Investigation of Structure-Property-Boiling Enhancement Mechanisms of Copper/Graphene Nanoplatelets Coatings

In this work, we present an exceptionally high heat transfer coefficient (HTC) and critical heat flux (CHF) achieved by graphene nanoplatelets (GNPs) and copper composite coatings with tunable surface properties. These coatings were created by a combination of powder metallurgy and manufacturing processes including ball milling, sintering, electrodeposition, and salt-patterning. We demonstrated correlations between various coating processes, resultant surface morphologies, properties, and improved boiling mechanism. Electrodeposition of GNP and copper particles led to formation of tall ridge-like structures and valleys to contain the boiling fluid in between. Higher CHF achieved for these coatings was attributed to the microlayer evaporation. It was observed that ball milling of GNP and copper particles prior to their sinter-coating enhanced their surface roughness that resulted in very high HTC, nearly 5.4 times higher than plain copper surfaces. Additional salt-patterning along with sinter-coating yielded interconnected porous networks with high nucleating activity that rendered record-breaking HTC of 1,314°kW/m2-°C. Combination of these coating processes can be adopted to tailor the surfaces and achieve better boiling performance. Novel techniques developed in this work can be applied to a variety of thermal engineering applications.

Experimental and CFD Analysis of Two-Phase Forced Convection Flow in Channels of Various Rib Shapes

This paper investigates numerically and experimentally heat transfer forced convective two-phase flow (i.e. air and water) over a rectangular ribbed channel with a vertical orientation. Three distinct rib–groove shapes have been examined. Ribs - groove shapes are; Triangle, Trapezoid, and Semi-Trapezoid ribs-groove. The present study has been performed with continuous heat flux through range of water and air superficial inlet velocity values between 0.105 – 0.316m/s, and 0.263 – 1.320 m/s, respectively. Continuity, momentum and energy calculations have been formulated using the Finite Volume Approach (FVM). Results indicate that the triangle rib-groove has the high heat transfer coefficient and lower temperature difference than other cases against a different number of Reynolds. The experimental data has been compared to numerical results for ribs –grooved channel with deviation of about 1.0% - 7.5%. The channel fitted with triangle ribs shows the highest heat transfer, which is about 59% higher than the smooth channel; 56% for trapezoidal rib, and 44% for channel fitted by semi-trapezoidal rib. Finally, the triangle rib-groove gives a better heat transfer improvement value in comparison with trapezoidal and semi trapezoidal rib-groove channel at constant pumping power.

Influence of tip clearance and cavity depth on heat transfer in a cutback squealer tip

Numerical simulations are conducted to present the aerothermal performance of a turbine blade tip with cutback squealer rim. Two different tip clearance heights (0.5%, 1.0% of the blade span) and three different cavity depths (2.0%, 3.0%, and 6.0% of the blade span) are investigated. The results show that a high heat transfer coefficient (HTC) strip on the cavity floor appears near the suction side. It extends with the increase of tip clearance height and moves towards the suction side with the increase of cavity depth. The cutback region near the trailing edge has a high HTC value due to the flush of over-tip leakage flow. High HTC region shrinks to the trailing edge with the increase of cavity depth since there is more accumulated flow in the cavity for larger cavity depth. For small tip clearance cases, high HTC distribution appears on the pressure side rim. However, high HTC distribution is observed on suction side rim for large tip clearance height. This is mainly caused by the flow separation and reattachment on the squealer rims.

Optimization of Heat Transfer Coefficient for Al2O3 (75%) – CuO (25%) / Water Hybrid Nanofluid using Taguchi

To have the maximum benefits of nanofluid for high heat transfer coefficient, like hybrid composite materials in the material’s revolution, the hybrid nanofluid was prepared and its performance was realized by experimentation. In this investigation, the prepared Al2O3 (75%)– CuO (25%) / Water hybrid nanofluid was used as a coolant for making pen barrel in injection molding machine. For experimentation, the three process parameters viz., Volume Fraction (VF), Volume Flow Rate (VFR) and Temperature (Temp) were controlled and optimized by using Taguchi’s L9 orthogonal array to yield the maximum heat transfer coefficient. To optimize it, total nine different experiments were conducted by controlling these factors. The considered all three parameters were kept three levels. Regression equation was established to predict heat transfer coefficient by incorporating independently controllable process parameters. Based on the optimization result, it was found that the high heat transfer coefficient was achieved at 0.2 %, 6 LPM and 35 °C of VF, VFR and Temp of hybrid nanofluid respectively

Effect of Quench Severity and Hardness of Aluminium 2585 Alloyusing Eco Friendly Quenchants

