Heat Exchange Coefficient Research Articles

Разработка эффективного водогрейного котла-утилизатора

Introduction. Problems of waste gas heat recovery are relevant in the course production activities. Secondary thermal ener­gy resources are the most widely spread type of energy waste. Efficient recovery of waste heat will reduce energy costs. The building of a cafeteria, that has a water-heating waste heat boiler (WHB) represents a widely spread type of industrial buildings in eastern countries, where hot water and heating can be provided by using heat waste recovered from groups of tandoor furnaces. The purpose of the research is to study unsteady convective flows of heat passing through the pipe of a tandoor heat exchanger and to develop a simple design of a small-sized, easy to manufacture, economical and safe model of a water heating device for the needs of the national economy. Materials and methods. The research is based on a comprehensive methodology employed to study, analyze and gene­ralize thermophysical processes based on the study of convective unsteady heat flows in heat exchanger pipes of tandoor furnaces. Results. The research result represents higher thermal efficiency of the WHB installed in the building of a cafeteria due to the heating, accumulation and heat transfer by vertical finned steel heat-exchanger pipes in the cylindrical boiler in the course of convective heating by the outlet gas used as the heat carrier without returning heat to the water heating boiler. Conclusions. The cafeteria building has scientifically and practically grounded design of a WHB tandoor group, which is a vertical cylindrical tank filled with water, in which vertical outlet heat exchange pipes are placed. Heat, emitted during the operation of tandoors, is used to bake flatbreads and bread by burning wood, coal, natural gas or electric heaters. This heat heats boiler sections to supply hot water to consumers and heat the building premises. The method of finned pipes extends the field of application of the device, increasing the coefficient of heat capacity and heat exchange, as well as the capacity of equipment.

Experimental and numerical study on tube-side flow and heat transfer characteristics of superheated vapor flow in catalyst-filled LH2 spiral wound heat exchanger

High energy consumption is considered to be one of the most persistent problems in liquid hydrogen (LH2) plants. The combination of heat exchanger and ortho-para (O–P) hydrogen conversion has attracted considerable attention as a cutting-edge technology to reduce energy consumption. The flow and heat transfer characteristics of O–P hydrogen conversion catalyst-filled spiral wound heat exchanger (SWHE) were investigated in this study in two steps. In the first step, pressure-drop experiments were performed in a tube filled with porous media. The results indicated that the pressure drop was overestimated when using Ergun's equation. Therefore, a new empirical pressure-drop correlation for a channel filled with O–P catalyst was formulated. Subsequently, a novel heat transfer model was established based on this correlation for further numerical simulations. The distributions of the temperature, pressure, and para hydrogen content in a catalyst-filled tube were determined. In addition, the influence of the flow rate on the heat exchange coefficient and outlet para hydrogen was clarified; it was found that, with an increase in the flow rate, the heat exchange coefficient increased, whereas the outlet para hydrogen content decreased. At a flow rate of 0.5 m3/h, the para hydrogen content increased by 44% after hydrogen flowed through the channel filled with the O–P catalyst. Furthermore, a prediction model for the para hydrogen content with a flow rate range of 0–1.5 m3/h was derived. This study provides promising theoretical evidence for the engineering application of SWHEs filled with O–P catalysts in large-scale hydrogen liquefaction units.

Improving the performance of steam power cycle through thermo-photovoltaic device: A novel combined system and thermodynamic analysis

In this study, a new system consisting of a thermophotovoltaic device and steam Rankine cycle system is proposed to prevent the mismatch between the combustion temperature and the steam maximum temperature to achieve photo-thermal energy cascade utilization and improve the fuel conversion efficiency. The energy balance model of the proposed system is established, and the influence of parameters such as emitter area and heat exchange coefficients on the system’s performance is investigated. Exergy analysis of the system is performed based on the second law of thermodynamics. The results show that the proposed system has 11–13% higher efficiency than the steam Rankine cycle system. The addition of a thermophotovoltaic device mainly reduces the exergy loss of the boiler due to the temperature difference between the combustion flue gas and the steam. Increasing the emitter area improves the system efficiency, and a system with Si cells is more efficient than a system with GaSb cells. Increasing the heat transfer coefficient of the air heat exchanger and the outlet flue gas temperature to generate a higher flame temperature is crucial to improving the performance of the combined system. The addition of a thermophotovoltaic device does not reduce the exergy loss during combustion. Thus, further energy cascade utilization should consider the efficient conversion of high-order chemical energy of a fuel. This study contributes to the theory of photo-thermal energy cascade conversion and provides new insights into improving the performance of the steam Rankine cycle.

