Browsing by Author "Hegde, R.N."

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A model study on accelerated consolidation of coir reinforced laterite and blended shedi soil with vertical sand drains for pavement foundations
(2012) George, V.; Santosh, G.; Hegde, R.N.; Durga Prashanth, L.; Gotamey, D.; Ravi Sankar, A.U.
Sub-grade soils of lateritic origin are frequently encountered in the construction of highway embankments in various regions of India, often comprise intrusions of soft lithomargic soils that result in large settlements during constructions, and differential settlements at later stages. This necessitates the use of appropriate soil improvement techniques to improve the load-carrying capacity of pavements. Coir is a natural fiber that can be used in place of geosynthetics and geogrids, and it is biodegradable and environment friendly. This work deals with the accelerated consolidation of un-reinforced and coir-reinforced laterite and blended lithomargic soils, provided with three vertical sand drains. The load-settlement characteristics were studied for various preloads ranging from 50kg (0.0013 N/mm2) to 500kg (0.013N/mm2) using circular ferro-cement moulds. It was observed that at lower preloads up to 300kg, the relative increase in consolidation (Cr) for randomly reinforced soil with vertical drains was significantly higher than that of un-reinforced soil without vertical drains. Also, the Cr for un-reinforced soil with vertical drains was quite higher than that of un-reinforced soil without vertical drains, with values above 38.71%. However, in the case of higher preloads of 450kg and 500kg, the Cr for randomly reinforced soil with vertical drains was insignificant, and the Cr for un-reinforced soil with vertical drains remained slightly higher at around 9.59% for similar comparisons. The aspect-ratio of coir fibers used was 1: 275. © 2012 Cafet-Innova Technical Society. All rights reserved.
Accelerated consolidation of coir reinforced lithomargic laterite soil blends with vertical sand drains for pavements
(2012) George, V.; Hegde, R.N.; Vardhana, M.V.; Santosh, G.; Gotamey, D.
It is found that sub-grade soils of lateritic origin encountered in the construction of highway embankments in various regions of India, often comprise intrusions of soft lithomargic soils that result in large settlements during constructions, and differential settlements at later stages. This necessitates the use of appropriate soil improvement techniques to improve the load-carrying capacity of pavements. This work deals with the accelerated consolidation of un-reinforced and coir-reinforced laterite and blended lithomargic soils, provided with three vertical sand drains. The load-settlement characteristics were studied for various preloads ranging from 50kg (0.0013 N/mm2) to 500kg (0.013N/mm2). Studies were performed using circular ferro-cement moulds. It was observed that at lower preloads of up to 250kg, the relative increase in consolidation (Rct) for randomly reinforced soil with vertical drains was significantly higher than that of un-reinforced soil without vertical drains. Also, the Rct for un-reinforced soil with vertical drains was quite higher than that of un-reinforced soil without vertical drains, with an average value of 20.84%. In the case of higher preloads the Rct values for randomly reinforced soil with vertical drains were moderate with an average value of 22.67%. An additional increase of up to 27% at lower pre-loads and 11.83% at higher pre-loads was observed due to the effect of random reinforcement when compared to use of vertical drains alone. © 2012 ejge.
Behavioral study of alumina nanoparticles in pool boiling heat transfer on a vertical surface
(2011) Hegde, R.N.; Reddy, R.P.; Rao, S.S.
Experiments were carried out to investigate the pool boiling of alumina-water nanofluid at 0.1 g/l to 0.5 g/l of distilled water, and the nucleate pool boiling heat transfer of pure water and nanofluid at different mass concentrations were compared at and above the atmospheric pressure. At atmospheric pressure, different concentrations of nanofluids display different degrees of deterioration in boiling heat transfer. The effect of pressure and concentration of nanoparticles revealed significant enhancement in heat flux and deterioration in pool boiling. The heat transfer coefficient of 0.5 g/l alumina-water nanofluid was compared with pure water and clearly indicates deterioration. At all pressures the heat transfer coefficients of the nanofluid were lower than those of pure water. Experimental observation revealed particles coating over the heater surface and subsequent SEM inspection of the heater surface showed nanoparticles coating on the surface forming a porous layer. To substantiate the nanoparticle deposition and its effect on heat flux, investigation was done by measuring the surface roughness of the heater surface before and after the experiment. While SEM images of the heater surface revealed nanoparticle deposition, surface roughness of the heater surface confirmed it. Based on the experimental investigations it can be concluded that an optimum thickness of nanoparticles coating favors an increase in heat flux. Higher surface temperature due to the presence of nanoparticles coating results in the deterioration of boiling heat transfer. 2011 Wiley Periodicals, Inc.
