Abstract:
An electric power generation system employs a thermoelectric generator placed between an aircraft inner skin and an aircraft outer skin. The thermoelectric generator is configured to utilize a thermal differential between the inner and outer skin to generate electricity. An electrical interface is provided for access to the electricity generated by said thermoelectric generator.

Description:
BACKGROUND INFORMATION 
     1. Field 
     Embodiments of the disclosure relate generally to the field of electrical power generation for aircraft and more particularly to a system employing a thermoelectric generator engaged between aircraft interior and exterior surfaces for generation of electricity using temperature differential between the surfaces. 
     2. Background 
     Modern aircraft employ electrical power for numerous on board systems. Conventional generation of electricity for such usage is accomplished with engine or auxiliary power unit (APU) driven generators located in the aircraft. Power from the generators is then routed through the aircraft for use with standard electrical cabling in numerous wire harnesses. Issues of weight for the extensive wiring systems as well as the potential for undesirable electrical discharge within the circuit system have prompted examination of alternative power routing techniques. 
     As an example, a system that uses a laser powered by the conventional centralized generation system to inject power in the form of light into a fiber optic cable and a photovoltaic (PV) array to convert the light back into electricity for powering devices has been developed. This system avoids the issues associated with undesirable electrical discharge in the power distribution system but still results in significant weight in the aircraft since fiber optic cables must replace the conventional wiring harnesses throughout the aircraft. Additionally, the amount of power the laser optical system can produce and transmit is limited. 
     It is therefore desirable to provide an electrical generation system which is distributed to avoid extensive wiring harnesses and which is efficient, low-maintenance, robust, reliable, solid-state and yet providing sufficient power for operation of selected aircraft systems. 
     SUMMARY 
     Embodiments disclosed herein provide an electric generator which employs a thermoelectric generator placed between an aircraft inner skin and an aircraft outer skin. The thermoelectric generator is configured to utilize a thermal differential between the inner and outer skin to generate electricity. An electrical interface is provided for access to the electricity generated by said thermoelectric generator. 
     For the exemplary aircraft embodiments, the inner skin and outer skin are on the fuselage of the aircraft and the aircraft is operated at altitudes providing a temperature differential between the outer skin and inner skin warmed by heated cabin air. 
     The embodiments provide a method for generating electrical power for use by a device on an aircraft through positioning a thermoelectric generator between an inner skin and an outer skin of an aircraft. Cabin air proximate the inner skin is heated at operating altitudes to maintain the temperature differential between the inner skin and outer skin. Electricity is then generated using the thermoelectric generator based on a temperature differential between the inner skin and the outer skin. The generated electricity may then be used to at least partially power the device. 
     The features, functions, and advantages that have been discussed can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top schematic view of an aircraft with cabin air conditioning; 
         FIG. 2  is a front section view of a fuselage wall with inner and outer skins and a thermoelectric generator; 
         FIG. 3  is a cabin interior pictorial view showing the thermoelectric generator generalized location and operating devices to be powered; 
         FIG. 4A  is a side view of an example thermoelectric generator operating element; 
         FIG. 4B  is a top view of the operating element of  FIG. 4A ; 
         FIG. 5  is a block diagram of the thermoelectric generator with power conditioning, battery and outlet; 
         FIG. 6A  is a front section view of the fuselage skins with the thermoelectric generator incorporating a finned heat exchanger; 
         FIG. 6B  is a top section view of the fuselage skins with the finned heat exchanger ducted for forced convection with a fan; 
         FIG. 6C  is a top section view of the fuselage skins the finned heat exchanger ducted for forced convention using pressure differential; and, 
         FIG. 7  is a flow chart of operation of the thermoelectric generator for distributed generation of power for on board device use. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments disclosed herein provide electrical power for a device using a thermoelectric generator located near the receiving device. The thermoelectric generator is able to produce electrical power using the potential energy that exists between the warm cabin air of the aircraft and the external cold air at cruising altitudes. 
     A descriptor for the embodiments has been coined as “Electricity Over Air (EOA)” because the thermoelectric generator employs the temperature differential of the cabin air in order to make electricity. To maintain passenger comfort, the cabin air must be kept warm. Since aircraft warm the cabin air by circulation throughout the cabin using natural and/or forced convection, the power consuming device is essentially receiving its electrical power through the air. 
     Commercial aircraft cruise at altitudes above the tropopause and extending well into the stratosphere. Air temperatures in this region of the atmosphere are nominally between −20° and −60° C. Operating altitudes even during climb and descent regularly provide significantly cooler air temperatures. 
