PTC heater and design method thereof

Abstract

The invention relates to the technical field of electric heaters, and provides a PTC heater and a design method thereof.The PTC heater comprises a PTC heating rod and a radiator attached to the PTC heating rod; and the PTC heating rod and the radiator are brazed into a whole. The PTC heating rod comprises at least two PTC heating chips, and a dummy piece is arranged between every two adjacent PTC heating chips. The PTC heating chips and the dummy chip are the same in structural size, and the dummy chip is embedded between the two PTC heating chips. According to the PTC heater provided by the invention, the heat insulation partition structure is arranged between the adjacent PTC heating chips. According to the structure, the two PTC heating chips are physically separated, the longitudinal heat conduction path of the PTC heating chips is effectively blocked, the heat superposition effect between adjacent units is essentially eliminated, meanwhile, under the heat dissipation effect of the heat dissipation strips, the heat dissipation area of the radiator and the air flowing path are enlarged, and heat generated on the heating chips in unit time is further effectively taken away.

Description

Technical Field

[0001] This application relates to the field of heater technology, and more specifically, to a PTC heater under natural convection conditions and its design method. Background Technology

[0002] The content in this section provides only background information related to this application and may not constitute prior art.

[0003] PTC electric heaters, as highly efficient electrothermal conversion devices, have significant application value in indoor heating. Their core working mechanism lies in achieving a stable conversion of electrical energy into heat energy through the resistive characteristics of PTC thermistor ceramic materials. A typical PTC heater consists of several parallel-arranged PTC heating chips. The Joule heat generated by each chip after being energized is transferred to a metal radiator via heat conduction, and then heats the indoor environment through thermal radiation and convection, thereby improving the thermal comfort of the space.

[0004] In current product design, high-density integrated design schemes are commonly adopted to pursue better heating performance parameters. This scheme theoretically achieves a linear increase in heating efficiency by increasing the number of PTC heating chips per unit volume and providing a strong convection heat dissipation environment. However, this high-density layout results in excessively small spacing between adjacent PTC heating units, leading to a significant thermal superposition effect in actual operation, especially under natural convection conditions. In addition to effectively conducting heat to the radiator, the heat from each PTC heating chip also causes adjacent PTC heating chips to heat each other, resulting in a rise in PTC heating chip temperature. This heat accumulation phenomenon triggers a vicious cycle of temperature rise: when the ambient temperature exceeds the Curie point temperature of the PTC material, its resistance exhibits an exponential growth characteristic, and under constant operating voltage, the current intensity dominated by Ohm's law will decrease significantly (I = U / R). Although this negative feedback mechanism has temperature self-limiting characteristics, it directly leads to an irreversible decrease in the system's effective power (P = VI). More seriously, the temperature gradient distortion caused by heat accumulation will disrupt the linear operating range of the PTC material's resistance characteristics, ultimately leading to a decrease in the thermal efficiency and a deterioration in the heating performance of the entire heating system.

[0005] In summary, existing PTC heaters face a fundamental technical contradiction in the pursuit of high power density: while increasing the chip density can improve the theoretical heating power, it inevitably leads to thermodynamic imbalances in actual operation due to limitations in material properties and heat transfer mechanisms, forming a technical bottleneck that urgently needs to be addressed to restrict the continuous improvement of equipment thermal efficiency. Under natural convection conditions, existing PTC heaters are clearly unusable, necessitating a complete redesign of the PTC heating chip distribution and PTC heater structure. Summary of the Invention

[0006] In view of this, the purpose of this application is to provide a PTC heater and its design method, which can solve the technical problems raised in the background art.

[0007] On one hand, the present invention proposes a PTC heater, comprising:

[0008] PTC heating rod;

[0009] The radiator is in contact with the PTC heating rod;

[0010] The PTC heating rod includes: at least two PTC heating chips, with several dummy chips arranged between adjacent PTC heating chips;

[0011] The radiator includes a mounting shell and a heat dissipation structure;

[0012] The heat dissipation structure includes multiple bottom-to-top through-holes to create natural convection from the bottom up within the radiator.

[0013] The innovative technical solution proposed in this application innovatively sets up a thermal insulation isolation structure between adjacent PTC heating chips. This structure effectively blocks the heat conduction path between the two PTC heating chip units by physically separating them, fundamentally eliminating the thermodynamic coupling phenomenon between adjacent units. The dummy chip avoids the formation of localized heat accumulation areas by blocking radiative heat transfer and air convection conduction paths. By eliminating parasitic heat exchange between adjacent PTC heating chips, it ensures that each PTC unit is always within the preset temperature-resistance characteristic linear range, maintaining the stability of its positive temperature coefficient of resistance. This solution fundamentally avoids the temperature rise hysteresis effect caused by heat storage in the air layer in traditional structures, preventing temperature rise runaway induced by thermal resistance mismatch between the heat sink and the mounting substrate, thereby ensuring that the resistivity transition characteristics of the PTC material below the Curie temperature threshold are always in a controllable operating state.

[0014] In some possible embodiments, the heat dissipation structure includes a plurality of heat dissipation strips, which are wavy metal sheets.

[0015] In some possible embodiments, the heat dissipation structure is a heat dissipation cylinder with multiple interconnected sidewalls, heat dissipation holes formed at both ends of the heat dissipation cylinder, and the central cross-section of the heat dissipation cylinder is circular.

[0016] In some possible embodiments, the heat dissipation structure is a heat dissipation column with multiple interconnected sidewalls, with heat dissipation holes formed at both ends of the heat dissipation column, and the central cross-section of the heat dissipation column is a regular polygon.

[0017] In some possible embodiments, the PTC heating chip has the same structural dimensions as the dummy chip, including the same length, width, and height.

[0018] Furthermore, the dummy sheet is a ceramic insulating sheet.

[0019] In some possible embodiments, the PTC heating chip and the dummy chip are alternately arranged.

[0020] In some possible embodiments, the length of the PTC heating rod is 800mm to 850mm, the number of PTC heating chips is 7 to 11, the length of the heat sink after it is straightened is L1, the width is h, and the length of the heat sink when it is folded into a wave shape is L2; ​​a = L1 / L2; b = h / L2; where a ∈ [1.5, 2.5], b ∈ [0.015, 0.02].

[0021] On the other hand, the present invention also provides a design method for designing the aforementioned PTC heater, comprising the following steps:

[0022] The length of the PTC heating rod, the thermal conductivity of the heat sink, the thermal conductivity of the dummy plate, and the width of the air inlet are used as fixed parameters.

[0023] The length of the PTC heating chip, the number of heat sinks, and the size of the heat sinks are used as variable parameters.

[0024] A heat dissipation model of the PTC heating chip in the central region is established based on fixed and variable parameters to predict the temperature of the PTC heating chip under steady state.

[0025] Based on the steady-state temperature of the PTC heating chip, the optimal range of variable parameters is generated.

[0026] The technical solution proposed in this application achieves dual technical optimizations by constructing a heat dissipation model for the PTC heating chip: firstly, it employs a feature region dimensionality reduction modeling method to simplify the three-dimensional heat transfer field into an axisymmetric two-dimensional model, reducing the complexity of model construction; secondly, it accurately analyzes the thermal accumulation effect of the PTC heating chip, effectively improving the temperature field simulation accuracy compared to traditional homogenized models. This modeling strategy, through deterministic calculation of the temperature extrema in the central region, can accurately pinpoint the point of maximum temperature rise within the system, thereby deriving the corresponding maximum resistance value of the PTC heating chip. Based on this, the parameter optimization algorithm can quickly converge to the optimal solution domain under limited computational resource constraints, achieving optimal matching between system power density and thermal stability parameters.

[0027] Furthermore, the dimensions of the heat dissipation strip include a length ratio a and a width ratio b, where a = L1 / L2; b = h / L2; where L1 is the length of the heat dissipation strip after it is straightened, L2 is the length of the heat dissipation strip when it is folded into a wavy shape, and h is the width of the heat dissipation strip, where a ∈ [1.5, 2.5] and b ∈ [0.015, 0.02].

[0028] The solution provided in this application uses length ratio 'a' and width ratio 'b' to describe the size of the heat sink. In practice, this allows for the description of the entire heat sink's size information with a relatively small amount of information, thereby avoiding redundant information when building the heat dissipation model.

[0029] Furthermore, the construction method of the heat dissipation model includes the following steps:

[0030] Calculate the heating power Q1 of all PTC heating chips, where Q1 = nP; and P is the power of the PTC heating chip, P = U / R. 2 U is the rated voltage of the PTC heating chip, R is the resistance of the PTC heating chip, and n represents the number of PTC heating chips;

[0031] Calculate the heat dissipation power Q2 of the central region per unit time, Q2=E×S×T`; where E represents the heat transfer coefficient, S represents the heat transfer area, and T` represents the temperature difference between the corrugated pipe surface and the air.

[0032] The heat dissipation power equals the heat generation power as the steady-state condition, and a heat dissipation model is constructed based on the heat generation power and the heat dissipation power.

[0033] In the technical solution provided in this application, the equalization of heat dissipation power and heat generation power is creatively used as a steady-state condition when constructing the heat dissipation model, thereby avoiding the need to calculate the heat accumulation effect. The dynamic equilibrium characteristics that change constantly during the heat dissipation process are simplified into a static equation model, which effectively reduces the complexity of the heat dissipation model.

[0034] The technical solution of this application embodiment has at least the following advantages and beneficial effects: The innovative technical solution proposed in this application innovatively sets up a thermal insulation partition structure between adjacent PTC heating chips. This structure effectively blocks the heat conduction path of the two PTC heating chip units by physically separating them, fundamentally eliminating the thermodynamic coupling phenomenon between adjacent units. On the one hand, the dummy chip avoids the formation of local heat accumulation areas by blocking the radiation heat transfer and air convection conduction paths; on the other hand, by completely covering the gap space between the PTC heating chips, it forces all the heat flow generated by the PTC heating chips to be directionally conducted to the heat sink surface. Thus, by eliminating parasitic heat exchange between adjacent PTC heating chips, it can ensure that each PTC unit is always within the preset temperature-resistance characteristic linear range, maintaining the stability of its positive temperature coefficient of resistance; the setting of the closed thermal insulation cavity blocks the dissipation of heat to non-heat dissipation paths, enabling efficient coupling between the working temperature field of the PTC heating chip and the heat sink of the heat sink. This solution fundamentally avoids the temperature rise hysteresis effect of the PTC heater caused by heat storage in the air layer in the traditional structure, and prevents the temperature rise runaway phenomenon induced by thermal resistance mismatch between the heat sink and the mounting substrate, thereby ensuring that the resistance transition characteristics of the PTC material under the Curie temperature threshold are always in a controllable working state. Attached Figure Description

[0035] Figure 1 A schematic diagram of the structure of a PTC heater provided for some embodiments of this application.

