Heat Capacity
Just as we have so far considered the valences and the equilibrium of atoms and coefficients or indices in reaction equations. Now we turn to the so-called reaction energy. Energy, when measured, is the result of
work done.
Energy is never lost according to the first principal of thermodynamics, but, for the most part, is converted from e.g. well-usable chemical to bad-usable heat energy. Heat is, in principle, the simplest transferable
energy. It only requires for example the touch of two media and it already works, different temperatures required.
| For 'heat transfer' look at the video above. |
The temperature thus indicates in this case the direction of the heat transfer. It can be measured in Kelvin (K) or degrees Celsius (°C). When Celsius defined his scale in 1742, it was not yet known that there is an
absolute zero point of temperature. This was then found at about -273°C. and was chosen as the origin for the Kelvin scale at equal distances (0 K = -273°C.).
Unfortunately, today's calorie is only a measure of food in the general public and no longer standard for the specific heat. However, it is as dependent on the substance and was defined as the amount of heat required
to heat 1 gram of a specific substance by 1°C (or 1 K), and that was for water just 1 calory. This is expressed in Joule (J) (1 cal = 4.184 J) nowadays.
| The 'calories' turned into 'joule', when one realized that heat is just an energy. |
The specific heat (capacity) could also be seen as a measure of the ability to transport heat, that is, e.g. absorb heat in the engine and dispense in the radiator. Why does this happen with water which is unfavorable
for corrosion and freezing temperatures? Simply because water can absorb much more heat compared to all other media, may be because of the mobility of the hydrogen molecules. Engine oil does not even reach
half the specific heat with 1.8 J/(g*K) or 1.8 kJ/(kg*K).
If, therefore, only oil would be used instead of water for the cooling of a combustion engine, the cooling would have to be at least twice as large. Motor oil is used for cooling, but only because it comes closer to the hot
spots of the engine, but generally together with air cooling or even as an emulsion of oil and water (not in motor vehicles).
The fan has to perform enormously in the air cooling in relation to a water pump and takes much more energy. The more intense exchange of heat at the respective system limits is relevant here. And it is also a fact,
that antifreeze reduces the efficiency of a cooling system. The specific heat capacity of glycols is as far from reaching the one of water.
If you also want to know how much heat is required to bring 6.5 liters of water as a coolant from 20°C to 90°C, you must multiply its specific heat 4.181 J / (g * K) with the temperature difference of 70°C (or 70 K) and
the mass of 6,500 g and receive 1,902,355 J or 1,902 kJ. This measure is referred to as the heat quantity Q.
How nice that fuel has such a high energy density. You can check it out here. Tthe caloric value of super gazoline is 42.3 MJ /kg (=
42,300 kJ/kg). The 1,902 divided by the 42,300 discloses that one, assuming a heat
transfer without losses, is only 0.022 Kg (22 g - 0.03 liter) of gasoline. 02/17
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