     As shown in  FIG. 1  for an exemplary aircraft system, the aircraft  10  has a fuselage  12  encompassing the cabin  14 . Engines  16  (shown as mounted on the wings  18  for the present example but mounted on the empennage of the aircraft in alternative configurations) include a compressor section which receives incoming air (shown as element  19 ) and provides hot bleed air (shown as element  20 ) to an air conditioning system  22  that employs heat exchangers to appropriately heat incoming cabin air (shown as element  24 ) which is then routed into the cabin  14  through appropriate ducting to a mixing manifold  26  where it is mixed in an approximate 50/50 ratio with existing cabin air which has been cleaned by routing through one or more high efficiency air filtration systems  28 . An exiting air volume (shown as element  30 ) equal to the incoming cabin air volume is discharged from the fuselage  12  through one or more exit ducts. Cabin air is maintained at operating altitudes including cruise at temperatures of approximately +20° C. 
     As shown in  FIG. 2 , the aircraft fuselage  12  is typically constructed with an inner skin  32  and an outer skin  34  for both structural and insulation considerations. A thermoelectric generator  36  is placed in the intermediate volume  38  between the inner and outer skins. Such thermoelectric generators can be placed at multiple locations through the fuselage  12 . Heat, represented by arrows  40 , is transmitted through the thermoelectric generator  36  from the cabin  14  to the external air mass  42 . Electrical power generated by the thermoelectric generator  36  is then provided to an outlet  44 . 
     As shown in  FIG. 3 , the thermoelectric generator  36  is located immediately adjacent the desired usage location such as passenger seating  46  where it may be employed for personal devices of the passenger, operation of current seat mounted devices such as television displays  48 , music system indicators  49 , or seat lighting systems (not shown). While shown for the described example as providing power for passenger compartment devices, the thermoelectric generators  36  may be placed in alternative locations for powering of galley equipment or other electrical systems in the aircraft. 
     The operating elements  50  of the thermoelectric generator  36  as shown in  FIGS. 4A and 4B  employ a cold plate  52  and a hot plate  54  fabricated from alumina ceramic or similar material which may be metalized. The hot plate  52  and cold plate  54  are mounted on opposite sides of a thermoelectric stack  56  fabricated from bismuth telluride (Bi2Te3) semiconductor p-n junctions. Electrical power generated by the stack  56  is then provided through leads  58   a  and  58   b.  For an exemplary embodiment, a thermoelectric generator  36  may be created using one or an array of single stage operating elements  50  such as the model NL1010T produced by Marlow Industries Inc., Dallas, Tex. The hot and cold plates  52 ,  54  are thermally interfaced to the inner and outer skins  32 ,  44  either directly or on conductive extensions using thermal grease such as that produced by Marlow Industries with part no. #860-3079-001 for optimal thermal conductivity. The cold plate  52  conductively engages the outer skin for heat transfer and the hot plate  54  interacts with the heated cabin air either through direct conductive engagement of the inner skin  32  with natural convective heat transfer from the cabin air to the inner skin or with heat exchange elements for natural or forced convection. 
     As shown in  FIG. 5 , the thermoelectric generator  36  provides generated power to a power conditioning module  60  which converts the generator output to desired current and voltage values (such as 12 volt or 28 volt DC or 110 volt AC) for the operating devices at the outlet  44 . A battery  62  is connected to the generator through the power conditioning system for power storage to allow usage of the powered devices when thermal gradients may not be present for operation of the thermal generator  36  or to supplement the power provided by the thermal generator when the temperature differential is small. 
     The configuration of the thermoelectric generator  36  may incorporate a direct conductive connection to the inner and outer skins of the fuselage as shown in  FIG. 2  which relies on natural convective heat transfer between the inner skin and the warm air of the cabin. In alternative configurations, the thermoelectric generator  36  may incorporate a finned heat exchanger  66  as shown in  FIG.6A  which either extends into the aircraft cabin  14  on the interior of inner skin  32  to enhance natural convective heat transfer into the thermoelectric generator or is incorporated in a duct  68  which employs a fan  70  interconnected to receive cabin air and directing flow across the finned heat exchanger  66  for forced convective heat transfer as shown in  FIG. 6B . In a further alternative configuration, the duct  68  may be included as a portion of the cabin air exit duct  72  as shown in  FIG. 6C  to utilize pressure differential between the pressurized cabin and exterior pressure at altitude to create airflow for forced convective heat transfer to the heat exchanger. 
     The embodiments disclosed provide a method for generation of electrical power on an aircraft as shown in  FIG. 7 . A thermoelectric generator is mounted between the inner and outer skins of an aircraft fuselage, step  702 . The aircraft is then operated at a cruising altitude providing a low temperature external to the fuselage, step  704 . The cabin air within the fuselage is warmed using engine bleed air, step  706 . Electrical power is then generated by the thermoelectric generator through the temperature differential between the cabin air acting on the inner skin at cabin temperature and external air acting on the outer skin at external temperature, step  708 . As previously described, the differential temperature may be employed by the thermoelectric generator using natural convection or forced convection. The forced convection may be induced using a fan or relying on pressure differential between the cabin and external air. Power generated by the thermoelectric generator can then be conditioned for proper voltage, step  710 , and provided to devices in the aircraft for power usage, step  712 . 
     Having now described various embodiments of the disclosure in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present disclosure as defined in the following claims.