Patent Description:
Heat exchangers generally include a tubular vessel and a plurality of heating elements disposed inside the tubular vessel. Working fluid enters the tubular vessel at one longitudinal end and exits at the other longitudinal end. The working fluid is heated by the plurality of heating elements as the working fluid flows inside the tubular vessel. In fluid-to-fluid heat exchangers, the heating elements are tubes through which a heating fluid flows. The heat is transferred from the heating fluid to the working fluid via the walls of the tubes. In electric heat exchangers, the heating elements are electric heating elements (e.g., resistance heating elements).

<CIT> represents a document which reflects the closest prior art.

In order to more quickly and efficiently heat the working fluid, a typical heat exchanger may increase the total heat exchange area or increasing the heat flux of the heating elements, to increase the heat output. However, typical methods of increasing the total heat exchange area can take more space in the heat exchanger that could otherwise be used for containing the working fluid and typical methods of increasing the heat flux of the heating elements can be limited by the materials and design of the heating elements, as well as other application specific requirements.

In one form, a heater assembly is provided, which includes a continuous series of helical members and a plurality of heating elements. Each helical member defines opposed edges and a predetermined pattern of perforations extending through each helical member and parallel to a longitudinal axis of the heater assembly. The plurality of heating elements extend through the perforations (and in one form through all of the perforations) of the continuous series of helical members. The continuous series of helical members define a geometric helicoid.

In another form, an electric heat exchanger includes a body defining a cavity, a heater assembly disposed within the cavity, and a proximal flange configured to secure the heater assembly to the body. The heater assembly defines a longitudinal axis and includes a continuous series of helical members and a plurality of heating elements. Each helical member defines opposed edges and a predetermined pattern of perforations extending through each helical member and parallel to the longitudinal axis. The plurality of heating elements extend through the perforations of the continuous series of helical members. The continuous series of helical members define a geometric helicoid.

In still another form, in an electric heat exchanger, a device provides a consistent linear temperature rise along a length of the electric heat exchanger. The device includes a continuous series of helical members. Each helical member defines opposed edges and a predetermined pattern of perforations extending through each helical member and parallel to a longitudinal axis of the electric heat exchanger. The continuous series of helical members define a geometric helicoid and the perforations are configured to receive heating elements.

In one form, a heater assembly includes a continuous series of perforated helical members and a plurality of heating elements. The perforated helical members cooperate to define a geometric helicoid disposed about a longitudinal axis of the heater assembly. Each perforated helical member defines opposed edges and a predetermined pattern of perforations. The perforations extend through each perforated helical member parallel to the longitudinal axis. The heating elements extend through the perforations.

According to another form, each heating element includes a first segment, a second segment, and a bend connecting the first and second segments. The first segment extends through a first set of the perforations. The second segment extends through a second set of the perforations. The second set of the perforations are parallel to and offset from the first set of the perforations.

According to a further form, the plurality of heating elements are arranged in a concentric pattern.

According to yet another form, the heater assembly further includes a central support member. Each of the perforated helical members defines a central aperture and the central support member extends through the central aperture.

According to another form, the heater assembly further includes a temperature sensor that extends through an interior of the central support member, the temperature sensor including a probe external of the central support member.

According to another form, the heater assembly further includes a proximal flange configured to secure the heater assembly to a heat exchanger body. The flange defines a plurality of flange apertures and a central groove. The flange apertures are aligned with the perforations of the perforated helical members. The heating elements extend through the flange apertures. The central support member are received in the central groove.

According to another form, the heater assembly further includes a vent aperture providing fluid communication between an exterior of the central support member and an interior of the central support member proximate to the flange.

According to another form, the central support member includes at least one additional heater.

According to another form, the heater assembly further includes a non-perforated helical member disposed at a distal end of the continuous series of perforated helical members, the non-perforated helical member forming an extension of the geometric helicoid.

According to another form, each of the heating elements is secured to at least a portion of each perforation through which each heating element extends.

According to another form, the opposed edge from one helical member overlaps with the opposed edge from an adjacent helical member.

According to another form, the opposed edge from one helical member is spaced apart from the opposed edge from an adjacent helical member and connected thereto by a bridging member.

According to another form, the heater assembly further includes a plurality of rods extending parallel to the longitudinal axis. A periphery of each perforated helical member defines a plurality of grooves, and the rods are at least partially disposed within a corresponding set of the grooves.

According to another form, the rods extend outward from the grooves beyond the periphery of each perforated helical member. The heater assembly is configured to be received within a cylindrical cavity of a body and the rods are configured to provide sliding contact with a wall of the body that defines the cylindrical cavity.

According to another form, the heater assembly further includes a shroud disposed about at least one of the perforated helical members and coupled to the rods.

According to another form, the rods do not extend outward beyond the periphery of each perforated helical member.

According to another form, the shroud is a heat shield configured to reflect radiant energy radially inward relative to the longitudinal axis.

According to another form, the shroud includes at least one skirt defining a plurality of deformable flaps that extend radially outward relative to the longitudinal axis.

According to another form, the at least one skirt is disposed proximate to a proximal end portion or a distal end portion of the heater assembly.

According to another form, the at least one skirt includes a first skirt and a second skirt. The first skirt is disposed at a proximal end portion of the heater assembly and the second skirt is disposed at a distal end portion of the heater assembly.

According to another form, the continuous series of perforated helical members defines a variable pitch.

According to another form, the continuous series of perforated helical members has a longer pitch proximate to an inlet end of the heater assembly than an outlet end of the heater assembly.

According to another form, the heating elements are electrical resistance heating elements.

According to another form, the electrical resistance heating elements are one of the group of: a tubular heater, a cartridge heater, or a multi-cell heater.

According to another form, the plurality of heating elements includes a first heating element and a second heating element, the first heating element having a different length than the second heating element.

According to another form, the heater assembly further includes an alignment plate disposed coaxially about the longitudinal axis. The alignment plate defines a plurality of plate apertures that align with perforations of the perforated helical members.

In another form, a heat exchanger includes a body, a heater assembly, and a proximal flange. The body defines a cylindrical cavity. The heater assembly defines a longitudinal axis. The heater assembly includes a continuous series of perforated helical members and a plurality of heating elements. The perforated helical members are disposed within the cylindrical cavity and defines a geometric helicoid. Each perforated helical member defines opposed edges and a predetermined pattern of perforations extending through each perforated helical member and parallel to the longitudinal axis. The heating elements extend through the perforations of the perforated helical members. The proximal flange secures the heater assembly to the body.

According to another form, the heat exchanger further includes a plurality of rods extending longitudinally parallel to the longitudinal axis. A periphery of each perforated helical member defines a plurality of grooves, and the rods are partially disposed within a corresponding set of the grooves and have a thickness that extends radially outward of the periphery of the perforated helical members so that the rods are in sliding contact with an interior wall of the body that defines the cylindrical cavity.