Behavioral study of alumina nanoparticles in pool boiling heat transfer on a vertical surface
(2011) Hegde, R.N.; Reddy, R.P.; Rao, S.S.
Experiments were carried out to investigate the pool boiling of alumina-water nanofluid at 0.1 g/l to 0.5 g/l of distilled water, and the nucleate pool boiling heat transfer of pure water and nanofluid at different mass concentrations were compared at and above the atmospheric pressure. At atmospheric pressure, different concentrations of nanofluids display different degrees of deterioration in boiling heat transfer. The effect of pressure and concentration of nanoparticles revealed significant enhancement in heat flux and deterioration in pool boiling. The heat transfer coefficient of 0.5 g/l alumina-water nanofluid was compared with pure water and clearly indicates deterioration. At all pressures the heat transfer coefficients of the nanofluid were lower than those of pure water. Experimental observation revealed particles coating over the heater surface and subsequent SEM inspection of the heater surface showed nanoparticles coating on the surface forming a porous layer. To substantiate the nanoparticle deposition and its effect on heat flux, investigation was done by measuring the surface roughness of the heater surface before and after the experiment. While SEM images of the heater surface revealed nanoparticle deposition, surface roughness of the heater surface confirmed it. Based on the experimental investigations it can be concluded that an optimum thickness of nanoparticles coating favors an increase in heat flux. Higher surface temperature due to the presence of nanoparticles coating results in the deterioration of boiling heat transfer. © 2011 Wiley Periodicals, Inc.
Boiling induced nanoparticle coating and its effect on pool boiling heat transfer on a vertical cylindrical surface using CuO nanofluids
(2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
Experiments were performed to study boiling induced nanoparticle coating and its influence on pool boiling heat transfer using low concentrations of CuOnanofluid in distilled water at atmospheric pressure. To investigate the effect of the nanoparticle coated surface on pool boiling performance, two different concentrations of CuO nanofluids (0.1 and 0.5 g/l) were chosen and tests were conducted on a clean heater surface in nanofluid and nanoparticle coated surface in pure water. For the bare heater tested in CuO nanofluid, CHF was enhanced by 35.83 and 41.68 % respectively at 0.1 and 0.5 g/l concentration of nanofluid. For the nanoparticle coated heater surface obtained by boiling induced coating using 0.1 and 0.5 g/l concentration of nanofluid and tested in pure water, CHF was enhanced by 29.38 and 37.53 % respectively. Based on the experimental investigations it can be concluded that nanoparticle coating can also be a potential substitute for enhancing the heat transfer in pure water. Transient behaviour of nanofluid was studied by keeping heat flux constant at 1,000 and 1,500 kW/m2 for 90 min in 0.5 g/l concentration. The boiling curve shifted to the right indicating degradation in boiling heat transfer due to prolonged exposure of heater surface to nanofluid. Experimental outcome indicated that pool boiling performance of nanofluid could be a strong function of time and applied heat flux. The longer the duration of exposure of the heater surface, the higher will be the degradation in heat transfer. Springer-Verlag 2012.
