单回路紫铜_水脉动热管传热性能的实验研究

实验研究了单回路紫铜—水脉动热管在水冷方式和定传热功率时,冷却水流量、倾角、管径和充液率4种因素对热管传热性能,包括管壁测点温度、冷热段均温、传热温差、传热热阻和温度振幅的影响规律,得到提高传热性能的一些措施。结果显示:水平放置的单回路脉动热管无法启动;30°以上倾角管内可产生振荡,增加倾角可降低传热热阻;定加热功率下,冷却水流量存在最佳值,过大和过小都会增加传热热阻;在脉动热管允许管径范围内,增加管径可大大降低传热热阻;相同传热功率时,30%充液率热管的传热热阻明显低于70%充液率管;小而均匀的壁温振荡比大幅锯齿状振荡时的传热性能好。     

脉动热管水平及小倾角条件下的传热性能

为了研究脉动热管放置方式对其传热性能的影响,以超纯水作为工质,对水平及倾角为30°放置的脉动热管的传热性能进行研究,用壁面温度振荡性能和传热热阻来描述其传热能力。在不同的放置条件下,着重分析不同加热功率和充液率(35%,50%,70%)对其传热性能的影响。研究表明：水平放置时,充液率为35%和50%时脉动热管不能启动,充液率70%时可以启动运行;脉动热管在运行时存在临界热量输入值,倾角为30°时,临界值为60 W,但水平放置条件下临界值为90 W;水平放置下的脉动热管传热热阻在不同加热功率下,显著高于倾角为30°的情况;倾角为30°,充液率为35%时的脉动热管适合在低加热功率范围运行,此时传热热阻要低于充液率为50%的情况,但传热范围很窄,传热极限低;30°倾角时,与充液率35%和50%相比,高充液率70%的脉动热管整体传热性能最优。     

乙醇_水双工质脉动热管传热性能实验研究

通过对乙醇-水双工质脉动热管在风冷条件下进行的实验研究,探讨了加热功率、体积配比和充液率对热管振荡和传热性能的影响。结果显示,在实验条件下,功率小于100 W时,充液率、体积配比和加热功率对热管传热性能的影响较明显;中高功率时热管稳定性与热管中液态水体积份额有关,且随水份额增大热阻降低。而水份额低于21%时,热管稳定性较差,且水的份额越小,不稳定出现时的功率越低。50%~70%充液率热管的传热性能要优于30%充液率的热管,体积配比相当的热管振荡特性和传热性能相对较差。     

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。     

石墨烯/丙酮纳米流体振荡热管传热特性研究

通过实验研究了不同质量浓度的石墨烯/丙酮纳米流体振荡热管不同充液率下的传热性能。结果表明,小充液率(45%)下,石墨烯/丙酮纳米流体振荡热管的热阻均小于纯工质丙酮,但烧干现象并没有得到明显改善;中等充液率(62%~70%)下,石墨烯/丙酮纳米流体振荡热管较纯工质丙酮来说不再发生烧干现象,纳米流体振荡热管的热阻随着加热功率的增加而明显降低,浓度为0.01%时具有较为明显的传热优势;大充液率(90%)下,石墨烯/丙酮纳米流体振荡热管的传热性能则普遍优于纯工质,且随着加热功率的增加,传热性能的优势更加明显。     

甲醇乙醇混合工质振荡热管传热性能研究

混合工质可为振荡热管带来独特的传热性能．比较甲醇、乙醇纯工质以及甲醇-乙醇混合工质振荡热管在不同充液率时的热阻随加热功率的变化情况,结果发现：在小充液率（45％）时甲醇-乙醇混合工质和乙醇振荡热管开始烧干时的加热功率高于甲醇工质振荡热管;在加热功率不是很大（低于65W）和大充液率（62％～90％）时,甲醇以及甲醇-乙醇混合工质振荡热管的传热性能优于乙醇振荡热管;在大加热功率（高于65W）和大充液率（62％～90％）时甲醇以及甲醇-乙醇混合工质振荡热管的热阻十分接近,均低于乙醇工质振荡热管的热阻,且热阻随着充液率的增加曲线变化越来越平缓．     

铜-R22分离式热管传热特性的试验研究

采用铜管模拟分离式热管蒸发段,以R22为工质,在热流密度1～5 kW/m2、蒸发温度30～60℃和蒸发段倾角10°～90°范围内,研究了这种分离式热管的传热特性.分析了热管的启动特性以及热流密度、蒸发段倾角和充液率对其传热特性的影响.结果发现:以R22为工质的分离式热管具有良好的启动性,蒸发段合理的充液率为80%～100%,在试验参数范围内,热流密度、蒸发段倾角和充液率对热管的传热性能没有明显影响.     

