The outer circulation is to pump the water in the water tank to the circulating water outlet through a circulating pump. The circulating water outlet is generally connected to the water inlet of the temperature-controlled container through a hose, and the water outlet of the air-temperature container is also through the hose It is connected to the water inlet of the outer circulation of the water tank to realize the temperature control of the temperature-controlled container. What are the benefits of external circulation? Water baths vary in size due to differences in manufacturing process, temperature control range, and tank capacity. Now let me give an example: We use a rotational viscometer to measure the viscosity of silicone oil at 25 degrees: If the height of the water bath we buy is higher than the height that the viscometer can withstand, the beaker cannot be placed in a constant temperature water tank to measure it directly. This is why we have to use the external circulation to realize the temperature control of the silicone oil. The steps are as follows: the water bath circulation outlet is connected to the water inlet of the hollow sandwich cup through a hose, and the water outlet of the hollow sandwich beaker is also connected to the water inlet of the outer circulation of the sink through a hose, and the silicon oil to be tested is put into the beaker ,that's it. The simple point is that if the temperature cannot be controlled in the water tank, the temperature can be controlled in the outer container of the water tank with the external circulation.