scholarly journals CALCULATION METHODS OF RADIATIVE HEAT TRANSFER COEFFICIENT FOR DIVIDED AIRSPACES

2002 ◽  
Vol 67 (561) ◽  
pp. 13-20
Author(s):  
Hiroshi AKASAKA
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Calculation Methods ◽  
Radiative Heat Transfer Coefficient

Average Wall Radiative Heat Transfer Characteristic of Isothermal Radiative Medium in Inner Straight Fin Tubes

2021 ◽  
Author(s):  
Wenping Peng ◽  
Min Xu ◽  
Xiaoxia Ma ◽  
Xiulan Huai
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Radiative Heat Transfer ◽  
Calculation Method ◽  
Radiative Heat ◽  
Solid Surfaces ◽  
Design Calculation ◽  
Radiative Heat Transfer Coefficient ◽  
Fin Tubes

Abstract Wall radiative heat transfer in inner straight fin tubes is very complex considering the coupling of heat conduction in fins and radiative heat transfer of medium with solid surfaces, influenced by a number of factors such as fin parameters, radiative pro perties and run conditions. In this study, a simplified method is used.The average radiative heat transfer between radiative medium and solid surfaces is firstly studied by simulation with fins assumed having a constant temperature. Then an approximate correlation of this radiative heat transfer coefficient is proposed using the traditional radiative heat transfer calculation method with a view coefficient, having a error within 15%. A calculation method of average wall radiative heat transfer coefficient is further proposed by fin theory with an average temperature of fin surface used to consider the varying of the temperature along the fin when the conductivity of fins is finite. Using the predicting method proposed, a method for design calculation of fins in tubes to optimize wall radiative heat transfer is also given with three dimensionless numbers of p/n, 2H/D and nt/pD defined. Three cases of are analyzed in detail based on the design calculation method. It is verified that the radiative heat transfer could be enhanced twice by introducing fins. Under the same h0, conductivity and emissivity are two important factors to choose the material for fins.The micro-fins or the special treatments on the tube wall are a best choice for the fin material having a relatively small conductivity.

scholarly journals Determination of Radiative Heat Transfer Coefficient at High Temperatures Using a Combined Experimental-Computational Technique

2015 ◽  
Vol 15 (2) ◽  
pp. 85-91 ◽  
Author(s):  
Václav Kočí ◽  
Jan Kočí ◽  
Tomáš Korecký ◽  
Jiří Maděra ◽  
Robert Č Černý
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Computational Modeling ◽  
Transfer Coefficient ◽  
High Temperatures ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Calculated Data ◽  
Radiative Heat Transfer Coefficient

Abstract The radiative heat transfer coefficient at high temperatures is determined using a combination of experimental measurement and computational modeling. In the experimental part, cement mortar specimen is heated in a laboratory furnace to 600°C and the temperature field inside is recorded using built-in K-type thermocouples connected to a data logger. The measured temperatures are then used as input parameters in the three dimensional computational modeling whose objective is to find the best correlation between the measured and calculated data via four free parameters, namely the thermal conductivity of the specimen, effective thermal conductivity of thermal insulation, and heat transfer coefficients at normal and high temperatures. The optimization procedure which is performed using the genetic algorithms provides the value of the high-temperature radiative heat transfer coefficient of 3.64 W/(m2K).

Calculation of Convective and Radiative Heat Transfer Coefficient Using Thermography During a Physical Exercise

2020 ◽  
Author(s):  
Sathish K. Gurupatham ◽  
Priyanka Velumani ◽  
Revathy Vaidhya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Human Body ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Convective Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Air Velocity ◽  
Heat Transfer Coefficients

