Time Calculation of the Temperature Rise in an Electric Iron

Objectives:To calculate the time required by an electric iron to raise

the temperature from the room temperature to 65 degree Celsius. We first measured three sets of data experimentally and then compared the data to the value that we calculated though our assumptions.

Equipment usedProctor SileX Iron (model #17400)StopwatchThermocoupleVernier Caliper

ThermocoupleIron & Vernier Caliper

Problem: We want to calculate the time required for thetemperature rise to 65 degree Celsius (final

temperature of the electric iron after heating) from 23 degree Celsius (initial temperature of the iron before heating).

We assumed to have heat transfer as convention and radiation. The heated plate of electric iron is assumed to be Aluminum Alloy 195, cast(4.5 % Cu). The properties of the aluminum alloy were noted at 300K from the ‘Fundamental of Heat and

Mass transfer’ book. Density(rho)=2790 kg/m^3 C=883 J/kg.K K=168 W/m.K Assume emissivity( ) =0.80 T(surf)=22 Degree Celsius Tf=65 Degree Celsius Area of the aluminum plate(approx.) =0.02m^2 Power rated of electric iron=1200W

Solution Assuming efficiency to be 50%, For a 1200W electric Iron; q =0.50*1200=600W; Uniform heat flux (qꞌꞌ) =600/0.02= 3*10^4 W/m^2 Let convention coefficient at outer surface be (h)=10W/m^2.K

Bi=h L/K=10*0.00235/168=1.4*10^-4

For radiation, =0.8*(5.67*10^-8)(338+295)*(114244+87025) =5.779 W/m^2.K Bi r =hr L/k=5.779*0.00235/168=8*10^-5

Continue….. Using the lumped capacitance analysis, we have;

With Eg =0, we can write the equation as,

Solving in Matlab, we get; t = 39 sec.

Experimental data: From the experiment, we found that the required time for the raise in temperature to 65 Degree Celsius from room temperature of 22 degree Celsius were 26, 28 and 25 seconds respectively in three consecutive experiments, which is close to the value we calculated.Now the average of the three experimental data is 26.33 s.

=(39-26.33)/26.33*100 =48.12%

Conclusion and Recommendation:The percentage error that we calculated was

reasonable considering our assumptions in the calculation model.

If possible get all the necessary data from the manufacturer so that the error associated with modeling the calculation will be minimal.

Possible Reasons of ErrorThe assumption of the material properties of

the ironing surface. The assumption of the efficiency of the iron. Human error associated with reading the

time and temperature rise. The assumption of uniform heat flux. The calculation of the surface area of ironing

surface.

Referenceshttp://laundry.manualsonline.com/manuals/

mfg/hamilton_beach/14700.html?idRes=12120817

Incropera (2006) Fundamentals of Heat and Mass Transfer

http://eartheasy.com/live_energyeffic_appl.htm