多级增湿太阳能海水淡化的实验研究

基于多级增湿和分级冷凝原理,设计搭建了一台新型利用太阳能的多级增湿海水淡化装置,实验研究了喷水温度、不同的空气循环方式、分级冷凝对系统产水率和热耗的影响变化规律。研究结果表明,由于采用了分级冷凝和多级增湿技术,系统产水率提高了25%～50%,产水热耗得以降低。     

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0.015 m的管式降膜太阳能海水蒸馏器单位冷凝面积产水速率为0.696 kg/(h·m~2),比特征尺寸为0.035 m的蒸馏器增加10.48%,冷凝温度T_4为81.94℃,比特征尺寸为0.035 m的蒸馏器高3.83℃,在测试范围内蒸发冷凝温差最小为1.9℃,该研究可为强化管式太阳能海水淡化装置热质传递过程提供技术参考。     

不凝气体对竖管太阳能海水淡化装置性能的影响

针对太阳能海水淡化装置内不凝气体抑制气水混合物冷凝换热的问题,设计一种竖管太阳能海水淡化装置,通过分别填充氦气和空气作为蒸发冷凝腔工作介质,研究2种不凝气体对装置产水速率、蒸发冷凝温差、热扩散系数以及竖直温度梯度分布等性能的影响机理。结果表明,该淡化装置加热温度为80℃时,填充氦气的装置产水速率为245 g/h,比填充空气的装置产水速率增加15%,填充氦气的装置上测点温度与下测点温度相差约0.1℃,基于试验数据给出不凝气体为氦气运行条件下装置内Nu与Ra的经验关联式,二者呈指数函数关系,决定系数为0.9926。     

一种多级满液蒸发回热式太阳能海水淡化装置的设计

设计了一种多级满液型间接加热蒸发回热式太阳能海水淡化装置。装置中太阳能集热器与蒸发/冷凝部分通过热管联接为一整体,14个集热单元,分为7级;从第2级开始,均采用集热/蒸发/冷凝三位一体的单元,常压运行,不须使用真空泵。使用逐级降温回热法加强蒸汽的气化潜热回收利用,有效地提高了系统制水率和能量利用率。研究表明,在冬季运行工况下,装置的最高单位集热面积制水量为6.16 kg/m2,最大平均回热效率为65.83%。     

降膜蒸发多效回热吸收式太阳能海水淡化系统的实验研究

基于降膜蒸发与降膜凝结机理,设计建造了一台具有四效回热性能的吸收式太阳能海水淡化系统,用电加热水箱模拟太阳能集热系统,对该系统进行了模拟实验。实验中,对系统的瞬态和稳态性能进行了测试,给出了系统在不同运行温度、压力下的产水速率和性能系数。实验结果表明,由于在本系统中采用了横管、竖管降膜蒸发及降膜凝结技术,使其中大部分的蒸汽潜热及部分盐水的显热得到了多次重复利用,并由于吸收工质对最末效蒸汽进行了主动吸收,回收了蒸汽的焓,从而强化了最后一效的蒸发过程,因而系统具有较高的性能系数。在供热水温度为80℃、系统内部压力为15kPa时,四效装置的性能系数可达到3.0左右,体现出吸收式系统的良好优势。对影响产水率的其他因素也作了探索与分析,给出了合理的取值范围。     

多效鼓泡蒸发太阳能海水淡化系统的稳态实验研究

基于鼓泡蒸发和空气载湿气液相平衡机理,设计并实现了一台具有五级四效性能的鼓泡蒸发式太阳能海水淡化系统,对该系统的稳态产水性能进行研究,给出系统在特定的运行温度和压力环境中,不同鼓气量下各效的产水率、耗电当量及经济性能系数。实验结果表明,系统采用多效鼓泡蒸发技术并对各级采取鼓气量的优化组合措施,可提高系统的产水率。当各级载气流量分别为570、570、570、450L/h时的,装置的淡水产率为1.668L/h,GOR值为2.77,折算单位产量能耗4.93kWh/t,该点为装置的经济性能系数最高的工况点。     

几种不同类型太阳能蒸馏器的传热研究与性能分析

分析了几种不同类型太阳能海水淡化装置的结构、工作原理、传热传质等与装置产水率和性能相关的各种因素，指出了要提高装置的产水率、改善其性能，应从减小海水热容量、加强潜热利用、强化传热传质等方面来考虑，为太阳能海水淡化装置的进一步改进提供参考。     

