Total Heat Transfer Coefficient Research Articles

Advancements in design of radiant floor heating systems with an innovative simplified calculation method

The calculation accuracy of existing simplified methods for radiant floor heating systems (RFHS) is far from meeting the growing demand for energy saving. Therefore, an innovative steady-state simplified method is proposed based on conduction shape factors, equivalent thickness, and mirror principle. The new model is validated by experimental data and compared with an equally simple simplified method. Meanwhile, the effects of the total heat-transfer coefficient of radiant surfaces and fluid flow rate in heating pipes on the calculated results are discussed. The calculation flowchart is given. Parameter influence and sensitivity analysis are then performed. The results show that the new simplified model agrees well with experimental data, and the maximum relative error is 7.9% for heat flux and 2.0% for surface temperature. Standard deviation reduces by 68.5% and 66.8% for the heat flux and surface temperature, respectively, compared to the equally simple existing simplified method. With the same absolute increment of pipe pitch, the smaller the pipe spacing, the faster is the heat flux and surface temperature change. The order of importance of influential parameters is mean water temperature > indoor air temperature > pipe pitch > thermal conductivity of filling layer > thermal conductivity of pipe wall.

Analysis of billet temperature non-uniformity in a regenerative reheating furnace: Considering periodic combustion switching and misalignment contact of walking beams

Improving the billet temperature uniformity is crucial for the quality of rolled products. This paper investigated the heat and mass transfer processes in a regenerative reheating furnace by establishing typical heating unit models. The periodic combustion switching and misaligned water-cooled beams were considered. The effects of furnace temperature oscillation and skid marks on the total heat transfer coefficient distribution and billet temperature uniformity were analyzed. The results indicate that during the heating process of the billet, the periodic variation amplitude of furnace temperature decreases from 86 to 25 °C, and the depth of influence on the billet temperature is about 0.03 m. The total heat transfer coefficient on the billet bottom surface shows a wave distribution affected by beams shielding, but on the top surface, the closer it is to the furnace wall, the smaller the total heat transfer coefficient. The misalignment of water-cooled beams effectively eliminates the original skid mark and reduces the range of new skid mark. However, the cross-sectional temperature difference at the new skid marks remain at about 97 °C. Compared to extending the residence time, increasing the furnace temperature in the soaking zone is the optimal measure to reduce the influence of skid marks.

Heat-transfer characteristics of the two-phase-change process between a microencapsulated phase-change-material-slurry droplet and air: A numerical study

A concept is proposed for spray-heat exchangers with the aim of addressing the mismatch of heat supply-demand within and outside a water droplet. The concept involves using a microencapsulated phase-change-material (MPCM) slurry as the working medium, enabling two-phase-change heat transfer with air. The temperature of the water droplet rapidly decreases owing to continuous evaporation, leading to a rapid decrease in its heat-transfer capacity. The phase change of the MPCM particles not only provides sufficient heat for evaporation but also maintains a high surface temperature, thus sustaining effective evaporation. A numerical model was developed to theoretically investigate the effect of the MPCM phase change on external convection. The heat-mass transfer of a droplet with a radius of 0.25 mm composed of water and 20 vol% MPCM was simulated. The results indicate that the MPCM phase change effectively reduces the temperature decrease rate. However, when the overall surface temperature of the MPCM droplet exceeds that of water, the total heat-transfer coefficient is not necessarily higher. Further local analysis reveals that maintaining both an overall high surface temperature and a reasonable local temperature distribution is crucial to achieve a higher total heat-transfer coefficient. The MPCM phase change significantly influences the local surface-temperature distribution.

Machine-learning algorithms for predicting condensation heat transfer coefficients in the presence of non-condensable gases

