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Abstract

The article presents a novel method that allows measurement of thermal conductivity that is based on Stefan-Boltzmann law. The developed method can be used to determine thermal conductivity of ceramic investment casting molds. The methodology for conducting thermal conductivity tests of ceramic material samples is presented. Knowledge of the value of thermal capacity and thermal conductivity as a function of temperature enables computer simulations of the process of cooling and solidification of liquid metal in a mold.

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Authors and Affiliations

W. Leśniewski
E. Czekaj
P. Wieliczko
M. Wawrylak
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Abstract

The presence of more than one solute diffused in fluid mixtures is very often requested for discussing the natural phenomena such as transportation of contaminants, underground water, acid rain and so on. In the paper, the effect of nonlinear thermal radiation on triple diffusive convective boundary layer flow of Casson nanofluid along a horizontal plate is theoretically investigated. Similarity transformations are utilized to reduce the governing partial differential equations into a set of nonlinear ordinary differential equations. The reduced equations are numerically solved using Runge-Kutta-Fehlberg fourth-fifth order method along with shooting technique. The impact of several existing physical parameters on velocity, temperature, solutal and nanofluid concentration profiles are analyzed through graphs and tables in detail. It is found that, modified Dufour parameter and Dufour solutal Lewis number enhances the temperature and solutal concentration profiles respectively.

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Authors and Affiliations

Manjappa Archana
Bijjanal Jayanna Gireesha
Ballajja Chandrappa Prasannakumara
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Abstract

One of the most energy-intensive activities for a vehicle is space air conditioning, for either cooling or heating. Considerable energy savings can be achieved if this can be decoupled from the use of fuel or electricity. This study analyzes the opportunities and effectiveness of deploying the concept of passive cooling through the atmospheric window (i.e. the 8– 14 nm wavelength range where the atmosphere is transparent for thermal radiation) for vehicle temperature control. Recent work at our institute has resulted in a skylight (roof window) design for passive cooling of building space. This should be applicable to vehicles as well, using the same materials and design concept. An overall cooling effect is obtained if outgoing (long wavelength greater than 4 nm) thermal radiation is stronger than the incoming (short wavelength less than 4 nm) thermal radiation. Of particular interest is to quantify the passive cooling of a vehicle parked under direct/indirect sunlight equipped with a small skylight, designed based on earlier designs for buildings. The work involved simulations using commercial computational fluid dynamics software implementing (where possible) wavelengthdependency of thermal radiation properties of materials involved. The findings show that by the use of passive cooling, a temperature difference of up to 7–8 K is obtained with an internal gas flow rate of 0.7 cm/s inside the skylight. A passive cooling effect of almost 27 W/m2 is attainable for summer season in Finland. Comparison of results from Ansys Fluent and COMSOL models shows differences up to about 10 W/m2 in the estimations.
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Bibliography

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[2] Lambert M.A., Jones B.J.: Automotive adsorption air conditioner powered by exhaust heat. Part 1: Conceptual and embodiment design. P.I. Mech. Eng. D-J. Aut. Eng. Vol. 220(2006), 7, 959–972.
[3] Johnson V.H.: Fuel used for vehicle air conditioning: A state-by-state thermal comfort-based approach. SAE Tech. Pap. (2002), 2002-01-1957.
[4] Fayazbakhsh M., Bahrami M.: Comprehensive modeling of vehicle air conditioning loads using heat balance method. SAE Tech. Pap. (2013), 2013-01-1507.
[5] Zevenhoven R., Fält M.: Radiative cooling through the atmospheric window: A third, less intrusive geoengineering approach. Energy 152(2018), 27–33.
[6] Zevenhoven R., Fält M., Gomes L.P.: Thermal radiation heat transfer: Including wavelength dependence into modelling. Int. J. Therm. Sci. 86(2014), 189–197.
[7] Fält M., Pettersson F.: Modified predator-prey algorithm approach to designing a cooling or insulating skylight. Build. Environ. 126(2017), 331-338.
[8] Fält M.: The utilisation of participating gases and long-wave thermal radiation in a passive cooling skylight. PhD thesis. Åbo Akademi, Turku 2016.
[9] Kuczynski P., Białecki R.: Radiation heat transfer model using Monte Carlo ray tracing method on hierarchical ortho-Cartesian meshes and non-uniform rational basis spline surfaces for description of boundaries. Arch. Thermodyn. 35(2014), 2, 65–92.
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Authors and Affiliations

Umara Khan
1
Ron Zevenhoven
1

  1. Abo Akademi University, Process and Systems Engineering Laboratory, Henrikinkatu 2, 20500 Turku, Finland
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Abstract

The non-uniformity of temperature field distribution of long-span steel structure is proportional to the intensity of solar radiation. Based on the background of Guangzhou Baiyun Station large-span complex steel roof structure, this paper studies the non-uniformtemperature field distribution of large-span steel structure under the Summer Solstice daily radiation-thermal-fluid coupling action based on Star-ccm¸ finite element software, and uses Spa2000 software to analyze the stress and deformation of steel roof under temperature action. Combined with the on-site temperature monitoring, the maximum difference with the measured value is 2.5˚C compared with the numerical simulation results, which verifies the validity of the finite element simulation. The results show that: from 8:00, with the increase of solar altitude angle, the intensity of solar radiation increases, the temperature rises, and the temperature distribution of large-span steel structure becomes more and more non-uniform. From14:00 to18:00, the solar radiation weakens, and the temperature distribution tends to be uniform. Finally, reasonable construction suggestions and measures are proposed to reduce the adverse effects of temperature effects, which can provide theoretical references for the safe construction and normal operation of large-span steel structures located in the subtropics.
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Authors and Affiliations

Pengcheng Jiang
1
ORCID: ORCID

  1. Station Construction Command, China Railway Guangzhou Group Co., Ltd., Guangzhou, Guangdong, China

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