A Numerical Approach for the Evaluation of the Energy Efficiency in Ventilated Façade

2018 ◽  
Author(s):  
Massimo Milani ◽  
Luca Montorsi ◽  
Matteo Venturelli
Keyword(s):  
Heat Transfer ◽  
Energy Efficiency ◽  
Thermal Insulation ◽  
Radiative Heat ◽  
Fluid Dynamic ◽  
Electric Energy ◽  
Numerical Approach ◽  
Air Gap ◽  
Radiative Heat Exchange ◽  
Ventilated Facade

The paper studies the ventilated façade as a potential alternative to conventional coating technologies for the thermal insulation of building’s external walls. The ventilated façade is modeled by means of a CFD approach that accounts for the full 3D-geometry of the building, the walls thickness and materials’ thermal properties. The effects of the windows on the heat losses and in the performance of the ventilated façade are modeled in order to accurately characterize the thermal behavior of the system. The solar radiative heat transfer during two representative days of the year is considered in the analysis and a multiband thermal radiation is adopted to capture the different nature of radiative heat exchange according to the light wavelengths. The numerical approach enables to estimate the thermo-fluid dynamic behavior of the system and the temperature distribution and the velocity flow field within the air gap between the walls are addressed and their influence on the heat transfer through the building’s external walls is determined. The CFD analysis is employed to compare different configurations of the ventilated façade for improving the thermal insulation of the building; the performance of each scenario is determined in terms of electric energy and fuel consumption for the air conditioning and the heating system. Thus, the potential saving of the energy cost for ambient thermal conditioning is evaluated. The analysis investigates the effects on the energy efficiency of different geometrical features of the system such as the height of the building and the air gap thickness and theoretical correlations are derived in order to estimate the best tradeoff between the energy efficiency of the building and the investment of the ventilated façade configuration.

scholarly journals Change in Conductive–Radiative Heat Transfer Mechanism Forced by Graphite Microfiller in Expanded Polystyrene Thermal Insulation—Experimental and Simulated Investigations

Materials ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2626
Author(s):  
Aurelia Blazejczyk ◽  
Cezariusz Jastrzebski ◽  
Michał Wierzbicki
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Thermal Insulation ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Expanded Polystyrene ◽  
Transfer Mechanism ◽  
Total Thermal Conductivity ◽  
Heat Transfer Mechanism

This article introduces an innovative approach to the investigation of the conductive–radiative heat transfer mechanism in expanded polystyrene (EPS) thermal insulation at negligible convection. Closed-cell EPS foam (bulk density 14–17 kg·m−3) in the form of panels (of thickness 0.02–0.18 m) was tested with 1–15 µm graphite microparticles (GMP) at two different industrial concentrations (up to 4.3% of the EPS mass). A heat flow meter (HFM) was found to be precise enough to observe all thermal effects under study: the dependence of the total thermal conductivity on thickness, density, and GMP content, as well as the thermal resistance relative gain. An alternative explanation of the total thermal conductivity “thickness effect” is proposed. The conductive–radiative components of the total thermal conductivity were separated, by comparing measured (with and without Al-foil) and simulated (i.e., calculated based on data reported in the literature) results. This helps to elucidate why a small addition of GMP (below 4.3%) forces such an evident drop in total thermal conductivity, down to 0.03 W·m−1·K−1. As proposed, a physical cause is related to the change in mechanism of the heat transfer by conduction and radiation. The main accomplishment is discovering that the change forced by GMP in the polymer matrix thermal conduction may dominate the radiation change. Hence, the matrix conduction component change is considered to be the major cause of the observed drop in total thermal conductivity of EPS insulation. At the microscopic level of the molecules or chains (e.g., in polymers), significant differences observed in the intensity of Raman spectra and in the glass transition temperature increase on differential scanning calorimetry(DSC) thermograms, when comparing EPS foam with and without GMP, complementarily support the above statement. An additional practical achievement is finding the maximum thickness at which one may reduce the “grey” EPS insulating layer, with respect to “dotted” EPS at a required level of thermal resistance. In the case of the thickest (0.30 m) panels for a passive building, above 18% of thickness reduction is found to be possible.

