共查询到20条相似文献,搜索用时 0 毫秒
1.
SurfacesInvestigationofEnhancedBoilingHeatTransferfromPorousSurfaces¥LinZhiping;MaTongze;ZhangZhengfang(InstituteofEngineerin... 相似文献
2.
3.
A mechanism is proposed for nucleate pool boiling heat transfer along with a general model for both pure liquids and binary
mixtures. A combined physical model of bubble growth is also proposed along with a corresponding bubble growth model for pure
liquids on smooth tubes. Using the general model and the bubble growth model for pure liquids, an analytical model for nucleate
pool boiling heat transfer of pure liquids on smooth tubes is developed. 相似文献
4.
通过对五种尺寸的窄空间试验元件分别以水和乙醇做工质进行实验。研究了窄空间间距、窄空间尺寸、不同工质及不同热流密度对窄空间沸腾性能的影响。结果表明:当窄空间尺寸与热流通等因素组合恰当时。其换热系数可比大空间池沸腾提高3~6倍;临界热流密度有所降低。 相似文献
5.
为实现节能降耗,开发了多种强化沸腾传热的高效换热管。以水为工质,在0.1MPa下对垂直光管、烧结多孔管和T槽管进行了池沸腾传热实验研究,并分析了沿管子轴向的温度分布。实验结果表明,烧结多孔管与T槽管能显著降低起始沸腾过热度、强化沸腾传热:烧结多孔管和T槽管的起始沸腾过热度比光管的低1.5K左右;烧结多孔管和T槽管的核态沸腾传热系数分别为光管的2.4~3.2倍和1.6~2.0倍。此外,烧结多孔管和T槽管能降低相同热流密度下的壁面温度,且有利于降低管子轴向的温差。 相似文献
6.
窄空间只有在间距小于汽泡脱离直径时,对沸腾传热强化才有比较显的效果。窄空间沸腾强化传热的机理在于较大的泡底微层加速了蒸发传热和窄空间中被加热的液体周期性地与池液进行容积交换。水平圆盘窄空间中的汽泡生长分为性质完全不同的自由生长期和抑制长大期;在一个周期内,加热面的总传热量等于壁面传导给窄空间液体的热量与通过合体泡底微层蒸发潜热之和。在对圆形水平窄空间的沸腾传热的现象和机理进行分析的基础上,提出了窄空间的沸腾换热过程的数理模型;进而对窄空间沸腾的本质规律在理论上进行了初步探索,并得到分析解。理论计算结果与实验数据比较表明,该分析解适合于中低壁面过热度的情形。由于问题的复杂性,该模型仍需不断完善。 相似文献
7.
ln desalinization devices and some heat exchangers making use of low‐quality heat energy, both wall temperatures and heat fluxes of heated tubes are quite low and generally cannot cause boiling in flooded‐type tube bundle evaporators with a large tube spacing. But when the tube spacing is very small, boiling in restricted spaces can occur and induce a higher heat transfer than that of a falling film or pool boiling at the same heat flux. This study investigated experimentally the effects of tube spacing, positions of tubes, and heating status of tubes as well as surface status (smooth and roll‐worked) on boiling in restricted spaces in compact horizontal tube bundle evaporators under atmospheric pressure. The experimental results provide a restricted space boiling database for water in smooth and enhanced surface tube bundles. Of particular importance is information concerning the influence of tube spacing of flooded‐type tube bundle evaporators, especially for the case of zero pitch, when the neighboring tubes are contacting each other. © 2001 Scripta Technica, Heat Trans Asian Res, 30(5): 394–401, 2001 相似文献
8.
The two‐dimensional, steady, pool film boiling heat transfer from a horizontal circular plate facing downward to a stagnant saturated liquid is studied theoretically. It is assumed that the vapor‐liquid interface is smooth and that radiation can be disregarded. The relevant governing equations for the vapor film are solved for saturated water at atmospheric pressure using an improved two‐equation boundary‐layer integral method. It is shown that the dimensionless temperature profile is affected by the wall superheat ΔTsat and that the ratio of Nu to X0.2 is an increasing function of ΔTsat. Here, Nu represents the mean Nusselt number and X the film‐boiling Rayleigh number. In addition, it is revealed that the one‐equation boundary‐layer integral method developed by Nishio and colleagues is fairly accurate in predicting the film thickness, the representative radial velocity, and the mean Nusselt number. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(1): 72–84, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10071 相似文献
9.
Much progress has been made in high‐performance electronic chips, the miniaturization of electronic circuits and other compact systems recently, which brings about a great demand for developing efficient heat removal techniques to accommodate these high heat fluxes. With this objective in mind, experiments were carried out on five kinds of test elements with distilled water and ethanol as working liquids. The test elements used in these experiments consisted of five parallel discs with diameters varying from 5 mm to 40 mm. The experiments were performed with the discs oriented horizontally and uniform heat fluxes applied at the bottom surfaces. The influence of narrow spacing, space size, working liquid property, and heat flux on boiling heat transfer performance in narrow spaces has been investigated. Experimental results showed that the boiling heat transfer coefficient of a narrow space was 3 to 6 times higher than that of pool boiling when the narrow space size and heat flux combine adequately, but the critical heat flux was lower than that of pool boiling. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(5): 307–315, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20017 相似文献
10.
11.
Sand spots, attached to a copper ball surface by means of polyvinyl acetate adhesive and distributed over the surface with areal density that ranges between one spot per 1.18 cm2 (for low‐density spots) and one spot per 0.51 cm2 (for high‐density spots), serve as a temporary heat transfer enhancer during the quenching in liquid nitrogen. Highest heat flux densities, achieved during quenching, lie in the range 10.8 to 20.2 W/cm2, depending on the sand layer structure. Application of the temporary enhancer increases an amount of heat, evacuated by highly effective nucleate and transition boiling, by factor of 4.5 as compared with the bare sample. The process of sand layer preparation, data acquisition peculiarities, relationship between heat exchange efficiency and the spots areal density, along with sand grit size are discussed in this paper. 相似文献
12.
