Question

A hair dryer is basically a duct of constant diameter in which a few layers of electric resistors are placed. A small fan pulls the air in and forces it through the resistors where it is heated. If the density of air is 1.20 kg/m3 at the inlet and 1.015 kg/m3 at the exit, determine the percent increase in the velocity of air as it flows through the dryer

Answer 1

Therefore % increase in velocity is 18.23 %

Step-by-step explanation:

we use the equality of mass flow rate and the areas

`m_1 = m_2\\p_1v_1 = p_2v_2\\p_1A_1v_1 = p_2A_2v_2\\v_2 = (p_1)/(p_2) v_1`

The percentage increase in velocity is

Δ v% =
`(v_2 - v_1)/(v_1) \\`100%

=
`(p_1)/(p_2) v_1 - v_1`.100%

=
`((1.2)/(1.015) - 1)/(1)` . 100%

= Therefore % increase in velocity is 18.23 %