| Understanding the sediments is the base to know the vicissitudes and predict the future changes of the environment. As the host body of surface materials transported in basins, lakes has bad mobility. For this reason, environmental matters in lakes are stable relatively. And the hierarchical structures of sediments contain a great deal of environmental information. Therefore, sediment becomes the research hotspot of the natural environment change records. Due to the existing sampler is usually destroyed the original sequence of sediments, it resulted in the accuracy of the deposition period is generally low.The shortcomings of the existing sediment equipments are summarized and the structures of the sediment freeze corer inlaid with spiral tube are designed in detail based on the Function-Principle-Structure model in this article. And, we make the prototype. Numerical simulation about the freezing law of the sampler is carried out based on Fluent. The basic performance of the sampler is tested after the comparison between indoor experiment and numerical simulation. And the outdoor sampling operation scheme is formulated.The basic structure parameters are given. The length of the sampling tube is 1000 mm and its inside diameter is 137 mm. The width of the cold source is 250 mm. The distance between the lower boundary of the cold source and the sampling orifice is 200 mm. The sampling tube is made of 201 stainless steel. The spiral freezing pipe is made of brass and the waterproof casing is made of UPVC water supply pipe.Numerical simulation about the freezing law of the sampler is carried out. The result shows that the shape of temperature distribution near the wall of the tube is bow while the shape in the middle is “H”. And the shape of the phase transition sample is bow too. The position of theoretical closing point and the relationship curve between axial closing height and time are obtained. We compared the results between indoor experiment and numerical simulation and get four periods of the theoretical closing point during the freezing process. They are “uniform period” “plateau” “drop period” and “deceleration period”. The proportion of each period is 22.2%, 44.4%, 11.1% and 22.2% in turn and “plateau” controls the whole refrigeration cycle.The sediment with clear boundary and the overlying water are acquired from the indoor simulation lake sediment sampling test and it is proved that freezing sampling is feasible. The test lasts 8 hours and the initial temperature of the water is 12.7℃. The thickness of the sediment is 164.8mm, the thickness of overlying water is 151.4mm and the diameter of the sample is 137 mm. The relationship experiment of moisture content, freezing expansion rate and melting shrinkage rate is conducted and the outdoor sampling operation scheme is given in this paper. The correlation coefficient of water content and freezing expansion rate is 0.81. The correlation coefficient of water content and melting shrinkage rate is 0.97. The freezing expansion rate of sediment samplers is less than 5% while the melting shrinkage rate ranges from 10% to 40% totally. |
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