Abstract: A manipulator for handling operations for non-destructive testing in the vicinity of the nozzle of a vessel in the primary loop of a nuclear power plant includes a carriage being movable in circumferential direction of the nozzle of the vessel. A sled is disposed on the carriage and displaceable in the axial direction of the nozzle. A shoulder joint is disposed on the sled. A scissors half has an upper arm with one end supported in the shoulder joint and another end, a lower arm with a free end, another joint connecting the other end of the upper arm to the lower arm, a holder, and a further joint connecting the holder to the free end of the lower arm. A tool or a probe is disposed on the holder.

Abstract: A vehicle of the invention comprises at least two transfer arms including means for causing expansible positioning fingers to penetrate into the tubes of a steam generator and for extracting said fingers from said tubes. The vehicle also includes at least two pivoting fastening heads which contain said expansible positioning fingers. The heads are interconnected by one of the telescopic transfer arms, which arms extend perpendicularly to said pivoting heads. The other telescopic transfer arm is fixed to one of the heads and it extends perpendicularly therefrom with its opposite end carrying a tool support. Such a vehicle is particularly suitable for inspecting and maintaining tubes in tube apparatuses, e.g. the steam generators of pressurized water nuclear reactors.

Abstract: An apparatus is disposed below a tube plate in a chamber of a steam generator which is accessible through a manhole, for examining and/or repairing steam-generator tubes in the tube plate. A tool or inspection-instrument carrier of the apparatus includes a pneumatic swivel cylinder detachably connected to the apparatus. The swivel cylinder has a housing and an output shaft. A feed unit is supported on the output shaft. A flexible shaft is axially movable by the feed unit. A compressed-air motor is associated with the housing for driving the flexible shaft.

Abstract: Disclosed is a system for driving inspection probes through steam generator tubes of a nuclear power plant, particularly eddy current probes. The system utilizes a single conduit that is connectable to the tube sheet of a steam generator and comprises a multiple-unit probe pusher having a housing containing a plurality of independently actuable drive paths, a multiple-unit probe storage device including a plurality of independently movable take-up reels, and a guide or deflector device for directing any one probe that is driven from any one of the drive paths of the probe pusher to the single conduit. Preferably, the entire system is also remotely controllable. The system enables one probe to be in use for tube inspection while providing readily available spare probes to replace a defective probe with a minimum of downtime and worker radiation exposure.

Abstract: System and method for detecting and locating leaks in a steam condenser while the condenser is on-line and operating in its normal capacity. A tracer gas is mixed with water and introduced into the tubes of the condenser through an injector which can be positioned selectively to direct the gas toward different ones of the tubes. The occurrence of a leak is detected by monitoring for the presence of the tracer gas in the condensation chamber, and the location of the leak is determined from the position of the injector when the leak occurs.

Abstract: A method and apparatus for diffusing a liquid condensate return stream in an industrial steam condenser to reduce erosion and corrosion on the condenser structure. One or more diffuser screens are located intermediate a sparger nozzle and a condenser structure to diffuse the condensate screen prior to impact on the condenser structure.

Abstract: An apparatus for the inspection and/or repair of tubes discharging into a chamber of a heat exchanger includes a tube sensor. A manipulator provides remote-controlled positioning of the tube sensor. A plurality of mouthpieces disposed on the manipulator introduces the sensor into tubes of a heat exchanger. Tube connectors communicate with the mouthpieces and have two ends. One of the ends of the tube connectors is coaxially attachable to orifices of the tubes of the heat exchanger. The other of the ends of the tube connectors are bundled into a circular group at an adaptor. A distributor plate has orifices into each of which a respective one of the tube connectors discharge. A parallel turntable is supported on the distributor plate. A guide hose is introduced into the turntable for guiding the tube sensor. Incremental rotation of the turntable selectively aligns the axis of the guide hose with the axis of one of the orifices in the distributor plate.

Abstract: A system for helically driving an inspection probe within a tube of a nuclear steam generator is provided, wherein the system is particularly useful in driving a combination eddy-current and ultrasonic probe. The system generally includes a head assembly insertable with the tube for inspection, a drive frame assembly to be located external of the steam generator, and a conduit system connecting the head assembly and drive frame assembly. Particularly, the head assembly includes a portion fixable to the tube by a pressure bladder and a movable portion helically movable with a probe to the fixable portion. The drive motor and electrical pick-up are slidably movable on the drive frame assembly to move linearly with the probe during inspection so as not to limit the stroke of the probe, wherein the drive motor and pick-up are connected with the head assembly by way of two flexible coaxial conduits.