Boiling induced nanoparticle coating and its effect on pool boiling heat transfer on a vertical cylindrical surface using CuO nanofluids
(2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
Experiments were performed to study boiling induced nanoparticle coating and its influence on pool boiling heat transfer using low concentrations of CuOnanofluid in distilled water at atmospheric pressure. To investigate the effect of the nanoparticle coated surface on pool boiling performance, two different concentrations of CuO nanofluids (0.1 and 0.5 g/l) were chosen and tests were conducted on a clean heater surface in nanofluid and nanoparticle coated surface in pure water. For the bare heater tested in CuO nanofluid, CHF was enhanced by 35.83 and 41.68 % respectively at 0.1 and 0.5 g/l concentration of nanofluid. For the nanoparticle coated heater surface obtained by boiling induced coating using 0.1 and 0.5 g/l concentration of nanofluid and tested in pure water, CHF was enhanced by 29.38 and 37.53 % respectively. Based on the experimental investigations it can be concluded that nanoparticle coating can also be a potential substitute for enhancing the heat transfer in pure water. Transient behaviour of nanofluid was studied by keeping heat flux constant at 1,000 and 1,500 kW/m2 for 90 min in 0.5 g/l concentration. The boiling curve shifted to the right indicating degradation in boiling heat transfer due to prolonged exposure of heater surface to nanofluid. Experimental outcome indicated that pool boiling performance of nanofluid could be a strong function of time and applied heat flux. The longer the duration of exposure of the heater surface, the higher will be the degradation in heat transfer. © Springer-Verlag 2012.
Critical heat flux enhancement in pool boiling using alumina nanofluids
(2010) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
The pool boiling characteristics of dilute dispersions of alumina nanoparticles in water were studied. Consistent with other nanofluid studies, it was found that a significant enhancement in critical heat flux (CHF) can be achieved at modest nanoparticle concentrations (<0.1% by volume). During experimentation and subsequent inspection, formation of a porous layer of nanoparticles on the heater surface occurred during nucleate boiling. This layer significantly changes surface texture of the heater wire surface which could be the reason for improvement in the CHF value. © 2010 Wiley Periodicals, Inc.
Design of Small-Scale Vertical Axis Wind Turbine with Passive Blade Pitch Control
(Springer Science and Business Media Deutschland GmbH, 2025) Guhan Sidharth, M.; Sathyabhama, A.; Hegde, R.N.
The increase in global energy demand fuelled by the increase in global population along with the need for sustainable and environment-friendly methods of electricity generation has shifted the focus to renewable sources of energy. One such form of energy is the wind energy. It is important to achieve the best possible performance from wind turbines to extract maximum amount of energy from the wind flow. This research work aims at designing a small-scale Vertical Axis Wind Turbine (VAWT) with suitable blade pitch control which would be useful in improving its performance. A three-bladed H-type Darrieus VAWT is considered with the NACA0021 airfoil as the blade cross-sectional profile. The pitch angle is made to vary sinusoidally with the position of the blade with respect to the direction of wind flow. The pitch angle amplitude used is 16Â°. A four-bar mechanism in the double crank configuration has been designed to implement collective blade pitching. Computer-aided design (CAD) models for various parts of the VAWT and the four-bar mechanism have been developed. The designs of these parts were found to be safe based on finite element analysis (FEA) carried out in ANSYS. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
Experimental studies on CHF enhancement in pool boiling with CuO-water nanofluid
(2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
Critical heat flux enhancement (CHF) in pool boiling with CuO nanofluids was experimentally studied using a 36 gauge NiCr wire at atmospheric pressure. Experimentation included (1) subjecting the wire surface to multiple heating cycles with constant volume concentration of CuO nanofluid and (2) subjecting the wire surface to a single heating cycle with different volume concentrations of CuO nanofluid. Boiling of nanofluid in both the cases resulted in nanoparticle deposition and subsequent smoothing of the wire surface. To substantiate the nanoparticle deposition and its effect on critical heat flux, investigation was done by studying the surface roughness and SEM images of the wire surface. The experimental results show the evidence of nanoparticle deposition on the wire surface and its effect on CHF enhancement. Springer-Verlag 2011.
Experimental studies on CHF enhancement in pool boiling with CuO-water nanofluid
(2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
Critical heat flux enhancement (CHF) in pool boiling with CuO nanofluids was experimentally studied using a 36 gauge NiCr wire at atmospheric pressure. Experimentation included (1) subjecting the wire surface to multiple heating cycles with constant volume concentration of CuO nanofluid and (2) subjecting the wire surface to a single heating cycle with different volume concentrations of CuO nanofluid. Boiling of nanofluid in both the cases resulted in nanoparticle deposition and subsequent smoothing of the wire surface. To substantiate the nanoparticle deposition and its effect on critical heat flux, investigation was done by studying the surface roughness and SEM images of the wire surface. The experimental results show the evidence of nanoparticle deposition on the wire surface and its effect on CHF enhancement. © Springer-Verlag 2011.
