Physics
Heat Transfer Experiments
Heat transfer experiments involve studying the movement of thermal energy from one object to another. These experiments aim to understand the principles of conduction, convection, and radiation. By observing how heat is transferred through different materials and mediums, scientists can gain insights into the behavior of thermal energy and its effects on various substances.
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9 Key excerpts on "Heat Transfer Experiments"
eBook - PDFSolar Energy
Renewable Energy and the Environment
- Robert Foster, Majid Ghassemi, Alma Cota(Authors)
- 2009(Publication Date)
- CRC Press(Publisher)
55 3 Fundamentals of Engineering Thermodynamics and Heat Transfer 3.1 INTRODUCTION This chapter provides an introduction to heat transfer and engineering thermodynamics. The sci-ence of thermodynamics deals with energy interaction between a system and its surroundings. These interactions are called heat transfer and work. Thermodynamics deals with the amount of heat transfer between two equilibrium states and makes no reference to how long the process will take. However, in heat transfer, we are often interested in rate of heat transfer. Heat transfer processes set limits to the performance of environmental components and systems. The content of this chapter is intended to extend the thermodynamics analysis by describing the different modes of heat transfer. It also provides basic tools to enable the readers to estimate the magnitude of heat transfer rates and rate of entropy destruction in realistic environmental applications, such as solar energy systems. The transfer of heat is always from the higher temperature medium to the lower temperature medium. Therefore, a temperature difference is required for heat transfer to take place. Heat trans-fer processes are classified into three types: conduction, convection, and radiation. Conduction heat transfer is the transfer of heat through matter (i.e., solids, liquids, or gases) with-out bulk motion of the matter. In other words, conduction is the transfer of energy from the more energetic to less energetic particles of a substance due to interaction between them. This type of heat conduction can occur, for example, through the wall of a boiler in a power plant. The inside surface, which is exposed to gases or water, is at a higher temperature than the outside surface, which has cooling air next to it. The level of the wall temperature is critical for a boiler. Convection heat transfer is due to a moving fluid. The fluid can be a gas or a liquid; both have applications in an environmental process.
- Allan D. Kraus, James R. Welty, Abdul Aziz(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
19 Introduction to Heat Transfer Chapter Objectives • To introduce and describe the three modes of heat transfer: conduction, convection, and radiation. • To define thermal conductivity, a heat transfer property. • To develop the concept of thermal resistance. • To consider the overall heat transfer coefficient. 19.1 Introduction The remaining eight chapters of our study deal with heat transfer. The quantity, heat, was defined in earlier chapters and it was quantitatively related to work and system behavior through the first law of thermodynamics in Chapter 5. The first law remains a fundamental precept as we now devote our attention to the rate of heat exchange. As discussed earlier, heat will be exchanged between systems when they are at differ-ent temperatures. The second law of thermodynamics stipulates that this exchange will be from the higher-temperature body or system, toward the bodies or systems at lower temperatures. Practical considerations regarding heat transfer processes involve the rate at which heat transfer occurs. All decisions that involve equipment and material specifications require that heat transfer rates and process temperatures be determined. Our goal, in this chapter, is to examine the mechanisms of heat transfer and to introduce the equations that are fundamental to the evaluation of rates at which energy transfer, due to temperature difference, occurs. 19.2 Conduction Energy transfer by conduction is accomplished via two mechanisms. The first mechanism is by molecular interaction, in which the greater motion of a molecule at a higher-energy (temperature) level imparts energy to adjacent molecules at lower-energy levels. This type of energy transfer is present, to some degree, in all systems in which a temperature gradient exists and in which molecules of a solid, liquid, or gas are present. The second mechanism of conduction heat transfer is by “free” electrons.
eBook - PDF- Ethirajan Rathakrishnan(Author)
- 2012(Publication Date)
- CRC Press(Publisher)
That is, heat transfer can predict the temperature of both the metal bar and the water as a function of time. In other words, unlike ther-modynamics, heat transfer can answer the transient energy transfer questions such as the following: • Can heat be supplied to a system without employing high temperature difference? • How long would it take to supply a certain amount of heat energy to the 1 2 Basic Concepts and Definitions system? • How much heat energy is transferred between two specified instances of time during a process? • What sort of temperature distribution exists in the system? • How large an area is necessary to transfer the desired heat energy? Heat transfer finds application in all processes involving energy transfer. In this introductory text we will discuss heat transfer briefly, highlighting the basic principles of the subject. Basically there are three modes of heat transfer: conduction, convection and radiation. • Conduction is an energy transfer process from more energetic particles of a substance to the adjacent, less energetic ones as a result of the interaction between the particles. • Convection is the mode of heat transfer between a solid surface and the adjacent liquid or gas that is in motion. • Radiation is a heat transfer mode in which the energy is emitted by matter in the form of electromagnetic waves (or photons) as a result of the changes in the electronic configurations of the atoms or molecules, dictated by their temperature.
