Thermal performance of a building coupled to an evaporative cooling tower

The thermal performance of a building fitted with an evaporative cooling tower has been evaluated in terms of discomfort index for two climates, namely, composite and hot-dry, typified by New Delhi and Jodhpur, respectively. The effects of various evaporative cooling parameters (height and cross-sectional area of the tower, packing factor, area of the pads, resistance offered to the air flow and local wind conditions) on the performance of the building have been analysed. It was found that, for given parameters of the tower and wind conditions, there is an optimum height of the tower for which the thermal discomfort condition in the building is minimum. The optimum values of the tower height for comfort conditions in the building for various other tower parameters have been obtained for each climate.     

Thermal performance of an evaporatively cooled building: Parametric studies

A single-storey office building in a hot and dry climate is modelled for evaporative cooling. The counterflow cooling tower is modified to precool the tower inlet air by the tower exit air in a heat exchanger. Centralized evaporative air cooling, using the modified cooling tower, and roof evaporative cooling are considered to provide comfortable living conditions in the space. The thermal performance of such a building is analysed for various operating parameters. The study indicates that centralized evaporative air cooling is feasible, to maintain near-perfect comfort conditions in hot and dry climates. Modified cooling tower and roof evaporative cooling further enhance the scope of evaporative cooling for comfort applications.     

Numerical study of solar-wind tower systems for ventilation of dwellings

Numerical study is carried out of a simplified system of solar-wind tower for ventilation of dwellings. The conservation equations for mass, momentum and energy for mixed convection in two-dimensional coordinates are solved by the control volume method and Simpler algorithm. The governing parameters of the problem are Rayleigh number Ra, Reynolds number, Re (or Richardson number, Ri), the dimensionless conductivity of the solid medium, k_r and the geometrical parameters. Nusselt number Nu and dimensionless volume flow rate are calculated as a function of the governing parameters, and streamlines and isotherms are produced. The results show that the important parameters affecting the ventilation performance are Ra, Re (or Ri), and the geometrical parameters, the aspect ratio A, the exit port size h₁/L and to a lesser degree, the wall thickness ℓ₁/L.     

The first pilot demonstration: solar updraft tower power plant in Jordan

The high cost of importing heavy fuel oil from neighbouring countries of Jordan stimulated the need to consider renewable energy as an alternative to imported power. The paper describes a systematic experimental study on the pilot solar updraft tower power plant model system. Particular attention is given to measurements of air velocity, temperature, solar radiation and voltage difference. This is the first pilot solar updraft power plant that has been built in Jordan to evaluate such technology in Mutah Area. In this paper, all the experimental data were taken from a very small pilot project (compared with other prototypes that we constructed which were placed in the backyard of our faculty). For the experimental part, the solar updraft power plant was a pilot project with an updraft power plant height H=4(m), updraft power plant radius R _c=0.29(m), plastic solar collector area A _coll=36(m²), collector roof height=1(m), wind turbine that was a compensation of the suction fan with a diameter D _fan=0.5(m), and a small generator (6 V) The experimental results in this paper show that the maximum height (H _max) gradually increases with the solar irradiation (G). Also, in the same way, with the pressure difference (Δ p) increases with solar irradiation.     

Effects of acoustic barriers and crosswind on the operating performance of evaporative cooling tower groups

Most evaporative cooling towers are arranged on building roof due to the limitation of space and noise, and acoustic barriers are always installed around cooling towers in practical applications. The existence of acoustic barriers and crosswind may affect the recirculation phenomenon which is directly related to the operating performance of cooling towers. In this study, a physical and mathematical computation model is proposed to research the crosswind and distance between acoustic barriers and inlet of cooling towers. Both sensible and latent heat are considered in this research. The reflux flow rate and performance ratio are obtained to evaluate the recirculation and operating performance, respectively. The results show that the higher the crosswind velocity, the larger the reflux flow rate, and the lower the performance ratio of cooling tower groups. For high crosswind velocity, the presence of acoustic barriers is useful to inhibit reflux and improve operating performance, especially for ICE cooling tower groups. In addition, the optimum values are recommended for LiBr/ICE cooling tower groups in the research cases The variation of reflux flow rate and performance ratio with the acoustic barriers’ distance presents a parabolic tendency.     

Numerical study of the evaporative cooling of liquid film in laminar mixed convection tube flows

A numerical study is reported to investigate the evaporative cooling of liquid film falling along a vertical tube. A marching procedure is employed for solution of the equation of mass momentum, energy and concentration in the flow. Numerical results for air-water system are presented. The effects of flow conditions on the film cooling mechanism are discussed. Results show that a better liquid film cooling is noticed for a system having a higher inlet liquid temperature T_L0, a higher gas flow Reynolds number Re or a lower liquid flow rate Γ₀. Additionally, the results indicate that the convection of heat by the flowing water film becomes the main mechanism for heat removal from the interface.     

