Convective Heat Transfer Coefficient Distribution Research Articles

Computational Fluid Dynamics Prediction of External Thermal Loads on Film-Cooled Gas Turbine Vanes: A Validation of Reynolds-Averaged Navier–Stokes Transition Models and Scale-Resolving Simulations for the VKI LS-94 Test Case

Given the increasing role of computational fluid dynamics (CFD) simulations in the aerothermal design of gas turbine vanes and blades, their rigorous validation is becoming more and more important. This article exploits an experimental database obtained by the von Karman Institute (VKI) for Fluid Dynamics for the LS-94 test case. This represents a film-cooled transonic turbine vane, investigated in a five-vane linear cascade configuration under engine-like conditions in terms of the Reynolds number and Mach number. The experimental characterization included inlet freestream turbulence measured with hot-wire anemometry, aerodynamic performance assessed with a three-hole pressure probe in the downstream section, and vane convective heat transfer coefficient distribution determined with thin-film thermometers. The test matrix included cases without any film-cooling injection, pressure-side injection, and suction-side injection. The CFD simulations were carried out in Ansys Fluent, considering the impact of mesh sizing and steady-state Reynolds-Averaged Navier-Stokes (RANS) transition modelling, as well as more accurate transient scale-resolving simulations. This work provides insight into the advantages and drawbacks of such approaches for gas turbine hot-gas path designers.

A numerical investigation of hydrogen impingement-effusion array jet for a heat sink cooling using solid/porous fins: A thermo-hydrodynamic analysis

Increasing the aim of hydrogen use as fuel in vehicles motivates applying it to other critical requirements, such as cooling, owing to its thermal properties. Therefore, the effect of applying hydrogen impingement jets for cooling a hot surface of electrical devices, such as a prismatic battery, is investigated in this numerical study. The dependent variables are the volumetric flow rate, the jet distance from the target to the jet diameter, the coolant type, and the fins configuration, called in-line and staggered, and types, as solid or porous. The convective heat transfer coefficient, thermal resistance, pressure drop, and temperature and velocity distribution for the studied cases are considered. The simulation is conducted using the SST k-ω turbulence model, SIMPLE algorithm, and second-order method for discretization differential equations. Applying hydrogen as the coolant decreases the maximum temperature up to 2% and increases heat transfer by about 10%, while it mitigates the pressure drop by a factor of 1/12 if compared to air coolant. Further, inserting porous fins improves heat transfer by about 10% and 17%, respectively for air and hydrogen coolant in comparison with the case without fins. The fin decreases the temperature on the root and makes the recirculation zones.

Heat transfer and mechanical characteristics of the absorber in solar photo-thermal power generation system

In order to solve the problems of thermal fatigue, high temperature gasification and low temperature solidification of the heat receiver, a numerical calculation model for the heat transfer function of the tower type solar thermal power gener?ation high temperature receiver is proposed. A perfect analysis method is used for the simulation, and a thermal simulation program for predicting the heat gain of the solar thermal energy tower is compiled. In this paper, considering the various field connection characteristics, numerical value and distribution of convective heat transfer coefficient of the heat absorption medium, the temperature of the outer wall of the heat pipe absorption, and the thermal image conversion work in a non-uniform heat flow boundary area of a model of heat receiver was studied. The experiments show that when the flow rate of molten salt in the tube increases from 1 m/s to 2 m/s, the heat collection efficiency of the heat collection increases rapid?ly, while the flow time is more 3 m/s, the heat collection efficiency increases more gradually. The efficiency of heat absorption of the heat receiver is in the middle of the heat receiver, which can achieve 88 of the thermal image conversion. In the same large enough value, the heat collected at the inlet and outlet of the heat sink is about 82. It is clear that the numerical simulation provides a reliable basis for the design engineering, and provide guidance for the design of a full control model of tower solar photovoltaic power generation.

