Fluorinert FC-72 Research Articles

The Optical Spectra of a-Si:H and a-SiC:H Thin Films Measured by the Absolute Photothermal Deflection Spectroscopy (PDS)

The new absolute PDS setup allows to measure simultaneously the absolute values of the optical transmittance T, reflectance R and absorptance A spectra in the spectral range 280 2000 nm with the typical spectral resolution 10 nm in ultraviolet and visible spectral range and 20 nm in the near infrared region. The PDS setup provides the dynamic detection range in the optical absorptance up to 4 orders of magnitude using non-toxic liquid perfluorohexane Fluorinert FC72. Here we demonstrate the usability of this setup on a series of intrinsic as well as doped a-Si:H and a-SiC:H thin films deposited on glass substrates by radio frequency (RF) plasma enhanced chemical vapor deposition (CVD) from hydrogen, silane and methane under various conditions. The increase of the Tauc gap with increasing carbon concentration in intrinsic a-SiC:H was observed. The defect-induced localized states in the energy gap were observed in doped a-Si:H as well as undoped a-SiC:H below the Urbach absorption edge.

Slippery Liquid-Infused Porous Surfaces Showing Marine Antibiofouling Properties

Marine biofouling is a longstanding problem because of the constant challenges placed by various fouling species and increasingly restricted environmental regulations for antifouling coatings. Novel nonbiocidal strategies to control biofouling will necessitate a multifunctional approach to coating design. Here we show that slippery liquid-infused porous surfaces (SLIPSs) provide another possible strategy to obtaining promising antifouling coatings. Microporous butyl methacrylate-ethylene dimethacrylate (BMA-EDMA) surfaces are prepared via UV-initiated free-radical polymerization. Subsequent infusion of fluorocarbon lubricants (Krytox103, Krytox100, and Fluorinert FC-70) into the porous microtexture results in liquid-repellent slippery surfaces. To study the interaction with marine fouling organisms, settlement of zoospores of the alga Ulva linza and cypris larvae of the barnacle Balanus amphitrite is tested in laboratory assays. BMA-EDMA surfaces infused with Krytox103 and Krytox100 exhibit remarkable inhibition of settlement (attachment) of both spores and cyprids to a level comparable to that of a poly(ethylene glycol) (PEG)-terminated self-assembled monolayer. In addition, the adhesion strength of sporelings (young plants) of U. linza is reduced for BMA-EDMA surfaces infused with Krytox103 and Krytox100 compared to pristine (noninfused) BMA-EDMA and BMA-EDMA infused with Fluorinert FC-70. Immersion tests suggest a correlation between the stability of slippery coatings in artificial seawater and fouling resistance efficacy. The results indicate great potential for the application of this concept in fouling-resistant marine coatings.

Vertical coalescence during nucleate boiling from a single artificial cavity

In this experimental study bubble growth from an isolated artificial cavity micro-fabricated on a 380μm thick silicon wafer was investigated. The horizontally oriented boiling surface was heated by a thin resistance heater integrated on the rear of the silicon test section. The temperature was measured using an integrated micro-sensor situated on the boiling surface with the artificial cavity located in its geometrical centre. To conduct saturated pool boiling experiments the test section was immersed in degassed fluorinert FC-72. Bubble nucleation, growth, detachment and the evaporative heat flux at different pressures were analysed using high-speed imaging and temperature micro-sensors. Vertical coalescence was initially observed at the boundary between the isolated bubble and interference regimes. For wall superheats outside the isolated bubble regime, the occurrence of vertical coalescence is decreasing with increasing pressure. Although vertical coalescence seems initially more frequent with increasing wall superheat, the explicit dependency on temperature is covered by the scattering nature of the data. The applied heat flux was compared to the evaporative heat flux, nominally based on an arbitrary chosen area of influence on the boiling substrate.

