氧化石墨烯脉动热管传热性能实验研究

通过实验研究以氧化石墨烯分散液为工质的脉动热管的传热性能。实验采用1mg/m L的氧化石墨烯分散液,所得结果与以去离子水为工质的脉动热管传热性能进行比较发现:氧化石墨烯对以去离子水为工质的脉动热管传热性能具有强化作用,但是和脉动热管的加热功率密切相关。在加热功率低于20 W时,氧化石墨烯对脉动热管的强化作用较弱;当加热功率在30~60 W时,氧化石墨烯对脉动热管的强化作用较强,在3.71%~11.33%之间,且强化作用随加热功率的增大呈逐渐增强趋势;但随着功率继续增大,氧化石墨烯的强化作用逐渐减弱,当加热功率达到80 W后,热管传热性能减弱,原因可能是氧化石墨烯颗粒出现了沉降现象。     

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。     

不同充液率和加热功率下乙烷脉动热管传热性能研究

通过实验研究了在充液率为30%～70%,加热功率为10～60 W的工况下乙烷脉动热管的传热性能。结果表明:随着加热功率的增加,冷凝段和蒸发段的温度波动依次经历了低幅低频、低幅高频、高幅高频和高幅低频的振荡模式;在中低加热功率下,蒸发段和冷凝段的温度振荡波形相位角相差180°,而当高加热功率时,蒸发段和冷凝段的温度变化是同步的;在不同的加热功率下,脉动热管均在50%充液率时达到最佳传热性能;脉动热管的传热性能随加热功率的增大先增强后减弱,其存在最佳加热功率使得脉动热管的换热效率最高。     

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。     

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。     

基于响应面法分析氧化石墨烯对脉动热管传热性能的影响

响应面法（Response Surface Methodology,RSM）是评价多个自变量对过程及结果影响程度的有效工具。基于RSM方法,试验研究了氧化石墨烯（Graphene Oxide,GO）纳米流体对脉动热管（Pulsating Heat Pipe,PHP）的传热强化作用,分析了加热功率20~105 W、充液率25%~75%及GO纳米流体质量分数0%~0.1%时对PHP传热性能的影响。结果表明：氧化石墨烯/水脉动热管传热性能受加热功率、充液率及GO纳米流体质量分数的共同影响;加热功率（Q）的影响最大,其次是充液率（FR）,GO纳米流体质量分数（ω）的影响最小;Q与FR的交互作用较强时,对热阻影响显著;FR与ω的交互作用较弱时,对热阻影响则较小;Q与ω的交互作用及对热阻的影响最小;最佳运行参数为Q=96.4 W,FR=67.5%,ω=0.041%,对应的热阻值Rmin为0.463 K/W;应用RSM方法可大幅减少实验次数,有效分析GO/水PHP传热性能及影响因素,并预测最佳运行工况。     

基于表面活性剂水溶液的脉动热管可视化传热机理研究

脉动热管以质量浓度为1 440 mg/kg的十六烷基三甲基溴化铵（CTAB）水溶液为工质，固定充液率为50%，加热功率为10～105 W，通过可视化的角度探究CTAB/水PHP的作用机理，分析其在不同功率段的典型气泡行为，并与去离子水PHP进行比较。结果表明：CTAB/水PHP在流型方面具有较多气泡，主要以气泡簇的形式存在；加热功率为10 W时，去离子水PHP无法正常启动，其传热性能不如CTAB/水PHP；在低加热功率段，（10～30 W），二者均出现长液塞现象，且CTAB/水PHP能在加热功率更低时完成长液塞的隔断；在中等加热功率段（45～75 W）,CTAB/水PHP的蒸发段产生大量小气泡，且随着加热功率的增加，小气泡数量逐渐变多，去离子水PHP中未发现相同现象；高加热功率段（90～105 W）,CTAB/水PHP中更多观察到长液塞包裹着大量小气泡，而去离子水PHP在流型上与中等加热段无明显区别。     

