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Old Oct 15th 2018, 10:02 PM   #1
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Accelerated heat transfer test

Hi everyone! I want to keep a pharma product between 2-8C for 48 hrs in a 30C ambient using an insulated box with ice packs in it.

If I want to reduce my test time to 8 hrs, by how much should I raise the testing ambient temperature to get valid results as if it was a 48 hr 30C test?

As of the moment, it's taking so much time for me to determine if I got my ice pack volume and arrangement right. I need to shorten my test time to be more efficient.

Looking forward to your opinions, thanks a lot!
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Old Oct 15th 2018, 11:48 PM   #2
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this is all about heat conduction ... in the first case the inside temp is 5C aprox. outside temp 30C ....temp difference through the walls of the box is 25 C and this gives 48hrs .

for 8 hrs the heat transfer is 48/8 = 6 times greater ...

so the temp difference needs to be six times greater 150C so ambient is 155C

that's assuming the greater heat flow hasn't set up convection currents on the outside of the box.
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Old Oct 17th 2018, 12:26 AM   #3
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Thanks for the input @oz93666! I don't think my testing chamber will be able to safely create an ambient temperature of 155C. If my max ambient is 45C, how long should I run my test? That is again, to get the same results as a 48 hr 30C test would yield. Thanks!
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Old Oct 17th 2018, 02:25 AM   #4
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Originally Posted by juliusM View Post
Thanks for the input @oz93666! I don't think my testing chamber will be able to safely create an ambient temperature of 155C. If my max ambient is 45C, how long should I run my test? That is again, to get the same results as a 48 hr 30C test would yield. Thanks!
I'm not sure I fully understand what your doing?? or why ...

Anyway if ambient is 45C the temp difference between the inside and outside of the box has changed from 25C to 40C ...

so heat will dissipate 40/25 times quicker = 1.6 times quicker ...

the time the box stays cool should change from 48 hrs to about 30 hrs
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Old Oct 18th 2018, 07:40 PM   #5
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I'm making a soft case bag that will let sick people travel and have their temperature sensitive medicines with them as their carry on baggage. One of the main requirements and the worst case scenario is that the bag should hold a 2-8C internal temperature for 48 hrs in a +30C environment.

As I've said before, doing the tests take too long to finish only to find out that the design failed. So I asked here if there's any way I can shorten the test Thanks again for your input @oz93666, if you have something in mind which you think can help, please let me know!
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Old Oct 19th 2018, 12:35 AM   #6
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Well... to shorten test time put in a smaller ice pack ...

You could find out how many grams of ice-pack you need to keep cool for 10 hrs ...

Then you know doubling the ice-pack size will double the time the inside stays cool ...

The user can adjust the amount of ice pack depending on how long he need the box to stay cool .. No need to carry excessive ice around if you only need 10 hours of cooling.

Also you don't really need a controlled environment ... just do all your experiments at 25C in real use situation you can then know , that if one ice pack keeps it cool for 10 hrs at 25C ambient ...then the same ice pack will keep it cool for about 8hrs at 30C ambient.

It's important to conduct your experiments in the real world ...For example if the box is sitting on a car seat , this will help insulation and keep it cool longer , just putting the box in a plastic carrier bag will help insulation and get more hrs of cool time.

Last edited by oz93666; Oct 19th 2018 at 12:40 AM.
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