Study of Lateral Merger of Vapor Bubbles During Nucleate Pool Boiling

2004 ◽  
Vol 126 (6) ◽  
pp. 1023-1039 ◽  
Author(s):  
A. Mukherjee ◽  
V. K. Dhir
Keyword(s):  
Heat Transfer ◽  
Bubble Dynamics ◽  
Nucleate Boiling ◽  
Three Dimensions ◽  
Navier Stokes ◽  
Wall Heat Transfer ◽  
Navier Stokes Equation ◽  
Simple Method ◽  
Multiple Bubbles ◽  
Energy Equations

In the present work the bubble dynamics and heat transfer associated with lateral bubble merger during transition from partial to fully developed nucleate boiling is studied numerically. Complete Navier–Stokes equation in three dimensions along with the continuity and energy equations are solved using the SIMPLE method. The liquid vapor interface is captured using the Level-Set technique. Calculations are carried out for multiple bubble mergers in a line and also in a plane and the bubble dynamics and wall heat transfer are compared to that for a single bubble. The results show that merger of multiple bubbles significantly increases the overall wall heat transfer. This enhanced wall heat transfer is caused by trapping of liquid layer between the bubble bases during merger and by drawing of cooler liquid towards the wall during contraction after merger. Good agreement with data from experiments is found in bubble growth rate and bubble shapes obtained from numerical simulations.

Numerical Study of Lateral Merger of Vapor Bubbles During Nucleate Pool Boiling

2003 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Bubble Dynamics ◽  
Stokes Equations ◽  
Numerical Study ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Three Dimensions ◽  
Navier Stokes ◽  
Wall Heat Transfer ◽  
Simple Method

Nucleate boiling is one of the most efficient modes of heat transfer. At the start of nucleate boiling, isolated bubbles appear on the heating surface, the regime known as partial nucleate boiling. Transition from isolated bubbles to fully developed nucleate boiling occurs with increase in wall superheat, when bubbles begin to merge in vertical and lateral directions. The laterally merged bubbles form vapor mushrooms, which stay attached to the heater surface via numerous vapor stems. The present study is performed to numerically analyze the bubble dynamics and heat transfer associated with lateral bubble merger during transition from partial to fully developed nucleate boiling. The complete Navier-Stokes equations in three dimensions along with the continuity and energy equations are solved using the SIMPLE method. The liquid vapor interface is captured using the Level-Set technique. Calculations are carried out for multiple bubble-merger in a line and also in a plane and the bubble dynamics and wall heat transfer are compared to that for a single bubble. The results show that the merger process significantly increases the overall wall heat transfer. It is also found that the orientation of the bubbles strongly influences different heat transfer mechanisms.

Numerical investigation of thermal performance of key components of electric vehicles using nucleate boiling

2021 ◽  
pp. 1-33
Author(s):  
Shyamkumar P.I. ◽  
Suneet Singh ◽  
Atul Srivastava ◽  
Milan Visaria
Keyword(s):  
Heat Transfer ◽  
Bubble Dynamics ◽  
Cooling System ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Nucleate Boiling ◽  
Single Bubble ◽  
Scavenging Effect ◽  
Multiple Bubbles ◽  
Straight Flow

Abstract An efficient thermal management system is desirable for improving the performance of key components of electric vehicle (EV), such as battery packs and Insulated-Gate Bipolar Transistors (IGBTs). This paper investigates the application of single bubble nucleate boiling heat transfer in battery and IGBT component cooling pack. A semi mechanistic flow boiling model, which combines four main sub-models i.e. phase change model, micro-region model, Marangoni model, and contact angle model is developed to get the insight of various subprocesses like bubble inception, growth, departure, scavenging effect while the bubble departs and condensation. For model validation, simulations are carried out for single bubble flow boiling in a vertical rectangular channel and compared against the experimental data available in the literature. Thereafter, simulations are carried out for the battery and IGBT cooling pack to understand the physical phenomena associated with nucleate boiling in such systems. The choice of a single vapor bubble vis-à-vis multiple bubbles has been based on the objective of validating the developed numerical model. An enhancement of ∼30% in heat transfer is achieved for both battery and IGBT components when the system is subjected to a nucleate boiling cooling regime as compared to a conventional single-phase convection cooling system. Nusselt number variation due to the single bubble movement along the coolant path is studied in detail for both serpentine-shaped cooling path in a battery and straight flow path in an IGBT. Moreover, the influence of Reynolds number over bubble dynamics is analyzed.

scholarly journals Unsteady Heat Transfer from an Equilateral Triangular Cylinder in the Unconfined Flow Regime

