Simple method for realizing short-time saturated water vapor environment by using common environmental box

Abstract

The invention discloses a simple method for realizing a short-time saturated water vapor environment by using a common environmental box, which comprises the following steps of: setting the environmental box at a relatively high initial temperature, and keeping the humidity in a reachable maximum state, so that the environment in the box is close to the saturated water vapor environment as much as possible; and the temperature of the environmental box is reduced according to the calculated rate, so that a saturated water vapor environment is realized in the environmental box. The method is convenient to operate, the used equipment is simple in structure and low in price, and the short-time saturated water vapor environment can be achieved with low cost.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental testing of electrical products, and in particular relates to a simple method for realizing a short-term saturated water vapor environment by using a common environmental chamber. Background Art

[0002] Saturated water vapor environment refers to a state of dynamic equilibrium between humid air and water surface (or ice surface) at a given temperature and pressure. At this time, the content of water vapor molecules in the air reaches the maximum value at this temperature and pressure, that is, the water vapor pressure in the air is equal to the saturated water vapor pressure at this temperature, and the water vapor in the air can no longer increase, and is in a saturated state.

[0003] The saturated water vapor environment has the following characteristics:

[0004] Dynamic equilibrium: In a saturated water vapor environment, the number of water molecules leaving the water surface (or ice surface) is equal to the number of water molecules returning from the air to the water (or ice), reaching a dynamic equilibrium state.

[0005] Saturated water vapor pressure: At a certain temperature, when the water vapor in the air is in phase equilibrium with the water or ice below it, the water vapor pressure in the moist air is the saturated water vapor pressure at that temperature. The saturated water vapor pressure is a function of temperature and increases with increasing temperature.

[0006] Relative humidity: In a saturated water vapor environment, relative humidity is equal to 100%, indicating that the air is in a saturated state.

[0007] Condensation: If the water vapor content in the air exceeds the saturated water vapor pressure at that temperature, the excess water vapor will condense into liquid water or ice crystals.

[0008] In the field of environmental testing technology for electrical products, a saturated water vapor environment is an important testing environment. For example, in the anti-rust test, the sample needs to be placed in a container filled with air saturated with water vapor at a temperature of (20±5)℃ for 10 minutes. In theory, a saturated water vapor environment can be achieved by setting the relative humidity of the environmental chamber to 100%, but in reality, even if the relative humidity of a common environmental chamber is set to 100%, it can usually only reach 98%, making it difficult to achieve a saturated water vapor environment. Summary of the invention

[0009] The purpose of the present invention is to provide a simple method for realizing a short-term saturated water vapor environment by using a common environmental chamber, so as to solve the problem that the traditional saturated water vapor environmental chamber has a complex structure and is expensive.

[0010] The present invention utilizes the characteristic that saturated water vapor pressure is a function of temperature, increases with increasing temperature and decreases with decreasing temperature. The environmental chamber is first set at a relatively high starting temperature and the humidity is maintained at the maximum state that can be achieved, so that the environment in the chamber is as close to the saturated water vapor environment as possible; then, according to the calculated rate, the temperature of the environmental chamber is reduced. Since the saturated water vapor pressure decreases at the starting temperature at the reduced temperature, a saturated water vapor environment is achieved in the environmental chamber. However, due to the differences in the performance of different environmental chambers, factors such as water vapor loss need to be considered. Therefore, the set starting temperature and the rate of temperature reduction must be calculated to achieve an ideal saturated water vapor environment state.

[0011] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0012] A simple method of the present invention for realizing a short-term saturated water vapor environment by using a common environmental chamber is characterized by comprising the following steps:

[0013] S1, determine the maximum humidity Hum (unit %) that the environmental chamber can reach;

[0014] S2, calculate the test temperature T according to the relationship between saturated water vapor pressure and temperature test (Unit: °C) The saturated water vapor pressure E required to be reached test (unit: kPa);

[0015] S3, calculate the starting temperature T of the environmental chamber setting set (Unit: °C) required to reach saturated water vapor pressure E beg (unit kPa), E beg =E test / Hum;

[0016] S4, calculate E according to the relationship between saturated water vapor pressure and temperature beg The corresponding temperature is then increased by at least 18°C ​​(preferably 20-25°C) to obtain the starting temperature T of the environmental chamber. set (Unit: °C);

[0017] S5, measure the environmental chamber at the test temperature T test Water vapor loss at maximum humidity S (g / min);

[0018] S6, according to the comparison table of saturated steam pressure and water content per unit volume at different temperatures, the test temperature T is obtained. test The change rate of water content per unit volume under saturated water vapor environment ΔSv (unit g / (m 3 · ℃)), multiplied by the internal volume V (in m3) of the environmental chamber, and then the test temperature T testThe moisture content change rate of the environmental chamber under the saturated water vapor environment ΔS (unit: g / ℃);

[0019] S7, set the required temperature change rate ΔT (unit: °C / min), which should satisfy S / ΔS≤ΔT≤2*S / ΔS; usually ΔT will not exceed the actual cooling rate of the box;

[0020] S8, set the environmental chamber to the starting temperature T set and maximum humidity Hum, after the environmental chamber is stable, the temperature of the environmental chamber is gradually reduced according to the temperature change rate ΔT, and the environmental chamber can be at the required test temperature (T test Unit ℃) to achieve a short-term saturated water vapor environment.

