Thought Leadership

Beer Fridge – A Case Study in Thermal Design. Part 5 – Time for a FloBEER

By Robin Bornoff

All good things come to those who wait. For beer this entails a trade off between anticipation and satisfaction. If, too soon after you put the room temperature beer in the fridge, you get your child to grab a beer for you, your thirst might be quenched but your satisfaction might not be. Wait too long for it to cool down and you might forget you wanted one, or go to sleep, or hit the whisky instead. A transient thermal simulation will tell you how long, and how evenly, the beer cools down…

envelope_rcA time constant is a resistance multiplied by a capacitance. Maybe the combination of a resistance to refuse a free beer x your capacity to drink many. A back of the envelopeĀ  estimation as to how long it would take warm beer, placed in a cold environment, to achieve it’s cool temperature can be made. Thermal resistance = 1/heat transfer coefficient x area, a thermal capacitance = density x volume x specific heat, a time constant = thermal resistance x thermal capacitance. The time constant will be the time it takes for the beer to cool down to about 2/3 of the way to minimum. And here’s the envelope…

beer_time_cropped5When doing a transient simulation in FloTHERMone has to define for how long you wish to predict the behaviour of the system. Using the back of the envelope calc. helps set an initial guess for this duration. The rest is simply a matter of waiting for FloTHERM to crunch through the simulating. The end product is a series of predictions of the full 3D temperature distribution at many points in time (time steps). This information can be animated to show the how the cold penetrates the cans. There’s a bit of a cold bias towards the rear of the fridge, away from the door so either the bottom middle or bottom rear beer would be the best to grab first. Remember to move the remain cans to fill the hole you’ve just left and turn either to the envelope or FloTHERM if you want to estimate or simulate (respectively) how long you should take to drink the current one until the next one has cooled further down to acceptable levels.

Sit back, relax and have some on me!


31st January 2011, Ross-on-Wye

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This article first appeared on the Siemens Digital Industries Software blog at