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).     

Performance evaluation and comparison of multistage indirect evaporative cooling systems in two operation modes

The evaporative cooling technique is an efficient approach for cooling application. This study aims to establish a performance evaluation method to advance the appropriate design for multistage indirect evaporative cooling systems. A mathematical formulation has been developed for the indirect evaporative cooler (IEC). After the validation, the mathematical model was used to analyze the evaluation criteria by considering the simultaneous influence of the cooling effectiveness, the pressure drop, and the cooling capacity of the multistage IEC operating in two modes. The Mode-1 IEC is a conventional counterflow unit, while the Mode-2 IEC employs a regenerative M-cycle arrangement. The IECs are operated in a tandem arrangement. The multistage system is capable of improving the cooling performance and reducing the outlet air temperature. In addition, the multistage system displays a higher pressure drop resulting in a lager consumption of fan power. The analysis of performance evaluation criteria indicates that the appropriate maximum stage is suggested to be three-stage and two-stage for the Mode-1 and the Mode-2 IEC, respectively.     

不同蒸发冷却装置工作的影响因素及对比

采用CFD模拟了2种蒸发冷却装置,讨论了一次空气入口温度和喷淋水温度对蒸发冷却装置效率的影响。通过模拟一、二次空气出口处的温度分布,水蒸气相分布以及装置内整个通道的温度分布,得到影响2个蒸发冷却装置的传热性能的变化规律。同时,比较2个蒸发冷却装置的传热性能,给出了一种确定蒸发冷却装置性能的方法。对于管式蒸发冷却装置,选择管径为5 mm和10 mm,管间距为5 mm和10 mm的装置进行模拟。对于板式蒸发冷却,取板长度为500 mm和1 000 mm,并且板宽度为6 mm,8 mm和10 mm用于模拟。通过模拟得到装置尺寸对蒸发冷却效率的影响。     

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.     

蒸发冷却式冷水机组能耗模型实验研究

针对蒸发冷却式冷水机组能耗模型进行实验研究。比较蒸发冷却式冷水机组与普通冷水机组在工作原理存在的异同并分析室外气象参数对系统能耗影响的基础上,用冷凝器侧进口空气的焓值影响替代普通冷水机组能耗模型中的冷却水进口温度影响,建立了蒸发冷却式冷水机组的能耗模型,并利用实测数据进行了参数估计与误差检验,结果显示改进模型的验证误差在8%以内,在精度上比现有模型有了较大的提升。     

蒸发式冷凝器应用于户式空调的实验研究

将蒸发式换热器应用到户式空调机组中，室内机走冷却水，减少了泄漏的可能性，室外机应用蒸发式换热器，提高机组效率。通过建立实验台，测试空调机组性能，研究了对蒸发式换热器热质交换的各种影响因素，确定了蒸发式换热器的最佳范围，供工程设计、选型和生产参考。     

Experimental study of a direct evaporative cooling approach for Li-ion battery thermal management

A desirable operating temperature range and small temperature gradient is beneficial to the safety and longevity of lithium-ion (Li-ion) batteries, and battery thermal management systems (BTMSs) play a critical role in achieving the temperature control. Having the advantages of direct access and low viscosity, air is widely used as a cooling medium in BTMSs. In this paper, an air-based BTMS is modified by integrating a direct evaporative cooling (DEC) system, which helps reduce the inlet air temperature for enhanced heat dissipation. Experiments are carried out on 18650-type batteries and a 9-cell battery pack to study how relative humidity and air flow rate affect the DEC system. The maximum temperatures, temperature differences, and capacity fading of batteries are compared between three cooling conditions, which include the proposed DEC, air cooling, and natural convection cooling. In addition, a DEC tunnel that can produce reciprocating air flow is assembled to further reduce the maximum temperature and temperature difference inside the battery pack. It is demonstrated that the proposed DEC system can expand the usage of Li-ion batteries in more adverse and intensive operating conditions.     

