Browsing by Author "Liu, Yao-Hsien"

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Channel orientation effect on endwall heat transfer in rotating cooling passages with pin-fins
(2019-06-01)
Huang, Szu-Chi
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Wang, Chen-Chih
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Liu, Yao-Hsien
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機械工程學系
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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.
Comparison of the Trilateral Flash Cycle and Rankine Cycle with Organic Fluid Using the Pinch Point Temperature
(2019-12-01)
Lai, Kai-Yuan
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Lee, Yu-Tang
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Chen, Miao-Ru
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Liu, Yao-Hsien
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機械工程學系
Low-temperature heat utilization can be applied to waste heat from industrial processes or renewable energy sources such as geothermal and ocean energy. The most common low-temperature waste-heat recovery technology is the organic Rankine cycle (ORC). However, the phase change of ORC working fluid for the heat extraction process causes a pinch-point problem, and the heat recovery cannot be efficiently used. To improve heat extraction and power generation, this study explored the cycle characteristics of the trilateral flash cycle (TFC) in a low-temperature heat source. A pinch-point-based methodology was developed for studying the optimal design point and operating conditions and for optimizing working fluid evaporation temperature and mass flow rate. According to the simulation results, the TFC system can recover more waste heat than ORC under the same operating conditions. The net power output of the TFC was approximately 30% higher than ORC but at a cost of higher pump power consumption. Additionally, the TFC was superior to ORC with an extremely low-temperature heat source (<80 degrees C), and the ideal efficiency was approximately 3% at the highest work output condition. The TFC system is economically beneficial for waste-heat recovery for low-temperature heat sources.
DROPLET SIZE CHARACTERIZATION FOR MIST FLOW IN A SINGLE-SIDE HEATED VERTICAL SQUARE DUCT
(2014)
Liu, Yao-Hsien
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Lin, Chia-Cheng
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Chen, Chiao-Hsin
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機械工程學系
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Department of Mechanical Engineering
Cooling with mist flow can achieve higher heat transfer rates to meet the cooling requirements in recent industry applications. The mist flow was produced by introducing the dispersed water droplets in the air stream, and was used for cooling a heated surface in a vertical square duct with the hydraulic diameter of 4 cm. Digital image analysis method was developed to obtain the size of the droplets ranging from 20 to 110 mu m. The digital images were segmented using the optimal threshold gray level for droplets sizing. Droplet size variation subjected to a single-side heated wall with constant heat flux was investigated. Infrared thermography was applied to obtain the surface temperature distribution during the cooling test. The air-water mist flow gave much lower surface temperature compared to the air cooling, and the mean droplet diameter decreased as it flowed over the heated surface.
Effect of driven frequency on flow and heat transfer of an impinging synthetic air jet
(2015-01-22)
Liu, Yao-Hsien
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Tsai, Shu-Yao
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Wang, Chi-Chuan
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機械工程學系
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Department of Mechanical Engineering
In this study, impingement heat transfer from a synthetic air jet on a heated surface was experimentally studied. A synthetic jet provides a high heat transfer coefficient and a compact design, which is suitable for the thermal management of electronic devices. The synthetic jet is produced by the high frequency oscillating motion (200-800 Hz) of a piezoelectric actuator, and a jet Reynolds number ranging from 500 to 1300. The instantaneous and time-averaged velocity profiles of the synthetic jet issuing from the jet hole were measured using a hot wire anemometer. The jet hole diameter was 3 mm and the jet-to-surface spacing (Z/d) ranged from 0 to 25. The excitation frequency effect, jet-to-surface spacing, and jet Reynolds number were tested. The heat transfer enhancement of the synthetic jet was at least double the natural convective heat transfer. At a small jet-to-surface spacing, the warm air circulates inside small spaces, jeopardizing heat transfer. An optimal driven frequency of 600 Hz in this study provided the highest jet flow rates and heat transfer enhancement. (C) 2014 Elsevier Ltd. All rights reserved.
EFFECT OF MISSING FIN ON ENDWALL HEAT TRANSFER IN A ROTATING COOLING CHANNEL
(2017-01-01)
Wang, Chen-Chih
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Huang, Szu-Chi
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Liu, Yao-Hsien
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機械工程學系
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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.
