【摘要】：我國水資源在地域上分配不均勻,為了使水資源得到優(yōu)化配置,國家已興建了一批長距離引水工程,而渡槽是一種常見的輸水結(jié)構(gòu)。由于用水需求,渡槽有時候需要冬季輸水。西北地區(qū)冬季氣溫偏低,日溫差和年溫差較大,采用渡槽輸水時水易結(jié)冰,使整個輸水過程受阻,對保證輸水和結(jié)構(gòu)安全有不利的影響。寒冷地區(qū)輸水水溫對于結(jié)構(gòu)的凍脹破壞和安全運(yùn)行起到了至關(guān)重要的作用,而現(xiàn)在關(guān)于低溫工況下渡槽中水體的熱量損失與水溫變幅的研究甚少。本文以引大入秦工程莊浪河渡槽為例,研究渡槽在冬季低溫工況下輸水時的水溫變化及水的散熱,并進(jìn)行表面保溫計(jì)算,研究成果可為類同的工程提供參考。本文使用流固耦合原理,應(yīng)用ANSYS/FLOTEAN CFD計(jì)算軟件建立了渡槽的空間模型,計(jì)算出渡槽的溫度場分布、流速分布以及流體通過渡槽的熱通量。根據(jù)穩(wěn)態(tài)傳熱過程進(jìn)行理論分析,并引用導(dǎo)熱微分方程和牛頓冷卻公式進(jìn)行計(jì)算,采用模型和理論計(jì)算相結(jié)合的方式,計(jì)算出水溫的變化和熱量損失。通過對于不同工況下流體的計(jì)算,結(jié)果表明:渡槽水體的熱量損失及溫降的主要影響因素有渡槽的長度、流體的入口速度、大氣溫度、以及有無保溫措施。水溫降低主要是由于流體溫度與外界大氣溫度不一致,產(chǎn)生溫差導(dǎo)致的。流體與冷空氣進(jìn)行進(jìn)行對流換熱,并且通過渡槽進(jìn)行熱傳導(dǎo),流體與冷空氣的溫差越大,散熱速率更快,熱量損失更多,水溫降低幅度更大。隨著渡槽長度增加,水的熱量損失與溫度降低越多,水的散熱速率與溫降速率卻逐漸變小。外界環(huán)境溫度相同的情況下,水的入口流速越小,在同一長度處滯留的的時間越多,熱量損失相應(yīng)的增多。在所研究的幾種工況下,水溫最低降至0.561℃,接近于冰點(diǎn)0℃。因此應(yīng)該對渡槽采取相應(yīng)的保溫措施來防止水溫降低幅度過大。對比分析了在槽身外表面附有聚氨酯泡沫塑料和聚苯乙烯泡沫塑料兩種材料的保溫板分別以2cm、5cm、7cm的厚度進(jìn)行保溫時的熱通量。通過簡單的對比,表明:同種材質(zhì)的保溫板保溫效果隨其厚度的增加而增大,保溫板越厚,熱通量越小,保溫效果就越好;相同厚度的保溫板,聚氨酯保溫板的保溫效果優(yōu)于聚苯乙烯保溫板。進(jìn)而選出最優(yōu)的保溫措施�？紤]到經(jīng)濟(jì)性,莊浪河渡槽應(yīng)使用5cm厚度的聚氨酯保溫板。渡槽附有保溫層可有效阻止水體與冷空氣的熱交換和對流換熱,流體熱量損失和水溫降低幅度明顯小。
[Abstract]:In order to optimize the allocation of water resources, a number of long-distance water diversion projects have been built in China, and aqueduct is a common water conveyance structure. Because of water demand, aqueducts sometimes need to carry water in winter. The winter temperature in Northwest China is low, the daily temperature difference and annual temperature difference are big, the water is easy to freeze when using aqueduct to carry water, so the whole water conveyance process is blocked, which has adverse effect on ensuring the water conveyance and structural safety. The water temperature in cold regions plays an important role in the frost heaving damage and safe operation of the structure, but there is little research on the heat loss and water temperature variation in the aqueduct under low temperature conditions. This paper takes Zhuanglong River aqueduct as an example to study the variation of water temperature and the heat dissipation of the aqueduct under the condition of low temperature in winter, and to calculate the surface heat preservation. The research results can provide reference for similar projects. Using the principle of fluid-solid coupling, the spatial model of aqueduct is established by using ANSYS/FLOTEAN CFD software. The distribution of temperature field, velocity distribution and heat flux of fluid passing through the aqueduct are calculated. According to the steady-state heat transfer process, the heat conduction differential equation and Newtonian cooling formula are used to calculate the change of water temperature and heat loss. The results show that the main factors affecting the heat loss and temperature drop of the aqueduct are the length of the aqueduct, the inlet velocity of the fluid, the atmospheric temperature and the insulation measures. The decrease of water temperature is mainly due to the temperature difference between fluid temperature and ambient temperature. The temperature difference between the fluid and the cold air is larger, the heat dissipation rate is faster, the heat loss is more, and the temperature of water is decreased more greatly through the aqueduct heat transfer and convection heat transfer between the fluid and the cold air, and through the aqueduct, the temperature difference between the fluid and the cold air is larger. With the length of aqueduct increasing, the heat loss and temperature of water decrease more, but the heat dissipation rate and temperature drop rate of water become smaller. Under the same ambient temperature, the smaller the inlet velocity of water is, the longer the water stays at the same length, and the more the loss of heat is. Under several conditions studied, the lowest water temperature is 0.561 鈩，

本文編號：2217770