Enhanced Wall Treatment Research Articles

CFD ANALYSIS ON THE SINGLE-PHASE FLOW ELECTRICAL SUBMERSIBLE PUMP PERFORMANCE CURVE

Most of the industrial fields, especially oil and gas, involve the application of electrical submersible pump (ESP) for flow transport. The pump performance will deteriorate depending on conditions of usage. The main parameters that affect or influence the pump performance curve are pump types, fluid flow rates, gas fractions, the impellers’ geometry, rotational speeds and fluid properties. In this work, the pump performance curve was studied as the governing parameters such as flow rates, meshing elements and turbulence models were varied. A computational fluid dynamics simulation (CFD) was applied and the findings were compared with the manufacturer’s data for single-phase flows. The main purpose was focused on getting the right technique to investigate this problem. The various turbulence CFD models were analysed and sources of errors were explained. The corresponding pump head losses were discussed and the main improvement or the criteria to obtain the highest efficiency were suggested. The results show that the k-epsilon with enhanced wall treatment is the best CFD technique since it produces the most accurate results and the least errors by allowing flexibility in large pressure gradient and rapid changes in flow properties.Keywords: ESP, CFD simulation, head loss, performance curve, turbulence models

A numerical study of the effect of spiral counter grooves on a needle on flow turbulence in a diesel injector

In the paper, the necessity to improve the fuel injection process in diesel engines was shown. The purpose of the study is to quantitatively evaluate the increase of flow turbulence in a diesel injector caused by spiral counter grooves which are made on the injector needle and intend to improve fuel injection and atomization processes. Different parameters of the spiral counter grooves are considered from the point of view of the turbulization of fuel flow in the injector. The two-phase flow in such nozzles with different spiral grooves has been numerically investigated. Cavitation in the nozzle was modeled with using the Schnerr-Sauer equilibrium model and taking into account the influence of turbulence on the development of cavitation. The Realizable k-ε turbulence model along with Enhanced Wall Treatment for ε equation is used. The possibility of increasing the turbulence of fuel flow in the nozzle is demonstrated. It is noted that the existence of the spiral counter grooves leads to a reduction in flow velocity and improving the flow turbulence in the cylindrical space of the nozzle. The turbulence induced by the spiral grooves can lead to an increase in the cavitation intensity in the nozzle hole. The parameters of the spiral grooves which ensure the greatest flow turbulization in the nozzle have been determined. After replacing the standard nozzle with the modified nozzles No. 2 and 7, the effective turbulent kinetic energy at the nozzle hole outlet averaged over five nozzle holes increased from 2402 to 2464 and 2470 m2/s2, respectively.

Effects of Roughness on the Performance of a threaded Zigzag Demister Using RSM and k − ω turbulent models

In this paper, the effects of channel roughness on the droplet removal efficiency and pressure drop in a zigzag mist eliminator are investigated. The fluid flow, droplet dispersion and deposition through the demister are modelled using a commercial Computational Fluid Dynamics (CFD) tool. The turbulent airflow is simulated using two different Shear-stress Transport (SST) k-ω model and Reynolds Stress Model (RSM) with enhanced wall treatment. The Eddy Interaction Model (EIM) is also used to predict the trajectories of the droplets in the gas flow. The results show that inserting roughness increases the maximum velocity of the gas flow at the bends and enhances the removal efficiency with a little cost of an increase in the pressure drop for each bend. At the velocity inlet of 2 m/s with 6 μm droplets, the pressure drop and removal efficiency of the threaded zigzag demister with 5 threads increases by 22.7% and 16.08 %, respectively. Moreover, a higher value for the figure of merit is achieved for the threaded demister compared with the smooth unit which means that the effect of higher removal efficiency of the threaded unit is more pronounced than the effect of higher pressure drop showing the advantages of adding threads in demisters.

Numerical Study on Particles Deposition in the U-bend Ribbed Passage

Abstract The accumulation of particles in the internal cooling channel reduces the cooling effectiveness of the turbine blades and even affects the safe operation of the aero engine. Discrete phase-CFD simulations of particles deposition were performed in the U-bend ribbed passage by applying Euler–Lagrange method. Reynolds Average Navier–Stokes method was used for the gas phase calculation. The realizable k–ε turbulence model and enhanced wall treatment were adopted. The discrete phase was solved by using Lagrangian with random walk model. A particle deposition model was implemented by using user-defined functions. The Reynolds numbers of 30,000, 23,000, and 15,500 were studied. Particles diameters in the range 1–20 μm were considered. The particles deposition distribution of different locations is obtained in this study, and the influence of the Reynolds numbers and particle diameters on particles deposition performance are analyzed. Results show that the first row of ribs has a protective effect on the back row of ribs. The increased Reynolds number and increased particles diameter promote the deposition of particles on the wall.

