DE102010001566A1 - Flat tube for low temperature radiator used in car for indirect refrigeration of e.g. accumulator, has channels dimensioned such that hydraulic diameter ranges between specific values, where diameter amounts to quadruple of quotient - Google Patents

Abstract

The tube (1) has channels (2) arranged adjacent to each other, where liquid to be cooled flows through the channels. The channels are dimensioned such that a hydraulic diameter ranges from 0.68 mm to 0.97 mm. The hydraulic diameter amounts to a quadruple of a quotient from a cross section area and an inner periphery of each channel. A width (B) of each channel ranges from 0.47 mm to 0.66 mm. A depth (T) of the tube ranges from 14 mm to 18 mm. An outer wall thickness (W) of each channel ranges from 0.2 mm to 0.3 mm.

Description

The invention relates to a flat tube for a low-temperature cooler. In this case, the flat tube on several juxtaposed channels through which a liquid to be cooled can be performed.

Low temperature coolers are used in a vehicle for indirect cooling of heat exchangers such. B. when using indirect charge air coolers, stacked-plate oil coolers or more recently battery cooling or additionally required in the car electronics cooling used. In many cases, a low-temperature cooling section provided in a main cooler is used.

If the efficiency of such a low-temperature cooling section is insufficient, a separate low-temperature cooler can be used. For such coolers, a very high power dissipation of the low-temperature radiator is required for low coolant mass flows, also in relation to the "low-temperature cooling" with indirect intercooling, wherein the coolant mass flow is still very low compared to the conventional coolant radiator for engine cooling.

Conventional conventional coolant cooling technology (including but not limited to welding with / without turbulence) may be used for low temperature cooling, but with reduced power output since it is designed for high coolant mass flows.

Furthermore, extruded flat tubes or welded flat tubes with internal turbulence insert can be used, but they have a low efficiency and a reduced power output in common, since they are designed for refrigerant technologies.

All previous solutions show a low level of performance for the new application of "low-temperature cooling" in the automotive industry.

In contrast, it is an object of the invention to provide a flat tube for a low-temperature cooler, which has the highest possible cooling capacity.

This object is inventively achieved by a flat tube whose channels are dimensioned so that they have a hydraulic diameter of 0.68 mm to 0.97 mm, wherein the hydraulic diameter is four times the quotient of the cross-sectional area and inner circumference of the channels.

The use of flat tubes designed especially for the latest application of low-temperature coolers can increase the performance of low-temperature coolers while keeping the coolant mass flows low. This is made possible by an optimal dimensioning of the channels in the flat tube. It has surprisingly been found that this is achieved with a hydraulic diameter of 0.68 mm to 0.97 mm. With such a dimensioning, the highest power output occurs while the coolant mass flows continue to be low.

As provided according to one embodiment of the invention, this range of values can be advantageously limited to a hydraulic diameter (Dh) of 0.68 mm to 0.87 mm for further optimization.

It has also been found that the cross-section of the channels should advantageously not be made in a circular shape but, as provided according to a further embodiment of the invention, has a rectangular, triangular or oval cross-sectional area.

Further embodiments of the invention relate to the remaining advantageous efficiency-increasing dimensioning of the flat tube and its channels. In this case, the width of the channels dimension of 0.47 mm to 0.76 mm, preferably 0.47 mm to 0.66 mm, and the wall thickness of the channels dimensions of 0.2 mm to 0.35 mm, preferably 0.2 mm to 0.3 mm, on. Furthermore, the flat tube depth advantageously has dimensions of 12 mm to 20 mm, preferably 14 mm to 18 mm, and its height dimensions of 1.4 mm to 2.2 mm, preferably 1.6 mm to 2.0 mm. Thus, an optimum efficiency of the flat tube or of its channels for a low-temperature cooling is achieved in each case.

According to further embodiments of the invention, the flat tube according to the invention can be used advantageously in a low-temperature cooler. In this case, a plurality of flat tubes are arranged one above the other, with cooling fins being provided between them.

An embodiment of the invention will be explained in more detail with reference to the drawing. Show it:

1 a schematic cross section through a flat tube according to the invention,

2 a graph of the power and the internal pressure drop over the coolant velocity for different flat tube dimensions and for a first power point,

3 a graph of the power and the internal pressure drop over the coolant velocity for different flat tube sizing and for a second power point,

4 , a plot of the ratio of power to internal pressure drop for both power points plotted against the internal coolant velocity,

5 a graphical representation of the first derivative of the curves according to 4 for the first credit point,

6 a graphical representation of the first derivative of the curves according to 4 for the second credit and

7 a sketch of a low-temperature cooler with some flat tubes according to the invention.

