Question

What is sensible heat? How is the sensible heat loss from a human body affected by \((a)\) skin temperature, \((b)\) environment temperature, and \((c)\) air motion?

Short answer

Answer: Sensible heat is the heat energy associated with temperature changes in a substance without causing a change in its phase. Sensible heat loss from a human body can be affected by skin temperature, environment temperature, and air motion. Higher skin temperature increases heat loss, as there is a greater temperature gradient between the body and the environment. Higher environment temperature decreases heat loss as the temperature gradient decreases. Increased air motion enhances heat loss by removing the insulating layer of still air around the skin, increasing the heat transfer rate through convection.

Step-by-step solution

Define Sensible Heat

Sensible heat is the heat energy associated with changes in temperature in a substance without causing a change in its phase (i.e., solid, liquid, or gas). When an object's temperature changes, energy is either absorbed or released, causing a gain or loss of sensible heat.

Discuss the Effect of Skin Temperature on Sensible Heat Loss

(a) Higher skin temperature increases the sensible heat loss from a human body. When the skin temperature is higher, there is a greater temperature gradient between the body and the surrounding environment. This gradient causes the heat to flow from the body into the environment through conduction, convection, and radiation. The greater the temperature difference between the skin and the environment, the larger the amount of heat energy lost from the body.

Discuss the Effect of Environment Temperature on Sensible Heat Loss

(b) Higher environment temperature decreases sensible heat loss from a human body. As the temperature of the surrounding environment increases, the temperature gradient between the body and the environment decreases. As a result, the rate of heat flow from the body to the environment decreases, causing a reduction in the amount of sensible heat loss.

Discuss the Effect of Air Motion on Sensible Heat Loss

(c) Increased air motion around the body, such as wind or air circulation, enhances sensible heat loss. Faster moving air helps to remove the insulating layer of still air around the skin (called the boundary layer) through convection. This action increases the heat transfer rate from the skin to the air, thus amplifying the sensible heat loss from the body. In other words, the faster the air moves around the body, the more heat is lost to the environment through convection.