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Analytical Design and Estimation of Conventional and Electrical Aircraft Environmental Control Systems Hemanth Devadurgam , Soorya Rajagopal , Raghu Chaitanya Munjulury Division of Fluid and Mechatronic Systems, Department of Management and Engineering, Linköping University, Linköping, Sweden - 58183 Symbol Description Units ABSTRACT A Area m2 Environmental control system holds vital importance P Perimeter m as it is responsible for passenger’s ventilation and T Temperature degree C kg comfort. This paper presents an analytical design of k Thermal Conductiv- mK environmental control systems and represents the esti- ity mated design in three-dimensional. Knowledge-based K Kelvin K engineering application serves as the base for design- D Hydraulic Diameter m ing and methodology for the environmental control kg m Mass flow rate s systems. Flexibility in the model enables the user p Pressure Pa to control the size and positioning of the system and kg m Dynamics viscosity ms also sub-systems associated with it. The number of passengers serves as the driving input and three- dimensional model gives the exact representation with 1 Introduction respect to the volume occupied and dependencies on The Environmental Control System (ECS) is responsi- the number of passengers. It also provides a faster ble for passengers comfort and one of the most impor- method to alter the system to user needs with respect tant systems of an aircraft. Temperature and pressure to the number of air supply pipes, number of ducts and of the air vary on the altitude and ECS works on reg- pipe length. Knowledge-based engineering gives the ulating the air, takes-in the bleed air mixes it with the freedom to visualize various options in the conceptual recirculating air so that the pressure and temperature design process. of the air are safe for breathing. Also, the system pro- vides de-misting, anti-icing functions for the aircraft Nomenclature [1]. Conventional ECS, operates on an open loop sys- Abbreviation Meaning tem, with air acting as the refrigerant. Bleed air is ACM Air Cycle Machine conditioned and fed into the aircraft for passenger cmp Compressor survival. Further, this system is classified as a Low- CATIA Computer Aided Three Di- Pressure Water Separation System (LPWS) and High- mensional Interactive Applica- Pressure Water Separation System (HPWS). A com- tion monly used system in aircraft, where the air is used ECS Environmental Control Sys- as a refrigerant. Air is made to pass through heat ex- tem changers, Turbines, Condenser and water extraction HPWS High Pressure Water Separa- loop to give the conditioned air. tion System The difference between LPWS and HPWS is the LPWS Low Pressure Water Separa- water extraction loop, consisting of Reheater and tion System Condenser. Although LPWS has fewer components MHX Main Heat Exchanger and lesser weight, the absence of water extraction loop PHX Primary Heat Exchanger unit becomes the limiting factor. The absence of this RAPID Robust Aircraft Parametric In- loop can lead to icing near the Turbine unit. This ic- teractive Design ing is not a desirable effect and thus, HPWS becomes trb Turbine the better choice and is used commercially on a large 1 Devadurgam, Rajagopal, Munjulury Fig. 1 . Electrical ECS Schematic diagram [1] Fig. 2 . Low pressure water separation system schematic diagram [1] scale. gers. The user gets the freedom to choose the type On the other hand, electrical ECS mainly oper- of ECS system along with the air supply piping and ates on reducing power consumption, by using elec- diffusers(single-aisle). While fulfilling the goals, the tric power instead of pneumatic power. Air is taken objectives considered were, as the ram-air substitute and is conditioned before feeding into the fuselage. Electrical ECS comprises • Designing the ECS and components based on of two air conditioning packs, which are electrically the type of aircraft or number of passengers. powered and motor driven. Electrical ECS is gain- • Calculate inlet and outlet temperatures and ing importance due to the lesser fuel consumption and pressures of individual components. eco-friendliness when compared to the conventional ECS. Lack of bleed air inlet essentially means cabin • Validating the outputs temperatures (K) and pressurization is provided by electrical compressors. pressures (Pa) of bleed air. These compressors also act as the source of air for the ECS, illustrated in Figure 1. • Designing air supply piping for single and dou- ble aisle configurations, which could be instan- 2 Aims and Objectives tiated along the length of the fuselage. This paper aims at designing and sizing conventional & electrical ECS and air supply piping along with dif- 3 Methodology fusers. These