Showing papers by "John L. Monteith published in 1980"
4,943 citations
TL;DR: The variation in R′ between sowings was better correlated with the rate at which daylength was changing when the plants emerged than with the mean daylength while leaves were appearing, when plotted against ‘thermal time’.
Abstract: In the field successive leaves of winter wheat appear at a rate which varies because it depends strongly upon temperature. When plotted against ‘thermal time’, however (temperature accumulated above a fixed base of 0°C), leaf appearance was a strictly linear function of temperature. The mean rate of leaf appearance in thermal time, R′, was faster for a spring sowing than for an autumn sowing. The variation in R′ between sowings was better correlated with the rate at which daylength was changing when the plants emerged than with the mean daylength while leaves were appearing.
175 citations
TL;DR: In this paper, the dependence of coat or clothing insulation on windspeed u is usually described by a relation of the form I(u) = I(0) − au1/2, where a is a constant.
Abstract: Penetration of a layer of fibre by wind reduces its effectiveness as a barrier to heat flow. In the literature, the dependence of coat or clothing insulation I(u) on windspeed u is usually described by a relation of the form I(u) = I(0) − au1/2, where a is a constant. Re-analysis reveals that it is more appropriate to treat coat conductance (proportional to 1/I) as a linear function of windspeed. Vapour conductance can also be treated as a linear function of windspeed.
65 citations
TL;DR: The orientation of the model to the wind had little effect on the bulk resistance of the fleece, but the resistance on the windward side was substantially lower than on the leeward side.
Abstract: Penetration of an animal’s coat by wind reduces its thermal insulation and increases heat loss to the environment. From studies of the sensible heat loss from a life-sized model sheep covered with fleece, the average fleece resistance r¯ f (s cm -1 ) was related to windspeed u (m s -1 ) by 1/ r¯ f ( u ) = l/ r¯ f (0) + cu , where c is a dimensionless constant. As c is expected to be inversely proportional to coat depth I , the more general relation k¯ ( u ) = k¯ (0) + c9u was evaluated, where k¯ = I / r¯ f is the thermal diffusivity (cm 2 s -1 ) of the fleece and c9 = cI is another constant (cm). The orientation of the model to the wind had little effect on the bulk resistance of the fleece, but the resistance on the windward side was substantially lower than on the leeward side.
38 citations
TL;DR: A bulk Nusselt number should not be used to estimate heat loss from a live sheep in a hot environment if the windspeed is below about 4 m s-1 because the relation between mean surface temperature, Nusselst number and convective heat flux is not unique.
Abstract: A model sheep, made from metal cylinders and hemispheres, was heated electrically. Heat loss by forced convection in a wind tunnel was analysed in terms of the dependence of the Nusselt number ( Nu ¯¯ ) on Reynolds number ( Re ). For a bare trunk Nu ¯¯ = 0.095 Re 0.684 , but with fleece covering the trunk to a depth of 3.5 cm, Nu ¯¯ = 0.0112 Re 0.875 when the mean radiative temperature of the coat was taken as the surface temperature. Heat transfer by convection from the whole body, including legs, was described by Nu ¯¯ = 0.029 Re 0.80 . However, a bulk Nusselt number should not be used to estimate heat loss from a live sheep in a hot environment if the windspeed is below about 4 m s -1 because the relation between mean surface temperature, Nusselt number and convective heat flux is not unique.
33 citations