U.S. patent application number 11/664259 was filed with the patent office on 2007-11-01 for heat exchanger and a charge air cooling method.
This patent application is currently assigned to BEHR GmbH & CO. KG. Invention is credited to Roland Burk.
Application Number | 20070251249 11/664259 |
Document ID | / |
Family ID | 35447445 |
Filed Date | 2007-11-01 |
United States Patent
Application |
20070251249 |
Kind Code |
A1 |
Burk; Roland |
November 1, 2007 |
Heat exchanger and a charge air cooling method
Abstract
The invention relates to a heat exchanger (1) for a charge air
cooling, wherein water, in particular, condensation water in the
form of droplets and/or fog is supplied and the heat exchanger (1)
is provided with a hydrophobe surface in at least one partial area
thereof.
Inventors: |
Burk; Roland; (Stuttgart,
DE) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
BEHR GmbH & CO. KG
|
Family ID: |
35447445 |
Appl. No.: |
11/664259 |
Filed: |
September 30, 2005 |
PCT Filed: |
September 30, 2005 |
PCT NO: |
PCT/EP05/10586 |
371 Date: |
April 27, 2007 |
Current U.S.
Class: |
62/121 ; 165/133;
62/304 |
Current CPC
Class: |
F28F 13/02 20130101;
F28F 2245/02 20130101; Y02T 10/146 20130101; F28D 2021/0082
20130101; F02B 29/0462 20130101; F28F 13/10 20130101; F28F 3/027
20130101; Y02T 10/12 20130101; F28F 2245/04 20130101; F28F 13/18
20130101 |
Class at
Publication: |
062/121 ;
062/304; 165/133 |
International
Class: |
F28C 1/00 20060101
F28C001/00; F28F 13/18 20060101 F28F013/18; F28D 5/00 20060101
F28D005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2004 |
DE |
10 2004 048 207.1 |
Claims
1. A heat exchanger for cooling charge air to which water, in
particular condensation water, can be added in the form of droplets
and/or mist, wherein the heat exchanger has a hydrophobic surface
at least in a partial region.
2. The heat exchanger as claimed in claim 1, wherein, in the region
of the hydrophobic surface, the contact angle of a droplet is
greater than 90.degree., preferably greater than 120.degree. and in
particular greater than 150.degree..
3. The heat exchanger as claimed in claim 1, wherein separation
edges are provided on the heat exchanger.
4. The heat exchanger as claimed in claim 3, wherein the separation
edges are formed by ends of web fins or gills of gill fins.
5. The heat exchanger as claimed in claim 1, wherein the heat
exchanger can be electrostatically charged at least in a partial
region of the surface.
6. The heat exchanger as claimed in claim 5, wherein the
hydrophobic surface has dispersing, electrically conductive
constituents.
7. The heat exchanger as claimed in claim 1, wherein the heat
exchanger has at least one region with a neutral or hydrophilic,
electrically conductive surface.
8. The heat exchanger as claimed in claim 1, wherein the fins of
the heat exchanger have a spacing of a maximum of 2 mm, in
particular a maximum of 1.5 mm.
9. The heat exchanger as claimed in claim 1, wherein the fins have
separation edges with a spacing of a maximum of 5 mm.
10. The heat exchanger as claimed in claim 1, wherein the heat
exchanger is designed in terms of flow such that, in the operating
state which requires the admixture of condensation water, the flow
speed in the region of the separation edges exceeds a value of 3
m/s, in particular 6 m/s.
11. The heat exchanger as claimed in claim 1, wherein the heat
exchanger comprises at least one or two mechanical vibration
transducers.
12. A method for cooling charge air, the charge air flowing through
a heat exchanger and the charge air having water in the form of
condensation water added to it, wherein the air flowing through the
heat exchanger entrains condensation water which forms on the heat
exchanger.
13. The method as claimed in claim 12, wherein the condensation
water which is entrained in the heat exchanger is conveyed onward
in the charge air in the form of droplets or mist.
14. The method as claimed in claim 1, wherein the condensation
water accumulates in the heat exchanger in the form of droplets on
hydrophobic faces, with the droplets which form having a contact
angle of greater than 90.degree., preferably greater than
120.degree. and in particular greater than 150.degree..
