Nucleate pool boiling of R134a on cold sprayed Cu–CNT–SiC and Cu–CNT–AlN composite coatings

Pialago, Edward Joshua T.,Kwon, Oh Kyung,Jin, Jae Sik,Park, Chan Woo Elsevier 2016 Applied Thermal Engineering Vol.103 No.-

<P><B>Abstract</B></P> <P>Ternary copper–carbon nanotube–silicon carbide (Cu–CNT–SiC) and copper–carbon nanotube–aluminum nitride (Cu–CNT–AlN) composite coatings, which were fabricated by mechanical alloying and cold gas dynamic spraying, were used as heating surfaces for boiling heat transfer enhancement. The surfaces of these composite coatings had randomly distributed micro- and nano-sized cavities, which served as active sites for bubble nucleation. Nucleate boiling heat transfer tests on the composite coatings were investigated in a pool of saturated R134a refrigerant at 4.8±0.04°C. Boiling inception on the Cu–CNT–SiC and Cu–CNT–AlN coatings started at heat flux values of about 10–20kW/m<SUP>2</SUP> and at wall superheats that were about 4°C lower than that of the plain Cu plate. The Cu–CNT coating had maximum boiling heat transfer enhancement ratio <I>E</I> <SUB>h,max</SUB> of 1.48 as compared to the plain Cu plate. With the addition of SiC and AlN particles into the composition of the Cu–5CNT composite, the enhancement was augmented further. The coating with 20vol.% AlN exhibited the highest enhancement with an <I>E</I> <SUB>h,max</SUB> of 2.83. This was followed by the coating with 10vol.% SiC with an <I>E</I> <SUB>h,max</SUB> equal to 2.52. Although the Cu–CNT–ceramic coatings had high <I>E</I> <SUB>h,max</SUB>, the <I>E</I> <SUB>h</SUB> decreased at high heat fluxes. The maximum enhancement by achieved by each of the composite coatings was observed at heat fluxes within 100–200kW/m<SUP>2</SUP>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cu–CNT–SiC and Cu–CNT–AlN coatings were fabricated by mechanical alloying and cold spraying. </LI> <LI> The coatings were used as heating surfaces for the enhancement of nucleate boiling of R134a. </LI> <LI> The ternary composite coatings showed boiling enhancement ratios of up to 2.83. </LI> <LI> The (Cu–5CNT)–20AlN composite coating exhibited the highest boiling enhancement. </LI> <LI> Maximum enhancement by each composite coating was observed at heat fluxes within 100–200kW/m<SUP>2</SUP>. </LI> </UL> </P>

핵비등에서 열전달 특성과 기포발생의 광학적 관찰에 관한 연구

윤준규,임종한 한국기계기술학회 2009 한국기계기술학회지 Vol.11 No.1

This study is experimentally to analyze the heat transfer characteristics and photographic observation of bubble generation in saturated nucleate pool boiling. The photographs were taken of water boiling from heated nickel wires. The attempts is made to explain the different nucleate boiling of water. Some of the bubbles photographed were very close to the spherical shape, while others were close to the hemispherical. Also, a number of bubble had intermediate shapes that were called oblate bubbles. At least, heat transfer regions of three and possibly four were found to exist in nucleate boiling depended upon the mode of vapor generation. The vapor structure on the surface progressed through a sequence of first discrete bubbles, then vapor columns and vapor mushrooms, and finally vapor paths, as the surface temperature was increased. These individual vapor structures or combinations of them determine the mechanism of heat transfer in the four nucleate boiling regions.

Effect of chemical etching of fuel cladding surface on crud deposition behavior in simulated primary water of PWRs at 328 °C

Baek, Seung Heon,Shim, Hee-Sang,Kim, Jung Gu,Hur, Do Haeng Elsevier 2018 Annals of nuclear energy Vol.116 No.-

<P><B>Abstract</B></P> <P>The purpose of this work is to evaluate the effect of chemical etching of fuel cladding surface on crud deposition and sub-cooled nucleate boiling behavior in simulated primary water of a PWR at 328 °C (601 K) and 13.0 MPa. Crud deposition tests were conducted using an as-received cladding tube and a chemically etched cladding tube under sub-cooled nucleate flow boiling conditions. The boiling behaviors on the two different cladding tubes were also monitored through the acoustic emission technique during the crud deposition tests. The number of boiling events was much smaller on the chemically etched cladding tube than on the as-received cladding tube. The amount of deposit decreased by about 51% on the chemically etched cladding tube compared to that on the as-received cladding tube. The effect of chemically etched surface is discussed from the viewpoint of surface roughness, wettability, and the degree of sub-cooled nucleate boiling.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of chemical etching of fuel cladding surface on crud deposition is presented. </LI> <LI> Boiling behavior on cladding tubes is monitored using acoustic emission technique. </LI> <LI> Boiling signals decreases significantly on the chemically etched cladding. </LI> <LI> The amount of crud deposits decreases on the chemically etched cladding. </LI> </UL> </P>

Experimental Study of Heating Surface Angle Effects on Single Bubble Growth

Jeongbae Kim,Hyung Dae Kim,Jangho Lee,Young Chul Kwon,Jeong Hoon Kim,Moo Hwan Kim 대한기계학회 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.11

Nucleate pool boiling experiments were performed using pure R11 for various surface angles under constant heat flux conditions during saturated pool boiling. A 1-㎜-diameter circular heater with an artificial cavity in the center that was fabricated using a MEMS technique and a high-speed controller were used to maintain the constant heat flux. Bubble growth images were taken at 5000 frames per second using a high-speed CCD camera. The bubble geometry was obtained from the captured bubble images. The effects of the surface angle on the bubble growth behavior were analyzed for the initial and thermal growth regions using dimensional scales. The parameters that affected the bubble growth behavior were the bubble radius, bubble growth rate, sliding velocity, bubble shape, and advancing and receding contact angles. These phenomena require further analysis for various surface angles and the obtained constant heat flux data provide a good foundation for such future work.