Dynamics and flow coupling in two-layer turbulent thermal convection

AbstractWe present an experimental investigation of the dynamics and flow coupling of convective turbulent flows in a cylindrical Rayleigh–Bénard convection (RBC) cell with two immiscible fluids, water and Fluorinert FC-77 electronic liquid (FC77). With the lighter water above FC77, the latter is under the condition of constant heat flux at its top and bottom boundaries. It is found that one large-scale circulation (LSC) roll exists in each of the fluid layers, and that their circulation planes have two preferred azimuthal orientations separated by ${\sim }\mathrm{\pi} $. A surprising finding of the study is that cessations/reversals of the LSC in FC77 of the two-layer system occur much more frequently than they do in single-layer turbulent RBC, and that a cessation is most likely to result in a flow reversal of the LSC, which is in sharp contrast with the uniform distribution of the orientational angular change of the LSC before and after cessations in single-layer turbulent RBC. This implies that the dynamics governing cessations and reversals in the two systems are very different. Two coupling modes, thermal coupling (the flow directions of the two LSCs are opposite to each other at the fluid–fluid interface) and viscous coupling (the flow directions of the two LSCs are the same at the fluid–fluid interface), are identified, with the former as the predominant mode. That most cessations (in the FC77 layer) end up as reversals can be understood as a symmetry breaking imposed by the orientation of the LSC in the water layer, which remains unchanged most of the time. Furthermore, the frequently occurring cessations and reversals are caused by the system switching between its two metastable states, i.e. thermal and viscous coupling modes. It is also observed that the strength of the LSC in water becomes weaker when the LSC in FC77 rotates faster azimuthally and that the flow strength in FC77 becomes stronger when the LSC in water rotates faster azimuthally, i.e. the influence of the LSC in one fluid layer on the other is not symmetric.

Linear instability analysis of thermocapillary convection in a bilayer system

The linear instability analysis of thermocapillary convection in a bilayer system consisting of silicon oil 10cS and fluorinert FC70 liquids was discussed in this paper. The bilayer system was bound below by a rigid plate and above by a free surface with a passive gas. The two immiscible liquids were separated by an interface. A constant horizontal temperature gradient was imposed along the interfaces. Two typical cases were studied: (i) streamwise homogeneous disturbances (the streamwise disturbance wave number α=0); (ii) spanwise homogeneous disturbances (the spanwise disturbance wave number β=0). When α=0, it was found that convection in the two layers may occur in the form of stationary mode or oscillatory mode. The oscillatory mode takes the form of traveling wave, which propagates in either spanwise direction. When β=0, convection in the two layers occurs in the form of oscillatory mode, which takes the form of traveling wave propagating in the same direction as base flow. The three dimensional analysis suggested that disturbance in the spanwise direction was the major cause of destabilization in the system. The influences of Biot number Bi and the depth ratio h on the unstable modes in the bilayer system were discussed.

Microfluidic Based Ka-Band Beam-Scanning Focal Plane Array

An eight-element 1-D Ka-band focal plane array (FPA) capable of beam scanning based on microfluidic principles is presented. The FPA is placed at the back surface of an 8-cm-diameter extended hemispherical Rexolite ( $\varepsilon_{\rm r}=2.56$ , $\tan\delta=0.0026$ ) lens and consists of interconnected microfluidic reservoirs and channels constructed by bonding polydimethylsiloxane (PDMS) ( $\varepsilon_{\rm r}=2.8$ , $\tan\delta=0.02$ ) and liquid crystal polymer (LCP) ( $\varepsilon_{\rm r}=2.9$ , $\tan\delta=0.0025$ ) substrates. The antenna element of the array is a small volume (2.5 $\mu$ L) of liquid metal residing inside a low-loss Fluorinert FC-77 ( $\varepsilon_{\rm r}=1.9$ , $\tan\delta=0.0005$ ) solution. The array beam is scanned by moving the liquid-metal antenna among the reservoirs using an external pump. The proximity-coupled feed network of the array is passive and designed strategically to accommodate the position variation of the liquid-metal antenna element. The array operates with measured $7^{\circ}$ half-power beamwidth (HPBW), $>$ 21 dB realized gain, and 3.3% $\vert{ S}_{11}\vert dB bandwidth and provides $\pm 30^{\circ}$ beam-scanning range. The presented microfluidic-based beam-scanning technique operates without resorting to RF switches. Consequently, it is promising for high-power handling and low-cost realization of millimeter-wave high-gain beam-scanning antenna arrays.