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%。     

不同加热功率下充液率对无芯环路热管性能的影响

设计了以铝为管材、丙酮为传热工质的无芯环路热管。其蒸发段采用加热带加热,冷凝段用风冷降温。热管依靠蒸发压头使工质循环,并依靠重力作用,使冷凝液回流到蒸发段。搭建试验台并研究了不同加热功率下充液率对无芯环路热管的传热温差、传热量、热效率、热阻和当量导热系数的影响。结果表明:加热功率为150.00 W、充液率为30%时,无芯环路热管的均温性最好;传热温差和热阻均最小,分别为6.75℃、0.045 K/W。传热量132.00 W、热效率0.88、当量导热系数168 125 W/(m·K),均达到最大值。所以,该无芯环路热管在本实验研究范围内的最佳工作条件为加热功率150.00 W、充液率30%。     

基于中子成像技术环路热管的可视化试验研究

基于中子成像(NR)技术对铜-丙烯环路热管(LHP)在不同加热功率(0、5和10 W)下的运行进行了可视化研究。结果表明:在加热功率为5 W时蒸发器内液体工质在减少,冷凝器能够充分冷凝,液体管线充满液体工质;在加热功率10 W时热管内部冷凝的液体工质量在减少,蒸发器开始出现烧干现象;环路热管能够成功启动并稳定运行,且随加热功率增加启动时间减少;LHP在5 W时内部的气液分布使得传热性能最佳,在10 W时风扇的强制对流并不能达到充分冷凝的效果,导致热管热阻增大,性能变差;LHP运行过程中气体管线部分存在残留液体工质,这会减少LHP的工质实际循环量,降低其传热性能。     

Influence of filling ratio and working fluid thermal properties on starting up and heat transferring performance of closed loop plate oscillating heat pipe with parallel channels

Using ethanol or acetone as the working fluid, the performance of starting up and heat transfer of closed-loop plate oscillating heat pipe with parallel channels(POHP-PC) were experimentally investigated by varying filling ratio, inclination, working fluids and heating power. The performance of the tested pulsating heat pipe was mainly evaluated by thermal resistance and wall temperature. Heating copper block and cold water bath were adopted in the experimental investigations. It was found that oscillating heat pipe with filling ratio of 50% started up earlier than that with 70% when heating input was 159.4 W, however, it has similar starting up performance with filling ratio of 50% as compared to 70% on the condition of heat input of 205.4 W. And heat pipe with filling ratio of 10% could not start up but directly transit to dry burning. A reasonable filling ratio range of 35%-70% was needed in order to achieve better performance, and there are different optimal filling ratios with different heating inputs- the more heating input, the higher optimal filling ratio, and vice versa. However, the dry burning appeared easily with low filling ratio, especially at very low filling ratio, such as 10%. And higher filling ratio, such as 70%, resulted in higher heat transfer( dry burning) limit. With filling ratio of 70% and inclination of 75°, oscillating heat pipe with acetone started up with heating input of just 24 W, but for ethanol, it needed to be achieved 68 W, Furthermore, the start time with acetone was similar as compared to that with ethanol. For steady operating state, the heating input with acetone was about 80 W, but it transited to dry burning state when heating input was greater than 160 W. However, for ethanol, the heating input was in vicinity of 160 W. Furthermore, thermal resistance with acetone was lower than that with ethanol at the same heating input of 120 W.     

Experimental study on heat transfer performance of pulsating heat pipe with refrigerants

The effects of different refrigerants on heat transfer performance of pulsating heat pipe(PHP) are investigated experimentally.The working temperature of pulsating heat pipe is kept in the range of 20℃-50℃.The startup time of the pulsating heat pipe with refrigerants can be shorter than 4 min,when heating power is in the range of 10W-100W.The startup time decreases with heating power.Thermal resistances of PHP with filling ratio 20.55% were obviously larger than those with other filling ratios.Thermal resistance of the PHP with R134a is much smaller than that with R404A and R600a.It indicates that the heat transfer ability of R134a is better.In addition,a correlation to predict thermal resistance of PHP with refrigerants was suggested.     

