多入口多孔介质燃烧器的数值模拟

在多入口燃烧器内加入多孔介质,以甲烷/空气为燃料,采用非预混燃烧的数值模拟方法,探究多入口燃烧器的燃烧情况.对比多孔介质燃烧与空间自由燃烧,分析了"超焓燃烧"现象;在多孔介质燃烧基础上,探究不同当量比对燃烧温度的影响;在多孔介质燃烧和不同当量比的基础上探究污染物CO和CO_2的排放情况.结果表明:多孔介质燃烧可以实现"超焓燃烧"特性,燃烧火焰温度高于自由空间燃烧温度;当量比对燃烧温度影响很大,随着当量比的增大,燃烧器内最高燃烧温度升高,但燃烧过程存在一个最佳当量比0.6,超过该当量比后最高温度将不再变化;多入口多孔介质燃烧有助于减少CO和CO_2的生成量.     

渐变型多孔介质中预混燃烧温度分布试验

进行了预混天然气在等孔隙率渐近变孔径的多孔介质中的燃烧试验，用热电偶测量了燃烧室温度分布，并与单一孔径（d=1mm）的均匀多孔介质中燃烧结果进行了比较。结果表明，渐变型多孔介质燃烧器比均匀型多孔介质燃烧器具有更多的优点：燃烧室温度分布更加均匀，燃烧更加稳定，并能更好的适应当量比和流量／功率的变化，由于孔径的变化，多孔介质中气流扰动增加，有利于火焰的稳定，当量比和流速变化范围增大。     

有序堆积床内预混气体燃烧特性实验研究

为研究预混气体在多孔介质燃烧器中的火焰燃烧特性,设计了一种新型多孔介质燃烧器,其中多孔介质区域由氧化铝圆柱体有序堆积而成。分别研究了当量比和入口速度对甲烷/空气预混气体在多孔介质燃烧器中的火焰温度分布、火焰最高温度以及火焰传播速度的影响。结果表明:在当量比0.162~0.324、入口速度0.287~0.860 m/s的实验工况下火焰均可以稳定向前传播,并且都发生了超绝热燃烧;当量比越大,入口速度越大,火焰最高温度越高;当入口速度为0.430 m/s时,贫可燃极限的当量比可以扩展到0.162;火焰传播速度随着入口速度的增加和当量比的减小而增大,其数量级为0.100 mm/s,属于一种十分典型的低速过滤燃烧。     

天然气在渐变型多孔介质中的预混燃烧启动特性

针对天然气在渐变型多孔介质燃烧器中的点火启动过程进行了试验研究,通过监测燃烧器壁面或气体温度在点火后的变化,得到了影响启动时间的因素及特性,对特定的燃烧器而言,启动时间与预混气体当量比、流速以及点火位置有关,在冷态下点火,随着当量比接近理论当量比,启动时间减小;混合气体流速增大,启动时间增大;点火位置从燃烧器外移到燃烧器人口时,启动时间可大大缩小,采用小流速、近理论当量比条件下点火,对多孔介质层预热,有利于火焰迅速向上游移动,然后再调整到需求当量比或流速,可以大大减小燃烧器启动时间,采用孔径变化率高的渐变型多孔介质结构,也可以达到缩短启动时间的目的。     

多孔介质微小燃烧器的传热特性分析

采用计算流体力学软件Fluent,对H_2/空气预混气在全填充多孔介质平板微燃烧器内的燃烧过程进行数值模拟.研究了多孔介质导热系数、壁面导热系数、当量比、孔隙率对微燃烧器回热循环的影响规律.模拟结果表明:预热区对流回热效率、多孔介质导热效率与多孔介质导热系数呈正相关趋势;壁面导热系数增大会使预热区对流回热效率下降,壁面对流回热效率上升;预热区对流回热效率、壁面对流回热效率与当量比呈负相关趋势;多孔介质孔隙率是影响回热效率的重要因素,随着孔隙率的增大,预热区对流回热效率下降,壁面对流回热效率上升.     

基于多孔介质燃烧的端部辐射器的实验研究

设计了基于多孔介质燃烧技术的端部辐射器,研究不同预混气体流速(功率)下当量比对燃烧器燃烧稳定性、多孔介质内部温度、辐射器表面温度及其均匀性、污染物排放、辐射效率等特性的影响.结果表明,燃烧器辐射表面的温度均匀性较好.最大相对温差小于3%:多孔介质燃烧器可实现最低当量比0.33的稳定可持续燃烧;小功率燃烧时.多孔介质内部温度及端部辐射表面温度都随当量比增大而增加,且流量越大增加程度越大,可据此提出实现更高辐射表面温度的方案.实验工况范围内.最大辐射效率达23%;NO<,x>排放体积分数低于25×10<'6>,在当量比大于0.45时,CO排放体积分数均低于10×10<'6>.     

