KR100795375B1 - Apparatus for enhancing heat transfer by attached nano tube - Google Patents

Abstract

An apparatus for enhancing heat transfer through attached nano tubes is provided to reduce thickness of a thermal boundary layer to enhance heat transfer to improve the thermal efficiency, thereby improving the economical efficiency and reducing carbon dioxide emission. Nano tubes(4) are deposited in accordance with a flow direction of a thermal medium within a range of a thermal boundary layer(3) formed at a top side of a plate(1) or a wall of a pipe to increase a heat transfer area by a shape of deposited needles and to disturb and break down development of the thermal boundary layer to enhance heat transfer. The plate where the nano tubes are mounted is a coated thin plate.

Description

Apparatus for Enhancing Heat Transfer by Attached Nano Tube}

1 is a schematic view showing a thermal boundary layer developed on the wall of the heat transfer apparatus plate along the flow direction.

Figure 2 is a schematic diagram showing a thermal boundary layer developed in the wall of the inner tube for heat transfer mechanism according to the flow direction.

Figure 3 is a schematic diagram showing a thermal boundary layer equipped with nanotubes grown and deposited on the flat wall surface of the heat transfer mechanism according to the present invention.

Figure 4 is a schematic diagram showing another form of nanotubes grown and deposited on the wall of the apparatus for heat transfer according to the present invention.

<Explanation of symbols for the main parts of the drawings>

1: plate 2: tube

3: thermal boundary layer 4: nanotubes

The present invention relates to a heat transfer mechanism, and more particularly, in a heat transfer mechanism in which a heat medium flows inside an inner tube or an upper surface of a smooth plate and transfers heat to the outside, a temperature boundary layer formed on the tube or plate wall surface. Within this range, the present invention relates to a nanotube-deposited heat transfer apparatus configured to coat and deposit nanotubes along a heating medium flow direction to promote heat transfer in the shape of an animal's hair or a needle. For reference, the thermal boundary layer and the flow boundary layer have a relatively large and small thickness depending on the dimension number of the plant.

Generally, an air conditioning system, a bus cooler, a heat pump, a heat pipe, and the like are provided with a heat exchanger for cooling / heating a fluid or a refrigerant. Such a heat transfer mechanism can be formed in various shapes to increase the contact area with the outside air, and can also reduce the heat resistance in the Reynolds water flow region limited by the flow velocity, hydraulic diameter, and gas density. Evaporator provided with the.

Therefore, in air conditioning systems, bus coolers, refrigeration systems, heat pumps, heat pipes, and steam generators in nuclear power plants, the working fluid cools by radiating heat while passing through the condenser and absorbing heat from the outside while passing through the evaporator. Is cooling the outside air while evaporating.

Normally, the smooth plate or cylindrical pipes of a heat exchanger are formed of metal sheet or copper tube, aluminum, etc. and can be rolled or stamped into a desired structure.

1 is a schematic diagram showing a thermal boundary layer developed on the wall of the heat transfer mechanism according to the flow direction, Figure 2 is a schematic diagram showing a thermal boundary layer developed on the wall of the inner tube for heat transfer according to the flow direction, Same as

In the heat transfer surface area exposed to the fluid flow formed on the upper surface of the flat plate 1 or inside the inner tube 2, the flow and thermal boundary layer 3 mature and develop gradually on the wall surface of the flow passage, which is very low in this boundary layer region. Results in heat transfer.

Thermal fluid developed on the top or inside of these plates includes the ability to transfer heat to or absorb heat from other parts of the plate. All heat transfer is through the wall. Due to the temperature boundary layer developed on the wall there is a problem that the heat transfer efficiency is reduced.

As described above, the heat transfer in the heat transfer mechanism is such that the heat resistance of the outside air contacting the fin occupies most of the total heat resistance, so that the performance of the fins ultimately determines the performance of the heat transfer mechanism. One such type of fins widely applied to conventional heat exchangers is a louver fin called a LF fin.

However, the conventional louver fin has a problem that low heat transfer performance is limited because the impact angle of air is limited to 90 ° and vortices are not generated in the width direction and the axial direction, and the boundary layer is thickened at low speed to form duct flow.

There is also an offset strip fin, also called OSF, as one of the other types of conventional fins.

However, such an offset strip fin provides only a one-dimensional staggering effect, which also has a problem of low heat transfer effect.

Since the size of the fin mounted on the wall surface of the conventional heat exchanger includes a relatively much larger size than the temperature boundary layer, there is a problem in that it does not provide an efficient fin shape in promoting heat transfer.

Accordingly, the present invention has been made to improve the above conventional problems,

The present invention provides a flow collapse means for disturbing and collapsing the thermally developed temperature boundary layer on the flow channel wall of the heat transfer apparatus, through which the flow resistance is minimized, disturbance and mixing occur, and the boundary layer collapses. do. This means that the flow collapse means improves the specific heat transfer performance and the overall heat transfer performance of the flow channel walls.

The present invention is intended to provide a heat transfer promoting effect by growing, coating / depositing nanotubes, which have been actively developed recently, on the wall surface of a heat transfer apparatus as a fluid collapse means. Nanotubes are typically considered carbon nanotubes, but can be made of similar materials, such as TiO2, to make nanotubes or nanofibers, coating, depositing, and growing them on cotton.

