CN112984804A - Shell-and-tube heat exchanger started by heat source - Google Patents

Abstract

The invention provides a heat source started shell-and-tube heat exchanger, which comprises a shell, wherein tube plates are respectively arranged at two ends of the shell, a heat replacement part is arranged in the shell, the heat exchange part comprises a lower tube box, an upper tube box and a heat exchange tube, the heat exchange tube is communicated with the lower tube box and the upper tube box to form closed circulation of heating fluid, two ends of the lower tube box and the upper tube box are arranged in openings of the tube plates, and an electric heater is arranged in the lower tube box; filling phase-change fluid in the lower channel box; the electric heaters are arranged in a plurality of numbers, each electric heater is independently controlled, and the starting number of the electric heaters changes periodically along with the change of time; in the previous period of the cycle, the starting number of the electric heaters is gradually increased along with the time until all the electric heaters are started; during the latter part of the cycle, the number of electric heaters activated is gradually reduced over time until all are deactivated. The invention increases the heating power of the heat exchange tube periodically and continuously and reduces the heating power, so that the heated fluid can generate the volume which is continuously in a changing state after being heated, and the free end of the heat exchange tube is induced to generate vibration, thereby strengthening heat transfer.

Description

Shell-and-tube heat exchanger started by heat source

Technical Field

The invention relates to a shell-and-tube heat exchanger, in particular to a shell-and-tube heat exchanger with high heat exchange efficiency.

Background

The invention relates to a project which is developed by cooperating with Qingdao science and technology university and relates to descaling of a heat exchanger, and the project is a novel invention which is applied to a shell-and-tube heat exchanger on the basis of the development of the Qingdao science and technology university (application number 2019101874848).

The shell-and-tube heat exchanger is widely applied to industries such as chemical industry, petroleum industry, refrigeration industry, nuclear energy industry and power industry, and due to the worldwide energy crisis, the demand of the heat exchanger in industrial production is more and more, and the quality requirement of the heat exchanger is higher and more. In recent decades, although compact heat exchangers (plate type, plate fin type, pressure welded plate type, etc.), heat pipe type heat exchangers, direct contact type heat exchangers, etc. have been rapidly developed, because the shell and tube type heat exchangers have high reliability and wide adaptability, they still occupy the domination of yield and usage, and according to relevant statistics, the usage of the shell and tube type heat exchangers in the current industrial devices still accounts for about 70% of the usage of all heat exchangers.

After the shell-and-tube heat exchanger is scaled, the heat exchanger is cleaned by adopting conventional modes of steam cleaning, back flushing and the like, and the production practice proves that the effect is not good. The end socket of the heat exchanger can only be disassembled, and a physical cleaning mode is adopted, but the mode is adopted for cleaning, so that the operation is complex, the consumed time is long, the investment of manpower and material resources is large, and great difficulty is brought to continuous industrial production.

The mode of passively strengthening heat exchange is to strictly prevent the fluid vibration induction in the heat exchanger from being changed into effective utilization of vibration, so that the convective heat transfer coefficient of the transmission element at low flow speed is greatly improved, dirt on the surface of the heat transfer element is restrained by vibration, the thermal resistance of the dirt is reduced, and the composite strengthened heat transfer is realized.

In application, it is found that continuous heating can cause the internal fluid to form stability, i.e. the fluid does not flow or has little fluidity, or the flow is stable, so that the vibration performance of the heat exchange tube is greatly weakened, thereby affecting the descaling of the heat exchange tube and the heating efficiency. There is therefore a need for improvements to the above-described heat exchangers.

Meanwhile, in application, the heat exchange efficiency can be improved by adjusting corresponding structural parameters. There is therefore a need for improvements to the above-described heat exchangers.

Disclosure of Invention

The invention provides an electric heating shell-and-tube heat exchanger with a novel structure, aiming at the defects of the shell-and-tube heat exchanger in the prior art. The shell-and-tube heat exchanger can realize the periodic frequent vibration of the heat exchange tube, and improves the heating efficiency, thereby realizing good descaling and heating effects.

