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ACTIVE BRAKE COOLING 67
Appendix H: Liquid Distribution System
Objective
Electronically control spray of a liquid
Analysis
Positive displacement or non-positive displacement pump?
1. Flow and pressure relationship of a (non-positive displacement) pump
When the flow increases, the discharge pressure of the pump decreases, and when the flow
decreases the discharge pressure increases (ref. tutorial2.htm).
Flow rate would be unsteady in our application
2. Do not let a (non-positive displacement) pump run at zero flow
Do not let a centrifugal (non-positive displacement) pump operate for long periods of time
at zero flow. In residential systems, the pressure switch shuts the pump down when the
pressure is high which means there is low or no flow
(http://www.pumpfundamentals.com/centrifugal-pump-tips.htm)
The period of running, waiting for pressure relief valve to open would be difficult for a non-positive
displacement pump. A
Therefore, we should use positive displacement pump type.
Flow Control
Positive displacement pumps do not slip: If they are turning, they are moving fluid.
Rate of fluid delivery to nozzle must be within range of flow rates the nozzle is capable of
delivering.
With positive-displacement pumps, flow rate is proportional to pump rpm, allowing control of flow
rate through control of pump rpm. Requires PWM or voltage control...possible with the Arduino but
would require different electronic hardware than we’re been expecting and programming--not our
specialty.
A mechanical control method is simple:
ACTIVE BRAKE COOLING 68
…method varies the net forward flow of the pump via an external recycle loop. This most
closely resembles flow control of a centrifugal pump. The recycle valve opens to allow flow
to return to the pump suction. Downstream pressure defines the available pressure drop for
the control valve. The recycle rate will change based on the pump differential pressure and
the control valve opening. This method works best for systems with a high pressure rise and
a constant downstream pressure, e.g., pumping from makeup tanks into a high-pressure
process system.
The recycle system works well with screw, gear and progressive cavity pumps. It is
acceptable for most vane pumps. However, don’t use the method for cyclic pumps such as
reciprocating or diaphragm ones; rapidly changing outlet velocities easily can cause
problems with cyclic pump inlet-head requirements.
(http://www.chemicalprocessing.com/articles/2015/effectively-control-pd-pumps/)
System Schematic
ACTIVE BRAKE COOLING 69
When electric pump is powered, fluid is moved from the reservoir to the nozzle at a controlled flow
rate. When the pressure at the nozzle reaches a pre-set magnitude, the nozzle sprays liquid.
Required Materials
Description Part # Sold By Price ($) Qty.
Liquid Reservoir 603-001 Amazon 11.74 1 11.74
Tube 6519T13 McMaster-Carr 3.30/ft 10 ft. 33
Tube Clamps 5435K11 McMaster-Carr 5.02 25 (1 pkg.) 5.02
Adjustable spray angle high pressure spray nozzle 3480K21 McMaster-Carr 35.2 1 35.2
In-Line Pressure Relief Valve (brass) RVi-05 Straval 67.15 1 67.15
Brass close nipple 4568K131 McMaster-Carr 1.66 4 6.64
Adjustable sprayer heads - 3.75 5 (1 pkg.) 3.75
Precision Flow-Adjustment Valve for Chemicals 4981K11 McMaster-Carr 58.97 1 58.97
Hose Tee with Barbed Ends 91355K47 McMaster-Carr 6.34 2 (1pkg.) 6.34
Hose Barb Female 1/4 NPT-1/4 Hose Barb 5346K42 McMaster-Carr 14.43 10 (1 pkg.) 14.43
Liquid Pump G2-H 12V 2.5L US Solar Pumps 46.38 1 46.38
Total 288.62
ACTIVE BRAKE COOLING 70
Plus Tax: 331.913
Description Link
Liquid Reservoir https://www.amazon.ca/Dorman-603-001-Coolant-
ReservoirBottle/dp/B000E35UV2
Tube https://www.mcmaster.com/#standard-plastic-and-
rubbertubing/=1544w7w
Tube Clamps https://www.mcmaster.com/#standard-plastic-and-
rubbertubing/=1544w7w
Adjustable spray angle high pressure spray nozzle https://www.mcmaster.com/#spray-tips/=156irs6
In-Line Pressure Relief Valve (brass) http://straval.com/products/relief-valves/rvi-05/?size=19#size_table
Brass close nipple https://www.mcmaster.com/#brass-close-nipples/=157jtsi
Adjustable sprayer heads
