Optimization of Heat Fluxes on the Heater and the Design Surfaces of a Radiating-Conducting Medium

In a radiating-conducting planar medium with a boundary as the heater surface using an inverse analysis, this work deals with the design methodologies to understand the inherent relationship between heater surface temperature/flux, design surface temperature/flux, and medium properties. The heat flux on the heater surface is chosen as the fitness function. Subsequently, to achieve maximum and minimum design surface heat fluxes, an optimization was done to evaluate the zone of operation of the heater. In addition, the effect of medium properties on the temperature-flux relationships on both surfaces has been studied. The distance between the two surfaces is also considered a parameter. The medium properties, the distance between the surfaces, and the heater surface temperature have been found to have a great impact on the design surface heat flux. The inverse mixed boundary problem has been solved using the lattice Boltzmann method (LBM), the finite-volume method (FVM), and the genetic algorithm (GA). Results of the present study provide a guideline towards the efficient design of a heater in which conduction and radiation are the dominant modes of heat transfer.     

暖风器及其相关蒸汽和疏水系统设计研究

  [目的]  针对目前多个火电厂一次风机和送风机进出口的暖风器运行中存在的极端低温情况下暖风器出口风温偏小、管道振动、疏水不畅等问题,提出解决方案。  [方法]  文章拟通过对几个工程暖风器及其关的汽水系统和布置设计与实际运行情况进行分析比较。  [结果]  在技术规范书编制时要求厂家核算在极端低温环境温度下暖风器的面积要满足空预器冷端风温要求。在施工图设计阶段,应优化暖风器汽水系统,使其达到便于控制和节能的要求;暖风器宜高位布置,让暖风器本体疏水能通过自流的方式到达疏水排放点;在调试阶段,对于疏水管道布置存在U型时,在启动初期、疏水压力不足时在低位点设放水管。在运行维护阶段,需要充分利用控制系统,把暖风器的疏水和风温控制结合起来,确保系统安全、稳定、经济运行。  [结论]  文章的中分析和研究是基于理论和其它工程优化的案例进行的,有实际应用价值,可供其它工程参考。     

热网加热器泄漏原因分析及防止措施

热网加热器是供热电厂的主要辅助设备,对提高电厂热效率和安全稳定起着重要作用,但由于系统设计、运行和检修等原因,热网加热器普遍存在泄露损坏现象,严重影响电厂热网首站正常运行,文中对热网加热器泄露产生的原因进行分析并提出防止措施,为防范泄露提供指导.     

蛇形管高压加热器用于1 000 MW二次再热机组的可行性分析

随着1 000 MW二次再热机组设计参数越来越高、采用传统单列U形管高压加热器也越来越受到限制,当前新上二次再热机组不得不采用双列U形管高压加热器,从而使得主给水系统复杂、运行困难。结合U形管高压加热器,对比分析了新型高压加热器(即蛇形管高加)技术特点及国产化现状,指出在1 000 MW二次再热机组应用蛇形管高压加热器是可行的,并具有结构及系统简单、热适应性好、可靠性高等优势,推荐在同类工程中应用,为适应末来更高参数超超临界机组的高压加热器制造技术发展打下基础。     

Model-based design and analysis of heat pipe working fluid for optimal performance in a concentric evacuated tube solar water heater

In this study, a semi-dynamic model of a concentric evacuated tube solar water heater is developed to investigate the effect of working fluid design on technical and economic performance of a typical solar water heater in a household located at Sydney, Australia. The model is validated against experimental data. The effects of using water, ammonia, acetone, methanol, and pentane as working fluids of the built-in heat pipe are discussed comparatively during a typical day of operation. Water is identified as the best working fluid amongst the others. The variation of thermal resistance and critical heat flux of the heat pipes due to change in weather condition is presented and discussed. Three hypothetical working fluids are then proposed for further analysis which led to a working fluid design superior to water in performance. It is shown that the performance of the solar water heater can be significantly enhanced up to 28% and 50% from economical and technical points of view, respectively.     

燃煤锅炉暖风器的改进

对燃煤锅炉原有盘管式暖风器结构特点及存在问题进行了分析,提出了新型套管式暖风器的设计思路,探讨了新型套管式暖风器设计制造过程中的几个具体问题。新型暖风器投用后可以有效地防止管内介质的泄漏,大大提高暖风器运行的可靠性,减少燃煤锅炉尾部受热面的低温腐蚀,减缓了锅炉空气预热器的堵灰速率,具有较高的推广价值。     

高压加热器投入率低原因分析与改进

高压加热器投入率低是影响电厂机组安全经济运行的一个重要方面。以某电厂300MW机组高压加热器为例,分析了高压加热器投入率低的原因,运用等效热降法对机组的运行经济性进行计算,提出并落实了具体的改进措施,保证了高压加热器的正常运行,取得了良好的经济效果。     

脱硝尿素热解系统炉内烟气换热器运行分析及设计优化

脱硝尿素热解制氨系统一般通过电加热器提供所需的高温热解空气热量,采用锅炉烟道内布置烟气换热器,可以有效提供高温热解空气加热所需热量,降低电加热器运行功率从而节省高品质电能.通过对某350 MW机组实际运行数据分析,总结锅炉内置烟气换热器尿素热解系统的运行特点,提出烟气换热器优化设计方案,保证尿素热解制氨系统的运行经济性...     

Carbon monoxide emissions of combined pellet and solar heating systems

Emissions are an important aspect of a pellet heating system. Low harmful emissions, particularly carbon monoxide, are a measure of a well performing system. High carbon monoxide emissions are often caused by unnecessary cycling of the burner and when the average load is below the lowest possible combustion power of the burner. Combining pellet heaters with a solar heating system can significantly reduce cycling of the pellet heater and avoid the inefficient summer operation of the pellet heater.Five combined systems representing the range of typical solutions of this system type and one recently developed system have been studied, modelled and simulated. These systems are compared to a reference system, which is based on a pellet boiler and is not combined with a solar heating system. The aim was to study CO-emissions of the different types of systems and to analyse the potential of CO-emission reduction when the pellet heater is combined with a solar heating systems. Another aim was to compare the yearly CO-emissions obtained from simulations under realistic dynamic conditions with the yearly CO-emissions calculated based on the values that are obtained by the standard test methods and with the limit values of different regulations. The results from the simulations show that it is possible to almost halve the CO-emissions if the pellet heater is combined with a solar heating system. The results also show that the CO-emissions of existing combined solar and pellet heating systems can be drastically reduced if the pellet heater is properly controlled and some basic design rules are observed. Comparing the yearly CO-emissions obtained from the simulations with the yearly CO-emissions calculated based on the standard test methods shows that using the latter give too low CO-values for the whole year. It is also shown that for the existing systems the average emissions under these realistic annual conditions were greater than the limit values of two eco-labels.     

Experimental and theoretical studies of recyclic flat-plate solar water heaters equipped with rectangle conduits

A recycle operation design using a flat-plate solar water heater with rectangle flow conduits was theoretically and experimentally investigated. Devices with differing flow-conduit geometries (i.e. aspect ratio) and external recycle were designed to create a solar heater with low heat-transfer resistance between the absorber and working fluid to increase the convective heat-transfer coefficient. Considerable solar water heater collector efficiency improvement has been obtained employing rectangle flow conduits and a recycle operation, instead of recycle solar collector constructed with circular pipes operated at the same total mass flow rate. Under a fixed absorber area and distance between the flow conduits, the collector efficiency increases with increasing flow conduit aspect ratio, total mass flow rate and recycle ratio but with decreasing inlet water temperature. The incident solar radiation, mass flow rate, recycle ratio and flow conduit aspect ratio influences on the collector efficiency and energy consumption are also discussed.     

Performance and Service Life Considerations—Closed Feedwater Heaters

Because of the potential restriction of plant capacity and increases in fuel consumption cost that result from the removal of closed feedwater heaters from service, there is a need for the application of new design and operation concepts that enhance both the thermal performance and the availability of heaters and their associated systems. Practical operating practices, which take into consideration the highly localized environments in closed feedwater heaters and the individual susceptibilities to failure of the various tube materials in common use, have evolved from direct experience with closed feedwater heater problems. Many electric utilities have adapted these operating concepts in their standard operating procedure. Life extension programs for feedwater heaters that are repaired or to be replaced must include the provision for new operating concepts. Heaters that are subjected to the same operation conditions that led to the original failures may be expected to fail for the same reasons, often in a much shorter time. The acquisition of accurate data on operating performance, the location of tube distress, combined with the application of new, successful practices in feedwater heater design, operation, and maintenance, have provided the best assurance of a satisfactory service life of closed feedwater heaters.     

Thermal performance study of two-pass solar air heaters

The operation of a conventional solar air heater with two covers in a two-pass mode offers an inexpensive method of improving the collector efficiency by about 10–15 per cent. Heat transfer models are developed for two such two-pass flow arrangements and are compared with the performance of the single pass design. The computer models are validated by comparing with the experimental data from a series of collector testing experiments. The collector performance is examined over a wide range of design and operating conditions and the two-pass designs are found to perform better than the single pass system. For closed-loop systems with air recirculation the two-pass designs have some limitations in performance. Design curves for two-pass systems over a range of variables are presented.     

Experimental observations on a continuous flow type domestic solar water heater

The operation of a continuous flow type domestic solar water heater is explained with the help of a schematic diagram. Steady state thermal analysis of such a water heater is carried out. A water heater of this type with a collector area of 1 m² is subjected to tests. The experimental results are compared with predicted results. The experimental results have also been compared with those obtained from a water heater operating on thermosiphon flow. The performance of the continuous flow type water heater is shown to be comparable to that of the thermosiphon flow type. It is concluded that, in the Indian context, the continuous flow type water heater has more advantages than the thermosiphon flow type water heater in view of its low capital cost and the ease of operation and maintenance.     

