Concept about Heat – Introduction to fundamental concepts of Biological Science including the organization and common characteristics of living matters, cell structures and functions, food production by photosynthesis, harvesting energy, mechanism of cells reproduction, genetics, evolutions, and Human Biology. Introduction to general chemistry including basic concepts about matter, atomic structure, chemical bonds, gases, liquid, and solids, solutions, chemical reactions, acid, bases, and salt;
organic and biochemistry including hydrocarbons and their derivatives, carbohydrates, lipids, proteins, enzymes, vitamins, and minerals, nucleic acids; principles of physics and applications to nursing including gravity and mechanics, pressure, heat and electricity; nuclear chemistry and nuclear physics, effects of radiation on human beings, and protection and disposal. The aim of the course is to acquire knowledge and skills in general biological science, general chemistry and physics.
Concept about Heat
Heat is a form of energy that is related to the motion of molecules. Every form of energy in nature can be transformed into heat energy.
Nature of Heat: Rubbing the hands together results the transformation of mechanical energy into heat energy. Body heat also results in part from friction of the blood against the walls of the blood vessels. Light energy from the sun strikes a body on the earth increases molecular motion within the body therefore, increases the temperature of the body.
Electric iron, electric stove, electric heater, are the examples of the transformation of electric energy into heat energy. Food is oxidized into carbon dioxide, water, and heat which maintain body temperature and supplies it with energy to work.
Definition of Heat:
In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than macroscopic work or transfer of matter.
Measurement of Quantity of heat
In a study of Basal Metabolism, it is important to know not only the body temperature but also the quantity of heat produced by the body. In FPS system, The Btu (British Thermal Unit) is the quantity of heat that enters or leaves one pound of mass of water when its temperature changes 1°F. Whereas in metric system the Calorie is defined as the quantity of heat that enters or leaves one gram of mass of water when its temperature changes by 1°C (or the 1° change is from 14.5° to 15.5°C).
The Kilogram – Calorie is used for calculating the energy value of foods and in BMR of the body.
Thermal Capacity and Specific Heat:-
Thermal capacity is the number of heat units required to raise a unit mass of a substance by 1° of temperature. Specific heat of a substance is the ratio of its thermal capacity to that of water at 15°c.
If the thermal capacity (s) of a substance is known, the heat (H) necessary to change temperature of the mass (m) from an initial temperature (t₁) to a final temperature (12) can he calculated by the following formula:
- H = ms (t2-t1)
Transmission of Heat:
When there is a difference in temperature between objects or between an object and its surroundings, heat is transferred from the warmer to the cooler region, e.g., heating of iron rod. There are three processes by which heat is transferred. These are (i) conduction, (ii) convection, and (iii) radiation.
(i) Conduction: In this process, heat energy is passed through a substance. The energy moves
from the warmer to cooler molecules of an object without producing any apparent motion. Substances conduct heat at different rates. Those conduct heat rapidly are called good conductors of heat and others that conduct heat slowly within them are called poor conductors. Poor conductors are used as insulators where the passage of heat is not required, e.g., nonmetals, cork fiberglass etc.
(ii) Convection: In this process, heat is transported by the actual movement of a portion of a heated liquid or gas, e.g., heating a water. Convection may be exemplified as “the hot air rises”. In clinical purposes, a Thermos bottle is used and sedative bath is prescribed to help emotionally disturbed patients. Steam inhalations and colonic irrigations transfer heat by convection.
(iii) Radiation: Heat is transferred from Sun to the earth without requiring any material medium. Heat energy can be transmitted through a vaccum from some source of heat. The process of emitting energy is called the radiation of an object.
Applications of Heat Transfer in the Human Body:
1. The temperature of the human body is the result of a balance between heat energy produced and heat energy lost. Heat energy produced in the body is from the oxidation of foodstuffs in the tissues whereas heat energy lost from the body is by conduction, convection, and radiation.
2. Most of the heat of the body is lost through the skin. Usually the surface temperatures of the body are 4° to 5°C lower than the internal temperatures.
3. A hot bath transfers heat to the body and increases metabolism. Bathing in cold water causes a loss of body heat from the skin.
4. The body loses heat by radiation from the skin. Under ordinary circumstances, radiation loses account for about 60% of the total heat loss of the body;
5. Body temperature may be raised or lowered artificially. It may be lowered artificially by refrigeration therapy to produce hypothermia.
6. The body temperature may be raised-artificially by increasing the environmental temperature. The rise in temperature is accomplished by special heating cabinets, hot water and steam bath, and heavy blankets. Muscular contraction is another source of heat energy.
Effects of Heat
1. Freezing and Melting Points: The temperature at which a liquid changes to a solid is called its freezing point. The temperature at which the same solid is changed back to a liquid is its melting point.
2. Vapour pressure: When a liquid is heated, its molecules leave the surface of the liquid. Pressure developed by the molecules of the liquid as it is changing to a gas is known as the vapour pressure of that liquid.
3. Boiling point: The boiling point of the liquid is the temperature at which its vapour pressure is equal to atmospheric pressure.
A certain quantity of heat is absorbed by the molecules of a liquid when it changes from a liquid to a vapour at the boiling point. This same amount of heat is liberated when the vapour (gas) condenses to a liquid.
The terms used for specifying heat absorbed or released during a change from one physical phase to another are heat of fusion, heat of solidification, heat of Vaporization, and heat of condensation.
Dry heat
- Red heat
- Flaming
- Hot air oven
- Incineration
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