Convective Heat Flux Research Articles

Investigation on the DNB-type critical heat flux in a fuel assembly with 5 by 5 rods

In this paper, Eulerian two-phase model coupled with wall boiling model was employed to simulate the departure from nucleate boiling (DNB) in a 5 × 5 fuel assembly. The numerical simulation accurately predicted the critical heat flux (CHF) and also its location. Compared with the calculated results from W-3 formula and FLICA subchannel code, the CFD (Computational Fluid Dynamics) calculations showed good agreement against experimental measurements with the deviation of 5%, but presented more detailed flow distribution. Based on CFD results, the method of CHF prediction was discussed with an eye on wall superheat, void fraction and vapor convective heat flux in rod surfaces. The distribution of flow field and liquid–vapor fraction affected by mixing vane were further studied. Mixing vane can continually influence the downstream thermal hydraulic characteristics, forming the diagonal circulation and square circulation with the flow development. As a result, the bubble aggregation firstly occurred on the surface of corner hot rod instead of central hot rod, which induced the local heat transfer crisis. The CFD calculations presenting the evolution process of physical parameters can provide guidance for rod bundle CHF test and fuel assembly design.

Human scalp hair as a thermoregulatory adaptation

Humans are unique among mammals in having a functionally naked body with a hair-covered scalp. Scalp hair is exceptionally variable across populations within Homo sapiens. Neither the function of human scalp hair nor the consequences of variation in its morphology have been studied within an evolutionary framework. A thermoregulatory role for human scalp hair has been previously suggested. Here, we present experimental evidence on the potential evolutionary function of human scalp hair and variation in its morphology. Using a thermal manikin and human hair wigs at different wind speeds in a temperature and humidity-controlled environment, with and without simulated solar radiation, we collected data on the convective, radiative, and evaporative heat fluxes to and from the scalp in relation to properties of a range of hair morphologies, as well as a naked scalp. We find evidence for a significant reduction in solar radiation influx to the scalp in the presence of hair. Maximal evaporative heat loss potential from the scalp is reduced by the presence of hair, but the amount of sweat required on the scalp to balance the incoming solar heat (i.e., zero heat gain) is reduced in the presence of hair. Particularly, we find that hair that is more tightly curled offers increased protection against heat gain from solar radiation.

Measurement of the turbulent heat fluxes in mixed convection using combined stereoscopic PIV and PIT

The results of simultaneous measurements of velocity and temperature fields in a turbulent mixed convection airflow are analyzed and discussed. To access local temperature and velocity fields in airflows, we present a combination of stereoscopic particle image velocimetry and particle image thermometry. The obtained flow fields make it possible to determine the local convective heat fluxes, thus giving insight into the dynamics of plumes and Taylor–Görtler-like vortices. The evaluated mean local heat fluxes further reveal that the main convection roll transports a substantial amount of heat along the cooling plate and back to the heated bottom plate. Yet, the associated mean turbulent heat fluxes remain positive as they are dominated by the correlation of the temperature and the vertical velocity component. More specifically, a statistical analysis of the local heat flux distribution reveals that Taylor–Görtler-like vortices lead to more skewed distributions of the turbulent convective heat fluxes than plumes.Graphical abstract

Review of Jackson Herring’s Early Work on Thermal Convection

Jack Herring had three mid-1960s numerical papers on Rayleigh-Bénard thermal convection that might seem primitive by today’s standards, but already encapsulated many of the questions that are still being asked. All of them use severely truncated versions of the incompressible Navier–Stokes–Boussinesq equations with only one, or just a few, horizontal Fourier modes. In the first two papers, 1963 and 1964, the presented results used only one Fourier mode α and three variables. The single mode’s variables are its vertical velocity profile wα(z,t), its temperature profile θα(z,t) and the horizontally uniform vertical profile of the background temperature ψ(z,t). All of the second- and third-order terms are ignored except the convective heat flux wθ¯. The objective was to find asymptotic steady-state solutions. Each paper found evidence for the one-third Nusselt versus Rayleigh scaling of Nu∼Ra1/3, originally derived from Malkus’ maximum flux principle. The 1963 paper uses free-slip upper and lower boundaries, with magnitudes of Nu that are a factor of three larger than the experiments. In the 1964 paper, by introducing no-slip/rigid boundary conditions, the magnitude of Nu dropped to within 20% of the experimental values. Both Nu(Ra) relations are in good agreement with circa-1990 direct numerical simulations (DNS). This dependence upon the boundary condition at the walls suggests that to obtain physically realistic scaling, no-slip boundary conditions are necessary. The third paper is discussed only in terms of what it might have been aiming to accomplish and its relation to the earlier free-slip results.

