boiling heat transfer ppt and advanced heat transfer ppt and heat and mass transfer powerpoint slides
Dr.TomHunt,United States,Teacher
Published Date:22-07-2017
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A Short Course on Heat Transfer
Intended as a repetition from previous courses
by
Björn Palm,
Royal Institute of Technology, Stockholm Course Contents,
based on Holman’s book Heat Transfer
Chapter 1: Introduction
Chapter 2: Steady-State Conduction - One Dimension
Chapter 3: Steady-State Conduction - Multiple Dimensions
Chapter 4: Unsteady-State Conduction
Chapter 5: Principles of Convection
Chapter 6: Empirical and Practical Relations for Forced-Convection
Heat Transfer
Chapter 7: Natural Convection Systems
Chapter 8: Radiation Heat Transfer
Chapter 9: Condensation and Boiling Heat Transfer
Chapter 10: Heat Exchangers
(Chapter 11: Mass Transfer)
2 Part 1
Introduction
3 Introduction
What is heat?
Heat is energy transfer caused by temperature difference
4
The four laws of thermodynamics:
• Zeroth law:
If two bodies both are in thermal equilibrium with a third
body, they are also in thermal equilibrium with each other,
and they then are said to have the same temperature.
5
• First law: (Energy principle)
Energy cannot be generated or destroyed, only converted to
different forms.
(”Energy consumption” is the transfer of ”prime” energy to
thermal energy in the surrounding)
6 • Second law:
Heat cannot by itself pass from one body to another body
with higher temperature.
(Entropy disorder strives to a maximum in a closed system.
Shows the direction of time.)
7 •
8 Third law:
The entropy of a pure, crystalline material takes its lowest
value at absolute zero temperature, where it is 0.
(There is a lowest limit to the temperature, 0K = -273.15°C.
World record: 0.00000017 K = 170 nanokelvin)
9 Three modes of heat transfer:
• Conduction
Through solid bodies and ”still” fluids hot cold
• Convection
Through moving fluids
(also boiling and condensation)
• Radiation
Between surfaces, through gas or vacuum
hot cold
10
What do we know about conduction?
11 Conduction, thermal conductivity, Fourier´s law:
Fourier’s law:
q = -k⋅A⋅δT/δx
where, q = heat flow (W)
2
A = area perpendicular to heat flow (m )
δT/δx = temperature gradient in the direction
of heat flow(°C/m)
k = thermal conductivity (W/(m °C))
Fourier´s law is the defining equation for the thermal
conductivity.
12 Conduction, thermal conductivity, Fourier´s law:
For one-dimensional heat transfer (a plane wall,) with
constant thermal conductivity, Fourier´s law is simplified to
q = k⋅A⋅ΔT/δ
where ΔT = temperature difference (°C)
δ = distance or thickness (m).
13
fig. 1
Temp
δT/δx0
x
Hot Cold
q0
14 Fig. 2 Heat transfer through a plane wall
T1
ΔT
T2
δ
15 Table 1
Material
Thermal conductivity (20°), (W/m⋅°C)
Diamond, type IIa 2600
Copper 386
Iron, wrought, 0.5% C 60
Stainless steel, 18/8 16.3
Brick 0.69
Water 0.6
Pine wood, 0.15/0.33 (cross/along fibres)
Cork 0.045
Glass wool 0.038
Mineral wool 0.04
Polyurethane 0.02
Air 0.026
Argon gas 0.018
16
Example to solve:
Conduction:
Calculate the heat flow per square meter (heat flux) through a
mineral wool insulation, 5 cm thick, if the temperatures on the
two surfaces are 30 and 200°C, respectively.
17 Heat transfer by convection, Newton’s law of cooling
Convection is a general term for heat transfer through a
moving fluid.
18
Fig 3, Different types of convection heat transfer
Boiling
Forced
convection
Diffusion,
mass
transfer
Condensation
19
What do we know about convection?
20
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