scholarly journals Heat Transport Capacity of an Axial-Rotating Single-Loop Oscillating Heat Pipe for Abrasive-Milling Tools

Energies ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2145 ◽  
Author(s):  
Ning Qian ◽  
Yucan Fu ◽  
Marco Marengo ◽  
Jiuhua Xu ◽  
Jiajia Chen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Theoretical Analysis ◽  
Thermal Performance ◽  
Slow Motion ◽  
Positive Influence ◽  
Rotational Axis ◽  
Centrifugal Acceleration ◽  
Oscillating Heat Pipe ◽  
Single Loop

In order to enhance heat transfer in the abrasive-milling processes to reduce thermal damage, the concept of employing oscillating heat pipes (OHPs) in an abrasive-milling tool is proposed. A single-loop OHP (SLOHP) is positioned on the plane parallel to the rotational axis of the tool. In this case, centrifugal accelerations do not segregate the fluid between the evaporator and condenser. The experimental investigation is conducted to study the effects of centrifugal acceleration (0–738 m/s2), heat flux (9100–31,850 W/m2) and working fluids (methanol, acetone and water) on the thermal performance. Results show that the centrifugal acceleration has a positive influence on the thermal performance of the axial-rotating SLOHP when filled with acetone or methanol. As for water, with the increase of centrifugal acceleration, the heat transfer performance first increases and then decreases. The thermal performance enhances for higher heat flux rises for all the fluids. The flow inside the axial-rotating SLOHP is analyzed by a slow-motion visualization supported by the theoretical analysis. Based on the theoretical analysis, the rotation will increase the resistance for the vapor to penetrate through the liquid slugs to form an annular flow, which is verified by the visualization.

Experimental Investigation of a Flat-Plate Oscillating Heat Pipe With Modified Evaporator and Condenser

2014 ◽  
Author(s):  
M. J. Rhodes ◽  
M. R. Taylor ◽  
J. G. Monroe ◽  
S. M. Thompson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flat Plate ◽  
Thermal Performance ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Oscillating Heat Pipe ◽  
Lower Heat ◽  
Operating Temperatures

The thermal performance of a flat-plate oscillating heat pipe (FP-OHP) - with modified evaporator and condenser was experimentally investigated during high heat flux conditions. The copper FP-OHP (101.6 × 101.6 × 3.18 mm3) possessed two inter-connected layers of 1.02 mm2 square channels with the evaporator and condenser possessing two parallel, 0.25 × 0.51 mm2 square microchannels. The microchannels were integrated to enhance evaporation and condensation heat transfer to improve the FP-OHP’s ability to transport high heat flux. The FP-OHP was oriented vertically and locally heated with a 14.52 cm2 heating block at its base and cooled with a water block that provided either: 20 °C, 40 °C, or 60 °C operating temperatures. A FP-OHP without embedded microchannels was also investigated for baseline performance comparison. Both FP-OHPs were filled with Novec HFE-7200 (3M) working fluid at a filling ratio of approximately 80% by volume. The maximum temperature of each FP-OHP was recorded versus time for various heat inputs for the investigated operating temperatures. The results indicate that the integrated microchannels enhance the FP-OHP’s thermal performance for all operating temperatures. At 20 °C, 40 °C, and 60 °C, the microchannel-embedded evaporator and condenser dissipated 80 W, 65 W, and 55 W more than the baseline control with a minimum thermal resistance of 0.219 °C/W, 0.205 °C/W, and 0.170 °C/W, respectively — corresponding to a percent enhancement on-the-order of 25%. This percent enhancement increased with operating temperature. It has also been shown that Novec HFE-7200 allows the FP-OHP to start at relatively lower heat inputs — as low as 35 W, demonstrating that this working fluid can enhance heat transfer even at lower heat flux applications.

scholarly journals Thermal Assessment of Nano-Particulate Graphene-Water/Ethylene Glycol (WEG 60:40) Nano-Suspension in a Compact Heat Exchanger