Effect of nonuniform pin size on heat transfer in a rotating rectangular channel with pin-fin arrays
(2019-12-25)
Hung, Shuo-Cheng
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Huang, Szu-Chi
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Liu, Yao-Hsien
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機械工程學系
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Department of Mechanical Engineering
Internal channels to cool the trailing edges of gas turbine blades were typically installed with pin-fin arrays for higher heat transfer enhancement. In this study, the heat transfer characteristics in a rotating rectangular channel (aspect ratio = 4:1) with differently sized pin-fin arrays were experimentally investigated. Liquid crystal thermography was used to measure heat transfer on the endwall in a staggered pin-fin array at a channel orientation of 135 degrees. The staggered array was composed of four or three pins in a row. Pins of varying diameters were inserted in every row exhibiting four pins; either two or four pins were replaced. The rotation numbers ranged from 0 to 0.33, and the Reynolds numbers ranged from 10,000 to 20,000. The results revealed that flow acceleration, separation, and wake flow contributed to various heat transfer contours. Larger pins contributed to higher local flow velocities through fin spacing and produced higher heat transfer distributions. The effect of rotation improved heat transfer enhancement on both trailing and leading surfaces. The friction factor ratio increased when more large-sized pins were installed in the array.
Enhanced dehumidification via hybrid hydrophilic/hydrophobic morphology having wedge gradient and drainage channels
(2019-11-01)
Yang, Kai-Shing
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Huang, Yu-Yang
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Liu, Yao-Hsien
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Wu, Shih-Kuo
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Wang, Chi-Chuan
Heat transfer performance under dehumidifying conditions for hydrophilic, and hybrid surfaces (hydrophilic/hydrophobic) within ambient are reported. The hybrid surface features star-shape morphology that contains hydrophilic interior inside star-shape while maintains a hydrophobic nature in the exterior of the star-shape. The star-shape offers comparatively good collecting capability of water condensate for its wedge gradient can effectively manipulate the surface energy. The mobility of the condensate within the star-shape interior is improved, leading to enhanced condensation heat transfer performance of 3.7 similar to 11.4% when compared to the hydrophilic surface. However, the contact angle hysteresis of the star-shape surface also retains the condensate inside the star-shape interior to some extent. To tackle this problem, a drainage channel alongside the gravity direction is added to the star-shape surface (star_I), and it offers a much better condensate removal, thereby improving the dehumidifying heat transfer performance up to 15.3 similar to 30.4%.
Enhancement of Mist Flow Cooling by Using V-Shaped Broken Ribs
(2019-10-01)
Huang, Kuan-Tzu
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Liu, Yao-Hsien
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機械工程學系
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Department of Mechanical Engineering
Substantial heat transfer enhancement can be achieved by cooling with air/water mist flow because of droplet impingement and liquid film/fragment evaporation on the heated surface, which leads to a high heat-removal rate. An experimental investigation was conducted in a square channel with continuous and broken V-shaped ribs. To generate a mist flow, micro droplets were introduced into the gas stream. The rib angle of attack was 45 degrees, and the rib spacing-to-height ratios were 10 and 20. The air Reynolds number ranged from 7900 to 24,000, and the water-to-air volume flow ratio was less than 0.1%. The net heat inputs ranged from 1.1-3.1 W/cm(2) and 3.4-9.4 W/cm(2) for the air and mist flow cases, respectively. Because the deposited liquid fragments produced uneven temperature distribution on the heated surface, steady-state infrared thermography was used to visualize the heat transfer distribution. Two to seven times higher heat transfer was attained for the broken ribs when using the mist flow than when using air flow. This increase was mainly attributed to the broken structure, which facilitated liquid transport and enhanced liquid coverage. In addition, the broken ribs produced a smaller friction factor than continuous ribs. The broken structures were beneficial for higher thermal performance in the mist flow.
EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER ON THE INTERNAL TIP WALL IN A ROTATING TWO-PASS RECTANGULAR CHANNEL
(2019-01-01)
Chia, Kai-Chieh
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Huang, Szu-Chi
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Liu, Yao-Hsien
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機械工程學系
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Department of Mechanical Engineering
The current study experimentally studied heat transfer characteristics of the blade tip wall in a rotating internal cooling channel. The aspect ratio of this rectangular channel was 1:4, and the hydraulic diameter was 25.6 mm. Due to the impact of the 180 turn, complex three dimensional flow significantly affected heat transfer on the internal tip surface. The liquid crystal method is used to capture the heat transfer contour on the internal tip surface. In this study, the leading and trailing surfaces of the channel wall were either smooth or roughened with 45 angled ribs. The Reynolds number inside the pressurize two-pass cooling channel ranged from 10,000 to 30,000 at both stationary and rotating conditions. Furthermore, two channel orientations (90 and 135) were tested. The effect of Coriolis force on heat transfer is studied with the rotation number up to 0.53. The tip heat transfer from the smooth channel wall was more sensitive to rotation and the largest heat transfer enhancement as a result of rotation was 68%.
