Question

Suppose it is a particularly hot summer day and you want to make some popsicles to help cool off. You fill a popsicle mold with 0.15kg of juice (suppose it is the same thermal energy as water). The juice starts out at a temperature of 30 °C and the freezer will cool it to -20  °C.

a. How much heat must be removed from the popsicles in order to bring them to their final temperature.

b. Draw an energy flow diagram to show the heat and work flows in this situation, and determine the minimum work needed by the freezer to remove this amount of heat from the inside of the freezer Assume the inside of the freezer remains a stable -20 °C and the outside remain 30 °C.

c. If a gas fired power plat operated with 40% of efficiency, how much heat would have to be added, QH, to produced this much work? If the exhaust temperature is at 20 °C, what is the minimum TH needed to achieve this efficiency.

I know this problem involve phase change. I have tried it but got wrong answer. Would you please explain to me each step of your work so I understand how to do this.

Thank you

Answer 1

in this solution instead of giving complete written solution i would like to give more ideas about these types of questions.

Beware about phase changes ( check answer to A part)..

I don't get idea of energy work diagram instead of that i drawn temp-time(heat) diagram . i think that's most promising here.

idea of minimum work is when freezer working reversibly .use reversible equation here
a) rn z -15 kg, c.=4-1ghjו//01,-30% b) om 30 to owex dam

-239 CTi ive let Cienc 8 3 O.165 225

C) cp rceey to ceol juice is 2A3+20
try to solve these types of questions . thanks for reading