分离式热管蒸发段的试验研究

该文采用加热石英玻璃管和无缝钢管模拟分离式热管的蒸发段。对例题的充液。流和传热特性进行了系统的试验和理论分析。作者着重分析了核态沸腾传热区及飞溅降膜区的换热原理，试验数据回归整理李相应了换热系数无量钢准则关系式，与试验数据吻合较好；同时将这两个关系式分别与大空间沸腾传热及整体式热管蒸发段降膜传热区传热进行了比较，得出了极为有用的结论。     

柴油机非水冷却介质自然对流沸腾传热特性研究

对于采用非水冷介质的高温冷却及少冷却柴油机的研究，目前尚需了解冷却介质温度的提高及冷却介质的性质差异，对柴油机的传热及零部件热状况的影响。本文模拟柴油机工作条件，对机油、柴油及不同配比的乙二醇水溶液等液体的自然对流沸腾传热特性进行了试验研究，揭示了各种因素对传热的影响，通过对试验数据的回归分析得出了３种非水冷却介质自然对流沸腾传热关系式。为机油、柴油及乙二醇水溶液用于柴油机高温冷却及少冷却提供了理论依据。     

三维内花瓣形螺旋肋管式油加热器强化传热的试验研究

简要介绍了一种新型的三维内花瓣形螺旋肋管式油加热器的强化传热机理、特点、试验研究及在某电 厂油系统中实际应用的效果。试验获得的传热及流阻关系式为设计使用单位提供了依据。     

内螺纹管传热和压力损失

在高压试验装置上对蒸发管中内螺纹对传热和压力损失的影响进行了试验研究。试验研究的参数范围包括了矿物燃料锅炉全负荷及部分负荷的运行范围。研究结果与光管所得的数据及文献中提出的试验结果进行了比较。对沸腾危机的位置、CHF后传热及     

分离式热管蒸发段传热特性的研究

在研究分离式热管蒸发段流动特性的基础上,对其传热特性进行了系统的试验研究和理论分析,首先分析了核态沸腾传热区及飞溅降膜传热区的换热原理;根据数据回归整理了核态沸腾传热区和飞溅降膜传热区的换热系数无量纲准则关系式,与试验数据吻合较好;并将它们与其它关系式进行了比较,得出了有用的结论,其结果为分离式热管的研究及工程应用提供了理论依据。     

管内复合强化传热技术及机理分析

文中对管内强化传热及复合强化传热技术进行了在紊流流动下的阻力和传热特性分析，并给出了几种复合强化传热技术的试验研究结果。提出了螺旋槽带中插入旋向相反的部分管长扭带是行之有效，效果明显的复合强化传热技术。     

高温固液相变蓄热容器的研究与发展

介绍了近年来国内外空间太阳能动力装置PCM蓄热容器的研制情况，分析了PCM蓄热容器的传热过程及热分析方法，概括了研究中存的主要问题，认为进一步完善传热模型，寻求强化传热新途径，提高效率和可靠性及进一步的试验研究是今后发展及研究的主要方向。     

内表面烧结型多孔管的流动沸腾换热

采用流动沸腾传热试验平台,研究了2 m长铁基烧结型内表面多孔管竖直管内流动沸腾传热特性,利用流动沸腾传热学基本原理及公式计算了传热过程中的热通量、沸腾传热系数及相关参数,并考察了过热度和流速对多孔管流动沸腾传热性能的影响.结果表明:烧结型表面多孔管的流动沸腾传热能力优于同条件下的光滑管,内表面沸腾传热系数是同尺寸光滑管...     

单回路脉动热管传热特性研究

试验研究了单回路紫铜-水脉动热管在3种充液率下的传热性能,理论分析了不同加热功率和充液率下工质的干度、流速、显热和潜热及其份额的变化特性。结果显示:较小传热功率时,减小充液率或增大加热功率会提高热管的传热性能;而较高传热功率时,充液率和加热功率对热管的传热性能影响较小。增加传热功率或减小充液率,会提高管内工质的流速及流量,提高热管的潜热传热量及潜热传热份额;显热量随加热功率和充液率的增加而增大。     

单向开缝翅片管换热器传热与阻力性能的数值模拟及试验研究

对一种单向开缝翅片管换热器进行了数值模拟及试验研究,分析了不同翅片间距及管径下单向开缝翅片管换热器的传热与阻力性能的变化规律。数值模拟和试验结果的对比表明,采用数值模拟方法研究单向开缝翅片管换热器的传热与阻力性能是可行的。     

Comparison of Heat Transfer and Pressure Drop for the Helically Baffled Heat Exchanger Combined with Three-Dimensional and Two-Dimensional Finned Tubes

Experiments were performed to compare the shell-side heat transfer coefficient and pressure drop of a helically baffled heat exchanger with petal-shaped finned tubes to those of low-finned tubes for oil cooling using water as a coolant. The experimental results showed that for the heat exchanger with petal-shaped finned tubes, the shell-side heat transfer coefficients were augmented by 28–48%, yet the shell-side pressure drops were reduced by 35–75% at the same volumetric flow rates of oil. The possible mechanisms responsible for this heat transfer enhancement were analyzed for helically baffled heat exchanger combined with petal-shaped finned tubes.     

