The Principle And Technologies For Sampling Deep-Sea High-Fidelity Hydrothermal Fluids

The discovery of seafloor hydrothermal activities is one of the most significant events in the 20th century marine science research.It is of great scientific interest and economic importance to study the hydrothermal system since it yields unique biological communities under extreme environment as well as abundant metal sulfide deposits.To date,the collection of high-quality hydrothermal fluid samples is still the most effective and important method. As a result,a variety of hydrothermal fluid sampling devices have been developed in the world.However,in addition to obvious obstacles of the high temperature and pressure,the corrosive nature of hydrothermal fluid and high loads of particle in the fluid prevent a lot of samplers from collecting high-fidelity fluid samples.At present,the research of sampling technology of deep-sea hydrothermal fluid in our country is still in backward state.As the investigation of hydrothermal activities is progressed,the development of high-quality hydrothermal fluid sampler is the impending requirement.The sampling valve and the valve's underwater actuator are the key components of a hydrothermal fluid sampler.Most of the present samplers adopt commercially available items, which are usually difficult to obtain satisfying practical application.To address these issues, the principles and some key technologies for sampling deep-sea high-fidelity hydrothermal fluids have been discussed and investigated in this dissertation.In order to obtain the high-purity,free of contamination and one-phase hydrothermal fluids,the principles for so-called "high-fidelity" sampling were discussed in three aspects: the gas-tight performance of sampler,the principle of regulating the flow rate and corrosion protection.Main emphasis has been put on the study of the cooling process of the hydrothermal fluid inside the sampling tube when collecting a fluid sample with high temperature(such as 400℃),as to ensure the corrosion resistance performance of the material of sampler.A novel bidirectional self-tightening sealing structure and a pressure-balanced sealing structure of the sampling valve were put forward to solve the bidirectional sealing problem under high temperature and pressure.The valve poppet-seat contact sealing performance of different contact models and materials was studied by means of finite element analysis and experiments.Furthermore,based on the bidirectional self-tightening sealing structure,a novel sampling valve with titanium alloy poppet-to-pure titanium seating structure has been successfully designed,fabricated and tested,thus greatly improving the performance of high temperature tolerance and corrosion resistance.According to the application requirements and characteristics of the sampling valve in the deep sea,a hydraulic actuating mechanism based on the ram on the manipulator was developed.This actuating mechanism transforms the output force and displacement of the ram to match the opening force and stroke of the sampling valve.And it features the simple design,high reliability and the effect of force amplification.Moreover,a novel underwater electronic control actuator for the sampling valve was also presented.Theoretical analysis and experiments were carried out to study the performance of this new kind of actuator, including the actuating force,response time and power consumption.The results indicated that the actuator is capable of providing significant force while keeping a small size and low power consumption,which is quite suitable for the deep-sea application.Based on the sampling valve and underwater actuators,the system integration of deep-sea hydrothermal fluid sampler was studied.Two different kinds of samplers were presented,namely,the hydraulically actuated sampler and the electronic controlled sampler. Base on these system integration schemes,four sets of hydraulically actuated samplers and two sets of time-serial samplers have been successfully designed and constructed.The laboratory experiments and sea trial were carried out to study the integrated performance of the hydrothermal fluid sampler.Firstly,all of the four sets of hydraulically actuated samplers and two sets of time-serial samplers were tested in the high pressure vessel, which indicated that the samplers have good bidirectional sealing performance and high reliability.Secondly,four sets of hydraulically actuated samplers have been successfully deployed at four different hydrothermal vent areas along the Mid-Atlantic Ridge during sea trial.Fluid samples were successfully collected from hydrothermal vents with the highest depth and temperature of 3622m and 370℃,respectively.The analysis results of the fluid samples showed that the samplers have a good integrated performance to collect reasonable high-fidelity hydrothermal fluid samples.In summary,the successful development and sea trial of the hydrothermal fluid sampler indicated that the technologies of high-pressure bidirectional sealing,high temperature tolerance and corrosion resistance,valve's underwater actuating mechanism and the real-time temperature measuring technique studied in this dissertation are practical and reliable for applications in deep-sea hydrothermal fluid sampler.The study achievements also have wide application prospects in the related areas of high temperature and pressure sealing and water sampling.