According to another form, the heat exchanger further includes a skirt that includes elastically deformable flaps that extend radially between the perforated helical members and an interior wall of the body that defines the cylindrical cavity.

According to another form, the body includes an inlet at a proximal end of the cylindrical cavity and an outlet at a distal end of the cylindrical cavity. The heater assembly further includes a non-perforated helical member coupled to a last one of the continuous series of perforated helical members. The non-perforated helical member forms an extension of the geometric helicoid and begins along the geometric helicoid at or before the outlet.

According to another form, the non-perforated helical member has a pitch equal to a diameter of the outlet.

In another form, a heater assembly includes a continuous perforated helical baffle and a plurality of heating elements. The baffle defines a geometric helicoid about a longitudinal axis. The perforated helical baffle defines a predetermined pattern of perforations extending through the perforated helical baffle and parallel to the longitudinal axis. The heating elements extend through the perforations.

According to a further form, the geometric helicoid has a pitch that varies along the longitudinal axis.

According to a further form, the pitch is continuously variable.

Referring to <FIG>, a heater assembly <NUM> constructed in accordance with the teachings of the present disclosure is configured to be disposed inside a tubular body <NUM> or shell of a heat exchanger <NUM> (shown in <FIG>) to heat a working fluid flowing through the electric heat exchanger <NUM>. The heater assembly <NUM> may be mounted to the tubular body <NUM> of the heat exchanger <NUM> by a proximal end plate or mounting flange <NUM>. The heater assembly <NUM> includes a flow guiding device <NUM> and a plurality of heating elements <NUM> extending within and secured relative to the flow guiding device <NUM>. The heater assembly <NUM> defines a proximal end portion <NUM> and a distal end portion <NUM> that define a longitudinal axis X of the heater assembly <NUM>. The mounting flange <NUM> is disposed at the proximal end portion <NUM> of the heater assembly <NUM>. The plurality of heating elements <NUM> extend along the longitudinal axis X of the heater assembly <NUM>.

Referring to <FIG>, the flow guiding device <NUM> includes a plurality of perforated helical members <NUM> or helical baffles that are connected in a linear array along the longitudinal axis X of the heater assembly <NUM> to define a continuous geometric helicoid. The continuous geometric helicoid is such that each perforated helical member <NUM> defines a surface that follows a helical path about the longitudinal axis X. Optionally, the flow guiding device <NUM> further includes a helical end baffle or non-perforated helical member <NUM> disposed adjacent to the distal end portion <NUM> of the heater assembly <NUM> and connected to an adjacent perforated helical member <NUM> to form an extension of the continuous geometric helicoid. The plurality of perforated helical members <NUM> and the non-perforated helical member <NUM> define a continuous helical flow guiding channel <NUM> to guide the working fluid to flow therein and to create a helical flow within the tubular body <NUM> of the heat exchanger <NUM> (<FIG>).

Referring to <FIG>, the perforated helical members <NUM> each are in the form of a metal sheet that is bent to form one complete helical turn. While not shown in the drawings, it is understood that the metal sheet may be bent to form only a portion of one helical turn or more than one helical turn. The perforated helical members <NUM> each define opposed edges <NUM> and <NUM> and a predetermined pattern of perforations <NUM> extending through each perforated helical member <NUM>. An opposed edge <NUM> or <NUM> from one perforated helical member <NUM> can be welded to an opposed edge <NUM> or <NUM> from an adjacent perforated helical member <NUM>. In one form, as shown in <FIG>, the opposed edge <NUM> or <NUM> of one perforated helical member <NUM> can overlap an opposed edge <NUM> or <NUM> from the adjacent perforated helical member <NUM>. In the example shown in <FIG>, this overlap is equal to about <NUM> rotations to provide additional coverage. In another form, as shown in <FIG>, the opposed edge <NUM> or <NUM> from one perforated helical member <NUM> can abut and be welded to an opposed edge <NUM> or <NUM> from an adjacent perforated helical member <NUM> so that surfaces of the adjacent perforated helical members <NUM> form a continuous surface. In another example, not specifically shown, the opposed edge <NUM> or <NUM> from one perforated helical member <NUM> can be joined to the opposed edge <NUM> or <NUM> of the adjacent perforated helical member <NUM> by a bridging member (not shown). The bridging member can be helicoid in shape or can be another shape, such as extending a short distance in a circular manner for example.

Therefore, the perforated helical members <NUM> are connected along the longitudinal axis X of the heater assembly <NUM> to form a linear array (a continuous series) of the perforated helical members <NUM>. The perforations <NUM> in the plurality of perforated helical members <NUM> are aligned along a direction parallel to the longitudinal axis X of the heater assembly <NUM>, or normal to a radial direction, thus resulting in an angle relative to each face of the perforated helical members <NUM>. The non-perforated helical member <NUM> is connected to a distal end of the continuous series of perforated helical members <NUM>. The non-perforated helical member <NUM> is structurally similar to the perforated helical member <NUM>, but is not perforated.

Each of the perforated helical members <NUM> and the non-perforated helical member <NUM> has an inner peripheral edge <NUM>, which is contoured in a way such that when viewed in a direction parallel to the longitudinal axis X of the heater assembly <NUM>, the inner peripheral edge <NUM> defines a circular aperture <NUM> coaxial with the longitudinal axis X. In the example provided, the perforated helical members <NUM> each define a plurality of peripheral grooves <NUM> along the outer periphery of the perforated helical members <NUM>. Similarly, the non-perforated helical member <NUM> defines a plurality of peripheral grooves <NUM> along its outer periphery. The peripheral grooves <NUM> of the plurality of perforated helical members <NUM> (and the non-perforated helical member <NUM>) are also aligned along a direction parallel to the longitudinal axis X of the heater assembly <NUM>.

The helical pitch, the outer diameter of the perforated helical members <NUM>, the diameter of the central aperture <NUM> of the perforated helical members <NUM> and the thickness of the perforated helical members <NUM> may be properly selected depending on a desired flow rate and a desired flow volume of the working fluid. The number of the heating elements <NUM> and the number of the perforations <NUM> in the perforated helical member <NUM> may be properly selected depending on a desired heat output and heat efficiency.

Referring to <FIG>, the heater assembly <NUM> further includes a central support member <NUM> that extends through the central apertures <NUM> of the perforated helical members <NUM> and the non-perforated helical member <NUM> to connect the plurality of perforated helical members <NUM> and the non-perforated helical member <NUM> together and to provide structural support for the heater assembly <NUM>. The central support member <NUM> and the non-perforated helical member <NUM> may also be configured to provide additional heating to the working fluid. In one form, the central support member <NUM> is an additional heating element (e.g., an electric heating element). When also used as an additional heating element, the central support member <NUM> may include one or more electric resistance heating elements, such as a cartridge heater, a tubular heater or any conventional heater with an elongated configuration to provide both heating and structural support.

