Bài giảng Chapter 1: Introduction

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Bài giảng Chapter 1: Introduction CHAPTER 1: INTRODUCTION ƒ `` Lecturer :Th.S Nguyễn Duy Tuệ12/2015 1 Chapter 1 : Introduction OBJECTIVES - Student can understand the history of refrigerant - Understand the benefits and kinds of refrigerant system12/2015 Chapter 1 : Introduction 2 REFERENCE [1]. 4O LESSONS ON REFRIGERATION AND [1] AIR CONDITIONING FROM IIT KHARAGPUR. ( Useful training material for mechanical engineering students/college, or reference for engineer ) - Indian Institute of Technology (IIT) [2]. Danfoss document12/2015 Chapter 1 : Introduction 3 CONTENT Applications of refrigerant History of refrigerant system Types of refrigeration system12/2015 Chapter 1 : Introduction 4 Applications of refrigerant - The job of a refrigeration plant is to cool articles or substances down to, and maintain them at a temperature lower than the ambient temperature. Refrigeration can be defined as a process that removes heat. - The oldest and most well-known among refrigerants are ice, water, and air. In the beginning, the sole purpose was to conserve food.12/2015 Chapter 1 : Introduction 5 Applications of refrigerant - It had been discovered that the growth of microorganisms is temperature-dependent, that growth declines as temperature falls, and that growth becomes very slow at temperatures below +10 °C.12/2015 Chapter 1 : Introduction 6 Applications of refrigerant There are countless applications for refrigeration plants now. Examples are: - Foodstuff conservation - Process refrigeration - Air conditioning plants - Drying plants - Fresh water installations - Refrigerated containers - Heat pumps - Ice production - Freeze-drying - Transport refrigeration12/2015 Chapter 1 : Introduction 7 History of refrigerant 1. Natural Refrigeration : (page 3, [1]) - In olden days refrigeration was achieved by natural means such as the use of ice or evaporative cooling. In earlier times, ice was either: + Transported from colder regions, + Harvested in winter and stored in ice houses for summer use or, + Made during night by cooling of water by radiation to stratosphere.12/2015 Chapter 1 : Introduction 8 History of refrigerant -In Europe, America and Iran a number of icehouses were built to store ice. Materials like sawdust or wood shavings were used as insulating materials in these icehouses. Later on, cork was used as insulating material. - In 1806, Frederic Tudor, (who was later called as the “ice king”) began the trade in ice by cutting it from the Hudson River and ponds of Massachusetts and exporting it to various countries including India.12/2015 Chapter 1 : Introduction 9 History of refrigerant a. Art of Ice making by Nocturnal Cooling (at night): - The art of making ice by nocturnal cooling was perfected in India. In this method ice was made by keeping a thin layer of water in a shallow earthen tray (baked clay), and then exposing the tray to the night sky. - Compacted hay (dried grass) of about 0.3 m thickness was used as insulation. The water looses heat by radiation to the stratosphere, which is at around -55°C -> the water in the trays freezes to ice. -> Very popular in India.12/2015 Chapter 1 : Introduction 10 History of refrigerant b. Evaporative Cooling: - Evaporative cooling is the process of reducing the temperature of a system by evaporation of water. - Used in India for centuries to obtain cold water in summer by storing the water in earthen pots. The water permeates through the pores of earthen vessel to its outer surface where it evaporates to the surrounding, absorbing its latent heat in part from the vessel, which cools the water. -> Better in hot and dry air condition12/2015 Chapter 1 : Introduction 11 History of refrigerant12/2015 Chapter 1 : Introduction 12 History of refrigerant c. Cooling by Salt Solutions: - This reduces the temperature of the solution(water+salt). Sodium Chloride salt (NaCl) can yieldtemperatures up to -20°C and Calcium Chloride(CaCl2) up to - 50°C in properly insulated containers. - However, as it is this process has limitedapplication, as the dissolved salt has to be recoveredfrom its solution by heating.12/2015 Chapter 1 : Introduction 13 History of refrigerant12/2015 Chapter 1 : Introduction 14 History of refrigerant12/2015 Chapter 1 : Introduction 15 History of refrigerant 2. Artificial Refrigeration : (page 5, [1]) - Professor William Cullen of the University ofEdinburgh demonstrated this in 1755 by placingsome water in thermal contact with ether under areceiver of a vacuum pump. The evaporation rate ofether increased due to the vacuum pump and watercould be frozen. -> The temperature of ether will remain constant aslong as the vacuum pump maintains a pressureequal to saturation pressure at the desiredtemperature.12/2015 Chapter 1 : Introduction 16 History of refrigerant - U.F. Clouet and G. Monge liquefied SO2 in1780 while van Marum and Van Troostwijk liquefiedNH3 in 1787. Hence, a compressor is required tomaintain a high pressure so that the evaporatingv ...