Electronic device

Abstract

The present application provides an electronic device, comprising a body, at least one heat source, a circuit board, at least one first fan and at least one second fan. The body has a front compartment and a rear compartment, the rear compartment extends from the front compartment and is higher than the front compartment. The heat source, the circuit board and the first fan are arranged in the front compartment. The first fan has a first air outlet and a second air outlet facing in different directions. The circuit board, the first fan and the body form at least one air chamber space, which communicates with the external environment through a first opening of the rear compartment. The heat source is located in the air chamber space. The first air outlet of the first fan is adjacent to and faces the air chamber space to provide a first air flow to the air chamber space. The second air outlet of the first fan faces at least one second opening of the rear compartment to generate a second air flow to discharge the body. The second fan is arranged in the rear compartment to supply air or exhaust air to the air chamber space.

Description

Technical Field

[0001] This invention relates to an electronic device. Background Technology

[0002] As electronic devices continue to improve in performance and shrink in size, they generate more heat during operation. However, electronic devices often lack sufficient space to install appropriate heat dissipation modules, making it difficult for them to dissipate the waste heat accumulated inside the casing. Consequently, the internal temperature of the electronic device rises. In high-temperature environments, the computing performance of the central processing unit and graphics processing unit will be affected, and they may even overheat, crash, or burn out.

[0003] Therefore, how to provide an optimized airflow and heat dissipation path inside electronic devices to improve heat dissipation efficiency and avoid the aforementioned waste heat accumulation has become a topic that relevant technical personnel need to consider. Summary of the Invention

[0004] The present invention relates to an electronic device that utilizes the rear compartment space of the device body to provide an optimized air chamber space within the device body to improve heat dissipation efficiency without increasing the overall thickness of the device.

[0005] According to an embodiment of the present invention, an electronic device includes a body, at least one heat source, a circuit board, at least one first fan, and at least one second fan. The body has a front compartment and a rear compartment, the rear compartment extending from and being higher than the front compartment. The heat source, circuit board, and first fan are disposed in the front compartment. The first fan has a first air outlet and a second air outlet facing opposite directions. The circuit board, the first fan, and the body form at least one air chamber space, which communicates with the external environment through a first opening in the rear compartment. The heat source is located in the air chamber space. The first air outlet of the first fan is adjacent to and faces the air chamber space to provide a first airflow to the air chamber space. The second air outlet of the first fan faces at least one second opening in the rear compartment to generate a second airflow to exit the body. The second fan is disposed in the rear compartment to supply or exhaust air to the air chamber space.

[0006] Based on the above, the electronic device is configured with a front compartment and a rear compartment, and the rear compartment's higher structural feature provides space for the installation of a first fan and a second fan. The circuit board, the first fan, and the main body in the front compartment form an air chamber, which connects the rear compartment to the external environment. In this way, the second fan in the rear compartment can enhance the heat dissipation effect of the air chamber by supplying or exhausting air, thus preventing waste heat from remaining inside the device. Attached Figure Description

[0007] Figure 1 This is a schematic diagram of an electronic device according to an embodiment of the present invention;

[0008] Figure 2 Showing it from another perspective Figure 1 Electronic devices;

[0009] Figure 3 yes Figure 1 A partial cross-sectional view of an electronic device;

[0010] Figure 4 Shown from a top-down perspective Figure 1 Some internal components of electronic devices;

[0011] Figure 5 This is a partial cross-sectional view of an electronic device according to another embodiment;

[0012] Figure 6 This is a top view of some components of an electronic device according to another embodiment;

[0013] Figure 7 This is a top view of some components of an electronic device according to another embodiment;

[0014] Figure 8 This is a top view of some components of an electronic device according to another embodiment;

[0015] Figure 9A and Figure 9B These are partial cross-sectional views of electronic devices according to different embodiments.

