Tag Archives: Heat capacity

WATER PIPES BURST ~ CAUSE AND PREVENTION

WATER PIPES BURST

BRRR!!! ~ IN THE DEEP FREEZE NOW!!!

   Right now, like many other Canadians, we are in a deep freeze and should be aware of the following causes and prevention steps we can take to avoid costly and heart-breaking damage to our homes from burst water pipes – here or away on holiday.  I’ve added ‘Prevention of Burst Pipes’ and ‘Tips on preventing your pipes from freezing while on vacation’ Why Do Pipes Burst the Way They Do? at the end of this blog.

The following are excerpts from Why Cold Weather Makes Your Water Pipes Burst written by Nick Berry – DataGenetics – 12/11/13
We’re currently experiencing colder-than-seasonal weather here in Seattle. This is causing a lot of problems with burst water pipes. Here is a picture of a couple of issues suffered by a friend of mine Ian.

Why do water pipes burst, and why do they always fail the same way? These are two interesting questions.
Water pipes burst because the water inside them expands is it gets close to freezing, and this causes an increase in pressure inside the pipe. When the pressure gets too high for the pipe to contain, it ruptures.
We grew up with water all around us and so this expansion phenomenon seems natural, but interestingly, it is a chemical anomaly. Most liquids do not expand just before transition to solid. You should be thankful for this; it is one of the reasons that life exists.
When a liquid cools the molecules slow down (temperature really is just a measure of the average kinetic energy of the molecules). This slowing down allows the molecules to get closer together and increases the density of the liquid. This happens with water too, and when water is cooled down, it gets denser and denser, down to 3.98°C then, something interesting occurs; it starts to expand again.
DENSITY OF WATERYou can see this effect on the graph …which shows how the density of pure water changes with temperature (at one atmosphere). You can see how density reaches a maximum at 3.98°C.

 

Because of the shape of a water molecule, it is slightly polarized. The electrons buzzing around it are more likely to be on one side of the molecule than the other (called a dipole), and this asymmetry creates a slight potential. Water molecules are attracted to each others’ opposite sides. These potentials create weak bonds that are called Hydrogen Bonds. Hydrogen bonds, whilst not as strong as covalent bonds or ionic bonds, are stronger that van der Vaals forces.

WATER MOLECULE2This extra hydrogen-bond ‘glue’ holding water molecules together is the reason why water is a liquid at everyday temperatures and pressures (another one of the reasons life exists). Other chemical compounds similar to H2O, but without the benefit of Hydrogen bonds, are all gases in typical Earth temperature ranges.
The Hydrogen-bonds in water are also the reason why water has such a high specific heat capacity (the amount of energy required to raise the temperature of water one degree); this helps dampen our weather and stops the Earth changing in temperature too rapidly. It also means that water is great for carrying energy around (like in power stations and hydronic central heating systems). It’s also why it takes a lot of energy to boil a kettle to make a nice cup of tea!
As water cools, like other liquids, the molecules slow down and get denser. A competing force, however, is the desire for the water molecules to align with other water molecules based on their Hydrogen bonds, and this causes expansion. Below the temperature of 3.98°C down to 0°C, this alignment expansion process wins out against the desire of slower molecules to get closer, and density decreases.
Whilst not completely understood, it is this expansion that causes beautiful snowflakes to form with their characteristic six points.
This decrease in density continues until the water finally freezes to form ice. Water expands to form ice which has a volume up to 9% greater than the water it came from. It is this reason that icebergs float (being less dense than the water they displace).
Again, it seems natural to us that ice floats, because we grew up this all effect all around us, but this is atypical.
Most other liquids, when freezing, do not form a solid ‘crust’ on top. As they cool, the solid formed, being denser, drops to the bottom of the cooling liquid and the solid grows up from the bottom!
This irregular behavior of water is yet another reason that life exists. When water freezes, it floats to the top, forming a skin which insulates the water below. When a river or lake freezes on top, life continues below in the liquid left underneath.
Why Do Pipes Split Longitudinally?
We know now that is it the expansion of water causing excess pressure inside the pipe that causes it to rupture. The second question to answer is why they always seem to burst parallel to the direction of the pipe?
SAUSAGES(Regular readers of my blog will find a lot of duplication in this topic to my posting about why sausages split the way they do. It’s the same reason).

