In physics, the word heat brings to our minds a feeling of hotness, for instance the type of feeling we experience during a cloudless harmattan afternoon or during vigorous exercises. Apart from making us feel uncomfortable during afternoon, heat makes more comfortable during a cold harmattan morning.

In general, heat serves man in various ways, in cooking, drying clothes, warming our homes. In industries, heat is used in extraction of metals from their ores, for shaping, softing, cutting, hardening, coating of metals and lot more.

Definition

 

Heat is the form of kinetic energy which cause a rise in temperature in a body as it is absorbed or a reduction in temperature as it is lost to the environment.

Heat physics is an essential aspect of physics. Since is applied in various aspect (field) of physics as a course of study. For instance, if a block of heat copper is placed in a beaker containing cold water we know from experience that the block of copper cools down and the water warms up until they come to equality of temperature. What causes this decrease in the temperature of the copper block and the increase in the temperature of water?. We say that this was caused by the fact that (heat) energy was transfer from the copper block to the water.

Heat is a form of energy that is transferred across a boundary by virtue of a temperature difference or temperature gradient. (Adapted from). Thermodynamics Gordon J (1959).

Implied in this definition is the very important fact that a body dose not contains heat, but that heat is transient phenomenon.

If we consider the hot block of copper as one system and the (cold) water

In the beaker s another system. When the copper is placed in the water and the two are in thermal communication, heat is transferred from the copper to the water until equilibrium of temperature is established. At that point we no longer have heat transfer, since there is no temperature difference. If follows that heat is identified at the boundaries of the system, hence heat is defined as energy being transferred across the system boundary.

Other definition has it as follows

(a) Heat is a measure of the total internal energy of a body. (b) Heat defined as energy in transit (motion).

(c) Heat is a form of energy possessed by a substance by virtue of the vibration movement, i.e. kinetic energy of its molecules or atoms.

The significance and common factors in these definitions is that,

1. A form of energy
2. A measure or internal energy
3. Energy in motion (transit)
4. Energy of a body as a result of the vibration movement of its molecules

Heat is measured in joule J after the scientist who worked on heat other units as the BTU (British thermal units) have been in place but the generally accepted unit is the joule (J) or calories. For instance one BTU is equivalent to 252 calories

Definition of Relevant Terms in Thermal Physics

1. The study of heat energy for effectiveness, there must be absolute consideration of relevant terms in thermal (heat) physics. Some are as follows
2. Meat flow: this represent the movement of thermal energy from place to place
3. Thermal conductively: this is the property of material related to its ability to transfer heat through itself
4. Heat transfer rate: this is the quantity of heat energy flowing per unit of tie through an object
5. Temperature: this is the amount of their(heat) thermal energy available. It is measured in celcius or Kevin scale.
6. Conductors: these are materials which allow the passage of heat and electricity
7. Thermodynamics: this is the terms used to designate the science of relational between heat and power. It is concerned with the amount of heat transfer as a system undergoes a process from one equilibrium state to another

Historical Background

Heat has always been perceived to be something’s that produces in us a sensation of warmth and one would think that the nature of heat is one of the first things understood by mankind. But it was only in the middle of the nineteenth century that we had a true physical understanding of the nature of heat, this owed to the development at that time of the kinetic theory, which creates molecules as my balls that are in motion and thus posses kinetic energy.

Heat is then defined as the energy associated with the random motion of atoms and molecules. Although it was suggested in the eighteenth centuries that heat is the manifestation of motion at the molecules level (called the live for a), the prevailing view of heat until the middle of the nineteenth century was based on the calorie theory proposed by the French chemist Antoine Lavoisier (1743-1794)

In 1789. The calorie theory asserts that heat is a fluid like substance called the caloric that is a mass less, colorless, odourless and tasteless substance that can be poured from one body into another. When calorie was added to a body, its temperature increased, and when caloric was removed from a body, its temperature decreased. When a body could not contain any more caloric, much the same was as when a glass of water could not dissolved any more salt or sugar, the body was said to be saturated with caloric. This interpretation give rise to saturated liquid and vapour which are still in date to day.