[0016] Explanation of icon numbers

[0017] 100: Electronic devices

[0018] 110: Body

[0019] 111: Host

[0020] 111a: Front compartment

[0021] 111b: Rear compartment

[0022] 112: Screen

[0023] 120: Heat source

[0024] 130: Circuit board

[0025] 140A, 140B, 140C, 140D: First Fan

[0026] 150: Second Fan

[0027] 160: Thermal conductive component

[0028] 161: Heat dissipation fins

[0029] 170, 172, 173, 174: Retaining wall

[0030] 181: Touchpad

[0031] 182: Keyboard

[0032] 183: Heat pipe

[0033] E1, E3: First air outlet

[0034] E2: Second air outlet

[0035] F1: First airflow

[0036] F2: Second airflow

[0037] P1: First opening

[0038] P2: Second opening

[0039] P3: Third opening

[0040] P41, P42: Fourth opening

[0041] P5: Fifth Opening

[0042] R1, R2, R3: Air chamber space

[0043] S1: Top surface

[0044] S2: Bottom surface

[0045] XYZ: Rectangular coordinates Detailed Implementation

[0046] Reference will now be made in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same component reference numerals are used in the drawings and description to denote the same or similar parts.

[0047] Figure 1 This is a schematic diagram of an electronic device according to an embodiment of the present invention. Figure 2 Showing it from another perspective Figure 1 Electronic devices. Figure 3 yes Figure 1 A partial sectional view of the electronic device. Cartesian coordinates (XYZ) are also provided here to aid in component description. Please also refer to... Figures 1 to 3In this embodiment, the electronic device 100, such as a laptop computer, includes an openable body 110, which is divided into a main unit 111 and a screen 112 pivotally connected to each other. The main unit 111 is further divided into a front compartment 111a and a rear compartment 111b according to its structural features. The rear compartment 111b extends from and is higher than the front compartment 111a, and the screen 112 is pivotally connected to the rear compartment 111b. The electronic device 100 also includes a touchpad 181 and a keyboard 182, both of which are located in the front compartment 111a. In this embodiment, the plane of the main unit 111 is the XY plane or a plane parallel to the XY plane, and this is used as a reference for describing the relevant components within the main unit 111.

[0048] Figure 4 Shown from a top-down perspective Figure 1 Some internal components of the electronic device. Please also refer to... Figure 3 and Figure 4 To avoid excessive complexity and interference between lines, the relevant components are depicted in simplified drawings. In this embodiment, the electronic device 100 also includes a circuit board 130, a heat source 120, first fans 140A and 140B, and a second fan 150. The first fans 140A and 140B each have a first air outlet E1 and a second air outlet E2 facing opposite directions. The circuit board 130, the first fans 140A and 140B, and the main unit 111 of the casing 110 form an air chamber space R1, which spans the front compartment 111a and the rear compartment 111b, and communicates with the external environment through a first opening P1 in the rear compartment 111b. Figure 3 , Figure 4 As shown, the circuit board 130 is located in the XY plane, and the first fans 140A and 140B are arranged in a direction approximately parallel to the circuit board 130 within the main body 111 of the housing 110. In this embodiment, since the first fans 140A and 140B are fitted into the circuit board 130, the air chamber space R1 can cover the space above and below the circuit board 130 on the Z-axis.

[0049] Heat sources 120 (two are shown, for example, the CPU and GPU of a laptop) are located within the air chamber space R1. A first air outlet E1 is adjacent to and faces the air chamber space R1 to provide a first airflow F1 to R1. The second air outlets E2 of each of the first fans 140A and 140B face the second opening P2 of the rear compartment 111b to generate a second airflow F2 to exhaust the main unit 111 of the chassis 110. A second fan 150 is located in the rear compartment 111b, specifically in the space above the front compartment 111a, and is used to supply or exhaust air to the air chamber space R1 to achieve a cooling effect.

[0050] It should be noted that the supply fan directly cools the heat source 120 of the air chamber space R1, such as the heat pipe 183 and heat dissipation fins 161, by introducing cool air from the external environment; while the exhaust fan forcibly exhausts the heat absorbed by the air chamber space R1 to the external environment, increasing the flow of cool air (such as the first airflow F1 and the cool air drawn from the fourth openings P41 and P42) by generating negative pressure. This invention does not limit the choice between supply and exhaust cooling strategies for the air chamber space R1 to a single approach; rather, both can be combined to dynamically adjust the cooling strategy based on real-time temperature and system load, achieving an optimal balance between efficiency, noise, and energy consumption. For example, if the laptop is under high-performance load or in a high-temperature external environment, the second fan 150 can use an exhaust cooling strategy; if the laptop is under medium or low-performance load or in a low-temperature external environment, the second fan 150 can use a supply cooling strategy.

