Post on 24-Feb-2016
description
Subsystem Design Review
Agenda
1. Goals of Review2. Updates from SDR3. Review of our System4. Input Desired5. Functions6. Engineering Analyses Conducted7. Next Steps
Goals of Review
• Confirm acceptability of mechanical design• Get advice on areas of uncertainty:
o Smart battery procuremento Aluminum vs Stainless enclosureo Pressure sensors for clampingo Isothermal heat spreader
Review: System Goals
Our task is to create an underwater thermoelectric generator that generates 20W of electrical power from 500W of heat.
The main driver of this project is efficiency.
Updates From SDR
1. The electrical system will be out of the water.2. Mechanical system
a. Contains only thermoelectrics and a heat sourceb. Waterproofc. Tethered to the (out of water) electrical system.
3. We chose a very simple system design:a. Easier to assemble and troubleshootb. Few disadvantages compared to other options.c. Like a submarine environment.
Mechanical System
Input Desired
1. Batteries.a. We can’t find the smart batteries we wanted
2. Enclosure Material.a. Aluminum or Stainless Steel?
3. Heat Spreadera. How do we know it will be isothermal?
4. Clamping Testa. Is there a way to determine whether the clamping
pressure is uniform?
5. TEGa. Should we purchase them now so we can test them?
FunctionsWe tried to analyze every item in our functional decomposition. Our main functions were:
1. Protect System2. Generate Heat3. Transfer Heat4. Generate Electricity5. Store Electricity6. Monitor System
Our Analysis
1. Thermoelectrics [Generate Electricity]
2. Heat Sinking [Transfer Heat]
3. Insulation [Protect System, Transfer Heat]
4. Clamping Thermoelectrics [Transfer Heat]
5. Max Power Point Tracking [Store Electricity]
6. Battery Charging [Store Electricity]
7. Monitoring [Monitor System]
8. Heater [Generate Heat]
9. Heat Spreading [Transfer Heat]
10.Seals [Protect System]
Thermoelectrics: Last Time
• We planned to use the Taihuaxing TEP1-1264-1.5 modules from the Sustainable Energy Lab
• We thought we could generate 20W, but Dr. Stevens had some concern about our numbers.
Thermoelectrics
Analysis:1. Determine number of modules required to stay
within allowable temperatures and for which Q<480W
2. Iterate heat balance equations to find power3. Taihuaxing Thermoelectric makes some modules
that meet our requirements. Need more research to confirm their specs.
Heat Sinking
• First calculated a desired heat sink thermal resistance using a basic model
Heat Sinking
• Next, set up equations to determine heat sinking needso Found number of fins needed by varying fin size,
spacing and array type (rectangular vs pin)
Heat Sinking
• Results show that plate fin array with reasonable dimensions is sufficient
Heat Sinking
• Found a fin array in the Thermoelectrics Lab• Plugging in dimensions in the spreadsheet:
o Rsink = 0.094 K/W - better than needed! Could decrease the resistance by modifying fins
Heat Sinking
• Increasing fin spacing increases convection coefficiento Removing 8 of the 16 fins increases the convection
coefficient from 58.6 W/m^2K to 142 W/m^2K, but resistance is unchanged
o Other modificationscould lower theresistance
Insulation
• Created a basic thermal circuit to determine the thermal conductance needed for the insulation
Insulation• Using the equation, , we found a few
options for insulation that met a compressive strength of ~10 Mpa (1450psi)
Insulation
• Top of heat spreader insulation:o 310M Silica Ceramic from Cotronics Corp
Compressive Strength = 1200 psi Thermal Conductivity = 0.187 W/mK Trial Kit contains 2 pieces of 4.5” x 3” x 3” at
$84.65( http://www.cotronics.com/catalog/58%20%20310M%20%20311.pdf )
• Sides of heat spreader insulation:o 2600F Ultra Temperature Tape from Cotronics Corp
Thermal Conductivity = 0.06 W/mK at 500F 391W-1 Tape, Size = 0.02” x 1” x 20’ at $124.50
( http://www.cotronics.com/vo/cotr/pdf/391.pdf )
Insulation
• Created a detailed thermal circuit to determine insulation needs
Insulation
• Analyzed heat flow through each node to come up with a system of equations we could solveo Calculated heat that flows through the
thermoelectrics out of the total 500Wo Used solver in Excel to optimize insulation
thicknesses vs cost while maintaining 96% energy delivered through thermoelectrics (480W/500W)
• Results:o ½” of primary insulation (Ceramic)o 1 ¼” of secondary insulation (Fiberglass)
Insulation
Start of needing insulation between
clamp and heat sink
Clamping ThermoelectricsAnalysis Assumptions:
• Compression assembly achieved by 4 bolts threaded into aluminum bolt housing
• 2 56 x 56 mm TEMs clamped at 200 psi
• Evenly distributed clamping pressure
• Max Thermal Expansion load of 500 lbfBolt Grades Considered:● A307● A354● A499
Aluminum Alloys Considered:● 3004 H38● 5052 O● 5052 H32● 5083 H112
Alu
min
um
Hou
sing
Stee
l Bol
t
Clamping Analysis Approach
• Calculate EL to ensure bolt fails before threads strip.