Numerical Assessment of Safe Separation Distance in the Wildland–Urban Interfaces

A safe separation distance (SSD) needs to be considered during firefighting activities (fire suppression or people evacuation) against wildfires. The SSD is of critical interest for both humans and assets located in the wildland–urban interfaces (WUI). In most cases, the safety zone models and guidelines assume a flat terrain and only radiant heating. Nevertheless, injuries or damage do not result exclusively from radiant heating. Indeed, convection must be also considered as a significant contribution of heat transfer, particularly in the presence of the combined effects of sloping terrain and a high wind velocity. In this work, a critical case study is considered for the village of Sari-Solenzara in Corsica (France). This site location was selected by the operational staff since high-intensity fire spread is likely to occur in the WUI during wind-blown conditions. This study was carried out for 4 m high shrubland, a sloping terrain of 12° and a wind speed of 16.6 m/s. The numerical simulations were performed using a fully physical fire model, namely, FireStar2D, to investigate a case of fire spreading, which is thought to be representative of most high wildfire risk situations in Corsica. This study is based on the evaluation of the total (radiative and convective) heat flux received by two types of targets (human bodies and buildings) located ahead of the fire front. The results obtained revealed that the radiation was the dominant heat transfer mode in the evaluation of the SSD. In addition, the predictions were consistent with the criterion established by the operational experts, which assumes that in Corsica, a minimum SSD of 50 m is required to keep an equipped firefighter without injury in a fuelbreak named ZAL. This numerical work also provides correlations relating the total heat flux to the SSD.

Analysis of heat transfer characteristics of a sandwich cylindrical shell with a metal-rubber core

This work aims to analyze the heat transfer characteristics of a sandwich cylindrical shell with a metal-rubber core (SCS-MR) using both finite element analysis and experimental techniques. The SCS-MR is a lightweight and high-temperature resistant material that is suitable for construction in environments with varying conditions, such as rocket launchers, aircraft injectors and ships. The heat transfer, heat flux, and thermal convection loss were first analyzed using thermal resistance and Fourier law. Subsequently, a representative volume element of the SCS-MR was established to simulate thermal transfer, followed by a series of comparative experiments that measured the temperature gradients, the boundary conditions, and the density of the SCS-MR. Additionally, three types of metal spirals were examined using differential scanning calorimeter (DSC). The convective thermal conductivity, heat flux, and heat convection loss of the SCS-MR were analyzed experimentally, revealing that the metal spiral exhibited an exothermic peak in the DSC. Furthermore, the heat transfer rate of the SCS-MR was faster than that of the solid cylindrical shell (CS) when the set temperature was reached. The insulation cover was capable of providing boundary conditions to minimize the impact of natural convection. In the high-temperature environment, the thermal conductivity decreased with increasing density of the scaled model SCS-MR.

Upslope fire spread and heat transfer mechanism over a pine needle fuel bed with different slopes and winds

The surface fire spread involved slope and wind effects are significantly important in wildland fires, while very limited attention has been paid on the heat transfer mechanism, especially for different fire line conditions. This work experimentally evaluates the effects of slope angle (0˚ to 30˚) and wind velocity (0 to 2 m/s) on spread of surface fire over a pine needle fuel bed. Flame length, flame angle, rate of fire spread, fuel consumption rate and heat flux are acquired and quantitatively analyzed. Two different fireline shapes of sheet and inverted ‘v’ are observed and assumed for different wind velocities and slope angles, respectively. The flame length, rate of spread, mass loss rate and heat flux increase with the increasing wind velocity and slope angle, while flame angle and fuel consumption efficiency vary in the opposite way. The extreme fire can be observed with the external manifestations of a steep increase in flame length, rate of spread and heat flux under conditions of larger wind velocity and slope angle, which is similar to an eruptive fire. In addition, the heat transfer of convection and radiation heat flux is quantitatively analyzed with wind velocity and slope angle to explore heat flux control mechanism. Moreover, the modified models of radiation heat flux considering fire line shape are presented, which demonstrates good effectiveness in predicting radiation heat flux by comparing the calculated values and experimental data.

