JP7148118B2 - heat transfer device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat transfer device, and more particularly to a heat transfer device having a plurality of heat transfer fins arranged in parallel.

Conventionally, as this type of technology, a heat sink in which a plurality of heat radiation fins are arranged in parallel has been proposed (see, for example, Patent Document 1). The radiation fins of this heat sink are formed in a plate shape from a metal material with high thermal conductivity such as aluminum, aluminum alloy, or copper. Further, since the radiation fins are required to have high heat transportability, it has been proposed to form the radiation fins from a graphite material (see, for example, Patent Document 2).

A heat exchanger having corrugated fins formed by cutting and raising a plurality of louvers has also been proposed (see Patent Document 3, for example). In this heat exchanger, heat transfer performance is improved by forming a plurality of louvers on the corrugated fins.

JP 2018-098396 A JP 2018-093119 A JP 2015-017776 A

High heat transfer performance is desired for heat transfer fins such as heat dissipation fins and corrugated fins, as in the above technology. For this reason, the space between the heat transfer fins is narrowed, the flow velocity of the heat transfer medium such as air or liquid flowing between the heat transfer fins is increased, the heat transfer fins are cut and raised, or the heat transfer fins are wavy. Various techniques have been proposed to improve the heat transfer, such as forming the heat transfer medium into a thin layer.

A main object of the heat transfer device of the present invention is to increase the heat transfer of the heat transfer fins by suppressing the pressure loss of the heat transfer medium flowing between the heat transfer fins.

The heat transfer device of the present invention employs the following means in order to achieve the above main object.

The heat transfer device of the present invention is
A heat transfer device having a plurality of heat transfer fins arranged in parallel,
The heat transfer fins are made of a porous material that is permeable to a heat transfer medium that flows as a flow path between adjacent heat transfer fins.
It is characterized by

In the heat transfer device of the present invention, when the heat transfer medium flows between the heat transfer fins arranged in parallel as a flow path, the speed difference between the low speed region near the heat transfer surface and the high speed region far from the heat transfer surface is As a result, an unstable wave due to Kelvin-Helmholtz instability is generated, and a high-pressure part with high pressure and a low-pressure part with low pressure are alternately formed in the heat transfer medium, and this flows downstream as a traveling wave that propagates in the mainstream direction. . Since the heat transfer fins are made of a porous material that allows the heat transfer medium to pass through, the heat transfer medium permeates the heat transfer fins in the high pressure section and flows out into the adjacent flow path, while in the low pressure section, the heat transfer medium flows out into the adjacent flow path. flows through the heat transfer fins from the During this transmission, heat transfer occurs between the heat transfer medium and the heat transfer fins. The traveling wave generated by these heat transfer fins has the effect of propelling the flow downstream, and has the effect of keeping the flow resistance between the heat transfer fins relatively low. Heat transfer promotion can be realized. As a result, the pressure loss of the heat transfer medium flowing between the heat transfer fins can be suppressed and the heat transfer of the heat transfer fins can be enhanced.

In the heat transfer device of the present invention, when the distance between the heat transfer fins is 2H and the plate thickness of the heat transfer fins is δ, the dimensionless plate thickness β represented by the formula (1) and the entire heat transfer fin The formula ( 2) and the Reynolds number Re represented by Equation (3) where Ub is the bulk velocity of the heat transfer medium and ν is the kinematic viscosity coefficient of the heat transfer medium. (4) may be satisfied. In this way, a more appropriate heat transfer device can be designed according to the size and spacing of the heat transfer fins and the type of heat transfer medium.

β=δ/H (1)
K=(ε/32)·(Dh/H) ² (2)
Re=Ub·H/ν (3)
K/β>0.08×Re ^−1.5 (4)

In the heat transfer device of the present invention that satisfies the formula (4), the Reynolds number Re may satisfy Re≧50. This condition is based on the fact that when the Reynolds number Re is less than 50, the heat transfer medium flows slowly, and thus traveling waves due to Kelvin-Helmholtz instability are often not generated.

Further, in the heat transfer device of the present invention satisfying the formula (4), the pore hydraulic diameter Dh may satisfy Dh≦0.1H. This condition is based on the fact that the holes of the heat transfer fins through which the heat transfer medium passes are sufficiently small relative to the dimension of the mechanically formed flow passages. That is, in the numerical calculation of heat transfer, instead of solving the flow and heat transfer in individual holes of the heat transfer fins, an average flow is generated inside the heat transfer fins according to the transmittance. This is to establish the assumption.