3 is a schematic view showing a thermal boundary layer equipped with nanotubes grown and deposited on a flat wall surface of a heat transfer apparatus according to the present invention, and the present invention is an outer surface in which a heat medium flows inside an upper surface of a plate (1) or a tube (2). In the heat transfer mechanism for transferring heat to the furnace,

The nanotubes 4 are grown and deposited in the heat medium flow direction within the range of the thermal boundary layer 3 formed on the upper surface of the plate 1 or on the wall of the tube 2, and the heat transfer area is changed by the shape of the grown deposited needles. The present invention relates to a device for heat transfer, on which nanotubes are deposited, which are designed to increase heat dissipation and disrupt the development of the thermal boundary layer (3), thereby facilitating heat transfer, and the coating plate on which the nanotubes (4) is mounted is made of thin plate.

      As shown in FIG. 2, the plate 1 or tube is fixed to the plate 1 or tube 2 because the heat exchanger is fixed to a position to transfer heat to the outside where the heat medium flows, and the surface is smooth. (2) When the heat medium flows on the smooth surface of the wall, the thermal boundary layer 3 is naturally formed on the wall with a considerable thickness, so that heat cannot be effectively taken out from the heat exchanger.

This is because the stagnant fluidized bed in the thermal boundary layer acts as a resistance to heat transfer, thereby inhibiting heat transfer from the surface of the heat transfer mechanism. The heat resistance in this stagnant fluidized bed is greater near the surface, and at the surface of the device for heat transfer, fluid flow is completely stopped, only the heat transfer effect by diffusion, and no convection effect.

That is, as shown in Figs. 1 and 2, the heating medium forcibly proceeds to the wall at a flow average speed, Vo, and proceeds at a speed Vo approximately entered at a part far from the stagnant thermal boundary layer 3 on the wall. The air passing through the thermal boundary layer 3 proceeds at a rate of V1 lower than Vo, and at a rate of V2 lower than V1 in the stagnant boundary layer below it, and at the surface of the heat transfer mechanism virtually no heat flow occurs. It is completely stopped.

This flow stoppage is due to the action of friction and viscous forces between the heat medium and the fin (FIN) in hydrodynamic terms. Therefore, large fins are required to discharge a large amount of heat, and as the fin size increases, the thermal resistance increases and the surface area becomes large, thereby increasing the overall cooling system and decreasing the heat transfer rate per unit volume. It goes against the form of the flag.

As shown in FIG. 3, the present invention relates to a cooling fin of a nanotube, and more particularly, by arranging turbulent flow promoting protrusions on a wall surface of a heat transfer mechanism at regular intervals in the direction of the flow mainstream of a heat medium, the flow of heat medium In addition, it is possible to form turbulence, and the incoming heat medium is peeled off the top of the turbulent acceleration protrusion and reattached to the wall to thin the existing thermal boundary layer, thereby increasing the coefficient of friction and promoting the heat transfer rate to improve cooling or heat dissipation efficiency. It relates to a (carbon) nanotube type cooling fin that can be improved. Since the nanotubes are very large in length compared to their diameters, they have flexibility and thus shake due to flow, causing disturbance of the flow and thermal boundary layers.

In order to implement this, Figure 4 shows a schematic view showing another form of nanotubes grown and deposited on the wall of the heat transfer mechanism according to the present invention.

Nano-tubes are attracting much attention due to their unusual structure and excellent mechanical and electrical properties. Especially, the thermal conductivity of carbon nanotubes is 10 times higher than that of copper, silver, or gold. It is so large that it is almost superconductor in terms of heat transfer.

As shown in FIG. 4, two-dimensional or one-dimensional alignment is necessary. At this time, the two-dimensional alignment method is a method of applying spin coating (dip coating) or dip coating (dip coating). One-dimensional alignment methods include extrusion or elongational flow, magnetic fields, or stretch drying. In addition, it may be formed as a bucky block according to the shape of the aggregate in which the nanotubes 4 are formed.

When these nanotubes are applied to a plate or tube with an ideal flow, the nanotubes can act as a nucleus that causes condensation and evaporation to start. Can be used.

When coating a plate or tube using the material of the nanotube, the nanotube is freely coated on the surface, and a part of the hair is randomly created on the surface. In this way, the fabrication of the heat transfer surface is economical and simple, but a large number of hairy nanotubes are present in the thermal boundary layer, and thus the heat transfer surface is improved.

While the invention has been particularly shown and described with reference to the above embodiments, it has been used only for the purpose of illustration and those of ordinary skill in the art to which the invention pertains have the invention as defined in the appended claims. It should be understood that various modifications may be made without departing from the spirit and scope of the invention.

As described above, in the present invention, the thickness of the boundary layer is reduced by growing and depositing nanotubes in a predetermined arrangement direction within the range of the thermal boundary layer grown on the wall of the heat transfer mechanism, disturbing and breaking the developed thermal boundary layer. It is to provide a heat transfer apparatus that promotes heat transfer. This heat transfer promotion increases the thermal efficiency of the apparatus used in the general industry, thereby improving economic efficiency and reducing carbon dioxide emissions.

Claims (2)

A heat transfer promoting mechanism for transferring heat to a surface of a plate (1) or the inside of a tube (2) to the outside of the heat medium flows, Within the range of the thermal boundary layer 3 formed on the upper surface of the plate 1 or on the wall of the tube 2, The nanotubes 4 are grown and deposited along the heating medium flow direction to reduce the thickness of the thermal boundary layer 3 by the shape of the grown-deposited needles to promote heat transfer. A heat transfer facilitating apparatus on which nanotubes are deposited, wherein the mounted coating plate is a thin plate. delete

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