Sensible Heating

Sensible heat is heat that is exchanged by a body or thermodynamic system in such a way that the exchange of heat changes the temperature of the body or system, as well as some macroscopic variables of the body or system while leaving certain other macroscopic variables of the body or system, such as volume or pressure, unchanged.

In contrast to latent heat, which is the amount of heat exchanged that is hidden, or that takes place without a change in temperature, sensible heat is the amount of heat that is exchanged. For instance, during a phase change such as the melting of ice, the temperature of the system that contains the ice and the liquid remains the same until all of the ice has melted. This holds true until all of the liquid has been absorbed by the ice. The concepts of latent and sensible are related to one another.

Both sensible heat and latent heat are just different expressions of the same type of energy. Instead, they are used to describe the transfer of heat under conditions that have been stated in terms of the influence that these conditions have on a substance or a thermodynamic system.

In the works of the early scientists who were responsible for laying the groundwork for thermodynamics, the term “sensible heat” had a distinct meaning in the context of calorimetry. In 1847, James Prescott Joule provided a definition for it by stating that it was an energy that was indicated by the thermometer.

Sensible heat

A sort of energy known as sensible heat can either be released into the atmosphere or taken in by it. Only the rise or fall in temperature of a substance or gas is relevant to the concept of sensible heat; phase change is not taken into account. The phase transition that occurs between the solid, the liquid, and the gas is important to understand in relation to latent heat. For the purpose of determining how much air moves through the electric furnace, the sensible heat formula is applied.

The formula for calculating sensible heat in the presence of a change in temperature is written as

Q sensible= 1.10 x cfm x (to – ti)

Where

Q Sensible = Heat gain from outside in Btu/h

1.10 equals the product of air’s heat capacity, which is 0.018 Btu per degree Fahrenheit.

Cfm = rate of flow of air entering from outside

to= The current temperature in degrees Fahrenheit

ti = Temperature inside in oF

Example 1

Determine the amount of sensible heat gained by a ventilation flow rate of 10,000 cfm when the temperature (to) of the air outside is 88 degrees Fahrenheit and the temperature (ti) of the air inside is 78 degrees Fahrenheit.

Solution

Q Sensible = 1.10 x cfm x (to – ti)

Q Sensible = 1.10 x 10000 x (88 – 78)

Q Sensible = 110,000 Btu/h

As a result, the gain in sensible heat is equal to 110,000 Btu/h.

Newton’s Law of Heating/Cooling

To begin, it is necessary to examine Newton’s Law of Heating and Cooling. This provides information regarding the transmission of thermal energy, also known as the energy associated with heat, from one source to another. The transfer of thermal energy always occurs from a source that is warmer to a source that is cooler, and this transfer will continue until the two things are at the same temperature, also known as the temperature of equilibrium.

When we return to the example of the pot of water, we notice that when we place it on a hot stove, the hot burner on the stove serves as the heat source and transfers thermal energy into the pot of water. This energy then leads the molecules of water to become excited and move at a quicker pace, which results in an increase in the temperature of the water.

Even after the burner is turned off, thermal energy is still being transferred from a hot source to a cold source while the pot is removed from the heat. In this scenario, the source of the hot water is the kettle, and the source of the cool water is the surrounding surroundings. Therefore, the hot water is making an effort to warm the environment around it; however, due to the fact that the environment is so much larger than the pot of water, it will require a great deal more thermal energy to raise the temperature of the surrounding environment than the pot of water can give off. Because of this, we are more likely to take note of the decrease in temperature of the water rather than the rise in temperature of the surrounding surroundings.

Latent and Sensible Heat

There are two types of heat that can be given out or taken in by the atmosphere: sensible heat and latent heat. There is a connection between changes in phase between solids, liquids, and gases and latent heat. Changes in the temperature of a gas or substance that do not result in a transition in phase are referred to as sensible heat.

The term “latent heat” refers to the energy that is either taken in by a substance during the transition from a gas to a liquid or solid or vice versa, or that is given off by the substance. For a substance to change from a solid into a liquid, for example, it needs to take in energy from the environment around it so that the molecules can be spread out into a volume that is larger and more fluid. This requires the substance to absorb energy. When a material goes from a phase that has a lower density, like a gas, to a phase that has a greater density, like a liquid, the molecules in the substance come closer together, which causes them to lose energy as a result of motion and vibration. This results in the substance emitting energy.

For instance, when water is brought to a boil over a stovetop, energy is drawn from the stovetop’s heating element and used to convert the liquid’s molecular structure into a gas known as water vapour. When water is frozen in ice cube trays and then placed in a freezer, the water emits energy as it changes from a liquid to a solid-state. This process is called entropy. This energy is extracted by the system that operates the freezer in order to maintain the freezer’s cold temperature.

Conclusion

Changing the temperature of a substance without causing any phase transitions requires a certain amount of energy, which is referred to as sensible heat. The soil or the air itself may be responsible for the change in temperature brought on by the sun’s radiation being absorbed. Alternatively, it may be the result of coming into contact with the warmer air that is a direct result of the release of latent heat (by direct conduction). The movement of air molecules, which in turn creates wind and vertical motions, is what drives the transfer of energy through the atmosphere. This transfer occurs as a result of both latent and sensible heat acting on the atmosphere. In the SI system, the unit of sensible heat is the joule (J), however, in the FPS system, the unit is the British thermal unit (Btu).