[0021] The saturated water vapor pressure is a function related to temperature, so the relationship between saturated water vapor pressure and temperature is the modified Tetens formula:

[0022] Where, E is the saturated water vapor pressure, the unit is hPa; t is the environmental chamber temperature, the unit is ℃.

[0023] The determination method of step S5 is: by setting the environmental box at the test temperature T test and maximum humidity Hum, run for 1 hour, and check the water consumption of the environmental chamber, which is the water vapor loss S of the environmental chamber.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] The method of the present invention is easy to operate, uses a simple device with a low price, and can achieve a short-term saturated water vapor environment at a relatively low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a calculation flow chart of the present invention.

[0027] Figure 2 This is a comparison table of saturated steam pressure and water content at different temperatures. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. Those skilled in the art should recognize that the present embodiments are only used to illustrate the present invention, and are not used to limit the present invention. As long as the embodiments are changed and modified within the scope of the present invention, they can be within the scope of the claims of the present invention.

[0029] Example 1

[0030] The internal volume of the existing environmental chamber is 1m 3, the maximum humidity is 98%, and the test purpose is to maintain a saturated water vapor environment at a temperature of (20±5)℃ for 10 minutes.

[0031] A simple method for achieving a short-term saturated water vapor environment using a common environmental chamber includes the following steps:

[0032] S1, through the calibration certificate, determine that the maximum humidity Hum (unit %) that the environmental chamber can reach is 98%;

[0033] S2, test temperature T test The test temperature T is calculated based on the relationship between saturated water vapor pressure and temperature (Formula 1). test (Unit: °C) The saturated water vapor pressure E required to be reached test 1.70405 kPa;

[0034] S3, calculate the starting temperature T of the environmental chamber setting set (Unit: °C) required to reach saturated water vapor pressure E beg (unit kPa), E beg =E test / Hum=1.70405kPa / 98%=1.73883kPa;

[0035] S4, calculate E according to formula 1 beg The corresponding temperature, and on this basis, add 20℃ to get the starting temperature T of the environmental chamber setting set is 36°C;

[0036] S5, measure the environmental chamber at the test temperature T test Water vapor loss S (g / min) at maximum humidity: by setting the environmental chamber at the test temperature T test and maximum humidity Hum, run for 1 hour, check the water consumption of the environmental chamber, that is, the water vapor loss of the environmental chamber S = 0.3g / min;

[0037] S6, it is known that the internal volume V of the environmental chamber is 1m 3 , according to the comparison table of saturated vapor pressure and water content at different temperatures (see Figure 2 This comparison table is a commonly used empirical parameter. The unit of water content in the table is g / m3. Therefore, the internal volume V of the environmental chamber is required to calculate the water content change rate of the environmental chamber. The test temperature T can be obtained by looking up the table. test The change rate of water content per unit volume ΔSv in a saturated water vapor environment is about 0.8g / (m 3 · ℃)), multiplied by the internal volume V of the environmental chamber, and then the test temperature T test The moisture content change rate ΔS of the environmental chamber in the saturated water vapor environment is about 0.8g / ℃;

[0038] S7, calculate S / ΔS=0.375°C / min, set the required temperature change rate ΔT according to S / ΔS≤ΔT≤2*S / ΔS, which is set to 0.5°C / min this time;

[0039] S8, set the environmental chamber to the starting temperature T set =36℃ and maximum humidity Hum = 98%. After the environmental chamber is stable, the temperature of the environmental chamber is gradually reduced at a temperature change rate of ΔT = 0.5℃ / min. The environmental chamber can be at the required test temperature T test A short-term saturated water vapor environment is achieved at (20℃±5℃) to meet the established test requirements.

[0040] Example 2

[0041] The internal volume of the existing environmental chamber is 0.48m 3 , the maximum humidity is 98%, and the test purpose is to maintain a saturated water vapor environment at a temperature of (25±5)℃ for 10 minutes.

