The pressure compensation technology of deep-sea sampling based on the real gas state equation
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The pressure compensation technology of deep-sea sampling based on the real gas state equation Shuo Wang1, 2, Shijun Wu1*, Canjun Yang1 1 State Key Laboratory of Fluid Power and Mechatronic Systems, Zhejiang University, Hangzhou 310027, China 2 Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, Sanya 572000, China
Received 12 July 2019; accepted 18 December 2019 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
Compressed gas is usually used for the pressure compensation of the deep-sea pressure-maintaining sampler. The pressure and volume of the recovered fluid sample are highly related to the precharged gas. To better understand the behavior of the gas under high pressure, we present a new real gas state equation based on the compression factor Z which was derived from experimental data. Then theoretical calculation method of the pressure and volume of the sample was introduced based on this empirical gas state equation. Finally, the proposed calculation method was well verified by the high-pressure vessel experiment of the sampler under 115 MPa. Key words: gas state equation, deep-sea sampler, pressure compensation, sample pressure, sample volume Citation: Wang Shuo, Wu Shijun, Yang Canjun. 2020. The pressure compensation technology of deep-sea sampling based on the real gas state equation. Acta Oceanologica Sinica, 39(8): 88–95, doi: 10.1007/s13131-020-1637-6
1 Introduction The deep sea is the largest habitat on earth, with at least 50% of the total biosphere lying below a depth of 1 000 m in the ocean. Our knowledge of deep-sea ecosystems remains very limited compared to that for continental shelf ecosystems (Drazen and Yeh, 2012). This extreme environment is characterized by the absence of light, low temperature, and high hydrostatic pressure (Koyama et al., 2002; Pavithran et al., 2007). A variety of topographical features exist in deep-sea environments, such as hydrothermal vents, cold seeps, oceanic trenches, seamounts, and bathyal plains, which possess different physical and chemical properties (Zhang et al., 2018). Extremophiles could be sensitive to drastic changes in pressure and temperature and may be sensitive to changes in atmospheric pressure (Kim and Kato, 2010). Studies on microbes in extreme environments can deepen the understanding of deep-sea microbes’ survival principles and deep-sea microbes’ functions in the food chain (Huang et al., 2006). Humans currently do not understand the ecology and biology of the deep-sea biota because this remote environment is difficult and expensive to access and sample (Shillito et al., 2015). There are numerous methods to obtain samples from the deep sea, such as trawls, water samplers, microbe samplers, multibottle rosette samplers, bellows type samplers, box-core sediment samplers and grab samplers equipped with a camera (Koyama et al., 2002; Kim and Kato, 2010; Bianchi et al., 1999). Researchers have enabled investigations of seabed sulfides by developing near-bottom vehicl
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