Numerical study on the heat transfer deterioration and its mitigations for supercritical CO2 flowing in a horizontal miniature tube

Responding to the rapid growth of size reduction in engineering systems, it is crucial to explore the safety performance of supercritical fluid systems in miniature tubes. In this paper, numerical studies are conducted to explore the performance of baffles on heat transfer deterioration (HTD) mitigations for supercritical CO2 (sCO2) flowing in a horizontal mini tube using RNG k-e turbulence model with enhanced wall treatment (EWT). Three kinds of baffle arrangements: in-lined, staggered and centred, with the same blockage ratio (BR = 0.25) are selected to explore their performance on HTD mitigation. Thethermo-hydraulic performances of the baffled tubes are examined using the dimensionless parameters based on normalized Nusselt numbers and Fanning friction factors,Nu/Nu0,f/f0andPEC=(Nu/Nu0)/(f/f0)1/3. The results reveal that unlike the in-lined and staggered baffles, the centred baffles induce jet impingements directly onto the tube walls and generate significant amounts of transverse fluid velocity near the tube wall (which exceeds that in the core region),making it the most influential baffle arrangement on the HTD mitigations. The effects of baffles on buoyancy flow under a wide range of heat and mass fluxes are explored based on Jackson’s criterion (Gr/Re2<103). It is observed that the Gr/Re2 increases at a relatively lower rate in baffled tube than in the smooth tube under increased heat flux variation whereas it decreases at a higher rate than the smooth tube under increased mass flux variation, thus revealing the buoyancy weakening effects of baffles. Finally, the baffle’s performance on HTD mitigation when the tube is further miniaturized is explored and the results unveil that miniaturization weakens buoyancy, and there exists a certain mini size (D = 0.5 mm) at which buoyancy influence completely vanishes, and the effect of baffles on HTD mitigation becomes insignificant.

Numerical approach of a fully developed flow in a solar collector adapted to the climate of southwest Algeria

The present work has been conducted with the aim of contribution to the study of heat transfer phenomena in an air solar collector, which deal with transient heat transfer properties and mechanisms.The improvement of heat transfer in the studied system is characterized by the development of the flow between the absorption of cold air and the evacuation of hot air.The equations, which govern the problem dealt with, are those of turbulent and incompressible flows written in Reynolds decomposition for velocity, pressure and temperature, in a mean component and a term of fluctuation, and expressing the conservation of the mass, of the amount of movement and energy.To close the set of transport equations, the turbulence model k-E was used. We will therefore use this model of turbulence with an improved treatment of wall laws (Enhanced wall treatment), with the intention of solving the laminar sub-layer. The simulation results obtained are valid for temperature values between (30 °C - 50 °C) for heating flows between (200 w / m2 - 800 w / m2), the average volume flow obtained is equal to: 0.3 m3/s. These results are essential for the passive heating of buildings and the drying of agrifood products.

Heat Transfer and Fluid Flow in Double Pipe Heat Exchanger, Part II: Numerical Investigation

Analysis of thermo hydraulic characteristics in a simple configuration of the double-pipe heat exchangers adds a great value to the design of heat exchangers. This paper presents a comparison of the experimental observations and numerical predictions for the thermal characteristics of the double pipe heat exchanger. A CAD design was developed and the Realizable k-ε mathematical model coupled with enhanced wall treatment gave the closest results. Experiments were performed for 60 ≤ Re ≤ 240 for two different inlet temperatures of the hot fluid, 50°C, and 70°C keeping the inlet temperature of the cold fluid constant at 31°C. Temperature gradients extracted from ANSYS Fluent were compared with the experimental data. Further, pressure and temperature contours for the hot and cold streams were generated to analyze the performance parameters.

