Variation Of Heat Transfer Coefficient Research Articles

Performance assessment of firefighter protective clothing under different thermal environments: Impact of the variation of thickness in inter-layer airgap and microclimate

Personal protective equipment for firefighters can effectively prevent skin burns and ensure firefighters' safety. Considering a variety of fire environments faced by a firefighter, the present study is devoted to showing the role of the inter-layer fabric airgap and its variation in thickness on skin burns under high intensity heat flux. The present numerical model is formulated by considering a coupled conduction and radiation heat interaction in the porous fabric medium and the Pennes bioheat transfer model for the multi-layered skin. The study considers the effect of variation in airgap thickness, variation in heat transfer coefficient, and duration of exposure on the thermal damage of the firefighter's skin subjected to different harsh thermal environments. The results found that increasing the thickness of AG1 and AG2 does not yield a significant impact during the exposure time. Conversely, AG3 and AG4 lead to considerable temperature reductions at the basal layer, with AG3 causing a decrease of 2.6 °C to 2.9 °C and AG4 causing a decrease of 11.9 °C to 17.0 °C under all exposure conditions. Additionally, when the heat transfer coefficient increases during post-exposure, temperature drops of 9.17 °C to 10.72 °C, 9.81 °C to 11.46 °C, 10.0 °C to 11.64 °C, and 8.68 °C to 10.07 °C are observed for AG1, AG2, AG3, and AG4, respectively, across all exposure conditions. However, both the airgaps have a substantial effect on thermal protection during the post exposure period. In addition, the nature of the variation of stored and transmitted energy in fabric assembly shows an opposite trend during both the exposure and post exposure period in contrast to the third and fourth airgaps for all the considered thermal environments.

Effect of knock on piston thermal load of a high compression ratio natural gas engine based on stepwise decoupling calculation

High compression ratio natural gas engine (NGE) is prone to knock at high load, which aggravates the thermal load of piston. Therefore, accurately evaluating the piston thermal load in the practical design is essential to enhance engine reliability and improve performance. The typical piston thermal load simulation adopts uniform wall boundary conditions, making it difficult to reveal the influence of turbulent flame and knock on the piston thermal load. In this paper, a stepwise decoupling method is applied to calculate the piston thermal load. The advancement of this method lies in its integration of chemical reaction mechanism with computational fluid dynamics (CFD) to calculate the spatial variations in heat transfer coefficient (HTC) and near-wall gas temperature at the piston top. Moreover, the conjugate heat transfer (CHT) method is adopted to solve the piston thermal load by coupling the thermal boundary conditions (TBC) obtained in the first step with the cooling oil boundary conditions. Based on this method, the effect of knock on piston thermal load of a high compression ratio NGE under different knock intensities is explored in this paper. It is found that turbulent combustion causes uneven distribution of thermal load at piston top. The decrease in knock intensity significantly reduces the gas temperature, heat flux and thermal load at piston top. Particularly under severe knock, the average temperature of piston is 22.9 K and 32.4 K higher than that of light knock and normal combustion, respectively. Furthermore, the main factor affecting the piston temperature field distribution is the gas temperature rather than the HTC. The gas temperature at piston top is overall the highest on the side near the inlet valve pit, which leads to a higher temperature on this side. Compared to light knock and normal combustion, when severe knock occurs, the thermal load on the exhaust valve pit increases significantly. This study provides an effective method for analyzing the heat transfer of the piston under knocking combustion, which is of guiding significance for controlling the thermal load of the high-temperature components in the combustion chamber.

Application of semiempirical correlations for multidimensional heat transfer in rocket engine cooling channels

Heat transfer in cooling channels of liquid rocket engine thrust chambers is an intrinsically multidimensional problem due to the geometry of the channels, often rectangular in section, and the asymmetric distribution of heat input from the hot combustion gas. In this study, the possibility of addressing this problem with semiempirical correlations for the coolant heat transfer and multidimensional numerical simulations for the heat conduction in the wall is investigated. Using experimental data from a test campaign of a cooling channel representative of liquid rocket engine conditions, semiempirical correlations are derived. Both cases of constant and variable heat transfer coefficient along the perimeter of the channel section are considered. The resulting correlations are then used to evaluate their reliability in reproducing the experimental wall temperature data from the same test campaign. For comparison, a correlation taken from the open literature and obtained with experimental data of circular heated tubes is also considered. The results demonstrate that correlations based on a constant heat transfer coefficient fail to reproduce with sufficient accuracy the test cases characterized by higher wall temperatures, while correlations based on a variable heat transfer coefficient overestimate the wall temperature in the initial sections of the channel.

