Heat Transfer in Building Materials

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Questions and Answers

What is the required thickness of insulation to ensure heat loss does not exceed 1830W given the thermal conductivities mentioned?

5 cm

2.5 cm

7.5 cm (correct)

10 cm

For the hot steam pipe insulated with two layers, what is the overall heat lost per meter of length?

180 W/m (correct)

230 W/m

300 W/m

120 W/m

What is the overall heat-transfer coefficient when water flows at 50 ℃ in the given tube?

25 W/m²·℃

35 W/m²·℃

20 W/m²·℃ (correct)

30 W/m²·℃

What is the interface temperature between the tube and insulation of the thick-walled stainless steel pipe when the inside wall temperature is 600 ℃?

400 ℃ Signup and view all the answers

Which statement accurately reflects the heat loss characteristics of the wall described at the beginning?

Thermal conductivity affects heat loss but is not the sole factor Signup and view all the answers

What is the rate of heat loss through a red brick wall with a length of 5m, height of 4m, thickness of 0.25m, and temperature difference of 70℃?

3.92 kW Signup and view all the answers

What is the thermal conductivity of plywood, used in a composite wall for calculating heat flow?

0.052 W/m-K Signup and view all the answers

Given a copper plate of 3cm thickness with one side at 400℃ and the other at 100℃, how does the thermal conductivity affect heat transfer?

Higher thermal conductivity equates to higher heat transfer rate. Signup and view all the answers

What would be the heat transfer from a hot plate of dimensions 50 by 75 cm at 250℃ with a convection heat-transfer coefficient of 25 W/m2K, when the air is at 20℃?

625 W Signup and view all the answers

What is the expression for the rate of heat transfer through a wall heated and cooled by convection on opposite sides?

$rac{T_1 - T_2}{rac{1}{h_1} + rac{ riangle x}{k} + rac{1}{h_2}}$ Signup and view all the answers

In a material where thermal conductivity varies as the square of temperature, what is the general form of the relationship?

$k = k_o (1 + eta T^2)$ Signup and view all the answers

For a steel tube with a thermal conductivity of 46 W/m-K and an inside convective coefficient of 1500 W/m2℃, what is the significance of the outside convective coefficient of 197 W/m2℃?

It increases the total resistance to heat transfer. Signup and view all the answers

What parameters are crucial for calculating the rate of heat flow through a composite wall containing steel, plywood, and glass-wool?

Thermal conductivities, thicknesses, and temperatures. Signup and view all the answers

Study Notes

Heat Transfer Through Red Brick Wall

A red brick wall, 5m long, 4m high, and 0.25m thick, has a temperature difference of 70℃ between its surfaces.
The thermal conductivity of red brick is 0.7 W/m-K.
The heat loss through the wall is calculated to be 3.92 kW.

Heat Transfer Through a Composite Wall

A composite wall comprises a 1.5mm steel sheet, 10mm plywood, and 2cm of glass-wool.
The steel sheet has a thermal conductivity of 23.23 W/m-K.
The plywood has a thermal conductivity of 0.052 W/m-K.
The glass-wool has a thermal conductivity of 0.014 W/m-K.
The temperature difference across the composite wall is 10℃.
The rate of heat flow is calculated to be 6 W/m².

Heat Transfer Through a Copper Plate

A copper plate, 3cm thick, has a temperature difference of 300℃ between its faces.
The thermal conductivity of copper is 370 W/mK at 250℃.
The heat transferred through the plate is not calculated in the problem statement.

Convective Heat Transfer from a Hot Plate

A hot plate, 50cm by 75cm, is maintained at 250℃ and exposed to air at 20℃.
The convection heat transfer coefficient is 25 W/m²K.
The heat transfer from the plate is not calculated in the problem statement.

Heat Transfer Through a Wall with Convective Boundary Conditions

A wall experiences convective heat transfer on both sides.
The heat transfer rate through the wall is determined by the temperature difference between the two fluids, the wall thickness, the thermal conductivity, and the convection heat transfer coefficients on each side.
The equation q = (T1 - T2) / (1/(h1A) + ∆x/(kA) + 1/(h2A)) represents the heat transfer rate.

Heat Transfer Through a Wall with Variable Thermal Conductivity

A plane wall has a thermal conductivity that varies with temperature according to the equation k = k₀(1 + βT²).
The expression for the heat transfer through the wall is not derived in the problem statement.

Heat Transfer Through a Composite Wall (Figure Required)

The problem refers to a composite wall with a figure for reference.
The figure is required to understand the wall's construction and materials.
The heat transfer per unit area through the wall is not calculated without the figure.

Heat Loss from a Steel Tube

A steel tube, with an inside diameter of 3.0 cm and 2 mm thickness, experiences fluid flow both inside and outside.
The thermal conductivity of steel is 46 W/mK.
The inside fluid temperature is 223℃, and the outside fluid temperature is 57℃.
The inside and outside convection coefficients are 1500 W/m²℃ and 197 W/m²℃, respectively.
The heat loss per unit length of the tube is not calculated in the problem statement.

Insulation Required for a Wall

A 2 cm thick wall with an average thermal conductivity of 1.3 W/m℃ needs insulation to limit heat loss to 1830 W/m².
The insulation material has an average thermal conductivity of 0.35 W/m℃.
The inner and outer surface temperatures are 1300℃ and 30℃, respectively.
The required thickness of insulation is not calculated in the problem statement.

Heat Loss from a Steam Pipe With Insulation

A steam pipe with an inside surface temperature of 250℃ has an inside diameter of 8 cm and a wall thickness of 5.5 mm.
The pipe has a thermal conductivity of 47 W/m℃.
The pipe is covered by two layers of insulation: 9 cm with k = 0.5 W/m℃ and 4 cm with k = 0.25 W/m℃.
The outside insulation surface temperature is 20℃.
The heat loss per meter of length is not calculated in the problem statement.

Overall Heat Transfer Coefficient and Heat Loss for a Water-Flowing Tube

Water flows at 50℃ inside a 2.5 cm inner diameter tube with a wall thickness of 0.8 mm.
The tube has a thermal conductivity of 16 W/mK.
The inside convection coefficient is 3500 W/m²℃.
The outside convection coefficient is 7.6 W/m²℃ due to free convection.
The surrounding air temperature is 20℃.
The overall heat transfer coefficient and heat loss per unit length are not calculated in the problem statement.

Heat Loss Through Insulated Stainless Steel Tube

A stainless steel tube with a 2 cm inner diameter and 4 cm outer diameter is insulated by a 3 cm layer of asbestos.
The stainless steel has a thermal conductivity of 19 W/mK.
The asbestos insulation has a thermal conductivity of 0.2 W/mK.
The inside wall temperature of the pipe is maintained at 600℃, and the outside asbestos surface temperature is 100℃.
The heat loss per meter of length and the tube–insulation interface temperature are not calculated in the problem statement.

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Description

This quiz explores various principles of heat transfer through different materials including red brick walls, composite walls, and copper plates. You will analyze conductivity, temperature differences, and heat loss rates in practical scenarios. Test your understanding of thermal properties essential for engineering and design.