JP2001065801A - Heat exchangers and boilers - Google Patents

Abstract

(57) Abstract: An object of the present invention is to provide an extremely simple apparatus configuration without installing an additional structure such as a baffle, to easily manufacture the apparatus, and to discharge the heat from a heat transfer tube. An object of the present invention is to provide a heat exchanger capable of sufficiently suppressing noise by preventing air column resonance between a vortex and gas present in a container, and a boiler provided with the heat exchanger. A heat transfer tube group of a heat exchanger is configured by arranging two types of tube groups in which the heat transfer tube arrangement is changed to a staggered arrangement and a square arrangement, in the fluid flow direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat exchanger and a boiler, and more particularly to a heat exchanger and a boiler used in thermal and nuclear power plants.

[0002]

2. Description of the Related Art FIG. 2 is a schematic horizontal sectional view of a heat exchanger used for a boiler and a waste heat recovery boiler in a conventional thermal power plant. The heat exchanger has a configuration in which a heat transfer tube group configured by regularly arranging a plurality of heat transfer tubes 1 is arranged in a gas flow path formed by a duct wall 2.

[0003] In a tube bank structure such as a heat exchanger, under certain conditions, an air column resonance phenomenon to be described later may occur, and loud noise may occur. Therefore, the baffle 3 is inserted as a measure for preventing the air column resonance phenomenon. The installation of the baffle 3 is very expensive. But baffle 3
Is a structure that does not contribute to the heat exchange that is the original purpose of the heat exchanger at all, and is a structure that is not originally required for the heat exchanger.

In the heat transfer tube group, when a fluid flows around the heat transfer tube 1, a vortex 4 as shown in FIG. The cycle (frequency) of the vortex 4 is called a vortex emission frequency, and mainly depends on the diameter of the heat transfer tube, the flow velocity around the heat transfer tube, the arrangement of the heat transfer tubes, the pitch of the heat transfer tubes, and the like.

On the other hand, in the heat exchanger, a box-shaped container is required to form a flow path in which the fluid flows through the tube group. When the fluid is a gas, these containers have a plurality of discrete natural column vibration modes generally called standing waves corresponding to their dimensions. The frequencies in these modes are called natural air column frequencies, and the vibrations in these modes are hardly attenuated. Therefore, the gas filling the container is likely to vibrate strongly at the natural column frequency.

[0006] The gas oscillates under the influence of the force generated in the tube by the discharge of the vortex. At this time, the period of the force generated in the tube becomes the vortex emission frequency. The vortices emitted as they flow through the tube bundle are strengthened and certain frequency components become dominant. When the dominant frequency of the vortex coincides with the natural column frequency of the vessel containing the entire tube group, the gas will resonate, generating loud noise within the vessel.

In general, resonance noise often occurs in a vertical direction in a gas flow which is susceptible to a force generated in a pipe. Also, if the generated sound pressure is large, it may induce severe vibrations in the pipes, which may lead to breakage. In the design of the tube bank structure, prevention of the generation is important from the viewpoint of noise prevention and equipment damage prevention. Becomes

As a first prior art for preventing the air column resonance phenomenon, Japanese Patent Application Laid-Open No. H5-141891 discloses a heat exchanger provided with a baffle in or around a tube bank. As a second prior art, JP-A-52-1654 describes a heat exchanger in which small-diameter tubes are arranged between large-diameter tubes.

A third prior art is disclosed in Japanese Unexamined Patent Application Publication No. 10-2057.
In Japanese Patent Publication No. 02, two kinds of pipes having different pipe outer diameters, two kinds of pipes provided with fins having different heights, and two kinds of pipes having elliptical cross sections and different directions of a long axis and a short axis are respectively randomized. Are described. This publication also describes a tube bank structure in which the arrangement pitch of tubes having the same outer diameter is randomly changed.

The tube group of the heat exchanger as described above is mainly composed of heat transfer tubes 1 as shown in FIGS. The arrangement shown in FIG. 4 is called a square arrangement, and the arrangement shown in FIG. 5 is called a staggered arrangement.