Multiple hot spot cooling with flow boiling of HFE-7000 in a multichannel pin fin heat sink

Electronics cooling applications require a high cooling performance due to increasing power consumption. Phase change heat transfer is a popular approach for offering high heat flux cooling. Controlling temperature distribution and mitigating boiling instabilities under high heat flux conditions present a significant challenge. While numerous studies investigated the effect of pin fins in a minichannel with single hotspots on boiling enhancement, few research studies are available for minichannels with multiple segmented hotspots. This study's primary objective is to dissipate high heat (1.4 kW) using flow boiling of a dielectric fluid, namely HFE-7000, which has lower thermophysical properties than water, to achieve a uniform temperature distribution, and to suppress boiling instabilities. The boiling performance of a pin fin multichannel heat sink with dimensions of 3 × 14 × 300 mm (H × W × L) subjected to 8 hotspots with uniform heating was investigated in this regard. Flow boiling experiments were performed over a wide range of input heat power from ∼0.1 to ∼1.4 kW with a coolant mass flux of 500 kg/m2 s in the three parallel minichannels having staggered elliptical pin fins with no tip clearance on each hotspot and distribution pins at the inlet. High-speed visualization was used to relate the heat transfer coefficient variations along the channel to flow patterns. The heat transfer performance and flow regimes at different locations were obtained and discussed. Thanks to the mixing effect of elliptical micro pin fins with optimum geometrical parameters along the heat sink, the presence of distribution pin fins at the inlet for suppressing boiling instabilities and early transition to stable annular flow, the temperature uniformity (∼2.3 °C, temperature difference between the inlet and outlet hotspots) could be achieved at the highest heat input. Heat transfer coefficient reduction upto 27 % was reported along the channel when comparing inlet (1st) and outlet (8th) hotspots.

Modeling of cryogenic cracking behavior of tight sandstone under confinement

Stimulation is a must for commercial development of tight sandstone hydrocarbon reservoirs. Cryogenic fracturing using liquid nitrogen (LN) is a promising clean technique for efficiently stimulating reservoir rocks given its waterless nature. We developed a fully coupled thermo-mechanical (TM) model that incorporates strain-based damage theory for simulating LN cryogenic cracking in tight sandstone. Particularly, the compressive and tensile strengths, Young’s modulus, and thermal expansion coefficients and conductivity are designated as dynamic functions of the damage variable during the TM coupling process. Then the initiation, propagation, and cessation of multiple cracks from a borehole within a 2D heterogeneous tight sandstone plate were systematically scrutinized. Cryogenic cracks are found to emerge in short and long forms. In accordance with experiments, multiple long cracks emanate radially from the borehole along the maximum horizontal stress direction. In the investigated parameter ranges, the fracture morphology, including numbers, lengths, and coverage, is susceptible to changes in in-situ stress, Young's modulus, and thermal conductivity, but relatively insensitive to the variations of heat transfer coefficient and sandstone density. These results deepen our understanding of cryogenic shock on tight sandstone and provide a theoretical reference for designing cryogenic treatment operations.

Experimental investigation on the flow boiling of R134a in a plate heat exchanger with mini-wavy corrugations

As a common component in various applications, the two-phase heat transfer of plate heat exchanger has been frequently studied. However, further investigations are still required on the flow pattern, especially for those with new plate structures brought with the emergence of new applications. This study presented an experimental investigation on the flow boiling of R134a in a plate heat exchanger with mini-wavy corrugations designed for thermal management system of electric vehicle (EV). The flow pattern transitions in the test section were captured and discussed, meanwhile the effects of vapor quality and mass flux on the variation of heat transfer coefficient (HTC) were analyzed. Based on the observation, the two-phase flow pattern developed from pulsating film flow, then rough stream flow and finally to thin stream flow with the increase of vapor quality. The flow pattern map was determined with the superficial momentum of the liquid and vapor phase refrigerant, while the empirical correlations were developed based on two-phase Weber number to predict the transitions between the flow patterns. The HTC showed an intermediate increase firstly under low vapor qualities, and rapidly decreased after reaching the peak value at the vapor quality of 0.45–0.6. In addition, the experimental data were compared with the present correlations, and a new Nu correlation was developed considering the transitions of flow patterns, showing an optimal prediction on the experimental data with the mean absolute error of 11.3%.