Thermal enhancement study of a transverse inverted-T shaped ribbed solar air heater

In the present study, the heat transfers and flow fields analysis in solar air heater duct having of transverse inverted-T shaped ribs is performed. The significant outcomes are presented in terms of Nusselt number, friction factor, thermal enhancement factor, and visualization of different fluid properties for the solar air heater (SAH). The computational exercise is done by considering various non-dimensional parameters like Reynolds number (Re), relative roughness pitch (P/e), and relative roughness height (e/Dh) for the test to enhance the rate of heat transfer through the rectangular SAH duct. The relative roughness pitch and Reynolds number are varied from 7.14 to 17.86 and 3800 to 18,000 respectively, considering a fixed value of relative roughness height of 0.042. A two-dimensional computational domain is selected for the study where an absorber plate made up of aluminum is subjected to a constant and uniform heat flux of 1000 W/m2. Among the various turbulence models, the RNG k-ɛ model with enhanced wall treatment is accepted as the most appropriate model to simulate the governing eqs. A Thermal enhancement factor of 1.87 is obtained as a result of enhancement in heat transfer for the SAH with an inverted T-shaped rib roughened absorber plate. The correlations are obtained for the Nusselt number and friction factor as a function of Reynolds number and relative roughness pitch by carrying out a non-linear regression analysis.

Heat Transfer Enhancement of Supercritical Nitrogen Flowing Downward in a Small Vertical Tube: Evaluation of System Parameter Effects

In this paper, the heat transfer enhancement (HTE) of supercritical nitrogen flowing downward in a vertical small tube (diameter 2 mm) is studied using the commercial software CFX of Ansys16.1, to provide theoretical guidance on the design of high-performance heat transfer systems. An effective numerical simulation method, which employs the SSG Reynolds stress model with enhanced wall treatment, is applied to study the heat transfer of supercritical nitrogen under typical working conditions. The objective is to evaluate the effect of the main parameters taking into account the buoyancy and flow acceleration effects. Simulation results are compared with results calculated from three well-known empirical correlations and the applicability of empirical correlation is discussed in detail. It is discovered that the Watts and Chou correlation accurately fits the simulation results of supercritical nitrogen and the Dittus-Boelter and Jackson correlations can only be used for high-pressure conditions. The HTE of supercritical nitrogen is closely related to the laminar sub-layer and buffer layer of a boundary layer. The buoyancy effect on the HTE should be considered at low mass flux conditions, and thermal acceleration can be completely ignored for the cases studied. The special HTE featured by the increment in heat transfer coefficient with increasing heat flux is discovered at low pressure, and simulation results proved that this HTE is caused by the combined actions of buoyancy as well as significant variations in specific heat and viscosity.

Experimental Study on the Film-Cooling Characteristics of the Cylindrical Holes Embedded in Sine-Wave Shaped Trench

Abstract An experimental investigation has been performed to study the film-cooling performance of the cylindrical holes embedded in the sine-wave-shaped-trench. The sine-wave-shaped-trench is obtained by changing the trailing edge of the transverse trench into sine-wave shape; the holes are located next to the peaks of the wave. The sine-wave-shaped-trench is expected to get a wider spread of the cooling jet in the spanwise direction. The film-cooling effectiveness, heat-transfer coefficient, and discharge coefficient of the sine-wave-shaped-trench hole configurations with different trench depths (0.75D, 1D) and wave peaks (1D, 2D) are measured by the transient thermal liquid measurement technique. The blowing ratio covers a range from 0.5 to 2.0. The transverse trench hole is investigated as a basis of the comparison. Thermal and hydrodynamic fields are investigated numerically using Reynolds-averaged Navier–Stokes (RANS) simulations with Realizable k–ε turbulence model and enhanced wall treatment. Results show that broadening the wave peak of the sine-wave-shaped-trench improves the spanwise uniformity of the injection. There is a pair of anticounter-rotating vortices formed downstream of the sine-wave-trailing-edge. Increasing the trench depth shows positive effects on the heat-transfer coefficients ratio of the sine-wave-shaped-trench. The discharge coefficients of the sine-wave-shaped-trenches are higher than that of the transverse trench which means the sine-wave shape trench has a lower flow resistance.