Optimization of power distribution for electrothermal anti-icing systems by differential evolution algorithm

Ice accretion on windward components of aircraft will seriously threaten flight safety. Electrothermal anti-icing systems can prevent icing on the critical components. They have great potential for lightweight and energy-saving aircraft. This paper develops a numerical anti-icing model coupled with heat conduction in a multi-layer composite structure to evaluate the anti-icing performance. Furthermore, a differential evolution algorithm is adopted to optimize the power distribution of an electrothermal anti-icing system with a fixed heating element layout to find the minimal power consumption to ensure that no runback water flows out of the protection area. The maximum anti-icing surface temperature, runback water range, and the maximum temperature in the multi-layer composite structure are selected as constraints during optimization to guarantee the effectiveness of the anti-icing protection system. The feasibility rule based on a constraint violation is deployed to handle the constraints. The distributions of internal temperature of the multi-layer structure, anti-icing surface temperature, and runback water are chosen to evaluate the performance of the electrothermal anti-icing system. Comparing these performance parameters of optimized and baselines cases shows that the differential evolution algorithm can obtain minimal power consumption based on the anti-icing model under fixed icing conditions and heating element layout. The analysis of different heat flux terms indicates that the heat power distribution of the electrothermal anti-icing system should match convection heat transfer coefficient distribution on the surface to increase the energy efficiency.

Cooling Characteristics of the Hot-Rolled Seamless Steel Tube Impinged via Inclined Jet

The characteristics of flow field distribution and temperature variation of an inclined jet impinging on a steel tube surface at different positions in circumferential directions were studied via numerical simulation. By analyzing the local convective heat transfer coefficient in circumferential direction, it was shown that the downstream and upstream regions had the characteristics of typical asymmetry. As the inclination angle increases, the local convective heat transfer coefficient gradually increases in the downstream region and gradually decreases in the upstream region. When the θ of the top and bottom jet is 30°, the increases in the downstream region are 40.2% and 54.6%, respectively. Based on the study of the local convective heat transfer coefficient and temperature distribution in the circumfluence direction of a steel tube during the cooling process, it was shown that the optimal inclination angle is 0~10°. With the increase in inclination angle, the average heat transfer coefficient shows a decreasing trend overall. With the increase in jet Reynolds number, the decrease in the average heat transfer coefficient gradually decreases. When the inclination angle increases to 30°, the effect of inclination angle on steel tube cooling is obviously stronger than that of jet position.

Experimental assessment of the gap width effect on turbulent flow and forced convective heat transfer around a single rod suspended in a channel

The present work presents the experimental campaign carried out to assess the convective heat transfer around a single rod suspended in a rectangular channel under axial turbulent flow. The distance between the rod and the upper wall of the channel forms a rod-wall gap, whose width, d, can be varied. The experiments were performed for the dimensionless gap widths that yield W/D = 1.050, 1.100, 1.150 and 1.200. Hot-wire anemometry was used to measure mean velocities, the RMS velocity fluctuations and the velocity spectra. The rod is equipped with a heated cell that provides the local temperature and convective heat transfer coefficient distributions around the rod’s surface. The local convective heat transfer distribution is in good agreement with the literature. The lowest value for the heat transfer coefficient was not found right in the narrow gap for W/D = 1.050, but, slightly away from the gap. As W/D increases, the minimum local convective heat transfer coefficient occurred closer to the narrowest gap width. The Reynolds-Colburn analogy was investigated for all configurations through the measured convective heat transfer coefficient and the skin friction distributions. A linear relationship was found between the Stanton number and the skin friction coefficient. Moreover, data scattering was seen to decrease significantly when the local velocity was used instead of the global one. It suggests that the heat transfer process is governed, mainly, by the local parameters.

Design a cooling pillow to support a high-speed supercritical CO2 turbine shaft

• High speed supercritical CO 2 turbine rotor shaft cooling zone. • Modeling a cooling pillow to cool the shaft and to provide dynamic support. • Design charts and figures for the cooling zone. • Rotor dynamic analysis through the Campbell diagram. • Trade-off analysis in designing the cooling zone. Supercritical CO 2 cycles offer a new thermal power generation paradigm but their commercial deployment has been slow due to significant turbine design challenges. Rotor bearings and seal design are identified as the critical challenges due to the high temperatures, high pressures, and high rotational speeds, a combination of extreme values not encountered in any other past turbine applications. This paper presents a new supercritical CO 2 turbine configuration that addresses these challenges by introducing a rotor shaft cooling zone to control the temperatures encountered by the seals and the bearings. This makes it possible to use proven conventional seal and bearing technology. The salient feature is referred to as a ‘cooling pillow’ that cools the rotor shaft to a tolerable seal temperature by circulating supercritical CO 2 fluid through the annulus and at the same time provides dynamic support to the rotating shaft against vibration. Turbulent heat transfer and frictional heat generation correlations for the annuli have been employed to evaluate the cooling performance and the simplified Reynolds equation for hydrodynamic fluid film lubrication has been employed to evaluate the dynamic performance. Design charts and figures are presented using non-dimensional parameters to help with the design of supercritical CO 2 turbines at different temperatures and sizes. The COMSOL rotor-bearing system simulator consisting of bearing and disks with the main shaft has been employed to produce Campbell plots and carry out a parametric study of rotor vibration frequencies varying with the cooling zone design. The cooling capacity is found to be significantly higher than the cooling load required. Moreover, the convection heat transfer coefficient and dimensionless temperature distribution are independent of radial clearance and this offers trade-offs in terms of controlling rotor vibrations. Through the pursuit of such trade-offs, it is demonstrated that dynamic performance can be improved by up to 55% and 60% for the 0.5 MW and 10 MW turbine sizes, respectively.

