Chapter 1, Problem 126P

A 40-cm-long, 800-W electric resistance heating element with dieter 0.5 cm and surface temperature ${120}^{\text{o}}\text{C}$ is immersed in 75 kg of water initially at ${20}^{\text{o}}\text{C}\text{.}$

Determine how long it will take for this heater to raise the water temperature to ${80}^{\text{o}}\text{C}\text{.}$ and Also, determine the convection heat transfer coefficients at the beginning and at the end of the heating process.