Convective Transfer Coefficient Research Articles

Experimental Investigation of Tip Design Effects on the Unsteady Aerodynamics and Heat Transfer of a High-Speed Turbine

Abstract While modern engine manufacturers devote significant efforts to the development of reliable and efficient machines, the introduction of novel, optimized components in the hot gas path represents a risky opportunity. Accurate experimental and numerical data are critical to assess the impact of new technologies on the harsh engine environment. The present study addresses the impact of a selection of high-performance rotor blade tips on the aerodynamic and heat flux field of a high-pressure turbine (HPT) stage. A combined numerical and experimental approach is employed to characterize the interaction of the tip leakage flow with the rotor secondary flows and the casing heat transfer mechanisms for each individual tip geometry. The turbine stage is tested at engine-scaled conditions in the rotating turbine facility of the von Karman Institute. In the present study, the turbine rotor is operated in rainbow configuration to allow the simultaneous testing of multiple blade tip geometries. Reynolds-averaged Navier–Stokes (RANS) simulations are employed to predict the aerodynamic and thermal fields of the individual profiles using test-calibrated boundary conditions. Isothermal steady computations are performed at different wall temperatures to compute the adiabatic wall temperature and the heat transfer convective coefficient. Low-order models are used to represent the over-tip thermal field and the driving heat transfer mechanisms. The time-resolved outlet flow is characterized using a vortex tracking technique and high-frequency aerodynamic measurements to identify the rotor secondary flow structures.

Techno-economic and environmental analysis of a hybrid PV/T solar system based on vegetable and synthetic oils coupled with TiO2 in Cameroon

To assess the production potential, economic profitability and ecobalance of the photovoltaic/thermal (PV/T) system in Cameroon, different configurations of HTF based on water, vegetable and synthetic oils, coupled with different forms of titanium dioxide (TiO2) are used. A numerical code is written in Matlab. The PV/T model connected in direct contact PV-absorber is validated and a multi-objective optimization of the system is performed. The hourly evolution of PV cell temperature for the six HTF configurations revealed a value below 36 °C with Coton/TiO2. The platelets-and spherical-shaped nanoparticles increase the convection transfer coefficient between the fluids and the tubes. TiO2 showed a higher thermal influence in vegetable and synthetic oils than in water at a volume concentration of 4 %. The cotton/TiO2 configuration showed a 12.08 % improvement in electrical efficiency over conventional PV systems with low exergy efficiency compared to water. Configurations with therminolVP-1/TiO2 are better, with the proposed energy cost reduced to 33 % of the price of electricity in Cameroon. The PV/T-Palm/TiO2 system showed an energy cost of $0.03 with a net present value of $568.45, an emission rate of 7.78 kg, a reversibility index of 1.95, an annual cost of $7.07 and a payback time of 5.97yr. This shows that PV/T systems based on vegetable oils are economical.

Numerical Study of the Effect of the Ejection Angle on the Cooling Performance of a High-Pressure Gas Turbine

In modern gas turbines, the purge flow plays an important role in improving the performance of the gas turbine, as it is adapted against the problem of the ingestion of hot gases in the inter-disc cavity of the turbine. The performance of this purge flow is necessarily influenced by some geometrical and physical parameters. This paper presents a 3D numerical study on the influence of the ejection angle on the cooling performance in a high pressure transonic gas turbine with the presence of the cavity. Five inclination cavity angles are compared (𝝓 = 30°, 45°,60°,75°and 90°) by using ANSYS Fluent, a steady flow Reynolds average Navier-Stokes equations are solved, and the turbulence model k-ω SST has been chosen based on comparison of the distribution of velocity and heat transfer convective coefficient with experimental results in a previous work. It was seen that that cooling is limited to the suction side because of the non-uniform pressure distribution of the main flow and the high pressure of the stagnation point. The optimal configuration was determined for an ejection angle of 30°.

How to design the drying of porous materials?

The convective drying of porous materials is studied at the pore scale using a two-component two-phase Lattice Boltzmann model. Capillary pumping from coarse to fine pores is found to enhance the drying in first drying period at high rate. A ‘toy’ model of four connected channels is developed to design the drying of porous materials. This approach has to be seen to supplement the continuum modelling of drying using known moisture transport properties and convective moisture transfer coefficient, allowing to better understand convective drying and design the pore structure to optimize the drying rate.