Condensation on surfaces in the presence of non-condensable gas (NCG) is a ubiquitous and critical phenomenon in many industrial fields. However, current empirical correlations for predicting condensation heat transfer coefficients in the presence of NCG may exhibit significant deviations from reality. Machine learning algorithms are now being dedicated to this field, but the models developed can only predict the condensation heat transfer coefficients of steam or vapor of a non-aqueous working fluid with similar physical properties to water in the presence of NCG. In the present study, a comprehensive theoretical analysis was conducted to investigate the total condensation heat transfer coefficients with NCG, and 16 dimensionless numbers were identified as input variables for machine learning models. Based on a filtered database consisting of 4377 data points extracted from 37 papers, the Spearman correlation coefficients were calculated to evaluate the relationship between the total heat transfer coefficients and the input variables, indicating the magnitude of the impact of the 16 dimensionless variables. Four machine learning models, namely Gradient Boosting Regression (GBR), Extreme Gradient Boosting (XGBoost), Random Forest Regression (RFR), and Multilayer Perceptron (MLP), were developed to predict the total heat transfer coefficients for water and non-aqueous working fluids. The mean absolute percentage errors for the four models were 1.38%, 1.63%, 3.00%, and 4.42%, respectively, with the GBR model exhibiting the highest degree of accuracy. The determination of the application scope of these models was conducted by analyzing the value ranges for each dimensionless parameter and its corresponding frequency distribution.

Energy and exergy-based degree-hours in estimation of heat requirements for heating and cooling purposes

This study presents an innovative exergy-based methodology to revolutionize the assessment of heating and cooling energy utilization, transcending the limitations of traditional heating and cooling degree-hours (HDH and CDH) analyses. The study’s distinctiveness stems from its investigation into variations in HDH and CDH concerning critical parameters such as ambient temperature, solar-air temperature, solar absorptivity, surface emissivity, and total heat transfer coefficient. This fosters a profound comprehension of the thermodynamic performance of building heating and cooling systems, empowering decision-makers with the insights needed to optimize energy utilization effectively. As demonstrated through a case study conducted in Antalya, Turkey, this study uncovers significant findings. A mere 1 °C increase in ambient temperature results in an average 14 % surge in heating demand and an average 17 % decline in cooling demand, leading to a substantial 1000°-h discrepancy between heating and cooling requirements. Furthermore, we underscore the sensitivity of energy demand to temperature fluctuations, the substantial impact of design temperature on energy consumption, the notable influence of solar effects on environmental conditions, and the potential for optimization in parameters such as solar absorptivity, surface emissivity, and total heat transfer coefficient. These insights underscore the significance of exergy-based systems, offering heightened energy efficiency, swift adaptability to temperature changes, integration of renewable energy sources, and intelligent control features that contribute to sustainability and energy savings.

Determining energy, exergy and enviroeconomic analysis of stand-alone photovoltaic panel under harsh environment condition: Antarctica Horseshoe-Island cases

It is considered that some of the energy needs of the Turkish Science Base, which will be established on the Antarctic Horseshoe Island, will be supplied from solar energy. In this study, the performance of the PV panel was experimentally tested on the Antarctic Horseshoe Island. Energy, exergy and enviroeconomic analysis of the PV panel were performed. In the experiments carried out for three days, the energy efficiency was determined as 5.40%, 7.39% and 11.35%, respectively. The exergy efficiencies were calculated as 4.53%, 6.58% and 10.25%, respectively. At the end of three experiments, the amount of CO2 blocked to the atmosphere was determined as 3.06 kg on average. The study used meteorological parameters (solar radiation, wind speed, humidity, and ambient air temperature) and other data (current-voltage, panel surface temperature, convection and radiation heat transfer coefficients, sky temperature, total heat transfer coefficient, total heat loss and exergy destruction) that can only be calculated using these variables to estimate the electrical efficiency of the PV module. This was achieved using the multilayer perceptron and decision tree method. The process of approximating the values estimated by statistical evaluations to the values calculated experimentally for energy efficiency was found to have error rates of 5.6% and 12.5%, respectively.

On the performance of a latent heat thermal storage unit integrated with a helically coiled copper tube and organic phase change materials: A lab-scale experimental study

In this study, the performance of a latent heat thermal storage (LHTS) unit integrated with a helically coiled copper tube and organic phase change materials is investigated using a lab-scale experimental setup. The effects of various operating conditions such as the coil thickness, testing fluid temperature/flow rate, PCM type, turbulator, and stirrer rotational speed on phase change behavior are investigated. The evaluation is based on PCM temperature variations, total heat transfer coefficient, and thermal effectiveness. The effects of testing fluid temperature, PCM type, turbulator, and stirring speed on phase change behavior are found to be more pronounced compared to those of the coil thickness and the fluid volume flow rate. Considering the melting process, it is found that the average temperature of the PCM in the LHTS unit with a turbulator is higher than that of the case without turbulator by nearly 10 °C which indicates an improvement in the heat transfer between water-PCM. The average PCM temperature is found to increase by 2 °C and 3.5 °C when a stirrer with a rotational speed of 200 and 400 rpm is employed, respectively. The total heat transfer coefficient for the LHTS unit at a stirring speed of 400 rpm (200 rpm) shows a significant increase of 39.6% (27%) compared to the scenario without a stirrer.

