GB1578505A

GB1578505A - Heat exchangers

Info

Publication number: GB1578505A
Application number: GB4228/78A
Authority: GB
Original assignee: GULDAGER CONSULT
Current assignee: GULDAGER CONSULT
Priority date: 1977-02-02
Filing date: 1978-02-02
Publication date: 1980-11-05
Also published as: FR2379785A1; NL7800936A; SE7801135L; NO146511B; CH626983A5; FR2379785B3; NO146511C; NO780248L; DE2803664A1

Abstract

The heat exchanger has a storage container (1) and a tube system, which is arranged in the latter and through which a heat-dissipating medium flows. In order to achieve the best performance of such a heat exchanger, it is important that, on the one hand, the heat-dissipating medium leaves the heat exchanger with the lowest achievable temperature and, on the other hand, that the temperature of the medium in the container which absorbs the heat is as uniform as possible over its entire volume. In order to achieve this, the tube system has a heating medium inlet distributor tube (4) situated at the top in the storage container (1) and an outlet manifold (5) situated at the bottom in this container, which are connected by a number of vertical tube elements which extend helically. Each of these tube elements has an upper part (7, 7') whose heat exchange surface is substantially smaller than the entire heat exchange surface of the lower part (8, 8') of the tube element. This heat exchanger is used, in particular, in the form of a hot water container for heating service water. <IMAGE>

Description

(54) IMPROVEMENTS IN OR RELATING TO HEAT EXCHANGERS (71) We, GULDAGER CONSULT ApS of Rypevang 4, DK-3450 Allerd, Denmark, a Danish company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to heat exchangers.

Such heat exchangers may be used as hotwater boilers for heating utility water and may comprise a storage tank, at the bottom of which is placed an inlet pipe branch for water or another liquid which is to be heated, and at the top an exhaust branch for the heated liquid, together with a pipe-system intended for the flow of a heat emitting medium, such as steam or hot water, which system has an upper inlet distributor tube and a lower outlet-collecting tube, each of which has an external connecting branch and which are mutually connected through a number of vertical elements of spiral tubes, i.e. helical tube coils which together form the heating unit of the storage tank.

Such heat exchangers can be used for heating utility water and other liquids not only by district heating water or -steam, but also by exploitation of solar heat, groundheat or heat from any kind of waste water. In order to obtain economical exploitation it is important that the heating medium used (usually cooled water or condensate) leaves the heat exchanger with the lowest possible temperature, and that the temperature nowhere in the water of the tank is higher than necessary in order that the drawn off utility water can have the required temperature.In other types of heat exchangers than the one in question, it has been tried to obtain this by dividing the tank into two compartments by means of an intermediate bottom so as to obtain a colder lower compartment for cooling and heat receipt from the heating medium immediately before it leaves the heat exchanger, and an upper warmer compartment for the supplementary heating of the utility water through the top of the heat exchanger.

According to the invention, there is provided a heat exchanger comprising a storage tank with an inlet pipe branch at its bottom for water or another fluid to be heated and an exhaust branch at its top for the heated fluid and a pipe system for flowing heat emitting medium, such as steam or hot water, which system has a top-inlet-distributor and a bottom outlet-collecting tube each having an external connecting branch and each being mutually connected through a plurality of vertical elements of spiral tubes formed by helical tube coils which together form a heating element of the storage tank, each element having a top part the total heating-surface of which is substantially smaller than the total heating-surface of the bottom part of the element.

A preferred heat exchanger provides an appropriate distribution of temperature in the water of a tank, which is a plain tank with a single inner compartment in which there is room for appropriate electrolytic protection of the pipe system and cathodic protection of the tank, at the same time avoiding complications in placing intermediate bottom and pipe connections between the thereby separated compartments.

In the lower part of each element of spiral tubes a considerably higher cooling of the heating medium can be obtained and, by dividing the heating element into two steps, a further favorable stratification of the water in the tank according to the temperature can be obtained as a result of the suppression of the thermosiphonical effcct. In other words, without using an intermediate bottom and without creating obstructions for the electrolytic protection of the tank and pipe system, a division is obtained, by which the top part of the tank contains hot water, e.g. with temperatures of approximately 50"-60"C ready for draught, while the lower part contains colder water, which is not heated until it is needed.

