cooling and corrosion

Explain the terms ( Kinetic energy) Conduction, convection and radiation.
Indirect cooling?
Direct cooling?
What are the the problems you get with indirect and direct cooling?
What is the purpose of a thermostat?
Pressure cap?
Why is engines fitted with a core plug, and what is the purpose of a core plug
What is the purpose of a heat exchanger?
How does the heat exchanger work?
How does the centrifugal circulating water pump work?
Why is it important to lubricate the impellor when fitting from new?
When fitting a impellor what should you check before refitting the housing and why?
What is the process of a intercooler/after cooler how does it work?
Why do we have Inhibitors & antifreeze?
How do you test Antifreeze?
What is galvanic corrosion?
Describe the terms
Stray corrosion?
Stress corrosion?
Corrosion Fatigue?
Crevice corrosion?
What is Electrolysis?
How do you prevent corrosion?
What are sacrificial anode made off?

 

Conduction:

Heat spontaneously flows from a region of higher temperature to a region of lower temperature, temperature differences over time, approaching thermal equilibrium.

Info from: http://en.wikipedia.org/wiki/Conduction_%28heat%29

Radiation

Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation.

Examples of thermal radiation include visible light emitted by an incandescent light bulb, infrared radiation emitted by animals and detectable with an infrared camera, and the cosmic microwave background radiation.

Info from: http://en.wikipedia.org/wiki/Thermal_radiation

Convection:

Convective heat transfer, often referred to as convection, is the transfer of heat from one place to another by the movement of fluids. The presence of bulk motion of the fluid enhances the heat transfer between the solid surface and the fluid. Convection is usually the dominant form of heat transfer in liquids and gases.

Info from: http://en.wikipedia.org/wiki/Convective_heat_transfer

An image showing the different types of heat transfer:

Image from: http://www.beodom.com/en/education/entries/principles-of-thermal-insulation-heat-transfer-via-conduction-convection-and-radiation

And a song from YouTube about this stuff

Direct cooling:

The difference between direct cooling systems and indirect cooling systems, also known as secondary refrigeration, lays in the physical separation between  the primary circuit, where the cold is generated, and the secondary system, where cooling takes place.

Info from: http://www.zitrec.com/Applications_indirect_cooling_systems.htm

Image from: http://www.betterbricks.com/building-operations/cooling-towers

Indirect cooling:

Indirect cooling in supermarkets

The combination of these benefits is why typically in public buildings, such as supermarkets, indirect systems are promoted.  In supermarkets, the cold needs to be transported to a variety of fresh and frozen displays in an effective, safe and economical way.  All the cooling effect required is produced in the machine room, far from the display cases, resulting in high flexibility and a lower risk of leakage. A heat recovery system, also situated in the machine room, can provide heating for the supermarket when required. In this way  the use of unwanted refrigerant such as ammonia in a public place is avoided, although it can still be used in the primary system, kept in a safe sealed room, away from the public.  

  (info from: http://www.zitrec.com/Applications_indirect_cooling_systems.htm)

 

The purpose of a Thermostat:

The thermostat acts as a valve that stays closed during engine warm-up. When the thermostat is closed, it prevents coolant from leaving the engine and circulating through the radiator. When the engine gets warm, the thermostat’s spring valve opens, allowing coolant to circulate through the radiator to be cooled.

(Info from: http://www.matthewsvolvosite.com/replace-thermostat-volvo-850-s70-v70-c70-or-xc70.html)

(Image from: http://www.matthewsvolvosite.com/replace-thermostat-volvo-850-s70-v70-c70-or-xc70.html)

Pressure cap:

(image from: http://www.motorera.com/dictionary/pr.htm)

The radiator cap actually increases the boiling point of your coolant by about 45 F (25 C). How does this simple cap do this? The same way a pressure cooker increases the boiling temperature of water. The cap is actually a pressure release valve, and on cars it is usually set to 15 psi. The boiling point of water increases when the water is placed under pressure.

