310 Final Exam.docx

Exam Date: Monday 12/9 10:30 - 12:30

What to study:

• Equations and units
  • Define the units if there are similarities
  • If there is math associated it will appear in that section
  • Lighting, turbines, PV cells
• Types
  • Which to use if there are varieties/options
• How they work
• The parts that make it up
• Advantages and Disadvantages
• Understand and explain scientific concepts

Sections and possible points

1. Heat Pumps (20 points) (needs to be finished)

• A heat pump function:
  • Summer: pumps heat from inside to outside
  • Winter: pumps heat from outside to inside, heat is extracted from the air outside
• Energy Balance:
  • Q_h = W_NET + Q_c
    • ∴W_NET = Q_h - Q_c

• Key Components of a heat pump system
  • Compressor: Compresses refrigerant to raise temp and pressure
  • Reversing valve: Directs refrigerant flow to indoor or outdoor unit for depending if heating or cooling mode in use
  • Indoor heat exchanger: Transfer heat between refrigerant and indoor air
  • Outdoor heat exchanger: Transfer heat between refrigerant and outdoor air
  • Expansion valves: Control refrigerant flow and reduces temp and pressure
  • Check valves aka non-return valves: prevent reverse flow of refrigerant
  • Filter Drier: removes moisture and contaminants form refrigerant
  • Sight glass: allows for visual inspection
  • Temperature and pressure sensors: monitor system operation
• Refrigeration cycle basics:
  • Evaporation: Refrigerant absorbs heat and turns into gas
  • Compression: Refrigerant pressure is increased therefore increasing temperature
  • Condensation: Refrigerant releases heat and condenses back to liquid
  • Expansion: refrigerant passes through expansion valve to reduce pressure and temp
• Heating mode process:
  • Refrigerant compression
    • Starts as low pressure and temp vapor
    • Refrigerant compress to be high temp high pressure vapor
  • Flow directed by reverse valve
    • Reversing valve directs hot refrigerant to indoor heat exchanger
  • Heat transfer to indoor air
    • At indoor heat exchanger fan blows cool air over coil
    • Heat from refrigerant transfer to indoor air
    • Refrigerant cools and compresses
  • Flow through expansion valve
    • Flow to expansion valve, in heating process by passes this first valve to bypass and non-return valve
    • Passes through filter drier and sight glass
  • Expansion and cooling
    • Pressure and temperature is reduced making a mix of liquid and vapor in second expansion valve
  • Heat absorption in outdoor heat expansion
    • Cold refrigerant flow to outdoor heat exchanger
    • Fan blows outdoor air over coil transferring thermal energy to refrigerant
    • Refrigerant absorbs heat and evaporates
  • Cycle repeats
    • Warmed vapor returns to reversing valve and goes back to compressor
• Cooling mode process:
  • Switch to cooling mode
    • Reverse valve changes position direction vapor to outdoor heat exchangers
  • Heat transfer to outdoor air
    • Outdoor exchanger blow cooler air over coil, carrying heat away from refrigerant and it cools and condenses
  • Flow through expansion valve
    • Refrigerant flows toward the second expansion valve, the first one is closed so it passes through the non-return valve and goes through the filter drier and sight glass
  • Cooling process
    • Goes through a second expansion valve where it expands and lowers pressure and temperature
  • Heat absorption in indoor heat exchanger
    • Cooled refrigerant flows into indoor heat exchanger
    • Fan blows warm hard over coil and transfers heat from air to refrigerant cooling the space
    • Refrigerant absorbs heat and evaporates becoming a low-pressure, low temperature vapor
  • Cycle repeats
    • Cooled vapor flows back into reserve valve which directs to compressor and continues the cycle

2. Compressors (15 points) (done)

• Convert mechanical power into fluid air power
• Compressed air produced can be stored
• Critical components in industries and systems that rely on pneumatic tools, air-driven machinery, and industrial air systems
• 2 major designs
  • Positive displacement
    • Pressure is increased by decreasing volume
    • Types:
      • Rotary:
        • Vane: cylindrical housing with an off-center drive shaft and adjustable vanes