In order to achieve the purpose, the invention adopts the following technical scheme:

a shell-and-tube heat exchanger with reasonably optimized space comprises a shell, wherein tube plates are respectively arranged at two ends of the shell, a heat exchange component is arranged in the shell and comprises a lower tube box, an upper tube box and a heat exchange tube, the heat exchange tube is communicated with the lower tube box and the upper tube box to form closed circulation of heating fluid, two ends of the lower tube box and the upper tube box are arranged in openings of the tube plates, and an electric heater is arranged in the lower tube box; filling phase-change fluid in the lower channel box; the heat exchange tube is one or more, and every heat exchange tube includes many convex tube bundles, and the central line of many convex tube bundles is following pipe case for the circular arc of concentric circles, the tip intercommunication of adjacent pipe bundle to make the tip of pipe bundle form the pipe bundle free end, its characterized in that, lower pipe case and upper tube case set up along casing length direction, the heat exchange tube sets up to a plurality ofly, along the fluidic flow direction in the casing, the interval of adjacent heat exchange tube constantly diminishes.

Preferably, the distance between adjacent heat exchange tubes is gradually decreased and gradually increased along the flowing direction of the fluid in the shell.

Preferably, the two ends of the shell are respectively provided with a tube plate, a heat exchange component is arranged in the shell, and the heat exchange component comprises a lower tube box, an upper tube box and a heat exchange tube.

A shell-and-tube heat exchanger comprises a shell, wherein tube plates are respectively arranged at two ends of the shell, a heat replacement component is arranged in the shell, the heat exchange component comprises a lower tube box, an upper tube box and a heat exchange tube, the heat exchange tube is communicated with the lower tube box and the upper tube box to form closed circulation of heating fluid, two ends of the lower tube box and the upper tube box are arranged in openings of the tube plates, and an electric heater is arranged in the lower tube box; filling phase-change fluid in the lower channel box; the heat exchange tube is characterized in that the electric heaters are arranged in a plurality, each electric heater is independently controlled, and the starting number of the electric heaters is periodically changed along with the change of time; in the previous period of the cycle, the starting number of the electric heaters is gradually increased along with the time until all the electric heaters are started; during the latter part of the cycle, the number of electric heaters activated is gradually reduced over time until all are deactivated.

Preferably, the preceding period of time is 3 times the following period of time.

Preferably, assuming that there are m electric heaters, one electric heater is turned on every 3/4m periods in one cycle until the heater is turned on all at 3/4 periods, and then one electric heater is turned off every 1/4m periods until the heater is turned off all at one period.

Preferably, the heating power of each electric heater is the same.

Preferably, the inner diameter of the heat exchange tube bundle is increased along the flowing direction of the fluid in the shell.

The invention has the following advantages:

1. through the flowing direction of fluid in the shell, the reasonable change of the internal diameter and the interval of the tube bundle of the heat exchange tube improves the heat exchange efficiency.

2. The shell-and-tube heat exchanger provided by the invention can realize periodic frequent vibration of the elastic heat exchange tube by intermittently exchanging heat in a period, thereby realizing good descaling and heat exchange effects.

3. The invention increases the heating power of the heat exchange tube periodically and continuously and reduces the heating power, so that the heated fluid can generate the volume which is continuously in a changing state after being heated, and the free end of the heat exchange tube is induced to generate vibration, thereby strengthening heat transfer.

4. The invention designs a layout of a heat exchange component with a novel structure in the shell, and can further improve the heating efficiency.

5. The invention optimizes the optimal relation of the parameters of the heat exchange tube through a large amount of experiments and numerical simulation, thereby realizing the optimal heating efficiency.

Drawings

FIG. 1 is a top view of a heat exchange member of the present invention.

Fig. 2 is a front view of the heat exchange part.

Fig. 3 is a coordinate schematic diagram of the intermittent heating of the heat exchange part.

Fig. 4 is a graph illustrating the coordinates of the periodic increase and decrease in heating power of the heat exchange member.

FIG. 5 is a schematic diagram of the periodic increase and decrease of heating power of another embodiment of the heat exchange component.

Fig. 6 is a coordinate diagram illustrating linear variation of heating power of the heat exchange part.

Fig. 7 is a schematic layout of heat exchange components arranged in a circular shell.

Fig. 8 is a schematic view of the structure of a heat exchange tube.

Fig. 9 is a schematic view of the housing structure.

In the figure: 1. the heat exchange tube comprises a heat exchange tube 2, a lower tube box 3, a free end 4, a free end 5, a shell pass inlet connecting tube 6, a shell pass outlet connecting tube 7, a free end 8, an upper tube box 9, a connecting point 10, a heat exchange part 11, a shell, a tube bundle 12, an electric heater 13, a front tube plate 14, a support 15, a support 16, a rear tube plate 17 and end parts 18-20.