15. The method as claimed in claim 1, wherein in at least one
operating state in which condensation water is to be added to the
charge air, the charge air in the heat exchanger flows, at least in
the region of separation edges, at a flow speed of over 3 m/s, in
particular over 6 m/s.
16. The method as claimed in claim 1, wherein mechanical vibrations
are generated in the heat exchanger, in particular by means of at
least one vibration transducer which is coupled to the
evaporator.
17. The method as claimed in claim 16, wherein the mechanical
vibrations are aligned substantially perpendicular to a heat
transmitting face of the heat exchanger.
Description
[0001] The invention relates to a heat exchanger according to the
preamble of claim 1 and to a method for cooling charge air
according to the preamble of claim 11.
[0002] In order to increase the performance of engines,
turbochargers are used to compress the air. Here, however, the air,
referred to in the following as charge air, is heated to
temperatures of over 150.degree. C. as a result of the compression
in the turbocharger. In order to reduce such heating of the air,
air coolers are used which are arranged at the front of the cooling
module and serve to cool the charge air. Here, the charge air flows
through a heat exchanger which has ambient air flowing through it,
and said charge air is thus cooled. This makes it possible to cool
the charge air to a temperature which is approximately 20-90 K
above the temperature of the ambient air. Cooling the charge air
permits an increase in engine performance.
[0003] A two-stage device for cooling charge air and a method for
operating such a device is known, for example, from DE 102 54 016
A1, said device permitting a further increase in performance as a
result of improved charge air cooling.
[0004] A method and a device for operating a supercharged internal
combustion engine are known from DE 28 14 593 C2, said method and
device being used to accumulate the condensation water precipitated
in the charge air cooler, discharge said condensation water out of
the charge air cooler, accumulate said condensation water in an
accumulation tank arranged separately from the charge air cooler,
and supply the accumulated condensation water into the exhaust line
of the internal combustion engine upstream of the exhaust gas
turbine in the flow direction. For this purpose, a pump or at least
a sufficient pressure drop is provided which conveys the
condensation water from the accumulation tank into the exhaust
line.
[0005] Heat exchangers which are used to cool air are provided with
a hydrophilic coating in order to better discharge the condensation
water which is accumulated from said air, since it is
conventionally sought to avoid liquid water components in the
cooled air.
[0006] Heat exchangers of said type, however, leave something to be
desired.
[0007] It is an object of the invention to improve a heat exchanger
of the type mentioned in the introduction.
[0008] Said object is achieved by means of a heat exchanger having
the features of claim 1 and by a method having the features of
claim 11. Advantageous embodiments are the subject matter of the
subclaims.
[0009] According to the invention, a heat exchanger is provided for
cooling charge air to which water, in particular condensation
water, can be added in the form of droplets and/or mist, the heat
exchanger having a hydrophobic surface at least in a partial
region. By providing a hydrophobic surface in contrast to the known
provision of a hydrophilic surface which is effective in conveying
the condensation water downward under the force of gravity, the
condensation water accumulates on the hydrophobic surface in the
form of droplets, with the droplets projecting into the flow duct,
and therefore being easily entrained and ultimately separated and
being conveyed in the charge air flow in the form of droplets
and/or mist. Here--in contrast to the prior art--no specific device
is required to add condensation water to the charge air, in order
to supply the condensation water in the form of droplets or mist to
the charge air flow. The condensation water which is fed back to
the charge air cools the charge air and therefore contributes to an
increase in engine performance.
[0010] In contrast to conventional discharging of the water which
is condensed out, targeted admixture of water takes place according
to the invention, with the result that the cooling power can be
increased, said conventional method being dispensed with.
Conventional cooling of charge air by means of a second cooling
stage, whose cooling power is, for example, generated by a
refrigerant circuit, is therefore associated with considerable
impairment of the efficiency of the cooling system. On the other
hand, it is however undesirable to supply the water which is
condensed out to the motor vehicle engine in an uncontrolled
fashion, that is to say inhomogeneously in terms of space and
time.
[0011] In the region of the hydrophobic surface, the contact angle
of a droplet is preferably greater than 90.degree., preferably
greater than 120.degree. and particularly preferably greater than
150.degree., so that the condensation water accumulates on the
surface in the manner of a pearl and can be easily entrained by the
charge air flow. The hydrophobic surface permits the formation of
approximately spherical droplets which are transported and
entrained by the charge air flow when they are of a small size.
[0012] Separation edges are preferably provided on the heat
exchanger, at which separation edges the droplets which have
collected on the hydrophobic surface detach from the heat exchanger
as a result of the prevailing charge air flow. Here, the separation
edges are preferably also provided with a hydrophobic coating, so
that the low adhesion forces allow the droplets to be easily
detached from the surface. The separation edges are preferably
formed by ends of web fins or gills of gill fins.
[0013] The detachment is supported by flow speeds of preferably
over 3 m/s, particularly preferably over 6 m/s, for which the heat
exchanger is correspondingly designed in terms of flow. High flow
speeds additionally assist in the residence times on the
hydrophobic surfaces being short, which can prevent a plurality of
droplets coalescing, and makes the droplet size at the time of
separation smaller.
[0014] To assist the formation of droplets, the heat exchanger can
be electrostatically charged at least in a partial region of the
surface, so that the droplets which are formed impact against one
another as a result of the electrostatic charge and can, as a
result, detach from the fin structure of the heat exchanger more
easily. In addition, the tendency is reduced for the droplets to be
trapped again by heat exchanger structures arranged in the flow
direction. Electrostatic charging of the droplets also prevents
said droplets joining together in the air flow, so that the
droplets do not coalesce to form larger droplets. Here, the
tendency for the droplets to be trapped again by subsequent fin
structures is considerably greater for larger droplets as a result
of the larger inertial forces, so that it is desirable for the
droplets to be as small as possible.
[0015] The hydrophobic surface preferably has dispersing,
electrically conductive constituents, for example in the form of
nanoparticles which permit electrically conductive contact between
the charged hydrophobic surfaces and the droplets rolling over the
hydrophobic coating, so that the electrical charge can be better
transmitted to said droplets.
[0016] As an alternative to the electrically conductive
constituents, the heat exchanger can have at least one region with
a neutral or hydrophilic, electrically conductive surface which
permits electrostatic charging of the droplets. Here, the
hydrophilic region is preferably considerably smaller, than the
hydrophobic region.
[0017] The fins of the heat exchanger preferably have a spacing of
a maximum of 2 mm, in particular a maximum of 1.5 mm, and can
therefore be situated considerably closer together than the fins of
conventional heat exchangers.
[0018] Good distribution of the droplets in the charge air is
achieved by the fins having separation edges with a spacing of a
maximum of 5 mm.
[0019] One preferred embodiment involves combining the features of
a hydrophobic surface with mechanical vibration generation,
preferably in the inaudible ultrasound range.
[0020] In a further embodiment, it is proposed to couple a
vibration transducer to the evaporator, with the aim of detaching
the condensate droplets which form primarily on the transmitting
face of the heat exchanger from the surface by means of mechanical
vibrations, and if appropriate, of separating said droplets into
smaller droplets.
[0021] The vibration direction of the vibration transducer which
couples vibrations in is preferably selected such that it is
aligned perpendicular to the heat transmitting face. In a further
embodiment of the concept, at least two vibration transducers are
coupled to the evaporator, said vibration transducers being
distributed locally such that the body-borne noise vibration field
which permeates the evaporator is as homogeneous as possible and/or
said vibration transducers complementing one another in terms of
their vibration direction and phase position such that circular
body-borne noise vibration is generated. This makes it possible for
all the heat transmitting faces to vibrate with a vibration
component perpendicular to the surface.
[0022] In a further embodiment, the vibration transducer can be
adapted in terms of its frequency and amplitude such that resonant
effects occur which preferably detach droplets of a particularly
certain size from the surface. As a result, the power of the
required ultrasound transducer can be limited to small values, and
the detachment of small droplets can be assisted. In addition, the
frequency and arrangement of the one or more vibration transducers
in combination with the mounting of the heat exchanger and/or the
connection of further noise conducting components can be adapted in
terms of impedance in such a way that stationary waves with a
particularly advantageous amplitude distribution are generated.