Numerical Investigation of Film Coefficient Approximation for Chemically Reacting Boundary-Layer Flows

Aerothermal analysis of spacecraft planetary entry is heavily dependent on heritage engineering models. The film coefficient heat transfer model examined in this paper estimates the convective heating to the vehicle for a laminar, dissociated, chemically reacting boundary layer for an Earth atmosphere. This model requires information about the vehicle and flowfield for a given trajectory point and estimates a proportional relationship between enthalpy potential and convective heat flux. In practice it is the aerothermal engineer who must decide which assumptions are appropriate for his/her application. This work looks at numerous CFD simulations for an arbitrary, axisymmetric flight vehicle to analyze the relative importance of both the mass and energy constraints imposed at the wall boundary, as well as the effect of various diffusion models. Within the subset of tested energy boundary conditions, it is found that the most desirable energy boundary condition is the radiative equilibrium boundary condition, which permits conservative estimates of convective heat flux, but also generates flowfield-dependent spatial thermal distributions along the surface. Other key findings are presented in an effort to make the film coefficient engineering model readily available to design engineers across industry.

Research on the Energy Characteristics of a Transferred Arc Plasma-Chemical Reactor for Waste Treatment

This study has been performed to reveal the main characteristics of operating a direct current (DC) plasma-chemical reactor (PChR) designed for hazardous waste treatment. The PChR employs thermal plasma as the operating environment. The investigations presented in this paper were conducted to study the electrical and energy characteristics of the plasma torch and plasma-chemical reactor during the destruction of inorganic waste. The PChR is equipped with a plasma torch with a nominal capacity of 50 kW and a free-burning arc. The zone of heat release from the atmospheric pressure DC arc cathode and arc anode (melted waste) spot is combined with the area of chemical reactions. The plasma torch (PT) parameters vary in the range of arc current I = 120–180 A, arc voltage U = 250–280 V, arc length x = 0–100 mm, and gas flow rate G = 1–3 g/s at atmospheric pressure, using air as the plasma-forming gas. The experimental results confirmed that plasma technology has several advantages over conventional incineration, including higher temperatures, heat source independence from the waste being processed or additional fuel, and a shorter exposure time in the high-temperature area. It was determined that the arc current increases with increasing arc length. With increasing arc length, the initial part begins to operate in a turbulent regime. This study determines the dependence on the heat flux transferred by electrons to the anode on the arc current. The convective heat flux density distribution over the anode heating spot was measured and discussed.

Time-dependent mixed stagnation point hybrid nanofluid flow with radiative heat flux and viscous dissipation effects over a movable EMHD Riga plate

This research communication scrutinizes the time-dependent radiated stagnation point flow by a movable Riga surface in the presence of porous medium, mixed convection, viscous dissipation and radiative heat flux. Both electro-magneto effects are accounted for. The considered flow problem comprises Copper (Cu) as a nanoparticle in a continuous phase fluid water (H2O). The mathematical modeling depends on two main expressions, i.e., momentum equation of Navier-Stokes equation under certain conditions and temperature expression. The coupled system is further simplified via similarity transformations. Computational outcomes are computed by implementing bvp4c technique with the shooting concept. The obtained results are displayed graphically. It is noticed from the computations that both Nusselt number (NN) and skin friction coefficient (SFC) declined subject to increasing estimations of the unsteady variable. The final outcomes and main key points are listed in the conclusion section.

Numerical simulation of subcooled flow boiling for nuclear engineering applications using OpenFOAM

Abstract This work is focused on the development and validation of models and methods for the simulation of wall boiling in nuclear engineering applications with the computational fluid dynamics (CFD) code OpenFOAM. The new chtMultiRegionReactingTwoPhaseEulerFoam solver was developed based on the reactingTwoPhaseEulerFoam solver of OpenFOAM Foundation version 7. The solver is used for the simulation of two-phase flow under consideration of wall boiling and conjugate heat transfer (CHT) between solid structure and two-phase fluid regions. The Euler–Euler approach for two-phase flows was used. The heat flux during wall boiling was calculated with the help of the extended Rensselaer Polytechnic Institute wall heat flux partitioning model, in which the convective heat flux between solid wall and two-phase flow with high void fractions was also considered. The solver was validated against experimental data from the OECD/NEA PWR Subchannel and Bundle Tests benchmark. This Nuclear Power Energy Corporation (NUPEC) database provides data for different fuel assembly subchannel geometries at different thermal-hydraulic conditions. 10 experimental runs with different boundary conditions of the benchmark exercise I-1 were simulated with the chtMultiRegionReactingTwoPhaseEulerFoam solver. The solver showed good numerical stability in all examined cases, which captured different boiling regimes with up to cross-section averaged void fractions of 0.6. The results were compared with measured data for the averaged over the cross-section of the investigated geometry void fractions. Good agreement with experimental data was observed.

