Average Convective Heat Transfer Coefficient Research Articles

Analysis and optimization of the heat transfer behavior in the melt-spinning process of Nd-Fe-B ribbons

Heat transfer plays a significant role on the quality of Nd-Fe-B ribbons in the melt-spinning (MS) process. In this paper, the heat transfer behavior in the MS process of Nd-Fe-B ribbons was investigated by experiment and simulation. A full flow channel heat transfer model with high accuracy is established using the “fluid-thermal” coupling method. The temperature distribution of the cooling roller and fluid field in steady-state is obtained. The simulated and experimental results of the outlet temperature are compared and the relative error is within 5%. The microstructures of the free surface and roller-sticking surface of Nd-Fe-B melt-spun ribbons are characterized by FE-SEM, and the refined grains are formed on the roller-sticking surface of Nd-Fe-B ribbons due to rapid solidification caused by the heat transfer from the roller. Moreover, a multi-nozzle structure is proposed for the MS process. The temperature distribution on the surface of the cooling roller in the axial direction is more uniform compared with the original single-nozzle structure, and the average convective heat transfer coefficient is increased by about 1.27 times after the modification of multi-nozzle structure, with a productivity of three times. Finally, the experimental design method of Latin hypercube sampling response surface design is used to obtain the response surface relationships of rotational speed, inlet flow rate, and water inlet temperature on the surface temperature of the cooling roller, respectively. NSGA-II multi-objective genetic algorithm (MOGA) is adopted for multi-objective optimization of process parameters. The optimized combination of process parameters is obtained with a relative error of about 0.41%. The research results are helpful to understand the heat transfer behaviors in the MS process of Nd-Fe-B ribbons, improve the utilization rate of the cooling roller and enhance the production efficiency in the actual application.

Convective heat transfer of falling film around the horizontal half-oval tube with reverse airflow in an evaporative condenser

Horizontal falling-film evaporation is frequently used in industrial air conditioning system to improve its thermal performance. Transient heat transfer characteristics on the surface of a circular tube have been investigated, while the non-circular tube such as half-oval tube has been rarely reported. This study aims to investigate the thermal performance of liquid film around a half-oval tube by adopting transient simulations with laminar and SST k-ω models, respectively. Simulations consider varying wind velocity, liquid Reynolds number, heat flux and length-width ratio of the tube. Simulated results are quantitively validated by comparing with reported experimental results, and the average differences are below 9.5 %. Results indicate that the local convective heat transfer coefficient (CHTC) increases with wind and the average CHTC is at least 5.98 % higher than the case without wind. Although the influences of liquid Reynolds number and heat flux show slight differences, they still can improve the convective heat transfer. The local CHTC exhibits an escalating trend with length-width ratio of 1–5. Meanwhile, the average CHTC for the four tested half-oval tubes is at least 6.8 % higher than the values of the circular tube. An empirical correlation for predicating the average CHTC is established by regression fitting with a mean deviation of 4.6 %. These findings help to design the falling-film evaporation system by adopting the half-oval tube in industrial air conditioning system.

Multi-tiered configurations improved flow boiling performance: Comparation investigation of leaf vein inspired two-tiered and three-tiered open microchannels

Microchannel heat sinks with expanding flow area along with the flow direction are able to suppress flow instability and reduce pressure drop during two-phase flow boiling by offering broadening volume for bubble elongation and growth that suppress the slug blockage and flow reversal. In this regard, microchannels with expanding area perpendicular to flow direction are supposed to obtain the comparable results, as the bubbles migrate to the downstream and top of microchannels simultaneously. However, the relevant study about multi-tiered microchannel heat sinks was limited and the corresponding flow boiling characteristics remained elusive. In this work, leaf vein inspired two-tiered open microchannel (LTWOMC) and three-tiered one (LTHOMC) were proposed and comparative flow boiling experiments were carried out. The outcomes indicated that LTWOMC obtained earlier ONB, which was 6.4 °C lower than LTHOMC at G = 220 kg/m2·s, the average local convective heat transfer coefficient (hcon) and average two-phase one (htp) of LTWOMC were maximumly enhanced up to 36.3% and 148.7% at G = 150 kg/m2·s, respectively. The pressure drop (ΔP) of LTWOMC was generally larger than LTHOMC at all mass fluxes, which led to the cooling coefficient of performances (COPs) of LTHOMC superior compared to LTWOMC under all working conditions. Moreover, LTHOMC exhibited better flow stability than LTWOMC with lower amplitudes and standard deviations of both wall temperature and pressure drop. In general, the three-tiered hierarchical configuration is more suitable than two-tiered one for flow boiling heat transfer.

