Study On Water Temperature Prediction Of Rectangular Aqueduct In Winter

Uneven distribution of water resources in the region in our country,and in order to make the optimized allocation of water resources,the country has built a batch of long distance water diversion project, the aqueduct as an indispensable water building.Because of the demand of wate,aqueduct sometimes needs to be transported in winter.In Northwest China,the winter temperature is low,the daily temperature difference and the annual temperature difference are larger,and the water is easy to freeze when the aqueduct is used to carry water,which makes the whole water delivery process blocked,and has a negative influence on the water conveyance and the structural safety. The water temperature in the cold area plays an important role in the frost heaving damage and the safe operation of the structure.However,the research on the heat loss of the water body and the water temperature in the aqueduct under the condition of low temperature is very low.In this paper,Yindaruqin project of Zhuanglang river aqueduct as an example,change of water temperature and water on the aqueduct under low temperature condition in winter when the water cooling,and the surface insulation calculation,the research results can provide reference for similar engineering.In this paper,the three-dimensional numerical model of aqueduct is established by using.the finite element software of ANSYS/FLOTEAN CFD,and the temperature field distribution,velocity distribution and the heat flux of the fluid passing through the aqueduct are calculated.According to the theoretical analysis of the steady heat transfer process,the heat conduction differential equation and the Newton cooling formula are used to calculate the variation of water temperature and heat loss.Through the calculation of the fluid under different working conditions,the calculation results of surface water heat loss:aqueduct temperature drop and main influence factors of aqueduct length,fluid entrance velocity,atmospheric temperature,and there is no insulation measures.Water temperature reduction is mainly due to the fluid temperature is not consistent with the outside air temperature,resulting in temperature difference.The convection heat transfer between the fluid and the cold air,and the heat conduction through the aqueduct,the greater the temperature difference between the fluid and the cold ai,the faster the heat transfer,the more the heat loss,the greater the water temperature reduction. With the increase of the length of the aqueduct,the heat loss and the temperature decrease,the water cooling rate and the temperature drop rate become smaller. Under the condition of the same ambient temperature,the smaller the inlet velocity of water is,the more time it stays at the same length,and the corresponding increase of heat loss. In the study of several conditions,the lowest water temperature to 0.561 degrees,close to freezing point of 0 degrees ?.Therefore,it is necessary to take heat preservation measures on the outside surface of the aqueduct to prevent the water temperature decrease too much.Comparison and analysis of the insulation board with polyurethane foam and polystyrene foam and two kinds of material in the outer surface of the groove respectively by 2cm,5cm, 7cm of the thickness of the insulation heat flux. By simple comparison shows that the thermal insulation effect of the same material increases with the thickness of the insulation layer is thick,heat flux is small,heat preservation effect;thermal insulation material with the same thickness,polyurethane insulation board insulation effect is better than that of polystyrene insulation board.Then choose the best insulation measures. Taking into account the economy,the use of 5cm thickness of polyurethane polyurethane insulation board.The insulation layer can effectively prevent the heat exchange and convection heat transfer between the water and the atmosphere, and the heat loss of the fluid and the water temperature decrease obviously.By comparing and analyzing the water temperature and heat dissipation of the rectangular aqueduct in winter,when there are no external insulation measures,a series of conclusions are obtained,which provides a valuable reference for similar projects.