The Flow-Heat Coupling Study of Cooling Circulating Channel of Magnetic Drive Pump

The medium in the cooling circulation channel of the magnetic drive centrifugal pump will take away the heat generated by the magnetic eddy current and bearing friction in time to avoid the high temperature demagnetization phenomenon of the permanent magnets. Therefore, the reasonable design of the cooling circulation channel directly affects the stable operation of the magnetic drive centrifugal pump. In this paper, the heat exchange and temperature distribution in the cooling circulating channel of magnetic drive pump are studied by means of numerical calculation of fluid-heat coupling and external characteristic test. The temperature distribution and development law of the isolation sleeve clearance, the bottom of the isolation sleeve and the reflow hole are analysed emphatically, and the convection heat transfer coefficient distribution in the isolation sleeve clearance is studied.

Determination of convective heat transfer coefficient for hot gas torch (HGT)-assisted automated fiber placement (AFP) for thermoplastic composites

In-situ manufacturing of thermoplastic composites using the automated fiber placement (AFP) process consists of heating, consolidation and solidification steps. During the heating step using hot gas torch (HGT) as a moving heat source, the incoming tape and the substrate are heated up to a temperature above the melting point of the thermoplastic matrix. The convective heat transfer occurs between the hot gas flow and the composites in which the convective heat transfer coefficient h plays an important role in the heat transfer mechanism which in turn significantly affects temperature distribution along the length, width and through the thickness of the deposited layers. Temperature is the most important process parameter in AFP in-situ consolidation that affects bonding quality, crystallization and consolidation. Although it is well known the convective heat transfer coefficient h is not constant and has a distribution, most studies have assumed a constant value for h for heat transfer analysis which leads to discrepancy between numerical and experimental results. In this study a new function is proposed to approximate the distribution of the convective heat transfer coefficient h in the vicinity of the nip point. Using the proposed convective heat transfer coefficient distribution, a three-dimensional finite element transient heat transfer analysis is performed to predict temperature distribution in the composite parts. An optimization loop is employed to find the free parameters of the distribution function so that the predicted temperature match experimental data. It is shown that, unlike other studies assuming constant h value, not only maximum temperature can be well predicted, but also predicted heating and cooling curves agree well with experimental results. The cooling rate is of significant importance in crystallization behavior and residual stress calculation.

Laser-Scanning-Based Method for Estimating the Distribution of the Convective-Heat-Transfer Coefficient on Full-Scale Building Walls

We propose a method for estimating the convective-heat-transfer coefficient (CHTC) distribution on building walls by using the water-evaporation method involving filter paper and three-dimensional laser scanning, and demonstrates consistency with the gravimetric evaporation method. The theory and method are established based on the convective heat- and mass-transfer analogy and a near-infrared laser-scanning system. The equations to remotely estimate the CHTC distribution are obtained empirically, and the proposed method is applied to the walls of a penthouse during winter. The spatial distribution of the surface reflection intensity that determines the evaporation rate is successfully retrieved with 0.2–0.3% accuracy from a measurement distance of 5 m. The comparison of evaporation rates with a gravimetric measurement does not show a statistically significant bias. The results show that the crucial factors for the precision of the CHTC estimation are errors in the laser-scanning system and their amplification when dividing the evaporation rate by the vapour pressure deficit to obtain the convective-mass-transfer coefficient. The estimated CHTC distributions on the target walls have approximately ≤ 2–3 W m−2 K−1 errors in the 95% confidence interval after applying spatial and/or temporal averaging. Although the error in the convective-heat-transfer coefficient is larger in winter during minimal vapour pressure deficits, it is generally well explained in the range of the random error in laser scanning. The correlation between the spatially-averaged convective-heat-transfer coefficient and near-wall wind speed is comparable to existing methods (R = 0.71–0.79), and the regression relation agrees with that obtained in previous studies performed in similar conditions.