Triple diffusive free magneto-convection of electro-conductive nanofluid from a vertical stretching sheet

In the present investigation, an analysis is carried out to study the MHD triple diffusive free thermo-solutal convection boundary layer flow of an electro-conductive nanofluid flow over a vertical stretching sheet. This problem is relevant to magnetic nanomaterials fabrication operations in which multiple species in addition to nanoparticles are present. In addition to the nanoparticle diffusion, two different salts (species) having different properties are considered. A variable magnetic field is applied transverse to the vertical sheet. It is assumed that the surface is in contact with the hot magnetic nanofluid at a temperature which provides a variable heat transfer coefficient. Buongiorno’s model is employed for the nanofluid. It is also assumed that the Oberbeck-Boussinesq approximation is valid and the mixture of nanofluid and salts is homogenous and is in local thermal equilibrium. In addition, the thermal energy equation features cross-diffusion (Soret and Dufour) terms for both components of salts having different concentration. Appropriate similarity transformations are deployed to render the model non-dimensional. The emerging transformed dimensionless non-linear non-dimensional ordinary differential boundary value problem is solved with the robust bvp4c method in MATLAB. Validation with previous studies has been included for special cases of the general model. The simulations show that the addition of nanoparticles and salts, strongly modifies Temperature and nanoparticle and salt 1 and 2 concentrations. With stronger magnetic field the velocity is suppressed as is momentum boundary layer thickness whereas temperatures are boosted.

Nonlinear Estimators for Hypersonic Heat Flux Reconstruction

A novel class of nonlinear estimators that minimizes the projection of the error on a multiresolution basis is developed to improve the accuracy and efficiency of the multidimensional reconstruction of the heat flux from discrete temperature sensors in nonplanar hypersonic boundary layers. This approach uses the local temperature time derivative as the pre-estimator of the heat flux estimation risk in the inverse heat conduction problem. This new approach leads to improved results both in terms of computational efficiency and signal-to-noise ratio when compared to both regularization of the linear response operator and filtering of the temperature measurements. The approach is verified against an analytical verification test case, which shows significant accuracy improvement compared to optimal linear estimators and L2 regularization. It is then applied to experimental data to resolve the heat flux from noisy temperature data collected using fast-response sensors in the Virginia Tech hypersonic wind tunnel at Mach 6. The heat flux agrees very well with the Fay–Riddell approximation. Moreover, the heat transfer coefficient variation over the surface of the test is consistent with computational fluid dynamics simulations of the Reynolds-averaged Navier–Stokes equations.

Numerical simulation study of impact of polydispersity on biomass pyrolysis in draft-tube spouted reactor with fountain confiner

During biomass pyrolysis within spouted reactor, particles exhibit behavior characterized by polydispersity. To explore the impact of polydispersity of bed materials on the biomass pyrolysis, the multiphase particle-in-cell model is constructed to simulate such process. The focus of the study is examining the impact of size distribution of solid materials and the presence of a draft tube on the particle-level properties. The results show that the yields of Gas1 and tar during the first pyrolysis increase about 13.1 % and 14.8 %, respectively, as the PSD width of sand increase from 0.1 to 0.7. In addition, the influence of the draft tube is primarily centered on enhancing interphase interactions rather than pyrolysis yields when a fountain confiner is applied. Fine particles mainly distribute along the interphase of annulus and its vicinity while coarse particles mainly accumulate along the interphase of annulus and spout. Expanding the PSD widths of bed materials from 0.1 to 0.7 results in an approximate temperature increase of 10 K in the floating biomass. The variation of particle slip velocity and heat transfer coefficient exhibits similar trend, mainly due to their interrelation in convective heat transfer. These findings hold valuable insights that can guide optimization design and parameter selection in the conical fountain confined spouted bed reactors.

