包覆吸水膜的管式蒸发散热器性能的实验研究

应用间接蒸发散热的原理,在空调冷凝器表面包覆吸水膜,利用水蒸发带走热量.这样蒸发面积达到了最大值,并且能够通过毛细力自动补充蒸发的水分.空调冷凝器中热工质的温度和热容比间接散热器中的一次空气大,能够提高蒸发表面温度,提高蒸发量,进而提高散热效率.通过对通有热水的表面覆盖吸水纸膜的单铜管的实验研究,得出了该方式的传热系数以及水膜的导热系数,证明了该散热方式较空调冷凝器空气强制对流和其它蒸发散热方式的优势.     

一种过滤-蒸发式家用空调器装置

介绍一种过滤-蒸发式家用空调器,通过布水器系统对室外空气进行加湿降温,然后用处理过的空气与冷凝器进行换热,不仅能有效降低空调能耗,充分利用冷凝水,实现冷凝水零排放,同时空气经过布水网时,空气中的大部分灰尘被吸附在布水网上,也能减少冷凝器表面的积灰现象,进而减少对空调的清洗次数,提高空调器使用寿命。经分析,在干旱少雨地区该空调器节能效果更加明显,由于结构简单,设备改造添加材料成本较低,易于实现产品化。     

一种基于太阳能与蒸发冷却的新型新风处理机组

新风负荷约占空调能耗的30％,减少新风处理能耗对降低空调能耗有重要作用.本文提出了一种将太阳能空气集热器与间接蒸发冷却器相结合的新型新风处理机组,夏季采用间接蒸发冷却器对新风预冷,喷淋水以循环水为主,利用冷凝水作为其补充水,降低了喷淋水的水温,并利用室内排风作为间接蒸发冷却器的二次空气,提高了换热效率;冬季采用太阳能空气集热器对新风预热,并利用间接蒸发冷却器作为一次空气与二次空气的显热换热器来承担部分冬季新风负荷,从而大大减少了新风处理机组的能耗.能耗计算分析结果表明,与传统新风处理机组相比,新型新风处理机组夏季节能36.9％,冬季节能64.0％,静态投资回收期为3.7年,动态投资回收期为4.7年.     

空调冷凝水利用实验研究

本文对空调器冷凝水的生成量及蒸发量进行了理论分析;通过KC-20/2011型空调验证,在相同条件下,采用不同喷洒冷凝水方式,冷凝器铜管同点温度能降低4.0~12.9℃不等;在广州夏季通常天气,洒冷凝水后冷凝器散热效率可提高约64.8%;实验与分析表明利用空调冷凝水冷却冷凝器不仅能解决冷凝水滴水问题还能大幅提高空调制冷效率,是提高空调节能的一种有效途径。     

空气源热泵

空气源热泵在运行中．蒸发器从空气中的环境热能中吸取热量以蒸发传热工质．工质蒸气经压缩机压缩后压力和温度上升．高温蒸气通过永久黏结在贮水箱外表面的特制环形管冷凝器冷凝成液体时．释放出的热量传递给了空气源热泵贮水箱中的水。冷凝后的传热工质通过膨胀阀返回到蒸发器,然后再被蒸发,如此循环往复。     

蒸发冷却空调技术在住宅建筑中的研究进展

介绍蒸发冷却空调技术在住宅领域的研究进展。主要包括:直接蒸发冷却空调技术在住宅建筑的应用、间接蒸发冷却在住宅建筑的应用以及蒸发冷却与其他技术相结合在住宅建筑领域的应用几个部分。参考国内外相关文献及其专利,得出蒸发冷却空调技术在部分地区住宅领域应用效果较好的结论,特别是将蒸发冷却空调技术与其他技术相结合的应用过程中,这项技术能够提高整个机组的运行能效比,使机组运行更加节能、环保。在广阔的农村住宅领域以及"干空气能"丰富的部分地区,蒸发冷却空调技术值得被大力推广。     

用于汽轮机排汽冷却的蒸发式冷凝器模型及性能分析

蒸发式冷凝器兼具传热性能好和节水的优势,在大型动力系统冷却中具有广阔的应用前景。建立了蒸发冷凝器的理论分析模型,提出了蒸发式冷凝器用于冷却小型汽轮机排汽的设计方案;获得了喷淋水温度、空气和蒸汽的焓值在冷凝器内沿程的变化规律,并对喷淋水量、配风量和空气温度等影响冷凝器性能的影响因素进行了分析。研究结果对蒸发式冷凝器在火力发电行业的应用具有参考意义。     

不同管径组合的冷凝器换热数值研究

基于对传统空调用铜管翅片式冷凝器的研究分析，提出了一种新型的冷凝器形式，其迎风侧和背风侧采用不同直径的铜管和不同宽度的翅片，通过对两种形式的冷凝器的流动和换热进行的数值分析，新设计的冷凝器具有比传统冷凝器高的换热能力和低的空气流动阻力，适合于空调器的使用，而且该设计思路可以推广到空调用蒸发器的优化设计中。     

节能型冷却除湿复合式空调系统

介绍了冷却除湿空调的基本原理,对已有系统提出了改进.利用热回收装置,对除湿过程中的吸附热进行回收,并采用室内回风作为间接蒸发冷却器的二次风,能够更有效的降低处理空气的温度.对两种方案的热利用效率进行了实例计算,改进系统更有效.     