Pool boiling on surfaces with mini-fins and micro-cavities

The experimental studies presented here focused on pool boiling heat transfer on mini-fin arrays, mini-fins with perforated covering and surfaces with micro-cavities. The experiments were carried out for water and fluorinert FC-72 at atmospheric pressure. Mini-fins of 0.5 and 1 mm in height were uniformly spaced on the base surface. The copper foil with holes of 0.1 mm in diameter (pitch 0.2/0.4 mm), sintered with the fin tips, formed a system of connected perpendicular and horizontal tunnels. The micro-cavities were obtained through spark erosion. The maximal depth of the craters of these cavities was 15 – 30 μm and depended on the parameters of the branding-pen settings. At medium and small heat fluxes, structures with mini-fins showed the best boiling heat transfer performance both for water and FC-72. At medium and high heat fluxes (above 70 kW/m2 for water and 25 kW/m2 for FC-72), surfaces with mini-fins without porous covering and micro-cavities produced the highest heat transfer coefficients. The surfaces obtained with spark erosion require a proper selection of geometrical parameters for particular liquids – smaller diameters of cavities are suitable for liquids with lower surface tension (FC-72).

Nucleation site interaction between artificial cavities during nucleate pool boiling on silicon with integrated micro-heater and temperature micro-sensors

Nucleate boiling is commonly characterised as a very complex and elusive process. Many involved mechanisms are still not fully understood and more detailed consideration is needed. In this study, bubble growth from micro-fabricated artificial cavities with varied spacing on a horizontal 380μm thick silicon wafer was investigated. The horizontally oriented boiling surface was heated by a thin resistance heater integrated on the rear of the silicon test section. The temperature was measured using 16 integrated micro-sensors situated on the boiling surface, each with an artificial cavity located in its geometrical centre. Experiments with three different spacings 1.5, 1.2 and 0.84mm in between cavities with a nominal mouth diameter of 10μm and a depth of 80μm were undertaken. To conduct pool boiling experiments, the test section was mounted inside a closed stainless steel boiling chamber with optical access and completely immersed in degassed fluorinert FC-72. Bubble nucleation, growth and detachment at 0.5 and 1bar absolute pressure were investigated using high-speed imaging. The effect of decreasing inter-site distance on bubble nucleation frequency, bubble departure frequency and diameter with increasing wall superheat is presented. Furthermore, the frequency of horizontal bubble coalescence was determined. The regions of influence on the measured frequencies and bubble departure diameter were compared with recently published findings.

Pool boiling heat transfer on vertical fins with wire mesh structures

Experimental investigations into pool boiling heat transfer on finned arrays with internal tunnels limited by copper wire mesh were conducted. The experiments were carried out for water, ethanol and fluorinert FC-72 at atmospheric pressure. The wire net with mesh aperture of 0.3 and 0.5 mm, sintered with the vertical side of the 10 mm high rectangular fins and horizontal inter-fin surface formed a system of connected tunnels. Tunnel width was 0.6 and 1.0 mm. Substantial enhancement of heat transfer coefficient was observed for the investigated surfaces. In water, ethanol and FC-72 boiling the highest increase in the heat transfer coefficient was obtained for the surface with mesh aperture of 0.5 mm and tunnel width of 0.6 mm. The ratio of boiling heat transfer coefficients for the investigated fins with mesh covering and smooth fins (10 mm height), at the heat flux 100 kW/m 2 , was about 3 for water and ethanol as working fluids. NOMENCLATURE a - mesh aperture (opening size), mm h - height (depth), mm, N,NTS - narrow tunnel structure, p - pitch, mm, q - heat flux, kW/m 2 , s - width of space between fins, mm, w - width, mm,

Flow boiling heat transfer of refrigerant FC-72 in microchannels

The design of technological devices and systems, with reduced size but unchanged or increased performances, has been one of the most important scientific challenges faced in the last decade by many fields of the world industry. The capability to remove and exchange heat in more compact components has allowed great advantages in the optimization of all final products as well as in industrial processes. However the never-ending race to miniaturization of appliances has been taking into account problems concerning computational models and design criteria developed in the past for macro-systems. Nowadays most of these methods are no longer reliable for emerging micro-systems because of the substantial differences in transport phenomena and heat exchange, mainly in two-phase flow (scaling effects). This paper aims to provide its contribution to the burgeoning research activity on boiling heat transfer under forced convection in microchannels. The BO.E.MI.A. experimental facility was designed and specifically developed to perform different regimes heat transfer tests on mini and microchannels: a total of 150 tests were performed using a fluorinert fluid FC-72 as coolant. The test section consists of a horizontal 1 mm inner diameter stainless steel tube having a heated length (Joule effect) of approximately 60 mm. The mass flux range is between 1000 and 2000 kg m −2 s −1 while the applied heat flux is between 10 and 150 kW m −2. By means of a preheater we are able to change coolant inlet temperature and by setting the operating pressure in a range between 3 and 7 bar, a broad spectrum of subcooling degree at inlet test section is achieved. The local heat transfer coefficients were evaluated for both subcooled and saturated flow boiling regimes. The experimental data show an increase of local heat transfer coefficient for increasing values of heat flux, with a weak dependence on the vapour quality. The experimental values obtained were compared with those from the adoption of one of the main heat transfer correlations in the literature.