[0051] Furthermore, such as Figure 4 As shown, the electronic device 100 also includes a baffle 170, which abuts against the circuit board 130 and the main unit 111 of the housing 110 and is adjacent to the two first fans 140A and 140B, forming an air chamber space R1 with the first fans 140A and 140B, the circuit board 130 and the main unit 111 of the housing 110. The baffle 170 can be considered as one of the multiple boundaries forming the air chamber space R1. A first opening P1 is located between two second openings P2, and the first opening P1 and the two second openings P2 are located on the same side of the rear compartment 111b. The two first fans 140A and 140B are located on opposite sides of the air chamber space R1, and the two first air outlets E1 face each other and are adjacent to the air chamber space R1. Therefore, when the first fans 140A and 140B are activated, they can respectively provide a first airflow F1 to the air chamber space R1. A second fan 150 corresponds to the air chamber space R1.

[0052] Furthermore, the second fan 150 is positioned higher within the main unit 111 of the chassis 110 than the first fans 140A and 140B are within the chassis 110. The rear compartment 111b has a third opening P3, which connects to the external environment and corresponds to the second fan 150. This third opening P3 is actually located at a higher point in the rear compartment 111b (relative to the front compartment 111a) and differs from the first opening P1 and the second opening P2. (See also...) Figures 2 to 4 It can be seen that, along the height direction (positive Z-axis direction) of the fuselage 110, the second fan 150 is actually located between the third opening P3 and the first opening P1. Here, the second fan 150 includes multiple fan units, all of which are axial fans. For example... Figure 3 As shown, the top surface S1 and bottom surface S2 of the front compartment 111a each have multiple fourth openings P41 and P42 for connecting to the external environment. For example, the fourth opening P41 on the top surface S1 is... Figure 1 The keyboard 182 shown has gaps between its keys. The first opening P1 on the bottom surface S2 is, for example, an opening on the bottom shell of the host 111, which allows cool air from the outside environment to be drawn into the host 111 through the fourth openings P41 and P42 respectively when the first fans 140A and 140B are running.

[0053] In addition, the electronic device 100 also includes a heat-conducting element 160 and a heat sink 161. One end of the heat-conducting element 160 is located in the air chamber space R1 and is in thermal contact with the heat source 120 through a heat pipe 183. The heat pipe 183 is in thermal contact between the heat sink 161 and the heat source 120. The heat-conducting element 160 extends from the front compartment 111a to the rear compartment 111b, with the other end of the heat-conducting element 160 adjacent to the second fan 150. The heat sink 161 is disposed inside the main unit 111 of the casing 110 and is adjacent to the second opening P2 and the second air outlet E2.

[0054] Please check at the same time Figure 3 , Figure 4 The airflow diagram shows that the second airflow F2 generated by the first fans 140A and 140B sequentially passes through the second air outlet E2, the heat dissipation fins 161, and the second opening P2 before being discharged from the rear compartment 111b. This serves as the first heat dissipation path, dissipating the heat from the heat dissipation fins 161 (transferred from the heat source 120 to the heat dissipation fins 161 by the heat pipe 183) to the outside of the chassis 110. Furthermore, the first airflow F1 generated by the first fans 140A and 140B is first transferred to the air chamber space R1 to absorb the heat from the heat source 120, and then pushed by air pressure through the first opening P1 to be discharged from the main unit 111 of the chassis 110. This can be considered a second heat dissipation path. More importantly, in this embodiment, the second fan 150 blows air into the air chamber space R1, thus drawing in cool air from the external environment into the air chamber space R1 from the third opening P3 of the rear compartment 111b. As... Figure 4 The second fan 150 shown corresponds to the position of the air chamber space R1. The cold air drawn into the air chamber space R1 by the second fan 150 can further cool the first airflow F1 that has absorbed heat, the heat conductor 160 and the heat pipe 183, and also provide air pressure pushing force that can expel the first airflow F1 from the body 110, thereby enhancing the heat dissipation effect of the second heat dissipation path.

