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Project Sponsor: Abraham Fansey / VP Office of Finance and Administration Team Members:

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Multidisciplinary Engineering Senior DesignProject 05424High Temperature Pizza Oven2005 Critical Design ReviewMay 13, 2005

Project Sponsor:

Abraham Fansey / VP Office of Finance and Administration

Team Members:

Izudin Cemer – Electrical Engineering

Adam George – Mechanical Engineering

Nathan Mellenthien – Mechanical Engineering

Derek Stallard – Mechanical Engineering

Team Mentor:

Dr. Satish Kandlikar

Kate Gleason College of Engineering

Rochester Institute of Technology

- Design and build a high temperature pizza oven to replicate the unique results of a coal oven
- High temperature
- Crispy crust
- Fast cook time

- For use at R.I.T.’s future pizzeria or other universities

- Define problem
- Data collection/Research
- Concept development/Brainstorming
- Feasibility assessment
- Performance objectives & specifications
- Analysis & synthesis
- Prototype detailed design

- Achieve comparable results to a coal oven
- No coal
- High internal temperatures
- Mixture of traditional baking methods and current technology
- Evenly cooked pizza
- User friendly
- Capable of high production
- Safe Oven

- Time
- 20 weeks

- Money
- Budget

- Suppliers
- Reliability

- Manpower

- Cooking time: no longer than five minutes per pizza
- Stone deck must reach a minimum temperature of 650°F
- Internal air temperature must reach a minimum temperature of 850°F
- Deck must be rotating and have a variable speed
- Oven insulation: outside surface is no higher than 120°F
- Minimum production capacity: 40 pizzas/hour

- Thermal Analysis
- Mechanical Analysis
- Electrical Analysis

- Thermal Model
- Pizza Heat Transfer Methods
- Heat loss
- Heat generation

Flue

Dome

Flame

Door

Pizza

Stone Deck

IR Burner

Radiation from dome

Convection from air

Pizza

Conduction from stone

- Assume
- 1-D conduction
- Standard pressure
- Constant Area and Thickness
- Avg. temp of pizza=330.7 K

- Values
- λ(k)=3.43 W/mK (Experiment)
- A=.07297 m2 (D=.3048m)
- W=.00635m
- T1=616.5 K
- T2=330.7 K

- Q=11264.9 J/s

- Assume
- 1-D radiation
- Standard pressure
- Constant Area and Thickness
- Avg. temp of pizza=330.7 K

- Values
- ε=.75 W/m2K
- A=.07297 m2 (D=.3048m)
- σ=5.67x10-8 W/m2K4
- T1=697.3 K
- T2=330.7 K

- Q=710.7 J/s

- Assume
- 1-D convection
- Steady State
- Standard pressure
- Constant area and thickness
- Free Convection
- Avg. temp of pizza=135.5°F

- Values
- α=3.43 W/mK
- A=.07297 m2 (D=.3048m)
- W=.00635m
- T=727.6 K
- TW=330.7 K

- Q=144.8 J/s

- Conduction
- 11264.9 J/s
- 92.9% of total heat transfer

- Radiation
- 710.7 J/s
- 5.9% of total heat transfer

- Convection
- 144.8 J/s
- 1.2% of total heat transfer

Heat Loss Through Flue

Heat Loss Through Dome

Dome

Flue

Heat Loss to Pizza

Heat Loss Through Door

Flame

Door

Pizza

Stone Deck

IR Burner

- Heat loss to pizzas*: 50,222 J/s
- Heat loss through walls: 176.32 J/s
- Heat loss through door:
- Open: 942.5 J/s
- Closed: 26.81 J/s

- Heat loss through flue: 44.42 J/s
- Total Heat loss Range during operation:
- 50,469 J/s to 51,385 J/s
*Oven is operating at capacity of 100 pizzas/hour

- 50,469 J/s to 51,385 J/s

- Mass rate of propane required
- Preheat conditions

- Propane rate required=mp
- mp=Qneeded/HHV
- HHV=50,350 kJ/kg (Incropera & Dewitt)

- Qneeded=Qwalls+Qpizza
- Equations developed via curve fitting in Excel
- Closed Door
- mp=236.94·(pizzas/hour)-0.9868
- 3.607 kg/hr / 2.515 hr tank life*

