Temperature and humidity test chamber knowledge

In the field of environmental testing, test equipment is one of the key elements, which requires us not only only know the test standards, but also to be familiar with the basic principles of the test equipment, this post is to share some knowledge about the temperature and humidity test chamber.

NO.1 Temperature and humidity chamber

Relative to the temperature test chamber, constant temperature and humidity test chamber needs to increase the humidity generated and control devices. Most manufacturers in the equipment factory must confirm whether the humidity function, has been produced after the expansion of the function is not possible or the expansion of the function of the cost is particularly high and does not have the feasibility. But there are some manufacturers of humidity function as a separate component design, which means that if you first buy the temperature test chamber, the later demand for humidity function can be purchased humidity function of the component to upgrade the existing equipment.

NO.2 Rapid-Rate Thermal Cycle Chamber

For temperature and humidity chambers with a high rate of temperature change, they are also known as Rapid-Rate thermal cycle chamber. As the humidity control requires the cooperation of the compressor, so in its corresponding refrigeration capacity will be affected, so its temperature change rate is only for the conditions without humidity. For mechanical refrigeration TEMAK can do 30 ℃ / min or even higher, if the temperature change rate requirements are particularly high only to be able to use liquid nitrogen refrigeration and other ways to achieve.

NO.3 Temperature and humidity explosion-proof chamber

With the increasing importance of consumer electronics batteries, coupled with the rise of electric vehicles, the environmental testing of batteries more and more demand, but due to the high chemical activity of the batteries themselves, belonging to the explosive products, so in the temperature and humidity test need to use explosion-proof temperature and humidity box for the test, rather than ordinary temperature and humidity box, so as to ensure that in the case of abnormalities will not lead to safety accidents.

NO.4 Temperature and humidity test chamber humidity control

Temperature and humidity test chamber temperature control and temperature test chamber consistent, just need to take into account the additional impact of humidity on the temperature to optimize the temperature control.

There are three methods of humidity control, respectively, steam engine humidification, spray humidification and sink heating humidification.

Humidifier U.S. and China Taiwan brands mostly use boiler humidification, mainland China, Europe and Japan brands use water tray humidification. Boiler humidification and water tray humidification have their own advantages and disadvantages. Boiler humidification, humidity constant control is easy, the studio is relatively easy to achieve low humidity, long-term constant operation of low energy consumption, but the humidity linear change control fluctuations, overshoot is not easy to control, cleaning and maintenance is not convenient, high unit cost. Water pan humidification linear change and overshoot control is easy, easy to clean and maintain, unit cost is low, but low humidity is not easy to achieve, long-term operation of energy consumption is slightly higher, thermostat matching requirements are high.

Steamer humidification:

Steamer is to heat the water in the tank to produce steam, after the steam reaches a certain amount will push the valve to release steam. The released steam will be carried out in the air intake system of the temperature and humidity test chamber so as to humidify the temperature and humidity test chamber. According to the humidity control needs of the temperature and humidity test chamber to control the output of heating steam.

Advantages of the steamer: It can provide a large amount of steam continuously, which is suitable for large-size humidity test chambers.

A. The ability to provide a continuous large amount of steam, which is suitable for large-size temperature and humidity test chamber to achieve high temperature and high humidity;

B. Placement of the steam engine on the outside of the inner chamber of the temperature and humidity test chamber makes it easier to achieve low humidity conditions;

C. Placing the steamer outside the inner chamber of the test avoids safety hazards;

D. Strict control of the amount of humidification reduces the consumption of humidification water.

Disadvantages of steamers:

A. It takes time to produce a large amount of steam, so there is a certain delay;

B. Continuous heating will cause the minerals in the water to precipitate and adhere to the container wall (if equipped with a water purifier can solve this problem);.

C. Steamers require high power heating to produce steam;

D. Steam tanks need to be disassembled in order to perform maintenance, which is costly if assistance is sought from the equipment manufacturer or a third party.

By optimizing the size of the steamer, it can be applied to different sizes of temperature and humidity chambers, so as to give better play to its advantages, which can now be seen widely used in different sizes of standard temperature and humidity chambers and rapid temperature change test chambers.

Spray humidification:

Spray humidification is relatively simple, there can be a water spray device can be atomized, which has a wide range of applications in other areas, such as plant irrigation. Spray directly to the temperature and humidity test chamber in the air intake channel on the heater, water spray contact with the heater into water vapor and mixed into the air intake, so that the control of the air intake has a certain humidity to control the humidity of the temperature and humidity test chamber.

The advantages of spray humidification:

A. The function is very simple to realize;

B. Can provide a large amount of water mist;

C. Will not produce dry burning;

D. can save electricity, because it is not heated and then output steam.

Disadvantages of spray humidification:

A. Since the head of the spray is very fine, it will be clogged if there are more impurities in the water, so the quality of the water is very high;

B. The spray must be completely heated before it can be turned into water vapor;

C. it is difficult to produce high humidity at high temperatures;

D. Minerals in the water will be heated by the air to be brought to the temperature and humidity test chamber on the test sample contamination.

Sink heating and humidification:

The principle of sink heating and humidification is the same as that of steam engine, the difference is that one is closed and the other is open. The sink is located in the air inlet of the temperature and humidity test chamber, the air into the temperature and humidity test chamber from the top of the sink when passing through the steam so as to achieve humidity control.

Advantages of sink heating and humidification:

A. Because the amount of water in the sink is small, the corresponding humidification work delay is very short;

B. No boiling is required to provide water vapor;

C. The shorter boiling time will reduce the maintenance effort of the sink and equipment;

D. Easy and simple cleaning of the sink.

Disadvantages of sink-heated humidification:

A. Because of the small amount of water in the sink, it is not possible to produce large amounts of water vapor, and high temperature and high humidity conditions in large volumes may not be possible;

B. The heater for sink humidification runs the risk of dry firing and is more easily damaged;

C. It is more difficult to control the generation of low humidity because the sink is located in the channel of the air intake and water is present at any temperature above zero;

D. Since the sink is in an internal cavity, it is necessary to drain whoever is at each low temperature, otherwise the water in the sink will freeze. If carry out temperature cycle test its water consumption will be much larger, no automatic water replenishment system basically can not be used.

NO.5 Dehumidification and low humidity test conditions

There are two types of dehumidification in temperature and humidity test chamber: mechanical refrigeration dehumidification and desiccant dehumidification. Mechanical refrigeration dehumidification dehumidification is to cool the air below the dew point temperature, so that more than saturated moisture content of water condensation precipitation, which reduces the humidity. Desiccant dehumidification is the use of air pumps will be the temperature and humidity test box air pumped out, and will be injected into the dry air, while the wet air into the dryer can be recycled for drying, drying and then sent to the temperature and humidity test box, and so on repeated cycles for dehumidification. Now most of the temperature and humidity test chamber using the former method of dehumidification. The latter dehumidification method, can make the dew point temperature below 0 ℃, suitable for special requirements of the occasion, but the cost is more expensive.

If you need to achieve low humidity test conditions, usually need to add additional auxiliary devices to achieve low humidity, general standard temperature and humidity test chamber is not to support low humidity test conditions, especially below 20% humidity. Usually there will be few low humidity test demand, if the enterprise has low humidity test demand need to be clearly put forward in the procurement of temperature and humidity test chamber corresponding requirements. The following is TEMAK temperature and humidity test chamber temperature and humidity can be controlled capacity range table.

Constant temperature and humidity test chamber indicators are basically 30% ~ 98% RH or 20% ~ 98% RH. Low temperature and low humidity is relatively difficult to control, because at this time the absolute humidity per unit volume is very low, many times will be much lower than the absolute content of the ambient atmosphere. Low temperature and low humidity will require dehumidification of the air in the box, so that the air becomes dry. If the method of cooling dehumidification, is in the box air pre-conditioning room with a set of refrigeration tubes, when the wet air through the refrigeration tube, due to the reduction in air temperature makes the relative humidity will reach 100% RH, part of the water vapor precipitation in the refrigeration tube on the formation of condensation, and then become dry. Although this dehumidification method can theoretically reach the dew point temperature below zero, but when the surface temperature of the refrigeration tube reaches 0 ℃, the surface of the refrigeration tube condensation will freeze, thus affecting the heat exchange, making the dehumidification ability to decline, and at the same time, because the box can not be absolutely sealed, the wet air in the atmosphere will penetrate into the box, so that the dew point temperature rises. This dehumidification method can not make the box dew point temperature down to below 0 ℃, the actual minimum dew point temperature of about 5 ~ 7 ℃, the dew point temperature of 5 ℃ its corresponding absolute moisture content is 0.0055g / kg, corresponding to the temperature of 30 ℃, the relative humidity is 20% RH. If the temperature is required to 20 ℃, the relative humidity reaches 20% RH, at this time, the dew point temperature is If the temperature is 20℃, the relative humidity reaches 20%RH, and the dew point temperature is -3℃, it can't be realized by this method, and the desiccant must be used to realize it, but the desiccant belongs to the consumables, and it needs to be replaced regularly, and the cost of using it in the later stage is high.