scholarly journals Pool Boiling of Nanofluids on Biphilic Surfaces: An Experimental and Numerical Study

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 125
Author(s):  
Eduardo Freitas ◽  
Pedro Pontes ◽  
Ricardo Cautela ◽  
Vaibhav Bahadur ◽  
João Miranda ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Model ◽  
Heat Dissipation ◽  
Numerical Study ◽  
Pool Boiling ◽  
Temperature Drop ◽  
Surface Cooling ◽  
Average Temperature ◽  
Gold Silver

This study addresses the combination of customized surface modification with the use of nanofluids, to infer on its potential to enhance pool-boiling heat transfer. Hydrophilic surfaces patterned with superhydrophobic regions were developed and used as surface interfaces with different nanofluids (water with gold, silver, aluminum and alumina nanoparticles), in order to evaluate the effect of the nature and concentration of the nanoparticles in bubble dynamics and consequently in heat transfer processes. The main qualitative and quantitative analysis was based on extensive post-processing of synchronized high-speed and thermographic images. To study the nucleation of a single bubble in pool boiling condition, a numerical model was also implemented. The results show an evident benefit of using biphilic patterns with well-established distances between the superhydrophobic regions. This can be observed in the resulting plot of the dissipated heat flux for a biphilic pattern with seven superhydrophobic spots, δ = 1/d and an imposed heat flux of 2132 w/m2. In this case, the dissipated heat flux is almost constant (except in the instant t* ≈ 0.9 when it reaches a peak of 2400 W/m2), whilst when using only a single superhydrophobic spot, where the heat flux dissipation reaches the maximum shortly after the detachment of the bubble, dropping continuously until a new necking phase starts. The biphilic patterns also allow a controlled bubble coalescence, which promotes fluid convection at the hydrophilic spacing between the superhydrophobic regions, which clearly contributes to cool down the surface. This effect is noticeable in the case of employing the Ag 1 wt% nanofluid, with an imposed heat flux of 2132 W/m2, where the coalescence of the drops promotes a surface cooling, identified by a temperature drop of 0.7 °C in the hydrophilic areas. Those areas have an average temperature of 101.8 °C, whilst the average temperature of the superhydrophobic spots at coalescence time is of 102.9 °C. For low concentrations as the ones used in this work, the effect of the nanofluids was observed to play a minor role. This can be observed on the slight discrepancy of the heat dissipation decay that occurred in the necking stage of the bubbles for nanofluids with the same kind of nanoparticles and different concentration. For the Au 0.1 wt% nanofluid, a heat dissipation decay of 350 W/m2 was reported, whilst for the Au 0.5 wt% nanofluid, the same decay was only of 280 W/m2. The results of the numerical model concerning velocity fields indicated a sudden acceleration at the bubble detachment, as can be qualitatively analyzed in the thermographic images obtained in this work. Additionally, the temperature fields of the analyzed region present the same tendency as the experimental results.

A Numerical Model of a Reciprocating-Mechanism Driven Heat Loop for Two-Phase High Heat Flux Cooling

2016 ◽  
Vol 8 (4) ◽  
Author(s):  
Olubunmi Popoola ◽  
Ayobami Bamgbade ◽  
Yiding Cao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Model ◽  
Performance Optimization ◽  
Numerical Study ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Two Phase ◽  
Transfer Device

An effective design option for a cooling system is to use a two-phase pumped cooling loop to simultaneously satisfy the temperature uniformity and high heat flux requirements. A reciprocating-mechanism driven heat loop (RMDHL) is a novel heat transfer device that could attain a high heat transfer rate through a reciprocating flow of the two-phase working fluid inside the heat transfer device. Although the device has been tested and validated experimentally, analytical or numerical study has not been undertaken to understand its working mechanism and provide guidance for the device design. The objective of this paper is to develop a numerical model for the RMDHL to predict its operational performance under different working conditions. The developed numerical model has been successfully validated by the existing experimental data and will provide a powerful tool for the design and performance optimization of future RMDHLs. The study also reveals that the maximum velocity in the flow occurs near the wall rather than at the center of the pipe, as in the case of unidirectional steady flow. This higher velocity near the wall may help to explain the enhanced heat transfer of an RMDHL.

scholarly journals Model of heat transfer in the stagnation point of rapidly evaporating microjet

2012 ◽  
Vol 33 (1) ◽  
pp. 139-152 ◽  
Author(s):  
Dariusz Mikielewicz ◽  
Tomasz Muszyński ◽  
Jarosław Mikielewicz
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Steady State ◽  
Theoretical Model ◽  
Stagnation Point ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Surface Cooling ◽  
Nozzle Size ◽  
Good Consistency

Model of heat transfer in the stagnation point of rapidly evaporating microjetThe paper presents investigation into the single water microjet surface cooling producing evaporating film. Reported tests were conducted under steady state conditions. Experiments were conducted using the nozzle size of 70 and 100 μm respectively. In the course of investigations obtained were experimental relations between heat flux and wall superheating. It was proved that the phenomenon is similar to that of pool boiling but the boiling curves are showing a smaller value of critical heat flux (CHF) that the stagnant pool boiling. Values of CHF are also reduced with decreasing liquid subcooling. Theoretical model of surface cooling by evaporating microjet impingement in the stagnation point was described theoreticaly. Results of experiments were compared with predictions by the model showing a good consistency.