https://www.amazon.ca/Adjustable-Sprayer-Misting-Watering- Irrigation/dp/B014FCRUT2/ref=s9_simh_gw_g86_i1_r?pf_rd_m=A3DW
YIK6Y9EEQB&pf_rd_s=&pf_rd_r=5R18V10XZRBE1PG4QRH9&pf_r d_t=36701&pf_rd_p=b420c7ed-0dc7-4f64-
becab1a9f89477f6&pf_rd_i=desktop
Precision Flow-Adjustment Valve for Chemicals https://www.mcmaster.com/#flow-control-needle-valves/=15bs9se
Hose Tee with Barbed Ends https://www.mcmaster.com/#hose-tees/=15bsf2a
Hose Barb Female 1/4 NPT-1/4 Hose Barb https://www.mcmaster.com/#barbed-hose-fittings/=1544pbj
Liquid Pump https://www.ussolarpumps.com/product/g2-h-direct-drive-gear-pump/
Appendix E: Pneumatic Cooling System
Objective
Maximize cooling effectiveness while minimizing air consumption and intricacy of a pneumatic
cooling system.
ACTIVE BRAKE COOLING 71
Figure 1.Candidate configurations
Configuration A B
Flow Rate Control Manually adjusted control
valve
Alter nozzle size or pump rpm
On/Off Energize solenoid valve Energize/de-energize pump
Table 1. Flow rate and on/off mechanism descriptions
Introduction
Two outputs derived from this design work: the scale model, and design of a full-scale,
practical system. Modeling heat transfer and cooling medium flows analytically aids in
S
Compressed Air
Source
Manual Valve
Solenoid Valve
Flow Nozzle
Centrifugal Pump
Flow Nozzle
Configuration B
Configuration A
ACTIVE BRAKE COOLING 72
development of both systems. The scale model should represent the practical system to the highest
degree permitted by constraints in order to maximize the relevance of knowledge developed
through design, construction, and operation of the scale system to a full scale system design.
It has been found analytically that convective heat transfer with turbulent flow is
significantly more effective in heat transfer per unit of air than laminar flow. This is illustrated in
Figure 2: note the significant increase in rate of cooling at the expense of very little increase to flow
represented by the sudden y-axis shift of theTurbulent series relative to the Laminar.
Figure 2. Laminar vs Turbulent flow
The analytical model was based on an Example from Heat and Mass Transfer: A Practical
Approach, by Yunus A. Cengel (p.428), attached as Appendix A . The knowledge that flow
velocity has such a significant effect on effectiveness of cooling has initiated further investigation
into flow nozzles, and enforces that any optimized cooling system prioritizes flow velocity.
Electronic control of volume flow of cooling fluid is not considered necessary because the
volume of cooling fluid delivered at the optimum velocity may be altered by an existing
mechanism: duration of cooling medium delivery periods.
y = 0.209x + 13.25
y = 0.586x + 24.02
0
20
40
60
80
100
120
140
0 50 100 150 200
Flow Velocity (m/s)
Laminar
Turbulent
ACTIVE BRAKE COOLING 73
Configuration A
As drawn, the manual valve is used to control flow rate, and the solenoid valve flow
periods. It would be possible to control both flow rate and flow period electronically using a
different type of solenoid, but this would complicate the control system further and what this would
allow control of, is already controllable by other, simpler means. Namely, the manual valve, also
the duration of periods of airflow.
It is possible that the existing air system of a transport truck can handle the additional load
of this cooling with little to no modification. That is, the compressed air source would be the
existing system of the large truck the cooling system is installed on. This may significantly reduce
system hardware cost, a concern of ours included in the Goals, Objectives, and Constraints
document which is guiding design decisions.
Another advantage of this sytem would be the size of air lines running to each brake would
be smaller than that of configuration B for any volume flow rate of gas, due to the gas being more
compressed. As there would be many of these lines in a practical application which would need to
be custom installed and consume real volume of a trucks undercarriage, smaller diameter lines with
their tighter turn radius and smaller diameter may be preferrable over the energy efficiency of
Configuration B.
