Conduction is the transfer of heat by touch from one solid object to another. Convection is the transfer of heat by movement through liquid and gases. Radiation is transfer of heat from an object travelling through a space until absorbed by another object.
Direct Cooling?
Direct cooling is a water cooling system. The water is drawn into the water jackets to cool the engine. The water absorbs the heat from an engine and cools it. The picture above also has a radiator which cools off the coolant. Marine engines just pull in water and pump it back out.
Indirect Cooling?
The picture above is a heat exchanger. This type uses coolant to cool the engine. The coolant is circulated through the engine and the heat exchanger. The heat exchanger takes the heat off the coolant. Raw water is drawn into the heat exchanger jackets to cool off the heat exchanger and then pumped out the exhaust. The cool raw water absorbs the heat from the heat exchanger and the heat exchanger abosrbs the heat from the engine.
What is the purpose of the thermostat?
The thermostat controls the temperature of the engine. The valve opens when the engine has reached its maximum operating temperature. The cool coolant then circulates through the water jackets cooling the engine. The valve is then closed again when there is cool coolant in the jackets.
Pressure cap?
The pressure cap is on top of the radiator at the fill port. The pressure cap increases the boiling point of the coolant. The cap is a pressure release valve.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 valve open excess coolant returns to the resavoir. When the radiator cools back down a vacuum is created sucking the excess coolant back into the radiator.
Why are engines fitted with a core plug and what is the purpose?
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There are holes in engine block that were required to cast the engine upon manufacture. Plugs were installed at the end of this process. These plugs are designed to POP out if the engine freezes due to lack of antifreeze. They can save the engine from requiring total replacement if this condition happens.
How does the centrifugal circulating water pump work?
Why is it important to lubricate the impeller when fitted from new?
When the impellor is fitted it is dry and there is no lubrication , all impellors rely on being wet as a way of lubrication, so a little silicone or grease is to be used so that the impeller can turn easily in the housing before it is meets water.
When fitting a impellor what should you check before refitting the housing and why?
It is important to check the gaskets are good and in place Also to check for cracks.. Because there is a lot of force in the water when the impeller is working. The pressure can cause it to fail.
What is the purpose of a oil cooler and how does it work?
The oil cooler works like the radiator. Instead of the coolant, it circulates the engine oil which takes the heat of the oil and helps keep the engine cool.
Why do we have Inhibitors and Antifreeze?
Antifreeze are used in radiator to help raise the boiling point, and lower the freezing point of the coolant. The inhibitors are used to stop rust and sludge build up in the system.
How do you test antifreeze?
What is Cavitation Corrosion?
Cavitation corrosion occurs when steam pockets or bubbles eat away into the metals. This form of corrosion will eat out the volutes and impellers of centrifugal pumps with ultrapure water as the fluid. It will eat valve seats. It will contribute to other forms of erosion corrosion, such as found in elbows and tees. Cavitation should be designed out by reducing hydrodynamic pressure gradients and designing to avoid pressure drops below the vapor pressure of the liquid and air ingress. The use of resilient coatings and cathodic protection can also be considered as supplementary control methods.
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.
Describe the terms:
Stray Corrosion ?
Stray current corrosion refers to corrosion damage resulting from current flow other than in the intended circuit.
Corrosion Fatigue?
Corrosion fatigue is damage in a corrosive environment. It is the mechanical degradation of a material under the joint action of corrosion and cyclic loading.
Stress Corrosion?
By cracking under a sudden unexpected failure of normal ductile metals in a corrosive environment. This happens when the temperatures of metals are high.
Crevice Corrosion?
Crevice corrosion is a corrosion occurring in spaces to which the access of the working fluid from the environment is limited. These spaces are generally called crevices. Examples of crevices are gaps and contact areas between parts, under gaskets or seals, inside cracks and seams, spaces filled with deposits and under sludge piles. Common with stainless steels.
What is electrolysis?
is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially highly important as a stage in the separation of elements from naturally occurring sources such as using an electrolytic cell.
What are sacrificial anodes made off?
Sacrificial anodes are made off zinc, and are very common in the marine industry, to help protect components in the salty environment.
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