Transfer Instability Research Articles

Experimental investigation of the flow and heat transfer instabilities in n-decane at supercritical pressures in a vertical tube

The fuel may be used in hypersonic vehicles to cool various surfaces; however, supercritical pressure fuels have been found to have deteriorated heat transfer rates and instabilities for some flow conditions. The flow and heat transfer instabilities in supercritical pressure n-decane were investigated experimentally in this work, with pressure of 2.5 and 3.0 MPa and inlet temperature of 16–225 °C. The heat flux was slowly increased to observe the flow in different stages as well as to obtain the boundary lines for a stability map. Seven stages were observed with different stability features. The transition to turbulence was found to be the main reason for the instability for stage b with slightly irregular oscillations, while dramatic variations of the thermal properties caused Helmholtz oscillations with regular frequencies and large amplitudes. The heat transfer deterioration in conjunction with an instability with buoyancy due to the density variation was found to be the reason. Higher pressures, inlet mass flow rates or fluid temperatures or downward flow weakened the instabilities, so these should be used in engineering designs to reduce the heat transfer deterioration and instability. The stability map provides further support for the nonlinear dynamic theory explaining the oscillations.

Evolution of Angular Momentum and Orbital Period Changes in Close Double White Dwarf Binaries

We have presented the evolution of angular momentum and orbital period changes between the component spins and the orbit in close double white dwarf binaries undergoing mass transfer through direct impact accretion over a broad range of orbital parameter space. This work improves upon similar earlier studies in a number of ways: First, we calculate self-consistently the angular momentum of the orbit at all times. This includes gravitational, tides and mass transfer effects in the orbital evolution of the component structure models, and allow the Roche lobe radius of the donor star and the rotational angular velocities of both components to vary, and account for the exchange of angular momentum between the spins of the white dwarfs and the orbit. Second, we investigate the mass transfer by modeling the ballistic motion of a point mass ejected from the center of the donor star through the inner Lagrangian point. Finally, we ensure that the angular momentum is conserved, which requires the donor star spin to vary self-consistently. With these improvements, we calculate the angular momentum and orbital period changes of the orbit and each binary component across the entire parameter space of direct impact double white dwarf binary systems. We find a significant decrease in the amount of angular momentum removed from the orbit during mass transfer, as well as cases where this process increases the angular momentum and orbital period of the orbit at the expense of the spin angular momentum of the donor and accretor. We find that our analysis yields an increase in the predicted number of stable systems compared to that in the previous studies, survive the onset of mass transfer, even if this mass transfer is initially unstable. In addition, as a consequence of the tidal coupling, systems that come into contact near the mass transfer instability boundary undergo a phase of mass transfer with their orbital period.

Effects of heat flux, mass flux and channel width on flow boiling performance of porous interconnected microchannel nets

This study presents an experimental investigation of flow boiling heat transfer performance in porous interconnected microchannel nets (PIMNs) as an effective cooling solution for microelectronic devices. Three PIMNs with different microchannel widths, i.e., 0.25, 0.4 and 0.55 mm, were fabricated via copper powder sintering and wire electric discharge machining. The effects of heat flux, mass flux and channel width on flow boiling characteristics, i.e., two-phase heat transfer, pressure drops and two-phase flow instabilities were evaluated for the optimization design. Flow boiling experiments were conducted using deionized water as the coolant with variation in the heat flux and mass flux of 200–500 kg m−2 s−1 under an inlet subcooling of 40 K. The high speed visualization showed the flow pattern transition from bubbly flow to annular flow was accompanied with the change of boiling heat transfer mechanisms. Both the heat flux and the mass flux have significant effect on the two-phase heat transfer performance of the PIMNs. The PIMN-2 with the medium channel width of 0.4 mm presented the highest heat transfer coefficients and best capability to mitigate the severe two-phase flow instability, as well as the favorable pressure drop penalty, which achieved the best overall flow boiling performance in this study.

Instability of the IncFII-Type Plasmid Carrying blaNDM-5 in a Klebsiella pneumoniae Isolate.