Experimental Investigation of Heat Transfer and Resistance Characteristics of a Finned Oval-Tube Heat Exchanger With Different Air Inlet Angles

The air inlet flow direction is not orthogonal to the heat exchanger surface in many cases. To study the performance of the heat transfer and pressure drop of a heat exchanger with different air inlet angles, this paper shows the experimental system about a finned oval-tube heat exchanger inclined toward the air incoming flow direction. The heat transfer and pressure drop characteristics of four air inlet angles (90°, 60°, 45°, and 30°) are studied separately for the Reynolds number ranging from 1300 to 13000 in this study. The experimental correlations of Nusselt number and resistance coefficient of the air side are acquired. The results show that the overall heat transfer coefficients become smaller and smaller with the decrease of the air inlet angles, while the pressure drops have significant changes. The heat transfer performances of the heat exchanger under the three inclined air inlet angles are worse than that at 90°. Among the three inclined angles, the performance at 45° is the best under identical mass flow rate criterion and at low Reynolds number under identical pressure drop criterion; that at 60° is the best at large Reynolds under identical pressure drop criterion. Finally, some conclusions are attained about the effects of the air inlet angles on the heat transfer and pressure drop performance of the finned oval-tube heat exchanger.     

Experimental determination of shell side heat transfer coefficient and pressure drop for an oil cooler shell-and-tube heat exchanger with three different tube bundles

In this paper, the heat transfer coefficient and pressure drop on the shell side of a shell-and-tube heat exchanger have been experimentally obtained for three different types of copper tubes (smooth, corrugated and with micro-fins). Also, experimental data has been compared with theoretical data available. Correlations have been suggested for both pressure drop and Nusselt number for the three tube types. A shell-and-tube heat exchanger of an oil cooler used in a power transformer has been modeled and built for this experimental work in order to investigate the effect of surface configuration on the shell side heat transfer as well as the pressure drop of the three types of tube bundles. The bundles with the same geometry, configuration, number of baffles and length, but with different external tube surfaces inside the same shell were used for the experiment. Corrugated and micro-fin tubes have shown degradation of performance at a Reynolds number below a certain value (Re < 400). At a higher Reynolds number the performance of the heat exchanger greatly improved for micro-finned tubes.     

A study on the simulation and experiment of a microchannel counter-flow heat exchanger

Numerical simulations and experimental tests were carried out to study the fluid flow and heat transfer characteristics for a rectangular-shaped microchannel heat exchanger. Moreover, influences of gravity to heat transfer and pressure drop behaviors of the microchannel heat exchanger were presented by variation of the physical inclinations of the microchannel heat exchanger system used for experiments. For experimental results, a heat flux of 17.4 W/cm² was achieved for the heat exchanger. Besides, the results obtained for the actual effectiveness and for the effectiveness (the so-called effectiveness-NTU method) were determined. In this study, the pressure drop decreases as the water temperature rises. As the pressure drop increases from 880 to 4400 Pa, the mass flow rate increases from 0.1812 to 0.8540 g/s. In addition, the results obtained from numerical analyses were in good agreement with those obtained from experiments, with discrepancies of the heat transfer coefficient estimated to be less than 9%.     

Heat Transfer and Pressure Drop Characteristics of Angled Spiraling Tape Inserts in a Heat Exchanger Annulus

Heat transfer augmentation in heat exchangers has received much attention in recent years, mainly due to energy efficiency and environmental considerations. Many active and passive techniques are currently being employed in heat exchangers, with twisted tape inserts providing a cost-effective and efficient means of augmenting heat transfer. This article describes how the single-phase heat transfer and pressure drop characteristics were determined for an angled spiraling tape that was inserted into the annulus of a tube-in-tube heat exchanger. Four sets of experimental measurements were taken: a normal tube-in-tube heat exchanger that was used as a reference and three heat exchangers with different angled spiraling tape inserts. Semiempirical heat transfer and pressure drop correlations were derived that predict the experimental data to within 4.3%. The angled spiraling tape inserts resulted in an increase in the heat transfer coefficients and pressure drop penalties, which varied with tape pitch and the direction of flow relative to the tape curvature. The smallest pich (25 mm) produced the greatest heat transfer enhancement (206%) and pressure drop penalty (203%). The heat exchanger with the largest pitch (100 mm) produced the lowest heat transfer enhancement (70%) and a corresponding low pressure drop penalty (58%).     

