1 Introduction
In scientific research practice, it is well known that the temperature stability of the incubator and the evenness of the temperature distribution directly affect the accuracy of scientific experiments. Therefore, we have performed a series of dynamic observations and analytical studies on different types of constant temperature incubators. To guide scientific experiments.
We use precision thermometers, thermocouples and 852OA digital multimeters for large-scale water-isolated incubators (studio size 500x500x60mm, power 660w, hereinafter referred to as the water tank) and DNP-9052 type electric heating equipment manufactured by Zhejiang Top Equipment. Intensive and systematic dynamic observation was performed at 10 points on the same position in a constant temperature incubator (studio size 350x350x410~, power 200w, hereinafter referred to as electric heating box), and the observation results thereof are as follows.
2 Dynamic observations
2.1 Using the rated temperature range (36 ± 0.5 °C) as a standard, compared with the average temperature curve of the two incubators, although the temperature profiles of the two incubators are all within the rated temperature range, compared to The temperature curve of the water tank is much smoother than that of the electric heating tank (illustration), which shows that the average temperature of the former is more stable than the latter.
2.2 In the same observation point, the temperature dispersion in the two incubators was compared. The coefficient of variation (Cv.) of the temperature in the water tank is less than the coefficient of variation (Cv) of the electric heating box, which indicates that the temperature of the former is better than the latter.
2.3 For the comparison of the dispersion of the upper temperature in the same incubator with the dispersion of the temperature in the lower layer, the two types of incubators have a common feature, that is, the coefficient of variation (CV) of the upper temperature is less than the coefficient of variation of the temperature of the lower layer. Cv, this shows that the upper temperature uniformity is better than the lower layer.
2.4 In the electric heating box, the average temperature in the upper layer was lower than the average temperature in the lower layer (p<0.05).
2.5 In the watertight tank, the average temperature of the upper layer is slightly higher than the average temperature of the lower layer (p<0.05).
3 Discussion
In summary, the constant and uniform degree of the tank temperature is better than the large electric heating box. The reason for the difference in the above results is that the materials used to manufacture the two large-scale incubators are different and their structures are different.
3.1 The inner wall of the tank is made of copper with good thermal conductivity, while the inner wall of the tank is made of steel with poor thermal conductivity. The thermal conductivity of copper is 6 times larger than that of copper.
3.2 The cubicle made of copper in the gutter box is filled with water with good thermal conductivity, while the electric heating box does not have a sandwich wall or water to conduct heat, and only the air with poor thermal conductivity conducts heat energy. The thermal conductivity of water is 25 times greater than air.
Therefore, the heat generated by the heat source at the bottom of the water trap can be quickly and uniformly transmitted to the inside of the box through the copper and water and air with good thermal conductivity. The heat transfer medium of the electric heating box is poor in thermal conductivity of steel and air, so its thermal conduction speed is greatly limited, so the temperature uniformity of the former is better than the latter.
3.3 Since the specific heat of water is five times larger than that of air, the total heat capacity of the watertight tank is twice as large as that of the electric heat tank, so the former has better thermal stability than the latter.
3.4 The temperature of the upper layer of the watertight tank is slightly higher than that of the lower layer. The reason why the temperature of the lower layer of the electric heating tank is higher than the upper layer is determined by the three modes of heat propagation—the laws of conduction, radiation, and convection. Although the heat sources of both are installed at the bottom of the tank, the thermal conductivity of the latter is far inferior to that of the former, so that the heat generated at the bottom of the tank cannot be quickly conducted to the upper layer of the tank.
Second, the upper layer is farther away from the heat source than the lower layer, and the amount of heat radiated by the heat decreases with distance. Therefore, the upper layer receives less heat radiation and the temperature is lower. The third way of re-heating - convection is also subject to certain restrictions, so the lower temperature of the electrothermal incubator is higher than the upper layer.
On the contrary, the three heat transmission methods of the water tank are better than the electric heating box, so the former temperature uniformity is better than the latter, and the hot convection has the law of cold drop heat rise, resulting in a slightly higher temperature of the upper layer of the large water incubator In the lower level.
4 Suggestions
In scientific experiments with high requirements on temperature stability and uniformity, in order to reduce system errors and improve experimental accuracy, the following issues should be noted:
(1) Use a watertight tank with good performance as much as possible to avoid using electric heating tanks.
(2) Since the temperature uniformity of the upper layer is superior to the lower layer, the specimen should be placed on the upper layer as much as possible during the experiment.
(3) If both upper and lower layers are to be placed with experimental specimens, control specimens should be set separately on the upper and lower layers.
(4) Since the temperature distributions of the two large thermostats have opposite characteristics and the degree of difference is not the same, they should also be considered when analyzing the relevant experimental results.
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