Effect of an Exhaust Heat Exchanger with Inserts on the Performance of Thermoelectric Generators

A thermoelectric generator is used as a waste heat recovery system for generating electric power. The thermoelectric generator system consists of an exhaust heat exchanger, a thermoelectric module, and a water heat exchanger. The aim of the current work is to explore different types of inserts used in the test section of the exhaust heat exchanger and power generation of thermoelectric generators at different operating conditions. An experimental setup has been developed for conducting experimental investigation on thermoelectric generators to find the effect of the exhaust heat exchanger (EHE) with inserts on the performance of thermoelectric generators. The cone (G-type test section) and cone-cylinder (H-type test section) type inserts were introduced to enhance the performance of the thermoelectric generator. Compared with an insert-free (empty, F-type) thermoelectric generator with cone and cone-cylinder type inserts in terms of the output power, the average heat transfer rate and convection heat transfer coefficient of F-type, G-type, and H-type test sections of the EHE are 358, 468, and 459 W and 76, 100, and 97 W/m2K, respectively. It shows that the G-type test section of EHE exchanges more heat from engine exhaust to the hot surface of the thermoelectric module through the wall of the EHE. The G-type test section created more temperature difference; obviously, it generated more power output. It was observed that the G-type and H-type test sections of exhaust heat exchangers improved average maximum output power by 29.49% and 26.11% than that by the F-type test section of heat exchanger, respectively. The F-type, G-type, and H-type test sections of exhaust heat exchangers showed a maximum average efficiency of 0.80, 0.78, and 0.70%, respectively.

Methodology for determining convective heat transfer coefficients on the tubesheet surface of shell-and-tube heat exchangers under single-phase flow

Designing shell-and-tube heat exchangers requires reliable methods to calculate the convective heat transfer coefficient (CHTC) on the tubesheet, due to its impact on thermal stress. To address this, we established numerical models for both the tube and shell sides of the tubesheet. Using computational fluid dynamics (CFD), we systematically investigated the distribution of convective heat transfer on the tubesheet surface and its variations with structural and process parameters. The results showed that when fluid flowed into the tubesheet, the average convective heat transfer coefficient on the tube side of the tubesheet surface was 26% higher than when it flowed out. Additionally, the average convective heat transfer coefficient in the perforated region of the tubesheet was 1.39 to 2.57 times greater than in its periphery. Furthermore, the local CHTC on the shell side of the tubesheet surface gradually decreased along the downstream direction from the inlet of the shell-side fluid. Through simulations conducted across various structural and process parameters, we derived empirical formulas to rapidly calculate the average CHTC on the tubesheet surface. These formulas incorporated a tubesheet porosity factor for the tube side and introduced a new method for calculating the equivalent tubesheet diameter on the shell side. Random testing verified that our proposed formula reliably predicted the numerical simulation results.