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1929 ◽  
Author(s):  
M. Sarafraz ◽  
Mohammad Safaei ◽  
Zhe Tian ◽  
Marjan Goodarzi ◽  
Enio Bandarra Filho ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Ethylene Glycol ◽  
Thermal Performance ◽  
Evaluation Criteria ◽  
High Heat ◽  
Operating Conditions ◽  
Working Fluid ◽  
High Heat Flux ◽  
Micro Channel

In the present study, we report the results of the experiments conducted on the convective heat transfer of graphene nano-platelets dispersed in water-ethylene glycol. The graphene nano-suspension was employed as a coolant inside a micro-channel and heat-transfer coefficient (HTC) and pressure drop (PD) values of the system were reported at different operating conditions. The results demonstrated that the use of graphene nano-platelets can potentially augment the thermal conductivity of the working fluid by 32.1% (at wt. % = 0.3 at 60 °C). Likewise, GNP nano-suspension promoted the Brownian motion and thermophoresis effect, such that for the tests conducted within the mass fractions of 0.1%–0.3%, the HTC of the system was improved. However, a trade-off was identified between the PD value and the HTC. By assessing the thermal performance evaluation criteria (TPEC) of the system, it was identified that the thermal performance of the system increased by 21% despite a 12.1% augmentation in the PD value. Furthermore, with an increment in the fluid flow and heat-flux applied to the micro-channel, the HTC was augmented, showing the potential of the nano-suspension to be utilized in high heat-flux thermal applications.

scholarly journals Thermal-Performance Evaluation of Bicycle Helmets for Convective and Evaporative Heat Loss at Low and Moderate Cycling Speeds

2019 ◽  
Vol 9 (18) ◽  
pp. 3672 ◽  
Author(s):  
Shriram Mukunthan ◽  
Jochen Vleugels ◽  
Toon Huysmans ◽  
Kalev Kuklane ◽  
Tiago Sotto Mayor ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Loss ◽  
Thermal Performance ◽  
Frontal Zone ◽  
Thermal Manikin ◽  
Evaporative Heat Loss ◽  
Cooling Efficiency ◽  
Bicycle Helmets ◽  
Evaporative Heat Transfer

The main objective of the study was to investigate the thermal performance of five (open and closed) bicycle helmets for convective and evaporative heat transfer using a nine-zone thermal manikin. The shape of the thermal manikin was obtained by averaging the 3D-point coordinates of the head over a sample of 85 head scans of human subjects, obtained through magnetic resonance imaging (MRI) and 3D-printed. Experiments were carried out in two stages, (i) a convective test and (ii) an evaporative test, with ambient temperature maintained at 20.5 ± 0.5 °C and manikin skin temperature at 30.5 ± 0.5 °C for both the tests. Results showed that the evaporative heat transfer contributed up to 51%–53% of the total heat loss from the nude head. For the convective tests, the open helmet A1 having the highest number of vents among tested helmets showed the highest cooling efficiency at 3 m/s (100.9%) and at 6 m/s (101.6%) and the closed helmet (A2) with fewer inlets and outlets and limited internal channels showed the lowest cooling efficiency at 3 m/s (75.6%) and at 6 m/s (84.4%). For the evaporative tests, the open helmet A1 showed the highest cooling efficiency at 3 m/s (97.8%), the open helmet A4 showed the highest cooling efficiency at 6 m/s (96.7%) and the closed helmet A2 showed the lowest cooling efficiency at 3 m/s (79.8%) and at 6 m/s (89.9%). Two-way analysis of variance (ANOVA) showed that the zonal heat-flux values for the two tested velocities were significantly different (p < 0.05) for both the modes of heat transfer. For the convective tests, at 3 m/s, the frontal zone (256–283 W/m2) recorded the highest heat flux for open helmets, the facial zone (210–212 W/m2) recorded the highest heat flux for closed helmets and the parietal zone (54–123 W/m2) recorded the lowest heat flux values for all helmets. At 6 m/s, the frontal zone (233–310 W/m2) recorded the highest heat flux for open helmets and the closed helmet H1, the facial zone (266 W/m2) recorded the highest heat flux for the closed helmet A2 and the parietal zone (65–123 W/m2) recorded the lowest heat flux for all the helmets. For evaporative tests, at 3 m/s, the frontal zone (547–615 W/m2) recorded the highest heat flux for all open helmets and the closed helmet H1, the facial zone (469 W/m2) recorded the highest heat flux for the closed helmet A2 and the parietal zone (61–204 W/m2) recorded the lowest heat flux for all helmets. At 6 m/s, the frontal zone (564–621 W/m2) recorded highest heat flux for all the helmets and the parietal zone (97–260 W/m2) recorded the lowest heat flux for all helmets.

