The effects of the design of the cap of a natural gas-fired cooktop burner on flame stability

Results of an investigation aiming to study the effects of the burner cap design factors on flame stability are presented in this paper. Flame stability is an essential part of the operation of all domestic burners, including natural gas-fired cooktops. At high thermal inputs flame lifts are encountered above certain levels of primary aeration, whereas flashback only takes place at low thermal inputs, due to natural gas' low flame speed, above certain levels of primary aeration. In this work, flame lift limits were measured at 3·3 kW thermal input and the highest primary aeration above which flame lifts started to become visible was the stability limit at this thermal input. Around 60% primary aeration was desired to minimize pollutant emissions. Turndown tests were done at 40% primary aeration. The lowest thermal input below which the flame flashed back in less than 30 s was the turndown limit. A turndown ratio of at least 5 was aimed for (i.e. 0·67 kW or less would be desirable). The cap design factors studied were: the angle under the cap, the angle under the overlap, the shape under the cap, the size of the cap overlap, the height of overlap above the burner, cap material and cap thickness. The only feature of the burner head included in the tests was the angle at the top of the burner head, the part which comes into contact with the cap. The ‘Factorial Experimental Design’ method with statistical analysis was used. This enabled detection of interactions between factors as well as the effects of each single factor. The results show that combinations of factors which gave a balance between the performance at 3·3 kW and a satisfactory turndown ratio of 5 would be preferred. Those which gave very high turndown ratios were usually operable only at very low primary aerations (well below 60%) at 3·3 kW. Overall, the preferred combination of factors would be: 15° burner head top angle and angle under the cap, indent under the cap, 2·2 mm overlap with 15° angle at zero height above the burner, and thin aluminium caps. For the burner used in the experiments, such a combination should have no problem operating at up to 61% primary aeration at 3·3 kW and having a turndown ratio of 5·3. © 1998 John Wiley & Sons, Ltd.     

旋流燃烧器螺旋伸展长度对高温空气燃烧特性的影响

以工业炉的高温空气燃烧技术应用为背景,对一个同心式轴向旋流高温空气燃烧器单烧嘴燃烧室内的高温空气燃烧特性进行了数值研究.燃烧室尺寸为600 mm×600 mm×1000 mm,燃烧器烧嘴由位于中心的圆形直射流燃气喷口和其外围的同心轴向旋流高温预热空气射流喷口构成.湍流输运方程采用RSM模型,气相燃烧模型采用β函数的PD...     

Performance simulation of a low‐swirl burner for a Stirling engine

A new type of gas burner for Stirling engine that can recover adequate heat from exhaust gas was designed based on the plate heat exchanger and low‐swirl combustion technology, which consists of three components: a cyclone, a burner, and a circular plate heat exchanger. The circular plate heat exchanger tightly wound around the combustion chamber plays a high efficiency of heat recovery role. In consideration of the radial symmetry of the burner, a three‐dimensional numerical simulation was carried out by Ansys15. The velocity distribution, temperature distribution, and pressure distribution of the combustion gas were presented respectively. Strong backflow that came from the exhaust gas around the root of the flame in the combustion chamber and a vortex below the inlet of the exhaust gas channel were found, which were beneficial for the combustion and improving the uniformity of temperature distribution. Combustion behaviors of the burner under standard operating conditions were obtained, the highest temperature was about 2200 K in burner and the exhaust gas entered the plate heat exchanger at the temperature of 1375 K and exited at 464 K, with the waste heat recovery efficiency over 65.8%. And, the air‐fuel ratio and combustion power had negligible effect on the waste heat recovery efficiency.     

蓄热式烧嘴在大型加热炉上的应用

１前言 本文将介绍日本钢管公司开发并投入实用的节能效果显著的蓄热式烧嘴。该烧嘴采用紧凑型陶瓷蜂窝状蓄热体,与传统金属式蓄热体相比,预热空气的温度可从最高７００℃提高到１３００℃,其节能效果是不言而喻的。这种最新蓄热式烧嘴已实用于热轧连续加热炉和厚板分批加热炉,与传统烧嘴相比,节省燃料分别为２５％和４０％。该技术曾获１９９８年日本全国优秀节能技术进步奖。 作为加热炉热回收装置,向来采用金属式蓄热体。其缺点是由于受耐热温度的制约,热回收能力有限。加上传热面积不足而影响热回收能力,另外,燃烧空气配管长,…     

罩式退火炉加热罩改造

针对罩式退火炉加热罩存在助燃空气的换热效果不理想、煤气和空气混合不均匀、煤气燃烧不充分、煤气消耗高等系列问题,对换热器进行了改造,即将“单一箱型集中换热方式”改为“顶部环形对称换热方式”,空气预热温度由改造前的最高350℃增至430℃,换热效率提高明显.同时对烧嘴结构进行改进,在煤气管路内部靠近出口端处增设上、下空气导入支管,将原单一集中的煤气出口通道改为5路分散布置的煤气出口通道,使一次点火成功率由82％提高到91％,吨钢煤气消耗由104m3减少到81m3.     

