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Conduction and materials

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Introduction

Chris mullet Conduction-: There are lots of different types of conduction. The main theory behind conduction is where vibrating molecules come into contact with adjoining molecules and set them vibrating faster and hence they become hotter; this process is carried on throughout the substance without appreciable displacement of the particles. This is commonly known as Conduction. There is also Thermal Conductivity. This is as follows; because some materials allow heat to pass through them quite quickly. Most non-metals allow heat to pass through them slowly. Materials that allow heat to pass through more slowly are called poor Conductors of heat or Insulators. Stripping knives, soldering irons, cooker or oven doors are made of metal and, when heated, quickly become too hot to be held or touched. ...read more.

Middle

Heat travels through all materials but some will allow it to travel through quickly while through others it may be very slow. This heat movement is known as COONDUCTION. Materials, which allow fast movement of heat, are known as good Conductors. When the movement is slow they are called Poor Conductors. Copper is a very good conductor of heat and is called a material of high TTHERMAL CONDUCTIVITY (Thermal means heat). In comparison, still air is a poor conductor of heat so has a low thermal conductivity. The amount of heat, (Q), transmitted between the surfaces of a slab of material of uniform thickness and composition varies: (a) Directly with the area (A) (b) Directly with the temperature difference between the faces ((2-(1) (c) Directly with the time of flow (T) ...read more.

Conclusion

Typical values of 'k' for different materials when dry are given in figure that ive produced (thermal conductivity increases with moisture content). Find how much heat is conducted per second through 1m2 of sheet glass, 5mm thick, when the temperature difference between the faces is 10 deg C. (k=1.05W/m deg C) Materials Thermal Conductivity k W/m deg C Resistivity r (=1/k) Asphalt 1.2 0.9 Asbestos Cement 0.3 3.5 Brickwork (in commons) 1.3 3.5 Dense Concrete 1.4 0.7 Clinker Concrete 0.4 2.8 Sandstone 1.3 0.8 Granite 2.7 0.4 Plaster 0.6 1.8 Wood 0.1 7.7 Glass 1.1 1.0 Plaster Board 0.2 6.3 Slag wool 0.1 20.0 Cork Board 0.1 20.0 Fiber Glass 0.0 25.0 Expanded Polystyrene 0.0 3.3 Table of thermal Conductivity and Resistivity (Typical Values for dry Materials) Q=kAT((2-(1) D =1.05x1x1x10 =2100J 0.005 This is a rate of heat loss of 2100W (2100J/s) per square meter. ...read more.

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