Detailed Description

A shell-and-tube heat exchanger, as shown in fig. 9, comprises a shell 11, a heat exchange component 10, a shell-side inlet connecting pipe 5 and a shell-side outlet connecting pipe 6; the heat exchange component 10 is arranged in the shell 11 and fixedly connected to the front tube plate 14 and the rear tube plate 17; the shell side inlet connecting pipe 5 and the shell side outlet connecting pipe 6 are both arranged on the shell 11; fluid enters from a shell side inlet connecting pipe 5, exchanges heat through a heat exchange part and exits from a shell side outlet connecting pipe 6.

The end parts 18-20 at both ends of the lower and upper tube boxes are arranged in the openings of the front and rear tube plates 14, 17 for fixation.

Fig. 1 shows a top view of a heat exchange part 10, as shown in fig. 1, the heat exchange part 10 includes a lower tube box 2, an upper tube box 8 and a heat exchange tube 1, the heat exchange tube 1 is communicated with the lower tube box 2 and the upper tube box 8, a fluid is circulated in the lower tube box 2, the upper tube box 8 and the heat exchange tube 1 in a closed manner, an electric heater 13 is arranged in the heat exchange part 10, the electric heater 13 is used for heating the fluid in the heat exchange part 10, and then the fluid in the shell is heated by the heated fluid.

As shown in fig. 1-2, an electric heater 13 is provided in the lower header tank 2; the lower tube box 2 is filled with phase-change fluid; the heat exchange tubes 1 are one or more, each heat exchange tube 1 comprises a plurality of circular arc-shaped tube bundles 12, the central lines of the circular arc-shaped tube bundles 12 are circular arcs which are concentric with the lower tube box 2, the end parts of the adjacent tube bundles 12 are communicated, and fluid forms serial flow between the lower tube box 2 and the upper tube box 8, so that the end parts of the tube bundles form tube bundle free ends 3 and 4; the fluid is phase-change fluid, vapor-liquid phase-change liquid, the heat exchange component is in data connection with the controller, and the controller controls the heating power of the heat exchange component to periodically change along with the change of time.

Preferably, the lower header 2 and the upper header 8 are provided along the length of the shell side. The shell side preferably extends in the horizontal direction.

It has been found in research and practice that the continuous power-stable heating of the electric heater can result in the stability of the fluid formation of the internal heat exchange components, i.e. the fluid is not flowing or has little fluidity, or the flow rate is stable, and the vibration performance of the heat exchange tube 1 is greatly weakened, thereby affecting the descaling of the heat exchange tube 1 and the heating efficiency. Therefore, the following improvements are required for the above-mentioned electric heating heat exchange pipe.

Preferably, the heating power is a batch type heating method. Namely, heating is firstly carried out for a period of time, then heating is stopped for a period of time, and then heating is carried out again, and continuous circulation is carried out. Preferably, the heating time is 3 times the time without heating.

As shown in fig. 3, the heating power P of the electric heater varies regularly during one period time T as follows:

0-3T/4, i.e. three quarters of a period, P ═ n, where n is a constant number in watts (W), i.e. the heating power remains constant;

p =0 in a quarter period of 3T/4-T. I.e. the electric heater does not heat.

Preferably T is 50-80 minutes, wherein the heating power P is 3500-5500W, preferably 4000W < n < 5000W.

Through the heating with the time variability, the fluid can be frequently evaporated, expanded and contracted in the elastic tube bundle, so that the vibration of the elastic tube bundle is continuously driven, and the heating efficiency and the descaling operation can be further realized.

Preferably, the electric heater 13 is provided in a plurality, each electric heater is independently controlled, and the number of the activated electric heaters is periodically changed along with the change of time.

Preferably, the number of the electric heaters is n, one electric heater is started at intervals of 3T/4n within one period T until the heaters are all started at 3T/4, and then one electric heater is stopped at intervals of T/4n until the heaters are all stopped at T.

Preferably, the heating power of each electric heater is the same. The relationship diagram is shown in fig. 4.

Through the heating with the time variability, the fluid can be frequently evaporated, expanded and contracted in the elastic tube bundle, so that the vibration of the elastic tube bundle is continuously driven, and the heating efficiency and the descaling operation can be further realized.

Preferably, the electric heater is arranged in a plurality of sections along the length direction of the tube shell, each section is independently controlled, and the electric heater is sequentially started along the direction opposite to the fluid flowing direction in the shell side (for example, the right end of the figure) along with the change of time until all the sections are started, and then is sequentially closed from the fluid flowing direction until the period is ended, and all the sections are closed.