• Calculate Relative Strength, R:
• If R > 1:
• Fatigue Factor of Safety based on:
Steel Bolts in Aluminum Bolt Housing
Varying Grade of Steel bolts assuming 3004 H38 Aluminum Housing
Varying Aluminum Alloys for Bolt Housing
Clamping - Bolted Connection Design
Pressure PlateAssuming:• Plate as 1” wide beam
bolted on each end
• Low carbon steel (E = 29 Msi)
⅜” thick beam:y at center = 0.015”
½” thick beam:y at center = 0.0065”
Clamping ConclusionsA307 ¼ - 20 bolt in 3004 H38 Aluminum best meets design requirements. EL = 0.362” and Fatigue Safety Factor = 6.7
Low grade ¼ - 20 bolts are easily obtained, and the Thermoelectric Lab has a supply of them
3004 H38 Aluminum bolt housing requires an OD of 0.5” for n = 12 (not fatigue safety factor) McMaster sells 0.5” by 1’ rods of 6061 T6511 (similar properties) for $6.29
Pressure Plate bending appears manageable with low carbon steel, but more analysis is required.
Alternative Materials
• What if we used Stainless Steel instead of Aluminum Alloy?
• Easier to weld Stainless Steel, minimal increase in prices, increased strength, minimal power loss, less corrosion
• Potential problem with bending since it must be thinner than aluminum to get required thermal resistance
• Increased weight
Electrical Systems
TEG 20WMPPT
(Perturb and Observe)
VARIABLE LOAD
CHARGING CIRCUIT
LI-ION BATTERY
BANK
(1)
LI-ION BATTERY
BANK
(2)
...LI-ION
BATTERYBANK
(N)
20W {
62.5% Power Unused
11.9% Power Unused
Battery Model
Simulink Model
Simulation Results
Battery Charging
More parallel batteries = less power lost through internal resistance
Battery Charging
Different battery voltages have similar results on power loss
Loading Analysis
• Short circuit Protection• Overcharge Protection voltage• Overdischarge Protection voltage• Overcurrent detection Protection
Battery Protection Circuit
http://www.freepatentsonline.com/6768289.html
• Used in laptops,cameras, cell phones,electric wheelchairs,scooters, and military applications
• Reports temperature,voltage, currentand SoC
Smart Batteries
Smart Batteries (GenPort)
• SMBus 1.1 compliant
• Cell balanced
• Protectiono Primary and secondary
over and under voltage protection
o over current protectiono short circuit protectiono over temperature protectiono cell imbalance protectiono and more...
http://www.genport.it
Battery Test Plan
• Use TI EV2300 to communicate from battery to the computer using SMBus communication protocol.
• Test the standard charging algorithm (CC/CV), slow charge current condition, constant power charging condition
• Compare to Simulink model, adjust Simulink model (if required), and repeat
http://www.batteryspace.com
Step Up/Down Converters BUCK-BOOST NON-INVERTING BUCK
BOOSTCUK SEPIC ZETA
# Switches 2 4 2 2 2
# Capacitors 1 1 2 2 2
# Inductors 1 1 2 2 2
Inverted Output + x + x x
Continuous Iin x x + x +
Continuous Iout x x + + x
MPPT AlgorithmP&O
● Fixed output voltage from Batteries
● Vary the current via DC/DC duty cycle
Electrical Schematic
Monitoring
• Thermocouples & DAQ system - from lab• “Smart Batteries” with State-Of-Charge
sensors
Monitoring
• Moisture Sensoro Need to monitor moisture level inside enclosure to
make sure no water ingress has occured
• Sparkfun Humidity and Temperature Sensor - SHT15 - $28.95o Measurement range: 0-100% RHo RH accuracy: +/- 2% RHo Power Consumption: 30 uW
https://www.sparkfun.com/products/8227
Heater
• Need a 500W electric heater• Cartridge heaters are available and
compact.• Size Constraints:
o Length - ~80mm (3.15in)o Diameter - <30mm (1.18in)
• Options:o 3.5” x 0.370” - $25.63o 4.5” x 0.370” - $28.72o 3.0” x 0.495” - $29.85
Heat Spreader
• Need to spread the heat (uniformly) from the cartridge heater to the TEGso Copper: k=400 W/mKo Aluminum: k=210 W/mK
o Need detailed model (ANSYS) to do isothermal check
Seals• To seal the cover plate and enclosure,
different methods of static sealing were investigated.
• Face seal gland is the best choice with flange design
• Areas of concern: o O-rings are typically designed for applications with oilo Finding an O-ring that is square shaped
Seals
• O-Ring Cord Stock - Material: EPDM (~$0.60/foot)
- Can customize shape
- Good resistance to water- Can withstand temperatures up to 212F- Would need to purchase Silicone Adhesive ($5.39)
Seals
• Sealed enclosure connectionso Glands
Cheap Limited waterproofing
o Underwater Connectors More expensive Good waterproofing Easy to repair
• Underwater connectors better fit our needs
Next Steps
• Full analysis of pressure plate including thermal loads
• Weld design, and final geometries of clamping components
• Choose O-Ring dimensions and design groove for seal
• Design enclosure flange once sealing design is finished
• Preliminary Testing / Model Validationo TEM powero Battery Testingo Clamping Force
Questions?
ThermoelectricsTaihuaxing Thermoelectric makes TEGs and supplies the efficiency information. Two TEP1-12656-0.8 deliver 18W of power from 480W of heat input.
Model width alpha R K n Power
TEP1-1263-3.4 30 0.0489 7.0 0.33 8 18.0
TEP1-12635-3.4 35 0.0489 6.5 0.36 8 17.1
TEP1-1264-3.4 40 0.0489 7.0 0.33 8 18.0
TEP1-1264-1.5 40 0.0478 3.0 0.78 4 15.1
TEP1-12656-0.8 56 0.0483 1.7 1.33 2 18.0
TEP1-12656-0.6 56 0.0478 1.2 1.94 2 12.4
Thermoelectrics
Functional Decomposition