Abstract: A gas/liquid, parallel flow heat exchanger in a waste-heat tank which is constructed as a pressure tank, is charged with coolant, and is connected after a pressure gasification. The waste-heat tank includes conduit-like elements of equal length which serve as heat transfer surfaces and are installed in conduit-like components or wall units. The wall units divide the interior of the waste-heat tank into regions having upwardly and downwardly directed fluid flow. A central, coaxial, polygonal, preferably hexagonal, cylindrical displacement body is provided, with the number of surfaces of the displacement body depending upon the number of heat transfer surface elements. Also provided are wall units which project out of the wall of the container of the waste-heat tank into the interior thereof across from the corners of the polygonal displacement body. Cylindrical displacement bodies are located centrally between the corners of the polygonal displacement body on an imaginary circle.

Abstract: Exhaust gas treatment method and apparatus extract heat from an exhaust gas by operating in a water-condensing mode which allows more heat to be recovered, removes particulate matter and condensed acid from the exhaust gas, and washes heat exchange surfaces to keep them clean and wet to improve heat transfer. Systems for heating water, air, and both water and air are disclosed. Methods of constructing and assembling improved heat exchangers are disclosed.

Abstract: Apparatus in the form of a multi-unit cooler for cooling liquid samples of steam or water in boiler water feed systems or other process apparatus for the purpose of testing or measuring various inorganic and other components of the cooled samples as for example oxygen content, carbonates, sulfates, etc.

Abstract: Exhaust gas treatment method and apparatus extract heat from an exhaust gas by operating in a water-condensing mode which allows more heat to be recovered, removes particulate matter and condensed acid from the exhaust gas, and washes heat exchange surfaces to keep them clean and wet to improve heat transfer. Systems for heating water, air, and both water and air are disclosed. Methods of constructing and assembling improved heat exchangers are disclosed.

Abstract: An energy storage and recovery system designed for storing excess over demand energy generated by a steam cycle electrical generating plant during slack electricity demand periods and for recovering the stored energy to provide supplemental electricity during peak demand periods.The system utilizes one or more moving bed heat exchangers for transferring heat between the steam cycle of the power plant and a moving bed of refractory particles. Pipes and valves establish fluid communication between the heat exchangers and the steam cycle to supply fluid to selectively heat the moving bed of refractory particles or to cool them as the case may be.One or more insulated silos are provided for storing the refractory particles and means are provided for transporting the particles between the silos and the heat exchangers.

Abstract: A heat exchanger block includes a series of rows of tubes, the end rows of which are joined to form walls, and two further rows of tubes at the opposite sides of the series, also formed as walls. The tubes of the further rows are shorter than the other tubes and, at one side, are spaced downwardly from the top and, at the other side, are spaced upwardly from the bottom. A pair of lateral openings at the opposite sides and ends of the block results. The blocks may be joined to provide composites or they may be separate although joined at one pair of their lateral openings. A pressure vessel may enclose the blocks to relieve them of rupturing pressure.

Abstract: In a heat exchanger having tubes arranged in latticed pattern in a frame and serving to conduct a medium for heat exchange and enclosed in a housing wherein the space defined by the housing and the frame is divided into a collector and a distribution chambers, each chamber being subdivided with a partition wall defining a further chamber, namely a collector and a distribution chambers respectively. These chambers intercommunicate through corresponding tubes to form separate flow paths for the medium for heat exchange. The heating or cooling medium is flowing through the exchanger transversely to the longitudinal direction of the tubes.

Abstract: A heat exchanger with at least one main tube, closed off at one end, into which compressed air, which is to be heated, is admitted and, after being heated, is removed. The main tube has at least two channel guideways which are separated from one another in the longitudinal direction. U-shaped or curved compressed air lines project from the main tube and contact the hot gases. Each compressed air line is connected at one end to the channel guideway of the main tube into which compressed air is admitted, and at its other end with the channel guideway through which the heated compressed air is removed. The compressed air lines are formed primarily from hollow bodies, which extend in the direction of flow of the hot gas and which preferably are tapered at the inflow and outflow ends in order to aid the flow.

Abstract: An evaporator for producing wet steam in a cogeneration plant wherein the evaporator is a multiple pass unit having continuous in-tube flow paths from inlet to outlet. The evaporator is a shell and tube type with the clean steam on the shell side and water in the tubes. The evaporator is particularly useful in a cogeneration plant used in a secondary recovery process using contaminated wet steam.