Thermal Hydraulics Simulation of a Water Spray System for a Cooling Fluid Catalytic Cracking (FCC) Regenerator

Olefins are crucial building blocks for petrochemical industry, serving as raw materials for the production of various products such as plastics, synthetic fibers, detergents, solvents, and other chemicals. In FCC, heavy petroleum feedstocks are injected into a catalytic cracking unit, where they are mixed with a catalyst. The catalyst aids in breaking down the large hydrocarbon molecules into smaller fragments, including olefins like Propylene and Ethylene. These polymerization reactions occur at high temperatures. They demand that heat removal occurs as quickly as possible in order to control the reactor temperature and to avoid “hot spots” in the Regenerator or localized oxidation reactions (and to avoid creep rupture of the regenerator steel cladding). The cooling of the regenerator cladding surface can be achieved by impinging water droplets (spray), ejected from a spray nozzle. Spray cooling can provide uniform cooling and handle high heat fluxes in both a single phase and two phases. This research provides a thermal hydraulic design of regenerator spray cooling systems. In the framework of this research, Fire Dynamics Simulator (FDS) software was applied in order to simulate the temperature field and the water vapor mass fraction. A COMSOL Multiphysics finite element code was used in order to calculate the temperature field inside the regenerator cladding. The calculated surface temperatures and heat transfer convective coefficient, obtained using FDS software, were validated successfully against COMSOL numerical results and previous results in the literature. The numerical simulations were carried out for two cases. The first case was carried out at a distance of 0.5 m, and the second case was carried out at a distance of 0.2 m. A grid sensitivity study was carried out on the FDS model. Numerical integrations were carried out over time in order to calculate the average temperatures. The difference between these four average temperatures, calculated by applying different grids, is less than 7.4%. The calculated surface temperatures and heat transfer convective coefficient were validated successfully against COMSOL numerical results and previous research. It was shown that the calculated temperatures decrease in the second case. The water spray system managed to cool the steel wall more effectively as the water spray system approaches the steel cladding.

The Phenomenon of Flow and Heat Transfer in Annular Heat Exchanger on Plain Tube Condition

Advanced industrial development in technology necessitates using equipment that can effectively and efficiently transfer heat energy. A heat exchanger is the most common device used in industry to transfer heat energy. The Annular Heat Exchanger is one of the heat exchangers used in industry that is simple to manufacture and inexpensive to finance. The annular heat exchanger is commonly found in the food, beverage, chemical process, pharmaceutical, and refrigeration technology industries. This type of heat exchanger is used due to its simple design, easy to manufacture, and low cost. The presence of a heater in a concentric pipe with a straight construction is the general form. Experimentation was carried out in this study. A heater is used to transfer the heat, and there is a cold fluid flow through the annulus. The heater is linked to an AC Voltage Regulator and has five heat settings ranging from 400 W to 600 W. Simultaneously, cold fluid flows in the annulus via a closed system with six flow variations ranging from 2.5 GPM to 5 GPM. A cooling system is used to keep cold fluids at a constant temperature. The purpose of this research is to demonstrate the flow and heat transfer phenomena in an annular heat exchanger. This study obtained the average heat transfer convection coefficient, h, and Nusselt number, Nu. The steady-state conditions for the heat variations of 400 W, 500 W, and 600 W are 2400 s, 3600 s, and 5400 s, respectively. The flow calibration results in this apparatus experiment have an error of 0.05%. At a heat variation of 500 W and Reynolds number 10669, the highest average heat transfer convection coefficient (h) reaches 6703 W/m2K, and the average Nusselt number (Nu) of 314 is obtained. The Reynolds number of critical transition points for heat variations of 400 W, 450 W, 500 W, 550 W, and 600 W are 6986, 7125, 8444, 8616, and 10009, respectively.

