A Possible Mechanism for the Formation of Unwettable Dry Spots on the Heated Surface under Nucleate Boiling: Part I. Basic Models and Characteristics of Heterogeneous Nucleate Pool Boiling at a Low Pressure

2019 ◽  
Vol 82 (8) ◽  
pp. 1194-1205
Author(s):  
Yu. M. Zhukov ◽  
D. S. Urtenov
Keyword(s):  
Heated Surface ◽  
Pool Boiling ◽  
Low Pressure ◽  
Nucleate Boiling ◽  
Nucleate Pool Boiling

scholarly journals Variations of nanoparticle layer properties during nucleate pool boiling

2021 ◽  
Vol 2116 (1) ◽  
pp. 012002
Author(s):  
Tomio Okawa ◽  
Koki Nakano ◽  
Yutaro Umehara
Keyword(s):  
Heat Transfer ◽  
Heated Surface ◽  
Pure Water ◽  
Pool Boiling ◽  
Qualitative Change ◽  
Nucleate Boiling ◽  
Heat Transfer Surface ◽  
Nucleate Pool Boiling ◽  
Capillary Suction ◽  
Nanoparticle Layer

Abstract The nanoparticle layer detachment during nucleate pool boiling and its influences on heat transfer surface properties were explored experimentally. The material of the heat transfer surface was copper and the nanoparticle layer was formed on the heat transfer surface by nucleate boiling in the water-based TiO2 nanofluid. It was found that the detachment of the nanoparticle layer during nucleate boiling in pure water is significant. In the present experiment, more than half of nanoparticles deposited on the heated surface were detached before the CHF condition was reached. The thickness and roughness decreased accordingly. However, the wettability and wickability that are the influential parameters on the CHF value were maintained even after the occurrence of nanoparticle layer detachment and deteriorated only after the CHF condition was reached. It is therefore considered that the onset of CHF brings qualitative change to the capillary suction performance of the layer of nanoparticles. In exploring the effect of the nanoparticle layer properties on the nucleate boiling heat transfer, sufficient attention should be paid to the variation of the nanoparticle layer properties during nucleate boiling.

Inverse Determination of the Local Heat Transfer Coefficients for Nucleate Boiling on a Horizontal Cylinder

2003 ◽  
Vol 125 (6) ◽  
pp. 1087-1095 ◽  
Author(s):  
H. Louahlia-Gualous ◽  
P. K. Panday ◽  
E. A. Artioukhine
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pool Boiling ◽  
Gradient Methods ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Nucleate Boiling ◽  
Nucleate Pool Boiling ◽  
Transfer Coefficients ◽  
Iterative Regularization

This article treats the local heat transfer for nucleate pool boiling around the cylinder using the inverse heat conduction analysis. The physical model considers a half section of a cylinder with unknown surface temperature and heat flux density. The iterative regularization and the conjugate gradient methods are used for solving the inverse analysis. The local Nusselt number profiles for nucleate pool boiling are presented and analyzed for different electric heat. The mean Nusselt number estimated by IHCP is closed with the measured values. The results of IHCP are compared to those of Cornewell and Houston (1994), Stephan and Abdelsalam (1980) and Memory et al. (1995). The influence of the error of the measured temperatures and the error in placement of the thermocouples are studied.

scholarly journals Lattice Boltzmann Simulation of Nucleate Pool Boiling in Saturated Liquid

2011 ◽  
Vol 9 (5) ◽  
pp. 1347-1361 ◽  
Author(s):  
Yoshito Tanaka ◽  
Masato Yoshino ◽  
Tetsuo Hirata
Keyword(s):  
Lattice Boltzmann ◽  
Solid Wall ◽  
Bubble Diameter ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Bubble Nucleation ◽  
Immiscible Fluids ◽  
Nucleate Pool Boiling ◽  
Two Phase ◽  
Boiling Process

AbstractA thermal lattice Boltzmann method (LBM) for two-phase fluid flows in nucleate pool boiling process is proposed. In the present method, a new function for heat transfer is introduced to the isothermal LBM for two-phase immiscible fluids with large density differences. The calculated temperature is substituted into the pressure tensor, which is used for the calculation of an order parameter representing two phases so that bubbles can be formed by nucleate boiling. By using this method, two-dimensional simulations of nucleate pool boiling by a heat source on a solid wall are carried out with the boundary condition for a constant heat flux. The flow characteristics and temperature distribution in the nucleate pool boiling process are obtained. It is seen that a bubble nucleation is formed at first and then the bubble grows and leaves the wall, finally going up with deformation by the buoyant effect. In addition, the effects of the gravity and the surface wettability on the bubble diameter at departure are numerically investigated. The calculated results are in qualitative agreement with other theoretical predictions with available experimental data.

