One Black coffee please!

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I was asked on a very sleepy morning how does the house coffee machine work and could I simulate the thermostat which works overtime in most hourseholds. So off I went to hunt for some facts. Assuming that initially, (before turning the machine on) everything pot, and surrounding air is at 72F. The initial temperature of coffee is 195 F. The coffee pot is heated at the bottom by a 2000 Watt heat power source to keep the temperature of the coffee between 190 F and 200 F.  A thermostat is placed at the top surface of the coffee machine, which turns the power off if the temperature at the thermostat location exceeds 200F. The heat power remains off until the temperature in the previous step drops below 190F.

Pot2 
Once the basic information was in place, next step was fairly simple using SOLIDWORKS Simulation, I was able to look assign power to be bottom face of the coffee pot. The transient analysis helped simulate the thermostat.

Heatpower-thermostat

Temperature-distribution 
 

To make sure the thermostat was working, I probed the top surface of coffee and check the temperature variation with time. The temperature at the thermostat location increases until it reaches the maximum allowed temperature. In the following calculation steps, the thermostat turns off the power source until the temperature at the thermostat location drops below the minimum allowable value. After that coffee goes through similar cycles of cooling and heating.

Thermostat 

Now that I have convinced myself and a very special critque of mine….how about that coffee.?

Rajat Trehan

Product Manager – Design Validation

Computer Aided Technology Inc.