热管置入式墙体传热优化研究

提出一种新型被动式太阳能利用技术——热管置入式墙体。通过理论分析和实验测试对其传热性能进行优化研究,考察热管管径、蒸发段长度比、充液率等因素对热管置入式墙体传热性能的影响。研究表明,平均等效传热系数与热管外径近似成线性关系,在热管置入式墙体结构允许的条件下宜选用较大管径,蒸发段长度比的最佳范围为67%~80%;重力热管充液率对热管置入式墙体等效传热系数的影响显著,最佳充液率范围为30%~40%。     

纳米悬浮液热虹吸管的传热性能试验研究

在相同的试验条件下,对比研究了纳米CuO-去离子水(DW)悬浮液重力热管与普通DW重力热管的启动性和等温性,研究了纳米工质热管的充液率和颗粒浓度对热管工作特性的影响,对纳米工质热管的强化传热机理进行了初步探讨。研究表明:纳米工质热管比普通热管启动快;纳米工质热管蒸发段外壁温的高低与充液率、纳米浓度和加热条件有关;纳米颗粒浓度和充液率对热管的传热性能影响较大,且存在最佳浓度(本研究为5%)和最佳充液率(本研究为44.3%);高浓度纳米工质热管比普通DW重力热管易于达到传热极限;试验中纳米悬浮液重力热管的传热强化率为16.19%～146.27%。     

倾角对复合中空热管传热性能的影响

为了研究倾角对复合中空热管传热性能的影响,建立了复合中空热管传热性能实验装置,对相同充液比(33％)不同倾角(分别为60°、75°、90°)和不同工质(分别为纯水和无水乙醇)复合中空热管的传热性能进行了实验研究.研究结果表明:对于充液比为33％,工质为纯水和无水乙醇的复合中空热管,倾角为90°时传热性能最佳.实验研究为复合中空热管换热器的工业应用提供基础.     

Natural Convection Heat Transfer in an Inclined Enclosure Filled with a Water-Cuo Nanofluid

This article presents the results of a numerical study on natural convection heat transfer in an inclined enclosure filled with a water-CuO nanofluid. Two opposite walls of the enclosure are insulated and the other two walls are kept at different temperatures. The transport equations for a Newtonian fluid are solved numerically with a finite volume approach using the SIMPLE algorithm. The influence of pertinent parameters such as Rayleigh number, inclination angle, and solid volume fraction on the heat transfer characteristics of natural convection is studied. The results indicate that adding nanoparticles into pure water improves its heat transfer performance; however, there is an optimum solid volume fraction which maximises the heat transfer rate. The results also show that the inclination angle has a significant impact on the flow and temperature fields and the heat transfer performance at high Rayleigh numbers. In fact, the heat transfer rate is maximised at a specific inclination angle depending on Rayleigh number and solid volume fraction.     

Influence of Inclination Angle on the Start-up Performance of a Sodium-Potassium Alloy Heat Pipe

ABSTRACT

Alkali metal heat pipes play significant role in various high-temperature engineering applications because of their excellent heat transfer capacity. Inclination angle is one of major factors which significantly affect start-up and heat transfer characteristics especially for thermosiphons. A sodium-potassium alloy (Na-K) gravity-driven heat pipe (GHP), in which the content of potassium in Na-K is wt. 55%, was fabricated to study the effect of inclination angle on start-up and heat transfer capacities of high-temperature GHPs. The Na-K GHPs was fixed by the adjusting bracket in 9 inclination angles (0°, 10°, 20°, 30°, 40°, 50°, 60°, 70° and 80°). Outside wall temperature was measured by eleven thermocouples which calibrated by the China Institute of Metrology prior to using them in the experiments. Results show that inclination angle has a significant impact on start-up and heat transfer performances of the Na-K GHP because of the impact of gravity on the two-phase flow inside the heat pipe and effective heating area in the evaporator. Start-up and heat transfer characteristics are dramatically improved and temperature difference significantly decreases as the inclination angle increases from 0° to 50°, but slightly decreases when the inclination angle exceeds 60°.     

重力对微槽平板热管传热性能的影响

系统地研究了重力对微槽平板热管传热性能的影响,分析了工作温度、冷却方式和倾角等影响因素。通过对比实验发现重力对热管的轴向液膜分布影响非常明显,在周向只在大充液率时有明显的影响,从而使得倾角较大地影响了热管的传热能力。研究表明深槽平板热管具有优良的传热性能,在微电子器件冷却等微小空间散热方面有着良好的应用前景。     

Heat transfer performance in 3D internally finned heat pipe

An experimental study of heat transfer performance in 3D internally finned steel-water heat pipe was carried out in this project. All the main parameters that can significantly influence the heat transfer performance of heat pipe, such as working temperature, heat flux, inclination angle, working fluid fill ratio (defined by the evaporation volume), have been examined. Within the experimental conditions (working temperature 40 °C–95 °C, heat flux 5.0 kw/m²–40 kw/m², inclination angle 2–90°), the evaporation and condensation heat transfer coefficients in 3D internally finned heat pipe are found to be increased by 50–100% and 100–200%, respectively, as compared to the smooth gravity-assisted heat pipe under the same conditions. Therefore, it is concluded that the special structures of 3D-fins on the inner wall can significantly reduce the internal thermal resistance of heat pipe and then greatly enhance its heat transfer performance.     

Flow and Heat Transfer Characteristics of Two‐Phase Fluid in Inclined Pipes on a Rotation Platform

A rotating platform was used to create dynamic load, and the mixture air–water two‐phase flow and boiling steam–water two‐phase flow were obtained in an inclined test pipe. By changing the parameters, such as inclination of the test pipe, rotational speed, inlet temperature, flow rate, and so on, the experiments for two‐phase flow in the pipe at inclination of 0°, 45°, and 66° were conducted, respectively. The effects of acceleration and inclination on their flow and heat transfer characteristics were investigated. The two‐phase flow patterns in inclined pipes under rotation conditions were caught with a video camera. The images show that the impact mixed flow and churn flow were found in this research. The results show that the acceleration and pipe inclination significantly influence the flow characteristic and heat transfer of the two‐phase pipe flow. As the directions of the dynamic load and the gravity are opposite to the flow direction, the greater the dynamic load and inclination, the higher the pressure drop and the heat emission, and the lower the flow rate, the void fraction, and the fluid temperature. Therefore, the dynamic load and gravity will improve the flow resistance, enhance heat emission and reduce the heat gained by the fluid.     

Thermal performance of inclined grooved heat pipes using nanofluids

An experimental study was performed to investigate the thermal performance of an inclined miniature grooved heat pipe using water-based CuO nanofluid as the working fluid. This study focused mainly on the effects of the inclination angle and the operating pressure on the heat transfer of the heat pipe using the nanofluid with the mass concentration of CuO nanoparticles of 1.0 wt%. The experiment was performed at three steady sub-atmospheric pressures. Experimental results show that the inclination angle has a strong effect on the heat transfer performance of heat pipes using both water and the nanofluid. The inclination angle of 45° corresponds to the best thermal performance for heat pipes using both water and the nanofluid. The present investigation indicates that the thermal performance of an inclined miniature grooved heat pipe can be strengthened by using CuO nanofluid.     

Heat (mass) transfer in rectangular cross-sectioned two-pass channels with an inclined divider wall

Heat transfer characteristics in rectangular cross-sectioned two-pass channels with an inclined divider (inner) wall have been examined experimentally. Local heat (mass) transfer rates were measured by the naphthalene sublimation method; seven kinds of divider inclination angles were tested for three turn clearances under the Reynolds numbers of (2.0-5.0)×10⁴. The influence of the inclined divider wall on the local heat transfer characteristics is discussed in detail. Then, the optimum combination of the inclination angle and the turn clearance is examined based on the trade-off between the heat transfer enhancement and pressure loss penalty, and on the improvement of uniformity in the distribution of local heat transfer rates.     

Numerical Analysis of Baffle Cut on Shell Side Heat Exchanger Performance with Inclined Baffles

In this work, an attempt has been made to decrease the pressure drop and to increase the heat transfer rate in a shell and tube heat exchanger (STHX) by tilting the baffle angle and by varying the baffle cut. The process of solving the simulation includes modeling, meshing, and analyzing the geometry of the STHX by using Pro-E, hypermesh, and computational fluid dynamics package of ANSYS Fluent, respectively. The objective of this study is to find a suitable baffle inclination and baffle cut for the efficient performance of the STHX. The baffle inclinations of 25°, 30°, 35°, and 40° were considered for three different baffle cuts of 25%, 30%, and 35% of shell inside diameter and the results were compared with segmental baffle of inclination angle 0°. The shell side flow with different inclination angles and baffle cuts results in a significant variation in heat transfer rate and pressure drop in the STHX. The results provide a clear idea that the heat transfer rate is maximum in inclined baffle heat exchanger compared to that of segmental baffle heat exchanger. Further it is found that the STHX with the configuration of 35º baffle inclination angle and baffle cut of 30% of shell inside diameter provides higher heat transfer rate with minimum pressure drop compared to all other configurations.     

脉动热管传热性能的实验研究

对脉动热管的运行进行了可视化实验,分析了影响脉动热管运行性能的因素,并且在不同的充液率、传热量和不凝性气体含量的条件下,对脉动热管的运行进行了测试,实验结果表明:脉动热管的整体热阻受充液率、传热量、不凝性气体的影响,存在最佳的充液率,在一定的条件下脉动热管的运行达到最佳。