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? – 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

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

Questions?