Experimental investigation on heat transfer of nitrogen flowing in a circular tube

Average and local convective heat transfer coefficients of nitrogen are measured experimentally in an electrically heated circular tube for a range of Reynolds number from 1.08 × 104 to 3.60 × 104, and wall-to-bulk temperature ratio from 1.01 to 1.77. The exit Mach number is up to 0.17, and the heat flux is up to 46 kW·m−2. The molybdenum test section has a 62 diameters heated section with an inside diameter of 5 mm and a 30 diameters entrance section to ensure the fully-developed flow. Uncertainty of Nusselt number is less than 1.6 % in this study. The results indicate that the average heat transfer correlations evaluated by both the bulk and the modified film Reynolds numbers agree well with the experimental data. The local heat transfer results based on bulk properties are compared with previous empirical correlations. New prediction correlations are recommended which are significantly affected by the property variation and heated length. The comparison between the proposed correlations and experimental points shows that 88 % of experimental data fall into an error of 10 %, and almost all data are within an error of 20 %.

Flow and heat transfer in rotating smooth and ribbed multi-channel double-wall structure with multiple-jet impingement cooling

In this study, the heat transfer of multiple-jet impingement in rotating smooth and ribbed multichannel double-wall cooling structure with film extraction are investigated. The dimensionless jet-to-target spacing is 1, and the dimensionless jet-to-jet spacing is 3.55. In ribbed channel, the rib height is 1 mm and rib spacing is 8 mm. The experimental jet Reynolds number ranges from 2000 to 8000, and the maximum jet rotation number is 0.22. The test section contains five impingement channels. The local average convective heat transfer coefficient is measured by the “copper plate method”. The SST k-ω model is used to study the effect of rotation on the flow in channels. The results show that the heat transfer gap between high and low radius is more evident with an increase of the Roj. This is because the rotation effect increases and decreases the mass flow rate at high and low radius, respectively. Moreover, rotation can strengthen the impingement effect of the trailing side (TS) while weakening the effect of the leading side (LS) when the Roj is less than 0.06, Which causes differences in the heat transfer between the LS and TS of the impingement channel. Furthermore, affected by the ribs, the average heat transfer of ribbed target surface is improved. The area of high heat transfer region generated by impingement decreases, and an inverted butterfly-shaped high heat transfer region is generated near the film hole. Finally, the rib weakens the effect of rotation on the flow of target surface to some extent.

Study on dynamical characteristics of cooling fluid in engine piston

The cooling of engine piston is very important, and the fluid vibration characteristics of its internal cooling oil is the key to affect the heat transfer efficiency. In order to effectively ensure that the piston temperature will not be overloaded and avoid the reduction of sealing performance, a two-phase flow model in the piston cooling chamber is established in the paper. The flow field and heat transfer characteristics of the cooling oil are simulated by finite element method using FLUENT. In terms of model selection, VOF multiphase flow calculation and SST k-ω model are selected as turbulence model. The setting of boundary conditions combines the piston stroke characteristics of the hydraulic cylinder, so as to obtain accurate inlet parameters, and obtain the oil liquid phase proportion distribution, oil velocity field and the change law of convective heat transfer coefficient under different piston positions. The results show that the instantaneous ratio of cooling oil is closely related to the speed, and increasing the oil speed is an important means to improve the heat transfer performance. The multiphase flow model has high reliability, and there is no obvious difference between the average convective heat transfer coefficient obtained by the near-wall model method and the wall function method.

A novel convective heat transfer enhancement method based on precise control of Gyroid-type TPMS lattice structure

Innovative single-phase flow heat transfer enhancement technologies can improve heat dissipation efficiency and reduce the weight and volume of heat dissipation equipment. Triply Periodic Minimal Surfaces (TPMS) hold promise as a outstanding single-phase heat transfer enhancement structure. To further improve the convective heat transfer performance of TPMS, this study independently presents a novel lattice structure control method specifically designed for Gyroid-type TPMS, along with the corresponding mathematical equation. By adjusting the parameter “α” in the equation, the Gyroid lattice geometry can be controlled. This study named “α” as the “Lattice deformation control parameter of Gyroid”. Numerical simulations indicate that increasing α from 0 to 0.25 within the Reynolds number range of 282–2579 can lead to a 19.9–28.9% increase in the average convective heat transfer coefficient (h¯) of the Gyroid, a 0.3%-4.5% increase in the Nusselt number (Nu), and a 13.0%-20.3% decrease in the average friction factor (f¯). The research results suggest that optimizing α is a promising new technology for enhancing convective heat transfer of Gyroid-type TPMS, as it not only improves its heat transfer performance but also reduces its flow resistance. The main reason for the convective heat transfer enhancement of Gyroid-type TPMS with increasing α is the increase in the heat transfer area, while the reduction of flow resistance is mainly due to the formation of the “flow-guiding structure” inside the Gyroid.