scholarly journals Influence of fluid flow characteristics and heat transfer in a tube heat exchanger using H-shape inserts with circular ring

2021 ◽  
Author(s):  
Satyendra Singh ◽  
◽  
Tarun Joshi ◽  
Himanshi Kharkwal ◽  
◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fluid Flow ◽  
Heat Exchanger ◽  
Thermal Performance ◽  
Flow Characteristics ◽  
Circular Ring ◽  
Main Section ◽  
Tube Heat Exchanger ◽  
Fluid Flow Characteristics

The heat transfer and fluid flow characteristics in a tube heat exchanger using H-shape inserts with circular ring (CRWHS) has been done by computationally and experimentally. In this investigation parameters like ratio of the diameters and pitches are considered. The value of diameter and pitch ratios are (DR=0.8, 0.9), (PR=3, 4) respectively. The main section in which investigation was done is 1.5m long and the hydraulic diameter of the tube is 68.1mm. 1000 W/m2 heat flux was provided in the main section. Heat flux was constant throughout the investigation. Air is used as a working medium in which 6000 to 21000 Reynolds number was used for the investigation. The observation revealed that the increment in heat transfer rate is 4.56 times as compare to smooth tube for the circular ring with H-shape inserts. In case of DR=0.8 and PR=3, maximum thermal performance factor was obtain which is 3.24. In GIT the deviation in Nusselt number & friction factor is limited to ±0.4% & ±0.1% respectively. CFD analysis result comparisons with experimental one are presented in which the maximum deviations for thermal performance factor are limited to ±3.6%.

scholarly journals On the Thermal Performance of a Microparallel Channels Heat Exchanger

2018 ◽  
Vol 11 (2) ◽  
Author(s):  
Ivana Fernandes de Sousa ◽  
Carolina Palma Naveira Cotta ◽  
Daduí Cordeiro Guerrieri ◽  
Manish K. Tiwari
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Exchanger ◽  
Theoretical Analysis ◽  
Transfer Problem ◽  
Heat Transfer Problem ◽  
Coolant Fluid ◽  
Differential Formulation ◽  
Micro Heat Exchanger ◽  
Conjugated Heat Transfer

Abstract This paper presents the experimental and theoretical analysis of a micro heat exchanger designed for the waste heat recovery from a high concentration photovoltaic (HCPV) system. A test bench was built to analyze the thermal behavior of a heat exchanger targeted to work in a similar condition of an existing HCPV panel. A high power heater was encapsulated inside a copper cartridge, covered by thermal insulation, leading to dissipated heat fluxes around 0.6 MW/m2, representative of the heat flux over the solar cell within the HCPV module. The experimental campaign employed water as the coolant fluid and was performed for three different mass flow rates. An infrared camera was used to nonintrusively measure the temperature field over the micro heat exchanger external surface, while thermocouples were placed at the contact between the heat exchanger and the heater, and at the water inlet and outlet ports. In the theoretical analysis, a hybrid numerical–analytical treatment is implemented, combining the numerical simulation through the comsolmultiphysics finite elements code for the micro heat exchanger, and the analytical solution of a lumped-differential formulation for the electrical heater cartridge, offering a substantial computational cost reduction. Such computational simulations of the three-dimensional conjugated heat transfer problem were critically compared to the experimental results and also permitted to inspect the adequacy of a theoretical correlation based on a simplified prescribed heat flux model without conjugation effects. It has been concluded that the conjugated heat transfer problem modeling should be adopted in future design and optimization tasks. The analysis demonstrates the enhanced heat transfer achieved by the microthermal system and confirms the potential in reusing the recovered heat from HCPV systems in a secondary process.

