Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02343380 2001-03-09
WO 00/08403 _ . 1 PCT/EP99/05760
Device for the heating of free-flowing substances and processes for its manu-
facture
This invention refers to a device for the heating of free-flowing substances,
especially
diesel fuel, and to a process to manufacture such a device.
Substances in liquid or gaseous states are normally transported in containers
and
pipe systems. Whenever the temperature drops below .a defined value, the
medium in the
container or the medium to be transported in a pipe system starts to change
its (physical)
state and becomes more dense (which is not desired). In the case of gaseous
substances
this will lead to the formation of droplets and to a condensing precipitation
on the inner walls.
Liquid substance tends to flocculate thus preventing the emptying of the
container or its
transport in pipes. A known example for this is the flocculation of diesel
fuel at low tempera-
tures.
This undesired effect, however, could be counteracted by reducing the pressure
in-
side the container or the pipes. Normally, this is not possible. By adding
chemical additives
one can try to maintain the desired physical state (e.g. winter diesel fuel).
Known as well are various forms of supplying heat to keep the temperature of
the
substance at a defined level in order to suppress these undesired effects.
Corresponding
heating devices are known from DE 32 43 809 A1 and DE. 35 16 253 A1. However,
supplying
a very large amount of heat within a short time can lead to undesired side
effects. The con-
cerned liquid may be damaged in its substance. Due to local temperature peaks
it is also
possible that the substance will not change from the thicH; flowing state to
the standard liquid
state but will change directly and undesired into the gaseous state.
Supplying heat too quickly - especially with local temperature peaks - may
lead to
explosions whenever highly flammable substances are concerned.
As a matter of course, heat can be supplied slowly as well. The main advantage
is
that the desired liquid or gaseous state will only be reached after an
increased period of time.
If the (ambient) temperature drops below a critical value, the required
temperature has rap-
idly to be reached again to avoid interruptions of running engines which
subsequently would
deteriorate the operation of a plant.
Aim of this invention is to create a device which enables the heating of free-
flowing
substances and which allows to supply liquid or gaseous substances that are
kept in con-
tainers (e.g. tanks), pipe systems or other receptacles with large amounts of
heat within a
short period of time and by avoiding the undesired side effects mentioned
earlier. An addi-
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WO 00/08403 , 2 PCT/EP99/05760
tional aim of this invention is to have a process available for the
uncomplicated manufacture
of a combined heat supply and transfer element.
The aim mentioned first has been solved by the device which is described in
patent
claim Ns 2.
The preferred further development and design of the device invented are
subject
matter of patent claims N~ 2 to 12.
The aim mentioned second has been solved by the measures described in patent
claim Ns 13. The further development of this process is subject matter of
patent claim N~ 14
According to the invention, a heat transfer element has to be mounted to at
least one
part of the container or pipe, e.g. fuel tank. Suitable materials are copper
or aluminum, for
example.
If, according to claim N~ 2, the heat transfer element consists of a bundle of
steel
wool, of metal shavings or metal threads as long as po:>sible andlor a wound
or folded ex-
panded metal mesh (see EP 0 340 619 A) or wire mesh, the heat transfer element
is char-
acterized by a very large surface area but very low volume and a reduced flow
resistance. A
known expanded metal mesh will only require 2 % of the container volume.
Whenever the
heat transfer element is mounted preferably in the outlet area of the tank
there will be no cir-
culatory problems whatsoever. This results from the fact that the drain
opening of a tank is
generally smaller than the diameter of the tank. If the heat transfer element
fills the entire
tank, it provides the additional advantage of reducing the surge movements of
a liquid due to
the countless tittle chambers of the element. In addition, 'these chambers
prevent explosions
as flame propagation will not be possible. Local overheating is not dangerous.
Should the
heat transfer element cause flow perturbations (unchanged flow diameter) in
the case of
gaseous substances, for example, the diameter of the pipe concerned can be
increased as
required - according to the invention - within the area of the heat element.
Compacting the outer areas of the heat conducting element will improve its
positional
stability.
If, according to claim N~ 4, a cavity is formed in t;he heat transfer element
that is lo-
sated directly in front of the container drain outlet, an increased amount of
the substance
stored in the container will be available in cases of increased substance
demands. In the
case of diesel engines, a sufficient amount of fuel will be; available at the
cavity of the heat
transfer element after a preheat period of that heat transfer element which is
then able to
reheat the downstream pipe system even up to the injection nozzle to such a
point that fuel
will arrive at the nozzle prior to reaching the flocculation temperature.
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The heat transfer element can be supplied with the required heat in various
ways
(claims 5 till 12).
An electrically operated heater can be designed .as heating element which is
in ther-
mal contact with the heat transfer element of the container or pipe.
Another type of heating element would be a thermal conductor which is in
thermal
contact with the heat transfer element. This conductor' is connected to heat
source and
passes through the container or pipe wall. In this case, the thermal conductor
is preferably a
ring- or rod-shaped conductor that passes through the container or pipe wall.