Flow regime-based modeling of heat transfer and pressure drop in microchannel flow boiling

Local heat transfer coefficients and pressure drops during boiling of the dielectric liquid fluorinert FC-77 in parallel microchannels were experimentally investigated in recent work by the authors. Detailed visualizations of the corresponding two-phase flow regimes were performed as a function of a wide range of operational and geometric parameters. A new transition criterion was developed for the delineation of a regime where microscale effects become important to the boiling process and a conventional, macroscale treatment becomes inadequate. A comprehensive flow regime map was developed for a wide range of channel dimensions and experimental conditions, and consisted of four distinct regions – bubbly, slug, confined annular, and alternating churn/annular/wispy-annular flow regimes. In the present work, physics-based analyses of local heat transfer in each of the four regimes of the comprehensive map are formulated. Flow regime-based models for prediction of heat transfer coefficient in slug flow and annular/wispy-annular flow are developed and compared to the experimental data. Also, a regime-based prediction of pressure drop in microchannels is presented by computing the pressure drop during each flow regime that occurs along the microchannel length. The results of this study reveal the promise of flow regime-based modeling efforts for predicting heat transfer and pressure drop in microchannel boiling.

Cooling the Electronic Brain

This article discusses findings of some immersion cooling studies carried out to define the potential of direct liquid cooling of three-dimensional chip stacks. Four possible immersion cooling strategies were assessed. These included two active cooling strategies and two passive cooling strategies. The cooling densities for all four immersion cooling techniques were determined assuming the use of Fluorinert FC-72, a commonly used perfluorinated dielectric liquid. For passive systems, the cooling densities ranged from 25 W/cm3 for natural convection to 200–400 W/cm3 for pool boiling. For active technologies, the densities were 100–300 W/cm3 for forced convection and more than 2000 W/cm3 for flow boiling. It was found that the optimum die spacings for both single- and two-phase direct cooling was in the range of 0.2–0.6 mm for typical microelectronics geometries, though substantial cooling densities could be achieved at less-than-optimum spacings.

Properties and Transport Behavior of Perfluorotripentylamine (FC-70)-Doped Amorphous Teflon AF 2400 Films

Teflon AF 2400 films are known to imbibe solvents, making films in the presence of solvents less fluorous than they might otherwise be. Herein, we demonstrate that doping films with perfluorotripentylamine (Fluorinert FC-70) maintains the fluorous nature of Teflon AF 2400 and improves transport selectivity for fluorine-containing organic compounds. Density measurements on the FC-70-doped films reveal that free volume decreases dramatically as the dopant concentration increases (0-12 wt %) and then increases to approach that of pure FC-70. Remarkably, films from 0 to 12 wt % FC-70 have the same w/v concentration of Teflon AF 2400, indicating that FC-70 fills the free volume of Teflon AF 2400. This is consistent with the observed increased storage modulus and significant decrease (compared to undoped films) of solute diffusion coefficients in the same range of FC-70 concentrations. In contrast, FC-70 at concentrations greater than 12 wt % dilutes Teflon AF 2400, leading to a decrease of storage modulus and dramatic increase in solute diffusion coefficients. Sorption of chloroform decreases from 11.8 g of chloroform/100 g of film (pure Teflon film) to 3.8 g of chloroform/100 g of film (27 wt % FC-70-doped Teflon film), less than the solubility of chloroform in pure FC-70 (4.06 g of chloroform/100 g of FC-70). Solute partition coefficients from chloroform to FC-70-doped films generally decrease with increased dopant concentration. However, within a series of toluenes and nitrobenzenes, selectivity for F-containing solutes over analogous H-containing solutes increases as dopant concentration increases if the substitution is on the aromatic ring but not if it is on the methyl group (toluene). Transport (partitioning × diffusion) rates, as they involve both thermodynamic and kinetic factors, are not simply related to composition.

