ThermoAcoustic Refrigeration

1
ThermoAcoustic Refrigeration
TARGET

• ThermoAcoustic Refrigeration Generation
  Engineering Team

2
Team Members
TARGET

• Trevor Bourgeois
• Mike Horne
• Peter Smith
• Erin MacNeil
• Supervisor Dr. Murat Koksal

3
Design Description
TARGET

• Thermoacoustic Refrigerator
• Unpressurized System
• Air as Gas Medium
• Loudspeaker as Acoustic Driver
• Variable design (stacks)
• Advantages of Thermoacoustic Refrigeration
• No Environmentally-Harmful Refrigerants
• Mechanically Simple

4
Summary of Fall Term
TARGET

• Work to understand Theory
• Development of Mathematical Model
• Construction of two Prototypes
• Standing wave created
• No DT
• Identification of Stack as most important
  component

5
Main Prototype Components
TARGET

• Speaker
• Gas
• Tube
• Stack
• Heat Exchangers

6
Speaker
TARGET

• Considerations
• Power Capacity
• Frequency Response
• Choice
• 10 inch
• Operates At Low Frequencies (100 Hz)
• 400 W Maximum Power

7
Gas Medium
TARGET

• Considerations
• Physical Properties
• Sealing
• Cost
• Choice
• Air
• Atmospheric Pressure

8
Tube
TARGET

• Considerations
• Length
• Diameter
• Sound Reflection
• Low Acoustic Losses
• Sound Transmission
• Choice
• 1.5 PVC Tube
• Flat End

9
Stack
TARGET

• Considerations
• Gap Size
• Material properties
• Material thickness
• Location
• Length
• Does not impede wave
• Choice
• Paper
• Aluminum Screen

10
Heat Exchangers
TARGET

• Considerations
• Material
• Type
• Choice
• Aluminum
• Water Circulated

11
Stack
TARGET

• Solid Porous Material
• Give And Takes Heat From Gas
• Heat Transfer
• DT Across

12
Design Considerations
TARGET

• Gap Size
• Solid Thickness
• Position
• Length
• Ability Of Sound To Pass Through
• Physical Properties

13
Stack Designs
TARGET

• Foil
• Paper
• Foam
• Lexan
• Screen

14
Foil
TARGET

• Aluminum Foil
• Crimped
• Rolled Up Around Centre Post

15
Foil
TARGET
16
Paper
TARGET

• Couragrated Paper
• Rolled Up

17
Paper
TARGET
18
Foam
TARGET

• Open Cell Foam
• Cut To Approximate Shape
• Tape To Hold Two Pieces Together

19
Foam
TARGET
20
Lexan
TARGET

• Strips Thin Lexan
• Monofilament Fishing Line Used As Spacers
• Rolled Up Around A Pencil

21
Lexan
TARGET
22
Screen
TARGET

• Aluminum Screen
• Punch To Cut Circles
• Many Layers

23
Screen
TARGET
24
Experimental Setup

• To better understand how measurements were taken,
  we will look at the stack area
• Pressure measurements were taken in the tube by
  attaching pressure transducers in the locations
  shown in red
• Temperature measurements were taken using
  thermocouples. They were fed through the tube
  through small drilled holes and mounted on the
  stack face. They are shown in blue.

TARGET
25
Maximum Pressure vs. Frequency

• The first experiment conducted was a test to
  determine the operating frequency of the design
• A frequency scan in increments of 20 Hz was
  applied to determine the frequency that creates
  the highest pressure values in the tube
• Two high pressure zones were evaluated from the
  experiment and are located in the 130 Hz and 220
  Hz region shown in red

TARGET
26
Stack Temperature vs. Time _at_130Hz

• Once an operating frequency was selected from the
  previous experiment, temperature tests were
  conducted for the 130 Hz zone
• Up until this point in the group was not
  convinced that temperature results could be
  obtained
• Fortunately temperature results appeared within a
  short time period of 10 seconds
• Each stack was tested, with the results better
  described on the following slide