Experimental investigation of the effect of compound protrusion-pin array on heat transfer in an internal rotating cooling channel
(2018-07-25)
Ullal, Ankith
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Hung, Shuo-Cheng
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Huang, Szu-Chi
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Liu, Yao-Hsien
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機械工程學系
An experimental investigation was conducted to study the effect of protrusions and their combination with pins on heat transfer enhancement in a rotating internal passage with an orientation angle of 90 degrees for Reynolds numbers (Re) of 10,000 and 20,000. The trailing surface showed the highest Nusselt number (Nu). The highest and lowest local Nusselt number was at the front and back of the protrusion respectively. A short disturbed wake region was observed behind the protrusion as a result of complex three dimensional flow. Addition of pins in the configuration resulted in an increase of the average Nusselt number, specifically a 35%, 50% and 142% for trailing, static and leading surfaces respectively, compared to protrusions only case for Re of 10,000. On removal of the third column of protrusions, average Nusselt number showed a decrease of 8.25%, 3.1% and 2.3% for trailing, static and leading cases respectively, compared to the protrusion-pin case for Re of 10,000. It also caused elongation of the stagnation and wake flow fields around the fourth column comprising of pins. Pressure drop results indicated that the protrusion only case was the lowest compared to protrusion-pin.
Flow field investigation in a rotating disk chemical vapor deposition chamber with a perforated showerhead
(2017-11-01)
Liu, Yao-Hsien
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Peng, Guan-Jhong
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Lai, Wei-Chia
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Huang, Chih-Yung
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Liang, Jin-Hsing
A flow field in a simulated rotating disk chemical vapor deposition chamber in which the inflow gases entered through a showerhead inlet was experimentally investigated using particle image velocimetry. The deposition uniformity was highly related to the flow pattern, which was influenced by the buoyancy, centrifugal, and flow inertia forces. This study investigated flow patterns for different processing parameters, namely chamber heights (20 and 40 mm), jet-to-disk temperature differences (0-500 degrees C), and disk rotational speeds (0-500 rpm). The time-averaged axial and radial velocity profiles were determined for examining the effects of rotation and heating on flow uniformity above the rotating disk. The Reynolds stress and turbulence intensity was found to be influenced by the buoyancy and rotation induced flow. At a high jet-to-disk temperature difference, the upward buoyancy force lifted the flow and prevented the inlet flow from reaching the disk surface. The buoyancy-induced flow can be suppressed through disk rotation or chamber height reduction. Moreover, the nondimensional parameters (Grashof number and rotational Reynolds number) can be used to construct flow regime maps and quantify the effects of rotation and heating even with the contribution from different chamber heights, disk temperatures, and rotational speeds. (C) 2017 Elsevier Inc. All rights reserved.
Heat Transfer and Friction in a Square Channel with Ribs and Grooves
(2016-01)
Liu, Yao-Hsien
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Lo, Yuan-Hsiang
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Li, Xin-Xian
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Huh, Michael
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機械工程學系
Turbulence promoters have been widely applied to enhance heat transfer in internal flow channels, although they cause pressure loss. This study employed the transient liquid-crystal technique to measure the heat transfer distribution in a square channel with compound turbulence promoters with orthogonal (90deg), continuous angled (45deg), discrete angled (45deg), V-shaped, and inverted-V-shaped rib configurations. The rib height-to-hydraulic diameter ratio (e/Dh) and the rib pitch-to-height ratio (P/e) were 0.1 and 8, respectively. Variations in the Nusselt number were observed after adding grooves between the ribs. The Reynolds number tested in this study ranged from 15,000 to 35,000. Adding grooves between the ribs enhanced the heat transfer. The convective heat transfer coefficient increased by up to 40%, whereas the friction factor ratio increased by less than 30%. The discrete angled configuration of grooved ribs exhibited the maximal heat transfer enhancement and thermal performance, whereas the orthogonal configuration attained the minimal heat transfer enhancement and thermal performance. The frictional loss of the V-shaped and inverted-V-shaped configurations was higher than that of the continuous or discrete arrangements for both ribs-only and ribbed-grooved configurations.