[0036] Figure 2 This is a partial schematic diagram of a PTC heating rod.

[0037] Figure 3 This is a cross-sectional view of a PTC heating rod.

[0038] Figure 4 This is an exploded view of a PTC heater.

[0039] Figure 5 for Figure 1 A partial schematic diagram of point A in the middle.

[0040] Figure 6 This is a partial schematic diagram of another heat dissipation structure.

[0041] Figure 7 This is a partial schematic diagram of another heat dissipation structure.

[0042] Figure 8 A structural diagram of the housing has been added for the PTC heater.

[0043] Figure 9 This is a cross-sectional view of a PTC heater.

[0044] Figure Labels

[0045] 1. PTC heating rod; 101. First electrode plate; 102. Second electrode plate; 103. Insulating film;

[0046] 2. PTC heating chip;

[0047] 3. Radiator; 31. Mounting shell; 32. Heat dissipation strip; 32a. Heat dissipation structure; 32a1. Heat dissipation cylinder; 32a2. Heat dissipation column;

[0048] 33. Partition; 34. Heat dissipation holes;

[0049] 4. Housing; 41. Air inlet; 42. Air outlet;

[0050] 5. Fake films; Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments. The same reference numerals in the accompanying drawings represent the same components. It should be noted that the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the described embodiments of this application without creative effort are within the scope of protection of this application.

[0052] Compared to the embodiments shown in the accompanying drawings, feasible embodiments within the scope of this application may have fewer components, other components not shown in the drawings, different components, differently arranged components, or components with different connections, etc. Furthermore, two or more components in the drawings may be implemented in a single component, or a single component shown in the drawings may be implemented as multiple separate components.

[0053] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this application pertains. The terms “first,” “second,” and similar terms used in this specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms “an” or “a” and similar terms do not necessarily indicate a quantity limitation. Terms such as “upper” and “lower” are used only to indicate relative positional relationships, and these relative positional relationships may change accordingly when the absolute position of the described object changes.

[0054] Example 1:

[0055] refer to Figure 1 and Figure 4 The PTC heater disclosed in the first embodiment of this application includes a PTC heating rod 1 and a radiator 3. The PTC heating rod 1 is used to generate heat, and the PTC heating rod 1 and the radiator 3 are connected as one piece by brazing.

[0056] The PTC heating rod 1 includes a first electrode plate 101, a second electrode plate 102, a PTC heating chip 2, and dummy plates 5. The first electrode plate 101 and the second electrode plate 102 are elongated metal strips with identical dimensions. They are preferably made of stainless steel or copper alloy, and their dimensions are matched to the PTC heating chip 2, which has a rectangular block structure. In this embodiment, multiple PTC heating chips 2 and multiple dummy plates 5 are arranged at intervals along the length of the first electrode plate 101. The PTC heating chip 2 heats up when powered on. The first electrode plate 101 is connected to the positive terminal of the power supply, and the second electrode plate 102 is connected to the negative terminal. The front side of the PTC heating chip 2 is in contact with the first electrode plate 101, and the back side is in contact with the second electrode plate 102. In this way, multiple PTC heating chips 2 between the first electrode plate 101 and the second electrode plate 102 can be simultaneously powered synchronously. The multiple PTC heating chips 2 are connected in parallel circuit structure, and the rated voltage of each PTC heating chip 2 is equal.

[0057] refer to Figure 3 Furthermore, the PTC heater also includes an insulating film 103 and a protective shell 104. The insulating film 103 is wrapped around the outside of the first electrode plate 101 and the second electrode plate 102, serving an insulating function. The insulating film 103 is a polyimide film. The protective shell 104 is made of metal and is wrapped around the outside of the insulating film 103 to protect the insulating film 103 and prevent it from being worn.

[0058] refer to Figure 2 In designing PTC heating chips 2, the length of the PTC heating rod 1 is usually determined first, and then the required number of PTC heating chips 2 is obtained according to the power requirements. Each PTC heating chip 2 and the dummy chip 5 are then arranged alternately. The heat from adjacent PTC heating chips 2 can transfer to each other, resulting in a thermal superposition effect. Therefore, in this solution, adjacent PTC heating chips 2 are separated by dummy chips 5, thus avoiding heat exchange between adjacent PTC heating chips 2 and preventing a thermal superposition effect.

[0059] Furthermore, the length, width, and height dimensions of the PTC heating chip 2 are the same as those of the dummy chip 5, and the two are arranged in a periodic alternation along the length of the PTC heating rod 1. This layout maximizes the number of PTC heating chips 2 per unit length while eliminating longitudinal heat conduction paths through the thermal decoupling effect of the dummy chip 5. Moreover, the thickness of the dummy chip 5 is equal to the thickness of the PTC heating chip 2, which avoids voids between the second electrode plate 102 and the first electrode plate 101, allowing the second electrode plate 102 and the first electrode plate 101 to fit tightly against the PTC heating chip 2.