Mechanisms of enhanced heat transfer of piston oscillating cooling in a heavy-duty diesel engine

The thermal load and reliability of pistons become major concerns with the increase of power density of internal combustion engines. The oscillating cooling technology is often adopted to enhance the heat transfer of pistons in heavy-duty diesel engines. To understand the heat transfer mechanisms, this study developed an optical oscillating cooling piston based on a real heavy-duty engine. The characteristics of two-phase oscillating flows were optically observed under different conditions. As engine speed increased from 100 to 700 r/min or oil supply pressure decreased from 0.2 to 0.8 bar, the oscillation intensity of the two-phase flow gradually increased and the oscillating flow pattern developed from slug to intermittent mist flow. Furthermore, computational fluid dynamics simulations were performed to analyze the heat transfer mechanisms of oscillating cooling and optimize the structure of the piston. The results showed that the heat transfer coefficient of oscillating cooling can be decomposed into three components, namely conventional flow, oscillation enhanced and jet flushing parts. The conventional flow part accounts for the largest proportion of the total heat transfer coefficient, whose value is positively correlated with oil flow rate. The oscillation enhanced part is optimal when the oil filling rate is between 40 % and 60 %. The jet flushing part can lead to a higher temperature gradient in the outer cooling gallery and thus increased thermal stress. The cooling capacities of inner and outer galleries are mainly influenced by the diameters of the oil outlet and distributor pipes, respectively. The jet flushing part can be controlled by changing the inclination angle of the distributor pipe. Finally, optimization achieved an improvement of 8.3 % in cooling capacity of inner cooling gallery and a reduction of 27.5 % of heat dissipation inhomogeneity in the piston.

Investigation on the thermal-fluidic characteristics of ice slurry in sinusoidal corrugated plate heat exchangers

The sinusoidal plate heat exchangers (SCPHEs) using ice slurry as coolant have a critical role for building air conditioning. However, the thermal-hydraulic properties of ice slurry in SCPHEs are still unclear. Therefore, its flow and heat transfer performances in SCPHEs are studied using Euler-Euler model in this paper. The results show that with increasing corrugation pitch (P), the velocity of the mainstream direction and the flow dead zone decrease. As enlarging the corrugation amplitude (H), the low-velocity flow zone and flow dead zone increase. The average resistance coefficient (fave) of ice slurry reduces with increasing P and volume flow rate. When volume flow rate is between 0.144 m3/h and 1.44 m3/h, fave decreases more significantly than other stages. In addition, fave increases with increasing H and ice concentration (αin). The mass transfer of ice particles is increased at higher H and smaller P. The average Nusselt number (Nuave) of ice slurry, heat transfer rate (Qw) and total heat transfer coefficient (U) of SCPHEs increase as enlarging H, αin and volume flow rate, and decrease with increasing P. While the U and Qw are less affected by ice particle concentration. In addition, the empirical correlations of fave and Nuave in SCPHEs are developed.

Towards an improved thermometric method: Convective and radiative heat transfer for heat flux measurement through an indirect approach

Actual thermal performance of building walls need to be assessed through on-site tests. Several measurement procedures have been proposed during the last decades. Nonetheless, among them the Thermometric (THM) method has been poorly explored in literature, hence opportunities for improvements can be highlighted. The THM technique is a quite a new and non-standardized procedure for wall thermal characterization, based on the well-known Newton’s law of cooling. This law needs the heat transfer coefficient knowledge and there is no agreement about the value to apply when the THM method is used. In this work, a low-cost experimental apparatus characterized by a heated wooden sample was realized. Sensors were installed to measure heat fluxes through a common heat flux plate. The obtained values were compared with the heat flows achieved via the THM method, where dimensionless groups analysis was performed for computing suitable heat transfer coefficients obtained from data processing. The aim of this work is to lay the groundwork for overcoming the disagreement related to the value of the total heat transfer coefficient in the THM method by proposing and consolidating an alternative approach. The results show that the proposed data processing for the THM method can provide satisfying results in terms of indirect heat flux measurements, showing extremely low percentage differences (ranging from + 1.16 % to + 3.56 %) if compared with the HFM method.