Smooth and free of vibrations

• • • • • Screw: ambient air intake -> cleans the air

• • • • • Scroll: used in refrigeration

• • • • Reciprocal
        • Cylindrical housing with piston connected to crankshaft
        • Piston moves up and down
        • Single stage: air becomes hot and makes compressor less efficient
        • Multi-stage: avoids overheating and increases pressure
  • Dynamic compressor
    • Use rotating elements to accelerate the gas by diffusing action, velocity is converted into static pressure
    • Total energy in flowing gas is constant
    • Entering an enlarged section, flow speed is reduced and some velocity turns into pressure energy -> static pressure is higher in enlarged section
    • Centrifugal compressor
      • Converts kinetic energy into potential energy
      • Bernoulli’s principle
      • Radial acceleration
• Efficiency and safety concerns:
  • Heat can reduce efficiency or even blow up
  • Cooling system is essential
    • Air or water cooled
• Applications:
  • Industrial and commercial
  • Pneumatic tools, air systems in factories, transportation
  • Chemical manufacturing, HVAC, and energy production
  • Displacement -> quiet and smooth
  • Reciprocating -> high compression ratios

3. Chillers (15 points) (done)

• Used to generate cool water for AC
• Normally on roof or basement
• Closed-loop system
• Remove heat from building
  • Can come from: people, lighting, plug loads, solar radiation
• Basic operation:
  • Chilled water circuit: water leaves evaporator, circulates through the building, and absorbs heat
  • Heat rejection: heat is transferred from chilled water to refrigerant
• Key components:
  • Evaporator: cools water
  • Compressor: drives refrigerant through system
  • Condenser: transfer heat from refrigerant to condenser water loop
  • Expansion valve: expands refrigerant, lowering pressure and temp
• Cycles:
  • 1. Refrigeration circuit: transfers heat from evaporator to condenser
    • Loop: evaporator -> compressor -> condenser -> expansion valve -> evaporator
  • 2. Chilled water circuit: absorbed heat from building via AHU (air handling unit)
    • Loop: AHUs -> evaporator -> AHUs
  • 3. Condenser water circuit: rejects heat to cooling tower
    • Loop: condenser -> cooling tower -> condenser
• Step-by-step process
  • 1. Evaporator: starting point where chilled water is produced
    • chilled water circulates through the building, absorbing heat and returning to the evaporator for heat transfer
    • refrigerant within the evaporator absorbs this heat, causing it to vaporize
    • evaporator is insulated to minimize energy losses and maintain efficiency
  • 2. Compressor: refrigerant, now a low-pressure, low-temperature vapor, enters the compressor through suction line
    • the refrigerant is compressed, increasing its pressure and temperature
    • process transforms the refrigerant into a high-pressure, high-temperature superheated vapor
    • compressor is the driving force of the system
  • 3. Condenser: from the compressor, the refrigerant flows into the condenser
    • it releases the heat absorbed in the evaporator
    • Cooling water from the cooling tower circulates through the condenser, removing this heat
    • water always inside the pipe, refrigerant and water ever actually meet
    • refrigerant condenses into a high-pressure liquid
  • 4. Expansion valve: high-pressure liquid refrigerant moves to the expansion valve, where it experiences a dramatic pressure drop
    • process causes a portion of the refrigerant to vaporize, creating a low-pressure, low-temperature liquid-vapor mixture
    • expansion valve regulates the flow of refrigerant into the evaporator, ensuring efficient operation
    • Prepares refrigerant to re-enter evaporator for heat absorption
• Chiller load:
  • = water flow rate
  • = water density
  • = water specific heat capacity
• Types:
  • Water-cooled: use a water loop and cooling towers
    • Advantages: efficiency, temp stability, scalability
    • Disadvantages: high initial costs, maintenance requirement, water dependency
    • Installation considerations: installed on roof or ground level -> structural requirement; maintenance
  • Air-cooled: use fans to dissipate heat directly into the air
    • Advantages: ease of installation, lower maintenance, suitable for dry climates
    • Disadvantages: low efficiency, affected by ambient air, noise levels
    • Installation considerations: pipe routing, aesthetics, space
• Applications:
  • Commercial and institutional: buildings and data centers
  • Industrial: manufacturing, power generation

