Basics of heat trasfer and heat exchanger
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HEAT TRANSFER and HEAT EXCHANGERS Collected and Rearranged By Mohamed Saad – Mohamed Adel
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this presentation provides a basic and brief knowledge about heat transfer methods, and also a quick lock about heat exchanger design and types.
Transcript of Basics of heat trasfer and heat exchanger
HEAT TRANSFERand
HEAT EXCHANGERS
Collected and Rearranged
By Mohamed Saad – Mohamed Adel
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HEAT TRANSFER LAW APPLIED TO HEAT EXCHANGERS
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Heat Transfer by Conduction
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• The transfer of energy between objects that are in physical contact
• Transfer of energy by touch
Thermal Conductivity of solids
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Thermal Conductivity of gases
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Thermal conductivity of liquids
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The Heat Conduction Equation
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Rate of heat generation inside control volume
Rate of energy storage inside control volume
Rate of heat conduction into control volume
+ =
Rate of heat conduction out of control volume
+
Heat Transfer by Convection
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The transfer of energy between an object and its environment, due to fluid motion
Natural Convection
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• Hot air rises cool air falls
• Convection – heat transferred by the circulation of a fluid (or gas), such as in a heating system at home; important near the surface of the Sun.
Heat Transfer by Radiation
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q = ε σ (Th4 - Tc4) Ac
Th = hot body absolute temperature (K)
Tc = cold surroundings absolute temperature (K)
Ac = area of the object (m2)
σ = 5.6703 10-8 (W/m2K4)
The Stefan-Boltzmann Constant
The transfer of energy to or from a body by means of the emission or absorption of electromagnetic radiation
Emissivity coefficient for several selected material
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Surface MaterialEmissivity Coefficient
- ε -
Aluminum Commercial sheet 0.09
Aluminum Foil 0.04
Aluminum Commercial Sheet 0.09
Brass Dull Plate 0.22
Brass Rolled Plate Natural Surface 0.06
Cadmium 0.02
Carbon, not oxidized 0.81
Carbon filament 0.77
Concrete, rough 0.94
Granite 0.45
Iron polished 0.14 - 0.38
Porcelain glazed 0.93
Quartz glass 0.93
Water 0.95 - 0.963
Zink Tarnished 0.25
Heat Exchanger
The main concept is “heat economy”
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• A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another
1) Double pipe heat exchanger
The simplest design for heat exchanger consist of two concentric pipes One fluid flow inside the small pipe and the second
fluid flows in the space between the two pipes
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2) Shell and tube heat exchanger
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• Shell and tube heat exchangers consist of a series of tubes. One set of these tubes contains the fluid that must be cooled. The second fluid runs over the tubes that are being heated so that it can absorb the heat required
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Baffle type and spacing
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General design consideration
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Factor Tube-side Shell-side
Corrosion More corrosive fluid Less corrosive fluids
Fouling Fluids with high fouling
and scaling
Low fouling and scaling
Fluid temperature High temperature Low temperature
Operating pressure Fluids with low pressure
drop
Fluids with high pressure
drop
Viscosity Less viscous fluid More viscous fluid
Stream flow rate High flow rate Low flow rate
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3) plate and frame heat exchanger
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• the plate heat exchanger is composed of multiple, thin, slightly separated plates that have very large surface areas and fluid flow passages for heat transfer. This stacked-plate arrangement can be more effective, in a given space, than the shell and tube heat exchanger.
4) Spiral heat exchangers :
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Temperature profile for different types of heat exchangers
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Thank you for attention
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