## 20161205

### Online reading assignment: heat transfer applications

Physics 205A, fall semester 2016
Cuesta College, San Luis Obispo, CA

Students have a bi-weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing a presentation on heat transfer applications.

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"How the Coffee Joulies work--their melting point is 140 and they turn into liquid and absorb the heat from the coffee and release it back when it begins getting cooler."

"We will be testing out some stuff related to the transfer of heat between different objects. I know that heat goes from hot to cold, so I am curious to see how the different things mentioned perform when tested."

"A Cooper Cooler chills wine in six minutes by spraying the bottle with ice water transferring heat to the ice water from the bottle. Coffee Joulies keep coffee at a comfortable 140° because the material inside the joulies has a melting temp of 140°. The solid material absorbs the heat of the coffee and releases a little bit at a time as the environment removes heat from the coffee."

"I've heard about space blankets before and how they are so light weight and not even expensive. They are a heat-reflective thin plastic sheet."

"That you lose a lot of body height from emitting it so an emergency space blanket should be silver."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.
"There are no equations so I am confused if this will mostly be conceptual rather than a numerical section?"

"I am confused about carbonation when using a Cooper Cooler. Why does pressure build in a soda can when you shake it and not when you spin it?"

"I'm a little confused how spinning a bottle is any different than shaking it. It seems like the drink would still explode because it was still shaken up."

"How do I know it's conduction, convection or radiation for the questions below? I wasn't sure on how to know."

"I don't really understand how something can cool off faster by being spun and sprayed. It doesn't seem like it should work that well."

"It seems super interesting this method of adding Coffee Joulies to cool down your hot coffee while keeping it at a constant temperature. I don't fully understand how the coffee joulies work though and the chemical processes behind it."

The primary heat transfer process that the Cooper Cooler™ uses to chill beverages is:
 conduction. ***************** [17] convection. ************** [14] radiation. [0] (Unsure/guessing/lost/help!) **** [4]

How plausible do you think these claims for the Cooper Cooler™ are?
(Only modal responses shown.)
"The Cooper Cooler™ can chill a soda in one minute": somewhat plausible [43%]
"Because it's spinning and not shaking your carbonated beverages, you don't have to worry about them exploding": not very plausible [43%]

The primary heat transfer process that the Coffee Joulies™ uses to moderate and maintain coffee temperatures is:
 conduction. ********************** [22] convection. ********* [9] radiation. ** [2] (Unsure/guessing/lost/help!) ** [2]

How plausible do you think these claims for Coffee Joulies™ are?
(Only modal responses shown.)
"One 'bean' for every four ounces of coffee cools right down to 140° in a few seconds": somewhat plausible [49%]
"Keeps coffee at 140° for two full hours": not very plausible [37%]

The primary heat loss process that any blanket (regardless of type) should prevent in typical "emergency survival conditions" (on Earth) is:
 conduction. **** [4] convection. ******* [7] radiation. ******************** [20] (Unsure/guessing/lost/help!) **** [4]

How plausible do you think heavy-duty garbage bag material will be just as effective as a space blanket for typical "emergency survival conditions" on Earth?
 Implausible. ***** [6] Not very plausible. ******* [7] Somewhat plausible. ************** [14] Very plausible. ***** [5] (Unsure/guessing/lost/help!) [3]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"The negative sign that is applied to the power equation for radiation--is that strictly for when energy is taken from the object?" (Yes, since a positive sign is for when energy (heat) is given to an object.)

"It says the emergency space blankets are perfect for space because radiative heat loss is the primary means of heat loss. What is the primary means of heat loss on Earth?" (Medical research says for a patient on an operating room table, it's radiation. But if you're wearing clothes, then you've minimized radiation and conduction (by covering up exposed skin and adding layers), and then you would need to minimize convection by sheltering yourself from the wind, and wearing a hat on your head. Heat loss via evaporation is an additional factor if you are perspiring (or even just exhaling), and are surrounded by dry (and cooler) air.)

"Could you just use a few extra trash bags instead, and it would be just as effective as a space blanket?" (Let's test this in lab, before you need to resort to this in the wilderness.)

"Would silverbody blankets be ideal for space?" (NASA seems to think so. And they use gold foil instead of aluminum foil, because, reasons.)

"I might need this Cooper Cooler if it really works." (Let's test this in lab, before you ask Santa for one of these.)