Laminar Heat Transfer in the Entrance Region of Internally Finned Square Ducts

2001 ◽  
Vol 123 (6) ◽  
pp. 1030-1034 ◽  
Author(s):  
V. D. Sakalis ◽  
P. M. Hatzikonstantinou
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
High Heat ◽  
Axial Distance ◽  
High Heat Transfer ◽  
Developing Flow ◽  
Temperature Boundary ◽  
Internal Fins ◽  
High Heat Transfer Coefficient ◽  
Square Ducts

The laminar, incompressible, hydrodynamically fully developed and thermally developing flow is studied in straight ducts of square cross section, containing four equal, symmetrical, straight, thin and with 100 percent efficiency internal fins. Both the duct wall and the fins are subjected successively to constant temperature boundary condition. Numerical results are obtained using an iterative ADI scheme for the friction number, the temperature distribution and the Nusselt number for the thermally developing and developed regions as functions of axial distance and fin height. Results obtained are in good agreement with the corresponding literature values. In the thermally developing region a high heat transfer coefficient is obtained. Friction number and Nusselt number in the thermally developed limit increase as the fin height increases until they reach their critical values at fin heights near 0.85 and 0.73 respectively.

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

2020 ◽  
pp. 095441002096469
Author(s):  
Weijie Wang ◽  
Shaopeng Lu ◽  
Hongmei Jiang ◽  
Qiusheng Deng ◽  
Jinfang Teng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Suction Side ◽  
High Heat ◽  
Tip Clearance ◽  
Tip Leakage Flow ◽  
Trailing Edge ◽  
Cavity Depth ◽  
High Heat Transfer ◽  
Blade Tip ◽  
High Heat Transfer Coefficient

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.

A Photographic Study of Flow Boiling Stability on a Plain Surface With Tapered Manifold

2015 ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Speed ◽  
Flow Boiling ◽  
High Heat ◽  
Bubble Nucleation ◽  
High Heat Transfer ◽  
Plain Surface ◽  
High Heat Transfer Coefficient

Flow boiling in microchannels offers many advantages such as high heat transfer coefficient, higher surface area to volume ratio, low coolant inventory, uniform temperature control and compact design. The application of these flow boiling systems has been severely limited due to early critical heat flux (CHF) and flow instability. Recently, a number of studies have focused on variable flow cross-sectional area to augment the thermal performance of microchannels. In a previous work, the open microchannel with manifold (OMM) configuration was experimentally investigated to provide high heat transfer coefficient coupled with high CHF and low pressure drop. In the current work, high speed images of plain surface using tapered manifold are obtained to gain an insight into the nucleating bubble behavior. The mechanism of bubble nucleation, growth and departure are described through high speed images. Formation of dry spots for both tapered and uniform manifold geometry is also discussed.

Numerical and experimental analysis of microchannel heat transfer for nanoliquid coolant using different shapes and geometries

2014 ◽  
Vol 229 (11) ◽  
pp. 2056-2065 ◽  
Author(s):  
Harry Garg ◽  
Vipender Singh Negi ◽  
Nidhi Garg ◽  
AK Lall
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Fluid Flow ◽  
Transfer Coefficient ◽  
Experimental Analysis ◽  
High Heat ◽  
Heat Transfer Analysis ◽  
Flow And Heat Transfer ◽  
High Heat Transfer ◽  
High Heat Transfer Coefficient

As part of the liquid cooling, most of the work has been done on fluid flow and heat transfer analysis for flow field. In the present work, the experimental and numerical studies of the microchannel the fluid flow and heat transfer analysis using nanoliquid coolant have been discussed. The practical aspects for increasing the high heat transfer coefficient from conventional studies and the different geometries and shapes of the microchannel are studied. The Aspect Ratio has significant effect on the microchannels and has been varied from AR 2, 4 and 8 to choose the optimum one. Three different fluids, i.e. de-ionized water, ethylene glycol, and a custom nanofluid are chosen for study. The proposed nanofluid almost interacts as another solid and has reduced thermal resistance, friction effect, and thus it almost vanishes high hot spots. Experimental analysis shows that the proposed nanofluid is excellent fluid for high rate heat removals. Moreover, the performance of the overall system is excellent in terms of high heat transfer coefficient, high thermal conductivity, and high capacity of the fluid. It has been reported that the heat transfer coefficient can be increased to 2.5 times of the water or any other fluid. It was also reported that the AR 4 rectangular-shaped channels are the optimum geometry in the Reynolds number ranging from 50 to 800 considering laminar flow. Examination and identification is based upon the practical result that includes fabrication constraints, commercial application, sealing of the system, ease of operation, and so on.