Experimental study on the discharge characteristics of two eutectic solder packed bed latent heat storage systems

Metallic solder based PCMs possess higher thermal conductivities, larger storage masses and exhibit lower subcooling effects compared to their organic or inorganic counterparts. It is thus justified to investigate their potential usage for medium temperature applications. These solders are relatively expensive and can be combined with cheaper PCMs in cascaded storage systems which are more thermodynamically efficient compared to single PCM systems as reported recently. The aim of the research is thus to compare two packed bed storage systems during discharging cycles using eutectic solder (Sn63/Pb37), that is widely available worldwide. The single PCM system (40 capsules) consists of encapsulated spheres of eutectic solder, whereas the second cascaded system consists of encapsulated spheres of eutectic solder and erythritol in an equal storage ratio in the tank. For the cascaded system, the eutectic solder capsules are placed at the top and erythritol at the bottom of the storage tank (20 capsules at the top and 20 at the bottom). The effect of the discharging flow-rates of 4 mL/s, 6 mL/s and 8 mL/s is investigated in relation to the temperature profiles, energy rates and exergy rates. Increasing the flow-rate, increases heat transfer rate thus shortening the discharging time as well as increasing thermal profile reversals during discharging. The peak energy and exergy rates increase with the increase in the flow-rate for the two storage systems. The single PCM system shows slightly higher average energy and exergy rates compared to the cascaded system possibly due to its higher thermal conductivity. The cascaded PCM system shows higher average stratification numbers at all the flow rates considered. The non-cascaded system exhibited slightly higher exergy recovery efficiencies compared to the cascaded PCM system possibly due to its higher thermal conductivity at all flow-rates considered. The effect of the initial discharging temperature is also investigated with a discharging flow-rate of 6 mL/s after charging with set heater temperatures of 260°C, 280°C and 300°C, respectively. Comparable thermal profiles are seen for both systems for the three set temperatures; however, the single PCM system shows slightly higher storage temperatures. The single PCM shows slightly higher but comparable peak and average discharging energy rates compared to the cascaded system. The exergy rates for the two systems are also comparable. However, the cascaded system shows slightly higher exergy rate values for the lowest set temperature whereas the single PCM system shows slightly higher exergy rate values for the other two set temperatures. Energy and exergy rates are almost independent of the initial storage tank temperatures induced by different set charging temperatures. The average stratification number shows no correlation with set temperature for both storage systems. The cascaded system shows slightly higher average stratification numbers at different set temperatures. Exergy recovery efficiencies for different set heater temperatures are comparable for the two storage systems and vary only marginally with the increase in the set temperature. Overall, the effect of the flow-rate is more pronounced than the effect of the set heater temperature.     

Experimental study on the impact of mass moisture content on the evaporative cooling effect of porous face brick

Porous face bricks on the outside of a building wall exhibit evaporative cooling after absorbing water. Thus, these bricks are promising for use as a passive energy-saving building technology. Artificial watering is an effective method to ensure a sufficient water supply for effective evaporative cooling. However, improper watering measures may result in the waste of water resources while failing to achieve the evaporative cooling effect. In this paper, studies were conducted on a composite wall composed of a facing layer and a base layer as follows. (1) The mass moisture content variations in the porous face brick with respect to soaking time were measured, and the feasibility of using this type of face brick as an evaporative cooling carrier was investigated. (2) The relationship between mass moisture content and the evaporation capacity of the porous face brick was determined under stable conditions. A critical mass moisture content for the porous face brick was determined through analysis of the measurement data. (3) A field measurement was performed to verify the feasibility of using the critical mass moisture content as a criterion for watering. The results indicate that the temperature and heat flows at the inner and outer surfaces of the composite wall were reduced significantly. However, when the mass moisture content exceeded the critical mass moisture content, the evaporative cooling capability tended to stabilize with further watering. Therefore, the critical mass moisture content of the porous face brick can be used as a criterion for watering to conserve water while facilitating the evaporative cooling effect.     

Experimental investigation into the thermal-flow performance characteristics of an evaporative cooler

This study investigates the thermal-flow performance characteristics of an evaporative cooler. The derivation of the Poppe [1] and Merkel [2] analysis for evaporative coolers are presented and discussed. Performance tests were conducted on an evaporative cooler consisting of 15 tube rows with 38.1 mm outer diameter galvanized steel tubes arranged in a 76.2 mm triangular pattern. From the experimental results, correlations for the water film heat transfer coefficient, air–water mass transfer coefficient and air-side pressure drop are developed. The experimental tests show that the water film heat transfer coefficient is a function of the air mass velocity, deluge water mass velocity as well as the deluge water temperature, while the air–water mass transfer coefficient is a function of the air mass velocity and the deluge water mass velocity. It was found that the correlations obtained for the water film heat transfer coefficient and the air–water mass transfer coefficient compare well with the correlations given by Mizushina et al. [3]. Relatively little published information is available for predicting the air-side pressure drop across deluged tube bundles. The present study shows that the pressure drop across the bundle is a function of the air mass velocity and the deluge water mass velocity.     

