Conditions and speed of sublimation of four-ring lyophilization experimental lyophilizer

The conditions and speed of the sublimation of the four-ring lyophilization experimental lyophilizer can begin to sublimate when the saturated vapor pressure of the ice at a certain temperature is greater than the partial pressure of the water vapor in the environment; The suction and capture of water vapor by a condenser with a lower temperature than the product is a necessary condition
for maintaining the liter.

The distance traveled by the gas molecules between two consecutive collisions is called the mean free path, and it is inversely proportional
to the pressure.

At atmospheric pressure, its value is very small, and the sublimated water molecules can easily collide with the gas and return to the surface of the steam source, so the sublimation rate is very extensive
.

With the pressure reduced by less than 13.
3Pa, the average free path increased by a factor of 105, which significantly accelerated the sublimation speed, and the water molecules that flew out rarely changed their aspects, thus forming a directional steam flow
.

Vacuum pumps act as gas pumps in lyophilizers to maintain the low pressures
necessary for sublimation.

1g of water vapor is 1.
25L at atmospheric pressure and 10,000 liters at 13.
3Pa, and it is impossible
for an ordinary vacuum pump to extract such a large volume in a time.

The condenser actually forms a vacuum pump
that specializes in capturing water vapor.

The temperature of the product and condensation is usually -25 °C and -50 °C
.

The saturated vapor pressure of ice at this temperature is 63.
3Pa and 1.
1Pa, respectively, so there is a considerable pressure difference between the sublimation surface and the condensing surface, if the partial pressure of the non-condensable gas in the system is negligible at this time, it will promote the sublimation of the water vapor from the product to reach the surface of the condenser at a certain flow rate to form frost
.

The sublimation heat of ice is about 2822J/g, if the sublimation process does not supply heat, then the final product can only reduce the internal energy to compensate for the sublimation heat, until its temperature is balanced with the temperature of the condenser, and the sublimation is stopped
.

In order to maintain the temperature difference between sublimation and condensation, sufficient heat
must be provided to the product.

Four-ring lyophilization experimental lyophilizer for the cold trap temperature setting cold trap is a machine that captures water during the freeze drying process, theoretically speaking, the lower the temperature of the cold trap, the higher its ability to catch water, but if the temperature of the cold trap is low, then the operating cost of the machine itself will increase
.

So let's talk about some types of cold traps for freeze dryers, so that you can choose the devices you need and save costs
better.

Lyophilization with a cold trap temperature of -45 °C is suitable for some products that are easy to freeze dry, the lyophilizer with a cold trap temperature of about -60 °C is suitable for lyophilization of most products, and the freeze drying of cold trap temperature of -80 °C is suitable for lyophilization
of some special products.

The influence of cold trap temperature on water catching capacity experimentally shows that the cold trap temperature drops from -35 °C to -55 °C, the water catch capacity is significantly improved, the cold trap temperature is lower than -55 °C, and the water catch capacity of the cold trap is not significantly improved
.

Therefore, in the absence of special needs, the choice of cold trap temperature of about -60 °C is the ideal choice
.