TARGET
27
Stack Temperatures at 36 Watts

• Stack alternatives were Aluminum Screen, Lexan,
  Aluminum Foil, Paper, and Foam
• After extensive testing of all stack options, the
  following maximum and minimum temperature values
  were obtained
• Results favor the Aluminum Screen and Paper stack
  because of their low cold side temperature, and
  large temperature difference

TARGET
Aluminum Foil
Aluminum Screen
Foam
Paper
Lexan
Temperature Difference
19 C
30 C
18 C
15 C
26 C
28
Temperature vs. Frequency

• A scan of temperature difference across the stack
  at various frequencies was also conducted
• A comparison of this graph with the previous
  pressure vs. frequency scan reveals the
  correlation between pressure and temperature
  results, although it is surprising that a
  temperature difference is possible at frequencies
  other than optimum

TARGET
29
Temperature vs. Speaker Power

• The effectiveness of each stack to create a
  temperature difference was also investigated
• From this graph, we can see that the Paper and
  Aluminum Screen versions were again top
  performers, but this plot also tells us the
  effectiveness of each stack to create a
  temperature difference
• Example, twice as much power for the Lexan stack
  to create a temperature difference equivalent to
  that of the aluminum foil

TARGET
30
Temperature vs. Radial Distance

• The effects of temperature vs. radial distance of
  the stack was also examined
• Thermocouples were placed at various locations on
  the hot stack face
• The two best stack options were tested by this
  method the Aluminum Screen and Paper model
• It was discovered that the Paper stack had
  temperature deviations in the radial direction,
  while the Aluminum Screen remained constant
  radially values are indicated in the slide
• It can be determined that the Aluminum Screen
  version has higher radial heat transfer than that
  of the Paper stack

TARGET
31
Stack Ranking

• From the experiments conducted, the results were
  used to properly rank each choice by the pairwise
  ranking method, and aggregate scoring method
• Variables considered were the compatibility into
  the design, cost, low side temperature,
  manufacturability, power and efficiency, and
  temperature difference
• The pairwise ranking was first applied to
  determine importance of each variable
• A group evaluation determined that compatibility
  and temperature difference were the most
  important factors in the design of an effective
  stack

TARGET

• Pairwise Ranking Method
• Important Attributes Determined
• Ranked According to Importance For Each Stack

32
Stack Ranking

• An aggregate scoring system was then applied
  using the pairwise data
• This system uses a scoring system based on
  effectiveness to meet each variable
• As a group, it was determined that the Aluminum
  Screen and Paper stacks were most likely to meet
  the design requirements stated earlier with
  scores significantly greater over the other
  choices

TARGET

• Aggregate Scoring System
• 10 Highly Effective 0 Not Effective

33
Stack Temperature Results

• Well, most of you are wondering how we are
  actually going to cool an air space with the
  experimental results
• The left stack shown, indicates what the group
  thought was going to happen to the stack before
  the experimentation, where we achieve an equal
  temperature difference about the ambient
  temperature
• Experimental results show that this is not the
  case (shown on the right) where a hot side is
  achieved with a small drop in temperature for the
  cold side (3 degrees below ambient)
• Regardless, it is believed that once a heat
  exchanger is implemented (to remove heat), it
  will reduce the hot side temperatures and cold
  side temperatures accordingly
• To further discuss the adaptation of the heat
  exchanger into our design, I will now pass the
  presentation over to Pencil Pete

TARGET
34
Heat Exchanger
TARGET

• We decided to go with two HE
• From experimentation we believed that if.
• Zoom on top of model
• Developed two heat exchangers separated by wooden
  cartridge
• Acts as insulating material to prevent conduction
  between the two HE.
• Now like to present the evolution of our HE
  design.