[0011]

In the first prior art,
Although a baffle is provided as an additional structure in the tube bank, it is desirable that the baffle is not provided because the baffle is a structure that is not originally required for the heat exchanger and is very expensive. Further, in the second and third prior arts, pipes having different pipe diameters and the like are arranged in a mixed manner, so that the configuration of the apparatus is somewhat complicated, and the manufacture of the apparatus is not always easy.

An object of the present invention is to provide a very simple apparatus configuration without any additional structure such as a baffle, to facilitate the manufacture of the apparatus, and to realize the vortex discharged from the heat transfer tube and the vortex discharged from the vessel. It is an object of the present invention to provide a heat exchanger capable of sufficiently suppressing noise by preventing air column resonance with generated gas and a boiler including the same.

[0013]

In order to achieve the above object, according to the present invention, a heat exchanger tube group, which is a constituent element of a heat exchanger, is replaced with a plurality of types of heat exchanger tube arrays in which gas (fluid) is used.
It is constituted by being arranged adjacent to the flow direction. Here, changing the arrangement of the heat transfer tubes means changing the arrangement of the heat transfer tubes, the outer diameter (tube diameter) of the heat transfer tubes, and the pitch of the heat transfer tubes.

That is, in the first aspect, the heat transfer tube group is configured by arranging at least two types of tube groups having different arrangements (arrays) of heat transfer tubes adjacent to each other in the direction of fluid flow.

In the second invention, the heat transfer tube group is constituted by arranging at least two types of tube groups having different outer diameters of the heat transfer tubes adjacent to each other in the flow direction of the fluid.

In the third aspect, the heat transfer tube group is constituted by arranging at least two types of tube groups having different pitches of the heat transfer tube in the fluid flow direction adjacent to each other in the fluid flow direction.

In the fourth aspect, the heat transfer tube group is constituted by arranging at least two types of tube groups having different pitches of the heat transfer tube in a direction perpendicular to the flow direction of the fluid adjacent to the flow direction of the fluid. .

In the fifth invention, the heat exchanger of any one of the first to fourth inventions is used as a heat exchanger constituting a boiler.

According to the present invention, by changing the arrangement of the heat transfer tubes, the flow state around the heat transfer tubes represented by the flow velocity changes. For this reason, the vortex emission behavior changes, and vortices having different frequencies are emitted from each heat transfer tube array. Thereby, the intensity of the dominant frequency component of the emission vortex can be reduced.

FIG. 6 is a conceptual diagram showing the generation of resonance and the method of avoiding resonance according to the present invention. In the figure, the horizontal axis is frequency, and the PSD on the vertical axis is power spectrum density (Power Spectrum Density) representing the intensity of each frequency component. The solid line 5 is the PSD distribution according to the present invention, the dashed line 6 is the PSD distribution when air column resonance occurs in the conventional heat exchanger, and the dashed line 7
Is a PSD threshold value for generating air column resonance.

Since the generation of resonance requires a force having energy equal to or greater than the attenuation of the sound field to be generated in the heat transfer tube, there is a limit value of the PSD for generating resonance indicated by the dashed line 7.
According to the present invention, the intensity of the most dominant vortex emission frequency component can be made lower than the PSD threshold for resonance occurrence. As a result, the energy generated by the discharge of the vortex is insufficient for resonance generation, so that air column resonance does not occur and noise can be sufficiently suppressed.

Further, it is not necessary to install an additional structure such as a baffle, and by arranging a plurality of types of tube groups in which the arrangement of the heat transfer tubes is adjacent to each other in the fluid flow direction, one type of tube group can be provided. Different pipes are not mixed. That is, since one kind of tube group can be constituted by the same tube, the device configuration becomes extremely simple, and the device can be easily manufactured.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 7 is a schematic configuration diagram of a heat exchanger to which the present invention is applied. Hereinafter, the basic operation will be described. Wall 2
The heat energy absorbed from the fluid by the plurality of heat transfer tubes 1 installed perpendicular to the flow direction of the fluid in the flow path formed by the heat exchanger 1 Supplied outside.