Comparison of cooling performance of nanofluid flows in mini/micro-channel stacked double-layer heat sink and single-layer micro-channel heat sink

Mini/micro-channel heat sinks are the advanced cooling method to fulfill the cooling demand of electronic equipment integrated with high-power circuit packages. Many designs are provided to enhance the thermal performance of micro-channel. In the present experimental study, the mini/micro-channel stacked double-layer heat sink is designed and tested for the first time. The mini/micro-channel stacked double-layer heat sink is composed of a single-layer micro-channel heat sink stacked with a mini-channel heat sink. The pure water and alumina-water nanofluid are considered as the coolant. A comparison is conducted between the heat dissipation performance of mini/micro-channel stacked double-layer heat sink and single-layer micro-channel heat sink. The results showed that as compared with the case of single-layer micro-channel heat sink, the pressure drop can be reduced considerably by using the mini/micro-channel stacked double-layer heat sink. For the flow rate ratio less than 2.0, the average convection heat transfer coefficient of the mini/micro-channel stacked double-layer heat sink is higher than that of the single-layer micro-channel heat sink. Finally, the FOM ratios are greater than unity for all cases. This indicates that the use of mini/micro-channel stacked double-layer heat sinks has more advantages in engineering applications than the single-layer micro-channel heat sinks.

Heat transfer characteristics of nanofluid under the action of magnetic field based on molecular dynamics and flow states

Theoretical analysis, numerical simulations, and experimental studies are used to comprehensively investigate the changes in the heat transfer characteristics of Fe3O4–water magnetic nanofluid under different types of magnetic fields and the heat transfer mechanism, providing new ideas for its practical application. By combining the fundamental conservation theorem and the Boussinesq approximation, dimensionless control equations have been established. The analysis of the variation pattern of the calculated values of the source terms under different boundary conditions, as well as the order of magnitude analysis, concludes that: the enhanced trend of Brownian motion and thermophoretic motion is the main reason for the enhanced heat transfer capability of the magnetic nanofluid; where the thermophoretic motion contributes slightly more to the heat transfer; the increase in Joule heat is the reason for the further enhancement of the heat transfer capability by the magnetic field. Volume fraction, temperature, and magnetic field strength are positively correlated with the average convective heat transfer coefficient. The reason for magnetic fields to enhance heat transfer is revealed by the deflection of the magnetic nanofluid by the magnetic body flow under local magnetic fields to form localized reflux. The alternating magnetic field further enhances the ability of magnetic fields to enhance heat transfer in magnetic nanofluids. Overall, the effect of the applied magnetic field on the motion of the magnetic nanoparticles causes the disruption of the thermal boundary layer, which is responsible for the enhanced heat transfer capacity of magnetic nanofluids.

Numerical study on the influence of input power and tube shape on a single-phase natural circulation for passive residual heat removal heat exchanger

