Patent Description:
Utility model <CIT> discloses a heat exchanger comprising a container for liquid with an inlet tube for cold water and an outlet tube for hot water, and a heat-releasing tube coil wound around the outer side of the container, and an adhesive thermally conductive layer is added between the contact part of the inner side of the coil with the container and the outer side of the container. The profile of the tube coil is oval or D-shaped. The container for liquid and the coil are made of different materials. The container is made of low-carbon or stainless steel, and the coil is made of aluminum, copper or their alloy. A disadvantage of this heating tube coil for water heater is that it has low coefficient of heat transfer from the heating fluid due to the indirect contact with the container for liquid, and hence the coefficient of performance (COP) is reduced, because when the operational temperature of the heating fluid is reached, respectively when the coil is heated, the contact between the coil and the container deteriorates, due to the different linear thermal expansions of the metals included in the construction. In addition, the adhesive thermally conductive layer reduces its characteristics over time and further worsens heat transfer.

The object of the invention is to create a heat exchanger with an increased coefficient of heat transfer and heat release from the heating fluids, leading to an increased coefficient of performance (COP).

This object is achieved by creating a heat exchanger, according to the invention, consisting of a container for liquid with an inlet pipe for cold liquid, and an outlet pipe for hot liquid and a heat-releasing tube coil for heating fluid. The heat-releasing tube coil for heating fluid has an inlet tube, a heat-releasing tube wound in the form of a coil around the container for liquid, and an outlet tube. There is a thermal insulation layer and an outer protective jacket around the container for liquid and heat-releasing tube coil. The heat-releasing tube of the heat-releasing tube coil is tensioned around the container for liquid by preheating to the operating temperature of a heat transfer fluid intended to circulate in the coil before winding the heat-releasing tube around the container for liquid. According to the invention, only the coil is heated to the corresponding temperature, which is higher than the temperature of the other components included in the construction, which remain at an unchanged temperature.

In a preferred embodiment, the liquid in the container for liquid is water. Alternatively, it may be glycol or another liquid, which is to be heated.

Preferably, the heat-releasing tube of the heat-releasing tube coil wound around the container for liquid is covered with fixing protective tape with adhesive layer, resistant to a temperature at least as high as the temperature of the heat transfer fluid in the heat-releasing tube of the heat-releasing tube coil.

In a preferred embodiment of the invention, a layer of thermal paste is applied between the heat-releasing tube coil and the container for liquid, which improves the thermal conductivity between the container for liquid and the heat-releasing tube coil.

According to the invention, the container for liquid and the heat-releasing tube coil are made of materials with different coefficients of linear expansion. The container for liquid is made of steel, such as low carbon or stainless steel, and the heat-releasing tube coil is made of aluminum, copper, or an aluminum or copper alloy. This choice of metals allows obtaining the desired linear temperature expansions of said metals in order to achieve the desired tension of the heat-releasing tube of the heat-releasing tube coil around the container for liquid without causing plastic deformation as it cools contacting the container for liquid during manufacture.

It is known from the physics of metals that the linear temperature expansions of two different metals and their alloys are different and are function of their temperature.

When an object changes its temperature, that is, heats up or cools down, its length changes by an amount proportional to the initial length and to the change in temperature. The linear thermal expansion, or change in length, of an object can be expressed as: <MAT>.

The final length of the object can be calculated by L1 = L0 + dl = L0 + L0 α (t1 - t0) (<NUM>)
where L1 = final length of the object (m, inches).

The coefficients of linear expansion of most materials vary with temperature.

In the case under consideration, the linear temperature coefficients α for these common metals are:.

Accordingly, the preheating of the tube compensates for the different expansion of the container for liquid and the coil.

An additional object of the invention is to create a method for manufacturing a heat exchanger with an increased coefficient of heat transfer and heat release by the heating fluids, leading to an increased coefficient of performance (COP).

This object is met by creating a method for manufacturing a heat exchanger, comprising the steps of:.

Preferably, the heat-releasing tube of the heat-releasing tube coil wound around the container for liquid is covered with fixing protective tape with adhesive layer resistant to a temperature at least as high as the temperature of the heating fluid in the heat-releasing tube of the heat-releasing tube coil.

In a preferred embodiment of the invention, before winding the heat-releasing tube around the container for liquid, a layer of thermal paste is applied between the heat-releasing tube coil and the container for liquid.

The heating of the coil to the operating temperature of the heating fluid can be done by induction, infrared radiant heating, gas flame, or hot air, above the ambient temperature during its assemble with the container for liquid.

In the state of the art, it is known that, through the process of condensing the fluid (for example, refrigerant), the resulting heat in the coil is released by means of heat transfer along the following chain: Fluid > Wall > Body. The coil (body) through the process of thermal conduction transfers heat to the contact area between the coil and the container for liquid. The heated area of the container for liquid heats the fluid inside it (e.g. water) by the process of heat transfer. Accordingly, tensing the heat-releasing tube of the heat-releasing tube coil by preheating increases the coefficient of heat transfer and heat release by the heating fluids, which leads to an increase in the COP of the device, which is the main advantage of the heat exchanger according to the invention.

In a preferred embodiment of the invention, the liquid in the container for liquid <NUM> is water.