FIG. 1 shows a first example of a heat exchanger to which the present invention is applied.
2 shows a tube arrangement of a heat transfer tube group in an example. In this embodiment, a tube group is formed by combining a staggered arrangement and a square arrangement as the tube arrangement. As shown in FIG. 1, the tube group constituted by the heat transfer tubes 1 installed in the flow path formed by the wall 2 has a staggered arrangement of seven rows on the upstream side in the gas flow direction and three rows on the downstream side. The array is a square array. Since the discharge behavior of the vortex is affected by the flow velocity around the pipe determined by the arrangement of the pipes, by changing the pipe arrangement in this way, the vortex discharge frequency differs between the upstream and downstream sides in the gas flow direction of the pipe group. it can.

Next, the effect of this embodiment will be described with reference to FIG. FIG. 8 shows the results of frequency analysis of forces generated in the third and tenth tubes from the upstream in the gas flow direction in the tube arrangement of FIG. As the analysis conditions, the Reynolds number was set to 1.0 × 10 ⁴ assuming the operating conditions of the actual machine. In FIG. 8, the horizontal axis represents the frequency St (= f · d / U _in ) dimensionlessly determined by the pipe diameter d and the inflow velocity U _in , and the vertical axis represents the power spectral density PSD.

From FIG. 8, the dominant frequency in the third column is St.
= 0.41 but the dominant frequency in the tenth column is St
= 0.59. This is because by changing the arrangement of the pipes on the upstream side and the downstream side in the gas flow direction, the local flow velocity is remarkably different from that of a tube group having a uniform arrangement. As described above, there are a plurality of frequency components that govern the vortex emission frequency, but the intensity of each frequency component decreases. As a result, the energy generated by the discharge of the vortex can be sufficiently reduced, so that the occurrence of air column resonance can be prevented and the noise can be sufficiently suppressed.

Further, the tube banks composed of the seven rows on the upstream side in the gas flow direction are unified in a staggered arrangement, and the tube banks composed of the three rows on the downstream side are unified in a square arrangement, so that heat exchange is performed. The device configuration of the container becomes extremely simple, and the device can be easily manufactured.

In FIG. 1, for simplicity, the cross section of the heat transfer tube 1 is shown as a solid, but the actual heat transfer tube 1 is a hollow tube in which a heat exchange medium is provided. It has a flowing structure. The same applies to the following embodiments.

Next, FIG. 9 shows a tube arrangement of a heat transfer tube group in a second embodiment of the heat exchanger to which the present invention is applied. In this embodiment, a tube group is configured by combining two types of tube rows having different tube diameters (outer diameters) in the same tube arrangement as the entire tube group.

That is, in the tube group composed of a plurality of heat transfer tubes 1 installed in the flow path formed by the wall 2, the entire tube group is arranged in a staggered arrangement, but up to seven rows on the upstream side in the gas flow direction. than the pipe diameter D _a, it is to reduce the tube diameter D _B of the downstream three rows.

Since the vortex shedding behavior is affected by the tube diameter,
By changing the tube diameter in this way, the vortex shedding frequency can be made different between the upstream side and the downstream side of the tube group. As a result, similarly to the first embodiment, generation of air column resonance can be prevented and noise can be suppressed. In addition, a tube group composed of seven rows on the upstream side in the gas flow direction has the same diameter D _A , and a tube group composed of three rows on the downstream side has the same diameter D _B. The device configuration of the exchanger becomes extremely simple, and the device can be easily manufactured.

Next, FIG. 10 shows a tube arrangement of a heat transfer tube group in a third embodiment of the heat exchanger to which the present invention is applied. In the present embodiment, a tube group is formed by combining two types of tube rows having different heat transfer tube pitches in a direction perpendicular to the gas flow direction (hereinafter, referred to as a gas flow vertical direction) in the same tube arrangement as the whole tube group. are doing.

That is, in a tube group composed of a plurality of heat transfer tubes 1 installed in a flow path formed by the wall 2, the heat transfer tube pitch T in the gas flow vertical direction up to seven rows on the upstream side in the gas flow direction.
_The heat transfer tube pitch T _B in the vertical direction of the gas flow in the three rows on the downstream side is set smaller than _A. However, the pitch L of the heat transfer tubes in the gas flow direction is constant.

Since the vortex discharge behavior is affected by the flow velocity around the pipe determined by the pipe pitch, by changing the heat transfer pipe pitch in this way, the vortex discharge frequency differs between the upstream side and the downstream side of the tube group. it can. As a result, similarly to the first embodiment, generation of air column resonance can be prevented and noise can be suppressed. Also configured tube group on the upstream side 7 column gas flow direction has the same heat transfer tube pitch T _A, since the formed tube group on the downstream side third column has the same heat transfer tube pitch T _B In addition, the apparatus configuration of the heat exchanger becomes extremely simple, and the apparatus can be easily manufactured.