Preferably, the electrical heater is sequentially activated in the opposite direction of fluid flow in the shell side (e.g., beginning at the right end of the figure) for three quarters of a period 3T/4 until all segments are activated, and then sequentially deactivated from the direction of fluid flow for the next quarter of a period T/4 until all segments are deactivated at the end of the period.

That is, assuming that the electric heater is n segments, in a period T, every 3T/4n, starting one segment from the right end until all segments are started at 3T/4n, and then every T/4n, starting from the left end, closing one segment until all segments are closed at T.

Preferably, the heating power is the same for each section. The relationship diagram is shown in fig. 4.

The electric heater is gradually started along the flowing direction of the fluid, so that the heating temperature at the rear end is high, a similar counter-flow effect is formed, the flowing of the fluid is further promoted, and the elastic vibration effect is increased. Through the change of the heating power with time variability, the fluid can be frequently evaporated, expanded and contracted in the elastic tube bundle, so that the vibration of the elastic tube bundle is continuously driven, and the heating efficiency and the descaling operation can be further realized.

Preferably, the number of the electric heaters 13 is multiple, each electric heater 13 has different power, one or more electric heaters can be combined to form different heating powers, in the front period of the cycle (preferably three-quarter cycle), according to the time sequence, the single electric heater is started first, the single electric heater is independently started according to the sequence that the heating power is sequentially increased, then the two electric heaters are started, the two electric heaters are independently started according to the sequence that the heating power is sequentially increased, then the number of the started heat exchange parts is gradually increased, and if the number is n, the n electric heaters are independently started according to the sequence that the heating power is sequentially increased; and ensuring that the heating power of the heat exchange parts is increased in sequence until all the electric heaters are started finally. In the later period of the period (preferably, a quarter period), firstly, the single electric heater is not started, the single electric heater is not independently started according to the sequence that the heating power is sequentially increased, then the two electric heaters are not started, the two electric heaters are not independently started according to the sequence that the heating power is sequentially increased, then the number of the heat exchange parts which are not started is gradually increased, and if the number is n, the n electric heaters are not started independently according to the sequence that the heating power is sequentially increased; and (3) until all the electric heaters are not started, ensuring that the heating power of the electric heaters is reduced in sequence.

For example, the heat exchange parts are three, namely a first heat exchange part D1, a second heat exchange part D2 and a third heat exchange part D3, and the heating powers are P1, P2 and P3, wherein P1< P2< P3, P1+ P2> P3; the sum of the first heat exchange component and the second heat exchange component is larger than that of the third heat exchange component, the first, the second, the third, the first plus the second, the first plus the third, the second plus the third, then the first, the second and the third are started in sequence according to the time sequence, and the sequence which is not started in the rest period time is the first, the second, the third, the first plus the second, the first plus the third, the second plus the third, then the first, the second and the third.

The heating power is gradually increased and decreased through the electric heater, the flowing of the fluid is further promoted, and the elastic vibration effect is increased. Through the change of the heating power with time variability, the fluid can be frequently evaporated, expanded and contracted in the elastic tube bundle, so that the vibration of the elastic tube bundle is continuously driven, and the heating efficiency and the descaling operation can be further realized.

Preferably, the heating power of the heat exchange part is linearly increased in the front period of the cycle, and the heating power of the heat exchange part is linearly decreased in the rear period of the cycle, as shown in fig. 6.

Preferably, the linearly increasing growth amplitude is smaller than the linearly decreasing growth amplitude.

The linear variation of the heating power is achieved by a variation of the input current or voltage.

By arranging the plurality of electric heaters, the starting of the electric heaters with gradually increased quantity is realized, and the linear change is realized.

Preferably, the period is 50 to 300 minutes, preferably 50 to 80 minutes; the average heating power of the heat exchange part is 2000-4000W.

Preferably, the pipe diameter of the lower pipe box 2 is smaller than that of the upper pipe box 8, and the pipe diameter of the lower pipe box 2 is 0.5-0.8 times of that of the upper pipe box 8. Through the pipe diameter change of lower tube case and upper tube case, can guarantee that the fluid carries out the phase transition and in the internal time of first box short, get into the heat exchange tube fast, fully get into the heat transfer of second box.

Preferably, the connection position 9 of the heat exchange tube at the lower tube box is lower than the connection position of the upper tube box and the heat exchange tube. This ensures that steam can rapidly enter the upper header.

