SOLUTION FOR HEATRANSFERIN HYPERLOOP PODAdvanced Heat Transfer Term ProjectYASH NAIKStudent Id: 108947812P a g e | 1HEAT TRANSFER PROJECT – Solution for Heat transfer in Hyperloop PodTable of contents• Abstract• Introduction• Current Systemo Componentso Operationo Calculation• Alternate solutions• Increasing Radiative Heat Transfer• Increasing Convective Heat Transfer• ReferencesP a g e | 2ABSTRACT:This report contains current method of cooling used in Hyperloop Pod with calculation andafter that some other methods to increase heat transfer rate is discussed. Focus is to enhanceradiative heat transfer as mostly it is taken for granted in system designs but can play majorrole. Many Article and papers are reviewed for this as radiative heat transfer can also contributetowards convective heat transfer also. Each method is reviewed, and conclusion is it can usedor not in pod with what changes and to what length.

INTRODUCTION:SpaceX Hyperloop pod Competition requires each Team to Design and build a pod which iswithin competition parameters and passes all preliminary as well as final design testing. So asa member of Hyper Lynx team, representing UC Denver, I am working on designing theHyperloop pod for the competition. The original design intent was to avoid using a coolingsystem and keep the design as simple as possible. But it is necessary for some of theComponents.CURRENT SYSTEM:Only few components generate heat that must be dissipated. Selected components wereresearched to determine the estimated temperature rise and any cooling requirement.The low voltage battery, Raspberry Pi, and Arduino components do not require cooling.

Eachwas vacuum tested to 0.14psi (7torr) at SpaceX in 2016, and no adverse heat rise was recorded.The high voltage battery manufacturer has confirmed that cooling is unnecessary for thebatteries.

The motor and motor controller both explicitly require cooling. We assume the nearvacuumconditions provide no effective air convection.As per the manufacturer, the EMRAX 208 liquid-cooled motor requires 7L/min of coolant flowduring operation, at a nominal pressure of 8.7psi (0.

6bar). The maximum pressure is200kPa. The listed motor efficiency is 92-98%. For heat generation calculations, a 90%efficiency was assumed, resulting in 8kW of maximum heat generation. The motor is not likelyto spend the entire flight at maximum power, so these numbers are conservative.

The UnitekBAMOCAR-D3 motor controller lists a maximum flow of 12L/min, a maximum pressure of130kPa. The maximum power loss (and assumed heat generation) is listed at 3kW. Theassumed time of flight will be 60sec, and this is conservative. The motor and motor controllerwill generate 66kJ of heat during operation.P a g e | 3The cooling system will serve as a heat sink.

No radiator will be used due to the near-vacuumconditions and short time of flight. Distilled water will be used as coolant. The system will besealed during very pre-flight and the reservoir tank will maintain an internal pressure ofapproximately 100kPa during flight. A 1gal reservoir of distilled water exposed to 66kJ of heatwill result in a 4°C temperature rise.

The system requires a pump head of 0.7m. During longtermstorage, the coolant system will be filled with a glycol mixture for anti-freezing and antimicrobialprotection.COMPONENTS:The motor and motor controller will have individual pumps, tubing, and sensors. This ensureswe can monitor and control coolant flow to the motor and controller independently.

The pumpis a 12VDC water pump with maximum flow of 13L/min, a 4m, a maximum temperature of60°C, and a maximum power draw of 1.2A. Each pump will receive 12VDC from the LVpower system, fused at 2.5A. Tubing is 0.375″ (9.

525mm) ID nylon, rated to 450psi (3103kPa)at 70°F (21°C) and a maximum temperature of 212°F (100°C). Fittings are High-DensityPolyethylene with a maximum pressure of 125psi (862kPa) and maximum temperature of190°F (88°C).The reservoir has two sensors.

A pressure sensor will verify the reservoir is maintaining tankpressure during vacuum conditions, and a temperature sensor will monitor the fluid temperaturerise during operation. The motor and motor controller will each have a pressure sensor at theirrespective inlets to monitor delivered coolant pressure.OPERATION:Before flight and during the INIT state, the Hyper lynx crew will activate the coolant pumpsand adjust them to reach desired motor and motor controller pressures. The pumps arecontrolled by variable 12VDC signal, which will be controllable through the Mission Controlinterface. The pumps will continue to run for the duration of the flight, and are only deactivatedby the crew after verifying reservoir, motor, and motor controller temperatures have stabilizedto safe levels.CALCULATIONS:Reservoir Temperature Rise (4.1°C)?T=(Q/M*C) (1)?T is the temperature rise in CelsiusQ is the heat input (66kJ)M is the mass of coolant (3.