could be used for different sizes and The various components that make an ECS are types of aircraft with a varying number of passen- sized/modeled and presented below. Also, the as- 2 Analytical Design and Estimation of Conventional and Electrical Aircraft Environmental Control Systems Fig. 3 . High pressure water separation system schematic diagram [1] sisting equations are illustrated with numerical val- • Fin tube hydraulic diameter on hot and cold side ues along with the assumptions made to in the de- of the heat exchanger [2]. sign process. Initial assumptions are based on Moir & Seabridge [1]: 4At Dh = (1) Pt • Cruising altitude of 11277m where, • Mach number of 0.78 2 • At = Inside cross section area of the tube, (m ) • Inlet bleed air temperature at PHX (Tbleed) is • Pt = Perimeter of the tube, (m) 473.15 K • Density of air on hot and cold side of the heat • Ram air temperature (Tram) is 217.15 K exchanger [2]. MP 3.1 Analytical component sizing r = (2) RT Heat exchangers form the backbone of ECS. Cross- flow heat exchangers are considered and only dry where, bleed air is made to pass through the ECS[2]. Each Kg component of ECS is illustrated with the sizing equa- • r = Density, ( m3 ) tions along with the assumptions. These equations in- • M = Molar mass of the air = 29 crease the flexibility and adaptability of the system. The number of passengers (NPax) acts as the driv- • P = Pressure of air, (bar) ing input for the ECS sizing. Other limitations like J stresses, size, servicing, material, and cost were ne- • R = Gas constant=0.0831 ( mol:K ) glected during the sizing/modeling of the individual • T = Temperature of air, (K) ECS components. 3.1.1 Heat Exchanger • For dynamic viscosity, Sutherland’s law is used The Primary heat exchanger (PHX) & Main heat ex- [2]. changer(MHX) are not the only heat exchangers in T 1:5 Tre f + S ECS, even Reheater & Condenser are also cross-flow m = mre f ∗ ( ) ∗ ( ) (3) Tre f T + S type heat exchangers. Thus, PHX, MHX, Reheater, and Condenser have the same sizing equations. These where, are discussed in this section with emphasis on the Kg method employed for the sizing. • m = Dynamic Viscosity, ( m:s ) 3 Devadurgam, Rajagopal, Munjulury Kg • mre f = Reference Dynamic Viscosity, ( m:s ) • Prandtl number of air on cold and hot side of the heat exchanger [4]. • T = Temperature of air, (K) Pr = (m ∗Cp)=Kair (7) • Tre f = Temperature of air at sea level, (K) • Nusselt number of air [2]. • S = Sutherland’s Temperature, (K) f = (0:790 ∗ (log(Re)) − (1:64))−2 (8) mre f Tre f S 0:5 2 Gas Kg Nu = (( f =8)∗(Re−1000)∗Pr)=(1+12:7∗(( f =8) )∗(Pr 3 )−1) ( ):s (K) (K) m (9) Air 1:76 ∗ 10−5 288.15 110.4 • W K Table 3. Sutherland’s Constant Heat transfer coefficient ( m2 ) of hot and cold side of the heat exchanger [3]. • Flow velocity of air on hot and cold side of the h = (Nu ∗ Kair)=(Dh) (10) heat exchanger [3]. m • Number of tube passes in the heat exchanger V = (4) [3]. r ∗ A Nt = (La − Dh)=SL (11) where, where, m • V = Flow Velocity of air, ( s ) • SL = Longitudinal fin pitch distance, (m) Kg • r = Density, ( m3 ) • Total heat transfer area at hot and cold side of the heat exchanger [2] . • A = Cross sectional area of the tube = 2 (Pt ∗ Dh)=4, (m ) AHS = 2∗(Nt )∗(Lb)∗(Lc)∗(((s f −Th f )+(2∗ finh))=s f ) (12) Kg • m = Mass flow rate of air, ( s ) ACS = 2∗(Nt )∗(La)∗(Lb)∗(((s f −Th f )+(2∗ finh))=s f ) • Reynolds number of air on hot side and cold (13) side of the heat exchanger [2]. where, r ∗V ∗ D • Nt = Number of tube passes Re = h (5) m • finh = Fin height in, (m) where, • Th f = fin thickness, (m) m • V = Flow Velocity of air, ( s ) • La;Lb;Lc are the length,breadth and height, (m) Kg • Total surface temperature effectiveness of fin • r = Density, ( m3 ) [4]. • Dh = Hydraulic Diameter of the tube, (m) E ft = 1 − ((1 − h fin)) ∗ (AHS=ACS)) (14) Kg • m = Dynamic Viscosity, ( m:s ) where, • Thermal conductivity of air on hot side and cold side of the heat exchanger (W/m.K) [2]. • h fin = Isentropic efficiency of fin −11 3 −8 • Overall thermal resistance [4]. kair = (((1:52∗10 )∗(Tbleed))−((4:86∗10 )∗ R = (1=(E ∗ h)) + (1=((A =volume ) (T_bleed^2))+((1.02*10^-4)*(T_bleed))- TR ft hs hx (3.93*10^-4)) (6) /(A_hs/volume_hx)*h))+(( T_hf/ K_fin)) (15) 4 Analytical Design and Estimation of Conventional and Electrical Aircraft Environmental Control Systems where, • Pressure drop at the heat exchanger [4]. • K = Thermal conductivity of fin , ( W ) 2 fin mK Um = (4 ∗ m)=((rho ∗ p ∗ (Dh))) (25) • volume = (L ) ∗ (L ) ∗ (L ),(m3) hx a b c −2 f riccoe f f = (1:58 ∗ (log(Re)) − (3:28)) (26) • Overall heat transfer coefficient [4]. 2 U = (1=RTR) (16) DP = ( f riccoe f f ∗ ((rho ∗ (Um))=(2 ∗ Dh))) ∗ Ltube (27) • Heat capacity rate for both bleed and ram air [3].
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