Numerical Investigation on Pool Boiling Over a Vertical Tube Coupled With In-Tube Condensation

2019 ◽  
Author(s):  
Shuai Ren ◽  
Wenzhong Zhou
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Boiling Heat Transfer ◽  
Power Plants ◽  
Pool Boiling ◽  
Heat Removal ◽  
Vertical Tube ◽  
Two Phase ◽  
Maximum Heat ◽  
Maximum Heat Transfer

Abstract Pool boiling and in-tube condensation phenomena have been investigated intensively during the past decades, due to the superior heat transfer capacity of the phase change process. In passive heat removal heat exchangers of nuclear power plants, the two phase-change phenomena usually occur simultaneously on both sides of the tube wall to achieve the maximum heat transfer efficiency. However, the studies on the effects of in-tube condensation on external pool boiling heat transfer are very limited, especially in numerical computation aspect. In the present study, the saturated pooling boiling over a vertical tube under the influences of in-tube steam condensation is investigated numerically. The Volume of Fluid (VOF) interface tracking method is employed based on the 2D axisymmetric Euler-Euler multiphase frame. The phase change model combining with a mathematical smoothing algorithm and a temporal relaxation procedure has been implemented into CFD platform by user defined functions (UDFs). The two-phase flow pattern and bubble behavior have been analyzed. The effects of inlet steam mass flow rate on boiling heat transfer are discussed.

A New Perspective on Heat Transfer Mechanisms and Sonic Limit in Pool Boiling

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Superheated Liquid ◽  
Heater Surface ◽  
Liquid Stream ◽  
Maximum Heat ◽  
Pool Boiling Heat Transfer ◽  
Maximum Heat Transfer ◽  
Secondary Evaporation

Pool boiling is postulated as a single-phase heat transfer process with nucleating bubbles providing a liquid pumping mechanism over the heater surface. This results in three fluid streams at the heater surface—outgoing vapor and liquid streams, and an incoming liquid stream. Heat transfer during periodic replacement of the liquid in the influence region around a nucleating bubble is well described by transient conduction (TC) and microconvection (MiC) mechanisms. Beyond this region, free convection (FC) or macroconvection (MaC) contributes to heating of the liquid. A bubble growing on the heater surface derives its latent heat from the surrounding superheated liquid and from the microlayer providing a direct heat conduction path. Secondary evaporation occurs in the bubbles rising in the bulk after departure, and at the free surface. This secondary evaporation does not directly contribute to the heat transfer at the heater surface but provides a means of dissipating liquid superheat. A sonic limit-based model is then presented for estimating the theoretical upper limit for pool boiling heat transfer by considering the three fluid streams to approach their respective sonic velocities. Maximum heat transfer rates are also estimated using this model with two realistic velocities of 1 and 5 m/s for the individual streams and are found to be in general agreement with available experimental results. It is postulated that small bubbles departing at high velocity along with high liquid stream velocities are beneficial for heat transfer. Based on these concepts, future research directions for enhancing pool boiling heat transfer are presented.

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.

scholarly journals Enhancement of Nucleate Pool Boiling Heat Transfer with Sodium Oleate

2017 ◽  
Vol 29 (1) ◽  
pp. 44-48
Author(s):  
KM Tanvir Ahmmed ◽  
Sultana Razia Syeda
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Sodium Oleate ◽  
Surfactant Concentration ◽  
Chemical Engineering ◽  
Pool Boiling ◽  
Nucleate Pool Boiling ◽  
Maximum Heat ◽  
Maximum Heat Transfer

In this study saturated nucleate pool boiling of water with sodium oleate surfactant on a horizontal cylindrical heater surface has been investigated experimentally and compared with that of demineralized water. The concentration of sodium oleate in water was 100-300 ppm. The experimental results show that a small amount of surfactant enhances the heat transfer coefficient significantly. At low surfactant concentrations, heat transfer coefficient increases with increasing surfactant concentration in water. The maximum heat transfer enhancement is found to be at 250 ppm of sodium oleate solution. By adding more surfactant to water, heat transfer coefficient is found to be lowered. Surface tension of different concentration of sodium oleate solutions is measured. It is observed that the maximum heat transfer coefficient is obtained at a surfactant concentration that corresponds to the critical micelle concentration (cmc) of the sodium oleate solution.Journal of Chemical Engineering, Vol. 29, No. 1, 2017: 44-48