2011 ◽  
Vol 2011 ◽  
pp. 1-13 ◽  
Author(s):  
Amit Dhiman ◽  
Radhe Shyam
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Prandtl Number ◽  
Flow Regime ◽  
Cross Flow ◽  
Navier Stokes ◽  
Central Difference ◽  
Simple Method ◽  
Energy Equations

Effects of Reynolds number on the heat transfer characteristics of a long (heated) equilateral triangular cylinder are investigated for the range of conditions Re = 50–150 (in the steps of 10) and Prandtl number = 0.71 (air) in the unconfined unsteady cross-flow regime. In order to simulate the present situation, the computational grid is created by using commercial grid generator GAMBIT and the numerical computations are carried out by using FLUENT (6.3). The SIMPLE method is used to solve continuity, Navier-Stokes and energy equations along with the appropriate boundary conditions. The second order upwind scheme is used to discretize the convective terms, while the central difference scheme is used to discretize the diffusive terms in the governing equations. The present results are in an excellent agreement with the literature values. The temperature isotherms and temporal history of Nusselt number are presented in detail. The local as well as time-averaged Nusselt numbers are calculated. The time-averaged Nusselt number increases with increasing Reynolds number for the fixed value of the Prandtl number. Finally, the present numerical results are used to develop the simple heat transfer correlation for the range of conditions covered here.

Numerical Study of an Evaporating Meniscus on a Moving Heated Surface

Volume 3 ◽  
2004 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Stokes Equations ◽  
Numerical Study ◽  
Heated Surface ◽  
Nucleate Boiling ◽  
Two Dimensions ◽  
Temperature Fields ◽  
Navier Stokes ◽  
Wall Heat Transfer ◽  
Parallel Plates

The present study is performed to numerically analyze an evaporating meniscus on a moving heated surface. This phenomenon is similar to the one observed at the base of a vapor bubble during nucleate boiling. The complete Navier-Stokes equations along with continuity and energy equations are solved. The liquid vapor interface is captured using the level set technique. A column of liquid is placed between two parallel plates with an inlet for water at the top to feed the meniscus. The location of water inlet at the top is kept fixed and the bottom wall is imparted with a velocity. Calculations are done in two-dimensions with a fixed distance between the plates. The main objective is to study the velocity and temperature fields inside the meniscus and calculate the wall heat transfer. The results show that the wall velocity creates a circulation near the meniscus base causing increased wall heat transfer as compared to a stationary meniscus. The local wall heat transfer is found to vary significantly along the meniscus base, the highest being near the advancing contact line.

Conjugate Free Convection Heat Transfer and Thermodynamic Analysis of Infrared Suppression Device with Cylindrical Funnels

2022 ◽  
Author(s):  
Vikrant Chandrakar ◽  
Arnab Mukherjee ◽  
Jnana Ranjan Senapati ◽  
Ashok Kumar Barik
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Convection Heat Transfer ◽  
Navier Stokes ◽  
Bejan Number ◽  
Navier Stokes Equation ◽  
Ansys Fluent ◽  
Geometric Ratio ◽  
Flow Rate Increase ◽  
Free Convection Heat

Abstract A convection system can be designed as an energy-efficient one by making a considerable reduction in exergy losses. In this context, entropy generation analysis is performed on the infrared suppression system numerically. In addition, results due to heat transfer are also shown. The numerical solution of the Navier-stokes equation, energy equation, and turbulence equation is executed using ANSYS Fluent 15.0. To perform the numerical analysis, different parameters such as the number of funnels, Rayleigh number (Ra), inner surface temperature, and geometric ratio are varied in the practical range. Results are shown in terms of heat transfer, entropy generation, irreversibility (due to heat transfer and fluid friction), and Bejan number with some relevant parameters. Streamlines and temperature contours are also provided for better visualization of temperature and flow field around the device. Results show that heat transfer and mass flow rate increase with the increase in Ra. Entropy generation and the irreversibility rise with an increase in the number of funnels and geometric ratio. Also, the Bejan number decreases with an increase in Ra and the number of funnels. A cooling time is also obtained using the lumped capacitance method.

Flow Characteristics in a Three-Dimensional Rectangular Channel With a Pair of Ribs Placed Symmetrically at the Channel Walls

2000 ◽  
Author(s):  
M. Singh ◽  
P. K. Panigrahi ◽  
G. Biswas
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Energy Equations

Abstract A numerical study of rib augmented cooling of turbine blades is reported in this paper. The time-dependent velocity field around a pair of symmetrically placed ribs on the walls of a three-dimensional rectangular channel was studied by use of a modified version of Marker-And-Cell algorithm to solve the unsteady incompressible Navier-Stokes and energy equations. The flow structures are presented with the help of instantaneous velocity vector and vorticity fields, FFT and time averaged and rms values of components of velocity. The spanwise averaged Nusselt number is found to increase at the locations of reattachment. The numerical results are compared with available numerical and experimental results. The presence of ribs leads to complex flow fields with regions of flow separation before and after the ribs. Each interruption in the flow field due to the surface mounted rib enables the velocity distribution to be more homogeneous and a new boundary layer starts developing downstream of the rib. The heat transfer is primarily enhanced due to the decrease in the thermal resistance owing to the thinner boundary layers on the interrupted surfaces. Another reason for heat transfer enhancement can be attributed to the mixing induced by large-scale structures present downstream of the separation point.

