[Chemistry Class Notes] on Sensible Heat Formula Pdf for Exam

To explain what is sensible heat, it is a form of energy emitted into the atmosphere or absorbed. The concern of sensible heat is given as only the change in the temperature of the gas or the material but not in the phase shift. The phase shift between the solid, liquid, and gas phases is relevant to the latent heat. The airflow in an electric furnace can be calculated using the sensible heat formula. This is a simple sensible heat definition.

Sensible Heat Formula

Besides the sensible heat definition, the sensible heat formula having a change in temperature is expressed as follows:

[Q_{Sensible}=1.10times cfmtimes (t_{0}-t_{i})]

Where

Q sensible  is the Heat gain from outside in Btu/h,

1.10 is the product of heat capacity of air 0.018 Btu/oF, Cfm is the rate of flow of air entering from the outside, to is the Temperature outside in oF, and ti is the Temperature inside in oF.

Sensible Heat Examples

Let us suppose the water at 30℃ is heated with the gas stove. The portion of the thermal energy till the temperature reaches 100℃ is the sensible heat meaning And the thermal energy portion that converts water to steam without changing the temperature (100℃ is constant) is known as the latent heat. Here, the saturation temperature is 100℃ because the process occurred at atmospheric pressure.

Sensible Heat vs. Latent Heat

The internal energy portion of a system associated with the molecules’ kinetic energy is known as the sensible heat or sensible energy. The degree of activity and the average velocity of the molecules is proportional to the temperature. Therefore, at higher temperatures, the molecules will possess higher kinetic energy, and as a result, the system will hold higher internal energy.

Also, the internal energy is associated with the intermolecular forces between the system’s molecules. If sufficient energy is added to the molecules of either a solid or liquid, they will overcome these particular molecular forces and just break away, turning the system into gas. This is the phase change process and due to this added energy, a system in the gas phase is at a very higher internal energy level than it is available either in the solid or the liquid phase. The internal energy associated with the phase of a system is referred to as latent heat or latent energy.

Example

Calculate the sensible heat gain of the ventilation flow rate of 10,000 cfm when the temperature (to) of the outside air is given as 88oF and the inside air temperature (ti) is given as 78oF.

Solution

Qsensible = 1.10 cfm (to – ti)

= 1.10 10,000 (88 – 78)

= 110,000 Btu/h

Thus, the sensible heat gain is given as 110,000 Btu/h.