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。     

Experimental study of passive systems thermal performance

In geographical zones with a continental Mediterranean climate, the convenience of passive systems becomes doubtful, when one takes into account real thermal performance throughout the different seasons of the year. It is assumed that these systems stay shut down during summer thus avoiding undesirable solar gains. This study contributes answers to some questions about this topic by means of a comparative experimental analysis on the thermal performance of three passive systems (Massive/Trombe Wall, Direct Gain and Sunspace) and two traditional constructive systems (with/without low energy measures) for various situations (with/without night/day protection and ventilation) and climatic seasons (winter, summer and one neutral-times of spring and autumn). The measured variables are solar irradiance, outdoor temperature and indoor temperature taken from different points of the physical models. The applied procedures, technics and instruments are explained and some conclusions are drawn based on the obtained results.     

Experimental study of effect of an inner thermal curtain in evaporative cooling system of a cascade greenhouse

In this paper experimental study has been carried out in a cascade greenhouse with inner thermal curtain to see the effect of thermal curtain. A thermal model has also been developed to predict the air temperature in a cascade greenhouse. The fan-pad system has been used for evaporative cooling and an inner thermal curtain has been used to divide the greenhouse in two zones. Experiments have been conducted in hot summer conditions at Solar Energy Park, IIT Delhi, New Delhi, India for empty greenhouse. Statistical analysis has been carried out to validate the agreement of experimental observations with predicted values. The values of the root mean square percent deviation and coefficient of correlation has been found out 9.0%, 0.90; 5.0%, 0.95 and 7.0%, 0.97 for April, May and June in case of evaporative cooling without curtain in greenhouse-2. The degree of freedom for the experimental work is 10.0. It is found that the use of evaporative cooling with a thermal curtain reduces the temperature of greenhouse by 5 °C and 8 °C in the second zone of greenhouse-1 and 2 in comparison to greenhouse without curtain in May.     

Optical characterisation of materials and systems for daylighting

The measurement of BRTF (Bi-directional reflectance and transmittance function) is described using a new instrument which is capable of supplying BRTF data and algorithms for use in computer simulations directly on diffuse materials and indirectly on large samples and sub-systems. A high sensitivity and dynamic range is needed to achieve low minimum observable BRTF and the role of angular resolution are discussed with examples. Forward scattering with extended tails is found to dominate pigmented polycarbonate. Slatted blinds are discussed as examples of systems where azimuth is important.     

多周期蒸汽动力系统运行优化研究

结合考虑锅炉效率随负荷的变化,汽轮机作功的非线性以及各设备的启停费用来研究的蒸汽动力系统优化运行问题,并采用改进的遗传算法求解。通过一算例求解结果表明算法可行,模型更切合实际。     

Thermal efficiency of evaporative heat loss for open and closed cycle systems

The authors present an analytical expression for the thermal efficiency of evaporative heat loss for open and closed cycle systems in terms of system design and climatic parameters. The derived analytical expression can be used for optimum design of evaporative cooling (open cycle) and distillation system (closed cycle). The theoretical results have also been validated experimentally for open cycle system.     

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.     

Experimental study of CPC type ICS solar systems

Extensive experimental study on solar water heaters, which were developed in our laboratory, is presented. These solar devices are integrated collector storage (ICS) systems with single horizontal cylindrical storage tank properly placed in symmetric CPC type reflector trough. In this paper we study ICS solar systems, which differ in storage tank diameter and correlate their thermal performance and the ratios of the stored water volume per aperture area and also per total external surface area. Based on the results of this study and aiming to achieve improved ICS systems, we considered an effective tank diameter and we extracted by outdoor tests the performance of a number of experimental models differing in the absorbing surface, reflector and transparent cover. We calculated the mean daily efficiency and the thermal loss coefficient during night of each system combination. In addition, 24 h and four days operation diagrams of the variation of water temperature of the studied ICS systems are compared with the corresponding diagrams of two flat plate thermosiphonic units with mat black and selective absorbing surface, respectively. The experimental results show that ICS system with selective absorbing surface, high transmissivity of the transparent cover and high reflectance of its reflector surface performs efficiently enough, both during the day and night operation, approaching the thermal performance of the corresponding thermosiphonic unit of flat plate collector with selective absorber.     

Experimental validation of a thermal model of an evaporative cooling system

A periodic thermal model for an evaporative cooling system over the roof has been presented. Open roof pond, water film and flowing water layer are the the special cases of the analysis. The time dependency of solar radiation, ambient air, sol-air and room air temperatures has explicitly been taken into account by expressing as a Fourier series of time for a 24 h cycle. Experimentally observed air temperature of rooms, treated with and without evaporative cooling over the roof, has been found in good agreement with theoretical results.