Heat is sup-
plied by a heat accumulator or by means of a heating medium that flows through
heating
canals.
The heat conductor, for instance, could be connE:cted to a heat recovery
system, i.e.
a heat accumulator. When combustion engines are used, the heat energy required
for the
element could be taken from the cooling system and/or from the waste gas heat
of the oper-
ating engine. Fuel will not pass through the heat conducting element during
standstill of the
engine. To drive off, the heat transfer element can be heated by means of the
car's auxiliary
heating (e.g. via a heat conductor).
The use of so-called Q-pipes representing a the~rmosiphon or a closed gravity
heat
pump loop is especially advantageous. Q-pipes are hollow, closed=type vacuum
pipe sys-
tems. They are only partially filled with an easily evaporating liquid. Due to
gravity it gathers
in the lower part of the Q-pipe. By supplying heat to the lower part of the Q-
pipe the liquid will
evaporate and its vapor rises to the top. When the upper portion of the Q-pipe
cools down,
vapor will condensate, dissipate heat and drop down to the bottom. To
facilitate the forming
of condensate there are countless constructive suggestions regarding the
design of drip
noses on the inside walls of the Q-pipes. The heat conductivity of Q-pipes is
50 times higher
than the conductivity of massive copper. Within the Q-pipes heat is
transported "mechani-
cally" from the lower to the upper portion. If there is no heat demand and
subsequently no
condensating process in the upper portion of the Q-pipe there will be no heat
taken out in the
lower portion as well. Whenever one or several Q-pipes of a heat accumulator
are arranged
below the heat transfer element in such a way that they are extending into the
heat transfer
element, a heat transport from the heat accumulator andlor heating element to
the heat
transfer element is possible. If the heat transfer element /has attained the
same temperature
as the liquid within the Q-pipes there will literally be no mechanical
transport of heat. Ac-
cording to the invention, there will be no cooling and subsequently no heat
supply to the heat
transfer element whenever the liquid does not flow through the heat transfer
element.
If the container or the pipe consists of a material with good heat conducting
proper-
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ties, a heat collar can be designed to heat the heat tran~;fer element. The
heat collar is pref-
erably in thermal contact with the ring- or rod-shaped conductor extending
through the con-
tainer or pipe wall.
Another preferred method of heating the heat transfer element consists of
wrapping
the container or pipe with an induction coil close to the area of the heat
transfer element.
An additional preferred method consists of a microwave generator whose field
is di-
rected onto the heat transfer element.
The use of the described heat conducting elements has an additional advantage.
Whenever vapor bubbles are formed due to an increased heat supply, these
bubbles will rise
undisturbed through the liquid and reach the gaseous ai:mosphere on top of the
liquid. The
endless number of small canals of the heat transfer element will prevent large
bubbles from
rising to the top. Whenever a large vapor bubble is formed this one will be
divided into a
large number of small vapor bubbles. The total surface .area of many little
vapor bubbles is
definitely greater than the surface area of a single vapor' bubble. Due to
this increased sur-
face area the heat energy contained in the vapor will be~ given off more
rapidly to the envi-
ronment , i.e. to the heat element and the liquid. As a result of the
labyrinth-shaped countless
canals of a heat transfer element, rising vapor bubbles have to pass a
considerably in-
creased distance on the way to the top of the liquid - c;ontrary to rising
through an undis-
turbed environment. This increased distance corresponds to an increased time
of surface
contact with the heat transfer element and with the liquid. As each vapor
bubble can only
dissipate heat to the heat element and the liquid during the time of surface
contact, this in-
creased contact time will lead to an increased emission of heat. All in all,
the heat transfer
element will transfer the vapor inherent heat energy in a better and more
advantageous way
to the liquid.
The explanation of the invention is given by the construction examples of the
draw-
ing. Shown are:
Fig. 1 schematic longitudinal cut of the container with heat transfer element
Fig. 2 to 9 schematic longitudinal cuts of various construction forms of the
heat transfer
element and the heating installation as well as
Fig. 10 schematic drawing of a device to implement a process of manufacturing
a com-
bined heating and heat transfer element.
According to fig. 1, the heat transfer element (Na 3) is arranged inside a
container,
e.g. a fuel tank. It consists of a bundle of expanded metal, for instance,
that fills the entire
cross-sectional area of the tank (N~ 1) and which is located directly in front
of the drain outlet.
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If the tank (Ns 1 ) is filled with flocculated diesel fuel, for example, the
heat transfer element
(Ns 2) can be supplied with heat energy. The fuel will be liquefied - at least
in the area of the
heat transfer element (Ns 2) - in order to be drained in a normal way.
Design example fig. 2 shows the electrical heatinc,~ rod (N~ 4) mounted inside
the tank
(No 1) and inside the heat transfer element (Ns 2) and being in thermal
contact with the heat
transfer element (Ns 2).
