Research On Development And Distribution Law Of Temperature Field Of Underwater Artificial Freezing Device

Given certain feasible traditional schemes for river dredging are conducted in China,the effect is limited under certain special circumstances or conditions.Underwater artificial freezing method is a newly-invented idea for river dredging and salvaging.Little research has been done on the application of the method.In the paper,real overseas cases of underwater small-scale fixed-point dredging and salvage with artificial freezing method and the patent of two domestic underwater artificial freezing devices are studied.Numerical modeling for the temperature field of the freezing device is conducted by ADINA finite element analysis software to analyze the law of development and regularities of distribution of temperature field of the soil layer under the action of the device,explore the influence law of impact factors on the final freezing effect,verify the correctness of the law with the temperature field theory in a drive to provide references for practical application.The main conclusions can be drawn as follows:(1)Although heat transfer in the soil layer during the freezing process by a frozen plate is non-steady heat conduction,the process is cruelly slow.When the temperature is between-200 and-10℃,within the scope of a short distance to the normal direction of the freezing plate(e.g.,0.5～1.0m,1.0～1.5m,etc.),the distance-temperature curve is approximately straight.The shorter the distance range is,the straighter the line is.The closer the area is to the board,the more obvious the phenomenon is.The heat transfer in the frozen soil curtain within this range can be regarded as one-dimensional steady-state heat conduction in a short period of time(e,g.,1h).(2)When the nature of the soil is constant,under the same salt water cooling plan,the final freezing depth depends solely on the freezing time.The shape and size of the plate can only affect the horizontal freezing range rather than the freezing depth.(3)When the freezing plate is at any temperature,and at any time,the ratio of the distance between any two isotherms and the freezing plate in the frozen soil curtain is equal to the ratio of the temperature difference between the isotherm and the freezing plate,namely:The distance between the isotherm a and the freezing plate The distance between the isotherm b and the freezing plate The temperature difference between the isotherm a and the freezing plate The temperature difference between the isotherm b and the freezing plateFrom this formula,a simple method for predicting the maximum freezing depth in real time using the artificial freezing plate for underwater freezing is obtained:the temperature T1 and the distance x1 in the place near the vertical dimension of the plate are measured to determine the vertical distance x2 from maximum frozen area covered by isotherm T2 to the plate.The maximum freezing depth χ2=x1·T2-T3/T1-T3,among which,T3 is the temperature of the artificial freezing plate.(4)When the final brine temperature is-10℃～-50℃,the frozen soil curtain is significantly affected by the final temperature.Adjusting the final temperature of the brine cooling plan within this temperature range can effectively regulate the freezing depth;In actual construction,the best economical way is to keep the final brine water temperature at-10℃～-50℃.(5)For the artificial freezing device Ⅱ,the freezing plate on the top affects the freezing depth in the vertical direction,but the influence range is limited.The temperature field in the range of about 1.5 m is greatly affected while the impact range by the long freezing tube is approximately 4.5m.(6)The maximum freezing range of the four artificial freezing devices II is small.The longitudinal freezing depth of the shortest lm-short pipe freezing device is only 0.7 m shorter than that of the 4 m-long pipe freezing device.In the short pipe artificial freezing device,The point where the short tube is radially downward by lm is minimally affected by the longitudinal direction of the short tube.The main influence comes from the lateral heat conduction through the surrounding long tube.(7)When the maximum thickness of the frozen soil curtain is strictly required,the 4m long tube freezing device has the best freezing effect to meet the dredging requirements.When the thickness of the frozen soil curtain is not critically requested,the four kinds of freezing tube devices realize favorable freezing effect,among which the 1m short freezing tube artificial freezing device has the lowest manufacturing cost and the best economic benefit.