In a preferred heat exchanger, there is obtained a thermal effective heating element consisting of the top part of the elements combined with a thermal braking heating element consisting of the bottom part of the elements in one and the same tank, as the mutual capacity or the capacity of the transmission of heat of the heating elements is adapted to the operating conditions met with.

The elements of spiral tubes, which are part of the two heating elements, can suitably be standard elements, and a heat exchanger can then be constructed in a simple way by placing a middle distributing pipe between the inlet distributor tube and the outletcollecting tube, which middle distributing pipe is connected with the bottom end of the top part of each element of spiral tube and with the top end of the bottom part of each element of spiral tube, as an example the bottom heating element consists of a greater number, e.g. twice as many, of elements of spiral tubes as the top one.

It is also possible to use differently shaped elements of spiral tubes in the two heating elements, e.g. the diameter of the bottom part of the elements of spiral tube can be bigger than the top part. In this way it is possible to obtain not only a desired large heating surface of the lower part, but there is also a greater possibility that calcium which is deposited at the top part of the elements and which works loose by a change of the temperature therein, can sink right down to the bottom of the tank, from where it can be eliminated through a purging cock.

The flow rate of the heating medium through the bottom part of the elements can be obtained by a greater tube diameter for the spiral tubes here than at the top part.

The invention will be further described, by way of example, with reference to the accompanying drawings, wherein Figure 1 shows schematically a vertical section through a preferred heat exchanger; Figure 2 shows a horizontal section along the line II-II in Figure 1; and Figure 3 a vertical section through a second preferred heat exchanger.

The heat exchanger shown is a hot-water boiler for storage and heating by means of a heating medium such as steam or hot water, which flows through a pipe system in the boiler and can, e.g., be delivered from a district heating plant or a central-heating boiler.

The heat exchanger comprises a storage tank 1 at the bottom of which is fitted a pipe branch 2 for connection to cold-water piping and at the top of which is fitted a pipe branch 3 for connection to piping, which leads to the draining points of hot utility water. Hot water or steam as heating medium is led into the tank through an external pipe branch which is fitted on a ring-shaped inlet distributor tube 4 in a top part of the boiler and, when cooled, the heating medium escapes through an external pipe branch fitted to outlet-collecting tube 5 at the bottom of the tank. A suitable distance from the top of the tank at which to place the inlet distributor 4 would equal approximately 1/4 of the capacity of the tank.

The surface of the transmission of heat through which the heating medium emits heat to the water in the storage tank 1, is formed by the walls of a number of helical tubes, which are referred to below as elements of spiral tubes.

In the heat exchanger in Figs. 1 and 2, the surface of the transmission of the heat exchanger is divided into two heating elements, i.e. a first heating element, which is inserted between the outlet-collecting tube 5 and a ring-shaped middle distributor pipe 6 for a first heating of the cold water coming in through pipe branch 2, and a second heating element, which is inserted between the middle distributor pipe 6 and the inlet distributor tube 4 for supplementary heating of the hot utility water, which is drawn off through the pipe branch 3. In the embodiment shown, the second heating element consists of three elements of spiral tubes 7, while the first heating element consists of six elements of spiral tubes 8 with a diameter a little bigger than that of the elements 7.