CH4/air combustion in a microscale recirculating heat exchanger: Sizing design using the heat transfer approach

Microcombustors are microscale combustion devices that can be used to power microelectromechanical systems. Many combustor configurations are reported in the literature and, among them, combustion in a microscale recirculating heat exchanger is a feasible option. In this work, a simple, double-channel, recirculating heat exchanger is considered. The novelty of the present work lies in the heat transfer analysis approach to design a microcombustor. A combustor is designed using thermal resistance networks for a premixed fuel containing a methane–air mixture in stoichiometric ratio. The length of the combustor is designed based on the position of the combustion flame. Computational fluid dynamics is utilized to validate the theoretical results. The analysis is carried out for adiabatic and nonadiabatic conditions. The combustor lengths for adiabatic and nonadiabatic (ceramic) combustors vary from 39 to 242 mm and 49 to 276 mm, respectively, for variations in the mass flow rate of the premixed gases from 6 to 10 mg/s. A minimum limiting flow rate of 6 mg/s was identified. The average error in the maximum combustion gas temperatures between the theoretical and CFD results obtained in this work is 4.2%. The theoretical approach presented can be suitably applied to more complex geometries involving multichannels and variations in geometrical properties.     

工业炉发展与蓄热式燃烧器的应用

简要叙述了工业炉发展取得的成就,并指出,工业炉采用蓄热式燃烧器系统是20世纪工业炉技术进步的一项重大成就。重点介绍了俄罗斯和乌克兰等国在蓄热式燃烧器方面的研究成果及应用特色。     

高效节能型锻造炉的设计

介绍了安钢机构制造公司锻造的结构特点,应用ＳＬ型煤气平焰烧嘴型辐射对流换热器入烧混合煤气后的效果。     

Operational characteristics of a parallel jet MILD combustion burner system

This study describes the performance and stability characteristics of a parallel jet MILD (Moderate or Intense Low-oxygen Dilution) combustion burner system in a laboratory-scale furnace, in which the reactants and exhaust ports are all mounted on the same wall. Thermal field measurements are presented for cases with and without combustion air preheat, in addition to global temperature and emission measurements for a range of equivalence ratio, heat extraction, air preheat and fuel dilution levels. The present furnace/burner configuration proved to operate without the need for external air preheating, and achieved a high degree of temperature uniformity. Based on an analysis of the temperature distribution and emissions, PSR model predictions, and equilibrium calculations, the CO formation was found to be related to the mixing patterns and furnace temperature rather than reaction quenching by the heat exchanger. The critical equivalence ratio, or excess air level, which maintains low CO emissions is reported for different heat exchanger positions, and an optimum operating condition is identified. Results of CO and NO_x emissions, together with visual observations and a simplified two-dimensional analysis of the furnace aerodynamics, demonstrate that fuel jet momentum controls the stability of this multiple jet system. A stability diagram showing the threshold for stable operation is reported, which is not explained by previous stability criteria.     

太钢热连轧新增3#加热炉的优化设计

介绍了太钢1549mm热连轧新增3#步进梁式炉的必要性。由于在设计中采用了新技术和有效的节能降耗措施，采用了全自动控制，炉子冷却系统采用汽化冷却，其各项指标达到国际先进水平。经过一年的运行，使用效果很好，满足了生产工艺要求。     

蓄热式燃烧器的开发及在现代工业炉中的应用

综述了蓄热式燃烧器的研制开发过程，明确了该燃烧器的工作原理、结构特点及其在节能和减少环境污染方面的主要效果，重点介绍了国外典型的蓄热式燃烧器系统及其主要应用领域。     

螺旋翅片管换热器的优化设计

本文以试验为基础,对螺旋翅片管换热器的管束结构进行了优化设计,建立了数学模型。对建模 过程中有关目标函数确定、变量分析、约束条件等进行了讨论。得到了一定限制条件下的最佳结构参 数,可为电站锅炉的省煤器、空气预热器等设备的优化设计提供参考。     

燃烧模型在NexGen燃烧器出口流场模拟中的应用

通过求解三维定常雷诺平均的N-S方程,对NexGen燃烧器的出口流场进行数值模拟。首先,利用冷态流场的实验数据验证燃烧器几何模型和数值计算方法的有效性。然后,在计算中分别选取火焰面模型、混合分数PDF模型和涡耗散模型3种燃烧模型,比较燃烧模型对燃烧器出口流场模拟结果的影响。研究结果表明:燃烧模型对Nex Gen燃烧器出口的速度场、火焰形状和热流密度分布基本没有影响,但是对火焰长度、火焰最高温度、最高热流密度及校准面上温度分布和温度值有较大影响。相比火焰面模型和涡耗散模型,混合分数PDF模型的计算结果与实验结果吻合较好,可以为防火试验方案设计提供参考。     

