Investigation of turbulent convective heat transfer and pressure drop of TiO2/water nanofluid in circular tube

Turbulent heat transfer behavior of titanium dioxide/water nanofluid in a circular pipe was investigated experimentally where the volume fraction of nanoparticles in the base fluid was less than 0.25%. The experimental measurements have been carried out in the fully-developed turbulent regime for various volumetric concentrations. The results indicated that addition of small amounts of nanoparticles to the base fluid augmented heat transfer remarkably. There was no much effect on heat transfer enhancement with increasing the volume fraction of nanoparticles. The measurements also showed that the pressure drop of nanofluid was slightly higher than that of the base fluid and increased with increasing the volume concentration. In this paper, experimental results have been compared with the existing correlations for nanofluid convective heat transfer coefficient in turbulent regime. Finally, a new correlation of the Nusselt number will be presented using the results of the experiments with titanium dioxide nanoparticles dispersed in water.     

钝体燃烧器湍流预混燃烧的数值模拟

采用湍流火焰封闭燃烧模型(TFC)模拟了钝体燃烧器的湍流预混燃烧,比较了基于火焰褶皱率和湍流燃烧速度2种源项解法对钝体预混燃烧的预测,对3个不同湍流燃烧速度表达式模拟的性能进行了比较,采用粒子成像测速技术(PIV)测量了燃烧器中心射流出口的速度分布,并将其作为边界条件代入计算.结果表明:不同湍流燃烧速度公式的计算结果在火焰刷厚度、位置及火焰前锋位置方面存在较大差别;Gulder公式的计算结果最接近试验数据,火焰刷厚度与试验结果吻合较好,但火焰刷位置与试验结果差别较大;Dinkelacker的火焰褶皱率模型主要模拟燃烧器在高压条件下的燃烧,在运行压力接近标准大气压的情况下,计算结果与试验值存在较大误差.     

利用进气反吹缸内燃烧再生的柴油机微粒过滤器

开发了一种以耐高温滤袋为过滤元件的柴油机排气微粒过滤器系统。采用相同的两个滤袋,一个用于过滤柴油机排气中的微粒,把微粒沉积在滤袋的外表面,另一个利用自然进气流反方向把已沉积在滤袋外表面的微粒吹掉,使微粒随进气流再回到气缸内,在燃烧室中燃烧,达到袋滤器再生的目的。通过系统中各阀门的开关保证二个滤袋在规定的时间间隔按"过滤"和"再生"模式轮换工作。所开发的系统在一台单缸柴油机上进行了验证性试验。结果表明,袋滤器能保证90%的过滤效率。在过滤时间和再生时间相等的稳定工况下,可保证袋滤器的阻力不超过允许值。当再生间隔为10 min时,维持最大过滤阻力为13.3 kPa。这表明进气过程不仅能把滤袋捕集的微粒重新吸回气缸中,而且微粒能在燃烧室中烧掉,使滤袋不需辅助手段自行再生。     

加热炉采用蓄热式燃烧技术的可行性分析

以某钢厂加热炉为例,分析了加热炉采用蓄热式燃烧技术的适用性,提出了加热炉蓄热式改造的基本前提.     

A computational study and correlation of premixed isooctane–air laminar reaction front properties under spark ignited and spark assisted compression ignition engine conditions

To address the need for reliable premixed laminar burning velocity and thickness information within the spark assisted compression ignition (SACI) combustion regime, a large dataset of simulated reaction fronts has been generated in this work. A transient one dimensional premixed laminar flame simulation was applied to isooctane–air mixtures using a 215 species chemical kinetic mechanism. The simulation was exercised over fuel–air equivalence ratios, unburned gas temperatures and pressures ranging from 0.1 to 1.0, 298 to 1000 K and 1 to 250 bar, respectively, a range that extends beyond that of previous researchers. Steady reaction fronts with burning velocities in excess of 5 cm/s could not be established under all of these conditions, especially when burned gas temperatures were below 1500 K and/or when characteristic reaction front times were on the order of the unburned gas ignition delay. Steady premixed laminar burning velocities were correlated using a modified two-equation form based upon the asymptotic structure of a laminar flame, which produced an average error of 2.5% between the simulated and correlated laminar burning velocities, with a standard deviation of 3.0%. Additional correlations were constructed for reaction front thickness and adiabatic flame temperature. The resulting premixed laminar burning velocity correlation showed good agreement with experiments and existing correlations within the spark-ignited (SI) regime. Analysis of the simulated characteristic reaction front times and ignition delays suggests that homogeneous SACI combustion is most useful under medium and high load operating conditions.     

Heat transfer in helical channels with two-sided heating in gas flow

Experimental results and analysis of heat transfer from convex and concave walls (surfaces) and average heat transfer from both walls to hydrodynamically and thermally stabilized air flow in rectangular helical channels with two-sided heating over a wide range of flow hydrodynamic (Re = 10³-2 × 10⁵) and geometric parameters (relative curvature D/h = 5-90 and relative width b/h = 2-20) are presented. It is established, that in case of two-sided heating the heat transfer (Nu numbers) from convex and concave walls increases up to 20% in comparison with one-sided heating. Average heat transfer in helical channels increases up to 50% for laminar-vortex flow regime, and up to 20% for turbulent flow regime in comparison with heat transfer in straight flat channel. Correlations are proposed for stabilized heat transfer for different flow regimes.     

阻燃抗紫外线复合功能窗帘交织物的性能

为探讨复合交织工艺对织物性能的影响,通过对试样织物的燃烧性能、紫外线防护系数(UPF)等测试,探讨了纬纱不同交织比对织物阻燃性能及抗紫外线性能的影响。研究表明3种功能纤维相互协调、优势互补,提高了织物的阻燃性能和抗紫外线性能。阻燃腈纶含量与织物阻燃性能呈非线性关系,阻燃腈纶与蜂窝抗紫外涤纶交织比为1∶1时,织物经纬向阻燃性能最好,且没有熔滴。蜂窝抗紫外线含量在15.69%~35.3%时,紫外线透过率与蜂窝抗紫外线涤纶含量呈负相关关系;蜂窝抗紫外线涤纶含量超过15.69%时,紫外线防护系数UPF与蜂窝抗紫外线涤纶含量呈非线性正相关关系,阻燃腈纶与蜂窝抗紫外线涤纶交织比为1∶3时,织物抗紫外性能最好。     

无烟煤在黑火药中的初步应用

文章介绍了无烟煤在工业黑火药中的应用。研究表明,无烟煤作为黑火药可燃剂组分可以在现有工艺设备不变的条件下完成制药和制索过程。无烟煤的引入可以大大地稳定导火索燃速,使用3%～5%的无烟煤制成全通过40目筛的黑火药,存储5个月后再用于制索,其燃速仅下降9 m/s,远低于现行导火索;温、湿度影响试验表明,相同条件下其燃速变化只是现行导火索的一半。     

一种新型高段延期药的研制及应用

文中采用一种新型缓燃剂,调整合适的配比,代替铅丹—硅系延期药中的硫化锑,组合成一种新型延期药剂。该药剂具有良好的化学安定性和长储稳定性,良好的耐高温高湿性和可靠的火焰感度,成本低廉,工艺简单,代替通常高段别使用的钨系延期药,有很高的实际应用价值。     

蓄热式加热炉燃烧系统的设计研究

主要针对蓄热式加热炉在设计和操作中出现的问题,对蓄热体形式、换向阀及换向控制系统、烧嘴布置方式、管道设计以及炉体结构等进行了优化设计,提出了改进措施,并对优化操作提出了建议。