Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
7~
~N ARRANGEMEN~ FOR ENSURING -rHA~ ~C~ ~IILL F~
SUBSTANT~ALLY UNIFORMLY ON A TUBULAR HEAT ~XCHANGER
PLACED IN WATER
The present invention relates ~o an arrangement
according to the preamble of Claim 1. The invention can
be applied in conjunction with heat-pump systems Gf the
kind which take energy fro~ an energy-absorbing closed loop ~Ihich lies
.~ partially in water and through which there is circulated
a liquid whose freezing point is lower than that of the
water in which the loop is placed. That part of the loop
which lies in water will hereinafter be referred to as the
heat exchanger while the liquid passing through the loop
10 will be called the heat carrier. The heat exchanger may
comprise any number of tubular members connected in paral-
lel.
Thus, the heat pump takes energy from the heat carrier,
therewith lowering the temperature thereof, whereafter the
lS temperature of the heat carrier is raised again in the heat
exchanger, by taking energy from the water in which the
heat exchanger is placed. The invention can be applied when
the temperature of the water is so lcw that part of the
energy taken from the water occurs through formation of ice
20 on the outer surfaces of the heat exchanger. This naturally
implies that the temperature of the heat carrier is below
the freezing point of the water.
A few years ago, the formation of ice on the heat ex-
changer was considered a disadvantage and should be avoided,
25 since structural dam~ges had occurred as a result thereof.
Often, the heat exchanger, either in part or as a who1e,
rose to the surface of the water, which normally resulted
in leakage of heat carrier. In recent times it has been
observed that important advantages can be obtained in re-
spect of energy-producing heat-pump systems when ice is per-
mitted to form on the heat exchanger. The energy production
plant is always able to take energy from the water, even
though the temperature thereof lies close to its freezing
2 1~ 7~
poir,t. Ih~ ~,lant is normclly ~t,l~ to run at ~ull caF, ~7~y.
irrespective of whether the ten-~perature of the water falls
to its freezing point during certain periods of operation
The problem encountered when perrnit~ing ice to form is th~t
it is often necessary to secure the hea-t exchanger against
the buoyancy forces imparted thereto by the ice, which forces
can be quite large; Maximum ice-diameters can reach to
between 4û and 70 cms, implying a buoyancy force of about
ll - 33 kg per meter of heat exchanger tubing of conventional
o sizes. The problem is not lessened by the fact that the
extent to which ice forms varies along the heat exchanger
tubing, owing to the fact that the temperature of the heat
carrier increases progressively therealong. The result is
an ice formation of conical configuration, which may have a
diameter of say 50 cm at the beginning of the heat exchanger,
and may terminate at a distance of 2ûO m therefrom. Uneven
icing is disadvantageous from the aspect of anchoring down
the heat exchanger and also from the point of view of
capacity in terms of heat transfer, and also in terms of the
ability to accumulate a large quantity of ice.
Several methods of creating uniform icing of heat ex-
changers immersed in water are known to the art. For
example, the direction of flow of the heat carrier can be
reversed periodically. Although icing is then relatively
~s uniform, the ice is thickest at the beginning and at the end
of the heat exchanger, if the heat carrier is allowed to move
in both directions for the same length of time. Icing will
be relatively uniform when heat is taken from the heat car-
rier intermittently while constantly circulating the same,
3~ provided that the heat pump is working for less than about
65 % of the time. When the pump is switched off, cold will
be transmitted from the initial parts of the heat exchanger
to its remaining parts, resulting in almost uniform icing.
In a third method, a tube-part for outgoing heat carrier is
3s brought into contact with the tube part for incoming heat
carrier. This contact can be made along the whole of the
tube-parts or at given locations therealong. The tube-parts
are thus caused to freeze together and an ice-cylinder is
:
formed around the two tube-parts, w~,ich c~rltribute~ to~,ards
uniform icing.