The passive residual heat removal heat exchanger (PRHR HX) plays an important role in cooling the reactor core under accident conditions. However, few studies have considered the exact conditions of the natural circulation loop (NCL) for the PRHR HX, such as different initial temperatures of fluid in the NCL and the cooler, and configuration of the heat exchanger tubes. In this study, analyses with these considerations are conducted. Influences of different heating power inputs and the two configurations (spiral-shaped and C-shaped heat exchanger tubes) on heat transfer performance are discussed. The CFD computational setting was qualitatively verified and transient computations of 600 s were conducted. The computational results suggest that the oscillation of the first 40 s is associated with difference of the initial temperatures of the fluid in the NCL and the cooler. It is found that the frequency increases first and then the amplitude with increase of heating power. The system reaches a neutrally-stable condition with heating power between 500 W and 750 W, and then it reaches a neutrally-stable condition earlier with an increasing heating power, which also results in a higher frequency and a larger amplitude. In addition, the loop flow rate is positively correlated with the average convective heat transfer coefficient. On the other hand, replacing a C-shaped tube with a spiral-shaped tube insignificantly affects the flow oscillation in the loop, and the more complex heat exchanger tube structure could enhance its heat transfer performance. The results of the study reveal the characteristics of the NCL for the PRHR HX.

Experimental investigation of convective heat transfer in the aircraft cabin environment at low air pressure

The heat transfer capacity of the cabin environment under low air pressure is significantly different from that under normal pressure. The existing research on the low-pressure environment of aircraft cabins has not provided a reliable convective heat transfer correlation to guide the design of the cabin thermal environment. This investigation evaluated the heat transfer in an actual aircraft cabin under different pressures. A laboratory test was designed in a cabin mockup with controllable boundary conditions for air temperature and pressure. Based on the measurement results, the quantitative effects of low pressure on the convective heat transfer coefficient (CHTC) of the heating surface were analyzed. According to the experimental results, the CHTC of the horizontal surface in natural convection increased from 3.26 W/(m2·K) to 5.10 W/(m2·K) when the heat flux increased from 100 W/m2 to 400 W/m2, and the CHTC dropped by 23–30% when the pressure dropped from 101 kPa to 61 kPa. With the same heat flux, the average CHTC value for the vertical plate was slightly lower than that for the horizontal heating plate under normal pressure, and the trend became significant as the air pressure decreased. In general, the average CHTC for forced convection was substantially higher than that for natural convection. Consequently, correlation equations for calculating natural and forced convection on horizontal and vertical plates under low air pressure were proposed, which will aid the design of the cabin thermal environment.

Temperature Field Analysis and Cooling Structure Optimization for Integrated Permanent Magnet In-Wheel Motor Based on Electromagnetic-Thermal Coupling

Aiming at the impact of heat generation and temperature rise on the driving performance of a permanent magnet (PM) motor, taking the PM in-wheel motor (IWM) for electric vehicles as an object, research is conducted into the temperature distribution of the electromagnetic–thermal effect and cooling structure optimization. Firstly, the electromagnetic–thermal coupling model considering electromagnetic harmonics is established using the subdomain model and Bertotti’s iron loss separation theory. Combined with the finite element (FE) simulation model established by Ansoft Maxwell software platform, the winding copper loss, stator core loss and PM eddy current loss under the action of complex magnetic flux are analyzed, and the transient temperature distribution of each component is obtained through coupling. Secondarily, the influence of the waterway structure parameters on the heat dissipation effect of the PM-IWM is analyzed by the thermal-fluid coupled relationship. On the basis, the optimization design of waterway structure parameters is carried out to improve the heat dissipation effect of the cooling system based on the proposed chaotic mapping ant colony algorithm with metropolis criterion. The comparison before and after optimization shows that the temperature of key components is significantly improved, the average convection heat transfer coefficient (CHTC) is increased by 23.57%, the peak temperature of stator is reduced from 95.47 °C to 82.73 °C, and the peak temperature of PM is decreased by 14.26%, thus the demagnetization risk in the PM is improved comprehensively. The research results can provide some theoretical and technical support for the structural optimization of water-cooled dissipation in the PM motor.

