板式间接蒸发冷却器热工特性的实验研究

对自行研制设计的间接蒸发冷却换热试件开展了实验,研究了影响换热器换热性能的因素。结果表明：板式间接蒸发冷却器换热效率随二次空气入口的速度升高、一次空气入口的温度、二次空气入口的湿球温度升高而变大,随一次空气入口的速度变大而变小。实验结果对于深入认识间接蒸发冷却器的换热机理及开展换热器的优化设计有着很大的指导意义。     

Energy-saving potential of an indirect evaporative cooler

In many parts of the world, large differences between the dry-bulb and wet-bulb temperatures during the summer season can be used advantageously to pre-cool fresh air for air-conditioned space using an indirect evaporative cooler (IEC). This paper presents an analytical evaluation using the field performance results of a 1180 L/s (2500 ft³/min) IEC unit and the recorded weather data in coastal and interior locations in Kuwait. Estimated cooling capacity of the IEC is 3.1 and 2.4 tons of refrigeration (RT, 1 RT=3.517 kW of heat absorption), for the interior and the coastal areas, respectively. Furthermore, the power requirements of a conventional packaged unit air-conditioner (PU) to produce this cooling in these respective areas are 4.93 and 3.85 kW compared with only 1.11 kW needed by the IEC. Also, the seasonal energy savings of the IEC are 12,418 and 6320 kWh, for the interior and coastal areas, respectively.     

Experimental investigation on the performance of air cooler under frosting conditions

Evaluation of heat transfer performance of the air cooler under frosting conditions is of great importance for the refrigeration industry. In this paper, effects of frost growth on the performance of the air cooler have been studied with an experimental air cooler of industrial size with different fin spacings, i.e., 6, 8 and 10 mm. Results showed that factors affecting the heat transfer performance of the air cooler include the evaporation temperature, the frost height, the fin spacing and the air velocity. The overall heat transfer coefficients based on a logarithmic mean temperature difference (LMTD) and the energy transfer coefficients based on a logarithmic mean enthalpy difference (LMED) were calculated. As the frost accumulated on the air cooler, the overall heat transfer coefficient and energy transfer coefficient will drop gradually.     

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.     

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.     

Thermal and hydraulic performance of a modified two-stage evaporative cooler

The thermal and hydraulic performance of a modified two-stage evaporative cooler is evaluated. Variables considered are the mode of operation, packing thickness, mass flow rate of the water flowing to the precooler, and the mass flux of water flowing over the packing media. The effectiveness of the system increased with the increase of the mass flow rate of water flowing to the precooler, decreasing the mass flux of water flowing to the packing, and with the increase of the packing thickness. The effectiveness of the system with structured packing was higher than that with sheathy leaf base or natural fiber packing.The air-side pressure drop per unit length in the direction of air flow was nearly constant when the structured packing was used. For the sheathy leaf and natural fiber packings, the air pressure drop increased at a uniform rate as the mass flux of water flowing over the packing increased. The air pressure drop was lowest for the setup with the structured packing.     

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.     

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.     

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).     

Experimental and theoretical investigation of an innovative evaporative condenser for residential refrigerator

In this study, an innovative, evaporative condenser for residential refrigerator was introduced. A vapor compression cycle incorporating the proposed evaporative condenser was tested to evaluate the cycle performance. To allow for evaporative cooling, sheets of cloth were wrapped around condenser to suck the water from a water basin by capillary effect. The thermal properties at the different points of the refrigeration cycle were measured for typical operating conditions. The experimental results showed that the condenser temperature increases 0.45 °C for each degree increase in evaporator temperature when the air velocity is 2.5 m/s, and the ambient condition is 29 °C and the relative humidity is 37.5%. Meanwhile, the condenser temperature increase is 0.88 °C in the case of air velocity 1.1 m/s and ambient conditions of 31 °C and relative humidity of 47.1%. A theoretical model for the evaporative condenser was developed, and validated by experimental results. The theoretical model showed that the evaporative condenser can operate at a condensing temperature of 20 C lower than that of the air-cooled condenser for heat flux of 150 W/m², and at air velocity 3 m/s. The effect of the different parameters on the condenser temperature was studied too.     

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.     

Experimental investigation of the performance characteristics of a counterflow wet cooling tower

An experimental investigation of the performance characteristics of a counter flow wet cooling tower represented by the heat rejected by the tower and its thermal effectiveness is presented in this paper. The tower is filled with a “VGA.” (Vertical Grid Apparatus) type packing which is 0.42 m high and contains four (04) galvanised sheets having a zigzag form, between which are disposed three (03) metallic vertical grids in parallel with a cross-sectional test area of 0.15 m × 0.148 m. The investigation is concerned mainly on the effect of the air, water flow rates and the inlet water temperatures on the thermal effectiveness of the cooling tower as well as the heat rejected by this tower from water to be cooled to the air stream discharged into the atmosphere. The two operating regimes which were observed during the air/water contact inside the tower, a Pellicular Regime (PR) and a Bubble and Dispersion Regime (BDR) appear to be important, as The BDR regime enables to cool larger amount of water flow rates, while the Pellicular regime results with higher thermal effectiveness.     

