High Temperature Pizza Oven: Multidisciplinary Engineering Senior Design Project

1. 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

2. Mission Statement • 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

3. Design Process • Define problem • Data collection/Research • Concept development/Brainstorming • Feasibility assessment • Performance objectives & specifications • Analysis & synthesis • Prototype detailed design

4. Key Requirements & Critical Parameters • 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

5. Major Design Challenges • Time • 20 weeks • Money • Budget • Suppliers • Reliability • Manpower

6. Performance Specifications • 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

7. Analysis of Design • Thermal Analysis • Mechanical Analysis • Electrical Analysis

8. Thermal Analysis • Thermal Model • Pizza Heat Transfer Methods • Heat loss • Heat generation

9. Thermal Model Elements Flue Dome Flame Door Pizza Stone Deck IR Burner

10. Pizza Heat Transfer Model Radiation from dome Convection from air Pizza Conduction from stone

11. Conduction Detail • 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

12. Radiation Detail • 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

13. Convection Detail • 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

14. Pizza Heat Transfer Summary • 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

15. Heat Loss Elements 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

16. Heat Loss Summary • 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

17. Heat Generation • Mass rate of propane required • Preheat conditions

18. Mass Rate of Propane • 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

19. Preheat Conditions • 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%

20. Design of Prototype

21. Design of Prototype • Total weight of dome = 495 lbs

22. Design of Prototype • Oven base support • Constructed of 3”x3”x3/8” angle iron • Total height = 30”

23. Design of Prototype

24. Design of Prototype

25. Mechanical Analysis • Using COSMOS finite element analysis • Top load of 600 lbs • Concrete dome • Lower load of 50 lbs • Deck, deck support, shaft, etc.

26. Strain Max of 3.807e-005

27. Mechanical Design Concerns • Thermal Expansion • Enough clearance during thermal expansion of deck shaft • Oven being top heavy • Extended base footprint • Cracking of concrete dome • Un-reinforced concrete

28. Thermocouple and Microcontroller Based Temperature Monitoring • Use of thermocouples and microcontroller to measure, and display temperature • Send data through RS232 to a PC

29. Electrical Overview • 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

30. Introduction to Microcontrollers • 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

31. Temperature Sensors • 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

32. Advantages/Disadvantages of a Thermocouple • Advantages • Wide operating temp. range • Low cost • Disadvantages • Non-linear • Low sensitivity • Reference junction compensation required • Subject to electrical noise

33. Thermocouple

34. Thermocouples • 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.)

35. Thermocouples Continued • 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

36. Cold Junction Compensation • 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

37. Compensating Circuitry

38. Linear Approximation • 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

39. Electrical Conclusion • Electrical Block Diagram

40. 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= Results

41. Questions?

42. Backup Slides and References

43. Trial 1 • Toven=232.2 °C • Mi=.805 kg • Mf=.715 kg • T=11 minutes • Heat=2034 kJ

44. Trial 2 • Toven=260 °C • Mi=.655 kg • Mf=.585 kg • T=10 minutes • Heat=1582 kJ

45. Trial 3 • Toven=287.8 °C • Mi=.800 kg • Mf=.720 kg • T=8 minutes • Heat=1808 kJ (back)

46. Determination of Thermal Conductivity • 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)

47. Experimentation • 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)

48. Heat Loss to Pizza • 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

49. Heat Transfer Through Door (Open) • 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

50. Heat Transfer Through Door (Closed) • 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