Experimental investigation for heat transfer augmentation method of jet impingement using a fluid of different concentrations of water and ethylene glycol (EG)

In the modern world, with rapid inventions in microscale electronics, devices suffers undesirable internal heat generation and, due to their tiny shapes, undergo large heat flux conditions. This emphasizes the development of effective and efficient heat dissipation methods to boost their performance and keep them in safe working conditions. The jet impingement cooling method is used for cooling purposes in many engineering applications, and is popular for quick removal of heat from the solid surfaces. The present experimental study is an investigation of effect impingement of jet of water and ethylene glycol mixture over a heated surface. The blending of ethylene glycol (C2H6O2) with water (H2O) as a base fluid enhances the average (convective) heat transfer coefficient (HTC). The cooling fluid with different concentrations of C2H6O2 varying from 10%, 25%, 50%, and 100% shows higher values of average convective coefficient at similar flow conditions than pure water. The fluid having mixture proportions 50% C2H6O2 and H2O shows an optimum value for heat transfer enhancement in the range of 30% to 75% than pure water at the same flow rates. It can be noted that based on mechanical stability and the cost associated, the experimental results reveal that the optimum value of the concentration of C2H6O2 in water is 50% for maximum heat transfer and at higher values of C2H6O2 hamper the mechanical stability and causes higher pumping power due to increase in viscosity of the fluid.

Local and overall convective heat transfer coefficients for human body with air ventilation clothing: Parametric study and correlations

Convective heat transfer coefficient associated with various human body parts plays an important role in the prediction of physiological responses with the help of human thermoregulation models. The primary goal of this work is to develop correlations for the convective heat transfer coefficients associated with various segments and whole torso of the human body in sleeve opening (SO), collar opening (CO), and both sleeve and collar opening (SCO) scenarios of air ventilation clothing. For this, a 3D CFD model of the air ventilation clothing is developed and validated with experimental data. Detailed parametric study is performed to analyze effect of openings in the air ventilation clothing, air flow rate, fan diameter and inlet (ambient) air temperature on the local and overall convective heat transfer coefficients. Results indicate that the area-weighted average convective heat transfer coefficient associated with whole torso is 36% and 5% higher in the case of CO and SCO, respectively, as compared to the SO case. The convective heat transfer coefficient is highest in the lower-back segment and lowest in the upper-chest segment of the body for SO and SCO scenarios. Whereas in CO scenario, the upper-chest segment has the highest and stomach segment has the lowest convective heat transfer coefficients. Effects of fan diameter and inlet air temperature are found to be least significant on the convective heat transfer coefficients as compared to the effect of opening and air flow rate. Further, correlations for segment-wise and whole torso convective heat transfer coefficients are proposed in the present work.

Investigation of convective heat transfer at the facade with balconies for a multi-story building

As a common building appendage, balconies can significantly alter the flow pattern near the building façade, thus greatly affecting the convective heat transfer coefficient (CHTC) of façades. In the present study, computational fluid dynamics (CFD) simulations are performed with the 3D steady Reynolds-averaged Navier-Stokes (RANS) SST k-ω model to evaluate the convective heat transfer at the building façade with balconies. This model is systematically validated by a reduced-scale wind tunnel experiment and then utilized to conduct simulations with high-resolution grids. The effects of the balcony height (height of balcony parapet walls), depth, and length on the forced convective heat exchange at the façade and balcony surfaces are analyzed in detail. The results show that with the presence of balconies, the surface-averaged CHTC (CHTCavg) is reduced by about 17.5% at the windward facade, while it is reduced by 35.2% at the leeward façade. Furthermore, when the height of the balcony (Hp) varies from 0.5 to 1.5 m, CHTCavg decreases by up to 39%, 48.8%, and 50% on the leeward facade, the inner surfaces of windward and leeward balconies, respectively. However, balcony depth and length have relatively non-significant effects on the CHTCavg of building facades and balconies' surfaces. Finally, new correlations are established to describe the average CHTC along the façade and balconies’ surfaces. The difference in CHTCavg obtained from the correlations and the simulations is less than 6%. The findings of the present study would facilitate the calculation of the cooling and heating loads of buildings with balconies.