Abstract: A steam condenser system for a turbine, which system includes: a condenser having an outlet for conveying uncondensed products out of the condenser; an exhauster having a housing, an inlet connected between the housing and the condenser outlet, and exhaust outlet connected to the housing, and a rotatable member, disposed in the housing and rotatable about an axis for propelling uncondensed products from the exhauster inlet to the exhauster outlet; and an electric motor having an output shaft connected for rotating the rotatable member. The motor is disposed relative to the exhauster such that the motor shaft forms an angle with the horizontal and extends in a downward direction from the motor to the exhauster. Preferably, the motor shaft and the axis of rotation of the rotatable member have a substantially vertical orientation and the motor is positioned above the rotatable member.

Abstract: In order to carry out interventions, particularly for inspection and maintenance purposes, within heat exchangers, such as the steam generators equipping nuclear power stations, a device is proposed, which has an articulated arm formed from at least two rigid segments (24a, 24b), which are articulated to one another about an axis (A), as well as two plates (30a, 30b) mounted at the ends of the articulated arm via two handles (28a, 28b), each authorizing two rotations about two orthogonal axes (B, C), whereof one (B) is parallel to axis (A) and the other (C) is perpendicular to the surface (31a, 31b) of the corresponding plate. Each plate (30a, 30b) carries fastening members (32) able to engage in perforations (20a) of a tube plate (12) of the exchanger, as well as a support (34) for an intervention tool.

Abstract: In a steam condenser in which the steam is condensed on tubes which are grouped together in separate nests (2) and through which cooling water flows, the tubes, arranged in rows, of a nest enclosing a hollow space (13), a cooler (14) for the non-condensable gases in arranged in the hollow space. Two nests (2) are provided which are at a distance from one another and to which steam is admitted over their entire periphery, the nest form, irrespective of the external form of the condenser, being selected in such a way that first of all a convergent flow channel (15)--accelerating the steam--and then adjoining it a divergent retaining part (16)--deflecting the steam--are formed between the nests (2) on the one side and also between one nest each and the condenser wall. The cooler (14) for the non-condensable gases is located inside a nest in the plane in which, outside the nest, the convergent steam channel merges into the divergent part.

Abstract: A condenser for the water-steam loop of a power plant includes a condensate-filled lower portion. A heating pipe system is disposed in the lower portion and nozzles are disposed on the heating pipe system through which heating condensate or heating steam is forced into the condensate for heating the condensate and thereby expelling dissolved gases from the condensate. A heating valve is connected to the heating pipe system and a proportional regulator is connected to the heating valve for adjusting heating output of the heating pipe system through the quantity of hot condensate or hot steam. A measurement variable converter connected to the proportional regulator acts upon the proportional regulator at least as a function of oxygen content of the condensate and as a function of subcooling of the condensate, the subcooling being equal to the difference between the temperature of the condensate and the temperature of condensation of steam to be condensed.

Abstract: An apparatus for introducing and/or positioning a device in a chamber of a heat exchanger includes an assembly yoke with ends and a middle. The yoke may manually be introduced into the chamber of the heat exchanger with a pole. At least three remotely-actuatable clamping fingers are disposed on the assembly yoke. The clamping fingers are designed such that they may be locked or braced in tubes of the heat exchanger. For this purpose, respective locking devices that are remotely controllable may be used. A lifting cylinder holds one of the clamping fingers at least approximately at the middle of the yoke. Remotely-actuatable clamping devices each hold at least one of the clamping fingers on a respective one of the ends of the yoke. Toothed belts each have an end connected to a respective one of the clamping fingers positioned on the ends of the yoke. Two synchronously controllable elevators each have a toothed belt drive in engagement with a respective one of the toothed belts.

Abstract: The invention provides a method of positioning a robot intended to perform inspection and maintenance operations within a nuclear plant, and especially within a vessel of a pressurized-water reactor. The robot, which comprises an articulated arm, is controlled so that it initially attaches its head at one end of the arm to a support point having known coordinates. Then, supported on this point, the robot brings and attaches a foot-plate at the other end of the arm to a working support position having known coordinates adjacent the access opening of the vessel. The head is then released and the robot operated to move and position the head through the access opening and into the operating zone in the vessel.

