EXCHANGER OF HEAT

Technical Field

The invention relates to exchanger of heat of a desk type the adjacent desk of which defining channels for hot and cold media flows

Background of the Invention

Exchangers of heat comprise evenly spaced and mutually parallel arranged desks defining channels for hot and cold media flows In principle there exist two basic designs, the first one featuring media cross flow and the other one media counter-flow, the inlet and outlet of the media being arranged either at the same side of the exchanger or at its opposite sides The exchanger with media counter-flow having inlet and outlet of the media being arranged at the same side is often named as U-type exchanger while the one with inlet and outlet of the media on opposite sides is called a Z-type exchanger Typical constructions are known from the paper WO 92/09859 describing an exchanger with a media cross-flow and from the paper WO 96/19708 dealing with an exchange of heat with media counter-flow The said designs manifest uneven distribution of temperature at both media outlets By conventional exchangers the channels for hot media flow have constant cross-section and amounts of media flowing through the center and through side portions of the exchanger are substantially the same The hot media flow along the cold media inlet is cooled by still non-heated cool media and therefore more than the flow in the exchanger middle part or the flow at the side of already heated, originally cold media The cooled original hot, now warm medium therefore shows uneven temperature distribution along its outlet cross- section A so called cold corner appears at the place where in-coming cold media flow meets the out-coming warm media Similarly a so called hot corner appears in the opposite place, where the hot media flow comes in and the heated media flow leaves the exchanger The differences between both side parts of flowing media are considerable, the temperature at one side may become more than double the temperature at the opposite output side

It is an object of the invention to improve the distribution of temperatures inside the exchanger and to achieve higher efficiency of the transfer of heat between both media

Disclosure and Obiect of the Invention

The foregoing problems are solved by an exchanger of heat of a desk type the adjacent desk of which define channels for hot and cold media flows designed in accordance with the present invention, where a cross profile of channels for hot media flow and/or longitudinal profile of channels for cold media flow is variable along the respective media flow In a preferred embodiment the cross profile of the channels for hot media flow at the near side of cold media inlet is of the greater cross-section than at the one at the near side of heated media outlet and the cross profile of channels cold media flow at the side of inlet of this media is of a smaller cross-section than it is at its outlet Further according to the invention the cross profile of the hot media flow channels is of a trapezoid shape, the wider basis of which is positioned at the side of cold media inlet, while the longitudinal profile of cold media flow channels increases along the media floe from the inlet to its outlet from the exchanger Still further according to the invention the cross profile of hot media flow channels and/or cold media flow channels may have a shape of a closed curved line

It is a preferred aspect of the present invention that any distribution of temperature at the heated media outlet is possible, advantageously fully even distribution of the said temperature along the whole heated media outlet cross-section

Bnef Description of the Drawings

By way of examples the invention will be now described with reference to the accompanying drawing

Fig 1 illustrates temperature distribution by a conventional exchanger of heat with media-cross flow and Fig 2 presents temperature distribution by a

conventional exchanger of heat with media counter-flow Fig 3 schematically illustrates shape of channels for media flow designed according to the invention and on Fig 4 there is a sketch of one part of which the exchangers is made of Fig 5 presents an axonometric view on a part of the exchanger core according to the Fig 3

Description of Preferred Embodiments

In further presented descriptions of exchangers of heat comprising the invention the term heat-exchanging media means cold medium and hot medium which flow into the exchanger and flow out as heated and cooled liquids resp The term warm medium describes originally cold medium partially warmed during transport through an exchanger The heat- exchanging media may be represented by water or gas the term warm medium applies for any matter which is to be heated As a typical hot medium we can take waste heat, the energy of which an exchanger transfers to another medium The uneven temperature distribution by conventional exchangers is presented on Fig 1 and Fig 2 Quite a different temperature behaviour occurs by exchangers of heat according to the invention as described below Fig 3 schematically illustrates an exchanger of heat of the desk type with a cross arrangement of channels for heat-exchanging media flow The cross arrangement of the channels means that both flows run mutually perpendicular Individual desks 1 define alternately arranged first channels 2 for cold media flow and second channels 3 for hot media flow According to the invention the cross-section of both the first and second channels 2,3 is of a trapezoidal shape The individual desks 1 are arranged in such a way that the first channels 2 vertically enlarge along the media flow, while the second channels 3 is wider at the cold media inlet 4 than at the side of heated media outlet 5, but his cross-section along the hot media flow, from the hot media inlet 6 towards the cooled media outlet 7 remains unchanged The hot media flow along the cold media inlet 4 thus passes through larger cross-section which results in a higher flow volume in this part of the second channel 3 and

thus in a higher amount of heat energy transferred to the cold media flow than it happens on the opposite side, at the side of heated media outlet 5, where less energy is necessary for heating When leaving the exchanger the originally hot medium therefore shows even temperature distribution along the whole cooled media outlet 7 As far as a temperature distribution across the heated media flow is concerned, it is significantly more favourable than it is by current constructions having constant cross-section of the exchanger channels The hot medium flowing along heated media outlet 5 passes through smaller cross-section than at the side of cold media inlet 4, therefore the flow of heated, originally cold medium receives less heat energy than it is the case at the opposite, cold medium inlet side By appropriate design of a profile of the second channel 3 it possible to achieve even, regular temperature distribution not only at the side of cooled medium outlet 7 but also at the side of heated medium outlet 5 Fig 4 shows a shape of the desk 1 to be applied for a construction of a core of an exchanger according to the invention The desk 1 is made of a single piece, a pressed steel sheet A section of a core consisting of such desks 1 is shown on Fig 5 Interconnection of individual desks 1 into the unit and the construction of a complete exchanger is provided by a method known as such, e g as described in the paper WO 92/09859

The above described exchanger of heat with media cross flow has substantially a shape of a cube or prism with a square base The invention is nevertheless not limited to such an exchanger shape The above presented principle may be applied also by exchangers with heat- exchanging media counter-flow, either of the U-type or the Z-type The construction of means for direction of media flows by such exchangers is generally known and therefore is not discussed in this paper Application of the means does not anyhow limit the design of heat-exchanging media flow channels according to the invention The first and second channel 2,3 shapes discussed above are basically of a trapezoidal shape

The here presented principle can be further applied in a way, that walls of both channels 2,3 are not made by flat surfaces, but they may be waved In

such a case a cross profile of the second channel 3 and/or the first channel 2 may be in a shape of a closed curve as illustrated on Fig 6 Such a design allows for any random temperature distribution at heat-exchanging media outlets 5,7 of the exchangers by a suitable curve of the warm media flow channel it is possible to achieve the same flow pattern as known by Ventuπ tube

The above described embodiments of channels 2,3 for heat-exchanging media flows eliminate the problem of extremely hot and extremely cold places inside the exchanger On the other hand, by special circumstance it may be functional to achieve an uneven temperature distribution Then it shall be sufficient to use the construction in a reversed arrangement, i e the cross profile of the second channels 3 will have at the near side of cold media inlet 4 smaller cross-section than at the near side of heated media outlet 5