- Frank P. Incropera, David P. DeWitt, Theodore L. Bergman, Adrienne S. Lavine(Authors)
- 2017(Publication Date)
- Wiley(Publisher)
C H A P T E R Introduction 1 2 Chapter 1 ■ Introduction From the study of thermodynamics, you have learned that energy can be transferred by interactions of a system with its surroundings. These interactions are called work and heat. However, thermodynamics deals with the end states of the process during which an inter- action occurs and provides no information concerning the nature of the interaction or the time rate at which it occurs. The objective of this text is to extend thermodynamic analysis through the study of the modes of heat transfer and through the development of relations to calculate heat transfer rates. In this chapter we lay the foundation for much of the material treated in the text. We do so by raising several questions: What is heat transfer? How is heat transferred? Why is it important? One objective is to develop an appreciation for the fundamental concepts and principles that underlie heat transfer processes. A second objective is to illustrate the man- ner in which a knowledge of heat transfer may be used with the first law of thermodynamics (conservation of energy) to solve problems relevant to technology and society. 1.1 What and How? A simple, yet general, definition provides sufficient response to the question: What is heat transfer? Heat transfer (or heat) is thermal energy in transit due to a spatial temperature difference. Whenever a temperature difference exists in a medium or between media, heat transfer must occur. As shown in Figure 1.1, we refer to different types of heat transfer processes as modes. When a temperature gradient exists in a stationary medium, which may be a solid or a fluid, we use the term conduction to refer to the heat transfer that will occur across the medium. In contrast, the term convection refers to heat transfer that will occur between a surface and a moving fluid when they are at different temperatures. The third mode of heat transfer is termed thermal radiation.
- Gerald Miller(Author)
- 2022(Publication Date)
- Springer(Publisher)
Thermal conduction is the process by which heat transfer occurs by molecular interaction. It can occur in gases, liquids and solids. An example is heat transfer across a closed window or across a wall. In the human body, the example of conductive heat transfer is across tissue from the core towards the periphery (skin). Thermal convection is the process by which heat transfer occurs via bulk motion of a fluid. An example might be forced air flow from an air conditioner vent or wind chill on a windy day. In the body, examples of convective heat transfer include blood flow from the core towards the periphery or air flow in the lungs from the alveoli though the trachea and out the mouth and nose. Both conduction and convection require that there be a material involved, although convection does not occur in solids, whereas conduction can. The third method of heat transfer is thermal radiation, which occurs as a result of electromagnetic transport processes. An example is heat gain from the sun to the earth (and your own skin). Radiation is a surface to surface phenomenon and does not require a material interaction. The greenhouse effect is an example of thermal radiation. 42 3. BIOMEDICAL HEAT TRANSPORT As an example, Figure 3.1 depicts the three types of heat transfer from a campfire. Conduction Radiation Convection Figure 3.1: The three types of heat transfer: conduction, convection and radiation (Wikipedia). 3.2 THERMAL CONDUCTION Conduction (or heat conduction) is the transfer of thermal energy between neighboring molecules in a substance due to a temperature gradient. It always takes place from a region of higher temperature to a region of lower temperature, and it acts to equalize temperature differences. Conduction takes place in all forms of matter including solids, liquids, and gases, but it does not require any bulk motion of matter. In solids, it is due to the combination of vibrations of the molecules in a lattice and the energy transport by free electrons.
eBook - PDF- Richard W. Hartel, D.B. Hyslop, D.B. Hyslop, T.A. Howell Jr.(Authors)
- 2008(Publication Date)
- CRC Press(Publisher)
153 chapter ten Heat transfer Heat transfer is arguably the most important transport process in the food industry, since processing of most foods requires either an increase or a decrease in temperature. Thermal processing, or heating to destroy unde-sirable microorganisms, is one of the main techniques a food technologist utilizes to ensure safety of the food supply. Sterilization and pasteurization require that a food be heated to a certain temperature and held there for suf-ficient time to destroy microorganisms before being cooled again. Both the heating and cooling steps require an understanding of heat-transfer prin-ciples. There are numerous other examples of heat transfer in the food indus-try, from baking a food in an oven, to solidification of chocolate in a cooling tunnel. Nearly every food processing system utilizes heat transfer in some form or another. Thus, knowledge of the principles of heat transfer is critical for the food technologist. Furthermore, using the principles of heat transfer together with enthalpy balances provides a powerful tool for the food tech-nologist to solve complex food-processing problems. Heat transfer occurs in one of three modes: conduction, convection, or radiation. Sometimes all three modes of heat transfer may occur at the same time. Conduction heat transfer involves transfer of thermal energy from one molecule to another. A metal rod placed in proximity to a heat source will begin initially to heat up on the end near the heat source. However, after some time, the other end will also be hot, as the molecules of the metal trans-fer the heat along the length of the rod. Materials that are good heat conduc-tors have high thermal conductivity, k ; whereas insulators, materials with low k , do not transfer heat very well by conduction. Convection heat transfer occurs when a fluid carries thermal energy from one place to another.
