1. What is free space?
When the sample tube is mounted on a static volumetric instrument, the volume of the remaining tube space is referred to as the free space volume, except for the sample volume removed from the sample tube. During the test, the free space volume needs to be accurately understood and the free space volume must be kept constant. Under normal circumstances, the free space will be tested first at room temperature, then the Dewar will be raised and the free space will be tested at the temperature of the liquid coolant (usually liquid nitrogen). The latter is called cold free space. If the cold free space changes during the analysis, there is a considerable error in the calculation of the amount of gas in the sample tube.
In the mid-1980s, Mike Instruments introduced the patented isothermal jacket technology for cold free space temperature control.
Second, the United States Mike Instrument Company 1987 isothermal jacket product introduction
The BET technique for material specific surface area and pore size distribution analysis needs to be accomplished by low temperature gas adsorption. In this process, it is necessary to accurately understand the pressure, volume and temperature of all components of the test system in order to accurately calculate the amount of test gas. Since the gas adsorption occurs at a low temperature and the other components of the test system are at a normal temperature, the temperature must be stabilized when the low temperature sample is connected to the normal temperature system. If proper control is not possible, in such an interconnected and extremely temperature gradient, the volatilization of the coolant will cause a change in the size of the cooling zone, thereby affecting the gas volume test and the gas adsorption test results.
As shown in the figure below, the sample tube loaded with the sample is immersed in liquid nitrogen and directly connected to other components of the instrument. The temperature gradient space will increase with the evaporation of liquid nitrogen and the liquid nitrogen level. Increased temperature volume of the sample tube is increased.
One method is to maintain a constant volume in the cooling zone by adjusting the position of the dewar, mainly by continuously raising the Dewar with the liquid nitrogen level. This method does effectively maintain a constant volume of the sample tube immersed in liquid nitrogen, but it must be ensured that the height of the sample tube initially exposed at room temperature is sufficient. But even with this method, the temperature gradient still exists and only partial evaporation compensation can be obtained.
In the mid-1980s, Mike Instruments used a traditional way to maintain a liquid nitrogen level, using a transfer tool that directly connected the Dewar and liquid nitrogen tanks with the evaporation of liquid nitrogen. , continuously add fresh liquid nitrogen to the Dewar. As shown below. This method is very effective, but you need to prepare the following transfer device:
In 1987, Mike Instruments introduced a patented isothermal jacketing technology that provides excellent stability for maintaining a constant cold free space. The isothermal jacket is made of a porous material and can be placed directly around the sample tube during use. As long as the bottom end of the isothermal jacket is immersed in liquid nitrogen, the porous material ensures that liquid nitrogen is maintained around the sample tube and at a constant height. In this way, even if only a small amount of liquid nitrogen remains in the dewar, the sample tube cold free space can be maintained. If the test time is too long, fresh liquid nitrogen can be replenished at the right time. The isothermal jacket has no loss during use and is a true long-term solution, as shown in the following figure:
Stock Pot With Compound Bottom
Stock Pot With Compound Bottom,All Clad Stock Pot,Stock Pot With Compound Bottom Of Foot,Large Stock Pot
Jiangmen Junerte Stainless Steel Kitchenware Co.,Ltd , https://www.junertejm.com