Hello

Recently i had a strange thought which i hope you all can help me. I was drinking coke from the bottel just taken out from the Refrigerator. The room temperature was 38 degrees. During discussion, i was just rotating the bottle the bottle in the vertical plane,(i mean the bottles axis was vertical) and i found out that the coke tasted warmer ( even though the bottle was cold) compared to teh one that was not shaked. Now my question is if i were to shake the bottle continuously, how long will it take for the coke inside the bottle to come to room temperature and with what angular velocity should the bottle be rotated? Can we model it using CFD? If so, how? I hope youcan help me in this issue.

Thanks for your kind suggestion, beforehand

Ram

If coke has this effect on you, maybe you should drink something else ... Anyway, in theory you saw right. I mean, if you rotate the bottle you cause a molecular movement that makes temperature rise and moreover the skin friction between liquid and bottle walls and between two different (=different radial distance from the axis) layer of fluid with different velocity has the same effect. But I think that the exponential law that regulate the temperature variation of a body in a different ambient temperature will always prevail ... It's not a simple study. I have just a question ... Did you enjoy you coke? Bye

I have a question to you as well. Where do you live? I mean the temperature in your room is 38 degrees - uph, a bit too hot.

As for the Coke, I am sure the dissipation of mechanical energy into heat (as was mentioned in another response) is negligible here. The mechanism behind the incresed heat transfer is the forced convection (due to the rotation of the bottle). And yes, you can model it using CFD, although it wouldn't be a simple problem to solve. You know, Coke is sparkling, besides the flow is likely to be turbulent. Also you have a free surface. Uph

(1). The bottle temperature should be colder than the Coke temperature, this is how the Coke gets cooled in the refrigerator. (2). And I have noticed that it takes a long time for the whole bottle of drink to cool down in a refrigerator. That means, the bottle probably has not sitting in the box long enough to reach the equilibrium temperature of the refrigerator. (3). In other words, when you remove the bottle , the bottle itself is cold, but not the Coke itself. When you drink the Coke, directly with mouth, you drink the cold layer of the Coke around the bottle wall and near the top surface. (4). On the other hand, if you shake the bottle, it will mix the Coke inside the bottle with the cold layer of Coke around the wall, thus the temperature of the Coke will increase. (5). The feeling of the temperature also depends on the conductivity of the material, whether it is the plastic bottle, or the glass bottle, or the Coke itself. And Coke with a lot of bubbles (Co2) tends to be less conductive than the liquid Coke. Because you are drinking a lot of gas bubble, the lower conductivity will let you feel the Coke warmer. (6). I think, if you drink the Coke slowly, and then shake your body to release the gas bubble, it will remove the body heat quickly. Thus you will likely feel cooler in your stomach.

i liked ur analysis a lot, it accurate and amusing. cox

Hi Ram,

Did You shake the Coke to the extent that it lost a lot of gas? The evolution of carbon dioxide gas from aqueous carbonic acid is an endothermic process that helps draw heat away from Your body when You consume the drink.

When You ingest the drink, electrolytes and other "stuff" present in Your saliva and in digestive secretions immediately promote the nucleation of carbon dioxide bubbles, and as Your body heat is quickly drawn away to fuel the degassing process, You get the instant satisfaction of gulping down a cold one. This doesn't happens when You drink a flat liquid.

Try shaking all the gas out of a bottle of Coke, put it back in the refrigerator with an unopened bottle, let them both chill for some time, and then do a taste test. I don't think simple conductive or convective heat transfer was an important factor in giving You the experience that You described.

Dewey Yin

-- Mr. De-Wei Yin, MASc, PEng Computational Fluid Dynamics Software Developer Directed Development Group AEA Technology Engineering Software Limited 554 Parkside Drive Unit 4, Waterloo, Ontario N2L 5Z4 Canada Tel: +1 519 886-8000 x 223

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(1). Would you like to try the cfd simulation, from the cfd code vendor side? (2). It would be interesting to know the results of the cfd simulation, if it is possible at all.

Hello Everyone..

Thanks for your responses. That coke seems to have a Burp effect on me. Anyway I would like to have some more clarifications.

1. If the flow is turbulent inside the bottle, how do one characterise it using Non-dimensional numbers?

2. Assuming that the dissolved carbondioxide in the coke as a seperate medium, taking it to be a % of the volume of coke, Can we model it using VOF?

3.Does the dissipation / energy conversion depend on the angle of rotation of the bottle w.r.t the vertical? If so, why?

4. Now if we vibrate the bottle vertically instead of rotating it, does it have the same effect? If yes, at what angle of rotation w.r.t the vertical corresond to the same degree of heat loss with the vertical vibration at a given amplitude?

5.In the present case, the human body(myself) is stationary

6. If we put the bottle in the refigerator vertically, due to natural convection, the warmer fluid will be at the top ( due to air space and its less thermal conductivity compared to that of base fluid), shoudn't one get a warmer sip compared to that of a colder one? Isnt it right John?