湿式冷却塔进风口加装导风板的优化设计

基于两相流传热传质理论,利用Fluent软件模拟300 MW机组冷却塔填料区使用多孔介质时的通风率,采用离散相模型（DPM）在配水区上表面加入热水,模拟研究新型旋流型叶片导风板的优化能力,给定不同弧度及安装角,分别在0、3和7 m·s^-1风速下计算冷却塔出塔水温,并分析侧风对冷却塔冷却性能的影响。研究结果表明：加装导风板可以降低侧风引起的不利影响,导风板数量为50块时效果最好,旋流型叶片导风板的最佳安装角为20°,此时旋流型叶片的最佳弧度为15°,最大温降可达0.787 4 K。研究结果为火电厂选择导风板提供了依据。     

The Connectedness of Some Varieties and the Deligne—Simpson Problem

The Deligne—Simpson problem (DSP) (respectively, the weak DSP) is formulated as follows: give necessary and sufficient conditions for the choice of the conjugacy classes C_j GL(n, ) or c_j gl(n, ) so that there exist irreducible (respectively, with trivial centralizer) (p + 1)-tuples of matrices M_j C_j or A_j c_j satisfying the equality M₁ ... M_p+1 = I or A₁ + ... + A_p+1 = 0. The matrices M_j and A_j are interpreted as monodromy operators of regular linear systems and as matrices-residua of Fuchsian ones on the Riemann sphere. For ((p + 1))-tuples of conjugacy classes one of which is with distinct eigenvalues we prove that the variety {(M₁, ..., M_p+1) | M_j C_j, M₁ ... M_p+1 = I} or {(A₁, ..., A_p+1) | A_j c_j, A₁ + ... + A_p+1 = 0| is connected if the DSP is positively solved for the given conjugacy classes and give necessary and sufficient conditions for the positive solvability of the weak DSP.2000 Mathematics Subject Classification. 15A30, 15A24, 20G05.     

湿式瘦高冷却塔淋水装置节能技术应用

主要叙述了一种基于FLUENT UDF方法设计湿式冷却塔淋水装置的节能技术,并介绍其应用于电厂冷却塔的情况。该节能技术的应用研究主要包括,环境侧风对超大型自然通风冷却塔热力性能的影响;塔群效应和塔群效应与环境侧风叠加等条件下,超大型逆流式自然通风冷却塔的热力计算方法;基于FLUENT UDF方法准确分析塔内每个区域的热力参数(喷头实际出流能力、填料实际淋水密度和对应区域的集水池平均水温)等工艺性能关键技术研究;冷却塔新材料(不同波形、不同片距)、新设备的研发制造;冷却塔环境保护关键技术研究等。     

Gas-phase saturation and evaporative cooling effects during wet compression of a fuel aerosol under RCM conditions

Wet compression of a fuel aerosol has been proposed as a means of creating gas-phase mixtures of involatile diesel-representative fuels and oxidizer + diluent gases for rapid compression machine (RCM) experiments. The use of high concentration aerosols (e.g., ∼0.1 mL_fuel/L_gas, ∼1 × 10⁹ droplets/L_gas for stoichiometric fuel loading at ambient conditions) can result in droplet–droplet interactions which lead to significant gas-phase fuel saturation and evaporative cooling during the volumetric compression process. In addition, localized stratification (i.e., on the droplet scale) of the fuel vapor and of temperature can lead to non-homogeneous reaction and heat release processes – features which could prevent adequate segregation of the underlying chemical kinetic rates from rates of physical transport. These characteristics are dependent on many factors including physical parameters such as overall fuel loading and initial droplet size relative to the compression rate, as well as fuel and diluent properties such as the boiling curve, vaporization enthalpy, heat capacity, and mass and thermal diffusivities. This study investigates the physical issues, especially fuel saturation and evaporative cooling effects, using a spherically-symmetric, single-droplet wet compression model. n-Dodecane is used as the fuel with the gas containing 21% O₂ and 79% N₂. An overall compression time and compression ratio of 15.3 ms and 13.4 are used, respectively. It is found that smaller droplets (d₀ ∼ 2–3 μm) are more affected by ‘far-field’ saturation and cooling effects, while larger droplets (d₀ ∼ 14 μm) result in greater localized stratification of the gas-phase due to the larger diffusion distances for heat and mass transport. Vaporization of larger droplets is more affected by the volumetric compression process since evaporation requires more time to be completed even at the same overall fuel loading. All of the cases explored here yield greater compositional stratification than thermal stratification due to the high Lewis numbers of the fuel–air mixtures (Le_g ∼ 3.8).     