When the fluid in the cooling system heats up, it expands, causing the pressure to build up. The cap is the only place where this pressure can escape, so the setting of the spring on the cap determines the maximum pressure in the cooling system. When the pressure reaches 15 psi, the pressure pushes the valve open, allowing coolant to escape from the cooling system. This coolant flows through the overflow tube into the bottom of the overflow tank. This arrangement keeps air out of the system. When the radiator cools back down, a vacuum is created in the cooling system that pulls open another spring loaded valve, sucking water back in from the bottom of the overflow tank to replace the water that was expelled

(info from: http://auto.howstuffworks.com/cooling-system7.htm)

Core plugs and their purpose:

Core plugs, sometimes wrongly called freeze plugs or frost plugs, are plugs that fill the core holes found on water cooled internal combustion engines. The sand casting cores are used to form the internal cavities in the engine block or cylinder head(s), usually forming the coolant passages. The traditional plug is a thin, domed, disc of ferrous metal which is pressed into a machined hole in the casting. Alternatively a non-ferrous metal such as brass offers improved corrosion prevention.

(Info from: http://en.wikipedia.org/wiki/Core_plug)

(Image from: http://www.pauls-place.com/products-chevy-block-accessories.asp)

The purpose of a heat exchanger:

The classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils and air flows past the coils, which cools the coolant and heats the incoming air.

(info from: http://en.wikipedia.org/wiki/Heat_exchanger)

(Image from: http://en.wikipedia.org/wiki/File:Straight-tube_heat_exchanger_1-pass.PNG)

How the heat exchanger works:

There are two primary classifications of heat exchangers according to their flow arrangement. In parallel-flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. In counter-flow heat exchangers the fluids enter the exchanger from opposite ends. The counter current design is most efficient, in that it can transfer the most heat from the heat (transfer) medium. In a cross-flow heat exchanger, the fluids travel roughly perpendicular to one another through the exchanger.

(Info from: http://en.wikipedia.org/wiki/Heat_exchanger#Flow_arrangement)

Parallel flow heat exchanger:

(image from: http://en.wikipedia.org/wiki/File:Heat_exc_1-1.svg)

Cross flow heat exchanger:

(image from: http://en.wikipedia.org/wiki/File:Heat_exc_2-1.png)

How does the centrifugal circulating water pump work?

The centrifugal pump is powered by an electric motor in a waterproof housing. That motor drives a device called an impeller. The impeller is a wheel with angled blades. When water gets caught in it, it is driven by centrifugal force to the outside of the spinning wheel. The shape of the blades then compresses the water and shoots it out in a jet

(info from: http://www.ehow.com/how-does_4963320_circulator-pump-work.html)

(Image from: http://media.web.britannica.com/eb-media/58/3658-004-061948E8.gif)

Why is it important to lubricate the impellor when fitting from new?

When the impellor is fitted from new, it will be dry, and all impellors rely on being wet as a way of lubrication, so a little silicone is to be used so that the impellor can turn/slip easily in the housing before it is surrounded by water.

When fitting a impellor what should you check before refitting the housing and why?

When refitting a new impellor, check to see if there isn’t any shredding or cracks, because when the impellor turns, the force of the water will have a possibility of stressing the weakened area and cause it to get bigger until a blade is torn off and jams the pump.

What is the process of a intercooler/after cooler how does it work?

An intercooler (sometimes referred to as an aftercooler) is designed to remove heat from the compressed air coming from the supecharger (or turbo) before it enters the engine's induction system. An intercooler works just lie a radiator - air is cooled by fins, bars, louvres, and plates inside the intercooler that are cooler than the compressed air coming from the supercharger. The reduction in air temperature increases the density of the air (more air molecules per cupic foot), which consequently increases your engine's ability to make more horsepower and torque. The decreased air temperature allows you to run more boost on a given octane of fuel before detonation occurs..

(Info from: http://www.angelfire.com/hiphop3/ppddaiddddyy/Intercoolers.html)

(image from: http://heatexchanger-design.com/wp-content/uploads/2011/02/intercooler.jpg)

Why do we have Inhibitors & antifreeze?

Antifreeze (engine coolant) performs several functions in addition to providing freeze protection. Antifreeze contains chemicals that inhibit corrosion and scale formation in the engine and radiator. Antifreeze (engine coolant) provides protection against boiling in the summer. At one atmosphere pressure pure water boils at 212 °F (100 °C) but a 50/50 blend of water/ethylene glycol boils at 223 °F (106 °C).