Numerical analysis of thermo hydro-dynamics behavior of solar flat plate collector with square and V-cut twisted tape inserts

Numerical analysis has been conducted for a solar collector with two circular pipes having semi-circular contact with absorber plate. The tubes are analyzed with and without the inclusion of twisted tape inserts of twist ratio Y = 3 and Y = 4. The comparison between the heat transfer and pressure drop characteristics of a plain tube to that fitted with the twisted tape inserts is done and validated against experimental results with good agreement. Additionally, helical twisted tape is modeled with square- and V-cut to analyze its influence on flow and heat transfer phenomenon. V-cut twisted tape inserts act as turbulence promoters, increasing fluid flow and inducing vortex-like motion. As a result, boundary layer around the absorber plate is disrupted with decrease in stagnation temperature, resulting in better heat transfer and more effective absorption and conversion of solar energy. The Nusselt number, friction factor, and heat transfer coefficient variation with the Reynolds number have been studied for the given heat fluxes. It is found that the Nusselt number of the fluid flowing in the plain tube is increased by 76.44% when the tube is fitted with twisted tape inserts. The pressure drop in the tube is found to increase with the presence of the twisted tapes. The average temperature along the length of the circular tube and absorber plate has also been reported.

Green roof heat transfer coefficient measurement and impact of plant species and moisture

Green roofs attract wide attention for building energy conservation and sustainable development. However, the heat transfer coefficient of green roofs is not well defined. In this study, we developed a non-contact steady-state method for green roof heat transfer coefficient measurement. The apparatus required 16 min to reach the steady state, with a measurement variation of 2.84 ∼ 3.47 %. The impacts of plant species and substrate moisture on the heat transfer coefficient of green roofs were defined. The green roof with Sedum lineare (a CAM plant) performed the widest variation of heat transfer coefficient, from 2.847 W/m2 K (at the wilting point) to 5.401 W/m2 K (at the field capacity). The green roof with Paspalum vaginatum (a C4 plant) performed the least variation of heat transfer coefficient, with only 2.807 ∼ 3.069 W/m2 K from the wilting point to the field capacity. The green roof with Festuca arundinacea showed mediate variation in heat transfer coefficient, with 2.849 ∼ 4,372 W/m2 K. This work provides a method to determine green roof heat transfer coefficient and defined dynamics of heat transfer coefficients in three different green roofs, which is crucial to further elucidate the green roof heat transfer mechanism and the impact factors.

Significance of Pressure Drop, Changing Molar Flow, and Formation of Steam in the Accurate Modeling of a Multi-Tubular Fischer–Tropsch Reactor with Cobalt as Catalyst

A Fischer–Tropsch (FT) fixed-bed reactor was simulated with reactor models of different complexities to elucidate the impact of a pressure drop, a change in the total molar volume rate (induced by the reaction) along the tubes, and a change in the axial variation of the external radial heat transfer coefficient (external tube wall to cooling medium, here, boiling water) compared to disregarding these aspects. The reaction kinetics of CO conversion for cobalt as a catalyst were utilized, and the influence of inhibition of syngas (CO, H2) conversion reaction rate by steam, inevitably formed during FT synthesis, was also investigated. The analysis of the behavior of the reactor (axial/radial temperature profiles, productivity regarding the hydrocarbons formed, and syngas conversion) clearly shows that, for accurate reactor modeling, the decline in the total molar flow from the reaction and the pressure drop should be considered; both effects change the gas velocity along the tubes and, thus, the residence time and syngas conversion compared to disregarding these aspects. Only in rare cases do both opposing effects cancel each other out. The inhibition of the reaction rate by steam should also be considered for cobalt as a catalyst if the final partial pressure of steam in the tubes exceeds about 5 bar. In contrast, the impact of an axially changing heat transfer coefficient is almost negligible compared to disregarding this effect.

Experimental investigation of flow orientation effects on cryogenic flow boiling

Cryogenic flow boiling physics is of paramount importance for future cryogenic space applications employing Cryogenic Fluid Management (CFM) technologies. This experimental study investigates the two-phase flow and heat transfer performance of LN2 flow boiling across five distinct flow orientations: vertical upflow, vertical downflow, horizontal flow, 45° inclined upflow, and 45° inclined downflow. The study employed the steady-state heating method within a circular heated tube featuring an 8.5-mm inner diameter and a 680-mm heated length. High-speed video recordings were utilized to capture two-phase flow patterns and interfacial behaviors across various flow orientations. The experiments covered a wide range of operating conditions, including mass velocities ranging from 351.80 to 1572.77 kg/m²s and inlet pressures from 297.14 to 1032.97 kPa, primarily with near-saturated inlet subcooling. Distinct two-phase flow patterns and regime transitions were identified for each flow orientation. Symmetrical flow patterns were evident in vertical orientations, whereas non-vertical orientations exhibited asymmetric flow stratifications, primarily influenced by the buoyancy force in a terrestrial gravity environment. Bubble dynamic parameters were quantified, and bubble collision and dispersion phenomena were visualized. Analyzing heat transfer performance based on local flow boiling curves and variations in heat transfer coefficients (HTCs), it was observed that vertical upflow demonstrated the most enhanced heat transfer performance, while vertical downflow exhibited the lowest. As mass velocity exceeded 830 kg/m²s, the differences in heat transfer among orientations became less distinct, emphasizing the role of flow inertia in mitigating the influence of flow orientation. A direct comparison of microgravity HTC data from a recent study by the authors against the 1-ge HTC data indicated enhanced heat transfer performance in microgravity for flow orientation configurations in terrestrial gravity. However, this enhancement progressively diminished as the heat flux increased. Distinct HTC trends were observed as mass velocity increased for different flow orientations and gravity levels.

