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Title:
METHOD OF REDUCING THE AMOUNT OF COOLING FLUID, PARTICULARLY A FLUID WHICH UNDERGOES PHASE CHANGES IN TUBE HEAT EXCHANGERS, AND A DEFLECTOR FOR THE EXECUTION OF THE SAID METHOD
Document Type and Number:
WIPO Patent Application WO/2019/059789
Kind Code:
A1
Abstract:
The invention is related to a method of reducing the amount of cooling fluid, particularly a fluid which undergoes phase changes in tube heat exchangers, and a deflector for the execution of the said method. According to the method, inside exchanger tubes that are smooth or notched on the inside or outside at least two deflectors of varying diameters are placed in each of the exchanger tubes, each shaped like a section of a rod with a circular section, and are installed in a coaxial concentric arrangement in a tube by means of spacer projections present in the deflector, the diameter and length of the deflector are so adjusted to the inner diameter of the tube that the cooling fluid flow in the annular chamber created by placing a deflector in the tube facilitates efficient heat exchange.

Inventors:
MATUSIAK, Kazimiera (ul. Kanałowa 35, 40-748 Katowice, PL)
Application Number:
PL2018/000086
Publication Date:
March 28, 2019
Filing Date:
September 06, 2018
Export Citation:
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Assignee:
NORMAX - INVEST SP. Z O.O. (ul. Jana III Sobieskiego 11/18, 40-082 Katowice, PL)
International Classes:
F28F1/42; F28F1/14; F28F13/08; F28F13/12; F28D21/00
Foreign References:
DE102016102690A12017-08-17
GB2069676A1981-08-26
US20010003309A12001-06-14
GB1361421A1974-07-24
US4784218A1988-11-15
Attorney, Agent or Firm:
KLASSEK, Maciej Adam (INVENTCONSULT Patent & Trademark Agency, Sowińskiego 1, 40-272 Katowice, PL)
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Claims:
Claims

1. The method of reducing the amount of the cooling fluid, and in particular a fluid which undergoes phase changes in tube heat exchangers characterized in that inside exchanger tubes that are smooth, notched on the outside or inside at least two deflectors of varying diameters, each shaped like a section of a rod preferably with a circular section are placed in each tube of the exchanger, and are fixed in a coaxial concentric arrangement in a tube by means of spacer projections located on the deflector, the deflector diameter and length is so adjusted to the inner diameter of the tube as to ensure that the flow of the cooling fluid in the annular chamber created by placing a deflector in the tube facilitates efficient heat exchange.

2. The method according to claim 1, characterized in that if several deflectors installed in series are used, change of the sectional area of the annular chamber on each successive deflector installed is between 10% to 70% of the sectional area of the exchanger tube, whereas the length of each successive deflector of a given diameter in a series of deflectors remains constant or changes within the range from 10% to 70% against adjacent deflectors.

3. The method according to claim 1, characterized in that diameters of deflectors installed in series in the evaporator decrease gradually from the inlet so that the sectional area of the annular chamber created following the installation of deflectors increases on each deflector installed by 10 % to 70 % of the sectional area of a deflector installed on the inlet of the evaporator tube, whereas the length of each successive deflector of a given diameter in a series of deflectors is constant or increases by 10 % to 70 % against the length of the preceding deflector, the diameter and length of the deflector is so adjusted with respect to the inner diameter of the tube so that the flow of the cooling fluid in the peripheral annular area of the tube facilitates efficient heat exchange.

4. The method according to claim 1, characterized in that the diameters of deflectors installed in series in a condenser increase gradually from the inlet so that the sectional area of the annular chamber created following the installation of deflectors decreases on each deflector installed by 10 % to 70 % of the sectional area of a deflector installed on the inlet of the condenser tube, whereas the length of each successive deflector of a given diameter in the series of deflectors is constant or decreases by 10 % to 70 % against the length of the preceding deflector, the diameter and length of the deflector are so adjusted with respect to the inner diameter of the tube that the flow of the cooling fluid in the peripheral annular area of the tube facilitates efficient heat exchange.

5. Deflector for reducing the amount of cooling fluid, and in particular a fluid which undergoes phase changes in tube heat exchangers characterized in that each has a body 1 in the shape of a section of a rod of a circular section equipped with spacer projections 2 located on the side surface whose outline together with the cross-sectional area of the cylinder fits within the sectional area of a portion of the heat exchanger tube.

Deflector according to claim 5, characterized in that it has a shape of a section of a cylinder or a another figure inscribed within a circle, cylinder, preferably a portion of a tube sealed on both sides.

Deflector according to claim 5, characterized in that it is made of metal or plastic whose surface shows a slight resistance of the cooling fluid flow.

