倾斜降膜蒸发特性实验研究

以电加热作为供热热源来模拟太阳能,研究了不同工况下倾斜降膜蒸发特性,通过对蒸馏器吸热面和冷凝面划分等间距小区段,根据液膜和冷凝面的温度分布,利用Dunkle模型预测了蒸馏器的产水速率.结果表明:热流密度、单位长度给水质量流量、倾斜角度和单位长度冷却水质量流量是影响蒸馏器产水速率的主要因素;产水速率随着热流密度的增大呈线性增加;在单位长度给水质量流量为5.5～10.0kg/(h.m)时,产水速率随着单位长度给水质量流量的减小呈线性增大,单位长度给水质量流量为0.7～5.5kg/(h.m)时,产水速率波动较小;在倾斜角度为15°～60°时,产水速率随着倾斜角度的增大而增大;冷却水均匀地流过冷凝面上表面有助于增大蒸馏器的产水速率;蒸馏器吸热面和冷凝面划分的区段越多,模型预测值与实验值吻合越好.     

不同特征尺寸管式降膜太阳能海水蒸馏器热性能分析

为提高小型太阳能海水蒸馏器热能利用效率和产水速率,设计一种管式降膜太阳能海水蒸馏器,基于小高径比环形封闭空间水蒸气传热传质特性,分析特征尺寸和运行温度对装置单位冷凝面积产水速率的影响机理,研究不同特征尺寸管式降膜太阳能海水蒸馏器蒸发冷凝温差、竖直方向冷凝温度梯度等变化规律.结果表明,运行温度为85℃时,特征尺寸为0.0...     

锥台式降膜蒸发太阳能苦咸水淡化装置实验研究

针对传统太阳能苦咸水淡化装置运行过程中水体热容量大、传热距离长的问题,文章提出并设计了新型锥台式降膜蒸发太阳能苦咸水淡化装置,通过倾斜冷凝面以拦截浮升水蒸气,从而缩短了苦咸水液膜蒸发传热距离,减少了蒸发冷凝腔内不凝气体量,实现了封闭环形空间内小特征尺寸传热,通过对比分析冷凝面倾斜角度为70°（装置一）和冷凝面倾斜角度为45°（装置二）两装置产水速率和性能系数（GOR）,得到影响该装置性能的关键因素。结果表明,在进水流量为0.30 kg/h时,装置一最大稳态产水速率为0.24 kg/h,比装置二增加了8.33%,其最大蒸发冷凝温差为3.8℃,竖直方向冷凝温度差为1.7℃,性能系数为0.63,该研究为提升小型太阳能苦咸水淡化技术热能利用效率做了有益的探索。     

降膜蒸发过程的传热性能研究

对圆管和平壁的降膜蒸发过程的传热机理及影响因素进行了分析,并对已有的实验结果进行了比较;已有的实验研究主要是围绕圆管或平壁来进行,不利于找出最佳加热元件;提出在平壁表面加圆管型肋的复合加热元件,对其进行研究有利于找出最佳加热元件,对提高降膜蒸发传热效率极具实用价值。     

功能表面降膜蒸发传热特性的实验研究

研究了处理表面镀铬铝管、PTFE铜管和纯铝氧化管水平管降膜蒸发传热，研究了喷淋密度、热流密度、管内蒸汽速度和管表面处理对降膜蒸发传热特性的影响。实验结果表明：在表面蒸发区，水平管降膜蒸发传热系数随热流密度的增加而提高，随喷淋密度增大先降低后升高，冷凝例传热系数基本保持不变。总传热系数对操作条件变化很不明显，表面阳极氧化膜使传热系数略有下降，但由于其优良的抗垢时蚀性能，非常有必要再进行深入地研究。     

环形布膜器垂直管内R113降膜蒸发换热特性数值研究

通过建立垂直管内降膜蒸发物理数学模型,对环形插头型布膜器管内R113的气液两相逆流降膜蒸发换热特性进行二维非稳态数值研究,分析了管内液膜流动分布以及壁面温度和液膜表面温度分布,对比了加热前后液膜厚度的变化.结果表明:随着降膜蒸发过程的进行,液膜下端开始出现液滴飞溅,且不断向上端发展;R113在管内降膜蒸发过程中壁面温度和液膜表面温度沿流动方向逐渐升高,气相温度变化趋势则相反;从壁面到管中心,温度沿径向逐步降低,在近壁面1mm前后其分布趋势相反;加热后液膜厚度明显减小,且下游液膜厚度变得相对均匀.     

