Experimental Investigation on Convective Heat Transfer Characteristics in Ribbed Channel

The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments.Reynolds numbers studied in the channel range from 1 400 to 8 000.The ratios of rib height to hydraulic diameter (e/D) are 0.2and 0.33,respectively.The ratio of rib spacing to height (P/e) ranges from 5to 15.The rib orientations in the opposite surfaces are symmetrical and staggered arrangements.The results show that the heat transfer coefficients are increased with the increase of rib height and Reynolds number,though at the cost of higher pressure losses.When the rib spacing to height ratio is 10,it keeps the highest heat transfer coefficient in three kinds of rib spacing to height ratios 5,10 and 15.The heat transfer coefficient of symmetrical arrangement ribs is higher than that of the staggered arrangement ribs,but the pressure loss of the symmetrical arrangement ribs is larger than that of the staggered arrangement ribs.

EXPERIMENTAL RESEARCH AND DESIGN ON HEAT TRANSFER OF EVAPORATOR USED IN THE LARGE QUICK FREEZE PLANT

The evaporator is the main part of a quick-freeze equipment. There are many factors influencing the heat transfer coefficient of an evaporator. The most important factors among them are the fin shape, tube diameter, distance of fin space, frost, and velocity of air flow etc. They mainly influence the thermal efficiency of an evaporator, and therefore its thermal efficiency has direct relationship with the whole efficiency of the quick freeze plant. Evaporators with different structural types have different heat transfer efficiency, in order to obtain high efficiency structure of evaporator, 8 evaporator models with different fin shape, tube diameter and tube arrangement are analyzed and compared. The calculation results show that the integral waved fins, equilateral-triangle arranged small diameter tubes and varying fin-spacing has the highest heat transfer coefficient. The experimental result also shows that the evaporator with this type of structure has better thermal efficiency. The experimental result is in good agreement with the calculation result, it can instruct engineering design for usual designer. A real quick-freeze equipment is designed and put into production. The result shows that, compared with traditional domestic quick-freeze equipments, this equipment decreases by 40% in size and by 20% in energy consumption.

Experimental Study of Heat Transfer in a Real Scale Building Incorporating PCM in the Air Layer of the Vertical Walls

The purpose of this paper is to study the energy efficiency of a local living space exposed to solar radiation in the subtropical climate of Casablanca. The study was mainly focused on the contribution of a phase change material (PCM), inserted into a 7-cm thick air layer of a double brick wall, in two different locations. We note that the experimental study was conducted using two real-scale test cavities, located in the Faculty of Science Ain Chock-Casablanca. Two PCM mounting methods were used for the south and west walls, in order to test its energy efficiency as a storage and retrieval means of the solar flux coming from the outside. In the case of the southern wall, the PCM is put directly on the internal side of the outside part of the double wall (Case 1). For the west wall, the PCM is placed 1.2 cm away from the internal side of the outer part of the double wall (Case 2). The first result shows that the PCM placed to the wall allows storing the solar heat during the day and releasing it to the outside of the building at night. While in the second case, the PCM keeps the heat stored day and night.

Analysis of Heat Transfer Performance of Oscillating Heat Pipes Based on a Central Composite Design

Oscillating heat pipes (OHPs) are very promising cooling devices. Their heat transfer performance is af- fected by many factors, and the form of the relationship between the performance and the factors is complex and non-linear. In this paper, the effects of charging ratio, inclination angle, and heat input and their interaction effects on heat transfer performance of a looped copper-water OHP are analyzed. First, suppose that the relationship between the response and the variables approximates a second-order model. And use the central composite design to arrange the ex- periment. Then, the method of least squares is used to estimate the parameters in the second-order model. Finally, multi- variate variance analysis is used to analyze the model. The results show that the assumption is right, that is to say, the re- lationship is well modeled by a second-order function. Among the three main effect variables, the effect of inclination angle is the most significant, but their interaction effects are not significant. In the range of the considered factors, both the optimum charging ratio and the optimum inclination angle increase as the heating water flow rate increases.

