Heat pipe evacuated tube solar collectors (HPETCs) are an integral part of solar water heating (SWH) technologies. In order to better design and optimize HPETCs, fast and robust numerical tools are needed that can provide accurate predictions while not sacrificing much accuracy. Due to the complexity of the heat transfer processes involved in modeling a collector’s performance e.g., coupled radiative, convective and conductive heat transfer, direct numerical analysis solutions (DNS) are computationally cumbersome. RN models have been shown to be suitable tools for studying the performance and thermal behavior of HPETCs. While RN models can be used for studying the performance of HPETCs from a system point of view, they are generally unable to provide an in-depth knowledge of the collectors’ thermal behavior. Furthermore, their temporal accuracy is limited to the availability of meteorological and ambient data. This study aims to improve upon RN models by combining them with both a proper orthogonal decomposition (POD) reduced order modeling technique and Lattice Boltzmann method (LBM) for evaluating the thermal performance of an HPETC during a complete 24 hour cycle of operation. LBM has been chosen because of several advantages in comparison to other CFD techniques including (a) suitability for integrating with parallel computing algorithms due to local nature of its collision process (b) being naturally explicit, there is no need for solving coupled pressure-velocity equations (c) simple calculation procedure along with easy handling of complex geometries and easier treatment of boundary conditions. By combining the advantages of both RN and computational fluid dynamics (CFD) models, this novel method is not only able to consider the geographical and meteorological characteristics of the ambient surroundings, but also the peripheral temperature distribution of a single HPETC can be accounted for with acceptable accuracy and as little computational cost as possible. Once the temperatures at a handful of instances in time have been calculated with the RN model, POD method is used to predict the thermal behavior of the collector with desired temporal accuracy, without the need for any further input data for day time operation. Finally, LBM has been employed, as an auxiliary method, to model thermal behavior during night time operation. For validation, the temperature distribution inside the HPETC has been compared with the previous experimental work of the authors and the results show that the model is able to predict the temperature distribution with a maximum error of less than 15%, and several orders of magnitude faster than DNS.

Keywords: Evacuated tube solar collectors, resistance network, proper orthogonal decomposition, Lattice Boltzmann method, thermal behavior


An Innovative Thermal Analysis Model for Continuous Operation of a Solar Collector

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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