Configuration B
Flow is turned on and off by energizing and de-energizing the pump, and flow rate is a
function of pump rpm and back-pressure provided by the flow nozzle, in the case of the nonpositive
displacement, centrifugal pump.
Since end use is a low pressure, high flow application, it is possible to use a blower, instead
of a compressor to drive airflow. The processes of compression and decompression with associated
entropy changes, yields higher energy consumption in delivering a certain flow rate of air than a
ACTIVE BRAKE COOLING 74
blower. The major advantage of this system is its reduced energy (operating) cost, if . It is not yet
understood whether the energy cost associated with moving the air is significant. In a multi-brake
system, configuration B may still require solenoids to direct the air to only the brakes requiring
cooling.
If it turns out by regulation or capacity that the existing truck air system cannot be used to
supply the brake cooling system with air, configuration B is preferred for the simplicity and
corresponding low cost of blowers relative to compressors.
Conclusions
Depending on results of future analysis and further information gathering regarding
auxillary use of truck air systems, a configuration of an air delivery system will chosen for use in
large scale practical applications, and our system model. It is favorable for the small system to
represent the large scale system, in that this maximizes the relevance of the knowledge developed
from the scale model to full scale applications.
Appendix A
ACTIVE BRAKE COOLING 75
Appendix J: Full Scale Model
Part I
ACTIVE BRAKE COOLING 76
Objective
Determine air volume flow required at each brake to maintain safe brake temperature under
worstcase circumstances through development of an analytical heat transfer truck braking system
model.
Assumptions:
• Velocity of vehicle is constant
• 10 brakes per truck, share load exactly
• No heat is conducted from the brake drum to neighboring components
Conditions
• Research indicates one of the most difficult sections of road for transport truck drivers in
Canada is a 9 km length of Highway 20 which contains grades up to 18%.
• British Columbia regulations dictate that the mass of any truck and trailer must not exceed
63 500 kg.
• In summer, outdoor temperatures in British Columbia can easily reach 30ºC.
• Brake temperature is 100ºC at beginning of descent, and heat transfer from the drum takes
place at 300ºC.
• Brake drums operate best at 250º C, and temperature should not exceed 450ºC. (Yukon PDF)
• The truck is equipped with 10 identical drum brakes and no engine brake.
Properties
Air properties at 160ºC, 1atm:
(Cengel, p.926)
Analysis
ACTIVE BRAKE COOLING 77
Total change in elevation:
Period of time over which this change in elevation occurs:
Total potential energy recovered during this descent:
Recovered over a period of 270s corresponds with a power of:
Divided across 10 brakes:
Assume approaching the decline with a brake temperature of 100ºC, all ten drums of this type:
Figure 1. Brake Drum (http://www.truckcomponentsonline.com/HEAVY-
DUTYDRUMS_c_1101.html)
The initial energy possessed by this drum of cast iron and 48kg is:
9 km
arctan 0 . 18 = 10 . 20 ̊
h
ACTIVE BRAKE COOLING 78
Now to calculate the rate at which energy is leaving the plate
Convection From Outside of Drum
The velocity at which air moves over the outer surface of the drum is approximated as the linear
velocity of the vehicle, though the drum is truly in complex motion relative to the ground, rotating
as it translates linearly. Any “nozzling” effect of components near the brake drum on fluid velocity
is neglected.
The drum is approximated as a hollow cylinder of two different inside diameters.
Figure 2. Approximated brake drum
The area of the drum from which heat transfer by convection and radiation is significant does not
include the area normally bolted against the truck wheel, and is approximated as a plate:
ACTIVE BRAKE COOLING 79
Figure 3.Heat transfer plate
The area of heat transfer is:
L is considered the width of this plate (depth of the drum).
313 053>10 000 therefore heat transfer equations for turbulent flow are used
Assume heat transfer from drum to environment is occurring at an average temperature of 300ºC
Radiation
Not affected by change in fluid velocity, so calculated as occurring from both the inside and outside
of the drum. For cast iron, Emissivity
In the case of conventional braking systems which are passively cooled, the total rate of heat
transfer from the brake drum to the environment is equal to:
Figure 4.Conventional brake heat transfer
Yielding an increase of temperature of the brake drum to --------- under the stated conditions,
which exceeds safe operating limit of 450ºC (Yukon PDF). This increase in temperature occurs
because . The rate of heat loss can be made to equal or exceed the rate of heat
ACTIVE BRAKE COOLING 80
generation by the addition of forced convection through the inside of the brake drum. To maintain
a brake temperature of 300ºC throughout the decline, .