A dynamic model of the packed dehumidifier

Liquid desiccant dehumidification, a clean energy technique for creating comfortable environments has received a lot of interest. Several dynamic models have been proposed to predict the outlet air humidity ratio and temperature, however, a study on presenting variations of heat and mass transfer coefficients and thermal mass of desiccant during the dynamic dehumidification process was not encountered according to authors’ best knowledge. This gap is primarily due to the complex nature of the coupled heat and mass transfer processes, which make it challenging to capture the evolution of heat and mass transfer coefficients over time. In this study, variations of these parameters are analyzed at first. A theoretical study is conducted to show the thermal mass of the desiccant can be considered constant when changing the inlet air humidity ratio or desiccant temperature, simplifying the dynamic modeling process. While the variation of heat and mass transfer coefficients show significant impact in such conditions. Subsequently, a new method based on mass conservation is provided to determine the thermal mass of desiccant. By examining the cause-and-effect relationships between heat and mass transfer coefficients and outlet air humidity ratio, the evolution of heat and mass transfer coefficients following exponential laws is deduced by inversion. Then a dynamic model of packed dehumidifiers can be completed easily based on above derivations, and its viability is confirmed by experimental results. Compared to the existing method, the prediction accuracy can improve by 50% based on the proposed methods. This study characterizes evolution rules of heat and mass transfer coefficients over time, and with this, evolutions of outlet air parameters during the dynamic dehumidification process can be acquired conveniently based on the existing steady dehumidification model.

Approximate Analytical Solution of the Problem of Thermal Conductivity for a Tube Wall with Variable Heat-Transfer Coefficients along the Perimeter

Approximate Analytical Solution of the Problem of Thermal Conductivity for a Tube Wall with Variable Heat-Transfer Coefficients along the Perimeter

A modified decomposition method for the analysis of porous triangular fin with a power exponent of thermal properties and magnetic effect

A closed-form solution of the triangular porous fin with a simultaneous variation of power law-dependent heat transfer coefficient, internal heat generation, and surface emissivity parameters under the influence of external magnetic and electric fields is carried out. Darcy’s model has been used to simulate flow in the porous triangular fin with insulated boundary conditions. The governing singular value equation is nondimensionalized and solved by modified Adomian decomposition method (MADM) and the results of MADM are compared with the numerical solution obtained from the finite difference method (FDM) in the limiting conditions. The graphical analysis of the significant power law variation of thermophysical parameters, Hartmann number and important design parameters such as the half-thickness parameter of the triangular fin are performed and physically interpreted. A comparative study has been carried out with multiple power law parameters at different values while other thermophysical parameters were kept at a fixed level and it has been found that fin temperature is highest at higher values of power index parameters. From this study, it has been found that with the increasing value of the Hartmann number as well as the porosity parameter, the efficiency of the triangular porous fin increases rapidly.

A hybrid study of a 4-stage compressed solar distiller based on experimental, computational and deep learning methods

In the present study, a hybrid technique is employed to demonstrate the thermal performance of a 4-stage compressed solar distiller with hydrophilic evaporators (CSDHE) regarding the role of natural convection in the air gap domain. Initially, the test is conducted under simulated solar radiation of 2.13 W·m−2 over 5400 s. A thermodynamic model incorporating diffusion is developed for the next step to analyze internal transient temperatures. In the third step, a 3D single-phase natural convection model of the CSDHE is simulated to achieve the research objectives. Based on experimental, thermal modeling, and computational results, a dual deep neural network is developed to predict the thermal behavior of the system and the variation of convection heat transfer coefficient for different air gap thicknesses over 10,000 s. The experimental results revealed a distilled water production rate of 3.806 kg·m−2h−1 with a gained output ratio (GOR) of 112 %. Moreover, the findings demonstrate that conduction accounts for 84.23 % of total heat transfer, while convection accounts for 6.36 % during 5400 s. We also found that, by employing a convolutional neural network (CNN) and directly harvesting data from pre-defined contours, the hybrid training dataset for deep forward neural network (DFNN) is trained 28.35 % faster than conventional methods.

