If there is a bulk mixing of the layers of gas in the tube by mechanical stirring or because of a density gradient, mass transfer occurs primarily by the mechanism of forced or natural convection.

如果是受到机械式的搅拌或者是密度梯度发生了变化而使得管中有大量的分层的气体，那么传递就主要通过强制对流或自然对流而发生。

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A new method, on-line measurement of the density of natural gas, has been established by researching on vibrating element density transducer tests.

通过应用振动式密度计试验研究，在国内建立起一种天然气密度在线测量的新方法。

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A new method, on-line measurement of the density of natural gas, has been established by researching on vibrating element density transducer tests.

前言： 通过应用振动式密度计试验研究，在国内建立起一种天然气密度在线测量的新方法。

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Nor can they compare to the power density of sources like natural gas, oil and nuclear.

FORBES: Magazine Article

While conspiracy theorists may want to believe that Big Oil, Big Coal and Big Nuclear are stifling the growth of renewables, the simple truth is that coal, oil, natural gas and nuclear can satisfy the Four Imperatives: power density, energy density, cost and scale.

FORBES: Magazine Article