An experimental study was conducted to investigate the effects of acoustic cavitation on natural convective heat transfer from a horizontal circular tube. The experimental results indicated that heat transfer could be enhanced by acoustic cavitation and had the best effect when the head of the ultrasonic transducer was over the midpoint of the circular tube, and the distance between the head and the tube equaled 15 mm. The augmentation at low heat flux was better than that in the case of high heat flux. Based on experimental results, the correlation formula of Nusselt number for water was obtained. 相似文献
13.
14.
15.
INTanDUCTI0NBoilingheattransferandcriticalheatflux(CHF)inaconfinednarrowspacehavebeenstudiedexperi-melltallybyanumberofinvestigatorsinthepastfewdecades.However,thereisnoanypopularlyacceptedmodelintheheattransferinnarrowspaceboiling,althoughsomepopularknowledgeabouttheboilingheattransferinthenarrowspacehavebeenacceptedbymanyresearchers.Theknowledgecanbecon-cludedasthatthenucleateboilingheattransferisenhancedatlowheatfluxregionanddeterioratedathighheatfiuxregi0nespeciallyatCHF.Theenhanceme… 相似文献
16.
Katsuhide Ohira 《亚洲传热研究》2003,32(1):13-28
Slush hydrogen is a mixture of liquid hydrogen and solid hydrogen particles, and is being considered as a spaceplane fuel or as a means of transport for hydrogen used as a source of clean energy. This paper describes nucleate boiling heat transfer characteristics of slush hydrogen and slush nitrogen. For the visual observation of heat transfer states, a heat transfer unit was placed in a glass Dewar designed to minimize the heat loss from an atmospheric environment. The heat transfer unit used was a circular flat plate 0.025 m in diameter made of electrolytic tough pitch copper. During testing, three different orientations of the heat transfer surface were used: horizontal facing up, vertical, and horizontal facing down. Heat transfer data for the normal boiling point (NBP) of liquid hydrogen, the triple point (TP) of liquid hydrogen, the NBP of liquid nitrogen, and the TP of liquid nitrogen were obtained up to the critical heat flux (burnout). These data for slush hydrogen and nitrogen, including the results of observation of the heat transfer surface were compared. This clarified the nucleate boiling heat transfer characteristics of slush hydrogen and slush nitrogen, which have rarely been investigated. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(1): 13–28, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10068 相似文献
17.
An experimental study was conducted to investigate transient local heat transfer around a bubble at onset of boiling on a thin glass heating plate immersed in saturated n-hexane at low pressure. Eight rapid response Cu-Ni thermocouples consisting of a vacuum deposited thin film were used to measure the temperature change of the heating surface. Simultaneous high-speed video photographs were also obtained. The surface temperatures near a nucleation site decreased rapidly owing to the evaporation of a thin layer (microlayer) of liquid formed beneath the bubble in the early period and the rate of bubble growth increased with increasing incipient boiling superheat (ΔTIB). The thickness of the microlayer decreased markedly with increasing ΔTIB. © 1998 Scripta Technica, Heat Trans Jpn Res, 26(7): 484–492, 1997 相似文献
18.
微尺度通道内流动沸腾研究综述 总被引:1,自引:0,他引:1
阐述了微尺度通道内传热问题出现的工程背景——高密度微电子器件的冷却。对当前国内外微尺度通道内流动沸腾换热特性的研究现状进行了归纳。突出分析了工质种类、微尺度通道的几何参数和工质的工况参数等对微尺度通道内流动沸腾换热特性的影响。同时分析了微尺度通道内流动沸腾换热的强化机理、流动阻力特性、压降关联式和沸腾换热关联式的理论和实验研究。最后根据分析对今后的工作提出了一些建议。 相似文献
19.
Transient and steady state natural convection heat transfer for D-mannitol on a horizontal cylinder was investigated experimentally at various liquid temperatures and heat input conditions. To clarify the natural convection phenomena of D-mannitol, transient and steady heat transfer coefficients were measured under various liquid temperatures of D-mannitol and periods of heat generation rates from a horizontal platinum cylinder. The platinum cylinder with a diameter of 1 mm and a length of 43.5 mm was used as the test heater in this experiment. Experimental results indicated that the steady heat transfer coefficient of D-mannitol was affected by the liquid temperature. As the liquid temperature increased, it was understood that the effect of liquid temperature weakened. When the period of the heat generation rate was changed, the heat transfer process was divided into natural convection heat transfer and conductive heat transfer. It was considered that the conductive heat transfer was more dominant as the period of the heat generation rate decreased. The empirical correlations of steady and transient heat transfer coefficients for D-mannitol were obtained. 相似文献
20.
Experimental studies were made on heat transfer on a horizontal platinum wire during nucleate pool boiling in nonazeotropic refrigerant binary mixtures at pressures of 0.25 to 0.7 MPa and at heat fluxes up to CHF. The boiling features of the mixtures and the single-component substances were observed by photography. The relationship between the boiling behavior and the reduction of heat transfer coefficients in binary mixtures is discussed in order to propose a correlation useful for predicting the present experimental data over a wide range of low to high heat fluxes. It is shown that the correlation is applicable to alcoholic mixtures. The physical meaning of k, which was introduced to evaluate the effect of heat flux on the reduction of a heat transfer coefficient, is clarified based on measured nucleate pool boiling heat transfer data and visual observations of the boiling features. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(7): 535–549, 1998 相似文献