Numerical study of pool boiling heat transfer in a large-scale confined space

2017 ◽  
Vol 118 ◽  
pp. 188-198 ◽  
Author(s):  
Yongsheng Tian ◽  
Keyuan Zhang ◽  
Naihua Wang ◽  
Zheng Cui ◽  
Lin Cheng
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Large Scale ◽  
Numerical Study ◽  
Pool Boiling ◽  
Confined Space ◽  
Pool Boiling Heat Transfer

Oscillatory Heat Transfer in a Pipe Subjected to a Laminar Reciprocating Flow

1996 ◽  
Vol 118 (3) ◽  
pp. 592-597 ◽  
Author(s):  
T. S. Zhao ◽  
P. Cheng
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Nusselt Number ◽  
Numerical Study ◽  
Temperature Cycle ◽  
Uniform Heat Flux ◽  
Fluid Temperature ◽  
Cycle Space ◽  
Reciprocating Flow

An experimental and numerical study has been carried out for laminar forced convection in a long pipe heated by uniform heat flux and subjected to a reciprocating flow of air. Transient fluid temperature variations in the two mixing chambers connected to both ends of the heated section were measured. These measurements were used as the thermal boundary conditions for the numerical simulation of the hydrodynamically and thermally developing reciprocating flow in the heated pipe. The coupled governing equations for time-dependent convective heat transfer in the fluid flow and conduction in the wall of the heated tube were solved numerically. The numerical results for time-resolved centerline fuid temperature, cycle-averaged wall temperature, and the space-cycle averaged Nusselt number are shown to be in good agreement with the experimental data. Based on the experimental data, a correlation equation is obtained for the cycle-space averaged Nusselt number in terms of appropriate dimensionless parameters for a laminar reciprocating flow of air in a long pipe with constant heat flux.

Boiling Heat Transfer and Critical Heat Flux Enhancement of Upward- and Downward-Facing Heater in Nanofluids

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Muhamad Zuhairi Sulaiman ◽  
Masahiro Takamura ◽  
Kazuki Nakahashi ◽  
Tomio Okawa
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Flux Enhancement ◽  
Optimum Configuration ◽  
Wall Superheat ◽  
Nucleate Boiling Heat Transfer

Boiling heat transfer (BHT) and critical heat flux (CHF) performance were experimentally studied for saturated pool boiling of water-based nanofluids. In present experimental works, copper heaters of 20 mm diameter with titanium-oxide (TiO2) nanocoated surface were produced in pool boiling of nanofluid. Experiments were performed in both upward and downward facing nanofluid coated heater surface. TiO2 nanoparticle was used with concentration ranging from 0.004 until 0.4 kg/m3 and boiling time of tb = 1, 3, 10, 20, 40, and 60 mins. Distilled water was used to observed BHT and CHF performance of different nanofluids boiling time and concentration configurations. Nucleate boiling heat transfer observed to deteriorate in upward facing heater, however; in contrast effect of enhancement for downward. Maximum enhancements of CHF for upward- and downward-facing heater are 2.1 and 1.9 times, respectively. Reduction of mean contact angle demonstrate enhancement on the critical heat flux for both upward-facing and downward-facing heater configuration. However, nucleate boiling heat transfer shows inconsistency in similar concentration with sequence of boiling time. For both downward- and upward-facing nanocoated heater's BHT and CHF, the optimum configuration denotes by C = 400 kg/m3 with tb = 1 min which shows the best increment of boiling curve trend with lowest wall superheat ΔT = 25 K and critical heat flux enhancement of 2.02 times.

Forced Convective Boiling of Refrigerant HCFC123 in a Mini-Tube

2010 ◽  
Author(s):  
Koichi Araga ◽  
Keisuke Okamoto ◽  
Keiji Murata
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Pool Boiling ◽  
Constant Heat Flux ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Convective Boiling ◽  
Frictional Pressure Drop ◽  
Heat Transfer Coefficients

This paper presents an experimental investigation of the forced convective boiling of refrigerant HCFC123 in a mini-tube. The inner diameters of the test tubes, D, were 0.51 mm and 0.30 mm. First, two-phase frictional pressure drops were measured under adiabatic conditions and compared with the correlations for conventional tubes. The frictional pressure drop data were lower than the correlation for conventional tubes. However, the data were qualitatively in accord with those for conventional tubes and were correlated in the form φL2−1/Xtt. Next, heat transfer coefficients were measured under the conditions of constant heat flux and compared with those for conventional tubes and for pool boiling. The heat transfer characteristics for mini-tubes were different from those for conventional tubes and quite complicated. The heat transfer coefficients for D = 0.51 mm increased with heat flux but were almost independent of mass flux. Although the heat transfer coefficients were higher than those for a conventional tube with D = 10.3 mm and for pool boiling in the low quality region, they decreased gradually with increasing quality. The heat transfer coefficients for D = 0.30 mm were higher than those for D = 0.51 mm and were almost independent of both mass flux and heat flux.