(info from: http://www.eetcorp.com/antifreeze/antifreeze-faq.htm#q2)

(image from: http://mypetshappiness.com/wp-content/uploads/2009/07/iStock_000001212761XSmall.jpg)

How do you test Antifreeze?

What is galvanic corrosion?

Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical contact and immersed in an electrolyte. The same galvanic reaction is exploited in primary batteries to generate a voltage.

(info from: http://en.wikipedia.org/wiki/Galvanic_corrosion)

Describe the terms
Stray corrosion: Stray current corrosion refers to corrosion damage resulting from current flow other than in the intended circuit(s).
Stress corrosion: Failure by cracking under the conjoint action of a constant tensile stress, which is applied to residual, in certain chemical environments specific to the metal.
Corrosion Fatigue: Damage to or failure of a metal due to corrosion combined with fluctuating fatigue stresses.
Crevice corrosion: Corrosive degradation of metal parts at the crevices left at rolled joints or from other forming procedures; common in stainless steel heat exchangers in contact with chloride-containing fluids or other dissolved corrosives. Also known as contact corrosion.

(Info from: http://calvinbayley.blogspot.com/search?updated-max=2011-06-27T13%3A16%3A00-07%3A00&max-results=7)

What is Electrolysis?

In chemistry and manufacturing, electrolysis is a method of using a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction.

(Info from: http://en.wikipedia.org/wiki/Electrolysis)

How do you prevent corrosion?

10 ways to prevent corrosion:

Choose products that are made of non-corrosive metals like stainless steel and aluminum.

Metal Corrosion can be best controlled by maintaining a dry environment using suitable moisture barriers and drying agents.

Make sure that your electrical connections are clean.

To prevent metal corrosion on a car or truck, apply a thin coating of petroleum jelly after you clean the terminal.

Always clean and dry the blades of garden tools after every use as this eliminates moisture. Also wash away soil from shovels, hoes and rakes before storing them in a cool and dry place. In addition, wash your garden tools with soap and water, dry them and rub motor oil on the metal parts before you put them away for winter season.

Coat metals with oil, paint, grease or varnish because it can prevent corrosion.

Utilize cleaning agents like soaps, solvents, emulsion compounds and chemicals to efficiently get rid of oil, grease, dirt and other unwanted foreign deposits and follow the correct procedures in applying them.

Metal Corrosion that has already formed on car batteries can be removed by using a mix of cola and baking soda to create a paste. The paste will eat at the corrosion.

To prevent soil corrosion, install correctly copper or copper alloy plumbing underground. The main reasons that lead to corrosion of copper pipelines are poor drainage and moisture. A loose layer of backfill such as limestone or pea level must be put down in the trench before laying copper pipes.

Galvanizing also provides metal corrosion protection. This is the process of giving a thin coating of zinc or steel material by immersing the object in a bath primarily composed of molten zinc. Galvanizing is an efficient way to protect steel because even if the surface is scratched, the zinc still protects the underlying layer. This process is widely used by the automotive industry.

(info from: http://www.smithandarrow.com.au/blog/rust-corrossion/10-ways-prevent-corrosion-metals/)

What are sacrificial anode made off?

Sacrificial anodes are made off zinc, and are very common in the marine industry, to help protect components in the salty environment.

(info from: http://calvinbayley.blogspot.com/search?updated-max=2011-06-27T13%3A16%3A00-07%3A00&max-results=7)

Marine transmissions

1. Explain the different type of gear selection systems (in outboard gearcases and stern drivers and Inboard marine gearboxes)

For outboard… a dog clutch is used which consists of a gear which is on the output shaft that slides in either direction to lock the forward or reverse gear to the shaft. the gears are in what’s called a gear case which is in the bottom of the outboard system, different to the set up of a sternleg or an outboard where the gearcase is in the top of the leg. The stern leg uses a similar dog clutch system, except it uses coned syncro hubs similar to that as the syncro cones on a manual gearbox. this is so there is smooth sync as the gears are selected instead of the rough clacking made by the teeth from dog clutch as on an outboard. The gear is engaged once the cone/selector is pushed more into the gear and becomes tight enough for the two components to engage.

