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## PowerPoint Slideshow about 'Convection Experiment' - parker

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Presentation Transcript

What will you hear today?

- Introduction
- Theory
- Equipment and Procedure
- Results and Discussion
- Conclusions
- Questions

Introduction

- What is convection?
- Heat transfer from fluid flowing over solid surface

- Why study convection?
- Occurs in almost every process plant
- Example: Heat Exchangers, Tray Dryers, etc.

Theory – Newton’s Law of Cooling

- Flat Plate:
- Finned Plate (Resistances in Parallel):

Theory – Forced Convection

- Physical Situation:
- Solving Boundary Layer Equations
- Continuity Equation -
- Momentum Balance -
- Thermal Balance –
- Rigorous analytical solution

Theory – Forced Convection

- Forced Convection – analytically developed
- Dimensionless Parameters
- Reynolds:
- Prandtl:
- Nusselt:

- Flat Plate:

- Dimensionless Parameters

Theory - Natural Convection

- Physical Situation:
- New Momentum Equation:
- Must now solve all three boundary layer equations simultaneously

- New Momentum Equation:

Theory - Natural Convection

- Experimental Correlation:
- Churchill and Chu
- Dimensionless Parameters
- Grashoff:
- Rayleigh:

- Correlation:

Equipment and Procedure

Figure 9: Front view of convection duct.

Figure 10: Side view of convection duct.

Results and Discussions

- Flat Plate: Laminar Flow

Results and Discussions

- Turbulent Mix
- New Correlation -

Results and Discussions

- Flat Plate: Turbulent Mix

Results and Discussions

- Finned Plate: Laminar

Results and Discussions

- Turbulent Mix
- New Correlation -

Results and Discussions

- Finned Plate: Turbulent Mix

Results and Discussions

- Effectiveness of Fin Addition

Conclusions – What we learned

- The convective heat transfer coefficient increases linearly with the square root of air velocity
- Predictive Equations are useful for predicting trend in data, but not the absolute numbers
- Natural Convection is the limit to forced convection, though it is difficult to predict
- The addition of fins will increase the heat transfer rate substantially at low air velocities, but not as much at higher air velocities

Conclusions – Significance?

- Aid in design of heat exchangers
- How to increase heat transfer coefficient
- How to increase heat transfer rate
- Realize presence of natural convection for cheap ways to cool electronic equipment

- Confidence of Predictive Equations
- Use for other experiments, such as tray dryer
- Only if can perfectly match geometry, or can run a short scale experiment to obtain correction factor

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