On the Mechanism of Pool Boiling Critical Heat Flux Enhancement in Nanofluids

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Hyungdae Kim ◽  
Ho Seon Ahn ◽  
Moo Hwan Kim
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Heated Surface ◽  
Pure Water ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Titania Nanoparticles ◽  
Nanoparticle Layer ◽  
Wall Superheat ◽  
Dry Spot

The pool boiling characteristics of water-based nanofluids with alumina and titania nanoparticles of 0.01 vol % were investigated on a thermally heated disk heater at saturated temperature and atmospheric pressure. The results confirmed the findings of previous studies that nanofluids can significantly enhance the critical heat flux (CHF), resulting in a large increase in the wall superheat. It was found that some nanoparticles deposit on the heater surface during nucleate boiling, and the surface modification due to the deposition results in the same magnitude of CHF enhancement in pure water as for nanofluids. Subsequent to the boiling experiments, the interfacial properties of the heater surfaces were examined using dynamic wetting of an evaporating water droplet. As the surface temperature increased, the evaporating meniscus on the clean surface suddenly receded toward the liquid due to the evaporation recoil force on the liquid-vapor interface, but the nanoparticle-fouled surface exhibited stable wetting of the liquid meniscus even at a remarkably higher wall superheat. The heat flux gain attainable due to the improved wetting of the evaporating meniscus on the fouled surface showed good agreement with the CHF enhancement during nanofluid boiling. It is supposed that the nanoparticle layer increases the stability of the evaporating microlayer underneath a bubble growing on a heated surface and thus the irreversible growth of a hot/dry spot is inhibited even at a high wall superheat, resulting in the CHF enhancement observed when boiling nanofluids.

Experimental and Numerical Study of the Effects of Asymmetric Micro Ratchets on Pool Boiling Performance

2013 ◽  
Author(s):  
Lance Brumfield ◽  
Sunggook Park
Keyword(s):  
High Performance ◽  
Numerical Study ◽  
Heated Surface ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Industrial Applications ◽  
Heat Fluxes ◽  
Working Fluid ◽  
High Heat Flux ◽  
Central Processing

Nucleate boiling is an attractive method for achieving high heat flux at low superheat temperatures. It is frequently used for industrial applications such as heat exchangers and is being considered to cool advanced central processing units (CPU) which produce heat fluxes on the order of 1 MW/m2 and are becoming increasingly less efficient to cool via forced conduction of air. The issues with implementing nucleate boiling as a cooling mechanism lies in the difficulty of quantifying the complex and numerous mechanisms which control the process. A comprehensive nucleate boiling model has yet to be formulated and will be required in order to safely and reliably cool high performance electronics. Spatially periodic systems with localized asymmetric surface structures (ratchets) can induce directed transport of matter (liquid/particles) in the absence of net force. It was hypothesized that ratchets may enhance pool boiling heat transfer by aiding in the removal of vapor which forms on the heated surface. Therefore, experiments on pool boiling using asymmetric micro ratchets of various geometries, with FC-72 as the working fluid, were investigated. Additionally, various numerical pool boiling simulations were performed using FLUENT to better understand the underlying physical principles behind pool boiling.

Experimental Studies on Pool Boiling Characteristics of Titanium Dioxide-Water Nano-Fluids

2010 ◽  
Author(s):  
Tomio Okawa ◽  
Takahito Kamiya
Keyword(s):  
Heat Flux ◽  
Time Scale ◽  
Base Fluid ◽  
Heated Surface ◽  
Pool Boiling ◽  
Experimental Studies ◽  
Nucleate Boiling ◽  
High Heat Flux ◽  
Nanoparticle Concentration ◽  
Wall Superheat

It is known that dispersion of a small amount of nanometer-sized particles in liquid can cause substantial improvement of the critical heat flux in pool boiling. Nanofluids (colloidal suspensions of nanoparticles in a base fluid) may therefore be used as the coolant in industrial applications in which high-heat-flux removal is needed. If it is supposed that the deposition of nanoparticles onto the heated surface during nucleate boiling is the main cause of the CHF enhancement in nanofluids, a certain time period is considered to be necessary for the CHF to be improved. In view of this, preliminary experiments were performed in the present work to investigate the time scale of CHF improvement; here, distilled water was used as a base fluid, and TiO2 and copper were selected as the materials of nanoparticles and heated surface, respectively. Under a particular experimental conditions of nanoparticle concentration and nucleate boiling heat flux (40 mg/l and 500 kW/m2), an approximate time scale of CHF improvement was 10 min; this value might not be negligibly short in some nanofluid applications. The measured time-variations of the wall superheat during the nucleate boiling in nanofluid suggested that longer time periods are required for the CHF enhancement at lower heat fluxes and lower nanoparticle concentrations. In particular, 40 min was not sufficient for the wall superheat to reach a steady-state value at the lowest nanoparticle concentration of tested in this work (9 mg/l).

