The walls of a house are made of a 10 cm layer of brick, 10 cm of fiberglass insulation and 1cm of drywall. Thermal conductivity values: Brick: 1.31 W/mA-1K Fiberglass : 0.04 W/mA-1K dry wall : 0.17 W/mA-1K
a) Calculate the thermal conductivity of a 1 m2 section of wall.
b) Find the relationship between the thermal conductivity, k, in W/mA-1K and the thermal resistance = R in (m2A-1K)/W.
In order to be energy efficient, the air intake for the home is passed through a countercurrent heat exchanger with the indoor air going the other direction. The system is designed to absorb heat from the outgoing air and use it to warm the incoming air. In order to accomplish this, the outgoing air is passed through a radiator which has ethylene glycol flowing through it. As the ethylene glycol warms, its density decreases and it flows upward into the radiator through which the incoming air passes. density = 1.1153-.0007*T ; T in A-1C. Cp = 2.43 J/kgA-1K viscosity (cP = mPa)
| T(oC) |
-17.8 |
4.4 |
26.7 |
48.9 |
71.1 |
93.3 |
| n(mPa) |
310 |
48 |
14 |
7 |
3.8 |
1.4 |
To approximate this process, assume the glycol enters the lower radiator at a temperature of 10A????1C through a 30 cm long pipe with an inner diameter of 2 cm. It then warms to 18A????1C and flows to the upper radiator through a 1.0 meter long pipe.
c) Find an expression for viscosity as a function of temperature. [I would use Excel and a curve fit, you may use whatever you want.]
d) Using the temperatures and pipe dimension given, determine the inner diameter for the 1.0 meter long pipe so the flow rate is the same as for the 30 cm long pipe. Don't forget that the viscosity and density are different for the two temperatures.
Show transcribed image text The walls of a house are made of a 10 cm layer of brick, 10 cm of fiberglass insulation and 1cm of drywall. Thermal conductivity values: Brick: 1.31 W/m K Fiberglass : 0.04 W/m K dry wall : 0.17 W/m K
a) Calculate the thermal conductivity of a 1 m2 section of wall.
b) Find the relationship between the thermal conductivity, k, in W/m K and the thermal resistance = R in (m2 K)/W. In order to be energy efficient, the air intake for the home is passed through a countercurrent heat exchanger with the indoor air going the other direction. The system is designed to absorb heat from the outgoing air and use it to warm the incoming air. In order to accomplish this, the outgoing air is passed through a radiator which has ethylene glycol flowing through it.
As the ethylene glycol warms, its density decreases and it flows upward into the radiator through which the incoming air passes. density = 1.1153-.0007*T ; T in C. Cp = 2.43 J/kg K viscosity (cP = mPa) To approximate this process, assume the glycol enters the lower radiator at a temperature of 10 C through a 30 cm long pipe with an inner diameter of 2 cm. It then warms to 18 C and flows to the upper radiator through a 1.0 meter long pipe.
c) Find an expression for viscosity as a function of temperature. [I would use Excel and a curve fit, you may use whatever you want.]
d) Using the temperatures and pipe dimension given, determine the inner diameter for the 1.0 meter long pipe so the flow rate is the same as for the 30 cm long pipe. Don't forget that the viscosity and density are different for the two temperatures.