[0060] The heat sink 3 has a structural feature with the same width as the PTC heating rod 1, and its longitudinal coverage must meet the basic requirement of completely covering all PTC heating chips 2. When the first electrode plate 101 and the second electrode plate 102 are energized, the Joule heat generated by the PTC heating chip 2 is transferred to the surface of the heat sink 3, and the air medium temperature rises in the form of natural convection. The heat sink structure of the present invention can form several micro-channels to produce a flue effect, which can accelerate the flow of air from bottom to top under natural convection conditions.

[0061] Example 2:

[0062] Example 2 provides a specific structure of a radiator 3 and an arrangement of the radiator 3 based on the PTC heater of Example 1;

[0063] like Figure 5 As shown, the radiator includes a fixed shell and a heat dissipation structure. The heat dissipation structure includes several heat dissipation strips 32, which are wavy metal sheets. The heat dissipation strips 32 can divide the through space of the fixed shell 31 into multiple heat dissipation holes 34, thereby increasing the heat dissipation area of ​​the entire radiator 3. The more heat dissipation strips 32 there are, the more heat dissipation holes 34 can be divided. In order to fix the heat dissipation strips 32, partitions 33 are provided between adjacent heat dissipation strips 32. The front and rear ends of the partitions 33 are fixedly connected to the fixed shell 31, and the heat dissipation strips 32 are fixedly connected to the partitions 33.

[0064] Both the mounting shell 31 and the heat sink 32 are metal components with excellent thermal conductivity, such as aluminum alloy and copper. The mounting shell 31 has a square structure and is arranged vertically. One side of the mounting shell 31 is fixedly connected to the PTC heating rod 1, for example, by bonding with thermally conductive resin.

[0065] refer to Figure 5 Because the heat dissipation strip 32 is corrugated, it can isolate multiple small heat dissipation holes 34 within the fixed shell 31. However, relatively speaking, the edges of these heat dissipation holes 34 are not regular enough and there is a certain concave area. When natural convection is formed, turbulence is easily formed in the concave area of ​​the edges, which affects the heat exchange efficiency.

[0066] refer to Figure 6 To address this, an alternative radiator structure 32a is provided. The radiator structure 32a consists of multiple interconnected heat dissipation cylinders 32a1 with their sidewalls connected. Both ends of the heat dissipation cylinders 32a1 are through-holes, and the cylinders are arranged vertically upwards. The central cross-section of the heat dissipation cylinders 32a1 is circular. This results in a more regular inner wall of the heat dissipation channel formed by the structure, without abrupt reductions in cross-section. The upward airflow velocity is more stable, turbulence is less likely to form, airflow wear is reduced, and heat exchange is increased.

[0067] refer to Figure 7 In a more specific embodiment, the contact area between the cylindrical heat dissipation structure and the fixed shell 31 is small, resulting in low efficiency in transferring heat from the PTC heating rod 1 to the heat dissipation structure. To address this, another heat sink structure is provided, consisting of multiple interconnected heat dissipation columns 32a2, with both ends of the columns extending vertically upwards. The central cross-section of each column is a regular polygon. Because the heat dissipation columns 32a2 are constructed as regular polygons, their sidewalls have more contact surface with the fixed shell, enabling better heat absorption. Furthermore, the regular edges of the heat dissipation cylinder prevent turbulence and promote better upward air convection, increasing heat dissipation efficiency.

[0068] refer to Figure 8 and Figure 9 In a further design, the PTC heater also includes a housing 4, which is used to fix the entire PTC heater. In practice, the PTC heater is not made infinitely large and needs to be installed in a heating system. Therefore, the size of the PTC heater is limited by the housing 4. The PTC heating rod 1 and the radiator 3 are both fixedly connected inside the housing 4.

[0069] The housing 4 has an air inlet 41 and an air outlet 42 that run vertically through it. The heat dissipation hole 34 has the same penetrating direction as the air inlet 41 and the air outlet 42. The air inlet 41 and the air outlet 42 have a vertically upward penetrating direction.

[0070] In this scheme, by setting the through direction of the shell 4 and the through direction of the heat dissipation hole 34 to be vertically upward, the density of air decreases after heating, and warm air rises and cold air falls, so that natural air convection can be formed inside the shell 4, thus forming a good heat exchange circulation even without a fan.

[0071] Example 3:

[0072] Example 3 provides a further design scheme for the PTC heater based on Example 2. In this design, natural convection is used for heat dissipation to reduce noise, which limits the heat dissipation performance. Furthermore, an excessive number of PTC heating chips 2 leads to a significant heat accumulation effect between them, resulting in a decrease in the overall heating power of the PTC heater.

[0073] Based on this, this application provides the following specific technical solution, which, under the conditions that the areas of the air inlet 41 and the air outlet 42 are constant, the length of the PTC heating rod 1 is constant, and the thermal conductivity of the heat sink 3 material is constant, gives the optimal number and position of the PTC heating chips 2 and the number of heat sink strips 32.