Heat Transfer and Friction Measurement in Pin-Fin Arrays Under Mist Flow Condition
(2019-04-01)
Wang, Szu-Kai
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Liu, Yao-Hsien
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機械工程學系
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Department of Mechanical Engineering
Effects of air/water mist flow on endwall heat transfer in a square channel were experimentally investigated using infrared thermography. The purpose was to study the detailed heat transfer contour variation caused by the generation of the liquid films. The surface was roughened with staggered partial pin-fin arrays to enhance flow mixing and liquid entrainment. Two streamwise spacings (Xp/d= 3 and 6) of the fin array were investigated. The gas Reynolds number ranged from 7900 to 24,000. The calculated droplet deposition velocity was comparable to the literature results and was not substantially affected by the gas Reynolds number or fin spacing. For the pin-fin array, heat transfer was dominated by the water accumulation and liquid film formation, which was dependent on the carrier gas flow rate and fin spacing. Furthermore, thick liquid fragments entrained between the fins substantially enhanced local convective heat transfer coefficients. The average heat transfer enhancement on the finned surfaces using mist flow was four times as high as the air flow. The pressure drop from the mist flow was two times as high as the air flow.
Heat transfer and pressure drop of air/water mist flow in horizontal Minichannels
(2019-05-01)
Ho, Ping-Tse
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Liu, Yao-Hsien
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機械工程學系
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Department of Mechanical Engineering
The heat transfer, friction factor, and flow pattern of air/water mist flow in a rectangular minichannel heat sink were experimentally investigated. The channel size effect was studied using three horizontal minichannels exhibiting cross-sections measuring 0.5mmx3mm, 1mmx3mm, and 3mmx3mm. The gas Reynolds number ranged from 1000 to 6000, and the wall temperature ranged from 40 to 60 degrees C. For the single-phase air flow, the flow transition was comparable with the conventional flow channel. For the mist flow, the flow patterns observed in the current minichannel were dry-wall mist flow and wavy annular flow. The mist cooling performance decreased with increase in wall temperature, mainly because of the extended dryout regions. The heat transfer from the mist flow was 1.5-4 times higher than the air flow, and higher enhancement ratios were observed in larger minichannels at lower gas Reynolds numbers. Because of droplet accumulation in the minichannel, the friction factor due to the mist flow was 2-3 times higher than the air flow. The friction factor decreased with increase in wall temperature because of the low volume of liquid in the minichannel.
Heat Transfer Augmentation in Rotating Triangular Channels with Discrete and V-Shaped Ribs
(2012-10-01)
Liu, Yao-Hsien
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Lai, Shi-Yu
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機械工程學系
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Department of Mechanical Engineering
Heat transfer has been experimentally measured in a rotating triangular-shaped cooling channel with the rotation number up to 0.65. Continuous, discrete, V-shaped, and discrete-V ribs are applied on the leading and trailing surfaces to augment heat transfer. The rib spacing-to-height ratio (P/e) is 9 and rib height-to-hydraulic diameter ratio (e/D-h) is 0.085. Regionally averaged heat transfer coefficients are measured along the streamwise and spanwise directions with the Reynolds numbers from 15,000 to 25,000. Effects of secondary flow induced by ribs and rotation in this channel give distinct local heat transfer distributions. Results show that V-shaped and discrete-V ribs have comparable heat transfer distributions, and both have the highest heat transfer enhancement at stationary condition as well as rotating conditions.
Heat transfer enhancement of an impinging synthetic air jet using diffusion-shaped orifice
(2016-02-05)
Liu, Yao-Hsien
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Chang, Tsung-Han
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Wang, Chi-Chuan
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機械工程學系
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Department of Mechanical Engineering
Impingement heat transfer from a synthetic air jet through a diffusion-shaped orifice was investigated in this study. The effect of the opening angle (60 degrees and 90 degrees), orifice thickness (1-3 mm), and driven frequencies (400-800 Hz) were examined. Hot-wire anemometry was used to measure the instantaneous and average flow velocities ejected from the jet holes. At a small jet-to-surface spacing, synthetic jets from a diffusion-shaped orifice produced higher heat transfer than that from a round orifice. The highest heat transfer enhancement from using a diffusion-shaped orifice was approximately 30% compared with the round orifice at an opening angle of 60 degrees. The diffusion-shaped orifice achieved the highest area averaged heat transfer coefficient and Nusslet number of 80 W/m(2).K and 8.9, respectively. When the opening angle increased to 90 degrees, heat transfer enhancement was degraded because of increased flow circulation and reduced ejection flow velocity. The effect of orifice configuration on the heat transfer diminished as the jet-to-surface spacing increased. (C) 2015 Elsevier Ltd. All rights reserved.