8kg)C is the heat capacity of the coolant (4184J/kg)P a g e | 4Fluid Velocity (3.68m/s)v=Q/A (2)v is the fluid velocity in m/sQ is the desired flow rate (1.1667×10-4m3/s)A is the cross-sectional area of the coolant tubing (3.1669×10-5m2)Required Pump Pressure (76456Pa)P1=P2+?g(z2-z1) +?v2/2(f*L/D+?K) (3)P1is the required pump pressure in PaP2 is the desired line pressure at the motor (76443Pa)? is the density of water at 30°C (995.7kg/m3)g is the gravitational acceleration, (9.

81m/s2)z2 is the elevation of the motor from the datum (0.1m)z1 is the datum elevation of the system (0m)v is the velocity of the coolant from Eq.1f is the friction factor for a smooth pipe, derived from the Moody chartD is the diameter of the tubing (0.0064m)L is the length of tubing (0.2m)?K is the sum of the minor loss constantsRequired Pump Head (0.7m)hp=P2-P1/?g+(z2-z1) +v2/2g(f*L/D+?K) (4)hp is the pump head in mP2is the desired line pressure at the motor (76443Pa)P1is the required pump pressure from Eq.

2? is the density of water at 30°C (995.7kg/m3)g is the gravitational acceleration, (9.81m/s2)z2 is the elevation of the motor from the datum (0.1m)z1 is the datum elevation of the system (0m)v is the velocity of the coolant from Eq.1f is the friction factor for a smooth pipe, derived from the Moody chartD is the diameter of the tubing (0.0064m)L is the length of tubing (0.2m)?K is the sum of the minor loss constantsP a g e | 5ALTERNATE SOLUTIONS:As for cooling system we are using is more practical and easy to implement. But it not the onlysolution that can be applied to solve the problem.

There are numerous ways (solution) that canbe used here but might not be practical to use them because they might be experimental orrequires lot more effort. I have found some other ways to increase the heat transfer from motor.There are two modes by which we can increase heat transfer inside pod.1) Increase radiative heat transfer.2) Increase convective heat transfer.INCREASING RADIATIVE HEAT TRANSFER:Heat transfer by radiation between two surfaces at different temperature is given by the StefanBoltzmannequation: q = ??A (TH4- TC4)Where? = Stefan-Boltzmann Constant=5.

67*E-08 (W/m2K4)TH = temperature of the hot surface(K)Tc = temperature of cooler surface (K)? = emissivityA= surface area of heat sinkNow this equation indicates that the temperature difference between two surface has thegoverning effect in the radiative heat transfer. But there are other constrains as emissivity andsurface area of heat sink.But inside pod, as heat transfer occurs between motor and our surface, surface temperature willrise constantly, and heat transfer will begin to reduce significantly as, it depends on power 4 oftemperature.

So, even small temperature rise will reduce the heat transfer rapidly.Other way to increase radiative heat transfer rate is to increase surface area. But since that canincrease weight of pod also and with limited space available it cannot be done.But, as mentioned in this article, effective surface area can be increased without increasingactual area of heat sink surface.”An innovative is solution must be developed to increase the effective surface. area withoutincreasing the size of the parts. Microscopic texturing is such a solution.

Microscopic surfacetexturing not only increases the surface area; it also increases the emissivity of the surface atthe same time. This is because radiation heat transfer is primarily a surface phenomenon. Thus,certain texturing. processes that provide sufficient control over surface feature morphology canincrease surface emissivity.

” {1}P a g e | 6Article talks about using surface treatments to increase surface area. Chemical etching is oneof the treatments used frequently and another common treatment is Ion beam texturing.In theory later, technique can be used to generate any type of texture on surface as we required.Images of textures”The larger surface area will enhance radiation as well as convection heat transfer, providedthat the texturing can provide an excellent surface for pool boiling heat transfer, which is oftenseen in cooling of high power electronics.” {1}There is one technique which emphasizes on increasing emissivity of surface called Anodizing.It is an electrochemical process that thickens and toughens the naturally occurring protectiveoxide layer on the surface of metal parts.

“To demonstrate the contribution of anodizing in low airflow velocity applications, two ATSmaxi FLOW heat sinks, one anodized and the other non-anodized, were thermally,characterized using the exact same method. The heat sink tested, ATS-440-C1-R0, has afootprint of 45 x 38 mm, its overall height is 24 mm and its fin offset on each side is 21mm. The heat sink was thermally characterized at natural convection and airflow velocities upto 3 m/s at increments of 0.5 m/s. Figure 3 compares the thermal resistance of thetwo heat sinks at different velocities. As shown, the thermal resistance of the anodized heatsink at all airflow velocities is lower than that of the non-anodized heat sink. However, thedifference is most significant at natural convection and becomes smaller as the airflowincreases.

