Numerical study on the bulk heat transfer coefficient for a variety of vegetation types and densities

✍ Scribed by Junsei Kondo; Atsuko Kawanaka

• Publisher: Springer
• Year: 1986
• Tongue: English
• Weight: 588 KB
• Volume: 37
• Category: Article
• ISSN: 0006-8314
• DOI: 10.1007/bf00122990

✦ Synopsis

The relationship between the geometrical structure of a canopy layer and the bulk transfer coefficient was investigated using a numerical canopy model. The following results were obtained:

(1) The bulk transfer coefficients for momentum and heat, CM and C,, change with non-dimensional canopy density C, ; each has a maximum.

(2) The value of CM is always larger than the value of C, for a canopy with c, > ch, c, and c,, being the drag coefficient and the heat transfer coefficient of an individual canopy element, respectively.

(3) The value of C, at which C, has its maximum value is larger than the value of C, at which CM has its maximum. Therefore, the reciprocal of the sublayer Stanton number BN r ranges between 50 and 65 for C, around 0.1 while it ranges between 0 and 30 for C, < 10-z and C, > 2 (when c, = 0.5).

(4) The value of B;' in the present study is consistent with most available observations, except for canopies of medium density (when C, is around 0.1) for which no observational value has been obtained. IUNSEI KONDO AND ATSUKO KAWANAKA Zb height of canopy bottom. S roughness length of ground ( = 0.001 m, nearly equal to the value for a smooth surface). zo9 ZT roughness length for wind and temperature profile above the canopy layer, respectively. a molecular temperature diffusion coefficient of air ( = 2.15 x 10 -5 m2 s -I). P density of air ( = 1.29 kg m -3). Y kinematic viscosity of air ( = 1.53 x 10m5 m2 s -'). 0 Stefan-Boltzmann constant (= 5.67 x lo-* W m-2 Km4). t momentum flux at the top of canopy layer.