On the Growth Behavior of Bubble during Saturated Nucleate Pool Boiling at Sub-atmospheric Pressure

Jeongbae Kim(김정배),Moo Hwan Kim(김무환) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11

Nucleate pool boiling analysis was performed using previous experimental results obtained with subatmospheric pressure and previous analytical results proposed by authors of this paper. To reveal the differences between the bubble growth behavior of atmospheric pressure and that of sub-atmospheric pressure is the main objective. The second is to show the effect of the system pressure on the bubble growth behavior. To do so, we correlated experimental data using the non-dimensional parameters of the characteristic radius and time scales proposed by previous study, and found that the growth behavior at sub-atmospheric pressure was basically different from that at atmospheric pressure during saturated nucleate pool boiling.

수평관내 3성분 혼합냉매의 핵비등 및 강제대류증발 열전달

오종택 麗水大學校 産業基術硏究所 1999 産業基術硏究所 論文集 Vol.8 No.-

The forced convective boiling heat transfer coefficients of R-407C were measured inside a horizontal tube 6.0 mm I.D. and 4.0 m long. Because of the nucleation was completely suppressed in the two-phase flow region with high quality heat transfer coefficient in forced convective evaporation was higher than it in nucleate boiling. The average heat transfer coefficients were about 30 percent lower than the pure refrigerant correlation due to the mass transfer resistance near the gas-liquid interface. The total experimental data shows agreement with the predicted heat transfer coefficients for ternary refrigerant mixtures within mean deviation of 30%.

일정 벽면 온도 조건에서 이성분 혼합물의 핵비등시 벽면 열유속 거동

배성원,이한춘,김무환,Bae, Sung-Won,Lee, Han-Choon,Kim, Moo-Hwan 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.9

The objective of this work is to measure space and time resolved wall heat fluxes during nucleate pool boiling of R113/R11 mixtures using a microscale heater array in conjunction with a high speed CCD. The microscale heater array is constructed using VLSI techniques, and consists of 96 serpentine platinum resistance heaters on a transparent quartz substrate. Electronic feedback circuits are used to keep the temperature of each heater at a specified temperature and the variation in heating power required to keep the temperature constant is measured. Heat flux data around an isolated bubble are obtained with triggered CCD images. CCD images are obtained at a rate of 1000frames/second. The heat transfer variation vs. time on the heaters directly around the nucleation site is plotted and correlated with images of the bubble obtainedby using the high speed CCD. For both of the mixture(R11/R113) and pure system(pure R11, pure R113), the wall heat fluxes are presented and compared to find out the qualitative difference between pure and binary mixture nucleate boiling.

Experimental Study of Heating Surface Angle Effects on Single Bubble Growth

Kim, Jeong-Bae,Kim, Hyung-Dae,Lee, Jang-Ho,Kwon, Young-Chul,Kim, Jeong-Hoon,Kim, Moo-Hwan The Korean Society of Mechanical Engineers 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.11

Nucleate pool boiling experiments were performed using pure R11 for various surface angles under constant heat flux conditions during saturated pool boiling. A 1-mm-diameter circular heater with an artificial cavity in the center that was fabricated using a MEMS technique and a high-speed controller were used to maintain the constant heat flux. Bubble growth images were taken at 5000 frames per second using a high-speed CCD camera. The bubble geometry was obtained from the captured bubble images. The effects of the surface angle on the bubble growth behavior were analyzed for the initial and thermal growth regions using dimensional scales. The parameters that affected the bubble growth behavior were the bubble radius, bubble growth rate, sliding velocity, bubble shape, and advancing and receding contact angles. These phenomena require further analysis for various surface angles and the obtained constant heat flux data provide a good foundation for such future work.

국소 열유속 및 온도 측정을 통한 물 풀 핵비등에서의 열전달 메커니즘 연구

김민창(Minchang Kim),김성진(Sung Jin Kim) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11

The local heat flux and temperature on the boiling surface are measured to determine the heat transfer mechanism in nucleate pool boiling. Using infrared thermometry, the temperature distribution can be measured when mid-wave(3-5.5 ㎛) optical access to the surface is possible. The heat flux is calculated by the heat equation with this temperature information. The contact line length density(CLD) and the time-averaged wetted area fraction(WF) are also measured for an infrared opaque indium-tin-oxide surface over an electrically heated silicon substrate which is transparent to infrared. With this information, the dominant heat transfer mechanism during the nucleate pool boiling of water is evaluated. In conclusion, the convection heat transfer on the liquid area based on the micro-convection model is the predominant heat transfer mechanisms during the nucleate pool boiling of water.

Numerical Study on a Sliding Bubble During Nucleate Boiling

Son, Gihun The Korean Society of Mechanical Engineers 2001 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.15 No.7

A numerical method for simulating bubble motion during nucleate boiling is presented. The vapor-liquid interface is captured by a level set method which can easily handle breaking and merging of the interface and can calculate an interfacial curvature more accurately than the VOF method using a step function. The level set method is modified to include the effects of phase change at the interface and contact angle at the wall as well as to achieve mass conservation during the whole calculation procedure. Also, a simplified model to predict the heat flux in a thin liquid microlayer is developed. The method is applied for simulation of a sliding bubble on a vertical surface to further understand the physics of partial boiling. Based on the computed results, the effects of contact angle, wall superheat and phase change on a sliding bubble are quantified.