Thermal analysis of a Trombe wall in various climatic conditions: An experimental study

The soaring energy prices incite us to value any available and free energy source. This paper is a contribution to improving the integration of passive solar systems in buildings. It consists in an experimental study of a Trombe wall in the Abha region of Saudi Arabia under real climatic conditions. The recorded experimental results are used to evaluate the solar gains collected by a room during the heating season.The experimental results combined with predictions based on thermal analysis are used to evaluate the different heat exchange coefficients, the thermo-circulation in the gap, and the total amount of heat captured during the sunshine hours. The influence of climatic factors such as wind and cloud cover has been analysed.The results show that the fraction of solar radiation transmitted inside is lower than losses to the outside, radiative exchanges are more important than convective ones. The quantity of heat collected during the days of experimentation varies according to climatic conditions. The Trombe wall can meet 80% of the heating needs of the room during a sunny day with low wind, 42% in the case of a sunny day with strong wind, and 37% during a day with scattered or low-density clouds. Even in the case of heavy cloud cover, the Trombe wall can provide 14% of heating needs.

Steady-state simulation and optimization of an air cooled chiller

In this paper, we propose a rigorous model for representing the operation of an air cooled chiller of a large office building and some simple correlations for predicting global heat exchange coefficient and pressure drop of the evaporator. The proposed models and a simplified physical one that assumes constant evaporator's heat exchange coefficient and pressure drop are used to simulate and optimize the operation of the chiller. The rigorous model shows that large variations of the order of 10% can be observed in the prediction of global heat exchange coefficient of the evaporator. We also present correlations for predicting specific enthalpies and entropies of superheated R-410, capable of representing Chemour's tabulated values within a maximum error of 2,5% for the entire expected operating region of chillers for air conditioning systems. All models are programmed as non-linear programming problems and solved by a sequential quadratic programming algorithm. Simulation and optimization results show that all physical models are easily and rapidly solved and that the more rigorous model should be preferred to optimize the operation of the chiller and to adequately predict limiting operating points and off-design situations. CPU time for all simulations was below 0,3 s using an Intel Centrino Duo type processor. Optimizing the operational point by means of the rigorous model might enable significantly reducing energy consumption depending on the disturbances affecting the operation of the chiller (e.g. of the order of 7%). We further show that the simple correlations are capable of predicting the operation of the chiller within acceptable deviations (predicting errors in compressor's power are up to 3%) and might be used to preliminarily test advanced control applications. It is also shown that evaporator's pressure drop should not be neglected as is a common practice, since prediction errors in superheating might be of the order of 3 °C. Finally, the rigorous model should be used to analyze limiting operating points and the effect of changing manipulated variables on important process constraints like superheating.

A new causative heat supply for exertional heat stroke on runners in cold air.

The dysregulation in heat balance, the main cause of exertional heat stroke, occurs not only in midsummer but also in the cold season. Possible causes of this are a reduction in convection and evaporation due to tailwinds and an acceleration of radiant heat inflow. Although the amount of radiant heat that reaches the surface can be estimated, the actual amount of heat that flows into the body cannot be specified yet. This paper made an experimental attempt at this. A device is made up of a temperature controllable heat sink and heat flow detector, which keeps the surface temperature constant and has a heat exchange coefficient comparable to that of the human body surface. The output of this device (total heat exchange) was divided into radiant heat exchange and other heat exchange using a standard radiant heat calibrator, Leslie cube. A phenomenon, in which a wet surface while the surface temperature was low absorbed larger heat than that of the dry surface, was found. And authors named this "hidden heat inflow". As a result of multiple regression analyses, both radiant heat exchange and other heat exchanges are closely related to the surface temperature, and the maximum difference in total heat exchange during the experiment reached 200kcal/m2/h. It has been suggested that this phenomenon may also occur on the surface of human skin. One of the causes of this "hidden heat inflow" is considered to be the decrease in evaporative cooling due to the decrease in surface temperature. However, this alone cannot explain all of the phenomena, so water vapor aggregation may also be involved. A "hidden heat inflow" as a sufficient heat source for exertional heat stroke or collapse during a marathon race on a cold day was evidenced experimentally.

