Cooling - Revision history

SpookySimon: /* Simulation/Analysis */

2024-04-02T13:48:58Z

Simulation/Analysis

SpookySimon: /* Fluid Flow Rates */ gormatting

2024-04-02T13:37:23Z

Fluid Flow Rates: gormatting

SpookySimon: /* Hosing */

2024-03-21T18:45:57Z

Hosing

SpookySimon: /* Routing */

2024-03-21T18:45:02Z

Routing

SpookySimon: /* Water */

2024-03-21T18:43:32Z

Water

SpookySimon: /* Thermal Resistance Circuit */

2024-03-21T18:42:15Z

Thermal Resistance Circuit

SpookySimon: /* EV */

2024-03-19T17:32:09Z

SpookySimon: /* Radiator Choice */

2024-03-19T17:30:47Z

Radiator Choice

SpookySimon: /* Simulation/Analysis */

2024-03-14T13:09:52Z

Simulation/Analysis

SpookySimon: /* Thermal Resistance Circuit */ little more words, dont want to have to write a whole text books baout it tho

2024-03-14T13:06:33Z

Thermal Resistance Circuit: little more words, dont want to have to write a whole text books baout it tho

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 The system can be modeled parametrically to analyze how sensitive your setup will be to changes in each of these parameters. You will need to have the correct (or close enough) values for your mass flow rates for water and air, coefficient for thermal conductivity, area and heat input.
 In order to verify the model, tests will have to be performed, either on a dyno or on a vehicle. You must gather temperature data before and after the radiator.
 ===Thermal Resistance Circuit===
 The easiest way to model heat transfer is with a resistance based electrical analogy. A thermal mass can be looked at as a single capacitor, a heat transfer boundary can be looked at as a resistor, and a heat source, unsurprisingly, as a DC source. This allows a number of elegant simplifications to heat transfer analysis.
 ===Battery Thermal Analysis===

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 <!--rephrase: As far as I know, teams that run multiple rads use one for water and one for oil. -->Common FS/FSAE electric mounting scheme is to run two symmetric radiators<ref>https://www.instagram.com/p/B8jcYNqhux2/?igshid=1hwa03kwfnw3</ref>.
 ==Fluid Flow Rates==
-Tuning radiator performance is largely balancing the flow rates of the water and the air passing through the radiator. For analysis, heat exchangers use a term called capacity rate which is the mass flow rate times the specific heat of the fluid. An over-simplified way to think about this is as if the fluid are conveyer belts for "heat units", the specific heat capacity is how many "heat units" can fit on the belt at a time and the mass flow rate is how fast the belt is going.
+Tuning radiator performance is largely balancing the flow rates of the water and the air passing through the radiator. For analysis, heat exchangers use a term called capacity rate which is the mass flow rate times the specific heat of the fluid. An over-simplified way to think about this is as if the fluid are conveyer belts for "heat units", the specific heat capacity is how many "heat units" can fit on the belt at a time and the mass flow rate is how fast the belt is going. Heat capacity rate is defined as:
-: C = ṁ * c<sub>p</sub>The maximum possible heat transfer by a heat exchanger will be limited by the smallest heat capacity rate as seen by the equation:
+: C = ṁ * c<sub>p</sub>
 : Q<sub>max</sub> = C<sub>min</sub> * (t<sub>hot,inlet</sub> - t<sub>cold,inlet</sub>)The limiting factor in our analogy will be whichever conveyer belt is filled up first. The ratio of flow rates is called Capacity-Rate Ratio and is the lower flow rate C<sub>min</sub> over C<sub>max</sub>. The effectiveness of the heat exchanger will be a function of this ratio. A few assumptions will be important in the flow rate discussion here: (1) The engine is designed such that the water inlet temperature to the radiator (t<sub>hot,inlet</sub>) will be the same temperature regardless of the water flow rate and (2) The inlet air temperature will be independent of the air flow rate.
 The above equation tells us two things: heat transfer is limited by one of the mass flow rates, and that increasing the lowest heat capacity rate will increase our heat transfer rate.
 We can discuss the impact of changes to a single fluid flow rate interchangeably with capacity rate if we assume the heat capacity of the fluid stays constant, but not when comparing the capacity rates of two fluids.

