Electrohydrodynamic heat sink

Abstract

The invention relates to an electrohydrodynamic heat sink, formed by a conductive wire (5) disposed near to and parallel to a series of ground fins (4), in an elongate case (1) with an inlet hole (2) at a central point and two outlet holes (3) at the ends.(5 The case (1) has a larger flat face (11) that holds the ground fins (4), which are disposed between the outlet holes (3), and the internal space of the case (1) has a substantially triangular shape, with a greater height corresponding to the distance between the larger flat face (11) and the inlet hole (2) and a width corresponding to the distance between the outlet holes (3).

Description

[0001] DESCRIPTION

[0002] Electrohydrodynamic heatsink

[0003] TECHNICAL SECTOR

[0004] This application relates to an electrohydrodynamic heatsink for cooling components, especially electronic ones. It offers improved heat dissipation efficiency by optimizing the flow of fluid through the collector electrode, which, in addition to its function, acts as a heat sink.

[0005] STATE OF THE ART

[0006] The present invention relates to the cooling of electronic components. An electrohydrodynamic (EHD) device has a corona electrode and a collector electrode. The corona effect allows the ionization of a fluid surrounding the corona electrode and produces movement of this fluid.

[0007] Electrohydrodynamic devices offer advantages due to their reduced size, low weight and power consumption, as well as reduced noise and vibration. These characteristics lead them to be used in small-scale component cooling applications, replacing conventional heat sinks or fans.

[0008] Electrohydrodynamic devices currently used in cooling use the corona effect to direct an air stream toward a finned heat dissipation element located downstream of the electrohydrodynamic device. Thus, the electrohydrodynamic device is used to generate air movement inside the component to be cooled, while the heat sink's fins are responsible for receiving and dissipating the heat.

[0009] Electrohydrodynamic devices used in refrigeration are often known as electrohydrodynamic pumps, since their function is to propel air, while the heatsink performs the dissipation function. See, for example, document US2012314334A1. Document CN113188106 is known in the state of the art, where the device is arranged in a T-shaped housing and has central fins and three corona electrodes, one on each arm of the T. This system requires several corona electrodes, so its construction and efficiency are reduced. It is also noted that the fluid has vague passageways that do not perform the function of capturing and removing heat from the fins.

[0010] KR101513402 is also known, where the collector electrodes are fins parallel to the corona electrode. These fins vary in height, depending on their distance from the corona electrode. This system better connects the fluid to the fins, but heat exchange is not optimized because the temperature difference is small at the end of the air path. These applications also do not include sufficient dimensional information to obtain the best results. As will be demonstrated later, displaying the entire length of the conductive wire, as this document does, yields worse dissipation results than the invention.

[0011] The applicant is not aware of any system that would solve all these problems as effectively as the invention.

[0012] BRIEF EXPLANATION OF THE INVENTION

[0013] The invention consists of an electrohydrodynamic device according to the independent claims and whose variations solve the problems of the state of the art.

[0014] This device allows for optimal heat exchange, ensuring that the fluid comes into contact with the fins, maximizing heat exchange and reducing the volume required per calorie dissipated.

[0015] In this application, two values ​​will be considered “similar” if the difference is less than 15%, preferably 10%, of the largest value.

[0016] The electrohydrodynamic heatsink is of the type formed by a conductive wire close and parallel to a series of ground fins, all within an elongated housing with an inlet orifice at a central point and two outlet orifices at the ends. This generates a T-shaped flow, generally inverted depending on its orientation over the element to be cooled. The housing has a flat larger face that carries the ground fins, arranged between the outlet orifices. The interior cavity of the housing has a substantially triangular shape, with a greater height corresponding to the distance between the flat larger face and the inlet orifice, and a width corresponding to the distance between the outlet orifices. These outlet orifices truncate the triangle, which is normally isosceles and with a zenith angle greater than 90°, preferably greater than 120°.

[0017] Preferably the area of ​​the inlet hole is similar to the total area of ​​the outlet holes.

[0018] The fins can all act as ground fins or include secondary fins, parallel to the ground fins and electrostatically independent of the conducting wire. That is, they either do not carry an electrostatic charge or are too far from it to generate any appreciable effect. These secondary fins serve solely as heat dissipation, in contrast to the main or "ground" fins, which also act as electrodes.

[0019] As will be indicated later, the housing may have a triangular shape or may comprise inserts that define the triangular shape. These inserts may have a wall facing the housing cavity (between the inlet and each outlet), either straight or curved, preferably convex.

[0020] The triangular shape can be optimized by modifying the height of the fins at the ends, by having the top of the housing recessed between the fins, reducing the usable flow rate for the fluid, or by any other means. In these cases, the effective height of the fins in the center is greater than at the ends.

[0021] Other variations can be seen in the rest of the report.