Theoretical and experimental investigation on vertical tank technology for sinter waste heat recovery

In the present work, the gas flow pressure drop and gas–solid heat transfer characteristics in sinter bed layer of vertical tank were studied experimentally on the basis of the homemade experimental setup. The gas flow pressure drop through the sinter bed layer was measured with different gas velocity and particle diameters, as well as the sinter and air temperatures. The influences of gas superficial velocity and particle diameter on the gas flow pressure drop and gas solid heat transfer in sinter bed layer were analyzed in detail. The revised Ergun's correlation and gas solid heat transfer correlation were obtained according to the regression analysis of experimental data. It is found that, the pressure drop of unit bed layer height gradually increases as a quadratic relationship with increasing the gas superficial velocity, and decreases as an exponential relationship with the increase of sinter particle diameter. For a given sinter temperature, the heat transfer coefficient in sinter bed layer increases with increasing the gas superficial velocity, and increases with decreasing the sinter particle diameter. In addition, the heat transfer coefficient also gradually increases with increasing the sinter temperature at the same gas superficial velocity and sinter particle diameter. The mean deviations between the experimental data obtained from this work and the values calculated by the revised Ergun's correlation and the experimental heat transfer correlation are 7.22% and 4.22% respectively, showing good prediction.

Industrially Experimental Investigations and Development of the Curve-ROD Baffle Heat Exchanger

The conventional heat exchanger with segmental baffles is prone to bring forth fluid-induced vibration of heat transfer tubes and increase the pressure drop of shell-side greatly at higher fluid flow velocity. In order to avoid the above defects, the ROD-baffle heat exchanger has been developed. However, its collocation of heat transfer tubes is conventionally in square, which leads to fewer heat transfer area per unit volume. Based on the ROD-baffle heat exchanger, a new type curve-ROD baffle has been developed, and an industrial investigation of the curve-ROD baffle heat exchanger with normal triangular collocation has been carried into execution. In this paper, two equations using the Reynolds number were acquired to predict the heat transfer coefficients of the shell-side and tube-side. The experimental results show that the shell-side heat transfer and pressure drop characteristics of the curve-ROD baffle heat exchanger are superior to those of the segmental baffle one.

Heat transfer analysis of the bent cooling channels in SSRF light-blocked components

The front end light-blocked components of the third generation of synchrotron radiation facility,which are subjected to high heat load,are cooled with flowing water through the cooling channels.The convective heat transfer coefficient and the flow resistance(or pressure drop) are two important parameters for evaluating the heat transfer performance of the cooling channels and should be strictly quantified.In this research,two typical bent cooling channels in Shanghai Synchrotron Radiation Facility(SSRF) were modeled and their in-pipe turbulent flows were simulated.The two criteria obtained under different channel water velocities met the SSRF technical requirements.To reduce the total pressure drop,arc transitions were proposed to replace the right angle transitions in the cooling channels.At the same time,an experiment was performed to measure the convective heat transfer coefficient of a typical bent channel unit.The experimental results were in good agreement with the simulation ones.

A NEW METHOD TO JUDGE THE ENHANCEMENT OF HEAT TRANSFER IN THE TRAILING EDGE OF TURBINE BLADES

An experimental investigation of heat transfer and friction loss with taper pin fin configurations were dealed with. Three kinds of configurations-full cross pin fins (FCF), shorter round pin fins (SRF) and taper pin fins (TPF), with different height md spacing of the fins and friction loss are compared with each other. Besides, a new dimensionless number, the ratio of f to Nu, cslled here the specific friction loss, is put forward to judge the validity of configurations. The comparison obviously shows that:

电厂锅炉实验虚拟仿真系统建设与应用

为开展能动专业核心课程“锅炉原理”的实验教学,校企合作开发了电厂锅炉实验虚拟仿真系统。基于两相流动与辐射对流传热原理构建的仿真系统,由风烟和汽水两大模型构成,严格遵守质量、能量、动量守恒方程。变负荷虚拟实验显示,随锅炉负荷增加,热效率降低、燃料耗量增加。根据辐射传热原理,结合火焰平均温度计算发现:只有炉膛出口烟温增加,才能保证炉膛传热负荷增加,继而抬升排烟温度,导致排烟热损失变大、锅炉热效率降低。锅炉原理实验虚拟仿真,可训练学生运用锅炉本体热力计算原理分析问题的思维,是落实创新能力培养的重要举措。