It is an explanatory view showing an outline of composition of heat sink 20 as a heat transfer device of one embodiment. 4 is a schematic diagram schematically showing a state in which an unstable wave (traveling wave) is generated near the surface of the heat radiating fin 40. FIG. 4 is a schematic diagram schematically showing alternately occurring high-pressure portions and low-pressure portions in an unstable wave (traveling wave) generated near the surface of the heat radiating fin 40. FIG. FIG. 7 is an explanatory diagram showing, using contour lines, simulation results of the pressure of the heat transfer medium in the flow path sandwiching the heat radiating fins 40 ; FIG. 4 is an explanatory diagram schematically showing the dimensions of the heat radiating fins 40 and the flow velocity of the heat transfer medium flowing between the heat radiating fins 40; 4 is a list showing an example of simulation results of the relationship between Reynolds number Re, non-dimensional transmittance/non-dimensional plate thickness (K/β), pressure loss, and heat transfer. 4 is a table showing simulation results of the relationship between minimum dimensionless transmittance/dimensionless plate thickness (K/β) and Reynolds number Re at which traveling waves are generated; FIG. 4 is an explanatory diagram showing an example of the relationship between the minimum dimensionless transmittance/the dimensionless plate thickness (K/β) and the Reynolds number Re at which traveling waves are generated;

Next, the form for implementing this invention is demonstrated. FIG. 1 is an explanatory diagram showing the outline of the configuration of a heat sink 20 as a heat transfer device of the embodiment. The heat sink 20 of the embodiment includes a heat receiving portion 30 attached to a heating element, and a plurality of radiation fins 40 attached to the heat receiving portion 30 so as to be arranged in parallel.

The heat-receiving portion 30 is formed in a plate shape from a metal material having good thermal conductivity, such as aluminum, copper, or stainless steel.

The radiating fins 40 are made of a porous metal such as aluminum, copper, stainless steel, or the like having good thermal conductivity so as to pass through a heat transfer medium such as air or a coolant that flows between the adjacent radiating fins 40 as a flow path. It is made of material and formed into a thin plate.

Next, the function when the heat sink 20 configured in this way is attached to a heat generating body and a heat transfer medium such as air or refrigerant (liquid or gaseous refrigerant) is caused to flow between the plurality of radiation fins 40 will be described. When the heat transfer medium is caused to flow as a flow path between the adjacent heat dissipating fins 40, the velocity of the main flow of the heat transfer medium becomes uneven near and far from the surface of the heat dissipating fins 40. Therefore, due to Kelvin-Helmholtz instability, an unstable wave is generated. occurs. Such unstable waves are generated by subsequent amplification of pressure fluctuations caused by minute disturbances in the vicinity of the inflow portions of the heat radiating fins 40 of the heat transfer medium, and become traveling waves that advect in the flow direction. Therefore, in the vicinity of the surface of the heat radiating fins 40, a high pressure portion with a high pressure and a low pressure portion with a low pressure of the heat transfer medium alternately occur. It progresses in the direction of flow of the medium. FIG. 2 is a schematic diagram schematically showing a state in which an unstable wave (traveling wave) is generated near the surface of the radiation fins 40, and FIG. FIG. 2 is a schematic diagram schematically showing alternately occurring high-pressure portions and low-pressure portions in a wave (traveling wave); As described above, the radiation fins 40 are made of a porous material such as a metal that allows the heat transfer medium to pass through. The heat transfer medium flows out to the adjacent flow passage, and conversely, the heat transfer medium in the adjacent flow passage passes through the heat radiating fins 40 and flows into the low pressure section. As shown in FIG. 3, the distribution of the high pressure portion and the low pressure portion is such that when one of the two flow paths sandwiching the heat radiating fin 40 is in the vicinity of both surfaces of the heat radiating fin 40, the heat is dissipated when one becomes the high pressure portion. The other one facing across the fin 40 becomes a low pressure section, and when one becomes a low pressure section, the other becomes a high pressure section. FIG. 4 is an explanatory diagram showing, using contour lines, simulation results of the pressure of the heat transfer medium in the flow path sandwiching the heat radiating fins 40 . In the figure, the thick solid line in the center indicates the heat radiating fins 40, the plus indication in the contour lines of -1.4 to 1.4 indicates that the pressure is higher than the average pressure of the heat transfer medium, and the minus indication indicates the heat transfer medium. indicates that the pressure is lower than the average pressure of As shown in the figure, the pressure fluctuates in the order of high pressure, low pressure, high pressure, and low pressure on the upper side of the radiation fins 40 in the drawing, and low pressure from the left side on the lower side of the radiation fins so as to be paired with the upper side. The pressure fluctuates in the order of part, high pressure part, low pressure part, and high pressure part. Therefore, as indicated by the arrows drawn on the heat radiation fins 40 in FIG. 3, the heat transfer medium passes through the heat radiation fins 40 from the high pressure section toward the low pressure section. Since the waves generated by such alternating high-pressure and low-pressure portions travel along the flow of the heat transfer medium, in each portion of the radiating fins 40, the heat transfer medium permeates from one channel side to the other channel side and passes through the other. permeation from the channel side to one side alternately. Such permeation of the heat transfer medium through the heat dissipation fins 40 causes heat transfer between the heat transfer medium and the heat dissipation fins 40 . For this reason, heat transfer can be enhanced as compared with the case where the radiation fins 40 are formed of a material impermeable to the heat transfer medium. On the other hand, the unstable wave due to Kelvin-Helmholtz instability has the effect of driving the fluid downstream, which can keep the flow resistance relatively small. As a result, the pressure loss of the heat transfer medium flowing between the heat radiating fins 40 can be suppressed, and the heat transfer of the heat radiating fins 40 can be increased.

