A numerical and experimental investigation of flow maldistribution in a micro-channel heat sink

A study of flow mal-distribution in U-type micro-channel configuration is presented. Numerical simulations indicate that flow deceleration and associated pressure recovery in the inlet header lead to flow separation and recirculation which cause oscillations in channel-wise mass flow distribution. Increase in flow resistance by decrease in channel depth, width or number of channels or increase in channel length, results in a more uniform distribution. Mal-distribution increases at high flow rate or low viscosity due to the dominance of inertial phenomena. Experiments performed on a 25-channel setup illustrate that small manufacturing variations in channel dimensions introduce random fluctuations in flow distribution.     

Performance of a single‐duct portable propane air conditioning system under different refrigerant charge levels

The effects of the refrigerant charge on the performance of a portable propane air conditioning system have been evaluated and compared to nonportable systems in which the surrounding temperatures of the evaporator and condenser are not equal. This study aims to determine the similarities and differences in the performance of the two types of propane air conditioners under different charge levels, and to serve as a source of reference for future designs of portable air conditioners. The refrigerant charge was changed from ?12.3% to +30% of its normal charge at several room temperatures ranging from 20 °C to 35 °C. The performance parameters include the refrigerant temperature, mass flow rate, maximum velocity of refrigerant, maximum pressure, cooling capacity, compressor work, specific cooling capacity, and coefficient of performance of the system. It has been found that an increase in charge level was found to increase the cooling capacity, coefficient of performance, and maximum velocity of refrigerant in the system while decreasing specific cooling capacity. The increase in the charge caused a relatively insignificant rise in the maximum pressure of the system and useful work of the compressor.     

空调水系统节能改造及分析

针对北京西城区青少年图书馆空调冷冻水系统运行高能耗问题 ,根据具体条件 ,分析了各种解决方案及其适用性 ,确定采用切削水泵叶轮改造方案。经过计算和实测 ,认为改造后取得了较好的节能效果。     

几何结构对径向引入集箱系统气液两相流量分配特性影响的实验研究

在空气-水实验台上,针对集箱中存在的气液两相混合物分配不均问题,研究了入口条件对双纵向引入多分支并联管水平集箱系统分支管中流量分配特性的影响。为了改善气液两相流在集箱中的分配特性,通过在集箱内部加装"笛型管"结构,并将两集箱系统的分配特性进行了比较。实验研究证明:新型集箱的两相流量分配均匀性得到了极大的改善,并且当入口条件改变时,新型集箱的分配特性依旧良好。     

Experimental investigation of an automotive air-conditioning system driven by a small biogas engine

A compact air conditioning module run on biogas for rural use is proposed. The research study is to investigate the use of small biogas engine to drive the automotive vapour-compression air-conditioning system. The engine used is single-cylinder, four-stroke gasoline engine with capacity of 125 cm³ and compression ratio of 11:1. The biogas engine can be used to run the air-conditioning system with acceptable operation over a range of speeds and loads. The modular system can operate at a range of cooling loads above 3.5 kW at high coefficient of performance, with the proper speed ratio between the engine and the compressor. Overall primary energy ratio of the modular refrigeration system driven by the biogas engine was found to be maximum at about 1.0–1.2. The performance of the modular system tends to decrease with an increase in engine speed.     

空调水系统管路间耦合特性的分析及试验研究

为了探讨压差控制方式的可靠性 ,提高该控制方式的节能效果 ,通过控制领域中相对增益的概念 ,阐述了相对增益值与管路间耦合程度的关系 ,根据试验对一空调水系统的相对增益进行了计算 ,并分析了压差控制方式下变流量空调水系统中压差设定值及定压点位置对各支路间耦合特性的影响。最后得出结论 :压差控制回路对支路间的耦合起一定的改善作用 ,压差设定值大小对支路间的耦合程度没有影响 ,对耦合程度严重的回路 ,有必要采取解耦控制     