Geometrical Evaluation of a Pair of Elliptical Tubes Subjected to a Flow with Forced Convection Heat Transfer

2019 ◽  
Vol 396 ◽  
pp. 155-163
Author(s):  
Ana Paula Del Aghenese ◽  
Eliander Manke Heinemann ◽  
Gabriel de Avila Barreto ◽  
Filipe Branco Teixeira ◽  
Liércio André Isoldi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Degrees Of Freedom ◽  
Fluid Dynamic ◽  
Convection Heat Transfer ◽  
Numerical Approach ◽  
Angle Of Incidence ◽  
Prandtl Numbers ◽  
Forced Convective Flow ◽  
Volume Method

In the present work it is performed a study on the geometric evaluation of a pair of elliptical tubes subjected to external flow with forced convection by means of numerical approach. The objectives are the maximization of Nusselt number (NuD) and the minimization of drag coefficient (CD). The degrees of freedom for the pair of tubes arrangement are: the ratio between the transverse pitch and characteristic length of tubes (ST/D), where D = (A)1/2, the ratio of the main and secondary axes of the elliptical tube (a/b) and the angle of incidence of the flow on the pair of tubes (α). The simulations were carried out considering two-dimensional forced convective flows, in the laminar regime and incompressible conditions. For all configurations, Reynolds and Prandtl numbers are constant, ReD = 100 and Pr = 0.71. The Finite Volume Method (FVM) is used to solve conservation equations of mass, momentum and energy. The software Gmsh is used for creation of the geometries and generation of the meshes. Results showed that the degrees of freedom affected the fluid dynamic and thermal performance of the forced convective flow. According to the objectives outlined in this study, the best performance for the maximization of heat transfer was obtained when α = 0o, a/b = 1⁄2 and ST/D = 3.5. In the case of the fluid dynamics study, the optimal result for CD minimization occurred when α = 0o, a/b = 2.0 and ST/D = 4.0. Thus, the optimal geometry will depend on the indicator performance where the problem is evaluated.

Numerical Investigation on the Heat Transfer Enhancement due to Coolant Extraction on the Cold Side of Film Cooling Holes

2014 ◽  
Author(s):  
A. Andreini ◽  
G. Caciolli ◽  
R. Da Soghe ◽  
B. Facchini ◽  
L. Mazzei
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Fluid Dynamic ◽  
Numerical Approach ◽  
Test Case ◽  
Cold Side ◽  
Engine Design ◽  
Starting Point ◽  
Sst Model ◽  
Film Cooling Holes

Film cooling represents one the most widely-used cooling techniques for hot gas path components. In particular, effusion cooling has recently become an important focus of attention in the context of aero-engine design due to its high cooling performance. Notwithstanding the huge amount of work dedicated to the heat transfer on the hot side of effusion cooling plates, it has been demonstrated that up to 30 % of the total cooling effectiveness of a typical effusion cooling configuration can be ascribed to cold side convective cooling. Nevertheless, in open literature it is possible to notice a lack of knowledge as far as this topic is concerned. This paper describes a numerical activity aimed at investigating the phenomenology of the heat transfer at the entrance of film cooling holes. First of all the accuracy of the numerical approach has been validated through a comparison of enhancement factor measurements on a test case available in literature. Steady state RANS simulations have been performed, modeling turbulence by means of the k–ω SST model. The use of a transition model has been taken into account, since in these configurations the transitional behavior of the boundary layer has been highlighted in literature. Subsequently, the attention has been turned to the comprehension of the phenomena involved in the heat transfer augmentation, focusing the attention to the influence of fluid dynamic parameters such as suction ratio and Reynolds number. A good agreement has been highlighted with experimental data, therefore this work provides a starting point for future investigations on more representative configurations.

Optimization of a Small Size CHP System by Means of a Fully Transient Numerical Approach

2017 ◽  
Author(s):  
Luigi Chiantera ◽  
Massimo Milani ◽  
Luca Montorsi ◽  
Matteo Stefani
Keyword(s):  
Energy Efficiency ◽  
Ad Hoc ◽  
Electric Energy ◽  
Numerical Approach ◽  
Combined Heat And Power ◽  
Battery Capacity ◽  
Energy Conversion Systems ◽  
One Year ◽  
Chp System

