Question

A vacuum gauge fixed on a steam condenser reads 80 kPa vacuum. The barometer indicates 1.013 bar. The absolute pressure in terms of mercury head is, nearly 

(a) 160 mm of Hg 

(b) 190 mm of Hg 

(c) 380 mm of Hg 

(d) 760 mm of Hg

Answer 1

(a) 160 mm of Hg 

Absolute pressure = Atmospheric pressure + Gauge pressure 

\(\therefore\) P_a = P_o + P_g

Since the condenser pressure is vacuum.

P_g = –80 kPa

p_a = 101.3 – 80 = 21.3 kPa

\(\rho\)_mgh_m = 21.3 × 10³

13.6 × 10³ x 9.81 h_m = 21.3 x 10³

\(\therefore\) Mercury head, h_m = \(\frac{21.3}{136\times4.81}\) = 0.15965 m

= 159.65 mm

= 160 mm