Question

Define the following terms using equations and explain all terms used in the equation:

(a) Reynolds number (Re)

(b) Grashof’s number (Gr)

(c) Convective heat loss or gain from a body  

Answer 1

a)

$$Re=\frac{uL}{\nu}$$

u is the flow speed

L is a characteristic linear dimension

ν is the kinematic viscosity of the fluid

b) The Grashof number is:

$$Gr=\frac{g\beta (T_s-T_\infty)L^3}{\nu^2}$$

where:

g is acceleration due to Earth's gravity

β is the coefficient of thermal expansion

T_s is the surface temperature

T_∞ is the bulk temperature

L is the vertical length

ν is the kinematic viscosity.

c)

$$H=kA(T_s-T_a)$$

where H is the loss, k is the cooling constant, A is the surface area, and T_s–T_a is the difference between skin temperature and air temperature.