A heat exchanger for cooling fluid passing through the heat exchanger. The heat exchanger includes a hot fluid flowpath and a cold air flowpath. At least a portion of the cold air flowpath has a thermally conductive wall transferring thermal energy from hot fluid flowing through the hot fluid flowpath to cold air flowing through the cold air flowpath. The cold air flowpath includes a separator for separating ice particles from the cold air flowing through the cold air flowpath. The separator includes a passage having a bottom wall, an end wall, and a side wall including a porous wall through which a majority of cold air entering the separator passes. The end wall has an ice particle discharge opening adjacent the bottom wall permitting a minority of the cold air entering the separator to carry ice particles separated from the majority of cold air through the opening.

BACKGROUND

The present disclosure generally relates to heat exchangers, and more particularly, to a heat exchanger having anti-icing provisions.

Aircraft use cooling systems to manage thermal loads resulting from equipment operation. These cooling systems frequently include heat exchangers having separate hot and cold flowpaths. Heat from fluid in the hot flowpath is transferred to fluid in the cold flowpath, thereby cooling the fluid in the hot flowpath and heating the fluid in the cold flowpath. For example, air from compartments having equipment giving off heat can be directed through the hot flowpath and air from a cooling turbine of an air cycle machine (i.e., a refrigeration unit) can be directed through the cold flowpath. The heat exchanger transfers thermal energy from the hot flowpath air to the cold flowpath air, thereby cooling the air from the equipment compartment. The cooled air is returned to the equipment compartment, cooling the equipment to ensure proper performance.

Air entering conventional heat exchangers from cooling turbines must be maintained at a temperature above a freezing temperature of water to prevent ice from accumulating on surfaces of the cold flowpath in the heat exchanger. If the temperature of the air entering the heat exchanger is below the freezing temperature of water, multiple layers of ice can accumulate on surfaces along the cold flowpath. These layers of ice impair the heat exchanger by increasing power required to pump air through the heat exchanger and insufficiently cooling fluid in the hot flowpath. However, if colder air could be used in the heat exchanger without ice accumulating, then the air cycle machine efficiency could be increased and the heat exchanger size and weight could be reduced. Thus, there is a need for a heat exchanger that reduces the potential for ice accumulation.

SUMMARY

In one aspect, the present disclosure includes a heat exchanger for cooling fluid passing through the heat exchanger. The heat exchanger comprises a hot fluid flowpath for carrying a hot fluid from a hot fluid inlet to a hot fluid outlet downstream from the hot fluid inlet. At least a portion of the hot fluid flowpath is defined by a thermally conductive wall permitting thermal energy to transfer from hot fluid flowing through the hot fluid flowpath. The heat exchanger further comprises a cold air flowpath for carrying a cold air from a cold air inlet to a cold air outlet downstream from the cold air inlet. At least a portion of the cold air flowpath is defined by the thermally conductive wall permitting thermal energy to transfer from the hot fluid flowing through the hot fluid flowpath to cold air flowing through the cold air flowpath. The cold air flowpath includes a separator for separating ice particles from the cold air flowing through the cold air flowpath. The separator includes a passage having a bottom wall, an end wall, and a side wall defined at least in part by a porous wall through which a majority of cold air entering the separator passes. The end wall has an ice particle discharge opening adjacent the bottom wall permitting a minority of the cold air entering the separator to carry ice particles separated from the majority of cold air through the opening.

In another aspect, the present disclosure includes a heat exchanger for cooling air passing through the heat exchanger. The heat exchanger comprises a thermally conductive hot air conduit for carrying hot air from a hot air inlet to a hot air outlet downstream from the hot air inlet. The heat exchanger further comprises a cold air flowpath for carrying a cold air from a cold air inlet to a cold air outlet downstream from the cold air inlet. The cold air flowpath includes an upstream passage having a bottom wall, a porous side wall, and an end wall including an ice particle discharge opening adjacent the bottom wall. A majority of cold air entering the cold air inlet passes through the porous side wall and enters a downstream passage in thermal communication with the hot air conduit so thermal energy transfers from hot fluid flowing through the hot fluid flowpath to cold air flowing through the downstream passage of the cold air flowpath. A minority of cold air entering the cold air inlet sweeping ice particles through the discharge opening and out of the heat exchanger.

