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DRYING METHODS & REMOVING WATER
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Objectives
- To learn that water can be separated from a
mixture by evaporation.
- To appreciate that both of these methods are
used in the colour industry at various stages of colour-making.
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Curriculum links
English National Curriculum:
Science 3: 3e
| Gateway story
In industry, many methods are used for removing water. The images
on this gateway introduce children to some of those methods.
Gateway elements
- Drying a car
- Drying rolls of dyed yarn
- The chameleon drying lettuce.
Drying a car: This car is being dried in an industrial laboratory,
using hot air from what look like hair driers. Cars would not usually
be dried in this way. On this occasion, the paint is undergoing
testing.
Drying rolls of dyed yarn: This rollover set of two images
shows the yarn in the metal tub which is the dye bath, followed
by the damp rolls being placed on a conveyor belt ready to go through
a microwave oven for drying. In between these two stages, the yarn
is spun dry to remove the bulk of the water.
The chameleon drying lettuce: The image of the chameleon
being sprayed with water from the salad spinner demonstrates how
a 'centrifuge' spins water from dyed yarn (amongst other things)
in the colour industry. A centrifuge is also similar to the spin
cycle on a washing machine.
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Approximate time required: 60 minutes (plus
observation time)
Resources needed
Per group:
What
do they have in common? sheet
Desk lamp
Radiator
Microwave oven (if available)
Hair drier
3-4 saucers
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SAFETY NOTE
Appliances must have been safety
checked before children use them
All mains appliances used in schools must be checked annually and
equipment brought from home must be checked too.
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Suggested organisation
Whole class introduction followed by work in
pairs and then groups for investigations and plenary.
Carrying out the activity
The children are shown the What
do they have in common? pictures of wet clothes on a washing
line, a hair drier in use, paintings left to dry on a drying rack, a towel
on a radiator and a draining rack of dishes. They are asked:
- What do these pictures all have in common?
(water is being removed)
- What happens to make wet things dry and
where does the water go?
Introduce the word 'evaporation' if it is not
suggested as a reason for the water 'disappearing'. Ask the children to
try putting the methods of water removal in order, starting with the one
in which evaporation (drying) occurs the slowest.
Children may raise factors such as the quantity
of water in the wet object; whether water is trapped inside or on the
surface; and the size of the wet object - which can lead to a discussion
of the need for a controlled investigation to answer the question more
accurately. However, the teacher should not introduce these factors, as
they can lead to confusion if the children are not ready for them.
The children can now plan and carry out an investigation
to find out the most effective drying methods. Children can be given the
following 'handy hints' to help plan their investigation:
- 1 tablespoon of water is a sufficient quantity
for comparison.
- 1 tablespoon of water can take between 30
minutes (hair dryer) or 8 hours (sunny window sill position) to evaporate.
- When using a hair drier the air should initially
be directed across the surface of the water, to avoid blowing the water
off the saucer. As the water evaporates, the hot air can be blown directly
at and closer to the water. Children can take it in turns to hold the
hair drier or it could be supported in some way.
Note: Filtration
methods can also be tested. Although these do not 'dry' the remaining
material,a large quantity of water is removed very quickly and cheaply.
Filtration is used a great deal in industry for this reason.
Plenary
Sharing the results of each group will probably highlight the need (as
in industry) for tested, controlled methods of water removal so that the
continuous processes of dyeing and drying fabrics and yarns is not held
up. It is important for workers to know what time each process is expected
to take.
Children are shown pictures of
industrial
drying methods to discuss and compare with the different
methods they have tested.
Background information
In industry, methods of water removal include:
- Filter press: demonstrated by rolling a
wet (saturated) fabric item in a dry towel and twisting firmly to squeeze
it so that water runs out - the towel gets wet, the object gets drier.
- Centrifuge: demonstrated by using a salad
spinner to remove water from wet lettuce leaves.
- Drying racks or a hot air oven: all involving
evaporation through heating of the surrounding air.
- Microwave oven: involving direct heating
of the water to boil it off while the air remains cool.
Extensions / links
Science
Challenge the children to design an investigation into removing water
from wet fabric or yarn using some of the above ideas and others of their
own. For example, they could use a rolling pin like a mangle or paper
towels like a press.
Science
Carry out the Drying
times investigation.
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