Comprehensive Comparisons Between Evaporation and Pool Boiling on Thin Micro Porous Coated Surfaces

2006 ◽  
Author(s):  
Chen Li ◽  
G. P. Peterson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Porous Media ◽  
Heated Surface ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
Coated Surfaces ◽  
Dry Out

The evaporation and pool boiling on micro porous coated surfaces have been shown to provide among the highest heat transfer rates achievable from any type of surfaces. The heat transfer modes in these surfaces, present a number of interesting similarities and also, some fundamental differences, which are the result of the liquid supply methods to the heated surface. For the evaporation from porous coated surfaces, the liquid return to the heated surface is assisted by the capillary pressure at the liquid-vapor interface; while for pool boiling, gravity is the principal driving force that rewets the surface. In order to better understand the physical phenomena that governs the flow behavior of both the liquid and vapor phases, and the heat transfer process inside the porous media, comprehensive comparisons between these return mechanisms and their respective characteristics, and the performance and the critical heat flux (CHF) for each have been made, based on similar physical situations. These systematic comparisons illustrate that at a lower heat flux, the evaporation and pool boiling curves are almost identical due to the similar heat transfer modes, i.e., convection and nucleate boiling. While with further increases in heat flux, the heat transfer performance of the evaporation on micro porous media is generally superior to pool boiling on an identical surface. This shift is believed to be due to the fact that for evaporation on micro porous media, the heat transfer mode is dominated by the film evaporation, while in pool boiling, it is principally the result of fully developed nucleate boiling. It was also observed that the impact of the effective thermal conductivity of the porous coating on pool boiling performance is larger than for evaporation heat transfer on the identical micro porous coated surfaces. In general, the experimental data indicated that the CHF for evaporation heat transfer is much higher than for pool boiling on the same surfaces. The mechanism of CHF for evaporation on porous coated surfaces is believed to be the capillary limit; while for pool boiling the limit is the result of the hydrodynamic instabilities. This difference in mechanisms is clearly demonstrated by the experimental observations, where initially, the dry out process of the porous coated surfaces during evaporation is gradual, while for pool boiling; the entire surface reaches dry out in a very short time. In addition, the sensitivity of the CHF to the thickness of the porous coatings at a constant volumetric porosity and pore size, as well as the various optimal volumetric porosity of the CHF at a given thickness, are clearly the results of the differences induced by the various CHF mechanisms.

Bubble Dynamics for Nucleate Pool Boiling of Electrolyte Solutions

2010 ◽  
Vol 132 (8) ◽  
Author(s):  
Seyed Ali Alavi Fazel ◽  
Seyed Baher Shafaee
Keyword(s):  
Experimental Data ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
Close Relation ◽  
Electrolyte Solutions ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Experimental Results ◽  
Nucleate Pool Boiling ◽  
Wide Range

Bubble dynamics is the most important subphenomenon, which basically affects the nucleate pool boiling heat transfer coefficient. Previous investigations state that the effect of physical properties of liquid and vapor phases on bubble departure diameter are often conflicting. In this article, extensive new experimental data are presented for the bubble departure diameter for various electrolyte aqueous solutions over a wide range of heat fluxes and concentrations. Experimental results show that the bubble detachment diameter increase with increasing either boiling heat flux or electrolyte concentration. Experimental results also present a close relation between the dimensionless capillary and bond numbers. A new model for the prediction of vapor bubble departure diameter in nucleate boiling for the electrolyte solutions is proposed, which predicts the experimental data with a satisfactory accuracy.

scholarly journals Predicting Conduction Heat Flux through Macrolayer in Nucleate Pool Boiling

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3893
Author(s):  
Mohd Danish ◽  
Mohammed K. Al Mesfer ◽  
Khursheed B. Ansari ◽  
Mudassir Hasan ◽  
Abdelfattah Amari ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Current Model ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
High Heat ◽  
High Heat Flux ◽  
Nucleate Pool Boiling ◽  
Conduction Heat Transfer ◽  
Wall Superheat

In the current work, the heat flux in nucleate pool boiling has been predicted using the macrolayer and latent heat evaporation model. The wall superheat (ΔT) and macrolayer thickness (δ) are the parameters considered for predicting the heat flux. The influence of operating parameters on instantaneous conduction heat flux and average heat flux across the macrolayer are investigated. A comparison of the findings of current model with Bhat’s decreasing macrolayer model revealed a close agreement under the nucleate pool boiling condition at high heat flux. It is suggested that conduction heat transfer strongly rely on macrolayer thickness and wall superheat. The wall superheat and macrolayer thickness is found to significantly contribute to conduction heat transfer. The predicted results closely agree with the findings of Bhat’s decreasing macrolayer model for higher values of wall superheat signifying the nucleate boiling. The predicted results of the proposed model and Bhat’s existing model are validated by the experimental data. The findings also endorse the claim that predominant mode of heat transfer from heater surface to boiling liquid is the conduction across the macrolayer at the significantly high heat flux region of nucleate boiling.

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