Refrigeration, Air Conditioning and Heat Pumps

G F Hundy

• Verlag: Butterworth-Heinemann
• Jahr: 2016
• ISBN:
  9780081006665
• Auflage: 5
• Thema: Scienze fisiche
• Thema: Termodinamica

Refrigeration, Air Conditioning and Heat Pumps, Fifth Edition, provides a comprehensive introduction to the principles and practice of refrigeration. Clear and comprehensive, it is suitable for both trainee and professional HVAC engineers, with a straightforward approach that also helps inexperienced readers gain a comprehensive introduction to the fundamentals of the technology. With its concise style and broad scope, the book covers most of the equipment and applications professionals will encounter. The simplicity of the descriptions helps users understand, specify, commission, use, and maintain these systems.

It is a must-have text for anyone who needs thorough, foundational information on refrigeration and air conditioning, but without textbook pedagogy. It includes detailed technicalities or product-specific information. New material to this edition includes the latest developments in refrigerants and lubricants, together with updated information on compressors, heat exchangers, liquid chillers, electronic expansion valves, controls, and cold storage. In addition, efficiency, environmental impact, split systems, retail refrigeration (supermarket systems and cold rooms), industrial systems, fans, air infiltration, and noise are also included.

• Full theoretical and practical treatment of current issues and trends in refrigeration and air conditioning technology
• Meets the needs of industry practitioners and system designers who need a rigorous, but accessible reference to the latest developments in refrigeration and AC that is supported by coverage at a level not found in typical course textbooks
• New edition features updated content on refrigerants, microchannel technology, noise, condensers, data centers, and electronic control

Chapter 1

Fundamentals

Abstract

An introduction to the relationships between temperature, work and heat and the minimum amount of energy required to lift heat from a low temperature to a higher one is given. This results in a definition of ideal or Carnot coefficient of performance. The behaviour of fluids in the liquid/gas phase region is explained with reference to a temperature/enthalpy diagram and the variation of boiling point with pressure. The general gas laws are covered. A detailed description of the pressure/enthalpy diagram is given together with how plots of various processes can be made. Heat transfer in the form of conduction, convection and radiation is described. There is an elementary introduction to the use of non-dimensional groups in dealing with convection problems, and log mean temperature difference in dealing with heat transmittance. Finally, transient heat flow and two-phase heat transfer are introduced. Worked numerical examples are provided.

Keywords

temperature

work

heat

Carnot COP

sensible heat

latent heat

boiling point

Boyle’s law

Charles’ law

Dalton’s law

pressure/enthalpy diagram

Mollier diagram

heat transfer

conduction

convection

radiation

heat transmittance

log mean temperature difference

heat exchanger effectiveness, transient heat flow

two-phase heat flow

1.1. Introduction

Refrigeration is the action of cooling, and in practice this requires removal of heat and discarding it at a higher temperature. Refrigeration is therefore the science of moving heat from low temperature to high temperature. In addition to chilling and freezing applications, refrigeration technology is applied in air conditioning and heat pumps, which therefore fall within the scope of this book. The fundamental principles are those of physics and thermodynamics, and these principles, which are relevant to all applications, are outlined in this opening chapter.

1.2. Temperature, work and heat

The temperature scale now in general use is the Celsius scale, based nominally on the melting point of ice at 0°C and the boiling point of water at atmospheric pressure at 100°C (by strict definition, the triple point of ice is 0.01°C at a pressure of 6.1 mbar).

The law of conservation of energy tells us that when work and heat energy are exchanged there is no net gain or loss of energy. However, the amount of heat energy that can be converted into work is limited. As the heat flows from hot to cold, a certain amount of energy may be converted into work and extracted. For example, it can be used to drive a generator.

The minimum amount of work to drive a refrigerator can be defined in terms of the absolute temperature scale. Fig. 1.1 shows a reversible engine E driving a reversible heat pump P; Q and W represent the flow of heat ...