In this study, we characterized the blaNDM-5-bearing plasmid in a Klebsiella pneumoniae isolate that had lost the plasmid during serial passage. We determined the complete sequences of the plasmid pCC1410-2, which was extracted from a K. pneumoniae ST709 isolate collected at a Korean hospital from which two NDM-5-producing K. pneumoniae isolates were subsequently isolated. As a result, the pCC1410-2 plasmid had a backbone structure that was similar to those of two plasmids previously reported from the same hospital, but lacked some antibiotic resistance genes (blaTEM-1, rmtB, mphR(A), mrx(A), and mph(A)). A 9-bp repeating unit encoding three amino acids (Gln-Gln-Pro) was inserted in TraD in pCC1410-2. Thus, the pCC1410-2 plasmid might be transferred from the previously identified carbapenem-resistant K. pneumoniae, but some delections and inversions might have occurred during the process. We compared the transfer frequency and stability of the plasmids. The relative frequency of conjugative transfer and stability in the host were significantly lower in pCC1410-2 than in previously reported blaNDM-5-bearing plasmids in Korea. A low transfer frequency and instability in the host may cause underestimation of carbapenemase-producing Enterobacteriaceae in the clinical setting and in surveillance studies.

Spectral and photometric behavior of SU UMa during quiescence and outburst states

We report the results of spectral and photometric observations of SU UMa. Available spectra from International Ultraviolet Explorer (IUE) and CCD photometry of five nights were used. Some profiles revealing the variations of some spectral lines at different times are presented. There is variation with time for photometric observations and the brightness of SU UMa is changed from 12.9 mag. to 15.6 mag in 5 nights with clear display of burst. The ultraviolet luminosity for emitting region is in the range of (6.9*1030erg s−1). The mass accretion rate is in the range of (9.8*10−13M⊙yr−1). The line flux modulations at different times can be explained in terms of the mass transfer instability model (Bath 1973).

Fluid flow and heat transfer characteristics of separation and reattachment flow over a backward-facing step

In this study, a direct numerical simulation of the fluid flow and heat transfer characteristics of separation and reattachment flow at a backward-facing step is presented. A computer program of FORTRAN code is used to solve the governing equations according to finite volume method. The effects of the Reynolds number and expansion ratio on the fluid flow and heat transfer characteristics are investigated. The size of the primary recirculation zone increases with the reduction of expansion ratio and the fluctuation of isotherms increased with the increase of Reynolds number. The periodic characteristics and the dissimilarity between Nu and Cf appear in the transitional flow regime. The rotating fluids in the reattachment region increase the flow instability and the interchange of the hot and cold fluids increases heat transfer instability. The combined effects of flow instability and heat transfer instability play an important role in the formation of the dissimilarity between Nu and Cf.

Effects of structural parameter on flow boiling performance of interconnected microchannel net

Developed thermal management solutions for microelectronic fields have got extensive attentions these years. In this study, an interconnected microchannel net (IMN) was developed via micro wire electrical discharge machining process to explore the feasibility of flow boiling heat transfer enhancement. The experiments for the IMNs with different structural parameters were conducted using deionized water as the coolant with variation in the heat flux and under an inlet subcooling of 40°C and constant mass flow rate of 180kgm−2s−1. Four IMN samples with different channel width, i.e., 0.25, 0.4, 0.55 and 0.7mm, were investigated to study the effects of channel size and heat flux on flow boiling characteristics, i.e., two-phase heat transfer, pressure drops and two-phase flow instabilities, were proceeded in order to optimize the structural design of the IMN. Test results indicate that the sample IMN-2 with the channel width of 0.4mm manifests the overall best flow boiling performance, which exhibits more favorable two-phase heat transfer and pressure drop characteristics, as well as the prominent superiority for the mitigation of two-phase instability. This reveals a highlight for the potential application in the flow boiling enhancement of microchannel heat transfer.

Charge transfer instability in a mixed Ir/Rh honeycomb lattice in Li2Ir1−xRhxO3 solid solution

The solid solution series Li2Ir1-xRhxO3 is synthesized for several values of x between 0 and 1. The compounds possess a monoclinic layered structure (space group C2/m) throughout the solid solution range with the lattice constants following Vegard's relationship. Magnetization and resistivity data below room temperature are presented. The effective magnetic moment (μeff) is reduced below the value obtained by interpolating between the end-members, presumably due to nearest neighbor charge exchange leading to non-magnetic Ir5+/Rh3+ pairs. Surprisingly, the degree of reduction of μeff cannot be explained by a random mixture of Ir and Rh and, in particular, is strongly asymmetric around x = 0.5. This anomalous moment reduction possibly results from the difference in on-site Coulomb repulsion between Ir and Rh ions.

