CUED Publications database

"A car gets very hot when left in the sun, but only on a hot day when heat is not lost by convection to air"

Hunt, H (2017) "A car gets very hot when left in the sun, but only on a hot day when heat is not lost by convection to air". NEW SCIENTIST, 235. p. 57. ISSN 0262-4079

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Abstract

Radiation from the sun is more than matched by convection to the air. Face the sun and your bare skin receives heat by radiation. The sun delivers about 1400 watts of energy per square metre (W/m2) to the Earth but the atmosphere absorbs and reflects much of this. On a very good day in the UK perhaps 300 W/m2 will reach the ground. Your face presents about 0.03m2 to the sun so will receive about 9W of solar heat. When your skin and air temperatures are both around 25oC you don't lose heat to the air but on a cool 10oC day then your face will lose about 5W, and substantially more if there's a breeze. Also your face will radiate 3W to nearby cold walls if they are at 5oC. A car gets very hot when left in the sun, but only on a hot day when heat is not lost by convection to the air. Just like the car your skin is only interested in the total energy balance, so don't strip off in the Spring.

Item Type: Article
Subjects: UNSPECIFIED
Divisions: Div C > Applied Mechanics
Depositing User: Cron Job
Date Deposited: 30 Aug 2017 20:06
Last Modified: 28 Dec 2017 01:54
DOI: