A CO2 incubator produces condensation, is the relative humidity too high?
When we use CO2 incubator to cultivate cells, due to the difference in the amount of liquid added and the culture cycle, we have different requirements for the relative humidity in the incubator.
For experiments using 96-well cell culture plates with a long culture cycle, due to the small amount of liquid added to a single well, there is a risk that the culture solution will dry out if it evaporates for a long period of time at 37 ℃.
Higher relative humidity in the incubator, for example, to reach more than 90%, can effectively reduce the evaporation of liquid, however, a new problem has arisen, many cell culture experimentalists have found that the incubator is easy to produce condensate in high humidity conditions, condensate production if uncontrolled, will accumulate more and more, to the cell culture has brought a certain risk of bacterial infection.
So, is the generation of condensation in the incubator because the relative humidity is too high?
First of all, we need to understand the concept of relative humidity, relative humidity (Relative Humidity, RH) is the actual content of water vapor in the air and the percentage of water vapor content at saturation at the same temperature. Expressed in the formula:
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the percentage of relative humidity represents the ratio of the water vapor content in the air to the maximum possible content.
Specifically:
* 0% RH: There is no water vapor in the air.
* 100% RH: The air is saturated with water vapor and cannot hold more water vapor and condensation will occur.
* 50% RH: Indicates that the current amount of water vapor in the air is half the amount of saturated water vapor at that temperature. If the temperature is 37°C, then the saturated water vapor pressure is about 6.27 kPa. Therefore, the water vapor pressure at 50% relative humidity is about 3.135 kPa.
Saturated water vapor pressure is the pressure generated by vapor in the gas phase when liquid water and its vapor are in dynamic equilibrium at a certain temperature.
Specifically, when water vapor and liquid water coexist in a closed system (e.g., a well-closed Radobio CO2 incubator), water molecules will continue to change from the liquid state to the gaseous state (evaporation) over time, while also gaseous water molecules will continue to change to the liquid state (condensation).
At a certain point, the rates of evaporation and condensation are equal, and the vapor pressure at that point is the saturated water vapor pressure. It is characterized by
1. dynamic equilibrium: when water and water vapor coexist in a closed system, evaporation and condensation to reach equilibrium, the pressure of water vapor in the system is no longer changing, at this time the pressure is saturated water vapor pressure.
2. temperature dependence: saturated water vapor pressure changes with temperature. When the temperature increases, the kinetic energy of water molecules increase, more water molecules can escape to the gas phase, so the saturated water vapor pressure increases. Conversely, when the temperature decreases, the saturated water vapor pressure decreases.
3. Characteristics: saturated water pressure is a purely material characteristic parameter, does not depend on the amount of liquid, only with the temperature.
A common formula used to calculate saturated water vapor pressure is the Antoine equation:
For water, the Antoine constant has different values for different temperature ranges. A common set of constants are:
* A=8.07131
* B=1730.63
* C=233.426
This set of constants applies to the temperature range from 1°C to 100°C.
We can use these constants to calculate that the saturated water pressure at 37°C is 6.27 kPa.
So, how much water is in the air at 37 degrees Celsius (°C) in a state of saturated water vapor pressure?
To calculate the mass content of saturated water vapor (absolute humidity), we can use the Clausius-Clapeyron equation formula:
Saturated water vapor pressure: At 37°C, the saturated water vapor pressure is 6.27 kPa.
Converting the temperature into Kelvin: T=37+273.15=310.15 K
Substitution into the formula:
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the result obtained by calculation is about 44.6 g/m³.
At 37°C, the water vapor content (absolute humidity) at saturation is about 44.6 g/m³. This means that each cubic meter of air can hold 44.6 grams of water vapor.
A 180L CO2 incubator will only hold about 8 grams of water vapor. When humidification pan as well as culture vessels are filled with liquids, the relative humidity can easily reach high values, even close to saturation humidity values.
When the relative humidity reaches 100%, the water vapor begins to condense. At this point, the amount of water vapor in the air reaches the maximum value it can hold at the current temperature, i.e. saturation. Further increases in water vapor or decreases in temperature cause the water vapor to condense into liquid water.
Condensation may also occur when the relative humidity exceeds 95%, but this depends on other factors such as temperature, the amount of water vapor in the air, and the surface temperature. These influencing factors are as follows:
1. Decrease in temperature: When the amount of water vapor in the air is close to saturation, any small decrease in temperature or increase in the amount of water vapor may cause condensation to occur. For example, the temperature fluctuations in the incubator may lead to the generation of condensate, so the temperature is more stable incubator will have an inhibitory effect on the generation of condensate.
2. local surface temperature below the dew point temperature: local surface temperature is lower than the dew point temperature, water vapor will condense into water droplets on these surfaces, so the temperature uniformity of the incubator will have a better performance in the inhibition of condensation.
3. Increased water vapor: for example, humidification pan and culture containers with a large amount of liquid, and the incubator is better sealed, when the amount of water vapor in the air inside the incubator increased beyond its maximum capacity at the current temperature, even if the temperature remains unchanged, condensation will be generated.
Therefore, a CO2 incubator with good temperature control obviously has an inhibiting effect on the generation of condensate, but when the relative humidity exceeds 95% or even reaches saturation, the possibility of condensation will increase significantly, therefore, when we cultivate cells, in addition to choosing a good CO2 incubator, we should try to avoid the risk of condensation brought about by the pursuit of high humidity.
Post time: Jul-23-2024