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Search Results (3)

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Keywords = overall heat transfer coefficient (OHTC)

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16 pages, 2758 KiB  
Article
Study on Flow and Heat Transfer in Single Rock Fractures for Geothermal Heat Extraction
by Duanru Li, Gang Liu and Shengming Liao
Processes 2024, 12(2), 363; https://doi.org/10.3390/pr12020363 - 9 Feb 2024
Cited by 2 | Viewed by 1929
Abstract
A full understanding of the fluid flow and heat transfer behaviors within a single fracture is important for geothermal heat extraction. In this study, models of single fractures with varying aperture and inner surface roughness (characterized by fractal dimension) are constructed, and a [...] Read more.
A full understanding of the fluid flow and heat transfer behaviors within a single fracture is important for geothermal heat extraction. In this study, models of single fractures with varying aperture and inner surface roughness (characterized by fractal dimension) are constructed, and a compound fracture aperture (CFA) is proposed to describe the coupled effect of fracture aperture and inner surface roughness. The effect of the fluid flow Reynolds number on heat transfer was investigated as it ranged from 4.84 to 145.63. The results show that the overall heat transfer coefficient (OHTC) in a single fracture significantly increases with the rise in fluid velocity and the compound fracture aperture. Particularly, the OHTC in a single fracture with an inner surface fractal dimension of 2.09 can be up to 1.215 times that of a parallel flat fracture when the flow velocity reaches 0.18 m/s. Moreover, for a fracture with a smaller CFA, enhancing the fracture aperture plays a decisive role in increasing the OHTC. Aperture emerges as a more sensitive optimization parameter for efficient heat extraction compared to the flow velocity. Meanwhile, based on simulation results, a convective heat transfer correlation equation is derived to provide more accurate estimates of the OHTC in rock fractures with different geometries and morphological features. Full article
(This article belongs to the Special Issue Green Manufacturing and Low-Carbon Control of Mechanical and Electrical Products)
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24 pages, 5765 KiB  
Article
Modelling and Analysis of Plate Heat Exchangers for Flexible District Heating Systems
by Serafym Chyhryn
Energies 2019, 12(21), 4141; https://doi.org/10.3390/en12214141 - 30 Oct 2019
Cited by 3 | Viewed by 4368
Abstract
Seamless integration of district heating (DH) and power systems implies their flexible operation, which extends their typical operational boundaries and, thus, affects performance of key components, such as plate heat exchangers (PHXs). Despite that the heat transfer in a PHX is regulated by [...] Read more.
Seamless integration of district heating (DH) and power systems implies their flexible operation, which extends their typical operational boundaries and, thus, affects performance of key components, such as plate heat exchangers (PHXs). Despite that the heat transfer in a PHX is regulated by mass flows, flexible operation and demand variations cause shifts in temperature levels, which affects the system operation and must be efficiently accounted for. In this paper, an overall heat transfer coefficient (OHTC) model with direct relation to temperature is proposed. The model is based on a linear approximation of thermophysical components of the forced convection coefficient (FCC). On one hand, it allows to account for temperature variations as compared to mass flow-based models, thus, improving accuracy. On the other hand, it does not involve iterative lookup of thermophysical properties and requires fewer inputs, hence, reducing computational effort. The proposed linear model is experimentally verified on a laboratory PHX against estimated correlations for FCC. A practical estimation procedure is proposed based on component data. Additionally, binding the correlation to one of varying parameters shows reduction in the heat transfer error. Finally, operational optimization test cases for a basic DH system demonstrate better performance of the proposed models as compared to those previously used. Full article
(This article belongs to the Special Issue Modelling, Simulation and Control of Thermal Energy Systems)
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16 pages, 8850 KiB  
Article
Thermal Characteristics of a Primary Surface Heat Exchanger with Corrugated Channels
by Jang-Won Seo, Chanyong Cho, Sangrae Lee and Young-Don Choi
Entropy 2016, 18(1), 15; https://doi.org/10.3390/e18010015 - 30 Dec 2015
Cited by 22 | Viewed by 8051
Abstract
This paper presents the heat transfer and pressure drop characteristics of a primary surface heat exchanger (PSHE) with corrugated surfaces. The PSHE was experimentally investigated for a Reynolds number range of 156–921 under various flow conditions on the hot and cold sides. The [...] Read more.
This paper presents the heat transfer and pressure drop characteristics of a primary surface heat exchanger (PSHE) with corrugated surfaces. The PSHE was experimentally investigated for a Reynolds number range of 156–921 under various flow conditions on the hot and cold sides. The inlet temperature of the hot side was maintained at 40 °C, while that of the cold side was maintained at 20 °C. A counterflow was used as it has a higher temperature proximity in comparison with a parallel flow. The heat transfer rate and pressure drop were measured for various Reynolds numbers on both the hot and cold sides of the PSHE, with the heat transfer coefficients for both sides computed using a modified Wilson plot method. Based on the results of the experiment, both Nusselt number and friction factor correlations were suggested for a PSHE with corrugated surfaces. Full article
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