MET 214 Heat exchanger module-1
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1. Heat transfer occurs through three methods: conduction, convection, and radiation. 2. Conduction involves the transfer of heat through direct contact of particles. Convection involves the transfer of heat by fluid motion. Radiation involves heat transfer through electromagnetic waves without a medium. 3. Heat transfer is important across several engineering disciplines for applications like cooling systems, fluid heating/cooling, building design, and engines.
MET 214 Heat exchanger module-1
- 1. MODULE-1 According to thermodynamic concept , the energy that is transferred as a result of a temperature difference is called HEAT THREE DIFFERENT TYPES OF HEAT TRANSFER: 1.CONDUCTION 2.CONVECTION 3.RADIATION
- 2. Itmportances of heat transfer: 1.electrical engineerg:cooling system for motors,generators and transformor 2.chemical engineering: evaporation,condensation,heating and cooling of fluid 3. civil engineering: constructions dams,structures,building design. 4.mechanical engineering:heat transfer in internal combustion engine,steam generations,refrigeration and heating and ventillation.
- 3. Conduction:it is the process by which heat flows from a region of higher temperature to a region of lower temperature within the substance. Conduction take place by two mechanism: a)by lattice vibration:molecules at higher temperature imparts energy to adjacent molecules at lower temperature. b)by free electrons: transfer of heat by free electrons, the free electrons concentration in non-metals is very low.Hence conduction is found in solids
- 4. Convection:it is possible only in the presence of fluids( liquid and gases).As fluid passes over hot objects,they pick up heat energy and carry it to colder area. Two types of convection: 1.free convection 2.forced convection
- 5. RADIATION:RADIATION HEAT TRANSFER BETWEEN TWO SUBSTANCES TAKE PLACE EVEN WITHOUT ANY MEDIUM THROUGH ELECTROMAGNETIC WAVES
- 6. Heat flux: it is the amount of heat flow per unit area through a body=Q/A W/m2 the materials having higher thermal conductivity are conductors, while material having lower thermal conductivity are called as insulators
- 7. Radiation is the only way that heat can move through a vaccum.Radiant heat can be felt by holding a hand near any hot object,higher the temperature of the object, more energy being released. The denser the solid, the faster heat will be transferred from the hottest regions to coldest.
- 8. Convection: Is the way heat flows through fluids, whether they are liquids or gases.
- 9. THE LAWS OF HEAT TRANSFER. 1.Fourier’s law of heat conduction. The rate of heat flow is proportional to the product of the area of flow A, and the temperature gradient (-dt/dx),the constant of proportionality being the thermal conductivity k, which is a property of material. Unit is j/s or W Qx=-kA(dt/dx)
- 10. 2.NEWTONS LAW OF HEAT CONVECTION Q=hA(t1-t2) heat transfer is occuring from a surface area A at temperature t1, to a fluid at a lower temperature t2. h is the convection co-efficient in w/m2K
- 11. STEFAN-BOLTZMANN LAW OF RADIATION: Q=EσAT4 T-absolute temperature, A-surface area, E-emissivity σ-stefan boltzmann constant,5.67*10-8w/m2k4 It states that the radiant energy emitted by a black body is proportional to the surface area and fourth power of its absolute temperature.
- 12. Thermal conductivity: thermal conductivity, k is the property of a material's ability to conduct heat PURE METALS HAVE HIGHER VALUES OF THERMAL CONDUCTIVITY WHILE GASES AND VAPORS HAVE LOWEST.
- 14. K for a pure metals decreases with temperature. K=ko(1+bф+cф2) where ф=T-Tref. K for a non homogeneous materials increases both with increasing temperature and increasing density.
- 21. Thermal conductivity: it is defined as the ability of a substance to conduct heat. It is expressed in w/m-k or w/moC. Heat transfer co-efficient(h): ability of the fluid carry away heat from the surfaces which in turn depends upon velocities and other thermal properties.unit w/m2 k or w/m2oC