As shown in the figures, the heat exchanger according to the invention consists of a container for liquid <NUM> with an inlet tube for cold water <NUM>, and an outlet tube for hot water <NUM>, a heat-releasing tube coil for heating fluid, which has an inlet tube <NUM>, a heat-releasing tube <NUM>, wound in the form of a coil around the container for liquid <NUM>, and an outlet tube <NUM>. A thermal insulation layer <NUM> is arranged around the container for liquid <NUM> and the heat-releasing tube coil. An outer protective jacket <NUM> is slipped on the entire structure. The heat-releasing tube <NUM> of the heat-releasing tube coil is tensioned around the container for liquid <NUM> by preheating it to the operating temperature of the heat transfer fluid that will circulate in the heat-releasing coil before winding the heat-releasing tube <NUM> around the container for liquid <NUM>.

In a preferred embodiment, the container for liquid is made of stainless steel. Alternatively, it can be made of low carbon steel.

In a preferred embodiment, the heat-releasing tube coil is made of aluminum. Alternatively, it can be made of copper, or aluminum or copper alloy.

In the particular embodiment, the thermal insulation layer <NUM> is made of hard or soft polyurethane. Alternative materials are expanded polystyrene EPS, extruded polystyrene XPS, stone or polymer wool.

In the particular embodiment, the jacket <NUM> is made of a polymer material or a metal, for example steel. The polymer material, which can be used, is, for example, ABS, PS, PC, PE, PVC, or other suitable polymer material known in the art. Alternatively, it can be made of textile material.

The types of heat transfer fluid that can be used in the heat-releasing tube coil are known in the art.

Before winding the heat-releasing tube <NUM> around the container for liquid <NUM>, a layer of thermal paste is applied between the heat-releasing tube coil and the container for liquid <NUM>, which improves the thermal conductivity between them.

After being mounted around the container for liquid <NUM>, the heat-releasing tube coil is covered with a fixing protective tape with an adhesive layer (not shown in the figures), the tape being arranged with the adhesive layer facing the heat-releasing tube coil. The fixing tape is resistant to a temperature at least as high as the temperature of the heating fluid in the heat-releasing tube <NUM> of the heat-releasing tube coil. For example, the fixing tape must withstand a temperature of at least <NUM>. An example of a suitable fixing tape is a highly conformable polyolefin copolymer tape with special adhesive coating on the backside for good adhesion during mounting processes involving the use of polyurethane foam. The adhesive coating of the tape can be, for example, based on synthetic rubber with high adhesion. The fixing tape is used to prevent the thermal insulation polyurethane foam from entering between the container for liquid <NUM> and the heat-releasing tube <NUM>, which can reduce the contact between them, and hence the coefficients of heat transfer and heat release from the heating fluids to the container for liquid <NUM>.

An alternative to the fixing tape is to use fixing clamps which are welded to the container for liquid <NUM> and then bent around the heat-releasing tube <NUM> to prevent displacement of the heat-releasing tube <NUM> and reduction of the contact between the container for liquid <NUM> and the heat-releasing tube <NUM>, and respectively, the coefficient of heat transfer and heat release from the heating fluids to the container for liquid <NUM>.

The method for manufacturing the heat exchanger, according to the invention, includes the steps of:.

During operation, the heat exchanger condenses, wherein the heat transfer fluid in the heat-releasing tube coil is heated, respectively the heat-releasing tube coil heats, which in turn heats the container for liquid <NUM> and respectively the heated fluid therein. During this heating, the two materials expand linearly, but due to the preliminary tensioning of the heat-releasing tube <NUM> of the heat-releasing tube coil, when it reaches its operating temperature, it does not separate from the container for liquid <NUM>; due to the greater extension of the heat-releasing tube <NUM> in length and diameter relative to the container for liquid <NUM>, the resulting linear thermal expansions are compensated accordingly, and the contact, and hence the conduction, are more efficient.

After being wound around the container for liquid <NUM>, the heat-releasing tube <NUM> of the heat-releasing tube coil is preferably covered with fixing protective tape with adhesive layer resistant to a temperature at least as high as the temperature of the heating fluid in the heat-releasing tube <NUM> of the heat-releasing tube coil.

The heat-releasing tube <NUM> is wound in the form of a coil around the container for liquid <NUM>, the turns of the coil being optionally spaced far or close apart. Densely spaced turns form a longer coil and have a smaller degree of planar curvature, while sparser turns form a shorter coil and have a greater degree of planar curvature. It is possible for the entire coil to be wound with the same pitch between the turns. It is also possible for the pitch between the turns to vary in different parts of the coil, e.g. the turns are denser at the bottom of the container for liquid <NUM> and sparser at the top of the container for liquid <NUM>.

It will be clear to those skilled in the art that various embodiments of the heat exchanger are possible, which also fall within the scope defined in the appended claims.

Claim 1:
Heat exchanger consisting of a container for liquid (<NUM>) with an inlet pipe for cold liquid (<NUM>) and an outlet pipe for hot liquid (<NUM>), a heat-releasing tube coil for heating fluid, which has an inlet tube (<NUM>), a heat-releasing tube (<NUM>), wound in the form of a coil around the container for liquid (<NUM>), and an outlet tube (<NUM>), wherein there is a thermal insulation layer (<NUM>) and an outer protective jacket (<NUM>) around the container for liquid (<NUM>) and the heat-releasing tube coil, characterized in that the heat-releasing tube (<NUM>) of the heat-releasing tube coil is tensioned around the container for liquid (<NUM>) by preheating only the heat-releasing tube coil to the operating temperature of a heat transfer fluid, intended to circulate in the coil, before winding the heat-releasing tube (<NUM>) around the container for liquid (<NUM>).