The flow rate of the heating medium in the first heating element, which is the spirals 8, provided that all the spirals have the same tube diameter, is only half the flow rate in the spirals 7, because more cooling of the heating medium takes place at the bottom heating element than at the top one. The flow of the heating medium is controlled by means of a thermostat 9, depending on the temperature of the water in the top part of the storage tank.By tapping water through the pipe branch 3, colder water from the bottom part of the tank will flow around the thermostat, which admits the heating medium through inlet-distributor tube 4 by means of which the water at the top part of the tank is heated to a suitable temperature by the heating medium flowing relatively quickly through spirals 7, while the admitted cold water at tie bottom of the tank is pre-heated by the more slowly flowing heating medium in the spirals 8, which heating medium leaves the tank only at a relatively low temperature through the outlet-collecting tube 5.The heating medium can be hot water, which, for instance, flows into the inlet-distributor tube 4 at a temperature of approximately 60"C before it flows into the middle distributor pipe 6 and finally is cooled to about 25-30"C leaving the tank through the outlet-collecting tube 5. The water in the storage tank 1 enters, for example, at a temperature of approximately 1 00C and escapes through the outlet-pipe branch 3 at a temperature of approximately 60"C.

In the heat exchanger shown in Fig. 3, the surface of the transmission of heat in each element of spiral tube is distributed between a lower part 8', which is connected to an outlet-collecting tube 5, and an upper part 7', which is connected to an inlet-distributor tube 4. In the embodiment shown, the bottom part 8' of each element of spiral tube is made of a pipe with a greater flowing diameter and with a greater winding diameter than the upper part 7'.

This construction too, results in a considerably slower flow of the heating medium in the bottom part 8' of the elements of the spiral tubes, for example half of the flow rate at the top part 7', so that greater cooling of the heating medium takes place at the bottom part than at the top part. The water at the top part of the tank is heated to the desired temperature by the heating medium flowing relatively quickly through the top part 7' of the spirals, while the admitted cold water at the bottom of the tank is pre-heated by the more slowly flowing heating medium at the bottom part 8' of the elements of spiral tubes, which medium leaves the tank at a relatively low temperature through the outlet-collecting tube 5.

It will be understood that the balancing of the two parts of the elements of spiral tubes so that the fall in temperature of the heating medium in each part is adjusted to the present operating conditions, can be made in other ways than those shown in the drawing.

For example, the surface of the transmission of heat at the bottom part 8' can be increased by the use of a finer pitch angle, i.e., more tight winding of the spirals.

Besides obtaining an effective exploitation of the heat of the heating medium by the greatest possible cooling thereof it is possible by the preferred heat exchangers to keep the advantages by heating the utility water by means of elements of spiral tubes, while the stratification of the storage water has made it possible to obtain the advantages of tanks in two pieces at the same time maintaining an adjoining compartment having room enough for means for electrolytic protection of tank and pipe system.

WHAT WE CLAIM IS: 1. A heat exchanger comprising a storage tank with an inlet pipe branch at its bottom for water or another fluid to be heated and an exhaust branch at its top for the heated fluid and a pipe system for flowing heat emitting medium, such as steam or hot water, which system has a top-inletdistributor and a bottom outlet-collecting tube each having an external connecting branch and each being mutually connected through a plurality of vertical elements of spiral tubes formed by helical tube coils which together form a heating element of the storage tank, each element having a top part the total heating-surface of which is substantially smaller than the total heating-surface of the bottom part of the element.

2. A heat exchanger as claimed in claim 1, in which between the inlet-distributor tube and outlet-collecting tube there is a middle distributor which is connected with the bottom end of each top part of each element of the spiral tube and with the top end of the bottom part of each element of spiral tube.

3. A heat exchanger as claimed in Claim 2 in which the middle distributor is connected with an outlet-collecting tube through a number of the elements of spiral tubes, which are considerably greater than and preferably twice as big as the number of elements of the spiral tubes, by which it is connected with the inlet distributor tube.

4. A heat exchanger as claimed in any one of claims 1 to 3 in which the diameter of the bottom part of the elements of the spiral tubes is greater than the diameter of the top-part of the elements of the spiral tubes.

5. A heat exchanger as claimed in any one of claims 1 to 4 in which the bottom part of the elements of the spiral tubes has a tube diameter, which is greater than the tube diameter at the top part of the elements of the spiral tubes.

6. A heat exchanger substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 or Figure 3 of the accompanying drawings.

7. A hot water system including a heat exchanger as claimed in any one of the pre

Claims

ceding claims.