Experimental Investigation of a Thermosyphon With Microstructure on the Boiling Surface

2018 ◽  
Vol 11 (1) ◽  
Author(s):  
Y. Chai ◽  
W. Tian ◽  
J. Tian ◽  
L. W. Jin ◽  
X. Z. Meng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Dissipation ◽  
Pool Boiling ◽  
High Heat ◽  
Primary Concern ◽  
Heat Transfer Efficiency ◽  
Heater Wall ◽  
Micro Structures ◽  
Thermal Physical Properties ◽  
Graphite Foam

Abstract In recent years, a primary concern in the development of electronic technology is high heat dissipation of power devices. The advantages of unique thermal physical properties of graphite foam raise up the possibility of developing pool boiling system with better heat transfer efficiency. A compact thermosyphon was developed with graphite foam insertions to explore how different parameters affect boiling performance. Heater wall temperature, superheat, departure frequency of bubbles, and thermal resistance of the system were analyzed. The results indicated that the boiling performance is affected significantly by thermal conductivity and pore diameter of graphite foam. A proposed heat transfer empirical correlation reflecting the relations between graphite foam micro structures and pool boiling performance of Novec7100 was developed in this paper.

Heat Transfer Behavior of Silica Nanoparticles in Pool Boiling Experiment

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Denitsa Milanova ◽  
Ranganathan Kumar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Chemical Composition ◽  
Particle Deposition ◽  
Ph Value ◽  
Pool Boiling ◽  
High Heat ◽  
Boiling Regime ◽  
High Heat Transfer ◽  
The Wire

The heat transfer characteristics of silica (SiO2) nanofluids at 0.5vol% concentration and particle sizes of 10nm and 20nm in pool boiling with a suspended heating Nichrome wire have been analyzed. The influence of acidity on heat transfer has been studied. The pH value of the nanosuspensions is important from the point of view that it determines the stability of the particles and their mutual interactions toward the suspended heated wire. When there is no particle deposition on the wire, the nanofluid increases critical heat flux (CHF) by about 50% within the uncertainty limits regardless of pH of the base fluid or particle size. The extent of oxidation on the wire impacts CHF, and is influenced by the chemical composition of nanofluids in buffer solutions. The boiling regime is further extended to higher heat flux when there is agglomeration on the wire. This agglomeration allows high heat transfer through interagglomerate pores, resulting in a nearly threefold increase in burnout heat flux. This deposition occurs for the charged 10nm silica particle. The chemical composition, oxidation, and packing of the particles within the deposition on the wire are shown to be the reasons for the extension of the boiling regime and the net enhancement of the burnout heat flux.

scholarly journals Numerical investigation of fluid flow and heat transfer characteristics on the aerodynamics of ventilated disc brake rotor using CFD

2014 ◽  
Vol 18 (2) ◽  
pp. 667-675 ◽  
Author(s):  
Karuppa Raj ◽  
R. Ramsai ◽  
J. Mathew ◽  
G. Soniya
Keyword(s):  
Heat Transfer ◽  
Numerical Analysis ◽  
Heat Dissipation ◽  
Rotational Symmetry ◽  
Temperature Drop ◽  
Brake Disc ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Ansys Cfx ◽  
Brake Rotor

Ventilated brake discs are used in high speed vehicles. The brake disc is an important component in the braking system which is expected to withstand and dissipate the heat generated during the braking event. In the present work, an attempt is made to study the effect of vane-shape on the flow-field and heat transfer characteristics for different configurations of vanes and at different speeds numerically. Three types of rotor configurations circular pillared, modified taper radial and diamond pillar vanes were considered for the numerical analysis. A rotor segment of 20? was considered for the numerical analysis due to its rotational symmetry. The pre processing is carried out with the help of ICEM-CFD and analysis is carried out using ANSYS CFX 12.1. The three dimensional flow through the brake rotor vanes has been simulated by solving the appropriate governing equations viz. conservation of mass, momentum and energy using the commercial CFD tool, ANSYS CFX 12. The predicted results have been validated with the results available in the literature. Circular pillar rotor vanes are found to have more uniform pressure and velocity distribution which results in more uniform temperature drop around the vanes. The effect of number and diameter of vanes in the circular pillared rotor is studied and the geometry is optimized for better mass flow and heat dissipation characteristics.

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