Next, preferable conditions for the radiation fins 40 of the heat sink 20 of the embodiment will be described. FIG. 5 is an explanatory diagram schematically showing the dimensions of the heat radiating fins 40 and the flow velocity of the heat transfer medium flowing between the heat radiating fins 40 (flow paths). Now, the plate thickness of the heat radiation fins 40 is δ, the interval (channel width) of the heat radiation fins 40 is 2H (half channel width is H), the bulk velocity (average flow velocity) of the heat transfer medium is Ub, and the total volume of the radiation fins is V The void ratio (Vv/V), which is the ratio (Vv/V) of the void volume Vv, is ε, and the void hydraulic diameter (4Vv/S ) is Dh, and the kinematic viscosity coefficient of the heat transfer medium is ν, the dimensionless plate thickness β represented by Equation (1), the dimensionless transmittance K represented by Equation (2), and Equation (3) Define a Reynolds number Re represented by At this time, it is preferable to satisfy the condition of formula (4).

β=δ/H (1)
K=(ε/32)·(Dh/H) ² (2)
Re=Ub·H/ν (3)
K/β>0.08×Re ^−1.5 (4)

FIG. 6 is a table showing simulation results of the relationship between Reynolds number Re, dimensionless transmittance/thickness (K/β), pressure loss, and heat transfer. FIG. 7 is a table showing simulation results of the relationship between the minimum dimensionless transmittance/the dimensionless plate thickness (K/β) and the Reynolds number Re at which traveling waves are generated. In FIG. 6, hatched areas indicate areas where traveling waves are generated. When the Reynolds number Re is 10 (RE=10), pressure loss and heat transfer do not increase unless K/β becomes infinite. This means that no traveling wave is generated. When the Reynolds number Re is 50 (RE=50), pressure loss and heat transfer increase when K/β is a value between 10 ^-3 and 10 ^-2 (3.0×10 ^-3 ) or higher. This means that traveling waves are generated above this value. Similarly, when the Reynolds number Re is 100 (RE=100), 500 (Re=500) and 1000 (Re=1000), K/β is a value between 10 ⁻⁴ and 10 ⁻⁵ (9.0× 10 ⁻⁴ ) or more, a value between 10 ⁻⁵ and 10 ⁻⁶ (8.0×10 ⁻⁵ ) or more, a value between 10 ⁻⁵ and 10 ⁻⁶ (3.0×10 ⁻⁵ ) or more Pressure loss and heat transfer increase, and above this value a traveling wave is generated.

