Patent Publication Number: US-2021163124-A1

Title: Heat exchanger for an aircraft

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Patent application claims priority from European Patent Application No. 18187435.5 filed on Jun. 8, 2018, the disclosure of which is incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a heat exchanger for an aircraft, in particular a helicopter. 
     More specifically, the exchanger is a liquid-gas heat exchanger, an oil-air one in the case shown. 
     BACKGROUND ART 
     As is known, helicopters are normally equipped with a plurality of transmission units that are adapted to transmit drive from one or more turbines to the main and/or tail rotors, and/or from the turbine to a plurality of accessory devices, i.e. assigned, for example, to provide the power necessary for operation of the flight instruments. 
     In a known manner, a lubricating fluid, typically oil, circulates inside the transmission unit, both for lubricating the moving parts of the transmission unit and for cooling said moving parts. 
     In order to ensure the effectiveness of lubrication and cooling, it is necessary to cool the lubricating fluid circulating inside the transmission units. 
     To this end, helicopters are fitted with cooling systems that basically comprise: 
     a heat exchanger to exchange heat between the oil of the transmission unit and air circulating inside the cooling system; and 
     a fan adapted to create air circulation from the heat exchanger to the fan. 
     In known solutions, the heat exchanger comprises: 
     an oil conveying circuit running from a first inlet station to a first outlet station; and 
     an air conveying circuit running from a second inlet station to a second outlet station. 
     In particular, the oil has a first temperature value at the first inlet station and a second temperature value, lower than the first temperature value, at the first outlet station. 
     Contrariwise, the air has a third temperature value at the second inlet station and a fourth temperature value, higher than the first temperature value, at the second outlet station. 
     In other words, the oil yields heat to the air, cooling itself inside the heat exchanger while the air simultaneously heats up. 
     Known types of heat exchanger also comprise a plurality of modules, each formed by: 
     a wall lapped by the oil and by the air on respective mutually opposite faces; 
     a plurality of first fins facing the inside of the oil conveying circuit and projecting in a cantilever fashion from the first face; and 
     a plurality of second fins facing the inside of the air conveying circuit and projecting in a cantilever fashion from the second face. 
     In particular, the second fins extend orthogonally to the wall and have a certain length along a first direction running from the second inlet station to the second outlet station. 
     The second fins are also arranged so as to form a plurality of consecutive rows, proceeding along a first direction. 
     The second fins of mutually immediately consecutive rows are staggered, along a second direction orthogonal to the first direction. 
     In particular, the fins of each row are arranged on a median section of the immediately consecutive row. 
     Due to the aforesaid configuration, the air is partially heated at the end of each row, reducing the residual heat exchange capacity of the air. 
     More specifically, the peripheral regions of the portion of air flow that lap the second fins heat up through thermal conduction while the central region of this portion heats up when it laps the second fins of the next row. 
     This partial heating is repeated at the end of each row, until a condition is attained in which the air substantially reaches the same temperature of the rows of second fins it strikes against. In this condition, there is essentially no heat exchange between the air and the second fins and, therefore, there is no cooling of the oil. 
     There is thus awareness in the industry of the need to optimize the heat exchange between air and oil, for the same heat exchanger weight and pressure drop between the second inlet section and the second outlet section. 
     Furthermore, known types of heat exchangers are made through brazing, i.e. by welding various parts together. The use of this technology defines a constraint with respect to shapes and configurations achievable for the first and second fins. 
     There is also awareness in the industry of the need to provide a heat exchanger that is particularly flexible with regard to the shape and arrangement of the first fins and the second fins. 
     US 2016/0115864, EP-B-2712805, FR-A-29988822 and WO2016/018498 describe heat exchangers for known types of aircraft. GB-A-2496692 discloses a heat exchanger according to the preamble of claim  1 . 
     DISCLOSURE OF INVENTION 
     The object of the present invention is to provide a heat exchanger for an aircraft that satisfies at least one of the above-specified needs in a simple and inexpensive manner. 
     The aforesaid object is achieved by the present invention, in so far as it relates to a heat exchanger for a transmission unit of an aircraft, according to claim  1 . 