海水淡化中降膜蒸发过程的实验研究

由于横管降膜蒸发具有传热系数高、热耗低、可利用低品位能源等优点,横管降膜蒸发技术成为低温多效海水淡化技术中应用最广泛的方法.搭建了单管横管降膜试验台,观测了横管降膜蒸发的流动过程,研究了横管降膜蒸发过程中的流动特性和传热特性,归纳了管间距、喷淋密度对横管降膜蒸发过程中流动特性和传热特性的影响.实验结果表明:喷淋密度的增...     

紧凑高效型水平管束降膜蒸发换热器的实验研究

在大气压条件下使用单列和3列叉排光滑管和滚压强化换热管紧凑管束进行了水降膜蒸发换热实验,确认了滚压管在中,低热负荷范围内能够增强换热系数3～4倍,有很好的沸腾强化换热性能。管间距及液膜溅射损失对蒸发换热特性影响很小。同时也考察了单列和3列管束换热特性闯的差异。实验发现这种差异在低雷诺数区域时更加明显。     

氨水竖管降膜蒸发实验和理论研究

为了增强氨水竖管降膜蒸发过程中的热质传递效果,建立了降膜蒸发过程的数学模型,基于有限容积法对模型进行了求解,并通过实验验证了模型的准确性,用数学模型计算了溶液的速度场、浓度场、膜厚和换热量,得出结论:降膜蒸发过程的入口段小于100 mm,在入口段,溶液的流速和膜厚都发生剧烈的变化;最佳的布膜厚度是由溶液进口流量决定的;单位管长氨气的蒸发量随管长由上而下逐渐减小,前3 m管长的蒸发量占整个蒸发量的80.64%。基于建立的数学模型,可以确定不同流量下的布膜器最佳布膜厚度和管道最佳长度,为降膜换热器的优化设计提供参考。     

Experimental investigation of falling film evaporation on horizontal tubes

This paper presents the results of an experimental investigation relating to heat transfer during evaporation of thin liquid films falling over horizontal tubes. Experiments were conducted using 25 mm o.d. copper tubes heated by internal electrical cartridge heaters so that a uniform heat flux was generated on the outside tube surface. Five heated tubes were arrayed on a vertical plane with a pitch of 50 mm. Freon R-11 preheated to the saturation temperature at 0.2 MPa was supplied to the topmost heated tube through feeding tubes. Heat transfer characteristics on each heated tube were clarified in a range of film Reynolds number from 10 to 2000 and the measured data are presented in the form of correlations. Deterioration of heat transfer due to film break down was also considered. © 1999 Scripta Technica, Inc. Heat Trans Jpn Res, 27(8): 609–618, 1998     

Steady-state experimental study of a closed recycle solar still with enhanced falling film evaporation and regeneration

An active regenerative solar still with an area of 1.03 m², enabling one to reuse the latent heat of condensation and sensible heat of brine, is constructed and tested indoors, using a solar simulator for irradiation. In this still, a considerable fraction of the latent and sensible heat is successfully recycled and utilized for preheating the feedstock and recycling air via a falling film evaporator–condenser. The forced thin layer evaporation and film condensation, which are the efficient enhanced processes for heat transfer, are applied in this unit. As a result, the performance ratio of the unit is about two to three times greater than that of a conventional basin-type solar still (single-effect).     

Experimental study on a horizontal tube falling film evaporation and closed circulation solar desalination system

A specifically designed solar desalinization system with a solar collector (about 2.01 m² in area) has been developed and tested under practical weather conditions. In this system, a considerable fraction of the latent and sensible heat is successfully recycled and utilized for preheating the feedstock and recycling air via a condensation cavity and heat exchangers. The thermal performance of the system is greatly improved because of the falling film evaporation technology used. As a result, the yield is about two to three times more than that of a conventional single basin type solar still under the same conditions. The transient-state performance of the system, the relationships with the solar radiation, the operating temperature, the feedstock flow rate and the productivity are presented. Other factors influencing the freshwater are also discussed.     

