P17487: Kontiki Kiln Heat Recovery System
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Preliminary Detailed Design

Table of Contents

Team Vision for Preliminary Detailed Design Phase

In this phase, our team intended to determine the initial feasibility of our design through both testing and simulation. To do this, we tested last year's project to get transient temperature data, and then used this information to run a simulation to determine the feasibility of using a convection loop to move the water in our design.

Feasibility: Prototyping, Analysis, Simulation

After running initial tests on last year's project, we analyzed the temperature data and used the results to run a CFD simulation to determine the feasibility of using a passive convection loop to move water through our system.

Analysis: Temperature Data

Our team completed a second burn trial to collect temperature data with thermocouples for the water and kiln over time. The details of the testing conditions are outlined in the timeline below:

Timeline of events

Timeline of events


The schematic and actual setup images below shows the placement of the thermocouples and modifications to last year's design to complete this test:

public/Detailed Design Documents/Schematics/system_schematic2.png public/Detailed Design Documents/Schematics/kiln_2nd_burn_schematic.png

The final results from the test are summarized below:

Parameter Values
Starting water temperature 19.9 °C 67.8 °F
Increase +10.1 °C +18.2 °F
Ending water temperature 30.0 °C 86 °F
Amount of water heated
Time elapsed 1.3 hours
Date completed 10/9/16
Location Victor, NY
Ambient temperature 11.67 °C 53 °F

In addition to temperature data, our team conducted a crude estimate of the volumetric flow rate by collecting data for volume and time:

Volumetric Flow Rate Estimate

Volumetric Flow Rate Estimate

With this parameter, other needed parameters for heat flux analysis were calculated and are summarized below:

Parameter Measurement Units Equation
Minimum temperature 12.6 °C Took min. temp. from data file
Avg. Volumetric Flow Rate 0.00012045 m³/s Calculated with discrete values (see graph above)
Density of water 999.8 kg/m³ Lookup value
Specific Heat Coefficient 4.192 KJ/kgK Lookup value
Coil Surface Area 0.4445 public/Detailed Design Documents/Temperature Data/10-09-16/equation_surface_area.JPG
Mass Flow Rate 0.1206 kg/s public/Detailed Design Documents/Temperature Data/10-09-16/equation_massflowrate.JPG

Using this data, heat transfer rate and heat flux equations were applied to each temperature reading data to generate the following:

Parameter Measurement Units Equation
Average Heat Transfer 5.2979 kW public/Detailed Design Documents/Temperature Data/10-09-16/equation_heattransfer.JPG
Average Heat Flux 12.041 kW/m² public/Detailed Design Documents/Temperature Data/10-09-16/equation_heatflux.JPG

The average heat flux was compared to the heat flux at each temperature in the graph below. The standard deviation is ±3.033kW/m² which is used to create the upper and lower bounds, which account for 75% of the data.

Average heat flux: 12.041 ± 3.033kW/m²

Average heat flux: 12.041 ± 3.033kW/m²

Due to flame dynamics being highly variable, our team will use this base heat flux measurement to create our simulation, which is discussed in the next section.

Additionally, the density change for the discrete water temperature values were analyzed in the graph below. This shows that the water density changes due to changing temperature are negligible, so a constant water density value can be assumed during analysis:

Density changes are within 1% of 999.8kg/m³, which was the chosen value for the analysis

Density changes are within 1% of 999.8kg/m³, which was the chosen value for the analysis

Fluent Simulation

To determine if a convection loop was a viable way to move water through our system, a CFD simulation was created to determine the temperature of the water as well as its velocity as it moves through a system. First, a CAD model was created using the drawings of last year's project, which can be seen below:
SolidWorks CAD model of last year's design

SolidWorks CAD model of last year's design

This model was then imported into ANSYS, which is a finite element software that is used to set up Fluent simulations, which is a computational fluid dynamics solver. After the initial geometry was imported into ANSYS, and a fluid domain was created to run the simulation on. This was done by filling in all the empty space in the previous CAD model, then suppressing all of the geometry used to create the fluid domain to make converging on a solution easier. A picture of the fluid domain can be seen below:

Screenshot of the fluid domain

Screenshot of the fluid domain

Next, the fluid domain was meshed using ANSYS, as this is a necessary step in using a finite element solver. The mesh can be seen below. Note that the mesh is much finer in the coils than it is in the reservoir, as it was expected that more elements would be necessary in the coil to properly capture the rapidly changing temperatures and velocities in the coil.

Screenshot of the mesh

Screenshot of the mesh

Next, a Fluent simulation was created using the mesh. Using the information we calculated from testing last years project, a boundary condition of 10 kw/m² was applied to the copper coils. Additionally, a heat loss of 100 W/m² was applied to the walls of the reservoir, to account for conductive heat losses through the side, and a convection boundary condition was applied to the top of the reservoir. The simulation being run is a transient one, and was run for 800 seconds with a time step size of 2 seconds. Temperature contours for the water, as well as velocity vectors, can be seen below:

Screenshot of the temperature contours

Screenshot of the temperature contours

Screenshot of the velocity vectors

Screenshot of the velocity vectors

Using this simulation, it can be seen that the water is flowing at a rate of approximately 10 cm/s, and has an average temperature in the reservoir of about 36°C. The simulation needs to be refined further, and will be after talking with professors who know more about CFD simulation. However, these results are approximately in line with what is expected, since the test we ran had a velocity of approximately 1 m/s, and an average temperature of 23°C. It makes sense that a lower flow rate would result in a higher temperature, since the slower moving water will have more time to absorb heat from the fire. Further refining of the simulation will likely result in adding more heat losses to the system, which means that the simulation will be able to run for a longer time without the temperatures getting to extreme values.

Drawings, Schematics, Flow Charts, Simulations

This is an updated schematic of the selected design. A raised platform is used to elevate the reservoir and the coils are then connected:

public/Detailed Design Documents/Schematics/system_schematic.png
Part Name Main Parameters Material
A Kiln Diameter, height Fixed: Stainless Steel AISI 304
B Coils Pipe diameter Low-cost conductive metal (e.g. Copper)
C Reservoir Height, diameter Lightweight non-conductive material
D Platform Height, width Any sturdy material

Potential failure modes associated with this construction include:

Test Plans

The next step for testing is to physically test how effective the passive convection loop is. While the simulation done in a previous section shows that it is likely to work, the simulation itself is not a perfect representation of reality since it is likely missing several boundary conditions. Additionally, testing data done on an actual convection loop will allow us to further refine the model, which will in turn allow us to better make future design decisions. 3 different sets of temperature data will be taken: one at the "inlet", where water is flowing into the reservoir, one at the "outlet", where water is flowing out of the reservoir, and then one set of temperature data taken far away from either of these points to determine the bulk temperature of the reservoir. Additionally, if we can locate the proper testing equipment, the volumetric flow rate of the water through the coils will also be measured to see how effective the passive convection loop is at driving flow through the system.

Design and Flowcharts

Below is an updated flowchart of the system architecture. Teal boxes indicate a material source:
Coil design process

Coil design process



Additionally, an updated functional decomposition breaks down the main functions further for this specific design:

Updated functional decomposition

Updated functional decomposition

Bill of Materials

Current Bill of Materials with a net cost of $56.29

Current Bill of Materials with a net cost of $56.29

Risk Assessment

A list of the new and updates risks for this phase

A list of the new and updates risks for this phase

A link to the live risk assessment sheet can be seen here.

Design Review Materials

Include links to:

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