8. Deflector according to claim 5, characterized in that the spacer projections 2 have the shape of longitudinal pyramids arranged axially whose base is essentially rectangular, adjacent with their bases to the side surface of the deflector's body 1, placed at a distance of 3 - 10 diameters of the deflector D, with maximum circumferential shift against each other by angle a of 90° to 120°.

Description:
Method of reducing the amount of cooling fluid, particularly a fluid which undergoes phase changes in tube heat exchangers, and a deflector for the execution of the said method

The invention is related to a method of reducing the amount of cooling fluid, particularly a fluid, which undergoes phase changes, in tube heat exchangers, and a deflector for the execution of the said method.

Thermal engineering discloses shell and tube heat exchangers being non- contact exchangers, in which two fluids in parallel or in counter flow enter into contact through a wall of a profiled tube which separates them and at the same time transfers heat. The said exchangers are manufactured as bundles of profiled tube portions connected with each other in parallel at their ends with connecting pipes to form sets.

A particular example of the said tube exchangers are evaporators and condensers which use at least one fluid as a working medium which undergoes a phase change during its flow through the tube.

Known tube exchangers whose tubes are covered with lamellas being radiators, function as air exchangers which operate in a stream of natural or forced air flow. Exchangers in which a tube heat exchanging unit is placed in a shell or is directly immersed in a tank filled with a flowing fluid, which is subject to heat exchange, are known as shell and tube exchangers in which the second medium is most often a liquid. Exchangers of this type are widely used in air-conditioning systems, for feeding heat pumps, in refrigeration and in vapor cooling installations.

A condition required to ensure a good heat exchange, which has a direct impact on the efficiency of the tube exchanger, is the creation and maintenance of turbulent flow of working fluid along its entire length, and the largest possible heat exchange area between fluids entering into contact through the tube wall.

In practice, there are known units i.e. the so-called turbulators, placed inside tubes in tube exchangers to improve heat transfer efficiency whose role is to force turbulent flow of the working fluid. Those known elements often have the form of creases, embossed areas and notches made on the inner surface of exchangers' tubes. A variation of turbulators also includes exchangers' tubes with adequately adjusted section which is obtained as a result of assembling the tube of the exchanger from segments varying in diameter coupled with each other. Turbulators in form of inserts placed inside exchanger tubes are also known to be used to force and maintain the turbulent flow.

Turbulators known from US patent application US 2,252,045 usually take the form of cylinder sections in which longitudinal dimples were made in the shape of a multi-turn helical line along the entire circumference of the cylinder's side surface, or have series of notches, embossed areas and creases as disclosed by US patent application US 2007089873A1 which make the cooling fluid flow turbulently in a rotational flow. Turbulators create high flow resistance.

All elements of turbulators contacting the inner walls of the exchanger tubes reduce the active heat transfer area of the exchanger and create zones where heat transfer efficiency is lower. Moreover, through their interference in the structure of tubes, they deteriorate their strength. At the same time turbulators increase the resistance of the working fluid flow while reducing the amount of cooling medium in exchangers only to a small extent. Changes of tube diameters made to reduce the volume of the exchanger are costly and significantly reduce the exchanger's active heat exchange area thus deteriorating performance parameters.

Technical development enforces the introduction of new highly-effective organic cooling fluids such as low-boiling hydrocarbons e.g. propane, propylene and their non-flammable fluoric derivatives, the so-called freons, as well as other such as ammonia. The use of those modern cooling fluids classified as the so-called greenhouse gases is however connected with a number of inconveniences and hazards i.e. explosiveness in the case of hydrocarbons, and an adverse impact on the human body and the environment, involving contribution to the reduction of ozone in upper layers of the atmosphere and worldwide climate change, in the case of fluorinated hydrocarbons. The negative impact of modern cooling fluids results in an attempt to maintain and even increase the heat efficiency of modern tubular structures of heat exchangers while at the same time reducing the amount of cooling fluids used and decreasing the volume of the working medium in the installation. The reduction of the amount of the cooling medium in heat exchange installations resulting in a decreased emission of fluorinated greenhouse gases is a particular and extremely important technical problem in the context of environmental protection. As yet there are no effective designs reducing the internal volume of tube heat exchangers.

In the operation of a tube heat exchanger acting as an evaporator in which a fluid which undergoes phase changes is used, the fluid gradually passes from the liquid to the gaseous state (vapor) as it flows along the exchanger tube. Tube portion as an element of the exchanger through which the cooling medium flows is an element that has a constant cross-sectional area and a constant volume along its entire length. The cooling fluid fills the entire volume of the exchanger tube and flows through the entire section of the exchanger tube. In turn, the cooling fluid, which expands due to temperature increase and gradually changes its state of aggregation as the temperature goes up, changes its thermodynamic properties, ability to transfer thermal energy, specific heat and the flow speed. Heat exchange between the cooling fluid and the cooling medium in the tube heat exchanger occurs only on the inner surface of the exchanger tube and only part of the cooling fluid, which is in contact with the inner wall of the exchanger tube, is involved in this process.