Referring to <FIG>, the plurality of heating elements <NUM> are inserted through the perforations <NUM>. Only a couple heating elements <NUM> are shown in <FIG> for clarity of illustration, but when fully assembled, all of the perforations <NUM> receive heating elements <NUM> therethrough, such that fluid travels along the helical flow guiding channel <NUM> and not through the perforations <NUM>. In the example provided, the plurality of heating elements <NUM> each have a tongs-like configuration and includes a pair of straight portions <NUM> extending through the perforations <NUM> of the perforated helical members <NUM>, and a bend portion <NUM> connecting the pair of straight portions <NUM>. The heating elements <NUM> may be any suitable type of heating element, such as electric resistance heating elements.

For example, electric tubular heaters, electric cartridge heaters, or multi-cell heaters can be used. When the heating elements <NUM> are electric heating elements, they can contain resistance heating elements (e.g., heating coils, not specifically shown) that can be disposed within the straight portions <NUM> and, when included, the bend portion <NUM>. In the example provided, an electric resistance heating coil can extend through the straight portions <NUM> and the bend portion <NUM> and have opposite leads (not specifically shown) extending from the proximal ends of respective straight portions <NUM>. With additional reference to <FIG>, one example of a cartridge-type heater is illustrated. In this example, the heating elements only include the straight portions <NUM>. Each straight portion <NUM> is terminated at the distal end and the heating element <NUM> does not bend to connect to two of the straight portions <NUM>. Instead, a resistance heating element (not shown) is disposed in each straight portion <NUM> and the electrical leads extend from the proximal end of each straight portion <NUM>.

Returning to <FIG>, each of the heating elements <NUM> is secured to at least a portion of each perforation <NUM> through which each heating element <NUM> extends. In the example provided, the heating elements <NUM> are secured by welding over approximately one-half of a periphery of each perforation <NUM> so that a weld joint <NUM> is formed along half periphery of the perforation <NUM>.

Referring to <FIG>, the working fluid is guided by the perforated helical members <NUM> in the flow guiding channel <NUM> to flow in a helical direction F and is continuously heated by the heating elements <NUM>. By using the flow guiding channel <NUM>, the working fluid can be guided to flow transversely across the heating surface of the heating elements <NUM>. Therefore, the working fluid can be more efficiently heated by the heating elements <NUM> within a predetermined length of the heat exchanger <NUM>, as opposed to a typical heat exchanger (not shown) where the working fluid flows in a direction parallel to the longitudinal axis X of the heat exchanger. Because the working fluid is properly guided to flow transversely across the heating surface of the heating elements <NUM>, a dead zone where the working fluid is not heated can be avoided. In traditional heat exchangers, not specifically shown, dead zones can lead to fouling in which the working fluid breaks down and causes material buildup and deposits on the heating elements. Accordingly, the heat exchangers of the present teachings can reduce fouling and increase heat transfer efficiency by increasing flow uniformity and decreasing the radiative heat loss to the shell or vessel (e.g., body <NUM> shown in <FIG>).

Referring to <FIG>, the heating elements <NUM> may be inserted into the perforations <NUM> in a way such that the bend portion <NUM> of the heating elements <NUM> form a concentric pattern around the central support member <NUM> (<FIG>), or to form a symmetric pattern relative to a diameter of the perforated helical member <NUM> (<FIG>). Between the configurations shown in <FIG>, a greater density of heating elements <NUM> can be fit in the same space using the concentric pattern, though other configurations and patterns can be used. Between the configurations shown in <FIG>, the concentric pattern generally has tighter bend radii connecting the straight portions <NUM>. Thus, the pattern can also be chosen based on design criteria, such as element density or bend radii. As best shown in <FIG>, the heating elements <NUM> can have different lengths, such that some of the heating elements <NUM> extend further along the longitudinal axis X than others. The length of the heating elements <NUM> can be based on their location relative to the non-perforated helical member <NUM>. In one configuration, the one or more of the heating elements <NUM> can be a first set of heating elements that all have a first length, while one or more different heating elements <NUM> can be a second set of heating elements that all have a second length that is different from the first length. In this example, the heating elements <NUM> are not limited to only two sets with only two lengths, and additional sets and lengths can be included.

Referring to <FIG> and <FIG>, the heater assembly <NUM> can further include a plurality of support rods <NUM> extending through the peripheral grooves <NUM> of the perforated helical members <NUM> and the non-perforated helical member <NUM> and parallel to the longitudinal axis X of the heater assembly <NUM>. The support rods <NUM> may extend outward (i.e., in the radial direction relative to the longitudinal axis X) beyond a periphery of the peripheral grooves <NUM> and may be configured as glide rods for installation of the heater assembly <NUM> into a cylindrical cavity <NUM> of the tubular body <NUM> of the heat exchanger <NUM> (<FIG>). In other words, the support rods <NUM> can reduce the direct surface contact between the heater assembly <NUM> and the inner wall of the tubular body <NUM> (<FIG>) to reduce friction and, thus, the force needed to slide the heater assembly <NUM> into the tubular body <NUM>. Alternatively, the support rods <NUM> may be configured to not extend beyond a periphery of the peripheral grooves <NUM> and merely function as a structural support for the heater assembly <NUM>. In the example provided, the support rods <NUM> are welded to the perforated helical members <NUM> and the non-perforated helical member <NUM>.

Referring back to <FIG>, the heater assembly <NUM> may further include a pair of shrouds <NUM> that are provided at the proximal end portion <NUM> and the distal end portion <NUM> for surrounding the perforated helical members <NUM>, the non-perforated helical member <NUM>, the heating elements <NUM>, and the support rods <NUM>. At the proximal end, the shroud <NUM> is generally located between an unheated portion <NUM> and a heated portion <NUM>. While <FIG> shows two shrouds <NUM>, any number of shrouds <NUM>, including one, may be provided to surround the perforated helical members <NUM>, the heating elements <NUM>, and the support rods <NUM>. When one shroud <NUM> is provided, the shroud <NUM> may be provided at the distal end portion <NUM> or the proximal end <NUM>.

Referring to <FIG>, the shrouds <NUM> can each define a cylindrical shroud member <NUM> and a plurality of deformable flaps <NUM> that form a skirt about the cylindrical shroud member <NUM>. The cylindrical shroud member <NUM> can wrap a portion of the perforated and/or non-perforated helical members <NUM>, <NUM>. In the example provided, each cylindrical shroud member <NUM> extends along the longitudinal axis X a length that is at least one full helical pitch of the corresponding perforated or non-perforated helical members <NUM>, <NUM> that it surrounds. The deformable flaps <NUM> are generally formed by cutting a radially outward flanged portion of the shroud <NUM> such that the flaps <NUM> can extend radially outward from the cylindrical shroud member <NUM>. Contact with the inner wall of the tubular body <NUM> can elastically deform the flaps <NUM> such that the flaps <NUM> are biased into contact with the inner wall of the tubular body <NUM> to inhibit flow from escaping between the tubular body <NUM> of the heat exchanger <NUM>, thus mitigating blow-by. In the example provided, the flaps <NUM> of the distal shroud <NUM> shown in <FIG> can be positioned axially near the distal end of the heater assembly <NUM>, such as just before an outlet <NUM> of the tubular body <NUM> of the heat exchanger <NUM>. For example, the flaps <NUM> of the distal shroud <NUM> can be positioned approximately at dashed line <NUM> shown in <FIG> before the outlet <NUM> of the tubular body <NUM>. In the example provided, the flaps <NUM> of the proximal shroud <NUM> shown in <FIG> can be positioned axially near the start of the perforated helical members <NUM> such as after an inlet <NUM> of the tubular body <NUM>. For example, the flaps <NUM> of the proximal shroud <NUM> can be positioned approximately at dashed line <NUM> shown in <FIG> after the inlet <NUM> of the tubular body <NUM>.