Next, FIG. 11 shows a tube arrangement of a heat transfer tube group in a fourth embodiment of the heat exchanger to which the present invention is applied. In the present embodiment, a tube group is configured by combining two types of tube rows having different heat transfer tube pitches in the gas flow direction with the same tube arrangement as the whole tube group.

That is, in the tube group composed of the plurality of heat transfer tubes 1 installed in the flow path formed by the wall 2, the heat transfer tube pitch LA in the gas flow direction up to seven rows on the upstream side in the gas flow direction is larger than the pitch L _A. , and to reduce the heat transfer tube pitch L _B of the gas flow direction of the downstream side three columns. However, the pitch T of the heat transfer tubes in the vertical direction of the gas flow is constant.

Since the vortex discharge behavior is affected by the flow velocity around the pipe determined by the pipe pitch, by changing the heat transfer pipe pitch in this way, the vortex discharge frequency differs between the upstream side and the downstream side of the tube group. it can. As a result, similarly to the first embodiment, generation of air column resonance can be prevented and noise can be suppressed. Also configured tube group on the upstream side 7 column gas flow direction has the same heat transfer tube pitch L _A, since the formed tube group on the downstream side third column has the same heat transfer tube pitch L _B In addition, the apparatus configuration of the heat exchanger becomes extremely simple, and the apparatus can be easily manufactured.

Next, FIG. 12 shows a tube arrangement of a heat transfer tube group in a fifth embodiment of the heat exchanger to which the present invention is applied. In this embodiment, a tube group is configured by combining the features of the tube arrangement of the first to fourth embodiments.

That is, in the tube group composed of a plurality of heat transfer tubes 1 installed in the flow path formed by the wall 2, the first tube group up to seven rows on the upstream side in the gas flow direction is arranged in a staggered arrangement, Three rows of second tube banks are arranged in a square array. Furthermore, the pipe diameter D _A of the first tube bank, as compared to the heat transfer tube pitch L _A and the gas flow vertical heat transfer tube pitch T _A gas flow direction, of the second tube bank pipe diameter D _B, the gas flow direction the heat transfer tube pitch L _B and the gas flow vertical heat transfer tube pitch T _B is made smaller.

Since the discharge behavior of the vortex is affected by the pipe arrangement, the flow velocity around the pipe determined by the pipe pitch, and the pipe diameter, by changing the pipe arrangement, the heat transfer pipe pitch and the pipe diameter in this manner,
The vortex shedding frequency can be different between the upstream side and the downstream side of the tube bank. As a result, similarly to the first to fourth embodiments, generation of air column resonance can be prevented and noise can be suppressed. Also configured tube group on the upstream side 7 column gas flow direction, in staggered, have the same pipe diameter D _A, the same heat transfer tube pitch L _A and T _A, tube composed of the downstream side third column The group is a square array with the same tube diameter D
_B , since they have the same heat transfer tube pitches L _B and T _B ,
The apparatus configuration of the heat exchanger becomes extremely simple, and the apparatus can be easily manufactured.

Here, with respect to the first and fifth embodiments and the three cases of the uniform staggered arrangement, the fluid force generated in the entire tube group is obtained, and the result of frequency analysis of this fluid force is shown in FIG. The uniform staggered arrangement is a comparative example in which 10 rows of heat transfer tubes of the same size as those of the first and fifth embodiments are provided in the gas flow direction.

FIG. 13 shows that the PSDs at the dominant frequencies in the first and fifth embodiments are smaller than those in the uniform staggered arrangement. In particular, in the fifth embodiment, the PSD at the frequency St = 0.70, which was dominant in the uniform staggered arrangement, is 1
It can be seen that it decreases to about / 10. As described above, since the dominant frequencies are dispersed according to the above-described embodiment, the energy intensity at the dominant frequencies can be sufficiently reduced, and the occurrence of air column resonance can be prevented. Next, FIG. 14 shows a schematic configuration of a sixth embodiment in which the present invention is applied to a boiler of a thermal power plant. In this boiler, the exhaust gas generated by the combustion of the coal in the furnace 13 and the burner 14 is supplied to the superheater 9 and the reheater 1 installed in the duct wall 2a forming the gas flow path.
After passing through the zero and the economizer 11, it is discharged to the outside of the boiler. Among them, the superheater 9, the reheater 10, and the economizer 11 are heat exchangers, and absorb heat from passing exhaust gas.

