What is Specific Heat of Substances? Specific Heat of Water

In thermodynamics and fluid mechanics, this value of substances is very important in such applications. We use this property to calculate the different kinds of engineering systems. Also, we are using these values in different theoretical calculations. But before using it, we need to understand what specific heat is and what it means on a thermodynamical basis. So, you can find this information here;

• What is specific heat?
• What are the types of it?
• What are the specific heats of general substances?
• In which applications do we use it?
• FAQs

What is the Specific Heat Capacity?

Heat transfer and energy are very common terms in engineering calculations. They are very important in the development of engineering systems. So, we need to know how much heat substances can absorb or carry. Because of this reason, people or scientists developed a term which is specific heat capacity.

This is the capability of a substance and how much energy that can absorb. We compare the substances by comparing them on a unit mass basis. Similarly, this capacity means, the energy value to raise a unit mass of substance in unit temperature. The unit of mass and the temperature can change.

For example, we need 4.5 kJ energy to raise the temperature of 1kg iron to 10°C. So, we can calculate it by using the specific heat capacity of iron.

Specific Heat Capacity in Constant Volume and Constant Pressure

Furthermore, there are two common types of these capacities of substances. These types are specific heat capacity in constant volume and constant temperature.

We need this distinction. Because in engineering calculations both in thermodynamics and fluid mechanics, we have constant pressure and constant volume processes. And also, the specific heat capacities of substances change in constant volume and constant temperatures.

Specific Heat Capacity in Constant Volume

In constant volume processes, the pressure can change. For example, if you give energy to a gas inside a constant volume cylinder, the pressure of the gas will increase. But volume does not change. So, in the calculations, we use specific heat capacity in a constant volume.

So, capacity in constant volume is the value in the constant volumes. We can not use this value under constant pressure.

Specific Heat in Constant Pressure

Also, this logic is the same for this value in constant pressure. For example, think about a piston-cylinder system. If we give energy to this system, the piston will move upward. But the pressure of this system will not change. So, we will use the constant temperature value for that gas.

Why There is a Difference between Constant Volume and Constant Pressure?

Always, the constant pressure specific heat is greater than the constant volume. Because to raise the temperature of the substance we need to give energy. But also, we need to give some additional energy to hold the pressure of the system constant.

For example in the piston cylinder system, we need to give the energy to raise the temperature of the gas inside it. Also, we need to give the energy to move the piston upward. Because of this additional energy, the constant pressure value is greater than in constant temperature.

Units

Units are very important. But also, a unit of this value is very important. You need to use the proper set of units while you are making your calculations.

The units of specific heat in constant volume and constant temperatures are the same. This is the kJ/kg°C or kJ/kg.K. Also in English units, it is Btu/oF.

Specific Heats of Certain Substances

In general, we are using the specific heat values of certain substances such as water. Also in heat transfer analyses, we are using metal elements.

What is the Specific Heat Capacity of Water?

The capacity of water is 4.184 kj/kg.K. This value is for the liquid state of the water.

Specific Heat Capacities of Other Substances

• Ice: Ice is the solid form of water. This value is 2.39 kj/kg.K.
• Ethylene Glycol: We use Ethylene Glycol as antifreeze in our cars. This value is 2.39 kj/kg.K.
• Glass: The capacity of glass is very important in melting processes. It is 0.8 kj/kg.K.
• Iron: Iron is also a very important element in the metal industry. For example in casting operations, we are using this capacity value which is 0.45 kj/kg.K.
• Aluminum: Aluminum is also a very important element in heat transfer applications. This value of aluminum is 0.897 kj/kg.K.
• Copper: Also, we use copper elements in different heat transfer applications such as tubings in heat exchangers. This value is 0.385 kj/kg.K for copper.

Thermal Conductivity and Specific Heats

There is a strict relation between the thermal conductivity and the specific heat of substances. With the increasing thermal conductivities, this value of substances decreases. It represents the total energy that a material can absorb. So, we need to give lots of energy to raise the temperature of all portions.

So, the thermal conductivity will be very low for materials with high values. Materials with low specific heat will heat up more rapidly. This means they will conduct more rapidly.

For example, if you take a look at the values above, metals have very low values. Also, metals are the best in conduction.

Engineering Applications

There are various kinds of engineering applications where we use specific heat capacities of substances generally. There are various kinds of thermodynamical and heat transfer applications in which we use constant volume and constant pressure values.

Heat Transfer Calculations

If there is a heat transfer between bodies or environments, we’ll use this value. Because we need to calculate the final temperature of the substance. So, we need to know the specific heat capacity of that substance. It is giving information about how much Celsius this body will raise by given energy.

For example, if we are calculating the temperature rise of solids or open environment, we use the capacity of constant pressure. Because the pressure of the environment does not change with the increasing temperature.

For example, we are using this formula in energy transfers to bodies generally;

In this equation,

Q: This is the total heat energy in kJ or BTU.

m: Total mass of the body which is kg or lb.

C: Specific heat of the body

ΔT: Total temperature change in K or °F.

You can see here, that with the increasing specific value, we need to give much more energy to increase the temperature of the body.

Thermodynamical Applications

In thermodynamical calculations, specific heats of substances have a very big importance. For example, in the calculation of the total work of a piston-cylinder system, we need to calculate the total temperature raises and drops of gas. Also, we are using constant pressure values of gases in these situations.

And also in pressurized vessel systems, we use constant volume value. If we give energy to pressurized vessels, we need to calculate the total temperature change by using the constant volume value of that gas.

Heat Exchangers

The tubing systems of heat exchangers must conduct heat very well. So, we need to use materials that have specific heats that are very low. These tubing materials are generally copper and copper alloys. Because this value of the copper alloy is one of the lowest one. This means the thermal conductivities of copper are very high.

Conclusion

So, we tried to give answers to the question of what is the specific heat of substances. It is a very important phenomenon in physics and engineering. There are various kinds of applications of these values in engineering.

Also, there are two types of this value; constant volume and constant temperature. It is very important to use the correct one in engineering calculations.

We use these values in heat transfer, thermodynamics, and practical applications.

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