1 shows a schematic representation of a flat tube according to the invention 1 in cross section. There are several channels in the tube 2 through which a liquid to be cooled can be passed. In the present embodiment, there are eight channels in the 1 are shown in cross section transverse to their main extension direction.

The channels have a rectangular, triangular or oval cross-sectional area for optimum cooling effect; In the embodiment, they have a rectangular cross-section.

The channels 2 have a width B whose optimal dimensioning will be the subject of further consideration.

The flat tube has a depth T (in the direction transverse to the main extension direction of the channels 2 ), which is about 16 mm. The height H of the flat tube is 1.8 mm and the outer wall thickness W of the flat tube 1 in the region of the channels 2 and thus also the outer wall thickness is dimensioned to about 0.2 mm.

The following quantities can be derived mathematically from these dimensioning values:
channel height HC = H - 2 · W,
Cross-sectional area A of the channels 2 : A = B × HC and
Circumference U of the cross-section of the interior of the channels 2 (transverse to their main extension direction): U = 2 * (B + HC).

From the cross-sectional area and circumference, in turn, the so-called hydraulic diameter Dh of the channels can be determined: Ie = 4 · A / U.

It has been found to be 0.68 mm to 0.97 mm or preferably 0.68 mm to 0.87 mm for optimum cooling effect.

This will be explained in more detail below. Here, of the above dimensions, the flat tube 1 and the channels 2 went out.

Furthermore, the considerations relate to a constellation in which several flat tubes 2 are installed in a cooler with intermediate corrugated fins. The block dimension with B × H = 439.2 mm × 620 mm and the corrugated fin height with 8 mm and rib density with 85 Ri / dm are kept constant.

Furthermore, the following considerations are based on two performance points, Performance 11 and Performance 2: m-KL [kg / m ² s] m-KM [kg / s] Te-KM [° C] Te-KL [° C] Performance 1 8th 0.2 80 25 Performance 2 8th 0.4 80 25 with m-KL: mass flow density air
m-KM: Coolant mass flow
Te-KM: Coolant inlet temperature
Te-KL: Cooling air inlet temperature

Thus, in the previously mentioned dimensions and in the two power points, further parameters which relate to the cooling capacity and which are explained in more detail below are considered.

Depending on the dimensioning, depending on the choice of the width B of the channels, differing speeds of the flow of the liquid to be cooled in the channels result for these two power points.

The following table shows the available "internal velocities", ie the flow velocity of a liquid to be cooled in the channels, at the different channel widths in the flat tube for Performance 1 and Performance 2: B in mm Performance 1 U in m / s Performance 2 U in m / s 1.51 0.299 0.482 1.08 0.312 0.502 0.98 0.317 0.509 0.90 0,322 0.517 0.83 0.327 0.525 0.76 0.332 0.534 0.66 0.344 0.552 0.61 0.349 0.561 0.53 0.362 0,581 0.47 0,375 0.603

It can be seen that the flow rate of the liquid in the channels decreases with increasing channel width. Furthermore, these speed values are needed for the following considerations.

In 2 are plotted in a graph, the cooling capacity and the internal pressure drop across the coolant velocity in the different flat tubes for the power point Performance 1. The curve marked with diamonds shows the cooling capacity in kW, plotted against the coolant velocity in the channels in m / s. The value of the width B of the flat tubes is varied over the course of the curve. Correspondingly, the rectangular curve shows the internal pressure drop in 0, 1 · mbar also plotted against the coolant velocity in the channels in m / s and for different values of B.

3 shows a diagram corresponding to that in FIG 2 , but for the second credit performance 2.

The two 2 and 3 It can be seen that with increasing coolant velocity on the inside of both the performance and the internal pressure drop increase. The following is now considered for the power points, the ratio of cooling capacity to internal pressure drop.

4 , again shows for both power points and for varied values of B the ratio of power to internal pressure drop in kW / 0.1 · mbar above the internal coolant velocity in m / s. The diamond-marked curve shows this curve for the first and the rectangle-shaped curve for the second power point.

In the 4 The curves shown can each be exactly described by means of a polynomial of degree 3 with a coefficient of determination of 1.