水平管降膜蒸发中强迫对流传质过程实验研究

对水平横管束降膜吸收器中,溴化锂溶液表面自然对流和强迫对流传质现象,分别在常压和负压下进行了实验研究。以惠特曼提出的双膜模型为基础,对实验结果做出了分析;以图线的方式,直观的比较了传质系数与压力,溶液表面对流情况的关系。得出了强迫对流对传质系数有很大提升的结论。     

横管降膜蒸发过程中管间距对传热系数影响的实验研究

针对横管降膜蒸发器的4种主要布管方式(三角形、正方形、转角三角形、转角正方形)所对应的3种管间距下,以海水和纯水作为实验工质的传热系数进行了实验研究。研究结果表明:转角正方形布置(管间距为45.7mm)下的传热系数最高,三角形布置(管间距为57.2mm)次之,正方形、转角三角形布置(管间距为33.02mm)的传热系数最低;随着蒸发温度的升高,纯水作为实验工质时的三种管间距传热系数差异减小,而海水实验结果则正好相反;不同管间距传热系数产生差异的主要区域为管周向0~135°区域。     

Experimental study of flash evaporation of a water film

This experimental study of the flash evaporation phenomenon of a water film was carried out with an initial water height of 15 mm, superheats ranging from 1 to 35 K and initial temperatures from 30 to 75 °C. During a sudden pressure drop, temperature measurements of the water film allowed us to determine the water mass evaporated by this phenomenon as well as the mass flow rates. A correlation between the water mass evaporated by flashing and the superheat was then obtained. Evolution of the flash evaporation rate coefficient let us estimate the duration of the flash evaporation phenomenon.     

Transient theory of double slope floating cum tilted-wick type solar still

A double slope floating cum tilted-wick solar still has been fabricated and transient theory of floating cum tilted-wick type solar still has been proposed. Analytical expressions have been derived for the different temperatures components of the proposed system. For elocution of the analytical results, numerical calculations have been carried out using the meteorological parameters for a typical summer day in Coimbatore. Analytical expression results are found to be in the close agreement with the experimental results.     

Mathematical modeling and the thermal performance of floating cum tilted-wick type solar still

In this paper, mathematical modeling for the thermal performance of floating cum tilted-wick type solar still has been presented. Explicit expressions for the temperatures of various components of the proposed system and its efficiency have been developed. The effect of mass flow rate due to capillary action of jute wick has been investigated for evaporative, convective, and radiative heat transfer from the evaporating surface to the condensing surface.It has been found that the mass flow rate of 2.5 x 10^?3 kg/s is optimum for effective distillation. Also, the effect of absorptivity of the wick surfaces (floating and tilted-wick) on the productivity of the solar still has been studied and found that α_w1 (absorptivity of the tilted-wick surface) and α_wf(absorptivity of the floating-wick surface) of 0.85 have given higher productivity.For enunciation of the analytical results, numerical calculations have been made using meteorological parameters for a typical winter and summer day in Coimbatore.The theoretical results are in good agreement with the experimental results.     

A spray evaporation type solar still

The single effect basin type solar still has been for long the cheapest way to produce drinkable water from sea water using solar equipment (Howe and Tleimat, 1977). Nevertheless the operating efficiency is low, around 35 %, due mainly to the rejection to the atmosphere of the latent heat of condensation and consequently the production is also low, less than 5 1/m² day for a good insolation climate. Furthermore the device presents some operation problems like condensation on the inner side of the glass and algae growth both decreasing the radiation absorption of the basin, and others.Several attempts have been made to increase production, based mainly on the utilization of several evaporation stages using in each stage the latent heat of condensation rejected by the preceding stage (Férnandez and Chargoy, 1990, Joyce et al., 1993).Together with the recover of the latent heat one can increase the evaporation area either by utilizing a fabric where the previously heated salt solution circulates (Baumgartner et al., 1991) or by using some kind of high contact surface material like sponges or thorn bushes (AQUASOLAR, 1988).Another possibility of increasing the evaporation area is just by spraying the salt solution in air and then condensate the moisten air.The present paper describes the details of construction of a device based on spray evaporation and presents the results obtained in laboratory using water previously heated by electric resistances.The experimental results where then used to tune a computational model of the chamber [6] to obtain the performance (daily production and energy consumption) of the system when connected to a CPC solar collector. Testing of the device with CPC collectors will be carried on in the summer of 94.