Presentacion 1 lab heat final
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Transcript of Presentacion 1 lab heat final
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Polytechnic University of Puerto RicoChemical Engineering Department
Winter 2016
Ashley M. Ramirez Quiles Stephanie P. Rivera Ares Edgared M. Troche Muñiz Jorge Sepulveda November 29, 2016 CHE 3321- 22 Prof. Pablo Traverso
Heat Transfer Linear Conductivity Effect
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AgendaObjectives
Theory
Equipment
Procedure
Data
Calculations
Security
References
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Objectives
Determine thermal conductivity and temperature difference in stainless steel, brass, aluminum and isolators for a steady state conduction.
Contact resistance effect in the interphase and thermal paste
Conduct analysis and comparison of the resistance effects
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TheoryConduction Heat Transfer
Energy is transferred as heat due to a temperature potential difference in a body, or between bodies in contact with each other.
Figure 1. Representation of heat flow [1]
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Theory
Thermal proportionality constant :
; Heat transfer rate is proportional to the temperature gradient.
; Fourier’s Law
Wiedemann-Franz Law:
, and
Figure 2. One-dimensional steady state heat transfer, temperature gradients. [2]
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TheoryEnergy Balance:
+
For constant Thermal Conductivity:
+;
Figure 2. Volume element for one dimensional heat-conduction. [2]
T1>T2
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Theory Under steady state conditions, the
temperature distribution is linear, and the temperature gradient may be expressed as:
Fourier’s Rate Equation;
Experimental
Figure 3. Linear direction of heat flow. [3]
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TheoryHeat Flow:
Figure 4. One-dimensional heat transfer through a composite wall, and its equivalent electrical analog. [3]
;
(𝐴∗𝑅𝑡 h)=𝑅𝑣𝑎𝑙𝑢𝑒=∆𝑇𝑞𝐴
=∆𝑥𝑘
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Theory
Overall Heat-Transfer Coefficient (U)
In a composite wall we can state that;
Figure 5. Composite wall. [4]
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TheoryReduced cross-sectional area of heat transfer between thermocouples:
From Fourier’s Law;
Rearranging the equation;
;
Figure 6. Composite wall with reduced area. [5]
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TheoryThermal Contact Resistance:
From the energy balance equation;
Figure 8. Joint-roughness model for the analysis of hc . [3]
𝑞=𝑇 2𝐴−𝑇2 𝐵
𝐿𝑔
2𝑘𝐴 𝐴𝑐+
𝐿𝑔
2𝑘𝐵 𝐴𝑐
+𝑘 𝑓 𝐴𝑣𝑇 2 𝐴−𝑇 2𝐵
𝐿𝑔=𝑇 2 𝐴−𝑇 2𝐵
1h𝑐 𝐴
h𝑐=1𝐿𝑔
( 𝐴𝑐
𝐴2𝑘𝐴𝑘𝐵
𝑘𝐴+𝑘𝐵+𝐴𝑣
𝐴 𝑘 𝑓 );Figure 7. Illustration of the thermal contact resistance effect, temperature profile. [5]
Figure 9. Ideal and actual thermal contact. [2]
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Theory
Figure 11. Effect of metallic coatings on thermal contact surfaces. [2]
Figure 10. Contact conductance of typical surfaces. [3]
MaterialThermal
Conductivity - k -
W/(m K)
Temp.(oC)
Air, atmosphere (gas) 0.024 25
Aluminum 205 25
Aluminum Brass 121 25
Beef, lean (78.9% moisture) 0.43 - 0.48 25
Brass 109 25
GM280 (Si, thermal
paste)1.2 -45
Stainless Steel 16 25
Water 0.58 25
Figure 12. Thermal conductivities of various materials. [6][7]
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Equipment
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Equipment
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Procedure Measure the temperature distribution for
the steady state conduction of energy through a uniform flat wall and demonstrate the effect of a change in the heat flow.
Understand the use of the Fourier Frequency equation to determine the rate of heat flux through solid materials for one-dimensional heat flow.
Measure the temperature distribution for steady-state energy conduction through a composite flat wall and determine the global heat transfer coefficient for a heat flow through a combination of different materials in series.
Determine the thermal conductivity (k) of a sample of metal.
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Procedure Show that the temperature gradient is
inversely proportional to the cross-sectional area for one-dimensional heat flow in a solid material of constant thermal conductivity.
Demonstrate the effect of contact resistance on thermal conduction between adjacent materials.
Understand the application of poor conductors (insulators) and determine the thermal conductivity k (the proportionality constant) of an insulation.
Observe the conduction of the heat in an unstable state (qualitative only with a graphic recorder or a connected PC).
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Data
Heater Voltage (V)Heater current (Amps)
Heated Section Temperature (°C)Cooled Section Temperature (°C)
Cooling Water Flowrate (L/min)Heat Flow (Watts)
V I T1, T2, T3 T6, T7, T8 Fw Q=VI
• As the electrical supply to the heater is Direct Current the power supplied to the heater is simply obtained from the product of the Voltage and Current, i.e. [5]
Heater Power (Q) = Voltage (V) x Current (I)
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Calculations Steady-State Heat
Conduction:
The Fourier Rate Equation:
(m2 , cross sectional area of bar)
The Overall Heat Transfer Coefficient:
(m2 ) cross sectional area
(∘C)
Temperature difference across composite wall
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Calculations Thermal Conductivity:
(Constant of Proportionality)
Inverse Proportionality of Temperature Gradient to Area:
Effect of Contact Resistance on Thermal Conduction:
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Calculations Thermal Conductivity and
Application of Insulators: Unsteady State Conduction
of Heat:
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Safety
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References
[1] http://philschatz.com/physics-book/contents/m42228.html
[2] Dr. Balku, Ş. (2015). STEADY HEAT TRANSFER AND THERMAL RESISTANCE NETWORKS. Retrieve from http://slideplayer.com/slide/6638492/
[3] J P Holman, S. B. (2011). HEAT TRANSFER (In SI Units). (10). (M.-H. G. Holdings, Ed.) New York, United States.
[4] http://www.engr.iupui.edu/~mrnalim/me314lab/lab02.htm
[5] Manual Lab.
[6] http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/thrcn.html
[7] http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html
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ANY QUESTIONS?