Heat transfer enhancement using 40 kHz ultrasound and metal foams inside a horizontal mini-channel

The aim of this experimental and numerical study using COMSOL Multiphysics is to analyze the effects of the metal foam and the acoustic streaming generated by ultrasonic waves of 40 kHz on heat transfer in forced convection over a heated plate. The results of the literature show that the metallic foam, and the ultrasonic acoustic streaming, improve heat transfer independently. For this purpose, we carried out a comparative study of different configurations. In the first configuration, aluminum foam occupies the entire surface of the heating body and the cooling fluid passes through it. However, in the second configuration, two aluminum foams of 10 mm thickness, spaced 10 mm apart, arranged in a manner that a quantity of air passes above and the other through its pores. Flow regime is maintained laminar for velocities ranging between 0.2 and 1 m/s. A heat flux of 50 W is kept constant in the bottom of test section.The results revealed that the insertion of aluminum foams improved the heat transfer by a factor of 227% and 125% respectively for a fully and partially porous channel, compared to an empty channel for equal flow velocities. While an enhancement factor of 42% was obtained by the acoustic streaming effect generated by ultrasonic waves of 40 kHz in an empty channel. The coupling of these two intensifying methods showed a slight increase in heat exchange coefficient in a partially porous channel configuration with an enhancement factor of 7% compared to a flow without ultrasound, Otherwise, no ultrasound influence on heat transfer in a fully porous channel configuration, this is explained by the impedance of wave propagation medium which attenuates the acoustic streaming effect.

RETRACTED:Increasing electricity generation—Installing photovoltaic cells coupled to a battery pack, to provide the electricity

By 2050, renewables should increase the share of electricity generation to 70 %. According to the net-zero long-term plan, solar energy is at the forefront of renewable sources. The concreted solar plant is one of the best renewable-based electricity generation utilities that can combine with solar cells and battery systems. In this study, basic modelling for counter flow shell-tube type heat exchanger is developed in which melted salt and steam/water are the two-working fluid of the heat exchanger. A two-phase heat transfer analysis has been considered for the boiling phenomena in the saturated steam region. The study is performed for 5 kg·s−1 flow rate of steam/water and for different flow rate of melted salt varying from 75 kg·s−1 to 300 kg·s−1. Thermodynamic characteristics of the heat exchanger, such as, vapor quality and convective coefficient variation of the steam/water along the length of the heat exchanger has been presented. In addition, temperature profile of the melted salt and the steam/water along the length of the heat exchanger is determined in this study. Numerical analysis affirmed that the battery cooling was successful at Reynolds number of 200–500 as the maximum temperature was lower 320 K.

Numerical study of two heat exchangers for the cooling of a battery pack for an electric vehicle

Background: The thermal management of a battery pack designed for an electric vehicle is a key to prevent accidental events and ensure a long lifespan of the batteries. A typical accident is a thermal runaway of one or more cells in the battery which can cause fire or explosion of the battery pack. This paper presents a numerical modelling of a battery pack (BP) and its heat exchanger (HE) for an electric vehicle. The heat produced in the battery is evacuated by the HE. Methods: Two different kinds of modelling have been realized: a computational fluid dynamic (CFD) modelling and a coarse (called MOD3 for 3D Model) modelling. The CFD modelling allows the creation of fine numerical simulations of a BP, but uses large meshes, therefore the cost of each calculation is important. In order to make a large number of quite long transient simulations, a second tool called MOD3, employing only a coarse mesh, was developed in this study at the Commissariat à l’énergie atomique et aux énergies alternatives (CEA). Results: Two measurement campaigns corresponding to two different versions of the HE have been conducted at CEA. The temperature measurements allow comparisons of MOD3 to a real battery pack and to fit some heat exchange coefficients. The cells temperatures as well as the cooling liquid temperature are compared. Conclusions: The MOD3 tool has been fitted partly on CFD calculations, and partly on experimental measurements. It will be integrated in a machine learning environment by CIDETEC to take into account the thermal management of the BP in real car simulations.