Abstract: A remotely operable boiler tube wall cleaning and inspection system including a collapsible "H" frame capable of being inserted through the boiler manway access ports and being positioned at will over the full area of the tube wall.

Abstract: An automatic tube circumference scanning apparatus automatically performs inspections, repairs and other operation on a group of tubes arrayed in a narrow space and extending in horizontal directions. The apparatus includes an upper support/traverse section mounted on an upper tube in the group of tubes so as to be able to travel along a tube axis and to stop and grip the upper tube, a lower support/traverse section mounted on a lower tube so as to be able to travel, stop and grip the lower tube, a flexible rail extending vertically between the upper and lower support/traverse sections and fixed thereto, and a probe scanning section mounted on the flexible rail so as to be able to move up and down and which grips any arbitrary tube between the aforementioned upper and lower tubes for making a probe scan around such tube.

Abstract: An apparatus and method for remotely inserting and positioning a sleeve-loaded mandrel within a damaged tube mounted in the tubesheet of a nuclear steam generator is disclosed herein. The apparatus of the invention generally comprises a frame, a mounting mechanism for detachably and pivotally mounting the frame to the open end of one of a first tube in the tubesheet, an advancing assembly supported by the frame for remotely inserting and advancing the sleeve-loaded mandrel to a position across a damaged section of the selected tube, and a drive train for pivotally positioning the advancing assembly into alignment with the open end of the selected tube. In the preferred embodiment, the advancing means is formed from the pair of hydraulically operated grippers, one of which is reciprocably movable with respect to the other.

Abstract: A remotely installed, operated and removed manipulator for steam generator includes a mast, an articulating arm attached to the mast, capable of operating in the bottom or top head of a once through steam generator or the head of a recirculating steam generator. Each embodiment can be remotely installed and removed. The manipulator provides precise access to tubes and can sustain substantial loads, so the apparatus can perform much of the tube work that must be performed inside a steam generator.

Abstract: A plug removal apparatus for removing a mechanical plug fixed in an end of each heat exchange tube of a heat exchanger includes a plug removing mechanism which engages with and pulls out a cylindrical member of the mechanical plug. The plug removing mechanism includes a mandrel insertable into and threadedly engageable with the cylindrical member, a push rod coaxially extending through the mandrel for pushing a cone member of the mechanical plug, an actuating means for selectively moving the mandrel and the push rod towards and from the mechanical plug, and a drive means for selectively rotating the mandrel into engagement with the cylindrical member.

Abstract: The feed device comprises a housing (10) of sufficient size to contain a cylindrical piece (15), equipped with a removable cover (20), through which passes a nozzle (24) connected to a compressed-air distribution source (25, 26). A flexible pipe (11) is fastened at one of its ends to the housing (10). A loading unit (12) consisting of a fixed part (28) and of a rotary arm (29) is connected to the end of the flexible pipe (11) opposite the housing (10). The pieces (15) can, in particular, be plugs for plugging the tubes of a steam generator of a pressurized-water nuclear reactor.

Abstract: An automatic indexer assembly provides a constant axial and rotational movement of a signal-producing-sensor probe through a zone of a tube to be inspected with minimum signal distortion by means of threadedly connected fixed and movable hollow shafts. A probe tail is clamped to move with the movable shaft as it is driven by a constant speed drive motor and gear reducer mounted on a platform and guide plates which move with the movable shaft along a track parallel to the shaft axis. A water swivel and electrical slip ring also move on a platform with the movable shaft. Twisting of a fluid supply line and an electrical supply line is minimized. Constant sensor movement can be accomplished to permit accurate recording of the signal produced on a recording means with a minimum of backlash, acceleration, deceleration, or intermittent variables distorting the signal.

Abstract: The present invention is a transport system for an inspection system that includes a flexible controller end effector for carrying inspection and gripping devices. The transport system includes a hollow flexible conduit through which control cables for the effector can pass unobstructed. A rotatable deflector assembly helps guide the end effector as it enters the steam generator using a rotatable deflector channel and an extension. A drive assembly provides axial movement control for the end effector allowing easy insertion and retrieval. The axial movement is provided by friction rollers coupled to an axial drive mechanism and mounted in a drive box. The drive assembly also provides orientation control to allow the end effector to be rotated by rotating the drive box which rotates the conduit held in place by the direction rollers. The drive assembly further provides two spatially fixed locations from which the axial and rotational motions can be provided.

