Thermo-buoyancy Driven Flows and Pouring Characteristics of a Kyusu
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2023
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University of Hawaii at Manoa
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The Japanese teapot, also known as the kyusu, has a unique design for its handle, allowingfor it to be cool to touch while pouring. The handle acts as a fin and the traditional hollow, cylindrical design is hypothesized to be cooled by a thermo-buoyancy driven flow. Though fins are ubiquitous in practical heat transfer applications, the underlying heat transfer mechanism for these geometries are not well understood. Analytical solutions are only available for simple fins, often with assumptions of constant cross section, one-dimensional and steady state. Infrared thermography was used for investigation of spatial distribution of the temperature in the pot handles. Four different kyusu designs were studied. Simplified models, such as solid cylinders, hollow cylinders of uniform and varying cross-sectional geometry, and 3D models of actual handle designs were used for analysis and comparison with data. Temperature profiles were compared against each other for the different handle designs conditions. The solid handle acted as a fin and matched the model’s predictions during steady state. The transient response deviated from predictions. The hollow ones maintained a degree of temperature variation in length and did not agree well with the simplified model of a constant diameter cylinder. A modified Nu correlation was proposed in which the curvature of the handle was incorporated. Results of preliminary CFD and experimental flow visualization suggested that there exists a re-circulation flow within the handle. The pouring mechanism of the kyusus were also investigated. The well-known ‘teapot effect’ was observed for all pouring angles. Computational analysis and image processing edge detection were employed in an attempt to correlate volume fraction with angle of pour. An experimental setup, inspired by previous pouring experiments, was used to record inclination angle and residual volume. It was found that geometry, handle placement, water temperature and other factors affected pouring ability. A critical angle of pour was discovered in which it is hypothesized that surface tension effects along with momentum and energy balance lead to an optimal angle to avoid the teapot effect.
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Fluid mechanics
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