In the conventional case;
With the addition of convection to the inside of the drum;
Figure 4. Brake heat transfer with forced convection
Convection From Inside of Drum
3.
Consolidating and algebraically manipulating Eq. 1 through 4, a formula is made which will
indicate flow velocity required to remove energy from the drum at any specific rate.
𝑄 𝑜𝑢𝑡 , 𝑡𝑜𝑡𝑎𝑙 = 𝑄 𝑖𝑛 = 𝑄 𝑐𝑜𝑛𝑣 , 𝑜𝑢𝑡𝑠𝑖𝑑𝑒 + 𝑄 𝑟𝑎𝑑 + 𝑄 𝑐𝑜𝑛𝑣 , 𝑖𝑛𝑠𝑖𝑑𝑒
ACTIVE BRAKE COOLING 78
Conclusion
At an internal drum airflow velocity of 51 988.7 m/s, the rate of energy leaving the plate matches
the rate of energy added to the plate.
This sample calculation may be used to develop an Excel sheet which can be used to experiment
with system parameters.
ACTIVE BRAKE COOLING 82
Part II
Objective
Determine the volume flow and corresponding power required to deliver 51 988.7 m/s air to the
drum
Assumptions
• The flow area of the drum is reduced by 30% by mechanical components of the brake
Air behaves as an ideal gas
• The energies required to overcome pipe friction, for elevation changes, and of the kinetic
energy of the gas are negligible
Given
Analysis
Reducing flow area by 30% and calculating Volume flow:
Figure 5. Cooling medium flow area
Using the ideal gas law to estimate the effect of increasing pressure on volume flow required:
T, R, m are assumed constant.
ACTIVE BRAKE COOLING 83
The power required to compress and supply adequate volume flow of air is
Converting to a more familiar unit of power
Multiplying by 10 brakes
Conclusion
The power required to supply enough air to maintain constant brake temperature through forced
convection under conditions listed above is approximately 1.6 million horsepower.
Increasing the delivery pressure significantly reduces the required volume flow, but does not affect
required supply power, in this model.
ACTIVE BRAKE COOLING 84
Appendix K: Custom Stand
ACTIVE BRAKE COOLING 85
ACTIVE BRAKE COOLING 86
Appendix L: Model Specifications
Brake drums are commonly made from Grey Cast Iron Ht250, g3000. Mechanical properties are
listed below. Performance indicators of the Model are also listed. Please note that these values were
obtained ignoring the systems energy losses such as surface roughness/friction
ACTIVE BRAKE COOLING 87
Mechanical
property Value Units
Elastic modulus 150 Gpa
Density 7100
kg/m^
3
Possion ratio 0.26 -
Thermal
conductivity 53 W/m K
Specific heat 0.46 kJ/kgK
Weight 43 kg
Parameter Calculated
Quantity
Units Detail
Volume Flow Rate 20.8 CFM 166/8outlets
Volume Flow Rate of
Blower
166 CFM Given
Speed of Impeller 2660 RPM Given
Amps 4.1 Amps Given
Volts 12 Volts Given
Wire Gauge 22 gauge Arbitrary Length is less than
10 feet does not
pose threat
Power 49.2 W P=V*I
Power 0.065 hp conversion
factor(1kW=1.34hp)
Velocity 1056.42 ft/min Volume Flow Rate /
Area
Mass Flow Rate 0.0533 Slug/min Volume Flow Rate
*Density of Air
Mach Number 0.015650667 <3 V/C
Density of air 2.571 *10^-3 Slug/ft^3 Room temperature
Outlet diameter 1.9 inch inch Measured in
Machine Shop
Max Voltage Drop 0.36 - 0.3*12
ACTIVE BRAKE COOLING 88
Outlet Area 0.019689 ft^2 ((3.14)* outlet
diameter ^2)/4