Referring to <FIG>, the proximal mounting flange <NUM> is configured to secure the heater assembly <NUM> to a tubular body <NUM> of the heat exchanger <NUM>. The proximal mounting flange <NUM> includes a plate body <NUM>, a plurality of apertures <NUM> and a plurality of bolt holes <NUM> through the plate body <NUM>. The plurality of apertures <NUM> are aligned with the perforations <NUM> of the continuous series of perforated helical members <NUM> and are configured to route the plurality of heating elements <NUM> through the proximal mounting flange <NUM>. While not specifically shown, the heating elements <NUM> can be sealed to the apertures <NUM> so that fluid is prevented from flowing through the apertures <NUM>. The plurality of bolt holes <NUM> are defined along the periphery of the plate body <NUM>. The proximal mounting flange <NUM> may be mounted to the tubular body <NUM> of the heat exchanger by inserting bolts (not shown) into the bolt holes <NUM> and through bolt holes in a mating flange (e.g., mating flange <NUM> shown in <FIG>) of the tubular body <NUM>. A gasket (not shown) or other sealing material can be used to form a fluid-tight seal between the mounting flange <NUM> and the mating flange (e.g., flange <NUM> shown in <FIG>). In another configuration, not shown, the end plate or mounting flange <NUM> can be mechanically attached to the mating flange by a different manner, such as welding, latches, clamps, etc..

The proximal mounting flange <NUM> can further define a circular central recess or groove <NUM> configured to align the central support member <NUM>. The central groove <NUM> is coaxial with the longitudinal axis X and a proximal end of the central support member <NUM> is configured to be received in the central groove <NUM>. In the example provided, the central support member <NUM> is welded to the proximal mounting flange <NUM>.

Referring to <FIG>, the heat exchanger <NUM> configured in accordance with the teachings of the present disclosure includes the tubular body or shell <NUM> defining the cylindrical cavity <NUM>, the inlet <NUM>, the outlet <NUM>, and a heater assembly <NUM> disposed inside the tubular body <NUM>. The heater assembly <NUM> defines a proximal end portion <NUM> and a distal end portion <NUM>. A proximal mounting flange <NUM> is configured to secure the heater assembly <NUM> to the body <NUM>.

The heater assembly <NUM> is structurally similar to that of <FIG> except that the continuous series of perforated helical members <NUM> and the non-perforated helical member <NUM> are connected in a way such that the helicoid defined by the perforated helical members <NUM> and the non-perforated helical member <NUM> has a variable pitch. Therefore, like elements are indicated by like reference numbers and the detailed description thereof is omitted herein for clarity. In the example provided, the outlet <NUM> is a radial outlet such that it is open to the flow path <NUM> through the radial direction. In an alternative configuration, not specifically shown, the outlet <NUM> can be an axial end outlet that is open through an axial end <NUM> of the body <NUM>.

Returning to the example provided, the helicoid defined by the perforated helical members <NUM> and the non-perforated helical member <NUM> may have a pitch which is the largest at the proximal end portion <NUM> (near the inlet <NUM> of the heat exchanger <NUM>) and the smallest at the distal end portion <NUM> (near the outlet <NUM> of the heat exchanger <NUM>). In one form, the pitch is a continuously varying pitch with the pitch gradually decreasing from the proximal end portion <NUM> to the distal end portion <NUM>. Alternatively, as shown in <FIG>, the heater assembly <NUM> may define a plurality of zones along the longitudinal axis X of the heater assembly <NUM>. The pitch can be fixed within a particular zone, while different zones can have different pitches. For example, the heater assembly <NUM> may define three heating zones with a first fixed pitch P1 in the first zone, a second fixed pitch P2 in the second zone, and a third fixed pitch P3 in the third zone. The second fixed pitch P2 is larger than the third fixed pitch P3 and smaller than the first fixed pitch P1. The first pitch P1 is located at the proximal end portion <NUM>. The third pitch P3 is located at the distal end portion <NUM>. The second pitch P2 is located between the first and third pitches P1, P3. While three zones are illustrated, more or fewer zones can be used. In one form, each perforated helical member <NUM>, or a group of perforated helical members <NUM>, can have a constant helical pitch along its particular length, while different perforated helical members <NUM>, or a different group thereof, can have a different pitch to form a variable pitch geometric helicoid.

In an alternative configuration, not specifically shown, the perforated helicoid can be formed, not from individual members connected together, but from a single continuous helicoid member spanning from the proximal end to the distal end of the heater assembly. For example, the single helicoid member can be extruded, formed by feeding strip stock sheet metal through opposing conical dies, or 3D printed.

Referring to <FIG>, a diagram shows a temperature distribution of the heating elements <NUM> along the longitudinal axis X for one particular configuration of the heater assembly <NUM>, <NUM>. The temperature of the portions of the heating elements <NUM> that are adjacent to the proximal end portion of the heater assembly is approximately <NUM> in the particular example. As the working fluid is guided by the flow guiding channel <NUM> of the perforated helical members <NUM> and flows to the distal end portion of the heater assembly <NUM>, <NUM>, the temperature gradually increases to approximately <NUM> in the example provided. While the example provided in <FIG> illustrates a temperature distribution for one particular inlet temperature, electric power load to the heating elements <NUM>, and mass flow rate of the fluid, other temperatures and distributions can result from different conditions or configurations. In general, a heater assembly constructed in accordance with the teachings of the present disclosure will have reduced heating element temperature without dead zones where the working fluid would not heated along its flow path.

Referring to <FIG>, a graph shows a relationship between the distance from the proximal mounting flange <NUM> and the heating element <NUM> temperature. The proximal mounting flange <NUM> is disposed proximate an inlet <NUM> of the heat exchanger <NUM>. As the working fluid enters the inlet <NUM> and flows away from the proximal mounting flange <NUM>, the temperature of the outer surfaces of the heating elements <NUM> steadily and gradually increases, as shown by line <NUM>. In contrast, the outer surfaces of the heating elements of a typical heat exchanger (not shown) have a higher temperature that also increases and decreases as the fluid flows away from the proximal flange (i.e., from the inlet to the outlet), as shown by line <NUM>. Accordingly, the teachings of the present disclosure provide a heater assembly and heat exchanger that provide for a consistent and lower linear temperature rise of the heating elements along a length of the heat exchanger.

