3A-2 Flashcards
How many kilograms of air are required to have 1kg of oxygen available for combustion?
4.35 kg of air equals 1 kg of oxygen
What is a kilomole?
Is the quantity of a substance that has a mass in kilograms that is numerically equal to its molecular mass
Difference between Higher and Lower Heating Values?
Higher heating value is determined through calorimetry or by Dulong’s formula. This higher heating value includes the latent heat of the water vapor in the fuel being measured. In real world conditions this latent heat is actually never absorbed into the boiler or steam.
So the lower heating value represents the reality of the heat supplied by the fuel. The lower heating value is ascertained by subtracting the latent heat of a evaporation that is contained within the water vapor of the fuel from the higher heating value.
K-Factor
Is a measure of a materials ability to conduct heat or its thermal conductivity. The higher its K value the more heat the material can transfer. A lower K fact means the material is a better insulator, such as materials with a K factor less then 1.
Valve Bonnet
Is the part which is attached to the top of the valve body. Removal of the bonnet gives access to the valve trim (Valve seat and Disc). Can be threaded, welded, or bolted.
Single Seated Versus Double Seated Valves?
Simply means that the valve in question either has one disc/plug or two discs/plugs. The double seat arrangement allows for twice the flow and divides the flow equally between the two control ports. The double flow arrangement also provides a balancing force on the valve which makes it much easier to open or close.
What are Jacketed Valves?
They are coverings over valves that supply heating fluid such as steam or glycol to prevent freezing or solidifying in the valve itself. Can be put over almost any valve type.
Difference between Mixing Valves and Diverting Vales?
Mixing valves have two inputs and one output for mixing two liquids together.
Diverting valves have one input and two outputs for sending fluids to different locations.
Diaphragm Valves
Used when handling corrosive, toxic, or abrasive fluids. A flexible diaphragm is pushed down onto the valve seat by the valve disc. No valve packing is required because it is not exposed to the process fluid like other valves.
Coulomb
Is equal to a charge on 6.242 x 10 ^ 18 electrons. Coulombs per seconds is equal to one ampere
Resistance
is defined as the opposition to the flow of electric current. Resistance is measured in ohms. One Ohm represents a resistance that develops one joule of heat when one ampere flows through it for one second.
Magnetic flux
Magnetic lines of force
Reluctance
Reluctance is the opposition to the establishment of magnetic flux or the magnetic lines of force
Field poles
Field portals are the are the means in which a generator creates magnetism for the conductor or armature to pass through. They require a power source or direct current which is called excitation in order to remain magnetized.
Interpoles
Interpol’s prevent armature reaction. They are placed in between the regular field poles and are connected to the armature current supply.
Armature reaction
Is the interaction of the armature conductors interacting with the main field flux produced by the field pole windings. The armature reaction causes the neutral plane within which the brushes have been placed to shift, so that the brushes are now shorting coils that produce voltage heavy sparking occurs at the brushes as a consequence.
Shunt excited!
In the shunt excited generator, the current in the schenfield whinings originates downstream of the armature and returns to the upstream side of the armature.
Compound excited generator!
The compound excited generator has two field Windings one is the shunt and the other is the series excited winding.
What is a generator actually generating?
A Generator develops voltage or electromotive force
What is a rheostat?
A rheostat or field regulator is used to control the output voltage of a DC generator
What is meant by the phrase in phase?
In phase refers to when in a AC circuit the voltage and the current reach their maximum values at the same time
What is lagging current?
Legging current is when current reaches its maximum later than the voltage in an AC circuit. This generally occurs when an inductive load such as a transformer, motor or generator. Windings is present on the circuit.
What is a leading current?
If the current reaches its maximum earlier than the voltage, it is said to be a leading current. This would occur in a circuit having a capacitive load such as a capacitor.
Inductance
the property of an electric conductor or circuit that causes an electromotive force to be generated by a change in the current flowing.
Self Inductance
the tendency of a coil to resist changes in current in itself. is an opposition to current flow. This causes inductive reactance which causes current to lag behind voltage. This can be corrected using a capacitor that will cause capacitive reactance. Capacitive reactance causes current to lead voltage.
How to cause current to lag?
An inductive load such as a motor, generator, or transformer will cause inductive reactance that will cause current to lag 90 degrees behind voltage.
How to cause current to lead?
The use of a capacitor that can store voltage will cause current to lead voltage by 90 degrees. A capacitor will cause capacitive reactance which will also increase the power factor.
What does a power factor of 1 mean?
It means both voltage and current are in phase with one another. On the other hand, a power factor less than one indicates an inductive reactance greater than the capacitive reactance is present within the circuit. Causing current to lag behind voltage by 90 degrees. A power factor above 1 means a capacitive reactance greater than inductive reactance is present causing current to lead voltage by 90 degrees.
What is required to send power over long distances?
It requires that the voltage is very high and the current is very low. This is because a larger current would require a much thicker conductor that would be too expensive to make. More current in a circuit produces a larger a mount of heat.