Performance of a solar-powered air conditioning system in Hong Kong

To study the feasibility of utilizing solar power for comfort cooling in Hong Kong, a solar-powered absorption air-conditioning system was designed and successfully constructed on the campus of the University of Hong Kong (HKU). The system consisted of a flat-plate collector array with a surface area of 38.2 m², a 4.7-kW nominal cooling capacity LiBr---H₂O absorption chiller, a 2.75-m³ hot-water storage tank, a cooling tower, a fan-coil unit, an electrical auxiliary heater, a data-acquisition system and the associated control systems. In the present paper, the design of the HKU solar-powered air-conditioning system is described in detail and its performance over an entire cooling season is also discussed and compared with similar systems in Italy and Singapore. It was found that the HKU solar air-conditioning system had an annual system efficiency of 7.8% and an average solar fraction of 55%.     

Experimental and numerical investigation of the flow in rotating diverging channels

This paper reports on an experimental and numerical study at low Reynolds number in order to evaluate the influence of the Coriolis forces on the flow in radial rotating channels.Operating conditions correspond to the flow in radial impellers for micro gasturbine applications.A comparison of detailed flow measurements with CFD results indicates that Navier Stokes solvers with standard k-ω and SST turbulence models predict the flow surprisingly well and that no extra corrections for Coriolis forces are required at these operating conditions     

A numerical solution for cooling and dehumidification of air by a falling desiccant film in parallel flow

The heat and mass transfer process between falling liquid desiccant film and air in parallel flow heat exchanger is investigated numerically. The governing equations with appropriate boundary and interfacial conditions describing the physical problem are derived. The control volume approach is used to predict the outlet conditions for both the air and the desiccant solution. The effect of inlet conditions, mass flow rates and channel geometry on the air cooling and dehumidification processes is also predicted. The average Nusselt and Sherwood numbers for air flow are correlated in terms of Prandtl number, Schmidt number and channel geometry. Typical numerical experiments showed good agreement of the present results with the available data in literature. Moreover, a parametric study is conducted to illustrate the general effects of various variables on heat and mass transfer processes in cooling and dehumidification of air.     

Boiling heat transfer coefficient of R22 and an HFC/HC refrigerant mixture in a fin‐and‐tube evaporator of a window air conditioner

The commonly used refrigerant in unitary type air conditioners is R22 and its phase out schedule in developing countries is to commence from 2015. Many alternatives to R22 are found in published literature in which R407C has similar characteristics to those of R22 except for its zeotropic nature. However, R407C which is an HFC is made compatible with the mineral oil lubricant in the system compressor by the addition of 20% of HC. This HFC/HC mixture called the M20 refrigerant mixture is reported to be a retrofit refrigerant for R22. Though its latent heat value is greater than that of R22, its refrigerating capacity is lower when it is used to retrofit R22 window air conditioners. Hence, a heat transfer analysis was conducted in the evaporator of a room air conditioner, for practically realized heat flux conditions during standard performance testing. The tests were conducted as per the BIS and ASHRAE standards. Kattan–Thome–Favrat maps are used to confirm the flow patterns, which prevail inside the fin‐and‐tube evaporator in the tested operating conditions. It is revealed that the heat transfer coefficient/heat fluxes are poorer for M20 because of the lower mass flow rate and higher vapor fraction at the entry of the evaporator than that of R22 in the prevailing operating conditions. The heat transfer coefficients of the M20 refrigerant mixture under various test conditions are lower in the range of 14% to 56% than those of R22. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20299     

新型中央空调节能控制系统研究

本文介绍了一种新型中央空调节能控制系统。系统基于变频技术,结合最优化控制、模糊控制以及计算机技术,具有负荷随动跟踪特性。结合专用管理专家系统软件,成为中央空调系统节能控制领域的发展趋势。     

溶洞气候的建筑空气调节系统设计

设计一种溶洞气候的建筑空气调节系统。在溶洞的上方修建房屋建筑,将溶洞中的空气先引入空气静压室,再将空气静压室内的空气通过送风井送入房屋建筑内的空调使用房,利用加热空气箱将经过置换的空气通过外墙排风道从空调使用房中抽出,并通过排风口将抽出的空气排入大气,从而实现利用溶洞气候对建筑内的空气进行调节。     