Experimental Evidence of the Coupling between the Energy Charge–Discharge and Natural Ventilation in a Full-Scale Passive Building

An experimental study was carried out on a full-scale passive building equipped with global and local instrumentation with the aim of characterizing the energy charge and discharge processes and their coupling to the outdoor thermal stresses, especially natural ventilation in the summertime. The characterization of both charge and discharge processes is necessary to understand the thermal behavior of a building. From the measurement campaigns, the coupling between the charge–discharge and natural ventilation was qualitatively highlighted by the dynamics of the convective heat flux at each instrumented surface of the envelope. From the analysis of the experimental data, during the charge process, the floor and ceiling play an essential role in the attenuation of the rising of the indoor air temperature, while the south-facing glazed facade contributes the most to the heating of the indoor air. During the discharge process, the floor surface also plays an important role in the discharge of the envelope elements since the floor is the colder surface of the envelope. A parametric analysis of the coupling was also performed and showed that it is necessary to consider the convective effects on the slab surface, the ceiling, and the glazed facade individually due to their behavior.

Unified formulation of convective heat flux and mass flux vectors with thermodynamic coupling and related transfer coefficients

Based on the inherent thermodynamic relations of compressible species in binary mixtures at constant pressure, the general three-dimensional (3D) convective heat flux and mass flux vectors are formulated including the contributions of simultaneous advection, thermal diffusion and mass diffusion and their coupling effects between temperature and concentration gradients. The novel expressions for the diffusion-thermo and thermo-diffusion effects do not require the meager data of thermal diffusion ratio and are valid for both gas and liquid mixtures in laminar flows. The unified flux forms of the Maxwell's electromagnetic equation type are obtained in convective processes. It is further shown that the surface convective heat and mass transfer coefficients can be expressed in terms of the convective heat fluxes and mass fluxes away from surfaces in steady laminar flows, and that the expression of each transfer coefficient yields the identical form on both impermeable and permeable surfaces.

Estimation of the local instantaneous heat flux inside a pulsating heat pipe for space applications

Pulsating Heat Pipes (PHP) are promising and effective passive two-phase heat transfer devices in terms of high heat transfer capability, efficient thermal control, adaptability and low cost and therefore they have been extensively studied in the last years. Many authors have estimated the heat fluxes at the evaporator and at the condenser area only in terms of the average values based on first principle considerations. In the present study the application of an inverse analysis technique to experimental infrared temperature data is proposed to investigate the local convective heat flux for forced convection flow inside these devices along the adiabatic zone. A PHP specifically designed to be hosted on board the heat transfer host of the International Space Station was tested in microgravity during the 67th Parabolic Flight Campaign organized by the European Space Agency. The device consists of an aluminium tube closed in a loop with 14 turns in the evaporator section, 3 mm inner diameter, half filled with FC-72 fluid. The external temperatures of the device are measured in the adiabatic zone with a high-speed infrared camera (50 Hz, 1280x1024 pixels). The images are thereafter post-processed and adopted as input data for the solution of the inverse heat conduction problem in the pipe wall (Tikhonov regularisation method) to extrapolate time-varying local heat fluxes on the tube internal surface in contact with the fluid.

Flow and radiation modeling over a Martian entry vehicle

The high-temperature shock layer around re-entry vehicles strongly emits radiation through atomic lines and molecular bands. Radiative heat transfer strongly affects boundary layer flow and heat transfer. A novel spectral model based on k-distribution is implemented and coupled with a hypersonic flow solver in OpenFOAM to simulate heat transfer over a Martian entry vehicle. The Navier-Stokes equations with finite rate chemistry are used to model hypersonic chemically reacting flows. The convective terms in the governing equations are treated with various flux schemes (HLL, AUSM+, Kurganov, and Tadmor). The non-gray radiative properties of shock layer gases were modeled with the Emission-weighted Full Spectrum k-distribution (EFSK) method. The Radiative Transfer Equation (RTE) is solved with the P1 radiative solver to calculate the wall heat flux and radiative heat source term. At a high Mach number, the radiative heat flux is dominant compared to the convective heat flux. The numerical results for Mach number 26 are compared with published data and are found to be in good agreement. All the flux schemes provided results in close agreement, with minor differences, especially near the wall for the AUSM+ flux scheme.

