Heat transfer coefficient calculation for forced convection refers to the process of determining the efficiency at which heat is transferred from a solid surface to a fluid when the fluid flow is induced or forced over the surface. It involves quantifying the rate of heat transfer and the temperature difference between the solid surface and the fluid.
The heat transfer coefficient (h) represents the ability of the fluid to extract heat from the solid surface. It is a key parameter in determining the overall heat transfer rate in forced convection scenarios. The calculation of the heat transfer coefficient involves considering factors such as fluid properties, flow conditions, surface characteristics, and the geometry of the system.
By evaluating the rate of heat transfer, surface area, and temperature difference, the heat transfer coefficient can be determined using appropriate equations or experimental correlations. This calculation helps in understanding and optimizing heat transfer processes in various engineering applications, such as cooling systems, heat exchangers, and HVAC systems, where forced convection is involved.
Accurate determination of the heat transfer coefficient enables engineers and researchers to design and optimize heat transfer systems, improve energy efficiency, and ensure adequate thermal management in various industries and applications.
2. • When heat flow is achived by mixing of warmer portions with cooler
portions of same material is known as convection.
TYPES:
1. Free convection : mixing of fluid accomplished by current set up when
body of fluid is heated such process known as free convection
2. Forced convection : mixing of fluids may be obtained by usinguse of
stirrers or agitator or pumping of fluid for recirculation such processes in
heat treansfer is designated as convective heat transfer.
What is CONVECTION ?
4. METAL WALL-
• Dotted lines HH and CC – boundaries
of hot fluid and cold fluid
• Temeperature gradient through the
line
𝑡𝑐 𝑡𝑑 through the metal wall whose
thermal conductvity is known
• Metal wall thickness is L
1. HOT FLUID SIDE
• 𝑡𝑎 - Maximum temperature in hot
fluid
• 𝑡𝑏 - Temperature at boundary
• 𝑡𝑐 - Temperature at actual interface
• Curve 𝑡𝑎 , 𝑡𝑏, 𝑡𝑐temperature gradient
from hot fluid to metal wall
• 𝑡𝑏- Average temperature on hot fluid
side
Metal
wall
𝑡𝑎
𝑡𝑏
𝑡1
M
𝑡𝑐
𝑡𝑑
𝑡𝑒
𝑡2
N
𝑡𝑓
L
HOT FLUID
(turbulenT)
COLD
FLUID
(turbulent)
Z
C H
5. 2. COLD FLUID SIDE
• 𝑡𝑓 - is minimum temperature on
cold fluid side
• 𝑡𝑒 - is temperature boundry at
cold fluid side
• 𝑡𝑑- Temprature at actual
interface
• Curve 𝑡𝑑, 𝑡𝑒, 𝑡𝑓is temperature
gradient metalwall to cold side
• 𝑡2- Average temperature on cold
fluid side
Metal
wall
𝑡𝑎
𝑡𝑏
𝑡1
M
𝑡𝑐
𝑡𝑑
𝑡𝑒
𝑡2
N
𝑡𝑓
L
HOT FLUID
(turbulenT)
COLD
FLUID
(turbulent)
Z
C H
6. SURFACE FILM COEFFICIENT
• The quantity of heat flowing through unit area of the film
for unit drop in temperature.
Let us consider :
• Q watt of heat flowing from hot fluid to cold fluid
• Area of metal wall on hot side - 𝐴1 𝑚2
• Area of metal wall on cold side - 𝐴2 𝑚2
• Average area of metal wall - 𝐴𝑚𝑚2
7. • Film coefficient on hot
side=
𝐴𝑚𝑜𝑢𝑡 𝑜𝑓 ℎ𝑒𝑎𝑡 𝑓𝑙𝑜𝑤𝑖𝑛𝑔 (𝑊)
𝑎𝑟𝑒𝑎 𝑚2 𝑋 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑖𝑛 𝑡𝑒𝑚𝑝𝑟𝑎𝑡𝑢𝑟𝑒 (𝑘)
• ℎ1 =
𝑞
𝐴1 (𝑡1−𝑡2)
•
𝑡1−𝑡2
𝑞
=
1
ℎ1𝐴1
• So =
1
ℎ1𝐴1
is known as thermal resistance on hot side
Similarly, film coefficient on cold side ℎ2 =
𝑞
𝐴2 (𝑡𝑑−𝑡2)
And
1
ℎ2𝐴2
is known as thermal resistance on cold side
8. OVERALL COEFFICIENT
•
1
ℎ1𝐴1
is the resistance on hot fluid side
•
𝐿
𝐾 𝐴𝑚
is the resistance of metal wall
•
1
ℎ2𝐴2
is the resistance on cold fluid side
So overall heat transfer may be written as
q=
Δ𝑡
1
ℎ1𝐴1
+
𝐿
𝐾 𝐴𝑚
+
1
ℎ2𝐴2
9. Right side of the equation multiplied by
𝐴1
𝐴1
q=
𝐴1Δ𝑡
1
ℎ1
+
𝐿𝐴1
𝐾 𝐴𝑚
+
𝐴1
ℎ2𝐴2
Overall heat transfercoefficient 𝑈1 is −
𝑈1=
1
1
ℎ1
+
𝐿𝐴1
𝐾 𝐴𝑚
+
𝐴1
ℎ2𝐴2
(1)
(2)
Compairing both equations (1) and (2)
q= 𝑈1𝐴1Δ𝑡
10. • q= 𝑈1𝐴1Δ𝑡
So,
Rate of heat
transfer
Overall heat
Transfer
coefficient
Temp.
Drop
Area of
heating
surface
11. FOR TUBULAR WALL
Area “A” replaced by diameter “D”
So, overall transfer coefficient 𝑈1is –
𝑈1=
1
1
ℎ1
+
𝐿𝐷1
𝐾 𝐷𝑚
+
𝐷1
ℎ2𝐷2
So,
Q= 𝑈1𝐷1Δ𝑡
12. REFRENCES
• Food Process Engineering and
Technology Zeki Berk Professor
(Emeritus) Department of
Biotechnology and Food
Engineering TECHNION Israel
Institute of Technology Israel
• https://youtu.be/v47uTuEGW9
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