Let’s model a section of water pipe as a thin-walled cylinder with hemispherical end caps.
What does that mean? It means that we’re only concerned with modelling the wall of pipe (the thing that fails). Thin-walled means that the thickness of pipe is considered negligible compared to the diameter of the pipe (in this way, we only need to consider the tension in the wall).
According to Pascal’s Principle we’ll assume the pressure of the fluid inside the pipe is uniform.
Stress is defined as Force per Area, and can be calculated by dividing the forces experienced over the cross-section upon which they are applied. We’ll use the Greek letter σ to represent stress.

HOOP STRESSHoop Stress
To calculate the hoop stress, we look at a slice down the center line of the pipe and consider the forces in a small hoop of width dx.

As before we calculate the force by the internal pressure multiplied by the area it is applied over:
Force = P.2r.dx
The area this force is applied over is the two parts of the ring at the top and bottom of the cylinder:
Area = 2.t.dx
Combining these, we can calculate the longitudinal stress:
σh = P.2r.dx / 2.t.dx
σh = Pr / t

HOOP STRESS_FIRST

LONGITUDINAL STRESS_FIRST

LONGITUDINAL STRESSResult: Comparing the two results, we can see that the hoop stress in the wall is twice that of the of the longitudinal stress. It should, therefore, be no surprise that pipes burst through a hoop failure and create a rupture that runs perpendicular to the line of maximum stress.
Hoop Stress: σe = Pr / 2t
Longitudinal Stress: σh = Pr / t

In other words, insulate your pipes this winter!
________________________________________
This post was originally published on Data Genetics, a site created by Nick Berry was educated as a rocket scientist and aircraft designer, graduating with a Masters Degree in Aeronautical and Astronautical Engineering, and currenty works as a Data Scientist at Facebook.

WHY

Prevention of Burst Pipes:

  • Make sure you know where your stop cock is. If you do not know where your stopcock is or how to operate it then please take a look at our blog on main stopcock.
  • Ensure that any outside taps and piping including drain pipes for heating or overflow pipes are insulated. You can use insulating lagging or foam to do this but make sure you do not leave any joints, bends or taps exposed. For outside taps fitted covers are available.
  • Any piping that are in unheated areas such as lofts, basements and garages all need to be lagged with good quality pipe lagging.
  • Any pipes buried in the ground outside such as pipes to garages or sheds need to be buried deep enough and/or lagged.
  • Insulate your cold water tank, this is so often forgotten and can be the major cause of Burst Pipes.
  • Leave your heating on at least 12 degrees centigrade at all times throughout cold spells. This will keep the system warm enough not to Burst Pipes and the water flowing.
  • Fix any dripping taps or existing leaks before the cold spell. Many Burst Pipes happen because of leaks.
  • Have your Central Heating System serviced regularly.
  • In particularly cold spells leave the loft hatch open as this will allow the warm air to circulate around the loft space and warms any pipes in that space, reducing the risk of a Burst Pipe.
  • If your home will be unoccupied for any space of time, turn off the stopcock, drain any water from the system and close the taps again (this is very important), leave your heating on. Most heating systems will continue to work without the mains water on for a period of time. Most importantly of all make sure that someone can check on the house from time to time. As much as you can do these actions to prevent a Burst Pipe sometimes Burst Pipes will occur and the sooner you can deal with them the better.
  • If you have any doubt or if you cannot do any of these measures yourself then make sure you get in touch with a good emergency plumber who will carry out these jobs and advise you further. Remember that the cost of a burst pipe can be thousands so a little preventative cost can save much more in the long run.

