Truncation method for calculating the resistance of ventilation air-conditioning duct systems under nonfully developed f
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Truncation method for calculating the resistance of ventilation air-conditioning duct systems under nonfully developed flow boundary conditions
School of Building Services Science and Engineering, Xi’an University of Architecture and Technology, Xi’an, Shaanxi 710055, China
Abstract
Keywords
Calculating the resistance of ventilation air-conditioning ducts under nonfully developed flow is a crucial problem that must be addressed. Based on the characteristics of the resistance in ventilation air-conditioning ducts, the truncation method—a computational method that is appropriate for nonfully developed flow boundary conditions—was proposed in this study. The resistance distributions in the upstream and downstream ducts from typical local components, including reducers, bends and tee ducts, were investigated. Using the resistance values of the local components under fully developed flow, the resistances that did not belong to nonfully developed flow were truncated and removed. Finally, the calculation steps of the proposed method were discussed, an engineering case study was presented, and the accuracy of the developed model was analyzed. The results showed that for the local components in the system (reducers, bends and tee ducts), their proportions of the total resistance exhibited similar trends under different width-to-height ratios. The resistance of these local components included upstream resistance, downstream resistance and their own resistance. The upstream resistance accounted for 2%–6% of the total resistance, whereas the downstream resistance of the reducers, bends and tee ducts accounted for 40%–60% of the total resistance. A functional relationship was established between the local resistance and cutoff distance of the reducers, bends and tee ducts. Hence, the truncation method can calculate the local resistance from the cutoff distance. Moreover, in the presented engineering case study, the error between the actual measured resistance values and those simulated with the truncation method was only 4.28%, which was far less than that of the results simulated with the traditional calculation methods (53.64%).
resistance,
Introduction
Over the last few decades, fully developed flow has been the basis of traditional research on duct resistance (Ceylan and Kelbaliyev 2003; Park 2016; Ramgadia and Saha 2019). However, in the field of ventilation air-conditioning ducts, the resistance variation from nonfully developed flow is significant (Miller 1978). For simplification, previous studies typically assume that the distance between local components is sufficiently far to avoid disturbing the flow fields between them, i.e., the flow fields at the inlets of local components are hypothetically fully developed flow. These components can be referred to as individual local components (or local E-mail: [email protected]
local components, nonfully developed flow, truncation method
Article History Received: 06 July 2020 Revised: 09 September 2020 Accepted: 28 September 2020 © Tsinghua University Press and Spri
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