Numerical study of unsteady flow and heat transfer of circular tangential direction jets flowing over the inner cylinder surface in the annular chamber

In order to understand the dynamics of vortices on heat transfer, the unsteady flow field of tangential direction jets flowing in the annular chamber is numerically investigated by scale-adaptive simulation (SAS). The jet Reynolds number is 332,000 based on the jet’s diameter and inflow velocity for a specific geometric model. The analogy theory is used to obtain the convective heat transfer coefficient distribution on the hub surface. Spectral analysis via fast Fourier transform (FFT) is used to analyze frequency information that flows inside the chamber. The proper orthogonal decomposition (POD) method is performed on the velocity field in the chamber and the convective heat transfer coefficient on the hub surface using a snapshot method. The fast Fourier transform helps find the dominant frequency of the unsteady flow in the chamber. The time sequence of velocity fields on the radial plane shows the presence of cyclic flapping of the jet. The proper orthogonal decomposition analysis indicates that the unsteady periodic flow phenomenon in the chamber and unsteady heat transfer on the hub surface are mainly related to the dynamics of the counter-rotating vortices caused by the jet.

Thermal structure design optimization and temperature control for worm gear grinding machine using flood cooling technology

For the worm gear grinding machine using flood cooling technology, the coolant absorbs the grinding heat in the machining process and flows on the machine bed, which directly affects the relative position between tool and workpiece. The existing thermal structure analysis and the temperature control research lack in-depth research on thermal problems related with the coolant flowing along the machine bed. In order to reduce the thermal deformation of the machine bed, this paper proposes a novel structure with double-layer coolant channel to improve the thermal characteristics of the machine bed, and the cooling fluid is controlled to maintain an even temperature distribution of machine bed through this structure. In addition, based on a comprehensive analysis of the machine bed heat sources and boundary conditions, a more accurate coolant convection heat transfer coefficient distribution was obtained by using CFX software, and a flow-thermal-structural multi-field sequential coupling finite element thermal characteristic analysis model was established to study the thermal characteristics of the machine bed. The results show that the maximum prediction error of the model is less than 6.77% compared with the experimental data under the same working conditions. The temperature distribution of the proposed machine bed structure is more uniform than that of the original one. The maximum temperature difference is reduced by 1.7 °C, which shows that this method can effectively reduce the relative deflection between the workpiece column and the column. The proposed machine bed structure decreases the thermal deformation’s sensitivity to the temperature of the coolant and has a high adaptability to external temperature fluctuations.

Experimental justification of poor thermal and flow performance of solar chimney by an innovative indoor experimental setup

Power generation of solar chimneys effectively depends on their thermal performance. The manufactured samples, available in the literature, have many functional weaknesses and their obtained output power is much lower than expected. Due to the variation of operating conditions (i.e. solar radiation, wind velocity, ambient temperature etc.) of outdoor experimental setups, the thermal performance and heat transfer coefficient cannot be properly evaluated for those systems. Herein, a new indoor test setup is employed to study the steady-state thermal performance of the solar chimney collector while the effects of environmental changes on the tests are minimized. The flexibility of the custom-designed experimental setup allows the investigation of effects of angle of collector, height of chimney, and the area of collector on the convection heat transfer coefficient, velocity and temperature distribution at various points, and the ratio of energy transferred to that introduced to the collector (RET). Our analyses show that the poor performance of common solar chimneys can be justified by existence of secondary flows beneath the collector. The results are important in designing the next generation of solar chimneys with optimized geometry and enhanced thermal efficiency. Results show that, high thermal and frictional losses, due to formation of secondary flows, cause less than 9% of the input energy to enter the chimney and generate power. The collector angle is known the most responsible parameter for controlling formation of the secondary flows. For the divergent collector, increasing the collector angle from 0 to 14 reduces the thermal losses by 1.72% and enhances the heat transfer coefficient by 41.6%. On the other hand, higher amounts of secondary flows in convergent collectors, increases thermal losses by 98.8%. Based on the obtained results, increasing the collector area, as commonly suggested by many researches, while increasing the suction velocity, significantly reduces thermal efficiency of the chimney; This issue along with increasing the manufacturing costs, indicate that increasing the area acts marginally and cannot be a good idea to improve chimney performance most of the times.

