scholarly journals Effect of Surface Structure Complexity on Interfacial Droplet Behavior of Superhydrophobic Titanium Surfaces for Robust Dropwise Condensation

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4107
Author(s):  
Je-Un Jeong ◽  
Dae-Yun Ji ◽  
Kwon-Yeong Lee ◽  
Woonbong Hwang ◽  
Chang-Hun Lee ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Surface Structure ◽  
Surface Structures ◽  
Superhydrophobic Surfaces ◽  
Dropwise Condensation ◽  
Exchange Performance ◽  
Droplet Behavior ◽  
Titanium Surfaces ◽  
Structure Complexity

In general, the dropwise condensation supported by superhydrophobic surfaces results in enhanced heat transfer relative to condensation on normal surfaces. However, in supersaturated environments that exceed a certain supersaturation threshold, moisture penetrates the surface structures and results in attached condensation, which reduces the condensation heat transfer efficiency. Therefore, when designing superhydrophobic surfaces for condensers, the surface structure must be resistant to attached condensation in supersaturated conditions. The gap size and complexity of the micro/nanoscale surface structure are the main factors that can be controlled to maintain water repellency in supersaturated environments. In this study, the condensation heat exchange performance was characterized for three different superhydrophobic titanium surface structures via droplet behavior (DB) mapping to evaluate their suitability for power plant condensers. In addition, it was demonstrated that increasing the surface structure complexity increases the versatility of the titanium surfaces by extending the window for improved heat exchange performance. This study demonstrates the usefulness of DB mapping for evaluating the performance of superhydrophobic surfaces regarding their applicability for industrial condenser systems.

Numerical Simulation of Temperature Field on Different Surface Structure of Bicycle Brake Pairs

2014 ◽  
Vol 697 ◽  
pp. 235-238
Author(s):  
Gang Wu ◽  
Can Chao Huang ◽  
Hong Ling Qin ◽  
Chun Hua Zhao
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Surface Structure ◽  
Surface Structures ◽  
Temperature Fields ◽  
Transfer Model ◽  
Pair Model ◽  
Layer Composite ◽  
Positive Effect ◽  
Heat Loads

Using the basic principle of heat transfer, tribology and numerical simulation, a two-dimensional heat transfer model of the three-layer composite brake pair materials were established. The temperature fields of brake pairs during the process of friction were analyzed. Applied given heat loads at different time node on the brake pair model, the temperatures of different bicycle brake pairs were compared and analyzed. Results show that the improved surface structures of brake pair have positive effect on decreasing the temperature of contact areas than that of ordinary surface structure.

Research on the Construction Technology of Radial Underground Heat Exchanger and its Heat Exchange Performance

2014 ◽  
Vol 580-583 ◽  
pp. 2488-2491
Author(s):  
Rong Hui Wang ◽  
Qing Hua Wang ◽  
Ye Feng
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Exchange ◽  
Surface Temperature ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Ground Heat Exchanger ◽  
Construction Technology ◽  
Exchange Performance ◽  
Radial Heat

5 radial heat exchange wells were designed, and the different angle drilling, drilling pipe, and grouting backfill construction technology was studied. In addition, the heat transfer performance of the buried radial heat exchange wells was tested. The results show that, design of pipe equipment is feasible, construction is convenient, and the ratio of backfill material is reasonable; the heat transfer performance of 90 °buried tube is the best. The smaller the angle with the ground heat exchanger, the greater the heat exchange performance is affected by the surface temperature.

3-D Numerical Simulation of Structure Optimization of Rectangular Fin Tube Economizer

2008 ◽  
Author(s):  
Yu-Kun Lu¨ ◽  
Quan Lu
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Transfer Characteristic ◽  
Correlation Equation ◽  
Exchange Performance ◽  
Tube Arrangement ◽  
Flow Through ◽  
Fin Tube ◽  
Heat Exchange Efficiency ◽  
Porous Medium Model

The FLUENT6.2 software is adopted for numerical simulating heat transfer and flow characteristic of the gas when it flow through rectangular tube bundles in transverse direction, the array separation of tubes effected to heat transfer and flow is analyzed, the correlation equation of heat transfer characteristic is derived, and bases on the velocity distributing the rational tube arrangement is adopt to optimize economizer. Taking a certain power plant’s 200MW boiler economizer as an example, the porous medium model and heat exchanger model are employed for simulating. The study result indicates that: the heat-exchange performance of the economizer taking variable-pitch tube arrangement is excelled than the primary one, the discrepancy of gas pressure drop of them is narrow. The essay has direct significance for the structure optimizing and increasing heat exchange efficiency of power plant economizer.

scholarly journals Thermal Performance of Cemented Paste Backfill Body Considering Its Slurry Sedimentary Characteristics in Underground Backfill Stopes

Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 7400
Author(s):  
Chao Huan ◽  
Sha Zhang ◽  
Xiaoxuan Zhao ◽  
Shengteng Li ◽  
Bo Zhang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Simulation Model ◽  
Flow Direction ◽  
Seepage Flow ◽  
Parameter Determination ◽  
Conductive Heat ◽  
Cemented Paste Backfill ◽  
Exchange Performance ◽  
Paste Backfill