[0055] Figure 5 This is a partial cross-sectional view of an electronic device according to another embodiment. Please refer to... Figure 5 And compare Figure 3The difference from the previous embodiment is that the second fan 150 in this embodiment exhausts air from the air chamber space R1. Specifically, in addition to the original first opening P1 as the exhaust path, the first airflow F1 that has absorbed heat in the air chamber space R1 is provided with an additional exhaust path through the third opening P3. This increases the negative pressure effect and more effectively enhances the heat dissipation effect of the second heat dissipation path.

[0056] In addition to the aforementioned dynamic adjustment of air supply or exhaust cooling strategies, the cooling strategy can also be dynamically adjusted according to the desired optimization parameters. Please refer to the table below, which shows the experimental data for a high-power laptop with the second fan 150 using exhaust mode. In both the control and experimental groups, the top surface S1 of the front compartment 111a was used as the measurement benchmark for temperature changes, and three small-sized second fans 150 were used side by side.

[0057]

[0058] In the control group, the second fan 150, when not running, achieved a top surface S1 temperature of 50°C, a noise level of 55 dB(A), and a thermal design power of 160 W. In the experimental groups 1-3 described below, different control variables will be tested when the second fan 150 is running.

[0059] In Experiment 1, the control variables were set to a noise level of 55 dB(A) and a thermal design power of 160 W to maintain the same conditions as the control group. After testing, the top surface temperature of the top surface S1 decreased to 47°C compared to 50°C in the control group, a reduction of approximately 3°C. This demonstrates that, while maintaining the original noise level and performance, activating the second fan 150 for exhaust in Experiment 1 effectively improves heat dissipation efficiency (i.e., optimizes cooling).

[0060] In Experiment 2, the control variable was set to a thermal design power of 160W to maintain the same conditions as the control group. After testing, the noise level decreased to 50 dB(A) compared to the control group's 55 dB(A), and the top surface temperature slightly decreased to 48.7 degrees Celsius compared to the control group's 50°C. This demonstrates that Experiment 2, without sacrificing operational performance, not only improves heat dissipation efficiency but also provides users with a quieter user experience (low-noise optimization).

[0061] In Experiment 3, the control variables were set to a top surface temperature of 50°C and a noise level of 55 dB(A) to maintain the same conditions as the control group. After testing, the thermal design power of Experiment 3 increased to approximately 170W~172W. This demonstrates that by maintaining the top surface temperature of S1 and ensuring tolerable noise levels, Experiment 3 can further improve processing performance by 6%~8% (operational performance optimization).

[0062] Figure 6This is a top view of some components of an electronic device according to another embodiment. Please refer to... Figure 6 And compare Figure 4 Unlike the previous embodiments, in this embodiment, the first fans 140A and 140B are arranged alternately, that is, each is paired with baffles 172 and 173 to form two independent air chambers R2. Simultaneously, two heat sources 120 are respectively disposed in the corresponding two air chambers R2, so that the first fan 140A, paired with baffle 172, dissipates heat from one heat source 120, while the first fan 140B, paired with baffle 173, dissipates heat from the other heat source 120. In this embodiment, the rear compartment 111b, in accordance with the configuration of the first fans 140A and 140B and the baffles 172 and 173, has two first openings P1 and two second openings P2 located on the same side of the rear compartment 111b, and arranged in an alternating pattern along the X-axis.

[0063] Figure 7 This is a top view of some components of an electronic device according to another embodiment. Please refer to... Figure 7 And compare Figure 6 In this embodiment, two independent air chambers R2 are formed by corresponding baffles 172 and 173, and the two first openings P1 and the two second openings P2 are located on the same side of the rear compartment 111b, with the two second openings P2 adjacent to each other and located between the two first openings P1. Unlike the previous embodiment, in this embodiment, the first fans 140A and 140B are adjacent and side by side, so that the air outlets E1 are oriented along the X-axis but facing away from each other, as shown in the figure.

[0064] In another embodiment, not shown, a single first fan 140A or first fan 140B may be configured instead, so that multiple heat sources 120 are all placed in the same air chamber space R2.