Recent research on an indirect evaporative cooler (IEC) Part 2: thermal performance of a non-conditioned building coupled with an IEC

The thermal performance of a non-conditioned building fitted with an indirect evaporative cooler (IEC) has been investigated in terms of hourly, monthly and seasonal discomfort index. The effect of various design parameters of the IEC on the discomfort index has been investigated for three different climatic areas of India, i.e. hot–dry, warm, humid and composite. The analysis has shown that the IEC is effective for creating thermal comfort conditions in buildings in dry–hot and composite climates. © 1997 by John Wiley & Sons, Ltd.     

Experimental insight into the performance characteristics of Ni-mesh semiconductor photo-electrochemical cells

The performance characteristics of two photo-electrochemical cells with different cell configurations were investigated at 25°C and within the illumination range of 70–100 W/m². These cells included a jacketed single cell (JSC) and a jacketed two-compartment cell (JTC). Ni-mesh was used as a counter electrode and as a backing material for semiconductor electrodes. Semiconductor electrodes were prepared by silk-screen painting technique using TiO₂, WO₃, PbO, Sb₂S₃, ZnO, Al₂O₃ or CuO powder mixed with Teflon. The electrolyte contained aqueous methylene blue (MB) and Fe (II)/Fe(III) compounds. Voltage–current characteristics of the cells were measured at 25°C. Energy conversion efficiencies were calculated. A best-performing cell was selected from each cell configuration. The effects of Ni-mesh, semiconductor properties, and electrolyte modification on cell performance were studied. Experimental observations are compared with those in the literature, and the performance of each cell configuration is discussed. The best performance was obtained from Ni–TiO₂-MB/MB, Fe(II)//MB, Fe(II)/Ni–C cell configuration with 13% efficiency from JTC, Ni-PbO/MB, Fe(II)/Ni cell configuration with 24% efficiency from JSC.     

Energy performance evaluation of an evaporative wind tower

The aim of this paper is to optimize the energy performance of cylindrical cross section evaporative wind towers as passive systems for thermal conditioning of urban spaces. Two theoretical models, a thermal model and a fluid model, have been developed to characterize the evaporative system and the tower design respectively. The thermal model evaluates the tower operation when the fan and the nozzles are working, giving as result the difference between the outlet temperature and inlet temperature. This model has been used to analyze the thermal response of the system to fluctuations in design parameters (water flow, air flow and absorption coefficient of the plastic). To that effect, three one-parametric and one multi-parametric optimization have been done. The fluid model describes the tower operation when the fan and the nozzles are not working, giving as result the wind behavior through the tower. Additional configurations of the wind tower have been evaluated: changing the number of the wind catcher openings, varying the height of the internal walls of the tower and modifying the geometry of the lower ventilation apertures.     

CFD方法与间接蒸发冷却换热器的三维数值模拟

采用计算流体力学(CFD)和数值传热学方法,对间接蒸发冷却器内流体流动与热质交换过程进行简化和假设,建立了换热器内三维层流流动与传热的数学物理模型。采用交错网格离散化非线性控制方程组,编制了三维simple算法程序。对间接蒸发冷却器内的流场、温度场及浓度场进行数值模拟研究,得到换热器内的流体流动状态和热流分布,并分析了通道宽度变化对换热器内流体流动与换热的影响。     

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。     

Recent research on an indirect evaporative cooler (IEC) Part 1: optimization of the COP

The paper presents an analysis for optimizing the coefficient of performance of an tube type indirect evaporative cooler (IEC) in terms of process stream air velocity and wet stream air velocity. Theoretical predictions of the optimum COP value have been compared with the experimental results obtained for an IEC at Indore in the summer months of May and June; the agreement is satisfactory. © 1997 John Wiley & Sons, Ltd.     

Experimental investigation of the performance of an elbow-bend type heat exchanger with a water tube bank used as a heater or cooler in alpha-type Stirling machines

In this work the effect of the elbow-bend geometry and the effect of the tube arrangement on the performance of air-to-water heat exchanger is studied experimentally. In elbow-bend heat exchanger, the direction of the working fluid is bended at 90 degrees to its inlet direction. The heating or cooling fluid flows inside straight tubes while the working fluid flows past the tubes along an elbow pass. Three different types of the geometry of the elbow with three different tube bank arrangements were studied. The results were plotted and analyzed to clarify the effects of the elbow-bend geometry, the tube bank arrangements and the dead volume in the heat exchanger on the heat transfer and pressure drop. Two empirical correlations were deduced for each design, one to predict the relation between Nusselt and Reynolds numbers, while the other relation is between the friction factor and Reynolds number. This work was done to select the more suitable design to be used as a heater or a cooler in Stirling machines.