Cold milk enters a small sterilizing unit and flows over an electrical heating element.
The temperature of the milk is raised from 11 °C to 75 °C. A mass of 73 g of milk enters the sterilizing unit every second.
Specific heat capacity of milk =
The milk flows out through an insulated metal pipe. The pipe is at a temperature of 75 °C. A small section of the insulation has been removed from around the pipe.
State how energy is transferred from the inside of the metal pipe to the outside of the metal pipe.
convection is likely to be a significant loss
due to reduction in density of air near pipe surface hot air rises and is replaced by cooler air from elsewhere
OR
due to conduction of heat or thermal energy from pipe to air
Outline one other method by which significant amounts of energy can be transferred from the pipe to the surroundings.
conduction/conducting/conductor through metals
The missing section of insulation is 0.62 m long and the external radius of the pipe is 0.042 m. The emissivity of the pipe surface is 0.35. Determine the energy lost every second from the pipe surface. Ignore any absorption of radiation by the pipe surface.
use of where
use of « = 0.164 »
Estimate the power input to the heating element. State an appropriate unit for your answer.
Outline whether your answer to (a) is likely to overestimate or underestimate the power input.
Discuss, with reference to the molecules in the liquid, the difference between milk at 11°C and milk at 84°C.
the temperature has increased so the internal energy / average of the molecules has increased OR temperature is proportional to average of the molecules
therefore the average speed of the molecules or particles is higher OR more frequent collisions between molecules OR spacing between molecules has increased OR average force of collisions is higher OR intermolecular forces are less OR intermolecular bonds break and reform at a higher rate OR molecules are vibrating faster.
