1. A polished copper sphere of 10-mm diameter, initially at a prescribed elevated temperature Ti, is quenched in a saturated (1 atm) water bath. Using the lumped capaci- tance method of Section 5.3.3, estimate the time for the sphere to cool (a) from Ti = 130°C to 110°C and (b) from Ti = 550°C to 220°C. Make use of the average sphere temperatures in evaluating properties. Plot the temperature history for each quenching process.
2. A tube of 2-mm diameter is used to heat saturated water at 1 atm, which is in cross flow over the tube. Calculate and plot the critical heat flux as a function of water velocity over the range 0 to 2 m/s. On your plot, identify the pool boiling region and the transition region between the low- and high-velocity ranges. Hint: Problem 10.20 contains relevant information for pool boiling on small-diameter cylinders.