- Open Door
- mp=190.08·(pizzas/hour)-0.9419
- 3.672 kg/hr / 2.470 hr tank life*
*100 pizza per hour load/20 lb tank

- Closed Door

- Mass of propane required
- m=300 kg
- Cp=900 J/kgK
- ΔT=434.4 K
- Mp=2.33 kg

- Preheat time (Based on 3.65 kg/hr mass rate) : 38 min
- Tank Drain (20 lb tank) : 25.7%

- Total weight of dome = 495 lbs

- Oven base support
- Constructed of 3”x3”x3/8” angle iron
- Total height = 30”

- Using COSMOS finite element analysis
- Top load of 600 lbs
- Concrete dome

- Lower load of 50 lbs
- Deck, deck support, shaft, etc.

- Top load of 600 lbs

Max of 3.807e-005

- Thermal Expansion
- Enough clearance during thermal expansion of deck shaft

- Oven being top heavy
- Extended base footprint

- Cracking of concrete dome
- Un-reinforced concrete

- Use of thermocouples and microcontroller to measure, and display temperature
- Send data through RS232 to a PC

- Introduction to microcontrollers and thermocouples
- Purpose of the microcontroller in the design
- How thermocouples work
- Implementation circuitry

- Representing thermocouple temperature voltage relationship
- Use of linear approximation

- Cold junction compensation
- Hardware
- Software
- Typical application circuitry used in the design

- General purpose microprocessors that control external devices
- The execute use program loaded in its memory
- Under the control of this program data is received as an input, manipulated, and then sent to an external output device

- Classical temp. sensors are thermocouples, RTDs and thermistors
- New generation of sensors are integrator circuit sensors and radiation thermometry devices
- Choice of sensor depends on the accuracy, temperature range, speed of response, and cost

- Advantages
- Wide operating temp. range
- Low cost

- Disadvantages
- Non-linear
- Low sensitivity
- Reference junction compensation required
- Subject to electrical noise

- Thermoelectric voltage is produced and an electric current flows in a closed circuit of two dissimilar metals it the two junction are held at different temperatures
- The current depends on the type of metal and temp. difference between hot and cold junction (not an absolute temp.)

- Voltage measuring device measures the temp
- To know the absolute temp. we need to keep the reference temp. stable and known
- Temperature of the reference junction is not known and not stable
- We used cold junction compensation method to take care of this problem

- Done through hardware using IC’s
- LT1025
- It has a built in temp. sensor that detects the temp. of the reference junction
- Produces voltage proportional to voltage produced by thermocouple with hot junction at ambient temp. and cold junction at 0 °C
- This voltage is added to thermocouple voltage and net effect is as if the reference junction is at 0 °C

- Method of representing thermocouple temp. voltage relationship
- V=sT + b
- V-thermocouple voltage
- S is the slope
- T is the temperature
- ‘b’ is an offset (b=0)

- Equation then becomes V= sT where s is now Seeback coeffcient
- In order to obtain a 10 mV output from an amplifier we will need a gain of G=10mv/51.71uV=193

- Electrical Block Diagram

Desired Outcomes

Cooking Time < 5 min.

Dome Temp. = x °C

Deck Temp. = x °C

Budget < $3000.00

Rotating Deck

Exterior Temp< 49 °C

Actual Outcomes

Cooking Time=

Dome Temp=

Deck Temp=

Budget=

Rotating Deck

Exterior Temp=

- Toven=232.2 °C
- Mi=.805 kg
- Mf=.715 kg
- T=11 minutes
- Heat=2034 kJ

- Toven=260 °C
- Mi=.655 kg
- Mf=.585 kg
- T=10 minutes
- Heat=1582 kJ

- Toven=287.8 °C
- Mi=.800 kg
- Mf=.720 kg
- T=8 minutes
- Heat=1808 kJ
(back)

- Lack of availability of specific k value for pizza
- Standard oven, pizza stone, and measuring devices required
- Set area and thickness
- dQ=(mi-mf)*L
- Values
- L=2260 kJ/kg
- A=.07297 m2 (D=.3048m)
- dt=240 s
- mi=.300 kg
- mf=.290 kg
- Ti=23.2°C
- Tf=65.5°C

- Solving for k yields k=3.43 W/mK
(back)

