Table of Contents
Introduction:
Thermal expansion is the increase in the volume of a material in response to an increase in its temperature. This phenomenon is observed in all materials and is a result of the increased kinetic energy of the material’s particles as temperature increases.
Thermal expansion is an important factor in the design of many different types of engineering and consumer products. Understanding the effects of thermal expansion on materials can help engineers and designers develop products that are strong, durable and resistant to changes in temperature.
The shape, volume, and area of matter can change as a result of temperature changes in thermal expansion. Temperature is defined as a monotonic function of a substance’s average molecular kinetic energy. When a substance is heated, its kinetic energy increases and a greater average spacing is maintained as the molecules begin to vibrate.
The unusual temperature rises as a result of material contraction, and the effect is small. It usually occurs within a short temperature range, which is referred to as strain, and temperature changes are used to divide it. This process is known as the materials coefficient of thermal expansion, and it usually varies with temperature. In the field of physics, Thermal expansion is the change in length, width, height, or volume of any material as a result of a change in temperature. Because atoms are closely packed in solids, thermal expansion is particularly noticeable. Thermal expansion of solids is used in a variety of situations in everyday life.
Overview:
Thermal expansion refers to the tendency of matter to change shape, area, and volume in response to temperature changes. Temperature is a monotonic function of a substance’s average molecular kinetic energy. The kinetic energy of a substance’s molecules increases when it is heated. As a result, the molecules begin to vibrate/move more and typically maintain a greater average separation. Materials that contract as the temperature rises are unusual; this effect is limited in size and occurs only within specific temperature ranges. The relative expansion (also known as strain) divided by the temperature change is known as the material’s coefficient of thermal expansion, and it varies with temperature.
There are three types of thermal expansion:
- Linear thermal expansion
- Aerial thermal expansion
- Volume thermal expansion
The coefficient of linear thermal expansion is defined as the relative expansion of the material divided by the change in temperature. In general, the coefficient of linear thermal expansion varies with temperature.
Thermal expansion of solids, liquids, and gases:
Thermal expansion is the tendency of matter to change shape, area, volume, and density in response to temperature changes, excluding phase transitions. The average molecular kinetic energy of a substance is a monotonic function of temperature. When a substance is heated, the molecules begin to vibrate and move more, usually increasing the distance between them. Substances that contract with increasing temperature are unusual and only occur in a few temperature ranges (see examples below). The relative expansion (also known as strain) divided by the change in temperature is known as the material’s coefficient of linear thermal expansion, and it varies with temperature. As the energy in particles increases, they begin to move faster and faster, weakening the intermolecular forces between them and thus expanding the substance.
When heated, all three states of matter (solid, liquid, and gas) expand. The atoms do not expand, but the volume they occupy does. When a solid is heated, the atoms around its fixed points vibrate faster. As a result, the relative increase in the size of solids when heated is small. Metal railway tracks are designed with small gaps so that when heated by the sun, the tracks expand into these gaps and do not buckle.
Liquids expand for the same reason as solids, but because the bonds between individual molecules are usually less tight, they expand more. This is the underlying principle of liquid-in-glass thermometers. A rise in temperature causes the liquid to expand, causing it to rise up the glass. Molecules in gases are farther apart and only weakly attracted to one another. Because heat causes molecules to move faster (heat energy is converted to kinetic energy), the volume of gas expands more than the volume of a solid or liquid. Gases in a fixed volume, on the other hand, cannot expand, so temperature increases result in pressure increases.
Thermal Expansion in Metals:
The kinetic energy of a material’s atoms causes it to expand (or contract). When a material is heated, the increase in energy causes the atoms and molecules to move faster and take up more space, causing the material to expand. This is true even for a solid, such as metal. However, different metals react to heat in different ways, depending on their individual coefficient of thermal expansion. For example, if you heated three wires of the same diameter but made of different metals — such as aluminium, steel, and tungsten — to the same temperature, each wire would expand by a different amount.
Naturally, the thermal properties of the material a customer selects for their metal components influence the potential for heat expansion. So, if you have a very tight tolerance part, you should probably choose a metal that is highly stable and does not vary a lot due to temperature changes.
When a part is measured, it can affect the temperature and, as a result, the dimensions of the part. A freshly cut part, for example, maybe hot or cold and thus have a slightly different dimension than if it was measured later in Quality Assurance (QA) or when inspected upon arrival at a customer’s manufacturing location. Metals expand when under less pressure, so atmospheric pressure can have a very subtle effect on the part measurement. That means that if you cut and inspect a part at sea level and then ship it to Denver, you may get a very slightly different measurement at the higher altitude — of course, this is only noticeable when measuring the smallest dimensions and tightest tolerances.
The coefficients of linear thermal expansion and volumetric thermal expansion V are related in isotropic materials by v=3α. Typically, the coefficient of volumetric expansion for liquids is listed, and linear expansion is calculated here for comparison. The thermal expansion coefficient of common materials, such as many metals and compounds, is inversely proportional to the melting point.
For metals, in particular, the relationship is: α≈0.020/Tm
Thermal Expansion Formula:
Thermal expansion is a common natural occurrence. It happens when an object expands and grows larger due to a change in temperature. This is due to the heat produced by the temperature. The average kinetic or movement of the energy of the molecules in a substance is defined as temperature. A higher temperature indicates that the molecules are moving more quickly on average. When we heat something, the molecules move faster. As a result, they occupy more room. The molecules tend to move into previously empty spaces. As a result, the size of the object grows.
Linear Expansion:
When there is a change in length, linear expansion occurs.
The linear expansion formula is as follows:
∆L/ L 0=αL∆T
When there is a change in volume due to temperature, this is referred to as volume expansion. The volume expansion formula is as follows:
∆V/ V 0=αV∆T
Area expansion occurs when there is a change in area as a result of a temperature change.
The formula for area expansion is as follows:
∆A/A 0=a A∆T
Volumetric Expansion Coefficient:
The fundamental relationship between linear expansion and temperature change, as well as the relationship between volume expansion and temperature change. Using these formulas in the volume expression will also yield the desired result. We will also cover the fundamentals of Archimedes’ principle, which describes how the volume of a liquid changes when a given mass is placed inside it.
Volume expansion is defined as the increase in the volume of a solid as the temperature rises, i.e., on heating.
If we consider and as the linear and volumetric expansions, the linear expansion is given by:
L→L(1+a∆T)
Similarly, volume expansion is denoted as follows:
V→V(1+γ∆T)
Here, we know that:
V=L³
When we plug the linear expansion value into this equation, we get:
V=L³(1+a∆T)³
V=L³ (1+3 a∆TO+2 a∆T+a²∆T²+a³∆T³)
We can ignore quadratic and cubic terms because the thermal expansion coefficient is of the order of parts per million per 0°.
V=L 3(1+a∆T)3 =3 a
The volume expansion coefficient is three times that of the linear expansion coefficient.
FAQs:
Question 1: What is thermal expansion?
Answer 1: Thermal expansion is the process by which an object or body expands when heated.
Question 2: Thermal expansion affects the properties of matter?
Answer 2: Thermal expansion has an impact on the body’s shape, volume, area, and density.
Question 3: What is the coefficient of linear thermal expansion?
Answer 3: The coefficient of linear thermal expansion is defined as the relative expansion of the material divided by the change in temperature.
