高效喷流式空气换热器的设计及应用

一、前言 近年来,加热炉的余热回收装置——空气换热器,在国内外得到了很快的发展和广泛的应用。炉子所用燃料不同,所选用的换热器种类也不尽相同,国内外大多数以粉煤为燃料的加热炉都采用高效喷流式空气换热器。该种换热器兼有套管式换热器和带插件式换热器的特点,被预热的空气在其内管内高速喷出,撞击外管内壁,大大提高了对流给热系数,强化了对流给热。因此,它具有     

波纹板式空气预热器的构想

提出了一种新型空气预热器的结构，采用波纹板片组成间壁式换热器，具有强化传热，结构紧凑，避免了回转式空气预热器存在的漏风问题。     

太阳辐射对室外空气换热器性能影响的研究

太阳辐射对热泵系统的室外空气换热器的热工性能有显著影响。提出了通过修正换热器传热系数以考虑太阳辐射作用的计算方法，设计出了热泵系统的实验装置并由实测数据进行了计算，得出了有与无太阳辐射时的传热系数之间的关系式。该方法不但可以提高热泵系统的热工性能模拟和能耗分析的准确性，而且对热泵系统及其室外空气换热器的设计与安装具有指导意义。     

基于E语言的管壳式换热器设计

管壳式换热器的传统设计过程计算工作量大、效率低。文中在Windows环境中,以E语言为平台,开发管壳式换热器的设计软件,包括工艺设计、热力校核和压降校核,界面友好。计算实例结果表明,所设计换热器的结构和压降都在合理范围内。软件可供工程设计或教学使用,也可为后续换热器的优化设计提供参考。     

椭圆管翅式换热器空气侧传热和流动特性的数值模拟

建立了椭圆管百叶窗翅片换热器三维模型,对椭圆管翅式换热器空气侧传热和流动特性进行了数值模拟,分析管径、管排数、翅片间距对椭圆管翅式换热器空气侧传热流动的影响。结果表明:管排数为1～3时,椭圆管百叶窗翅片换热器空气侧换热系数随换热器管排数的增加而降低,最大降幅达17.1%;椭圆率为2:3的椭圆管翅式换热器综合性能最好,与同周长圆管管翅式换热器相比,换热性能提高了10.1%,降阻幅度达32.3%;随着风速的提高,翅间距对管翅式换热器换热性能及阻力影响逐渐降低。     

热管式空气预热器系列化设计

本文讨论气—气型热管换热器的系列化设计问题,提出了利用中、小型工业锅炉及工业窑炉烟气余热预热空气的热管式空气预热器系列化设计方案。着重考虑了烟气含尘对热管换热器使用性能的重大影响,在系列设计中采取了相应的措施。     

热管式空气预热器的(火用)优化设计

“热管式空气预热器的(火用)优化设计”一文提出了热管换热器的一种新的设计计算方法。我们期望引起有关科技人员的注意和讨论。     

摩托车催化性能考核台架换热器的设计及试验

催化器性能评价试验中,需要调节、控制催化器的入口温度,本文设计了冷轧翅片管、整体轧制式、U型管壳式换热器和单程管壳式换热器,并对四种换热器进行了比较,选定冷轧翅片管换热器进行试验,试验结果表明设计的冷轧翅片管式换热器能够较好的对催化器入口温度进行控制,实用性较好。     

换热器设计计算及报价的计算机辅助系统

以光滑管换热器、片状管换热器及管状插入件换热器为例，开发了一个计算机辅助计算及报价的软件系统。运用该软件比较了三种换热器在相同设计条件下的设计计算结果，以及它们的制造成本和销售价格，结果表明该系统可减轻设计者的劳动强度，提高工作效率，为换热器的设计选型提供了依据。     

基于最大流速比的连续螺旋折流板管壳式换热器热力设计

管壳式换热器在石油、化工、中央空冷系统等工业领域中运用极为普遍,近年来的研究提出一种换热效果更好的新型连续螺旋折流板管壳式换热器。换热器的热力设计环节直接影响换热器的实际使用,然而由于可能涉及商业机密,公开文献中对于该新型换热器的热力设计环节研究较少。在传统弓形折流板设计过程的基础上,通过将连续螺旋折流板管壳式换热器与弓形折流板换热器经验关联式进行对比,提出一种新的基于最大流速比的连续螺旋折流板管壳式换热器热力设计方法;并通过对压缩机油冷器与中央空调系统干式蒸发器两个设计实例的测试验证了该设计方法的可靠性。该设计方法能够简化连续螺旋折流板管壳式换热器的设计流程,并为工业实际设计提供参考。     