Abstract: A heat recuperator comprises a cross-flow ceramic core within a housing. The housing includes an inlet conduit and an outlet conduit for a gas to be heated. The housing also includes means for thrice passing said gas through the ceramic core in order to improve the diffusion of the gas through the core.

Abstract: A triple pass heat exchanger for use in a solar energy heating or cooling system includes an assembly of four helically wound lengths of tubing. The helical tubes are arranged relative to each other in a substantially concentric manner so that the first tube is innermost, the second tube outward to the first tube, the third tube outward to the second tube and the fourth tube outward to the third tube. The first and third tubes are coupled in flow communication at a first common inlet and a first common outlet, and the second and fourth tubes are coupled in flow communication at a second common inlet and a second common outlet. A first liquid heat transfer medium flows through the first and third tubes and a second liquid heat transfer medium flows through the second and fourth tubes. A shell encloses the assembly within an inner chamber defined by the shell.

Abstract: A multiple module heat exchanger having a serpentine path for one fluid to flow transversely through adjacent modules while a second fluid flows longitudinally therethrough. A guide pin carried by one module and a mating receptacle carried by a module adjacent thereto cooperate to permit relative longitudinal movement between modules while precluding relative transverse movement therebetween. The mating guide pin and receptacle are located at the central axis of adjacent modules whereby there may be a limited amount of pivotal movement between adjacent modules.

Abstract: Apparatus for connecting tube banks in a shell and tube heat exchanger comprises a tube sheet co-extensive with the ends of a pair of adjoining tube banks into which tube sheet a plurality of aligned U-bends are fitted at their ends. The U-bends are positioned to connect each tube end in one bank with its mirror image tube end in the adjoining bank.

Abstract: A heat exchanger within a dense gravity layer comprises a vertical cylindrical container with a heating surface built thereinto. The heating surface is formed by a tubular housing containing a plurality of tubes mounted in tiers. A space between the inner surface of the container and the outer surface of the housing is divided by opposite seals into two vertical cavities. These cavities are divided along the height thereof by horizontal baffle members which are arranged in chessboard pattern relative one another to form chambers located along the height in a chessboard pattern, and to accomplish repeated variation of the direction of movement of one of heat carriers.

Abstract: A heat exchanger for exchanging heat between two different temperature fluids. The heat exchanger includes a sealed housing having first and second pairs of inlets and outlets. A first conduit is disposed within the housing. A second conduit is concentrically disposed within and spaced from the first conduit to define a first flow path between the spaced wall surfaces thereof which is disposed in fluid flow communication with the first inlet and first outlet for flow of a first fluid in a first direction through the housing. A second fluid flow path including first and second serially connected sections is provided for directing a second fluid between the second inlet and the second outlet over the exterior wall surface of the first conduit and through the second conduit in a second direction opposite to the direction of flow of the first fluid. In a preferred embodiment, a sealed chamber is formed interiorly within the housing about the first conduit.

Abstract: A heat exchange assembly is provided which employs concentric flat plate heaters, the heat exchange assembly having a common fixed tube sheet and floating tube sheet; the floating tube sheet comprising two concentric portions having frustoconical interface thereby, the frustoconical interface when projected has its apex in a plane containing the adjacent face of the fixed tube sheet in the axis of generation of the flat plate heater. Thermal stress on the floating tube sheet is thereby relieved. The heat exchanger is useful as a reactor particularly where the temperature profile of the material flowing therethrough is controlled or varied.

Abstract: A heat exchange assembly is provided which employs concentric flat plate heaters. The heat exchanger is useful as a reactor particularly where the temperature profile of the material flowing therethrough is controlled or varied.

Abstract: In a heat exchanger for the recovery of heat from hot shale ashes, having tubes arranged in a frame in latticed pattern and serving to conduct a gas, the frame is surrounded by a housing wherein the space enclosed by the frame and the housing is divided into a collector and a distribution chamber. The shale ashes move through the heat exchanger transversely of the longitudinal direction of the tubes. At the inlet for shale ashes there is provided an inlet space divided with a vertical partition wall into unequal compartments for receiving the ashes incoming through separate inlets under different pressures.

