共查询到20条相似文献,搜索用时 140 毫秒
1.
重力热管内部包含复杂的两相流动以及相变传热过程,传统理论分析及实验手段不能直观给出其内部流动、相变、热质传递的详细信息。采用VOF(volume of fluid)多相流模型对重力热管内气液两相流动及传热进行模拟,捕捉到蒸发段气泡产生、合并、长大、上升,以及冷凝段壁面附近液滴形成、合并、下滑、汇集到液池的全过程,得到的壁温分布与实验测量值对比体现良好一致性,表明数值模拟的正确性。同时,以热阻、传热量和热效率为评价标准,研究不同充液率和倾斜角度下对重力热管运行性能的影响。结果表明:在所研究的参数范围内,随着充液率的增加,热阻逐渐减小,冷凝段传热量逐渐增大。且工质初始充注量充满蒸发段时热管性能较好;倾角对热阻的影响不明显,冷凝段传热量和热效率均随倾角增加而增长。 相似文献
2.
将多片平板微热管阵列进行堆叠可以提高传热量。实验研究了不同叠加片数下平板微热管阵列在不同加热功率下的热阻、传热极限、温度分布及变化规律、不同层热管传热等运行特性。实验表明,随热管片数增加,热管整体的传热量增加,最大传热量由单片的60W提升至5片的180W;传热热阻降低,最小传热热阻由单片的1.09℃/W下降为5片的0.24℃/W。而且,随着片数增加,热管间的传热热阻开始影响多片平板微热管阵列的整体运行:外侧热管的传热量高于内侧热管,热阻低于内侧热管,且当片数为4片及以上时,热管整体性能提升会越来越不明显。在相同的加热功率下,多片平板微热管阵列的外侧蒸发段、外侧冷凝段和内侧蒸发段温度均随片数增加而降低,但内侧冷凝段温度先升高后降低。最理想的热管叠加片数为3-4片。 相似文献
3.
重力辅助平板型环路热管实验研究 总被引:1,自引:0,他引:1
研制了一套以不锈钢丝网为毛细芯的平板式蒸发器、风冷式冷凝器,以甲醇为工作工质的环路热管,并着重研究了其在不同热负荷条件下启动特性以及变工况条件下运行特征。实验结果表明,平板式LHP可以在1~10W/cm2热流密度范围内顺利启动,并有良好的适应变热负荷能力,在改变工况的时候系统一般能在3min内重新达到新平衡状态。系统在18~48W热负荷条件下出现波幅和周期不等的温度波动现象。实验系统的热阻在0.29~3.2℃/W之间,热阻与热负荷、系统倾角以及工质充灌量有关,并重点研究了倾角以及充灌量对系统启动及其变工况运行的影响。 相似文献
4.
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%。 相似文献
5.
6.
为研究分离式省煤器内循环工质的相变过程,使用Ansys Fluent中的mixture(混合流)模型对汽液两相流进行数值模拟。通过Lee's蒸发冷凝模型对分离式省煤器的传热传质过程进行了迭代计算,获得了瞬态的气相图和温度场。在相变系统的加热过程中,可观察到蒸发段的液池内气泡的形成、合并、生长和上浮的全过程和在冷凝段壁面上凝结成液膜,并汇集返回蒸发段的全过程,计算得到的壁面温度与工程现场测量值相吻合,验证了模型的正确性。研究了热流密度、相变段内径、相变段长度比、充液量和冷凝段参数对相变系统总传热系数的定性关系,研究表明:在蒸发段管径30 mm、冷凝段温度320 K、热冷段长度比为1、热流密度800 W/m~2情况下,充液率在0.2~0.8时分离式省煤器内循环系统可以稳定运行,充液率为0.4时,传热系数达到最大。研究结果为分离式相变换热系统的研究设计提供了参考。 相似文献
7.
8.
9.
文章针对不同充液量且长径比均为191的铜-水热虹吸管进行了实验研究,并对比分析了其在水平及微倾角状态下的传热特性。在冷却水流量恒定状态下,测量不同加热功率的热虹吸管轴向各测点温度及冷却水进出口水温,考察热虹吸管的轴向温度分布特点及变功率时各测点温度响应情况,计算对比分析热虹吸管的等效对流换热系数。实验结果表明,水平状态下,充液率为20%,30%和45%的热虹吸管,即使在低加热功率下也无法良好传热;充液率为14%的热虹吸管,在加热功率低于10 W时,传热性能良好。微倾角状态下,充液率为14%的热虹吸管传热性能大为改善,其蒸发段、冷凝段及等效对流换热系数均随着加热功率的增大而增大,但在加热功率达到40 W时会出现温度振荡现象。 相似文献
10.
满液型海水淡化蒸发器的换热特性研究 总被引:5,自引:2,他引:3
海水淡化装置,太阳能或余热吸收式制冷机中的蒸发换热器目前使用管排外降膜式蒸发方式。如将传热管束紧凑排列置于饱和状态液体中则变为满液式蒸发换热器,利用传热管束间受限空间内早期沸腾强化换热机理,将中小热负荷条件下的自然对流换热转化为核沸腾换热,在间隙尺寸适宜时,其换热性能可能优于降膜式蒸发换热器。该研究以盐水为实验工质,对紧凑传热管束受限空间的沸腾换热进行了实验研究,确认了满液式蒸发换热器也具有很好的换热性能,在中小热负荷条件下甚至超过降膜式蒸发换热器。 相似文献
11.
