Heat Transfer Enhancement During Pool Boiling of Water Over Horizontal and Vertical Tubes With Micro Structured Surfaces

2012 ◽  
Author(s):  
Jeet S. Mehta ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
High Speed ◽  
Pool Boiling ◽  
Bubble Nucleation ◽  
Steam Generation ◽  
Transfer Enhancement ◽  
Vertical Orientation ◽  
Structured Surfaces ◽  
Wide Range

Pool boiling is a stable and an efficient method for transferring large quantities of heat. This mode of heat transfer is used in a wide range of applications, including steam generation in boilers, petrochemical, pharmaceutical, cryogenic and many other industrial processes. It also holds promise for cooling of microelectronic devices, such as lasers, microprocessors and others. The objective of this work is to investigate the heat transfer augmentation due to an array of micro structured surfaces over a circular tube. The effects of horizontal and vertical orientation of the tubular test section on heat transfer enhancement are also studied. The bubble nucleation, growth and interactions over the micro structured surfaces are analyzed using high speed cameras to understand the bubble dynamics.

Large Eddy Simulations of Staggered Parallel-Plate Flows

2005 ◽  
Author(s):  
M. V. Pham ◽  
F. Plourde ◽  
S. K. Doan
Keyword(s):  
Heat Transfer ◽  
Numerical Simulations ◽  
Heat Transfer Enhancement ◽  
Parallel Plate ◽  
Large Scale ◽  
Primary Objective ◽  
Transfer Enhancement ◽  
Turbulent Structures ◽  
Wide Range ◽  
Large Eddy

Heat transfer enhancement is a subject of major concern in numerous fields of industry and research. Having received undivided attention over the years, it is still studied worldwide. Given the exponential growth of computing power, large-scale numerical simulations are growing steadily more realistic, and it is now possible to obtain accurate time-dependent solutions with far fewer preliminary assumptions about the problems. As a result, an increasingly wide range of physics is now open for exploration. More specifically, it is time to take full advantage of large eddy simulation technique so as to describe heat transfer in staggered parallel-plate flows. In fact, from simple theory through experimental results, it has been demonstrated that surface interruption enhances heat transfer. Staggered parallel-plate geometries are of great potential interest, and yet many numerical works dedicated to them have been tarnished by excessively simple assumptions. That is to say, numerical simulations have generally hypothesized lengthwise periodicity, even though flows are not periodic; moreover, the LES technique has not been employed with sufficient frequency. Actually, our primary objective is to analyze turbulent influence with regard to heat transfers in staggered parallel-plate fin geometries. In order to do so, we have developed a LES code, and numerical results are compared with regard to several grid mesh resolutions. We have focused mainly upon identification of turbulent structures and their role in heat transfer enhancement. Another key point involves the distinct roles of boundary restart and the vortex shedding mechanism on heat transfer and friction factor.

Subcooled Pool Boiling Studies on Nano-Textured Surfaces

2007 ◽  
Author(s):  
Vijaykumar Sathyamurthi ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Pool Boiling ◽  
Type A ◽  
Nucleate Boiling ◽  
Test Fluid ◽  
Type B ◽  
Textured Surfaces ◽  
Transfer Enhancement ◽  
Boiling Regime

Heat transfer in subcooled pool boiling on nano-textured surfaces is reported in this study. Silicon wafers coated with Multiwalled Carbon Nanotubes (MWCNT) forests 9 microns (Type-A), and 25 microns (Type-B) in height and 8–15 nm in diameter with a randomized pitch of 16–30 nm, form the test surfaces. The test fluid is a fluoroinert (PF-5060, Manufacturer: 3M Co.) with a boiling point of 56°C. The test rig is of the constant heat flux type. Heat transfer enhancement of approximately 1.3 to 32% is observed in the nucleate boiling regime for Type-A at subcooling levels of 20°C. Type-B CNT shows an enhancement of about 13–30% in the nucleate boiling regime for 20°C subcooling. Digital images acquired during the tests show increased nucleation occurring on surfaces coated with MWCNT. Potential factors that could explain the observed heat transfer enhancement are: the enhanced surface area (nano-fin effect), disruption of the “microlayer” region in nucleate boiling, an increase in the size of cold-spots and the high thermal conductivity of MWCNT.

Microstructured Surfaces for Enhanced Pool Boiling Heat Transfer

2011 ◽  
Author(s):  
Kuang-Han Chu ◽  
Ryan Enright ◽  
Evelyn N. Wang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Heat Removal ◽  
Design Guidelines ◽  
Complete Wetting ◽  
Structured Surfaces ◽  
Microstructured Surfaces ◽  
Wide Range

We experimentally investigated pool boiling on microstructured surfaces which demonstrate high critical heat flux (CHF) by enhancing wettability. The microstructures were designed to provide a wide range of well-defined surface roughness to study roughness-augmented wettability on CHF. A maximum CHF of 196 W/cm2 and heat transfer coefficient (h) greater than 80 kW/m2K were achieved. To explain the experimental results, a model extended from a correlation developed by Kandlikar was developed, which well predicts CHF in the complete wetting regime where the apparent liquid contact angle is zero. The model offers a first step towards understanding complex pool boiling processes and developing models to accurately predict CHF on structured surfaces. The insights gained from this work provide design guidelines for new surface technologies with higher heat removal capability that can be effectively used by industry.

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