[0065] Figure 8 This is a top view of some components of an electronic device according to another embodiment. Please refer to... Figure 8Unlike the previous embodiments, in this embodiment, the two first fans 140C and 140D are arranged side by side and connected. Therefore, the second air outlets E2 shown are adjacent to each other along the X-axis, and part of the airflow from the first fans 140C and 140D is discharged from the main unit 111 through the adjacent and side by side second air outlets E2 and second opening P2. On the other hand, for the first fan 140D on the left side of the figure, its first air outlet E3 is connected to the first fan 140C on the right side, so that part of the airflow from the first fan 140D can serve as the gain airflow for the first fan 140C. The airflow provided by the first air outlet E1 of the first fan 140C on the right side blows into the air chamber space R3 formed by the baffle 174, the circuit board 130 and the main unit 111 of the chassis 110, and then is discharged from the chassis 110 through the first opening P1 of the rear compartment 111b. This measure diverts some airflow to the first fan 140C via the first fan 140D, thereby increasing the airflow velocity and volume discharged from the first fan 140C. Accordingly, the rear compartment 111b needs to form multiple adjacent second openings P2 to correspond to the second air outlets E2 of the first fans 140C and 140D, and multiple adjacent first openings P1 to correspond to the air chamber space R3.

[0066] from Figure 8 The illustrated embodiment can be used to derive other similar fan configurations, in which multiple first fans are arranged side-by-side and connected to each other, with only the first or last first fan connecting its first air outlet to the air chamber space, thereby increasing the airflow velocity and flow rate of the first or last first fan through airflow accumulation. Correspondingly, the aforementioned baffle 174 is adjacent to the first air outlet of the first or last first fan.

[0067] Figure 9A and Figure 9B These are partial cross-sectional views of electronic devices from different embodiments. Please refer to them first. Figure 9A And compare Figure 3 Unlike the previous embodiment where the first fans 140A and 140B are embedded in the circuit board 130 along the Z-axis, the second fan 150 is positioned above the circuit board 130. In this embodiment, the second fan 150 is located at the same height as the first fans 140A and 140B within the housing 110, and is situated near the first opening P1 in the air chamber space R1. In other words, this is equivalent to placing the second fan 150 directly on the aforementioned second heat dissipation path, thereby accelerating the discharge of the first airflow F1 from the housing 110 within the air chamber space R1.

[0068] exist Figure 9AIn one embodiment, the rear compartment 111b has a fifth opening P5 located at the bottom, and the second fan 150 is arranged in a direction inclined to the direction in which the first fans 140A and 140B are arranged in the body 110. See also... Figure 9B The second fan 150 is repositioned perpendicular to the first fans 140A and 140B within the casing 110, with the first opening P1 of the rear compartment 111b serving as the heat dissipation path. Compared to Figure 9A , Figure 9B The exhaust path of the second fan 150 is the same as the aforementioned second heat dissipation path (i.e., the exhaust path is parallel and in the same direction). This allows the first airflow F1 in the air chamber space R1 to be discharged directly from the first opening P1 of the rear compartment 111b without having to turn to the third opening P3 or the fifth opening P5, thus enhancing the heat dissipation efficiency in the air chamber space R1.

[0069] In summary, in the above embodiments of the present invention, the electronic device is configured with a front compartment and a rear compartment, and the rear compartment being higher than the front compartment provides space for the installation of a first fan and a second fan. The circuit board, the first fan, and the main body in the front compartment form an air chamber space, which connects the rear compartment to the external environment. Simply put, this invention utilizes the dual-outlet characteristic of the first fan to provide two different heat dissipation paths within the main body. One path involves using heat pipes and cooling fins to transfer some of the heat from the heat source to the cooling fins for dissipation outside the main body. The other path involves the first fan, circuit board, and main body, along with a baffle, forming an air chamber space to expel heat from the air chamber space to the outside of the main body via airflow. More importantly, the second fan located in the rear compartment further enhances the air chamber space, accelerating heat dissipation and preventing heat accumulation within the main body.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electronic device, characterized in that, include: The body has a front compartment and a rear compartment, the rear compartment extending from the front compartment and being higher than the front compartment; A circuit board, at least one heat source, and at least one first fan are respectively disposed in the front compartment. The first fan has a first air outlet and a second air outlet facing opposite directions. The circuit board, the first fan, and the body form at least one air chamber. The air chamber communicates with the external environment through at least one first opening in the rear compartment. The heat source is located in the air chamber. The first air outlet is adjacent to and faces the air chamber to provide a first airflow to the air chamber. The second air outlet faces at least one second opening in the rear compartment to generate a second airflow to exhaust from the body. At least one second fan is provided in the rear compartment to supply or exhaust air to the air chamber space.