In still another aspect, the present disclosure includes a heat exchanger for cooling air passing through the heat exchanger. The heat exchanger comprises a cold air flowpath for carrying a cold air from a cold air inlet to a cold air outlet downstream from the cold air inlet. The cold air flowpath includes an upstream passage having a bottom wall, a foam side wall, and an end wall including an ice particle discharge opening adjacent the bottom wall. A majority of cold air entering the cold air inlet passes through the foam side wall and enters a downstream passage having a thermally conductive wall in thermal communication with hot fluid for transferring thermal energy from hot fluid to cold air flowing through the downstream passage of the cold air flowpath. A minority of cold air entering the cold air inlet sweeps ice particles through the discharge opening and out of the heat exchanger.

Other aspects of the present disclosure will be apparent in view of the following description and claims.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring toFIG. 1, a heat exchanger incorporating one embodiment is designated in its entirety by the reference number10. The heat exchanger10has a casing12including a plurality of cold air inlets14for receiving cold air (e.g., cold air from a cooling turbine), a hot fluid inlet16for receiving hot fluid (e.g., hot air from a cabin or a compartment having equipment), and a hot fluid outlet18for discharging the hot fluid after being cooled by the heat exchanger. The cold air exits the heat exchanger10through cold air outlets20(FIG. 2) and ice particle discharge openings22(FIG. 3) downstream from the cold air inlets14. In one embodiment, the casing12is made from aluminum sheet having a thickness of about 0.0625 inch.

As illustrated inFIGS. 2 and 3, cold air entering the heat exchanger10through the cold air inlets14travels along a cold air flowpath, generally designated by30, to the corresponding cold air outlet20. The cold air flowpath30is defined by an upstream passage32having a top wall34, a bottom wall36, an end wall38, and opposing side walls40. The top wall34, bottom wall36, and end wall38form at least a portion of the casing12. As illustrated inFIG. 3, the end wall38ends above the bottom wall36to form the ice particle discharge openings22. The opposing side walls40comprise a thermally conductive porous ceramic foam panel. In one embodiment the side walls40comprise Boeing Rigid Insulation (BRI). BRI is a hyper-porous, micro-channel ceramic foam having a pore size of about 35 microns and over 31,350 square feet of internal surface area per cubic foot. As will be appreciated by those skilled in the art, the large internal surface area of BRI provides good convective heat transfer. Further, BRI has a thermal conductivity of about 0.05 BTU/hr-ft-° R. BRI is available from The Boeing Company of Chicago, Ill. The rigid insulation has a high surface area, providing good heat transfer to the cold air passing through the rigid insulation. In one embodiment, the insulation has a thickness of about 0.150 inch. Boeing Rigid Insulation is described in more detail in U.S. Pat. No. 6,716,782.

As will be apparent to those skilled in the art, most of the air entering the cold air inlet14turns and passes through the porous side wall40. Any ice particles in the air are carried by their greater momentum to the end wall38. The ice particles strike the end wall38and fall under the influence of gravity to the bottom wall36where air sweeps the particles and droplets through the discharge openings22. Only a small fraction of air entering the cold air inlet14exits through the ice particle discharge opening22. Most of the air passes through the side walls40.

Thermally conductive elements60extend through the ceramic foam walls40at spaced intervals. In one embodiment, the thermally conductive elements60are made of aluminum nitride that is injected as a liquid into holes formed in the ceramic foam. Further, in one embodiment the elements60are cylindrical pins or rods having a diameter of about 0.141 inch. In one embodiment, the elements60are arranged in staggered rows. Although the elements may have another spacing, in one embodiment the elements in each row are vertically spaced about 0.49 inch apart and each row is spaced about 0.245 inch from adjacent rows. This element60size and spacing reduce the flow area through the porous side walls40by about twelve percent. The elements60span a downstream passage62formed between the foam side wall40and a thermally conductive wall64. In one embodiment, the elements60are connected (e.g., with aluminum nitride) to the thermally conductive wall64. Although the thermally conductive wall64may be made of other materials, in one embodiment the wall is made from aluminum nitride and alumina-silica cloth. The downstream passage62also includes a top wall66, a bottom wall68, and an end wall70. The top wall66, bottom wall68, and end wall70form part of the casing12.

