双斜向内肋对强化立式太阳能热气流电站的流动传热特性研究

为了加强立式太阳能热气流电站系统的传热,将矩形双斜向内肋对成对地布置在竖直烟囱通道的集热板上。通过数值计算,空气在流经肋对时温度梯度增大,换热增强。与原系统相比,加入双斜向内肋对后,气流的进出口温差增加21%,进出口速度差提高133%。进一步对双斜向内肋对的布置,包括肋对数和肋倾角进行研究,得到适合于本系统的内肋对的最佳设置为肋对数为2对、肋倾角为45°,此布置下气流的进出口温差增加8%,进出口速度差提高200%。利用场协同原理对结果进行分析验证,证明双斜向内肋对可以有效地减小速度矢量与温度梯度的夹角,增强系统换热。     

热管换热器内部流动与换热的数值模拟

单螺旋翅片热管管束的翅片结构中心对称处存在流体流动及换热不足,因此,将单螺旋翅片结构改为新型双螺旋翅片结构,并利用Fluent软件模拟分析改进后流场与温度场的变化情况。结果表明:在Re=500~6 500时,与未加翅片相比,单螺旋翅片热管换热增强33%~51%,摩擦阻力系数增加6%~24%;双螺旋翅片热管换热增强69%~84%,摩擦阻力系数增加19%~48%。且双螺旋结构的综合性能明显优于单螺旋结构的综合性能,且在Re=2 000时性能表现最优。根据场协同原理可知,双螺旋翅片结构对流体的强烈扰动可促使流体的速度矢量与温度梯度矢量协同程度更好。综合比较得知双螺旋翅片热管更有利于强化换热。     

丁胞型强化换热管内突起结构对流传热及阻力的数值模拟

采用SIMPLE算法求解RNG k-ε方程,分析丁胞强化换热管管内流动传热情况,研究管内侧突起结构对于单相气体流动过程的强化传热性能和压力损失,并和文献中的实验值进行对比.结果表明,丁胞管管内突起虽会使突起左右两侧局部换热系数减小,但总体上是增强了换热性能,且随着Re的增加强化换热效果更明显.同时也因形阻力增大了流动阻力.     

矩形翅片椭圆管气侧流动与换热规律的数值研究

利用Fluent软件,在矩形翅片椭圆管尺寸给定的情况下,对椭圆基管偏移位置不同的椭圆矩形翅片管外空气侧层流流动与换热进行数值研究,分析偏置距离与椭圆管短轴半径之比Δx/b和雷诺数(Re)对翅片管空气侧换热和流动的影响。结果表明:在计算的Re数范围内,随着Re数的增加,努谢尔特数(Nu)逐渐增加,阻力系数(f)变化不明显;Δx/b=0.5的翅片管(Nu)数比Δx/b=-0.5的翅片管增大约4.83%~8.7%,Δx/b=0.5的翅片管外空气侧阻力系数比Δx/b=-0.5的翅片管增加约4.3%。就翅片效率而言,Δx/b=-0.5时翅片的效率最高。     

三维内肋螺旋管内强化换热实验

采用实验方法测试了三维内肋螺旋管内的流动传热性能。实验用的螺旋管曲率δ=0．0663,测试段长1．15m,试验工质为水。对螺旋光管和两种不同结构尺寸的三维内肋管进行了测试,测量的雷诺数范围约为Re=1000～8500。结果表明,三维内肋对螺旋管内的对流换热仍然有较大的强化效果,同时流阻也有一定程度的增加。与未加肋的螺旋光管相比,在测试的流动范围内,两种三维内肋管的平均换热强化比达1．71和2．03．热力性能系数为1．2～1．66。     

圆柱形内肋强化换热数值模拟与火积耗散分析

对内肋管内部流体的湍流换热过程进行了数值模拟,讨论了肋高和肋的轴向夹角对换热的影响。相比于普通圆管,内肋圆管内的传热性能明显得到提高。无量纲肋高度和角度分别为0.8°和40°时传热效果最佳,而在0.1°和40°时换热与阻力的比值(Performance Evaluation Criteria,PEC)最大,综合换热性能最佳,可用于强化地源热泵地埋管换热。此外,本研究从火积耗散与传热效率的角度分析了内肋强化传热机理,得到管壁冷却管内流体的火积传递效率计算式,为内肋管强化换热的深入分析提供了依据。     

三维变形管与三维内肋管在管式空气预热器上的应用研究

本研究对比分析了三维内肋管及三维变形管的结构特点和强化传热机理,在相同工况下,揭示了光滑圆管、三维内肋管及三维变形管用于管式空气预热器时的传热性能和流动阻力性能,三维内肋管和三维变形管传热性能均优于光滑圆管,三维变形管管内传热系数和流动阻力系数随短长轴B/A的减小而增大,三维内肋管可增加每米肋数、肋宽和肋高以强化传热效果,但流体流动阻力也将增加,低Re下,三维变形管管内综合传热性能优于三维内肋管,三维变形管管外自支撑而防止管束振动的特点可以实现在管内外的冷热流体纯逆流动,提出一种传热温差高的逆流三维变空间管式空气预热器,在相同工况条件下,空气预热器重量减轻,体积减小约65%,节省大量的生产和运输成本以及安装空间,三维变形管空气预热器在烟气余热利用中具有推广应用价值。     