Quasi-Steady Simulation of Glaze Ice Accretion and Heat Transfer in the Supercooled Large Droplet Regime in Atmospheric Turbulent Air Flow

Abstract To avoid the use of a computationally intensive full unsteady simulation while providing an accurate solution, a quasi-steady simulation has been performed to study glaze and mixed ice accretion in the supercooled large droplet (SLD) regime in turbulent flow of atmospheric air. We have attempted to find the minimum time-step necessary to adequately simulate the icing process on an airfoil surface. Based on node displacement, a mesh morphing scheme has been adopted in the computations to account for the moving boundaries that are caused by the continuous ice buildup. We have modeled ice accretion on an airfoil surface for a time period of 232 s using several time steps. At each time-step we solved the steady-state conservation equations for the air and droplet phases and then used the results as initial conditions for the next time position. The magnitude of the time-step ranged from a least accurate two-shot simulation (where the time-step is 116 s) to a most accurate 2320-shot simulation (where the time-step is 0.1 s). In-between these two extreme time steps, we have performed a three-shot simulation (where the time-step is 77.33 s), a four-shot simulation (where the time-step is 58 s), a six-shot simulation (where the time-step is 38.67 s), a 46-shot simulation (where the time-step is 5 s), and a 232-shot simulation (where the time-step is 1 s). We have done so to find out the degree of accuracy (or inaccuracy) of the multishot simulation approach and to find out the appropriate time-step needed for a successful and valid quasi-steady simulation. A valid quasi-steady simulation needs to use a time-step that is small enough to reproduce the full time-dependent solution within a very small error band. We have found that both the 1 s and the 0.1 s time steps produce virtually identical results. This is the primary litmus test that proves the validity of the quasi-steady-state assumption. The results adopted in this paper are thus all based on the more conservative 0.1 s time-step. In the process of performing the simulations, remeshing was required in order to maintain the grid density in zones of high curvature to be able to capture the full physics in those zones. After successfully modeling glaze ice accretion over the airfoil surface using the 0.1 s quasi-steady simulation approach, the effects of supercooled large droplets (SLDs) impacting the surface have been examined and presented in terms of the variation of the local collection efficiency, the water film thickness, and the heat transfer rate. Examination of the variation of the angle that the ice horn makes with the airfoil chord line demonstrated a 20% improvement in angle prediction when the time-step is reduced from 116 s to 0.1 s. The analysis also reveals a 12% or 8.5% increase in the maximum collection efficiency, βmax, depending on whether the value of the liquid water content (LWC) has been doubled from 0.5 g/m3 to 1 g/m3, or the value of the freestream velocity has been doubled from 75 m/s to 150 m/s, respectively. Because of the need to monitor the local collection efficiency and convective heat fluxes at each shot (regardless of the number of shots employed), the approach adopted here was found to be effective in successively and successfully reproducing the curvature of the glaze ice horn.

Physics-based simulations of grassfire propagation on sloped terrain at field scale: flame dynamics, mode of fire propagation and heat fluxes†

The interaction of wind and fire on a sloped terrain is always complex owing to the mechanisms of heat transfer and flame dynamics. Heating of unburned vegetation by attached flames may increase the rate of spread. The relative intensities of convective and radiative heat fluxes may change fire behaviour significantly. This paper presents a detailed analysis of flame dynamics, mode of fire propagation and surface radiative and convective heat fluxes on sloped terrain at various wind speeds using physics-based simulations. It was found that with increasing slope angles and wind velocity, the plume inclines more towards the ground and becomes elongated in upslope cases, whereas in downslope cases, the plume rises from the ground earlier. For higher wind velocities, the flame and near-surface flame dynamics appear to show rising, even though the plume is attached. The flame contour results indicate that the near-surface flame dynamics are difficult to characterise using Byram’s number. A power-law correlation was observed between the simulated flame lengths and fireline intensities. The convective heat fluxes are more relevant for wind-driven fire propagation and greater upslopes, whereas both fluxes are equally significant for lower driving wind velocities compared with higher wind velocities.