The medium flowing in the heat transfer tubes of the reheater 10 and the economizer 11 absorbs thermal energy from the exhaust gas,
And stored in the drum 12. The medium stored in the drum 12 is sent to the superheater 9, where the medium is further absorbed in heat energy and sent to the steam turbine to be used for power generation. These components are supported by a support 15.

In this embodiment, at least one, preferably all, of the superheater 9, the reheater 10 and the economizer 11 uses the heat exchanger of any of the above-described first to fifth embodiments. . With such a configuration, it is possible to prevent the occurrence of air column resonance in the superheater 9, the reheater 10, the economizer 11, and the like, thereby suppressing noise, and the device configuration of the heat exchanger becomes extremely simple. The device can be easily manufactured.

Next, FIG. 15 shows a schematic configuration of a seventh embodiment in which the present invention is applied to an exhaust heat recovery boiler of a thermal power plant. Although the exhaust heat recovery boiler has the same basic performance as the boiler described with reference to FIG. 14, there is no component for burning fuel in the exhaust heat recovery boiler main body. In the exhaust heat recovery boiler, the exhaust gas discharged from the gas turbine is supplied to a superheater 9 and a reheater 1 installed in a duct wall 2a forming a gas flow path.
0, the denitration device 17, the evaporator 16, and the economizer 11 are discharged to the outside of the heat recovery steam generator. this house,
The superheater 9, the reheater 10, the evaporator 16, and the economizer 11 are heat exchangers and absorb heat from passing exhaust gas.

The medium flowing in the reheater 10, the evaporator 16, and the heat transfer tube of the economizer 11 absorbs thermal energy from the exhaust gas and is stored in the drum 12 through the pipe 8. The medium stored in the drum 12 is sent to the superheater 9, where the medium is further absorbed in heat energy and sent to the steam turbine to be used for power generation. The denitration device 17 removes nitrogen oxides contained in the exhaust gas. These components are supported by a support 15.

In this embodiment, at least one, preferably all, of the superheater 9, the reheater 10, the evaporator 16 and the economizer 11 is provided with at least one of the heat sources of the first to fifth embodiments. Use an exchanger. With this configuration, it is possible to prevent the occurrence of air column resonance in the superheater 9, the reheater 10, the evaporator 16, the economizer 11, and the like, thereby suppressing noise, and the device configuration of the heat exchanger is extremely reduced. It is simple and the device can be easily manufactured.

[0049]

According to the present invention, it is possible to easily manufacture an apparatus with an extremely simple apparatus configuration without installing an additional structure such as a baffle in a heat exchanger, and to prevent air column resonance. Noise can be sufficiently suppressed.

[Brief description of the drawings]

FIG. 1 is a view showing a tube arrangement of a heat transfer tube group of a first embodiment of a heat exchanger to which the present invention is applied.

FIG. 2 is a schematic horizontal sectional view of a conventional heat exchanger.

FIG. 3 is a diagram showing a state of vortex shedding in a tube bank.

FIG. 4 is a diagram showing a square arrangement of tube groups.

FIG. 5 is a diagram showing a staggered arrangement of tube groups.

FIG. 6 is a conceptual diagram of a resonance avoidance method according to the present invention.

FIG. 7 is a schematic configuration diagram of a heat exchanger to which the present invention is applied.

FIG. 8 is an explanatory diagram of an effect according to the first embodiment.

FIG. 9 is a view showing a tube arrangement of a heat transfer tube group according to a second embodiment of the heat exchanger to which the present invention is applied.

FIG. 10 is a view showing a tube arrangement of a heat transfer tube group according to a third embodiment of the heat exchanger to which the present invention is applied.

FIG. 11 is a view showing a tube arrangement of a heat transfer tube group according to a fourth embodiment of the heat exchanger to which the present invention is applied.

