PHYSICAL FUNDAMENTALS Chapter 4

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PHYSICAL FUNDAMENTALSChapter 4

• MARKKU LAMPINEN
• MAMDOUH EL HAJ ASSAD
• ERIC F. CURD

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Contents of Chapter 4

• FLUID FLOW
• Fluid Properties
• Constants for Water
• Constants for Gases
• Properties of Air and Water Vapor
• Liquid Flow
• Bibliography
• STATE VALUES OF HUMID AIR MOLLIER DIAGRAMS AND
  THEIR APPLICATIONS
• Properties of Air and Other Gases
• Fundamentals
• Water Vapor Pressure in the Presence of Air
• Vapor Pressure of Water and Ice and Calculation
  of Humid Air State Values
• Construction of Mollier Diagram
• Determination of Air Humidity
• State Changes of Humid Air
• Example of Cooling Tower Dimensioning

• HEAT AND MASS TRANSFER
• Different Forms of Heat Transfer
• Analogy with the theory of electricity
• Heat Conduction
• Heat Convection
• Thermal Radiation
• Mass Transfer Coefficient
• Heat and Mass Transfer Differential Equations in
  the Boundary Layer and the Corresponding Analogy
• Diffusion through a Porous Material
• Example of Drying Process Calculation
• Evaporation from Multicomponent Liquid System
• WATER PROPERTIES AND TREATMENT
• Introduction
• Common Water Impurities
• Cooling Water Systems
• Water Treatment
• References

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FLUID FLOW

• It is essential that the engineer involved in
  industrial ventilation have a good foundation in
  the subject of fluid mechanics, which involves
  the study of fluids at rest or in motion.
• The fields of application are wide involving
  computational fluid dynamics (CFD), flow in ducts
  and pipes, pumps, fans, collection devices,
  pollution dispersal, and many other applications.

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Properties of Air and Other Gases

• The analysis of dry atmospheric air varies with
  location, altitude, time of year,and other
  factors.

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Fundamentals

• Air is seldom dry it normally contains varying
  amounts of moisture.
• Humid air is a mixture of dry air and water
  vapor.
• The term dry air denotes the mixture of all gases
  present in air (nitrogen, oxygen, carbon
  monoxide, and inert gases), except water vapor.

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Different Forms of Heat Transfer

• For any method of heat transfer to take place, a
  temperature difference is necessary between two
  faces of a solid body, or at the boundaries of a
  gas or vapor.
• Heat transfer will take place only from a
  high-temperature source to a lower-temperature
  sink and is an irreversible process unless acted
  upon by another agency, as is the case with the
  refrigeration process.
• Heat transfer may occur by one or more of three
  different modes
• Conduction, which may be one-, two-, or
  three-dimensional or internally generated
• Convection, which may be natural or forced
• Radiation, which may be symmetrical or
  nonsymmetrical

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WATER PROPERTIES AND TREATMENT

• It is essential that the industrial ventilating
  engineer have a basic understanding of the
  properties of water and its treatment. This is to
  ensure an efficiently running and trouble-free
  plant.
• Additional to these issues are the problems
  relating to the discharge of contaminated water
  to the surrounding environment.

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Water Treatment

• In most engineering applications the supply water
  is not suitable for immediate use without
  treatment.
• It is essential that the method of water
  treatment selected be the one most suited to the
  application.
• If steam is used as the working medium for a
  process, it is essential that water treatment be
  used to prevent the precipitation of substances
  in the water from fouling pipe work and heat
  exchangers otherwise costly plant damage will
  result.

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WATER PROPERTIES TREATMENT
Ch 4.4
Water treatment necessary to reduce-

• Metal corrosion
• Scale formation on heat transfer surfaces
• Dezincification
• Plumbosolvancy
• Biological health hazards
• Microbiological fouling of surfaces

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COMMON WATER IMPURITIES

• Table 4.13 gives-
• Chemical constituent
• Chemical formula
• Problems caused
• Methods of treatment to overcome the problems

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HEAVY METALS

• Table 4.14 gives-
• A range of heavy metals encountered.
• Chemical formula
• The health and other problems caused by these
  metals.

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COOLING WATER SYSTEMS

• Heat rejection from process water is achieved
  by-
• Open recirculation.
• Closed recirculation.
• once through system.

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OPEN RECIRCULATION

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CLOSED RECIRCULATION

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ONCE THROUGH SYSTEM
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WATER TREATMENT

• Required to-
• Eliminate corrosion
• Improve heat transfer efficiency
• To eliminate health risks
• Ensure water is of the correct standard for a
  given process
• Biological control of surfaces

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METHODS OF TREATMENT

• Achieved by one or more of the following
  methods-
• External
• Sedimentation
• Oxidation
• Filtration
• Softening

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PLANT CLASSIFICATION

• Selection depends on many factors
• Lime soda
• Ion exchange which may be-
• Base Exchange
• Dealkalisation
• Demineralisation
• Precipitation softening
• Evaporation
• Reverse osmosis
• Magnetic water treatment
• Deaeration
• Oxygen scavenging
• etc

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BIOLOGICAL FACTORS

• Covering-
• Microbiological fouling in heat exchanging plant
• Microbiological corrosion
• Heath aspects on operators and others

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SEPARATION TECHNIQUES
1. Separation of a liquid from a solid 2.
Separation of a solid from a liquid
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SEPARATION OF A LIQUID FROM A SOLID

• Required to-
• Re-use liquid again
• Collect for recycling valuable particulates
• Ensure water courses are not contaminated

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LIQUID SEPARATION ACHIEVED BY

• Gravitational force
• Centrifugal force
• Vacuum
• Mechanical force
• Solvents
• Displacement
• Vaporisation

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SEPARATION OF SOLID FROM A LIQUID

• Achieved by one or more of the following
  methods-
• Relative solubility
• Reduction of solubility
• Chemical precipitation
• Ion exchange
• Electrolytic deposition
• Absorptive properties

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SEPERATION OF SOLIDS IN LIQUID SUSPENSION
Achieved by-

• 1.Density difference
• 2. Difference in cross section of particulate
  matter and
• liquid molecule
• Density differences work by-
• Particulate size
• Settling velocity
• Quantity of solids in suspension
• Aerobic process
• Anaerobic treatment

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DESIGN CONSIDERATIONS

• The owning and operating costs include-
• Initial cost
• Maintenance
• Energy cost
• Water treatment costs
• Corrosion costs
• Odour treatment
• Abrasion problems
• Slurry pumping problems
• Allowable discharge temperature into drains

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HEAT TRANFER FLUIDS

• Considers-
• Anti freeze fluids
• Heat transfer fluids
• Table 4.15 provides the characteristics of
  various solutions.

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Cooling Water Systems

• Cooling water systems used for process heat
  rejection can be classified under one of the
  following headings
• Open recirculation
• Closed recirculation
• Once-through system