Analysis of Nozzle cooling system in automobile

ANALYSIS OF NOZZLE COOLING SYSTEM IN AUTOMOBILE

Akshay GopinathDaehan WiDinesh SoundarajanHarikirupakar Kishore Kumar Keju AnContents

Introduction

Analytical Approach - Validation - Energy Analysis

CFD Simulation

Conclusion

Introduction

In US, the total fuel consumed for air conditioning amounts to 7 billion gallons a year. Air conditioning contributes to the fuel economy of a vehicle in a large way. Research is underway to improve the energy efficiency of the HVAC subsystem.Current cooling/heating system utilizes most of the energy to condition the large thermal mass of the vehicle and not the occupants. Nozzle Cooling is a newly developing system utilizes an efficient localized conditioning method.

Object of ProjectComparison Conventional system and Air nozzle System

Improve efficiency of refrigeration system

Calculate the time taken to reach Comfortable human temperatureAnalytical Approach : Validation

=>Finding Boundary condition The surface temperature of the car (T_s) Considering Areas : A_window (Glass), A_car body (Aluminum)

Ref > Energy Efficient HVAC system with spot cooling in an automobile Design and CFD Analysis, D. Ghosh and M. Wang, SAE International, 2012-10-0641Surface temperature prediction and validation in a realistic vehicle thermal environment!!

Solving equation : External forced convection and Radiation

Ref > Design of Dynamic Airvents and Airflow Analysis in a Passenger Car Cabin, Varad M. Limaye, SASTECH, Volume 11, Issue 1, Apr 2012.

Q=1100 W/m^2Given ValuesQ_sol1100 [W/m^2]T_310 [K]T__car309.203 [K}L0.5 [m]5.67*10^-8 [W/m^2-K^4]V_in0.029287 [m/s]V_out13.89 [m/s] _Aluminum0.9(anodized) _Glass0.92(Inside car)window(outside car)Q_rad_outQ_conv_outQ_sol_inQ_conv_out=>Surface temperature determination (using EES) ex) A_windscreen (Glass)

=>T_s_windscreen = 45.01 [C]

EES ResultFront_window(Glass)Back_window(Glass)Side_window(Glass)Car ceiling (Aluminum)T [C]45.0141.2332.9141.11Ref. ResultFront_window(Glass)Back_window(Glass)Side_window(Glass)Car body (Aluminum)T [C]4642.73440Our team matched Analytical Result and Ref. Result.Validation!!

So, We used these surface temperatures to run Fluent!

Using similar methods for other surfaces8Heat load considered from human body and Nozzle Locations

Conduction to seatsRadiation to/from windows and ceilingConvection to air

AC inletsFace nozzle inletChest nozzle inletLap nozzle inletOutletBoundary ConditionRoof, Windscreen, Rear screenConstant Temperature Specified in previous slidesHuman Body Constant Temperature 37 CSolver setupTurbulence modelRealizable K-EpsilonRadiation modelS2S modelNozzle Cooling systemTotal Flow rate (CFM)120Face Nozzle (CFM)36Chest Nozzle (CFM)48Lap nozzle (CFM)36AC SystemInlets (CFM)170Boundary Conditions and solver setupTransient setupTime step size1 secondTotal time simulated5 minutesInitial Temperature42 CMaterial PropertiesAirDensity (Kg/m3)1.225Conductivity (W/mk)0.0242Specific heat (J/kg.K)1006.43Viscosity (Kg/m.s)0.000017894

Breath surface (3cm above skin surface)Passenger and driver mid planePost Process planes and surfaces

Time 90 seconds Conventional system

Velocity contour at Passenger mid planeVelocity contour at Driver mid planeTemperature contour at Passenger mid planeTemperature contour at Driver mid plane

Time 90 seconds Nozzle systemVelocity contour at Passenger mid planeVelocity contour at Driver mid planeTemperature contour at Passenger mid planeTemperature contour at Driver mid plane

Time 280 seconds Conventional system Velocity contour at Passenger mid planeVelocity contour at Driver mid planeTemperature contour at Passenger mid planeTemperature contour at Driver mid plane

Time 280 seconds Nozzle system Velocity contour at Passenger mid planeVelocity contour at Driver mid planeTemperature contour at Passenger mid planeTemperature contour at Driver mid plane

Pathlines conventional systemPathlines Nozzle systemTemperature at breath surface conventional system at steady stateTemperature at breath surface Nozzle system at steady stateContours at breadth surface and Pathlines from inletNozzle cooling systemAC cooling system

Plot of Temperature v.s. Time for different partsEnergy Analysis (1)=>by using Refrigeration Cycle

The maximum achievable COP is 8.8 and Test results of the best systems are around 4.5 (Ref. Wikipedia)

Q_AC = 866.3 [W] Q_Nozzle = 937 [W] Q_in [W]W_in (fixed) [W]COPRAC866.3481.2771.8Air_Nozzle937481.2771.947COP_AC < COP_Air_Nozzle !Energy Analysis (2)

Q_in(W)AirNozzleAC90(Steady State)Time(sec)937 W649.7 W (75% of AC)649.7 W (75% of AC)866.3 W

ACACQ_in(W)Time(sec)Integration Area = Energy absorbed by evaporatorCASE(1)_5minQ_in = 408.84 [KJ]280(Steady State)CASE(2)_5minQ_in = 473.36 [KJ]=> 15.8 % Energy saved for 5min19CONLUSIONS AND FUTURE WORKIt has been found that efficiency of the system has been increased by about 0.3%.For a Nozzle system , Steady state was obtained after 90 seconds attaining a comfortable temperature .Local cooling can be considered a great supplement to the traditional centralized HVAC system to maintain passenger comfort with higher energy efficiency. The velocity of air from the nozzle plays an important role in its efficiency .Care must also be taken to ensure that the nozzles are strategically placed so that it does not cause discomfort. Combining these systems is effective in providing a comfortable cabin environment while reducing the HVAC system power.The combination of face, chest, abdomen was found to be most effective .Future work could be to smoothly integrate both conventional and nozzle air conditioning in a whole unit with control systems which could become both energy efficient and effective. Thank you