The paper investigates the performance of a combined heat and power system by means of a fully dynamic numerical approach. An ad-hoc library for the simulation of energy conversion systems is developed under the OpenModelica open source platform; the library includes the main components that usually equip a Combined Heat and Power (CHP) system and they can be connected as they are logically connected in the real plant. Each component is modelled by means of equations and correlations that calculate their performance on a time dependent basis. Therefore, many configurations can be evaluated not only in terms of cumulative annual results or average performance, but the instantaneous behavior can be investigated. The numerical library is constructed using the lumped and distributed parameter approach and it is validated by comparing the numerical results with the measured values over a one-year time period. The prediction capabilities of the proposed numerical approach are evaluated by simulating a case study of a health spa. This case study is selected since it is characterized by significant requirements of both thermal and electric energy. The comparison demonstrated that the calculated results are in good agreement with the measurements in terms of both annual values and distribution over the reference period. Furthermore, an optimization algorithm is adopted and linked to the developed library in order to estimate the best size of different components of the CHP system according to a number of constraints. This feature is particularly important when addressing the energy efficiency of a complete system that is depending on a number of interdependent variables. Therefore, the case study is investigated by accounting also for additional technologies that can be further enhance the performance of the system both in terms of energy consumption and economic investment. In particular, the numerical model is used to optimized the CHP energy efficiency by estimating the best trade-off between the reduction of the energy purchased and the overall cost of the system. The application of PV panels and electric energy accumulators is also investigated and the simulation demonstrates that the size of the cogeneration unit equal to 48 kW, the number of PV panels of 299 and the battery capacity of 45 kWh provide the lowest amount of energy purchased, while the best return of investment is obtained by the CHP unit of 40 kW along with 109 PV panels and a battery of 40 kWh.

Experimental Investigation of Thermoelectric Power Generation Using Radiative Heat Exchange

2014 ◽  
Vol 1025-1026 ◽  
pp. 1125-1133
Author(s):  
Niran Watcharodom ◽  
Withaya Puangsombut ◽  
Joseph Khedari ◽  
Narong Vatcharasatien ◽  
Jongjit Hirunlabh
Keyword(s):  
Power Generation ◽  
Experimental Investigation ◽  
Heat Exchange ◽  
Waste Heat Recovery ◽  
Radiative Heat ◽  
Waste Heat ◽  
Electrical Power ◽  
Air Gap ◽  
Radiative Heat Exchange ◽  
Thermoelectric Modules

This paper reports experimental investigation of a new concept of waste heat recovery for Thermoelectric Power Generation using Radiative heat exchange principle (TERX). To this end a small scale experimental setup was considered; it was composed of a heated plate, an absorber plate, thermoelectric modules and water cooled heat sink. The dimensions of absorber and heated plates were 0.2 m width and 0.3 m length. The air gap space between the two plates could be adjusted. Ten thermoelectric modules were connected in series parallel (5x2). Tests were made for different air gap spaces and fixed water flow rate (2L/min). A constant electric current (200W) was supplied to the heater of hot plate. Data collected included temperature at various positions and the electrical power generated. Experimental investigation confirmed that using radiative heat exchange principle could be considered for TE waste heat power generation. Increasing air gap decreased the electrical power generated as less radiative heat is absorbed by the thermoelectric modules. Under test conditions, the maximum measured electrical power is 0.3132 W at 0.5 cm of air gap, the corresponding temperature difference between the hot and cool sides of thermoelectric modules was about 35oC. Due to its simplicity of installation as no there is no need for direct contact between the thermoelectric generation set and the source of heat, the proposed concept offers a new alternative for waste heat recovery.

scholarly journals A simplified model of the thermal interaction of a Venetian blind located on the indoor glazing surface of a window

2021 ◽  
Author(s):  
Derek Roeleveld
Keyword(s):  
Heat Transfer ◽  
Radiative Heat ◽  
Numerical Data ◽  
Simplified Model ◽  
Radiative Heat Exchange ◽  
Empirical Correlations ◽  
Venetian Blinds ◽  
Model Sample ◽  
Heated Channel ◽  
Cold Walls

A simplified model was developed to predict the radiative and convective heat transfer in complex fenestration systems, including the effect of solar radiation. The focus of the current work was on Venetian blinds mounted adjacent to the indoor window surface. From the perspective of convection, the model used a convective flat plate flow between the blind and ambient surroundings and a convective channel flow between the window and blinds. It was necessary to develop new empirical correlations to predict the average channel Nusslet numbers of the hot and cold walls separately. Therefore, a CFG study of free convection in an asymmetrically heated channel was performed. Then, the new empirical correlations were used to develop a simplified one-dimensional model of the heat transfer in the system. The radiative heat exchange between the blind, window and room was calculated using a four surface grey-diffuse model. Sample predicted results were compared with existing experimental and numerical data from the literature.