Preferably, a return line is provided between the lower and upper headers, optionally at the ends 18-20 of the lower and upper headers, to ensure that condensed fluid in the upper header can enter the first line.

Preferably, the lower tube box and the upper tube box are arranged in the horizontal direction, the heat exchange tubes are arranged in a plurality along the flowing direction of the fluid in the shell side, and the tube diameter of the heat exchange tube bundle is continuously increased along the flowing direction of the fluid.

Preferably, the tube diameter of the heat exchange tube bundle is increased along the flowing direction of the fluid.

The pipe diameter range through the heat exchange tube increases, can guarantee that shell side fluid outlet position fully carries out the heat transfer, forms the heat transfer effect like the adverse current, further strengthens the heat transfer effect moreover for whole vibration effect is even, and the heat transfer effect increases, further improves heat transfer effect and scale removal effect. Experiments show that better heat exchange effect and descaling effect can be achieved by adopting the structural design.

Preferably, the heat exchange tubes are arranged in a plurality along the flowing direction of fluid in the shell side, and the distance between every two adjacent heat exchange tubes is gradually reduced along the flowing direction of the fluid.

Preferably, the interval between the heat exchange tubes becomes smaller and larger along the height direction of the lower header.

The interval amplitude through the heat exchange tube increases, can guarantee that shell side fluid outlet position fully carries out the heat transfer, forms the heat transfer effect like the adverse current, further strengthens the heat transfer effect moreover for the whole vibration effect is even, and the heat transfer effect increases, further improves heat transfer effect and scale removal effect. Experiments show that better heat exchange effect and descaling effect can be achieved by adopting the structural design.

Preferably, as shown in fig. 7, the casing is a casing with a circular cross section, and a plurality of heat exchange components are arranged in the casing.

Preferably, as shown in fig. 7, a plurality of heat exchange members are disposed in the housing, one of which is disposed in the center of the housing to become a central heat exchange member, and the others are distributed around the center of the housing to become peripheral heat exchange members. Through the structural design, the fluid in the shell can fully achieve the vibration purpose, and the heat exchange effect is improved.

Preferably, the heating power of the single peripheral heat exchange member is smaller than the heating power of the central heat exchange member. Through the design, the center reaches higher vibration frequency to form a central vibration source, so that the periphery is influenced, and better heat transfer enhancement and descaling effects are achieved.

Preferably, on the same horizontal heat exchange section, the fluid needs to achieve uniform vibration, and uneven heat exchange distribution is avoided. It is therefore necessary to distribute the amount of heating power among the different heat exchange members reasonably. Experiments show that the heating power ratio of the central heat exchange component to the peripheral tube bundle heat exchange component is related to two key factors, wherein one factor is related to the distance between the peripheral heat exchange component and the center of the shell (namely the distance between the circle center of the peripheral heat exchange component and the circle center of the central heat exchange component) and the diameter of the shell. Therefore, the invention optimizes the optimal proportional distribution of the pulsating flow according to a large number of numerical simulations and experiments.

Preferably, the radius of the inner wall of the shell is R, the center of the central heat exchange component is arranged at the center of the circular section of the shell, the distance from the center of the peripheral heat exchange component to the center of the circular section of the shell is S, the centers of adjacent peripheral heat exchange components are respectively connected with the center of the circular section, the included angle formed by the two connecting lines is a, the heating power of the peripheral heat exchange component is P2, and the heating power of a single central heat exchange component is P1, so that the following requirements are met:

P1/P2= a-b Ln (R/S); ln is a logarithmic function;

a, b are coefficients, wherein 2.0869< a <2.0875,0.6833< b < 0.6837;

preferably, 1.35< R/S < 2.1; further preferred is 1.4< R/S < 2.0;

preferably, 1.55< P1/P2< 1.9. Further preferred is 1.6< P1/P2< 1.8;

wherein 35 ° < a <80 °.

Preferably, the number of the four-side distribution is 4-5.

Preferably, R is 1600-2400 mm, preferably 2000 mm; s is 1150-1700 mm, preferably 1300 mm; the diameter of the heat exchange tube bundle is 12-20 mm, preferably 16 mm; the outermost diameter of the heat exchange tube is preferably 300-560 mm, preferably 400 mm. The tube diameter of the lower manifold is 100-116 mm, preferably 108 mm, and the length of the upper manifold and the lower manifold is 1.8-2.2 m.

The total heating power is preferably 5000-.

Further preferably, a =2.0872 and b = 0.6835.

