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.     

Recent researches in indirect evaporative cooler V: relative thermal performance of buildings coupled to direct and indirect evaporative cooler

A mathematical model has been developed to evaluate the relative thermal performance of a building coupled with an indirect or direct evaporative cooler. Using periodic analysis for taking into account thermal storage of building envelope, explicit expressions have been obtained for room air temperature and room air humidity. For comparing their performance under different climatic conditions, numerical calculations have been made taking meteorological parameters for a typical day for Delhi (composite climate), Jodhpur (hot-dry climate) and Madras (hot-humid climate). It is found that the indirect evaporative cooler is a more effective and energy efficient system than the air-conditioner; it can hence be commercially used for computer and electronic exchange applications as well as for human comfort in a variety of climatic conditions, whereas direct evaporative cooler has limited use (only in hot-dry and composite climates). © 1997 by John Wiley & Sons, Ltd.     

Design and performance analysis of a small solar evaporative cooler

In this paper, the process of design, manufacturing, and performance analysis of a simple yet innovative solar evaporative cooler is illustrated. This investigation aims to evaluate the performance of a very small cooler with minimum energy consumption (10 W). A solar evaporative cooler was made out of various simple electrical and mechanical components. The cooler was tested in a specified room with the volume of 510?×?310?×?320 cm³. In order to evaluate the performance of the cooler, the air temperatures at different locations in the room was measured and compared during five consecutive days. The results showed that the performance of the cooler is relatively reasonable during the summer. However, its performance can be improved using high-performance cooling pads and solar panels. This simple evaporative cooler benefits from the ease of manufacturing process, cost effectiveness, and high portability.     

Theoretical analysis of heat and mass transfer to fluids flowing across a flat plate

Analytical solutions for heat and mass transfer to fluids flowing across an isothermal flat plate were obtained. Laminar, inviscid and irrotational flow were assumed in the solution of the energy equation. The derived new relations were comparable with the experimental data and the solutions of other investigators.     

Measurement of thickness and heat transfer coefficient of water film out of tube in an evaporative air cooler

Thickness of falling water film out of tubes is one of critical factors of heat transfer of evaporative air cooler. A new method of resistance measurement was developed to measure thickness of the film. When the resistance probe on the tip of micrometer touches the surface and bottom of the film, two corresponding sudden reductions of resistance occurs, and the difference of two graduations on the micrometer displays the thickness of the film. The film thickness of eleven angles was measured in five kinds of water flows and results varies from 0.8933mm to 1.7233 mm. Mean thickness and mean heat transfer coefficient of the film out of the tube was calculated.     

Characterization of a semi-indirect evaporative cooler

This paper presents the experimental study of a semi-indirect evaporative cooler (SIEC), which acts as an energy recovery device in air conditioning systems. Experimental measurements were achieved for the characterization of the thermal performance of the device, employing the design of experiments (DOE) methodology and an analysis of variance (ANOVA).     

Heat and mass transfer from a single horizontal tube of an evaporative tubular heat exchanger

In this investigation, water side heat transfer coefficients without air flow from a single horizontal tubes are determined. Mass transfer coefficients are determined with water and air flow from the same tube. The total energy dissipated by inside hot fluid when only water is falling is compared with that when both the air and water flow past the tube. The water side heat transfer coefficient and mass transfer coefficient are given by empirical relations h_w = 6.0(Re_p)^0.18(Re_w)^0.87 and K = 3.5(Re_p)^0.18(Re_a)^0.28 (Re_w)^0.54, respectively. The ratio of energies dissipated with water and air flow and with only water flow increases with Re_w and Re_a and its maximum value is 1.72 in the range of variables used.     

窗式直接蒸发冷却器在干燥地区居住建筑的应用研究

为了对室内空气降温的同时增加大量新风的补充,采用直流式全新风模式的蒸发冷却空调给室内降温。对使用窗式直接蒸发冷却器降温的新疆乌鲁木齐市天山区某住宅房间送风温湿度进行测试,数据表明,进风口温度在29℃,出风口温度为22℃,湿球效率为72%,室内温度稳定在25℃,相对湿度为59%,温湿度满足舒适性要求。     

Theoretical analysis of heat transfer in laminar pulsating flow

Pulsation effect on heat transfer in laminar incompressible flow, which led to contradictory results in previous studies, is theoretically investigated in this work starting from basic principles in an attempt to eliminate existing confusion at various levels. First, the analytical solution of the fully developed thermal and hydraulic profiles under constant wall heat flux is obtained. It eliminates the confusion resulting from a previously published erroneous solution. The physical implications of the solution are discussed. Also, a new time average heat transfer coefficient for pulsating flow is carefully defined such as to produce results that are both useful from the engineering point of view, and compliant with the energy balance. This rationally derived average is compared with intuitive averages used in the literature. New results are numerically obtained for the thermally developing region with a fully developed velocity profile. Different types of thermal boundary conditions are considered, including the effect of wall thermal inertia. The effects of Reynold and Prandtl numbers, as well as pulsation amplitude and frequency on heat transfer are investigated. The mechanism by which pulsation affects the developing region, by creating damped oscillations along the tube length of the time average Nusselt number, is explained.     

Recent research on an indirect evaporative cooler. Part VI: evolution of design pattern for indirect evaporative cooler

A rule of thumb for indirect evaporative cooler has been derived in terms of the size of floor area to be cooled and design parameters of tube type IEC, viz. process stream air flow rate and number of tubes; the three Indian climate zones, namely hot–dry, composite and warm–humid, represented by three cities of Jodhpur, Delhi and Madras, respectively, have been considered. Copyright © 1999 John Wiley & Sons, Ltd.     