Effects of aspect ratio and inlet wind velocity on thermal characteristics of Trombe wall channel under different ventilation strategies: An indoor experiment

Due to the air flow channel's “C”-shaped structure with asymmetric thermal boundary conditions, the structural and operating parameters have unique intrinsic impacts on overall performance of Trombe wall. In order to match the engineering practice well, under laboratory conditions, an experimental research platform with adjustable channel width and fans was established to reveal the effects of aspect ratio and inlet wind velocity on thermal characteristics of air flow channel under different ventilation strategies. The results show that under natural ventilation strategy, the air flow channel's thermal performance has an extremum when the aspect ratio is about 0.05. Under forced ventilation strategy, with the growth of inlet wind velocity, the comprehensive average convective heat transfer coefficient rises while thermal efficiency shows different trends under various heat fluxes and reaches the maximum when heat flux is greater than 360 W/m2 and inlet wind velocity is 0.6 m/s. A larger aspect ratio leads to a lower comprehensive convective heat transfer coefficient and a smaller thermal efficiency. Compared with the natural ventilation strategy, except for the air temperature rise, the air flow channel's thermal performance is improved to a certain extent under forced ventilation strategy. The improvement of thermal efficiency is particularly significant when the heat flux is small, indicating that forced ventilation strategy has high application potential in areas with low solar radiation intensity. Finally, the Nusselt number correlations reflecting comprehensive average convective heat transfer performance of Trombe wall channel under two ventilation strategies were obtained for engineering design and performance evaluation of Trombe wall.

An experimental investigation on the radiant cooled wall’s heat transfer characteristics in a fully conditioned real-sized living environment

Radiant wall applications have been favored compared to floor and ceiling ones owing to their advantages. In the current work, the heat transfer characteristics of a radiant cooled wall, which are heat fluxes, and heat transfer coefficients, have been experimentally investigated by altering supplied water temperatures and using proper reference temperatures in a fully conditioned real-sized test chamber where the obstacles such as unrealistic room sizes and insufficient air conditioning processes have been eliminated. Detailed methodology for the determination of reference temperature, used thermocouples’ locations, and heat gains were revealed. As a result, investigated radiant cooled wall’s average total, radiative, and convective heat transfer coefficients were determined as 7.83, 5.14, and 2.57 W/m2K, in turn. 67 % of the total heat transfer rate in the mean was found to belong to radiation. Furthermore, novel empirical correlations on the total, radiative, and convective heat transfer coefficients were derived with the mean squared errors of 99 %, 98 %, and 99 %, respectively. There is no experimental investigation on radiant wall cooling excluding authors’ previous publications. Finally, a detailed measured and calculated dataset, obtained from the third investigation on the radiant cooling wall system in open sources, was presented for the sake of other researchers.

CFD and experimental study of heat dissipation from an anti-coning, pin vented, inboard mounted brake disc

Anti-coning brake discs are known for their superior NVH characteristics when compared to other disc designs, but also for poorer heat dissipation. Cooling characteristics of such a disc design are studied numerically and experimentally on a specially developed Thermal Spin Rig. The disc is installed inboard on a high-performance off-road vehicle, with portal axles and wheel drives, resulting in nearly fourfold higher disc rotational speeds in comparison to the wheel speeds. Being exposed to the free-flowing air and rotating much faster makes this application well worth the attention and deeper study in terms of disc cooling. Computational Fluid Dynamics (CFD) analyses show a detailed distribution of air velocities and pathlines, temperatures, pressures, and convective heat transfer coefficients. The results are all very coherent, conveying very useful information, both qualitatively and quantitatively. Their cumulative effect has been successfully validated by comparing the CFD predicted average convective heat transfer coefficients ( hconv) with the experimental results obtained on the Thermal Spin Rig, in a controlled environment. CFD results show to be very close to average hconv values calculated from measured cooling curves. The agreement is very good for the wide temperature and speed range. The overall relative differences are under 5%, and in most cases under 3%, except for the low disc rotation speeds, which show a maximum relative difference of 12.5% calculated at 200 rpm, for the disc heated to 300°C. Such outcomes give confidence in the CFD results for future work in both disc design and vehicle installations.