” {1}P a g e | 7Conclusion:Reviewing this article, suggests that use of Anodized textured surfaces can increase radiativeheat transfer for the same temperature difference between surfaces, by increasing emissivityand effective surface area of heat sink surface. This can be used in future for pod, as we canbuild a heatsink with anodizes etched surface around casing which contains liquid coolant. Notonly it will increase radiative heat extraction from motor, but it will also increase convectiveheat transfer.

As in mentioned in article, P a g e | 8• Now, there is one other article “Enhancing radiative energy transfer throughthermal extraction” which talk about extracting nearfield radiation from emitter via thermalextractor to increase radiative heat transfer.As we know One of the fundamental constraints in thermal radiation is the Stefan-Boltzmannlaw, which limits the maximum power of far-field radiation to Po = A?T4, where ? is theBoltzmann constant, A and T are the area and the temperature of the emitter(blackbody),respectively. It is said that near-field radiations could have an energy density that is orders ofmagnitude greater than the Stefan-Boltzmann law. Unfortunately, such near-field radiationtransfer is spatially confined and cannot carry radiative heat to the far field.

Article talks about “a new concept of thermal extraction was proposed to enhance far-fieldthermal emission, which, conceptually, operates on a principle like oil immersion lenses andlight extraction in light-emitting diodes using solid immersion lens to increase light output.”{2}Thus, it will allow a black body to radiate more energy which will be able to reach far fieldwithout breaking laws of thermodynamics. Basically, they put the thermal radiation extractorso close to the emitter body that the distance between emitter and extractor is less the thermalwavelength. The near field coupling is capable of transferring heat that has more energy densitythan predicted by Stefan-Boltzmann equation. Thermal extractor is made of such material thathas high transitivity which allows near-field radiation to reach far field without being absorbedor emitted by other surfaces. So, energy reached to far field well exceeds energy calculatedStefan-Boltzmann equation.The Article consists of series of experiments which consists using different material for thermalextractor to see if hypothesis made about nearfield radiation will reach far field as extractor ismade of transparent high index materials.They have run experiments with Thermal extractor made from natural material as well asstructured material.

Experiment setup consist of a standard blackbody sphere with a cavity,inside surface having high reflective index.Results show that,1) Thermal extractor must be in optical contact with emitter body meaning distancebetween extractor and emitter surface should be less than thermal wavelengths.Otherwise near field coupling will take place in between space.

2) Physical contact is not necessary, only optical contact. This will reduce or eliminateconduction between extractor and emitter.3) the thermal extraction device needs to provide enough radiation channels over the areaof the emitter to ensure that all internal modes of the emitter can out couple, which canbe achieved by making extractor density sates lighter than emitter.P a g e | 94) in the extraction device those optical modes that receive radiation from the emitter needto be accessible to far-field vacuum. This places a constraint on the geometry of theextraction device.

Example- A transparent high-index slab with a flat surface does not provide thermalextraction. Even though more radiations can enter the slab, those outside the escapecone cannot escape to far-field vacuum due to total internal reflection.Conclusion:This solution is still in experimental basis as it may not possible to implement it in everycase. To apply this solution, we may have to make adjustment for thermal extractorwhich are optically capable of transferring near- field couple to Fairfield outcoupled.

But also, these extractors must have high thermal insulation as in experiment they werearound room temperature whereas motor inside pod will around much highertemperature. Thus, it is limited by material constraints of thermal extractors.• A research paper,” Spectrally enhancing near-field radiative heat transferby exciting magnetic polariton in SiC gratings” also suggest that near field couples’ extractioncan be enhanced by presence of magnetic resonance or polariton.

Magnetic polaritons (MP)refer to the strong coupling of external electromagnetic waves with the magnetic resonanceexcited inside the nanostructures. But presence of electromagnetic waves may hinder motoroutput so cannot be used in my situation. Though it has immense application in real world likein energy-harvesting, near-field imaging, thermal modulation, and thermal switch andrectification we cannot use it. {3}There are numerous articles on extracting near filed Radiation, consisting experiments and theirresults are included using different material for thermal extractor like1) Enhancement of near-field radiative heat transfer using polar dielectric thin films2) Using high temperature liquid salts (Fluoride and Chloride salts)3) Nanostructures consisting nanoparticles that emit electromagnetic radiationMay be in future we can use these methods with convenient and with sure results.P a g e | 10INCREASING CONVECTIVE HEAT TRANSFER:Now as mentioned earlier that we are using a coolant to vacant produced heat which is doneby convection heat transfer mode. But still there are numerous ways to increase convectiveheat transfer which have more concrete data that they will work and have been tested by manyexperiments. As A review article “Recent Advances in Heat Transfer Enhancements”Has said that for”the mechanisms of heat transfer enhancement can be at least one of the following.

