A study on covection heat transfer

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Energy can exist in numerical forms such as thermal, mechanical, kinetic, potential, electrical, magnetic, chemical, and nuclear their sum constitutes the total energy E (or e on a unit mass basis) of a system. The forms of energy related to the molecular structure of a system and the degree of the molecular activity are referred to as the microscopic energy. The sum of all microscopic form of energy is called the internal energy of a system, and is denoted by U.

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A study on covection heat transfer

  1. 1. A STUDY ON COVECTION HEAT TRANSFER Prepared for: Dr. Mohammad Abu Taher Department of mathematics Dhaka University of Engineering and Technology, (DUET) Gajipur, Dhaka. E-mail: tahermath@yahoo.com, tahermath@duet.ac.bd Prepared by: Khairuzzaman Mamun ID No :112701P Contact no : 01761808592 Email : kpmmamun@gmail.com Presentation Date: 05-09-2012
  2. 2. LETTER OF TRANSMITTALSeptember 05, 2012Dr. Mohammad Abu TaherDepartment of mathematicsDhaka University of Engineering and Technology, (DUET)Gajipur, Dhaka.Dear sirHere is the report that you asked us to conduct on August 30, 2012 on A Study on Convection HeatTransfer.This study focused on different types of discussion and result about the Convection Heat TransferI will be pleased if you have any further query for this you can call me at your convenient time andplace.Sincerely yours,Khairuzzaman MamunID No : 112701PContact no : 01761808592Email : kpmmamun@gmail.com
  3. 3. OBJECTIVESEnergy can exist in numerical forms such as thermal, mechanical, kinetic, potential, electrical, magnetic, chemical, andnuclear their sum constitutes the total energy E (or e on a unit mass basis) of a system. The forms of energy related tothe molecular structure of a system and the degree of the molecular activity are referred to as the microscopic energy.The sum of all microscopic form of energy is called the internal energy of a system, and is denoted by U.Thermal energy is the sensible and latent forms of internal energy, and it is referred to as heat in daily life. The basicmechanism of heat transfer are the heat conduction, heat convection, heat radiation.This study aimed to analyze the Convection Heat Transfer and to discuss about heat transfer, classification of heattransfer, definition and mathematical explanation convection heat transfer, causes of convection heat transfer in thepoint of mathematical views. At the end, some example of convection process are described.
  4. 4. SEQUENCE OF CONTENTS Introduction Classification Definition & mathematical explanation of convection heat transfer Causes of convection heat transfer in the mathematical point of views Some Example of Convection Process Conclusion
  5. 5.  INTRODUCTIONThe transfer of heat is normally from a high temperature object to a lower temperature object. Heat transfer changesthe internal energy of both systems involved according to the First Law of Thermodynamics. The mechanism of heattransfer are conduction, convection, and radiation.Conduction is the transfer of energy from the more energetic particles of a substance to the adjacent less energetic onesas a result of interactions between the particles.Convection is the mode of energy transfer between a solid surface and the adjacent liquid or gas which is in motion,and it involves combined effects of conduction and fluid motion.Radiation is energy emitted by matter in the form of electromagnetic waves as a result of the changes in the electronicconfigurations of the atoms or molecules.
  6. 6.  CLASSIFICATION Heat can be transferred by three system. Heat Transfer Conductio Convecti Radiatio n on n
  7. 7.  DEFINITION & MATHEMATICAL EXPLANATION OF CONVECTION HEATTRANSFERConvection is the mode of energy transfer between a solid surface and the adjacent liquid or gas that is inmotion, and it involves the combined effects of conduction and fluid motion, the greater the convection heattransfer. In the absence of any bulk fluid motion, heat transfer between a solid surface and the adjacent fluidis by pure conduction. The presence of bulk motion of the fluid enhances the heat transfer between the solidsurface and the fluid, but it also complicates the determination of heat transfer rates.Consider the cooling of a hot block by the blowing cool air over its top surface. Heat is transferred to the airlayer adjacent to the block by conduction. This heat is then carried away from the surface by convection, thatis, by the combined effects of conduction within the air that is due to random motion of air molecules and thebulk or macroscopic motion of the air that removes the heated air near the surface and replaces it by thecooler air.Convection is called forced convection if the fluid is forced to flow over the surface by external means suchas a fan, pump, or the wind. In contrast, convection is called natural or free convection if the fluid motion iscaused by buoyancy forces that are included by density differences due to the variation of temperature in thefluid.Heat transfer processes that involve change of phase of a fluid are also considered to the convection becauseof the fluid motion induced during the process, such as the rise of the vapor bubbles during boiling or the fallof the liquid droplets during condensation.
  8. 8. Despite the complexity of convection, the rate of heat transfer is observed to be proportional to thetemperature difference, and is conveniently expressed by Newton’s law of cooling asWhere h is the convection heat transfer coefficient in is the surface area through which convection heat transfer takes place is the surface temperature and is the temperature of the fluid sufficiently far from the surface.Note that at the surface, the fluid temperature equals the surface temperature of the solid.The convection heat transfer coefficient h is not a property of the fluid. It is an experimentally determinedparameter whose value depends on all the variables influencing convection such as the surface geometry, thenature of fluid motion, the properties of the fluid, and the bulk fluid velocity.Some people do not considerate convection to be a fundamental mechanism of heat transfer since it isessentially heat conduction in the presence of fluid motion. But we still need to give this combinedphenomenon a name, unless we are willing to keep referring to it as “conduction with motion”. Thus, it ispractical to recognize convection as a separate heat transfer mechanism despite the valid arguments to thecontrary.
  9. 9.  CAUSES OF CONVECTION HEAT TRANSFER IN THE MATHEMATICAL POINTOF VIEWSConvection is heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away fromthe source of heat, carrying energy with it. Convection above a hot surface occurs because hot air expands, becomes lessdense, and rises (see Ideal Gas Law). Hot water is likewise less dense than cold water and rises, causing convection currentswhich transport energy.
  10. 10.  SOME EXAMPLE OF CONVECTION PROCESS Convection can also lead to circulation in a liquid, as in the heating of a pot of water over a flame. Heated water expands and becomes more buoyant. Cooler, more dense water near the surface descends and patterns of circulation can be formed, though they will not be as regular as suggested in the drawing.
  11. 11. Convection cells are visible in the heated cooking oil in the pot at left. Heating the oil produces changes in the index of refraction of the oil, making the cell boundaries visible. Circulation patterns form, and presumably the wall-like structures visible are the boundaries between the circulation patterns.Convection is thought to play a major role in transportingenergy from the center of the Sun to the surface, and inmovements of the hot magma beneath the surface of the earth.The visible surface of the Sun (the photosphere) has a granularappearance with a typical dimension of a granule being 1000kilometers. The image at right is from the NASA Solar Physicswebsite and is credited to G. Scharmer and the SwedishVacuum Solar Telescope. The granules are described asconvection cells which transport heat from the interior of theSun to the surface.
  12. 12.  CONCLUSIONBased on this study it can be said that among all processes of heat transfer, heat convection is a complexprocess as it involves combined effect of heat conduction and fluid motion. APPENDIX a. Wikipedia b. Book of heat and mass transfer Writer- Yunus A. Cengel University of Nevada, Reno. THANK YOU KHAIRUZZAMAN MAMUN ID No:112701P

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