Study of the isothermal drying characteristics of normal concrete subjected to low air velocity convection

The drying of capillary moisture from structural concrete used in enclosed areas takes place by free convection characterized by low air velocity. The slow drying results in the persistence of an unsaturated state in concrete rendering it susceptible to deterioration. The study of critical process parameters, such as, mass loss flux, convective transfer coefficients, critical and equilibrium moisture contents and their dependence on the pertinent process variables is fundamental to design of concrete elements for durability. While these parameters have been widely researched for non-cementitious porous building materials, studies related to concrete are not comprehensive and far apart in literature. This study addresses the gap by investigating the drying characteristics of OPC-based normal concrete for varying levels of water-to-cement ratio, curing age and characteristic length of concrete specimens besides the dry bulb temperature and relative humidity of air. Interestingly, the constant rate mass flux is noted to depend on water-to-cement ratio thereby revealing the dependence of the convective transfer coefficients on surface characteristics. It is also observed that the Anomalous diffusion model satisfactorily describes the change in degree of saturation of a specimen with drying time and allows a reliable estimation of the critical degree of saturation. The latter, when plotted as a critical point curve, exhibits a non-uniform increase, as has been reported previously for a wide variety of other porous materials. The modified Oswin model is shown to provide a suitable description of the degree of saturation at equilibrium attained under steady-state temperature and relative humidity conditions.

A Study of the Convective Cooling of Large Industrial Billets

The thermodynamic heat-transfer mechanisms, which occur as a heated billet cools in an air environment, are of clear importance in determining the rate at which a heated billet cools. However, in finite element modelling simulations, the convective heat transfer term of the heat transfer mechanisms is often reduced to simplified or guessed constants, whereas thermal conductivity and radiative emissivity are entered as detailed temperature dependent functions. As such, in both natural and forced convection environments, the fundamental physical relationships for the Nusselt number, Reynolds number, Raleigh parameter, and Grashof parameter were consulted and combined to form a fundamental relationship for the natural convective heat transfer as a temperature-dependent function. This function was calculated using values for air as found in the literature. These functions were then applied within an FE framework for a simple billet cooling model, compared against FE predictions with constant convective coefficient, and further compared with experimental data for a real steel billet cooling. The modified, temperature-dependent convective transfer coefficient displayed an improved prediction of the cooling curves in the majority of experiments, although on occasion a constant value model also produced very similar predicted cooling curves. Finally, a grain growth kinetics numerical model was implemented in order to predict how different convective models influence grain size and, as such, mechanical properties. The resulting findings could offer improved cooling rate predictions for all types of FE models for metal forming and heat treatment operations.

Effect of the solar roof chimney position on heat transfer in a room

This study reports a numerical-experimental analysis of heat transfer and airflow in a scaled room with a heated wall coupled with a double-channel vertical roof solar chimney. For the experimental study, a parametric study was performed in the thermal system, considering different values of heat flux supplied to a vertical wall of the scaled room and six different positions of the roof solar chimney. Experimental temperature profiles were obtained at six different depths and heights and experimental heat transfer coefficients were computed for both heated surfaces. The renormalization group k-ε turbulence model was evaluated against experimental data using computational fluid dynamics software. With the validated model, the effect of heat sources on temperature fields, flow patterns, and heat transfer convective coefficients is presented and discussed. The case with heat flux on the heated wall produces the biggest amount of air changes per hour, being the nearest position of the solar chimney to the air inlet the case with more air removal with 30.24 air changes per hour, corresponding to an output velocity of 0.13 m/s, compared to lower performance setting with 0.06 m/s muzzle velocity, likewise, this configuration presented the best thermal behavior for the configurations with and without the heated wall, with temperatures oscillating between 298 to 301 K. For this reason, it is important to consider this numerical-experimental (3D) study, to obtain the best use of natural ventilation and air changes per hour, offered by a double-channel roof solar chimney, being an efficient, economic, and ecological way of maintaining natural ventilation in buildings to live or work.

Analysis of the Performance of a Solar Thermoelectric Generator for Variable Leg Geometry with Nanofluid Cooling

In this study, the impact of nanofluid use in solar-thermoelectric generators (Solar-TEG) on thermal performance is investigated through analysis and simulation methodology. For conventional cooling analysis, we use air as a coolant and graphene nanoplatelet aqueous nanofluids (GNAN) for nanofluid cooling. We make a comparison between traditional and nanofluid cooling to find the best performance. GNAN at a dispersion of 0.025, 0.05, 0.075, and 0.1-wt% are added to the cooling system. GNAN has been used in the technological development of energy conversion. It has been proposed as a material to achieve better efficiency in Solar-TEG. Five different geometries are developed to analyze the efficiency in a Solar-TEG to find the optimal design. The impact of the thermal concentration relationship, substrate area, and convective transfer coefficient on Solar-TEG performance is investigated. To simplify and speed up simulations, we use equivalent models based on FEM. We are considering the properties of temperature-dependent semiconductors. For thermoelement materials, we use lead-tellurium. Lead-tellurium is an excellent material for thermoelectric study and supports large temperature ranges (up to 750 K). The thermal concentration relationship depends on the substrate area, which affects the efficiency of Solar-TEG. The maximum efficiency between the five geometry types is 5.53%, with a substrate of 110 × 100 mm2. The efficiency and output power using 0.1% wt GNAN as the refrigerant is enhanced by 14.74% and 26.39%. GNAN cooling improves compared to conventional fluid cooling in a Solar-TEG. Different convection coefficients are used to verify this fact.