Enhancing heat transfer ability of drag reducing surfactant solutions with static mixers and honeycombs

Solutions containing drag reducing additives also show reduced heat transfer which limits their use in district heating and cooling recirculation systems where heat exchange is critical. In this study, static mixers A and B and honeycombs were installed at the entrance to a heat exchanger to break the solution microstructure temporarily and thereby enhancing their heat transfer ability when passing through the heat exchanger. The effectiveness of the destructive devices in enhancing the heat transfer ability of drag reducing cationic and mixed zwitterionic/anionic surfactant solutions was investigated together with the microstructure recovery time and pressure drop penalty paid for the heat transfer enhancement.     

Design of A Single Tube Fuel Oil Preheater

This article presents design analysis of a fuel oil preheater. The preheater is a concentric tube heat exchanger where the fuel oil is on the tube-side and the heating medium flows in the annular space. Two situations were addressed in this study. In the first case, an analytical model was developed where the required heat exchanger length, diameter and the fluid velocity were determined for a given heat transfer duty and for an allowable pressure loss. A detailed study was conducted by individually varying parameters such as pressure loss, preheater discharge temperature, and mass flow rate of the fuel oil. In each instance their influence on the predicted design of the heat exchanger was investigated. In the second case, an optimization strategy was proposed for a certain heat transfer duty. The heat exchanger dimensions and the fluid flow rate were selected such that the annual operating cost of the heat exchanger was minimized. In addition, a detailed study was conducted to understand the total annual operating cost as a function of the fuel oil outlet temperature and the fuel oil mass flow rate.     

Analysis of effectiveness and pressure drop in micro cross-flow heat exchanger

A theoretical model that predicts the thermal and fluidic characteristics of a micro cross-flow heat exchanger is developed in this study. The theoretical model is validated by comparing the theoretical solutions with the experimental data from the relative literature. This model describes the interactive effect between the effectiveness and pressure drop in the micro heat exchanger. The analytical results show that the average temperature of the hot and cold side flow significantly affects the heat transfer rate and the pressure drop at the same effectiveness. Different effectiveness has a great influence upon the heat transfer rate and pressure drop. When the micro heat exchanger material is changed from silicon to copper, the thermal conductivity changes from 148 to 400 W/m K. The heat exchanger efficiency is also similar. Therefore, the (1 1 0) orientation silicon based micro heat exchanger made using the MEMS fabrication process is feasible and efficient. Furthermore, the dimensions effect has a great influence upon the relationship between the heat transfer rate and pressure drop. Therefore, the methodology presented in this paper can be used to design a micro cross-flow heat exchanger.     

The effect of heat transfer on the pressure drop through a heat exchanger for aero engine applications

This work is focused on the experimental study of the performance of a heat exchanger designed for aero engine applications. The heat exchanger is operating as a heat recuperator by taking advantage of the thermal energy of the exhaust gas of the aero engine in order to obtain a better combustion with less pollutant emissions. The experimental study has been performed in a wind-tunnel by taking detailed flow and thermal measurements on a 1:1 model of the heat exchanger under various operating conditions described by the hot gas inlet mass flow rates and its spatial direction (different angles of attack and inclination) towards the heat exchanger. The hot gas has been modeled with preheated air. Six sets of measurements have been carried-out for different hot gas inlet and outlet temperatures, including also isothermal measurements without any heat transfer in order to have a reference point for the pressure drop of the flow through the device. The experimental results showed that the effect of the angle of attack on the pressure drop is significant while the effect of the angle of inclination is negligible. Additionally, the pressure drop through the heat exchanger is greatly affected by the heat transfer.     

Development of a microchannel evaporator model for a CO2 air-conditioning system

This paper presents the development and verification of a heat exchanger model for evaluating the thermal performance of an evaporator for a CO₂ mobile air-conditioning system. The model has been developed, on the basis of the finite volume method, with emphasis placed on the air-side heat and mass transfer processes. The governing equations are derived from mass and energy balances using the newly developed air-side heat transfer and friction loss correlations for microchannel heat exchangers under both dry and wet conditions. The calculated air-side heat transfer and pressure drop data are in good agreement with measured data. However, the refrigerant-side pressure drop estimation for microchannel tubes usually underestimates the measured value. The simulation results and importance of selecting appropriate heat transfer and pressure drop correlations for the microchannel heat exchanger are addressed.