Lumped BurritoUsing Lumped Capacitance to Cook a Frozen Burrito

Chad Pharo & Chris Howald ME EN 340Heat Transfer Project

Lumped Burrito

Objective**In ME EN 340, we have to make many assumptions for our homework problems. Lumped capacitance is no exception several assumptions are made during a typical problem.For our project, we wanted to see how accurate the lumped capacitance method would be for predicting the cooking time of a frozen burrito.

Lumped Burrito

Lumped Burrito

Description of Experiment**We cooked 3 frozen burritos at different temperatures 300F, 350F, and 400FThe burritos were cooked for the time specified by the lumped capacitance calculations using Tfinal = 165FAt the end of the time period, we measured the interior temperature of the burrito and compared it to the interior temperature of a burrito cooked with the recommended time and oven temperature.

Lumped Burrito

Lumped Burrito

AssumptionsBurrito assumed to be a cylinderTsur = T for radiation calculationsOnly modes of heat transfer considered are free convection, radiation, and conduction through the burrito (ignore conduction through the cooking rack)Thermophysical properties of burrito were estimated as those of water (Table A-6) like the quizzes in classEmissivity value of plaster board was assumed ( = 0.92) since the outer tortillas are hardFinal temperature of Tfinal = 165F was chosen based on average food quality standards

**Lumped Burrito

Lumped Burrito

CalculationsVariables Defined**Lumped BurritoProperties of water @ 273 K: = 1000 kg/ m3 ; k = 0.569 W/m*K ; cp = 4217 J/kg*K ; = 1.3493e-7 m2 / s Ti = 0F = 255.37 KT,1 = 300F = 422.04 KT,2 = 350F = 449.82 KT,3 = 400F = 477.59 KTfilm,1 = 338.71 KTfilm,2 = 352.60 KTfilm,3 = 366.48 K

Lumped Burrito

CalculationsEquations UsedFree Convection:

Radiation:**Lumped Burrito

Lumped Burrito

CalculationsEquations ContinuedBiot Number:

Lumped Capacitance:**Lumped Burrito

Lumped Burrito

Carrying Out the Experiment**Lumped BurritoLumped Capacitance Burrito @ 400F was crispy on the outsideBurrito @ recommended settings burst in the oven (too hot for too long)Internal temperature was measured with food thermometer

Lumped Burrito

Results**Lumped Burrito

Lumped Burrito

ConclusionsWe did not reach the desired Tfinal = 165F using the lumped capacitance model; however, the burritos were still an acceptable temperature for consumption.The lumped capacitance results (in our opinion) were better than the recommended package directions because the package directions caused the burrito to burst open inside the oven.Overall, the lumped capacitance method is an acceptable way to cook a frozen burrito.**Lumped Burrito

Lumped Burrito

FYI**Lumped Burrito

Lumped Burrito

Appendices(Hand Calculations) *Lumped Burrito*

Lumped Burrito

Appendices**Lumped Burrito

Lumped Burrito

*Lumped Burrito*Iteration 1Iteration 2Iteration 3

Lumped Burrito

*Lumped Burrito*Actual temperaturesLumped Capacitancetimes

Lumped Burrito

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