Some mechanical aspects of low cost augmented integrated rock system

The development of an augmented integrated rock system is described in this paper. A unique AIRS (Flat Plate air heater connected in series with an integrated rock storage and collection system) concept is used as the absorber plate-to-air stream and then air stream-to-rock bed storage and collection unit heat transfer mechanism. The intention was to increase the efficiency of the air heater, over that of a ‘conventional’ type solar air heater by increasing the absorber area which includes the metallic absorber plate and the rock surface exposed directly to the sun. The programme objective was to design a device which can store the energy during its operation and supply it during the evening and late night hours when there is no sun in the sky. In order to achieve this goal, we have fabricated, tested and evaluated ‘AIRS’, and the results obtained are presented in this paper.     

Studies on thermal performance of electrical heaters by using porous materials

This paper is devoted to the subject of new configurations of electrical heaters that use porous media. Thermal performance of two innovative designs are estimated and compared with that of the conventional ones. In the first design, airway is filled with a porous insert while the second heater uses a porous heating element instead of the conventional solid ones. The coupled differential equations for both solid and gas phase are solved simultaneously by a control-volume based procedure along with the corresponding boundary conditions, using SIMPLE algorithm. Results reveal that for equal air flow rates, equal heater masses, and the same energy generation rates, the heating element in the porous heater attains the lowest temperature. Surprisingly, this heater also achieves the lowest pressure drop, which is a result of lower air velocity inside the heater. The results also show that at the same aforementioned conditions, the heater with porous insert suffers from the highest temperature while it has a medium pressure drop with respect to the other designs.     

新型镁砂加热器的设计及应用

着重介绍了新型镁砂加热器的结构特点、技术参数、设计要点、技术措施及生产使用效果。     

Cost optimization of a conical electric heater

Electric heaters are used extensively in many industrial applications including air conditioning, water heating, and drying of crop and other materials. There are several interacting parameters that affect heater performance and contribute to its operating and manufacturing costs. The design parameters of interest included coil length, coil diameter, helix diameter, coil pitch, number of turns, coil emissivity, heater wall emissivity, applied voltage, air flow rate, air temperature at the heater outlet, insulation thickness, and the heater dimensions. An objective function for the heater cost was defined in terms of the total annual costs for energy usage and manufacturing. The manufacturing cost included the material cost of the heater, the cost of coating the heater coil, and the cost of insulating the heater. A detailed model describing the performance of a conical heater was utilized to evaluate and minimize the objective function. The optimization problem was completely defined by introducing fourteen inequality constraints, three equality constraints, and ten design variables. The univariate search was used to reduce the number of inequality constraints. The direct search and variable metric methods were used to optimize the objective function at different values of the applied power and air temperature at the heater outlet, leading to the same results. The optimization results indicate that the optimum heater design was found at the minimum values of the coil diameter, conical angle, coil emissivity, and the maximum value of coil temperature. The maximum operating temperature of the optimum heater design (a heater with a silver coated coil) is substantially lower than the maximum normal operating temperature so that longer life for the heating element is expected. The effect of varying the applied power on the objective function showed that as the applied power increases the objective function may increase or decrease, depending on the combined effect of increasing the coil length and heater efficiency and decreasing the insulation thickness. The effect of varying the air temperature at the heater outlet on the objective function indicated that as the air temperature increases the objective function increases. Copyright © 2005 John Wiley & Sons, Ltd.     

阿尔法磁谱仪电源分配箱的加热系统设计和模拟

根据阿尔法磁谱仪(AMS-02)电源分配系统(PDS)的双路电源分配模式(BusA BusB),设计了一套能够3阶段逐次启动和关闭的自动控温加热系统,采用串并联容错技术控制上限开启和上限关闭两类温控开关的启闭,给出了加热片、温控开关、控温电路的关键参数及布局。对加热系统在5个典型冷工况下的启动特性和WAKE侧电子设备在ISS上最冷工况、最低电压运行模式下的温度响应特性进行了分析和校验,结果表明加热系统满足设计目标,温控器控温准确,不同冷工况下的功率分配合理。     

An experimental device for the simultaneous estimation of the thermal conductivity 3-D tensor and the specific heat of orthotropic composite materials

In this study, a new experimental design, which has the advantage of estimating simultaneously the three components of the thermal conductivity tensor and the specific heat of orthotropic polymer composite materials, is presented. Furthermore, no sample instrumentation is required, reducing substantially the global experimental procedure duration. The measurement technique consists in dissipating a known heat flux thanks to a home-designed thin heater, composed by two distinct heating elements and sandwiched between two cylindrical samples. The heater is also used as measurement instrument since micro-thermocouples are incorporated inside. The parameter estimation is performed by solving an inverse heat conduction problem. The method has been validated on a sample with known properties. The thermal properties of a unidirectional carbon-fiber composite have been then characterized. The results, obtained from a two-step estimation strategy are in good agreement with those determined within the framework of round-robin test.