Effect of silver nano-fluid on pulsating heat pipe thermal performance

This paper presents preliminary experimental results on using copper tube having internal and external diameter with 2.4 mm and 3 mm, respectively, to carry out the experimental pulsating heat pipe. The working fluids include the silver nano-fluid water solution and pure water.In order to study and measure the efficiency, we compare with 20 nm silver nano-fluid at different concentration (100 ppm and 450 ppm) and various filled ratio (20%, 40%, 60%, 80%, respectively), also applying with different heating power (5 W, 15 W, 25 W, 35 W, 45 W, 55 W, 65 W, 75 W, 85 W, respectively). According to the experimental result in the midterm value (i.e. 40%, 60%) of filled ratio shows better. In the majority 60% of efficiency is considered much better. The heat dissipation effect is analogous in sensible heat exchange, 60% has more liquid slugs that will turn and carry more sensible heat, so in 60% of filled ratio, heat dissipation result is better than 40%, and the best filled fluid is 100 ppm in silver nano-fluid.Finally, we observed through the measurement comparison in thermal performance with pure water. When the heating power is 85 W, the average temperature difference and the thermal resistance of evaporator and condenser are decreased by 7.79 °C and 0.092 °C/W, respectively.     

Experimental study on the start up performance of flat plate pulsating heat pipe

An experimental system of flat plate pulsating heat pipe was established and experimental research was carried out in this system to know the mechanism of heat transfer, start-up and operating characteristics. The factors, such as filling rate, heating power, heating method etc, which have great influence on the thermal performance of the plate pulsating heat pipe were discussed. The results indicate that heating power and filling rate are the important factors for the start-up of the plate pulsating heat pipe. The different start-up power is needed with different filling rate, and the start-up of the heat pipe in case of bottom heated is much easier than that of top heated. Increasing the heating power and enlarging the heating area can make the start-up easier. Heating power can also affect the start-up time of heat pipe under the condition of bottom heated, while it does not have some influence to the heat pipe of top heated. The thermal resistance of plate pulsating heat pipe is related with the heating power, and the higher the heating power is, the smaller the thermal resistance is. But the best filling rate which the heat pipe needs is different with different heating methods, and the performance of the heat pipe in the case of bottom heated is better than the others.     

An Experimental Investigation of Thermal Performance of a Polymer‐Based Flat Heat Pipe

A polymer‐based flat heat pipe (PFHP) was fabricated. The heat transfer performance was measured and analyzed when deionized (DI) water and acetone were used as the working fluid, separately. Input power ranging from 2.8 W to 14.2 W was provided to the evaporator section while the device was at different filling ratios. Experimental results revealed that, when the polymer‐based flat heat pipe was laid in a horizontal position, the thermal resistance (1.02 K/W) was much smaller than that (4.6 K/W) of a copper plate with the same thickness at the thermal power of 10.3 W and the value decreased as the tilt angle changed from 0° to 90°.     

Experimental research on heat transfer of pulsating heat pipe

Experimental research was conducted to understand heat transfer characteristic of pulsating heat pipe in this paper, and the PHP is made of high quality glass capillary tube. Under different fill ratio, heat transfer rate and many other influence factors, the flow patterns were observed in the start-up, transition and stable stage. The effects of heating position on heat transfer were discussed. The experimental results indicate that no annular flow appears in top heating condition. Under different fall ratios and heat transfer rate, the flow pattern in PHP is transferred from bulk flow to semi-annular flow and annular flow, and the performance of heat transfer is improved for down heating case. The experimental results indicate that the total heat resistant of PHP is increased with fill ratio, and heat transfer rate achieves optimum at filling rate 50%. But for pulsating heat pipe with changing diameters the thermal resistance is higher than that with uniform diameters.     