The present work presents a steady state two-dimensional theoretical analysis of laminar film condensation heat-transfer inside the condenser section of inclined wickless heat pipes flat-plate solar collector. A theoretical relation for the laminar film condensation heat-transfer coefficient is deduced and compared with the previous work. The comparison indicates good agreement between the present relation and most of the experimental results previously published. The present relation is preferred to the previously published empirical and theoretical relations. This is because it is valid for wide ranges of the wickless heat pipes inclination angles and the condenser section dimensions ratio. 相似文献
12.
13.
《International Journal of Heat and Mass Transfer》2007,50(7-8):1231-1237
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. 相似文献
14.
A mathematical model of evaporation and condensation heat transfer in a copper-water wicked heat pipe with a sintered-grooved composite wick is developed and compared with experiments. The wall temperatures are measured under different input power levels and working temperature conditions. The results show that the heat transfer in the condenser section was found to be only by conduction. In the evaporator, however, either conduction or boiling heat transfer can occur. The experimental data for the boiling heat transfer are well correlated by the theory of Stralen and Cole. Higher heat load drives the heat pipe to spend more time achieving the equilibrium state during the transient start-up process. The response curves of the evaporator thermal resistance are overlapped, and the condenser thermal resistance increases more sharply at the beginning. The total thermal resistance of the heat pipe ranges from 0.02 to 0.56 K/W. 相似文献
15.
The aim of this paper is to point out possible solutions to the further development of heat pipes by numerical modelling of phase-change heat transfer. Numerical modelling has now become a standard method that helps to reduce the economic costs of research and development of new and innovative devices. The article describes the procedures for using numerical simulation in phase-change heat transfer that occurs due to evaporation and condensation of the working fluid. The suggested procedure enables modelling of gravitational heat pipe under different changes in its geometry or under changes in the working fluid. From the simulation results we can find out how the heat pipe behaves under different geometric changes and how much heat output it transfers. The paper presents results obtained from modelling of heat pipes, such as classical gravitational heat pipe, heat pipe with capillary geometry, and closed loop pulsating heat pipe. The results gathered from numerical simulation of heat pipes were compared with measurement results. 相似文献
16.
Karim Alizad Kambiz Vafai Maryam Shafahi 《International Journal of Heat and Mass Transfer》2012,55(1-3):140-155
Thermal performance, transient behavior and operational start-up characteristics of flat-shaped heat pipes using nanofluids are analyzed in this work. Three different primary nanofluids namely, CuO, Al2O3, and TiO2 were utilized in our analysis. A comprehensive analytical model, which accounts in detail the heat transfer characteristics within the pipe wall and the wick within the condensation and evaporation sections, was utilized. The results illustrate enhancement in the heat pipe performance while achieving a reduction in the thermal resistance for both flat-plate and disk-shaped heat pipes throughout the transient process. It was shown that a higher concentration of nanoparticles increases the thermal performance of either the flat-plate or disk-shaped heat pipes. We have also established that for the same heat load a smaller size flat-shaped heat pipe can be utilized when using nanofluids. 相似文献
17.
Improvements of gravity assisted wickless heat pipes 总被引:2,自引:0,他引:2
The performance of conventional gravity assisted heat pipes and modified heat pipes with a separator in the adiabatic section is investigated experimentally. Heat pipes with a three layered wick in the evaporator section, in addition to the separator, are investigated. The performance of the modified heat pipes was compared to a reference gravity assisted heat pipe. Experiments were conducted on heat pipes of three lengths with a common diameter at constant evaporator and condenser lengths. The effect of varying the adiabatic length was, thus, investigated distinctly in normal heat pipes and in modified heat pipes with a separator. Water was employed as the working fluid in all heat pipes. The experimental program included five inclination angles and a heat flux range form 5 to 32 kW/m2. The presence of the adiabatic separator caused a marked improvement in all heat pipes tested for all lengths and inclination angles. A pronounced reduction in heat pipe evaporator temperature was obtained, which is accompanied by an improvement in the heat transfer coefficient. A correlation was developed for prediction of the heat transfer coefficient for gravity assisted heat pipes with an adiabatic separator. The correlation took into consideration the effect of the varying adiabatic length. The correlation was in good agreement with the experimental data. 相似文献
18.
19.
20.
To achieve a high heat-flux level and reduce manufacturing costs associated with conventional heat pipes, the concept of network heat spreaders employing a boiling heat-transfer mechanism in a narrow space had been proposed, and several flat-plate wickless heat spreaders had been designed and fabricated. The heat spreaders had been tested under different working conditions and orientations relative to gravity with very good results. The previously tested network heat spreaders, however, were based on plates with a relatively large size for general heat spreading purposes. In the present study, network heat spreaders with overall dimensions of 78 2 62 2 3.2 mm are designed and fabricated. Spreaders of this size are intended for use as heat sinks of high-power electronic components. External cooling fins are attached to enhance air-cooling heat transfer rate. The network heat spreaders are tested under various working conditions with water as the working fluid. The maximum heat input rate achieved is about 150 W with a corresponding heat flux of 60 W/cm 2 . Compared to the performance of a solid copper plate having the same overall size as the spreader, the maximum temperature difference over the surface is reduced from about 32°C to 3.3°C. The heat transfer performance of the spreader is also largely dependent on the filling ratio of the working fluid and the boiling heat transfer in the narrow space. For these reasons, boiling heat transfer mechanisms in a narrow space are analyzed, and a spreader design that would improve the performance in a horizontal position is described. 相似文献