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Heat Transfer


Total Normal Emissivities of Selected Materials
Total Normal Emissivities of Selected Materials

Radiative heat transfer between two or more surfaces can be approximated using the total, normal emissivity. This article provides empirically determined total normal emissivities for a number of materials including metals, metal oxides, common building materials and paints.


Calculation of Emissivity for Metals
Calculation of Emissivity for Metals

At any given temperature, real materials emit less energy than that of a black body. The effectiveness of a material at emitting energy is represented by a radiative property called emissivity, which is the ratio of the actual energy emitted by the material to that of a black body at the same temperature. This article will provide an overview of the methods available for calculating the spectral, spectral-directional, hemispherical and total hemispherical emissivity for metals.


Emissivity
Emissivity

At any given temperature, real materials emit less energy than that of a black body. The effectiveness of a material at emitting energy is represented by a radiative property called the emissivity factor, which is the ratio of the actual energy emission of the material to that of a blackbody at the same temperature. This article will provide an overview of emissivity and its many formulations.


Laws of Thermodynamics

The laws of thermodynamics are fundamental laws which describe the behaviour of heat and work in a thermodynamic system. These laws forbid phenomena such as perpetual motion machines, a hypothetical machine the development of which was pursued during the industrial revolution.


Heat of Combustion

The heat of combustion is the energy liberated when a substance undergoes complete combustion, at constant pressure usually in an environment with excess Oxygen. The heat of combustion is utilised to quantify the performance of a fuel in a combustion system such as furnaces, power generation turbines and motors. This article describes the heat of combustion and provides a list of heats of combustion for commons fuels and fuel components.


Calculating Thermal Relief Flow Rates

For long sections of pipe, the thermal expansion of trapped liquid can be significant. It is often required that the increase in volume of the fluid be determined in order to select suitable thermal relief valves to protect the integrity of the pipework. This article details how to calculate the required relief flow rate to prevent over pressure due to thermal expansion.


Flash Steam
Flash Steam

When condensate is discharged from a high pressure steam system to a system of lower pressure, a proportion of the condensate may vaporise to form low pressure steam. This is known as flash steam and may be utilised in low pressure heating systems to improve plant efficiency. This article discusses the generation of flash steam and presents a method by which it can be quantified.


Thermal Conductivity of Metals and Alloys

This article provides thermal conductivity data for a selection of metals and alloys. Thermal conductivity measures a materials ability to allow heat to pass through it via conductance.


Thermal Conductivity of Common Materials

This article provides thermal conductivity data for a selection of common materials. Thermal conductivity measures a materials ability to allow heat to pass through it via conductance.


Blackbody Radiation
Blackbody Radiation

A blackbody is an idealized volume which emits and absorbs the maximum possible amount of radiation at a given temperature in all directions over a wide range of wavelengths. Blackbodies are perfect emitters and absorbers of radiation and therefore useful as a standard when studying radiative heat transfer systems where the amount of radiation emitted and absorbed is a also a function of material properties. This article describes the basics of a black body and presents equations to describe its emissive characteristics.