4. Resistive Heat and Boilers (6 points) (done)

• Resistive heat (joule heating) is when an electric current passes through a conductor and encounters resistance. Converts electrical energy into heat
• Equations
  • P = I²R
  • Q = Pt
  • R =
• Types
  • Direct: the material to be heated carried the current and heat is developed within material. Basically the heat goes straight to workpiece
    • Ex. electric kettle: heating element is in contact with water
    • Others: toasters and electric underfloor heating
  • Indirect: heat is developed in separate conductor or heating element and the workpiece receives energy by a combination of conduction, convection, and radiation. Basically there is a middle man to get the heat to workpiece
    • Ex. ovens: resistive heat element heats the air and then the air cooks the food
    • Others: boilers and furnaces
  • Heat distribution can be enhanced with fans as it forces air over the element. It can also push heat further into a room
  • Safety: enclosed elements and design
• Materials used:
  • Nichrome: combo of nickel and chromium. Most common due to high resistivity and melting point of 1400 C
  • Kanthal: used in high temperature applications
  • Ceramic: used in some space heaters
• Boilers: A closed vessel or system of vessels and tubs where steam or hot water is generated by applying heat to water
  • Convert energy stored in fuels to generate heat
• How it works:
  • Fuel combustion: burns fuels like natural gas, oil, or biomass in the combustion chamber. Fuel reacts with oxygen to make heat
  • Heat transfer to water or steam: heat is transferred to water through heat exchanger which raises temp
  • Circulation: heated water circulates through a network of pipes. In a steam boiler steam is transported to required areas
  • Exhaust: by produced such as CO₂ and water vapor are expelled through pipe or flue
• Steam contains significant energy and is high efficient at powering turbines
• Heating boilers (hot water boilers) used for heating in domestic or commercial purposes and provide steam or hot water
• Power boilers (steam boilers) used for power plants or industrial application by generating steam or high temp hot water
• Types:
  • Fire-tube: hot combustion gas pass through tubes surrounded by water, used in low-pressure applications
    • Operation: furnace heats tubes, transfers heat to water in tank, steam is generated and sent downstream for use
    • Advantages: cheap and simple to construct
    • Disadvantages: limited to lower pressures
  • Water-tube: water flows through tubes surrounded by combustion gases, used in high pressure applications
    • Operation: fuel source burns in furnace heart water in tubes, when boiling point is reached steam is produced and moved downstream
    • Advantages: higher thermal efficiency
    • Disadvantages: more complex and require better water quality
  • Sectional
    • Water in sections and fire around them
• Boilers classified by: size, fuel type, steam vs water
• Boiler efficiency:
  • Combustion: how efficiently fuel is burned
  • Heat transfer: How well heat is transferred from gasses to water or steam
  • AFUE: Condensing have ratings of 90% and up, older boilers have as low as 70%
• Boiler safety:
  • Pressure relief valves
  • Temperature control
  • Ventilation
  • Routine maintenance
• Condensing boilers: higher efficiency by condensing water vapor
  • 9-% of energy is converted into sensible heat and 10% is converted into latent heat
  • Average efficiency is about 80% and can be increase to 86% and 98% when condensing water
• Equations:
  • Energy input = V x energy content of NG
  • Boiler efficiency = energy output / energy input
  • Energy required from fuel = energy required to produce / efficiency
  • Volume of gas required = energy required from fuel / energy content of NG
  • Q = mcT
  • Energy output = energy input x efficiency

5. Energy Storage (4 points) (done)

• Capture, store, and release energy back to the grid
• Pumped hydro storage is 95% of global storage capacity
• Pumped hydro for long term and battery storage for day to day
• Applications:
  • Grid stabilization
  • Frequency regulation
  • Backup power
• Types:
  • Pumped Hydro Storage: pumps water to an elevated reservoir and releases it to generate energy as needed
  • Lithium-ion batteries: store energy chemically and widely used in the grid
  • Compressed air energy: compressed air stored in underground caverns for later use
  • Flywheels: store kinetic energy and can provide fast-response power
  • Flow batteries: use liquid electrolytes to store energy and can scale up
  • Thermal energy storage: stores energy as heat for later use
• How each type works:
  • Pumped storage:
    • Use water falling to produce energy, after water falls through turbine it is collected in lower reservoir
    • A reverse turbine can pump the water back up to upper reservoir when energy demand is low
  • Lithium ion battery:
    • Anode and cathode store lithium
    • Electrolyte carry positive charge lithium ions from anode to cathode and vice versa through separator
    • The movement creates free elections in anode which makes a charge at positive current collector
    • Electrical current flows from collector through device being powered to negative current collector
    • Separator blocks flow of electrons inside battery
  • Characterized by:
    • Power vs energy: power is rate of discharge, energy is total amount stored
    • Cycle life: how many charge and discharge cycles a system can endure before degrading
    • Efficiency: how much energy can be extracted compare to how much is put in
    • Footprint: the physical space required for installation