[0023] In a further embodiment of the concept, the vibration
generation can also be utilized to increase the heat transfer
coefficient, or to reduce the pressure loss, on the inside of the
heat exchanger (that is to say the other fluid side). In
evaporators in particular, the formation of bubbles can be assisted
and/or laminar viscous underlayers can be broken up by means of
cavitation effects. This could prove to be particularly useful in
the evaporation of multi-component mixtures (for example
refrigerant/cooling oil).
[0024] Coupling mechanical vibrations into the heat transmitting
structure causes condensate droplets which form on the surface to
be detached at least at times, and as a result permits the gas flow
passing through the structure to be discharged out of the structure
faster.
[0025] The invention is explained in detail in the following on the
basis of two exemplary embodiments and with reference to the
drawing, in which:
[0026] FIG. 1 is a greatly enlarged schematic illustration of a
partial region (gill fins), which is provided with a coating
according to the invention, of a heat exchanger according to the
first exemplary embodiment,
[0027] FIG. 2 is a greatly enlarged schematic illustration of a
partial region (web fins), which is provided with a coating
according to the invention, of a heat exchanger according to the
second exemplary embodiment, and
[0028] FIG. 3 is an enlarged schematic illustration of a heat
exchanger according to the third exemplary embodiment.
[0029] According to the first exemplary embodiment, a heat
exchanger 1 for cooling charge air which is supplied to a motor
vehicle engine has a structure, which is known in principle, with
gill fins 2 which are arranged obliquely and parallel to one
another, with FIG. 1 illustrating only a greatly simplified and
enlarged section through part of the gill fins 2. According to the
invention, the gill fins 2 are provided with a hydrophobic surface
coating which has the effect that the condensation water which
accumulates on the gill fins 2, said condensation water
accumulating out of the charge air on the cooler surface of the
heat exchanger 1, accumulates in the form of droplets, as indicated
by approximately circularly illustrated droplets 3 in FIG. 1. Here,
the droplets 3, which have accumulated on the hydrophobic surface
of the heat exchanger 1, have a contact angle of more than
90.degree. relative to the surface of the heat exchanger 1, so that
they roll off the surface of the heat exchanger 1, are entrained by
the charge air flow, indicated by arrows, along the faces of the
gill fins 2 and--after separation at a separation edge 4--are
conveyed with the charge air flow as condensation water mist 5.
Here, the charge air flows in the region of the separation edges 4
at a flow speed of over 6 m/s, so as to ensure that the droplets 3
are separated and entrained.
[0030] Since the entrained condensation water in the charge air is
evaporated again during the suction and/or compression process, the
charge air is cooled further, with the result that the engine
performance can be further increased, for example by increasing the
injection quantity and by means of its timing.
[0031] According to the second exemplary embodiment illustrated in
FIG. 2, the heat exchanger 1 has a structure, which is known in
principle, with web fins 12 which are arranged parallel and offset
relative to one another. Corresponding to the gill fins 2 of the
first exemplary embodiment, the web fins 12 of the second exemplary
embodiment are provided with a hydrophobic coating which ensures
that the condensation water which accumulates on the relatively
cool web fins 12 rolls off.
[0032] The function of the hydrophobic coating is the same as in
the previously described first exemplary embodiment, so this is not
described in any more detail, but the flow profile of the charge
air is more uniform as a result of the shape of the fins, and the
charge air is not deflected significantly by the web fins 12 which
run parallel to the flow profile.
[0033] FIG. 3 shows, in the form of a section, a heat exchanger 21
having flow ducts 22, embodied here as tubes, through which a fluid
1 flows, and having fins 23 which are embodied here as corrugated
fins. A vibration 24 aligned perpendicular to the heat transmitting
face is generated by means of two vibration transducers (not
illustrated) with vibration directions (excitation 1 and excitation
2 respectively) which lie substantially perpendicular to one
another. The body-borne noise vibration field which permeates the
heat exchanger 21 is homogenized as a result.
* * * * *