Heat Transfer Project: Heat Transfer Project: The “Cooling Soup” DilemmaThe “Cooling Soup” Dilemma
Mike MantylaMike MantylaSteve HarstonSteve Harston
ME 340-1ME 340-1
The ProjectTest the effectiveness of cooling a hot liquid using
different cooling methods.
Cooling Methods tested:– Ambient air (small temperature difference)– Freezer (large temperature difference)– Mixing the fluid while cooling– Constant air flow over liquid– Constant air flow with stirring– Adding ice-cubes
Liquids tested: Water
ProcedureBoil water, cool to determined temperature,
measure time.
Assumptions:– Heat transfer through bowl neglected– Change in mass due to evaporation neglected– Bowl can be evaluated as a cylinder– Heat transfer to stirring spoon neglected
See Appendix for Calculations
Method 1: Ambient Air
CTi 95CT f 65CT 28
Description: Measure time for water to cool from initial temp to final temp in ambient air.
Average time to cool: 13.1 minutes
Method 2: FreezerDescription: Measure time for water to cool from initial temp to final temp in freezer.
Average time to cool: 5.6 minutes
CT 16
CTi 95CT f 65
Method 3: Air Flow over SurfaceDescription: Measure time for water to cool from initial temp to final temp with a constant air flow over liquid surface.
Average time to cool: 5.1 minutes
CTi 95CT f 65CT 28
smU 7 2
Method 4: Blowing/MixingDescription: Measure time for water to cool from initial temp to final temp while constantly stirring with a constant air flowover the surface.
Average time to cool: 4.4 minutes
CTi 95CT f 65CT 28
smU 7 2
Method 5: MixingDescription: Measure time for water to cool from initial temp to final temp while constantly stirring.
Average time to cool: 8.7 minutes
CTi 95CT f 65CT 28
Method 6: Ice CubesDescription: Measure time for water to cool from initial temp to final temp while placing ice cubes in the water one at a time.
Average time to cool: 3 minutes
CTi 95CT f 65CT 28
Results and DiscussionTime for Boiling Water to Cool with different Cooling
Methods
0
2
4
6
8
10
12
14
16
0 1 2 3 4 5 6
Trial Number
Tim
e (m
inut
es) Ambient Air
Freezer
Blowing
Blowing/Mixing
Mixing
Ice Cubes
Average Times for Water to Cool with different Cooling Methods
0
2
4
6
8
10
12
14
1 2 3 4 5 6
Aver
age
Tim
e (m
inut
es)
Ambient Freezer Blowing Blow/Mix Mix Ice Cubes
• The fastest way to cool the soup is not to increase the temperature difference as intuition might suggest.
• Combining cooling methods will cool the soup faster.
• Contrary to intuition, just blowing on the soup will cool it faster then putting it in the freezer while blowing and stirring will cool it faster still.
Conclusion
• Without calculations or experiments it is difficult to tell if the convection coefficient (h) is greater for a large temperature difference or greater for mixing and blowing on the liquid.
• Through the experiments it has been determined which method is most effective at cooling a hot liquid.
• If only one method is to be used, the ice cube method is the fastest.
• If ice is not available, blowing while mixing will have the best results.
Appendix: Calculations
121
20 1ln
CTTTTrt i
min2.161143.11
301328301368ln
9408.613.10136.0
27
2
et
Since the Biot > 0.1 an approximate analytical solution was used.
The Fourier number found after the calculations was approximately 0.851, which is greater than 0.2 signifying that these equations are valid to use for this situation.
For simplicity, only two calculations were shown. See authors for other calculations if desired.
min89.61143.11
267328267368ln
9408.613.10136.0
27
2
et
Room Temperature Cooling Method
Freezer Cooling Method
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