U.S. patent application number 10/542570 was filed with the patent office on 2006-10-12 for device and method for diagnosing obstructions in channels of a micro heat exchanger.
Invention is credited to Herbert Grieb, Astrid Lohf.
Application Number | 20060225864 10/542570 |
Document ID | / |
Family ID | 32667703 |
Filed Date | 2006-10-12 |
United States Patent
Application |
20060225864 |
Kind Code |
A1 |
Grieb; Herbert ; et
al. |
October 12, 2006 |
Device and method for diagnosing obstructions in channels of a
micro heat exchanger
Abstract
In order to diagnose obstructions in channels of a micro heat
exchanger, at least one temperature sensor is externally placed on
the micro heat exchanger and an evaluating device is connected to
this sensor. Said evaluating device diagnoses an obstruction based
on changes in the measured temperature in the event of unchanged
entry parameters of the fluids involved in the heat exchange.
Inventors: |
Grieb; Herbert; (Malsch,
DE) ; Lohf; Astrid; (Erlangen, DE) |
Correspondence
Address: |
SIEMENS CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
170 WOOD AVENUE SOUTH
ISELIN
NJ
08830
US
|
Family ID: |
32667703 |
Appl. No.: |
10/542570 |
Filed: |
January 21, 2004 |
PCT Filed: |
January 21, 2004 |
PCT NO: |
PCT/EP04/00464 |
371 Date: |
April 12, 2006 |
Current U.S.
Class: |
165/11.1 |
Current CPC
Class: |
F28F 19/00 20130101;
F28F 2260/02 20130101; F28F 27/00 20130101 |
Class at
Publication: |
165/011.1 |
International
Class: |
F28F 7/00 20060101
F28F007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 21, 2003 |
DE |
103 02 156.6 |
Claims
1.-4. (canceled)
5. A device for diagnosing obstructions in channels of a micro heat
exchanger, comprising: at least one temperature sensor arranged on
an outside of the micro heat exchanger; and an evaluation unit
connected to the at least one temperature sensor, wherein the
evaluation unit diagnoses an obstruction on the basis of changes of
a measured temperature, wherein entry parameters of fluids involved
in the heat exchange are unchanged.
6. The device according claim 5, wherein the device is a detachable
arrangement.
7. The device according claim 5, wherein the outside is an outer
surface of the micro heat exchanger.
8. A device for diagnosing obstructions in channels of a micro heat
exchanger, comprising: at least one temperature sensor arranged on
an outside of the micro heat exchanger; and a closed-loop control
device connected to the at least one temperature sensor, wherein
the closed-loop control device regulates a mass flow of fluids
involved in the heat exchange in the sense of keeping the measured
temperature constant, and wherein the closed-loop control device
diagnoses an obstruction on the basis of changes in the mass
flow.
9. The device according claim 8, wherein the device is a detachable
arrangement.
10. The device according claim 8, wherein the outside is an outer
surface of the micro heat exchanger.
11. A method for diagnosing obstructions in channels of a micro
heat exchanger, comprising: measuring a temperature of the micro
heat exchanger at an outside of the micro heat exchanger; and
diagnosing an obstruction on the basis of changes of the measured
temperature, wherein entry parameters of the fluids involved in the
exchange of heat remain unchanged.
12. The method according claim 11, wherein the measuring of the
temperature is accomplished at at least one point on the outside of
the micro heat exchanger.
13. The method according claim 11, wherein the outside is an outer
surface of the micro heat exchanger.
14. A method for diagnosing obstructions in channels of a micro
heat exchange, comprising: measuring a temperature of the micro
heat exchanger at an outside of the micro heat exchanger;
regulating a mass flow of one of the fluids involved in the heat
exchange such that the measured temperature is constant; and
diagnosing an obstruction on the basis of changes of the mass
flow.
15. The method according claim 14, wherein the measuring of the
temperature is accomplished at at least one point on the outside of
the micro heat exchanger
16. The method according claim 14, wherein more than one mass flows
are regulated.
17. The method according claim 14, wherein the outside is an outer
surface of the micro heat exchanger.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the U.S. National Stage of International
Application No. PCT/EP2004/000464, filed Jan. 21, 2004 and claims
the benefit thereof. The International Application claims the
benefits of German application No. 10302156.6 filed Jan. 21, 2003,
both applications are incorporated by reference herein in their
entirety.
FIELD OF THE INVENTION
[0002] The invention relates to a device and a method for
diagnosing obstructions in channels of a micro heat exchanger.