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%.     

Computational Analysis of Closed Wet Cooling Towers

The thermal and hydraulic performance of plain and oval tubes closed wet cooling tower (CWCT) are investigated numerically. Computational fluid dynamics (CFD), ANSYS Fluent 12.1, is implemented for the numerical solution. Species transport without reactions is adopted to simulate the mass transfer from the air-deluge water interface to the air. Different turbulence models and near-wall treatments are used to assess which model fits the data better. The mass transfer Colburn factor j _m , and friction factor f are presented and compared with experimental data. The proposed CFD model is also applied to predict the mass transfer coefficient of another CWCT and compares well with the experimental data.     

Design construction and test run of a solar powered solid absorption refrigerator

The intermittent system used CaCl₂ and NH₃ as absorbent and refrigerant, respectively. The absorbent was mixed with 20% by weight of CaSO₄, as cement, and prepared as hard porous granules of 5–10 mm sizes.The double glazed collector/absorber/generator unit used clear PVC and plane glass sheets, with the former as the outer cover. Overall collector plate exposed area was 1.41 m². A stagnant water evaporative condenser was designed and constructed of re-inforced sandcrete, with steel condenser tubes, and was coupled to the system. The evaporator was a spirally coiled steel tube immersed in a pool of stagnant water. Absorbent cooling during absorption was by natural convection of air over the collector plate and tubes, coupled with sky radiation. All construction, except the collector covers and porous condenser walls, were of steel sheets and tubes.Ambient temperatures during absorption and generation ranged over (25°–35°C). Tests indicated that cooling capacities of the NH₃ condensed were around 714 KJ m⁻², while effective cooling obtained was equivalent to an ice production of 1 kg m⁻², per day.     

Numerical model of evaporative cooling processes in a new type of cooling tower

A numerical model for studying the evaporative cooling processes that take place in a new type of cooling tower has been developed. In contrast to conventional cooling towers, this new device called Hydrosolar Roof presents lower droplet fall and uses renewable energy instead of fans to generate the air mass flow within the tower. The numerical model developed to analyse its performance is based on computational flow dynamics for the two-phase flow of humid air and water droplets. The Eulerian approach is used for the gas flow phase and the Lagrangian approach for the water droplet flow phase, with two-way coupling between both phases. Experimental results from a full-scale prototype in real conditions have been used for validation. The main results of this study show the strong influence of the average water drop size on efficiency of the system and reveal the effect of other variables like wet bulb temperature, water mass flow to air mass flow ratio and temperature gap between water inlet temperature and wet bulb temperature. Nondimensional numerical correlation of efficiency as a function of these significant parameters has been calculated.     

CO2 payback–time assessment of a regional-scale heating and cooling system using a ground source heat–pump in a high energy–consumption area in Tokyo

We present an assessment of installing a regional heating and cooling system in the Nishi(West)-Shinjuku area of Tokyo, Japan. In this assessment, we estimate the CO₂ payback–time, when air source heat–pumps (ASHP) are replaced with a ground–source heat–pump (GSHP) system. We calculate CO₂ emissions from transportation of the cooling tower, materials for the underground heat exchanger, and the digging loads and transportation loads incurred when the GSHP system is installed to replace the air source cooling system. The total CO₂ emission from the installation of the GSHP system was estimated to be 67,701t-CO₂, with 87% of the CO₂ emissions resulting from the digging process. CO₂ emissions from the operation of the GSHP system were estimated from the total energy-efficiency of the system and the heating and cooling demand in Nishi-Shinjuku area. Using the GSHP system, 33,935t-CO₂ would be emitted per year. We estimate that using the GSHP system would result in a reduction of 54% of the CO₂ emissions, or 39,519t-CO₂ per year. From these results, the CO₂ payback–time for replacing the conventional ASHP in the 1 km² studied region with the GSHP system is assessed to be 1.7 years.     

论冷却塔节能

冷却塔是冷却水循环的关键设备之一,也是能源消耗的重点设备.在目前要求节能减排的大背景下,冷却塔节能刻不容缓.探讨冷却塔如何节能,分别从依托新技术发展对冷却塔设计进行革新、对已有冷却塔技术进行改造以及控制冷却塔运行等方面进行分析,认为目前冷却塔行业的节能应从以下方面着手:一是冷却塔供应商提供高效节能优化的冷却塔;二是对已有冷却塔系统中效率低下的零部件进行替换或改进;三是冷却塔使用者对冷却塔的运行进行合理的管理.     