Investigation of Ester- and Amide-Linker-Based Porous Organic Polymers for Carbon Dioxide Capture and Separation at Wide Temperatures and Pressures.

Organic compounds, such as covalent organic framework, metal-organic frameworks, and covalent organic polymers have been under investigation to replace the well-known amine-based solvent sorption technology of CO2 and introduce the most efficient and economical material for CO2 capture and storage. Various organic polymers having different function groups have been under investigation both for low and high pressure CO2 capture. However, search for a promising material to overcome the issues of lower selectivity, less capturing capacity, lower mass transfer coefficient and instability in materials performance at high pressure and various temperatures is still ongoing process. Herein, we report synthesis of six covalent organic polymers (COPs) and their CO2, N2, and CH4 adsorption performances at low and high pressures up to 200 bar. All the presented COPs materials were characterized by using elemental analysis method, Fourier transform infrared spectroscopy (FTIR) and solid state nuclear magnetic resonance (NMR) spectroscopy techniques. Physical properties of the materials such as surface areas, pore volume and pore size were determined through BET analysis at 77 K. All the materials were tested for CO2, CH4, and N2 adsorption using state of the art equipment, magnetic suspension balance (MSB). Results indicated that, amide based material i.e. COP-33 has the largest pore volume of 0.2 cm(2)/g which can capture up to the maximum of 1.44 mmol/g CO2 at room temperature and at pressure of 10 bar. However, at higher pressure of 200 bar and 308 K ester-based compound, that is, COP-35 adsorb as large as 144 mmol/g, which is the largest gas capturing capacity of any COPs material obtained so far. Importantly, single gas measurement based selectivity of COP-33 was comparatively better than all other COPs materials at all condition. Nevertheless, overall performance of COP-35 rate of adsorption and heat of adsorption has indicated that this material can be considered for further exploration as efficient and cheaply available solid sorbent material for CO2 capture and separation.

Experimental investigation on the characteristics of thermo-acoustic instability in hydrocarbon fuel at supercritical pressures

In the investigation of forced-convection heat transfer in a small-scale channel, the phenomenon of thermo-acoustic instability was observed in hydrocarbon fuel (RP-3) at supercritical pressures. The heat transfer was obviously enhanced when thermo-acoustic instability occurred. To understand the relationship between the enhancement on heat transfer and thermo-acoustic instability, the characteristics of thermo-acoustic instability were firstly investigated. The pressure drop fluctuations were used to represent the characteristics of thermo-acoustic instability. And two pivotal characteristics of thermo-acoustic instability are amplitude and duration. The characteristics could be affected by three operating parameters: fuel mass flow rate, channel inlet temperature and channel operating pressure. A series of experiments were designed to study the effect of these three parameters on the characteristics. It is found that the amplitude increases with increasing mass flow rate, while the duration reaches the maximum value when mass flow rate is a certain value; the effects of operating pressure on the characteristics of thermo-acoustic instability are strongly interactive with the threshold power. And an increase in operating pressure causes the amplitude and duration to decrease since the variation trends of thermal physical properties become smooth; an increase in inlet temperature causes the amplitude and duration to decrease and increase, respectively, when operating pressure is below 3.0MPa. And the duration change indistinctively with increasing inlet temperature when operating pressure exceeds 3.5MPa.

Simultaneously precise frequency transfer and time synchronization using feed-forward compensation technique via 120 km fiber link.

Precision time synchronization between two remote sites is desired in many applications such as global positioning satellite systems, long-baseline interferometry, coherent radar detection and fundamental physics constant measurements. The recently developed frequency dissemination technologies based on optical fiber link have improved the transfer instability to the level of 10−19/day at remote location. Therefore it is possible to keep clock oscillation at remote locations continuously corrected, or to reproduce a “virtual” clock on the remote location. However the initial alignment and the correction of 1 pps timing signal from time to time are still required, besides the highly stabilized clock frequency transfer between distant locations. Here we demonstrate a time synchronization based on an ultra-stable frequency transfer system via 120-km commercial fiber link by transferring an optical frequency comb. Both the phase noise compensation in frequency dissemination and temporal basis alignment in time synchronization were implemented by a feed-forward digital compensation (FFDC) technique. The fractional frequency instability was measured to be 6.18 × 10−20 at 2000 s. The timing deviation of time synchronization was measured to be 0.6 ps in 1500 s. This technique also can be applied in multi-node fiber network topology.