[0074] Furthermore, the length of the PTC heating rod is 800mm to 850mm, the number of PTC heating chips is 7 to 11, the length of the heat sink 32 after straightening is L1, the width of the heat sink 32 is h, and the length of the heat sink 2 when it is folded into a wave shape is L2; ​​a = L1 / L2; b = h / L2; where a ∈ [1.5, 2.5], b ∈ [0.015, 0.02].

[0075] Specifically, the PTC heating chip 2 is 24mm long, 15mm wide, and 3.0mm thick. There are 16 PTC heating chips 2, and one dummy chip 5 is spaced between two adjacent PTC heating chips 2.

[0076] The following is the relevant experimental data:

[0077] During the experiment, the length of the PTC heating rod was 805mm, the size of the air inlet 41 and the air outlet 42 were equal, the length of the air inlet 41 was 1000mm, and the width of the air inlet 41 was 165mm.

[0078] The experimental data obtained through experiments are shown in the following tables: Table 1 shows the experimental data for different numbers of PTC heating chips; Table 2 shows the experimental data for adding two sets of heat sinks on each side of the PTC heating rod; and Table 3 shows the experimental data for adding one to four sets of heat sinks on each side of the PTC heating rod with a dummy chip between adjacent PTC heating chips.

[0079] Table 1: Experimental data for different PTC heating chip heating quantities:

[0080]

[0081] In Table 1, the ambient temperature is 8℃. Three sets of heat dissipation strips are set on each side of the PTC heating rod. "0 / 28" in the control group means that there are 0 dummy chips between adjacent PTC heating chips. A total of 28 PTC heating chips are installed. Two dummy chips are set at the beginning and end of the table. The total number of PTC heating chips and dummy chips is 34.

[0082] In Implementation Group 1, "1 / 16" indicates that there is one dummy chip between adjacent PTC heating chips, and a total of 16 PTC heating chips are installed. The number of dummy chips between the 16 PTC heating chips is 16, with one dummy chip at each end, for a total of 34 PTC heating chips and dummy chips.

[0083] In implementation group 2, "2 / 11" indicates that there are 2 dummy chips between adjacent PTC heating chips, and a total of 11 PTC heating chips are installed. The number of dummy chips between the 11 PTC heating chips is 20, with 1 dummy chip at the beginning and 2 dummy chips at the end. The total number of PTC heating chips 2 and dummy chips 5 is 34.

[0084] In implementation group 3, "3 / 7" indicates that the number of dummy chips is 3, and a total of 7 PTC heating chips are installed. The number of dummy chips between the 7 PTC heating chips is 18, with 5 dummy chips set at the beginning and 4 dummy chips set at the end. The total number of PTC heating chips 2 and dummy chips 5 is 34.

[0085] Based on the above 1 control group and 3 implementation groups, it can be seen that when the number of dummy chips is 1 to 2, the overall situation of steady-state power and heating power of a single PTC heating chip is optimal. Thus, the best effect can be obtained when PTC heating chips and dummy chips are arranged alternately.

[0086] Table 2: Experimental data for adding two sets of heat dissipation strips on each side of the PTC heating rod:

[0087]

[0088] Table 3: Experimental table with one dummy chip between adjacent PTC heating chips and 1-4 sets of heat sinks on each side of the PTC heating rod:

[0089]

[0090] According to the experimental data in Tables 1 to 3, the number of spacer 5 5s ranges from 1 to 3, showing good overall performance. When the number of spacer 5 5s is 1, the overall performance is the best. In Table 1, when the number of spacer 5 5s is 0, the maximum surge power is 2605W and the steady-state power is 880W. Therefore, after reaching the steady state, the total power of the PTC heating rod decreases by 1705W.

[0091] When the number of spacer 5 dummy plates is 1, the maximum incoming power is 1600 kW, and the steady-state power is 840 kW. Therefore, after reaching the steady state, the total power of the PTC heating rod decreases by 760 kW. Compared to the scheme when the number of spacer 5 dummy plates is 0, the decrease in the total power of the PTC heating rod is reduced by 1000 kW, while the steady-state power only decreases by 40 kW. Therefore, the scheme with 1 spacer 5 dummy plate is better than the scheme with 0 spacer 5 dummy plates.

[0092] When the number of spacer 5 dummy plates is 2, the steady-state power is only 652, which is 188 lower than the scheme with 1 spacer 5 dummy plate. Therefore, changing the number of spacer 5 dummy plates from 1 to 2 only reduces the steady-state power loss from 760 to 432, but the steady-state power decreases by 188. This excessive decrease in steady-state power reduces the heating efficiency, so the scheme with 1 spacer dummy plate is better than the scheme with 2 spacer dummy plates.

[0093] Therefore, when the number of fake lenses with intervals of 5 is 1 to 2, the overall performance is optimal.

[0094] As shown in Table 3, the steady-state power gradually increases with the increase in the number of heat sinks. However, the number of heat sinks is limited by manufacturing costs and space constraints, so in this scheme, the number of heat sinks is 2 to 4 sets. All six implementation groups in this scheme are preferred and feasible implementation methods, while the four control groups are poor implementation methods.

[0095] Example 4:

[0096] A design method is provided for designing the PTC heater described in Embodiment 3. Specific dimensional parameters of the PTC heater are provided in Embodiment 3. The length of the PTC heating rod, the width of the air inlet, the material of the heat sink, and the material of the dummy plate are related to production requirements and processes, and can be directly determined as fixed parameters. The materials of the heat sink and the dummy plate are both of high thermal conductivity.

