The external circulation is to pump the water in the water tank to the circulation outlet through the circulation pump. The circulation outlet is generally connected to the inlet of the temperature-controlled container through a hose, and the outlet of the temperature-controlled container is also through the hose Connect 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 the manufacturing process, temperature control range and tank capacity. Now let me illustrate with 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 handle, the beaker cannot be placed in a constant temperature water tank to measure directly at a constant temperature. We have to use the external circulation to realize the temperature control of the silicone oil. The steps are as follows: The circulating water outlet of the water bath is softly connected to the water inlet of the hollow sandwich cup, and the water outlet of the hollow sandwich cup 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 placed in the cup. 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.