Appropriate pressure-transmitting media for cryogenic experiment in the diamond anvil cell up to 10 GPa

We evaluated the qualities of pressure-transmitting media by the ruby fluorescence method at room temperature, 77 and 4.2 K in the diamond anvil cell (DAC) up to 10 GPa in order to find appropriate media for the low temperature experiment. Investigations were done on fourteen kinds of media: a 1:1 mixture by volume of Fluorinert FC-70 and FC-77, Daphne 7373 and 7474, NaCl, silicon oil (polydimethylsiloxane), vaselin, 2-propanol, glycerin, a 1:1 mixture by volume of n-pentane and isopentane, a 4:1 mixture by volume of methanol and ethanol, petroleum ether, nitrogen, argon and helium. We discuss the non-hydrostatic effects of the pressure in the media from the broadening effect of the ruby R1 fluorescence line. At the low temperature region, the non-hydrostatic effects develop continuously with increasing pressure from the low-pressure region in the all media. We reveal the relative strengths of the non-hydrostatic effects appeared in the media at 77K.

Evaluations of pressure-transmitting media for cryogenic experiments with diamond anvil cell

The fourteen kinds of pressure-transmitting media were evaluated by the ruby fluorescence method at room temperature, 77 K using the diamond anvil cell (DAC) up to 10 GPa in order to find appropriate media for use in low temperature physics. The investigated media are a 1:1 mixture by volume of Fluorinert FC-70 and FC-77, Daphne 7373 and 7474, NaCl, silicon oil (polydimethylsiloxane), Vaseline, 2-propanol, glycerin, a 1:1 mixture by volume of n-pentane and isopentane, a 4:1 mixture by volume of methanol and ethanol, petroleum ether, nitrogen, argon, and helium. The nonhydrostaticity of the pressure is discussed from the viewpoint of the broadening effect of the ruby R(1) fluorescence line. The R(1) line basically broadens above the liquid-solid transition pressure at room temperature. However, the nonhydrostatic effects do constantly develop in all the media from the low-pressure region at low temperature. The relative strength of the nonhydrostatic effects in the media at the low temperature region is discussed. The broadening effect of the ruby R(1) line in the nitrogen, argon, and helium media are significantly small at 77 K, suggesting that the media are more appropriate for cryogenic experiments under high pressure up to 10 GPa with the DAC. The availability of the three media was also confirmed at 4.2 K.

The critical role of channel cross-sectional area in microchannel flow boiling heat transfer

Experiments are conducted with a perfluorinated dielectric fluid, Fluorinert FC-77, to identify the critical geometric parameters that affect flow boiling heat transfer and flow patterns in microchannels. In recent work by the authors (Harirchian and Garimella, 2009), seven different silicon test pieces containing parallel microchannels of widths ranging from 100 to 5850 μm, all with a depth of 400 μm were tested and it was shown that for a fixed channel depth, the heat transfer coefficient was independent of channel width for microchannels of widths 400 μm and larger, with the flow regimes in these microchannels being similar; nucleate boiling was also found to be dominant over a wide range of heat fluxes. In the present study, experiments are performed with five additional microchannel test pieces with channel depths of 100 and 250 μm and widths ranging from 100 to 1000 μm. Flow visualizations are performed using a high-speed digital video camera to determine the flow regimes, with simultaneous local measurements of the heat transfer coefficient and pressure drop. The aim of the present study is to investigate as independent parameters the channel width and depth as well as the aspect ratio and cross-sectional area on boiling heat transfer in microchannels, based on an expanded database of experimental results. The flow visualizations and heat transfer results show that the channel cross-sectional area is the important governing parameter determining boiling mechanisms and heat transfer in microchannels. For channels with cross-sectional area exceeding a specific value, nucleate boiling is the dominant mechanism and the boiling heat transfer coefficient is independent of channel dimensions; below this threshold value of cross-sectional area, vapor confinement is observed in all channels at all heat fluxes, and the heat transfer rate increases as the microchannel cross-sectional area decreases before premature dryout occurs due to channel confinement.