- Value of k=3.43 W/mK
- Heat Required=(mi-mf)*L=1808 kJ
- Total Heat Supplied = Heat Rate * Cooking Time
- Cooking Time = 149s (2 min, 29 sec)

- Aim: 100 pizzas per hour
- Each pizza takes 1808 kJ to bake
- Experimentally Determined

- Average heat lost to pizzas=
- 180,800 kJ/hr=50,222 J/s
- 171,365 BTU/hr=47.6 BTU/s

Back

- Assume
- 1-D radiation
- Standard pressure
- Steady State

- Values
- ε=.75 W/m2K (concrete)
- A=.096774 m2 (door)
- σ=5.67x10-8 W/m2K4
- T1=697.3 K
- T2=293.2 K

- Q= 942.5 J/s

Back

- AISI 304 Stainless Steel
- k=16.6 W/mK
- .003175 m thick (1/8”) on both sides

- Insulation (Durablanket S Ceramic Fiber Blanket)
- k=.087 W/mK
- .1016 m thick (4”) between Stainless Steel plates

- Using Program
- Q=26.81 J/s
- TSurface=168.1 °F

Back

- Reflective Concrete
- k=.80 W/mK
- .1016 m thick (4”)

- Insulation (Durablanket S Ceramic Fiber Blanket)
- k=.087 W/mK
- .2032 m thick (8”)

- Air
- k=28.5*10^3 W/mK
- .0254m thick (1”)

- AISI 304 Stainless Steel
- k=16.6 W/mK
- .003175 m thick (1/8”)

- Using Program
- Q=176.32 J/s
- TSurface=123.0 °F

Back

- Compound Wall
- Unsure of insulation thickness desired
- Wanted to be able to try different values
- Plugging numbers into equations would be time consuming and inefficient

Private Sub CommandButton1_Click()

s = steelthickness.Value

t = insulationthickness.Value

ks = ksteel.Value

ki = kinsul.Value

q = (727.6 - 293.2) / ((1 / (5 * 0.09677)) + (s / (ks * 0.09677)) + (t / (ki * 0.09677)) + (s / (ks * 0.09677)) + (1 / (5 * 0.09677)))

tinsul = 727.6 - (q * ((1 / (5 * 0.09677)) + (s / (ks * 0.09677)) + (t / (ki * 0.09677)) + (s / (ks * 0.09677))))

tinsul = (9 / 5) * (tinsul - 273) + 32

tral = Format(tinsul, "#0.000")

qvalue = Format(q, "#0.00")

qval.Caption = qvalue

result.Caption = tral

End Sub

(back)

Private Sub CommandButton1_Click()

c = concretethickness.Value

t = feltthickness.Value

s = steelthickness.Value

kc = kcon.Value

ki = kinsul.Value

ks = ksteel.Value

q = (727.6 - 293.2) / ((1 / (5 * 1.162)) + (c / (kc * 1.162)) + (t / (ki * 1.162)) + (0.0254 / ((28.5 * 10 ^ 3) * 1.162)) + (s / (ks * 1.162)) + (1 / (5 * 1.162)))

tinsul = 727.6 - (q * ((1 / (5 * 1.162)) + (c / (kc * 1.162)) + (t / (ki * 1.162)) + (0.0254 / ((28.5 * 10 ^ 3) * 1.162)) + (s / (ks * 1.162))))

tinsul = (9 / 5) * (tinsul - 273) + 32

tral = Format(tinsul, "#0.000")

qvalue = Format(q, "#0.00")

qval.Caption = qvalue

result.Caption = tral

End Sub

Max of 6.888e-003 in

- Supply voltage- +5 V standard
- The clock- 20 MHz oscillator
- A/D converter- contains eight
- LCD drivers- enables microcontroller to be connected directly to an LCD display
- Current sink/source capability- up to 25 mA per pin
- EEPROM

- RISC instruction set
- Harvard architecture-code and data storage are on separate buses which allows code and data to be fetched simultaneously
- All of the ports are bidirectional

- Calibration errors-result of offset and linearity errors
- Electrical noise- thermocouples produce extremely low voltages
- Thermal coupling-need a good contact with a measuring surface

In order to obtain a 10 mV output from an amplifier we will need a gain of G=10mv/51.71uV=193

- Gas Valves
- Insulation
- Exterior (No sharp edges)
- Outdoor experiments
- Safe handling of propane containers