a man wraps himself in a flannel 4mm thick.how much heat is lost per square meter of his body per hour,if the atmospheric temperature is 293K and the body temperature is 310K? ( take k of flannel=0.0504W/m/K)
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use the formula,
dQ/dt = KA.dT/dx
where K is the thermal conductivity,
A is the cross section area,
dT is the temperature difference,
dx is the thickness of flannels.
dQ/A.dt = K.dT/dx
here, K = 0.0504 W/m/k
dT = (310-293)K = 17K
dx = 4mm = 4 × 10⁻³ m
heat lost per square metre per hour = 0.0504 × 17/ 4 × 10⁻³
= 0.0504 × 17/4 × 10³
= 50.4 × 17/4
= 214.2 J/m²/hr
dQ/dt = KA.dT/dx
where K is the thermal conductivity,
A is the cross section area,
dT is the temperature difference,
dx is the thickness of flannels.
dQ/A.dt = K.dT/dx
here, K = 0.0504 W/m/k
dT = (310-293)K = 17K
dx = 4mm = 4 × 10⁻³ m
heat lost per square metre per hour = 0.0504 × 17/ 4 × 10⁻³
= 0.0504 × 17/4 × 10³
= 50.4 × 17/4
= 214.2 J/m²/hr
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