Study On The Prediction Of Icing Depth Of Water And Temperature Effect Of Large Long Aqueduct In Winter

As is known to all that aqueduct is a kind of long-distance water conveyance structure.Due to the cold weather in northwest China in winter,the water temperature of aqueduct will drop during the process of water conveyance resulting in ice flowers and cracks in the tank,which is not conducive to the safe water conveyance of aqueduct.With the rise of a series of water diversion projects,research on the safety of aqueduct water diversion has gradually entered the public view.However,the prediction and analysis of freezing water depth in the process of water transport in winter is not profound enough.Therefore,the passage bases on the Zhuanglang river large long aqueduct project,research on the critical freezing water depth under different temperature and the temperature effect under the most adverse working condition,so as to meet the requirements of safety of aqueduct water diversion by controlling the depth of water in the actual water transfer process.Based on the theoretical analysis of steady state heat transfer process in ANSYS FLORTAN software to establish three-dimensional model of the aqueduct,and reference the heat conduction differential equation,Newton cooling formula and Manning's formula.The model and theoretical calculation are combined to analyze the fluid-solid thermal coupling field,so as to study the relationship between water temperature drop and water depth change under different ambient temperature as well as the temperature effect under extreme cold temperature.Finally,the passage analyses on water depth prediction and temperature effect under different ambient temperatures with and without insulation board,and the following conclusions can be drawn.(1)The elements that affect the freezing time of the water in the tank include the inlet water temperature,the ambient temperature,the water depth and the presence or absence of insulation measures.The temperature difference between the water in the tank and the gas outside is the essential reason for the decrease of water temperature.The heat loss of water in aqueduct can be divided into three parts,they are convection heat transfer between water and air,convection heat transfer between air and aqueduct wall and heat transfer of water along the aqueduct body.(2)In the case of the same ambient temperature,the lower the water depth is,the slower the corresponding velocity of the inlet water will be,the more time of the water to flow through the aqueduct will take,the more heat loss will consume,and the lower the outlet temperature will be.The higher the water depth is,the faster the corresponding velocity of the inlet water will be,the less time of the water to flow through the aqueduct will take,the less heat loss will consume,and the lower the watert temperature will drop.When the ambient temperature drops gradually,the greater the heat of the water will loss,the more the water temperature will drops,and the lower the temperature of the outlet water temperature will be.The tank water temperature decreases to low to below freezing point flowing through the aqueduct when the outside temperature reaches to 25? belw zero,that ice slag peoduce and rub and crash tank structure,which can not guarantee safety of water delivery.(3)The water temperature drop will decrease while the temperature and water depth increase.The water temperature drop will decrease by about 7 times when the water depth increases by 4.2 times,the external temperature drops by 5 times when the water temperature drops by about 3.3 times,indicating that the water temperature drop is sensitive to the depth change.Therefore,a relatively high flow should be maintained in the tank in order to ensure that the water in the tank does not freeze in winter.(4)The ambient temperature is 25?,that is to say the extreme cold temperature,while the water depth is less than one meter,the export water temperature decreases to below freezing point and ice flowers will generate which is positive to the safe of the aqueduct water.The measures of covering the top or attached with a thermal insulation board are taking to reduce heat loss,so as to ensure that aqueduct water temperature will not fall below zero even if it is the extreme cold temperatures.(5)The range of fluid heat loss and water temperature reduction is obviously reduced when the top of the aqueduct is covered or an insulation board is attached.Compared with no insulation measures,the heat loss and water temperature drop reduces about 0.34 times when the top of the aqueduct is covered.Compared with no insulation measures,the heat loss and water temperature drop reduces about 0.16 times.Compared with no insulation measures,the heat loss and water temperature drop reduces about 0.47 times when both measures are used simultaneously.The water temperature drops the least when the heat preservation board is added.(6)The aqueduct internal wall temperature is equals to the water temperature,the outer wall of aqueduct temperature is close to the atmospheric temperature,the temperature difference of internal and external will produce temperature stress.The temperature stress leads to the structure deformation and surface cracks which has adverse effects to the tank durability and service life.The passage should study the quantitative value of the temperature effect.Under extreme cold temperature,the temperature stress on the aqueduct wall surface is 5.14 Mpa.Therefore,the prestress is applied in advance to prevent the temperature stress in order to ensure the safety of the tank structure.