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Unformatted text preview: ot of power as a function of time: a. Find the time rate change of system energy at t=0.6 hours in kW. Start with the first law for a closed
system:
Next, evaluate this equation at t=0.6 hours. To do this, plug in the values for the heat transfer rate and
the power output at this time (in hours). b. Determine the change in system energy after 2 hours. To do this, first integrate the energy balance
equation. Remember to split up the integral for power, because it is a piecewise function. Also,
remember that we are integrating over time in seconds, so a unit conversion from hours to seconds
must be made to the first power integral (divide t by 3600). Next, evaluate the integrals: Also, the work output can be calculated by simply measuring the area under the curve for the plot of
power as a function of time. 4. Surfaces: Person(1), Surroundings (2)
Assume: emissivity, ε=1
Given: Surface area of body, A=1.7 m2
Temperature of person’s body, T1: 98.6 °F=310 K
Temperature of surroundings, T2: 20 °C=293 K
Boltzmann constant, σ=5.67e08 W/m2K4
Find: Rate of heat transfer from the body to the surroundings
Governing equation: Quantitative solution:...
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 Winter '14

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