Natural Convection Heat Transfer
Natural Convection Heat Transfer
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This is Non linear transient heat transfer analysis.
This is Non linear transient heat transfer analysis.
(Mechanical APDL Ansys)
(Mechanical APDL Ansys)
Objective:-
Objective:-
The objective is to study natural convection heat transfer through heat sink and to track the temperature distribution in aluminium heat sink during natural convection heat transfer process, which occurs over a duration of 11 hours.
Problem Description:-
Problem Description:-
The system comprises of heater and heat sink(plate and vertical fins). Heater is insulated from bottom all other sides of heater and heat sink are exposed to ambient air. All the materials are considered to be aluminium. Convection and radiation occurs between heater + heat sink and ambient air.
Heater and Heat sink
Volume is simplified from actual system
Base plate and Vertical fins(Heat sink)
Heat sink
Elements(Solid 278) ISO View
Elements(Solid 278) Oblique View
Heat Sink Elements
Thermal conductivity vs Temp Graph
(Aluminium)
All other material properties of aluminium and air are considered at film temperature for this analysis.
Some Calculation to estimate the initial and boundary condition which are required in analysis before starting this analysis:-
Some Calculation to estimate the initial and boundary condition which are required in analysis before starting this analysis:-
Heat generation
As, heater is insulated from bottom so heat loss due to conduction is considered negligible.
Initial temperature of heater = 800 K (Initial condition)
Ambient temperature of air = 300 K (Boundary condition)
To estimate time duration taken in analysis. Surface temperatures,Nu,h and Bi at the starting of analysis is calculated using following formulas:-
To estimate time duration taken in analysis. Surface temperatures,Nu,h and Bi at the starting of analysis is calculated using following formulas:-
Film temperature = 549.9 K
here, to calculate these surface temperature, the value of h=4 W/m2K is initially assumed by calculating experimental measured values.
- Temperature at top surface of heater = 799 K (Boundary condition)
- Temperature at top surface of heat sink base plate = 799.87 K (Boundary condition)
- Temperature at center of vertical fin = 799.8 K (Boundary condition)
- Temperature at top surface of vertical fin = 799.75 K (Boundary condition)
properties of aluminium is taken in GrL formula
RaL = 1.1427 x 109 (104<RaL<109 )
hence, Air flow will be laminar
The flow rate in natural convection heat transfer is established by the dynamic balance of buoyancy and friction
properties of ambient air are taken in Pr formula
h = 14.9 W/m2K (Boundary condition)
Qgen = 3188.33 W (Boundary condition)
Bi = 3.19 x 10-3 < 0.1
hence, this problem can be considered as lumped system for (aprox) time duration estimation in analysis.
Lumped system time estimation formula
∴ t = 38129.94 sec
t = 10.59 hours
800 K ( heater temperature) to 302 K(top surface of vertical fin temperature)
where,
also,
characteristic length
convection load
Solve
Result:-
Area no 62 selected to plot thermal graph result of analysis
Nodes of Area no 62
Node_3629 is selected to plot thermal graph results
Temp vs Time graph of Node 3629
Thermal gradient sum vs time graph of Node 3629
Area no 173 is selected to plot thermal graph results
Area no 173
Nodes of Area no 173
Node 190 is selected to plot thermal graph results
Temp vs Time graph for Node 190
Thermal flux sum vs Time Graph of Node 190
Thermal Gradient sum vs Time graph of Node 190
Temperature distribution animation
TEMP ISO.aviTEMP FRONT.aviTEMP TOP.aviTEMP OBLIQUE.aviTEMP SIDE.aviTEMP_BACK.aviThermal Flux sum animation
THERMAL FLUX SUM_FRONT.aviTHERMAL FLUX SUM_OBLIQUE.aviTHERMAL FLUX SUM_BACK.aviTHERMAL FLUX SUM_ISO.aviTHERMAL FLUX SUM_TOP.aviTHERMAL FLUX SUM_SIDE.aviThermal Gradient sum animations
THERMAL GRADIENT SUM_BACK.aviTHERMAL GRADIENT SUM_FRONT.aviTHERMAL GRADIENT SUM_OBLIQUE.aviTHERMAL GRADIENT SUM_TOP.aviTHERMAL GRADIENT SUM_SIDE.aviTHERMAL GRADIENT SUM_ISO.aviThank you
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