The caloric theory came under attack soon after its introduction. It maintained that heat is a substance that could not be created or destroyed. Yet it was known that heat can be generated indefinitely by rubbing one’s hands together or rubbing two pieces of wood together. In 1798, the American Benjamin Thompson (1753-1814) showed generated continuously through friction. The validity of the caloric theory was also challenged by several others. But it was the careful experiments of the Englishman James P. Joule (1818-1889)published in 1843 that finally convinced the skeptics that heat was not a substance after all, and thus put the caloric theory to a thing of the past. Although the caloric theory was totally abandoned in the middle of the nineteenth century, it contributed greatly to the development of thermodynamics and heat transfer.

The term thermodynamics was coined by James Joule in 1868 to designate the science of relations between heat and power.

Sources of Heat Energy

However, there are situation s in which heat generation occurs in a conducting medium. A few common examples are, a nuclear fuel element irradiated by high energy neurons to trigger nuclear fission, doctor in which heat generation occurs because of the flowing current (electric energy) and a catalyze pellet in which heat generation occurs because of a chemical reaction taking place inside the pellet, (chemical energy).

Conclusively, heat energy can be generated from Electrical energy, Nuclear energy, Chemical energy and mechanical energy, it occur through the functional forces between two solids in contract for example, two pieces of amber robbed together produces heat mechanically.

Heat Transfer Machanisms

 

Heat defined as a form of energy that can be transferred from one system to another as a result of temperature difference. Thermodynamic analysis is concerned with the amount of heat transfer as a system undergoes a process from one equilibrium states to another. The science that deals with the determination of the rate of such energy transfer is the heat transfer. As stated above, the transfer of nergy as heat is always from the higher temperature one, and heat transfer stops when the two medium reach equithermal state (equilibrium)

Heat can be transferred in three different modes. Conduction, convection and radiation. Below is a description of each mode

Heat Transfer-Conduction

Conduction is the transfer of energy from the more energy particles of a substance to the adjacent less energetic ones as a result of interactions between the particles.

Conduction can takes place in solids, liquid or gases. In gases and liquid conduction is a result of the to collisions and diffusion of the molecules during their random motion. In solids, it is due to the combination of vibrations of the molecules in a lattice and the energy transport by free electrons.

The rate of heat conduction through a medium depends. On the geometry of the medium, its thickness and the material of the medium, as well as the temperature difference across the medium. For instance rapping a hot water tank with glass wool (an insulating material) reduces the rate of heat loss from the tank the ticker the insulation, the smaller the heat loss. Also a hot water tank losses heat at a higher rate when the temperature of the room housing the tank is howered, precisely the larger the tank, the larger the surface are and thus the rates of heat loss.

The rate of heat conduction through a plane cayer is proportional to the temperature difference across the laver and the heat transfer areas, but is inversely proportional to the thickness of the layer. Represented as. Rte of heat conduct =(Area) (Temperature difference)

Thickness

This law is known as Fourier law of heat conduction after J. Fourier who expressed it first in his heat transfer text in 1822. (Y.A Cengel) 2007)

Convection

 

Convection is the mode of energy transfer between a solid surface and the adjacent liquid or gas that is in motion, and it involves the combined effect, of conduction and fluid motion. The faster the fluid motion, the greater the convection heat transfer. In the absence of any bulk fluid motion, heat transfer between a solid surface and the adjacent fluid is by pure conduction. The presence of bulk motion of the fluid enhances the heat transfer between the solid surface and the fluid, but it also complicates the determination of hat transfer rates.

Using a colling hot block by showing cool air over its top surface as a case study. The heat first is transferred to the air layer adjacent to the block by conduction. This heat is then carried away from the surface by convection that is by combined effect of conduction within the air that is due to random motion of air molecules and the bulk or macroscopic motion of the air that moves the heated air near the surface and replace it by cooler air.

Convection may be forced convection or natural, If the fluid is forced to flow over the surface by external means such as a fan, pump or the wind, in contrast convection is natural (or free) if the fluid motion is caused by buoyancy force that are induced by density differences due to the variation of temperature in the fluid, for example in the absence of a fan, pump or wind. Malted heat guns are example of affined convection.

Radiation

 

Radiation is the energy transferred or emitted by matter in the form of electromagnetic wave (or photons) as a result of the changes in the electronic configurations of the atoms or molecules. Unlike the corresponding conduction and convection, the transfer of heat by radiation dose not require the presence of an intervening medium (object in contact). In fact, heat transfer by radiation is faster (at the speed of light) and its suffers no attenuation in a vacuum. This is how the (heat) energy of the sun reached the earth.

