基于正交试验的扭转流换热器壳程结构优化

建立扭转流管壳式换热器周期性全截面数值计算模型,采用对比实验验证了数值模拟方法及其结果的可靠性。影响扭转流换热器壳程流体换热和流阻性能的主要因素有相邻两组类梯形导流板间距、导流板宽度、导流板倾斜角度以及每组导流板的数量。设计正交试验,综合研究各参数对扭转流换热器壳程流体传热系数、压降及综合性能的影响,并对影响显著的结构参数进行了优化。结果表明,在研究参数范围内,影响扭转流换热器壳程流体综合性能的主次顺序为:相邻两组导流板间距>每组导流板数量>导流板倾斜角度>导流板宽度。综合性能最优的结构参数组合是相邻两组导流板间距为100mm、每组导流板个数为2、导流板倾斜角度为52.5°、导流板宽度为100mm,综合性能最高为114.9。研究结果为管壳式换热器壳程结构参数进行多目标优化提供了一种新方法,具有一定的指导意义。

扭转流换热器结构参数对流场和温度场的影响

建立扭转流换热器和弓形折流板换热器两种周期性全截面模型,采用计算流体力学方法对两种换热器的传热系数、阻力、综合性能进行了数值研究。分析了扭转流换热器管束支撑物类梯形导流板结构参数对换热器传热和流阻性能的影响。结果表明:导流板倾角和相邻两组导流板间距对扭转流换热器传热性能的影响显著,导流板宽度的影响次之,每组导流板的数量的影响较小。扭转流换热器优化结构,压降较弓形折流板换热器降低42.5%~46.9%,综合性能提高7.2%~14.1%。研究结果为管壳式换热器结构优化和强化传热提供了新方案。

2类组合数学问题的算法形式化推导

组合数学问题算法的研究是计算机科学的重要研究内容,但在许多相关文献中,许多组合数学问题的算法只是经过简单分析得到,并未给出算法程序的详细设计过程,导致读者无法理解算法本质,更无法保证算法程序的正确性.该文在以组合数学中连续子序列最大乘积和第2类斯特林数变形问题为例的基础上,通过形式化描述问题的程序规约,使用规约变换规则,对程序规约进行一系列等价变换,获得问题求解序列的递推式,并以此为基础得到问题求解的算法程序,清晰地展示了从问题的需求到算法程序的详细推导过程.通过对相关组合数学问题的进一步深入研究,提炼了2类组合数学问题的求解策略,为提高组合数学问题算法程序的正确性提供了有效途径.

不动产存量数据清理整合重难点的分析与探讨

自2015年起全国各地陆续正式启动不动产统一登记,并开展了不动产存量数据清理整合工作。不动产存量数据清理整合项目实施过程中,会遇到基础资料薄弱、资料来源众多、数据体量大、登记业务复杂、与日常业务不协同等各种各样的问题。基于此,结合多地实际工作情况,针对最典型的几种重难点问题进行了分析,提出了有效可行的解决办法。

Characteristics of Fluid Flow and Heat Transfer in the Shell Side of the Trapezoidal-like Tilted Baffles Heat Exchanger

Periodic whole cross-section computation models are established for segmental baffle heat exchanger, shutter baffle heat exchanger, and trapezoid-like tilted baffle heat exchanger. The reliability of models is verified by comparing the simulated results to the results obtained from the Bell-Delaware method. Due to the orthogonal assembly of the baffles, the shell side fluid shows the twisty flow of trapezoid-like tilted baffle heat exchanger. The essential mechanism on disturbing flow and heat transfer enhancement is revealed by defining the non-dimensional factor η of the shell side fluid flow direction of heat exchanger and the field synergy principle. The results show that at the same Reynolds number, the shell side fluid convection heat transfer coefficient of trapezoid-like tilted baffle heat exchanger is 12.43%-24.33% and 6.71%-11.51% higher than those of segmental baffle heat exchanger and shutter baffle heat exchanger, respectively. The shell side fluid flow velocity field and the pressure gradient field of trapezoid-like tilted baffle heat exchanger and shutter baffle heat exchanger decreases compared with that of segmental baffle heat exchanger, so the shell side fluid flow resistance and pressure drop is increased; the shell side comprehensive performance of trapezoid-like tilted baffle heat exchanger is 5.85%-9.06% higher than that of segmental baffle heat exchanger, and 15.27%-23.28% higher than that of shutter baffle heat exchanger. In this study, a baffle structure with higher efficiency of the energy utilization for the heat exchanger is provided.

Selection of adsorbents for in-situ coupling technology of adsorptive desulfurization and biodesulfurization

In-situ coupling of adsorptive desulfurization and biodesulfurization is a new desulfurization technol- ogy for fossil oil. It has the merits of high-selectivity of biodesulfurization and high-rate of adsorptive desulfurization. It is carried out by assembling nano-adsorbents onto surfaces of microbial cells. In this work, In-situ coupling desulfurization technology of widely used desulfurization adsorbents of γ-Al2O3, Na-Y molecular sieves, and active carbon with Pseudomonas delafieldii R-8 were studied. Results show that Na-Y molecular sieves restrain the activity of R-8 cells and active carbon cannot desorb the sub- strate dibenzothiophene (DBT). Thus, they are not applicable to in-situ coupling desulfurization tech- nology. Gamma-Al2O3 can adsorb DBT from oil phase quickly, and then desorb it and transfer it to R-8 cells for biodegradation, thus increasing desulfurization rate. It is also found that nano-sized γ-Al2O3 increases desulfurization rate more than regular-sized γ-Al2O3. Therefore, nano- γ-Al2O3 is regarded as the better adsorbent for this in-situ coupling desulfurization technology.

Heat Transfer and Flow Resistance Characteristics of Helical Baffle Heat Exchangers with Twisted Oval Tube

To overcome the defect of the significant increase in pressure drop when the heat transfer performance of helical baffle heat exchanger is improved,a novel helical baffle heat exchanger with twisted oval tube is proposed.Numerical simulation was done to exhibit the shell side heat transfer and flow characteristics with CFD software Fluent.The field synergy principle was used to evaluate the shell side performance.The results show that the flow velocity distribution on the shell side of the spiral baffle heat exchanger is more uniform and the velocity near the tube wall increases in the range of research parameters,as the circular tube is replaced by a twisted elliptical tube with the same perimeter length.Moreover,the helical baffle heat exchanger with twisted oval tube has better field synergy of velocity and temperature gradient,velocity and pressure gradient.The helical baffle heat exchanger with helix angle of 15°has better performance than that of circular tube,and its heat transfer coefficient is improved about 3.3%and pressure drop is reduced by 17.1%–19.1%.Hence,the comprehensive heat transfer performance is improved by 21.5%–22.5%.When the helix angle is 20°,the comprehensive heat transfer performance is increased by 16.1%–18.0%with heat transfer coefficient improvement of 3.6%and pressure drop reduction of 13.9%–16.5%.