Experimental pool boiling investigations of FC-72 on silicon with artificial cavities and integrated temperature microsensors

In this experimental study, fluorinert FC-72 is boiled on a silicon chip with artificial cavities and integrated microsensors. The horizontal silicon chip with dimensions of 39.5 × 19 × 0.38 mm is completely immersed in FC-72. The integrated nickel–titanium temperature microsensors on the back of the chip are calibrated individually and exhibit a near-linear increase of electrical resistance with temperature. The applied heat fluxes and the resulting wall superheat at the boiling surface are varied by means of an integral thin-film resistance heater (95% Al, 4% Cu and 1% Si), also on the back of the silicon chip. Artificial cylindrical cavities with a mouth diameter of 10 μm and depths of 40, 80 or 100 μm situated above the microthermometers serve as artificial nucleation sites, due to trapped vapour. Bubble growth rates, frequencies, departure diameters of bubbles and waiting times between bubbles from an isolated cavity for different wall superheats and pressures were obtained by analysing high-speed video images and the simultaneously measured temperature below the artificial cavity.

Effects of channel dimension, heat flux, and mass flux on flow boiling regimes in microchannels

Experiments are conducted with a perfluorinated dielectric fluid, Fluorinert FC-77, to investigate the effects of channel size and mass flux (225–1420 kg/m 2s) on microchannel flow boiling regimes by means of high-speed photography. Seven different silicon test pieces with parallel microchannels of widths ranging from 100 to 5850 μm, all with a depth of 400 μm, are considered. Flow visualizations are performed with a high-speed digital video camera while local measurements of the heat transfer coefficient are simultaneously obtained. The visualizations and the heat transfer data show that flow regimes in the microchannels of width 400 μm and larger are similar, with nucleate boiling being dominant in these channels over a wide range of heat flux. In contrast, flow regimes in the smaller microchannels are different and bubble nucleation at the walls is suppressed at a relatively low heat flux for these sizes. Two types of flow regime maps are developed and the effects of channel width on the flow regime transitions are discussed.

A technique for precise electrical-transport measurements under pressure above 10 GPa

We report a technique for the precise measurement of electrical resistivity at high pressures up to 15 GPa by using Bridgman anvils. The relatively large size of the pressure chamber (1.0 mm in diameter) allows the use of large specimens and simple experimental procedures rather than using a standard diamond anvil cell. A SUS310 gasket is pressed by two tungsten carbide anvils. A sample with typical dimensions of approximately 0.5×0.2×0.1mm3 is placed in a small hole of the gasket. In order to obtain a quasi-hydrostatic pressure, the pressure chamber is filled with a 1:1 mixture of Fluorinert FC70 and FC77 as the pressure transmitting medium. Electrical leads are introduced through shallow grooves milled into the anvil. The grooves are filled with a mixture of alumina powder for insulation. Accurate data of the resistance values of Bi and Fe at room temperature are available. We observe sharp transitions for Bi at 2.55, 2.7 and 7.7 GPa. The electrical resistance of Fe shows a sudden increase due to a structural transition near 14 GPa.

Microchannel size effects on local flow boiling heat transfer to a dielectric fluid

Heat transfer with liquid–vapor phase change in microchannels can support very high heat fluxes for use in applications such as the thermal management of high-performance electronics. However, the effects of channel cross-sectional dimensions on the two-phase heat transfer coefficient and pressure drop have not been investigated extensively. In the present work, experiments are conducted to investigate the local flow boiling heat transfer of a dielectric fluid, Fluorinert FC-77, in microchannel heat sinks. Experiments are performed for mass fluxes ranging from 250 to 1600kg/m2s. Seven different test pieces made from silicon and consisting of parallel microchannels with nominal widths ranging from 100 to 5850μm, all with a nominal depth of 400μm, are considered. An array of temperature sensors on the substrate allows for resolution of local temperatures and heat transfer coefficients. The results of this study show that for microchannels of width 400μm and greater, the heat transfer coefficients corresponding to a fixed wall heat flux as well as the boiling curves are independent of channel size. Also, heat transfer coefficients and boiling curves are independent of mass flux in the nucleate boiling region for a fixed channel size, but are affected by mass flux as convective boiling dominates. A strong dependence of pressure drop on both channel size and mass flux is observed. The experimental results are compared to predictions from a number of existing correlations for both pool boiling and flow boiling heat transfer.