6. PV and Fuel Cell (6 points) (done)

• When a photon enter a PV cell it can be reflected, absorbed, or transmitted
• If photon energy is smaller than the band gap it will not be able to jump into the conduction band. Excess energy is converted into KE so energy is lost as heat
• E_p = hc / or E_p = 1239.8 (nm. eV) / (nm)
• = P_max / P_in = I_maxV_max / AI_insolation
• Fuel Cell: Electrochemical device that converts chemical energy from fuel into electricity through chemical reactions
• Hydrogen-Oxygen Fuel cell:
• Key components:
  • Electrolyte: ions pass through potassium hydroxide solution
  • Electrodes: sites of chemical reactions
    • Negative anode: on left, hydrogen is oxidized
    • Positive cathode: on right, oxygen is reduced
    • Wire connects anode to allow electron flow
• How it works:
  • Hydrogen gas enters cell at anode and get oxidized
  • Electrons from oxidation process move through wire to cathode which generates energy
  • Oxygen enters cathode and reacts with hydrogen and electrons to make water
• Equations:
• P_cell = V_cellI_cell for a single cell
• V_stack = NV_cell for a stack of cells
• P_stack = V_stackI_stack = N V_cellI_cell
• P_actual = P_theoretical
• Advantages:
  • Abundant fuel sources: only needs hydrogen and oxygen
  • No pollution: water only byproduct
  • Durability: last longer than batteries and simpler disposal
  • Environmental benefits: cleaner energy alternative
  • Scalability: can be scaled up or down
  • Quiet operation: no moving parts
• Disadvantages:
  • Cost: Expensive catalyst and components
  • Hydrogen supply: Hydrogen takes up more space in gas form than batteries and other fuels. It is also explosive when mixed with air
  • Energy-intensive fuel production: requires energy to produce
  • Durability: Membranes and catalysts degrade over time

7. Generators and Power (8 points) (done)

• Faraday’s Law: States voltage induced in the loop is directly proportional to the change in time of the flux
  • In simple terms: Over time a voltage will produce a field and when that field changes in a circuit a force is produced that is flux. The voltage is proportional to that of the rate of change for the flux
• Generator: How it works
  • A coil is (the rotor) rotated inside a field. The magnetic flux changes and induces a field (emf) that produces energy. The rotor's mechanical movement is driven by an energy source. The stator (stationary coil) produces a magnetic field and the rotor spins through it to generate a current.
• Key components of generator:
  • Rotor: Moving part in generator
  • Stator: Stationary part in generator
• AC Generator: Current changes direction
  • Slip rings: Wire connected to this and brush make contact with it
  • Brushes: Connect current to slip rings for continuous flow of current
  • How it works:
    • Turbine spins a coil inside a magnetic field. The coil rotates and the wires inside move through the field causing an induced current. The current reserves every half turn. Think flips
  • AC generators can be 3 phase, 3 alternating current, to provide a more stable, smoother, and efficient power supply. This means at any given point there is some level of power provided. There is not one peak time and one low time, there is variation.
  • 
  • Great for long distance transmission
• DC Generator: Current direction remains the same
  • Commuter (split rings): rotates with coil to keep flow of current in one direction
  • Brushes: connect current to commuter
  • How it works:
    • Similar to ac generator but the current only flows in one direction. Think a turn
• Equations
• P =
  • P = power output in watts
  • = emf or voltage in volts
  • I = current amps
• P = V_rms x I_rms x pf
  • Pf = power factor between 0 and 1 and accounts for the phase change difference as there is energy lost
• P_out = P_mechanical
  • = a decimal between 0 and 1

