On the Effective Driving Force for Transport in Cooling Towers
01 May 1995-Journal of Heat Transfer-transactions of The Asme (American Society of Mechanical Engineers)-Vol. 117, Iss: 2, pp 512-515
About: This article is published in Journal of Heat Transfer-transactions of The Asme.The article was published on 1995-05-01. It has received 5 citations till now. The article focuses on the topics: Heat transfer & Cooling tower.
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TL;DR: In this article, a theoretical investigation for the steady-state counter flow wet cooling tower with modified definitions for both the number of transfer units and the tower thermal effectiveness is presented, where the tower effectiveness is defined by the tower cooling range and the approach to equilibrium.
Abstract: The paper describes a theoretical investigation for the steady-state counter flow wet cooling tower with modified definitions for both the number of transfer units and the tower thermal effectiveness. The modified number of transfer units is dependent on both air and water heat capacity. The effectiveness is defined by the tower cooling range and the approach to equilibrium. A new expression relating the tower effectiveness to the modified number of transfer units and the capacity rate ratio has been developed. The model considered the resistance to heat transfer in the water film, the nonunity of the Lewis number, and the curvature of the saturated air enthalpy curve. A procedure for implementing the model in designing or rating cooling towers has been outlined and demonstrated through illustrative examples. The model compares very satisfactorily with other methods such as Logarithmic Mean Enthalpy Difference (LMED) and conventional effectiveness-NTU. Within the ranges used, the obtained results showed that substantial errors varied from +4.289 to -2.536 percent can occur in calculating the cooled water outlet temperature, and errors from +42.847 to -16.667 percent can occur in estimating the tower thermal characteristics.
49 citations
TL;DR: In this paper, a step-by-step approach is employed for numerical modeling of counterflow heat and mass exchangers in a natural draft wet-cooling tower, followed by reduced order modelling of heat transfer in cooling tower fills by means of proper orthogonal decomposition radial basis function networks.
Abstract: Numerical modelling of natural draft wet-cooling towers is considered in this paper. Development of a complete CFD model capable of predicting cooling tower performance under various operating conditions is presented. A step-by-step approach is employed, thus one-dimensional numerical modelling of counterflow heat and mass exchangers is extensively presented first. This is followed by reduced order modelling of heat and mass transfer in cooling tower fills by means of proper orthogonal decomposition radial basis function networks. Then the approaches in modelling of droplet zones (rain and spray zones) are discussed. Finally the two and three-dimensional CFD models are discussed.
44 citations
Cites background or methods from "On the Effective Driving Force for ..."
...The deficiencies of he Merkel method has motivated several authors to improve the formulation [6, 63, 78]....
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...Various developments and improvements, since its first appearance, have been reported in the literature, for example the works by Baker and Shryock [6], Bošnjaković [11], Kloppers and Kröger [44, 47, 48], Osterle [63], Poppe [70], Sadasivam and Balakrishnan [78], just to mention the few....
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22 citations
TL;DR: In this paper, a three-dimensional numerical model is established and validated for cooling performance optimization between a high-level water collecting natural draft wet cooling tower (HNDWCT) and a usual NVDWCT under the actual operation condition at Wanzhou power plant, Chongqing, China.
Abstract: A three-dimensional (3D) numerical model is established and validated for cooling performance optimization between a high-level water collecting natural draft wet cooling tower (HNDWCT) and a usual natural draft wet cooling tower (UNDWCT) under the actual operation condition at Wanzhou power plant, Chongqing, China. User defined functions (UDFs) of source terms are composed and loaded into the spray, fill and rain zones. Considering the conditions of impact on three kinds of corrugated fills (Double-oblique wave, Two-way wave and S wave) and four kinds of fill height (1.25 m, 1.5 m, 1.75 m and 2 m), numerical simulation of cooling performance are analysed. The results demonstrate that the S wave has the highest cooling efficiency in three fills for both towers, indicating that fill characteristics are crucial to cooling performance. Moreover, the cooling performance of the HNDWCT is far superior to that of the UNDWCT with fill height increases of 1.75 m and above, because the air mass flow rate in the fill zone of the HNDWCT improves more than that in the UNDWCT, as a result of the rain zone resistance declining sharply for the HNDWCT. In addition, the mass and heat transfer capacity of the HNDWCT is better in the tower centre zone than in the outer zone near the tower wall under a uniform fill layout. This behaviour is inverted for the UNDWCT, perhaps because the high-level collection devices play the role of flow guiding in the inner zone. Therefore, when non-uniform fill layout optimization is applied to the HNDWCT, the inner zone increases in height from 1.75 m to 2 m, the outer zone reduces in height from 1.75 m to 1.5 m, and the outlet water temperature declines approximately 0.4 K compared to that of the uniform layout.
10 citations
Dissertation•
01 Apr 2004
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References
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Book•
01 Jan 1955
TL;DR: In this article, the Mass Transfer Coefficients for Moleuclar Diffusion in Fluids and Interphase Mass Transfer in Solid-Fluid Operations are presented. But they do not consider the effect of ion exchange in solids.
Abstract: 1 The Mass-Transfer Operations Diffusion and Mass Transfer2 Moleuclar Diffusion in Fluids3 Mass-Transfer Coefficients4 Diffusion in Solids5 Interphase Mass Transfer6 Gas-Liquid Operations7 Equipment for Gas-Liquid Operations8 Humidification Operations, Gas Absorption9 Gas Absorption10 Distillation11 Liquid-Liquid Operations12 Liquid Extraction13 Solid-Fluid Operations14 Absorption and Ion Exchange15 Drying16 Leaching
2,184 citations
Book•
01 Jan 1960
TL;DR: In this article, the authors present an approach to unit operations in chemical engineering, including the following: Mass Transfer, Heat Transfer, Evaporation and Crystallization, Humidification, and Drying.
Abstract: Unit Operations in Chemical Engineering. STAGE OPERATIONS. Mass Transfer Operations. Phase Relations. Equilibrium Stage Calculations. Countercurrent Multistage Operations. Countercurrent Multistage Operations with Reflux. Simplified Calculation Methods. Multicomponent State Operations. MOLECULAR AND TURBULENT TRANSPORT. Molecular Transport Mechanism. Differential Mass, Heat, and Momentum Balances. Equations of Change. Turbulent-Transport Mechanism. Fundamentals of Transfer Mechanisms. Interphase Transfer. APPLICATIONS TO EQUIPMENT DESIGN. Heat Transfer. Mass Transfer. Simultaneous Heat and Mass Transfer--Humidification. Simultaneous Heat and Mass Transfer--Drying. Simultaneous Heat and Mass Transfer--Evaporation and Crystallization. The Energy Balance in Flow Systems. Fluid Motive Devices. Particulate Solids. Flow and Separation through Fluid Mechanics.
375 citations
TL;DR: The methode LMED (difference d'enthalpie logarithmique moyenne) as mentioned in this paper is a methode NUT-efficacite for the conception de tours de refroidissement.
Abstract: Developpement de la methode NUT-efficacite pour la conception de tours de refroidissement: introduction de l'enthalpie de l'air sature en parametre et definition du nombre d'increments correspondant a la precision desiree Presentation de la methode LMED (difference d'enthalpie logarithmique moyenne) et comparaison des deux methodes sur des exemples
199 citations
82 citations
"On the Effective Driving Force for ..." refers result in this paper
...Computations indicate that the L/G ratio does not have any effect on the change in heights obtained from the rigorous method and the c-NTU method at all values of r. This is in accordance with the results of Sutherland (1983) and Jaber and Webb (1989)....
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