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。     

四效管式降膜蒸发太阳能海水淡化装置性能研究

增加太阳能海水淡化装置的运行效数可显著地提升其热能利用效率和总产水量。为此,该文设计四效竖管式降膜蒸发太阳能海水淡化装置,对比研究运行效数对装置内环形封闭小空间中水蒸气热质传递的影响,理论分析装置内气体介质传热传质特性,采用试验测试数据对理论计算结果进行验证,同时还对不同运行温度条件下,装置各效产水速率、蒸发冷凝温度、竖直方向温度梯度以及排浓海水温度等参数进行测试分析。结果表明,四效海水淡化装置理论产水速率与试验产水速率变化趋势一致,二者最小偏差为6.08%,当运行温度为80℃时,装置总产水速率为0.95 kg/h,第1效产水速率是第4效产水速率的1.59倍,竖直方向温度差值最大为15.3℃,最高排浓海水温度为51.3℃。     

特征尺寸对竖管降膜太阳能海水蒸馏装置性能影响

针对小型太阳能海水蒸馏装置产水速率低等问题,设计竖管降膜太阳能海水蒸馏装置,理论推导单位冷凝面积产水速率ms的计算方法,分析特征尺寸对该太阳能海水蒸馏装置单位冷凝面积产水速率、二元混合气体对流传热温度、冷凝壁面温度梯度值等热特性的影响机理。结果表明,在输入功率为168 W,特征尺寸为15 mm的装置稳态运行时,单位冷凝面积最大产水速率为240.63 g/20 min,比特征尺寸为35 mm的装置增加了24.16%,二元混合气体稳态运行温度为85.37℃,比特征尺寸为35 mm的装置提高了7.21℃。     

横管降膜蒸发多效回热型太阳能海水淡化装置的性能分析

该文根据稳态实验结果，对实验装置的传热传质过程及火用过程进行了分析与计算。热分析表明，由于装置采取了多效回热措施，其热量的重复利用率接近100％，因而具有较高的热量利用系数；火用分析表明，系统的火用损来自多个方面，特别在蒸发腔及外冷凝器中，由于存在大量的不同逆传热过程，因而火用损失最大。因此，降低这两部分火用损是提高系统总火用效率的关键。     

A novel vacuum wastewater treatment plant integrated with a solar absorption system

In this investigation, a novel use of the solar absorption refrigeration systems was introduced by using it to enhance the operation of vacuum wastewater treatment plant. Wastewater treatment systems require a source of heat for evaporation, a cooling section for condensation and a mean of evacuation to facilitate evaporation. The solar absorption system can take over the first two tasks. Among the commercially available vacuum evaporators, one was selected and modified by replacing the conventional heat pump with the solar absorption system. Two validated mathematical models available in the literature, one for solar absorption subsystem and one for vacuum evaporation subsystem, were integrated together to perform the analysis. The impacts of solar absorption subsystem parameters along with vacuum evaporator subsystem parameters on the overall performance were investigated using the developed program. System performance was evaluated in terms of evaporation rate and condensate rate production. It was found that the degree of superheat had the greatest impact on the rate of evaporation. At low levels of supply temperature to the vacuum chamber, using only heat provided by the absorption system, the evaporation rate exceeded 60 kg/h. If the hot water was further heated by passing through the solar collector storage tank, the evaporation rate exceeded 200 kg/h.     

An energy saving atmospheric evaporator utilizing low grade thermal or waste energy

A specially designed compact thermal unit has been developed and tested for reducing the quantity of thermal energy required in evaporation and thickening processes. In this unit, a relatively large fraction of the heat of condensation and the sensible heat of the warm distillate is recycled and utilized for preheating the feedstock and evaporating the liquid phase within the evporation chamber. The yields obtained in such a thermal recycle unit can be increased by a factor of three relative to a simple single-effect (i.e. without recycling) evaporation unit operating under the same thermal energy input conditions. The proposed unit operates under atmospheric conditions and below the liquid boiling point. It resembles a multi-tubular film absorber. Since the evaporation chamber casing is heated (as opposed to being cooled), it performs as an air-blown film evaporator. A laboratory scale unit was built and tested to produce distilled water from city mains water. Its thermal efficiency corresponded to a three-stage vacuum evaporator. The main advantages of the proposed design are: simple construction, low fixed capital investment costs, low operation/maintenance costs and its amenability to utilize low grade thermal or waste (e.g. wet steam, exhaust gas, hot fluid) energy resources.     

Study on start-up characteristics of loop heat pipe under low-power

A series of experiments based on a flat loop heat pipe under low-power have been conducted in this work. It is found that the LHP can start up unfailingly under low heat power (Q = 6 W) and its thermal resistance is rather high in some cases of low-power. With the thickness of the sintered capillary interlayer increasing, the performance of start-up in the LHP becomes better because heat leak to compensation chamber is reduced and the temperature difference between compensation chamber and the evaporation room is increased. When compensation chamber in the LHP has a heat sink installed, the temperature difference and pressure difference between compensation chamber and evaporation room are augmented. As a result, it is beneficial to the improvement of start-up characteristics.     

