# Convection Experiment - PowerPoint PPT Presentation

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Convection Experiment. Leader: Tom Salerno Partners: Greg Rothsching Stephen Johnson Jen DiRocco. What will you hear today?. Introduction Theory Equipment and Procedure Results and Discussion Conclusions Questions. Introduction. What is convection?

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Convection Experiment

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## Convection Experiment

Partners:

Greg Rothsching

Stephen Johnson

Jen DiRocco

### 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:

### Theory - Natural Convection

• Physical Situation:

• New Momentum Equation:

• Must now solve all three boundary layer equations simultaneously

### 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

### 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