Heat Transfer Fluid

7 Key excerpts on "Heat Transfer Fluid"

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  eBook - PDF

  Introduction to Thermal and Fluid Engineering

  • Allan D. Kraus, James R. Welty, Abdul Aziz(Authors)
  • 2011(Publication Date)
  • CRC Press

    (Publisher)

  1 The Thermal/Fluid Sciences: Introductory Concepts Chapter Objectives • To introduce the component disciplines that comprise the thermal/fluid sciences—thermodynamics, fluid mechanics, and heat transfer. • To discuss the physical laws upon which the thermal sciences are based. • To present a list of products and/or processes whose analysis and design rely upon thermal/fluid science principles. 1.1 Introduction The subject areas of thermodynamics, fluid mechanics, and heat transfer comprise what are generally referred to as the thermal/fluid sciences. These subjects are often studied separately but are sufficiently interrelated that they are frequently taken sequentially by engineering students and, as with this text, are often treated in a single book. In this book, these subjects will be treated in a relatively fundamental fashion. Our goal is to provide a basic understanding of the physical laws and processes that involve energy utilization in ways that accomplish useful tasks. Thermal/fluid systems involve energy that can be stored, transferred, or converted within the system. Energy storage manifests itself in different forms such as gravitational or po-tential and kinetic energy as well as energy that is contained in the matter that constitutes the system. Energy can be transferred between a system and its surroundings via the flow of heat, work, and the flow of hot and/or cold fluid streams of matter. It may be converted from one form to another such as the conversion of the energy contained within fuels to elec-trical energy as in a power plant, or to mechanical energy, which is used to propel your automobile. A steam power plant (Figure 1.1) converts the chemical energy contained in a fossil fuel to electrical power, while the automobile and the turbojet engines contained in a fuel are converted to propulsive power.

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  Solar Receivers for Thermal Power Generation

  Fundamentals and Advanced Concepts

  • Amos Madhlopa(Author)
  • 2022(Publication Date)
  • Academic Press

    (Publisher)

  Section 1.5 ). Thus, the Heat Transfer Fluid is a key element of concentrating solar power (CSP) systems.

  There are different thermodynamic cycles, with variations in the range of their working temperatures. In view of this, properties of Heat Transfer Fluids should: (a) match the containment materials and storage media, (b) be capable of operating in the desired temperature range, (c) collect and transmit heat with little effort, and (d) flow well in confined spaces such as tubes (Benoit et al., 2016 ).

  5.1.1. Required characteristics of Heat Transfer Fluids

  To achieve a high performance of CSP systems, it is necessary for fluids that are exploited as heat transfer media in solar thermal devises to possess most of the characteristics of a good Heat Transfer Fluid. In brief, the major required characteristics of heat transfer media are as follows (Benoit et al., 2016 ; Bignon, 1980 ; Ho & Iverson, 2014 ):

  5.1.1.1. Working temperature range and thermal stability

  The efficiency of CSP power plants is predominantly restricted by the working fluid temperature. Consequently, a Heat Transfer Fluid should have a wide range of the working temperature. This implies that the candidate fluid should have a low melting point in order to avert its solidification in pipes or other flow channels, and a high upper limit of the working temperature that permits the exploitation of efficient thermodynamic cycles.

  Application of heat to a substance can cause physical and chemical changes to the properties of the material. A physical modification does not produce a fundamentally different substance, while a chemical change transforms a given substance into a chemically new substance. Both types of changes can alter the desirable properties of a fluid. For example, phase change is a physical transformation that affects the efficiency of thermodynamic cycles. Some important parameters of phase change are the critical temperature and pressure of a material (see Section 1.5

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  Solar 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.

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  Advances in Heat Transfer Augmentation Techniques in Single-Phase Flows

  • Varun Goel, Wei Wang, Bengt Sunden(Authors)
  • 2024(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 1 Introduction to heat transfer

  DOI: 10.1201/9781003229865-1

  1.1 Introduction

  It is of great importance to be able to determine temperature distributions and heat fluxes in most branches of engineering and technology. In design, sizing, and rating of heat exchangers, for example condensers, evaporators, radiators, and others, analysis of the heat transfer process is needed. Heat exchanger equipment appears frequently in heat and power generation, process industries of various kind, automotive engineering, etc. Design and sizing of air conditioning equipment, electronics cooling, and insulation of buildings require understanding and knowledge of heat transfer. For vehicles, many heat transfer problems are present.

  Successful stress and strain analysis in equipment exposed to high temperature requires accompanied analysis of the temperature distribution and heat loads. In manufacturing, production, and thermal or mechanical treatment of materials, heat transfer is an important issue.

  Equipment carrying electrical currents (electronics, electric motors, and transformers) commonly need cooling. In energy conversion devices like electrochemical apparatus (fuel cells, batteries, and electrolyzers) and combustion units, the significance of heat transfer is vital.

  Food processing and its treatment is another area where analysis of heat and mass transfer is required.

  1.2 Mechanisms of heat transfer

  Energy transferred from the hot to the cold part of a substance or from a high temperature body to another body kept at a lower temperature is generally labeled as heat.

  Application of basic relations of thermodynamics and fluid mechanics can in some cases easily determine the amount of transferred heat. When the mechanisms are not completely known, analogical or empirical methods based on experiments might be applicable.