     The present invention also relates to a method of cooling a first fluid to be cooled by means of heat exchange with a second cooling fluid inside an aircraft, according to claim  14 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, a preferred embodiment is described hereinafter, purely by way of non-limitative example and with reference to the accompanying drawings, in which: 
         FIG. 1  is a partially exploded perspective view of a helicopter comprising a heat exchanger made according to the teachings of the present invention; 
         FIG. 2  is a front view, on a highly enlarged scale, of the heat exchanger of  FIG. 1 , with parts removed for clarity; 
         FIG. 3  is an exploded perspective view of the heat exchanger of  FIGS. 1 and 2 , with parts removed for clarity; 
         FIG. 4  is a section view along line IV-IV of  FIG. 2 ; and 
         FIG. 5  is a section view along line V-V of  FIG. 2 . 
     
    
    
     Referring to  FIG. 1 , reference numeral  1  indicates a helicopter comprising a pair of turbines, a main rotor and a tail rotor (not fully shown). 
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The helicopter  1  also comprises: 
     a main transmission unit  3 , which is adapted to transmit power from the turbines to a mast  4  driving the main rotor; and 
     a plurality of secondary transmission units  6 , in themselves known and only schematically shown, which are adapted to transmit power from the main transmission unit  3 , i.e. assigned, for example, to provide the power necessary for the operation of respective on-board equipment or a drive shaft  5  of the tail rotor. 
     The helicopter  1  further comprises: 
     a heat exchanger  10  for cooling the lubricating fluid, oil in the case shown, circulating inside the transmission unit  3 ; and 
     a fan  11  (only schematically shown in  FIG. 1 ) adapted to create an air circulation through the heat exchanger  10 . 
     In the case shown, the heat exchanger  10  is a gas-liquid heat exchanger, in particular an air-oil one. 
     In other words, the heat exchanger  10  implements heat exchange between a flow of oil that is cooled and a flow of air that is heated. 
     In the accompanying figures, the flows of oil to be cooled and the air heated following the heat exchange with the oil are indicated by respective grey arrows. 
     Contrariwise, the flows of oil cooled after heat exchange with the air and cold air are indicated by respective white arrows. 
     The heat exchanger  10  basically comprises: 
     an oil feed circuit  20 ; and 
     an air feed circuit  30 . 
     The circuit  20 , in turn, comprises: 
     an inlet  21  for the oil to be cooled; 
     an outlet  22  for the cooled oil; and 
     a plurality of oil feed modules  23  ( FIGS. 2, 3 and 5 ), which are fluidically connected to the inlet  21  and the outlet  22 . 
     The circuit  30 , in turn, comprises: 
     an inlet  31  for the air still to be heated, fluidically connected to the fan  9 ; 
     an outlet  32  for the heated air, fluidically connected to the fan  9 ; and 
     a plurality of air feed modules  33  ( FIGS. 2 to 4 ), which are fluidically connected to the inlet  31  and the outlet  32 . 
     Referring to  FIGS. 2 and 3 , modules  23  and  33  alternate with one another along a direction Z and are elongated along a direction Y orthogonal to direction Z. 
     The oil flows inside each module  23  along a respective U-shaped path P formed by a pair of deliver and return sections Q and R both parallel to direction Y ( FIG. 5 ). 
     Each path P further comprises a section S interposed between sections Q and R. 
     Referring to  FIGS. 3 and 5 , each module  23  comprises an inlet section  24  fluidically connected to inlet  21  and an outlet section  25  fluidically connected to outlet  22 . 
     Each module  23  comprises: 
     a pair of parallel walls  26  opposite to each other along direction X, and lying on respective planes orthogonal to direction X; 
     a wall  27  interposed between walls  26 , opposite to sections  24  and  25  along direction Y, and lying on a plane orthogonal to direction Y; 
     a separator  28  orthogonal to wall  27 , extending from sections  24  and  25  towards wall  27  along direction Y and set apart from wall  27 ; and 
     a pair of walls  29 , extending between walls  26 , and between wall  27  and sections  24  and  25 . 
     In particular, walls  29  are opposite to each other and orthogonal to direction Z. 
     The separator  28  is also parallel to walls  26 . 
     Each module  23  further comprises a plurality of fins  15  elongated along direction Z and extending between walls  29 . 
     The separator  28 , walls  29  and the portion of wall  26  delimiting section  24  of each module  23  delimit the delivery branch Q of the path P of the oil inside the module  23 . 
     The separator  28 , walls  29  and the portion of wall  26  delimiting section  25  of each module  23  delimit the return branch R of the path P of the oil inside the module  23 . 
     The separator  28 , wall  27 , walls  29  and the portions of walls  26  immediately adjacent to wall  27  delimit the curved branch S of the path P. 