Computational Fluid Dynamics and Experimental Analysis of the Heat Transfer in a Room With a Roof Solar Chimney

Abstract This study reports a numerical-experimental analysis of heat transfer and airflow in a scaled room with a heated wall coupled with a double-channel vertical roof solar chimney. For the experimental part, a parametric study was performed in the thermal system, considering different values of heat flux supplied to a vertical wall of the scaled room (75 and 150 W/m2) and the absorber surface of the solar chimney (151 and 667 W/m2). Experimental temperature profiles were obtained at six different depths and heights, and experimental heat transfer coefficients were computed for both heated surfaces. The renormalization group k-ɛ turbulence model was evaluated against experimental data using computational fluid dynamics software. With the validated model, the effect of the heated wall and solar chimney on temperature fields, flow patterns, and heat transfer convective coefficients are presented and discussed. The cases with heat flux on the heated wall of the scaled room produce the biggest air changes per hour (ACH), being 30.1, 31.2, and 23.4 ACH for cases 1 to 3, respectively, while cases with no heated wall produce fewer ACH (11.72 and 12.28 for case 4 and 5). The comparison between cases with and without heat flux on one vertical wall but the same solar chimney heat flux shows that the ACH increases between 154% and 156%, respectively.

Analysis of Heat Transfer Performance in a Brayton Cycle Recuperator

Thermodynamic cycles are currently the most wanted means of converting nuclear power into available work due to the higher conversion efficiencies provided. Rankine cycles have been greatly applied for terrestrial reactors and nuclear submarines, while a lot of space projects have been using Brayton cycles for power conversion mainly due to mitigation in power-to-radiator area ratio. Regenerative Brayton cycles can present a considerable power conversion efficiency improvement when compared to the regular ones because of a reduction on the power demand from the hot heat exchanger of a cycle to achieve the same net output power. In this work, a cross-flow heat exchanger with He-Xe (40 g/mol) working fluid and Inconel 617 structural material used as the recuperator for the closed Brayton cycle of a nuclear reactor applicable for space systems is assessed in terms of heat transfer performance. The recuperator tubes are arranged in a staggered distribution around the exchanger axis. The matrix of tubes has a fixed count of 4 rows along the exchanger axis, while the number of tubes around the axis is variable, where the samples of 5, 7, 9, 12 and 16 are tested. The characteristic curves of heat transfer rate, effectiveness, convection coefficient and Colburn factor are built for each of the studied geometries in function of the Reynolds number. The obtained values for each of these parameters range between 1892.49 and 8493.21W (heat transfer rate), 0.165 and 0.325 (effectiveness), 60.3822 and 176.9682 W/m2K (cold side convection coefficient), 30.3276 and 104.3263 W/m2K (hot side convection coefficient), 0.0071 and 0.0109 (cold side Colburn factor), 0.0523 and 0.1370 (hot side Colburn factor).

Simulasi Thermal-Struktur Blade Stage Satu Turbin Geothermal

Condensing type geothermal turbine is a mechanical device that used to convert thermal energy into mechanical energy, then after converted to electrical energy in the generator by the rotation of the rotor’s magnetic field. Development of blade material for geothermal turbine application which using local content is crucial due to the blade’s turbine are 100% imported. So, efforts to produce blade material with high local content are very strategic to support national energy independence in the future. The Agency for the Assessment and Application of Technology (BPPT) started from 2020 until 2023 will focus on the development of the blade material for geothermal turbine application. As a starting point of the research, modelling and virtual testing of the stage-1 blade turbine were performed. In this study, the model is done in CATIAV5 software. Solid model is then imported to ANSYS workbench 15.0. Thermal-Structural analysis of turbine blade using the Stainless steel-based alloy with the ANSYS workbench 15.0 was carried out. In the thermal analysis, the model is given temperature, convective heat flux transfer coefficient and atmosphere gas temperature and then is solved for the heat flux distribution over the blade surface. The obtained heat flux distribution is taken as the thermal load into the Static structural analysis. In the static structural, the obtained model is given structural load, namely centrifugal force. The model is then conducted virtual testing in order to obtain stresses and deflections. The results showed that the model of stage one blade turbine is safe when operating at the determined loads.