• Cold Side
• To use the cold temperature produced and cool a
  cold space
• Hot Side
• Experiments heat conduction from hot side to
  cold side
• If we cool the hot side, we will be able to
  obtain a colder cold side

35
Heat Exchanger Evolution
TARGET

• Peter
• The HE must all be compatible with our present
  design.
• All our designs will consist of a circular disk
  will four holes designed for a floating fastener
  assembly and a center hole to hold part of the
  stack.

Heat exchanger must be compatible with our
present design
36
Heat Exchanger Evolution
TARGET
Drill Thru Channel Design

• Manufacturing
• Drill three thru holes
• Intersect at right angles
• Four ends tapped and plugged
• Front two ends tapped for a 1/8 NPT thread

37
Heat Exchanger Evolution
TARGET
Peter We werent confident that we could get a
long enough drill bit and if so prevent the tool
from wandering
Drill Thru Channel Design

• Pros Few manufacturing steps
• Low cost operation
• Cons Long enough drill bit
• Possible tool wandering

38
Heat Exchanger Evolution
TARGET
Tube Flow Design

• Manufacturing
• CNC machine a pocket for the tube insert
• Tube insert
• Machined block
• Connects five 1/16 diameter tubes.
• Seal with silicone
• Drill and tap two ends for a 1/8 NPT thread

39
Heat Exchanger Evolution
TARGET
Tube Flow Design

• Pros Greater heat transfer rate
• Cons Higher manufacturing costs
• Longer build time
• Sealing
• Larger pump ( )

40
Heat Exchanger Evolution
TARGET
CNC Milled Channel Design

• Manufacturing
• CNC end mill curved profile
• Thickness of wall is 2mm
• Front two ends drill and tap for a 1/8 NPT thread

41
Heat Exchanger Evolution
TARGET
CNC Milled Channel Design

• Pros Better rate of heat transfer than the
  first design.
• Lower machining costs than the second
  design.
• Cons Sealing

42
Heat Exchanger Setup

• Peter
• Plastic tubing was chosen to transport the water
  from the pumps to the heat exchangers and from
  the heat exchangers to the cold space or
  reservoir.
• The plastic tube was chosen based on its
  flexibility and ease of assembly with the
  fittings.

TARGET
Hot Side Heat Exchanger
Cold Side Heat Exchanger
Large Reservoir to keep water at a constant
temperature
43
Heat Exchanger Setup
TARGET
Hot Side Heat Exchanger
Represents our refrigerating capacity
Cold Side Heat Exchanger
44
Heat Exchanger Experiments
TARGET
5.5C
45
Heat Exchanger Experiments
TARGET
1.2C in 30 minutes
4.8C in 30 minutes
46
Heat Exchanger Experiments
TARGET
3.6C in 30 minutes
COP 0.185
47
Comparison with Project Goals
TARGET

• Less than ½ meter long, less than 20lb
• DT of 5-10ºC below ambient
• Sound Insulation
• Introduce Heat Exchangers
• 10-20 Watts Cooling
• Build for less than 2,000.00
• Users Manual

48
Recommendations
TARGET

• Theoretical Work
• Calculate Operating Frequency
• Heat Exchanger Calculations

49
Recommendations
TARGET

• Theoretical Work

• Experimentation
• Stack Gap Size
• Stack Location
• Stack Length

50
Recommendations
TARGET

• Theoretical Work

• Experimentation

• Equipment Improvements
• Pressure Transducers
• Signal Generator

51
Recommendations
TARGET

• Theoretical Work

• Experimentation

• Equipment Improvements

• Design Changes
• Speaker Funneling
• Helium
• Heat Exchangers
• Insulation (thermal, acoustic)
• Mechanical Resonator

52
Term Summary
TARGET

• Built prototype with variable stacks
• Performed comprehensive set of experiments
• Determined optimum stack
• Designed Heat Exchanger
• Heat Exchanger tests performed
• 16.7 W cooling power
• Coefficient of Performance 0.185

53
Thank You
TARGET

• Questions??