Comparison and evaluation of supercritical CO 2 cooling performance in horizontal tubes with variable cross‐section by field synergy theory

The cooling/heating performance improvement of supercritical carbon dioxide (sCO2) in heat exchange tube with changing cross-section is significant and crucial for solar-driven advanced thermal systems' application and development. The study introduced and constructed straight, diverging, and converging horizontal tubes with the changing cross-section. The analyzation and evaluation of the sCO2 cooling performance used the combination of SST k-ω turbulence model-based numerical method and the field synergy theory, including the influence of tube cross-sectional shape, inlet pressure and temperature on the cooling performance. As these simulation results indicate, the converging tube can enhance the flow field's synergy and increase the heat transfer ability by 13.15% under cooling conditions. Nevertheless, the heat transfer ability of the sCO2 decreases in the diverging tube under cooling conditions. Besides, the total heat transfer rate rises and the surface heat transfer coefficient has the opposite trends when the inlet temperature increases. Meanwhile, when inlet pressure varies from 11 to 12 MPa, the total heat exchange and surface convective heat transfer coefficient are the maximum. In conclusion, a converging horizontal tube and a suitable inlet pressure can effectively improve the cooling performance of the sCO2. The converging cross-section design will provide an alternative for its application in advanced thermal systems.

Numerical simulation of heat transfer performance of different heat exchange tubes in heat recovery steam generator

For the purpose of reducing the cost of hydrogen production in process engineering and practice and enhancing the heat exchange efficiency of heat recovery steam generator, a new spring-blade mixed heat exchange tube was creatively put forward, and the performance evaluation criterion (PEC) was used as evaluation index of comprehensive heat transfer performance. To explore the heat transfer performance, the velocity distribution, temperature distribution, pressure distribution and comprehensive heat transfer performance were analyzed, and heat transfer coefficient and the value of PEC were obtained. The addition of spring and blade in the mixed heat exchange tube has obvious positive impacts on the velocity, temperature and pressure drop. In the Reynolds number range of 20000–40000, the heat exchange coefficient increment of the mixed heat exchange tube is increased by 35% and 45% than that of the spring and blade heat exchange tube respectively. The pressure drop is positively correlated with the heat exchange coefficient, and its increase leads to the decrease of PEC value.

Scaling control by using ultrasonic guided waves

Fouling of heat exchanger surfaces is a major concern in the industry, resulting in performance losses through a decrease in the overall heat exchange coefficient. Control methods exist but are costly and have a strong environmental impact. Thus, the use of physical treatments is very promising, because the action is done on the clogged surface, in the bulk or in the solution. The present study shows the influence of ultrasonic guide waves on the crystallization of calcium carbonate inside a plate heat exchanger from scaled water. An experimental pilot was set up to study the scaling phenomenon. Several operating parameters such as flow rate, duration, and temperature were experimentally varied in order to identify their influence on the scale deposition in the heat exchanger. Subsequently, a thermodynamic prediction was performed by geochemical modeling using the Phreeqc software in order to get an idea of the nature of the deposit formed after the heating of scaled water. The main objective of this work was the determination of the impact of ultrasonic treatment on the mineral deposit, qualitatively and quantitatively. Therefore, four types of experiments lasting three days are presented in this paper to experimentally show the influence of ultrasound generated by a 35–50 kHz transducer on scale formation. The amount of solid deposited in grams/per day/area, the polymorphism of the formed crystals, and the number, size and size distribution of the particles were analyzed. Disassembly of the exchanger allowed access to the distribution of scale on the plates, and thus justified the choice of location for the 35–50 kHz transducer. It was also possible to estimate the thickness of the scale experimentally by 3D digital microscopy and to ensure the absence of microcrystals in the pores of the plate by analyzing the surface roughness. The results obtained were compared to the experimental measurements with and without the presence of the 35–50 kHz transducer. This allowed the evaluation of the effect of guided ultrasonic waves for the prevention of scale deposits. The presence of a single medium power transducer reduced mineral scale deposition in a plate and gasket heat exchanger by 76%.

STUDY OF THE THERMAL RESISTANCE OF HEAT TRANSFER IN TRANSIENT DYNAMIC REGIME IN AN INSULATING MATERIAL BASED ON TYPHA AND TWO-DIMENSIONAL (2D) CLAY: INFLUENCE OF THE HEAT EXCHANGE COEFFICIENT ON THE FRONT FACE

The objective of this study is to focus on the influence of local insulating materials in thermal insulation for a well-defined period. The material is a wall consisting of typha and clay. The main objective of this study is to see the behavior of the thermal resistance of the material as a function of the heat exchange coefficient at the front face. The typha and clay wall is modeled by applying the transient analytical method with the two-dimensional heat equation. This analytical resolution of the heat equation allows us to determine the detailed expression of the thermal resistance but also to visualize the curves of evolution of this resistance according to the depth under the influence of the heat exchange coefficient at the front side.