多孔介质蓄热系统动态蓄热特性试验与表征

为了解多孔介质蓄热材料热动态条件下的蓄热特性,得到表征蓄热材料的动态蓄热特性参数,在120 kW多孔介质热动态蓄热系统中,对不同孔径(2.9、4、5.5 mm)、长度(100～400 mm)的蜂窝多孔陶瓷蓄热体在不同热烟气条件下的动态蓄热特性包括蓄热速率、蓄热效率、蓄存单位热量所要克服的蓄热阻力进行了试验研究。结果表明:蓄热速率与时间的关系呈"抛物线"状,蓄热效率随蓄热时间的进行逐渐降低。相同时间下蓄热速率及单位蓄热阻损随蓄热体比表面积的增大或孔径的减小而增大,蓄热效率随蓄热体长度的增加而增大。根据试验研究和分析,采用蓄热速率、蓄热效率及单位蓄热阻损可以用来表征多孔蓄热体的动态蓄热特性。     

回热式多孔介质发动机的排放特性分析

研究了回热式多孔介质发动机的排放特性.使用Ferrenberg所提出的回热式发动机模型,其多孔介质面热器在气缸中作往复运动.用改进的KIVA-3V程序进行了二维模拟.探讨了在不同当量比和孔隙率条件下,气缸内燃烧和排放特性.结果表明,回热式多孔介质发动机在燃烧和排放方面较之常规都有明显的优势.采用低当量比能有效地降低污染物的排放,而孔隙率的影响则与当量比有关.分析证明,采用多孔介质回热器是发动机实现稀薄燃烧的一条可供选择的途径.     

多孔介质燃烧器的辐射输出效率和污染物

使用双温度体积平均模型、详细化学反应机理GRI3．0，对甲烷，空气预混气在多孔介质燃烧器内的预混火焰进行模拟．分析不同当量比和质量流量下的预热效率、辐射输出效率以及污染物排放情况，并对辐射输出效率随多孔介质热物性参数的变化进行敏感性分析．结果表明，增大相间对流换热系数或减小当量比、质量流量及固相消光系数都可以提高辐射输出效率，减小当量比或质量流量可以减少污染物排放．在所有的影响因素中，当量比的影响最大，发展超贫燃燃烧技术是获得高效低污染多孔介质燃烧器的关键．     

毛细管换热器在养殖水体温度调节中的应用

本文从传热学的基本原理出发,利用毛细管换热器的传热过程热量计算公式,探讨了不同毛细管长度、管间距及流量下的毛细管换热效果,为毛细管换热器在养殖水体温度调节提供参考。结果表明,管内介质流量和管长的增加,皆会增大毛细管换热量;管间距的增大伴随着换热面积的减小,换热效果降低。同时,根据毛细管换热的特点及海水温度和管内介质温度变化可知,进口温度与海水的温差越大,换热越明显。     

A review of the applications of heat pipe heat exchangers for heat recovery

The waste heat recovery by heat pipes is accepted as an excellent way of saving energy and preventing global warming. This paper is a literature review of the application of heat pipes heat exchangers for the heat recovery that is focused on the energy saving and the enhanced effectiveness of the conventional heat pipe (CHP), two-phase closed thermosyphon (TPCT) and oscillating heat pipe (OHP) heat exchangers. The relevant papers were allocated into three main categories, and the experimental studies were summarized. These research papers were analyzed to support future works. Finally, the parameters of effectiveness of the CHP, TPCT and OHP heat exchangers were described. This review article provides additional information for the design of heat pipe heat exchangers with optimum conditions in the heat recovery system.     

Internal heat generation in a discrete heat source: Conjugate heat transfer analysis

In the present work, we conduct an asymptotic and numerical analysis for the cooling process of a discrete heat source, which is placed in a rectangular-channel laminar cooling flow. In our physical model, the heated strip is embedded in a substrate, generating continuously a uniform volumetric heat rate. We assume that this heat-generation mechanism is due to an electrical current in the heat source. Hence, heat losses to the cooling fluid and to the substrate material during this process are presented. The governing equations of the cooling flow and the participating solid are reduced to an integro-differential equation that predicts the temperature variations of the heat source. We show that the conjugate heat transfer process is controlled by a conjugate nondimensional parameter, here denoted by α, which determines the basic heat transfer regimes between the cooling flow and the discrete heat source.     

