View Factors of Samples Tested in Cone and Cylinder Calorimeters

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Marcos J. A. Gemaque ◽  
Fernando S. Costa
Keyword(s):  
Thermal Radiation ◽  
Heat Input ◽  
Blackbody Radiation ◽  
View Factor ◽  
Exposed Surface ◽  
Solid Materials ◽  
Input Distribution ◽  
Total View ◽  
Flammability Characteristics ◽  
View Factors

Cone and cylinder calorimeters are devices used to determine flammability characteristics of solid materials under prescribed heat inputs. Temperature and heat input distribution on the exposed surface of a specimen in a calorimeter can be affected by variations of position or size of the specimen. This work analyzes the thermal radiation view factors of slabs and cylinders tested in cone and cylinder calorimeters, respectively. Blackbody radiation thermal interchange is assumed and reflections of neighbor objects are not considered. Uniformity of view factor distributions and total view factors are compared for slabs and cylinders tested in calorimeters, considering positioning and size variations.

scholarly journals Contactless and spatially structured cooling by directing thermal radiation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Nicola M. Kerschbaumer ◽  
Stefan Niedermaier ◽  
Theobald Lohmüller ◽  
Jochen Feldmann
Keyword(s):  
Thermal Radiation ◽  
Radiative Heat ◽  
Radiative Cooling ◽  
View Factor ◽  
Temperature Pattern ◽  
Thermal Gradients ◽  
Science And Engineering ◽  
Building Management ◽  
Temperature Manipulation ◽  
Novel Concept

AbstractIn recent years, radiative cooling has become a topic of considerable interest for applications in the context of thermal building management and energy saving. The idea to direct thermal radiation in a controlled way to achieve contactless sample cooling for laboratory applications, however, is scarcely explored. Here, we present an approach to obtain spatially structured radiative cooling. By using an elliptical mirror, we are able to enhance the view factor of radiative heat transfer between a room temperature substrate and a cold temperature landscape by a factor of 92. A temperature pattern and confined thermal gradients with a slope of ~ 0.2 °C/mm are created. The experimental applicability of this spatially structured cooling approach is demonstrated by contactless supercooling of hexadecane in a home-built microfluidic sample. This novel concept for structured cooling yields numerous applications in science and engineering as it provides a means of controlled temperature manipulation with minimal physical disturbance.

scholarly journals A Deep Neural Network Model of Particle Thermal Radiation in Packed Bed

2020 ◽  
Vol 34 (01) ◽  
pp. 1029-1036
Author(s):  
Hao Wu ◽  
Shuang Hao
Keyword(s):  
Neural Network ◽  
Heat Transfer ◽  
Thermal Radiation ◽  
Radiative Heat Transfer ◽  
Power Plants ◽  
Deep Neural Network ◽  
Radiative Heat ◽  
Particle Packing ◽  
View Factor ◽  
Pebble Bed

Prediction of particle radiative heat transfer flux is an important task in the large discrete granular systems, such as pebble bed in power plants and industrial fluidized beds. For particle motion and packing, discrete element method (DEM) now is widely accepted as the excellent Lagrangian approach. For thermal radiation, traditional methods focus on calculating the obstructed view factor directly by numerical algorithms. The major challenge for the simulation is that the method is proven to be time-consuming and not feasible to be applied in the practical cases. In this work, we propose an analytical model to calculate macroscopic effective conductivity from particle packing structures Then, we develop a deep neural network (DNN) model used as a predictor of the complex view factor function. The DNN model is trained by a large dataset and the computational speed is greatly improved with good accuracy. It is feasible to perform real-time simulation with DNN model for radiative heat transfer in large pebble bed. The trained model also can be coupled with DEM and used to analyze efficiently the directional radiative conductivity, anisotropic factor and wall effect of the particle thermal radiation.

View Factors to Grounds of Photovoltaic Collectors

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
J. Appelbaum
Keyword(s):  
Global Radiation ◽  
Appreciable Amount ◽  
View Factor ◽  
Solar Pv ◽  
Mathematical Expressions ◽  
Inclination Angles ◽  
View Factors ◽  
Solar Field ◽  
Analytical Expressions ◽  
General Configuration

Ground reflected radiation is one component of the global radiation on photovoltaic collectors in a solar field. This component depends on the view factor of the collector to ground, hence depends on the relative position of the collectors to each other. General analytical expressions and numerical values for the view factor to the ground were developed between flat-plate collectors positioned in a general configuration. Based on the general expression, the view factors to ground for particular collector configurations were derived. For deployment of photovoltaic collectors in multiple rows with common inclination angles, the view factor to ground is rather small, and hence, the reflected radiation from the ground on the collectors may be neglected compared to the direct beam and the diffuse components. However, in some cases the reflected radiation from the ground may constitute an appreciable amount as in snowy area. Bifacial photovoltaic (PV) panels can absorb solar radiation by both the front and the rear sides and are usually deployed vertically. In this case the reflected radiation from the ground on the panels may be appreciable depending on the ground albedo. The mathematical expressions of the different view factors may be used by the solar field designer to estimate the amount of reflected radiation from the ground reaching the collectors for different configurations of solar PV plants.

View Factors of Flat Solar Collectors Array in Flat, Inclined, and Step-Like Solar Fields

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
Nassar Yasser Fathi ◽  
Alsadi Samer
Keyword(s):  
Solar Radiation ◽  
Diffuse Radiation ◽  
Dynamic Parameter ◽  
Incident Radiation ◽  
Appreciable Amount ◽  
Design Parameters ◽  
View Factor ◽  
Solar Radiation Incident ◽  
View Factors ◽  
Reflecting Surfaces

Solar radiation consists of direct beam, sky diffuse, and reflected radiations from the ground and adjacent surfaces. The amount of diffuse radiation falling on solar collector depends on the view factor of the collector to sky. The reflected radiation striking the collector's surface depends on the reflectivity of the surface, as well as on view factors and the amount of solar radiation reaching the reflecting surfaces. The amount of reflected radiation coming from the ground can be of an appreciable amount, and can be amplified using special reflector surfaces. This study develops general analytical expressions for the sky's view factors as well as factors related to the ground and those between collectors for the deployment of collectors in multiple rows, in three types of solar fields: flat, inclined, and steplike solar fields. All parameters presented in these expressions are measurable (edge-to-edge dimension). The effects of the design parameters such as the tilt of the angle of the collector, the distance between the collectors, the height of the collector, the position of the collector above the ground (as in the case of step-like field), and the inclination of the land of the field (as in the case of an inclined field) on the view factors are numerically demonstrated. The current study also specifies new terms such as the sunny zone and the shadow zone; these zones control the amount of solar radiation reflected onto the collector. As a result, the ground-view factor that depends on the altitude of the solar angle is considered to be a dynamic parameter. The results obtained may be used to estimate the solar radiation incident on all types of solar fields, with the possibility of increasing the incident radiation on a collector by using planar reflectors.

A New Semianalytical Algorithm for Calculating Diffuse Plane View Factors

1998 ◽  
Vol 120 (1) ◽  
pp. 279-281 ◽  
Author(s):  
A. Mavroulakis ◽  
A. Trombe
Keyword(s):  
Exact Solutions ◽  
View Factor ◽  
View Factors ◽  
Plane View

A new semianalytical algorithm for calculating diffuse plane view factors which is based on an extension of Nusselt’s sphere method is presented. For simple cases of view factor calculations where exact solutions exist, the accuracy of the algorithm is tested and compared with the accuracy of others.

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