Effect of surface etching on condensing heat transfer

The effect of surface roughness on the pool boiling heat transfer of water was investigated on superhydrophilic aluminum surfaces. The formation of nanoscale protrusions on the aluminum surface was confirmed after immersing it in boiling water, which modified surface wettability to form a superhydrophilic surface. The effect of surface roughness was examined at different average roughness (Ra) values ranging from 0.11 to 2.93 μm. The boiling heat transfer coefficients increased with an increase in roughness owing to the increased number of cavities. However, the superhydrophilic aluminum surfaces exhibited degradation of the heat transfer coefficients when compared with copper surfaces owing to the flooding of promising cavities. The superhydrophilic aluminum surfaces exhibited a higher critical heat flux (CHF) than the copper surfaces. The CHF was 1650 kW/m2 for Ra = 0.11 μm, and it increased to 2150 kW/m2 for Ra = 0.35 μm. Surface roughness is considered to affect CHF as it improves the capillary wicking on the superhydrophilic surface. However, further increase in surface roughness above 0.35 μm did not augment the CHF, even at Ra = 2.93 μm. This upper limit of the CHF appears to result from the hydrodynamic limit on the superhydrophilic surface, because the roughest surface with Ra = 2.93 μm still showed a faster liquid spreading speed.

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Single-Phase Heat Transfer in Micro-Tubes: A Critical Review

ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference, Volume 2 ◽

10.1115/ht2007-32408 ◽

2007 ◽

Cited By ~ 6

Author(s):

Chandramoulee Krishnamoorthy ◽

Rahul P. Rao ◽

Afshin J. Ghajar

Keyword(s):

Heat Transfer ◽

Surface Roughness ◽

Single Phase ◽

Review Paper ◽

Measurement Techniques ◽

Data Bank ◽

Macro Scale ◽

Small Scales ◽

Gaseous Flows ◽

Effect Of Surface

This review paper specifically concentrates on heat transfer in micro-tubes and eleven experiments (on liquid flow) and two experiments (on gaseous flow) from 1991 to 2007 are reviewed critically with respect to measurement techniques, instrumentation; and factors like surface roughness and diameter that may play an important role at these small scales. Moreover, a comprehensive list of numerical and analytical results (for both liquid and gaseous flows) is presented in this paper. Interestingly, the effect of surface roughness on heat transfer does not seem to have been investigated thoroughly, as it has been observed to play a key role in influencing heat transfer at small diameters. The state-of-art review thus provides the contemporary experimenters in the field of mini-micro channel heat transfer, this tabulated data that can be used to understand how the different parameters affect the heat transfer in these small scales and a data-bank to validate future numerical and experimental work. The present study identifies the various factors that have contributed in the disparity of results found in the literature and finds that there is a need to investigate certain issues like the effects of roughness, diameter, and secondary flow due to buoyancy on heat transfer and transition. Moreover, it was observed that the start and end of the transition region at these small diameters are not validated by the any of the existing macro-scale correlations.

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CONDENSING HEAT TRANSFER IN VERTICAL CYCLONE

Experimental Heat Transfer ◽

10.1080/08916150290082667 ◽

2002 ◽

Vol 15 (4) ◽

pp. 221-228

Author(s):

C. B. Vijaya Vittala ◽

Sunirmal Ray ◽

S. Chaterjee ◽

T. Dharmavir Singh ◽

Kaushik Datta

Keyword(s):

Heat Transfer ◽

Condensing Heat Transfer

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Effect of surface etching on the magnetic properties and grain-boundary Dy-diffusion in DyH2-dip-coated sintered Nd-Fe-B magnets

Metals and Materials International ◽

10.1007/s12540-015-4337-6 ◽

2015 ◽

Vol 21 (3) ◽

pp. 600-606 ◽

Cited By ~ 8

Author(s):

Ju-Young Kong ◽

Tae-Hoon Kim ◽

Seong-Rae Lee ◽

Hyo-Jun Kim ◽

Min-Woo Lee ◽

...