The result is the polynomial for the first performance point Performance 1 (left curve) Y = -10,629.0x ³ + 11,478.2x ² - 4,167.9x + 510.9 and for the second performance point Performance 2 (right curve): Y = -1,906.7x ³ + 3,274.9x ² - 1,891.1x + 368.7.

From these third-order polynomials, their first derivatives are mathematically computable in a known manner.

5 shows the first derivative of the polynomial 3 , Degree above the internal coolant velocity for the first power point Performance 1. It can be seen from the curve that the optimum is at an internal velocity in the range of about 0.34 to 0.38 m / s, which has a channel width of 0, 47 ... 0.66 mm is achieved.

6 shows the first derivative of the polynomial 3 , Degree above the internal coolant velocity for the second power point Performance 2. It can be seen from the curve that the optimum is at an internal velocity in the range of about 0.54 to 0.60 m / s, which has a channel width of 0, 47 ... 0.66 mm is achieved.

This observation shows an optimum at a channel width of B = 0.47 to 0.76 mm, preferably of B = 0.47 to 0.66 mm by way of example at a depth of T = 16 mm and a nominal wall thickness of W = 0.2 mm.

These values are more generally tangible by means of the so-called hydraulic diameter Dh, which is optimally in the range Dh = 0.68 mm to 0.97 mm, preferably in the range 0.68 mm to 0.87 mm.

The values of the hydraulic diameter can also be transferred to other non-rectangular channel geometries.

7 schematically shows in view of a low-temperature cooler 3 with superimposed flat tubes according to the invention 1 , The view according to 8th shows the flat tubes in a side view, so that their longitudinal extent between a cooler inlet side 4 and a radiator outlet side 5 is recognizable. Inside the flat tubes 2 are in the illustration according to 8th the channels arranged in invisible side one behind the other. Between the flat tubes 1 are cooling fins 6 provided, which are indicated in the figure only in a part of the radiator.

For the above considerations of determining the optimum hydraulic cross-section of the channels, inter alia, a height of the corrugated fins 6 of 8 mm and a corrugated fin density of 85 corrugated fins per dm were assumed. Furthermore, it was assumed that the radiator would have a height of 439.2 mm and a length of the radiator and thus also the flat tubes of 620 mm.

LIST OF REFERENCE NUMBERS

1

flat tube

2

channel

3

Low-temperature cooler

4

Inlet side low temperature cooler

5

Outlet side low temperature cooler

6

cooling fins

Claims (10)

Flat tube for a low-temperature cooler, wherein the flat tube ( 1 ) several juxtaposed channels ( 2 ), through which a liquid to be cooled can flow, characterized in that the channels ( 2 ) are dimensioned to have a hydraulic diameter (Dh) of 0.68 mm to 0.97 mm, the hydraulic diameter (Dh) being four times the quotient of the cross-sectional area (A) and inner circumference (U) of the channels ( 2 ) is. Flat tube according to claim 1, characterized in that the hydraulic diameter (Dh) of the channels ( 2 ) Is 0.68 mm to 0.87 mm. Flat tube according to one of claims 1 or 2, characterized in that the channels ( 2 ) have a rectangular, triangular or oval cross-sectional area (A). Flat tube according to one of claims 1 to 3, characterized in that the width (B) of the channels ( 2 ) Is 0.47 mm to 0.76 mm, preferably 0.47 mm to 0.66 mm. Flat tube according to one of claims 1 to 4, characterized in that the flat tube depth 12 mm to 20 mm, preferably 14 mm to 18 mm. Flat tube according to one of claims 1 to 5, characterized in that the wall thickness of the channels ( 2 ) Is 0.2 mm to 0.35 mm, preferably 0.2 mm to 0.3 mm. Flat tube according to one of claims 1 to 6, characterized in that the flat tube height (H) is 1.4 mm to 2.2 mm, preferably 1.6 mm to 2.0 mm. Low temperature coolers with flat tubes ( 1 ) according to one of claims 1 to 7, characterized in that the flat tubes ( 1 ) in the cooler ( 3 ) are arranged one above the other and between the flat tubes ( 1 ) Corrugated ribs ( 6 ) are located. Low-temperature cooler according to claim 8, characterized in that the corrugated rib height is 4 mm to 10 mm, preferably 5 mm to 8 mm, and the corrugated rib density 85 corrugated ribs per dm. Low-temperature cooler according to claim 8 or 9, characterized in that the low-temperature cooler ( 3 ) has a width of about 439.2 mm and a height of about 620 mm.

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