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.

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.

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.

Numerical Investigations on the Heat Transfer Performance of Transonic Squealer Tip With Different Film Cooling Layouts

2020 ◽  
Author(s):  
Shijie Jiang ◽  
Zhigang Li ◽  
Jun Li ◽  
Liming Song
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Rate ◽  
Film Cooling ◽  
High Speed ◽  
Thermal Stresses ◽  
High Heat ◽  
Tip Leakage Flow ◽  
High Heat Transfer

Abstract Tip leakage flow in high speed turbine induce significant thermal loads and give rise to intense thermal stresses on blade tip, while increasing inlet pressure tends to accelerate leakage velocity beyond transonic regime. The present research quantifies heat transfer and film cooling effect on a squealer tip with three film cooling layouts, three coolant mass flow rates and a relative casing movement. The results indicate that area-averaged HTC of PS layout is higher than that of CAM layout by 6.9% and that of SS layout by 5.7% when coolant flow rate equals to 0.6% mainstream flow rate. By comparison, it is clearly observed that area of the high heat transfer coefficient regions are significantly enlarged when the flow rate of coolant is increased. With relative casing movement, a significant high HTC stripe parallel to pressure side rim is formed. In case of the PS layout, heat transfer coefficient is reduced by 7.3% with casing movement. While in case of CAM layout and SS layout, heat transfer coefficient increased by 4.8% and 2.3% with casing movement, respectively. Detailed flow patterns with three film cooling layouts are also illustrated.

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

Forced Convective Heat Transfer of Ionic Wind on Different Surface Conditions

2015 ◽  
Vol 793 ◽  
pp. 445-449 ◽  
Author(s):  
Lau Ee Von ◽  
Lee Jun Rong ◽  
Mohamed Ismail Harun
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Heat ◽  
Ionic Wind ◽  
Surface Conditions ◽  
High Heat Transfer ◽  
High Heat Transfer Coefficient ◽  
Transfer Properties ◽  
Source Array

The heat transfer enhancement of the forced convection due to ionic wind over different surface conditions including a smooth, rough ruface and a source array of rectangular blocks surface (representing electronic components) was studied. Under laminar flow, the highest heat transfer rate of 0.0736 W/m2.K per minute was observed for the source array surface. The average heat transfer coefficient during steady state of ionic cooling on smooth, rough and source array surfaces were observed to be 19.144 W/m2.K, 18.736 W/m2.K and 21.126 W/m2.K respectively. The heat transfer properties of ionic wind are similar to moving air, generating high heat transfer coefficient and Nusselt number on source array surface due to recirculation eddies.

Electrochemical Deposition of Copper on Graphene with High Heat Transfer Coefficient

2015 ◽  
Vol 66 (30) ◽  
pp. 55-64 ◽  
Author(s):  
A. Jaikumar ◽  
K. S. V. Santhanam ◽  
S. G. Kandlikar ◽  
I. B. P. Raya ◽  
P. Raghupathi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Electrochemical Deposition ◽  
High Heat ◽  
High Heat Transfer ◽  
High Heat Transfer Coefficient

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

2016 ◽  
Vol 5 (1) ◽  
pp. 11 ◽  
Author(s):  
Majid Joghatai ◽  
Dariush Semnani ◽  
Mohammad Reza Salimpour ◽  
Zahra Ashrafi ◽  
Davood Khoeini
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Heat ◽  
Vapor Compression ◽  
Compression System ◽  
High Heat Transfer ◽  
Vapor Compression System ◽  
High Heat Transfer Coefficient ◽  
Cooling Garments

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.

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