| 1. |
- Goos, Elke, et al.
(författare)
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Collisional energy transfer in CH3 radical decomposition—experiment versus theory
- 2002
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084. ; 4, s. 4372-4378
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Tidskriftsartikel (refereegranskat)abstract
- Experimentally determined incubation times in the thermal decomposition of methyl radicals were used to obtain collisional energy transfer probability information by adopting a discrete vibrational energy level masterequation scheme with specific rate constants from the statistical adiabatic channel model. The agreement with information from classical molecular dynamic, MD, simulations of CH3–Ar collisions was shown to be remarkably good. Results from MD simulations also support the assumption of thermally equilibrated rotations used here and in earlier work. The sensitivity of the pressure fall-off behaviour of the decomposition channels to remaining uncertainties in the energy transfer profiles is shown to be significant, in this case, as a consequence of the large number of collisions needed to reach activation. Nevertheless, we find classical molecular dynamics simulation to be useful and a good starting point in obtaining the collisional energy transfer kernel to be used in master-equation calculations treating the most obvious quantum effects through the use of discrete energy levels at low energies.
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| 2. |
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| 3. |
- Joudi, Ali, et al.
(författare)
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Energy Efficient Buildings with Functional Steel Cladding
- 2011
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Ingår i: World Renewable Energy Congress. - Linköping : Linköping University Electronic Press. - 9789173930703 ; , s. 2004-2009
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Konferensbidrag (refereegranskat)abstract
- The aim of the study is to develop a model for the energy balance of buildings that includes the effect from the radiation properties of interior and exterior surfaces of the building envelope. As a first step we have used ice arenas as case study objects to investigate the importance of interior low emissivity surfaces. Measurements have been done in two ice arenas in the north part of Sweden, one with lower and one with higher ceiling emissivity. The results show that the low emissivity ceiling gives a much lower radiation temperature interacting with the ice under similar conditions. The dynamic modelling of the roof in ice arenas shows a similar dependence of the roof-to-ice heat flux and the ceiling emissivity. A second part of the study focus on how to realise paints with very low thermal emissivity to be used on interior building surfaces.
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| 4. |
- Joudi, Ali, et al.
(författare)
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Energy efficient surfaces on building sandwich panels : a dynamic simulation model
- 2011
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Ingår i: Energy and Buildings. - : Elsevier BV. - 0378-7788 .- 1872-6178. ; 43:12, s. 3736-3736
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Tidskriftsartikel (refereegranskat)abstract
- The choice of building envelope is critical for the energy performance of buildings. The major part of the energy used by a building during its lifetime is used for maintaining a suitable interior thermal climate under varying exterior conditions. Although exterior heat radiation properties (i.e. total solar reflectivity and long wave thermal emissivity) have been well accepted to have a large impact on the need for active cooling in warmer climate, the effect of a reduced thermal emissivity on interior surfaces on the building thermal energy flux is rarely studied. This paper addresses the sensitivity of the thermal energy flux through a sandwich panel, by systematically varying the surface thermal emissivity (both interior and exterior) and total solar reflectance of exterior surface, for three geographical locations: southern, middle and northern Europe. A model is introduced for calculating the effect of both interior and exterior optical properties of a horizontal roof panel in terms of net energy flux per unit area. The results indicate potential energy saving by the smart choice of optical properties of interior and exterior surfaces.
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| 5. |
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| 6. |
- Joudi, Ali, et al.
(författare)
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Highly reflective coatings for interior and exterior steel cladding and the energy efficiency of buildings
- 2011
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 88:12, s. 4655-4666
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Tidskriftsartikel (refereegranskat)abstract
- The effect of surface heat-radiation properties of coil-coated steel cladding material on the energy efficiency of buildings in Nordic climate is addressed by parallel temperature and energy usage measurements in a series of test cabins with different exterior solar reflectivity and interior thermal reflectivity. During one year, a number of one- or two-week experiments with air conditioner cooling and electrical floor heating were made while logging air-, radiation- and surface temperatures, energy consumption and weather conditions. Measurements show significant energy savings in the test cabins by the use of high thermal reflectivity interior surfaces both during heating and cooling and a strongly reduced cooling demand by the use of high solar reflectivity exterior surfaces. Results are interpreted within the context of a steady-state energy flux model, to illuminate the importance of surface resistance properties (radiation and convective heat dissipation).
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| 7. |
- Joudi, Ali, et al.