In this heat transfer, the main subject here is the thermal radiation, which is the form of radiation emitted by bodies because of their temperature. It differs from other form of radiation such as x-rays, gamming rays, microwaves, radio waves and television waves that are not related to temperature. Radiation is a volumetric phenomenon and all solids, liquid and gas emit, absorb or transmit radiation to varying degrees. However radiation is usually considered to be a surface phenomenon or solids that are opaque to thermal radiation such as metal, wood and rock, since the radiation emitted by the interior regions of such material can never reach the surface and the radiation incident on such bodies is usually absorbed within few microns from the surface.

Effects of Heat Energy

 

1. Expansion. The size of most solids is altered when their temperature changes due to heat energy application. Solids expand when heated and contract (or decrease in size) when cooled. This can be explained considering the temperature depending on the kinetic energy and movement of molecules.

   For instance the cracking noise of galvanized iron sheet used in roofing, metal structure such as brings which expand during hot weather.

2. Changes of state: Addition of heat can bring about a change of state of a body. For example, in the form of solid like ice, it meets and changes to a liquid like water. When enough heat is added to a liquid, it may vaporize.
3. Chemical change: when heat is applied to a body, it may bring about changes chemically
4. Change in pressure: when heat is added to a gas, the pressure of the gas increases along side with its volume.
5. Change in the physical properties of a body: Addition of heat to a body may cause changes in the electrical resistance, magnetic properties, conductivity, elasticity, density and colour of a body.
6. Thermionic Emission:

Importance of Heat Energy

Infact one dose not need to go any where. The human body is maintained at a normal temperature of 36 oc and considerable alteration or reduction is abnormal, hence human comfort is closely tied to the rate of this heat change. We try to control this heat change by adjusting our clothing to the environmental conditions hence during cold weather (harmattan) we wear thick clothes to maintain this change.

Recent study have shown that combined heat and power (CHP) or Co-generation, takes the next step making use of both the electricity and recovering the heat from the generating plant. In this way different better use of fuel in this way has significant environment benefits with reduction in harmful gas emission of about 30%. Because it’s often difficult to make commercial use of heat in the kind of quantities involved (CHP) plant tends to be on a smaller scale than conventional generation. In U.K, there are a total electricity of about 1400 CHP installations, which contributes about six percent of the country’s total electricity demand.

Applications of Heat Energy

Heat energy is commonly encountered in different fields in both engineering, medicine, industries and lot more.

Engineering: Heat transfer in engineering systems is used in the designs of many house hold appliance, in whole or in part by using the principle of heat transfer. Some examples include the refrigerator, and freezer electric, Iron, the computer, the Tv, DVD, heater Energy-efficient homes are designed on the basic of managing heat loss in winter and heat gain in summer. Also it is applied in designs of other devices such as car radiator, solar collectors, various components of power plants and even space craft. The optimal insulation thickness in the walls and roof of the house, on hot water or steam pipes or on water heater is again determined on the basic of a heat transfer analysis with economic consideration medicine: An experimental technique that was developed in treatment of cancer has worked for virtually all of a select group patient. This treatments known as high intensity focused ultrasound (HIFU) and its uses aerobe inserted in the rectum to produce temperatures near the boiling point kill cancers cells.

So far, the approach has been used on about 440 patients in a four-year study performed by Christian chaussy, a German urologist. These patients, be cause of their age or health problem, were not candidates for surgical removal of the prostate (a walnut-size gland at the base of the bladder that is a leading site of cancer men). However since their disease had not spread throughout the gland, they were eligible for HIFU. This technique newly discovered compare to the surgery, it look very much that w can have an option for a cure with this technique. This finings were presented at a meeting of urologists recently.

Though there are side effects HIFU has not been around long enough to compare it with surgery. It has a quicker recovery time says chausses.

Industries: Heat energy is applied in the industries for many purposes e.g extraction o metals from their ores (iron), design of steam engines (heat energy to mechanical energy), in preservation processes like sterilization, stylization, pastenilization, and lot more.

Conclusion

The knowledge of heat physics (thermal) can be applied in every aspect of learning for effective usefulness.

Though most of our appliances and processes for our every day use are based on the principle of heat energy and it transfer; we need a detail knowledge of heat (thermal) physics for development in our present science and technology. Hence, it can be applied in different field of study.