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 Coolant hosing comes in 2 types: hard lines and soft  lines. Hard lines are often aluminum due to their low cost and ease of bending. Soft lines are often silicone or rubber hosing, but the use of water as coolant allows for lower spec lines than a production or high performance industry automobile. The stock motorcycle coolant lines are pre-formed rubber lines and are more than capable of being used for FSAE.
-Hard lines weight less per foot of distance and are often cheaper to purchase. However, they require more planning to execute. Soft lines can be routed around much more complicated geometry without planning the routing before hand.
+Hard lines weigh less per foot of distance and are often cheaper to purchase. However, they require more planning to execute. Soft lines can be routed around much more complicated geometry without planning the routing before hand.
 ===Filling and Bleeding===
 For the coolant system to run correctly, the system needs to be purged of air. A bleeder valve should be placed on the highest point in the system, often connected to the filler neck. You may have to turn the engine over a few times to flush it through the engine.

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 ==Routing==
-Coolant routing is largely a packaging concern. There are minor theoretical gains to be had in cooling performance if you minimize head losses. However, these are not big enough to gain points in competition, or seconds off in a dynamic event. Like most other fluid systems, routing can be done with hard lines or soft lines. The soft lines are often silicone similar to those seen in aftermarket applications, as they do not need to withstand high pressures or a caustic fluid like gasoline. Hard lines are often connected by short sections of silicone tubing.
+Coolant routing is largely a packaging concern. There are minor theoretical gains to be had in cooling performance if you minimize head losses. However, these are likely  not big enough to gain points in competition, or seconds off in a dynamic event. Like most other fluid systems, routing can be done with hard lines or soft lines. The soft lines are often silicone similar to those seen in aftermarket applications, as they do not need to withstand high pressures or a caustic fluid like gasoline. Hard lines are often connected by short sections of silicone tubing.
 Keeping routing short and straight will reduce weight. Reducing bends will drastically reduce the difficulty to bleed the system. In addition, any routing section that is not monotonic will trap air bubbles. It is recommended that the fill point of the system be the highest point to aid in complete filling.
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 DON'T TAKE THE RADIATOR CAP OFF WHEN IT'S HOT. If one was to hypothetically remove the rad cap when the system is dangerously hot, they could cover it with a heavy cloth to shield themselves from the coolant that will come out. Do not do this. Under no circumstances is it advisable to attempt to service the system until it has cooled down to a safe level.
 ==Catch Can==
 According to rules T.5.6, catch cans must meet the following criteria:

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 Note: The stock CBR 600RR water pump generates 30-60 Lpm<ref>https://www.facebook.com/photo/?fbid=10150829256503036&set=a.10150813204983036</ref>. With a few assumptions, we can calculate the maximum ballpark capacity rate for a CBR:
-* Mass flow rate of 60 LPM
+* Volumetric flow rate of 60 LPM
 * 1kg/L density of water
 * Temp near 100C<ref>c<sub>p</sub> of water is slightly temperature dependent at these temps. The higher the inlet water temp of the hot fluid, the higher the max heat transfer rate. We cannot use a higher temperature for FSAE coolant than 100C without cheating.</ref>

