Chapter 4.4 Notes Resistance in Thermal Systems. In fluid systems, resistance opposes the flow of Fluid. In thermal systems, resistance opposes the flow.

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Presentation transcript:

Chapter 4.4 Notes Resistance in Thermal Systems

In fluid systems, resistance opposes the flow of Fluid. In thermal systems, resistance opposes the flow of heat.

Thermal Resistance is a measure of an object’s ability to oppose heat transfer.Thermal Resistance Materials with high thermal resistance are used to insulate an object. In thermal systems, the prime move is temperature difference and the flow rate is heat flow rate.

Thermal resistance = Temperature drop / Heat flow Rate R thermal =  T / Hfr Thermal resistance 2 = thickness/(thermal conductivity x Area) R Thermal = x / kA

If the insulation is.5 m thick with a wall measuring 10 m by 10 m and the thermal conductivity of.00011, what is the Resistance? Which Equation? R Thermal = x / kA Area = 10 x 10 = 100 R Thermal =.5 / ( x 100) R Thermal =.5 /.011 = 45.5

What is our resistance if our heat flow rate is 5 with an initial temperature of 21 and final temperature of 45? Which Equation? R thermal =  T / Hfr = T f – T i / Hfr R thermal = (45 – 21) / 5 R thermal = 24/5 = 4.8

If you have several layers of different material in a wall, to get the total resistance, simply add the separate resistance of each layer. Resistance total = R 1 + R 2

Resistance of the sheet rock is.00032, resistance of the insulation is.031, and resistance of the brick is What is the total resistance of the wall? Resistance total = R 1 + R 2 + R 3 Resistance total = Resistance total =.0316

Virginia – 1900’s What was used for insulation?

Used by Romans – What is the insulation?