Heat transfer in rectangular channels with porous wire mesh under impinging jet conditions
(2017-12-01)
Sung, Hsiang-Chu
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Liu, Yao-Hsien
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機械工程學系
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Department of Mechanical Engineering
Detailed heat transfer distribution in a rectangular channel under an array of impinging air jets was experimentally investigated using transient liquid crystal technique. The jet-to-jet spacing was 4 and the jet-to-surface spacing Was 3. The rectangular channel was fully or partially filled with porous wire meshes (filling ratios = 100%, 50% and 25%) and the jet Reynolds numbers ranged from 2500 to 7700. Although the literature data indicated that the porous material enhanced the overall heat transfer rate, the regional heat transfer on the target surface was degraded because of the blockage and breakup of the core jet flow. The heat transfer coefficient was further reduced with an increase in the filling ratio. For the partially filled channel, the porous wire mesh located near the target surface contributed to even lower heat transfer. All the cases demonstrated that the porous material decreased regional heat transfer on the target surface, and the average Nusselt number for the fully filled case was only 50% of the unfilled case. Although the impingement heat transfer was hindered, the reduced variation in Nusselt number could prevent the development of local hot or cold spots in engineering applications. (C) 2017 Elsevier Masson SAS. All rights reserved.
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
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Wang, Chen-Chih
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Liu, Yao-Hsien
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機械工程學系
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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.
Heat transfer of impinging jet arrays onto half-smooth, half-rough target surfaces
(2018-01-05)
Lo, Yuan-Hsiang
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Liu, Yao-Hsien
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機械工程學系
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Department of Mechanical Engineering
Detailed heat transfer distributions from arrays of impinging jets on a half-smooth, half-rough target surface were experimentally investigated using a transient liquid crystal technique. The target surface was roughened through the creation of rectangular grooves aligned with the jet holes. The grooved regions were designed either parallel (longitudinal grooves) or orthogonal (transverse grooves) to the exit flow direction. let-to-jet spacing and jet-to-surface spacing (Z/d) were 4 and 3, respectively. In this experimental test, the effect of crossflow was investigated for three exit flow directions, each with a jet Reynolds number ranging from 2500 to 7700. Heat transfer was enhanced near the edge of grooves, whereas the heat transfer was degraded inside grooves. For the half-smooth, half-rough surface, the sudden change in surface geometry broke the flow development and caused intensified flow mixing in the impingement flow channel. Compared with traditional fully roughened surfaces, the half-rough surface is more effective for heat transfer, and an enhancement of more than 50% was achieved for the longitudinal grooves. The idea of partially roughened surfaces may be further extended to the other internal flow channels with different roughness elements. (C) 2017 Elsevier Ltd. All rights reserved.
High Rotation Number Effect on Heat Transfer in a Leading Edge Cooling Channel of Gas Turbine Blades With Three Channel Orientations
(2013-12-01)
Huang, Szu-Chi
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Liu, Yao-Hsien
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機械工程學系
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Department of Mechanical Engineering
Heat transfer in a leading edge, triangular-shaped cooling channel with three channel orientations under high rotation numbers is investigated in this study. Continuous ribs and V-shaped ribs (P/e = 9, e/Dh = 0.085), both placed at an angle (alpha = 45 deg) to the mainstream flow, are applied on the leading and trailing surfaces. The Reynolds number range is 15,000-25,000 and the rotation number range is 0-0.65. Effects of high rotation number on heat transfer with three angles of rotation (90 deg, 67.5 deg, and 45 deg) are tested. Results show that heat transfer is influenced by the combined effects of rib and channel orientation. When the rotation number is smaller than 0.4, rotation causes a decrease in the average Nusselt number ratios on the leading surface at a channel orientation of 90 deg. Heat transfer is enhanced gradually on the leading surface when the channel orientation varies from 90 deg to 45 deg for both ribbed cases. The highest heat transfer enhancement due to rotation is found at the highest rotation number of 0.65.