FIG. 12 is a view showing a tube arrangement of a heat transfer tube group according to a fifth embodiment of the heat exchanger to which the present invention is applied.

FIG. 13 is an explanatory diagram of the effects of the first and fifth embodiments.

FIG. 14 is a schematic configuration diagram of a sixth embodiment in which the present invention is applied to a boiler of a thermal power plant.

FIG. 15 is a schematic configuration diagram of a seventh embodiment in which the present invention is applied to an exhaust heat recovery boiler of a thermal power plant.

[Description of Signs] 1 ... heat transfer tube, 2 ... wall, 3 ... baffle, 4 ... vortex, 8 ... piping, 9 ... superheater, 10 ... reheater, 11 ... economizer, 12 ...
Drum, 13 ... furnace, 14 ... burner, 15 ... support,
16: evaporator, 17: denitration device.

Continued on the front page (72) Inventor Noriyuki Sadaoka 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture F-term in the Electric Power and Electric Development Laboratory, Hitachi, Ltd. 3L103 AA01 AA05 AA29 BB05 CC02 CC27 DD08 DD09 DD62 DD68

Claims (8)

[Claims] A heat transfer tube group comprising an array of a plurality of heat transfer tubes;
And a box-shaped container that houses the heat transfer tube group and forms a flow path of a fluid flowing therearound. The heat transfer tube group includes at least two types of tube groups having different arrangements of the heat transfer tubes. A heat exchanger characterized by being arranged adjacent to the flow direction of the fluid. 2. A heat transfer tube group comprising an array of a plurality of heat transfer tubes,
A heat exchanger including a heat transfer tube group and a box-shaped container that forms a flow path of a fluid flowing around the heat transfer tube group, wherein the heat transfer tube group has at least two types of tube groups having different outer diameters of the heat transfer tubes. Are arranged adjacent to each other in the flow direction of the fluid. 3. The heat transfer tube group according to claim 2, wherein the heat transfer tube group is composed of two types of tube groups, and an outer diameter of the heat transfer tube constituting the upstream tube group in the fluid flow direction is a downstream tube group. A heat exchanger having an outer diameter larger than the outer diameter of the heat transfer tube constituting the heat exchanger. 4. A heat transfer tube group comprising an array of a plurality of heat transfer tubes;
And a box-shaped container that houses the heat transfer tube group and forms a flow path of a fluid flowing therearound. The heat transfer tube group has at least two different heat transfer tube pitches in the fluid flow direction. A heat exchanger characterized in that a tube group of a kind is arranged adjacent to a flow direction of the fluid. 5. A heat transfer tube group comprising an array of a plurality of heat transfer tubes,
A heat exchanger comprising: a box-shaped container that houses the heat transfer tube group and forms a flow path of a fluid flowing therearound; wherein the heat transfer tube group has a pitch of the heat transfer tubes in a direction perpendicular to a flow direction of the fluid. A heat exchanger, wherein at least two types of tube groups differing from each other are arranged adjacent to each other in the flow direction of the fluid. 6. The heat transfer tube group according to claim 4, wherein the heat transfer tube group is constituted by two types of tube groups, and the pitch of the heat transfer tubes constituting the tube group on the upstream side in the flow direction of the fluid is the downstream side. A heat exchanger, wherein the pitch is larger than the pitch of the heat transfer tubes constituting the tube group. 7. A heat transfer tube group comprising an array of a plurality of heat transfer tubes;
A heat exchanger comprising: a box-shaped container that houses the heat transfer tube group and forms a flow path of a fluid flowing around the heat transfer tube group, wherein the heat transfer tube group is at least two of claims 1, 2, 4, and 5. A heat exchanger, characterized in that at least two types of tube banks having the features described in (1) are arranged adjacent to each other in the flow direction of the fluid. 8. A heat exchanger having a heat transfer tube group comprising an array of a plurality of heat transfer tubes, a box-shaped container accommodating the heat transfer tube group and forming a flow path of a fluid flowing around the heat transfer tube group, and the heat exchanger. A boiler comprising: a pipe for transporting a medium therein; and a duct for housing the heat exchanger and forming a gas flow path, wherein the heat exchanger according to any one of claims 1 to 7 as the heat exchanger. A boiler characterized by using.