Chapter 3 (Convection)

Flow is induced by an external source such as a pump, compressor, fan, etc.

• Forced convection

• Natural convection

Flow where fluid is confined by a surface.

• Internal Flow

• External Flow

• Boundary flow

Choose definition for velocity boundary layer

• The region in which flow adjusts from zero velocity at the wall to a maximum in the main stream of the flow.

• The region of the fluid in which these temperature gradients exist.

• Flow in which boundary layers develop freely, without constraints imposed by adjacent surfaces.

• Energy exchange mechanism between a surface and a fluid moving over a surface.

There are 3 type of geometries that cover external flow convection.

• 1. Parallel flow over a pyramid

  2. Flow across cylinder.

  3. Flow across sphere

• 1. 1. Parallel flow over a flat plate.

  2. 2. Flow across cylinder.

  3. 3. Flow across sphere

• 1. 1. Parallel flow over a flat plate.

  2. 2. Flow across cylinder.

  3. 3. Flow across oval

Air at 1 atm pressure and 20°C flows with a velocity of 8 m/s over a 1.5m x 6m flat plate whose temperature is 140°C. Determine the convective heat transfer rate from the plate if the air flows parallel to the 6m long side flat plate.

• 21.5 kW

• 50.6 kW

• 9.7 kW

• 10.2 kW

Inlet temperature of a fluid flow through a pipe is 26 degC. Outlet fluid temperature is 24 degC. Inlet pipe wall temperature is 30 degC. Calculate the average temperature using the formula.

• 2 degC

• 5 degC

• 12 degC

• 15 degC

What is the function of this formula?

• To calculate average Nusselt number for cross flow over a cylinder

• To calculate average Nusselt number for cross flow over a sphere

• To calculate average Nusselt number for cross flow over a plate

• To calculate average convective heat transfer coefficient number for cross-flow over a sphere

What is the blank step in the orange box?

• Calculate Reynold number

• Calculate Nusselt Number

• Calculate average temperature

• Calculate heat transfer rate

How to calculate film temperature?