[0042] A simple method for achieving a short-term saturated water vapor environment using a common environmental chamber includes the following steps:

[0043] S1, through the calibration certificate, determine that the maximum humidity Hum (unit %) that the environmental chamber can reach is 98%;

[0044] S2, test temperature T test is 15℃, and the test temperature T is calculated according to formula 1 test (Unit: °C) The saturated water vapor pressure E required to be reached test 2.33695 kPa;

[0045] S3, calculate the starting temperature T of the environmental chamber setting set (Unit: °C) required to reach saturated water vapor pressure E beg (unit kPa), where E beg =E test / Hum=2.33695kPa / 98%=2.38464kPa;

[0046] S4, calculate E according to formula 1 beg The corresponding temperature, and on this basis, add 20℃ to get the starting temperature T of the environmental chamber setting set (Unit: °C) is 41°C;

[0047] S5, measure the environmental chamber at the test temperature T test Water vapor loss S (g / min) at maximum humidity: by setting the environmental chamber at the test temperature T testand maximum humidity Hum, run for 1 hour, check the water consumption of the environmental chamber, that is, the water vapor loss of the environmental chamber S = 0.2g / min;

[0048] S6, it is known that the internal volume V of the environmental chamber is 0.48m 3 According to the comparison table of saturated steam pressure and water content at different temperatures, the test temperature T test The change rate of water content per unit volume ΔSv in a saturated water vapor environment is about 0.986g / ℃ · m 3 ), multiplied by the internal volume of the environmental chamber, and then the test temperature T test The moisture content change rate ΔS of the environmental chamber under the saturated water vapor environment is about 0.473g / ℃;

[0049] S7, calculate S / ΔS=0.422°C / min, set the required temperature change rate ΔT according to S / ΔS≤ΔT≤2*S / ΔS, which is set to 0.6°C / min this time;

[0050] S8, set the environmental chamber to the starting temperature T set =41℃ and maximum humidity Hum=98%. After the environmental chamber is stable, the temperature of the environmental chamber is gradually reduced at a temperature change rate of ΔT=0.6℃ / min. The environmental chamber can be kept at the required test temperature T test A short-term saturated water vapor environment is achieved at (25℃±5℃) to meet the established test requirements.

Claims

1. A simple method for achieving a short-term saturated water vapor environment using a common environmental chamber, characterized in that: The following steps are involved: S1, determine the maximum humidity Hum (unit %) that the environmental chamber can reach; S2, calculate the test temperature T according to the relationship between saturated water vapor pressure and temperature test (Unit: °C) The saturated water vapor pressure E required to be reached test (unit: kPa); S3, calculate the starting temperature T of the environmental chamber setting set (Unit: °C) required to reach saturated water vapor pressure E beg (unit kPa), E beg =E test / Hum; S4, calculate E according to the relationship between saturated water vapor pressure and temperature beg The corresponding temperature is then increased by at least 18°C ​​(preferably 20-25°C) to obtain the starting temperature T of the environmental chamber. set (Unit: °C); S5, measure the environmental chamber at the test temperature T test Water vapor loss at maximum humidity S (g / min); S6, according to the comparison table of saturated steam pressure and water content per unit volume at different temperatures, the test temperature T is obtained. test The change rate of water content per unit volume under saturated water vapor environment ΔSv (unit g / (m 3 · ℃)), multiplied by the internal volume V of the environmental chamber (in m 3 ), then the test temperature T test The moisture content change rate of the environmental chamber under the saturated water vapor environment ΔS (unit: g / ℃); S7, set the required temperature change rate ΔT (unit: °C / min), which should satisfy S / ΔS≤ΔT≤2*S / ΔS; usually ΔT will not exceed the actual cooling rate of the box; S8, set the environmental chamber to the starting temperature T set and maximum humidity Hum, after the environmental chamber is stable, the temperature of the environmental chamber is gradually reduced according to the temperature change rate ΔT, and the environmental chamber can be at the required test temperature (T test Unit ℃) to achieve a short-term saturated water vapor environment.

2. The simple method for realizing a short-term saturated water vapor environment using a common environmental chamber according to claim 1, characterized in that: In step S4, E is calculated according to the relationship between saturated water vapor pressure and temperature. beg The corresponding temperature, and on this basis, add 20 to 25 °C to get the starting temperature T of the environmental chamber setting set .

3. The simple method for realizing a short-term saturated water vapor environment using a common environmental chamber according to claim 1, characterized in that: The relationship between saturated water vapor pressure and temperature is the modified Tetens formula: Where, E is the saturated water vapor pressure, the unit is hPa; t is the environmental chamber temperature, the unit is ℃.

4. The simple method for realizing a short-term saturated water vapor environment using a common environmental chamber according to claim 1, characterized in that: The determination method of step S5 is: by setting the environmental box at the test temperature T test and maximum humidity Hum, run for 1 hour, and check the water consumption of the environmental chamber, which is the water vapor loss S of the environmental chamber.

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