The combined mine backfill–geothermal (CMBG) system can be used to effectively extract geothermal energy by installing a heat exchange tube (HET) in the underground backfilled stopes of mines, which can be used as the heat supply for buildings in mines and the surrounding areas. The efficient performance of this system strongly depends on the thermal exchange process between the HET and its surrounding cemented paste backfill body (CPB). In this study, a validated simulation model is established to investigate the heat exchange performance of CPB, in which the nonuniformly distributed thermal properties in CPB are fully considered. The results indicate that the increase in the porosity has a negative effect on the heat exchange performance of CPB. With the increase in the porosity, the decreased rate of the conductive heat transfer in CPB could be up to approximately 18%. In conditions with seepage flow, the heat transfer capacity of CPB could be effectively improved. Generally, a higher hydraulic conductivity corresponds to a higher heat transfer performance of CPB. When the seepage velocity rose from 2 × 10−6 to 6 × 10−6 m/s, the thermal conductivity of CPB achieved a 114% increase from 1.843 to 3.957 W/(m·K). Furthermore, it was found that the thermal energy accumulates along the seepage flow direction, enhancing the thermal influencing radius of the HET in this direction. Thus, the arrangement of HETs should fully take into account the seepage flow effect. This proposed simulation model could provide a reference for parameter determination and optimization of CMBG systems.

scholarly journals Modeling and Optimization of Superhydrophobic Condensation

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Nenad Miljkovic ◽  
Ryan Enright ◽  
Evelyn N. Wang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Contact Angle ◽  
Contact Angle Hysteresis ◽  
Unified Model ◽  
Transport Processes ◽  
Superhydrophobic Surfaces ◽  
Dropwise Condensation ◽  
Structured Surfaces ◽  
Nanostructured Surfaces

Superhydrophobic micro/nanostructured surfaces for dropwise condensation have recently received significant attention due to their potential to enhance heat transfer performance by shedding water droplets via coalescence-induced droplet jumping at length scales below the capillary length. However, achieving optimal surface designs for such behavior requires capturing the details of transport processes that is currently lacking. While comprehensive models have been developed for flat hydrophobic surfaces, they cannot be directly applied for condensation on micro/nanostructured surfaces due to the dynamic droplet-structure interactions. In this work, we developed a unified model for dropwise condensation on superhydrophobic structured surfaces by incorporating individual droplet heat transfer, size distribution, and wetting morphology. Two droplet size distributions were developed, which are valid for droplets undergoing coalescence-induced droplet jumping, and exhibiting either a constant or variable contact angle droplet growth. Distinct emergent droplet wetting morphologies, Cassie jumping, Cassie nonjumping, or Wenzel, were determined by coupling of the structure geometry with the nucleation density and considering local energy barriers to wetting. The model results suggest a specific range of geometries (0.5–2 μm) allowing for the formation of coalescence-induced jumping droplets with a 190% overall surface heat flux enhancement over conventional flat dropwise condensing surfaces. Subsequently, the effects of four typical self-assembled monolayer promoter coatings on overall heat flux were investigated. Surfaces exhibiting coalescence-induced droplet jumping were not sensitive (<5%) to the coating wetting characteristics (contact angle hysteresis), which was in contrast to surfaces relying on gravitational droplet removal. Furthermore, flat surfaces with low promoter coating contact angle hysteresis (<2 deg) outperformed structured superhydrophobic surfaces when the length scale of the structures was above a certain size (>2 μm). This work provides a unified model for dropwise condensation on micro/nanostructured superhydrophobic surfaces and offers guidelines for the design of structured surfaces to maximize heat transfer. Keywords: superhydrophobic condensation, jumping droplets, droplet coalescence, condensation optimization, environmental scanning electron microscopy; micro/nanoscale water condensation, condensation heat transfer.

Numerical Study of Fluid Flow and Heat Transfer in Plate-Fin Heat Transfer Exchanger of HTGR

2016 ◽  
Author(s):  
Wei Peng ◽  
Tao Chen ◽  
Xiaoyong Yang ◽  
Gang Zhao ◽  
Jie Wang
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Numerical Study ◽  
Steady State Solution ◽  
Fluid Temperature ◽  
Heat Transfer Characteristics ◽  
Inlet Velocity ◽  
Exchange Performance ◽  
Flow And Heat Transfer ◽  
Better Than

This paper numerically study the flow and heat transfer characteristics of fluids within the plate-fin heat exchangers with plain and serrated fins. The calculation result is steady-state solution. Effects of the parameters such as inlet velocity and fin type on heat exchange performance are analyzed. The result indicates that under the same inlet velocity, the fluid temperature would be more uniform for the serrated fins. Whereas for the plain fins, the stratified distribution of the fluid temperature is more obvious. Being different from the plain fins, the serrated fins can destroy the boundary layer periodically and strengthen the disorder of the flow field, so its heat exchange performance is better than the plain fins’, however, the pressure drop with serrated fins increases correspondingly.

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