Theory and experimental validation of cross-flow micro-channel heat exchanger module with reference to high Mach aircraft gas turbine engines

This study explores the design, analysis, and performance assessment of a new class of heat exchangers intended for high Mach aircraft gas turbine engines. Because the compressor air that is used to cool turbine blades and other components in a high Mach engine is itself too hot, aircraft fuel is needed to precool the compressor air, cooling is achieved with a new heat exchanger. The heat exchanger consists of a large number of miniature, closely-spaced modules. Within each module, the fuel flows through a series of parallel micro-channels, while the air flows externally over rows of short, straight fins perpendicular to the direction of fuel flow. A theoretical model was developed to predict the thermal performance of the module for various operating conditions. To confirm the accuracy of the model, a single module was constructed and tested using water to simulate the aircraft fuel. The theoretical model was used to predict the air temperature drop, water temperature rise, and heat transfer rate for each fluid stream. Comparisons between theory and experiment show good overall agreement in exit temperatures and heat transfer rates. This study shows the theoretical model is a reliable tool for predicting the performance of heat exchanger modules under actual fuel and air turbine engine conditions and for the design of aircraft heat exchangers of different sizes and design envelopes.     

Alternative Approach in Optimization of Plate Type Heat Exchangers

Plate type heat exchangers are widely used in process industries for gas/gas applications. Typically, these exchangers prove to be very efficient, especially as air preheaters in process furnaces or in equipment used in environmental protection (e.g., in units for thermal disposal of wastes).

For economic reasons, there is a need for a new optimization approach for plate type heat exchanger design and operation. The objective function is to achieve a minimal total annual cost of heat exchangers. Pressure drop and heat transfer are interdependent, and both of them strongly influence capital and operating costs of any heat transfer system. In designing a heat exchanger, it is necessary to determine the optimal dimensions of the apparatus with the given conditions of the equipment operation.

The goal is to obtain the most economically optimal design. An economic assessment allows a comparable estimation of various alternatives. The total annual cost consisting of fixed and variable costs of the heat exchanger was selected as a criterion that summarizes different factors of influence into one objective function. Major cost components of a heat exchange system are as follows: capital, operating and maintenance costs of air and flue gas fans, and capital and maintenance costs of the plate type heat exchanger.

The application of the developed optimization approach is demonstrated through practical industrial examples.     

内展翅片换热器应用在压缩空气系统中的节能效益分析

文中通过实验数据分析以及实际工程案例,就内展翅片换热器在压缩空气系统的相同工况下,采用光管换热器和外翅片换热器的换热效果及阻力特性进行了比较,结果表明,内展翅片换热器不仅具有较好的强化传热效果,而且单位压降损耗低,节能效果显著。     

内展翅片换热器在压缩空气系统中的应用分析

通过实验数据分析以及实际工程案例,对内展翅片换热器在压缩空气系统的相同工况下采用光管换热器和外翅片换热器的换热效果及阻力特性进行了比较。结果表明,内展翅片换热器不仅具有较好的强化传热效果,而且单位压降损耗低,节能效果显著。     

扭曲椭圆管换热器壳程强化传热的数值研究

基于扭曲椭圆管的换热器是一种新型的新风系统换热器,针对扭曲椭圆管及其应用特点,设计了两种不同结构参数的新风系统换热器。应用FLUENT软件,在夏季工况下对两种不同结构参数的新风系统换热器壳程进行模拟分析,并通过与实验数据的对比,验证计算模型的可靠性。结果显示在相同体积流量下,随着壳程开孔面积的增大,对流换热系数h不断减小,压降Δp不断减小,综合性能系数h/Δp^1/3变化不明显;随着螺距的减小,对流换热系数h不断增大,压降Δp不断增大,综合性能系数h/Δp^1/3也不断增大;流场分析显示,扭曲椭圆管换热器壳程流道内,呈现出明显沿着扭曲椭圆管壁面的螺旋流,使得空气在流道内充分扰动,增强换热效果。     