Thermal evaluation of heat exchanger and a dry-cooled supercritical CO2 mixture Brayton cycle based on three-dimensional and one-dimensional models: Key factors and potential applications

High ambient temperatures in the desert environment and heat capacity mismatch of printed circuit heat exchanger (PCHE) are always main factors that limited cycle efficiency of supercritical CO2 Brayton cycle (SCBC). The SCBC was established to obtain the operating parameters of precooler, low temperature recuperator (LTR) and high temperature recuperator (HTR) in this paper. The performance evaluation factors were developed and applied. The findings demonstrated that the precooler total heat transfer coefficient (HTC) peaked near the pseudo-critical temperature. Smaller hot-side pressure, larger hot-side and cold-side mass flux could improve heat transfer performance (HTP) of the precooler. The CO2-H2S in the precooler had larger HTC and pressure drop (ΔP), the CO2-Propane in the LTR and HTR had larger total HTCs and ΔP for the same critical temperature. Heat transfer correlations about the precooler of pure CO2 and CO2 mixtures were proposed. A conclusion was drawn by analyzing the performance evaluation factors that the PCHE using CO2-H2S for the precooler and CO2-Propane for the LTR and HTR could achieve better HTP under the same ΔP, but had the smaller effectiveness under the same ΔP. The CO2-H2S had the potential for practical application because of the larger cycle thermal efficiency and relatively good tolerance to the change of critical temperature.

Thermal analysis of tubular daylight guidance system on an insulated flat roof with overlying soil

As an emerging passive daylighting technology, tubular daylight guidance systems (TDGSs) are increasingly used in low-energy buildings. However, TDGS may become a thermal bridge to increase indoor air conditioning load. To avoid an increase in total energy consumption, the thermal analysis of a flat roof section with a TDGS is simulated using CFD in this work. Additionally, the simulation compares the heat transfer performance of a conventional TDGS with eight different designs TDGS that contain additional glass unit. The findings show that TDGS has a thermal bridging effect on an insulated flat roof with overlying soil. The additional glass unit in the middle of the conventional TDGS with diameter 500 mm decreases its overall heat transfer coefficient by 53 %. Further, the same thickness of glass is divided into 4 layers and evenly distributed inside the TDGS with diameter 500 mm, which can reduce the total heat transfer coefficient of the conventional TDGS by 67 %.

Multi-objective optimization of thermal and daylighting performance for sightseeing elevators without air conditioning system considering economic cost

In the study, the shape, size and structure of the sightseeing elevators were investigated, and a prototypical model was established by Grasshopper. Furthermore, the performance and prices of glass were used to construct the function of price, then the multi-objective optimization method was adopted to simultaneously optimize the predicted percentage of people dissatisfied, useful daylight illuminance and cost of the building envelope of the elevators. The results showed that the optimal values of the total heat transfer coefficient, solar energy heat gain coefficient and total transmission of the envelope are 0.799 W/(m2·K), 0.164 and 0.153, respectively. Compared with that of “6 mm ultralow light transmission thermal reflective glass +12 mm air +6 mm transparent glass”, the predicted percentage of people dissatisfied decreases about 5.412 %. Though useful daylight illuminance has a small decrease of 1.167 %, cost of building envelope decreases by 60.127 %. In addition, the suitable working hours for three positions, where the control cabinets can be set at, have been significantly improved among the using frequency. In addition, ventilation systems were considered to improve the internal environment of sightseeing elevators, and appropriate control methods were selected to ensure the maximum operation of sightseeing elevators.

Numerical simulation and experiment of laminar heat transfer characteristics in micro-channel collector

In response to the problems of high mass and high thermal resistance in traditional cold plate collectors, the author proposes a shaped and efficient micro-channel collector structure design for non-normal temperature control scenarios such as high power, multiple heat sources, and highly non-uniform power density. The author conducted numerical and experimental studies on the laminar heat transfer in a highly efficient micro-channel shaped collector for non-normal temperature control scenarios such as high power, multiple heat sources, and highly non-uniform power density, the results show that: The relative deviation between the simulated and experimental values of the pressure drop of the micro-channel collector using perfluorotriethylamine as the working fluid is within -20%, and the relative deviation between the simulated and experimental values of the surface temperature is within +3?C, the predicted trend of the pressure drop and temperature field of the collector is in good agreement with the experimental values, indicating the feasibility of using numerical simulation methods for performance analysis and design optimization of 3-D printed micro-channel collectors. As the flow rate increases, the pressure drop of the collector increases approximately linearly, while the value increase of the total heat transfer coefficient gradually decreases, and increasing inlet temperature or heating power will reduce pressure drop of collector and increase total heat transfer coefficient. The influence of gravity on the pressure drop and total heat transfer coefficient of micro-channel collectors is less than 1. The straight through micro-channel collector has lower pressure drop and stronger heat transfer ability compared to the folded type collector.

