Understanding Temperature, Heat, and Heat Transfer

Posted on Aug 26, 2024 in Physics

1.1 Temperature and Dilation

Temperature

Temperature (T) is a measurement of heat or thermal energy that indicates how cold (low temperature) or hot (high temperature) an object is. Temperature shifts produce variations in the properties of matter, such as volume.

The instrument used to measure temperature is the thermometer. This instrument works by detecting a change in the property of a substance; most thermometers detect the change in a substance’s volume: when temperature increases, the substance expands. Nowadays, the most common thermometer is made of a glass tube filled with mercury or red-colored alcohol; when the temperature increases, the liquid expands (more than glass), indicating the increase on a scale placed on the glass.

Temperature Scales

Relative temperatures (t) are defined by references to the fusion and boiling points, whereas absolute temperatures (T) are based on absolute zero (when the material’s particles are immobile).

Conversions

Fahrenheit to Celsius Degrees
Celsius to Fahrenheit Degrees
Celsius to Kelvin Degrees
Fahrenheit Degrees to Rankine
Kelvin to Rankine

Comparative Scale Chart

Dilation

Dilation is a solid’s most common change of size or dimension due to temperature shifts. There are three types:

1. Linear Dilation

   A solid’s dimension shift in one direction.

   			Length changes.
   		Linear dilation coefficient and a property of matter.

2. Superficial Dilation

   A solid’s dimension shift in two directions.

   			Area changes.
   		Superficial dilation coefficient ().

3. Volumetric Dilation

   A solid’s dimension shift in all directions.

   

Table 1.1 – Linear Dilation Coefficients

Example 1.1

A round iron sheet has a 20cm radius and is at 73°F. This sheet is submerged in boiling water. After a certain time, what will be the sheet’s area?

Answer

First, the initial area of the sheet is calculated at 73°F:

According to Table 1.1, iron’s dilation coefficient is 0.66×10^-5/°F; therefore, its superficial dilation coefficient would be:

The sheet’s area change would result as follows:

To calculate the new area, add the initial area to the area’s change:

1.2 Heat: Concepts and Applications

Heat is energy transferred from one material to another due to a difference in temperatures. Heat always flows from the object of higher temperature to the one with a lower temperature. Its measurement unit in the International System is the joule.

Therefore, temperature is the measurement of thermal energy, whereas heat refers to the transfer of energy.

Heat quantity (Q) needed for a temperature change (ΔT) depends on the material’s specific heat (c) and mass. The measurement unit of Q is joules (J).

Table 1.2 – Specific Heats

Latent heat of fusion (L_f): is the heat needed to change 1 kg of a substance from a solid to a liquid state.

Latent heat of vaporization (L_v): is the heat needed to change 1 kg of a substance from a liquid to a gas state.

The heat involved in a phase change depends on the substance’s mass and the latent heat of the process (L).

Table 1.3 – Latent Heats

Example 1.2

How much heat must be added to 0.5 kg of ice at -15°C to transform it into vapor?

The first step is to gather the data given in the problem and obtained from the tables:

Initial Temperature of Ice		Specific Heat of Water
Fusion Temperature		Latent Heat of Fusion
Boiling Temperature		Latent Heat of Vaporization
Specific Heat of Ice

Once you have all the information, you can start solving the problem:

1. Ice Temperature Increases from -15°C to 0°C

   

2. Ice Transforms into Water

   

3. Water’s Temperature Rises from 0°C to 100°C

   

4. Water Transforms into Vapor

   

The total heat addition required is the sum of the four previous amounts.

1.3 Heat Transfer

Heat transfer is a science that studies the speed at which heat flows through a medium due to temperature differences.

The following three phenomena intervene in heat transfer: