A Flexible Thermal Model for Solar Cavity Receivers Using Analytical View Factors

This paper presents advances to a thermal model for a cavity-type receiver that will be integrated into NREL’s System Advisor Model (SAM) software. Traditional concentrated solar power towers make use of an external cylindrical receiver where all active surfaces are fully exposed to the environment, resulting in significant convective and radiative losses. Cavity-type receivers promise to mitigate these losses by instead accepting solar flux through an aperture. In order to allow detailed resolution of the temperature distribution across the cavity, it is necessary to create refined meshes for different cavity geometries and determine the view factor accurately and quickly between any two elements in the mesh. To accomplish this, an analytical function is written to precisely calculate view factors between arbitrary planar polygons without requiring the use of computationally expensive Monte Carlo ray tracing. These view factors are modified using the F-hat method and used as the basis for a two-band radiation heat transfer model. Heat transfer fluid routing is handled through an elemental connectivity matrix, which specifies the elemental fluid temperature variation from inlet to outlet and allows the cavity mesh to interact with the fluid elements. The model is solved iteratively for panel and then fluid temperatures in order to account simultaneously for all energy transfers (convective, long wavelength, short wavelength, and fluid). This approach offers a computationally efficient but still detailed simulation of cavity receiver configurations making it suitable for use in an annual-hourly time series simulation tool such as SAM.

Relationship between Window and View Factors in the Workplace: A SEM Approach

Office occupants’ have always preferred workplaces that have windows that connects them to the outside. Window access to the outside can influence occupants’ satisfaction with the combination of other workplace features. This study aims to identify the window and view factors relationship in the workplace, to confirm the reliability and validity of the measurement and structural model. Adopting a cross-sectional survey design, primary data from five offices in the Kogi State of Nigeria with 267 respondents were collected by using the convenience sampling method and analysis was performed with the Statistical Package for Social Science version 23 and AMOS 22.0 version as the modelling tool. The study identified eleven vital factors that are interrelated in the relationship between windows and view in the workplace. They are referred to as latent construct namely; Window distance (WDB), Seating arrangement (SAB), Room height (FHB), Office size (OSB), Window position (WPB), Window Sill level (WLC), Window size (SWC), Window type (TWC), View content (CVC), View satisfaction (VSC), and Occupants’ satisfaction (SAT). The result showed a valid model using the Structural Equation Model, and the effect of the current workplace negligence on occupants’. This study improves the existing knowledge on the window and view relationship in the workplace, and provide suggestions for Facility Managers, Architects, and Interior Designers on maintaining a healthy workplace environment

Accuracy of view factor calculations for digital terrain models of comets and asteroids

Context. Detailed shape and topographic models coupled with sophisticated thermal physics are critical elements to proper characterization of surfaces of small bodies in our solar system. Calculations of self-heating effects are especially important in the context of thermal evolution of non-convex surfaces, including craters, cracks, or openings between “rocks”. Aims. Our aim is to provide quantitative comparisons of multiple numerical methods for computing view factors for concave geometries and provide a more rigorous criteria for the validity of their application. Methods. We contrasted five methods of estimating the view factors. First, we studied specific geometries, including shared-edge facets for a reduced two-facet problem. Then, we applied these methods to the shape model of 67P/Churyumov-Gerasimenko. Nevertheless, the presented results are general and could be extended to shape models of other bodies as well. Results. The close loop transformation of the double area integration method for evaluating view factors of nearby or shared-edge facets is the most accurate, although computationally expensive. Two methods of facet subdivision we evaluate in this work provide reasonably accurate results for modest facet subdivision numbers, however, may result in a degraded performance for specific facet geometries. Increasing the number of subdivisions improves their accuracy, but also increases their computational burden. In practical applications, a trade-off between accuracy and computational speed has to be found, therefore, we propose a combined method based on a simple metric that incorporates a conditional application of various methods and an adaptive number of subdivisions. In our study case of a pit on 67P/CG, this method can reach average accuracy of 2–3% while being about an order of magnitude faster than the (most accurate) line integral method.

Thermal Experiments for Validation of 3-AMADEUS Cubesat

There has been an increasing interest in CubeSats missions due to its small size, low cost and flexibility to accommodate different payloads. It enables CubeSats to perform a range of various missions. One of the causes of failure in a satellite in space are the temperature peaks suffered during a full orbital cycle. Therefore, proper thermal control system design and test should be performed to guarantee the reliability of a spacecraft prior to launch.The present work aims to analyze the main heat transfer processes within a satellite to validate the 3-AMADEUS CubeSat and current methodologies used by CEiiA for nano and micro satellites. Hence, with the purpose of developing thermal models with higher reliability, an experiment was devised to be performed in a controlled environment. The experimental test consists in a study of the heat exchange between two aluminum plates through radiation, using infrared lamps as heat source. Three distance configuration and two lamp types are tested. This would emulate the heat transmission between different components within the satellite. The view factors are changed. In parallel, a finite element software (MSC Nastran) is used to carry out a numerical study of the same experiments. The temperature distribution results of both numerical and experimental solutions are then compared, and the results are discussed. Keywords: Radiation, View factors, Experimental