The method of reducing the amount of cooling fluid, particularly a fluid which undergoes phase changes , in tube heat exchangers, consists in the reduction of the volume of a portion of a tube of the exchanger while at the same time keeping constant ability of the cooling fluid to exchange heat while it flows through tubes of the exchanger where it undergoes a gradual phase change from the liquid state to vapor, all intermediate states (liquid-vapor mixture) included.

In the method according to the invention, to reduce the amount of the cooling fluid in the tube heat exchanger, at least two deflectors shaped like a section of a rod with circular section of outer diameter smaller than the inner diameter of a portion of a tube of the exchanger are placed inside the tubes of the exchanger and installed in a coaxial concentric arrangement in the tube, the diameter of each deflector so adjusted to the inner diameter of the tube that the flow of the cooling fluid in the peripheral annular area of the tube shows efficient heat exchange. This makes it possible to control volume, speed and quality of the flow, as well as the cooling fluid heat exchange efficiency. If several deflectors arranged in series are used, the change of the sectional area of the annular chamber is between 10% to 70% of the sectional area of the exchanger tube for each successive deflector installed, whereas the length of each successive deflector of a given diameter in a series of deflectors is constant or changes by 10% to 70% against adjacent deflectors. The method according to the invention is also used in condensers and evaporators, which are types of heat exchangers, in which one of the working fluids evaporates or condenses.

If the method according to the invention is used in an evaporator, diameters of deflectors installed in series decrease gradually from the inlet so that the sectional area of the annular chamber created after the installation of deflectors increases on each installed deflector by 10% to 70% of the sectional area of the deflector installed at the inlet of the evaporator's tube, whereas the length of each successive deflector of a given diameter in a series of deflectors is constant or increases by 10% to 70% against the length of the preceding deflector.

If the method according to the invention is used in a condenser, diameters of deflectors installed in series increase gradually from the inlet so that the sectional area of the annular chamber created after the installation of deflectors decreases on each installed deflector by 10% to 70% of the sectional area of the deflector installed at the inlet of the condenser, whereas the length of each successive deflector of a given diameter in a series of deflectors is constant or decreases by 10% to 70% against the length of the preceding deflector.

The use of deflectors in exchangers with a alternate operating mode, which may function as a condenser or an evaporator, made it possible to reduce the volume of the cooling medium. Moreover, the unfavorable effect of the so-called liquid impact was eliminated. In an exchanger without a deflector, following the change of the operating mode from evaporator to condenser, the excess liquid that did not evaporate gets into the compressor and may result in its damage. Additional equipment e.g. a liquid separators, has been used so far to prevent this phenomenon. The use of deflectors in this type of exchangers makes it possible to eliminate additional protection equipment, speeds up the change of exchangers' operating modes and thus reduces installation costs and increases devices' efficiency, particularly in heat pumps and air conditioners with a reversed heating and cooling operating modes.

The invention is also related to the structure of the deflector for reducing the amount of cooling fluid in a tube heat exchanger. The deflector according to the invention has the shape of a section of a rod with a circular section and outer diameter smaller than the inner diameter of a portion of a tube of the exchanger which is equipped on its side surface with spacer projections whose outline together with the cross-sectional area of a cylinder fits in the sectional area of a portion of tube of the heat exchanger.

In a preferred embodiment, the deflector may have the form of a section of a cylinder, preferably a portion of a tube sealed on both sides.

A deflector may be made of metal or plastic whose surface shows slight resistance of the cooling fluid flow. To minimize the resistance of cooling fluid flow, spacer projections preferably have the shape of longitudinal pyramids arranged axially whose base is essentially rectangular, adjacent with their bases to the deflector's side surface.

For practical and design and assembly reasons, the spacer projections are preferably located at a distance of 3 - 10 diameters of deflector D, with maximum circumferential shift against each other by angle a of 90° to 120°.

The use of deflectors reduces the amount of the cooling medium. Deflectors installed concentrically in the exchanger tube create an annular flow area which forces a favorable flow of the fluid close to the walls of the exchanger tube i.e. in a zone where efficient heat exchange takes place. Deflectors made of materials with a low friction factor, equipped with spacer projections distributed evenly on the periphery, adjacent to the inner wall of the tube and keeping the deflector in the central tube position, create minimum flow resistance. Installation of deflectors composed of sections of varying diameters and lengths, selected depending on the cooling fluid, which changes its state of aggregation, volume and the speed of flow through the exchanger tube, does not deteriorate efficiency parameters of the exchanger.