榆林地区大中型商场蒸发冷却空调系统设计分析

以榆林某大型商场为例,对该商场使用蒸发冷却空调系统的设计方法进行研究,对蒸发冷却空调与传统机械制冷空调的优缺点进行对比,给出了具体的空调送风量数值、空调末端的送回风形式确定以及空调机房的设备布置和配管方式;并将适用于高温空调的层式通风方式与蒸发冷却空调系统结合,希望能够促进蒸发冷却在榆林乃至西北地区的推广应用。     

Numerical investigation on the heat and mass transfer in a direct evaporative cooler

A simplified mathematical model is developed to describe the heat and moisture transfer between water and air in a direct evaporative cooler. The mass of evaporated water is treated as a mass source of air flow, and the related latent heat of water evaporation is taken as a heat source in the energy equation. The momentum caused by water evaporation is taken into account in the momentum equations. The effective air viscosity and diffusion coefficient are decided experimentally. The models and methods are validated by comparing the numerical results with those of experiment for the same evaporative cooler. The influences of the inlet frontal air velocity, pad thickness, inlet air dry-bulb and wet-bulb temperatures on the cooling efficiency of the evaporative cooler are calculated and analyzed.The cooling effects of the direct evaporative cooler are predicted for use in four different regions in northwest China using the present numerical method and local weather data for air conditioning design. The predicted results show the direct evaporative cooler with high performance pad material may be well applied for air conditioning with reasonable choices for the inlet frontal velocity and pad thickness.     

Cooling enhancement in an air-cooled finned heat exchanger by thin water film evaporation

A theoretical analysis on the cooling enhancement by applying evaporative cooling to an air-cooled finned heat exchanger is presented in this work. A two-dimensional model on the heat and mass transfer in a finned channel is developed adopting a porous medium approach. Based on this model, the characteristics of the heat and mass transfer are investigated in a plate-fin heat exchanger with the interstitial surface fully covered by thin water film. Assuming that the Lewis number is unity and the water vapor saturation curve is linear, exact solutions to the energy and vapor concentration equations are obtained. The cooling effect with application of evaporative cooling was found to be improved considerably compared with that in the sensible cooler. This is because the thermal conductance between the fin and the air increases due to the latent heat transfer caused by the water evaporation from the fin surface. It is also found that the cooling enhancement depends greatly on the fin thickness. If the fin is not sufficiently thick, the cooling enhancement by the evaporative cooling decreases since the fin efficiency drops considerably due to the water evaporation from the fin surface. The fin thickness in the evaporative cooler should be increased larger than that in the sensible cooler to take full advantage of the cooling enhancement by the water evaporation.     

Going below the wet-bulb temperature by indirect evaporative cooling: Analysis using a modified ε-NTU method

The objective of this paper is to study a method to achieve sub-wet bulb temperature by indirect evaporative cooling of air (without using a vapor compression machine). For this purpose, an analytical model is developed based on the effectiveness-NTU method (ε-NTU). The main idea for achieving a sub-wet bulb temperature by indirect evaporative cooling of air is by indirectly pre-cooling the working air before it enters the wet passage. It is shown that a modified analytical model for indirect evaporative coolers could be based on the ε-NTU method for sensible heat exchangers when proper adjustments are made by redefining the potential gradients, transfer coefficient, heat capacity rate parameters and assuming a linear saturation temperature-enthalpy relation of air. This modified model is used to find the performance of a regenerative indirect evaporative cooler. The model results show very good agreement with results from experimental measurements and a numerical model.     