Tips on preventing your pipes from freezing while on vacation:

  • Ensure all windows and entry doors are closed tightly including crawl space doors if applicable.
  • You must NOT turn the heat off, but turn it down to 55 degrees.
  • Do not turn the hot water heater off but rather, setting your hot water heater on the lowest heat setting possible will keep it functioning at a minimum level, while saving you money on your energy bills. Some water heaters have a “vacation” setting which should be utilized.
  • Open all kitchen/bathroom cabinet doors under the sink and the door to the water heater closet to ensure circulation of warm air.
  • If you are going to be gone for a short period of time and a deep freeze is expected, turn on all hot and cold faucets including bath and kitchen to a slow drip. Tape a note on all dripping faucets reminding others to leave dripping.
  • If you are going to be gone for a week or more, shutting the water off to the whole house would be a great precaution. Others have recommended to turn off the water to your sinks, toilets, dishwasher and washing machine.
  • Undo all garden hoses from exterior faucets.
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OUR WORLD OF WATER

Physical Properties of Water

 The chemical formula for water is H20, which means it is a molecule consisting of two atoms of hydrogen and one of oxygen. These three atoms are bonded tightly together, more so than the atoms of most other substances. This tight bond and arrangement of atoms in the water molecule results in the following five unusual properties:

The water molecule – two hydrogen atoms and one oxygen atom bonded together

1. THREE FORMS: Water is the only substance that occurs naturally on earth in three forms: solid, liquid, and gas. In liquid water, the molecules of hydrogen and oxygen are close together but are able to slip past one another, which is why it flows. Examples of this are a river, a waterfall, or water coming out of your faucet.

When the temperature drops, the water molecules slow down and become sluggish. As it becomes cold enough for the water to freeze, the molecules rearrange themselves into hollow rings. This is why water expands when it freezes, unlike most other substances which contract. This expansion in the solid phase is the reason why ice cubes float in a glass of water. The ice is actually lighter or less dense than the liquid water.

Water also occurs in the gaseous phase, such as steam rising from a boiling tea kettle. As water is heated, the molecules move about violently, colliding with one another, until some break free and form a vapor, or gas.

EXPERIMENT #1
To see how easily water can change forms, try the following experiment. First melt some ice cubes in a pan on the stove. Bring the same water to a boil and place a cover on the pan to catch the steam. The steam should condense into small dropletsof water when it contacts the cover. Next, place the cover with the droplets of water into the freezer until the droplets freeze. Can you think of how humans use this ability of water to change forms? Think of how you change forms of water when you use it. Find out if it is possible for water to change from a solid form (ice) to the gaseous form (vapor) without becoming liquid.When various materials are dissolved in water, they can change the properties of the water. To see this, take two containers of equal size and put into each the same amount of water. Pour salt into one of the containers, label the container, stir until the salt dissolves and then place both containers in the freezer and mark the time. (Note: Do not use large amounts of water because it will take a long time for this to freeze.) See how long it takes for both to freeze. Can you think of why they put salt on icy roads during the winter? Ask your parents why anti-freeze is important for their car.

2. SURFACE TENSION: Water has a high surface tension. This is the ability of a substance to stick to itself. A drop of water falling from the rim of a faucet will stretch itself very thin before it drops off. Then it immediately forms a sphere and resists any kind of shape change. This high surface tension enables a water surface to support small objects like waterbugs, because their weight distribution will not permit them to break through.

EXPERIMENT #2
Can a needle float on water? Drop a sewing needleinto a container of water and watch it sink. Now, take a strip of paper and make a loop. Carefully rest the needle in the loop and lower it slowly onto the water, being careful not to break the water surface with the needle. Keep pushing the paper down slowly, and gently pull it away after the needle has floated. This may take several tries before it is accomplished. Look very closely at the contact between the needle and the water. Notice the indentation the needle makes on the water surface.Have you ever held water between your fingers? Place the tips of your thumb and index finger together in water. When you pull them out of the water, slowly open up a small space between them. You should catch some water between your fingers and be able to hold it there no matter how you move your hand. See what happens when you open up your fingers. Does the water stay between your fingers? Try this with very soapy water. Can you still capture some of the soapy water between your thumb and index finger? What does the soap do to the surface tension of the water?