2. The electronic device according to claim 1, characterized in that, It includes two first fans, located on opposite sides of the air chamber space, with the two first air outlets facing each other and adjacent to the air chamber space, to provide the first airflow to the air chamber space respectively, and the second fan corresponding to the air chamber space.

3. The electronic device according to claim 2, characterized in that, It also includes a baffle wall abutting between the circuit board and the body and adjacent to the two first fans, the baffle wall being one of the multiple boundaries forming the air chamber space.

4. The electronic device according to claim 2, characterized in that, The first opening is located between the two second openings, and the first opening and the two second openings are located on the same side of the rear compartment.

5. The electronic device according to claim 1, characterized in that, The electronic device includes two first fans arranged at intervals or side by side, and also includes multiple baffles that abut against the circuit board and the body and respectively correspond to the two first fans to form two independent air chamber spaces, and two second fans respectively correspond to the two air chamber spaces.

6. The electronic device according to claim 5, characterized in that, The two air chambers are connected to the external environment through the corresponding two first openings, and the two second openings are located on the same side of the rear compartment as the two first openings.

7. The electronic device according to claim 6, characterized in that, When the two first fans are spaced apart and side by side, the two first openings and the two second openings are staggered.

8. The electronic device according to claim 6, characterized in that, When the two first fans are adjacent and side by side, the two second openings are adjacent and located between the two first openings.

9. The electronic device according to claim 1, characterized in that, The rear compartment has at least one third opening communicating with the external environment, corresponding to the second fan, and different from the first and second openings, with the second fan located between the third and second openings.

10. The electronic device according to claim 1, characterized in that, At least one of the top and bottom surfaces of the front compartment has a plurality of fourth openings communicating with the external environment.

11. The electronic device according to claim 1, characterized in that, The first fan is positioned parallel to the circuit board within the housing.

12. The electronic device according to claim 1, characterized in that, The second fan is positioned higher within the housing than the first fan is within the housing.

13. The electronic device according to claim 1, characterized in that, The second fan is positioned at the same height as the first fan within the machine body, and is located in the air chamber space adjacent to the first opening.

14. The electronic device according to claim 1, characterized in that, The second fan is positioned perpendicular to or inclined to the first fan within the housing, and the second fan is located in the air chamber space adjacent to the first opening.

15. The electronic device according to claim 14, characterized in that, The second fan is configured in a direction perpendicular to that of the first fan within the housing, and the second fan discharges the first airflow from the air chamber space into the housing through the first opening.

16. The electronic device according to claim 1, characterized in that, The air chamber space spans the front compartment and the rear compartment.

17. The electronic device according to claim 1, characterized in that, The machine body includes a main unit and a screen. The main unit has a front compartment and a rear compartment, and the screen is pivotally connected to the rear compartment.

18. The electronic device according to claim 1, characterized in that, It also includes a heat-conducting element, one end of which is located in the air chamber space and in thermal contact with the heat source, the heat-conducting element extending from the front compartment to the rear compartment, with the other end of the heat-conducting element adjacent to the second fan.

19. The electronic device according to claim 1, characterized in that, It also includes heat dissipation fins, which are disposed in the body of the unit and adjacent to the second opening and the second air outlet. The second airflow passes sequentially through the second air outlet, the heat dissipation fins and the second opening and is discharged from the rear compartment.

20. The electronic device according to claim 1, characterized in that, The second fan includes multiple fan units, which are axial fans.

21. The electronic device according to claim 1, characterized in that, It includes a plurality of first fans that are connected side by side, with the second air outlets of each first fan adjacent to each other, and only the first or last position of the plurality of first fans is connected to the air chamber space via the first air outlet.

22. The electronic device according to claim 21, characterized in that, It also includes a baffle wall abutting between the circuit board and the body, the baffle wall being adjacent to the first air outlet of the first fan at the first or last position.

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