Abstract
Due to their ease of manufacture, high heat transfer efficiency and compact design, helically coiled heat exchangers are increasingly being adopted in a number of industries. The higher heat transfer efficiency over straight pipes is due to the secondary flow that develops as a result of the centrifugal force. In spite of the widespread use of helically coiled heat exchangers, and the presence of bubbly two-phase flow in a number of systems, very few studies have investigated the resultant flow characteristics. This paper will therefore present the results of CFD simulations for the two-phase bubbly flow in helically coiled heat exchangers as a function of the volumetric void fraction and the tube cross-section design. The CFD results are compared to the scarce flow visualisation experimental results available in the open literature.
Highlights
Coiled tube heat exchangers have seen extensive use in industrial applications such as in refrigeration, condensers and evaporators in the food industry, heat recovery systems, power generation, process plants and the nuclear industry where helically coiled heat exchangers are used for residual heat removal systems
This is due to the fact that helically coiled heat exchangers have a greater heat transfer rate as well as a more compact design compared to straight tube heat exchangers [1, 2]
The results shown in each series of simulations are very similar, in that the volume fraction distribution is spread throughout the pipe suggesting that the air and water phases are not separating
Summary
Coiled tube heat exchangers have seen extensive use in industrial applications such as in refrigeration, condensers and evaporators in the food industry, heat recovery systems, power generation, process plants and the nuclear industry where helically coiled heat exchangers are used for residual heat removal systems. This is due to the fact that helically coiled heat exchangers have a greater heat transfer rate as well as a more compact design compared to straight tube heat exchangers [1, 2]. In this paper we will investigate the phase distribution of bubbly flow in a helically coiled tube heat exchanger using computational fluid dynamics (CFD) at system conditions typical of domestic wet central heating systems. Due to the difficulties related to experimental methods and the cost and investment needed, the development and validation of a CFD simulation using existing experimental data, may prove beneficial for the development of helically coiled tube heat exchangers
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