[0022] DESCRIPTION OF THE FIGURES

[0023] For a better understanding of the invention, the following figures are included, which show exemplary embodiments.

[0024] Figure 1: Perspective view of an example of a heatsink (A) assembled, (B) partially exploded.

[0025] Figure 2: Longitudinal section of a second example, showing the internal triangular shape. Figure 3: Two examples of inserts (A) straight, (B) convex.

[0026] Figure 4: Two examples of fins, with secondary fins (A) and with mass fins only (B).

[0027] Figure 5: Example of the upper part of the housing with slots for inserting the fins.

[0028] Figure 6: Temperature curve according to the time elapsed in two tests (25 and 50W), each with and without insert.

[0029] Figure 7: Temperature curve according to the time elapsed in two tests, with 25W (7A) and with 50W (7B), without inlet hole, with hole but without triangular shape and with hole and triangular shape.

[0030] MODES OF EMBODIMENT OF THE INVENTION

[0031] Below, a brief description is given of an embodiment of the invention, as an illustrative and non-limiting example thereof.

[0032] The heatsink of the embodiment shown in the figures comprises a housing (1) with a long, flat major face (11), two major faces and two bases (12) approximately perpendicular to the flat major face (11). As can be seen, the shape represented is rectangular prismatic. The housing (1) is hollow and has three holes (2,3) that communicate its interior with the exterior. An inlet hole (2) facing a midpoint of the flat major face (11), on the other side of the housing (1) and two outlet holes (3) in the bases (12). The area of ​​the inlet hole (2) is approximately equal to the sum of the areas of the outlet holes (3).

[0033] On the flat major face (11) there are a series of ground fins (4) close to a conducting wire (5) that acts as a corona electrode. The ground fins (4) are parallel to the conducting wire (5), and occupy all or most (at least 80%) of the length of the flat major face (11). That is, they go from one base (3) to the other base (3). The conducting wire (5) is connected to a high voltage electricity source that allows it to be charged with an electrostatic charge. The ground fins (4) are charged with a charge in the opposite direction. It is possible to place secondary fins (6) between the ground fins (4) that do not interact with the conducting wire (5) (Figure 4A). For this purpose, they can be shorter than the ground fins (4) or have an insulating coating. These secondary fins (6) increase the heat exchange surface.

[0034] As can be seen, the mass fins (4) have a height similar to the height of the outlet holes (3), so that the fluid passing through them has been in contact with some fin (4,6).

[0035] The interior of the casing (1) has a substantially triangular shape, with a greater height corresponding to the distance between the larger flat face (11) and the inlet hole (2) and a width corresponding to the distance between the bases (12), that is to say the length of the larger flat face (11). In figure 2 it can be seen that two vertices are truncated by the presence of the outlet holes (3) and the third by the inlet hole (2). This interior of the casing (1) can have the sides between the inlet hole (2) and the two outlet holes (3) straight or concave.

[0036] The way to achieve this triangular shape inside the housing (1) can be done directly by the shape of the housing (1), which in this case is also triangular, or by using two inserts (7) that define the shape of the interior of the housing (1). These inserts (7) modify the shape of the housing (1), which has been represented as rectangular prismatic, so that its interior has the desired shape. Thus, in figure 2 the inserts (7) generate two chamfers. Figure 5 shows an embodiment in which the upper part of the housing (1) has internal slots (8) through which the mass fins (4) are inserted. This reduces the effective section at the ends, near the outlet holes (3), accelerating the passage of the fluid.

[0037] It can be seen, especially in figure 1, that the conducting wire (5) is external to the insulating housing (1), so that it only faces directly to the ground fins (4) in the entry hole. A notch in the surface of the housing (1) carries the conducting wire (5) to bring it closer to the ground fins (4) and ensure that it does not protrude from the surface of the device. The conducting wire (5) is anchored to the housing (1) to avoid accidental movements that modify the relative positions.

[0038] Figure 3 shows various ways of making the inserts (7). They can have flat walls (Figure 3A) or their curvature can be modified depending on the distance from the inlet hole (2). For example, in Figure 3B the slope of the insert (7) in the area close to the inlet hole (2) is perpendicular to it, while reaching the corresponding outlet hole (3) it is also perpendicular to it. Thus, the shape represented is a sector of an ellipse. Other curvatures are possible (sectors of an oval, ovoid, sinusoidal, hyperbola...).

[0039] Thanks to the more or less triangular shape of the interior of the casing (1), the fluid passing through the inlet hole (2) is directed directly to the fins (4,6) to carry out the heat exchange, without producing turbulence that reduces effectiveness by reducing the contact time and increasing the pressure loss. However, as can be seen in Figure 2, there is relatively cold fluid that reaches the end of the fins (4,6), so the temperature differential is maximum and that area also cools.

