Browsing by Author "Wang, Chen-Chih"

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Channel orientation effect on endwall heat transfer in rotating cooling passages with pin-fins
(2019-06-01)
Huang, Szu-Chi
;
Wang, Chen-Chih
;
Liu, Yao-Hsien
;
機械工程學系
;
Department of Mechanical Engineering
Heat transfer was experimentally measured using a rotating pin-fin channel involving two channel orientations, namely 90 degrees and 150 degrees, with respect to a rotating axis. A rectangular channel with an aspect ratio of 4:1 was selected to study internal cooling near the trailing edge of a turbine blade. A newly developed method of liquid crystal thermography along with stroboscopic photography was used to obtain detailed heat transfer contours on an endwall surface. The pin-fin arrays were designed in either inline or staggered patterns, and the Reynolds number ranged from 5,000 to 20,000. The pressurized air flow acted as the working fluid, and the highest rotation number was thus 0.39. The influence of rotation was greater on the inline array than on the staggered array, engendering higher heat transfer enhancement on the leading and trailing surfaces. Compared with the other orientation, the inclined orientation (150 degrees) engendered a larger spanwise heat transfer variation because of the shifted rotation-induced secondary flows. The inline array exhibited the highest rotation-induced heat transfer enhancement at the 90 degrees orientation, and the highest enhancement levels were 90% and 40% on the trailing and leading surfaces, respectively. (C) 2019 Elsevier Ltd. All rights reserved.
EFFECT OF MISSING FIN ON ENDWALL HEAT TRANSFER IN A ROTATING COOLING CHANNEL
(2017-01-01)
Wang, Chen-Chih
;
Huang, Szu-Chi
;
Liu, Yao-Hsien
;
機械工程學系
;
Department of Mechanical Engineering
This paper experimentally investigated the endwall heat transfer distribution in a rotating rectangular cooling channel (Aspect ratio = 4:1) using a newly developed steady-state liquid crystal thermography. Three Reynolds numbers (5000, 10000 and 20000) were tested, and the highest rotation number was 0.65. The buoyancy parameter ranged from 0 to 1.0 at a fixed density ratio of 0.1. Effect of missing fin (one fin missing) on heat transfer in a staggered pin-fin array was studied. For the stationary case, absence of the fin contributed to an undisturbed wake region from the adjacent upstream fins. Both leading and trailing surfaces produced the asymmetric heat transfer distribution along the spanwise direction because of the channel orientation (150 degrees) and rotation. At the highest rotation number, a highly irregular Nusselt number contour was observed on the missing fin region. This was mainly attributed to the intensified rotation induced secondary flow from the enlarged fin spacing, and the heat transfer enhancement of the missing fin case was 20% higher than the full fin case on the trailing surface.
Heat transfer measurement in a rotating cooling channel with staggered and inline pin-fin arrays using liquid crystal and stroboscopy
(2017-12-01)
Huang, Szu-Chi
;
Wang, Chen-Chih
;
Liu, Yao-Hsien
;
機械工程學系
;
Department of Mechanical Engineering
Endwall heat transfer in the stationary and rotating cooling channels with pin-fin arrays (inline and staggered pattern) were experimentally measured by wide band liquid crystal. The temperature measurement was performed with the stroboscopic photography to capture the reflected color from the liquid crystal coatings on the rotating object. A detailed calibration was performed to quantify the uncertainties in the liquid crystal measurement from the stroboscope frequency, flash duration, and viewing angle. The Reynolds numbers ranged from 5000 to 20000 and the rotation numbers ranged from 0 to 0.52. This measurement technique provided detailed heat transfer variations caused by the distinct secondary flow patterns from pin-fin and rotation. Results showed that the heat transfer from the staggered array was 25-30% higher than the inline array in the stationery channel. The rotation led to unsymmetrical heat transfer distributions along the spanwise direction. The heat transfer variation caused by rotation was more noticeable for the inline array, and the heat transfer in the rotating channel was more than 50% than that in the stationary channel. (C) 2017 Elsevier Ltd. All rights reserved.