Theoretical prediction of temperature difference between prefrontal cortex and forehead skin for fever screening

To improve reliability of fever screening, many studies have been conducted on the relationship between forehead skin and core temperatures. However, all studies thus far were based on only statistical analyses of temperature data, and it remains unsolved how forehead skin temperature is determined and controlled by environmental temperature as well as face details of individual. This study examined heat transfer in a free convection thermal boundary layer on the human forehead theoretically and experimentally to propose a theoretical model describing the relationship between prefrontal cortex (PFC) and forehead skin temperatures. Temperature distributions across the forehead boundary layer measured using a resistance thermometer probe showed that the convective heat flux on the forehead, including the case of wearing face mask, could be estimated similarly to that in a laminar free convection boundary layer on a heated vertical plate. It was also shown that the difference between PFC and forehead skin temperatures measured using a zero-heat-flux core-temperature monitoring probe and a thermocouple attached to the forehead was well represented by a simple formula derived from analyses of radiative and convective heat fluxes over a normal range of environmental temperature. Wearing a face mask little affected the temperature difference between PFC and forehead skin. These results provide a scientific basis for fever screening from thermo- and fluid-dynamics viewpoints.

Dust Devil Frequency of Occurrence and Radiative Effects at Jezero Crater, Mars, as Measured by MEDA Radiation and Dust Sensor (RDS)

AbstractThe Mars Environmental Dynamics Analyzer, onboard the Perseverance rover, is a meteorological station that is operating on Mars and includes, among other sensors, the radiometer Radiation and Dust Sensor (RDS). From RDS irradiance observations, a total of 374 dust devils (DDs) were detected for the first 365 sols of the mission (Ls = 6°–182°), which along with wind and pressure measurements, we estimated a DD frequency of formation at Jezero between 1.3 and 3.4 DD km−2 sol−1 (increasing as we move from spring into summer). This frequency is found to be smaller than that estimated at the Spirit or Pathfinder landing sites but much greater than that derived at InSight landing site. The maximum in DD frequency occurs between 12:00 and 13:00 local true solar time, which is when the convective heat flux and lower planetary boundary layer IR heating are both predicted to peak in Jezero crater. DD diameter, minimum height, and trajectory were studied showing (a) an average diameter of 29 m (or a median of 25 m) and a maximum and minimum diameter of 132 ± 63.4 and 5.6 ± 5.5 m; (b) an average minimum DD height of 231 m and a maximum minimum‐height of 872 m; and (c) the DD migration direction is in agreement with wind measurements. For all the cases, DDs decreased the UV irradiance, while at visible or near‐IR wavelengths both increases and decreases were observed. Contrary to the frequency of formation, these results indicate similar DD characteristics in average for the studied period.

Experimental estimation of the local heat transfer coefficient for thin liquid film evaporation in a capillary tube

• Local heat transfer coefficient was estimated for thin liquid film evaporation in a capillary tube. • Temperature infrared measurements were employed as input data of the inverse heat conduction problem. • A robust estimation procedure was adopted. • Procedure validation through the application to both synthetic and experimental data. • Original insight of thin liquid film evaporation was given. Two-phase heat transfer devices consisting of mini and microtubes represent a powerful solution to the continuous reduction of electronic components' dimensions and to the increase of the power to dissipate. Despite many studies on the two-phase heat transfer phenomenon in minitubes, most provided outcomes regarding the average heat transfer coefficient or Nusselt number. A technique to assess the local convective wall heat flux and heat transfer coefficient is proposed, validated, and then applied to the experimental case of thin-film evaporation in a heated capillary tube. The evaporation of the thin film of liquid plays a vital part in the two-phase heat transfer phenomenon inside mini/microtubes. Our study investigated this phenomenon by examining a semi-infinite slug flow. The estimation method used is represented by the inverse heat conduction problem solution in the tube wall, applying the Tikhonov regularisation method. The temperature distributions on the outer surface of the channel measured by an infrared camera were employed as input data for the inverse problem. The estimated heat transfer coefficient distributions confirm the available correlations in average values and provide insight into these complex phenomena in local and instantaneous quantities.