Keyword(s):

Magnetic Properties ◽

Grain Boundary ◽

Surface Etching ◽

Effect Of Surface

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Effect of Surface Conditions on the Adhesion of Crystallization Fouling

2010 14th International Heat Transfer Conference, Volume 4 ◽

10.1115/ihtc14-22313 ◽

2010 ◽

Author(s):

Yong Zou ◽

Yida Liu ◽

Gongming Xin ◽

Wen Liu ◽

Lin Cheng

Keyword(s):

Heat Transfer ◽

Surface Roughness ◽

Oxide Layer ◽

Crystalline Structure ◽

Lattice Parameter ◽

Hexagonal Structure ◽

Experimental Results ◽

Obvious Effect ◽

Surface Conditions ◽

Effect Of Surface

In this study, effects of surface conditions in terms of surface roughness and oxide layer, on adhesion of crystallization fouling on heat transfer surfaces were investigated. The experimental results showed that the surface roughness has no obvious effect on the adhesion of crystallization fouling. The polished sample did not present better anti-fouling properties compared to other rough samples. While the formation of Fe2O3 layer on the surface is proved to be able to accelerate the adhesion of calcite fouling with hexagonal structure, because there are similar crystalline structure and lattice parameter between the Fe2O3 and calcite fouling. Therefore, in order to improve the anti-fouling property of heat transfer surfaces, inhibiting the formation of oxide layer is more important than efforts to improve surface roughness.

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Effect of surface modification of a rectangular vortex generator on heat transfer rate from a surface to fluid

International Journal of Thermal Sciences ◽

10.1016/j.ijthermalsci.2018.01.004 ◽

2018 ◽

Vol 127 ◽

pp. 61-78 ◽

Cited By ~ 20

Author(s):

Uddip Kashyap ◽

Koushik Das ◽

Biplab Kumar Debnath

Keyword(s):

Heat Transfer ◽

Surface Modification ◽

Heat Transfer Rate ◽

Transfer Rate ◽

Vortex Generator ◽

Effect Of Surface

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The Impact of Fin Deformation on Condensation Heat Transfer Coefficients in Internally Grooved Tubes

Volume 2: Heat Transfer Enhancement for Practical Applications; Heat and Mass Transfer in Fire and Combustion; Heat Transfer in Multiphase Systems; Heat and Mass Transfer in Biotechnology ◽

10.1115/ht2013-17111 ◽

2013 ◽

Author(s):

Sunil Mehendale

Keyword(s):

Heat Transfer ◽

Heat Exchangers ◽

Thermal Contact ◽

Heat Pumps ◽

Condensation Heat Transfer ◽

Transfer Coefficients ◽

Heat Transfer Coefficients ◽

Condensing Heat Transfer ◽

The Impact ◽

Tube Expansion

In HVACR equipment, internally enhanced round tube (microfin) designs such as axial, cross-grooved, helical, and herringbone are commonly used to enhance the boiling and condensing performance of evaporators, condensers, and heat pumps. Typically, such tubes are mechanically expanded by a mandrel into a fin pack to create an interference fit between the tube outside surface and the fin collar to minimize the thermal contact resistance between tube and fin. However, during this expansion process, the internal enhancements undergo varying amounts of deformation, which degrades the in-tube thermal performance. Extensive data on condensing heat transfer coefficients in microfin tubes have been reported in the open literature. However, researchers have seldom used expanded tubes to acquire and report such data. Hence, it is always questionable to use such pristine tube data for designing heat exchangers and HVACR systems. Furthermore, the HVACR industry has been experiencing steeply rising copper costs, and this trend is expected to continue in coming years. So, many equipment manufacturers and suppliers are actively converting tubes from copper to aluminum. However, because of appreciable differences between the material properties of aluminum and copper, as well as other manufacturing variables, such as mandrel dimensions, lubricant used, etc., tube expansion typically deforms aluminum fins more than copper fins. Based on an analysis of the surface area changes arising from tube expansion, and an assessment of the best extant in-tube condensation heat transfer correlations, this work proposes a method of estimating the impact of tube expansion on in-tube condensation heat transfer. The analysis leads to certain interesting and useful findings correlating fin geometry and in-tube condensation thermal resistance. This method can then be applied to more realistically design HVACR heat exchangers and systems.

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