[0097] The optimal parameters for the PTC heating chip's single-chip size (single-chip power), the ratio of the straightened length of the heat sink to the wavy length of the heat sink in its working state (determining the size of the heat dissipation holes), and the number of heat sinks can be found directly through experiments and are easily adjusted in production as variable parameters.

[0098] In practice, changes in the size of a single PTC heating chip will lead to changes in local temperature rise, resulting in new trends in local heat generation. Consequently, the structure of the heat sink needs to be adapted accordingly. Conversely, changes in the heat sink structure will also alter the specific heat accumulation effect. Therefore, in practice, it is impossible to determine the size of the PTC heating chip and the dimensions of the heat sink using limited experiments. This approach employed computer simulations of numerous structures, selecting the four most likely control groups and six experimental groups mentioned above for testing, thereby determining the optimal parameter settings.

[0099] Based on this, this application provides the following design method, which includes the following steps:

[0100] S1: The length of the PTC heating rod, the material of the heat sink, the material of the dummy plate, and the width of the air inlet are set as fixed parameters. The material of the heat sink is its thermal conductivity, and the material of the dummy plate is its thermal conductivity. Thermal conductivity can be obtained directly from a database or experimentally.

[0101] Fixed parameters are specific parameters determined during the production of heat sinks based on demand and cost. The length of the PTC heating element and the size of the air outlet are mainly used to determine the size of the heat sink, the material of the fins is used to determine the insulation performance of the fins, and the material of the heat sink is used to determine the thermal conductivity of the heat sink.

[0102] S2: The length of the PTC heating chip, the number of heat sinks, and the size of the heat sinks are used as variable parameters;

[0103] The length of the PTC heating rod determines the arrangement range of the PTC heating chip. The length of the PTC heating chip determines the power of a single PTC heating chip and the maximum number of PTC heating chips that can be arranged. For example, in this scheme, the maximum number of PTC heating chips is 28. The heating power of the PTC heating chip is positively correlated with its length.

[0104] The dimensions of the heat sink include the length ratio 'a' and the width ratio 'b', where a = L1 / L2 and b = h / L2. L1 is the length of the heat sink when straightened, L2 is the length of the heat sink when bent into a wavy shape, and h is the width of the heat sink. The length of the heat sink when bent into a wavy shape refers to the length measured along the heat sink. The direct length is the length measured directly at both ends of the heat sink. The length of the heat sink when bent into a wavy shape is equal to the length of the PTC heating rod.

[0105] In this design, the heat sink is a wavy metal sheet. Since the bending frequency of the heat sink cannot be changed in actual production, each set of length ratio 'a' and width ratio 'b' corresponds to a set of heat dissipation hole sizes. In practice, the length of the heat sink in its wavy working state corresponds to the length of the PTC heating rod. Therefore, the length ratio 'a' and width ratio 'b' describe the actual structure of a single set of heat sinks, meaning each set of length ratio 'a' and width ratio 'b' corresponds to one heat dissipation area.

[0106] S3: Establish a heat dissipation model for the PTC heating chip in the central region based on fixed and variable parameters;

[0107] Furthermore, the construction method of the heat dissipation model includes the following steps:

[0108] S31: Calculate the heating power Q1 of all PTC heating chips, Q1 = nP; where P is the power of the PTC heating chip, P = U / R 2 U is the rated voltage of the PTC heating chip, R is the resistance of the PTC heating chip, and n represents the number of PTC heating chips;

[0109] When the PTC heating chip is below the Curie temperature, its resistance increases slowly with increasing temperature, showing an approximately linear relationship. When the temperature exceeds the Curie temperature, the resistance of the PTC heating chip increases exponentially. Therefore, it is necessary to limit the temperature of the PTC heating chip to near the Curie temperature, as close to the Curie temperature as possible.

[0110] S32: Calculate the heat dissipation power Q2 of the central region per unit time, Q2=E×S×T`; where E represents the heat transfer coefficient, S represents the heat transfer area, and T` represents the temperature difference between the radiator surface and the air.

[0111] Furthermore, Where N represents the Nusselt coefficient, k represents the thermal conductivity of the heat sink, and l represents the penetration depth of the heat dissipation hole; Ra = Gr × Pr;

[0112] Ra represents the Rayleigh number, Pr represents the Prandtl number, Gr represents the Glashoff number, v represents the fluid viscosity, α represents the thermal diffusivity, μ represents the dynamic viscosity, and c represents the fluid viscosity. p β represents the specific heat capacity at constant pressure, k represents the thermal conductivity of the radiator, g represents the acceleration due to gravity, and β represents the coefficient of thermal expansion.

[0113] Among them, Prandtl number, thermal diffusivity, fluid viscosity, dynamic viscosity, specific heat capacity at constant pressure, thermal conductivity, gravitational acceleration, penetration depth of heat dissipation holes, and coefficient of thermal expansion are all constant values ​​and will not change.

[0114] Therefore, when calculating heat dissipation power, it is necessary to focus on T'. That is, as T' increases, heat dissipation power Q2 will increase. In practice, because T' affects the Nusselt coefficient and Rayleigh number, the relationship between T' and heat dissipation power Q2 is not a simple direct proportional relationship.

