Exergy-based Planning and Thermography-based Monitoring for energy efficient buildings - Progress Report (KIT Scientific Reports ; 7632)

Designing and monitoring energy efficiency of buildings is vital since they account for up to 40% of end-use energy. In this study, exergy analysis is investigated as a life cycle design tool to strike a balance between thermodynamic efficiency of energy conversion and economic and environmental costs of construction. Quantitative geo-referenced thermography is proposed for monitoring and quantitative assessment via continued simulation and parameter estimation during the operating phase

Detailed Modeling of the Flash Hydrolysis of Algae for Biofuel-Production in COMSOL Multiphysics

Algae-derived biofuels are being commercialized as an important renewable energy source. Like any new technology, conversion improvements are desired, including reductions in process complexity and better utilization of the entire microalgae feedstock. The Old Dominion Biomass Laboratory has focused on flash hydrolysis for algae biofuel production. That process involves rapidly heating algae and water mixed as a slurry to a subcritical state. Results from small-scale bench tests are promising, but process scale up is a challenge. Currently there exists a pilot laboratory scale system utilizing induction heating in order to reach controlled reaction temperatures with a reaction duration of 10 seconds or less. However, the influence of the induction heating process on the resulting reactions had not been examined. That is the focus of this thesis. The pilot flash hydrolysis reactor system has been simulated utilizing COMSOL Multiphysics 5.1. The COMSOL model assumed fully developed laminar slurry flow with an electromagnetic field, rate sensitive chemical reactions, and diffusive transport of dilute species. Mesh refinement analysis, mass and energy balances, and experimental verification have been utilized to validate the model. This study has shown that industrial scale up challenges will include sensitivity to feedstock channel size, induction coil pitch, length and excitation frequency, process residence time, and algae concentration. Furthermore, process efficiency improvement may be possible by thermal management of the rapid heating and subsequent quenching process

Evaluation of Radiative Conductivity inside a Porous Media with the Effect of Participating Medium Based on Microscale Imaging

Space vehicles will experience high loads of heat while entering the planetary atmosphere. At such high temperature, radiation becomes the dominant mode of heat transfer. Since the atmospheric entry environment is nearly impossible to duplicate in a laboratory environment, a numerical model to evaluate thermal performance of the thermal protection system was established. The model simulates the radiative heat transfer process in highly porous media, and the process also takes into account the influence of the participating media. An iterative approach and periodic boundary conditions are used to solve The unbalanced heat flux problem. CT scanned microscale Fiberform and artificial fibers were used to study the thermal performance of heat shields. The anisotropic behavior of the material is highlighted through statistical analysis

PALM-USM v1.0: A new urban surface model integrated into the PALM large-eddy simulation model

Urban areas are an important part of the climate system and many aspects of urban climate have direct effects on human health and living conditions. This implies that reliable tools for local urban climate studies supporting sustainable urban planning are needed. However, a realistic implementation of urban canopy processes still poses a serious challenge for weather and climate modelling for the current generation of numerical models. To address this demand, a new urban surface model (USM), describing the surface energy processes for urban environments, was developed and integrated as a module into the PALM large-eddy simulation model. The development of the presented first version of the USM originated from modelling the urban heat island during summer heat wave episodes and thus implements primarily processes important in such conditions. The USM contains a multi-reflection radiation model for shortwave and longwave radiation with an integrated model of absorption of radiation by resolved plant canopy (i.e. trees, shrubs). Furthermore, it consists of an energy balance solver for horizontal and vertical impervious surfaces, and thermal diffusion in ground, wall, and roof materials, and it includes a simple model for the consideration of anthropogenic heat sources. The USM was parallelized using the standard Message Passing Interface and performance testing demonstrates that the computational costs of the USM are reasonable on typical clusters for the tested configurations. The module was fully integrated into PALM and is available via its online repository under the GNU General Public License (GPL). The USM was tested on a summer heat-wave episode for a selected Prague crossroads. The general representation of the urban boundary layer and patterns of surface temperatures of various surface types (walls, pavement) are in good agreement with in situ observations made in Prague. Additional simulations were performed in order to assess the sensitivity of the results to uncertainties in the material parameters, the domain size, and the general effect of the USM itself. The first version of the USM is limited to the processes most relevant to the study of summer heat waves and serves as a basis for ongoing development which will address additional processes of the urban environment and lead to improvements to extend the utilization of the USM to other environments and conditions