增压型鼓泡吸收输运特性实验装置的设计与研究

为探索真空环境下,气泡在溶液吸收过程中流动、传热特性及其机理,设计了一种增压型垂直管内溶液鼓泡吸收输运特性测量实验装置,并介绍了该装置的结构和工作原理,通过系统真空度维持、气泡流动和能量校核等实验分别验证系统的可靠性和准确性。结果表明,增压技术实现了负压环境下的鼓泡吸收。静置12 h系统真空度上升率仅为2.33%,系统气体泄漏量为2.4 mL/h,装置具有良好的可靠性。实验过程中的气泡产生、上升、碰撞、聚并和破裂行为与文献气泡流动行为一致。溶液和冷却水的出口温度、溶液出口质量分数测量结果最大相对偏差分别为0.08%、0.02%和0.01%;不同溶液入口温度和溶液流量的能量校核实验的最大误差分别为10.4 J和12.5 J,装置具有良好的准确性。为探究真空环境下鼓泡吸收的输运特性及揭示其传递机理奠定了良好的实验基础。

微通道内相变流动可视化教学实验系统研制

微通道相变换热技术可较好地解决集成电路散热问题,近年来已成为传热学领域的研究热点之一。为满足国家“双碳”人才培养需求,增强本科生对新型换热技术的深入了解,研制一套微通道内相变流动可视化教学实验系统。实验系统由加热系统、可视化热沉室、测量系统以及相关管路和元器件组成,其中通道宽度为1 mm,既能形成微通道沸腾流动,又便于学生观察实验现象。实验时通过调节水流量和加热功率来控制沸腾程度,以呈现独立气泡、塞状流、弹状流、环状流等典型气泡特征及其转变过程,实验过程生动有趣、启发思考,可增强学生对基础知识的理解,提高创新能力。

光伏组件多元复合相变材料控温特性研究与模拟

选取石蜡-十四醇掺混石墨作为多元复合相变材料,应用ANSYS软件建立光伏与相变控温模块的传热模型进行模拟分析与验证。研究不同质量分数的石墨、相变层热导率、热焓值以及厚度对光伏控温效果的影响。结果表明:上述因素都会不同程度地影响光伏组件的温度,其中石墨用量以及相变层厚度的影响最明显。当相变层中添加10%石墨时,光伏高于50℃的累计时间最少;当相变层厚度为50 mm时,控温效果最佳。

负压环境对喷雾冷却传热性能影响实验研究

为研究喷雾冷却实验系统在负压环境下的传热性能,搭建了一套以水为工质的闭式喷雾冷却系统,测试计算得到不同压力环境下表征系统传热能力的散热表面热流密度、传热系数及温度。结果表明:喷雾流量为0.45 L/min时热流密度及传热系数随喷雾腔内压力的降低呈增大趋势,当腔内压力降低至20 kPa时传热系数较常压下增加了95.2%;当喷雾流量为0.25 L/min时,随喷雾腔内压力的降低,热流密度及传热系数先增加后减小;当加热功率从100 W增加至1200 W时,热流密度及传热系数均随着腔内压力的降低而大幅增加,但适用热工况范围逐渐缩小;负压环境较常压环境下散热表面温度均匀性更差。研究结果可为喷雾冷却技术在航天器上的实际工程应用提供参考。

实验在传热学课程中的应用与优化

传热学是热力学和物理学中的一门重要学科,涉及热量和温度在物质内部和物质之间的传递和转换。在传热学的理论教学中,各高校更加关注如何提高学生的学习兴趣和学习效果,使学生更好地理解和应用传热学的相关知识。其中传热实验是启发学习传热学兴趣不可或缺的一部分。文章探讨了传热学实验课的教学目标、实验内容和实验方式。分析了传热学实验课教学的现状和存在的问题,结合传热学的基本知识和应用,提出了传热学实验课应具备的教学目标,立足于实验课堂,提出了教学优化策略。