As illustrated inFIGS. 2-4, a hot fluid flowpath, generally designated by80, is formed between opposing thermally conductive walls64and opposing end walls82. A bottom wall84closes a lower end of the hot fluid flowpath80. A porous foam panel110having spaced thermally conductive elements112distributed over the panel and extending through the panel and out from each face is positioned in the hot fluid flowpath80such that the conductive elements112are bonded to the opposing thermally conductive walls64. Although the panel110may be made of other materials and have other thicknesses, in one embodiment the porous panel comprises BRI having a thickness of about 0.150 inch. Although the thermally conductive elements112may be made of other materials, in one embodiment the thermally conductive elements are made of the same material as the thermally conductive elements60of the cold side. Further, the thermally conductive elements112of one embodiment have the same diameter and spacing as the elements60of the cold side. Although the elements112may extend beyond the panel110by other distances, in one embodiment the elements extend about 0.125 inch from each face. A dividing wall86extends from a top wall88to the bottom wall84on the side of the porous panel110open to an upstream chamber92but only extends to a location above the bottom wall84on the opposite side of the porous panel. The dividing wall86divides the hot fluid flowpath80into an inlet side94and an outlet side98.

Referring toFIGS. 1-4, hot fluid entering the hot fluid inlet16travels through tubing90to an upstream chamber92. The hot fluid flows through an inlet114and downward through an upstream section114of the hot fluid flowpath80. The hot fluid is nearly evenly distributed across the surface of the porous panel110due to the relatively high flow resistance of the panel. The hot fluid passes through the porous panel110along a first hot fluid direction95and continues downward on the other side, eventually turning around a lower end96of the dividing wall86. The hot fluid travels upward through a downstream section98of the hot fluid flowpath. Again, the fluid is almost evenly distributed across the surface of the porous panel110. The hot fluid passes through the porous panel110again along a second hot fluid direction99as it travels upward. Finally, the hot fluid travels through the downstream section98, out an outlet116, and into the downstream chamber100. From the downstream chamber100, the hot fluid travels through tubing102and out the hot fluid outlet18. As the hot fluid travels through the hot fluid flowpath90, heat is transferred to the cold flowpath by convection to the porous material and conduction from the porous material through the conductive elements112to the walls64, and by direct convection to the conductive elements, then conduction to the walls64, and finally, by direct convection to the walls64themselves.

Cold air entering the cold air inlet14travels through the upstream passage32generally parallel to the porous side walls40. A majority of cold air entering the inlet14turns orthogonally and travels through one of the opposing porous foam side walls40where it absorbs thermal energy from the BRI ceramic foam. This thermal energy is conducted from the wall64to the ceramic foam panels40by the thermally conductive elements60. The fluid becomes rarefied when forced through the BRI, decreasing fluid friction and the associated pressure drop. After exiting the porous foam side walls40, the cold air turns orthogonally again and travels along a first direction31through the downstream passage62generally parallel to the thermally conductive wall64where it absorbs more thermal energy by direct convective heat transfer from both the thermally conductive elements60and the conductive wall64.

As previously stated, a majority of cold air entering the inlet14travels through one of the opposing foam side walls40. Although the majority of cold air traveling through the porous foam side walls40may constitute other percentages of the cold air entering the inlet14, in one embodiment the majority constitutes at least 80 percent of the cold air entering the inlet. In another embodiment, the majority constitutes at least 90 percent of the cold air entering the inlet14, and in still another embodiment, the majority constitutes at least 95 percent of the cold air entering the inlet. The remainder of the cold air travels through the upstream passage32and out through the ice particle discharge opening22at the bottom of the end wall38.

In the event ice particles or water droplets enter the cold air inlet14, the momentum of the particles and droplets prevents them from turning orthogonally into the foam. Further, the pore size of the foam prevents ice particles from flowing through the foam. Instead of entering the foam, the ice particles and water droplets travel to the end wall38where they impinge on the wall. After striking the wall, gravity causes the particles and droplets to fall to the bottom wall36. The cold air traveling through the ice particle discharge opening22sweeps the ice particles and droplets out through the opening and into fluid streams exiting the cold air outlets20. Thus, the upstream passage32forms a separator for separating ice particles from the cold air.

The ice separator formed by the upstream passage32allows the heat exchanger10to be used with cold air having a temperature below a freezing temperature of water. Conventionally, the heat exchanger design would be limited to having cold air above the water freezing temperature to avoid ice accumulating in the heat exchanger. The colder air allows a smaller, lighter heat exchanger to be used to transfer a predetermined amount of heat from the hot fluid to the cold fluid. The reduced heat exchanger size and weight reduces fuel consumption and increases aircraft range.

As will be appreciated by those skilled in the art, the porous side walls40provide large surface areas that cause air traveling through the side walls to be at a low velocity. Further, the porous side walls40provide a low pressure differential across the walls.

Having described the embodiments in detail, it will be apparent that modifications and variations are possible without departing from the scope defined in the appended claims.