Abstract A detailed model of human thermoregulation and a numerical algorithm to predict thermal comfort is a novel field of research and has wide applications in the auto/transportation industry and in the heating, ventilating, and air-conditioning (HVAC) industry. Anatomically specific convective and radiative heat transfer coefficients for the human body will be required to understand the human thermal physiological and comfort models. It necessitates to create hygienic and thermally comfortable spaces for the best productivity of the users. The physiological nature of thermal comfort during a transient condition such as a physical exercise or travel in an automobile are not yet well understood. In this paper, thermography has been applied to measure the convective and radiative heat transfer coefficients which has not been done before. Three different recovery processes were considered after the running of a human model on a treadmill with a range of speeds starting from 2 miles/hour to 10 miles/hour for stretch of twenty minutes. The recovery process included, (a) fan-assisted cooling with an air velocity of 0.5 m/s for 30 minutes, (b) fan-assisted cooling with an air velocity of 1.5 m/s for 30 minutes, and (c) natural cooling with no assistance of fan for 30 minutes. Thermal images were taken for forehead, trunk, arms, hands, legs of the models and the convective heat transfer coefficient and radiative heat transfer coefficient were calculated. The human models included both male and female, and belonged to two different age groups of less than 15 and above 40 with a total of 24 participants. The results show that though the temperatures, measured using thermography, for various parts of the human body changed locally, the overall calculated radiative heat transfer coefficients matched with the ASHRAE handbook values, and the calculated convective heat transfer coefficient increased with the increase of air velocity, while the models cooled down after the workout. Interestingly, the skin temperature decreased, initially, as the exercise progressed. After the completion of exercise, the skin temperature exhibited a quick rise during the recovery period with a subsequent decrease in the temperature, later. This trend was the same with all different age groups and sex of the models. The results also confirm that thermal images can be relied on for calculating the convective and radiative heat transfer coefficients of the human body to determine the heat transfer rate.

Correlations and Theory for Microchannel Condensation

2008 ◽  
Author(s):  
Qian Su ◽  
Guang Xu Yu ◽  
Hua Sheng Wang ◽  
John W. Rose
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Theoretical Approach ◽  
Annular Flow ◽  
Fair Agreement ◽  
Calculation Methods ◽  
Fluid Property ◽  
The Heat Transfer Coefficient

In recent years several correlations have been proposed for calculating the heat-transfer coefficient during condensation in circular and non-circular channels of typical dimension around 1 mm where surface tension effects are important and correlations for larger diameter channels are inappropriate. A wholly theoretical approach applicable to annular flow has also been proposed. The correlations are all based on data for R134a, while the theory is applicable to any fluid. In this paper comparisons are made between the correlations for R134a and ammonia; plots based on theory are also included. Fair agreement is seen between all calculation methods for R134a but wide differences are seen for ammonia indicating that the correlations, based only on one fluid, do not capture the fluid property dependence accurately.

Near-Field Radiative Transfer Between Heavily Doped SiGe at Elevated Temperatures

2011 ◽  
Author(s):  
Z. M. Zhang ◽  
E. T. Enikov ◽  
T. Makansi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
State Energy ◽  
Radiative Heat ◽  
Elevated Temperatures ◽  
Near Field ◽  
Temperature Dependent ◽  
Heavily Doped ◽  
The Heat Transfer Coefficient

SiGe alloys represent an important type of high-temperature semiconductor material for solid-state energy conversion. In the present study, the near-field radiative heat transfer between heavily doped SiGe plates is investigated. A dielectric function model is formulated based on the previously reported room-temperature mobility and temperature-dependent electric resistivity of several silicon-rich alloys with different doping type and concentration. The fluctuational electrodynamics is used to evaluate the near-field noncontact heat transfer coefficient. The variation of the heat transfer coefficient with doping concentration and temperature is explained according to the change in the optical constants and in the spectral distribution of the near-field heat flux.

Casimir Friction and Near-field Radiative Heat Transfer in Graphene Structures

2017 ◽  
Vol 72 (2) ◽  
pp. 171-180 ◽  
Author(s):  
A.I. Volokitin
Keyword(s):  
Heat Transfer ◽  
Energy Transfer ◽  
Transfer Coefficient ◽  
Graphene Sheet ◽  
Drift Velocity ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Near Field ◽  
Radiative Energy ◽  
Phonon Polaritons

AbstractThe dependence of the Casimir friction force between a graphene sheet and a (amorphous) SiO2 substrate on the drift velocity of the electrons in the graphene sheet is studied. It is shown that the Casimir friction is strongly enhanced for the drift velocity above the threshold velocity when the friction is determined by the resonant excitation of the surface phonon–polaritons in the SiO2 substrate and the electron–hole pairs in graphene. The theory agrees well with the experimental data for the current–voltage dependence for unsuspended graphene on the SiO2 substrate. The theories of the Casimir friction and the near-field radiative energy transfer are used to study the heat generation and dissipation in graphene due to the interaction with phonon–polaritons in the (amorphous) SiO2 substrate and acoustic phonons in graphene. For suspended graphene, the energy transfer coefficient at nanoscale gap is ~ three orders of magnitude larger than the radiative heat transfer coefficient of the blackbody radiation limit.

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