Helmholtz共振腔强化换热的试验研究

为研究脉动流体对强化换热的影响，设计Helmholtz共振腔并分别在加装和不加装共振腔的情况下进行对比试验，发现水流经共振腔后变成了脉动流体，脉动的水经过单管换热器后强化了换热，在一定的共振腔参数的配合下，换热系数提高约10％～40％。     

中深层地热地埋管实际运行影响因素研究

为研究中深层地热地埋管运行的影响因素,分析西咸新区中深层地热地埋管供暖系统的长期运行结果,并结合关中地区地质数据,建立深度为2510 m的中深层地埋管换热器全尺寸模型,采用数值模拟法研究实际岩层分布下地埋管的运行、结构和材料因素对其取热能力的影响。结果表明,西咸新区某项目1号地埋管和2号地埋管两个地埋管,其平均取热功率均在310 kW以上,具有优良的取热能力。地埋管进水温度随季节变化明显,并引起用户侧负荷及热泵回水温度的波动。在结构方面,随内管径由63 mm增至125 mm,平均出口水温和换热功率分别降低1.9%和4.8%,但内管径过小将影响内管运行的安全性,综合安全和换热两方面因素,最佳内管径应选取ϕ110 × 10mm规格;随外管径由168.3 mm增至244.5 mm,平均出口水温和换热功率分别增加3.5%和9%,综合成本和换热两方面因素,最佳外管径应选取ϕ 177.8 × 19 mm规格;在运行方面,地埋管出口水温随着流量的增加而减小,换热功率随着流量增加而增加;出口水温随着进水温度的升高而上升,换热功率也随之减小。在材料方面,减小内管导热系数和增加固井材料导热系数均能增加地埋管出口水温和换热功率,考虑换热功率变化和成本因素,在工程中导热系数为0.42 W/（m∙K）的内管和导热系数为3 W/（m∙K）左右的固井材料。     

Experimental Investigation of Pulsating Heat Pipes and a Proposed Correlation

Pulsating heat pipes are complex heat transfer devices, and their optimum thermal performance is largely dependent on different parameters. In this paper, in order to investigate these parameters, first a closed-loop pulsating heat pipe (CLPHP) was designed and manufactured. The CLPHP was made of copper tubes with internal diameters of 1.8 mm. The lengths of the evaporator, adiabatic, and condenser sections were 60, 150, and 60 mm, respectively. Afterward, the effect of various parameters, including the working fluid (water and ethanol), the volumetric filling ratio (30%, 40%, 50%, 70%, 80%), and the input heat power (5 to 70 W), on the thermal performance of the CLPHP was investigated experimentally. The results showed that the manufactured CLPHP has the best thermal performance for water and ethanol as working fluids when the corresponding filling ratios are 40% and 50%, respectively. Finally, with the available experimental data set of CLPHPs, a power-law correlation based on dimensionless groups was established to predict their input heat flux. Compared with the experimental data, the root-mean-square deviation of the correlation prediction was 19.7%, and 88.6% of the deviations were within ± 30%.     

Experimental investigation of pulsating heat pipe performance with regard to fuel cell cooling application

A pulsating heat pipe (PHP) is a closed loop, passive heat transfer device. Its operation depends on the phase change of a working fluid within the loop. Design and performance testing of a pulsating heat pipe was conducted under conditions to simulate heat dissipation requirements of a proton exchange membrane (PEM) fuel cell stack. Integration of pulsating heat pipes within bipolar plates of the stack would eliminate the need for ancillary cooling equipment, thus also reducing parasitic losses and increasing energy output. The PHP under investigation, having dimensions of 46.80 cm long and 14.70 cm wide, was constructed from 0.3175 cm copper tube. Heat pipes effectiveness was found to be dependent upon several factors such as energy input, types of working fluid and its filling ratio. Power inputs to the evaporator side of the pulsating heat pipe varied from 80 to 180 W. Working fluids tested included acetone, methanol, and deionized water. Filling ratios between 30 and 70 percent of the total working volume were also examined. Methanol outperformed other fluids tested; with a 45 percent fluid fill ratio and a 120 W power input, the apparatus took the shortest time to reach steady state and had one of the smallest steady state temperature differences. The various conditions studied were chosen to assess the heat pipe's potential as cooling media for PEM fuel cells.