Background Notes on Measures - 5
 Contents are: Specific HeatCapacity ThermalConductance ThermalConductivity Heat FluxDensity
Additional information can be found in the Dictionary of Units
In all of this work on heat the SI unit is the degree kelvin [°K]
However, note that the °C is the same size as the °K so they may be freely interchanged.
(That applies only to the degree or temperature range and NOT to the actual temperature itself.)
The values of the Btu and calorie are those of the International Table.

SPECIFIC HEAT CAPACITY
It also referred to as Specific Entropy
For any particular substance, its Specific Heat Capacity is the measure of the quantity of (heat) energy needed to raise the temperature of a unit quantity of the substance through 1 degree of temperature. Note the 'unit quantity' may be either that of mass or volume. In the SI system use
joules [J] for the energy
kilograms [kg] OR cubic metres [m³] for the quantity
kelvin [K] for the temperature degree. (see Note above)

Other units often still seen are the British Thermal Unit [Btu] or calories for the energy, and the °F for the degree.

Solids and liquids usually have only one value for their Specific Heat Capacity which can be used for most practical work. Only in the most accurate work is there a need to seek a value adjusted to the prevailing conditions (pressure and temperature usually).
Gases however always have two values. One for the case when the pressure (of the gas) is kept constant, and one for when the volume is kept constant.

Approximate values in J / kg °K of the Specific Heat Capacities of some substances are
 air 1000 lead 125 aluminium 900 mercury 140 asbestos 840 nylon 1700 brass 400 paraffin 2100 brick 750 platinum 135 concrete 3300 polythene 2200 cork 2000 polystyrene 1300 glass 600 rubber 1600 gold 130 silver 235 ice 2100 steel 450 iron, cast 500 water 4200
Specific Heat Capacity can be thought of as a measure of how much heat is needed to warm the substance up. In the table above we can that it is easier to warm up gold and lead than it is to warm up concrete and water. The small values show that not a lot of energy is needed to produce a temperature change, whereas the large values indicate a lot more energy is needed.

Go to the MASS or VOLUME Specific Heat Capacity Conversion Calculator

THERMAL CONDUCTANCE
 Also known as Heat Transfer CoefficientIt is a measure of the rate at which heat energy flows through a surface. A typical use for this is in a building, when assessing the heat which is lost through the external walls.It is measured by the amount of energy which flows through a unit area, in unit time, when there is a unit temperature difference between the two sides of the surface. So, a logical expectation of its units would be something like *joules per square metre per second per degree kelvin* or J/m² s °KAnd, looking the 'older' types of units listed in the calculator it will be seen that they are of that form, like Btu/ft² sec °F However, when looking at the SI units it will be seen that there appears to be no unit of time. So what has happened?In the SI the units *joule/second* are equal to (are the definition of) a watt (which is a measure of power) and that fact has been used in reducing the units for Conductance to watts/sq.metre  degree kelvin [W/m² °K]So, more correctly, the definition should not refer to 'energy which flows' but to 'power which flows' and leave out the reference to 'unit time'.

Go to the THERMAL CONDUCTANCE Conversion Calculator

THERMAL CONDUCTIVITY
Very similar to, and often confused with, Conductance as described above. The difference to be noted is that Conductance involves area while Conductivity involves length.
For any particular substance, its Thermal Conductivity is the measure of the quantity of (heat) energy which flows through a unit length, in unit time, when there is a unit temperature difference between the two ends of the length.
The SI units for this measure are
watts/metre degree kelvin [W / m °K]
See the explanation given above, under Conductance, as to why there is no mention of time in those units. Once again, there is in the older units.

Thermal Conductivity can be thought of indicating how quickly the heat will get to you. Imagine holding a bar and putting one end of it in a fire (like a poker). The end you were holding would warm up until (eventually) it became too hot to hold. How long this would take would depend upon the length of the bar and the material of which it was made. The table shows that silver (with a high value) would be quicker in getting the heat to your hand than one made of steel (with a lower value). A bar of concrete would be much slower still. There are other materials whose values are even lower, but it might be rather difficult (or impossible) to use those.

Approximate values in W / m °K of the Thermal Conductivities of some substances are
 air 0.02 lead 35 aluminium 240 mercury 140 asbestos 0.2 nylon 0.3 brass 120 paraffin 0.2 brick 1 platinum 70 concrete 0.1 polythene 0.3 cork 0.05 polystyrene 0.08 glass 1 rubber 0.2 gold 300 silver 420 ice 2 steel 60 iron, cast 60 water, fresh 0.6

THERMAL RESISTIVITY is the inverse of Conductivity.

Go to the THERMAL CONDUCTIVITY Conversion Calculator

HEAT FLUX DENSITY
 Also known as Heat Flow Rate IntensityThis is a measure of the rate at which heat energy flows into or out of a surface.It is expressed simply as the amount of energy which flows through a unit area, in unit time. So, a logical expectation of its units would be something like *joules per square metre per second* or J/m² sAnd, looking the 'older' types of units listed in the calculator it will be seen that they are of that form, like Btu/ft² sec However, (as explained above in Thermal Conductance) when looking at the SI units it will be seen that there appears to be no unit of time. Why?In the SI the units *joule/second* are equal to (are the definition of) a watt (which is a measure of power) and that fact has been used in reducing the units for Flux Density to watts/sq.metre [W/m²]A typical example of the use of this measure is in working out anticipated ground temperatures as a result of the Sun's heat falling on the Earth's surface.

Go to the HEAT FLUX DENSITY Conversion Calculator

 Go to the the top OR the Dictionary of Units OR the Calculator Menu