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cold air falls and warm air rises. Why? Discuss!

Many of us experience the effects of falling cold air and rising warm air on a regular basis. It is happening all the time in the air above and around us and is one of the components in our weather systems. You may notice that when there is no heating or air conditioning operating in your house, the rooms upstairs are slightly warmer than those downstairs. Another example is the hot air balloon that works precisely to this principle. By heating the air inside the balloon, the craft will be lighter than the surrounding air and will rise. This is actually the result of cold air gushing downwards around the balloon at the same time as it is rising.

So why does cold air fall? That is simple: it is heavier than warm air. And why is it heavier? That is slightly less simple, but only slightly. As with any gas, the air (a generic term for the mixture of the gasses in our atmosphere), contains molecules that move (or agitate). This movement (or agitation) is greater as the temperature rises. The molecules move in ever greater orbits, taking up more space. This causes the mass of the air to expand. Although the total mass of a lump of air has not changed, the mass is more spread out and so any given cubic area of it will be lighter. An analogy is found with popcorn. A half pound of popcorn before being popped may fit into a cup. After popping, the same corn would fill a large saucepan. Its total weight will be more or less the same half pound that it always was, but if you filled up the original cup with the popped corn, it would weigh less than the unpopped corn as the rest of it would no longer fit into the cup. Expanding hot air is similar. A cup of cold air would weigh more than a cup of hot air.

As we are playing the why game, let's continue. Why do the molecules move about more when it is warmer? They absorb energy through electro-magnetic waves that smash into the molecules. In short, this is energy transfer by radiation. So we have a collection (several trillion, lets say) of molecules that are very agitated and another collection which are far less agitated. The agitated collection is spread out and thus light. The collection that are less agitated is heavier. The heavier stuff falls downwards, while the light stuff rises.

As well as being the main process behind hot air balloons, the movement of air according to its temperature is a critical factor with the weather. forecasters must ensure that these movements are factored into their modelling systems in order to produce a decent weather forecast. Air conditioning designers and must also take these factors into account as must architects. In order to preserve valuable heat, warm air must be prevented from escaping through the top of a building. As well as conserving heat, the movement of colder air downwards must also be considered when designing refrigerators and refrigeration systems.

If you have a few minutes, try this experiment. Firstly make sure nothing has been put into your refrigerator for at least 2 hours. Then, leave a thermometer inside the refrigerator, making sure it is placed at the bottom and then close the door. After 10 minutes, open the door and straight away and note the reading on the thermometer. Then place the thermometer on the top shelf and close the door. After 10 minutes, take the reading as soon as you open the door. You will notice a difference - perhaps as much as 1 to 2 degrees. This may not be such a big issue for us at home most of the time. For commercial kitchens, however, this difference maybe critical when ensuring food is kept at an optimum temperature. Commercial fridges are often fitted with a fan that evens out the colder and warmer air, thus negating the tendency for cold air to fall and warmer air to rise.

If you take large freezer stores - the ones that hold thousands of boxes of stock - the movement of air around the facility is an extremely important factor. The fans that blow frozen air into the store are always situated near to the ceiling, allowing it to diffuse downwards. Eventually, of course, the goods in the freezer store will need to be taken out and moved to another location, typically loaded onto a truck. If frozen goods are loaded onto a frozen truck this is no problem. Occasionally though, only a small quantity of frozen goods may be needed and the use of a large truck whose temperature is set at a frozen temperature would be wasteful if only a few boxes were being despatched. This is where insulated pallet shrouds or roll cage covers come into play. These enclose the pallet or roll cage, protecting frozen goods for up to 8 hours within an ambient environment (they also protect ambient goods such bakery products and bananas in a chilled or frozen environment). When a roll cage is used, the insulated roll cage cover works at its best when the cage is full of products. When it is half full then - you guessed it - the cold air falls to the bottom. This is fine at first (assuming the goods are in the bottom half), but after a while the warmer air that has risen to the top will start to affect the top layer of goods. This is where a temperature insulated divider must be used to make a seal and protect the goods in the half full roll cage.

So now you know the whys and hows of cold and warm air and now you also know why your feet get cold in winter!

Vernon Stent is the content writer for 5es.co.uk, where you can purchase or rent roll cage insulation covers and dividers and pallet covers.

# posted by 87468 : 9:53 AM  0 comments

Corrugated metal roofing is a rippled metal sheet used for roofing. It is not actually used in residential apartments; corrugated metal is more likely to be used in agricultural industry. It can be seen on the buildings like barns and industrial buildings. The major disadvantage of the corrugated metal roofing was that it rusted but galvanized corrugated metal does not rust. Galvanized metal is produced when a metal undergoes a chemical process to prevent it from corroding. The metal actually produced is treated chemically with an element known as zinc. The metal is mixed with liquid zinc which results in the fabrication of a coat over original metal. Zinc coating is used for this purpose because it wraps the metal and becomes the part of it. After the metal is coated, a layered structure is formed. Upper most layer is zinc, in the middle layer is metal and zinc and in the inner layer is the metal itself. This method is applied to prevent the rust from penetrating deep into the metal. Since a roof is a very important part of a building, rust can damage it to any extent like leakage, cracking of the metal and even breakage can be caused by the rusting. Hence using galvanized corrugated metal roofing is wise choice.

Basic Installation Galvanized corrugated metal roof consists of metal sheets, which are coated in zinc. These sheets are fitted over the wooden roof. The overlapping of the metal sheets is decided by the pitch of the wooden roof.

Some Benefits of Galvanized Corrugated Metal Roofing

There are numerous advantages of the galvanized corrugated metal roofs.

Toughness of the material

The first one is that they are extremely tough and durable provided the fact that rust cannot eat them up. The expect life of a galvanized corrugated metal roof is approximately fifty years and even more.

Light Weight material

Another advantage of the galvanized corrugated metal roofing is that it does not have much weight. With this quality they do not put much stress on the underlying materials and walls and ultimately their life is also increased.

Reusability of the Metal

Another advantage of the galvanized corrugated metal roofing is that the material used in the manufacturing is completely reusable; therefore galvanized corrugated metal roofing is also environment friendly.

Non-Combustible Material

Galvanized corrugated metal roofing is also a fire resistant material; this fact makes it appropriate for the people who have their buildings near flammable materials.

weather proof

Galvanized corrugated metal roofing is also suitable for the extreme weather conditions like rain, heat, snow, hailstorm and even hurricanes as it have the ability of contraction and relaxation with heat.

Cost Effective Solution

Galvanized corrugated metal roofing also help you in reducing your air conditioning expenditures as it partially reflects sunlight from your roof which results in producing less heat inside of your building. Eventually you save some money from your air conditioning expenses.

You can also find more info on sheet metal and structural metal roofing. Homeroofinghelp.com is a comprehensive resource to known about metal roofing.

# posted by 87468 : 1:36 AM  0 comments