Key components

8. ICE (4 points) (done)

• Convert chemical fuel into mechanical work
• Carnot cycle: most efficient
  • 
• Applications:
  • Transportation: cars, trucks, motorcycles, and airplanes
  • Industrial machines: generators, pumps
  • Marine engine: boats and ships used diesel-based ICEs
• Steps of 4 cycle (in own words):
  • 1. air/fuel mixture gets injected
  • 2. air/fuel mixture gets compressed
  • 3. air/fuel mixture gets ignited, pushing the piston down
  • 4. Piston moves up to push exhaust out
• Otto cycle: ideal cycle for spark-ignition engines
• Diesel cycle: ideal cycle for compression-ignition engines
  • V is engine displacement
  • B is bore
  • L is stroke length
  • N is number of cylinders

9. Motors (4 points) (done)

• Electric motors
  • Convert electrical energy into mechanical motion
  • Electromagnetic induction: moving magnet creates an electric field
  • Application: spinning motion for fans
  • AC motor: alternating current, changes direction periodically
  • AC vs DC: AC is more efficient, smoother, and easier to maintain. DC is simplier

10. Turbines (10 points) (done)

• Kinetic energy from moving fluid into mechanical energy
• Types: hydraulic, steam, gas, and wind
• Bernoulli’s Principle: At points along a horizontal streamline, higher pressure regions have lower fluid speed and lower pressure regions have higher fluid speed.
  • In own words: pressure differences cause the blade to spin to try and even it out
• Hydraulic turbine
  • Impulse turbine: only kinetic energy; blades in air
  • Reaction turbine: kinetic and pressure energy; blades fully submerged
• Gas turbine: basically an ICE, but continuous
  • Open-cycle: air is exhausted
  • Closed-cycle: exhaust is used again and again
• Power output = mass flow rate of a liquid x specific heat capacity of a gas x (initial temp - final temp) x efficiency
  • ṁ
• Steam turbine: thermal energy into mechanical energy
  • Rotors and stators
  • Energy forms in steam: kinetic, pressure, and thermal
• Power from wind: A= area, v = velocity, = air density
• Betz limit: 16/27, actual power
• EXAMPLES:
  • A gas turbine operates with an inlet temperature of 1200°C and an outlet temperature of 600°C. If the specific heat capacity of the gas is 1.005 kJ/kg·K and the mass flow rate is 20 kg/s, calculate the power output of the turbine. Assume no mechanical losses
  • 
  • A wind turbine with a rotor radius of 90 m operates in an area with an air density of 1.2 kg/m3 and a wind speed of 15 m/s. Calculate:
    • a. The total power in the wind approaching the turbine.
    • 
    • b. The theoretical maximum power that the wind turbine can extract from the wind.
    • 
  • A steam turbine operates with an inlet steam temperature of 500°C and an exhaust steam temperature of 100°C. Using Carnot's theorem, calculate the maximum possible efficiency of the turbine
  • 

11. Lighting (8 points) (done)

• Lumen: light output
• Efficacy =
• Incandescent:
  • Electricity heats a filament, which produces light
  • Advantages: high CRI values (excellent color rendering), cheap, and available in different sizes
  • Disadvantages: waste energy by consuming the same amount of energy for less lighting and making the cooling system work harder to off-put the heat; limited operation life; tungsten deposits reduce aesthetics and brightness
• Fluorescent
  • Glass tube with inert gas and electrodes that light up
  • High efficacies
  • Long lifetime
  • Emit more UV light than incandescent
• LED lamps
  • Semiconductor diodes emit light
  • Any range of colors
  • N-type: doped to have more electrons
  • P-type: doped to have more holes
  • Most energy efficient
  • Long life
• High intensity discharge
  • Similar to fluorescent
  • High power output
  • Advantages: long life, high lumen output, small
  • Disadvantages: require time to warm up
• EXAMPLES:
  • Given the list of materials and their bandgaps below, determine whether each material can be used for LEDs. If applicable, specify the color of light produced by each material
    • Bandgap of 2.9 eV
  • A large space is currently illuminated by 175 incandescent lamps, each with a rating of 60 W. How many (a) 24-W fluorescent lamps or (b) 40-W tubular fluorescent lamps are needed to supply the same level of lighting to the space? The efficacies of incandescent, compact fluorescent, and tubular fluorescent lamps are 20, 60, and 90 lm/W, respectively. Please neglect the power consumed by ballasts in fluorescent lamps