Effect of Operational Parameters on the Thermal Performance of Flat Plate Oscillating Heat Pipe

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Kamlesh K. Mehta ◽  
Nirvesh Mehta ◽  
Vivek Patel
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Flat Plate ◽  
Heat Pipe ◽  
Thermal Performance ◽  
Charge Ratio ◽  
Working Fluid ◽  
Operational Parameters ◽  
Oscillating Heat Pipe ◽  
Transfer Device

Abstract Flat plate oscillating heat pipe (FP-OHP) is a unique heat transfer device and considered as a promising candidate for effective heat transfer device in electronics industries. A number of theoretical studies and experimental investigations have been carried out on FP-OHP in the past decades after its invention. However, due to the operational characteristics of FP-OHP, the effect of various parameters on the thermal performance of FP-OHP has not been completely revealed so far. This paper attempts to discuss the effect of operational parameters on the thermal performance of FP-OHP. In this study, the FP-OHP was investigated with different charge ratios, orientations, working fluids, and heat loads from 10 W to 150 W. In order to investigate the effect, 18 parallel square channels of 2 × 2 mm2 are machined onto pure copper plate (93 × 70 × 8 mm3) to form FP-OHP. DI water, ethanol, methanol, acetone, and FC-72 are investigated. The measured thermal resistance was strongly dependent on operational parameters. The optimum performance was observed with acetone with a charge ratio of 70% in the vertical orientation. The lowest thermal resistance of 0.39 °C/W is achieved using acetone as a working fluid at 100 W. A Kutateladze number (Ku) was used to compare the experimental data and found to be suitable for prediction of the thermal performance of FP-OHP with standard deviation of 15%.

Effect of Microgrooved Surface and Surface Orientation on Spray Cooling Heat Transfer

2009 ◽  
Author(s):  
Dong-Fang Chen ◽  
Da-Wei Tang ◽  
Xue-Gong Hu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Thermal Performance ◽  
High Speed ◽  
Heat Transfer Performance ◽  
Flat Surface ◽  
Spray Cooling ◽  
Surface Orientation ◽  
Microgrooved Surface ◽  
Water Spray Cooling

Experiments were performed to investigate the flow structure and boiling heat transfer characteristics of water spray cooling on flat and microgrooved surfaces using a high-speed camera and a microscope. The heaters were made of cooper, with surface size of 2.0cm×7.4cm. Three orientations of the heater surfaces were selected: horizontal upward-facing, vertical, and horizontal downward-facing. A full-cone spray nozzle was placed normal to these heated surfaces. The heat transfer was directly measured using thermocouples within the heater. The experimental results show the bubble’s growth, coalescence along/between microgrooves, and break-up as wall heat flux reaches some higher values. It was found that the heat transfer for microgrooved surface is generally higher than that of flat surface at a given flow rate with the same surface orientation. The thermal performance of vertical microgrooved surface was highest at low temperatures; the thermal performance of the horizontal upward-facing was highest at higher wall temperature. The heat transfer performance for the horizontal downward-facing microgrooved surface had the highest critical heat flux (CHF).

