EP0000973A1

EP0000973A1 - Device for heating a liquid

Info

Publication number: EP0000973A1
Application number: EP78200156A
Authority: EP
Inventors: Gerrit Jan Heino
Original assignee: RHEEM BV; Rheem Nederland BV
Current assignee: RHEEM BV; Rheem Nederland BV
Priority date: 1977-08-26
Filing date: 1978-08-25
Publication date: 1979-03-07
Also published as: NL7709476A; GB1587589A

Abstract

A device for heating a liquid for example a central heating vessel, a boiler and so on, comprising an atmospherically ignited burner (2) operating for a limited period of time, a flue gas outlet channel (5) and a wall to be heated by the flue gases for transmitting heat to the liquid to be heated, the flue gas outlet channel (5) comprises a channel portion conducting the flue gases upwards (51) and a channel portion communicating with the former and conducting said gases downwards (52), the heatable wall being arranged both in the upwardly conducting channel and in the downwardly conducting channel, so preventing loss of energy due to a draught through the heating device when being out of operation.

Description

The invention relates to a device for heating a liquid, for example a central-heating vessel, a boiler and so on comprising an atmospherically ignited burner operating for a limited period of time, a flue gas outlet channel and a wall to be heated by the flue gases for transmitting heat to the liquid to be heated.
Atmospherically ignited burners require that the heating device should be provided with passages for the flue gases in order to obtain the desired resistance in the system. This resistance also produces a draught through the heating device when the heat souce is not operating. Such a draught per se is advantageous for evaporating and conducting away any moisture precipitated from the flue gases.
The disadvantage of such a draught resides in that, when the burner is switched off, the heating device starts operating in the reverse sence, since during operation the liquid is heated to a given temperature which is usually higher than the ambient temperature of the air.
Therefore, when the burner is inoperative the air passing through the heating device towards the chimney will be heated by the hot liquid, the resultant hot air leaving the chimney unhindered, which involves an appreciable loss of energy.
It has been proposed to provide a flap in the flue gas outlet channel in order to interrupt the natural draught through the heating system. This involves the disadvantage that any precipitated moisture is not evaporated and conducted away, whilst, moreover, the flaps need monitoring and after-care, which is usually not practised in domestic central-heating vessels and boilers so that damage.may occur.
The invention has for its object to provide a heating device, in which heat cannot get lost due to draught through the heating device and, on the contrary, the heat is maintained unhindered with a _'. natural draught so that the risk of condensed precipitates is avoided.
The device according to the invention is distinguished in that the flue gas outlet channel comprises a channel portion conducting the flue gases upwards and a channel portion communicating with the former and conducting said gases downwards, the heatable wall being arranged both in the upwardly conducting channel and in the downwardly conducting channel.
The invention is based on the phenomenon of a thermostatic equilibrium in the flue gas outlet channel, since when the burner is switched off the hot liquid will heat the flue gases in the two channel portions across the wall so that these flue gases tend to flow upwards. However, the closed communication of the two portions of the flue gas channel ensures a thermostatic equilibrium so that at a given heat of the gases in the flue gas channel the water will not give off heat any longer.
Since the flue gas outlet channel does not comprise means impeding the passages of gas, a natural draught can be maintained.
When the burner is switched on, a normal outlet of the flue gases will be automatically regained.
If the device is constructed in the form of a continuous flow heater, as is the case with a conventional central-heating vessel, in which the water to be heated is continuously pushed through a heat exchanger into the flue gas channel, it may be advantageous in accordance with the invention to arrange the heat exchanger section of the downwardly conducting channel portion at a lower level than the heat exchanger section of the upwardly conducting channel portion. In this way the desired thermostatic equilibrium in the channel portions can be better maintained. An intermittently operating burner is frequently provided with a pilot flame, which gives off such heat that together with one heat exchanger section it maintains the heat of a quantity of flue gas which has to be equal to the quantity of flue gas to be held in the hot state by the other heat exchanger section.
In a furhter embodiment of the invention it is proposed to seperate the upwardly conducting channel portion by means of a single partition from the downwardly conducting channel portion, which partition is at least partly permeable to heat. This expedient also contributes to maintaining the desired thermostatic equilibrium in the flue gas discharge channel.
The aforesaid partition may be formed by the refractory stones of the combustion space around the burner.
The invention will be described more fully with reference to two embodiments.
In the accompanying drawing:

Fig.l is a vertical sectional view of a first embodiment of a heating device in accordance with the invention.
Fig.2 is a vertical sectional view of a heating device of Fig.l in a modified form.
Fig.3 is a vertical sectional view of a second embodiment of a heating device in accordance with the invention.
Fig.4 is a sectional view on the line IV-IV in Fig.3.

