Heat
Let's clear your concept about Heat
An object decreases its temperature by releasing energy in the form of heat to its surroundings. And an object increases its temperature by gaining energy in the form of heat from its surroundings. Both the warming up and the cooling down of objects works in the same way - by heat transfer from the higher temperature object to the lower temperature object. So now we can meaningfully re-state the definition of temperature. Temperature is a measure of the ability of a substance, or more generally of any physical system, to transfer heat energy to another physical system. The higher the temperature of an object is, the greater the tendency of that object to transfer heat. The lower the temperature of an object is, the greater the tendency of that object to be on the receiving end of the heat transfer.
An object decreases its temperature by releasing energy in the form of heat to its surroundings. And an object increases its temperature by gaining energy in the form of heat from its surroundings. Both the warming up and the cooling down of objects works in the same way - by heat transfer from the higher temperature object to the lower temperature object. So now we can meaningfully re-state the definition of temperature. Temperature is a measure of the ability of a substance, or more generally of any physical system, to transfer heat energy to another physical system. The higher the temperature of an object is, the greater the tendency of that object to transfer heat. The lower the temperature of an object is, the greater the tendency of that object to be on the receiving end of the heat transfer.
Man and Heat
“A man is heat machine”
- Food is necessity of life, it is a source of energy that’s refers to maintain live activities.
- Every body movement or activities generates heat even the blink of an eye.
- Our body always tries to maintain a required level of temperature 98.6 Deg F or 37 Deg C either rejecting heat or absorbing.
- The rate at which heat is rejected by human body is called metabolic rate(while sleeping is called Basel metabolic rate).
- This rate may be increased up-to 10 times in hard working situation.
Modes of Heat Transfer
Thermal Conduction is the transfer of heat (internal energy) by microscopic collisions of particles and movement of electrons within a body. The microscopically colliding objects, that include molecules, atoms, and electrons, transfer disorganized microscopic kinetic and potential energy, jointly known as internal energy. Conduction takes place in all phases of matter, such as solids, liquids, gases and plasmas. The rate at which energy is conducted as heat between two bodies is a function of the temperature difference (temperature gradient) between the two bodies and the properties of the conductive medium through which the heat is transferred. Thermal conduction was originally called diffusion. Heat spontaneously flows from a hotter to a colder body. For example, heat is conducted from the hotplate of an electric stove to the bottom of a saucepan in contact with it. In the absence of an external driving energy source to the contrary, within a body or between bodies, temperature differences decay over time, and thermal equilibrium is approached, temperature becoming more uniform. In solids, conduction is mediated by the combination of vibrations and collisions of molecules, of propagation and collisions of phonons, and of diffusion and collisions of free electrons.
Convection is the concerted, collective movement of groups or aggregates of molecules within fluids (Example-liquids, gases) and Rheids, through advection or through diffusion or as a combination of both of them. Convection of mass cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids. Convective heat transfer is one of the major types of heat transfer, and convection is also a major mode of mass transfer in fluids. Convective heat and mass transfer take place both by diffusion – the random Brownian motion of individual particles in the fluid – and by advection, in which matter or heat is transported by the larger-scale motion of currents in the fluid. In the context of heat and mass transfer, the term "convection" is used to refer to the sum of advective and diffusive transfer. In common use the term "convection" may refer loosely to heat transfer by convection, as opposed to mass transfer by convection, or the convection process in general. Sometimes "convection" is even used to refer specifically to "free heat convection" (natural heat convection) as opposed to forced heat convection. However, in mechanics the correct use of the word is the general sense, and different types of convection should be qualified for clarity.
Radiation The heat transfer due to radiation takes place from one body to another without effecting to medium through which heat travels. Heat flow from sun to earth takes place in the same fashion. For this mode heat flow does not requires any medium also. The heat absorb by a body is depends upon the surface factor of body. This traveled in the form of electromagnetic waves (such as radio waves, visible light, x-rays, and gamma radiation (γ)).
Concept of Sensible Heat and Latent heat
Sensible Heat-Sensible heat is heat exchanged by a body or thermodynamic system that changes the temperature, and some macroscopic variables of the body, but leaves unchanged certain other macroscopic variables, such as volume or pressure.
Latent Heat-The heat required to convert a solid into a liquid or vapor, or a liquid into a vapor, without change of temperature-
Specific heat-It is defined as the amount of heat required to raise the temperature 10 C of substance with 1 kg mass without changing its state. It varies substance to substance.
Sensible Heat Factor- SHF is the ratio of total sensible heating load to that of the total heating load on air conditioning apparatus. SHF is used in the design process of the air conditioning apparatus.
Concept of Sensible Heat and Latent heat
Sensible Heat-Sensible heat is heat exchanged by a body or thermodynamic system that changes the temperature, and some macroscopic variables of the body, but leaves unchanged certain other macroscopic variables, such as volume or pressure.
Latent Heat-The heat required to convert a solid into a liquid or vapor, or a liquid into a vapor, without change of temperature-
- Latent heat of fusion.
- Latent heat of evaporation.
- Latent heat of sublimation.
Specific heat-It is defined as the amount of heat required to raise the temperature 10 C of substance with 1 kg mass without changing its state. It varies substance to substance.
Sensible Heat Factor- SHF is the ratio of total sensible heating load to that of the total heating load on air conditioning apparatus. SHF is used in the design process of the air conditioning apparatus.
SHF=SH/TH