Abstract: A combustion air preheater for heating combustion air with heat energy provided from flue gas includes both a heat pipe type heat exchanger for effecting low temperature heat transfer between the flue gas and the combustion air and a tube-and-shell type heat exchanger for effecting higher temperature heat transfer. The preheater includes a first heat exchanger, having first and second heat transfer compartments with a plurality of heat pipes extending therebetween and a second, connected heat exchanger which includes a plurality of heat tubes supported by tube sheets within a shell. Ducting is provided to direct flue gas over the tubes of the second heat exchanger and then through one of the compartments of the first heat exchanger and additional ducting is provided to direct combustion air through the other compartment of the first heat exchanger and through the tubes of the second heat exchanger.

Abstract: There is provided a ceramic heat exchange module 10 having fluid inlet and outlet conduits (12,20) extending from one side of horizontal manifolds (14,18). Serpentine tubes 16 extend from the opposed sides and connect the manifolds. In use, in a fluidized bed combustor 22, the manifolds are positioned between the base 30 and air inlets 32. Serpentine tubes extend into the fluidized bed 36, the fluid inlet and outlet conduits extend through the base for coupling to a working fluid supply.

Abstract: A liquid reservoir has a rectangular shell in which crossed first and second partitions form first, second, third and fourth rectangular liquid chambers. The partitions are impervious between the first and fourth chambers and apertured between the first and second, second and third, and third and fourth chambers. Liquid flows serially through the first, second, third and fourth chambers via the apertured partitions and such flowing liquid is subjected to a heat exchange in the first, second, third and fourth chambers.

Abstract: A methanol-synthesis reactor has a housing receiving a catalyst packing and coils of cooling tubes surrounding a core tube and disposed in helical radially spaced layers coaxial with the core tube. According to the invention, the internal diameters of the cooling tubes are from 4 to 50 mm, the distance between neighboring tubes in a direction transverse to the axis and the direction of fluid flow through the catalyst packing is between 2 and 20 times the smallest longitudinal dimension of the catalyst particles and the distance between neighboring tubes measured in the direction of the synthesis gas flow is less than 10 times the transverse distance.

Abstract: The invention provides a protective casing for a cube-shaped modular ceramic heat exchanger core, in which the core can easily be installed without danger of leakage between the fluid paths of the core. To this end the core rests in the casing with the edges of one face engaged with a suitable ceramic fibre composition gasket; the opposite face of the same flow path is engaged by another such gasket and the gasket is in turn engaged by a gasket compression member. The compression member is urged into this engagement by strong springs which thereby hold the gaskets in the necessary sealing engagement. In one aspect of the invention the casing is readily changed to provide single or multi-pass of one of the flow paths through the core; such a casing consists of a central portion of the thickness dimension of the core and replaceable end portions which provide the inlet, outlet and respective plenums.

Abstract: In an air heater, an initial group of passes on the airside is arranged in the form of a package wherein the passes consisting of banks of tubes are connected in parallel with the uptake gases.The passes of the package are located predominantly at the same horizontal level, are made of tubes of the same length and run in a zone of the same gas temperatures which is dangerous insofar as corrosion can be provoked therein.The width of the packaged passes progressively increases directly with the increase in the rates of air flow through the passes, and a feeding air duct admitting the last inflow of cold air is connected downstream of the last and widest pass to the connecting air duct serving the rest of the passes of the air heater.In an apparatus like this one, assembled from standard components, minimum overall dimensions and low weight are combined with high thermal efficiency.

Abstract: This invention relates to a hot water system which utilizes heat from the refrigerant of a refrigeration system to produce hot water. The utilized heat consists of the superheat of the refrigerant vapor, the latent heat of condensation, and part of the sensible heat of the liquid refrigerant. The water passing through a water-cooled condenser, which is part of the refrigeration system, is heated to a selected temperature by removal of both the superheat of refrigerant vapor, the latent heat of condensation, and part of the sensible heat of the liquid refrigerant as it passes through the condenser. The condenser has a water inlet and an outlet between which is connected to a hot water storage tank. As the water in the condenser is heated by absorption of the superheat of the refrigerant vapor, the latent heat of condensation, and part of the sensible heat of the liquid refrigerant passing therethrough, the heated water rises and flows by convection into the storage tank.

