Heat pipes have been used in various applications from cooling
electronics, energy recovery to enhancing dehumidification in air conditioning; most of
these applications have been in the High Tech domains. Today I would like to present to
you an exceptional application: heat pipes for rice drying, to help the Farmers of the
Why Rice? Of the various types of crops, rice is one of the most
important. Although one of the youngest species of grains cultivated by human, rice feeds
billions of people all over the world, and its consumption is ever increasing. Rice
combines so many virtues that it can be considered as the ultimate gift to mankind.
Why Rice Drying? The need comes from rices popularity: the demand
for rice is so paramount that farmers around the world, especially those in Asia, grow two
or even three crops per year. Traditional sun drying is no longer appropriate because it
is likely that at least one or two harvests will occur during the rainy season. Sun
drying, although the most traditional and natural way of drying rice paddy, in itself does
not yield the best or the highest production since it could not be effectively controlled.
Rain damage can take a heavy toll on the farmers who solely rely on the sun for drying.
BACKGROUND OF RICE DRYERS
The advantage of mechanical dryers has been established for many years. Just about all
the wheat and corn produced in America is mechanically dried. However, drying under a
tropical climate is much more difficult.
Most rice dryers rely on heating air, then blowing the air through wet rice paddy to
evaporate water from the rice. This process requires large amount of energy to supply the
heat for water evaporation as well as to heat the air, which is used as the carrier. The
performance of traditional dryers depends heavily on ambient conditions, especially
ambient relative humidity. On a sunny day, a batch of rice can be dried in six to ten
hours. On a rainy day, it could well take three times as long and three times as much the
energy. The irony is when you do have the need for drying, the dryers function efficiently
at their worst.
The drying system presented today is a complete departure from the traditional way to
build a dryer. This system uses two technologies to achieve an almost impossible task:
make dry air out of wet air, and make heat out of humidity. Dehumidifier heat pipes are
used to produce dry air, and a latent heat pump is used to produce low cost heat energy,
from the very ambient air.
BACKGROUND OF HEAT PIPES FOR DEHUMIDIFICATION
The concept of heat pipes for dehumidification is derived from a
NASA spin-off technology. In NASAs space program, the shuttle had to be dry upon its
landing in Florida, where the weather is quite humid. Our company has developed, almost 15
years ago, a special air-conditioning/dryer machine to perform such a task. That machine
was the first machine to use a Dehumidifier Heat Pipe. The concept is better explained in
the following illustrations:
With this concept in mind, the engineers at Heat Pipe Technology of Gainesville,
Florida developed a special dehumidification/air conditioning line of products which used
heat pipes to increase the dehumidification efficiency of vapor compression in air
conditioning. Such products are now widely available on the market to control humidity at
low energy cost.
|Custom Wrap-Around Heat
||U-Shaped Heat Pipes
Heat Pipe Technology has since become well known in the field of
heating, ventilating and air conditioning (HVAC) and dehumidifier heat pipes are used all
over the world to provide dry cool air at great energy savings. Several heat pipes are
installed in Thailand including one at an electronic manufacturing facility here in Chiang
Mai, and we have many other systems installed in Bangkok.
Some years ago I had the opportunity to present this application of heat pipes in
dehumidification at the Heat Pipe Symposium in Melbourne, Australia. Today I have the
opportunity and great pleasure to introduce to you a very "down to earth"
application, which can help many farmers in Asia to preserve and conserve the grains of
their hard labor, the DaikaTM Heat Pipe Rice Dryer.
THE DAIKA HEAT PIPE RICE DRYER
DAIKATM, which mean "great
goodness," is the trade name of this new rice dryer. This new invention is created
with the full faith of benefiting humankind, by facilitating the post harvest processing
and the storage of rice. This new invention promises to save energy, and to perform the
almost impossible: it works better when the air is most humid and it works best when it is
Let us now talk about rice drying. As harvested, rice with its husk (or paddy) from the
field contains about 25% to 30% moisture. To conserve paddy, one has to bring the moisture
content down to 13-15%. Huge amounts of water must be evaporated from the paddy. In the
process of drying rice, we need heat. But too much heat damages the quality of paddy: the
grain becomes brittle and breaks at the milling stage, and the polished rice could be
yellowed. Ideally rice paddy should be dried below 120°F (49°C) to prevent the loss of
quality and breakage at millings. Rice seeds have to be dried at even lower temperature of
around 100°F (38°C) to preserve the germs. At such low temperatures if the ambient air
is wet, drying times will lengthen. For example, when it rains, it can take a whole day to
dry at 120°F and even longer at 100°F. This results in high energy consumption and low
If we can create dry air, we can achieve faster drying rates at lower temperatures.
This is exactly what the DaikaTM Dryer does. It creates
dry air out of wet air and uses the heat of condensation of the water vapors as the source
The principle of operation relies on two technologies. First is a heat pipe enhanced
dehumidifier to extract moisture from the air. Second is a high efficiency latent heat
pump. The dehumidifier produces cool dry air, which is then heated up by the heat pump. In
this process the heat source comes from the heat of condensation of the water vapor in the
wet air. Therefore, the dryer is self-regulating, and the more humid the air, the better
the dryer works!
TRADITIONAL DRYING TECHNIQUES
Until today just about all dryers work on the principle as illustratred below.
Drying in Humid Climate
In this system, the drying air supplied to the grains depends on the ambient air.
The supply air is wet when the ambient air is wet. The drying psychrometric is as shown