Flow reversal prediction of a single-phase square natural circulation loop using symbolic time series analysis
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Sådhanå (2020)45:223 https://doi.org/10.1007/s12046-020-01466-3
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Flow reversal prediction of a single-phase square natural circulation loop using symbolic time series analysis RITABRATA SAHA* , KOUSHIK GHOSH, ACHINTYA MUKHOPADHYAY and SWARNENDU SEN Department of Mechanical Engineering, Jadavpur University, Kolkata 700032, India e-mail: [email protected] MS received 13 April 2018; revised 3 May 2019; accepted 6 June 2019 Abstract. In the field of thermal engineering, one of the biggest concerns is the cooling of heat producing systems. For this purpose, today’s world is encouraging to use such cooling systems which are free from any active components (passive systems) for its high reliability and compact size. For this reason, to establish cooling by transferring heat from one place (source) to another (sink) passive system like natural circulation loop (NCL) is highly used. Fluid flow dynamics of the NCL is changing with the increase in heater power which is used as the source for the simulation. We found steady flow dynamics for the comparatively low power of heat, and with the rise in the power first, we saw the oscillatory flow dynamics and then found flow reversal characteristics. This paper presents a novel strategy for the early prediction of flow reversal phenomenon in NCL using symbolic analysis of time series data. This time series data is found from the numerical simulation, and for the proper study, we are considering data after the initial transient part is overcome. Total time series data is transformed into a symbol string by partitioning into a finite number of specified symbolised groups. The state probability vector is calculated based on the number of occurrences of each symbol group. Present work is a single-phase study, and according to our geometry, we can provide a maximum 800 W heater power to stay in the single-phase. Therefore, for the early prediction of flow reversal in NCL, state probability vector evaluated at 800 W heater power which is the most undesirable state (chaotic data), and this is considered as the reference vector. The difference of the reference state vector from the current state vector is used as a parameter for early detection of flow reversal. It can be observed from the results that this difference changes significantly when the system is sufficiently away from the flow reversal. Keywords.
Natural circulation loop; flow reversal; instability; symbolic time series analysis.
1. Introduction In the field of thermal engineering, one of the biggest concerns is the cooling of heat producing systems. For this purpose, today’s world is encouraging to use such cooling systems which are free from any active components (passive systems) for its high reliability and compact size. For this reason, as a cooling system, natural circulation loop (NCL) has been used in various energy systems like electrical machine rotor cooling, solar water heater systems, geothermal energy systems and nuclear power plants, etc. [1]. Heat
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