Bioinspired radiative cooling coating with high emittance and robust self‐cleaning for sustainably efficient heat dissipation

AbstractTo overcome the overheating phenomena of electronic devices and energy components, developing advanced energy‐free cooling coatings with promising radiative property seem an effective and energy‐saving way. However, the further application of these coatings is greatly limited by their sustainability because of their fragile and easy contamination. Herein, it is reported that a bioinspired radiative cooling coating (BRCC) displayed sustainably efficient heat dissipation by the combination of high emittance and robust self‐cleaning property. With the hierarchical porous structure constructed by multiwalled carbon nanotubes (MWCNTs), modified SiO2 and fluorosilicone (FSi) resin, the involvement of the BRCC improves the cooling performance by increasing ≈25% total heat transfer coefficient. During the abrasion and soiling tests, the BRCC‐coated Al alloy heat sink always displays stable radiative cooling performance. Moreover, the simulation and experimental results both revealed that reducing surface coverage of BRCC (≈80.9%) can still keep highly cooling efficiency, leading to a cost‐effective avenue. Therefore, this study may guide the design and fabrication of advanced radiative cooling coating.

Numerical Study of the Influence of Different Bending Shapes on the Heat Transfer Characteristics of Annular Cross Wavy Primary Surface Recuperator (CW-PSR)

The cross-wave primary surface recuperator (CW-PSR) is a dependable option as a recuperator for micro gas turbines (MGT). The micro CW-PSR studied in this paper is composed of 171 stacked curved plates, with each plate containing 33 micro heat transfer channels with equivalent diameters of less than 1 mm. In this study, the influence of bending curvature on the thermal performance of CW-PSR plates is investigated through three-dimensional numerical simulation with fluid–solid–thermal coupling. The results indicate that the variation in bending curvature studied can result in a noteworthy 8% difference in the total heat transfer coefficient of CW-PSR plates. A direct correlation between heat transfer capacity and secondary flow strength is derived mathematically, explaining the mechanism by which secondary flow enhances heat transfer. By employing this relationship, a comprehensive analysis of CW-PSR plates with diverse bending curvatures is conducted, effectively showcasing how curvature influences the secondary flow pattern and enhances the channel’s heat transfer capacity. In addition, this paper considers the comprehensive influence of the size parameters of the heat transfer unit and the bending curvature of the heat transfer plate on the heat transfer and flow characteristics of the CW-PSR, and a dominant mathematical expression is obtained, which can be used for the design of similar heat exchangers of the same type.

Productivity amelioration of stepped solar still using phase change material and evacuated tube collector

AbstractThis study investigates the individual and cumulative effects of phase change material (PCM) and evacuated tube collector (ETC) on the performance of a stepped solar still (SSS). Experiments have been performed on SSS, SSS loaded with PCM (SSS‐PCM), SSS coupled with ETC (SSS‐ETC), and SSS loaded with PCM and coupled with ETC (SSS‐PCM‐ETC). An innovative way of loading paraffin wax as PCM is introduced to utilize solar energy efficiently for the distillation process during off‐sunshine hours. ETC is used to provide pre‐heated RO wastewater to the distillation unit. The distillate output was observed maximum for SSS‐PCM‐ETC (4.97 kg/m2 day) which is 99% more than that of the SSS unit. The PCM and ETC individually with SSS unit increases the distillate output by 31% and 24%, respectively. The working time of the distillation unit was observed to be increased by 3 h by the use of PCM. The total heat transfer coefficient was evaluated at the maximum for SSS‐PCM‐ETC and was observed in the range of 16.94–167.04 W/m2 °C. The thermal energy efficiencies of SSS, SSS‐ETC, SSS‐PCM, and SSS‐PCM‐ETC were evaluated as 28.65%, 35.59%, 43.88%, and 44.04%, respectively. SSS‐PCM‐ETC is found to be the most economic with the best environmental conservation having maximum values of daily productive cost ($0.69) and carbon credits earned ($184.8).