An indirect evaporative chiller

A novel indirect evaporative chiller driven by outdoor dry air to produce cold water as the cooling source for air conditioning systems is introduced, and the principle and the structure of the chiller is presented. The cold water can be produced almost reversibly under ideal working conditions, with its temperature infinitely close to the dew point temperature of the inlet air. The key components of the chiller are an air cooler and a padding tower. To improve the heat transfer performance inside the chiller, a quasi-countercurrent air cooler was designed; a subsection linear method was used for the mathematical model of the padding tower. The first indirect evaporative chiller, designed and developed in 2005, has been in use in Kairui Building, a big hotel in Shihezi, Xinjiang Autonomous Region. The tested temperature of the water produced is below the wet bulb temperature of outdoor air and reached the average value of the dew point temperature and the wet bulb temperature of outdoor air. As the running components are only pumps and fans, the COP (cooling energy for room divided by power cost) of this chiller is high, and the drier the outdoor air, the higher COP the chiller obtained. Since no CFCs are used in this chiller, it would not cause any pollution to the aerosphere. Finally, the application prospect of the indirect evaporative chiller in the world is presented.     

Indirect evaporative cooling of air to a sub-wet bulb temperature

Indirect evaporative cooling is a sustainable method for cooling of air. The main constraint that limits the wide use of evaporative coolers is the ultimate temperature of the process, which is the wet bulb temperature of ambient air. In this paper, a method is presented to produce air at a sub-wet bulb temperature by indirect evaporative cooling, without using a vapour compression machine. The main idea consists of manipulating the air flow inside the cooler by branching the working air from the product air, which is indirectly pre-cooled, before it is finally cooled and delivered. A model for the heat and mass transfer process is developed. Four types of coolers are studied: three two-stage coolers (a counter flow, a parallel flow and a combined parallel-regenerative flow) and a single-stage counter flow regenerative cooler.It is concluded that the proposed method for indirect evaporative cooling is capable of cooling air to temperatures lower than the ambient wet bulb temperature. The ultimate temperature for such a process is the dew point temperature of the ambient air. The wet bulb cooling effectiveness (E_wb) for the examples studied is 1.26, 1.09 and 1.31 for the two-stage counter flow, parallel flow and combined parallel-regenerative cooler, respectively, and it is 1.16 for the single-stage counter flow regenerative cooler. Such a method extends the potential of useful utilisation of evaporative coolers for cooling of buildings as well as other industrial applications.     

Theoretical analysis on heat and mass transfer in a direct evaporative cooler

The heat and mass transfer between air and water film in the direct evaporative cooler is theoretically analyzed in present paper. A simplified cooling efficiency correlation is proposed based on the energy balance analysis of air. The correlation may be applied to the water-drip cross-flow direct evaporative cooler, in which the wet special durable papers with different wave angles form the air channel. The Influences of the air frontal velocity and the thickness of pad module on the cooling efficiency of a direct evaporative cooler are discussed. An optimum frontal velocity of 2.5 m/s is recommended to decide the frontal area of pad module in the given air flow. The simplified correlation of cooling efficiency is validated by the test results of a direct evaporative cooler.     

Modelling of a direct evaporative air cooler using artificial neural network

This paper proposes the use of artificial neural networks (ANNs) to predict various performance parameters of a direct evaporative air cooler. For this aim, an experimental evaporative cooler was operated at steady‐state conditions, while varying the dry bulb temperature and relative humidity of the entering air along with the flow rates of air and water streams. Using some of the experimental data for training, a three‐layer feed‐forward ANN model based on back propagation algorithm was developed. This model was used for predicting various performance parameters of the cooler, namely the dry bulb temperature and relative humidity of the leaving air, mass flow rate of the water evaporated into the air stream, sensible cooling rate, and effectiveness of the cooler. Then, the performance of the ANN predictions was tested by applying a set of new experimental data. The predictions usually agreed well with the experimental values with correlation coefficients in the range of 0.969–0.993, mean relative errors in the range of 0.66–4.04%, and very low root mean square errors. This study reveals that, as an alternative to classical modelling techniques, the ANN approach can be used successfully for predicting the performance of direct evaporative air coolers. Copyright © 2007 John Wiley & Sons, Ltd.     

Experimental characterisation of the operation and comparative study of two semi-indirect evaporative systems

The study described in this paper aims to present the fundamentals in which the operation of two different evaporative cooling systems is based, as well as the experimental results developed to characterise their behaviour in different conditions of outside air. These results will permit to define, according to the ideas of the systems’ operation, appropriate parameters to characterise the heat and mass exchange processes that take place as well as to compare them, like cooling capacity, thermal or energetic effectiveness; and afterwards developing this comparative analysis. The first system consists of a bank of ceramic pipes arranged vertically and staggered acting as a heat exchanger (SIERCP). In the second case an evaporative cooler has been manufactured with hollow bricks filled with still water (SIECHB). Both systems are called “semi-indirect” because they are designed to act as either direct or indirect evaporative systems depending on the relative humidity of the outdoor and return air streams. Results show that parameters related to the air humidity should be considered; and that the second system behaves generally as a direct evaporative cooler and provides a better performance.