The heater assembly of the present disclosure is applicable to any heating device (e.g., electric heating device) to heat a working fluid. The continuous series of the perforated helical members <NUM> guide the fluid to create a uniform helical cross flow pattern. The helical channel <NUM> of the heater assembly <NUM>, <NUM> can change and increases the flow path of the working fluid without increasing the length of the heater assembly <NUM>, <NUM>. Therefore, the heater assembly <NUM>, <NUM> can improve heat transfer from the heater assembly <NUM>, <NUM> to the working fluid. With the increased heat transfer efficiency, the sheath temperature of the heating elements <NUM> and the temperature of the shell (e.g., tubular body <NUM>) of the heat exchanger can be reduced, and the physical footprint of the heat exchanger can be reduced.

Moreover, the perforated helical members <NUM> can be formed of a thermally conductive material. Since the perforated helical members <NUM> may be connected to the heating elements <NUM> (e.g., via welds <NUM> shown in <FIG>), they may be considered to be an extension of the heating elements <NUM> to function as extended heating surfaces or heat spreaders or fins to distribute the heat to the working fluid, thereby increasing heat transfer from the heating elements <NUM> to the working fluid. The central support member <NUM> may take the form of a cylindrical electric heating device to provide additional heating to the working fluid in the electric heat exchanger.

Furthermore, the heater assembly <NUM>, <NUM> is more rigid than that in a conventional heat exchanger due to the use of the continuous series of the perforated helical members <NUM> and the use of the central support member <NUM>. The central support member <NUM> is connected to the proximal mounting flange <NUM>, which in turn, is connected to the body of the heat exchanger. This continuous structure improves the vibrational characteristics of the heat exchanger, thereby increasing rigidity and dampening characteristics of the heater assembly. The support rods <NUM> can further increase rigidity and damping characteristics.

With additional reference to <FIG>, a heater assembly <NUM>, and <FIG>, a heat exchanger <NUM> with the heater assembly <NUM>, are illustrated. The heat exchanger <NUM> and the heater assembly <NUM> are similar to the heat exchanger <NUM> and the heater assembly <NUM>, <NUM>, except as otherwise shown or described herein. Therefore, like elements are indicated by like reference numbers and the detailed description thereof is omitted herein for clarity.

With reference to <FIG>, the heater assembly <NUM> can include a first lift member <NUM> and a second lift member <NUM>. The first lift member <NUM> is fixedly coupled to a periphery of the mounting flange <NUM>. In the example provided, the first lift member <NUM> extends from the top of the mounting flange <NUM> and defines an aperture <NUM>, through which a hook (not shown) or other lifting device can support the proximal end of the heater assembly <NUM>. The second lift member <NUM> is fixedly coupled to the distal end of the central support member <NUM>. In the example provided, the second lift member <NUM> extends from the top of the central support member <NUM> and is aligned with the first lift member <NUM>. The second lift member <NUM> defines an aperture <NUM>, through which a hook (not shown) or other lifting device can support the distal end of the heater assembly <NUM>. In the example provided, the second lift member <NUM> is disposed within the axial length of the non-perforated helical member <NUM>, though the second lift member <NUM> can be beyond the non-perforated helical member <NUM>. The first and second lift members <NUM>, <NUM> can be used to lift heater assembly <NUM> and position the heater assembly <NUM> in the tubular body <NUM> of the heat exchanger <NUM>.

The heater assembly <NUM> can further include a shroud <NUM>. The shroud <NUM> wraps around the perforated helical members <NUM>, the heating elements <NUM>, and the support rods <NUM>. The shroud <NUM> can be an axial length such that is extends along the entire length of the heated portion of the heater assembly <NUM> (e.g., including the shrouds <NUM> shown in <FIG>), or a length that is less than the entire heated portion. With additional reference to <FIG>, the shroud <NUM> can include a plurality of thin walled cylindrical shroud members <NUM>. The shroud members <NUM> can inhibit blow-by between the perforated helical members <NUM> and the tubular body <NUM>. The shroud members <NUM> can also be formed from or coated in a heat reflective material to form a heat shield that reflects heat radially inward toward the longitudinal axis X. Such a heat shield can further decrease heat loss to the body <NUM> and decrease the temperature of the body <NUM>. Adjacent cylindrical shroud members <NUM> can abut each other along the longitudinal axis X. In one form, any of the cylindrical shroud members <NUM> of the shroud <NUM> can optionally include the deformable flaps <NUM> (<FIG>) such that the shroud <NUM> can also function similar to the shrouds <NUM> (<FIG>, <FIG>).

In the example provided, the support rods <NUM> have a generally rectangular or cross-sectional shape and an outer surface <NUM> each support rod <NUM> is flush with the outer perimeter of the perforated and non-perforated helical members <NUM>, <NUM>. In one form, the outer surface <NUM> of each support rod <NUM> can have a curvature that matches the curvature of the outer perimeter of the perforated and non-perforated helical members <NUM>, <NUM>. The shroud <NUM> is attached to the support rods <NUM>. In the example provided, the support rods <NUM> include a plurality of bores <NUM> and each cylindrical shroud member <NUM> includes a plurality of bores <NUM> that are aligned with the bores <NUM> of the support rods <NUM>. Fasteners <NUM> (e.g., rivets, screws, etc.) or plug welds are received through the bores <NUM>, <NUM> and attach the cylindrical shroud members <NUM> to the support rods <NUM>.

With additional reference to <FIG>, the heater assembly <NUM> can further include an alignment plate <NUM>. The alignment plate <NUM> is a flat, circular disc that includes a plurality of apertures <NUM> and peripheral grooves <NUM>. The apertures <NUM> are the same size as and align with the perforations <NUM> of the perforated helical members <NUM>. The peripheral grooves <NUM> are the same size as and align with the peripheral grooves <NUM>. The support rods <NUM> are received in the peripheral grooves <NUM> similar to the peripheral grooves <NUM>. In the example provided, the alignment plate <NUM> defines a keyed center hole <NUM> having a diameter similar to the diameter of the central support member <NUM> and a key <NUM> that extends radially inward. In the example provided, the central support member <NUM> includes a key slot <NUM> that is open through the distal end of the central support member <NUM>. The key slot <NUM> extends through the wall of the central support member <NUM> and extends longitudinally parallel to the longitudinal axis X. The key slot <NUM> has a width in the circumferential direction of the central support member <NUM> that corresponds to the width of the key <NUM>. The central support member <NUM> is received through the center hole <NUM> and the key <NUM> is received in the key slot <NUM> to inhibit rotation of the alignment plate <NUM> relative to the central support member <NUM>. In one form, the center hole <NUM> can include more than one key <NUM>, spaced circumferentially about the center hole <NUM> and the central support member <NUM> can include a matching number of key slots <NUM>.