Abstract: A tube-bundle heat exchanger for cooling a medium having a high inlet temperature. The heat exchanger has an inlet tube bottom and an outlet tube bottom, in which are fastened the ends of tubes which connect the bottoms and through which the medium of high inlet temperature flows. An intermediate tube bottom, having insert tubes arranged concentrically in the tubes, is located in the inlet chamber, with these insert tubes projecting out on both sides from the tubes and forming annular spaces therewith. Toward the inlet chamber, the annular spaces open into an intermediate chamber limited by the inlet tube bottom and the intermediate tube bottom; in the opposite direction, the annular spaces open into a deflecting or reversing chamber sealingly covering the insert tubes.

Abstract: Abrasion-proof coke forms are produced from bituminous coal, brown coal, or peat in the form of briquets, by preheating the briquets, dehydrating or predrying them, carbonizing them and then cooling them in at least three separate stages in which the briquets are dehydrated indirectly by subjecting them to indirect temperature conditions, producing a temperature gradient in the briquets. The briquets are automatically fed into a shaft tower which includes an upper drying shaft portion made up of a plurality of stacked radiators which include tube elements for the passing of a heating fluid, such as steam, therethrough and which define vertical shaft passages through which the briquet forms are passed downwardly and into a carbonizing shaft which has separate gas channels for directing heating gases therethrough and to a heating flue and which subsequently includes a lower cooling zone through which the briquets pass and then into a discharge channel where they are delivered for classification.

Abstract: This invention relates to a group of modular heat exchangers of the type having a steam chamber, a feedwater chamber, and a feedwater tube passing through the steam chamber to establish fluid communication with the feed chamber.

Abstract: A heat exchanger comprises an outer chamber having an inlet and outlet for passing a flow of air through the outer chamber. An inner chamber is disposed within the outer chamber and has a second inlet and a second outlet for passing a flow of gas through the inner chamber. Heat exchange tubes are arranged in the inner chamber whereby the flow of gas contacts the outer surface of the tubes. A baffle device is disposed between the inner and outer chamber for directing the flow of air from the inlet, through a first section having heat exchange tubes, into the outer chamber and back into a second section having heat exchange tubes, so that air passes through the heat exchange tubes in the first and second sections.

Abstract: A heat exchanger for cooling a hot, high pressure gas and utilizing the heat removed therefrom for generating hot water comprising a first and a second vertically elongated pressure containment vessels, the second vessel disposed coaxially within the first vessel so as to establish an annular space between the outer surface of the second vessel and the inner surface of the first vessel. A gas inlet pipe penetrates through the bottom of the first vessel opening into the second vessel at the bottom thereof and a gas outlet pipe penetrates through the top of the first vessel opening into the second vessel at top thereof, thereby providing a passageway for the hot gas to flow through the second vessel. Water is circulated through the annular space between the first and second vessels and heated therein as it absorbs heat lost by the hot gas passing through the second vessel.

Abstract: A plate heat exchanger comprises a laterally arranged cylindrical container having an inlet and outlet for one of both media and those for the other medium and opening at one end, a plurality of heat exchange units each including a pair of opposite frames and a pack of plate elements therebetween and being inserted in sequence into the container, and a press lid attached to said one opening end of container under condition of thrusting said plurality of heat exchange units. The plate elements are clamped face to face through surrounding sealing surrounding sealing strips respectively to form between the plates interspaces through which the media flow. Every second interspace among the interspaces is closed with respect to the space within the container and communicates with said inlet and outlet for said one medium.

Abstract: A heat exchanger has a modular construction to create uniformity among several of its components. The heat exchanger utilizes concentric tubes, with one fluid flowing through the inner tube, and the other fluid flowing through the annular space in the outer tube. The inner tube fluid flows back over the outer tube, further exchanging heat, as it is discharged. The heat exchanger includes four cup-shaped modules that nest or slide together. Each module includes a sleeve with a port for one of the fluids. Each module also has a convex portion that slides sealingly into an adjacent module and contains holes for the tubes. The tubes are sealed into the holes in the convex portions, causing each module to define one of the four manifolds necessary for the operation of the heat exchanger.

Abstract: Each heat-exchange bank consists of at least two groups of flat, adjacent compartments provided for the circulation of a second fluid and separated by spaces for the circulation of a first fluid. Each compartment has lateral extensions placed in identical and opposite manner in two adjacent groups. The extensions are connected respectively in each group to a common admission manifold and to a common discharge manifold for the second fluid.

