scholarly journals Tuning Superhydrophilic Nanostructured Surfaces to Maximize Water Droplet Evaporation Heat Transfer Performance

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Claire K. Wemp ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Experimental Studies ◽  
Droplet Evaporation ◽  
Transfer Performance ◽  
Water Droplets ◽  
Model Framework ◽  
Droplet Spreading ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer

Spraying water droplets on air fin surfaces is often used to augment the performance of air-cooled Rankine power plant condensers and wet cooling tower heat exchangers for building air-conditioning systems. To get the best performance in such processes, the water droplets delivered to the surface should spread rapidly into an extensive, thin film and evaporate with no liquid leaving the surface due to recoil or splashing. This paper presents predictions of theoretical/computational modeling and results of experimental studies of droplet spreading on thin-layer, nanostructured, superhydrophilic surfaces that exhibit very high wicking rates (wickability) in the porous layer. Analysis of the experimental data in the model framework illuminates the key aspects of the physics of the droplet-spreading process and evaporation heat transfer. This analysis also predicts the dependence of droplet-spreading characteristics on the nanoporous surface morphology and other system parameters. The combined results of this investigation indicate specific key strategies for design and fabrication of surface coatings that will maximize the heat transfer performance for droplet evaporation on heat exchanger surfaces. The implications regarding wickability effects on pool boiling processes are also discussed.

Tuning Superhydrophilic Nanostructured Surfaces to Maximize Water Droplet Evaporation Heat Transfer Performance

2017 ◽  
Author(s):  
Claire K. Wemp ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Experimental Studies ◽  
Droplet Evaporation ◽  
Transfer Performance ◽  
Water Droplets ◽  
Model Framework ◽  
Droplet Spreading ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer

Spraying water droplets on air fin surfaces is often used to augment performance of air-cooled Rankine power plant condensers and wet cooling tower heat exchangers for building air-conditioning systems. To get the best performance in such processes, the water droplets delivered to the surface should spread rapidly into an extensive, thin film and evaporate with no liquid leaving the surface due to recoil or splashing. This paper presents predictions of theoretical/computational modeling and results of experimental studies of droplet spreading on thin-layer, nanostructured, superhydrophilic surfaces that exhibit very high wicking rates (wickability) in the porous layer. Analysis of the experimental data in the model framework illuminates the key aspects of the physics of the droplet spreading process and evaporation heat transfer. This analysis also predicts the dependence of droplet spreading characteristics on the nanoporous surface morphology and other system parameters. The combined results of this investigation indicate specific key strategies for design and fabrication of surface coatings that will maximize the heat transfer performance for droplet evaporation on heat exchanger surfaces. The implications regarding wickability effects on pool boiling processes are also discussed.

Droplet Spreading and Evaporation on Nanoporous Superhydrophilic Surfaces: Effects of Impact Parameters

2019 ◽  
Author(s):  
Emma R. McClure ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Weber Number ◽  
Incident Angle ◽  
Heated Surface ◽  
Droplet Evaporation ◽  
Droplet Spreading ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
Impact Parameters ◽  
Superhydrophilic Surfaces

Abstract Recent studies have indicated that droplet evaporation heat transfer can be substantially enhanced by fabricating a thin nanoporous superhydrophilic layer on a metal substrate. Earlier investigations have focused on how these surfaces affect low Weber number deposition of droplets and their subsequent evaporation on a horizontal, upward-facing heated surface. This investigation explores the effects of changing impact parameters — specifically how deposition, spreading, and vaporization on nanoporous superhydrophilic surfaces are affected by changing impact velocity and incident angle of the droplet motion relative to the surface. The results of droplet deposition and evaporation experiments are reported here for multiple droplet sizes (2–6 μL), and multiple incident angles (0–45°), and of 8 μL droplets from different drop heights (1.2, 40, and 80 mm). The results indicate that the strong capillary forces that enhance spreading on these surfaces remain dominant in the spreading and vaporization processes even when droplets strike the surface with significant velocity, and when the incident angle is oblique. The results indicate that increasing the Weber number has little effect on droplet evaporation and decreasing the incident deposition angle further enhances spreading and evaporation heat transfer. This paper also explores the implications of these results for spray cooling applications.

An Investigation of Evaporation Heat Transfer in Sintered Copper Wicks With Microgrooves

2006 ◽  
Author(s):  
Yuan Zhao ◽  
Chung-Lung Chen
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heat Transfer Performance ◽  
Pore Radius ◽  
Distilled Water ◽  
Transfer Performance ◽  
Sintered Copper ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
Effective Pore Radius

This paper presents an experimental study on the parameters that determine the thermal performance of sintered copper wicks with longitudinal micro grooves for heat pipe applications. The grooves, which provide passages to vent vapor, have a width in a range from 150 μm to 500 μm. The copper powder used here has a nominal diameter of 50 μm, which produces an effective pore radius of approximately 13 μm. The main wicks composed of pores and grooves present characteristics of bi-dispersed wick structures. Unlike traditional bi-dispersed wick structures, the sintered grooved wick structures provide undisrupted longitudinal liquid delivery passages and thus improve the boiling limit. Performance of the wick structures with distilled water was examined and the effects of the heat flux and groove geometries on the evaporation/boiling heat transfer performance were studied.

Experimental Investigation of Evaporation Heat Transfer Inside Horizontal Micro-Fin Tubes

2016 ◽  
Author(s):  
Xu Chen ◽  
Pengfei Mi ◽  
Peter R. N. Childs ◽  
Ekaterina Sokolova ◽  
Wei Li ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Geometric Parameters ◽  
Transfer Performance ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
Fin Tubes

Tubes with their features optimized to enhance heat transfer are routinely used in industry. A series of experimental investigations of evaporation heat transfer of widely used refrigerants inside a horizontal micro-fin cooper tube have been conducted and are reported here. The micro-fin tubes have different geometric parameters with inner diameter ranging from 4.98mm to 7.14mm. The helix angle of the tested tubes ranges from 18.858° to 35°. The apex angle of the tested tubes ranges from 11° to 40°. In addition, other geometric parameters of the tubes vary, such as the fin height, fin pitch and starts. Evaporation heat transfer experiments were conducted with the tubes and the working fluids include R22, R32 and R410A. The evaporation experiments were taken at a constant temperature of 6 °C for R22 and R410A, but 10 °C for R32. Moreover, the working conditions of the experiments varied with the mass flux ranging from 100 kg/(m2.s) to 400 kg/(m2.s). For the evaporation experiments, the inlet vapor quality is set as 0.1, while the outlet vapor quality is set as 0.9. The experimental data reveals that tubes with different geometric parameters have different heat transfer performance. The heat transfer coefficients, the reduced pressure and the changing trend of the heat transfer coefficients vary among these tubes. The experimental data has been compared with available models in the literature and an analysis of the effect of geometric parameters on the performance of the tubes undertaken. The influence of each geometric parameter on the heat transfer performance of the micro-fin tube has been analyzed and is reported.

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