DOI: /adfm Nature-inspired Boiling Enhancement by Novel Nanostructured Macro-porous Surface**

Transcription

1 Supporting Information for adfm Submitted to DOI: /adfm Nature-inspired Boiling Enhancement by Novel Nanostructured Macro-porous Surface** By Shanghua Li, Richard Furberg, Muhammet S. Toprak,* Björn Palm, and Mamoun Muhammed, [*] Dr. M. Toprak Corresponding-Author, S. Li Author-Two, Prof. M Muhammed Author-Five Division of Functional Materials Royal Institute of Technology, Stockholm, Sweden toprak@kth.se R. Furberg Author-Three, B. Palm Author-Four Division of Applied Thermodynamics and Refrigeration Royal Institute of Technology, Stockholm, Sweden Brief legend for the video: Enhanced NMp boiling.avi The video shows the difference of boiling performance between NMp surfaces and reference surfaces. The boiling surface is a round Cu surface. Heat is generated and monitored by a heater incorporated into the device. The boiling liquid is the widely used refrigerant, R134a (used in most A/C and domestic refrigerators). One quarter of the surface (Surface 1) is engineered to be the NMp surface while the rest of the surface (Surface 2) is plain copper reference surface (polished with 240 p, emery paper). The average ordered pore size of the NMp surface is 40 µm while the maximum pore size is around 55 µm. Some SEM images with different magnification are given for the NMp surface in the beginning of the video. As it can be seen from the video, most of bubbles are generated on the NMp surfaces which indicates a much higher heat transfer coefficient of NMp surface than the rest reference surface. The bubble generation frequency is high, which visually indicates a highly efficient nucleate boiling process. When the heat flux is decreasing from 4.5 to 0.5 kw/m 2, the 111

2 reference surface stops to boil while the NMp surface continues to boil vigorously. This video gives a visual support for that the NMp surface is an ideal enhanced surface for nucleate boiling. 222

3 Submitted to Supplementary Figures: Figure S1. Micrographs of (a) Cu deposited surface with no VEC; (b) closer view of dendritic Cu deposits on no VEC surface; (c) Cu depostied NMp surface; and (d) closer view of dendritic Cu deposits on NMp surface, (e, f) plain copper reference surface. As shown in the article Fig. 4a, three surfaces were compared for their performance in pool boiling experiments against plain copper reference surface (polished with 240 p, emery paper). These surfaces, having a thickness of 220 µm, are (i) as-made surface with dendritic Cu and no VEC; (ii) as-made typical NMp surface (with VEC); and (iii) annealed NMp surface. Fig. S1e shows typical micrographs of surfaces (i) and (ii) along with plain copper reference 33 3

4 surface. Overview of surface (i) with a close-up view of dendritic copper is presented in Fig. S1a and S1b respectively, whereas, surface (ii) with a close-up view of dendritic copper is presented in Fig. S1c and S1d. Deposited dendritic copper features are very similar for surfaces (i) and (ii). Despite having dendritic Cu with high surface area, surface (i) showed the same performance with the finely polished reference flat surface. This suggests that nano features alone are not enough to improve/enhance the heat transfer performance as reported earlier, and provision for the escape of vapor is also required. As-made and annealed NMp surfaces, having a combination of both nano features and vapor escape channels, HTC (W/cm 2 /K) Heat Flux (W/cm 2 ) Figure S2. HTC as a function of heat flux for NMp surfaces prepared under different conditions (Pool boiling tests are performed in R-134a under constant pressure of 4 bar). Dendritic surfaces with no vapor escape channels (VEC) [ ]; typical as-made dendritic NMp surface (with VEC) with a thickness of [ ] 50 µm, [ ] 80 µm, [ ] 120 µm, [ ] 220 µm; and annealed NMp with a thickness of [ ] 120 µm, [ ] 220 µm, [ ] 265 µm as compared with a reference Cu surface [+]. 444

5 showed a significant enhancement of HTC in the whole region of applied heat-fluxes. NMp surfaces, thus, dramatically enhance the boiling heat transfer performance. Improvement of the heat transfer coefficient (at 1 W cm -2 ) up to 17 times compared to the reference surface has been recorded. Various surfaces with thickness ranging from 50 to 265 µm have been tested for their HTC performance in pool boiling experiments. Fig. S2 shows the complete HTC data from pool boiling tests of nine different surfaces at a heat flux of 5 W cm -2. Thicker NMp surfaces showed higher HTC after annealing. Additional height of the structure increases the hydraulic resistance to the oscillating vapor front and the incoming liquid and therefore slightly inhibits the boiling performance, hence the positive relationship between structure thickness and performance only exists up to a thickness of 120 µm for the non-annealed structure after which thicker structures yield poor performance. The annealing treatment causes the dendritic grains to grow and interconnect whereby the thermal conductivity of the structure increases, resulting in enhanced micro-layer evaporation at the advancing vapor-liquid meniscus. 555