1,721,803 research outputs found
Modeling of dew-point evaporative coolers
No full textModeling is an essential approach to understanding the important physics that control dew-point evaporative cooling. It rationalizes the results from experimental investigations, gives insights into the physical mechanisms and relevant design parameters, and suggests ideas to improve the cooler performance further. This chapter details the state-of-the-art mathematical models developed for the dew-point evaporative coolers, which can be translated to different cooler geometries. The physics-based models of the dew-point evaporative coolers are developed based on thermodynamics, heat and mass transfer, and fluid mechanics. Depending on the physics and assumptions proposed, models with different levels of complexity can be developed, such as lumped parameter and computational fluid dynamics (CFD) models. The lumped parameter model can be solved analytically using the ε-NTU and LMTD method. In addition, data-driven models can be derived from the input–output data of the dew-point evaporative coolers, which can eliminate the need to physically understand the cooling process and respond in real time
Engineering of dew-point evaporative coolers
No full textThe concept of dew-point evaporative cooling brings about a new theoretical limit to evaporative cooling, attracting many research and engineering efforts to realize it in practice. The successful scientific progress of the dew-point evaporative cooler requires the excellent integration of many multiple disciplines. This chapter judiciously documents the engineering pathway in the development of dew-point evaporative cooling, highlighting the major points to consider to achieve efficient cooling. Different flow regimes, channel shapes, structural materials are tested during the design of the heat and mass exchangers. The geometric and operating conditions of the heat and mass exchangers must be determined according to the designated ambient conditions. In addition, the dew-point evaporative coolers can operate in different modes in order to optimize the fresh air intake or heat recovery from the room return air
Advanced dew-point evaporative cooling systems
No full textAs an effective sensible air-cooling technology, dew-point evaporative cooling has broad applications in air conditioning and can be integrated with many other air-conditioning systems. Ideally it can be coupled with a dehumidifier to achieve all-weather cooling. Beyond air cooling, dew-point evaporative cooling can be introduced to many devices and systems that need excellent heat and mass transfer for cooling and humidification. This chapter will present the advanced designs of air conditioners, condensers, cooling towers, and gas turbines with a dew-point evaporative cooling process. The innovative idea of dew-point evaporative cooling can substantially improve the energy efficiency of these systems by enhancing the degree of air and water cooling and air humidification
Fundamental analysis of dew-point evaporative cooler
No full textThe performance of dew-point evaporative cooling is controlled by the fundamental physical processes related to fluid flow and heat and mass transfer. Investigation of these processes is crucial to reveal the underlying mechanisms and dominant factors of the cooler. This chapter presents several important methods that can be used to fundamentally analyze the dew-point evaporative cooling based on its CFD model developed in the last chapter. The scaling and dimensional analyses are basic yet powerful approaches for identifying the dominant dimensionless numbers of the cooling process and quantifying their influence on the objective parameters of the cooler. They can also be applied to examine the complex heat and mass transfer phenomena in the cooler that deviate from conventional constant boundaries. In addition, the exergy analysis is another approach to gain key insights into the irreversibility and potential of the dew-point evaporative cooling. It is worth noting that the methods presented in this chapter are feasible to any energy system, and a comprehensive understanding of the physical principles can be obtained by integrating these techniques
State-of-the-art air-conditioning technologies
No full textAir conditioning is the process of regulating air’s temperature, humidity, ventilation and circulation, as well as cleansing air, for an enclosed space to achieve the desired comfortable environment. Modern air conditioning has existed for more than a century and plays an essential role in not only providing thermal comfort for human occupants, but also maintaining suitable thermal conditions for heat-sensitive devices and systems. The most common air-conditioning technology is developed based on the vapor-compression refrigeration cycle, which is also known as the conventional air conditioning in contrast to many other competing technologies. Despite the conventional air conditioner being the most widely adopted cooling technology and its market size still growing, its energy consumption and greenhouse gas emissions remain challenging issues. Therefore, a lot of efforts are being made to develop novel alternative approaches that are environmentally friendly and energy-efficient. This chapter will review some recent state-of-the-art air-conditioning technologies with a specific focus on cooling as this is the most difficult part in air conditioning from the thermodynamic perspective. Having a deeper appreciation on the importance of developing energy-efficient cooling technologies and their impacts on the environment, evaporative cooling, being as the key technological subject of this book, will be gradually introduced
Working principles of evaporative cooling
No full textEvaporative cooling is a clean and energy-efficient cooling technology that relies on the water’s latent heat of vaporization to cool the air. It has a long historical record for cooling applications before modern vapor-compression air conditioning was invented. Despite its history, there has not been a revolutionary change on evaporative cooling until the past century, where multiple designs of evaporative coolers were developed, tested and adopted. This chapter presents several key evaporative cooling technologies that have evolved, including direct, indirect, and dew-point evaporative cooling. Direct and conventional indirect evaporative cooling experience thermodynamic limits based on the air’s wet-bulb temperature, and hence have confined applications. To address this issue, an innovative indirect evaporative cooling, termed the dew-point evaporative cooling, has been proposed. Its unique feature of pre-cooling the air enables it to cool the air towards dew-point temperatures
Trip quality in peer-to-peer shared ride systems
Full text link© 2007 Lin-Jie Guan.In a peer-to-peer shared ride system, transportation clients with traffic demand negotiate with transportation hosts offering shared ride services for ad-hoc ridesharing in a continuously changing environment, using wireless geosensor networks. Due to the distinctive characteristic of this system—a complex and non-deterministic transportation network, and a local peer-to-peer communication strategy—clients will always have limited transportation knowledge, both from a spatial and a temporal perspective. Clients hear only from nearby hosts, and they do not know the future availability of current or new hosts. Clients can plan optimal trips prior to departure according to their current knowledge, but it is unlikely that these trips will be final optimal trip due to continuously changing traffic conditions. Therefore, it is necessary to evaluate the trip quality in this dynamic environment in order to assess different communication and wayfinding strategies. (For complete abstract open document
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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