A three-dimensional heat and mass transport model for a tree within a forest

A three-dimensional computational tool was developed that simulates the heat and mass transfer interaction in a soil-root-stem system (SRSS) for a tree in a seasonally varying deciduous forest. The development of the SRSS model involved the modification and coupling of existing heat and mass transport tools to reproduce the three-dimensional diurnal internal and external temperatures, internal fluid distribution, and heat flow in the soil, roots, and stems. The model also required the development of a parallel Monte-Carlo algorithm to simulate the solar and environmental radiation regime consisting of sky and forest radiative effects surrounding the tree. The SRSS was tested, component-wise verified, and quantitatively compared with published observations. The SRSS was applied to simulate a tree in a dense temperate hardwood forest that included the calculations of surface heat flux and comparisons between cases with fluid flow transport and periods of zero flow. Results from the winter simulations indicate that the primary influence of temperature in the trunk is solar radiation and radiative energy from the soil and surrounding trees. Results from the summer simulation differed with previous results, indicating that sap flow in the trunk altered the internal temperature change with secondary effects attributed to the radiative energy from the soil and surrounding trees. Summer simulation results also showed that with sap flow, as the soil around the roots become unsaturated, the flow path for the roots will be changed to areas where the soil is still saturated with a corresponding increase in fluid velocity

Image based analysis of visibility in smoke laden environments

This study investigates visibility in a smoke laden environment. For many years, researchers and engineers in fire safety have criticized the inadequacy of existing theory in describing the effects such as colour, viewing angle, environmental lighting etc. on the visibility of an emergency sign. In the current study, the author has raised the fundamental question on the concept of visibility and how it should be measured in fire safety engineering and tried to address the problem by redefining visibility based on the perceived image of a target sign. New algorithms have been created during this study to utilise modern hardware and software technology in the simulation of human perceived image of object in both experiment and computer modelling. Unlike the traditional threshold of visual distance, visibility in the current study has been defined as a continuous function changing from clearly discemable to completely invisible. It allows the comparison of visibility under various conditions, not just limited to the threshold. Current experiment has revealed that different conditions may results in the same visual threshold but follow very different path on the way leading to the threshold. The new definition of visibility has made the quantification of visibility in the pre-threshold conditions possible. Such quantification can help to improve the performance of fire evacuation since most evacuees will experience the pre-threshold condition. With current measurement of visibility, all the influential factors such as colour, viewing angle etc. can be tested in experiment and simulated in numerical model. Based on the newly introduced definition of visibility, a set of experiments have been carried output in a purposed built smoke tunnel. Digital camera images of various illuminated signs were taken under different illumination, colour and smoke conditions. Using an algorithm developed by the author in this study, the digital camera images were converted into simulated human perceived images. The visibility of a target sign is measured against the quality of its image acquired. Conclusions have been drawn by comparing visibility under different conditions. One of them is that signs illuminated with red and green lights have the similar visibility that is far better than that with blue light. It is the first time this seemingly obvious conclusion has been quantified. In the simulation of visibility in participating media, the author has introduced an algorithm that combines irradiance catching in 3D space with Monte Carlo ray tracing. It can calculate the distribution of scattered radiation with good accuracy without the high cost typically related to zonal method and the limitations in discrete ordinate method. The algorithm has been combined with a two pass solution method to produce high resolution images without introducing excessive number of rays from the light source. The convergence of the iterative solution procedure implemented has been theoretically proven. The accuracy of the model is demonstrated by comparing with the analytical solution of a point radiant source in 3D space. Further validation of the simulation model has been carried out by comparing the model prediction with the data from the smoke tunnel experiments. The output of the simulation model has been presented in the form of an innovative floor map of visibility (FMV). It helps the fire safety designer to identify regions of poor visibility in a glance and will prove to be a very useful tool in performance based fire safety design

Image based analysis of visibility in smoke laden environments

This study investigates visibility in a smoke laden environment. For many years, researchers and engineers in fire safety have criticized the inadequacy of existing theory in describing the effects such as colour, viewing angle, environmental lighting etc. on the visibility of an emergency sign. In the current study, the author has raised the fundamental question on the concept of visibility and how it should be measured in fire safety engineering and tried to address the problem by redefining visibility based on the perceived image of a target sign. New algorithms have been created during this study to utilise modern hardware and software technology in the simulation of human perceived image of object in both experiment and computer modelling. Unlike the traditional threshold of visual distance, visibility in the current study has been defined as a continuous function changing from clearly discemable to completely invisible. It allows the comparison of visibility under various conditions, not just limited to the threshold. Current experiment has revealed that different conditions may results in the same visual threshold but follow very different path on the way leading to the threshold. The new definition of visibility has made the quantification of visibility in the pre-threshold conditions possible. Such quantification can help to improve the performance of fire evacuation since most evacuees will experience the pre-threshold condition. With current measurement of visibility, all the influential factors such as colour, viewing angle etc. can be tested in experiment and simulated in numerical model.Based on the newly introduced definition of visibility, a set of experiments have been carried output in a purposed built smoke tunnel. Digital camera images of various illuminated signs were taken under different illumination, colour and smoke conditions. Using an algorithm developed by the author in this study, the digital camera images were converted into simulated human perceived images. The visibility of a target sign is measured against the quality of its image acquired. Conclusions have been drawn by comparing visibility under different conditions. One of them is that signs illuminated with red and green lights have the similar visibility that is far better than that with blue light. It is the first time this seemingly obvious conclusion has been quantified.In the simulation of visibility in participating media, the author has introduced an algorithm that combines irradiance catching in 3D space with Monte Carlo ray tracing. It can calculate the distribution of scattered radiation with good accuracy without the high cost typically related to zonal method and the limitations in discrete ordinate method. The algorithm has been combined with a two pass solution method to produce high resolution images without introducing excessive number of rays from the light source. The convergence of the iterative solution procedure implemented has been theoretically proven. The accuracy of the model is demonstrated by comparing with the analytical solution of a point radiant source in 3D space. Further validation of the simulation model has been carried out by comparing the model prediction with the data from the smoke tunnel experiments.The output of the simulation model has been presented in the form of an innovative floor map of visibility (FMV). It helps the fire safety designer to identify regions of poor visibility in a glance and will prove to be a very useful tool in performance based fire safety design