Aerothermal optimization of turbine cascade squealer tip with non-uniform squealer height

The squealer tip has significant influence on both the aerodynamic and heat transfer characteristics of the high-pressure turbine blade. However, due to the complexity of parameterization and meshing of the squealer and the complicated flow structure within the over-tip region, the existing squealer designs in the open literature have constant squealer heights. In this paper, the design space to the squealer height with non-uniform squealer height is extended and the new flow features it may bring are investigated. A parameterization system specifically designed for the non-uniform squealer height using five control parameters is implemented to automatically generate the geometry and hybrid meshes. Combining it with the multi-objective optimization system using genetic algorithms, a transonic turbine cascade squealer tip is optimized employing Reynolds-averaged Navier–Stokes k–ω shear stress transport model. The main objective of this study is to obtain a squealer configuration with the lowest total pressure loss coefficient and heat transfer coefficient. The optimum configuration with non-uniform squealer height achieves improvements in both the aerodynamic efficiency and the heat transfer performance, relative to the baseline conventional squealer tip geometry with the constant squealer height. Additionally, this work demonstrates that a flow structure in which the main flow forms a “blanket” below the leakage flow in the squealer is beneficial for aerothermal performance, especially reducing heat transfer losses, which provides valuable insight into the squealer tip design of advanced high-pressure turbines.

A comparative study of freeze-drying heat transfer in polymeric vials and glass vials

Implementation of polymeric vials for freeze-dried drug products has been practically non-existent because of unique moisture barrier and thermodynamic technical challenges. Hybrid vials, which combine the benefits of polymer and glass, have been shown to address the challenges of ordinary polymeric vials. Tackling thermodynamic challenges starts with a clear understanding of the heat transfer mechanism. To this end, multi-physics simulations and experimentation were used to compare the heat transfer between hybrid cyclic olefin polymer (COP) vials and borosilicate glass vials during freeze-drying. Parametric models were developed for hybrid COP and glass vials to systematically study the effect of five design parameters based on the arrangement of the vials on a tray inside a lyophilization chamber. Heat transfer in glass vials were dominated by heat conduction with the surrounding vapor, while hybrid COP vials were governed by conduction with the bottom shelf. Furthermore, hybrid COP vials exhibited more consistent heat flow rate and total heat transfer coefficient compared to glass vials, suggesting higher product quality as a result. The distance between adjacent vials and the drug product height were the most important parameters affecting heat transfer irrespective of vial type. Results indicated that hybrid COP vials can be filled to higher fill volumes with higher heat transfer and without the risk of breakage. Results of this study can help design innovative primary packaging systems for freeze drying or optimizing heat transfer for existing glass or hybrid COP vial systems regarding product consistency and drying time.

INFLUENCE OF THE DIAMETER OF CYLINDRICAL SAMPLES MADE OF DIFFERENT GRADES OF ALUMINUM ON THE COOLING KINETICS

The influence of the diameter of cylindrical samples from various grades of technical aluminum (A0, A5, A6), aviation AB98 and high-purity aluminum A5N on their characteristic cooling times and rates, as well as on heat transfer processes in a wide temperature range, was studied. It was revealed that cooling of the samples occurs due to convective heat transfer and radiation, which have characteristic times. An assessment of the magnitude of characteristic cooling times due to convective heat transfer and radiation has been carried out. It is shown that the characteristic cooling time due to radiation is less than the characteristic cooling time due to convection. Using experimental data on the cooling rate of the studied samples and theoretically calculated values of their heat capacity according to the Neumann-Kopp rule, heat transfer coefficients for the processes of convective heat transfer and radiation depending on temperature were determined. It has been established that with increasing temperature, the contribution of radiation to the total heat transfer coefficient increases, and the coefficient of convective heat transfer with increasing temperature first increases, then after passing a maximum it decreases. The contribution to the overall heat transfer coefficient from radiation is noticeable at high temperatures. It was revealed that the characteristic cooling times due to radiation and convection increase nonlinearly with increasing sample diameter (V/S). This dependence is explained by a decrease in the heat transfer coefficient with increasing sample diameter. Compared with the patterns of influence of sample size on the thermophysical properties of spherical samples. It was revealed that spherical samples cool faster than cylindrical samples of the same mass, and the heat transfer coefficients are higher.