地源热泵换热器可靠性设计方法研究

介绍地源热泵换热器传热模型和设计方法的研究现状,分析地源热泵换热器传热影响因素的随机特征,提出地源热泵换热器的可靠度分析方法,讨论采暖热能指标及设计值的变异性。结合工程实例提出基于可靠性理论的地源热泵换热器设计与分析方法。     

Numerical study on the effects of design parameters on the heat transfer performance of coaxial deep borehole heat exchanger

Deep borehole heat exchanger (DBHE) is attracting attention intensively owing to much more geothermal extraction, higher efficiency for heat pumps, and lesser land demand compared with shallow borehole heat exchanger. DBHE is usually dipped into several thousand meters in the subsurface, having a complicated heat transfer with surrounding rock–soil. However, the heat transfer characteristics below surface under different conditions are rarely studied. In this study, a numerical model considering the comprehensive effects of geothermal gradients and heat loss from inner pipe was proposed. The model was validated with experimental data and Beier analytical solution. Based on the model, the effects of primary design parameters on the heat transfer performance below surface along the pipe were investigated. The results indicate that temperature at pipe bottom increases with inlet flow rate decreasing, while the heat load cannot be extracted fully to the surface because of the heat loss of inner pipe. When the inlet flow rates decrease from 41.39 to 4.52 m³/h, the heat loss ratio increases from 25.5% to 63.7%. It is an effective way of insulating inner pipe to reduce heat loss under low inlet flow rates. Increasing the velocity in inner pipe by lessening the inner pipe diameter can also decline the heat loss well. While by this way, the increasing pumping power resulting from the higher velocity in inner pipe has to be considered. This study is significant to effective optimization of DBHE and energy conservation of buildings.     

A design methodology for small-scale bubbling fluidized-bed furnaces

A detailed methodology is presented for the design of small-scale fluidized-bed furnaces (SSFBF) in the 15–250 kW capacity range for domestic space and hot water heating. These bubbling fluidized-bed furnaces burn a beneficiated coal-water slurry mixture, and do not have heat exchange tubes in the bed or freeboard regions. Algorithms are developed, based on this methodology, to calculate furnace design and performance parameters. The heat transfer coefficients are calculated for the dense bed and freeboard of the SSFBF. These are then compared with theoretical and experimental heat transfer coefficients in the published literature. Excellent agreement is found between those in the SSFBF and those in the literature. The finding of this work is that the methodology and the heat transfer coefficients obtained provide excellent design tools for the scale-up of bubbling fluidized-bed furnaces in the 15–250 kW range.     

Numerical study of the effects of material properties on flame stabilization in a porous burner

Development of porous burners has been encouraged by lower emission standards as well as the advantages these burners offer; such as fuel flexibility, the ability to operate at low equivalence ratios, and effective flame speeds greater than the laminar flame speed. Although a burner may be constructed from a single section of porous media, a burner consisting of two sections with different characteristics has received significant attention in the last decade. Through proper selection of the properties of the two sections, the interface between the two sections serves as a flame holder preventing flashback for a range of conditions. In this paper, we present the results from a one-dimensional computational study on flame stabilization in a two section porous burner. The stable operating limits are predicted for a range of equivalence ratios and are compared to experimental values. A parametric study, in which the properties of the two sections are varied independently, is presented. The results indicate that matrix properties significantly affect the stable operating range. In addition, the upstream section acts primarily as a flashback arrestor and for the widest operating range, it should have a low conductivity, low volumetric heat transfer coefficient, and high radiative extinction coefficient. The downstream section acts primarily to recirculate heat through the matrix; it should have a high conductivity, high volumetric heat transfer coefficient, and an intermediate radiative extinction coefficient.     

管壳式相变储能换热器的优化设计

叙述了利用优化设计理论对管壳式相变储能换热器进行优化设计的方法。以该装置的成本为优化目标,储热量,放热时间,传热量,加工和防腐要求作为约束条件,得出了最佳的管子半径,厚度及管子根数,并给出了一个计算实例。     

间歇式热处理炉传热计算与分析

建立了台车式热处理炉炉膛传热数学模型和辐射换热器工作模型,分析了换热器的传热特性（空气预热温度、壁温、传热系数）随炉况的变化。结果表明,辐射换热器的传热特性随炉子的升温及保温过程变化而波动很大,因而对炉子的热工性能产生了影响。     

钝体高度变化对煤粉工业锅炉燃烧器流场特性影响的冷态实验研究

针对某新型适用于燃煤粉工业锅炉的燃烧器,冷态实验研究了其一次风出口处加装的钝体高度改变对燃烧器流场特性的影响。研究结果表明:钝体高度越高并不能使得回流效果越好,适当高度的钝体可以起到增加气流回流的效果。