Fig. 3 shows a device with rod- or ring-shaped heat conductor (N~ 4a). Rod or
ring
are passing through the walls of tank Ns 1 and are simultaneously in thermal
contact with the
heat transfer element Ns 2 and a heat accumulator (N~~ 5) which is heated by
the engine
block or by a heated medium flowing through canal N~ 6 (fig. 4). Canal Ns 6 is
flown through
by a heated liquid or gas, e.g. the waste gas of an engine.
The construction examples of fig. 3 and 4 are displaying a heat conductor
(No.4a)
designed as a Q-pipe system.
According to the invention, fig. 5 shows a device vvhich consists of a heat
collar (Ns 7)
that is wrapped around tank N~ 1 in the area of heat transfer element N~ 2.
The heat collar
can be heated electrically. It is also possible to design the heat collar N~7
similar to canal Ns
6 (see fig. 4), i.e. it is flown through by a heated liquid or heated gas. In
this case, it is an
advantage to wrap the heat collar helically around tank Ns 1 (not shown). The
heat collar
preferably covers the heat conductor (Ns 4a) if installed.
According to the invention, figure 6 shows a device where the outer areas (Ns
21 ) of
the material of the heat transfer element (Ns 2) have been compacted. This
material com-
paction enables an improved heat transfer between heating element and heat
transfer ele-
ment (Ns 2). In addition, this design improves the positional stability of the
heat transfer ele-
ment (Ns 2).
According to the invention, figure 7 shows a device with pipe (No. 8) that
consists of
non-conducting material and which is flown through by the medium to be heated.
A heat
transfer element (No. 2) e.g. made of expanded metal is amounted inside the
pipe. Within the
area of the heat transfer element (No. 2) an induction coil (N~ 12) is wrapped
around the pipe
(Ns 8). If the induction coil (Ns 12) preferably generates a high-frequency
alternating field, the
heat transfer element (Ns 2) will be heated and dissipate heat to the medium
flowing through
pipe Ns 8.
Figure 8 shows a totally different method of he<~t supply. One portion of the
non-
conducting pipe (Ns 8) is designed like a microwave oven. A microwave unit (Ns
9) covers the
pipe (Ns 8). On the inside, this unit is equipped with a fine'-meshed
conducting mesh (No 10)
which - in connection with the microwave generator (Ns 9) - constitutes a
Faraday cage. A
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microwave emitter (No.11) influences the heat transfer element (N~ 2).
Compared to the mi-
crowave emitter (Ns 11) the heat transfer element (Ns' 2) reacts like an
antenna and is
heated. This heat is used to heat the medium flowing through pipe Ns 8.
According to the invention, figure 9 shows a device with the heat element Ns 2
having
a cavity preferably within the vicinity of tank drain outlet N~ 13. If the
heat transfer element
(Ns 2) is heated according to one of the methods described earlier, the heated
liquid will rise
and gather within the cavity (Ns 13). If fuel is taken out oif the tank (Ns 1}
via the drain outlet,
(N~ 3) a fuel reserve will be available in the cavity (Ns 13) for the starting
phase of the engine.
Various heating methods are preferably combins;d in such a way to have fuel
avail-
able under most favorable conditions during the starting phase as well as
during sustained
operation.
Figure 10 shows a device to manufacture a combination of heat transfer element
(N~
2) and heating rod (Ns 4). A strip made of expanded metal (e.g. according to
EP 0 340 619)
is attached to and afterwards wrapped around the heating rod (Na 4). Figure 10
displays the
windings having a specific distance between layers. Actually, each layer is
tightly wound. As
the individual connecting links of the expanded metal are literally
perpendicular to the surface
of the metal there are - especially within the first layers of the winding -
only a few thermal
contact points. To improve the thermal contact at these positions, the first
few centimeters of
the metal strip to be wrapped around the heating rod (Ns 4) may consist of a
continuous, un-
punched metal strip followed by the expanded metal strip itself.
Alternatively, a metal film can
be positioned between the layers to improve the thermal contact within the
first windings.
According to the construction method shown in ifigure 10, a feeding device (N~
14)
will continuously add a liquid, curable and conducting material (e.g.
semiconducting polymer)
at least over first few layers. This material will pass through the pores of
the expanded metal.
After curing, the heat transfer element (Ns 2) will be filled with material
that covers the heat-
ing rod (N~ 4). This ensures an optimized heat transfer (between heating
element Ns 4 and
heat transfer element Ne 2 as the heat transfer of heating rod Ns 4 to the
individual connect-
ing links of the heat transfer element Ns 2 is guaranteed. The only important
thing is to im-
prove the thermal contact between the first layers of the resulting coil.
These additional
measures will no longer be required for subsequent layers as the number of
contact points
will increase with the increasing diameter of the coil.
i
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List of reference marks
01Containerltank 08 Pipe
02Heat transfer element 09 Microwave generator
03Tank drain outlet 10 Mesh
04Heating rod 11 Microwave emitter
05Thermal conductor 12 Induction coil
(ring- or rod-shaped)
06Canal 13 Cavity
07Heat collar 14 Feeding device
21 Compacted area