Abstract: An inspection system and process for inspecting a plurality of conduits mounted in a manifold is disclosed herein. The system generally comprises a probe carrier for driving an eddy current or ultrasonic probe throughout the conduits to be inspected, and a delivery assembly detachably mountable within the manifold for remotely delivering and inserting the probe carrier into the open ends of the conduits. The delivery system includes an insertion and pusher mechanism for selectively inserting and pushing the probe carrier through the open ends of the tubes, a rail assembly which is removably mountable within the manifold, and a carriage slidably mounted on the rail assembly for supporting and axially positioning the insertion and pusher mechanism. Angular and axial electric drive motors are also provided for rotating and moving the insertion and pusher to a selected angle around and point along the longitudinal axis of the manifold.

Abstract: The process consists in displacing a camera (15), provided with a sensitive support, parallel to the tubular plate (2) of the steam generator inside the water tank (3), successively taking photographs of the primary face (2a) of the tubular plate (2), making from the sensitive support, extracted from the water tank (3), pairs of photographic images of the ends of the tubes (8) flush with the tubular plate (2) with different angles of perspective, orienting the photographic images of the pairs in relation to one another to obtain a stereophotogrammetric view of the end of each of the tubes (8) to be checked, and making measurements and observations on the stereophotogrammetric view. The invention also relates to checking apparatus comprising a camera arrangement movable inside the water tank.

Abstract: A clamping element for fixation in a bore of a structural element and for carrying a load includes a clamping sleeve formed of a plurality of partial shells and having a central axis, a clamping bolt vertically movable in the clamping sleeve, the partial shells and the clamping bolt having mutually cooperating spreading surfaces converging and tapering toward the load, the clamping bolt permanently subjecting the partial shells to an automatically acting clamping force, the clamping bolt being axially movable to counteract and relieve the clamping force, the partial shells and the clamping bolt having surfaces adjacent the spreading surfaces converging obliquely toward the central axis and forcing the partial shells into a disengaged position.

Abstract: A steam generator having a tube sheet, tubes ending in the tube sheet, a chamber adjoining the tube sheet having an access opening formed therein and a device disposed in the chamber for inserting a sleeve into one of the tubes in a plurality of partial insertion strokes, the inserting device includes a movable clamping device holding and moving the sleeve in axial direction of the tube in one of the partial insertion strokes, and a stationary clamping device associated with the movable clamping device holding the sleeve during a backstroke of the movable clamping device.

Abstract: An apparatus for scanning header tube holes includes a probe assembly designed to engage the surface of the header encircling a header tube hole. The probe assembly includes a spring mounted sensor, in a preferred arrangement, an eddy current probe. A mechanism is provided for supporting and positioning the probe assembly. The mechanism is adapted, in operation, with resilient rings engaging the tube stub. A drive device is provided for imparting axial and circumferential movement to the probe relative to the surface of the hole which is to be inspected.

Abstract: A device for searching and retrieving objects on a tube sheet of a steam generator which includes a sled having a probe and a gripper thereon and connected to a flexible tube having control means therein for operating the probe and the gripper whereby the sled and flexible tube may be inserted through a handhole of the generator to an operating position on the tube sheet. Both the probe and the gripper may be angularly rotated to manipulate them between the tubes of the steam generator.

Abstract: A probe (10) for scanning the interior of a curved conduit (28) has a carrier (12) with a rotatable portion (12b). Sensor means (18) are secured to the rotatable portion (12b) and are aligned with respect to the curvature of the conduit by means of an elongated flat strip (20), secured to the rotatable portion (12b) and extending longitudinally therefrom. Driving means (14) is provided to urge the probe (10) longitudinally through the conduit (28).

Abstract: A mechanical feeding mechanism for delivering plugs seriatum from a cylindrical delivery chute having upper and lower latching mechanisms. Each of the upper and lower latching mechanisms are movable from a latching position wherein the latching mechanism engages a plug in the chute and an unlatching position. Linkage mechanism connects the upper and lower latching mechanisms such that when one of the latching mechanisms is in the unlatching position the other latching mechanism is biased toward the latching position.

