Passive Cooling Concept for Onboard Heat Sources in an Aircraft:- A passive cooling system based on heat pipe technology was tested in-flight in an Embraer test aircraft. Avionics thermal behaviour was simulated by employing electrical resistances with input power ranging from 40 to 850W. Heat is transported from the resistances to the evaporator of a recently patented heat exchanger system (HES) by intermediary heat transfer elements (IHTEs), consisting of one heat pipe and four thermosyphons. Heat pipes and thermosyphons are high efficient heat transfer passive devices used in a wide range of engineering applications such as heat exchangers, cooling of electronics components and solar energy systems. In aeronautics, the demand for effective cooling systems has been triggered by the advances in electro electronics systems. This scenario is more evident in recent full fly-by-wire aircrafts, where the heat dissipation requirement has increased considerably.

1. PASSIVE COOLING
CONCEPT FOR
ONBOARD HEAT
SOURCES IN AIRCRAFTS
Reported by:
Ashish Panda
1702293
RAC PPT GROUP
3

2. CONTENTS
INTRODUCTION
BEHAVIOURS
(in the form of graphs)
CONCLUSION
H.E.S AND IHTEs
EXPERIMENT
RESULTS

3. A passive cooling system based on heat pipe technology
was tested in-flight in an Embraer test aircraft. Avionics
thermal behavior was simulated by employing electrical
resistances with input power ranging from 40 to 850W.Heat
is transported from the resistances to the evaporator of a
recently patented heat exchanger system (HES) by
intermediary heat transfer elements (IHTEs),consisting of
one heat pipe and four thermosyphons. Heat pipes and
thermosyphons are high efficient heat transfer passive
devices used in a wide range of engineering applications
such as heat exchangers, cooling of electronics
components and solar energy systems. In aeronautics, the
demand for effective cooling systems has been triggered by
the advances in electro electronics systems. This scenario
is more evident in recent full fly-by-wire aircrafts, where the
heat dissipation requirement has increased considerably.
INTRODUCTION

4. The HES is a two-phase closed loop thermosyphon composed by a
shared evaporator and two parallel condensers. FUS and AC condensers
are installed at the aircraft fuselage and inside the air conditioning
system, respectively. Each condenser consists of inlet and outlet
manifolds connected by parallel pipes. This arrangement assures low
pressure drop at each condenser. Two vapor lines connect evaporator
and condensers inlet manifolds.Independent liquid lines connect
condensers outlet manifolds to the evaporator section.
Heat Exchanger System
Working Principle
The HES working principle is based on a two-phase closed loop, where
vapor fluxes flow up via the adiabatic lines towards the condensers due to
pressure differences between the evaporator and condensers.
Condensation takes place in the FUS and AC condensers and then liquid
flows down back to the evaporator due to gravitational forces. Heat is
removed by forced convection inside the AC duct when the aircraft air
conditioning system is operational. Heat is removed from the FUS
condenser by external forced convection in-flight and by natural
convection on ground. Condenser pipes were designed and constructed
according to geometrical constrains of the Embraer test aircraft. FUS
condenser is composed by two aluminum blocks designed to integrate
this condenser to the airplane fuselage. Each block is compressed
against each other reducing the contact thermal resistance between the
aluminum and the copper pipes compressed by these blocks.
.

5. Heat pipe technologies (here, one heat pipe and four thermosyphons) can also serve as intermediary heat transfer elements (IHTEs) between equipment inside
the airplane and the HES evaporator.Two types of shaped plugs (conical with fins and cylindrical) allow easy assembly between the IHTE condensers and the
HES evaporator. These plugs were designed to reduce the contact thermal resistance between these elements and theevaporator wall.Heat to the thermosyphon
evaporators (6-I and 6-II) is delivered by air forced convection. The idea is to mimic cooling of actual equipment, when the original design of the heat source
equipment cannot be modified to host the thermosyphon. Air flow temperature of the convective system is monitored by Resistance Temperature Detectors
(RTDs): Pt100 class 1/10 DIN sensor. Input power to the cartridge resistances is controlled virtually via Labview 2013.Each IHTE and the HES use water as
working fluid. Filling ratios, FR = Vw /Vevap, of 90 % and 80 % are used for the HES and IHTEs, respectively. Here, V is volume and the subscripts w and evap
stand for water and evaporator.
Intermediary Heat Transfer Elements (IHTEs)

6. The experimental apparatus was installed and tested in an aircraft in several flight
conditions. Since heat sink conditions vary with altitude, the HES and IHTEs thermal
performance was evaluated in several different test settings.
Vertical load factors, Nz=L/W, of about 0.5, 1.5 and 2.0
were experimented during aircraft maneuvers. Here, L and W are lift and aircraft weight,
respectively.
For tests in cruise conditions, a constant Mach number, M∞, of 0.78 was set. The test windows
were executed at altitudes, Hsl, of 9.1 and 10.6 km above the sea level, corresponding to air
static external temp., T∞, of about -30oC and -43oC, respectively;The thermal behavior of the
IHTEs was also evaluated during roller coaster and G-load turn maneuvers with an
approximated altitude of 4.5 km and Mach number of 0.55 the time lag from 140 to 168 minutes.
EXPERIMENT

7.  The input power effect on heat pipe thermal performance is
presented.
 Input power ranges from 40 to 120 W with an increment of 40
W. A period of 10 minutes in each power level sufficed to
approach steady state operation.
 Note that the HP temperatures in the LHS of y-axis are
approximately constant after 7-8 min once a test is initiated.
The heat pipe was cooled down between the first and second
test windows, corresponding to a total cooling time of 40 min.
 The reduction of the air static external temperature from -30
to -45ºC with increasing altitude barely modified the HES
evaporator average temperature for a given level of input
power.
 Notice that the HES evaporator is the heat sink for every
IHTE;Therefore, changes in the heat sink of the HES
fuselage condenser promoted by modifying the aircraft
altitude from 9.1 to 10.6 km weakly affect the heat pipe
thermal performance.
RESULT / DISCUSSION

8. BEHAVIOUR

9. CONCLUSION
 A cooling system concept to manage heat sources in
aircrafts was experimentally evaluated during
conventional cruise conditions and maneuvers.
 A heat exchanger system - HES (consisting of two
closed-loop thermosyphons), intermediate heat transfer
elements-IHTEs (heat pipe and thermosyphons) and heat
sources (simulating avionics) compose the setup.
 Heat conduction and forced convection were applied to
transfer heat from the sources to the evaporators of
IHTEs.
 Two types of shaped plugs were employed for thermal
coupling between the IHTE condenser and HES
evaporator: conical with fins and cylindrical.
 Heat is finally dissipated in the air conditioning system
and mainly in the aircraft fuselage.

10. THANKS
Reported by:
Ashish Panda
1702293