Referring to figures 1 and 2, a first embodiment of the heating device in accordance with the invention is used as a heating vessel of a central heating system. The vessel mainly comprises an envelope 1, which is suitably insulated from the surroundings in known manner. The vessel is provided with a burner 2, which may be fed by any suitable fuel, for example, gas or oil.
The fuel feeding duct is designated by reference numeral 3. Since the boiler concerned here is equipped with an intermittently operating burner a pilot flame 4 is constantly maintained an will ignite the main burner 2 each time when the fuel supply is released through a feed cock controlled by a thermostat (not shown).
With the burner communicates a flue gas outlet channel 5, which is constituted in accordance with the invention by two portions to wit an upwardly conducting section 51 and a section 52 communicating with former and conducting the flue gases downwards. The lower end of the latter section 52 joins a channel 6 leading to the chimney, which channel may be provided in a manner not shown with conventional draught- interrupting means, heat exchangers for preheating the water and the like.
The flue gases are conducted away in the direction indicated by the solid arrows in figures 1 and 2.
Both the upwardly conducting portion and the downwardly conducting portion 51 and 52 respectively of the flue gas channel 5 include a section 71 and 72 respectively of a heat exchanger 7.
The heat exchanger 7 communicates with the normal circulations of the water to be heated, said circulation including the conventional radiators and the like.
The heat exchanger 7 may be of any desired form, which does not constitute a subject- matter of the invention.
From figures 1 and 2 it will be apparent that, when the burner 2 is not operating an amount of flue gas and freshly sucked-in ambient air will be heated by the heat exchanger sections 71 and 72. The heated gases will rise in the directions indicated by the dotted arrows and are retained in the junction of the top ends of the two channel portions 51 and 52. Thus a heat trap is formed,since no heat can escape.
In the channels 51 and 52 a thermostatic equilibrium is established, which is maintained as long as the burner 2 remains inoperative.
However, as soon as the burner 2 is reignited by a pulse from the thermostat, the flue gases will follow their normal path through the channel 5 as indicated by the solid arrows.
Fig.2 shows that the levels of the sections 71 and 72 are different so that the section 72 in the downwardly conducting channel 52 is at a lower level than the other section 71. When the burner 2 is switched off, the heat of the pilot flame 4 is thus compensated for in order to maintain the desired thermostatic equilibrium in the channels 51,52.
An additional or alternate solution of the aforesaid problem consists in that the partition 8 between the two channels 51,52 is rendered partly permeable to heat. Fig.2 shows that the fire hearth is surrounded by refractory stones 9, the stones adjacent the channel portion 52 being capable of giving off heat to the gases in said channel.
Fig.3 and 4 show a second embodiment of a heating devise in accordance with the invention. It is abhot water system, for example, a boiler mainly comprising an insulated envelope 11, a water vessel 12 arranged therein and a central flue gas channel 13 arranged centrally in the water vessel 12. Beneath the water vessel 12 is provided a burner 14 having a pilot flame 15, which are operative in the manner described with reference to the preceding embodiment.
The heat transfer from the flue gases to the water takes place through the inner wall 16 of the water vessel 12.
According to the invention the flue gas channel 13 comprises an upwardly conducting channel portion 131 and a downwardly conducting channel portion communicating with the former, the lower end of the channel portion 132 communicating with the chimney joint 17.
Although the sectional area of the flue gas channel 13 may have any shape, it is shown in fig.4 that the channels 131 and 132 are formed by arranging a fitting, diametrical partition 18 in the circular flue gas channel 13.
The flue gases are conducted away in the direction of the solid arrows in fig.3 and when the burner is switched off, hot gas will accumulate in the upper part of the two channel portions 131 and 132, whilst a thermostatic equilibrium is established which is indicated by the arrow drawn in broken lines.
This embodiment operates in the manner described with reference to the preceding embodiment.
As a matter of course, the invention is not limited to the embodiments shown nor to the shape of the flue gas channel.

Claims

1. A device for heating a liquid for example, a central heating vessel, a boiler and so on comprising an atmospherically ignited burner intermittently operating for a limited period of time, a flue gas outlet channel and a wall heatable by the flue gases for transferring heat to the liquid to be heated characterized in that the flue gas outlet channel comprises a channel portion conducting the flue gases upwards and a channel portion communicating with the former and conducting the flue gases downwards, the heatable wall being arranged both in the upwardly conducting channel portion and in the downwardly conducting channel portion.

2. A device as claimed in claim 1 formed by a continuous flow heater comprising a heat exchanger traversed by the liquid characterized in that the heat exchanger section arranged in the downwardly conducting channel portion is disposed at a lower level than the heat exchanger section arranged in the upwardly conducting channel section.

3. A device as claimed in claim 1 or 2, characterized in that the upwardly conducting channel portion is separated from the downwardly conducting channel portion by a partition, which is at least partly permeable to heat for establishing the desired thermostatic equilibrium.

4. A device as claimed in claim 3, characterized in that the partition is formed by part of the wall of the fire hearth around the burner.