An experimental study of a solar-regenerated liquid desiccant ventilation pre-conditioning system

A solar-regenerated liquid desiccant ventilation pre-conditioning system has been installed and experiments were carried out for a period of nine months covering rainy, cold, and hot seasons in a hot and humid climate (Thailand). A heat exchanger was used to cool the dehumidified air instead of typical evaporative cooling to maintain the dryness of the air. The use of solar energy at the regeneration process and cooling water from a cooling tower makes the system more passive. The evaporation rate at the regeneration process was always greater than the moisture removal rate at the dehumidification process indicating that the concentration of the desiccant in the system would not decrease and so the performance would not drop during continuous operation. The system could reduce the temperature of the delivered air by about 1.2 °C while the humidity ratio was reduced by 0.0042 kg_w/kg_da equivalent to 11.1% relative humidity reduction. The experimental results were also compared with models in literature.     

Climatic model for prediction of below-grade heat loss: Influence of elevation

The aim of the paper is to create a new climatic model suitable for an energy balance analysis of the below-grade part of a building in a country with diverse topography, Slovakia, serving as an example. Slovakia is the eastern part of the former Czechoslovakia with a population and area similar to that of Denmark. Constants in the final relations — the mean annual temperature on the ground susrface T_o2, the mean annual temperature in 1 m and/or 2 m depth T₁₂, the average year temperature amplitude on the surface A_Y, and the day of occurrence of the minimal temperature t_o — were introduced on the basis of the statistical evaluation of the long-term temperature measurements of the Hydreometeorological Institute on 49 sites in Slovakia. The discussion of recommended values is given together with information on air and underground water temperatures. Through statistical analysis it was possible to quantify dependence of the T_o2, T₁₂ and A_Y, on elevation which was found to be the most important parameter for the climatic model of the country. The weighted average of the minimum daily temperatures from all the years recorded at 49 meteorological stations was determined as the day when minimum surface temperature occur in Slovakia. It was found to be in agreement with the results of long-lasting measuring of air temperature.     

The numerical computation of the evaporative cooling of falling water film in turbulent mixed convection inside a vertical tube

An analysis has been developed for studying the evaporative cooling of liquid film falling inside a vertical insulated tube in turbulent gas stream is presented. Heat and mass transfer characteristics in air–water system are mainly considered. A low Reynolds number turbulence model of Launder and Sharma is used to simulate the turbulent gas stream and a modified Van Driest model suggested by Yih and Liu is adopted to simulate the turbulent liquid film. The model predictions are first compared with available experimental data for the purpose of validating the model. Parametric computations were performed to investigate the effects of Reynolds number, inlet liquid temperature and inlet liquid mass flow rate on the liquid film cooling mechanism. Results show that significant liquid cooling results for the system with a higher gas flow Reynolds number Re, a lower liquid flow rate Γ₀ or a higher inlet liquid temperature T_L0.     

Theoretical and testing performance of an innovative indirect evaporative chiller

An indirect evaporative chiller is a device used to produce chilled water at a temperature between the wet bulb temperature and dew point of the outdoor air, which can be used in building HVAC systems. This article presents a theoretical analysis and practical performance of an innovative indirect evaporative chiller. First, the process of the indirect evaporative chiller is introduced; then, the matching characteristics of the process are presented and analyzed. It can be shown that the process that produces cold water by using dry air is a nearly-reversible process, so the ideal produced chilled water temperature of the indirect evaporative chiller can be set close to the dew point temperature of the chiller’s inlet air. After the indirect evaporative chiller was designed, simulations were done to analyze the output water temperature, the cooling efficiency relative to the inlet dew point temperature, and the COP that the chiller can performance. The first installation of the indirect evaporative chiller of this kind has been run for 5 years in a building in the city of Shihezi. The tested output water temperature of the chiller is around 14–20 °C, which is just in between of the outdoor wet bulb temperature and dew point. The tested COP_r,s of the developed indirect evaporative chiller reaches 9.1. Compared with ordinary air conditioning systems, the indirect evaporative chiller can save more than 40% in energy consumption due to the fact that the only energy consumed is from pumps and fans. An added bonus is that the indirect evaporative chiller uses no CFCs that pollute to the aerosphere. The tested internal parameters, such as the water–air flow rate ratio and heat transfer area for each heat transfer process inside the chiller, were analyzed and compared with designed values. The tested indoor air conditions, with a room temperature of 23–27 °C and relative humidity of 50–70%, proved that the developed practical indirect evaporative chiller successfully satisfy the indoor air conditioning load for the demo building. The indirect evaporative chiller has a potentially wide application in dry regions, especially for large scale commercial buildings. Finally, this paper presented the geographic regions suitable for the technology worldwide.