Aerothermal Investigation of Backface Clearance Flow in Deeply Scalloped Radial Turbines

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Ping He ◽  
Zhigang Sun ◽  
Baoting Guo ◽  
Haisheng Chen ◽  
Chunqing Tan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Recirculation Zone ◽  
High Heat ◽  
The Other ◽  
Leakage Flow ◽  
High Heat Transfer ◽  
High Heat Transfer Coefficient ◽  
Radial Turbines

A numerical investigation of flow structure and heat transfer in the backface clearance of deeply scalloped radial turbines is conducted in this paper. It is found that the leakage flow is very strong in the upper radial region whereas in the lower radial region, the scraping flow dominates over the clearance and a recirculation zone is formed. Pressure distributions are given to explain the flow structure in the backface clearance, and it is found that due to the sharp reduction of radial velocity and Coriolis force, the pressure difference in the lower radial region is reduced drastically, which is the mechanism for the domination of the scraping flow and the corresponding recirculation zone. There are two high heat transfer coefficient zones on the backface surface. One is located in the upper radial region due to the reattachment of the leakage flow and the other is located in the lower radial region caused by the impingement of the scraping flow. Increase of the clearance height reduces the high heat transfer coefficient caused by the impingement of the scraping flow, although it increases the leakage loss. On the other hand, the high heat transfer coefficient in the upper radial region can be reduced remarkably by using the suction side squealer geometry.

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

2019 ◽  
Vol 100 ◽  
pp. 00017 ◽  
Author(s):  
Paweł Gil
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Thermal Power ◽  
High Heat ◽  
Synthetic Jet ◽  
Industrial Environment ◽  
Synthetic Jet Actuator ◽  
Characteristic Temperatures ◽  
High Heat Transfer ◽  
High Heat Transfer Coefficient

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

2016 ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Dissipation ◽  
Flow Boiling ◽  
Low Pressure ◽  
High Heat ◽  
High Heat Transfer ◽  
High Heat Transfer Coefficient

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.

Submicron-Scale Condensation on Hydrophobic and Hydrophilic Surfaces

2013 ◽  
Author(s):  
Yutaka Yamada ◽  
Tatsuya Ikuta ◽  
Takashi Nishiyama ◽  
Koji Takahashi ◽  
Yasuyuki Takata
Keyword(s):  
Heat Transfer ◽  
Amorphous Carbon ◽  
High Heat ◽  
Industrial Applications ◽  
Carbon Surface ◽  
Environmental Scanning ◽  
Hydrophilic Surfaces ◽  
High Heat Transfer ◽  
Submicron Scale ◽  
High Heat Transfer Coefficient

Condensation heat transfer is a widely-used technique for industrial applications represented by heat exchanger because of its high heat transfer coefficient. To enhance its performance, a suitable surface is required, where both condensation and droplet removal smoothly occur. In this study, we compared wettability of a graphene surface and an amorphous carbon surface. The result shows that an amorphous carbon surface is more hydrophilic. Then we prepared a graphite surface which has nanoscale hydrophilic regions in large hydrophobic area. We observed the submicron-scale droplet condensation occurs preferentially on the hydrophilic graphite step by using environmental scanning electron microscope (ESEM).

Heat Transfer of Falling Film Flowing Around a Horizontal Tube With Nanofluids

2009 ◽  
Author(s):  
Binglu Ruan ◽  
Anthony M. Jacobi ◽  
Liansheng Li
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Horizontal Tube ◽  
High Heat ◽  
Working Fluid ◽  
Sodium Dodecylbenzene Sulfonate ◽  
Falling Film ◽  
High Heat Transfer ◽  
High Heat Transfer Coefficient ◽  
The Impact

Due to its high heat transfer coefficient and low working fluid inventory, the horizontal-tube, falling-film heat exchanger finds wide application as an absorber, condenser and evaporator. Recent advances in nanotechnology suggest the use of nanofluids in heat exchangers. Some researchers find an enhanced heat transfer with nanofluids, while others report no enhancement or a deleterious effect on heat transfer when applying nanoparticles in the working fluids. In the current work, the thermal conductivity and kinematic viscosity of aqueous alumina nanofluids are measured at concentrations of 0 vol%, 0.05 vol%, 0.5 vol%, 1 vol% (with and without sodium dodecylbenzene sulfonate, SDBS), and 2 vol%. For these nanofluids, the impact of nanoparticles on thermal conductivity and viscosity is small (less than 5% for thermal conductivity and 13% for viscosity). The heat transfer characteristics of these nanofluids are measured and compared to predictions from the literature for conventional fluids. The falling-film heat transfer for these nanofluids is in good agreement with predictions, and no unusual heat transfer enhancement is observed in the present studies. Although the findings with water-alumina nanofluids are not encouraging with respect to heat transfer, the results extend nanofluid data to a new type of flow and may help improve our understanding of nanofluid behavior. Moreover, this work provides a basis for further work on falling-film nanofluids.

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

2019 ◽  
Vol 9 (2) ◽  
pp. 2440-2444
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Process Parameters ◽  
Volume Fraction ◽  
High Heat ◽  
Hybrid Nanofluid ◽  
Maximum Heat ◽  
High Heat Transfer ◽  
High Heat Transfer Coefficient

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

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