(författare)
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Influence of reflective interior surfaces on indoor thermal environment and energy use using a coupling model for energy simulation and CFD
- 2015
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The importance of reducing the building energy use and maintaining the desired indoor climate has long inspired creative solution such as optimized optical properties for building surfaces. This paper aims to address the influence of interior thermal reflective surfaces on both indoor thermal environments with high spatial resolution and energy use. To do so, this work employs a coupling method using building energy simulation (BES) and computational fluid dynamics (CFD). The results indicate increase in the mean radiation temperature (MRT) and reduction in the floor heating energy use by the use of interior reflective surfaces. The study yields analysis of operative temperatures and interior surface heat fluxes. Overall, the interior reflective surfaces can contribute to improved building thermal performance and energy saving.
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| 8. |
- Joudi, Ali, et al.
(författare)
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Numerical and experimental investigation of the influence of infrared reflective interior surfaces on building temperature distributions
- 2017
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Ingår i: Indoor + Built Environment. - : Sage Publications. - 1420-326X .- 1423-0070. ; 26:3, s. 355-367
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Tidskriftsartikel (refereegranskat)abstract
- Radiative properties of interior surfaces can affect not only the building heat flux but also the indoor environment, the latter of which has not been thoroughly investigated. The aim of this study is to analyse the effect of surface emissivity on indoor air and surface temperature distributions in a test cabin with reflective interior surfaces. This was done by comparing experimental and simulation data of the test cabin with that of a normal cabin. This study employs transient computational fluid dynamics (CFD) using re-normalisation group (RNG) k-epsilon model, surface-to-surface radiation model and an enhanced wall function. Boundary conditions were assigned to exterior surfaces under variable outdoor conditions. The numerical and the measurement results indicate that using interior reflective surfaces will affect the indoor air temperature distribution by increasing the vertical temperature gradient depending on the time of the day. CFD simulations with high spatial resolution results show increased interior surface temperature gradients consistent with the increased vertical air temperature gradient. The influence of reflective surfaces is potentially greater with higher indoor surface temperature asymmetry. The vertical indoor air temperature gradient and surface temperatures are important parameters for indoor thermal comfort.
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| 9. |
- Joudi, Ali, 1980-
(författare)
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Radiation properties of coil-coated steel in building envelope surfaces and the influence on building thermal performance
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recent studies have shown that the optical properties of building exterior surfaces are important in terms of energy use and thermal comfort. While the majority of the studies are related to exterior surfaces, the radiation properties of interior surfaces are less thoroughly investigated. Development in the coil-coating industries has now made it possible to allocate different optical properties for both exterior and interior surfaces of steel-clad buildings. The aim of this thesis is to investigate the influence of surface radiation properties with the focus on the thermal emittance of the interior surfaces, the modeling approaches and their consequences in the context of the building energy performance and indoor thermal environment.The study consists of both numerical and experimental investigations. The experimental investigations include parallel field measurements on three similar test cabins with different interior and exterior surface radiation properties in Borlänge, Sweden, and two ice rink arenas with normal and low emissive ceiling in Luleå, Sweden. The numerical methods include comparative simulations by the use of dynamic heat flux models, Building Energy Simulation (BES), Computational Fluid Dynamics (CFD) and a coupled model for BES and CFD. Several parametric studies and thermal performance analyses were carried out in combination with the different numerical methods.The parallel field measurements on the test cabins include the air, surface and radiation temperatures and energy use during passive and active (heating and cooling) measurements. Both measurement and comparative simulation results indicate an improvement in the indoor thermal environment when the interior surfaces have low emittance. In the ice rink arenas, surface and radiation temperature measurements indicate a considerable reduction in the ceiling-to-ice radiation by the use of low emittance surfaces, in agreement with a ceiling-toice radiation model using schematic dynamic heat flux calculations.The measurements in the test cabins indicate that the use of low emittance surfaces can increase the vertical indoor air temperature gradients depending on the time of day and outdoor conditions. This is in agreement with the transient CFD simulations having the boundary condition assigned on the exterior surfaces. The sensitivity analyses have been performed under different outdoor conditions and surface thermal radiation properties. The spatially resolved simulations indicate an increase in the air and surface temperature gradients by the use of low emittance coatings. This can allow for lower air temperature at the occupied zone during the summer.The combined effect of interior and exterior reflective coatings in terms of energy use has been investigated by the use of building energy simulation for different climates and internal heat loads. The results indicate possible energy savings by the smart choice of optical properties on interior and exterior surfaces of the building.Overall, it is concluded that the interior reflective coatings can contribute to building energy savings and improvement of the indoor thermal environment. This can be numerically investigated by the choice of appropriate models with respect to the level of detail and computational load. This thesis includes comparative simulations at different levels of detail.