Modeling the transfer of low molecular weight plasma proteins during hemodialysis and online hemodiafiltration.

Replacing the renal excretion of low molecular weight proteins (LMWP) by extracorporeal dialysis (dialysis) treatment poses technological challenges. Hemodialyzers with sieving coefficients for LMWP that match or even exceed those of the glomerular membrane barrier are commercially available; however, the associated losses of albumin are much higher than physiological levels of renal albumin excretion. A unidimensional, convection-diffusion model of solute transfer has been developed to analyze and quantitate LMWP extraction and albumin loss during dialysis treatment. The model is applicable to any extracorporeal dialysis technique and any type of hemodialyzer. Clinical extraction data for beta 2 microglobin (β2M, 11.6kDa), myoglobin (16.7kDa) and interleukin 6 (IL6, 21-30kDa) from 15 patients on hemodiafiltration (HDF) using a Nipro Elisio H series high flux hemodialyzer were analyzed using the model and values for the convection and mass transfer coefficients were derived. The model predicts that under normal clinical operating conditions, given equal amounts of β2M removal, albumin losses are higher using pre-dilution rather than post-dilution HDF. The model can be used to provide estimates of the internal filtration rates of hemodialyzers operating in vivo.

Exact solution of the nonlinear fin problem with exponentially temperature-dependent thermal conductivity and heat transfer coefficient

This article studies a class of fin problems with two nonlinear terms arising from thermal conductivity and convection heat transfer coefficient. A one-dimensional convective straight fin is analysed for exponentially temperature-dependent thermal conductivity and exponentially temperature-dependent heat transfer coefficient. The exact fin temperature excess, heat transfer rate and fin efficiency are obtained and presented graphically. The obtained results show the strong influences of exponent indexes of thermal conductivity and convection transfer coefficient as well as thermogeometric fin parameter on the fin efficiency and heat flow.

Design and operation of the air-cooled beam dump for the extraction line of CERN’s proton synchrotron booster

A new beam dump has been designed, built, installed and operated to withstand the future proton beam extracted from the Proton Synchrotron Booster (PSB) in the framework of the LHC Injector Upgrade (LIU) Project at CERN, consisting of up to 1E14 protons per pulse at 2 GeV, foreseen after the machine upgrades planned for CERN's Long Shutdown 2 (2019-2020). In order to be able to efficiently dissipate the heat deposited by the primary beam, the new dump was designed as a cylindrical block assembly, made out of a copper alloy and cooled by forced airflow. In order to determine the energy density distribution deposited by the beam in the dump, Monte Carlo simulations were performed using the FLUKA code, and thermo-mechanical analyses were carried out by importing the energy density into ANSYS. In addition, Computational Fluid Dynamics (CFD) simulations of the airflow were performed in order to accurately estimate the heat transfer convection coefficient on the surface of the dump. This paper describes the design process, highlights the constraints and challenges of integrating a new dump for increased beam power into the existing facility and provides data on the operation of the dump.

Dynamical and optimal procedure to analyze the exhibition of physical attributes imparted by Sutterby magneto-nanofluid in Darcy medium yielded by axially stretched cylinder

This work aims to interpret the heat and mass transmission of Sutterby fluid by exploring the effects of a magnetic field. Flow field equations in cylindrical coordinates are obtained by incorporating Darcy resistance law. Afterwards, a mathematical structure for the physical problem is formulated. This formulation yields an intricate nonlinear set of partial differential expressions. A suitable scaling group of variables is employed on subsequent equations to convert them into non-dimensional form. Dynamical and optimal analyses are performed to achieve physical features of the present problem from the solution. A graphical depiction is presented for the flow behavior of convoluted physical parameters on velocity, temperature, and concentration profiles. Additionally, the quantities (local shear stress coefficient, thermal convective transfer coefficient, and local mass flux coefficient in the limiting case) that are responsible for extracting the physical phenomena in the vicinity of a stretched surface are computed and demarcated by varying controlling flow parameters.

