this process to keep the thermostat at the required constant temperature.
Various thermostats are widely used in fine chemical industry, bioengineering, medicine and food, metallurgy, petroleum, agriculture and other fields. To provide users with high-precision constant temperature field source, it is an ideal constant temperature equipment for scientific research institutes, universities, laboratories of industrial and mining enterprises and quality inspection departments. Therefore, it is very important to assemble and test the thermostat.
Second, the experimental purpose
1. Understand the structure and thermostatic principle of thermostatic bath, and preliminarily master the basic technology of its assembly and debugging.
2. Draw the sensitivity curve (temperature-time curve) of the thermostat and learn to analyze the performance of the thermostat.
3. Master the adjustment and use of Beckman thermometer and contact thermometer.
4. Understand the PID control technology of temperature.
Third, the experimental principle
A thermostatic bath generally consists of a bath, a heater, a stirrer, a thermometer, a temperature sensing element and a thermostatic controller.
Schematic diagram of thermostatic device:
1. bathtub
2. Heater
3. Agitator
4. Thermometer
5. Electric contact thermometer
6. Relay
7. Beckman thermometer
1. Bath: There are usually two kinds of bath: metal bath and glass bath. Its capacity and shape depend on needs.
2. Heater: usually an electric heater. The power of the electric heater is selected according to the capacity of the incubator, constant temperature and temperature difference with the environment.
3. Agitator: Generally, an electric agitator is used, and the stirring speed can be adjusted to keep the temperature in the tank as consistent as possible.
4. Thermometer: a thermometer with a common observation temperature of110℃. In order to measure the sensitivity of the thermostatic bath,1100℃ thermometer or Beckman thermometer can be used. Thermometers used should be standardized before use.
5. Temperature sensing element: it is the sensing center of the thermostat and the key to improve the accuracy of the thermostat. There are many kinds of temperature sensing elements, such as contact thermometer and thermistor temperature sensing elements.
6. Electronic relay: a device for controlling the "on" and "off" of the constant temperature heater.
The determination of the thermostat sensitivity is to observe the temperature fluctuation at a specified temperature, and the temperature control effect can be expressed by the sensitivity △t (t 1 is the highest temperature of the thermostat and t2 is the lowest temperature of the thermostat).
Usually expressed as a temperature-time curve:
Fourthly, the experimental part.
1. Main drugs and instruments and equipment
Main drugs: rosin, tin, distilled water, etc.
Instruments and equipment: glass jar, contact thermometer, Beckman thermometer, thermometer (110℃), stopwatch,
Agitator, electronic relay, heater.
2. Experimental steps
(1) thermostat assembly
Add distilled water to the glass jar to 2/3 of the volume, install all components and connect the lines according to the drawings.
(2) Adjust Beckman thermometer
Adjust Beckman thermometer so that its mercury column is about 2.5℃ at 25℃.
(3) Commissioning of thermostatic bath
Turn on the temperature control device, adjust the temperature to 25℃, turn on the agitator, put it at an appropriate speed, and turn on the heater.
Heater, put in a suitable power supply, and wait for constant temperature.
(4) Determination of the sensitivity of 30℃ thermostat.
After the thermostat is kept at 30℃, the temperature is read from Beckman thermometer every 0.5 minutes and measured.
Thirty minutes.
(5) Determination of the sensitivity of 35℃ thermostat.
Change the thermostat temperature to 30℃ and measure the thermostat temperature at 30℃ in the same way.
Sensitive. At the end of the experiment, turn off the temperature control device and agitator, and then unplug the power supply.
Verb (abbreviation of verb) data recording and processing
Time/minute temperature difference at 30℃, temperature difference at 35℃ and temperature difference at 35℃