     The fins  15  are arranged with lower density in section S with respect to branches Q and R, in order not to obstruct the curved path of the oil inside the associated module  23 . 
     The inlet  31  and the outlet  32  of circuit  30  are opposite to each other along direction X. 
     Referring to  FIGS. 2 to 4 , each module  33  comprises: 
     a pair of parallel walls  35 , opposite to each other along direction Z, lying on respective planes orthogonal to direction Z and thermally coupled to respective walls  29  of mutually immediately adjacent modules  23  along direction Z; 
     a plurality of walls  36   a  and  36   b  extending between walls  35  and extending along direction X; and 
     a pair of mutually opposite and parallel walls  37  and  38  lying on respective planes orthogonal to direction X, and defining a plurality of respective air inlets and outlets  39  and  40  spaced out along direction Y. 
     In particular, the walls  29  and  35  of respective modules  23  and  33  that are mutually consecutive along direction Z are superimposed on each other. 
     Each module  33  defines a plurality of cells  45  placed side by side along direction Y and having an extension mainly along direction X. 
     Each cell  45  is delimited by: 
     a pair of mutually parallel and opposite walls  36   a  and  36   b,  along direction X; 
     respective sections of a pair of walls  35 , along direction Z; and 
     respective sections of walls  37  and  38  extending between the respective walls  36   a  and  36   b.    
     Each cell  45  also comprises: 
     one of the inlets  39  defined by the respective section of wall  37 ; and 
     a pair of air outlets  40  defined by the respective sections of wall  38 . 
     The inlets  39  and outlets  40  of each cell  45  are fluidically connected to the inlet  31  and the outlet  32 , respectively, of circuit  30 . 
     Module  33  also comprises a plurality of fins  55  interposed between walls  36  and adapted to aid heat exchange between the air that flows in each module  33  and the oil that flows in modules  23  immediately adjacent to modules  33 . 
     Advantageously, each cell  45  comprises a row  61  of fins  55 , which lie on respective planes orthogonal to direction X; the fins  55  of the row  61  extend at a progressively increasing distances from wall  36   a  along direction Y, when proceeding along direction X from the respective inlet  39  towards the respective outlets  40 . 
     Each cell  45  also comprises a row  62  of further fins  55 , which extend at progressively increasing distances from wall  36   b  along direction Y, when proceeding along direction X from the respective inlet  39  towards the respective outlets  40 . 
     The rows  61  and  62  of fins  55  of each cell  45  converge towards one another when proceeding from the respective inlet  39  towards the respective outlets  40 , parallel to direction X. 
     Each cell  45  defines: 
     a chamber  52  delimited by the associated inlet  39  and the associated rows  61 ,  62 ; and 
     a pair of chambers  53 , each delimited by an associated wall  36   a,  an associated row  61  or  62 , and an associated section  51 . The fins  55  of each cell  45  extend along direction Z between the associated walls  35 . 
     The fins  55  of each cell  45  have a thickness along direction X and a length along direction Y. 
     In particular, mutually consecutive fins  55  of each cell  45  are spaced out along direction X by respective air passages  56 . 
     Mutually consecutive fins  55  along direction X of the same row  61  and  62  partially overlap each other along direction Y. 
     The passages  56  place chamber  52  and chambers  53  in fluidic communication. 
     Each passage  56  extends along direction Y, is open at its opposite end with reference to direction Y, and is closed along directions X and Z. 
     Due to this configuration, the air flows inside each module  33  along a path T comprising ( FIG. 4 ): 
     a section U substantially parallel to direction X and described, starting from inlet  39 , inside the chamber  52 ; 
     a section V substantially parallel to direction Y and described inside the passages  56 ; 
     a section W substantially parallel to direction X and described starting from inside chambers  53  to the respective outlets  40 . 
     The sum of the areas of the sections orthogonal to direction Y of the passages  56  is greater than the area of the inlet  39  of each cell  45 . 
     In consequence, the air is slowed down as it flows from chambers  52  to the passages  56  and laps fins  55  along section V of the respective path T. 
     The area of each outlet  40  is less than the area of the associated inlet  39 . 
     In the case shown, the perimeter of each cell  45  in section orthogonal to direction X is rhomboidal. 
     In particular, the walls  35  and walls  36   a  and  36   b  delimiting each cell  45  form between them an acute angle a of less than 45 degrees ( FIG. 2 ). 