Abstract: A tool holder robot makes it possible to carry out various interventions within a closed enclosure having an access opening. It comprises a cylindrical ferrule fixed to the opening, a cylindrical shaft mounted in rotary manner in the ferrule, a guide rail fixed to the inner wall of the shaft, in which a first arm is slidingly mounted, a second arm pivotably mounted to the free end of the first arm and a tool holder carriage slidingly mounted on the second arm. The second arm is in two parts and can rotate about its longitudinal axis.Application to the inspection and maintainance, without human intervention, of water boxes of nuclear power station steam generators.

Abstract: Device for inspection and repair of tubes of a nuclear reactor steam generator in a tube bundle being disposed in a tube sheet and opening into at least one chamber having an opening formed therein, including a manipulator being insertible in the chamber through the opening and being lockable to the tube sheet for carrying remotely controlled and monitored inspection instruments and tools, the manipulator including a support leg being adjustable in length in the axial direction, a main arm being connected to and movable relative to the support leg, and an equipment carrier being connected to the main arm and movable relative to and together with the main arm, and a mounting rod being connectible to and detachable from the manipulator.

Abstract: A motorized transporter is placed at the periphery of the tube bundle which extends up from the tube sheet within a nuclear steam generator shell. The transporter can be separated into parts as required to move it into and out of the limited space between the tube bundle and inside wall of the generator. A control station external the generator is connected by flexible cables to the transporter and its equipment in order to move the transporter, observe the transporter path for foreign objects, and retrieve such objects.

Abstract: A water leakage monitoring system has a carriage remotely controlled with a driving control signal to intermittently travel along an inspection rail, a plurality of discrete monitored members disposed adjacent to the inspection rail, an industrial color television camera hung from the carriage through an attitude adjusting mechanism so as to correctly oppose and monitor water leakage through each of the monitored members through the operation of the attitude adjusting mechanism in response to an attitude control signal, and a coating composition applied to the surface of each of the monitored members which changes in color when it is wet with water leaked through the associated monitored member.

Abstract: The invention relates to a device for selectively positioning a tool carried by a vehicle moving on the perforated plate of a bank of tubes, said device being composed of a vehicle comprising transfer members mounted to slide in a central body and comprising on either side thereof jacks extending at right angles to the planes in which said members move and of which the mobile rods of said jacks comprise at their free end positioning fingers, which vehicle is connected by swivel joint means to an articulated telescopic arm comprising means for fixation to the opening giving access to the enclosure, which arm maintains the vehicle, in the course of its displacements in the enclosure, permanently in contact with said perforated plate. The invention is more particularly applicable to the maintenance of apparatus comprising banks of tubes, in particular steam generators of nuclear power stations.

Abstract: A steam generator having a steam generator chamber, a tube plate bordering the chamber, tubes terminating in the tube plate being accessible through the steam generator chamber, a tubular column in the steam generator chamber having an end facing toward the tube plate, and a swivel arm extended from the tubular column being movable parallel to the tube plate for carrying a device for testing and/or repairing the steam generator tubes, includes a clamping element for positioning the tubular column relative to a tube of the tube plate, and a coupling being detachable from outside the steam generator chamber connecting the clamping element to the tubular column, the clamping element including a drive element disposed in the tubular column, an expansion plunger connected to the drive element for axially inserting the expansion plunger partially into a tube, an expansion sleeve formed of separate clamping jaws for engaging the tubes, the clamping jaws having ends being insertible into a tube, and a holding element

Abstract: A condenser for a steam turbine expels the oxygen-containing gas residing in the condensate passage in the hot well thereof by a scavenging steam. The oxygen-containing gas is expelled by the scavenging gas, which is introduced into the atmosphere in the condensate passage and arranged to flow counter to the condensate flow. The scavenging means includes a steam pipe attached in a vicinity of an outlet of the condensate passage in the hot well, and a valve device provided in the intermediate portion of the steam pipe.

Abstract: A device for positioning a member so as to face each of a plurality of perforations arranged in a given grid in a plate, especially for the inspection of the tubes of a steam generator in a nuclear power station. It comprises a body having at least two attachment members for fastening the device in the perforations. The device is rotatable around one or the other of these attachment members so as to displace it on the plate, and has a support carrying the member and pivotable with respect to the body in order to bring the member into a position facing several perforations without displacing the device.

