Physics Help Forum Accelerated heat transfer test

 Oct 15th 2018, 09:02 PM #1 Junior Member   Join Date: Oct 2018 Posts: 3 Accelerated heat transfer test Hi everyone! I want to keep a pharma product between 2-8°C for 48 hrs in a 30°C 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 30°C 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!
 Oct 15th 2018, 10:48 PM #2 Senior Member   Join Date: Apr 2017 Posts: 484 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.
 Oct 16th 2018, 11:26 PM #3 Junior Member   Join Date: Oct 2018 Posts: 3 Thanks for the input @oz93666! I don't think my testing chamber will be able to safely create an ambient temperature of 155°C. If my max ambient is 45°C, how long should I run my test? That is again, to get the same results as a 48 hr 30°C test would yield. Thanks!
Oct 17th 2018, 01:25 AM   #4
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Join Date: Apr 2017
Posts: 484
 Originally Posted by juliusM Thanks for the input @oz93666! I don't think my testing chamber will be able to safely create an ambient temperature of 155°C. If my max ambient is 45°C, how long should I run my test? That is again, to get the same results as a 48 hr 30°C 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

 Oct 18th 2018, 06:40 PM #5 Junior Member   Join Date: Oct 2018 Posts: 3 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 2-8°C internal temperature for 48 hrs in a +30°C 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!
 Oct 18th 2018, 11:35 PM #6 Senior Member   Join Date: Apr 2017 Posts: 484 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 18th 2018 at 11:40 PM.

 Tags accelerated, heat, test, transfer

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