SUMMARY OF THE INVENTION
[0003] It is known that deposits (fouling) in heat exchangers
disrupt the effectiveness of the heat transfer between the fluids
involved in the heat exchange. The same effects are to be observed
in micro heat exchangers with microchannels of which the diameter
is <1 mm, but in such devices this leads to the blockage of
individual channels or of all channels. Considering the fact that
micro reactors are also used in particular for extreme exothermic
reactions, explosive mixtures or toxic chemicals, it is
understandable that early detection is necessary as to whether a
safe tempering can no longer be guaranteed as a result of the
obstruction of the heat exchangers which are used for such purposes
as delay lines. To increase throughput microchannels are frequently
connected in parallel in micro heat exchangers. An even
distribution of the fluids on these microchannels is achieved by
their relatively high flow resistance. If individual microchannels
are now blocked, the heat transfer surface and thereby the
efficiency of the heat transfer is reduced. The efficiency is
calculated from the capacity flows (mass flow x specific heat
capacity) of the fluids involved in the heat exchange as well as
from their temperature on entry into and exit from the heat
exchanger. The fluid temperatures cannot however be recorded
directly in the microchannels since the temperature sensors
currently available are so large that they would block at least a
major part of the channel cross section and that even with slight
contact with the channel wall the temperature reading is likely to
be falsified as a result of heat conductance.
[0004] The underlying object of the invention is thus to make
possible a simple diagnosis of obstructions in channels of a micro
heat exchanger.
[0005] The object is achieved by the claims. In accordance with the
invention the object is particularly achieved by a device for
diagnosing obstructions in channels of a micro heat exchanger, with
at least one temperature sensor being arranged on the outside of
the micro heat exchanger, and an evaluation device being connected
to it, which, on the basis of changes to the measured temperature
with unchanged entry parameters of the fluids involved in the heat
exchange, diagnoses an obstruction. The object is further achieved
by method claims.
[0006] By contrast with conventional heat exchangers, the axial
heat conductance in the channel wall plays a major role in micro
heat exchangers, since the ratio of the wall cross sectional
surface to the channel cross sectional surface is greatly
increased. The consequence, particularly with materials with good
heat-conducting qualities, is greatly reduced efficiencies compared
to conventional heat exchangers. In the area of small NTUs (Number
of Transfer Units), i.e. for small ratios of the product of heat
transfer surface and heat transfer coefficient to heat capacity
flow, the efficiency drops as the NTU falls, while it remains
constant in the area of large NTUs. There is always a laminar
creeping flow in the micro channels so that the coefficient of heat
transfer is independent of the flow velocity. If a few micro
channels are now obstructed, the flow velocity actually increases
in the other channels; however the coefficient of heat transfer
remains constant and the transmitted heat volume falls because of
the reduced heat transfer surface. Since the heat capacity flow
remains constant, the efficiency decreases.
[0007] The invention now makes use of the fact that, because of the
high heat conductance, the temperature of the micro heat exchanger
wall with unchanged entry parameters of the fluids involved in the
heat exchange, which means with constant mass flows and constant
fluid entry temperatures, and with sufficiently small NTU (around
>5), is a measure for the efficiency of the heat exchanger. At
the same time the temperature, also because of the high heat
conductance in the wall, in micro heat exchangers is relatively
homogeneous, so the efficiency can be deduced on the basis of the
temperature of the micro heat exchanger, and the temperature in its
turn can be recorded significantly more easily since installing the
temperature sensor on the exterior of the micro heat exchanger does
not present any problem. A further advantage lies in the fact that
the temperature sensor does not come into contact with the fluids
so that it is not necessary to worry about the resistance to
chemicals or the catalytic effect of the temperature sensor. With
very large micro heat exchangers the temperature can be measured
with a number of temperature sensors at a number of points.
[0008] With an alternative device for diagnosing obstructions in
channels of a micro heat exchanger the obstructions are not
diagnosed on the basis of changes in the measured temperature;
Instead a closed loop control device is connected to the
temperature sensor which controls the mass flow of a fluid involved
in the exchange of heat in the sense of keeping the measured
temperature constant, with obstructions being diagnosed as a result
of changes to the mass flow.
[0009] If the micro heat exchanger is used as a delay element for
chemical reactions, the reaction heat to be fed in or removed must
additionally be taken into account, something which can be done by
a more complex evaluation (fuzzy logic, neuronal networks).
[0010] For further explanation of the invention reference is made
below to the figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 shows a first exemplary embodiment of the micro heat
exchanger in accordance with the invention, and
[0012] FIG. 2 shows a second exemplary embodiment of the micro heat
exchanger in accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0013] FIG. 1 shows a micro heat exchanger 1 with an inlet 2 and an
outlet 3 for a fluid to be cooled 4 and an inlet 5 and an outlet 6
for a cooling fluid 7. Within the micro heat exchanger 1 parallel
microchannels 8 are embodied in each case between the inlets 2 and
3 or 5 and 6, each with a channel diameter of <1 mm. On the
outside of the micro heat exchanger 1 a temperature sensor 9 is
arranged, which measures the temperature on the micro heat
exchanger wall and is connected to an evaluation unit 10. This
sensor detects a reduction in the efficiency of the heat exchanger
1 if the measured temperature changes with constant mass flows and
constant fluid entry temperatures.
[0014] The exemplary embodiment shown in FIG. 2 of the inventive
micro heat exchanger differs from the device shown in FIG. 1 in
that, instead of the evaluation unit 10, a closed-loop control unit
11 is provided, which uses a control element 12 to regulate the
mass flow of the cooling fluid 7 in the sense of keeping the
temperature of the micro heat exchanger 1 constant with the
temperature sensor 8.
* * * * *