[0115] S33: Take the equalization of heat dissipation power and heat generation power as the steady-state condition, and construct a heat dissipation model based on the heat generation power and heat dissipation power.

[0116] During operation, the temperature of the PTC heating chip continuously rises. In this design, the temperature of the PTC heating chip is approximated to the temperature of the heat sink. The heat generated by the PTC heating chip is mainly dissipated through the air. Therefore, as the temperature difference between the PTC heating chip and the air gradually increases, the heating power and the heat dissipation power tend to reach equilibrium. Initially, the air temperature is low, resulting in a higher heat dissipation power. As the air temperature rises, the heat dissipation power decreases, eventually falling below the heating power. Consequently, the temperature of the PTC heating chip rises again, leading to a decrease in heating power. After a period of time, the heating power and the heat dissipation power eventually become equal, and the entire system tends towards a dynamic stable state.

[0117] Furthermore, the heat dissipation model is as follows:

[0118] Q1 = Q2;

[0119]

[0120] S = q(l × L1);

[0121] R = L0R0

[0122]

[0123] Ra = Gr × Pr;

[0124] In the heat dissipation model: intermediate parameters are: heat generation power Q1, heat dissipation power Q2, heat transfer area S, resistance per unit length of PTC heating chip R0, heat transfer coefficient E, Nusselt coefficient N, Rayleigh number Ra, Prandtl number Pr, Grasshoff number Gr, and resistance of PTC heating chip R. Intermediate parameters are those that will not affect the heat dissipation model calculation and are used to simplify the model and balance the equations.

[0125] In the heat dissipation model, the constant parameters are: the rated voltage U of the PTC heating chip, the thermal conductivity k of the heat sink, the penetration depth l of the heat dissipation hole, the fluid viscosity v, the thermal diffusivity α, the dynamic viscosity μ, and the specific heat capacity at constant pressure c. pThe constant parameters are gravitational acceleration g and thermal expansion coefficient β. The material of the heat sink in the model will not change, and the object of heat dissipation is air, so the fluid properties will not change. Natural convection is used, so the corresponding dynamic viscosity, thermal diffusivity and thermal expansion coefficient will not be affected by wind speed. Thus, the constant parameters can be obtained directly and will not change during the heat dissipation process.

[0126] In the heat dissipation model: the variable parameters are: the number of PTC heating chips n, the length of the PTC heating chip L0, the number of heat sinks q, and the length of the heat sink after it is straightened L1;

[0127] The variable parameters are those that need to be solved in the heat dissipation model. Among them, the temperature difference T' between the heat sink surface and the air is a hypervariable parameter. This parameter does not need to be solved in practice, but it will be affected by the overall structure of the heat sink and the power of the PTC heating chip.

[0128] The heat dissipation model satisfies the following conditions:

[0129] (1): T` = T0 - T1, where T1 is the air temperature under steady-state conditions, T0 is the Curie temperature of the PTC heating chip, and R0 is the resistance value of the PTC heating chip at the Curie temperature. This condition indicates that under steady-state conditions, each PTC heating chip needs to be as close as possible to the Curie temperature in order to obtain the optimal resistance value.

[0130] (2) qh < Y, where Y represents the width of the air inlet. Y is a constant value. This constraint condition indicates that the width of all heat sink strips must be less than the width of the air inlet, and h is the width of the heat sink strip.

[0131] (3): L2=nL0+(n-1)L3, where, where, L3 represents the shortest length of the dummy chip. The dummy chip needs to have sufficient length to achieve the heat insulation effect. L3 is used to describe the shortest length of the dummy chip to achieve the heat insulation effect under the average working time of the PTC heater. The optimal value of L3 can be obtained through experiments or calculated by the thermal conductivity of the dummy chip. L2 represents the length of the PTC heating rod. This condition constrains the length and number of PTC heating chips under the condition that the length of the PTC heating rod is constant. L0 represents the length of the PTC heating chip.

[0132] In the technical solution provided in this application, a heat dissipation model is established based on the actual situation, and then the heat dissipation model is solved.

[0133] S4: Solve the heat dissipation model to obtain the optimal variation parameters;

[0134] Specifically, S4 includes the following steps:

[0135] S41: Collect the parameters required when building the heat dissipation model;

[0136] S42: Construct the aforementioned heat dissipation model using a modeling language supported by CPLEX;

[0137] S43: Configure the solution time limit, solution interval, and the level of detail in the output log;

[0138] The optimal solution found is evaluated, and iterative optimization is performed based on the evaluation results to find the solution that best meets actual needs and business objectives. The evaluation method is based on maximizing the heat dissipation power.

[0139] This solution already provides a method for constructing the heat dissipation model. Given a specific mathematical model, how to use the CPLEX algorithm to solve the mathematical model and iterate and update the solution results is common knowledge and will not be described further here.

[0140] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A PTC heater, comprising: PTC heating rod; The radiator is in contact with the PTC heating rod; The feature is that the PTC heating rod includes: at least two PTC heating chips, with a dummy chip disposed between adjacent PTC heating chips; The radiator includes a mounting shell and a heat dissipation structure; The heat dissipation structure includes multiple bottom-to-top through-holes to create natural convection from the bottom up within the radiator.