锥形内肋管传热与流阻性能的数值模拟

根据纵向涡强化传热技术提出了新型的强化换热管——锥形内肋管,运用数值模拟方法,研究了新型强化换热管结构参数锥底宽度a、导程P、肋深e和Re数对Nu、沿程阻力系数f及传热综合因子η的影响。结果表明：换热管内壁面边缘处产生了较多的微小涡流,有效破坏了流动边界层,强化了传热。在充分湍流的条件下,流体Re越小、e越小,其综合传热性能越强。当Re<15 000时,a对η的影响要大于P;在过渡点后, P对η影响较大。通过综合传热性能分析,给出了适合不同Re区间的锥形内肋优化参数。     

新型强化换热管管外流动与换热特性

针对新型强化换热管的几何特征,采用三维数值模拟方法,分别从速度—压力场协同性、综合评价因子ε、速度—温度场协同角三个方面对扭曲管、波节管、波纹管开展研究。对波纹管的实验测量结果与数值模拟结果最大相对偏差为2.35%。数值模拟结果表明,纹管管外Re从569~7 399变化,总压降从3.78增长到317.30Pa;扭曲管Re从508~7 622变化,总压降从0.84增大到62.50Pa;波节管Re为580~7 550变化,总压降从1.29增长到110.00Pa,波纹管阻力相比波节管最大提高186.7%,相比于扭曲管提高408.4%,Re<4 500时扭曲管Nu数比波纹管最大提高13.30%,比波节管最大提高6.97%,Re>4 500时波节管换热性能逐渐超越扭曲管以及波纹管,在计算范围内Nu比扭曲管最大提高5.17%,比波纹管最大提高5.40%;波节管的周期性波峰对于强化换热和减阻作用显著;波纹管的压降、强化换热表现均弱于波节管和扭曲管。根据计算结果拟合出Nu数与Re、Pr的实验关联式,为管壳式换热器设计提供一定的理论和依据。     

关于管内单相对流换热强化的极限问题

从场协同理论出发,分析了通道内表面全部为射流冲击换热表面时的极限换热率;将全射流冲击管内换热与普通流动管内换热进行了比较。给出了层流和紊流工况下全射流冲击换热可能达到的最大强化比。针对相同R e,分析得出:在层流充分发展段,全射流冲击通道的强化极限是16.9倍;在紊流充分发展段是3.5倍。综合现有各种通道内强化换热的研究结果进行比较,其换热率均低于全射流冲击管内换热率,其中层流工况以折流翅片式通道和交叉缩放椭圆管的换热率与极限换热率最为接近;紊流工况以内插螺旋丝强化管最为接近。     

余热回收用热管及热管式换热器的研究

简要介绍了热管及热管式换热器的工作原理,热管式换热器在工业余热回收中的应用,以及热管式换热器运行过程中防止积灰和低温腐蚀等问题的有效措施。     

On the steady‐state modelling of a two‐stage evaporator system

We develop and validate against experimental measurements a steady‐state two‐stage flooded refrigerant evaporator model for a heat pump drying system. A prototype two‐stage heat pump dryer test facility was designed, built and instrumented to provide the required measurements for the validation of the model. Repeatability and data quality tests were conducted to evaluate the accuracy of measurements. Experimental data could be reproduced to within ±6.5 per cent of replicated air and refrigerant side measurements for the same evaporator's air inlet conditions while the discrepancy of energy balance at the air‐side and refrigerant‐side was observed to be within ±8.9 per cent. The two‐stage evaporator model predicted the air‐side total heat and latent heat transfer of the two‐stage evaporator to within (?6.3 per cent, 7.6 per cent) and (?11.5 per cent, 9.5 per cent), respectively. On the refrigerant‐side, the model enabled the calculation of the degree of superheat to within (?10.6 per cent, 1.7 per cent). The model has shown that there is significant improvement in the heat recovered from a two‐stage evaporator system compared to a single evaporator system. In addition, the model demonstrated that the improvement in total heat recovery could be as high as 40 per cent over its base‐value when the latent to total load at the two‐stage evaporator is increased. Copyright © 2001 John Wiley & Sons, Ltd.     