椭圆型套管-管翅式蒸发式冷凝器传热传质性能及实验研究

介绍了一种椭圆型套管-管翅式蒸发式冷凝器,通过搭建的蒸发式冷凝器性能测试实验系统,研究该蒸发式冷凝器在不同循环水配比、不同地区环境以及“风冷”“水冷”“蒸发冷凝”和“全工况”4种不同运行模式下的传热传质性能与运行特性的变化规律。结果表明:在相同条件下“全工况”模式的热流密度高于“风冷”和“蒸发冷凝”两种模式,而“水冷”模式由于其传热面积远小于其它模式,所以其热流密度最高;“全工况”模式在保持配风量及循环水总量一定的条件下,热流密度随循环水配比的增大而先增大后减小,喷淋水与冷却水的流量最佳配比为2∶5;“全工况”模式在严寒干燥地区、寒冷地区以及夏热冬暖地区的总热流密度分别为5879.64、3964.28及2933.05 W/m^(2),因此不同地区环境运行的传热性能相差较大,该冷凝器“全工况”模式在空气干燥的地区,喷淋冷却水温度范围为13~18℃运行时传热性能较优。在相同的条件下,“蒸发冷凝”模式的水膜传质系数高于“全工况”模式,且两者均随喷淋密度的增大先增大后减小。

塔式太阳能吸热器中超临界CO_(2)流动换热研究进展

归纳总结了超临界CO_(2)在8 MPa、10 MPa和12 MPa下的热物性特点,并对超临界CO_(2)在水平管、竖直管以及螺旋管中流动与传热的实验研究和数值研究文献进行了总结,整理了非均匀热流边界条件下超临界CO_(2)流动换热研究文献。水平管中产生的二次循环可以强化超临界CO_(2)的流动传热;竖直管中由密度变化引起的浮力效应导致超临界CO_(2)的局部传热系数在沿管向上和向下流动中呈现不同的变化趋势;螺旋管中浮力和离心力的作用均能在圆周截面上产生二次流动,提高超临界CO_(2)的传热效率。此外,利用超临界CO_(2)替代传统的传热流体可以有效提高太阳能热发电的效率。太阳能吸热器的非均匀热流会导致热损失和热应力的增加,进一步调整超临界CO_(2)流量分布以匹配热流分布可以减少热损失、减少热应力分布不均匀。

A Cooperative Activity on Quenching Process Simulation Japanese IMS-VHT Project on the Benchmark Analysis and Experiment

Japanese IMS-VHT project on the Virtual Heat Treatment tool for monitoring and optimising HT process in relation with the international cooperative programs is briefly introduced. This project motivates to develop virtual tools for computer to optimize the heat treatment condition and to support decision for HT operation by knowledge based database in addition to process simulation. As one of the activities with the cooperation of the Society of Materials Science, Japan and the Japan Society for Heat Treatment, a benchmark project is undergoing. This includes simulation of carburized quenching process of a cylinder, disc, and ring as well as a helical gear by use of common data of materials properties and cooling characteristics by several available simulation programs. A part of the newly obtained results is presented as an interim report.

极地海洋工程装备圆管结构的对流换热影响

电伴热是极地海洋工程装备防寒主要措施,而热平衡是对流换热的关键问题.以圆管构件为研究对象,采用有限元数值仿真软件Fluent数值仿真与模型实验相结合的方法,分析了圆管构件在风速为0~40 m/s、温度为-40~0℃的极地环境条件下对流换热系数变化情况;基于数值仿真数据建立了电加热圆管构件对流换热系数的预测模型.结果表明:增大风速和降低温度都会增加圆管构件的对流换热系数;温度低于-30℃或风速大于25 m/s且温度低于-20℃时,温度对圆管的对流换热系数影响增大;实测数据验证了该模型的合理性.

永磁同步驱动电机温度场研究进展综述

永磁同步电机(PMSM)具有效率高、转速范围宽、功率密度大、控制性能好等优点,在电动汽车驱动系统中得到了广泛的应用。但是随着电机功率密度的提高,由于损耗发热而引起的温升问题成为永磁同步驱动电机发展的瓶颈之一。电机温升过高会损坏电机零部件,缩短电机的使用寿命,降低驱动系统的可靠性。为保证永磁同步驱动电机稳定可靠地工作,其温度场的研究至关重要。在回顾当前研究的基础之上,梳理了永磁同步驱动电机温度场研究中的关键问题,包括损耗来源与计算方法、热量传递路径及传热形式、温度场分布规律、温度场建模与测试方法,同时总结了各环节面临的问题与挑战。最后指出了车用永磁同步驱动电机温度场研究中亟待解决的关键问题。