2. The PTC heater according to claim 1, characterized in that, The heat dissipation structure includes several heat dissipation strips, which are wavy metal sheets.

3. The PTC heater according to claim 1, characterized in that, The heat dissipation structure consists of multiple interconnected heat dissipation cylinders with heat dissipation holes at both ends, and the central cross-section of the heat dissipation cylinder is circular.

4. The PTC heater according to claim 1, characterized in that, The heat dissipation structure consists of multiple heat dissipation columns with interconnected sidewalls. The two ends of each heat dissipation column are through-holes, and the central cross-section of each heat dissipation column is a regular polygon.

5. The PTC heater according to claim 1, characterized in that, The PTC heating chip has the same structural dimensions as the dummy chip, including the same length, width, and height.

6. The PTC heater according to claim 1, characterized in that, The PTC heating chip and the dummy chip are alternately arranged, and the dummy chip is a ceramic insulating sheet.

7. The PTC heater according to claim 4, characterized in that, The length of the PTC heating rod is 800mm to 850mm, the number of PTC heating chips is 7 to 11, the length of the heat sink after it is straightened is L1, the width is h, and the length of the heat sink when it is folded into a wave shape is L2; ​​a = L1 / L2; b = h / L2; where a∈[1.5,2.5], b∈[0.015,0.02].

8. A design method, characterized in that, The method for designing the PTC heater of claim 7 includes the following steps: The length of the PTC heating rod, the thermal conductivity of the heat sink, the thermal conductivity of the dummy plate, and the width of the air inlet are used as fixed parameters. The length of the PTC heating chip, the number of heat sinks, and the size of the heat sinks are used as variable parameters. A heat dissipation model of the PTC heating chip in the central region is established based on fixed and variable parameters; Solve the heat dissipation model to obtain the optimal variation parameters; The heat dissipation model is as follows: Q1 = Q2; S = q(l × L1); R = L0R0 Ra = Gr × Pr; The intermediate parameters are: heating power Q1, heat dissipation power Q2, heat exchange area S, resistance per unit length of PTC heating chip R0, heat transfer coefficient E, Nusselt coefficient N, Rayleigh number Ra, Prandtl number Pr, and resistance R of PTC heating chip; these intermediate parameters are used to simplify the model and balance the heat dissipation model. The set parameters are: rated voltage U of the PTC heating chip, thermal conductivity k of the heat sink, penetration depth l of the heat dissipation hole, fluid viscosity v, thermal diffusivity α, dynamic viscosity μ, and specific heat capacity at constant pressure c. p , gravitational acceleration g, thermal expansion coefficient β; The variable parameters are: the number of PTC heating chips n, the length of the PTC heating chips L0, the number of heat sinks q, and the length of the heat sinks after they are straightened L1; the variable parameters are the parameters that the heat dissipation model needs to solve. The temperature difference T' between the radiator surface and the air is a hypervariable parameter.

9. The design method according to claim 8, characterized in that, The dimensions of the heat dissipation strip include a length ratio a and a width ratio b, where a = L1 / L2; b = h / L2; where L1 is the length of the heat dissipation strip after it is straightened, L2 is the length of the heat dissipation strip when it is folded into a wavy shape, and h is the width of the heat dissipation strip, where a ∈ [1.5, 2.5] and b ∈ [0.015, 0.02].

10. The design method according to claim 8, characterized in that, The construction method of the heat dissipation model includes the following steps: Calculate the heating power Q1 of all PTC heating chips, where Q1 = nP; and P is the power of the PTC heating chip, P = U / R. 2 U is the rated voltage of the PTC heating chip, R is the resistance of the PTC heating chip, and n represents the number of PTC heating chips; Calculate the heat dissipation power Q2 of the central region per unit time, Q2=E×S×T`; where E represents the heat transfer coefficient, S represents the heat transfer area, and T` represents the temperature difference between the corrugated pipe surface and the air. Where N represents the Nusselt coefficient, k represents the thermal conductivity of the heat sink, and l represents the penetration depth of the heat dissipation hole; Day=Gr×Pr; Ra represents the Rayleigh number, Pr represents the Prandtl number, Gr represents the Glashoff number, v represents the fluid viscosity, α represents the thermal diffusivity, μ represents the dynamic viscosity, and c represents the fluid viscosity. p Let represent the specific heat capacity at constant pressure, k represent the thermal conductivity of the radiator, g represent the acceleration due to gravity, and β represent the coefficient of thermal expansion. The heat dissipation power equals the heat generation power as the steady-state condition, and a heat dissipation model is constructed based on the heat generation power and the heat dissipation power. The heat dissipation model satisfies the following conditions: T` = T0 - T1, where T1 is the air temperature under steady-state conditions, T0 is the Curie temperature of the PTC heating chip, and R0 is the resistance value of the PTC heating chip when it is at the Curie temperature. qh < Y, where Y represents the width of the air inlet, and Y is a constant; L2 = nL0 + (n-1)L3, where L3 represents the shortest length of the dummy chip. The dummy chip needs to have a sufficient length to achieve the heat insulation effect. L3 is used to describe the shortest length of the dummy chip to achieve the heat insulation effect under the average working time of the PTC heater. L0 represents the length of the PTC heating chip.

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