Numerical investigation of heat transfer and pressure drop characteristics in the micro-fin helically coiled tubes

The design of a compact heat exchangers is the challenging work in heat transfer research area. The enhancement of heat transfer can be achieved by increasing the surface area of the heat exchanger and changing the direction of fluid flow. Thus, in this study, the heat transfer and pressure drop characteristic in the micro-fin helically coiled tubes are investigated numerically by using ANSYS FlUENT 19.2. The realizable k − ε turbulence with enhanced wall treatment model was applied. These studies are carried out at different coil diameter from 100 mm to 200 mm, coil pitch of 25 mm to 45 mm and, Reynolds number varying from 10,000 to 25000. Effects of Reynolds number, fin number, coil diameter, and coil pitches on Nusselt number and pressure drop are discussed. At the same operating condition, the Nusselt number and pressure drop increase with an increase of fin number and Reynolds number. Compared to the smooth helical coiled tube, the micro-fin helical coiled tube having fin number Nf = 12 provides higher Nusselt number and pressure drop in the percentage of 39–51% and 22–36%, respectively. The coil pitches of helical tube have a small effect on Nusselt number. At the same Reynold number of 20000, the Nusselt number of smooth helical coiled tube with coil pitch 25 mm is about 0.86% and 1.71% higher than that of the tube with coil pitch of 35 mm and 45 mm, respectively. Moreover, the performance factor of micro-fin helical coiled tube with 8 fin declines from 1.08 to 0.96 with an increase of the coil diameter from 100 mm to 200 mm, respectively.

Numerical Analysis with Experimental Validation of Single-Phase Fluid Flow in a Dimple Pattern Heat Exchanger Channel

A plate heat exchanger with a dimple pattern heat plate has a large number of dimples. The shape of dimples defines the characteristics of the plate heat exchanger. Although such heat exchangers have become increasingly popular due to their beneficial characteristics, knowledge of the flow characteristics in such kind of channel is poor. A good knowledge of the flow conditions inside of such channel is crucial for the successful and efficient development of new products. In this paper single-phase water flow in dimple pattern plate heat exchanger was investigated with application of computational fluid dynamics and laboratory experiments. Numerical analysis was performed with two turbulence models, Realizable - with enhanced wall treatment function and - SST. The first predicts a slightly smaller pressure drop and the second slightly larger compared to the results of laboratory measurements. Our research found that despite the relatively low velocity of the fluid, turbulent flow occurs in the channel due to its shape. We also found that there are two different flow regimes in the micro plate heat exchanger channel. The first regime is the regime that dominates the heat transfer, and the second is the regime where a recirculation zone appears behind the brazing point, which reduces the surface for heat transfer. The size of the second regime does not change significantly with the velocity of the fluid in the volume considered.

Influence of secondary pass location on thermo-fluidic characteristic on the novel air-cooled branched wavy minichannel heat sink: A comprehensive numerical and experimental analysis

This paper presents a new fin pattern for air-cooled branched-wavy minichannel heat sink (BWMCHS) where three different secondary passes at a distance of 0.5λ, 1.0λ and 1.5λ have been considered (λ is the wavelength and equals to 20 mm). A comprehensive computational and experimental analysis is implemented to investigate the thermo-fluidic characteristics in detail. The RNG k-ε model with enhanced wall treatment with pressure and thermal effect has been used in the numerical analysis. Numerical investigations were validated with experiments. The numerical result is further examined to understand the phenomenological understanding of the air flow through these geometries. In the spanwise direction, BWMCHSs was observed to induce significant non-uniform distribution of air mass flow rate at the inlet and outlet. The pressure drop penalty exceeded the heat transfer enhancement due to flow migration. BWMCHS 0.5λ reported a higher pressure penalty among all the MCHSs. The BWMCHSs showed enhanced thermal performance over a straight minichannel heat sink (SMCHS). In conclusion, the overall performance of BWMCHS at 1.0λ secondary pass has been found superior over BWMCHS 0.5λ and BWMCHS 1.5λ in both numerical and experimental investigations.

Numerical analysis of heat transfer in tubular type heat exchangers of transport vehicles with pulsating flow

The shell and tube heat exchangers are widely used in many engineering applications. Tubular heat exchangers can be found in the transport, power engineering, food industry and etc. Therefore, the study of the characteristics of heat transfer and hydrodynamics in tubular heat exchangers is important. In this paper, numerical analysis of a heat transfer in a staggered tube bundle with steady and asymmetrical pulsating flow studied. The transverse and streamwise spacing-to-diameter ratios of the tube bundle were 1.3. The Reynolds number Re was 1100. Numerical simulation of the flow past the tube bundle with 7 longitudinal rows was carried out by solving the incompressible Navier-Stokes equations and energy conservation equation with two different modeling strategies. The simulation was carried out with the RNG k-ε turbulence model with enhanced wall treatment and laminar solver. The sensitivity of the Nusselt number to the mesh parameters is noted. The effect of the number of rows of the tube on the heat transfer rate for the tube bundle with the pulsating flow also was discussed. For the pulsating flow enhancement of the heat transfer in the tube bundle dependence from the row of the tube and modeling strategy. When RNG k-ε turbulence model was employed the heat transfer rate of the first row is increasing by 16 %, downstream rows by 6-7 %. When laminar solver was employed the heat transfer rate of the central rows are increasing by 53 %.