0.5 0. 125 30. 125 0.276 35.276
1.0 0. 109 30. 109 0. 10 1 35. 10 1
1.5 0.095 30.095 0.296 35.296
2.0 0.082 30.082 0.27 1 35.27 1
2.5 0.069 30.069 0.266 35.266
3.0 0.055 30.055 0.266 35.266
3.5 0.044 30.044 0.269 35.269
4.0 0.030 30.03 0.255 35.255
4.5 0.0 16 30.0 16 0.289 35.289
5.0 0.004 30.004 0.270 35.27
5.5 -0.0 12 29.988 0.246 35.246
6.0 -0.024 29.976 0.256 35.256
6.5 -0.038 29.962 0.245 35.245
7.0 -0.052 29.948 0.276 35.276
7.5 -0.066 29.934 0.270 35.27
8.0 -0.080 29.92 0.247 35.247
8.5 -0.094 29.906 0.245 35.245
9.0 -0. 107 29.893 0.250 35.25
9.5 -0. 12 1 29.879 0.243 35.243
10.0 -0. 132 29.868 0.277 35.277
10.5 -0. 145 29.855 0.260 35.26
1 1.0 -0. 156 29.844 0.232 35.232
1 1.5 -0. 168 29.832 0. 10 1 35. 10 1
12.0 -0. 178 29.822 0.246 35.246
12.5 -0. 189 29.8 1 1 0.24 1 35.24 1
13.0 -0.200 29.8 0.25 1 35.25 1
13.5 -0.2 1 1 29.789 0.247 35.247
14.0 -0.222 29.778 0.245 35.245
14.5 -0.23 1 29.769 0.255 35.255
15.0 -0.243 29.757 0.237 35.237
15.5 -0.252 29.748 0.24 1 35.24 1
16.0 -0.262 29.738 0.243 35.243
16.5 -0.27 1 29.729 0.252 35.252
17.0 -0.28 1 29.7 19 0.303 35.303
17.5 -0.26 1 29.739 0.25 1 35.25 1
18.0 -0.247 29.753 0.25 1 35.25 1
18.5 -0.256 29.744 0.24 1 35.24 1
19.0 -0.266 29.734 0.253 35.253
19.5 -0.276 29.724 0.240 35.24
20.0 -0.286 29.7 14 0.259 35.259
20.5 -0.233 29.767 0.24 1 35.24 1
2 1.0 -0.23 1 29.769 0.237 35.237
2 1.5 -0.242 29.758 0.262 35.262
22.0 -0.25 1 29.749 0.245 35.245
22.5 -0.260 29.74 0.303 35.303
23.0 -0.269 29.73 1 0.242 35.242
23.5 -0.279 29.72 1 0.243 35.243
24.0 -0.285 29.7 15 0.255 35.255
24.5 -0.248 29.752 0.245 35.245
25.0 -0.255 29.745 0.276 35.276
25.5 -0.265 29.735 0.255 35.255
26.0 -0.274 29.726 0.260 35.26
26.5 -0.283 29.7 17 0.245 35.245
27.0 -0.248 29.752 0.25 1 35.25 1
27.5 -0.252 29.748 0.256 35.256
28.0 -0.262 29.738 0.243 35.243
28.5 -0.27 1 29.729 0.27 1 35.27 1
29.0 -0.280 29.72 0.249 35.249
29.5 -0.260 29.74 0.263 35.263
30.0 -0.248 29.752 0.242 35.242
1. Draw the temperature-time curve at 30℃ with time as abscissa and temperature as ordinate.
Sensitivity of thermostatic bath: △ t = (t1-t2)/2 = (29.769-29.714)/2 = 0.0275.
Performance evaluation of thermostatic bath: the temperature is below 30℃ most of the time. According to four typical sensitivity curves, it can be concluded that the heater power is too small or the heat dissipation is too fast.
2. Draw the temperature-time curve at 35℃ with time as abscissa and temperature as ordinate.
Sensitivity of thermostatic bath: △ t = (t1-t2)/2 = (35.296-35.101)/2 = 0.0975.
Performance evaluation of thermostatic bath: the temperature is above 35℃ most of the time. According to four typical sensitivity curves, it can be concluded that the heater power is too high or the heat dissipation is slow.
Matters needing attention about intransitive verbs
1. The sensitivity of the temperature sensor should be very high.
2. The stirring speed of the stirrer should be large enough to ensure the uniform temperature in the thermostatic bath.
3. The heater has good heat conduction and proper power.
4. The stirrer, the temperature sensing element and the heater are close to each other, so that the heated liquid can be uniformly stirred at the same time.
The temperature is controlled in time by the temperature sensing element.
5. Beckman thermometer is an expensive glass instrument. The mercury ball has a thin glass wall and a small volume.
It is bulky and easy to be damaged, so be very careful when using it, don't put it casually, and put it in the temperature when not in use.
It's in the wooden box attached to the meter.
6. When the left hand pats the right wrist, pay attention to that the thermometer must be vertical, otherwise the capillary tube is easy to break and should be avoided.
Avoid heavy blows and stay away from the test bench.
Seven, thinking about the problem
1. What is the constant temperature principle of the incubator?
Thermostats are used to control the thermal balance of thermostats. When the water temperature drops due to external heat dissipation, the temperature indication controller will make the heater work, and when it is heated to the required temperature, the temperature sensor will control the heater to stop working, thus keeping the temperature of the water tank constant [1]. The thermostat also has the function of automatically adjusting the heater through the electronic relay to achieve the purpose of constant temperature. When the temperature of the thermostatic bath is lower than the set value due to the outward diffusion of heat, the relay forces the heater to work, and automatically stops heating when the system reaches the set temperature again. This cycle keeps the temperature of the system constant within a certain range.
2. Are the temperatures of all parts of the thermostat equal? Why?
The temperature in the thermostatic bath is not the same everywhere. Because the stirrer will not stir evenly, the temperature near the heater will be higher, while the place far away from heating will dissipate heat faster, and the place where the temperature is reduced and heated will be supplemented. Heat must be transferred from high temperature to low temperature, so it can't be the same.
3. How to improve the sensitivity of thermostatic bath? Try to analyze and discuss.
(1) Use components with higher sensitivity and shorter delay time.
A more uniform heating device, such as an electric heating jacket device, can be used. Or use a container with better thermal insulation performance. Or replace the contact thermometer with an element with higher sensitivity and faster reaction speed, so that the temperature change in the process is smaller and the reaction speed of the heater is improved, thereby improving the sensitivity.
(2) Optimize the liquid culture medium in the system.
Liquid with low viscosity coefficient and high thermal conductivity can be selected to reduce temperature fluctuation and improve sensitivity.
(3) adopt a more reasonable layout
From the summary of experimental results, it can be seen that the characteristics of reasonable layout are: the distance between heater and contact thermometer is as close as possible; Make each element located downstream of the stirrer in the stirring direction, but not too close to the stirrer, otherwise the temperature will be unstable.
(4) improve the stirring speed of the stirrer
This can make the heat transfer speed of the medium in the tank faster and the temperature of each part more uniform, thus improving the reaction speed of the system.
(5) Reduce the heating speed appropriately.
Reducing the heating voltage to a suitable value can weaken the heating delay and improve the sensitivity.
Eight. refer to
[1], Huang Guiping, Qu. Discussion on experimental conditions of constant temperature regulation and temperature control [J]. Jiangxi Chemical Industry, 2008,02:120-121.
[2] Chen Jun. Improvement of the thermostat assembly and performance test instrument [J]. Journal of Qiongzhou University, 2004,11(05): 40-41.
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