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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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[5] Zevenhoven R., Fält M.: Radiative cooling through the atmospheric window: A third, less intrusive geoengineering approach. Energy 152(2018), 27–33.
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[8] Fält M.: The utilisation of participating gases and long-wave thermal radiation in a passive cooling skylight. PhD thesis. Åbo Akademi, Turku 2016.
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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

Concentrator photovoltaic (CPV) systems have proven the capability of competing with traditional photovoltaic (PV) systems due to their high efficiency and low area occupancy. Such CPV systems require efficient heat removal auxiliary systems, especially for medium and high optical concentration ratios. Operating a CPV system under a high optical concentration (ratio > 200 X) might require active cooling techniques, which have high operating costs and maintenance. On the other hand, heat pipes (HPs) are widely used in electronic devices for cooling purposes. This work discusses the possibility of operating a CPV system coupled with HPs as a passive cooling technique. Two different HPs with different lengths are used to compare cooling efficiency. Each HP length was tested either in a single or double configuration. Long HPs showed better heat removal compared to a traditional fin-cooling system. CVP cooling with HP systems enhanced the entire electrical output of the cell, mainly at high optical concentration ratios.
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Authors and Affiliations

Mohammed Al Turkestani
1
ORCID: ORCID
Mohamed Sabry
1 2
ORCID: ORCID
Abdelrahman Lashin
1 3
ORCID: ORCID

  1. Physics Department, College of Science, Umm Al Qura University, Makkah, Kingdom of Saudi Arabia
  2. Solar Physics Lab, National Research Institute of Astronomy and Geophysics, Cairo, Egypt
  3. Physics Department, Faculty of Science, Mansoura University, Mansoura, Egypt

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