本文關(guān)鍵詞：高聚物對封閉方腔熱對流的流動與傳熱特性影響數(shù)值模擬　出處：《哈爾濱工業(yè)大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 高聚物 方腔自然對流 RB熱對流 Cross方程

【摘要】：在流體熱對流流動中,尤其當(dāng)流體處在湍流時,其流動情況比較復(fù)雜,此時對于熱對流中的流動特性和傳熱特性而言,因流體自身的復(fù)雜性而使其較為復(fù)雜。在此基礎(chǔ)上,在流體中添加一定量的高聚物后,高聚物可以改變該溶液的粘彈性特性,使得其流動特性和傳熱特性因此而發(fā)生變化。為了研究高聚物添加對熱對流流動和傳熱特性的影響,在本文中,選取自然對流和Rayleigh-Bénard(RB)兩種具有代表性的熱對流,分別對高聚物添加造成的影響進行研究與分析。首先,為了驗證高聚物添加后,Cross方程可以準(zhǔn)確的表示高聚物溶液的物性參數(shù),通過實驗測量了濃度為200ppm、500ppm、1000ppm高聚物溶液的粘度隨剪切速率變化的曲線;通過資料查得不同濃度高聚物的松弛時間?、零剪切粘度0?以及冪指數(shù)n,將其代入Cross方程中,取與實驗數(shù)據(jù)相同的剪切速率,根據(jù)公式得出對應(yīng)的粘度值。將相同濃度下實驗測得的粘度隨剪切速率變化的曲線與Cross方程得出的粘度與剪切速率變化曲線相比較。其次,本文在建立相應(yīng)不同熱對流的幾何模型后,對不同Ra數(shù)下的數(shù)值模型分別進行網(wǎng)絡(luò)無關(guān)性驗證來確保數(shù)值模擬計算的可行性與精確性,在得到不同工況下對應(yīng)的最佳的網(wǎng)格后,基于CFD模擬,分別模擬研究在不同Ra數(shù)、不同介質(zhì)下的流體流動和傳熱特性變化,綜合其速度變化以及溫度方面的變化,探討高聚物添加對熱對流的影響。再次,在封閉方腔自然對流中,當(dāng)Ra數(shù)逐漸增大時,對于任何介質(zhì)而言,流體的流動速度和傳熱能力都將增加,且增加幅度隨著Ra數(shù)的增加而變大。而高聚物的添加對方腔自然對流的流動和傳熱有著較大的影響,高聚物的添加降低了原流體流動的阻力而使得流體的整體速度增加,使得冷熱壁面處的速度邊界層變薄;同樣數(shù)值模擬結(jié)果顯示在高聚物添加后熱壁面處的Nu數(shù)變小,壁面處的溫度邊界層增厚,流體的傳熱減弱,根據(jù)不同Ra數(shù)下的Nu數(shù)得出不同介質(zhì)下這兩者之間的關(guān)系。最后,對于RB熱對流而言,高聚物添加對流體產(chǎn)生的影響與方腔自然對流結(jié)果一致,不同的是RB熱對流較方腔自然對流復(fù)雜。對RB熱對流整體而言,添加高聚物后,剪切特性占據(jù)主要地位,使得流體剪切變稀,溶液的流動阻力減弱,速度增加。同時,雖然速度整體增加,但是在流體傳熱方向上的速度值反而減小,在一定程度上抑制了溫度的傳遞,流體熱輸運能力降低,傳熱降低。同樣的,在同一Ra數(shù)下,高聚物添加使得RB熱對流壁面處的速度邊界層變薄、溫度邊界層增厚。
[Abstract]:In the case of thermal convection, especially when the fluid is in turbulent flow, the flow is complicated, and the flow characteristics and heat transfer characteristics in the thermal convection are discussed. On the basis of the complexity of the fluid, the viscoelastic properties of the solution can be changed by adding a certain amount of polymer to the fluid. In order to study the effect of polymer addition on the thermal convection flow and heat transfer characteristics, in this paper. Two kinds of representative thermal convection, natural convection and Rayleigh-B 茅 nardberg, were selected to study and analyze the effect of polymer addition. In order to verify that the cross equation can accurately represent the physical properties of polymer solution, the concentration of 200 ppm ~ 500ppm was measured experimentally. The curve of viscosity change with shear rate of 1000ppm polymer solution; The relaxation time of polymers with different concentrations was obtained by the data. , zero shear viscosity 0? The power exponent n is substituted into the Cross equation and the shear rate is the same as the experimental data. According to the formula, the corresponding viscosity value is obtained. The curve of viscosity changing with shear rate measured under the same concentration is compared with the curve of viscosity and shear rate obtained by Cross equation. Secondly. In order to ensure the feasibility and accuracy of the numerical simulation, the corresponding geometric models of different thermal convection are established in this paper, and the network independence of the numerical models under different Ra numbers is verified separately in order to ensure the feasibility and accuracy of the numerical simulation. After obtaining the best mesh under different working conditions, the fluid flow and heat transfer characteristics in different Ra numbers and different media were simulated based on CFD simulation. The influence of polymer addition on thermal convection is discussed by synthesizing the variation of velocity and temperature. Thirdly, in the closed square cavity, when the Ra number increases gradually, for any medium. The flow velocity and heat transfer capacity of the fluid will increase, and the amplitude of increase will increase with the increase of Ra number. The natural convection flow and heat transfer in the admixture of polymer have a great influence on the flow and heat transfer. The addition of polymer reduces the flow resistance of the original fluid and increases the overall velocity of the fluid, which makes the velocity boundary layer thinning at the cold and hot wall. The same numerical simulation results show that the Nu number at the hot wall becomes smaller, the temperature boundary layer at the wall becomes thicker and the heat transfer of the fluid decreases after the addition of polymer. According to the Nu number of different Ra numbers, the relationship between them is obtained in different media. Finally, for RB thermal convection, the effect of polymer addition on the fluid is consistent with the results of natural convection in square cavity. The RB thermal convection is more complex than the natural convection in the square cavity. For RB thermal convection as a whole, the shear characteristics play a major role after the addition of polymer, which makes the fluid shearing thinning and the flow resistance of the solution weakening. At the same time, although the velocity increases as a whole, the velocity value in the direction of heat transfer of the fluid decreases, to a certain extent, the transfer of temperature is restrained, the heat transfer capacity of the fluid decreases, and the heat transfer decreases. At the same Ra number, the addition of polymer makes the velocity boundary layer thinning and the temperature boundary layer thickening at the RB thermal convection wall.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TK124

【引證文獻(xiàn)】

相關(guān)會議論文 前1條

1 蘇耿輝;余佳佳;張錫文;何楓;;平板自然對流的溫度動態(tài)測量及分析[A];第九屆全國實驗流體力學(xué)學(xué)術(shù)會議論文集（上冊）[C];2013年

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本文編號：1436503