Preferably, the box body is of a circular section, and is provided with a plurality of heat exchange components, wherein one heat exchange component is arranged at the center of the circle of the circular section, and the other heat exchange components are distributed around the center of the circle of the circular section. The heat exchange tubes 1 are in one group or multiple groups, each group of heat exchange tubes 1 comprises a plurality of circular arc-shaped tube bundles 12, the central lines of the circular arc-shaped tube bundles 12 are circular arcs of concentric circles, and the end parts of the adjacent tube bundles 12 are communicated, so that the end parts of the heat exchange tubes 1 form tube bundle free ends 3 and 4, such as the free ends 3 and 4 in fig. 2.

Preferably, the heating fluid is a vapor-liquid phase-change fluid.

Preferably, the lower header 2, the upper header 8 and the heat exchange tubes 1 are all of a circular tube structure.

Preferably, the tube bundle of the heat exchange tubes 1 is an elastic tube bundle.

The heat exchange coefficient can be further improved by arranging the tube bundle of the heat exchange tube 1 with an elastic tube bundle.

Preferably, the concentric circles are circles centered around the center of the lower header 2. I.e., the tube bundle 12 of heat exchange tubes 1 is arranged around the center line of the lower header 2.

As shown in fig. 8, the tube bundle 12 is not a complete circle, but rather is left open to form the free end of the bundle. The angle of the arc of the mouth part is 65-85 degrees, namely the sum of the included angles b and c in figure 8 is 65-85 degrees.

Preferably, the ends of the tube bundle on the same side are aligned in the same plane, with the extension of the ends (or the plane in which the ends lie) passing through the median line of the lower header 2.

Further preferably, the electric heater 13 is an electric heating rod.

Preferably, the first end of the inner tube bundle of the heat exchange tube 1 is connected with the lower tube box 2, the second end is connected with one end of the adjacent outer tube bundle, one end of the outermost tube bundle of the heat exchange tube 1 is connected with the upper tube box 8, and the end parts of the adjacent tube bundles are communicated, so that a series structure is formed.

The included angle c formed by the plane of the first end and the plane of the central lines of the lower pipe box 2 and the upper pipe box 8 is 40-50 degrees.

The included angle b formed by the plane of the second end and the plane of the central lines of the lower pipe box 2 and the upper pipe box 8 is 25-35 degrees.

Through the design of the preferable included angle, the vibration of the free end is optimal, and therefore the heating efficiency is optimal.

As shown in fig. 8, the number of tube bundles of heat exchange tube 1 is 4, and tube bundles A, B, C, D are communicated. Of course, the number is not limited to four, and a plurality of the connecting structures are provided as required, and the specific connecting structure is the same as that in fig. 8.

The heat exchange tubes 1 are multiple, the heat exchange tubes 1 are respectively and independently connected with the lower tube box 2 and the upper tube box 8, and the heat exchange tubes 1 are in parallel connection.

Although the present invention has been described with reference to the preferred embodiments, it is not limited thereto. Various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (5)

1. A shell-and-tube heat exchanger comprises a shell, wherein tube plates are respectively arranged at two ends of the shell, a heat replacement component is arranged in the shell, the heat exchange component comprises a lower tube box, an upper tube box and a heat exchange tube, the heat exchange tube is communicated with the lower tube box and the upper tube box to form closed circulation of heating fluid, two ends of the lower tube box and the upper tube box are arranged in openings of the tube plates, and an electric heater is arranged in the lower tube box; filling phase-change fluid in the lower channel box; the heat exchange tube is characterized in that the electric heaters are arranged in a plurality, each electric heater is independently controlled, and the starting number of the electric heaters is periodically changed along with the change of time; in the previous period of the cycle, the starting number of the electric heaters is gradually increased along with the time until all the electric heaters are started; during the latter part of the cycle, the number of electric heaters activated is gradually reduced over time until all are deactivated.

2. The heat exchanger of claim 1, wherein the previous period of time is 3 times greater than the subsequent period of time.

3. The heat exchanger of claim 1, wherein assuming m electric heaters, one electric heater is activated every 3/4m periods in a cycle until 3/4 periods when the heater is fully activated, and then one electric heater is deactivated every 1/4m periods until the heater is fully deactivated in a cycle.

4. The heat exchanger of claim 3 wherein each of the electric heaters has the same heating power.

5. A tube plate is arranged at each of two ends of a shell, a heat exchange component is arranged in the shell and comprises a lower tube box, an upper tube box and a heat exchange tube.

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