Heat transfer and stress characteristics of additive manufactured FCCZ lattice channel using thermal fluid-structure interaction model

Lattice channels designed for hot stamping, metal injection, and die casting should have high heat transfer and structural performances. In this study, a thermal fluid-structure interaction (TFSI) one-way coupled model is developed to estimate the heat transfer and stress characteristics of a face-centered cubic with vertical struts (FCCZ) lattice channel. Based on the simulation model, the heat transfer and stress characteristics of the FCCZ lattice channel produced by metal additive manufacturing (AM) are analyzed in terms of the thermal fluid field, convective heat transfer coefficient, pressure drop, and stress distribution by varying the porosity and inlet velocity. Considering the thermal-structural performance factor (TSPF), the optimum porosity of the FCCZ lattice channel is determined as 0.8. In addition, the performances of the FCCZ lattice channels using 17-4 PH, H13, and maraging steel are compared. The performance of the H13 channel is superior to those of the 17-4 PH and maraging steel channels.

Unsteady numerical simulation on helium cooldown process for the 650 MHz two-cell superconducting cavity

Superconducting cavity is usually needed to be gradually cooled from room temperature to the superconducting temperature zone (4.2 K and below) in the testing and sophisticated operation process of superconducting cavity. The purpose of this paper is to study the cooling law on the helium cooldown process for the 650 MHz two-cell superconducting cavity with the unsteady numerical simulation. A three-dimensional coupled heat-flow model of 650 MHz two-cell superconducting cavity was established. The unsteady numerical simulation of different inlet temperatures, flow rates and pressure conditions was carried out. The equivalent convective heat transfer coefficient and temperature distribution of 650 MHz two-cell superconducting cavity during cooldown process were obtained. The effects of cooling time and entrance parameters on the cooldown process were analyzed. The temperature distribution of the lower intersection lines has a large drop in the initial stage of cooldown process (120 s), while the temperature near the flanges at the both ends is still higher (remaining at the initial temperature of 300 K). With the passage of time, the temperature of the upper and lower intersection lines decreases. The maximum temperature difference on the lower intersections is within 2 K in the final stage of cooldown process (3600 s). The maximum temperature difference increases by 180%, and the difference between the maximum temperature and the minimum temperature (dT) at the end of a cooldown stage increases by 130% after 1 h, respectively, when the inlet temperature drops from 290 to 270 K (under the condition of the initial temperature of 300 K). The maximum temperature difference and the dT at the end of a cooldown stage increase with the decrease in the inlet temperature. The maximum temperature difference increases with the increase in the inlet flow rate, while the dT at the end of a cooldown stage decreases with the increase in the inlet flow rate. The effect of changing the inlet flow rate on the cooling rate is not as obvious as changing the inlet temperature. Once there is a certain flow rate, the advantage of further increasing the flow rate to reduce the temperature of the superconducting cavity is not so great.

Numerical analysis of convective heat transfer coefficient for building facades

The latest architectural trends demand an extensive use of glazed curtain walls running from building floor to ceiling. While glazing poorly controls the heat flow, it is important for viewing, daylighting, and solar design features. In order to evaluate building energy consumption accurately, knowledge of convective heat transfer coefficient (CHTC) distribution over the façade of the building is important. In this article, high-resolution numerical simulations that use three-dimensional steady Reynolds-averaged Navier–Stokes and energy equations are performed. Convective heat transfer coefficient values at the windward facade of five buildings, with rectangular floor plans, and heights of 3, 10, 15, 20–30 stories, have been produced. The influence of building height on CHTC distribution is investigated at Reynolds numbers ranging from 0.7 × 106 to 33 × 106, and a correlation equation as a function of building height and a reference wind velocity is developed. For example, as the height increases from 10.1 to 101 m in the study cases, the surface-averaged convective heat transfer coefficient on the windward façade increases by 55%. The high-resolution spatial distribution of convective heat transfer coefficient over façade of the tallest building indicates that the top-corner zone convective heat transfer coefficient values are higher by 24% and the base-center zone values are lower by 27% compared to the average CHTC value, implying the necessity for zonal treatment.