     Furthermore, the heat exchanger  10  is made in a single piece. 
     In particular, the heat exchanger  10  is made of aluminium. 
     In the case shown, the heat exchanger  10  is made using an additive manufacturing technology. 
     In particular, the printing direction of the heat exchanger  10  is parallel to direction Y. 
     In use, operation of the transmission unit  3  causes overheating of the lubricating oil it contains. 
     The heat exchanger  10  performs heat exchange between an air current and the lubricating oil, enabling the latter to cool. In greater detail, the oil enters the heat exchanger  10  through inlet  21 , follows circuit  20  inside modules  23  and exits the heat exchanger  10  through outlet  22 . 
     Inside each module  23 , the oil flows from the associated section  24  along the branches Q, R and S of the associated path P until it reaches the associated section  25  and, from here, returns through outlet  22 . 
     Due to the presence of fins  15 , the oil gives out heat to walls  29  while it flows inside modules  23 . 
     At the same time, following operation of the fan  11 , the still cold air enters the heat exchanger  10  through inlet  31 , follows circuit  30  inside modules  33  and leaves the heat exchanger  10  in a heated state through outlet  32 . 
     Inside each module  33 , the air flows inside the associated cells  45  between the respective inlet  39  and respective outlets  40  along the respective path T. 
     Furthermore, the air laps the fins  55  of the rows  61  and  62  of each module  33 . 
     These fins  55  extend from the associated wall  29  and are therefore heated by the oil that flows in the modules  23  adjacent to each module  33 . 
     In other words, heat is given up by the oil in each module  23  to fins  15  and to wall  29 , from the latter to fins  55 , and from fins  55  to the air that flows in modules  33  adjacent to the aforementioned module  23 . 
     In greater detail, the still cold air flows inside each module  33 , first inside the chamber  52  along section U of the associated path T with a main velocity component substantially parallel to direction X. 
     Then, the air is diverted and flows in the passages  56  between fins  55  along section V of the associated path T with a main velocity component substantially parallel to direction Y. 
     In this situation, the air is slowed down, thus increasing the efficiency of the heat exchange with the fins  55 . 
     Finally, the air is again diverted and flows in chambers  53  of each module  33  along section W of the associated path T with a main velocity component substantially parallel to a direction 
     X, until it exits the module  23  through sections  52 . 
     The heated air then flows from sections  51  to outlet  32 . 
     From examination of the heat exchanger  10  and the cooling method implemented according to the present invention, the advantages that can be achieved therewith are evident. 
     In particular, the fins  55  of rows  61  and  62  lie on respective planes orthogonal to direction X and extend at progressively increasing distances from the respective walls  36   a  and  36   b  along direction Y, when proceeding along direction X from the associated inlet  39  to the associated outlets  40 . 
     In consequence, the trajectory of each particle of air that flows from inlet  39  to one of the outlets  40  passes through a single passage  56  and laps a single fin  55 . 
     It follows that the air is substantially always at a temperature lower than the temperature of the fins  55  that it laps against, as opposed to what happens in the previously described known solutions. 
     This results in a further improvement in heat exchange efficiency between oil and air with respect to the known solutions described in the introduction of this description, for the same weight of the heat exchanger  10  and air pressure drop between inlet  31  and outlet  32 . 
     Furthermore, the sum of the areas of the sections orthogonal to direction Y of the passages  56  is greater than the areas of the inlet  39  of each cell  45 . 
     In consequence, the air undergoes not only a diversion, but also a slowing down when it laps fins  55 . 
     This causes a further improvement in heat exchange efficiency between oil and water with respect to the known solutions described in the introduction of this description, for the same weight of the heat exchanger  10  and air pressure drop between inlet  31  and outlet  32 . 
     Finally, the cells  45  do not have undercuts, making the heat exchanger  10  adapted for manufacturing in a single piece using the technology known as additive manufacturing. This technology is particularly flexible regarding the possibility of making fins  55  of different shapes. 
     Finally, it is clear that modifications and variants can be made regarding the heat exchanger  10  and the cooling method described and illustrated herein without departing from the scope defined by the claims. 
     In particular, each cell  45  could comprise just one of the rows  61  and  62  of fins  55 . 
     The module  33  could be formed by a single cell  45  instead of a plurality of cells  45 . 
     The transmission unit  3  could be one of transmission units  6 . The heat exchanger  10  could be applied to types of aircraft other than the helicopter  1 , for example, a convertiplane or an aeroplane.