Experimental and numerical study on the effects of shaped multi-holes on the effectiveness of film cooling

In the present work, experimental and numerical study has been performed to investigate the effects of a novel film-cooling design with shaped multi-holes on the film-cooling effectiveness over a flat plate. A single cylindrical hole with 11.1 mm diameter has been replaced by multi-holes (14 holes with 2.97 mm diameter) with elliptical and fan-shaped configurations. The exit area, length to diameter ratio (L/D = 4.0) and injection angle (35°) of multi-holes are selected identical to the single cylindrical hole. The multi-holes were machined with a fixed spacing pitch (33.3 mm) between the centers of two adjacent holes. The surface temperature of the test plate was measured by an infrared camera. The experimental studies were performed at blowing ratios of 0.5 and 2. The numerical results based on the steady RANS with realizable k–e turbulence model and enhanced wall treatment were capable to predict the influence of the shape of multi-hole configurations on overall adiabatic film-cooling effectiveness. The experimental and numerical results showed that replacing a single hole with a shaped multi-hole leads to a considerable increase in film-cooling effectiveness in both axial and lateral directions. According to the results at blowing ratio of 2.0, the elliptical and fan-shaped configurations provide a higher area-averaged film-cooling effectiveness by 75% and 248.2% in comparison with the single hole, respectively.

Numerical modeling of heat losses in a line focusing solar compound parabolic concentrator with planar absorber

In this work, a three-dimensional steady state thermal model is developed for a compound parabolic concentrator of 2× concentration considering the effects of surface radiation and wall conduction. The performance of the compound parabolic concentrator is modeled to obtain the convective and radiative heat loss under the influence of different parameters such as absorber temperature, absorber emissivity, ambient temperature, external heat loss coefficient, aspect ratio and concentrator tilt. The turbulent natural convection in the concentrator is modeled using standard two equation k-ε turbulent model with enhanced wall treatment. For the surface radiation inside the concentrator, discrete ordinate radiation model is used. The thermo physical properties of air inside the cavity are assumed to be constant except the density which is modeled as incompressible ideal gas. The conduction at the walls is accounted by setting suitable wall thickness for reflectors, glass cover and end walls in the solver. This work clearly demonstrates the need for a three dimensional numerical simulation and coupled natural convection and radiation to exactly reproduce the velocity fields as would be obtained in experiments. The convective Nusselt number, radiative Nusselt Number and thermal stratification are obtained from the parametric study. This study on estimation of heat losses in compound parabolic concentrator is applicable to both solar thermal and solar photo-voltaic collectors with a view of modifying the concentrator design to optimize its thermal performance.

Numerical Analysis of the Aerodynamic Characteristics of NACA-4312 Airfoil

The aim of the work is to investigate the aerodynamic characteristics such as lift coefficient, drag coefficient, pressure distribution over a surface of an airfoil of NACA-4312. A commercial software ANSYS Fluent was used for these numerical simulations to calculate the aerodynamic characteristics of 2-D NACA-4312 airfoil at different angles of attack (α) at fixed Reynolds number (Re), equal to 5×10^5 . These simulations were solved using two different turbulence models, one was the Standard k-ε model with enhanced wall treatment and other was the SST k-ω model. Numerical results demonstrate that both models can produce similar results with little deviations. It was observed that both lift and drag coefficient increase at higher angles of attack, however lift coefficient starts to reduce at α =13° which is known as stalling condition. Numerical results also show that flow separations start at rare edge when the angle of attack is higher than 13° due to the reduction of lift coefficient.