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| 10. |
- Joudi, Ali, et al.
(författare)
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Reflective coatings for interior and exterior of buildings and improving thermal performance
- 2013
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Ingår i: Applied Energy. - Oxford : Elsevier. - 0306-2619 .- 1872-9118. ; 103, s. 562-570
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Tidskriftsartikel (refereegranskat)abstract
- The importance of reducing building energy usage and thriving for more energy efficient architectures, has nurtured creative solutions and smart choices of materials in the last few decades. Among those are optimizing surface optical properties for both interior and exterior claddings of the building. Development in the coil-coating steel industries has now made it possible to allocate correct optical properties for steel clad buildings with improved thermal performance. Although the importance of the exterior coating and solar gain are thoroughly studied in many literatures, the effect of interior cladding are less tackled, especially when considering a combination of both interior and exterior reflective coatings. This paper contemplates the thermal behavior of small cabins with reflective coatings on both interior and exterior cladding, under different conditions and climates with the aim to clarify and point out to the potential energy saving by smart choices of clad coatings.
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| 11. |
- Nordholm, Strure, et al.
(författare)
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Progress on the modeling of the collisional energy transfer mechanism in unimolecular reactions
- 1997
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Ingår i: Berichte Der Bunsen-Gesellschaft. - 0005-9021. ; 101, s. 574-580
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Tidskriftsartikel (refereegranskat)abstract
- The RRKM theory of unimolecular reaction rates is a statistical mechanical theory based on an assumption of microcanonical equilibrium in the reactant phase space. The energy transfer in reactant medium collisions was originally described by a canonical strong collision assumption, i.e., an assumption of full thermal equilibration in each collision. In our work we first introduce a microcanonical strong collision assumption which gives the RRKM theory a consistent form. We then introduce parametrizations of the degree of weakness (nonergodicity) of the collisions. A concept of collision efficiency is defined. The weakness of the collision is expressed in terms of reduced subsets of active reactant and medium degrees of freedom. The corresponding partially ergodic collision theory (PECT) yields physical functional forms of the collisional energy transfer kernel P(E,E). In order to resolve the energy and temperature dependence and the dependence on interaction strength a multiple encounter theory is introduced (PEMET). Initially each encounter may be described by a semiempirical PECT model. Eventually the encounters may be resolved by quantum dynamical calculations of the semiclassical or CAQE (classical approach quantum encounter) type. Simple statistical collision models only distinguish between hits and misses . In reality the energy transfer efficiency exhibits characteristic fall off with increasing impact parameter b. This b-dependence can be explicitly accounted for in the master equation for the reaction rate coefficient.
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| 12. |
- Nordholm, Sture, et al.
(författare)
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Simple analysis of intermolecular potentials : The mBq pair potential for collisions and energy transfer
- 2001
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084. ; 3:12, s. 2209-2215
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated and compared four different theoretical and empirical procedures for the generation of simple but reliable pairwise atomÈatom potentials to be used as components in the construction of intermolecular potentials. A method is proposed wherein the parameters of a modified Buckingham potential with atomic monopoles (mBq potential) is obtained by Ðtting to MP2 energies for interacting molecules confined to approach in selected symmetry directions. The results for 31 atomic pairs are compared with earlier results obtained by electron gas density functional theory, best available quantum chemical calculation or spectroscopic Ðt. The evidence is that the mBq potentials can be of signiÐcant practical value in a wide range of applications.
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| 13. |
- Svedung, Harald, 1970-, et al.
(författare)
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Collisional deactivation of CF3I - a molecular dynamics simulation
- 1999
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Ingår i: Chemical Physics. - 0301-0104 .- 1873-4421. ; 248:2-3, s. 195-211
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Tidskriftsartikel (refereegranskat)abstract
- The detailed mechanisms of ro-vibrational energy transfer in collisions between CF3I and argon or propane are investigated. Molecular dynamics simulations of collisions between a reactant CF3I molecule at energies from 50 to 200 kJrmol with medium argon or propane at selected initial temperatures are interpreted in terms of ergodic collision limits. The intramolecular potential used for CF3I is a Morse-stretchrharmonic-bend type function with parameters fitted to equilibrium structure, normal mode frequencies and dissociation energies. Simple generic Buckingham type pair-potentials are used for intermolecular atom–atom interactions. Energy transfer is related to i. geometry of collision, ii. impact parameter, iii. number of atom–atom encounters, iv. average dynamical hardness of interaction at atom–atom collisions, v. number of minima in the center of mass separation and vi. lifetime of the collisional complex. The energy transfer in our molecular dynamics calculations is compared with experimental results for the same colliders. The observed trends are interpreted in terms of detailed collisional mechanisms. Our results highlight the importance of rotational excitation and the repulsive part of the intermolecular potential.