With continued reference to <FIG>, the heater assembly <NUM> can further include one or more sensors (e.g., sensor <NUM>). In the example provided, the sensor <NUM> is a thermocouple or other temperature sensor, though other types of sensors can be used. The sensor <NUM> includes a probe end <NUM> that is disposed within the flow guiding channel <NUM>. In the example provided, the probe end <NUM> is disposed proximate to the outlet <NUM> (<FIG> and <FIG>) and attached (e.g., welded or clamped) to one of the heating elements <NUM>. The probe end <NUM> can be configured to detect a temperature of the heating element <NUM> to which it is attached. Similarly, additional sensors (not shown) can be attached to other the heating elements <NUM> to detect their temperatures. In an alternative configuration, not shown, the probe end <NUM> can be separate from the heating elements <NUM> and configured to detect the temperature of the working fluid at the probe end <NUM>.

The sensor <NUM> extends longitudinally from the probe end <NUM> generally along the longitudinal axis X on the outer side of the central support member <NUM> toward the distal end of the central support member <NUM>. In the example provided, the distal end of the central support member <NUM> includes a sensor slot <NUM> through the outer wall of the central support member <NUM> and separate from the key slot <NUM>. The sensor <NUM> has bends to extend through the sensor slot <NUM> and into the interior cavity of the central support member <NUM>. The sensor <NUM> then extends within the central support member <NUM> toward the proximal end of the central support member <NUM>. With additional reference to <FIG>, the sensor <NUM> extends through a bore <NUM> in the mounting flange <NUM>. The bore <NUM> is sealed around the sensor <NUM> to inhibit fluid flow through the bore <NUM>. The bore <NUM> is radially inward of the groove <NUM>. In this way, the electronic connections for the sensor <NUM> can be on the back side of the mounting flange <NUM>, along with electrical connections of the heating elements <NUM> when electrical heating elements are used.

In an alternative configuration, not shown, one aligned set of the perforations <NUM> can not have a heating element <NUM> and the temperature sensor <NUM> can extend through that set of perforations <NUM> and the corresponding flange aperture <NUM>. In such a construction, the probe can be disposed at any desired location along the longitudinal axis X. In an alternative configuration, one or more heating elements <NUM> can be used as a virtual sensor to detect temperature.

With additional reference to <FIG>, a vent aperture <NUM> can permit a small amount of fluid communication between the exterior and interior of the proximal end of the central support member <NUM>. In the example provided, the central support member has a slot through the proximal end that cooperates with the mounting flange <NUM> to define the vent aperture <NUM> when the central support member <NUM> is received in the groove <NUM> of the mounting flange <NUM>. Unlike the groove <NUM> of <FIG>, the groove <NUM> of <FIG> is an incomplete circle (i.e., does not extend a full circumference about the longitudinal axis X). Instead, the groove <NUM> has a start <NUM> and an end <NUM> that align with the slot in the proximal end of the central support member <NUM>. In the example provided, the groove <NUM> has a flat bottom that abuts a flat bottom surface of the central support member <NUM>. The start <NUM> and end <NUM> also form a key that ensures proper rotational alignment of the central support member <NUM>. In the example provided, the keys between the central support member <NUM> and the mounting flange <NUM> and the alignment plate <NUM> cooperate to position the continuous helicoid in the correct rotational position so that the perforations <NUM> align with the apertures <NUM> and <NUM>. In the example provided, the keys at both ends of the central support member <NUM> are aligned along the same line that is parallel to the longitudinal axis X, though other configurations can be used. In the example provided, the groove <NUM> also extends a small distance radially outward at the start <NUM> and end <NUM> of the groove <NUM>. In the example provided, the central support member <NUM> is welded to the mounting flange <NUM> from the start <NUM> to the end <NUM> of the groove <NUM>. In other words, the central support member <NUM> is welded about its circumference except for the circumferential region where the slot defines the vent aperture <NUM>. The vent aperture <NUM> can be aligned with the top of the mounting flange <NUM>. In another form, the vent aperture <NUM> can be a hole defined entirely by the central support member <NUM> near the proximal end.

With specific reference to <FIG>, the edge <NUM> of the first perforated helical member <NUM> (i.e., near the proximal end) can be disposed along the longitudinal axis X at or before the inlet <NUM> such that flow from the inlet enters the flow path <NUM>. With specific reference to <FIG>, the opposed edge <NUM> of the last perforated helical member <NUM> (i.e., near the distal end) can be disposed along the longitudinal axis X at or before the outlet <NUM>. In the example provided, the longest ones of the heating elements <NUM> extend along the longitudinal axis X to a position that is partially within the region aligned with the outlet <NUM>, though other configurations can be used. In the example provided, the last cylindrical shroud member <NUM> can extend along the longitudinal axis X to overlap axially with the ends of the longest ones of the heating elements <NUM>, to force the fluid to flow from the last heating elements <NUM> to the non-perforated helical member <NUM> before exiting from the outlet <NUM>, though other configurations can be used.

With additional reference to <FIG>, a portion of a heater assembly <NUM> of a third construction is illustrated. The heater assembly <NUM> is similar to the heater assembly <NUM>, <NUM>, or <NUM> except as otherwise shown or described herein. Therefore, like elements are indicated by like reference numbers and the detailed descriptions thereof are not repeated herein. In the example provided, the heating elements <NUM> are straight elements that terminate at a closed end <NUM>. In other words, the straight portions <NUM> are not connected by bent portions. In the example provided, the heating elements <NUM> are electric resistance heating elements such as cartridge heaters that have all of their leads or terminal pins <NUM>, <NUM> (<FIG>) extending from the same straight portion <NUM> on the opposite side of the mounting flange <NUM> (shown in <FIG>).

With additional reference to <FIG>, a portion of a heater assembly <NUM> of a fourth construction is illustrated. The heater assembly <NUM> is similar to the heater assemblies <NUM>, <NUM>, and <NUM> except as otherwise shown or described herein. Therefore, like elements are indicated by like reference numbers and the detailed descriptions thereof are not repeated herein.

In the heater assembly <NUM>, at least some of the heating elements <NUM> do not extend far enough in the longitudinal direction <NUM> to fully span the helical flow guiding channel <NUM> defined between the last perforated baffle <NUM> and the non-perforated baffle <NUM>.

In the example provided, the heating elements <NUM> include a first group <NUM> of heating elements <NUM> of a first length and a second group <NUM> of heating elements <NUM> of a second, longer length, though more groups of distinct lengths can be used. The heating elements <NUM> of the longer second group <NUM> terminate farther downstream along the helical flow guiding channel <NUM> than the heating elements <NUM> of the shorter first group <NUM>.