喷雾蒸发冷却器的原理及应用效果分析

简单介绍了蒸发冷却器的原理,通过对轮南燃气轮机电站喷雾蒸发冷却器的实例分析,考证了喷雾蒸发冷却系统在提高燃机出力,降低热耗及提高燃机电厂经济效益方面的作用。     

Monte Carlo simulation and experimental heat and mass transfer in direct contact membrane distillation

A Monte Carlo (MC) simulation model is developed to study heat and mass transfer through hydrophobic membranes applying direct contact membrane distillation (DCMD) process. In this study, the membrane pore space is described by a three-dimensional network model of inter-connected cylindrical pores with distributive pore size. Vapor flux through membrane pores is described by gas transport mechanism(s) based on the kinetic theory of gases. The present MC model can take into consideration the influence of temperature polarization phenomenon, membrane physical properties including pores interconnectivity and the DCMD fluid dynamic conditions. The developed model can simultaneously predict the DCMD process vapor flux and membrane surface temperatures, contrary to other models in which one of them has to be given in order to solve the other. The model is comprehensive in its approach and does not involve any adjustable parameter. The simulated results were compared with the experimental ones of different membranes and the comparisons were found to be in excellent qualitative and quantitative agreement.     

Recent researches in indirect evaporative cooler III: optimization of the cooling potential of a room–coupled indirect evaporative cooler

A mathematical model based on heat transfer principles, for characterizing the cooling performance of a room coupled indirect evaporative cooler (tube type) has been developed. Two dimensionless parameters, i.e. environment factor, ϕ and cooling factor, CF have been defined to characterize the performance of IEC coupled with a room. The optimum values of these parameters have been obtained for different environmental and thermal load conditions. In addition to this, a linear relationship has been obtained for the optimum size of a cooler to remove maximum heat from a room of given size. © 1998 John Wiley & Sons, Ltd.     

Theoretical analysis of convective heat transfer of Oldroyd-B fluids in a curved pipe

Perturbation methods are used to study steady, fully developed flow of Oldroyd-B fluids through a curved pipe of circular cross-section. A perturbation solution up to secondary order is obtained for a small value of curvature ratio. The range of validity of the perturbation method are discussed and chosen carefully. Variations of temperature distribution with Re and We are discussed in detail in order to investigate the combined effects of the two parameters on temperature distribution. Present studies also show the variations of the heat transfer rate with Re and We. This study explores many new characteristics of convective heat transfer of a kind of viscoelastic fluid through curved pipes.     

Theoretical analysis of fluid flow and heat transfer in stoichiometric combustion in a naturally-ventilated control-volume

Using the conservation equations for mass, momentum and energy, a theoretical analysis of buoyancy driven flow and heat transfer for a ventilated control-volume, with an internal heat-source, has been made. The special case of stoichiometric combustion in a naturally-ventilated brick walled room, with a single rectangular opening, has been used to demonstrate the numerical calculation procedure for the prediction of the histories of the fire temperature, gas flow rate, fuel burn rate, fire power and boundary-wall temperature. The analysis may be extended for more complex space geometries and wall structures; a typical case being a railway carriage with a composite wall.     

电机径向通风的空气—空气冷却器传热计算

针对径向通风、管束整体为矩形排列的电机空—空冷却器建立了分区域的传热计算模型,给出了针对不同的内风路温度条件所采取的传热计算方法,采用优选取值法计算方法用于空—空冷却器分区域的传热计算。该计算模型的计算数据通过与实验数据的对比进行了修正。根据该计算模型编制了计算软件进行冷却器设计,目前的冷却器设计软件从换热及与风扇匹配角度来讲均可满足设计要求。     

Study on the heat transfer characteristics of an evaporative cooling tower

In the present study, both experimental and theoretical results of the heat transfer characteristics of the cooling tower are investigated. A column packing unit is fabricated from the laminated plastic plates consists of eight layers. Air and water are used as working fluids and the test runs are done at the air and water mass flow rates ranging between 0.01 and 0.07 kg/s, and between 0.04 and 0.08 kg/s, respectively. The inlet air and inlet water temperatures are 23 °C, and between 30 and 40 °C, respectively. A mathematical model based on the conservation equations of mass and energy is developed and solved by an iterative method to determine the heat transfer characteristics of the cooling tower. There is reasonable agreement from the comparison between the measured data and predicted results.     

Life cycle assessment of a semi-indirect ceramic evaporative cooler vs. a heat pump in two climate areas of Spain

The aim of this study is to compare the environmental profile of a semi-indirect ceramic evaporative cooler (SIEC) with low environmental impact and heat pipe (HP) heat-exchanger battery with that of a Split class heat pump. The comparison is carried out for two different climate areas in Spain, one a continental or inland climate (Valladolid) and the other representative of a Western European climate (Bilbao). The environmental and economic study is conducted using life cycle assessment (LCA) with two software tools provided by SimaPro® 7.1 LCA suite (Eco-indicator‘99® and EPS 2000®). After the LCA sensitivity analysis results it can be clearly inferred that the major contribution to the categories of damage in both facilities (SIEC and heat pump) is the class of abiotic resources, followed by human health. The high contribution to environmental impact of the evaporative condenser, part of the SIEC-HP, should also be emphasized. With regard to the heat pump, electricity proves to be the main environmental burden, followed by the pump infrastructure, in which the compressor, the external battery, the external fan and the connection have the highest impacts, respectively.