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| 14. |
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| 15. |
- Svedung, Harald, 1970-, et al.
(författare)
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Pair-potential model for simulation of collisional energy transfer : quantum effects and hardness dependence
- 2001
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084. ; 3:12, s. 2216-2222
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Tidskriftsartikel (refereegranskat)abstract
- A study of the sensitivity of energy transfer efficiency in molecular collisions is reported with special focus on the hardness of repulsion in atomÈatom contact. An improved pair potential is proposed with independent parameters for atomic size, attraction and hardness determined speciÐcally for a chosen atom pair by supermolecular quantum chemistry or equivalent experimental interaction data. Colinear and full 3D collisions of atomÈdiatomic molecule collisions are simulated using classical or quantum (in the colinear case) mechanics to illustrate : (i) remarkable agreement between classical and quantum dynamics for VÈT energy transfer ; (ii) greater sensitivity to hardness than to attraction and (iii) suitability of MP2 energies in symmetry constrained axial directions as a data set for the determination of pair-potential parameters.
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| 16. |
- Svedung, Harald, 1970-, et al.
(författare)
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The mechanism of energy transfer in H2O-H2O collisions - a molecular dynamics simulation
- 1998
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Ingår i: Chemical Physics. - 0301-0104 .- 1873-4421. ; 236:1-3, s. 189-205
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Tidskriftsartikel (refereegranskat)abstract
- Earlier work on the activation-deactivation mechanism of gas phase unimolecular reactions is extended to the study of the detailed energy transfer mechanism in collisions of water molecules. Molecular dynamics simulations of binary collisions between a reactant water molecule at high internal energy with medium molecules at various selected initial temperatures are compared with results from approximate statistical theory. Energy transfer is related to i. interaction strength, ii. hard atom–atom encounters, iii. multiple minima in the center of mass separation, iv. collision lifetime and v. anharmonicity of the intramolecular potential function. The observed trends are interpreted within the framework of the partially ergodic multiple encounter theory PEMET. of collisional energy transfer. By comparison with typical stable molecule collisions the water–water collisions are more efficient as a reflection of the strong hydrogen bonding interactions. A good agreement between PEMET and molecular dynamics simulations over a wide range of interaction strengths and initial reactant energies is shown, indicating the possibility of a priori use of the PEMET model.
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| 17. |
- Wäckelgård, Ewa, 1957-, et al.
(författare)
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Optical characterization and modelling of paint top-coatings for low-emittance applications
- 2016
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Ingår i: Infrared physics & technology. - : Elsevier BV. - 1350-4495 .- 1879-0275. ; 78, s. 275-281
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Tidskriftsartikel (refereegranskat)abstract
- The study reports on characterization of low-infrared-emittance paint top-coatings for interior building applications in which the thermal radiation becomes important in comparison with thermal conductance. The top-coating that consist of a binder with aluminium flakes has been optically characterized in the infrared wavelength range in order to determine single flake and binder emittance from reflectance measurements. The single flake emittance was found to be 0.12 for non-leafing cornflake. The absorption coefficient that determines the binder emittance as a function of binder thickness was 0.060 [μm]−2 and 0.085 [μm]−2 for Lumiflon and polyester respectively. These results were used as parameters in a simple model of the flake-binder top-coating to investigate how the emittance of the top-coating was influence by the two components and compared with a state-of-art low-emittance commercial paint. It was found from the modelling that replacing the polyester binder with Lumiflon reduces the infrared emittance (at room temperature) from 0.36 to 0.30. Increasing flake reflectance from 0.88 to 0.96 and at the same time reduce flake thickness from 2 to 1 μm gives an emittance of 0.20. However, the real samples prepared with Lumiflon showed a severe degradation caused by the flakes floating up closer to the surface which indicates a viscosity problem that needs to be solved for practical use. Thinner flakes with higher reflectance can be found if vacuum metallised pigments are used instead of ball-milled.
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