In the example provided, the heating elements <NUM> have a pair of straight portions <NUM> that terminate in the longitudinal direction <NUM> at a bend portion <NUM>. In an alternative configuration, similar to <FIG>, the heating elements <NUM> can have a single straight portion <NUM> and terminate at an end <NUM> (<FIG>).

In the example provided, the bend portions <NUM> of some of the heating elements <NUM> align in the longitudinal direction <NUM> with the inlet/outlet <NUM>, though other configurations can be used. In one alternative configuration, not specifically shown, all of the heating elements <NUM> can terminate in the longitudinal direction <NUM> before the inlet/outlet <NUM>.

In other alternative configurations, the non-perforated baffle <NUM> can be omitted. <FIG> illustrate one such configuration where the non-perforated baffle <NUM> is not included. In this example, some of the heating elements extend farther in the longitudinal direction <NUM> than others, similar to <FIG>. As a result of the location of the inlet/outlet <NUM> relative to the end of the last perforated baffle <NUM> and the ends of the heating elements <NUM>, low pressure or low fluid flow regions can develop, schematically indicated by the regions circled in dashed lines indicated by reference numeral <NUM>. In this configuration, the heating elements <NUM> have lower watt density regions (e.g., regions <NUM> and <NUM> described in detail below with reference to <FIG>) in the regions of low pressure or flow <NUM>.

<FIG> illustrate another such configuration where the non-perforated baffle <NUM> is omitted. In this example, all of the heating elements <NUM> terminate at the same position in the longitudinal direction <NUM>. In this configuration, the heating elements <NUM> have lower watt density regions (e.g., regions <NUM> and <NUM> described in detail below with reference to <FIG>) in the regions of low pressure or flow <NUM>.

In still another configuration, not specifically shown, the non-perforated baffle <NUM> can be omitted and some or all of the heating elements <NUM> can terminate in the longitudinal direction <NUM> after the inlet/outlet <NUM>.

Returning to <FIG>, while the non-perforated baffle <NUM> is illustrated as having a pitch of approximately half the diameter of the inlet/outlet <NUM>, other configurations can be used. In one form, the non-perforated baffle <NUM> can have a pitch equal to or approximately equal to the diameter of the inlet/outlet <NUM>. In another form, the non-perforated baffle <NUM> can have a pitch greater than or less than half the diameter of the inlet/outlet <NUM>. The pitch of the perforated baffles <NUM> can be the same as the pitch of the non-perforated baffle <NUM> or the pitches can be different. The pitch of the perforated baffles <NUM> can be constant along the length of the heater <NUM> or can change along the length (e.g., as described above with reference to <FIG>).

In the example provided, the heating elements <NUM> have a non-uniform heating profile along their longitudinal length. Specifically, an end portion <NUM> of at least some of the heating elements <NUM> has a lower watt density than the remainder of the heating element <NUM>. The end portion <NUM> includes the bend portion <NUM> and, optionally, some of each straight portion <NUM> proximate the bend portion <NUM>.

Specifically, where the heating elements <NUM> do not extend far enough in the longitudinal direction <NUM> to fully span the helical flow guiding channel <NUM> defined between the last perforated baffle <NUM> and the non-perforated baffle <NUM>, more of the fluid flowing along the helical flow guiding channel <NUM> will tend to flow in the space not impeded by the heating elements <NUM>. Accordingly, less heat is able to be removed from the heating elements <NUM> in the end portions <NUM> that do not fill the entire helical flow guiding channel <NUM>. The lower watt density at the end portions <NUM> can inhibit overheating that may otherwise occur due to the decreased flow over the end portions <NUM>.

In one form, the length in the longitudinal direction <NUM> of the lower watt density end portions <NUM> can be the same for all heating elements <NUM>. In another form, the length in the longitudinal direction <NUM> of the lower watt density end portions <NUM> can be different depending on the position of the heating element <NUM> in the helical flow guiding channel <NUM>. For example, each heating element <NUM> may be constructed such that the lower watt density end portion <NUM> is only as long as the portion of that heating element <NUM> that extends beyond the last perforated baffle <NUM>.

In the example illustrated, the lower watt density end portions <NUM> of some of the heating elements <NUM> align in the longitudinal direction with the inlet/outlet <NUM>, though other configurations can be used.

With reference to <FIG>, a partial cross-sectional view of one of the heating elements <NUM> of <FIG> is illustrated. The heating element <NUM> includes an electrical resistance element <NUM>, an insulating material <NUM>, and a sheath <NUM>. The sheath <NUM> surrounds the electrical resistance element <NUM> and the insulating material <NUM> is disposed between the electrical resistance element <NUM> and the sheath <NUM> to electrically insulate the sheath <NUM> from the electrical resistance element <NUM>. The insulating material <NUM> is a material that conducts heat to permit heat transfer from the electrical resistance element <NUM> to the sheath <NUM>, such as magnesium oxide (MgO) for example.

In the example provided, the electrical resistance element <NUM> includes a high resistance region <NUM> and a low resistance region <NUM>. The low resistance region <NUM> corresponds to the end portion <NUM> of the electrical resistance heating element <NUM>. In the example provided, the last perforated baffle <NUM> is schematically illustrated by a dashed line. In the example provided, the low resistance region <NUM> is located predominantly downstream of the last perforated baffle <NUM>, though other configurations can be used.

In the example provided, the high resistance region <NUM> includes a resistance wire coil <NUM> in each straight portion <NUM> and the low resistance region <NUM> is a metal pin <NUM> having high conductivity (i.e., low resistance) such that current flowing through the pin <NUM> heats up the low resistance region <NUM> significantly less than current flowing through the coil <NUM> of the high resistance region <NUM>. For example, the heat produced in the low resistance region <NUM> may be negligible compared to the heat produced by the high resistance region <NUM>. In another form, the heat produced by the low resistance region <NUM> can be more than negligible but still be less than the heat produced by the high resistance region <NUM>.

In one form, the pin <NUM> is a solid piece of conductive material (e.g., metal) that curves around the bend <NUM> to connect the resistance coils <NUM> in the straight portions <NUM>. In one form, the pin <NUM> may be a solid wire of a larger diameter than the resistance wire coil <NUM>. In another form, the pin <NUM> may be a flat metal plate of low resistance. The low resistance region <NUM> can be formed of the same material as the high resistance region <NUM>.

In an alternative form, the low resistance region <NUM> may be a different material than the high resistance region <NUM> such that the low resistance region <NUM> is formed of a material with a lower electrical resistance (i.e., higher conductivity) than the high resistance region <NUM>. In the configuration where a different material is used, the low resistance region <NUM> may optionally also have a coil shape similar to the high resistance region <NUM> but less heat is produced due to the lower resistance material.

