Lectures - CHG 2314 Heat Transfer Part 1 Basic Concepts of...

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University of Ottawa, CHG 2314, B. Kruczek 1 CHG 2314 Heat Transfer Part 1 Basic Concepts of Heat Transfer - Physical origins and rate equations - Application of thermodynamics

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University of Ottawa, CHG 2314, B. Kruczek 2 Introduction | What is heat transfer ? z Heat transfer is thermal energy in transit due to a temperature difference. | What is thermal energy ? z Thermal energy is associated with the translation, rotation, vibration and electronic states of the atoms and molecules that comprise matter. z It represents the cumulative effect of microscopic activities and is directly linked to the temperature of matter. | Heat transfer is commonly encountered in engineering systems and other aspects of life
University of Ottawa, CHG 2314, B. Kruczek 3 Introduction | Engineering heat transfer deals in general with two types of problems: z Rating problems – calculating rates of heat transfer at a specific temperature difference for an existing problem z Sizing problems – determination of the size of a system in order to transfer heat at a specified rate for a specified temperature difference What is the condensation rate of steam at a given flow rate of cooling water which is available at certain temperature in a given heat exchanger? What should be the thickens of insulation to prevent a worker’s injury on accidental contact with a pipe surface?

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Nomenclature Quantity Meaning Symbol Units | DO NOT confuse or interchange the meanings of Thermal Energy , Temperature and Heat Transfer Thermal Energy Energy associated with microscopic behavior of matter Temperature A means of indirectly assessing the amount of thermal energy stored in matter Heat Transfer Thermal energy transport due to temperature gradients Heat Amount of thermal energy transferred over a time interval U t > 0 Heat Rate Thermal energy transfer per unit time Heat Flux Thermal energy transfer per unit time and surface area University of Ottawa, CHG 2314, B. Kruczek 4 or Uu J or J/kg T K or °C Q J q W 2 W/m " q
5 Modes of heat transfer | Conduction: Heat transfer in a solid or a stationary fluid (gas or liquid) due to the random motion of its constituent atoms, molecules and /or electrons Conduction Radiation Convection University of Ottawa, CHG 2314, B. Kruczek | Convection: Heat transfer due to the combined influence of bulk and random motion for fluid flow over a surface | Radiation: Energy that is emitted by matter due to changes in the electron configurations of its atoms or molecules and is transported as electromagnetic waves (or photons). NB1: Conduction and convection require the presence of temperature variations in a material medium.

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This note was uploaded on 05/30/2011 for the course CHG 2314 taught by Professor Kruz. during the Spring '10 term at University of Ottawa.

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Lectures - CHG 2314 Heat Transfer Part 1 Basic Concepts of...

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