3. HEAT CAPACITY: Another unusual property of water is displayed when it is heated. Water has an extremely high heat capacity, which is the ability of a substance to absorb heat without becoming extremely hot itself. This is why it takes a long time for water to boil. An empty pan placed over a hot flame will become red hot and then burn black. However, if some water is placed in the pan over the same flame, the pan will become hot, but not red hot as before since most of the heat will be absorbed from the pan by the water. In like manner, your body cools when you sweat because body heat is absorbed when sweat evaporates.

The heat capacity of water enables the oceans to act as huge reservoirs of solar warmth and keeps our weather from going to great extremes of heat or cold. The moderating effect of water is noticeably absent from a desert, where days tend to be very hot and nights cold.

EXPERIMENT #3
Collect rainwater in a clean glass or metal container and fill another container of similar shape with an equal amount of water from your faucet. Label the containers and place them in a warm place to evaporate. When all of the water has evaporated from both containers, check them for any residue. Which container has the most residue in it after the water evaporates?

4. SOLVENT ABILITIES: The most remarkable aspect of water is its ability to dissolve so many substances; that is, to act as a solvent. For example, some caves form when acidic ground water dissolves limestone bedrock. The substance that is dissolved is called the solute, and the liquid mixture is called a solution. Most water on the earth is actually a solution.

Rainwater is the purest naturally occurring solution of water and contains few dissolved substances.

The degree to which water has a distinctive taste or odor depends on the types of substances dissolved in it. Since water is not changed chemically when it acts as a solvent, it can be recovered for reuse after undesirable dissolved substances are removed. The amount of dissolved substances in water is affected by factors such as water temperature and the nature of the material water moves through.

EXPERIMENT #4
Take two containers of equal size and fill one with cold water and the other with hot water from your faucet. Make sure each container has an equal amount of water. Measure a ¼ teaspoon of salt into each container, stir to dissolve. Keep adding salt by the same amount to each container and see which temperature of water will dissolve the most salt. Keep a record of the number of times you added a ¼ teaspoon of salt to each container. Be sure to stir the water each time you add the salt. What would happen if you dissolved as much salt as possible in hot water and let the water cool to near freezing temperatures? Try this. Do you think that instant coffee or cocoa would dissolve as rapidly in cold water as hot water? Think of some environmental problems related to water’s ability to dissolve so many substances and the effects of dumping hot water containing dissolved pollutants into cooler river water.Mix some salt with water until it has a definite salty taste. Pour this into a pot and bring to a boil. Catch some of the steam using a pan lid. When it cools, taste the water collected on the pan lid. What happened to the salt? Find out what distilled water is and how it is prepared. Why is it best to use distilled water in a steam iron? If all the water in the oceans evaporated, what would be left? Look in an encyclopedia and find out how the Bonneville salt flats were formed.

Streams running through areas where there are few people will generally have a better quality of water than streams running through populated areas. Can you tell why? What do you think happens to the quality of polluted water when it evaporates? How would evaporation act as a natural purifier of polluted water?

CONDUCTIVITY: Conductivity is the ability of a substance to carry an electric current. Water will conduct an electric current only if dissolved ions are present because water molecules do not act as a conductor. Measuring conductivity is a good way to determine the amount of dissolved solids in a sample of water and, thus, to determine its purity.

EXPERIMENT #5
Construct an electric circuit using a flashlight bulb, wire, and a 6-volt dry cell battery. Wire the circuit such that two ends of the wire are submerged in a glass of water, as shown in the diagram. See if the bulb will light up when there is only water in the container. Start adding salt to the water, always stirring. Watch and see if the bulb starts to get brighter and brighter. Do you think that seawater would be a good conductor?

http://www.extension.umn.edu/distribution/youthdevelopment/components/0328-02.html