Abstract: An improved reheater for a moisture separator reheater includes an inlet header, an outlet header and a plurality of heat-exchange tubes connected therebetween. The inlet header is partitioned to provide at least two separate sections. Piping and control valves are also provided to supply steam to each section of the inlet header from the reheater inlet pipe. The improved reheater includes at least one bundle of tubes communicating with the header(s) via tubesheet(s). The inlet ends of the tubes may be differentially orificed whereby in combination with a nominal flow rate to the partitions, in-tube condensate subcooling is substantially eliminated with minimal scavenging steam at design conditions. At off-design, or low power level, conditions, where fixed resistances of orifices and fixed partitions cannot accommodate changes in heat transfer demand from tube to tube, the aforementioned control valves are automatically adjusted.

Abstract: A Moisture Separator Reheater (MSR) has a plurality of tube bundles which receive high-pressure saturated (tubeside) steam therein. Steam to be reheated (shellside steam) is passed in heat-exchange relationship with the tubes of the first and second reheater tube bundles after first being dried by the panels of a moisture separator. It emerges from the shell of the reheater dried and heated. In the reheater tube bundles saturated steam at temperatures and pressures substantially higher than the shellside steam transfers heat to the shellside steam by condensation within the tubes. The steam in the second stage tube bundle is at a temperature and pressure that is substantially higher than that of the steam in the first stage tube bundle and is heating shellside steam at a higher temperature than the shellside inlet steam to the first stage tube bundle. A greater quantity of tubeside steam than is theoretically necessary is passed through the tube bundles.

Abstract: A method of cooling beer, wherein beer contained in a cylindrical fermentation tank of a large capacity and undergoing a fermentation process extending from the beginning of fermentation to the termination of fermentation, is cooled by employing cooling jackets mounted on the external wall surface of the sidewall of the tank and on the bottom of the tank and wherein cooling is more intense at the lower layer of beer in the tank.

Abstract: A base housing section, a plurality of intermediate housing sections, and a head housing section are stacked one above the other in a gas-tight but readily removable manner, to form a hollow housing. The base housing section and head housing section are equipped with gas connections so that a gas from a coke plant may be circulated through the hollow housing. Each intermediate housing section has extending transversely across the interior thereof at least one group of a plurality of heat exchange tubes. Cooling fluid connection means are connected to the uppermost and lowermost groups of tubes for the passage therethrough of a cooling fluid. Adjacent ends of adjacent groups of the tubes are connected such that the heat exchange fluid passes through all of the tubes of the intermediate housing sections in a substantially sinusoidal manner.

Abstract: The two heating surfaces of the exchanger are both provided within a jacket. The first heating surface is formed, in part, by blind tubes which project into the casing through which the primary gas flows. The second heating surface is disposed in the space between the feed pipe and the jacket and receives the flow of primary gas after the primary gas has passed over the blind tubes. The secondary gas passes into the interior of the blind tubes while a working medium flows through the second heat exchanger in heat exchange relation with the primary gas. Some of the returning cooled primary gas can be tapped off and supplied as a coolant through the tube plate in which the blind tubes are mounted.

Abstract: This invention relates to a hot water system which utilizes heat from the refrigerant of a refrigeration system to produce hot water. A condenser as part of the hot water system is especially designed with greater heat exchange surface than would normally be provided with the refrigeration system so that water at convection flow and at a higher temperature than normal can be used in the condensing unit and yet achieve the necessary absorption of heat from the refrigerant passing through the condenser as required for proper operation of the refrigeration system.In one embodiment of the condenser unit a de-superheating coil is located at the top of the housing to overlie the top of an inverted can arrangement within the housing. Between the sides of the housing and the inverted can is located a sheet type heat exchange surface which is preferably pillowed.

Abstract: The system for condensing gases such as steam includes a housing with a gas inlet. At least one vertical column of vertically spaced separate tube bundles are in the housing. A separate water conduit is connected to the inlet of each of the separate tube bundles.

Abstract: This invention relates to an improved system of providing power having a unique generating means of the nuclear reactor variety adapted with a plurality of steam generators in the form of replaceable modular units of the expendable type for the attainment of the optimum in effective and efficient vaporization of fluid during the process of generating power.