The role of the heat exchange coefficient at the ice/ocean interface in Bohai Sea ice modeling

The role of the heat exchange coefficient (HEC) at the ice/ocean interface in Bohai Sea ice simulations using the HAMSOM ice-ocean coupled model has been studied by sensitivity research and mechanism analysis. Our simulations indicate that the HEC plays a major role during the ice melting period, and plays a very minor role during the ice growth period. The HEC can modulate ice freezing/melting at the ice/ocean interface through two important response mechanisms in the thermal ice-ocean fields. The magnitude of both freeze rate of newly formed ice and melt rate of ice base increases with the HEC. We also found that the values of the parameterized HEC and oceanic heat flux in the marginal ice zone (MIZ) are larger than those in the inner ice area in the Bohai Sea. The relationship between the HEC and friction velocity at the ice/ocean interface (i.e., the parameterization proposed by McPhee (1992)) was also introduced into the model to obtain the spatiotemporally varying HEC. The simulation result of ice area shows that the simulations using the parameterized HEC have the best performance, providing a 53% improvement compared with the simulations using a constant HEC (0.001, the value used in our previous study (Jia and Chen, 2020).

Investigations of Middle-Caliber Anti-Aircraft Cannon Interior Ballistics including Heat Transfer Problem in Estimation of Critical Burst Length

Numerical and experimental investigations of armament systems are an important part of modern design processes. The presented paper reports problems that were encountered on the theoretical analysis of the performance of 35 mm anti-aircraft cannon and the way in which they were solved. The first problem concerns the application of results of closed vessel tests of used propellant in interior ballistics simulations. The use of a nonstandard form of the gas generation rate equation solved this problem. The second problem concerned the assessment of projectile–barrel interaction. The barrel resistance was estimated making use of finite element analysis. The third problem arose from the need to determine the heat transfer from propellant gases to the barrel. The employed formula for the heat exchange coefficient and 2D modelling of the heat conduction in the barrel provided the solution. Selected elements of the theoretical model were validated by shooting range experiments and data provided by the ammunition producer. Using the considered approach, crucial ballistic parameters (maximum propellant gas pressure and muzzle velocity) were estimated with an error of less than 6.0%, without application of additional fitting coefficients. The numerical estimation of the barrel external surface temperature provided a relative discrepancy with the experimental data lower than 6% and enabled the estimation of the critical burst length, equal to 14 shots.

How Does Air‐Sea Wave Interaction Affect Tropical Cyclone Intensity? An Atmosphere‐Wave‐Ocean Coupled Model Study Based on Super Typhoon Mangkhut (2018)

AbstractCapturing TC intensity change remains a great challenge for most state‐of‐the‐art operational forecasting systems. Recent studies found TC intensity forecasts are sensitive to three‐dimensional ocean dynamics and air‐sea interface processes beneath extreme winds. By performing a series of numerical simulations based on hierarchical atmosphere‐wave‐ocean (AWO) coupling configurations, we showed how atmosphere‐ocean and atmosphere‐sea wave coupling can affect the intensity of super typhoon Mangkhut (2018). The AWO coupled model can simulate TC‐related strong winds, oceanic cold wake, and wind waves with high fidelity. With atmosphere‐ocean (AO) coupling implemented, the simulated maximum surface wind speed is reduced by 7 m s−1 compared to the atmosphere‐only run, due to TC‐induced oceanic cold wakes in the former experiment. In the fully coupled AWO simulations, the wind speed deficit can be completely compensated by the wave‐air coupling effect. Further analyses showed that, in the AWO experiment, two mechanisms contribute to the improvement of TC intensity. First, in the high wind scenario (>28 m s−1), the surface drag coefficient reaches an asymptotic level, assisting extreme wind speed to be maintained within the eyewall. Second, the wind speed distribution is modulated and becomes broader; higher wind within the TC area helps to offset the negative effect due to leveling off of the heat exchange coefficient as wind speed increases. Overall, the simulated TC in the AWO run can extract 8–9% more total heat energy from the ocean to maintain its strength, compared to that from the AO experiment.