A dog clutch system on an outboard

2. What type of gears are used in outboards and stern legs? (Give an explanation of why manufacturers choose this type of gear)

Helical type gears are used for gears in the outboards and sternlegs. The gears are angled at 45 degrees so that they can mesh properly as there is one shaft, meshing with another shaft at an angle of 90 degrees.

3. Explain what a duo propeller system is and how it works/operates

 

(Image from: http://www.volvopenta.com/SiteCollectionImages/VPC/Drives/758x228/ML_DPS_Duoprop_758x228.jpg)

Duo prop design:

• One of the main benefits of the IPS and DuoProp is highly increased propulsion efficiency. This means that less engine power and fuel consumption. In water, propellers function better when they are designed to pull, instead of push. Because of the placement of engines at the rear of most boats, however, this propeller orientation is rare. The DuoProp overcomes this limitation by using two propellers instead of one.

  Like traditional shaft-driven boat systems, the system features propellers that are fully submerged. This, however, is where most similarity ends. Instead of standard propellers, IPS employs two propellers per unit. These duo props are counter-rotating. One propeller spins clockwise, while the other rotates counterclockwise. This reduces wasted energy and results in better efficiency through the water.

(Info from: http://www.ehow.com/how-does_5336911_volvo-outdrive-duoprop-works.html)

Volvo IPS system:

(Image from: http://www.tomjenkinsyachtsales.com/img/news/13_Volvo%20Penta%20IPS.jpg)

4. Why would a V drive be used instead of a standard shaft drive system 

V-drive is a propulsion system for boats that consists of two drive shafts, a gearbox, and a propeller. In a "V-drive" boat the engine is mounted in the rear of the boat and the front of the engine faces aft. Connected to the rear of the engine is the transmission. The first drive shaft connects the rear of the transmission to a gearbox mounted in the centre of the boat. The second drive shaft extends from the gearbox to the rear and out the bottom of the boat to where a propeller is mounted.

(Info from: http://en.wikipedia.org/wiki/V-drive)

V drive diagram

 

(Image from: http://www.gknservice.com/typo3temp/fl_realurl_image/for-remote-v-drives-3c-17-91.jpg)

With the standard shaft drive setup, the engine is further forward in the hull with a shaft driven straight to the propeller.

(Image from: http://www.michiganmotorz.com/images/article/Inboard.jpg)

5. Compare a jet unit with a surface drive unit and give reasons why you would choose one system over the other

Jet unit:

In a boat hull the jet unit is mounted inboard in the aft section. Water enters the jet unit intake on the bottom of the boat, at boat speed, and is accelerated through the jet unit and discharged through the transom at a high velocity. The picture below shows where water enters the jet unit via the Intake (A). The pumping unit, which includes the Impeller (B) and Stator (C), increases the pressure, or "head", of the flow. This high pressure flow is discharged at the nozzle (D) as a high velocity jet stream. The driveshaft attaches at the coupling (F) to turn the impeller.

Reverse is achieved by lowering an astern deflector (E) into the jetstream after it leaves the nozzle. This reverses the direction of the force generated by the jet stream, forward and down, to keep the boat stationary or propel it in the astern direction.

(Info and image from: http://www.hamjet.co.nz/hamiltonjet_waterjet/how_a_waterjet_works)

Surface drive:

(Image from: http://www.francehelices.fr/surface-drive-system-uk.htm)

What are surface drives, and how do surface drives work? Put quite simply, surface piercing propellers operate half in and half out of the water in the planing wake region of a boat just behind the boats transom. Having the propeller at the surface level reduces drag and reduces the vessels draft, making the surface drive suitable for many applications where the owner is looking to reduce fuel costs, increase speed and create a more efficient vessel.
There are advantages and disadvantages for all propulsion systems for water craft. But for planing and semi-planing vessels, surface propulsion has several distinct advantages over its competitors in the propulsion marketplace.

(info from: http://www.seafury.com/a/About-Surface-Drives)

Over all, I would choose to have a Jet unit rather than a surface driver as the propeller is inside the mechanism and wont be disturbed by any external obstructions, and because the water is being sucked from under the hull,  so it doesn’t matter how shallow the water can be, it will still be able to drive without a propeller hitting the sea floor.