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

Answer:

Therefore % increase in velocity is 18.23 %

Explanation:

we use the equality of mass flow rate and the areas

$m_1 = m_2\\p_1v_1 = p_2v_2\\p_1A_1v_1 = p_2A_2v_2\\v_2 = \frac{p_1}{p_2} v_1$

The percentage increase in velocity is

Δ v% = $\frac{v_2 - v_1}{v_1}$100%

= $\frac{p_1}{p_2} v_1 - v_1$.100%

= $\frac{\frac{1.2}{1.015} - 1}{1}$ . 100%

= Therefore % increase in velocity is 18.23 %