Aerodynamics and Complicated Heat Transfer with the Mixed Motion of Air in the Flat Duct of a High-Temperature Heat Exchanger

The purpose of the research is to study the aerodynamics and heat transfer in the duct of a high-temperature recuperation system. The object of the research is a flat duct with a thickness-to-height ratio a:b = 1:10, length c = 400·a with one-sided heat input to the duct surface, complicated heat transfer and mixed air movement in the duct. The objectives of the research are to determine: (a) average temperatures on the duct surfaces; (b) air temperature distribution along the length of the duct; (c) local and average integral temperature values along the length of the duct; (d) local and average integral heat flow densities on the duct surfaces; (e) local and average integral heat exchange coefficients and Nusselt numbers on the duct surfaces; and (f) pressure distribution along the length and total pressure drop in the duct. The research method is based on conducting a mathematical numerical experiment in a stationary three-dimensional Cartesian formulation and physical modeling of processes on a prototype. It is established that the dominant heat transfer between the duct walls and the air is a complicated convective heat transfer, in which forced convection is affected by free convection. There is a 1.5–2.0-fold difference in the values of the heat flow density on the hot and non-heated surfaces of the duct. Generalizing dependences of Nusselt numbers, temperature pressures and friction resistance coefficients as functions of a dimensionless coordinate are obtained.

Study of the Optimum Thermal Insulation Thickness of a Calorimeter Wound with Linen Insulation

In this article, the object of the study is focused on the influence of local insulating materials in the design of a calorific model for the conservation of hot water for a fixed period. The short hollow cylinder is wound with thermal insulation flax between the two walls of the cylindrical device to insulate the interior temperature. The objective of this study is to see the behavior of the thermal resistance of the material as a function of the insulation thickness. The cylinder is modeled by applying the transient analytical method with the heat equation. This analytical resolution of the thermal equation makes it possible to determine the detailed expression of the thermal resistance but also to visualize the evolution curves of this resistance according to the thickness of the insulation under the influence of the contact resistance thermal and heat exchange coefficient on the outside cylinder wall. The results obtained show that the optimum insulation thickness of linen at a temperature of 90 °C is 3.7 cm under the influence of the thermal resistance of the material and 4 cm under the influence of the exchange coefficients thermal.

ОБ ИДЕНТИФИКАЦИИ КОЭФФИЦИЕНТА ТЕПЛООБМЕНА В СЛОИСТОЙ СРЕДЕ

In the article we consider the well-posedness in Sobolev spaces of the inverse problems of determining the heat exchange coefficient at the interface which is included in the transmission condition of the imperfect contact type. In a cylindrical spatial domain, a second-order parabolic equation is considered. The domain is divided into two sub-domains, on the common part of the boundary of which the transmission condition is set. The heat exchange coefficient included in the transmission condition is sought as end segment in series with time-dependent unknown Fourier coefficients. The equation is supplemented with general boundary conditions and initial conditions, as well as overdetermination conditions. The ovedetermination conditions are the values of a solution at some points lying in the spatial domain. Under natural smoothness conditions for the data and the location of the measurement points, the existence and uniqueness theorem local in time is demonstrated. The obtained solution to the problem is regular, i. e., all generalized derivatives included in the equation are summable to some power, and the equation holds almost everywhere. The method is constructive, and the approach allows to develop numerical methods for solving the problem. The proof is based on a priori estimates obtained and the fixed-point theorem.

Research on the Ratio between the Convection and Radiation Heat Exchange Amount of the Face and Head of Manikin in the Thermal Comfort Condition

In this paper, the radiation heat exchange coefficient of the exposed parts of human body is firstly obtained through pre-experiment, which is used to separate the total output heat exchange amount of the manikin. Then the heat exchange amount of manikin under different airflow organizations of personal ventilation, mixed ventilation and seat ventilation are respectively studied. The value of convection heat exchange and radiation heat exchange of the face and head of human body are compared. And variable conditions are studied for different air temperatures and volumes. It is concluded that when the supply air temperature changes between 22? and 30°C with human body thermally comfortable, the total heat exchange of the face and head changes from 38 W/m2 to 137 W/m2, and the range of the radiation heat exchange amount is 26 W/m2 to 67 W/m2. The convection heat exchange amount changes between 6 W/m2 and 110 W/m2, and the ratio of radiation heat exchange to convection heat exchange changes from 0.5 to 6.7.