Experimental study on CuO nanoparticles in distilled water and its effect on heat transfer on a vertical surface
(2011) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
The pool boiling characteristics of dilute dispersions of CuO nanoparticles in water were studied at atmospheric pressure on a vertical heating surface. Experimental investigation of different weight concentrations of nanoparticles revealed significant enhancement in heat flux and deterioration in pool boiling. Out of many reasons, nanoparticles coating the heater surface was believed to be the reason behind this. Subsequent inspection of the heater surface showed nanoparticles coating the surface, forming a porous layer. To substantiate the nanoparticle deposition and its effect on heat flux, an investigation was performed by measuring the surface roughness of the heater surface before and after the experiment. While SEM images of the heater surface revealed nanoparticle deposition, measurement of surface roughness of the heater surface confirmed it. Formation of the porous layer on the heater surface as revealed by SEM images provided an excellent location for nucleation sites enhancing heat transfer. However, deterioration in nucleate boiling at different weight concentrations indicated some phenomenon is working behind this. 2011 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
Experimental study on CuO nanoparticles in distilled water and its effect on heat transfer on a vertical surface
(2011) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
The pool boiling characteristics of dilute dispersions of CuO nanoparticles in water were studied at atmospheric pressure on a vertical heating surface. Experimental investigation of different weight concentrations of nanoparticles revealed significant enhancement in heat flux and deterioration in pool boiling. Out of many reasons, nanoparticles coating the heater surface was believed to be the reason behind this. Subsequent inspection of the heater surface showed nanoparticles coating the surface, forming a porous layer. To substantiate the nanoparticle deposition and its effect on heat flux, an investigation was performed by measuring the surface roughness of the heater surface before and after the experiment. While SEM images of the heater surface revealed nanoparticle deposition, measurement of surface roughness of the heater surface confirmed it. Formation of the porous layer on the heater surface as revealed by SEM images provided an excellent location for nucleation sites enhancing heat transfer. However, deterioration in nucleate boiling at different weight concentrations indicated some phenomenon is working behind this. © 2011 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
Flow visualization and study of critical heat flux enhancement in pool boiling with Al2O3-water nanofluids
(Serbian Society of Heat Transfer Engineers, 2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
Pool boiling heat transfer characteristics of Al2O3 -water nanofluids is studied experimentally using a NiCr test wire of 36 standard wire guage diameter. The experimental work mainly concentrated on (1) change of critical heat flux with different volume concentrations of nanofluid and (2) flow visualization of pool boiling using a fixed concentration of nanofluid at different heat flux values. The experimental work revealed an increase in critical heat flux value of around 48% andflow visualization helped in studying the pool boiling behaviour of nanofluid.Out of the various reasons which could affect the critical heatflux enhancement, surface roughness plays a major role in pool boiling heat transfer.
Flow visualization, critical heat flux enhancement, and transient characteristics in pool boiling using nanofluids
(2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
This paper presents the experimental outcome of a study of the pool boiling heat transfer characteristics of alumina and CuO nanofluid in distilled water using a 0.19 mm diameter NiCr wire. A series of experiments were conducted in order to visualize the flow, critical heat flux (CHF) enhancement, and transient characteristics of nanofluid. The boiling phenomenon was visualized using a 0.1 g/l concentration of alumina nanofluid. The average bubble diameter was measured and was found to increase with increased heat flux. The average bubble contact angle decreased from 69 during the initial stages of boiling to 33 at CHF. Massive vapour bubbles were observed on the test heater surface near the CHF, inducing vapour blankets and forming hot/dry spots. The increase in the CHF could be well explained by the hot/dry spot theory. Pool boiling experiments conducted using low volume concentrations of CuO-water nanofluid at atmospheric pressure in distilled water showed an increase in the CHF by 30 % at a 0.3 g/l concentration. The transient behaviour of nanofluid, examined by exposing the heater surface at a constant heat flux of 700 kW/m 2, indicated CHF enhancement of 5.21 % to 6.77 % for the two time durations. Based on the experimental investigations, it was concluded that the CHF enhancement is due to nanoparticle coating, which changes the thickness of the surface as a function of time and surface wettability and corroborates the hot/dry spot theory. Copyright 2012 by ASTM International.