FIG. 8 is an explanatory diagram showing an example of the relationship between the minimum dimensionless transmittance/the dimensionless plate thickness (K/β) and the Reynolds number Re at which traveling waves are generated. In the figure, the four plots are the points shown in FIG. 7, and the straight line is a straight line drawn so that the four plots are included in the upper right region (where the inequality sign in Equation (4) is replaced by an equal sign). According to the simulation results, an unstable wave (traveling wave) due to Kelvin-Helmholtz instability does not occur in the lower left region of the straight line in FIG. Therefore, in this region, it becomes difficult for the heat transfer medium to pass through the heat radiating fins 40, making it difficult to contribute to heat transfer. On the other hand, an unstable wave (progressive wave) due to Kelvin-Helmholtz instability is generated in the area on the upper right side of the straight line in FIG. Therefore, in this region, the heat transfer medium passes through the heat radiating fins 40, which also contributes to heat transfer.

In addition to the condition of the above formula (4), the Reynolds number Re is preferably 50 or more (Re≧50). This condition is based on the fact that when the Reynolds number Re is less than 50, the heat transfer medium flows slowly, which often makes it difficult to generate unstable waves (traveling waves) due to Kelvin-Helmholtz instability. Moreover, it is preferable that the pore hydraulic diameter Dh satisfies Dh≦0.1H. This condition is based on the fact that the pores through which the heat transfer medium of the heat radiating fins 40 permeates are sufficiently small relative to the channel dimensions that can be mechanically formed. That is, in the numerical calculation of the heat transfer of the heat radiating fins 40, instead of solving the flow and heat transfer in the individual pores of the heat radiating fins 40, according to the dimensionless transmittance K, an average This is to establish the assumption that a natural flow (flow due to permeation) occurs.

In the heat sink 20 of the embodiment described above, the radiation fins 40 are formed of a porous material through which a heat transfer medium can pass. , the heat transfer medium alternately permeates from one channel side to the other channel side and permeates from the other channel side to one side. As a result, the pressure loss of the heat transfer medium flowing between the heat radiating fins 40 can be suppressed, and the heat transfer of the heat radiating fins 40 can be increased.

In the heat sink 20 of the embodiment, the heat dissipation fins 40 are used to dissipate heat, but the heat sink 20 may dissipate cold heat, that is, absorb heat.

The heat transfer device of the present invention has been described with the heat sink 20 as an embodiment and applying it to the radiation fins 40 thereof. However, as an embodiment of the heat transfer device of the present invention, a corrugated fin type heat exchanger may be used and applied to corrugated fins. Further, as an embodiment of the heat transfer device of the present invention, a tube-type heat exchanger through which a heat exchange medium flows may be used and applied to fins attached to the tube. Alternatively, a corrugated fin or a fin attached to a tube may be used as an offset fin, and the offset fin may be applied to the portions arranged in parallel.

Although the embodiments for carrying out the present invention have been described above, the present invention is not limited to such embodiments at all, and can be modified in various forms without departing from the scope of the present invention. Of course, it can be implemented.

INDUSTRIAL APPLICABILITY The present invention is applicable to the manufacturing industry of heat transfer devices .

20 heat sink, 30 heat receiving part, 40 radiation fin.

Claims (2)

A heat transfer device having a plurality of heat transfer fins arranged in parallel,
The heat transfer fins are made of a porous material that is permeable to a heat transfer medium that flows as a flow path between adjacent heat transfer fins ,
The ratio of the dimensionless plate thickness β represented by the formula (1) when the distance between the heat transfer fins is 2H and the plate thickness of the heat transfer fins is δ, and the volume of the voids in the entire volume of the heat transfer fins. is the porosity, and Dh is the pore hydraulic diameter obtained by dividing 4 times the volume of the pore of the heat transfer fin by the area of the solid pore interface of the heat transfer fin. When using the coefficient K and the Reynolds number Re represented by the equation (3) where Ub is the bulk velocity of the heat transfer medium and ν is the kinematic viscosity coefficient of the heat transfer medium, the equation (4) is expressed as fill,
Reynolds number Re satisfies Re≧50,
A heat transfer device characterized by:
β=δ/H (1)
K=(.epsilon./32).(Dh/H)@2 (2)
Re=Ub·H/ν (3)
K/β>0.08×Re-1.5 (4) The heat transfer device of claim 1 ,
pore hydraulic diameter Dh satisfies Dh≦0.1H,
heat transfer device.

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