Modeling of coupled heat and mass transfer during drying of ebony wood using indirect natural convection solar dryer

This study presented the behavior of a laboratory scale solar dryer, which was designed with the objective of meeting the needs of low income carpenters of the tropical region of Africa. The following materials were used to build the solar dryer: aluminum sheets painted in black, a wooden support, and a plastic polyethylene used as a cover. Drying was carried out in the city of Yaoundé in Cameroon, and the tested boards were ebony (Diospyros crassiflora). Drying must be performed with the following conditions: slow process at a low temperature in order to maintain the proper air relative humidity. Since, no apparatus was used to force the circulation of the air, natural convection was the mode used by the dryer. The solar dryer was mathematically modeled by applying heat and mass transfer balance to the different components of the solar dryer. It is important to mention that the used heat and mass coefficients were proposed as variable with the operating conditions. The mathematical model was a reasonable description of the physical phenomena taking place in the dryer. The results show that the average relative error between numerical and experimental moisture contents was equal to 2.102%. Heat transfer convective coefficients and global mass transfer coefficients varied with drying time from 0.25 to 5.5 W/(m2K) and from 1 × 10−8 to 5.5 × 10−8 m/s, respectively. The proposed model allowed designing and dimensioning the solar dryer, to the industrial scale. It allowed following the evolution of the different temperatures and moisture content of the tested material and then optimizing the design of the dryer and the drying process conditions. Based on the model, proposing the opening of the drying chamber during the night time and the use of substances capable of retaining heat in the chamber were some proposed solutions in order to have more efficient drying process. The modeling results showed also that an improvement can be obtained at the addition of a solar collector.

Simultaneous hygrothermal performance assessment of an air volume and surrounding highly hygroscopic walls

Heat and mass transfers are becoming increasingly important in the field of building physics. They should be considered to predict building performance, especially for a wall containing highly hygroscopic materials. The moisture balance at the room scale is influenced by air leakage and moisture sources, by the vapour transfer within the material and by the interaction between the wall and the air volume. Therefore, to study the impact of mass transfers on the indoor climate, experimental data at different scales of study are needed. The present study adopts this approach to validate hygrothermal prediction. At the material scale, the hygric properties of wooden panels are estimated using an inverse method algorithm with transient experimental data. The phenomena within the wall and the interactions between the wall and the air volume are studied by designing an experimental device and characterising it in terms of air leakage to validate predictions obtained with model. The values of the material properties are validated at the wall scale by correctly simulating the hygrothermal behaviour before characterising the exchange between the wall surface and the air volume by estimating the convective transfer coefficient. Using this information, the indoor moisture level is correctly predicted by the developed model as well as the heat and mass flows through the walls. Finally, this numerical model highlights that taking into account coupled transfers has only a slight effect on the average energy consumed, while the heating power at the beginning of moisture steps is greatly decreased due to moisture adsorption.

Parametric Studies for Combined Convective and Conductive Heat Transfer for YASA Axial Flux Permanent Magnet Synchronous Machines

In this paper, the effect of some geometrical parameters on the steady state average temperature of the stator core, the winding and the permanent magnets of the yokeless and segmented armature (YASA) axial flux permanent magnet synchronous machine (AFPMSM) is studied. The geometrical parameters selected for the study are the air gap length, the inward heat extraction fin thickness and the permanent magnet thickness. These parametric studies make it possible to obtain a better trade-off between power density and efficiency. These investigations are very helpful in correlating the values of the geometrical parameters to some specific desired performance criteria like not going below some desired minimum efficiency, limiting the temperature of specific part to some maximum value for maximization of lifetime and also determination of the allowed speed range to limit the temperatures lower than the critical values. This is important specifically for the synchronous machines due to the fact that the speed value affects both the losses and the heat transfer convection coefficients. The air gap length has a direct effect on the overall machine losses and the air gap convection coefficient and hence on the temperature of the machine. As the fins are between the stator windings, a thicker fin reduces the space for copper windings and hence increases the losses, but at the same time improves heat evacuation. In addition, the effect on the temperature is studied of the speed variation, which influences both the losses and the convection coefficients of the machine. Every study is made based on coupled electromagnetic and thermal models. The results are obtained from analytical electromagnetic and thermal models verified by finite element simulations and validated experimentally on a 4 kW yokeless and segmented armature axial flux machine.