Experimental study on the heat exchange effectiveness of a dry coil indirect evaporation cooler under various operating conditions

In this study, a pilot Dry Coil IEC unit, an indirect evaporation cooler established by connecting a direct evaporation cooler and a sensible heat exchanger (SHE) in series, was made, and the effectiveness data of the pilot unit were acquired under various operation conditions in an environmental chamber realizing a wide-range of indoor and outdoor air conditions. The test result shows that over 40% effectiveness can be acquired even in hot and humid climates by using the Dry Coil IEC proposed in this paper. The Dry Coil IEC reduces the cooling coil size by pre-cooling the process air during the cooling season. It can also be used as an SHE reclaiming the sensible heat from the exhaust air during winter operation. The pilot unit recovered over 60% of sensible heat in the test. In addition, a simplified model of Dry Coil IEC returning the various operation conditions was developed based on existing models of an SHE and a direct evaporative cooler. A polynomial equation returning the effectiveness of the Dry Coil IEC was derived as a function of seven independent variables highly influencing the performance of the unit. The experimental data acquired by the pilot unit operation agree well with the effectiveness values of the Dry Coil IEC predicted by the proposed model. It was also identified that the proposed equation agrees well with the existing model of the Dry Coil IEC applied to the energy simulation program.     

A study of the influence of inlet air flow humidity and temperature on thermal efficiency of an evaporation chamber of a solar desalination plant

Results are presented of calculation studies of the influence of inlet air flow humidity and temperature on thermal efficiency of an evaporation chamber of a solar desalination plant where the process of humidification of the air inlet to an evaporation chamber occurs due to the heat and mass exchange with the saltwater surface in it.     

The experimental and numerical investigation of a grooved vapor chamber

An effective thermal spreader can achieve more uniform heat flux distribution and thus enhance heat dissipation of heat sinks. Vapor chamber is one of highly effective thermal spreaders. In this paper, a novel grooved vapor chamber was designed. The grooved structure of the vapor chamber can improve its axial and radial heat transfer and also can form the capillary loop between condensation and evaporation surfaces. The effect of heat flux, filling amount and gravity to the performance of this vapor chamber is studied by experiment. From experiment, we also obtained the best filling amount of this grooved vapor chamber. By comparing the thermal resistance of a solid copper plate with that of the vapor chamber, it is suggested that the critical heat flux condition should be maintained to use vapor chamber as efficient thermal spreaders for electronics cooling. A two-dimensional heat and mass transfer model for the grooved vapor chamber is developed. The numerical simulation results show the thickness distribution of liquid film in the grooves is not uniform. The temperature and velocity field in vapor chamber are obtained. The thickness of the liquid film in groove is mainly influenced by pressure of vapor and liquid beside liquid–vapor interface. The thin liquid film in heat source region can enhance the performance of vapor chamber, but if the starting point of liquid film is backward beyond the heat source region, the vapor chamber will dry out easily. The optimal filling ratio should maintain steady thin liquid film in heat source region of vapor chamber. The vapor condenses on whole condensation surface, so that the condensation surface achieves great uniform temperature distribution. By comparing the experimental results with numerical simulation results, the reliability of the numerical model can be verified.     

Calculations of the pulse combustion drying system

The paper describes modelling of spray drying system where valved and valveless pulse combustors were applied as a source of drying agent. Experimental analysis of pulse combustors operation was carried out in order to optimize their performance to achieve low emission of toxic substances, stable operation and high and smooth pressure oscillations. Optimized valved and valveless units were applied in the drying system.Extensive drying and evaporation tests were carried out to establish basic data required for modelling of the system. Laser techniques were applied to determine flow field in the drying chamber (LDA) as well as to analyse the structure of disperse phase (PDA).A modified mathematical model of heat, mass and momentum transfer in spray drying, developed earlier, was used to describe the pulse combustion drying system. The model enables to obtain temperatures of continuous and disperse phases, percent of evaporation and positions of particular fractions in the dryer. Air velocity profiles in the axial and radial directions in the drying chamber determined experimentally were substituted to the main programme calculating the spray drying process.A comparison of theoretical and experimental results shows good agreement also for complex hydrodynamics of pulsating flow in the drying chamber.Experimental investigations and mathematical modelling proved that the pulse combustion spray drying system could be effectively applied in dewatering of solutions with low content of solids, which could be important for waste disposal.     

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。     

某相变换热供汽系统的运行经济性分析及措施

某单位封闭循环相变换热供汽系统按给水温度20℃下的锅炉热功率与用热设备进行匹配,但在运行中却出现了供热不足、系统运行压力低、锅炉疲劳运行、年运行煤耗高等问题,致使用热终端不能正常工作。分析表明,导致系统运行经济性差的主要原因是锅炉蒸发量和实际可用热功率不足。计算表明,保持运行压力在设计控制范围,锅炉蒸发量由现2t／h增加到3．7t／h不仅可满足供热要求,而且年运行煤耗也可比目前情况节省130t。