Experiment 9 - Natural-convection melting of a slab of ice

Summary

Principle

The heat transfer across the air boundary layer that descends along a vertical ice slab causes melting at the surface.

Objective

The effect of heat transfer by boundary-layer natural convection over a vertical wall can be visualized and measured by experimenting with thin slabs of ice suspended vertically in still air. The uneven distribution of heat flux is demonstrated by the uneven thinning of the ice slab. The instantaneous flow rate of meltwater collected under the dripping ice is a measure of the overall heat transfer rate from the ambient to the isothermal surfaces of the slab. An additional objective of this experiment is to show that laboratory apparatuses can be built quite inexpensively, often by using kitchen utensils. This experiment teaches a group of students to critically evaluate each others' data, and to pool all their findings into a comprehensive report that may have engineering significance.

Apparatus

• Baking pan

• Refrigerator

• String

• Cardboard box

• Sheet-metal tray

• Thermometer

• Graduated beaker

• Clock

The heart of the apparatus is a vertical slab of ice, which is suspended by means of a string in still air. The manufacture of the ice slab and its suspension and the maintenance of a nearly motionless and isothermal ambient are the critical aspects of the apparatus construction.

An inexpensive way of producing ice slabs of one or more sizes is to use a flat-bottom baking pan (or cookie sheet) placed horizontally in the freezer of a household refrigerator.