Waste heat recovery using heat pipe heat exchanger for heating automobile using exhaust gas

The feasibility of using heat pipe heat exchangers for heating applying automotive exhaust gas is studied and the calculation method is developed. Practical heat pipe heat exchanger is set up for heating HS663, a large bus. Simple experiments are carried out to examine the performance of the heat exchanger. It is shown that the experimental results, which indicate the benefit of exhaust gas heating, are in good agreement with numerical results.     

地源热泵的套管式地下换热器传热研究

地源热泵是一种节能、对环境无害的绿色空调设备,可成为下个世纪冷暖技术的核心,采用能量平衡,建立了地下浅埋套管式换热器传热平衡式,进行求解,并分析了影响传热的各关联因子,提出了需研究的强化地下换热的措施,根据求解结果,给出了相应的函数关系图。对实验设计和工程实践有一定的指导作用。     

一种新颖简易的太阳能热动力转换装置--明托热机

明托热机(Minto Engine),俗称明托转轮,它 是通过液体活塞在转轮中不停地变换位置,产生不 同的动力矩,从而驱动转轮旋转的机器。明托热机 最早于1975年被维利·明托(Wally Minto)发明。 早期的明托热机结构十分简单,效率也很低,但由 于它能将低品位热能转变成高品位的动力。因而一 下子吸引了许多科学家的注意。之后,许多学者对 明托热机进行了研究,提出了许多改进的方向和应 用领域,推动了明托热机的发展。     

Frosting of heat pump with heat recovery facility

This paper aims to prolong the heat pump frost time and reduce its growth with heat recovery facility, which should mix the exhausted indoor and outdoor air before entering the evaporator. An ideal mathematic model is developed for heat transfer, frost generation and airside pressure drop. The properties of the mixture would be obtained by solving the mass and energy conservation equations. A parametric analysis is performed to investigate the effects of air inlet temperature, relative humidity and air mass flow rate on total heat transfer coefficient, frost thickness and airside pressure drop, respectively. The results show that rationalizing the ratio of indoor and outdoor air could prolong frosting time and reduce the frost thickness greatly. The total heat transfer coefficient, frost thickness and airside pressure drop increase monotonically with time going, but are not proportional. Decreasing the mixture inlet air temperature and relative humidity could essentially reduce frost growth on the tube surfaces. This can also be observed when increasing the air mass flow rate.     

Forced convection heat transfer in microchannel heat sinks

This paper presents an analysis of forced convection heat transfer in microchannel heat sinks for electronic system cooling. In view of the small dimensions of the microstructures, the microchannel is modeled as a fluid-saturated porous medium. Numerical solutions are obtained based on the Forchheimer–Brinkman-extended Darcy equation for the fluid flow and the two-equation model for heat transfer between the solid and fluid phases. The velocity field in the microchannel is first solved by a finite-difference scheme, and then the energy equations governing the solid and fluid phases are solved simultaneously for the temperature distributions. Also, analytical expressions for the velocity and temperature profiles are presented for a simpler flow model, i.e., the Brinkman-extended Darcy model. This work attempts to perform a systematic study on the effects of major parameters on the flow and heat transfer characteristics of forced convection in the microchannel heat sink. The governing parameters of engineering importance include the channel aspect ratio (α_s), inertial force parameter (Γ), porosity (ε), and the effective thermal conductivity ratio (k_r). The velocity profiles of the fluid in the microchannel, the temperature distributions of the solid and fluid phases, and the overall Nusselt number are illustrated for various values of the problem parameters. It is found that the fluid inertia force alters noticeably the dimensionless velocity distribution and the fluid temperature distribution, while the solid temperature distribution is almost insensitive to the fluid inertia. Moreover, the overall Nusselt number increases with increasing the values of α_s and ε, while it decreases with increasing k_r.     

石墨烯-PFA复合材料换热器与金属换热器的传热性能对比

氟塑料换热器以其耐腐蚀、耐磨损等优点而备受关注,但氟塑料热导率较低,换热能力差,限制了其广泛应用。石墨烯-PFA复合材料兼具石墨烯优异的导热性和可熔性聚四氟乙烯(PFA)良好的耐酸碱腐蚀性,是新一代的换热器材料。搭建了余热回收测试实验台,对石墨烯-PFA复合材料换热器和金属换热器的传热性能进行对比。研究了不同烟气流速、不同进口烟气温度以及不同石墨烯配比对复合材料传热性能的影响。结果表明:对于金属换热器和复合材料换热器,当烟气流速从2.0增加到4.0 m/s时,传热系数分别增加到原来的1.19和1.34倍;随着进口烟温的升高,两种材质的传热系数分别降低了15.6%和14.7%;随着石墨烯含量增加,复合材料的导热系数以及传热系数均增加。