[0040] The direction of fluid flow is ensured by the discharge itself and the channels formed between the insulating structure and the ground electrode or ground fins (4). The discharge is carried out on the tips of the ground fins (4) and the ionic wind is pushed towards the interior of the device, the channels formed between the structure and the ground fins (4) are what ensure that the flow is directed in that direction.

[0041] Figure 6 shows the time evolution of the temperature difference between the plate to be cooled and the environment in four tests. The dashed lines use a housing (1) with a rectangular prismatic interior, without an insert (7). The solid lines show the case with a straight-line insert (7) that makes the interior triangular. The upper curves correspond to a 50W heat source and the lower ones to a 25W heat source. It can be seen how modifying the shape of the interior of the housing allows an increase in performance of up to 24% (25W case).

[0042] The tests were carried out with an 80x80 mm aluminum plate heated by a resistance covering an area of ​​50x50 mm, and with a power of 25 and 50 W. The device coupled to the plate comprised eleven pairs of electrodes, covering 80x80 mm, either rectangular (control) or right triangular interior area. The ground fins (4) had a height of 19 mm and the central fins also acted as ground fins (4), with a height of 18.1 mm, and the width of all of them was 1 mm. The distance between extreme ground fins (4) is 6 mm and the central fins were centered in that space. The channels had a length of 80 mm. The length of the inlet hole (2) is 20 mm. The height of the outlet holes (3) is 10 mm, the total area of ​​the outlet holes (3) being equal to the area of ​​the inlet hole (2). The ground electrode is made of aluminum, by additive manufacturing, and the device power is 5W.Temperature measurement was performed by thermocouples inserted into the aluminum plate, comparing it with ambient temperature.

[0043] Also interesting is the test shown in Figure 7, which compares a model as claimed, with a 20 mm inlet hole, (solid line), a model with a 20 mm inlet hole, without the triangular shape (dashed line) and a model where most of the upper surface of the housing (1) is open, leaving the conductive wire (5) accessible along almost the entire length of the ground fin (4), that is, 75 mm of the 80 mm of the ground fin (4), (dotted and dashed line). This last model corresponds to the one shown in Korean patent KR101513402. These tests have been carried out by arranging heat sinks as described in the previous example to evacuate heat from an 80x80 mm metal plate using a 50x50 mm thermal resistance and supplying 25W (Figure 7A) or 50W (Figure 7B). The evolution of the temperature over time in these two cases is shown. The temperature of the plate is temporarily monitored through thermocouples.The device's power in all examples is approximately 5W. It can be seen that the Korean patent's solution produces the least dissipation.

[0044] Figure 1 shows how the housing (1) has two parts that fit together. A first part comprising the inserts (7) and the inlet hole (2) and a second part consisting of the flat larger face (11) and the fins (4,6).

[0045] The device may be modular, using several sets of fins (4, 6), housings (1), conducting wires (5)... in parallel, so that the element whose heat is to be dissipated can be cooled according to its needs. If necessary, the first part stated in the previous paragraph may be common to several modules.

Claims

CLAIMS 1- Electrohydrodynamic heatsink, formed by an elongated housing (1) that has a flat larger face (11) that carries ground fins (4), where the housing (1) has: an inlet orifice (2) at a central point facing the ground fins (4), a conducting wire (5), close and parallel to the ground fins (4), which passes through the inlet orifice (2), and two outlet orifices (3) of the housing at the ends of the ground fins (4), characterized in that the inner hollow of the housing (1) has a substantially truncated triangular shape, with a height corresponding to the distance between the flat larger face (11) and the inlet orifice (2) and a base corresponding to the flat larger face (11) between the outlet orifices (3). 2- Electrohydrodynamic heatsink, according to claim 1, characterized in that the area of ​​the inlet hole (2) is similar to the total area of ​​the outlet holes (3). 3- Electrohydrodynamic heatsink, according to claim 1, characterized in that it comprises secondary fins (6), parallel to the ground fins (4), and electrostatically independent of the conductive wire (5). 4- Electrohydrodynamic heatsink, according to claim 1, characterized in that the mass fins (4) have a height similar to the height of the outlet holes (3). 5- Electrohydrodynamic heatsink, according to claim 1, characterized in that the housing (1) comprises inserts (7) that define the triangular shape. 6- Electrohydrodynamic heatsink, according to claim 5, characterized in that the inserts (7) have a straight wall facing towards the hollow of the housing (1). 7- Electrohydrodynamic heatsink, according to claim 5, characterized in that the inserts (7) have a convex wall facing towards the hollow of the housing (1). 8- Electrohydrodynamic heatsink, according to claim 1, characterized in that the conducting wire (5) is outside the casing (1), such that it is insulating and is arranged between the ground fins (4) and the conducting wire (5) except at the inlet hole (2). 9- Electrohydrodynamic heatsink, according to claim 1, characterized in that the inner part of the casing (1) has inner slots (8) for inserting the ends of the ground fins (4).

Images