Abstract: A system for draining condensate from a temperature regulated, steam operated heat exchanger. A buffer tank having a volume at least equal to that of the steam compartment is connected to the steam side of the heat exchanger, and a drain line extends from the bottom of the buffer tank to a condensate collection pipe located above the buffer tank. The drain pipe from the heat exchanger includes an air venting device and a control pipe having a non-return valve linking the top of the tank to the steam side of the heat exchanger. During low load operation of the heat exchanger, air from the top of the buffer tank can flow back to the steam compartment of the heat exchanger to equalize the pressures and permit drainage of the condensate even during low load conditions.

Abstract: A steam duct (5) enclosing the preheater tube-bundle (6) leads, upwards, from the desuperheater box (2) and via a deflecting quarter-bend (9), opens into a flat steam-distribution duct (8). The heating steam flows from this distribution duct (8), through steam outlet openings (12) on the vertical narrow sides (11), and thereafter flows radially through the preheater tube-bundles (6), from the outside to the inside.

Abstract: The present invention relates to method and apparatus for preheating pulverous materials, such as glass batch constituents, prior to their introduction into a melting furnace to increase the efficiency and output of the melting installation. The pulverous materials are passed downwardly by gravity through a shell and tube preheater including an interior exhaust chamber to vent the contained moisture from the heated pulverous material. The venting prevents moisture condensation and build-up of the pulverous material within the tubes and batch materials, especially in cooler areas, which can cause tube pluggage. The subject invention is of particular utility to the glass industry and especially glass melting furnaces, but is also applicable to other types of furnaces.

Abstract: A process and an apparatus for recovering heat from a finely to coarsely divided hot material, such as carbide crushed on solidification, which contains particles and lumps of varying sizes. The hot material is separated by a classifier into a portion of lumps and a portion of particles, and the lump portion is cooled in a cooling bunker with a stream of cooling gas while the particulate portion is cooled in another cooling unit with a stream of cooling gas. The hot cooling gas resulting from the cooling is fed to a heat exchanger in which the gas is subjected to heat exchange with a working fluid for a turbine coupled to a power generator or the like. The heat exchanger is connected to the cooling bunker and unit by a closed circulating channel.

Abstract: The present invention relates to method and apparatus for preheating pulverous materials, such as glass batch constituents, prior to their introduction into a melting furnace to increase the efficiency and output of the melting installation. The pulverous materials are passed downwardly through a shell and tube preheater with sub-atmospheric pressure over the pulverous material to remove the contained moisture in vapor form from an upper region of the preheater. The decreased atmospheric pressure prevents moisture condensation and build-up on the pulverous material within the tubes, especially in cooler areas, which can cause tube pluggage. The subject invention is of particular utility to the glass industry, and especially glass melting furnaces, but is also applicable to other types of shell and tube heat-exchange applications.

Abstract: The present invention relates to method and apparatus for preheating pulverous materials, such as glass batch constituents, prior to their introduction into a melting furnace to increase the efficiency and output of the melting installation. The pulverous materials are passed downwardly through a shell and tube preheater with super-atmospheric gas pressure over the pulverous material to force the contained moisture downwardly to be vented from a lower region of the preheater. The increased gas pressure prevents moisture condensation and build-up on the pulverous material within the tubes, especially in cooler areas, which can cause tube pluggage. The subject invention is of particular utility to the glass industry and especially glass melting furnaces, but is also applicable to other types of furnaces.

Abstract: A feed water preheater is disclosed having warm and cold tube bundles. The warm tube bundle is divided into first and second warm tube bundles with the first warm tube bundle forming a desuperheater bundle and the second warm tube bundle forming a condenser bundle. The first and second warm tube bundles are isolated with respect to one another with a steam distribution duct arranged between the warm and the cold tube bundles. Preferably, the warm and cold tube bundles are U-shaped with a steam inlet arranged perpendicularly with respect to the tube bundles.

Abstract: There is disclosed a heat exchanger having one or more bundles of tubes through which steam or other vapor is passed and comprising horizontally arranged rows of tubes each of which is connected to a separate outlet header. Condensate from the outlet headers of each bundle is drained into a pot having individual water leg seals which isolate vapor pressure within such outlet headers from one another. The outlet headers are of generally rectangular cross section and staggered in a horizontal direction, with the lower end of each successive outlet header to be contacted by air extending below the upper end of the preceding outlet header. The tubes of each such successive row of tubes are longer than those of the preceding row to be contacted by air and extend over the upper end of the outlet header connecting with the tubes of the preceding row of tubes.