Effect of solute transfer and interfacial instabilities on scalar and velocity field around a drop rising in quiescent liquid channel

Physics of development of flow structures around the drop rising with solute transfer is highly influenced by the interfacial behaviour and is remarkably different than a particle rising under the same conditions. We report on the use of simultaneous particle image velocimetry-planar laser induced fluorescence technique to measure scalar and velocity fields around a drop rising in a quiescent liquid channel. The selected continuous phase is glycerol, and the drop consists of a mixture of toluene, acetone, and a dye rhodamine-6G, with acetone working as a interfacial tension depressant. The drop lies in the spherical region with Eötvös number, Eo = 1.95, Morton number, M = 78.20 and the particle Reynolds number being, Rep = 0.053. With Rep approaching that of creeping flow, we analyse the effect of interfacial instabilities solely, contrary to other investigations [M. Wegener et al., “Impact of Marangoni instabilities on the fluid dynamic behaviour of organic droplets,” Int. J. Heat Mass Transfer 52, 2543-2551 (2009); S. Burghoff and E. Y. Kenig, “A CFD model for mass transfer and interfacial phenomena on single droplets,” AIChE J. 52, 4071-4078 (2006); J. Wang et al., “Numerical simulation of the Marangoni effect on transient mass transfer from single moving deformable drops,” AIChE J. 57, 2670-2683 (2011); R. F. Engberg, M. Wegener, and E. Y. Kenig, “The impact of Marangoni convection on fluid dynamics and mass transfer at deformable single rising droplets—A numerical study,” Chem. Eng. Sci. 116, 208-222 (2014)] which account for turbulence as well as interfacial instabilities with Rep in the turbulent range. The velocity and concentration fields obtained are subjected to scale-wise energy decomposition using continuous wavelet transform. Scale-wise probability distribution functions of wavelet coefficients are calculated to check intermittent non-Gaussian behaviour for simultaneous velocity and scalar statistics. Multi-fractal singularity spectra for scalar and velocity fields are calculated using wavelet transform modulus maxima methodology to analyse the distribution of non-Gaussian flow structures and their effect on scalar transport. Further, Fourier spectra based on velocity and concentration are also reported. We found that vorticity and concentration fields became progressively non-Gaussian, as one moved from large scales to small scales. This turbulence like behaviour is attributed to interfacial instabilities developed because of the non-uniform shear at the interface. The multi-fractal singularity spectra had their Hurst exponent H > 0.5, which showed high correlation in the hierarchy of the flow structures. A strong correlation between concentration and velocity multi-fractal spectra was also seen.

Parametric Study on Flow Boiling Characteristics in <inline-formula> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula>-Shaped Re-Entrant Porous Microchannels With Structured Surface

This paper focuses on flow boiling performance of a type of $\Omega $ -shaped re-entrant porous microchannels for efficient thermal management of high heat-flux devices. The porous-based microchannels are totally constructed by sintered irregular shaped copper powders that featured microchannel walls with structured surface. Flow boiling experiments are conducted utilizing two coolants (deionized water and ethanol) at inlet subcoolings of 10 °C and 40 °C, mass fluxes of 125–300 kg $/\mathrm {m} ^{2}\,\cdot \, \mathrm {s}$ , and a wide range of heat fluxes. Flow boiling heat transfer, pressure drop, and two-phase flow instabilities are comprehensively evaluated to access the parametric effects, i.e., heat flux, mass flux, inlet subcooling, and coolants, on the flow boiling performance of re-entrant porous microchannels with structured surface (RPM-SS). It is found that for both water and ethanol, the two-phase heat transfer coefficients of RPM-SS generally decreased, while the pressure drop increased with the increase in heat flux and vapor quality. Though severe pressure drop instabilities with large magnitude of flow oscillations occurred for RPM-SS in the ethanol tests at large inlet subcooling cases, the RPM-SS can sustain fairly stable boiling at small inlet subcooling tests without the installation of inlet restrictors.