Practical design guidelines for heat transfer enhancement of condensers

Enhanced condensation is of great practical interest to further improve and miniaturize power generation and refrigeration systems. Studies in the literature that investigate enhanced condensation focus on increasing the heat flux at high vapor qualities; however, many thermodynamic cycles such as vapor compression and the Rankine cycle require complete condensation for cycle operation, and in such cases, low-quality condensation can be the limiting factor. Performance evaluation criteria (PEC) can be used to assess the relative improvement achieved by different enhancement methods, but most PEC are only applicable to single-phase flows. The present study therefore develops local design guidelines for condensing flows to determine the regions of the condenser that most need heat transfer enhancement. This is achieved by comparing the relative benefits and penalties associated with enhancing low-quality, medium-quality, and high-quality condensation equally. The effects of varying heat transfer coefficient, frictional pressure drop, temperature reduction due to pressure drop, driving temperature difference, and coupling fluid thermal resistance are considered. Three enhancement techniques are then analyzed with these approaches to determine their relative benefits and disadvantages. Cases that consider fixed geometries, fixed flow areas, and variable flow area are considered, along with comparing the relative benefits of size reduction, increased heat duty, and reduced temperature difference. Results show that heat transfer enhancement is achieved when the increase in heat exchanger conductance exceeds the reduction in the heat exchanger temperature difference induced by condensation pressure drop. Additionally, it is found that enhancement is typically most needed in the low vapor quality region of the condenser, except in situations where temperature pinching occurs along the heat exchanger.

Linear and Nonlinear Stability Analysis of Molten Salt Natural Circulation Loop

Abstract A molten salt natural circulation loop (MSNCL) has been setup to study the steady-state, transient, and stability characteristics of molten nitrate salt, mixture of sodium nitrate, and potassium nitrate in 60:40 ratios by weight. Natural circulation experiments in a temperature range of 290 °C–600 °C have been performed. A semi-analytical linear model was derived for stability analysis of rectangular natural circulation loops with conventional localized surface heating and cooling. The developed model includes the effect of wall thermal inertia, variable internal heat transfer coefficient, finite secondary side heat transfer coefficient at cooler, and heat losses for predicting the stability map. These effects are incorporated considering their significant role in modeling high-temperature molten salt-based natural circulation systems. The developed model has been first validated with the experimental data of water loop available in literature. The developed model is then validated with the experimental data generated in MSNCL. Validation of in-house developed nonlinear model has also been performed against the same experimental data. The comparison of both linear and nonlinear stability analysis with the experimental data shows good agreement and articulates the importance of various parameters which have been included in the developed model.

Saturated flow boiling heat transfer of R1233zd(E) in parallel mini-channels: Experimental study and flow-pattern-based prediction

The parallel channel is widely used in the two-phase flow boiling heat transfer due to its simple structure, but the existence of multiple flow patterns causes a complex and non-unified explanation of the heat transfer mechanisms. In this study, a saturated flow boiling experiment was designed in a parallel mini channel heat sink with R1233zd(E) as the working fluid. By controlling the vapor quality difference at the inlet and outlet to around 0.1–0.2, each single flow pattern was isolated and presented in the test section, and the corresponding variations of heat transfer coefficient (HTC) were discussed. The results showed that the flow pattern during the saturated flow boiling included bubbly flow, slug flow, wavy-annular flow and local dry-out. The transition boundaries between bubbly flow, slug flow and wavy-annular flow showed good agreement with the present criteria, while a modification was made on the transition from wavy-annular flow to local dry-out. The HTC showed a fast increase under low vapor qualities, then became stable and decreased with the increase of vapor quality. In addition, 6 correlations were selected to compare with the measured HTC classified according to the flow patterns. The comparison showed that the present correlations had different prediction accuracies on the HTC data under each flow pattern. The best prediction on the heat transfer during bubbly and slug flow was achieved by Liu and Winterton's model with the MAE of 16.4% and 12.9%, while Li and Wu's model showed the best agreement with the HTC data during wavy-annular flow with the MAE of 9.1%.