Cylindrical heat exchanger

#This invention relates generally to heat exchangers, and more particularly to a cylindrical heat exchanger member designed to be used in, for example, a commercial boiler/water heater. Boilers/water heaters in general are well known in the art, as are cylindrical heat exchanger members. In the context of heat exchangers, the term “cylindrical” denotes the general overall shape of the heat exchanger member.

#Early heat exchanger members have been configured from straight tubular members arranged in adjacent rows, forming a generally “flat” rectangular member. Water, typically, is circulated through the tubular members where it is heated, such as by a burner located in close proximity to the tubular members. The heated water is then circulated downstream for use elsewhere in the heating system. As requirements for heating capacity increased, cylindrical shaped heat exchanger members were created to increase the firing density of the boiler. Firing density is generally defined as the output in British Thermal Units (“BTUs”) divided by the combustion chamber volume. Operating the burner at a higher temperature can provide an increase in firing density since the BTU output can be increased without reducing combustion chamber volume. However, an off-setting consideration is the effect of combustion chamber volume on emissions. In particular, emissions, or waste products, such as CO and NOx, generally increase as a result of operating the burner at a higher temperature for a given volume combustion chamber. There is also another important factor which must be considered in regard to the relationship between BTU output and combustion chamber volume. This factor is the effective surface area of the heat exchanger member. Generally, the larger the surface area of the heat exchanger member, the higher the BTU output that can be achieved for a given combustion chamber volume and burner temperature. Consequently, it can be understood that the firing density of a boiler can be increased while maintaining a proper combustion chamber volume by designing a heat exchanger member with the largest possible surface area and the smallest overall size.

#In the prior art, firing density has been increased using a heat exchanger member configured by arranging straight tubular members in a circular pattern to form a cylindrical shaped member. In this manner, the overall volume of the heat exchanger member is reduced while maintaining surface area, thus increasing the firing density for a given combustion chamber volume. To circulate and control the flow of the water through the multiple straight tubes, a header is connected at both the top and the bottom ends of the straight tubes to control flow through each tube. One of the two headers commonly has both the inlet and outlet connections for circulating the water through the straight tubular members. The headers can be configured internally to provide desired flow paths through the tubular members.

#A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:

#FIG. 1 is a perspective view of a prior art type cylindrical heat exchanger member.

#FIG. 2 is a perspective view of a presently preferred embodiment of a cylindrical heat exchanger member.

#To aid in understanding the invention, it may be helpful to first describe a prior art type cylindrical heat exchanger member 20, such as shown in FIG. 1, having multiple straight tubular members 23 which are connected at each end to separate top 26 and bottom 29 headers. The tubular members can be arranged in a side-by-side, generally circular arrangement thus forming a cylinder, and hence the “cylindrical” designation. One of the two headers 26, 29, in this case the top header 26, has inlet 32 and outlet 35 connections adapted for connection to an external water source which will provide the water which is to be circulated through the individual tubular members 23. An opening 38 in the top header 26 is provided through which a burner element (not shown) can be inserted generally concentrically into the interior of the cylinder formed by the tubular members 23. In practice, the cylindrical heat exchanger member 20 will generally be housed in a combustion chamber/housing portion of a boiler/water heater, and the burner is fueled by an air/gas mixture to heat the multiple tubular members 23, and thus the water circulated within them. The heated water will thereafter be circulated from the heat exchanger member 20 for use downstream of the boiler elsewhere in the heating system.

#A disadvantage associated with the conventional heat exchanger member 20 is that the surface area relative to the combustion chamber volume can be less than desirable. Additionally, the use of more than one header 26, 29, and the related inability to access each end of the tubular members 23 at a single location, creates difficulties with regard to cleaning and maintenance of the heat exchanger member 20. For example, it can be difficult to access either the inside of the headers 26, 29 or the surface of the individual tubular members 23 facing the inside of the cylinder, which can be necessary for proper cleaning and maintenance. In particular, a large amount of boiler disassembly can be required, including the removal of both of the headers 26, 29 from each of the multiple tubular members 23. Such disassembly can also be needed in order to clean the outer surface of the tubular members 23 which face the inside of the cylinder. The radius of the cylindrical heat exchanger member 20 is generally made as small as possible, with due regard to surface area and combustion chamber volume, thus limiting access to the inside of the cylinder. Other significant disadvantages which can be associated with the conventional cylindrical heat exchanger member 20 are related to controlling the flow path of water through the various tubular members 23 and the external water connections. For example, the headers 26, 29 are initially configured to provide a particular flow path, which determines the amount of passes, i.e., the number of times the water is circulated through the tubular members 23 before being passed out of the heat exchanger member 20. This is normally specified by the customer at the time of purchase and cannot be altered thereafter. Thus, any change would require a new top 26 and/or bottom 29 header. Similarly, the headers 26, 29 of the conventional cylindrical heat exchanger member 20 also typically cannot be reconfigured for different external water connections. Thus, it can also be necessary for customers to specify the positioning of the external water connection, i.e., whether they will be on the right or left side when ordering the boiler. As a result, if the boiler is to be used with a different system, or the water connections are to be altered, the headers 26, 29 cannot simply be reconfigured to accommodate the changes.

#Generally, in regard to firing density, the use of multiple straight tubes 23 to form the cylindrical heat exchanger member 20 can result in a less compact design for the amount of surface area provided, resulting in a lower firing density than otherwise possible. This can be understood in one respect as owing to the space savings which can be achieved, according to an aspect of the present invention, by rolling the long straight tubes used in some prior art type heat exchanger designs into ring shaped tubular members and stacking them to form a more compact cylindrical shaped heat exchanger. The compromise between height and diameter accomplished using ring shaped tubular members can provide a larger surface area for a given volume, thus resulting in a higher firing density while retaining a proper combustion chamber volume for reduced CO and NOx emissions.