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# Conductive Heat Transfer

Conduction as heat transfer takes place if there is a temperature gradient in a solid or stationary fluid medium.

With conduction energy transfers from more energetic to less energetic molecules when neighboring molecules collide. Heat flows in direction of decreasing temperatures since higher temperatures are associated with higher molecular energy.

Conductive heat transfer can be expressed with "Fourier's Law"

q = (k / s) A dT

= U A dT                               (1)

where

q = heat transfer (W, J/s, Btu/hr)

k = Thermal Conductivity of material (W/m K or W/m oC, Btu/(hr oF ft2/ft))

s = material thickness (m, ft)

A = heat transfer area (m2, ft2)

U = k / s

=  Coefficient of Heat Transfer (W/(m2K), Btu/(ft2 h oF)

dT = t1 - t2

= temperature gradient - difference - over the material (oC, oF)

#### Example - Conductive Heat Transfer

A plane wall is constructed of solid iron with thermal conductivity 70 W/moC. Thickness of the wall is 50 mm and surface length and width is 1 m by 1 m. The temperature is 150 oC on one side of the surface and 80 oC on the other.

The conductive heat transfer through the wall can be calculated

q = [(70 W/m oC) / (0.05 m)] [(1 m) (1 m)] [(150 oC) - (80 oC)]

= 98000 (W)

= 98 (kW)

### Conductive Heat Transfer Calculator.

This calculator can be used to calculate conductive heat transfer through a wall. The calculator is generic and can be used for both metric and imperial units as long as the use of units is consistent.

### Conductive Heat Transfer through a Plane Surface or Wall with Layers in Series

The heat conducted through a wall with layers in thermal contact can be calculated as

q = dT A / ((s1 / k1) + (s2 / k2) + ... + (sn / kn))                                (2)

where

dT = t1 - t2

= temperature difference between inside and outside wall (oC, oF)

Note that heat resistance due to surface convection and radiation is not included in this equation. Convection and radiation in general have major impact on the overall heat transfer coefficients

#### Example - Conductive Heat Transfer through a Furnace Wall

A furnace wall of 1 m2 consist of 1.2 cm thick stainless steel inner layer covered with 5 cm outside insulation layer of insulation board. The inside surface temperature of the steel is 800 K and the outside surface temperature of the insulation board is 350 K. The thermal conductivity of the stainless steel is 19 W/(m K) and the thermal conductivity of the insulation board is 0.7 W/(m K)

The conductive heat transport through the layered wall can be calculated as

q = [(800 K) - (350 K)] (1 m2) / ([(0.012 m) / (19 W/(m K))] + [(0.05 m) / (0.7 W/(m K))])

= 6245 (W)

= 6.25 kW

### Thermal Conductivity Units

• Btu/(h ft2 oF/ft)
• Btu/(h ft2 oF/in)
• Btu/(s ft2 oF/ft)
• Btu in)/(ft² h °F)
• MW/(m2 K/m)
• kW/(m2 K/m)
• W/(m2 K/m)
• W/(m2 K/cm)
• W/(cm2 oC/cm)
• W/(in2 oF/in)
• kJ/(h m2 K/m)
• J/(s m2 oC/m)
• kcal/(h m2 oC/m)
• cal/(s cm2 oC/cm)
• 1 W/(m K) = 1 W/(m oC) = 0.85984 kcal/(h m oC) = 0.5779 Btu/(ft h oF) = 0.048 Btu/(in h oF) = 6.935 (Btu in)/(ft² h °F)

## Related Topics

### • Heat Loss and Insulation

Heat loss from pipes, tubes and tanks - with and without insulation - foam, fiberglass, rockwool and more.

### • Insulation

Heat transfer and heat loss from buildings and technical applications - heat transfer coefficients and insulation methods to reduce energy consumption.

### • Thermodynamics

Thermodynamics of steam and condensate systems.

### • Thermodynamics

Work, heat and energy systems.

## Related Documents

### Acetone - Thermophysical Properties

Chemical, physical and thermal properties of acetone, also called 2-propanone, dimethyl ketone and pyroacetic acid. Phase diagram included.

### Ammonia - Prandtl Number vs. Temperature and Pressure

Figures and table with changes in Prandtl number for ammonia with changes in temperature and pressure.

### Ammonia - Thermal Conductivity vs. Temperature and Pressure

Online calculator, figures and tables showing thermal conductivity of liquid and gaseous ammonia at temperatures ranging -70 to 425 °C (-100 to 800 °F) at atmospheric and higher pressure - Imperial and SI Units.

### Arithmetic and Logarithmic Mean Temperature Difference

Arithmetic Mean Temperature Difference in Heat Exchangers - AMTD - and Logarithmic Mean Temperature Difference - LMTD - formulas with examples - Online Mean Temperature Calculator.

