氨水吸收器热质交换面积计算方法的探讨

发布时间：2018-03-27 20:26

本文选题：氨水吸收式制冷　切入点：降膜　出处：《东南大学》2015年硕士论文

【摘要】：氨水吸收式制冷循环能够有效利用废热,是一种环境友好的制冷方式。但其体积庞大,机组金属消耗量较多。其中,吸收器的传热面积占机组总传热面积比重较大,对机组的性能影响也较大。在吸收器设计计算时,面积的确定影响机组的金属量消耗和占地面积,也决定系统是否能够正常运行。因此吸收器的设计计算应引起足够的重视。目前的设计计算中,吸收器平均温差一般按纯换热过程用的对数平均温差公式确定,并未考虑吸收器质交换引起的附加换热量,本文在深入分析吸收器热质交换过程的基础上,结合对数平均温差公式,提出了修正温差公式,结合数值计算以及实验结果分析温差公式的合理性,并进行了相关修正。开展的工作主要包括以下几个部分：1.针对制冷手册中计算吸收器传热面积时采用的对数平均温差公式,结合吸收器热质传递分析,提出对数平均温差修正公式。将竖直管降膜吸收过程简化为二维模型,在微元段热量平衡公式中加入由于吸收传质带来的热流通量,通过系列假设和简化,得出与对数平均温差公式形式接近的温差修正公式温差修正公式较对数平均温差公式多了一个系数C,C为待求量,与吸收过程的放热量,传热系数,溶液侧及冷却水侧的质量流量有关。2.单管式竖直管传热传质耦合吸收的理论分析。建立简化的物理模型,通过一系列假设,列出控制方程,并对所列方程组数值求解。根据求解结果分析溶液进口温度,冷却水温度,吸收压力,溶液浓度对液膜厚度,液膜浓度,降膜速度和液膜温度的影响。通过绘制不同影响因素下液膜厚度,浓度,速度和温度随管长的变换图像,得出结论：液膜温度,降膜速度随溶液进口温度的增大而增大,随冷却水进口温度的升高而升高,随稀溶液进口浓度的减小而减小,而膜厚,吸收终了浓度则相反；但吸收压力升高时,4个参数均对应增大。3.氨水降膜吸收实验研究。对已有的发生试验台作相应的改造,通过对冷却水侧水温的两次控制完成单管氨水降膜吸收实验。针对所做实验,取一定组数的实验数据进行分析。变化冷却水进口温度,稀溶液进口温度,稀溶液进口浓度及吸收压力这4参数,通过分析不同实验工况下稀溶液罐内温度T1、稀溶液进口温度T3、降膜终了浓溶液温度T4随时间的变化趋势发现,冷却水进口温度越低,稀溶液进口温度越低、初始稀溶液浓度越小、吸收压力越大,吸收越剧烈。4.数据分析整理,比较不同温差方法对吸收器设计的影响。结合对数平均温差方法,温差修正方法,数值计算方法以及实验数据,列出不同实验工况下,不同温差方法求得的平均温差及对应的吸收器面积,与实际的吸收器面积进行比较,指出修正温差方法相较于数值求解更方法为方便,而相较于对数平均温差方法能求得更接近于实际的吸收面积的结果。
[Abstract]:Ammonia-water absorption refrigeration cycle can utilize waste heat effectively and is a kind of environment-friendly refrigeration method. However, its volume is huge and the unit metal consumption is much. Among them, the heat transfer area of absorber accounts for a large proportion of the total heat transfer area of the unit. In the design and calculation of absorber, the determination of area affects the consumption of metal and the area of occupation of the unit. Therefore, the design and calculation of absorber should be paid more attention to. In the present design and calculation, the average temperature difference of absorber is generally determined by the logarithmic average temperature difference formula used in pure heat transfer process. The additional heat transfer caused by mass exchange of absorbers is not taken into account. Based on the in-depth analysis of the heat and mass exchange process of absorbers and the logarithmic average temperature difference formula, a modified formula of temperature difference is proposed in this paper. The rationality of the formula of temperature difference is analyzed with numerical calculation and experimental results. The work includes the following parts: 1. Aiming at the logarithmic average temperature difference formula used in calculating the heat transfer area of absorber in the refrigeration manual, Based on the analysis of heat and mass transfer of absorber, a correction formula of logarithmic average temperature difference is proposed. The absorption process of vertical tube falling film is simplified as a two-dimensional model, and the heat flux caused by absorption mass transfer is added to the heat balance formula of micro-element. Through a series of hypotheses and simplifications, it is concluded that the correction formula of temperature difference, which is close to the form of logarithmic mean temperature difference formula, has more coefficient C _ (C) than the logarithmic average temperature difference formula, and the coefficient of heat release and heat transfer in the absorption process. Theoretical analysis of heat and mass transfer coupling absorption of single tube vertical tube. A simplified physical model is established, and control equations are listed through a series of assumptions. According to the solution results, the inlet temperature, cooling water temperature, absorption pressure, solution concentration to the thickness of liquid film and the concentration of liquid film are analyzed. By drawing the transformation images of film thickness, concentration, velocity and temperature with the tube length, it is concluded that the film temperature and the falling film velocity increase with the increase of the inlet temperature of the solution. With the increase of inlet temperature of cooling water and the decrease of inlet concentration of dilute solution, the film thickness and the concentration at the end of absorption are opposite. However, when the absorption pressure is increased, the four parameters are all corresponding to increase .3.The experimental study of ammonia falling film absorption. Through twice controlling the water temperature of cooling water side, the experiment of falling film absorption of single tube ammonia water is completed. According to the experiment, the experimental data of a certain number of groups are analyzed. The inlet temperature of cooling water and the inlet temperature of dilute solution are changed. By analyzing the inlet concentration and absorption pressure of dilute solution, the temperature of dilute solution in tank T _ 1, the inlet temperature of dilute solution T _ 3, and the temperature of concentration solution T _ 4 at the end of falling film with time, it is found that the lower the inlet temperature of cooling water is, the lower the inlet temperature is. The lower the inlet temperature of dilute solution, the smaller the initial dilute solution concentration, the greater the absorption pressure, the more intense the absorption. 4. Data analysis, comparison of the influence of different temperature difference methods on the design of absorber, combining with logarithmic mean temperature difference method, temperature difference correction method, The average temperature difference and the corresponding absorber area obtained by different temperature difference methods under different experimental conditions are compared with the actual absorber area. It is pointed out that the modified temperature difference method is more convenient than the numerical method, and compared with the logarithmic mean temperature difference method, the results of the modified temperature difference method can be obtained more closely to the actual absorption area.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB616

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