7. If we rotate the coke bottle, due to centrifugal action the gas bubbles " might " be displaced to the centre of the bottle and heat transfer may be enhanced due to high conductivity of the base fluid. And taking into forced convection on the outer surface of the bottle due to rotation, heat transfer may be considerably increased and hence coke might be getting warmer soon. iSNT IT RIGHT?

8. Now as John was specifying that if we shake the human body to release the bubbles, body heat is removed completely.

Can we expect the same concept of the Coke bottle to that of Human body, after all Human body consists of 70% fluid !!!!!!!!

Thanks

ram

I would think that a back-of-the-envelope scale analysis provides much more physical insight into this problem than a CFD calculation does. It may take ten to twenty minutes and some educated guesses, but the result should be sufficient to show which of thermal conduction, thermal convection, and enthalpic change associated with gas desorption has the predominating thermal effect in this problem.

I'll do the scale analysis of this problem for six glass bottles of Coke (sorry, no PET bottles and no cans).

To get help on setting up a CFD simulation of this problem using our CFX software, please contact our consultancy department.

(1). I think, it would be interesting to know the transient temperature distribution of a bottle of Coke after it is removed from the regfrigerator ( and opened). No shaking involved. (2). The second part is the temperature history after the bottle is shaked a coupled of times. (3). If one shake the bottle until most of the bubbles are gone, what is the temperature difference before and after the shaking? (the same, hotter, or colder?)

(1). The bubbles are usually very small, and the bottle is only about 8 inches tall, the rising speed of the bubble also should be small, so, the flow is more likely laminar. (2).I think, the number of bubbles is not very large, so, it is possible to track individual particles, (crude way to represent the bubble). (3).The rotation should have very little impact on the natur of the flow inside the bottle. This is because, normally, your hand can only rotate the bottle by an angle,say 90 degrees. To reach 180 degrees you will have to twist your hand very hard. Thus the main body of the Coke will not be affected, except the thin layer of the fluid near the wall for a short period of time. (4).If you drink the Coke from a bottle and then shake the bottle up and down violently , then the Coke will form a bubbly jet and rush out of the bottle. Then you will have a huge loss of fluid (Coke) and you are likely to have very little left. (5).Do you count your hand as part of your body? (Do you think that hand can be considered as non-integral part of the body? in some countries?) Hard to understand, that the body is stationary while the Coke bottle is rotating. (6). Yah, it is possible. This is really very creative. It all depends on how you drink. If your mouth cover the mouth of the bottle completely, then I would imagine that the cold front would enter the mouth first. But then the cold layer near the bottle will touch the tongue and the inside wall of the mouth. So, you will get cooler feeling overall. The throat part probably will be on the warmer side. But if you suck only the layer of the Coke near the bottom of the mouth of the bottle, then it's all cool Coke. If you prefer the warmer part of the Coke, (better for your stomach, to keep the temperature difference to a minimum), you have to use a straw. You can try out three different ways to find out which way is better for you. (7). That is possible only if your hand is replaced by a motorized rotating device. Most mechanical arms can not rotate like a motor. And if you rotate it fast enough and long enough, you might be able to find some nuclear fuel on the Coke bottle wall? Do you think it's possible? (8).That is exactly the reason why people have been drinking the soda drink. The gas escaped will leave the body cool. The same is true that you can drink hot tea in a hot summer afternoon, to keep the body cool. Sometime, this is more effective though, because the water removed from the body will carry away more heat than that of the Co2. (9). But I prefer a cup of shaved ice with some sweet red bean or strawberry in a hot summer day. (by the way, if you have high blood pressure, it is a good idea to avoid the Coke or the similar drink.) (10). After the Coke, you may want to try the hot tea approach to keep your body cool in a hot summer day.

Thanks for your kind reply.

John, the body is stationary and only the movement is given to the bottle at various angles by the motion of the wrist. I hope you got it. The rotation angle may vary from zero degrees to thirty degrees w.r.t the vertical. Mind u the body is standing and the motion is only to the bottle through the wrists. Coming of your desposition of feeling cold on the tongue, it reminded me of one simple question asked by a kid. Why do we usually drink cold beer/cook drinks and warm/hot cofee/tea? Why not the reverse way like Warm Beer/cool drinks etc.? What do you think is the right answer for the kids question?

The concept of vapour bubbles coming to the centre of the bottle due to centrifugal motion of the bottle is due to their lesser density and hence the centrifugal force coming on the bubbles is less compared to the that of the base liquid. Same concept can be found in Centrifugal casting.

Yin, Can you kindly explain me what do you mean by back-of-the-envelope scale analysis? Its the first time i am hearing it. Thank you for your kind help in the scale analysis aspect.

John, How can you justify that the temperature distribution of the Bottle will shed some light in the present case?

Best Regards

ram

(1). It's the temperature distribution and histroy of the Coke and the bottle, together. (2). Science deals with numbers, not the feeling of the tongue. So, the temperature history and distribution will tell you the real fact.(3). Well, I guess, sometimes the body does not include the hand. Yes, I understand your problem.

Thanks for your kind help..

ram