The liquid level must be high enough to assure the gravity circulation of liquid. In the jet pipe, the flowing gas holds a turbulent state.

要求液面高度能保证净化液的自流，射流管内气体处于湍流状态，混合气流速度应达到连续射流所需的临界速度。

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This has allowed scientists to retrieve information about the Arctic Ocean region's gravity field, its surface circulation, and the thickness of its sea-ice cover.

BBC: Cryosat spots Arctic sea-ice loss in autumn

It uses so-called passive systems for cooling, such as the gravity flow of water and natural circulation based on thermodynamics.

WSJ: NRC Approves Toshiba Reactor Design