显热储热材料的制备及性能研究

采用水泥作为材料的胶凝剂,添加热容、热导率大的物质作为骨料来制备混凝土储热材料。研究表明:当铝酸盐水泥含量为10%时,材料的抗压、抗折强度能满足工业需求;材料的比热容随温度的升高先增大,在500℃时达到最大,后随着温度的升高反而降低;材料的热导率随着石墨粉含量的增加几乎成直线上升,当石墨含量为5%时材料的热导率大于1.7W/(m·K)。     

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。     

Quantification of the European industrial heat demand by branch and temperature level

We present the first comprehensive estimate of the final energy demand for heat in all EU28 member states for the reference year 2012, differentiated by temperature levels, comparing two different approaches. Two different calculation approaches based on different data sets yielded estimates of the total final energy demand for heat in the EU28 of 8150 PJ and 8518 PJ in 2012, respectively. Approach 1 distinguishes between three different process heat (PH) temperature levels and results in final energy demand for heat <100°C: 2077 PJ, 100–400°C: 2214 PJ and >400°C: 3859 PJ. The second approach distinguishes between low temperature space heat and hot water (<100°C: 1161 PJ) and four different PH temperature levels with a resulting energy demand of <100°C: 1027 PJ, 100–500°C: 1785 PJ, 500–1000°C: 1679 PJ and >1000°C: 2865 PJ. The high share of high‐temperature heat illustrates the limits to the potential decarbonisation of industrial thermal processes with renewable energy sources such as (non‐concentrating) solar thermal, geothermal or environmental heat. Therefore specific information on required temperature levels is of the essence. This, in turn, points out the relevance of renewable electricity and synthetic fuels based on renewable power for a significant reduction of CO₂ emissions from the industry sector in Europe. Considering current data quality, it is recommended to develop a consistent, comprehensive methodology to significantly improve the data basis on industrial heat demand. Copyright © 2015 John Wiley & Sons, Ltd.     

Heat pump dryer Part 1: Simulation of the models

Heat pump dryer is a complex system because of the interaction of heat and mass transfer of the working fluids. Since the system cannot be completely close, ambient conditions (temperature and humidity) influence the performance of the system. To investigate the performance of the heat pump dryer thoroughly, simulation models of heat pump dryer components have been developed. The finite-difference method was employed in the simulation to examine the state of the working fluids and heat and mass transfer. The simulation of each component can be used to construct different system configurations the results of which are reported in Part 2.     

国内分离式热管概况与热环研究的小结及展望

本文对我国分离式热管技术的研究进行了简要概况,针对工程中热源在上,冷源在下及冷热源相距较远时的热量传递问题,在分析了一般分离式热管及“水回路”等技术的基础上,对一种新型分离式热管－泵或风机驱动的动力型分离式热管（简称热环）的研究进行了小结和展望。     

Field test of a novel combined system of a high-efficiency heating/cooling heat pump and a clathrate cool storage unit

The Research Laboratory of Kyushu Electric Power Co., Inc. (KEPCO) installed a novel system in March 1992 which is a combination of a super heat pump with about twice the performance of a conventional one and a compact chemical storage-type clathrate cool storage unit. A field test was implemented by integrating these units into an actual air-conditioning system. As a result of the test, system performance was determined and the effectiveness of the system was confirmed. © 1998 Scripta Technica. Heat Trans Jpn Res, 26(6): 410–418, 1997     

Heat-spreading analysis of a heat sink base embedded with a heat pipe

A simplified model predicting the heat transfer performance of a heat sink base with a high thermal conductivity was developed. Numerical analysis was performed using the commercial software FLUENT. The investigation indicates that for heat sink bases with a high effective thermal conductivity, such as the base embedded with a typical heat pipe, the entire heat sink can be modeled as a flat plate with a uniform temperature and an effective convection heat transfer coefficient. This simplified model can be used to determine the heat transfer performance of a heat sink embedded with a typical heat pipe or vapor chamber.     

Augmentation of heat transfer through passive techniques

The thermal performance of energy preservation systems is greatly improved by increasing miniaturization and boosting. These are imaginative (or Promethean) techniques to enhance heat transfer. Enhancement methods of heat transfer draw great attention in front of the industrial sector because of their ability to provide energy savings and raise the economic efficiency of thermal systems. Three techniques these methods are categorized; those are active, passive, and compound. Different types of components are used in passive methods because of the transfer/working fluid flow path to the enhancement of the heat transfer rate. In this article, the subject of the review was the passive heat transfer enhancement methods including inserts (conical strips, winglets, twisted tapes, baffles), porous materials, coil/helical/spiral tubes, rough surfaces (corrugated/ribbed surfaces), extended surfaces (fins) and nanofluids (mono and hybrid nanofluid). Recent passive heat transfer enhancement techniques are studied in this article as they are cost-effective and reliable, and also comparably passive methods do not need any extra power to promote the energy conversion systems' thermal efficiency than active methods. In the passive approaches, various components are applied to the heat transfer/working fluid flow path to improve the heat transfer rate. The passive heat transfer enhancement methods studied in this article include inserts (twisted tapes, conical strips, baffles, winglets), extended surfaces (fins), porous materials, coil/helical/spiral tubes, rough surfaces (corrugated/ribbed surfaces), and nanofluids (mono and hybrid nanofluid). From the pioneers' research work, it is clear that a lower twist ratio and lower pitch, lesser winglet angles can provide more heat transfer rate and a little bit more friction factor. In the case of nanofluids, a little bit of pumping power is enhanced. Finally, heat transfer enhancement is compared with the thermal performance factor, which is more than unity.