### Benzene - Thermophysical properties

Chemical, physical and thermal properties of benzene, also called benzol. Phase diagram included.

### Butane - Thermal Conductivity vs. Temperature and Pressure

Online calculators, figures and tables showing thermal conductivity of liquid and gaseous butane, C4H10, at varying temperature and pressure, SI and Imperial units.

### Carbon dioxide - Thermal Conductivity vs. Temperature and Pressure

Online calculator, figures and table showing thermal conductivity of carbon dioxide, CO2, at temperatures ranging from -50 to 775 °C (-50 to 1400 °F) at atmospheric and higher pressure - Imperial and SI Units.

### Convective Heat Transfer

Heat transfer between a solid and a moving fluid is called convection. This is a short tutorial about convective heat transfer.

### Cooling Mode - Heat Flux

Heat fluxes for various cooling or heat transfer modes.

### Energy Transfer Equation

Fluid energy transfer.

### Ethane - Thermal Conductivity vs. Temperature and Pressure

Online calculator, figures and table showing thermal conductivity of ethane, C2H6, at varying temperature and pressure - Imperial and SI Units.

### Ethylene - Thermal Conductivity vs. Temperature and Pressure

Online calculator, figures and table showing thermal conductivity of ethylene, also called ethene or acetene, C2H4, at varying temperature and pressure - Imperial and SI Units.

### Ethylene - Thermophysical Properties

Chemical, physical and thermal properties of ethylene, also called ethene, acetene and olefiant gas. Phase diagram included.

### Foods - Thermal Conductivities

Thermal conductivity of selected foodstuff like apples, beef, sugar and more.

### Heat Exchangers - Fouling and Reduced Heat Transfer

Heat-transfer in heat exchangers are reduced by fouling.

### Hydrogen - Thermal Conductivity vs. Temperature and Pressure

Online calculator, figures and table showing thermal conductivity of hydrogen, H2, at varying temperature and pressure - Imperial and SI Units.

### Insulation Materials - Operating Temperature Limits

Temperature limits for commonly used insulation materials.

### International Standard Atmosphere

International standard atmosphere in elevation -2000 to 30000 metre - pressure, temperature, density, viscosity, thermal conductivity and velocity of sound.

### Liquids - Thermal Conductivities

Some fluids and their thermal conductivities.

### Metals, Metallic Elements and Alloys - Thermal Conductivities

Thermal conductivities of common metals, metallic elements aand alloys.

### Methane - Prandtl number vs. Temperature

Figures and table showing changes in Prandtl number for methane with changes in temperature and pressure.

### Methane - Thermal Conductivity vs. Temperature and Pressure

Online calculator, figures and table showing thermal conductivity of methane, CH4, at temperatures ranging from -160 to 725 °C (-260 to 1300 °F) at atmospheric and higher pressure - Imperial and SI Units.

### Nitrogen - Prandtl number vs. Temperature and Pressure

Figures and tables showing Prandtl number of nitrogen at varying temperarure and pressure, SI and Imperial units.

### Nitrogen - Thermal Diffusivity vs. Temperature and Pressure

Figures and tables showing thermal diffusivity of nitrogen at varying temperarure and pressure, SI and Imperial units.

### Overall Heat Transfer Coefficients

Walls or heat exchangers - calculate overall heat transfer coefficients.

### Pipes and Cylinders - Conductive Heat Losses

Conductive heat losses through cylinder or pipe walls.

### Plastics - Thermal Conductivity Coefficients

Thermal conductivity of plastics.

### Propane - Prandtl Number vs. Temperature and Pressure

Figures and tables with Prandtl Number of liquid and gaseous propane at varying temperarure and pressure, SI and Imperial units.

### Propane - Thermal Conductivity vs. Temperature and Pressure

Online calculator, figures and tables showing thermal conductivity of liquid and gaseous propane at varying temperarure and pressure, SI and Imperial units.

### Solids, Liquids and Gases - Thermal Conductivities

Thermal conductivity coefficients for insulation materials, aluminum, asphalt, brass, copper, steel, gases and more.

### Steel Pipes - Heat Loss Diagram

Heat loss from steel pipes and tubes - dimensions 1/2 to 12 inches.

### Thermal Conductivity - Online Converter

Convert between thermal conductivity units.

### Thermal Conductivity - Unit Converting Table

Convert between thermal conductivity units - table and diagram.

### Thermal Resistivity and Conductivity

The ability of a material to resist flow of heat.

### Thermal Transmittance vs. Thermal Resistance

The thermal transmittance U vs. the thermal resistance R.

### Thermoplastics - Physical Properties

Physical properties of thermoplastics like ABS, PVC, CPVC, PE, PEX, PB and PVDF.

### Water - Thermal Conductivity vs. Temperature

Figures and tables showing thermal conductivity of water (liquid and gas phase) with varying temperature and pressure, SI and Imperial units.

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