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Particle motion and heat transfer in an upward-flowing dense particle suspension: Application in solar receivers

Abstract : Concentrated solar power (CSP) plants conventionally make use of molten salt as the heat transfer medium, which transfers heat between the solar receiver and a steam turbine power circuit. A new approach uses particles of a heat-resistant particulate medium in the form of many dense upward-moving fluidised beds contained within an array of vertical tubes within the solar receiver. In most dense gas–solid fluidisation systems, particle circulation is induced by bubble motion and is the primary cause of particle convective heat transfer,which is themajor contributing mechanismto overall heat transfer. The current work describes experiments designed to investigate the relationship between this solids convection and the heat transfer coefficient between the bed and the tubewall, which is shown to depend on the local particle concentration and their rate of renewal at the wall. Experimentswere performed using 65 mmsilicon carbide particles in a tube of diameter 30mm, replicating the conditions used in the real application. Solidsmotion and time-averaged solids concentration were measured using Positron Emission Particle Tracking (PEPT) and local heat transfer coefficients measured using small probes which employ electrical resistance heating and thermocouple temperaturemeasurement. Results show that, as for other types of bubbling beds, the heat transfer coefficient first increases as the gas flow rate increases (because the rate of particle renewal at thewall increases), before passing through a maximum and decreasing again as the reducing local solids concentration at the wall becomes the dominant effect. Measured heat transfer coefficients are compared with theoretical approaches by Mickley and Fairbanks packet model and Thring correlation. The close correspondence between heat transfer coefficient and solids movement is here demonstrated by PEPT for the first time in a dense upward-moving fluidised bed.
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Submitted on : Monday, January 8, 2018 - 11:48:27 AM
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Pablo García-Triñanes, Jonathan Seville, Renaud Ansart, Hadrien Benoit, Thomas Leadbeater, et al.. Particle motion and heat transfer in an upward-flowing dense particle suspension: Application in solar receivers. Chemical Engineering Science, Elsevier, 2017, vol. 177, pp. 313-322. ⟨10.1016/j.ces.2017.11.041⟩. ⟨hal-01677355⟩

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