Page 45 - Basic Electrical Engineering

Substituting the values, length of wire, ℓ is

Example 1.3 It is required to raise the temperature of 12 kg of water in a
container from 15°C to 40°C in 30 min through an immersion rod connected

to a 230 V supply mains. Assuming an efficiency of operation as 80 per cent,
calculate the current drawn by the heating element (immersion rod) from the

supply. Also determine the rating of the immersion rod. Specific heat of
water is 4.2 kiloJoules/kg/°C.

Solution:

Output or Energy spent in heating the water, H is

H = m s (t − t )
2
1

Where m is the mass of water and s is the specific heat of water.

3
Here, H = 12 × 4.2 × 10 × (40 − 15) Joules
4
= 126 × 10 Joules

We know,

So, Energy input to immersion rod

The time of operation of the heater rod