Question

Water is boiled at sea level in a coffee maker equipped with an immersion-type electric heating element. The coffee maker contains 1 L of water when full. Once boiling starts, it is observed that half of the water in the coffee maker evaporates in 25 min. Determine the power rating of the electric heating element immersed in water. Also, determine how long it will take for this heater to raise the temperature of 1 L of cold water from 18 oC to the boiling temperature.

Answer 1

Answer:

The water is boiled at sea level and hence the saturation pressure and saturation temperature are at atmospheric conditions. Assuming 1 bar atmospheric pressure, the enthalpy of evaporation = 2257.63 KJ/kg. Quantity of water evaporated = 1/2Litre = 1/2 kg . Time taken for evaporation = 30minutes. Hence the power rating of the coffee heater = (1/2 * 2257.63)/30 *60 = 0.627 KW. Boiling temperature of water corresponding to these conditions = 99.6 degree celsius. Heat required to raise the temperature of 1 litre water to boiling temperature = mass * specific heat * increase in temperature = 1 * 4.18*...