Parametric Numerical Study of Flow and Heat Transfer in Microchannels With Wavy Walls

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Liang Gong ◽  
Krishna Kota ◽  
Wenquan Tao ◽  
Yogendra Joshi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fluid Flow ◽  
Thermal Performance ◽  
Numerical Study ◽  
High Heat ◽  
High Heat Flux ◽  
Laminar Fluid Flow ◽  
Flow And Heat Transfer ◽  
Wavy Channels

Wavy channels were investigated in this paper as a passive scheme to improve the heat transfer performance of laminar fluid flow as applied to microchannel heat sinks. Parametric study of three-dimensional laminar fluid flow and heat transfer characteristics in microsized wavy channels was performed by varying the wavy feature amplitude, wavelength, and aspect ratio for different Reynolds numbers between 50 and 150. Two different types of wavy channels were considered and their thermal performance for a constant heat flux of 47 W/cm2 was compared. Based on the comparison with straight channels, it was found that wavy channels can provide improved overall thermal performance. In addition, it was observed that wavy channels with a configuration in which crests and troughs face each other alternately (serpentine channels) were found to show an edge in thermal performance over the configuration where crests and troughs directly face each other. The best configuration considered in this paper was found to provide an improvement of up to 55% in the overall performance compared to microchannels with straight walls and hence are attractive candidates for cooling of future high heat flux electronics.

scholarly journals Visualization Study on Thermo-Hydrodynamic Behaviors of a Flat Two-Phase Thermosyphon

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2295 ◽  
Author(s):  
Chao Wang ◽  
Feng Yao ◽  
Juan Shi ◽  
Liangyu Wu ◽  
Mengchen Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Thermal Performance ◽  
Flow Behavior ◽  
Heat Transfer Process ◽  
Liquid Pool ◽  
Two Phase ◽  
Convective Boiling ◽  
Wick Structure ◽  
Vapor Liquid

The coupled effect of boiling and condensation inside a flat two-phase thermosyphon has a non-negligible influence on the two-phase fluid flow behavior and heat transfer process. Therefore, a flat two-phase thermosyphon with transparent wall was manufactured. Based on this device, a visualization experiment system was developed to study the vapor–liquid two-phase behaviors and thermal performance of the flat two-phase thermosyphon. A cross-shaped wick using copper mesh was embedded into the cavity of two-phase thermosyphon to improve the heat transfer performance. The effects of heat flux density, working medium, and wick structure on the thermal performance are examined and analyzed. The results indicated that a strong liquid disturbance is caused by the bubble motions, leading to the enhancement of both convective boiling and condensation heat transfer. More bubbles are generated as the heat flux increases; therefore, the disturbance of bubble motion on liquid pool and condensation film becomes stronger, resulting in better thermal performance of the flat two-phase thermosyphon. The addition of the wick inside the cavity effectively reduces the temperature oscillation of the evaporator wall. In addition, the wick structure provides backflow paths for the condensate owing to the effect of capillary force and enhances the vapor–liquid phase change heat transfer, resulting in the improvement of thermal performance for the flat two-phase thermosyphon.

Parametric Numerical Study of Flow and Heat Transfer in Microchannels With Wavy Walls

2010 ◽  
Author(s):  
Liang Gong ◽  
Krishna Kota ◽  
Wenquan Tao ◽  
Yogendra Joshi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fluid Flow ◽  
Thermal Performance ◽  
Numerical Study ◽  
High Heat ◽  
High Heat Flux ◽  
Laminar Fluid Flow ◽  
Flow And Heat Transfer ◽  
Wavy Channels

Wavy channels are investigated in this paper as a passive scheme to improve the heat transfer performance of laminar fluid flow as applied to microchannel heat sinks. Parametric study of three-dimensional laminar fluid flow and heat transfer characteristics in micro-sized wavy channels was performed by varying the wavy feature amplitude and wavelength at different Reynolds numbers between 50 and 150. Two different types of wavy channels were considered and their thermal performance for a constant heat flux of 47 W/cm2 was compared. Based on the comparison with straight channels, it was found that wavy channels can provide improved overall thermal performance. In addition, it was observed that wavy channels with a configuration in which crests and troughs face each other alternately (serpentine channels) were found to show an edge in thermal performance over the configuration where crests and troughs face each other. The best configuration considered in this paper was found to provide an improvement of up to 55% in the overall performance compared to microchannels with straight walls and hence are attractive candidates for cooling of future high heat flux electronics.

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