Improving the performance of the condenser fan in a subway train against the effects of crosswind flow by placing barriers

2019 ◽  
Vol 234 (2) ◽  
pp. 214-225
Author(s):  
Reza NB Abadi ◽  
Mahdi Deymi-Dashtebayaz ◽  
Niki Rezazadeh
Keyword(s):  
Heat Transfer ◽  
Numerical Modeling ◽  
Velocity Profile ◽  
Air Temperature ◽  
Rotating Flows ◽  
Navier Stokes ◽  
Rotational Flow ◽  
Parallel Lines ◽  
Subway Train ◽  
Energy Equations

In this paper, the effect of crosswind flow and barrier placement on the performance of the condenser fan in a subway train is investigated. In addition, the amount of heat transfer on the condenser tubes is also analyzed. At different velocities of the train, variations in the velocity profile and drag force are determined for various geometries including triangular, rectangular, symmetric triangular barriers, and a barrier with parallel lines outside of the fan. Navier–Stokes, energy equations, and k– ω turbulence model have been used for the numerical modeling of the turbulent and incompressible flow. The results show that due to the created vortices behind the triangular and rectangular barriers, a negative velocity on the outflow of the fan is observed. Also, the symmetric triangular barrier minimizes the rotational flow on the top of the fan, and parallel paths have the most impact on the improvement of the fan's performance due to the elimination of all rotating flows. Finally, variations in temperature on the condenser tubes in the presence of barriers that are placed in the middle gap between the holes on the top of the condenser tubes are determined. These barriers move the crosswind flow toward the condenser tubes and decrease the output air temperature of the condenser.

scholarly journals Calculation of Convective Heat Transfer in Square-Sectioned Gas Turbine Blade Cooling Channels

1998 ◽  
Author(s):  
Arash Saidi ◽  
Bengt Sundén
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Cross Sections ◽  
Turbine Blades ◽  
Solution Procedure ◽  
Navier Stokes ◽  
Internal Cooling ◽  
Turbine Blade Cooling ◽  
Cooling Channels ◽  
Energy Equations

Internal cooling channels are commonly used to reduce the thermal loads on the gas turbine blades to improve overall efficiency. In this study a numerical investigation has been carried out to provide a validated and consistent method to deal with the prediction of the fluid flow and the heat transfer of such channels with square cross sections. The rotation modified Navier-Stokes and energy equations together with a low-Re number version of the k-ε turbulence model are solved with appropriate boundary conditions. The solution procedure is based on a numerical method using a collocated grid, and the pressure-velocity coupling is handled by the SIMPLEC algorithm. The computations are performed with the assumption of fully developed periodic conditions. The calculations are carried out for smooth ducts with and without rotation and effects of rotation on the heat transfer are described. Similar numerical calculations have carried out for channels with rib-roughened walls. The obtained results are compared with available experimental data and empirical correlations for the heat transfer rate and the friction factor. Some details of the flow and heat transfer fields are also presented.

Characteristics of Fully Developed Flow and Heat Transfer in Channels With Varying Wall Geometry

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Abhishek G. Ramgadia ◽  
Arun K. Saha
Keyword(s):  
Heat Transfer ◽  
Time Dependent ◽  
Navier Stokes ◽  
Fully Developed Flow ◽  
Flow And Heat Transfer ◽  
Collocated Grid ◽  
Wall Profile ◽  
Energy Equations ◽  
Volume Method ◽  
Wall Geometry

Present study focuses on numerical investigation of fully developed flow and heat transfer through three channels having sine-shaped, triangle-shaped, and arc-shaped wall profiles. All computations are performed at Reynolds number of 600. Finite volume method on collocated grid is used to solve the time-dependent Navier–Stokes and energy equations in primitive variable form. For all the geometries considered in the study, the ratios Hmin/Hmax and L/a are kept fixed to 0.4 and 8.0, respectively. The thermal performances of all the three wall configurations are assessed using integral parameters as well as instantaneous, time-averaged and fluctuating flow fields. The geometry with the sinusoidal-shaped wall profile is found to produce the best thermal properties as compared to the triangle-shaped and the arc-shaped profiles though the obtained heat transfer is the highest for the arc-shaped geometry.

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