Flow visualization, critical heat flux enhancement, and transient characteristics in pool boiling using nanofluids
(2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
This paper presents the experimental outcome of a study of the pool boiling heat transfer characteristics of alumina and CuO nanofluid in distilled water using a 0.19 mm diameter NiCr wire. A series of experiments were conducted in order to visualize the flow, critical heat flux (CHF) enhancement, and transient characteristics of nanofluid. The boiling phenomenon was visualized using a 0.1 g/l concentration of alumina nanofluid. The average bubble diameter was measured and was found to increase with increased heat flux. The average bubble contact angle decreased from 69 during the initial stages of boiling to 33 at CHF. Massive vapour bubbles were observed on the test heater surface near the CHF, inducing vapour blankets and forming hot/dry spots. The increase in the CHF could be well explained by the hot/dry spot theory. Pool boiling experiments conducted using low volume concentrations of CuO-water nanofluid at atmospheric pressure in distilled water showed an increase in the CHF by 30 % at a 0.3 g/l concentration. The transient behaviour of nanofluid, examined by exposing the heater surface at a constant heat flux of 700 kW/m2, indicated CHF enhancement of 5.21 % to 6.77 % for the two time durations. Based on the experimental investigations, it was concluded that the CHF enhancement is due to nanoparticle coating, which changes the thickness of the surface as a function of time and surface wettability and corroborates the hot/dry spot theory. Copyright 2012 by ASTM International.
Flow visualization, critical heat flux enhancement, and transient characteristics in pool boiling using nanofluids
(ASTM International, 2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
This paper presents the experimental outcome of a study of the pool boiling heat transfer characteristics of alumina and CuO nanofluid in distilled water using a 0.19 mm diameter NiCr wire. A series of experiments were conducted in order to visualize the flow, critical heat flux (CHF) enhancement, and transient characteristics of nanofluid. The boiling phenomenon was visualized using a 0.1 g/l concentration of alumina nanofluid. The average bubble diameter was measured and was found to increase with increased heat flux. The average bubble contact angle decreased from 69° during the initial stages of boiling to 33° at CHF. Massive vapour bubbles were observed on the test heater surface near the CHF, inducing vapour blankets and forming hot/dry spots. The increase in the CHF could be well explained by the hot/dry spot theory. Pool boiling experiments conducted using low volume concentrations of CuO-water nanofluid at atmospheric pressure in distilled water showed an increase in the CHF by 30 % at a 0.3 g/l concentration. The transient behaviour of nanofluid, examined by exposing the heater surface at a constant heat flux of 700 kW/m2, indicated CHF enhancement of 5.21 % to 6.77 % for the two time durations. Based on the experimental investigations, it was concluded that the CHF enhancement is due to nanoparticle coating, which changes the thickness of the surface as a function of time and surface wettability and corroborates the hot/dry spot theory. Copyright © 2012 by ASTM International.
Flow visualization, critical heat flux enhancement, and transient characteristics in pool boiling using nanofluids
(2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
This paper presents the experimental outcome of a study of the pool boiling heat transfer characteristics of alumina and CuO nanofluid in distilled water using a 0.19 mm diameter NiCr wire. A series of experiments were conducted in order to visualize the flow, critical heat flux (CHF) enhancement, and transient characteristics of nanofluid. The boiling phenomenon was visualized using a 0.1 g/l concentration of alumina nanofluid. The average bubble diameter was measured and was found to increase with increased heat flux. The average bubble contact angle decreased from 69° during the initial stages of boiling to 33° at CHF. Massive vapour bubbles were observed on the test heater surface near the CHF, inducing vapour blankets and forming hot/dry spots. The increase in the CHF could be well explained by the hot/dry spot theory. Pool boiling experiments conducted using low volume concentrations of CuO-water nanofluid at atmospheric pressure in distilled water showed an increase in the CHF by 30 % at a 0.3 g/l concentration. The transient behaviour of nanofluid, examined by exposing the heater surface at a constant heat flux of 700 kW/m 2, indicated CHF enhancement of 5.21 % to 6.77 % for the two time durations. Based on the experimental investigations, it was concluded that the CHF enhancement is due to nanoparticle coating, which changes the thickness of the surface as a function of time and surface wettability and corroborates the hot/dry spot theory. Copyright © 2012 by ASTM International.