The use of a deflector in the evaporator tube decreases the tube volume to its minimum effective value. The obtained result i.e. the reduction of the amount of the medium in the system, does not reduce the exchanger efficiency parameters. The installation of a deflector on pyramid-shaped spacer projections inside tubes of the exchanger does not interfere with outer and inner walls of the tube nor does it deteriorate the material strength of the exchanger which is particularly important for the application in high-pressure installations.

The method according to the invention may be used in tube heat exchangers in which tube walls are smooth or have notches on the inside or outside which may support the energy exchange process but has no impact on the design of the deflector.

The method according to the invention makes it possible to significantly reduce the amount of the cooling medium.

The method according to the invention is used in tube heat exchangers, particularly in those in which a phase change of the cooling fluid and reversal of the cooling and heating operations take place e.g. in refrigeration, air conditioning, steam boilers and in the chemical and food sectors.

The subject of the invention is presented in embodiments in the attached drawing where

Fig. 1 - illustrates a cross-sectional view of a deflector,

Fig. 2 - illustrates a cross-sectional view of a portion of a tube of a heat exchanger with a deflector installed, Fig. 3 - illustrates a longitudinal sectional view of an example portion of a tube of a heat exchanger in which a set of two deflectors arranged in series, adjacent to each other and varying in size was installed,

Fig. 4 - illustrates an example diagram showing annular chamber area to length and width of a deflector, and a diagram showing flow speed to cooling liquid expansion level.

Example 1

Deflector according to the invention has a cylinder-shaped body 1 with outer diameter D smaller than the inner diameter 0 r of a portion of a tube of the exchanger equipped with spacer projections 2_located on the side surface which have the shape of pyramids whose basis is rectangular, adjacent with their bases to the side surface of the deflector's body 1.

Spacer projections 2 of the deflector are placed at distance I = 2.5 of deflector diameters D between them, with maximum circumferential shift against each other by angle a = 90°, their outline together with the cross-sectional area of the body fits in the sectional area of a portion of the exchanger's tube.

Deflector made of a corrosion-resistant metal alloy, has a polished surface showing slight resistance of cooling fluid flow, and was installed in a portion of a tube of the heat exchanger using propane as the cooling fluid. Reynolds number for the cooling liquid flow was R= 3200 - 3500.

In this embodiment the use of the method according to the invention made it possible to reduce 55% the volume of the cooling fluid necessary to fill the tube exchanger as compared to the amount of the cooling fluid used if there are no deflectors installed, without a drop in the heat exchange efficiency as compared to efficiency obtained without a deflector.

Example calculation regarding the selection of deflector sizes for a tube heat exchanger equipped with a set of five deflectors.

1. Formula used so far for the length of the exchanger tube:

L ( m) =< 2 x 0r ( mm)

0r - inner diameter of the tube in millimeters [mm] L - length in meters [m]

2. Formula for the length of the exchanger tube with deflectors:

L (m )= < 0r (mm)

0r - inner diameter of the tube in millimeters [mm]

L - Length of exchanger tubes and deflector in meters [m] 3. Minimum increase or decrease of the area of annular chambers occurring successively in the exchanger tube for evaporator and condenser respectively

PI - Area of inlet inner section [mm2]

P2 - Area of exchanger tube inner section [mm2]

Ye - number of deflector diameters (number of annular chambers)

Pe - annular chamber area change index

4. Ldw- indicant length of Ldw deflector

L - Length of the exchanger tube - total length of deflectors

Ye - number of deflector diameters (number of annular chambers)

Ldw =——

3Ye

5. Total length of deflectors depending on the number of their diameters Ye increasing from the inlet.

L= (0Del x lLdw)+ (0De2 x2 Ldw)+ (0De3 x3 Ldw)+ (0De4 x4 Ldw) + etc.

6. Selection table for the evaporator tube P2e - sectional area 66 [mm2] L - length 9m 0Ple - inlet diameter 3.4 [mm]; area 9,0 [mm2]

0 P2e - exchanger tube diameter 9.17 [mm] area 66,0 [mm2]

deflector diameters - 0De 1 - 0de 5

PD - deflector sectional area [mm2]

Ld - deflectors' length [m]

Deflector diameter 0Del 0De2 0De3 0De4 0De5

8,0 7,5 7,0 6,5 6,0

PD Deflector area 50,0 44,0 38,0 33,0 28,0 mm2

Difference 16,0 22,0 28,0 33,0 38,0 P2e - PD

Sectional area

of the annular

chamber mm2 Pe

Ld Deflectors' length l x Ldw 2 x Ldw 3 x Ldw 4 x Ldw 5 x Ldw in (m) total 9m 0,6 1,2 1,8 2,4 3,0