eBook - PDF- Jean-Maurice Vergnaud, Iosif-Daniel Rosca(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
21 2 General Study on Heat Transfer The laws of heat transmission are of controlling importance in the design of equip-ment and the operation of many diverse instruments in many different industries. This applies particularly to the rubber industry. 2.1 VARIOUS MEANS OF HEAT TRANSFER When different parts of a body are at different temperatures, heat flows from the hotter parts to the cooler. There are three distinct ways by which this transference of heat takes place: (i) conduction, in which the heat passes through the substance of the body itself, (ii) convection, in which heat is transferred by relative motion of portions of the heated body, and (iii) radiation, in which heat is transferred directly between distant portions of the body by electromagnetic radiation. 2.1.1 H EAT C ONDUCTION Conduction in a homogeneous opaque solid is the transfer of heat from one particle to another, under the influence of a temperature gradient, without appreciable displace-ment of the particles. Conduction involves the transfer of kinetic energy from one molecule to an adjacent molecule; it is the only mechanism of heat flow in an opaque solid. With gases and liquids, conduction may be supplemented by convection and radiation; within a fluid (motionless or in streamline motion), heat is transferred by conduction at right angles to the direction of fluid flow. Thus, heat is transferred by conduction either through the rubber materials or through the mold. 2.1.2 H EAT C ONVECTION Convection involves the transfer of heat by mixing one parcel of fluid with another. The motion of the fluid may be entirely the result of differences of density caused by temperature differences, as in natural convection, or it may be produced by mechani-cal means, as in forced convection. Energy is also transferred simultaneously by molecular conduction and, in transparent media, by radiation.
- A. V. Luikov(Author)
- 2014(Publication Date)
- Pergamon(Publisher)
CHAPTER 9 EXPERIMENTAL METHODS OF INVESTIGATION To APPLY the analytical solutions of heat and mass transfer to practical calculations, it is necessary to have the numerical values of the thermo-physical characteristics of the materials, which can be found from special experiments. Determination of the thermophysical characteristics of moist capillary-porous bodies presents great difficulty, especially with regard to the mutual effect of heat and mass transfer. Experimental methods for determining the coefficients of heat transfer X q , a q have been explained in numerous publications, therefore attention will be given mostly to those which are based on the laws of the non-sta-tionary temperature field in the first stage of its development. Such meth-ods are more acceptable for determining the thermophysical characteris-tics of wet materials owing to their short duration; for protracted ther-mal action in the presence of a temperature gradient causes redistribu-tion of the moisture in the specimen. A considerable part of this chapter will be devoted to consideration of experimental methods for determining mass transfer coefficients and the thermodynamic characteristics of mass transfer. A description of the well-known methods of finding porosity, the differential curve of pore distribution and the coefficient of air perme-ability will be omitted, because they have been described in sufficient detail in appropriate handbooks on physico-chemical experimental techniques and in special monographs. In conclusion, a short description will be given of some experimental equipment for the determination of heat and mass transfer coefficients in drying and calcination processes. § 1. Methods of Determining Some Thermal Properties Basic equations of methods of steady heat flow Determination of the thermal properties (coefficients of thermal con-ductivity and thermal diffusivity of heat insulators) presents great difficul-ties.
eBook - PDF- Carey Merritt(Author)
- 2022(Publication Date)
- Wiley(Publisher)
Process Steam Systems: A Practical Guide for Operators, Maintainers, Designers, and Educators, Second Edition. Carey Merritt. © 2023 John Wiley & Sons, Inc. Published 2023 by John Wiley & Sons, Inc. 3 UNDERSTANDING HEAT TRANSFER It is nearly impossible to fully grasp how a steam system works without a good understanding of heat transfer. A boiler in very simple terms converts fuel energy into steam. It does this by combustion and heat transfer. Overall system efficiency is directly related to heat transfer within the system. This chapter will show the reader what types of heat transfer take place within the steam system equipment and the importance of each. The reader should review this entire section before trying to apply any one heat transfer-type calculations as system heat balances should take into consideration the interrelationship of the three types of heat transfer. Once combustion takes place in the boiler furnace, the thermal energy must be transferred to the water to make steam. Similarly, the energy in the steam must be transferred to a product to complete the conversion of fuel energy to product energy. We know that whenever a temperature gradient exists, transfer of heat energy will occur. This may take the form of either conduction-, convection-, or radiation-type heat transfer. The three types are shown in Figure 3.1. To be able to fully appreciate the efficiency of a steam system we must understand where, when, and what affects these three types of heat transfer mechanisms. The efficiency of all steam systems is optimized by optimizing desirable heat transfer and preventing unwanted heat transfer. The Figure 3.2 below shows where heat energy transfer occurs in a typical steam system. RADIATION-TYPE HEAT TRANSFER The heat transfer due to the emission of energy from surfaces in the form of electromagnetic waves is known as thermal radiation.
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