(1) Use of a secondary heat transfer surface.(2) Disruption of the unenhanced fluid velocity.(3) Disruption of the laminar sublayer in the turbulent boundary layer.(4) Introducing secondary flows.(5) Promoting boundary-layer separation.

(6) Promoting flow attachment/reattachment.(7) Enhancing effective thermal conductivity of the fluid under static conditions.(8) Enhancing effective thermal conductivity of the fluid under dynamic conditions.(9) Delaying the boundary layer development.(10) Thermal dispersion.(11) Increasing the order of the fluid molecules.(12) Redistribution of the flow.(13) Modification of radiative property of the convective medium.

(14) Increasing the difference between the surface and fluid temperatures.(15) Increasing fluid flow rate passively.(16) Increasing the thermal conductivity of the solid phase using special nanotechnologyfabrications.” {4}As we can see first mechanism uses increased surface area technique which is very commonway to have more heat transfer. Now and no. (2) can be done increasing the surface area incontact with the fluid to be heated or cooled by using fins, intentionally promoting turbulencein the wall zone employing surface roughness and tall/short fins, and inducing secondary flowsby creating swirl flow using helical/spiral fin geometry and twisted tapes.Increasing turbulence can be help in some application to increase mixing of fluids, to increaseheat transfer by convection as turbulent flow will have more collisions between fluid particles,which increase contact time and transfer of energy from one particle to another.Arman and Rabas discussed the turbulent flow structure as the flow passes over a twodimensionaltransverse rib.

They noted that eddies are generated above the flow regions,particularly at the top of the rib and one in the downstream mixing zone. These zones have thehighest heat transfer rate because of the eddies. Which is basically experiment base don of no(6) mechanism.P a g e | 11Ding et al conducted an experiment and as result he got that, that fluids containing 0.5wt.%of carbon nanotubes (CNT) can increase heat transfer by 250% at Re = 800, which issignificant. report.

The increases in heat transfer due to presence of nanofluids are basicallyfollowing mechanisms, no (7 & 8).Heat transfer Enhancers:1) Creating extended surfaces (Fins)2) Use of Porous Media (As fluid)3) Use of Nanofluids4) Use of complex flexible seals5) Use of vortex generators (to get turbulent flow)6) Use of ultra-hight thermal conductive materialsHeat Transfer Enhancer Heat Transfer in presence of enhancer/HeatTransfer in absence of EnhancerRatio(unitless)Fins Inside Tubes 2Porous Media 12(approx.)Nano Fluids 3.

5Complex Flexible seals 3Vortex Generators 2.5Ultra-high thermal conductivity compositematerials 60 2 4 6 8 10 12 14Fins Inside TubesPorous MediaNano FluidsComplex Flexible sealsVortex GeneratorsUltra high thermal conductivity composite…Ratio of HT in presence of Enhancer to absence of enhancersEnhancersHeat Transfer EnhancersP a g e | 12REFERENCES & CITATION:{1} Radiation Heat Transfer and Surface Area Treatments Q pedia Thermal Magazine (Q pedia Thermal Magazine Volume II, Issues 1-12 2008){2} Enhancing radiative energy transfer through thermal extractionTan, Y., Liu, B., Shen, S., & Yu, Z.

(2016). Enhancing radiative energy transfer throughthermal extraction. Nanophotonics, 5(1). doi:10.1515/nanoph-2016-0008){3} Spectrally enhancing near-field radiative heat transferby exciting magnetic polariton in SiC gratingsYang, Y., & Wang, L. (2016). Spectrally Enhancing Near-Field Radiative Transfer betweenMetallic Gratings by Exciting Magnetic Polaritons in Nanometric Vacuum Gaps.

PhysicalReview Letters, 117(4). doi:10.1103/physrevlett.117.

044301{4} Recent Advances in Heat Transfer Enhancements: A Review ReportSiddique, M., Khaled, A. A., Abdul hafiz, N. I., & Boukhary, A. Y. (2010).

Recent Advancesin Heat Transfer Enhancements: A Review Report. International Journal of ChemicalEngineering, 2010, 1-28. doi:10.1155/2010/106461