Flow boiling performance of Ω-shaped reentrant copper microchannels with different channel sizes

This paper presents an experimental study of flow boiling performance in Ω-shaped reentrant copper microchannels for the efficient cooling of high heat flux devices. Three reentrant copper microchannels (RCMs) with different hydraulic diameters, i.e., 590, 781 and 858μm, were fabricated via micro wire electrical discharge machining (EDM) process. The channel size effects on flow boiling characteristics of such unique microchannels, i.e., two-phase heat transfer, pressure drops and two-phase flow instabilities, were accessed in order for the design optimization. Flow boiling tests were conducted utilizing the coolant of deionized water at inlet subcoolings of 10°C and 40°C. Test results showed that the reentrant copper microchannels presented a non-monotonic dependence of boiling heat transfer on microchannel size, whereas two-phase pressure drop can be reduced with the increase in microchannel size. Reentrant copper microchannels with the medium hydraulic diameter of 781μm were considered to be the optimum to achieve the best flow boiling performance, as they presented the maximum heat transfer rates and moderate pump power, as well as their superiority to alleviate the severe two-phase flow instabilities.

Flow Boiling Heat Transfer and Two-Phase Flow Instability of Nanofluids in a Minichannel

Single-phase convective heat transfer of nanofluids has been studied extensively, and different degrees of enhancement were observed over the base fluids, whereas there is still debate on the improvement in overall thermal performance when both heat transfer and hydrodynamic characteristics are considered. Meanwhile, very few studies have been devoted to investigating two-phase heat transfer of nanofluids, and it remains inconclusive whether the same pessimistic outlook should be expected. In this work, an experimental study of forced convective flow boiling and two-phase flow was conducted for Al2O3–water nanofluids through a minichannel. General flow boiling heat transfer characteristics were measured, and the effects of nanofluids on the onset of nucleate boiling (ONB) were studied. Two-phase flow instabilities were also explored with an emphasis on the transition boundaries of onset of flow instabilities (OFI). It was found that the presence of nanoparticles delays ONB and suppresses OFI, and the extent is correlated to the nanoparticle volume concentration. These effects were attributed to the changes in available nucleation sites and surface wettability as well as thinning of thermal boundary layers in nanofluid flow. Additionally, it was observed that the pressure-drop type flow instability prevails in two-phase flow of nanofluids, but with reduced amplitude in pressure, temperature, and mass flux oscillations.

Mass transfer from giant donors

The stability of mass transfer in binaries with convective giant donors remains an open question in modern astrophysics. There is a significant discrepancy between what the existing methods predict for a response to mass loss of the giant itself, as well as for the mass transfer rate during the Roche lobe overflow. Here we show that the recombination energy in the superadiabatic layer plays an important and hitherto unaccounted-for role in he donor's response to mass loss, in particular on its luminosity and effective temperature. Our improved optically thick nozzle method to calculate the mass transfer rate via $L_1$ allows us to evolve binary systems for a substantial Roche lobe overflow. We propose a new, strengthened criterion for the mass transfer instability, basing it on whether the donor experiences overflow through its outer Lagrangian point. We find that with the new criterion, if the donor has a well-developed outer convective envelope, the critical initial mass ratio for which a binary would evolve stably through the conservative mass transfer varies from $1.5$ to $2.2$, which is about twice as large as previously believed. In underdeveloped giants with shallow convective envelopes this critical ratio may be even larger. When the convective envelope is still growing, and in particular for most cases of massive donors, the critical mass ratio gradually decreases to this value, from that of radiative donors.

Effects of operation parameters on flow boiling characteristics of heat sink cooling systems with reentrant porous microchannels

Porous-based microchannel heat sinks offer potential and attractive solutions for efficient thermal management of high heat-flux devices. In this study, a unique type of reentrant porous microchannels (RPM) with Ω-shaped configurations was developed and tested in heat sink cooling systems. They were totally constructed by sintered copper powder, and were of a hydraulic diameter of 786μm. Flow boiling experiments of the coolant ethanol were conducted in RPM at inlet subcooling of 10°C and 40°C, mass fluxes of 125, 200 and 300kg/m2s, and a wide range of heat fluxes. Flow boiling heat transfer, pressure drop and two-phase flow instabilities were comprehensively evaluated. The operation parameter effects, i.e., inlet subcooling, heat flux, mass flux and coolants, on the flow boiling performance of RPM were accessed. The results show that the reentrant porous microchannels trigger the onset of nucleate boiling (ONB) at small wall superheat under all the ethanol boiling cases due to the significant increase of nucleation sites. The dependence of heat transfer performance on heat flux and mass flux were linked to the transition of dominated heat transfer mechanisms. The pressure drop and flow instabilities were found to be significantly dependent on the inlet subcooling and heat flux. Furthermore, the comparison of ethanol and water boiling performance were performed. The results in this study provide critical information for operation optimization of the newly developed heat sink cooling systems with reentrant porous microchannels, and are of considerable practical relevance.

