Introduction to Food Engineering

Home Syllabus
Material Balances Energy Balances
Fluids Laminar and Turbulent Flow Volumetric Flow and Friction Bernoulli's Equation and Pump Power Flow Measurement
Thermodynamic Properties
Modes of heat transfer Conduction in walls Conduction in multilayered walls Convection heat transfer Forced Convection Free Convection Overall Heat Transfer Coefficient Heat Exchangers Unsteady State Heat Transfer Heisler Charts
Decimal Reduction Time F value General Method Improved General Method
Properties of Air and Water Vapor Psychrometric Chart
Moisture Content and Drying Rates Drying Time
Single Effect Evaporator Multiple Effect and Industrial Evaporators
Refrigerants Vapor Compression Refrigeration System Ideal and Non-Ideal Cycle
Ice Crystallization Freezing Time Freezer Selection
Instructions List of Experiments

Free (Natural) Convection

Learning Outcomes

At the end of this module, you will be able to:

  1. describe the natural flow of fluid over a heated surface
  2. learn how to calculate Grashof and Rayleigh Numbers
  3. calculate rate of heat transfer in fluids under conditions of natural convection

In this module, we will learn how to determine the rate of heat transfer under conditions of free convection (also called natural convection). Free convection involves movement of a fluid over a solid surface only under the influence of gravity; there is no forced movement of fluid (no fans, pumps, blowers, etc.). In the following video, you will learn how to calculate two dimensionless numbers important in situations involving free convection, namely, Grashof Number and Rayleigh Number. One of the critical parameters in these numbers is the characteristic dimension. It is the dimension of the object that influences the movement of the fluid over it. To solve problems, you will require information on appropriate dimensionless correlations describing fluid flow over prevailing orientations such as inside or outside horizontal pipes or flow over vertical walls. This information is available in textbooks.

Recap

In this module, you learned how to calculate the rate of heat transfer for free convection. We considered relevant dimensionless numbers, Grashof Number, and Rayleigh Number.