Transferencia de calor en arquitectura: modelado y simulación por computadora de la temperatura del globo interior en Bogotá, Colombia

ilustraciones, fotografías a colorLa sensación térmica al interior de un edificio es el resultado de la interacción entre el espacio arquitectónico y su entorno a través de la transferencia de calor. En Colombia, aunque habitualmente se realizan simulaciones computacionales de la temperatura interior, sus predicciones raramente se comparan con las mediciones y, por tanto, no siempre se identifican los aspectos relevantes a considerar en las simulaciones. Este trabajo pretende aclarar qué aspectos deben incluirse en la simulación para obtener predicciones confiables de la temperatura interior para edificios en Bogotá, utilizando el software LadyBugTools y modelos numéricos en Python derivados de primeros principios. Los resultados se comparan con las mediciones de temperatura de globo al interior de dos espacios de la Universidad Nacional de Colombia en Bogotá. Nuestro estudio identifica los ingredientes relevantes a considerar en las simulaciones y aclara qué mecanismos de transferencia de calor son los más relevantes. El estudio es una contribución significativa para el uso de herramientas de simulación para evaluar el confort térmico interior en Colombia. (Texto tomado de la fuente)Thermal sensation inside buildings is the result of the interaction between the architectural space and its environment via heat transfer. In Colombia, although computational simulations of indoor temperature are usually performed, their predictions are barely compared with measurements and, therefore, the relevant aspects to take care in the simulations are not always identified. This work aims to clarify which aspects should be included in the simulation to obtain confident predictions of the indoor temperature for buildings in Bogotá using the LadyBugTools software and numerical models in Python derived from first principles. The results are compared with globe temperature measurements for two indoor spaces at the National University in Bogotá, Colombia. Our study identifies the relevant ingredients to be considered in the simulations and clarifies which heat transfer mechanisms are more relevant. The study is a meaningful contribution for the use of simulation tools to evaluate indoor thermal comfort in Colombia.MaestríaMagister en ciencias Físicafísica computaciona

Application of ray tracing in radiation heat transfer

This collection of presentation figures displays the capabilities of ray tracing for radiation propagation calculations as compared to an analytical approach. The goal is to introduce the terminology and solution process used in ray tracing, and provide insight into radiation heat transfer principles and analysis tools. A thermal analysis working environment is introduced that solves demanding radiation heat transfer problems based on ray tracing. This information may serve as a reference for designing and building ones own analysis environment

Lightweight, High-Temperature Radiator for In-Space Nuclear-Electric Power and Propulsion

The desire to explore deep space destinations with high-power and high-speed spacecraft inspired this work. Nuclear Electric Propulsion (NEP), shown to provide orders of magnitude higher specific impulse and propulsion efficiency over traditional chemical rockets, has been identified as an enabling technology for this goal. One of large obstacle to launching an NEP vehicle is total mass. Increasing the specific power (kW/kg) of the heat radiator component is necessary to meet NASA’s mass targets. This work evaluated a novel lightweight, high-temperature carbon fiber radiator designed to meet the mass requirements of future NEP missions. The research is grouped into three major sections: 1) a micro-scale radiation study, 2) bench-scale experimental and analytical investigations, and 3) large-scale radiator system modeling. In the first section, a Monte Carlo ray tracing model built to predict the effective emissivity of a carbon fiber fin by modeling the radiation scattering among fibers showed that the added surface area of the fibers over a flat fin surface increases the effective emissivity of the radiator area by up to 20%. The effective emissivity increases as the fiber volume fraction decreases from 1 to about 0.16 due to increased scattering among the fibers. For fiber volume fractions lower than 0.10, the effective emissivity decreases rapidly as the effect of radiation transmission becomes significant. In the second section, thermal analyses of the carbon fiber radiator fin predicted that these radiators could meet NASA’s performance targets by reducing the areal density to 2.2 kg/m2 or below. These models were validated through experimental tests conducted on sub-scale radiator test articles. This work elevated the technology readiness level (TRL) of the carbon fiber radiator fin from level 2 to 4. In the last section, a radiator system model for an NEP vehicle was built to analyze the dependence of radiator mass on selected system parameters. The model was used to minimize the radiator mass for test cases. The results predicted that carbon fiber fins operated near 600°C reduced the radiator mass by a factor of 7 as compared with traditional radiators operating near 100°C. This significant mass-reduction could enable future NEP systems