Pool Boiling Heat Transfer Characteristics of HFO-1234yf With and Without Microporous-Enhanced Surfaces

2011 ◽  
Author(s):  
Gilberto Moreno ◽  
Sreekant Narumanchi ◽  
Charles King
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Fundamental Study ◽  
Heat Transfer Coefficients ◽  
Hfc 134A ◽  
Lower Heat

This fundamental study characterizes the pool boiling performance of a new refrigerant, HFO-1234yf (hydrofluoroolefin 2,3,3,3-tetrafluoropropene). The similarities in thermophysical properties with HFC-134a and low global warming potential make HFO-1234yf the prospective next generation refrigerant in automotive air-conditioning systems. This study examines the possibility of using this refrigerant for two-phase cooling of hybrid and electric vehicle power electronic components. Pool boiling experiments were conducted with HFO-1234yf and HFC-134a at system pressures ranging from 0.7 to 1.7 MPa using horizontally oriented 1 cm2 heat sources. Results show that the boiling heat transfer coefficients of HFO-1234yf and HFC-134a are nearly identical at lower heat fluxes. HFO-1234yf yielded lower heat transfer coefficients at higher heat fluxes and lower critical heat flux (CHF) as compared with HFC-134a. To enhance boiling heat transfer, a copper microporous coating was applied to the test surfaces. The coating provided enhancement to both the boiling heat transfer coefficients and CHF, for both refrigerants, at all tested pressures. Increasing pressure decreases the level of heat transfer coefficient enhancements while increasing the level of CHF enhancements.

The Effect of Nanoscale Surface Modification on Boiling Heat Transfer and Critical Heat Flux

2010 ◽  
Author(s):  
Moo Hwan Kim
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Nuclear Power ◽  
Power Plants ◽  
Flow Boiling ◽  
Heated Surface ◽  
Pool Boiling ◽  
Working Fluid ◽  
Wetting Ability ◽  
Modified Surface

Recently, there were lots of researches about enormous CHF enhancement with the nanofluid in pool boiling and flow boiling. It is supposed the deposition of nanoparticles on the heated surface is one of main reasons. In a real application, nanofluid has a lot of problems to be used as the working fluid because of sedimentation and aggregation. The artificial surfaces on silicon and metal were developed to have the similar effect with nanoparticles deposited on the surface. The modified surface showed the enormous ability to increase CHF in pool boiling. Furthermore, under flow boiling, it had also good results to increase CHF. In these studies, we concluded that wetting ability of surface; e.g. wettability and liquid spreading ability (hydrophilic property of surface) was a key parameter to increase CHF under both pool and flow boiling. In addition, using wettability difference of surface; e.g. hydrophilic and hydrophobic, we conducted some tests of BHT (boiling heat transfer) enhancement using the oxide silicon which have micro-sized hydrophobic islands on hydrophilic surface. By using both of these techniques, we propose an optimized surface to increase both CHF and BHT. Also, the fuel surface of nuclear power plants is modified to have same effect and the results shows a good enhancement of CHF, too.

Boiling Heat Transfer Using Spatially-Variant and Uniform Microporous Coatings

2019 ◽  
Author(s):  
Quang N. Pham ◽  
Youngjoon Suh ◽  
Bowen Shao ◽  
Yoonjin Won
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Thermal Management ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Bubble Nucleation ◽  
Vapor Flow ◽  
Inverse Opal ◽  
Two Phase ◽  
Spatially Variant