The Transfer Instability Index: A Novel Metric of Emergency Department Transfer Relationships

In this study, the objective was to characterize emergency department (ED) transfer relationships and study the factors that predict the stability of those relationships. A metric is derived for ED transfer relationships that may be useful in assessing emergency care regionalization and as a resource for future emergency medicine research. Emergency department records at transferring hospitals were linked to ED and inpatient records at receiving hospitals in nine U.S. states using the 2010 Healthcare Cost and Utilization Project State Emergency Department Databases and State Inpatient Databases, the American Hospital Association Annual Survey, and the Trauma Information Exchange Program. Using the Clinical Classification Software to categorize conditions, high transfer rate conditions were placed into nine clinical groups. The authors created a new measure, the "transfer instability index," which estimates the effective number of "transfer partners" for each sending ED: this is designed to measure the stability of outgoing transfer relationships, where higher values of the index indicate less stable relationships. The index provides a measure of how many hospitals a transferring hospital sends its patients to (weighted by how often each transfer partner is used). Regression was used to analyze factors associated with higher values of the index. Sending hospitals had a median of 3.5 effective transfer partners across all conditions. The calculated transfer instability indices varied from 1 to 2.4 across disease categories. In general, higher index values were associated with treating a higher proportion of publicly insured patients: 10 and 12% increases in the Medicare and Medicaid share of ED encounters, respectively, were associated with 10 and 14% increases in the effective number of transfer partners. This public insurance effect held while studying all conditions together as well as within individual disease categories, such as cardiac, neurologic, and traumatic conditions. United States EDs that transfer patients to other hospitals often have multiple transfer partners. The stability of the transfer relationship, assessed by the transfer instability index, differs by condition. Less stable transfer relationships (i.e., hospitals with greater numbers of transfer partners) were more common in EDs with higher proportions of publicly insured patients.

Effects of structural parameters on flow boiling performance of reentrant porous microchannels

Flow boiling within advanced microchannel heat sinks provides an efficient and attractive method for the cooling of microelectronics chips. In this study, a series of porous microchannels with Ω-shaped reentrant configurations were developed for application in heat sink cooling. The reentrant porous microchannels were fabricated by using a solid-state sintering method under the replication of specially designed sintering modules. Micro wire electrical discharge machining was utilized to process the graphite-based sintering modules. Two types of commonly used copper powder in heat transfer devices, i.e., spherical and irregular powder, with three fractions of particle sizes respectively, were utilized to construct the porous microchannel heat sinks. The effects of powder type and size on the flow boiling performance of reentrant porous microchannels, i.e., two-phase heat transfer, pressure drop and flow instabilities, were examined under boiling deionized water conditions. The test results show that enhanced two-phase heat transfer was achieved with the increase of particle size for the reentrant porous microchannels with spherical powder, while the reversed trend existed for the counterparts with irregular powder. The reentrant porous microchannels with irregular powder of the smallest particle size presented the best heat transfer performance and lowest pressure drop.

Flow boiling heat transfer and pressure drop in stepped fin microchannels

Experiments on flow boiling were conducted in stepped fin microchannels. The test vehicles were made from copper with two different footprint areas, designated as SFMC1 and SFMC2. The microchannels were formed by wire cut Electro Discharge Machining process and have surface roughness (Ra) of about 2.0μm. Tests were performed, with deionized water, on channels having nominal width of 300μm and a nominal aspect ratio of four over different mass velocity and heat flux range and inlet temperature of 90°C. The experimental results of flow boiling in stepped fin microchannels and discussion on its heat transfer characteristics, instabilities and two-phase pressure drop are presented. The experimental data was plotted on Taitel–Dukler flow regime map to predict the flow boiling regimes existing within the channel under different operating conditions. The heat transfer mechanism and the flow boiling instabilities are explained based on the existent flow boiling regime. High speed visualizations are shown to validate the explanation.