Identification of radiative heat transfer parameters in multilayer thermal insulation of spacecraft

2017 ◽  
Vol 27 (3) ◽  
pp. 598-614 ◽  
Author(s):  
Aleksey V. Nenarokomov ◽  
Leonid A. Dombrovsky ◽  
Irina V. Krainova ◽  
Oleg M. Alifanov ◽  
Sergey A. Budnik
Keyword(s):  
Heat Transfer ◽  
Theoretical Model ◽  
Thermal Insulation ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Near Field ◽  
Radiative Properties ◽  
Problem Solution ◽  
Content Type ◽  
Field Effects

Purpose The purpose of this study is to optimize multilayer vacuum thermal insulation (MLI) of modern high-weight spacecrafts. An adequate mathematical simulation of heat transfer in the MLI is impossible if there is no available information on the main insulation properties. Design/methodology/approach The results of experiments in thermo-vacuum facilities are used to re-estimate some radiative properties of metallic foil/metalized polymer foil and spacer on the basis of the inverse problem solution. The experiments were carried out for the sample of real MLI used for the BP-Colombo satellite (ESA). The recently developed theoretical model based on neglecting possible near-field effects in radiative heat transfer between closely spaced aluminum foils was used in theoretical predictions of heat transfer through the MLI. Findings A comparison of the computational results and the experimental data confirms that there are no significant near-field effects between the neighboring MLI layers. It means that there is no considerable contradiction between the far-field model of radiative transfer in MLI and the experimental estimates. Originality/value An identification procedure for mathematical model of the multilayer thermal insulation showed that a modified theoretical model developed recently can be used to estimate thermal properties of the insulation at conditions of space vacuum.

scholarly journals Dependencies of heat transmittance through the ventilated wall system on thermal conductivity of connectors crossing thermal insulation layer

2019 ◽  
Vol 282 ◽  
pp. 02089 ◽  
Author(s):  
Aurelija Levinskytė ◽  
Raimondas Bliūdžius ◽  
Arūnas Burlingis ◽  
Tomas Makaveckas
Keyword(s):  
Heat Transfer ◽  
Stainless Steel ◽  
Thermal Insulation ◽  
Experimental Research ◽  
Experimental Studies ◽  
Insulation Material ◽  
Expanded Polystyrene Foam ◽  
Reinforced Plastic ◽  
Ventilated Facade ◽  
Wall System

The ventilated facade systems are widely used for improvement of energy efficiency and reducing of heat losses of newly built buildings and for existing buildings. To reduce the influence of point thermal bridges on heat transfer through the ventilated facades, previous often used aluminium alloy connectors as a change to stainless steel and reinforced plastic connectors. Different thermal characteristics of connectors using in ventilated facade systems, significantly influence the heat transfer coefficient of building’s walls. Previous empirical calculations of the heat transfer through ventilated facade walls with different connectors according to standard methodology and numerical modelling showed significant differences in results, therefore experimental research with the fragments of the ventilated facade systems were carried out using a guarded hotbox method. The aim of this experimental research was to analyse the heat flows through the ventilated wall system with different kind of heat-conductive connectors. Expanded polystyrene foam (λ – 0,031 W/(m∙K)) was used as thermal insulation material, thickness 300 mm, and three types of heat-conductive connections were installed: aluminum alloy (λ - 160 W/(m∙K)), stainless steel (λ - 17 W/(m∙K)) and glass fiber reinforced plastic (λ – 0,23 W/(m∙K)). The measurements in the guarded hotbox were useful for analysis of differences in results according to the standard and numerical calculations methods. The experimental studies showed that the results are very close to the numerical simulation results. The empirical calculation method gave similar results to the other two methods, except in the case of highly heat-conductive connectors.

scholarly journals Application of Nanofiber Technology to Nonwoven Thermal Insulation

2007 ◽  
Vol 2 (2) ◽  
pp. 155892500700200 ◽  
Author(s):  
Phillip W. Gibson ◽  
Calvin Lee ◽  
Frank Ko ◽  
Darrell Reneker
Keyword(s):  
Heat Transfer ◽  
Thermal Insulation ◽  
Radiative Heat Transfer ◽  
Protective Clothing ◽  
Radiative Heat ◽  
Glass Fibers ◽  
Small Diameter ◽  
Cold Environments ◽  
Thermal Protective Clothing ◽  
Biological Protection

Nanofiber technology (fiber diameter less than 1 micrometer) is under development for future Army lightweight protective clothing systems. Nanofiber applications for ballistic and chemical/biological protection are being actively investigated, but the thermal properties of nanofibers and their potential protection against cold environments are relatively unknown. Previous studies have shown that radiative heat transfer in fibrous battings is minimized at fiber diameters between 5 and 10 micrometers. However, the radiative heat transfer mechanism of extremely small diameter fibers of less than 1 micrometer diameter is not well known. Previous studies were limited to glass fibers, which have a unique set of thermal radiation properties governed by the thermal emissivity properties of glass. We are investigating the thermal transfer properties of high loft nanofiber battings composed of carbon fiber and various polymeric fibers such as polyacrylonitrile, nylon, and polyurethane. Thermal insulation battings incorporating nanofibers could decrease the weight and bulk of current thermal protective clothing, and increase mobility for soldiers in the battlefield.

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