Correlation of pore size distribution with thermal conductivity of precipitated silica and experimental determination of the coupling effect

Sonnick, Sebastian; Meier, Manuel; Ross-Jones, Jesse; Erlbeck, L.; Medina, Isabel Batista; Nirschl, Hermann; Rädle, Matthias

doi:10.1016/j.applthermaleng.2019.01.074

Cited by 28 publications

(14 citation statements)

References 25 publications

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“…• In comparison to literature only those results of Schäfer [60] agree with MD and the present experimental results. The data reported by McFall [5] and Sonnick [59] appear to be significantly lower for…”

Section: Resultsmentioning

confidence: 81%

Determination of Thermal Accommodation Coefficients on CaSiO3 and SiO2 using Molecular Dynamics and Experiments

Bayer-Buhr,

Vimal,

Prakash

et al. 2021

Preprint

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The thermal accommodation coefficient α has been assumed, although lacking any experimental proof, to be near unity for most gases so far, which denotes no influence. However, it plays a contributing role in the field of the effective thermal conductivity of highly porous insulation materials based on SiO 2 or CaSiO 3 as it is shown in this work. Besides, this work investigates a possible influence on α for Ar, N 2 , He within parameters like temperature, roughness and contamination as this has not been examined on such materials so far. More importantly, it answers the question whether the assumption of α = 1 is valid.By using a parallel plates device, very similar to the guarded-hot-plate, following EN 12667 it was possible to determine α on a dense CaSiO 3 . It occured that the assumptions α = 1 (for Ar, N 2 ) and α = 0.3 (for He) are valid for measurements near room temperature. Further, physical adsorption was found to increase α. The determination of the influence of roughness has been started showing an interesting effect, but it still remains an open topic.In a collaborative study molecular dynamics (MD) simulations were performed showing a strong equivalence of α between SiO 2 and CaSiO 3 . These results can be considered a lower limit of α as neither roughness nor adsorption processes have been included in the simulation. Therefore, any deviations between experiments and MD could be considered as an apperance of physical adsorption.

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Section: Resultsmentioning

confidence: 81%

Determination of Thermal Accommodation Coefficients on CaSiO3 and SiO2 using Molecular Dynamics and Experiments

Bayer-Buhr,

Vimal,

Prakash

et al. 2021

Preprint

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show abstract

“…It is calculated using the Gaussian error propagation law. Uncertainty analysis and error discussion of the used guarded hot plate apparatus can be looked up in the paper published by Sonnick et al [13] and is ≤ 2.07% of the measured value. For the pressure sensor, the number is ≤ 0.25% of the measured value.…”

Section: Sample Analysismentioning

confidence: 98%

“…For all tests performed with precipitated silica, the PERKASIL® GT 3000 GRAN obtained from W. R. Grace & Co. was used as basic material. Thereby, it has a maximum pore size distribution at a pore size of about 10 nm [13,14]. Furthermore, the silica gel Syloid® AL-1 was purchased from W. R. Grace & Co, whose pore size distribution is maximum at a pore size of 3.2 nm [15].…”

Section: Reagentsmentioning

confidence: 99%

“…pressure sensor. The measurement of the heat conductivity was carried out using a self-made guarded hot plate apparatus as mentioned by Sonnick et al [13], whereas the same test parameters were used. For this measurement, two separate samples were prepared as a plate or cuboid bulk with dimensions of around 160 × 160 × 20 mm and tested simultaneously.…”

Section: Sample Analysismentioning

confidence: 99%

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Impact of aeration and deaeration of switchable vacuum insulations on the overall heat conductivity using different core materials and filling gases

Erlbeck

Sonnick

Wössner

et al. 2020

Int J Energy Environ Eng

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Investigating switchable vacuum insulation panels might lead to a new type of insulation, which can be switched on to enable a low heat flow when a good insulation effect is desired and switched off when exchange with the environment is requested, during a cold summer night, for example. For this reason, different core materials for vacuum insulations as typical silica powder were investigated as well as silica agglomerates and silica gel. These materials were checked for the necessary time of aeration and evacuation and the corresponding change of heat conductivity along with the change of gas-pressure. Silica gel in combination with helium as filling gas showed best results corresponding to a high difference of the heat conductivities evacuated and aerated. Beside the solid backbone structure of the silica gel, this is caused by the high heat conductivity and small kinetic atomic diameter of the helium gas. Silica agglomerates decreased the aeration time as well as the deaeration time, but the improvement was neglected because of a lower change of heat conductivity during pressure drop or rise. Nevertheless, a good switchable vacuum insulation can be produced using silica gel and helium, for example.

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“…Through the porous grid, heat transfer through the panel can be reduced to values as low as the heat conduction of the branched structure plus radiation [27]. Thus, thermal conductivities five to ten times lower than for traditional insulation are achieved [34].…”

Section: Introductionmentioning

confidence: 99%

Numerical study on the application of vacuum insulation panels and a latent heat storage for refrigerated vehicles with a large Eddy lattice Boltzmann method

et al. 2019

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The development of sustainable trucks has drawn a lot of attention lately. However, the reduction of fuel consumption and emissions related to deep frozen food transports has not yet been satisfactorily considered. In this paper, a thermal Large Eddy Lattice Boltzmann Method (LES-LBM) is applied to investigate two concepts for optimized refrigerated vehicles: (a) the inclusion of vacuum insulation panels (VIP) in the refrigerated body's walls and (b) the introduction of a latent heat storage (LHS) to exchange fuel-driven air conditioning (AC), both with conveniently worth while potential to decrease fuel consumption and related emissions. The present numerical method allows for an accurate and efficient transient conjugate heat transfer simulation including the spatial and temporal resolution of the temperature distribution inside the insulation walls and the cargo in addition to the turbulent surrounding air flow induced by the AC. The present concept of VIP inclusion is found capable of halving the required cooling energy. In addition, it effectively reduces the variations in the temperature of the chilled goods during cooling operation, which is an important measure of the quality of the refrigerated body. The reduced required cooling energy is further found to enable the AC system to be replaced by a LHS mounted near the top of the refrigerator body and an additional ventilation system of lower total capacity. A comparison between simulations with conventional AC and LHS is conducted concerning the temperature homogeneity of loaded deep frozen food products. It is shown that a slight flow around the refrigerated goods is necessary and the maximum downtime of the AC system is 8 min in case of combined PUR and VIP insulation and 11 min in case of an additional LHS.

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Correlation of pore size distribution with thermal conductivity of precipitated silica and experimental determination of the coupling effect

Cited by 28 publications

References 25 publications

Determination of Thermal Accommodation Coefficients on CaSiO3 and SiO2 using Molecular Dynamics and Experiments

Determination of Thermal Accommodation Coefficients on CaSiO3 and SiO2 using Molecular Dynamics and Experiments

Impact of aeration and deaeration of switchable vacuum insulations on the overall heat conductivity using different core materials and filling gases

Numerical study on the application of vacuum insulation panels and a latent heat storage for refrigerated vehicles with a large Eddy lattice Boltzmann method

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