某工业园地源热泵空调系统改造方案及分析

以现有系统为基础,采用地埋管与冷却塔、地源热泵与水源热泵联合运行的方式对项目进行供暖与供冷改造。同时在机房内增加了混水换热水池,增大了地下水可利用温差,提高了地下水利用率,充分利用了现有设备与系统,节约了地下水资源,提高了系统有效性、经济性和环境效益。     

"中国太阳能第一楼"太阳能空调系统及试验研究

为开展太阳能空调系统设计、运行和控制的研究,建设了北苑太阳能空调示范项目.本文介绍该系统构成及设计特点,给出了国家空调设备质量监督检测中心的性能检测结果,以及UNDP项目对该项目全年运行监测结果.     

Simulation of an air conditioning absorption refrigeration system in a co-generation process combining a proton exchange membrane fuel cell

In this work, a computer simulation program was developed to determine the optimum operating conditions of an air conditioning system during the co-generation process. A 1 kW PEMFC was considered in this study with a chemical/electrical theoretical efficiency of 40% and a thermal efficiency of 30% applying an electrical load of 100%. A refrigeration-absorption cycle (RAC) operating with monomethylamine–water solutions (MMA–WS), with low vapor generation temperatures (up to 80 °C) is proposed in this work. The computer simulation was based on the refrigeration production capacity at the maximum power capacity of the PEMFC. Heat losses between the fuel cell and the absorption air conditioning system at standard operating conditions were considered to be negligible. The results showed the feasibility of using PEMFC for cooling, increasing the total efficiency of the fuel cell system.     

某综合楼空调通风节能设计

探讨移动通信综合楼的空调通风形式，着重阐述选用冷冻水型机房专用空调器的优点、应该注意的问题及本工程所采取的措施，并介绍了中央空调冷源、水系统、空调末端装置、通风防排烟系统及自控等的设置情况，以及空调系统节能设计的重要性。     

水蓄冷在空调节能设计中的应用

通过一工程实例说明了水蓄冷在空调设计中的应用。并通过水蓄冷方案与常规空调方案的设备初投资、运行电费、电网移峰等方面分析比较,证明水蓄冷具有初投资低、运行费用低和能有效实现电网的削峰填谷等特点,是空调节能设计的有力手段。     

A numerical investigation of evaporation characteristics of a fuel droplet suspended from a thermocouple

Numerical simulations of combined natural convection–conduction in a droplet of n-dodecane suspended from a thermocouple were carried out, taking into consideration evaporation, and the effect of thermocouple diameter on the evaporation characteristics was investigated. The calculated temperature history of the droplet is in good agreement with experimental results; both show that the rate of heating decreases with increasing thermocouple diameter. The maximum error in temperature due to the thermocouple increases linearly with increasing thermocouple diameter. Thus, in investigations involving a droplet suspended from a thermocouple, it is preferable to use a thermocouple with the smallest possible diameter.     

西安某办公楼蒸发冷却半集中式空调自控系统设计方案

以西安某办公楼为研究对象,提出了蒸发冷却半集中式空调系统即干工况风机盘管+蒸发冷却新风机组自控系统的设计方案,将蒸发冷却空调的具体应用和自动控制紧密的结合起来,保证了系统的安全和最佳节能效果。     

Experimental study and analysis of the application of ice‐storage capsules in an air conditioning system

Ice‐storage capsules are used in an energy‐efficient air conditioning system. Experiments and numerical simulations were conducted to investigate the effects of different structural configurations of the capsules on the freezing and melting processes of the refrigerant solution sealed inside the capsules. The predictions of the numerical simulation are in good agreement with the test results. The results show that the freezing speed of the capsules equipped with a metal core is 30% to 50% faster than for capsules without the metal core. In addition, it was found that the special refrigerant solution used in the experiment had a lower freezing point and a higher freezing speed than water. The effects of the size of the metal core, and the coolant temperatures are also investigated. © 2001 Scripta Technica, Heat Trans Asian Res, 31(1): 21–27, 2002