Heat transfer from a single and row of three dimensional wall jets - A combined experimental and numerical study

This paper reports the results of experimental and numerical studies to understand the heat transfer characteristics of three-dimensional wall jets exiting from a single and a row of circular jet openings over an unheated flat plate. Infrared thermography is employed to obtain the temperature distribution over the target surface, and the semi-infinite approximation methodology is used to estimate the heat transfer coefficients. Single wire constant temperature hot-wire anemometer is used to measure the flow characteristics. Additionally, computational studies have been performed to select a suitable low Reynolds number turbulence closure models among the following models, namely (i) Spalart Almaras (SA) (ii) Realizable k-ε with enhanced wall treatment (RKE-ewt) (iii) k-ω SST and (iv) Reynolds Stress Model with enhanced wall treatment (RSM-ewt) that predicts the experimentally obtained results for heat transfer characteristics accurately. Based on the investigations carried out, it is observed that RKE-ewt turbulence closure model is not only accurate but also faster in the prediction of heat transfer coefficient. Further, it is also seen that for a fixed mass flow rate, and at a given diameter of the jet opening, widely spaced jets show higher heat transfer coefficients. Furthermore, for a row of three-dimensional wall jets correlations based on the numerical results are developed for the Nusselt number for a Reynolds number range of 5000 to 15000.

Turbulent flames investigation of methane and syngas fuels with the perspective of near-wall treatment models

The near-wall treatment models play an important role in accurate turbulent flow simulation, particularly the ones close to the boundary layer. In the study, three k−ε epsilon near-wall treatment models, such as Enhanced Wall Treatment, Standard Wall Functions, and Scalable Wall Functions, have been numerically studied to verify the experimental results of methane combustion performed by Brookes and Moss within a laboratory-scale rig. Then, the turbulent flame of methane investigated at various wall distance (y∗) ranges specifically 0 < y∗ < 1, 1 < y∗ < 11.225, 11.225 < y∗ < 30, and 30 < y∗ < 500 to determine the effects of the mesh structures and y∗ on the numerical results. Following the validation of the near-wall treatment models and y∗, the turbulent combustion flame of methane and three syngas fuels were numerically investigated at the same thermal power, 8.6 kW. H2/CO ratios of the syngas 1, syngas 2, and syngas 3 are 2.36, 1.26, and 0.63, respectively. The maximum flame temperatures inside the chamber depend on the type of fuel, fuel species, and the percentage of the species. The results of the work show that Enhanced Wall Treatment presents better prediction as compared to the others, not only at 0 < y∗ < 1 but also at the other wall distance ranges. Standard Wall Functions demonstrates approximately the same results as compared to Scalable Wall Functions. Besides, the NO emissions in the flue gas of the syngas fuels are higher than methane due to higher flame temperatures and unburned hydrocarbon species. Furthermore, increment the H2/CO ratio for syngas fuels causes an increase in flame length, diameter, and temperature as well as NO emissions.

Numerical study on non-uniform heat transfer deterioration of supercritical RP-3 aviation kerosene in a horizontal tube

Abstract The convective heat transfer of supercritical-pressure RP-3 (Rocket Propellant 3) aviation kerosene in a horizontal circular tube has been numerically studied, focusing mainly on the non- uniform heat transfer deterioration along the circumferential direction. The governing equations of mass, momentum and energy have been solved using the pressure-based segregated solver based on the finite volume method. The re-normalization group (RNG) k-e turbulence model with an enhanced wall treatment was selected. Considering the heat conduction in the solid wall, the mechanism of heat transfer deterioration and the buoyancy effect on deteriorated heat transfer were discussed. The evolution of secondary flow was analyzed. Effects of the outer-wall heat flux, mass flux, pressure and tube thermal conductivity on heat transfer were investigated. Moreover, the buoyancy criterion and the heat transfer correlation were obtained. Results indicate that the poor flow performance of near-wall fluid causes the pseudo-film boiling, further leads to the heat transfer deterioration. The strong buoyancy has an effect of enhancing the heat transfer at the bottom of tube, and weakening the heat transfer at the top of tube, which results in the non-uniform inner-wall temperature and heat flux distributions. Decreasing the ratio of outer-wall heat flux and mass flux, increasing the pressure could weaken the heat transfer difference along the circumferential direction, while the effect of thermal conductivity of tube on the circumferential parameters distributions is more complicated. When the buoyancy criterion of (Grq/Grth)max ≤ 0.8 is satisfied, the effect of buoyancy could be ignored. The new correlations work well for non-uniform heat transfer predictions.