Investigations on boiling-induced nanoparticle coating, transient characteristics, and effect of pressure in pool boiling heat transfer on a cylindrical surface
(2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
Pool boiling experiments were conducted to study the heat transfer characteristics using low concentrations (0.0015 to 0.0077 vol%) of CuO nanofluids at and above atmospheric pressure in distilled water. The study included the following. (i) effect of pressure and concentration on heat transfer using CuO nanoparticles in distilled water, (ii) investigations on nanoparticle coating formed due to boiling-induced precipitation tested in CuO nanofluid and distilled water, and (iii) pool boiling behavior of CuO nanofluid subject to transient characteristics. The experimental outcome indicated that different concentrations of nanofluids display different degrees of deterioration in boiling heat transfer coefficients at and above atmospheric pressure. Boiling-induced precipitation of nanoparticles resulted in coating of nanoparticles. When tested in pure water, the nanoparticle-coated heater showed significant increase in critical heat flux compared with the critical heat flux of a bare heater tested in pure water. Study of the transient characteristics indicated degradation in boiling heat transfer due to prolonged exposure of the heater surface in nanofluid. Based on the experimental investigations, it can be concluded that nanoparticle coating can also be a potential substitute for enhancing the heat transfer if used in controlled quantities. 2012 Taylor & Francis Group, LLC.
Investigations on boiling-induced nanoparticle coating, transient characteristics, and effect of pressure in pool boiling heat transfer on a cylindrical surface
(2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
Pool boiling experiments were conducted to study the heat transfer characteristics using low concentrations (0.0015 to 0.0077 vol%) of CuO nanofluids at and above atmospheric pressure in distilled water. The study included the following. (i) effect of pressure and concentration on heat transfer using CuO nanoparticles in distilled water, (ii) investigations on nanoparticle coating formed due to boiling-induced precipitation tested in CuO nanofluid and distilled water, and (iii) pool boiling behavior of CuO nanofluid subject to transient characteristics. The experimental outcome indicated that different concentrations of nanofluids display different degrees of deterioration in boiling heat transfer coefficients at and above atmospheric pressure. Boiling-induced precipitation of nanoparticles resulted in coating of nanoparticles. When tested in pure water, the nanoparticle-coated heater showed significant increase in critical heat flux compared with the critical heat flux of a bare heater tested in pure water. Study of the transient characteristics indicated degradation in boiling heat transfer due to prolonged exposure of the heater surface in nanofluid. Based on the experimental investigations, it can be concluded that nanoparticle coating can also be a potential substitute for enhancing the heat transfer if used in controlled quantities. © 2012 Taylor & Francis Group, LLC.
Investigations on heat transfer enhancement in pool boiling with water-CuO nano-fluids
(2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
The main focus of the present work is to investigate Critical Heat Flux (CHF) enhancement using CuO nanofluid relative to CHF of pure water. To estimate the effect of nanoparticles on the CHF, pool boiling CHF values were measured for various volume concentrations of CuO nanofluid and compared with pure water. CHF enhancement of 130% was recorded at 0.2 % by volume of CuO nano-fluids. Surface roughness of the heater surface exposed to three measured heating cycles indicated surface modifications at different volume concentrations of nanofluid. SEM image of the heater surface revealed porous layer build up, which is thought to be the reason for CHF enhancement. Science Press and Institute of Engineering Thermophysics, CAS and Springer-Verlag Berlin Heidelberg 2012.