Effect of fin shape on the thermal performance of nanofluid-cooled micro pin-fin heat sinks

The study presents the combined effects of using nanofluid and varying fin cross-sectional shape on the heat transfer characteristics of a micro pin-fin heat sink by employing discrete phase model (DPM). Three fins configurations of the square, circular and hexagon cross-section with constant fin diameter and height have been analyzed for the inline arrangement of 17 × 34 fins. Aqueous nanofluid containing spherical shaped particle dispersions of TiO2 has been simulated for the particle concentration and size of 4.31 vol% and 30 nm respectively. Constant heat flux (192 W) boundary condition at the base of heat sink has been considered for the range of Reynolds number 250 ≤ Re ≤ 550. The influence of fin shape on the thermal efficiency of the heat sink has been analyzed by evaluating heat sink base temperature, Nusselt number, convective heat transfer coefficient distribution and temperature contours along the surface of the heat sink. Additionally the velocity streamlines and contours have also displayed to elaborate the fluid flow attributes. Results demonstrate that under identical flow conditions, the nanofluid cooled circular fins displayed most efficient thermal performance followed by the hexagon and square fins. While the water cooled square fins depicted lowest heat transfers characteristics. The best thermal performance of the circular fins is the response of the delayed flow separation along the smooth surface of fins and the subsequent uniform flow distribution along the whole sink. For all the cases, upstream fin rows played a primary contribution in flow distribution and hence thermal characteristics of the heat sink.

Numerical calculation of CHTC on end metal parts and flow in end region of a turbogenerator

The convection heat transfer coefficient (CHTC) distribution of surfaces of end metal parts directly affects the temperature distribution of end metal parts. In this study, a large turbogenerator is analysed. To study the CHTC distribution of surfaces of end metal parts in detail, a three-dimensional (3D) fluid and thermal analysis model of whole turbogenerator end region is established. The losses of end metal parts from 3D transient electromagnetic field calculation are provided to end metal parts as heat sources. Pressure values of end-region outlets and fluid velocity of fan outlet from flow network calculation are provided to end region as boundary conditions in the 3D fluid and thermal analysis model. CHTC distribution laws of the surfaces of the clamping plate, finger plate, and copper screen are studied in detail by the finite volume method. The fluid flow and temperature distribution of end metal parts are determined in the end region of the turbogenerator. The calculated results are compared with measured data.

Experimental study of the transitional flow regime in coiled tubes by the estimation of local convective heat transfer coefficient

The present work is focused on studying the transition between the laminar and turbulent flow regime in coiled tubes. Wall curvature is a popular heat transfer enhancement technique since it gives origin to a secondary flow in the flowing fluid due to the non-uniformity of the centrifugal force over the cross section. This phenomenon, both in the laminar and the turbulent flow regime, promotes local maxima in the velocity distribution that locally increase the temperature gradient at the wall by enhancing the heat transfer and, at the same time, leading to a significant variation in the convective heat-transfer coefficient along the circumferential angular coordinate. However, this geometry delays the transition from laminar to turbulent regime, transition that, in the majority of the papers available in the scientific literature, has been investigated on the basis of pressure drop data behaviour. In the present work the estimation of the local convective heat transfer coefficient distribution, based on the solution of the inverse heat conduction problem in the tube’s wall, is proposed as a complementary and detailed tool to investigate the transitional flow regime. Moreover, the present research, thanks to the application of the proposed approach to an experimental case, gives additional information on the phenomenon of transition in coiled tubes.

Effect of heat and mass flux on heat transfer characteristics of water forced convection inside vertical and inclined rifled tubes

Abstract In this paper the subcritical and supercritical water flow inside a rifled tube has been investigated experimentally. A comparison between vertical upward flow and a 20° inclined upward flow inside a specifically designed rifled tube for various heat and mass flux values has been conducted. The operating pressures for the tests were 15, 21.5, 22.5, 25 and 28 MPa, heat fluxes were 300, 400 and 500 kW/m2 and mass fluxes were 600, 800 and 1000 kg/m2 s. The low mass flux condition has been considered due to its important applications in boiler industries for once-through vertical and spirally wound tubes boilers. The results were shown as inner wall temperature versus fluid bulk enthalpies and convection heat transfer coefficient distribution for various fluid bulk enthalpies for various flow conditions inside the both vertical and inclined tubes. The results showed that the effect of inclination on heat transfer enhancement is incentive for subcritical pressure flows. Also the results showed the higher effect of mass flux on heat transfer in near-critical and supercritical pressures in comparison with the subcritical pressure conditions.