Abstract Two-phase thermal management offers cooling performance enhancement by an order of magnitude higher than single-phase flow due to the latent heat associated with phase change. Among the modes of phase-change, boiling can effectively remove massive amounts of heat flux from the surface by employing structured or 3D microporous coatings to significantly enlarge the interfacial surface area for improved heat transfer rate as well as increase the number of potential sites for bubble nucleation and departure. The bubble dynamics during pool boiling are often considered to be essential in predicting heat transfer performance, causing it to be a field of significant interest. While prior investigations seek to modulate the bubble dynamics through either active (e.g., surfactants, electricity) or passive means (e.g., surface wettability, microstructures), the utilization of an ordered microporous architecture to instigate desirable liquid and vapor flow field has been limited. Here, we investigate the bubble dynamics using various spatial patterns of inverse opal channels to induce preferential heat and mass flow site in highly-interconnected microporous media. A fully-coated inverse opal surface demonstrates the intrinsic boiling effects of a uniform microporous coating, which exhibits 156% enhancement in heat transfer coefficient in comparison to the polished silicon surface. The boiling heat transfer performances of spatially-variant inverse opal channels significantly differ based on the pitch spacings between the microporous channels, which dictate the bubble coalescent behaviors and bubble departure characteristics. The elucidated boiling heat transfer performances will provide engineering guidance toward designing optimal two-phase thermal management devices.

Effect of Gap Distance on Confined Boiling Heat Transfer Over a Saturated Porous Structure

2005 ◽  
Author(s):  
M. J. Schertzer ◽  
M. Khammar ◽  
D. Ewing ◽  
C. Y. Ching ◽  
J. S. Chang
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
High Speed ◽  
Imaging System ◽  
Porous Plate ◽  
Heat Removal ◽  
Heat Fluxes ◽  
Maximum Heat ◽  
Porous Wick ◽  
Maximum Heat Transfer

An experimental investigation was performed to study the effect that the introduction of a gap between a heated fin and a porous media would have on the heat removal characteristics of a capillary evaporator. In these experiments, a thin stainless steel resistive foil stretched between two copper electrodes was used to heat a saturated porous plate with an effective pore size of 50 microns. The temperature distribution on a 10 mm wide simulated fin was measured by a high-speed infra-red thermal imaging system. The heat removal performance was investigated for gap distances of 0.00 to 1.00 mm and for heat fluxes of 17 to 180 kW/m2. These results showed that the maximum heat transfer rate that could be achieved before persistent hot spots were observed on the surface increased with gap distance. Local temperature measurements made using thermocouples embedded in the porous media indicate that vapour penetration into the porous wick is intermittent, and that there is no stable single phase blanket of vapour. For a gap distance of 0.00 mm, this penetration is more uniformly distributed across the width of the heated fin than at a gap distance of 0.50 mm. In the latter case, the vapour distribution is much higher near the edge of the heated fin.

scholarly journals Enhancement of Pool Boiling Heat Transfer over Plain and Rough Cylindrical Tubes

2021 ◽  
Vol 39 (2) ◽  
pp. 329-336
Author(s):  
Farhan M. Haidary ◽  
Md. Rabbi Hasan ◽  
Mohammad Adib ◽  
Sadman H. Labib ◽  
Md. Jubayer Hossain ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Roughness ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Orientation Angle ◽  
Horizontal Tube ◽  
Vertical Tube ◽  
Smooth Tube ◽  
Pool Boiling Heat Transfer

This study investigates the pool boiling heat transfer of water over cylindrical heating tubes for different orientations and surface roughness of the tubes. First, two orientations of a smooth heating tube, horizontal and vertical, were used in the boiling chamber. For a given heat flux, the heat transfer coefficient achieved with the horizontal tube was always higher than that for the vertical tube. To investigate the influence of surface roughness, a rough heating tube with a fully rough outer surface was developed through a metal etching process. Under the same range of wall superheat, the rough tube enhanced the heat transfer rate significantly compared to the smooth tube. Finally, a modified heating tube (MHT) was developed by axially roughening half of the surface of an originally smooth tube. The orientation angle of the rough surface of this MHT was varied from 0° (horizontal-upward) to 180° (horizontal-downward) in the chamber. The heat flux increased significantly with the increase of orientation angles from 0° to 90° (the maximum of 80 kW/m2 at 90°), whereas the same decreased as the orientation angle is further increased from 90° to 180°. Results revealed that the bubble dynamics over the heating tubes play a vital role in pool boiling performance.

Sign in / Sign up

Export Citation Format

Share Document