Rate of cooling, hardness and severity during quenching of various media viz; cow urine, distilled water, tap water, engine oil (unused) SAE40 soap nut solution, shikakai nut solution for industrial heat treatment was investigated using 2585 Al alloy. For all media, nucleate boiling and convective heat transfer are being carried out and out of which maximum and minimum cooling rates are observed for cow urine. From the study it has been observed that cow urine, tap water and distilled water, cow urine has high heat transfer coefficient 6.577W/m2K, whereas Engine oil, Shikakai nut solution, Soap nut solution are considered Soap nut solution has high heat transfer coefficient 3.654 W/m2K. For all the quenchants, the hardness of Al 2585 alloy increased cow urine

Effect of Squealer Rim Slot Structure on Turbine Blade Aerothermal Performance

Recent studies have demonstrated that the turbine blade with a squealer tip has less aerodynamic loss than that with a flat tip. However, there exists an area of high heat transfer coefficient (HTC) in the frontal region of the cavity floor. The present study focuses on the effect of squealer rim slot structure on turbine blade aerothermal performance. An experiment of transient thermal measurement is carried out for a non-slot squealer tip to validate the numerical setup and the choice of turbulence model. ANSYS CFX is utilized to conduct the numerical simulations of cases with and without slot structure and they are both validated by the experimental data. Through the experimental and CFD results, it can be found that the case with a slot on the pressure side of the squealer rim has smaller area of high HTC region and the aerodynamic efficiency is raised. Moreover, the effect of different sizes of the slot is investigated numerically and it also has a great impact on the heat transfer and aerodynamics. The quantity of the flow passing through the slot can largely influence the flow field of the tip gap and the cavity. Thus, the heat transfer of these areas and the aerodynamic efficiency of the blade vary from the slot size.

Optimization of Helium Inflating on Heat Dissipation and Luminescence Properties of the A60 LED Filament Lamps

LED filament lamp has the characteristics of nearly 360° lighting angle, high brightness, and low energy consumption, turning it gradually into the best substitute for traditional incandescent lamps. At present, due to the limitations of heat dissipation, the development of high-power LED filament lamp is restricted. Helium is a rare gas with small density and high heat transfer coefficient. It can be used as a cooling and protective gas for LED filament lamp. In this paper, we investigated the effects of helium on the heat dissipation and luminescence performance of the A60 LED filament lamps by detecting the changes of junction temperature, color temperature, and luminous flux of different ratios helium inflating in the different power A60 LED filament lamps. Through the experiment, we found the most cost-effective ratio of helium gas in the A60 LED filament lamps without improving the lamp size and the filament diameter.

Performance of special type heat sink with an integrated synthetic jet actuator

The performance of special type heat sink with integrated synthetic jet actuator has been presented in this work. Synthetic jet is a flow technique which synthesizes stagnant air to a form of jet. Synthetic jet produces high turbulent flow and thus high heat transfer coefficient can be achieved. Standard heat sink with fan have limited applications in particular in a dusty industrial environment. Therefore, the use of new flow technique is optimistic. The paper presents preliminary results of heat sink thermal power and characteristic temperatures during synthetic jet switched on and off. The results show that under synthetic jet switched on, the dissipated heat is 3.7 times higher than when synthetic jet is switched off.

Heat Dissipation Beyond 1 kW/cm2 With Low Pressure Drop and High Heat Transfer Coefficient for Flow Boiling Using Open Microchannels With Tapered Manifold

Heat dissipation beyond 1 kW/cm2 accompanied with high heat transfer coefficient and low pressure drop using water has been a long-standing goal in the flow boiling research directed toward electronic cooling application. In the present work, three approaches are combined to reach this goal: (a) a microchannel with a manifold to increase critical heat flux (CHF) and heat transfer coefficient (HTC), (b) a tapered manifold to reduce the pressure drop, and (c) high flow rates for further enhancing CHF from liquid inertia forces. A CHF of 1.07 kW/cm2 was achieved with a heat transfer coefficient of 295 kW/m2°C with a pressure drop of 30 kPa. Effect of flow rate on CHF and HTC is investigated. High speed visualization to understand the underlying bubble dynamics responsible for low pressure drop and high CHF is also presented.

Comparison of heat transfer coefficient for different fabrics by vapor-compression system

The selection of a suitable fabric layer is an important aspect in the development of a cooling garment. One of the essential ingredients in selecting fabric for cooling garments is high heat transfer coefficient. In this study five different type of knitting fabrics with similar woven pattern were selected. The fabrics were attached to a vapor-compression system which is one of the most important systems in cooling garments. Heat transfer coefficient was calculated for each fabric for three different refrigerator flow rates. The most efficient fabric for applying in cooling garments was determined from the point of heat transfer coefficient.