Advanced Micro-Heat Exchangers for High Heat Flux

Three micro-heat exchangers for use in a liquid cooling system with a long offset strip, short offset strip, and chevron flow path based on the traditional heat transfer enhancement concepts were designed and tested. A straight channel heat exchanger was also made for comparison. The liquid crystal thermography method described by Lin and Yang (2005) was used to observe the flow and temperature distributions in the micro-heat exchangers. The test results show that the chevron channel heat exchanger provides the lowest thermal resistance. However, its pressure drop is also the highest, approximately five times higher than that for other three heat exchangers. The offset strip heat exchangers provide better thermal performance than does the straight channel heat exchanger. The performance of the heat exchanger with the shorter strip is better than that of heat exchanger with longer strip. From the above results, all of the three micro-heat exchangers with conventional heat transfer enhancement showed less thermal resistance than the straight channel heat exchanger. The conventional heat transfer techniques may be effectively applied in the high-flux micro-heat exchanger design.     

Heat Transfer Characteristics of a Quadratic Koch Island Fractal Heat Exchanger

Heat exchangers are widely used in the air conditioning and refrigeration industries, and any increase in their efficiency will have a positive effect on the industry as well. A new design of heat exchanger is proposed that will increase the heat transfer area significantly. The heat transfer area was increased by the use of fractals. Three techniques were used to investigate the heat transfer increase; analytical, numerical, and experimental methods. The results showed that the fractal heat exchanger has a higher heat transfer to overall volume ratio than a conventional tube-in-tube heat exchanger.     

Finned-Tube Heat Exchanger Optimization Methodology

Heat exchangers play a dominant role in the performance of most energy systems; however, optimization of these components is a complex task due to the coupled nature of the design parameters involved. Anytime the heat transfer coefficient is increased in these components, there is a corresponding increase in frictional pressure drop; therefore, a delicate balance is required between these two effects in heat exchanger optimization.

The finned-tube condenser heat exchangers used in residential air conditioning systems are examined in this study. Due to the intricate geometry of the finned-tube heat exchanger, there are no analytical optimization schemes available to optimize their design, while experimental trial and error is far too time consuming, considering the ten different design parameters that can be varied for optimization.

This study develops a system model using available analytical and empirical correlations for the entire air conditioning cycle with great detail in the condenser component. An optimization algorithm then uses this model to find an optimum design for ten condenser design parameters using various constraints with a system COP figure of merit. The design optimization methodology is fully developed and presented in the paper so that it can be applied to other energy systems' heat exchanger optimization opportunities.

The optimum condenser design was found to give the same performance as a coil optimized through a manual search costing 23% more. It is also shown that the optimum design is consistent with minimum entropy generation for the total system.     

Dynamic model of counter flow air to air heat exchanger for comfort ventilation with condensation and frost formation

In cold climates heat recovery in the ventilation system is essential to reduce heating energy demand. Condensation and freezing occur often in efficient heat exchangers used in cold climates. To develop efficient heat exchangers and defrosting strategies for cold climates, heat and mass transfer must be calculated under conditions with condensation and freezing. This article presents a dynamic model of a counter flow air to air heat exchanger taking into account condensation and freezing and melting of ice. The model is implemented in Simulink and results are compared to measurements on a prototype heat exchanger for cold climates.     

Detailed equipment design in heat exchanger networks synthesis and optimisation

In heat exchanger network synthesis, important features like pressure drop and fouling effects are usually neglected. In this work a new methodology is proposed to include these effects in grassroots as in retrofit designs. Heat exchangers are detailed designed during the heat exchanger network synthesis. Pinch analysis is used to obtain the heat exchangers network with the maximum energy recovery, and a new systematic procedure is proposed to the identification and loop breaking. Bell–Delaware method for the shell side is used to design the heat exchangers. An example of the literature was studied and the results show differences between heat exchangers, with and without the detailed design, relative to heat transfer area, fouling and pressure drop. The great contribution of this work is that individual and global heat transfer coefficients are always calculated, in despite of the current literature, where these value are assumed in the design step. Moreover, the methodology proposed to the heat exchangers design assures the minor heat exchanger according to TEMA standards, contributing to the minimisation of the heat exchanger network global annual cost. Finely, the new heat exchanger network considering pressure drops and fouling effects presents values more realistic then those one neglecting the equipment detailed design.