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 Finding average power output of the engine is one way to determine an approximate necessary cooling power for the engine. This can be accomplished by measuring fuel consumption or engine torque/vehicle velocity (P = FxV).
 ===EV===
-The main heat generating components are the motor and motor controller. Conservative rules of thumb put the ballpark efficiencies at about 90% for both components. The heat generated by this powertrain would be about 15 kW<ref>According to the equation Q = P<sub>electric,input</sub>*(1 - &eta;<sub>controller</sub> * &eta;<sub>motor</sub>) = 80*(1-0.9*0.9) = 15.2. Some papers use Q = P<sub>electric,input</sub>*[(1 - &eta;<sub>controller</sub>) + &eta;<sub>controller</sub> * (1 - &eta;<sub>motor</sub>)] which is numerically equivalent</ref> when running at max power. A better estimate is 30kW average draw<ref>Chiu, Harriet A. ''Design of a FSAE Cooling System''. 2019. MIT </ref> which yields a ballpark heat generation of ~6kW. This is likely higher than most teams will see.
+The main heat generating components are the motor and motor controller. Conservative rules of thumb put the ballpark efficiencies at about 90% for both components. The heat generated by this powertrain would be about 15 kW<ref>According to the equation Q = P<sub>electric,input</sub>*(1 - &eta;<sub>controller</sub> * &eta;<sub>motor</sub>) = 80*(1-0.9*0.9) = 15.2. Some papers use Q = P<sub>electric,input</sub>*[(1 - &eta;<sub>controller</sub>) + &eta;<sub>controller</sub> * (1 - &eta;<sub>motor</sub>)] which is numerically equivalent</ref> when running at max power. A better estimate is 30kW average draw for the traction system<ref>Chiu, Harriet A. ''Design of a FSAE Cooling System''. 2019. MIT </ref> which yields a ballpark heat generation of ~6kW. This is likely higher than most teams will see.
 A more thorough method is to use data from previous years, or that generated by a [[Introduction to VD Simulation | lap sim]], coupled with the efficiencies given on the motor/motor controller datasheets if available to model the generation over a lap<ref>LaMarre, Jeff. "FSAE Electric Vehicle Cooling System Design". 2015. UAkron</ref>.

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 ==Radiator Choice==
-The radiator for most teams is outside of the scope of custom design and production. Therefore, teams have limited to no ability to tune radiator parameters, and the choice of which radiator to run becomes the main design choice. Radiator selection can be done by size: length, width, and thickness. Radiator dimensions are not created equal as lower temperature water will be cooled less than high temperature water. The focus should be on getting more mass flow of hot water. On a downflow radiator, this means radiator width will often be more impactful than radiator length. A longer radiator forces water to travel further through the radiator, causing a greater ΔT between the inlet and outlet, and a lower average water temperature. The width of a radiator is analogous to the diameter of a pipe, the larger the width, the more water can flow through the radiator at a time. The thickness of the radiator will increase the massflow of the water through the radiator and the amount of time a quantity of air is in contact with the radiator, but can negatively impact the massflow of air through the radiator.
+The radiator for most teams is outside of the scope of custom design and production. Therefore, many teams have limited to no ability to tune radiator parameters, and the choice of which radiator to run becomes the main design choice. Radiator selection can be done by size: length, width, and thickness. Radiator dimensions are not created equal as lower temperature water will be cooled less than high temperature water. The focus should be on getting more mass flow of hot water. On a downflow radiator, this means radiator width will often be more impactful than radiator length. A longer radiator forces water to travel further through the radiator, causing a greater ΔT between the inlet and outlet, and a lower average water temperature. The width of a radiator is analogous to the diameter of a pipe, the larger the width, the more water can flow through the radiator at a time. The thickness of the radiator will increase the massflow of the water through the radiator and the amount of time a quantity of air is in contact with the radiator, but can negatively impact the massflow of air through the radiator.
 The two types of radiator are cross flow and down flow. The difference in performance is insignificant. A downflow radiator has water enter the top and go to the bottom in one pass. Crossflow radiators force water through the radiator sideways and can include multiple passes. Downflow radiators are most common in FSAE as they are usually taller and skinnier and will fit on the side of the vehicle without increasing frontal cross sectional area.
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 You can also purchase radiators by specifying the approximate engine power or by contacting a radiator supplier for assistance.
 ==Radiator Placement==
 '''Side'''<br />The most common radiator placement in FSAE is on the side of the vehicle, usually within the sidepod. This is a space that is usually free of other systems, somewhat unobstructed airflow, and for most bike engines it is a favorable routing position.

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 ===Thermal Resistance Circuit===
 The easiest way to model heat transfer is with a resistance based electrical analogy. A thermal mass can be looked at as a single capacitor, a heat transfer boundary can b looked at as a resistor, and a heat source, unsurprisingly, as a DC source. This allows a number of elegant simplifications to heat transfer analysis.
 ==Data and Data collection==