  Three different mechanisms of the transfer of heat have been identified. These are heat conduction, convection, and thermal radiation (see Figure 1.1

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  Process Engineering and Design Using Visual Basic®

  • Arun Datta(Author)
  • 2013(Publication Date)
  • CRC Press

    (Publisher)

  141 © 2010 Taylor & Francis Group, LLC chapter four Heat transfer Introduction Heat transfer is an important unit operation that is used in almost all chemical industries. In industries, heat is either gained or lost by a typical fluid stream. Once a particular fluid loses heat, there will be a stream that will gain heat. There are different types of heat-transfer equipment or heat exchangers, starting from a simple double-pipe exchanger to the highly complex multi-pass shell and tube exchanger. Conductive heat transfer Heat transfer per unit area through conduction is proportional to the tem-perature gradient and mathematically defined as [1]: Q kA dt dx = -      (4.1) The temperature gradient − dt / dx is the change in temperature in the x direction. Consider a heat conduction element in Figure 4.1 that receives Q x heat through the left face and rejects Q x+dx heat through the right face. Heat received and rejected by the element can be defined as Q k dz dy dT dx x = -      (4.2a) Q k dz dy dT dx d T dx dx x dx + = --      2 2 (4.2b) Heat gained by the element through the x direction will be Q Q k dz dy d T dx dx x x dx -=       + 2 2 (4.3) 142 Process engineering and design using visual basic ® © 2010 Taylor & Francis Group, LLC Now, heat gained by the element can also be defined as Q Q c dx dy dz dT d x x dx -= + 1 3 6 . ρ θ (4.4) From Equations 4.3 and 4.4 dT d k c d T dx θ ρ =       3 6 2 2 . (4.5) Equation 4.5 is Fourier’s general equation. The term 3.6 k / c ρ is called the thermal diffusivity, m 2 /h. Multiplication factor 3.6 is used to balance the unit. Equation 4.5 is the heat flow through one direction and if all three directions are considered, the general equation of heat flow will be dT d k c d T dx d T dy d T dz θ ρ = + +       3 6 2 2 2 2 2 2 . (4.6) Heat conduction through a composite wall Heat conduction through a composite wall is presented in Figure 4.2.

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  Rules of Thumb for Chemical Engineers

  • Stephen Hall(Author)
  • 2017(Publication Date)
  • Elsevier

    (Publisher)

  Physical and thermal properties are provided here for a wide range of proprietary Heat Transfer Fluids. The basic properties were obtained from information published by the manufacturers, converted to a consistent set of SI units, and fitted to formulae that relate properties to temperature. This gives a common basis from which to compare different Heat Transfer Fluids.

  The information in this chapter is specific to closed-loop systems that operate completely in the liquid state. Industry also uses condensing and evaporating systems. Some of the concepts in this chapter apply to those change-of-state systems, but the formulae and properties are limited to liquids.

  Safety Considerations

  Heat transfer systems typically operate at the temperature extremes of a plant. The fluids are engineered for their heat transfer properties, an important one being low viscosity. Many of the fluids are hydrocarbons that are combustible at ambient temperature but above their flash point when hot. For these reasons, closed-loop heat transfer systems present unique safety hazards that should be assessed throughout the life cycle of the system. Table 13.1 lists a few of the hazards; structured process hazard assessments (PHAs) should be conducted for these systems (see Refs. [1 ,2 ] for additional information).

  Table 13.1 Safety Considerations for Heat Transfer Systems

  Sizing and Specifications

  Carefully consider the toxicity and fire hazards for all Heat Transfer Fluids that may be introduced into the system (initially or potentially in the future). Thermal fluids should not be operated at a temperature above its atmospheric boiling pointProvide facilities for charging and draining fluid to/from the piping systemProvide adequate volume to contain thermal expansionProvide spill control, such as dikes around heaters and pumpsSpecify components and connections to be as fully contained as practicable, for example, by using sealless pumps, welded joints, and high-pressure flanges with flange coversAccount for pipe expansion or contraction that will occur when the system is heated or chilled

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  eBook - ePub

  Chemical Engineering for Non-Chemical Engineers

  • Jack Hipple(Author)
  • 2017(Publication Date)
  • Wiley-AIChE

    (Publisher)

  h, we see a relationship like the following:

  Without worrying about the exact numbers, we can look at the variables and how this equation predicts how the heat transfer coefficient would respond to a change in conditions or physical properties:

  1. If the Reynolds number increases, the heat transfer will increase by the 0.8 power. The greater the turbulence, the more efficient the heat transfer, but it does not increase linearly.
  2. If the pipe diameter increases, the heat transfer will decrease by the 0.2 power (the smaller the pipe diameter, the lower the velocity and less turbulent is the flow).
  3. If the viscosity increases, the heat transfer will decrease by the 0.5 power (if the fluid is “thicker,” the Reynolds number decreases and the ability to mix the fluid drops). Again, think about water versus maple syrup.
  4. If the thermal conductivity of the fluid increases, the heat transfer will increase by the 0.7 power.

  The point here is not to memorize the equation, but just to reinforce the natural logic that heat transfer will change in response to variables that can be affected and changed in the chemical engineering design of not only the heat exchanger but also the choice of fluids and their physical properties. This kind of general knowledge can also assist in estimating changes in heat transfer efficiency when changes to process systems are made.

  Utility Fluids

  It is easy to overfocus on the process stream that needs to be heated or cooled, but the utility fluid (water, steam, refrigerant, or Heat Transfer Fluid) is equally important. Their properties and availability may not be under complete control of the user, especially if they are supplied by a public utility. Even though we may specify 150 psig steam on a process flow sheet as well as on our calculations, the chances of the steam being at exactly 150 psig at any given time are slim to none, despite the best intentions of the utility manager or supplier. What happens if it’s 140 psig? 160 psig? Can the process fluid overheat? Are there any consequences to this? (Recall our discussions about HAZOP

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