Referring to <FIG>, an alternative construction of a heating element <NUM> is illustrated for use in the heater assembly <NUM> (<FIG>). The heating element <NUM> is similar to the heating element <NUM> (<FIG>) except as otherwise shown and described herein. In addition to the high resistance region <NUM> and the low resistance region <NUM>, the electrical resistance element <NUM> of the heating element <NUM> also includes an intermediate resistance region <NUM>. The intermediate resistance region <NUM> is between the low resistance region <NUM> and the high resistance region <NUM>. The intermediate resistance region <NUM> can have a watt density that is between the high resistance region <NUM> and the low resistance region <NUM>. In the example provided, the intermediate resistance region <NUM> is a coil <NUM> that is a continuation of the resistance wire coil <NUM> of the high resistance region <NUM> except that the pitch of the coil <NUM> in the intermediate resistance region <NUM> is longer than the pitch in the high resistance region <NUM>, though other configurations can be used to achieve an intermediate watt density. In the example provided, the pitch of the coil <NUM> is constant in the intermediate resistance region <NUM>. In an alternative configuration, the pitch of the coil <NUM> in the intermediate resistance region <NUM> can change. In one example, not specifically shown, the pitch of the coil <NUM> and/or the coil <NUM> may increase with proximity to the low resistance region <NUM>. In the example provided, the low resistance region <NUM> is located downstream of the last perforated baffle <NUM> and the intermediate resistance region <NUM> is also predominantly located in downstream of the last perforated baffle <NUM>, though other configurations can be used.

Referring to <FIG>, an alternative construction of a heating element <NUM> is illustrated for use in the heater assembly <NUM> (<FIG>). The heating element <NUM> is similar to the heating elements <NUM> (<FIG>) and <NUM> (<FIG>) except as otherwise shown and described herein. In the example provided, the low resistance region <NUM> is a coil <NUM> that is a continuation of the resistance wire coil <NUM> of the high resistance region <NUM> except that the pitch of the coil <NUM> is longer in the low resistance region <NUM> than the coil <NUM> of the high resistance region <NUM>. In one form, the pitch of the coil <NUM> is constant in the low resistance region <NUM>. In an alternative configuration, the pitch of the coil <NUM> in the low resistance region <NUM> can change. In one example, the pitch may increase with proximity to the bend <NUM>. In the example provided, the low resistance region <NUM> is located predominantly downstream of the last perforated baffle <NUM>, though other configurations can be used.

In the forms described above as having two straight portions <NUM> per heating element (e.g., <FIG>), the ends of each straight portion <NUM> opposite the bend <NUM> includes a lead or terminal pin <NUM>, <NUM> (<FIG>) on an opposite side of the flange <NUM> (<FIG>) to receive electrical power.

Referring to <FIG>, an alternative construction of a heating element <NUM> is illustrated for use in the heater assembly <NUM> (<FIG>). The heating element <NUM> is similar to the heating elements <NUM> (<FIG>) and <FIG> (<FIG>) except as otherwise shown and described herein. In the example provided, the heating element <NUM> includes a single straight portion <NUM> and lacks the bend portion <NUM> (<FIG>). The low resistance region <NUM> includes a pin <NUM> similar to that shown in <FIG> but being straight instead of going around the bend <NUM>. In the example provided, the low resistance region <NUM> is located predominantly downstream of the last perforated baffle <NUM>, though other configurations can be used.

Referring to <FIG>, an alternative construction of a heating element <NUM> is illustrated for use in the heater assembly <NUM>. The heating element <NUM> is similar to the heating elements <NUM> (<FIG>) and <NUM> (<FIG>) except as otherwise shown and described herein. In the example provided, the heating element <NUM> includes a single straight portion <NUM> and lacks the bend portion <NUM>. The low resistance region <NUM> includes a pin <NUM> similar to that shown in <FIG> but being straight instead of going around the bend <NUM> and the intermediate resistance portion <NUM> connects the low resistance portion <NUM> to the high resistance portion <NUM> similar to <FIG>. In the example provided, the low resistance region <NUM> is located downstream of the last perforated baffle <NUM> and the intermediate resistance region <NUM> is located predominantly downstream of the last perforated baffle <NUM>, though other configurations can be used.

Referring to <FIG>, an alternative construction of a heating element <NUM> is illustrated for use in the heater assembly <NUM> (<FIG>). The heating element <NUM> is similar to the heating elements <NUM> (<FIG>) and <NUM> (<FIG>) except as otherwise shown and described herein. In the example provided, the heating element <NUM> includes a single straight portion <NUM> and lacks the bend portion <NUM>. The low resistance region <NUM> includes a longer pitch coil <NUM> similar to that shown in <FIG> but being straight instead of going around the bend <NUM>. In the example provided, the low resistance region <NUM> is located predominantly downstream of the last perforated baffle <NUM>, though other configurations can be used.

In the forms described above with reference to <FIG>, in which a single straight portion <NUM> ends at a terminal end <NUM> instead of a bend <NUM>, one or more additional lengths of coil (not shown) or a straight wire (not shown) can extend from the pin <NUM> (or the end of coil <NUM> in the form shown in <FIG>), back in the direction opposite the longitudinal direction <NUM> (<FIG>) within the sheath to complete the circuit so that each heating element <NUM>, <NUM>, <NUM>, has a pair of terminal pins <NUM>, <NUM> (shown in <FIG>) proximate the flange <NUM> (<FIG>) to receive electrical power. For example, the coil <NUM> can terminate at a second coil (not shown) can be parallel to the coil <NUM> (and either coil <NUM> in the form shown in <FIG>, or coil <NUM> in the form shown in <FIG>).

In an alternative construction, not specifically shown, a third coil can be parallel to the first two coils and have a corresponding third terminal pin extending from the straight portion <NUM> such that three phase power can be used.

While the low resistance region <NUM> and/or the intermediate resistance region <NUM> is described above as being located at the end portions <NUM> of the heating elements <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, the low resistance region <NUM> and/or the intermediate resistance region <NUM> can be located elsewhere along the length of the heating elements <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. For example, the low resistance region <NUM> and/or the intermediate resistance region <NUM> can be aligned in the longitudinal direction <NUM> with the inlet/outlet <NUM> (<FIG> and <FIG>) or at a different location between the inlet/outlet <NUM> and the inlet/outlet <NUM>.

It should be understood that the heating elements described herein can be constructed using generally known techniques and constructions, except as otherwise described or shown herein. As a non-limiting example, the teachings of the following U. Patents can be used <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>.

Claim 1:
A heater assembly comprising:
a flow guide (<NUM>) defining a continuous geometric helicoid (<NUM>) disposed about a longitudinal axis of the heater assembly, the flow guide defining a predetermined pattern of perforations (<NUM>) that extend in a longitudinal direction through a first longitudinal length of the geometric helicoid, the longitudinal direction being parallel to the longitudinal axis; and
a plurality of electrical resistance heating elements (<NUM>) extending through the perforations, characterized in that at least one electrical resistance heating element of the plurality of electrical resistance heating elements has a first region (<NUM>) with a first watt density and a second region (<NUM>) with a second watt density, the second region being located farther in the longitudinal direction than the first region, the second watt density being less than the first watt density.