Abstract: A motionless mixer for combining different substances brought into communication therewith. The mixer includes at least two tubular members. Each tubular member has at least one spiral corrugated surface thereon. The members are arranged so that different substances brought into and out of communication therewith including the at least one corrugated surface will be mixed together.

Abstract: A system for supplying steam to equipment which uses the heat of the steam and not the pressure for performing work such as commercial laundry equipment. The system is a closed loop having a steam boiler which supplies steam directly to the equipment. A control valve regulates the amount of steam flowing through the equipment which determines the heat imparted to the equipment. The equipment is free of heat traps or other components which retard the flow of steam therethrough. The used steam flows into an improved condenser having a plurality of compartments which slows down the velocity of the steam to help facilitate the condensing process and to enable harmful air trapped in the condenser to be removed. Pumps remove the air from the condenser and maintain a vacuum within the condenser and steam return line from the equipment to maintain the steam flowing through the equipment at a desired rate.

Abstract: A heat exchanger has at least two cylindrical shells defining annular chambers lying one within the other. One of the annular chambers receives a tube bundle consisting of straight tubes while the other annular chamber receives a tube bundle of coiled tubes. The heat exchanger is particularly suitable for the heating of feed water (traversing the tubes) with steam (traversing the annular chambers) in a power plant in which the heat exchanger is disposed directly beneath the turbine on the turbine mount.

Abstract: A shell-and-tube heat exchanger comprises a shell which houses a tubular core, with an array of heat transfer tubes uniformly spaced between the shell walls and the core, said heat transfer tubes being secured in an inclined upper tube plate and an inclined lower tube plate. The shell-and-tube heat exchanger of the present invention is characterized by that each tube plate is made up of separate trapezoidal sections with gaps therebetween, which gaps are intended for passage of a heat transfer agent in the axial direction into the intertubular space at the inlet and outlet portions of the heat exchanger, inlet and outlet collectors being connected to each section of the upper and lower tube plates, respectively, for the supply of the heat transfer agent into the heat transfer tubes.

Abstract: A heat-exchanger for gases of greatly varying temperatures, especially for use in gas turbines, which essentially consists of a collective space, for example, of a pipe-shaped collective space for the cold gas and of a metal recuperator which is formed by a large number of preferably U-shaped pipes which are welded or brazed into the collective chamber, whereby the hotter gases flow through between the pipes of the recuperator to give off some of their heat to the compressor air flowing through these pipes; one or several protective sheet metal members are arranged within the area of the connecting places between the pipes of the recuperator and the collective chamber which protect the welded or brazed joints against the hot gases.

Abstract: An improved multi-section heat exchanger unit for use in combination with a radiant furnace unit or direct fired heaters which comprises a first heat exchange section having a plurality of bare heat exchange pipes positioned therein and in fluid communication with a first heat exchange fluid inlet and a first heat exchange fluid outlet to provide fluid flow through the bare pipes; and a second heat exchange section having a plurality of extended surface heat exchange tubes positioned therein in fluid communication with a second heat exchange fluid inlet being in fluid communication with the outlet of the first heat exchange section, the second heat exchange section being further characterized as having a gradually reduced internal cross section towards its upper portion so that the velocity of gas flow therethrough is maintained substantially constant.

Abstract: A heat exchanger (air preheater) comprising two series-connected sections, the section comprising the flue gas outlet having double-walled partitions with intermediate spaces in which a vaporizable medium is present for isothermalizing the said partitions in the flow direction in order to prevent the deposition of corrosive substances such as sulphur compounds.

Abstract: A pan for the continuous boiling of various liquids under vacuum includes an enclosed vessel divided into a series of interconnected compartments or stages provided with heating elements. During operation, boiling of the material is effected under optimum conditions as it flows continuously through the various stages from the feed end to the discharge end of the pan.

Abstract: The multi-pass heat exchanger comprises an open-ended shell for receiving a first fluid and at least one tube bank disposed in the shell and connected to pass a second fluid in indirect heat transfer with the first fluid. The tube bank may comprise one or more conduits each of which are of polygonal configuration in cross-section and have spaced rows of fins extending from the large sized surfaces of the conduits. Each of the conduits is formed into a flattened helical configuration consisting of substantially straight portions so arranged that alternate straight portions extend in substantial parallelism and having return bend portions interconnecting end-to-end next adjacent straight portions so that series flow of second fluid is provided through the straight portions.