Exam revision

Cry

Polytropic, Pressure increases, Volume decreases compression, Temperature increases

Adiabatic, Pressure decreases, Volume increases, Temperature decreases

Isobaric, Constant pressure, Temperature increases, Volume increases (expansion)

Isochoric, Pressure increases, Volume is constant, Temperature increases

Isothermal, Pressure decreases, Volume increases (expansion), Temperature is constant.

Briefly, explain superheated steam and give one application of superheated steam.

Superheated steam is the condition where it has absorbed additional heat energy above saturated conditon,

Used in steam turbine

True or false: In an adiabatic process, the work done (W) is equal to zero”.

False

Work done = Negative internal energy change

True or false: “In an Isothermal process, the work done (W) is equal to internal energy change”.

False

Work done = Heat

What does the acronym RTD stand for with reference to temperature measurement?

Resistance temperature device

Give brief description of the principle of operation of a thermocouple.

Based on the seebeck effect. Two different metals are connected and are in contact with a hot and cold junction. When there is a temperature change between the ends it will generate voltage across the junction.

State any three advantages and three disadvantages of Hydro electric energy

Advantages: Renewable, low emissions, reliable source.

Disadvantages: Enviromental consequences, expensive to build, drought potential if less or no rain.

Describe briefly about sustainability of energy in NZ context

Ulitilizing sources again and again without putting the source in danger of getting depleted

Describe any two applications of Green Hydrogen gas and include how these would benefit NZ’s environmental goals

Fuel cell vehicles, Alternate fuel

The nz enviroment goal is to achieve zero carbon emissions by 2050.

True or False: Heat transfer is maximum in Adiabatic Process.

False

Q=0

True or False: The internal energy change is equal to Work done in Isothermal Process.

False Q=W

Explain an RTD

A sensor whose resistance changes as its temperature changes. The resistance increases as the temperature of the sensor increases.

Forced convection

When a fluid is forced to flow over the surface by stirring or by an external source such as fans and pumps, creating an artificially induced convection current.

Natural Convection

When fluid motion is caused by buoyancy forces that result from the density variations due to variations of temperature in the fluid.

Sketch the T-H diagram at constant pressure

True or false: The work done is zero in an adiabatic process

False

Isobaric

Pressure is constant

Isochloric

Volume is constant

W=0

Modes of heat transfer for a person sitting quietly in a room?

Since the person is clothed, we need to account for conduction through the clothing and convection from the enclosed surface of the clothing, typically neglecting radiation.

Modes of heat transfer for a person sitting near an open fire

We need to consider that the person's surface facing the fire will absorb radiation from the flames.

Since the person is clothed, we need to account for conduction through the clothing and convection from the enclosed surface of the clothing, typically neglecting radiation.

2 Advantages of direct solar energy as an energy source?

Renewable and clean

2 Disadvantages of direct solar energy as an energy source?

Reliant on weather, not avalilable at night.

Explain adiabatic

Q=0

2 wire RTD

Thermocouple

3 wire RTD

single pane vs double pane glass

For the single-pane window, there is convection and radiation on both exterior surfaces of the glass, and conduction through the glass. For the double-pane window, in addition to these modes, there is radiation and convection between the facing surfaces of the panes.

The double-pane assembly's thermal network replaces single-pane conduction with two-pane conduction plus convection and radiation between the panes, increasing the overall thermal resistance. Therefore, we expect lower heat loss through the double-pane window.

4 methods of renewable energy for NZ plus examples

1. Recycle materials to reduce enenrgy requirements (Paper)

2. Use renewable energy whenever possible (Sun, wind for clothes drying)

3. Increase capacity of renewable energy resources (build more wind farms)

4. Reduce demand (New building standards, LED).

Define Conduction

The transfer of heat by physical contact, from one part of a substance to another without permanent displacement of the molecules.

Define convection

The transfer of heat from one place to another by the movement of fluids