All of the aforedescribed rnethods for producing uniform
icing are encumbered with disadvantages. None of the
methods facilitates anchoring of the ice-coated heat ex-
changer. The method in which the heat-carrier flow is re-
versed requires the provision of automatic devices and auto-
matically controlled valves, which costs money and reduces
reliability. In the method in which the heat pump is run
10 intermittently, the heat exchanger i5 not used to the whole
of its capacity, which means that a larger heat exchanger
must be used in order to obtain a certain given capacity.
The third method requires the tube-parts forming the heat-
exchanger loop to be placed closely together over a signi-
~5 ficant part of their lengths. This lowers the capacity ofthe heat exchanger, since when iced-up the double-laid
tube will have substantially the same heat transfer capacity
per meter as a single ice-covered tube. Consequently, a
larger heat exchanger is required to maintain the caDacitv
2~ desired.
The present invention. which is characterized by the
features set forth in the claims, ensures uniform icing ir-
respective of the length of the heat-exchanger tube or the
parallel-coupled heat exchanger tubes, by providing a cold
25 bridge between a selected number of locations on each heat-
exchanger tube. The cold bridge is produced by arranging
the heat-exchanger tube so that it contacts the bottorn of
the body of water at any number of locations, which are
spaced at any distance apart, normally 10-lOOcms. The tube,
or tubes, is or are then covered at these locations with a
layer of shingle or stone of suitable size, or with some
other lump ballast material, to a height which is normally
preferably equal to the distance between two mutually ad-
jacent contacting locations of the tube-parts with the
bottom of the body of water volume.
At low water temperatures and low heat-carrier tempera-
tures, ice will first form around those tube-parts which are
., , , , ~
~ ' ~
, ~ .
covered wilh ~ingle or stone, o~ing ~o the fact that ct
these lo~ations the intrinsic convective po~er transfer is
far smaller than with a tube located freely in water. ~Ihen
the distance between the locations at which the tube-parts
contact said bottom and the height of the shingle or stone
layer are appropriately selected, a cold bridge will de-
velop in the shingle or stone before any appreciable icing
occurs on those parts of the heat exchanger located freely
in water. This enables ice to form uniformly over the whole
~0 length of the heat-exchanger tubing located free]y in
water.
The invention will now be described with reference to
an exemplifying embodiment thereof illustrated in the
accompanying drawing, in which
Figure 1 is a schematic side view of an arrangement
according to the invention; and
Figure 2 is an end view of the arrangement illustrated
in Figure 1.
A heat-exchanger tube 3 is immersed in a body 1 of
water having a top defining surface 12 and a bottom 2.
The heat exchanger as a whole can comprise any selected
number of heat-exchanger tube members connected in parallel.
The heat-exchanger tube 3 is lain in a closed loop within
which there circulates a heat carrier 11. The temperature
of the heat carrier 11 in the initial, underwater part 7 of
the heat exchanger tube 3 is !ower than the freezing point
of the water. The cold heat carrier 11 is conducted in the
heat-exchanger tube 3 down to a pile 4 of shingle or gravel,
wherewith ice 5 is formed between the individual stones
forming said pile 4. The ice first forms around the in-
coming tube-~art 7, at its location beneath the pile 4 of
shingle, and is then gradually formed around the outgoing
tube-part 8, and its location within said pile 4. The ice
5 has finally frozen practically the whole of the pile 4 of
shingle, to form a coherent frozen block. When the pile 4
of shingle freezes, pronounced cold bridges form between
parts of the heat-exchanger tube 3 located in the frozen
pile 4 of shingle. For example, cold is transferred from
5~
the ingoing tube-part 7 to the out(~oing tube-part ~ by ttlF
transfer of cold frorn the locations ~ and 11 to the loca-
tion 10 on the heat exchanger tube 3. ~he continued supply
of cold heat carrier 11 will result in an even cylindrical
formation of ice along the whole of that part of the tubing
3 located freely in the water 1. The transfer of heat from
the water 1 to the heat carrier 11 is lower for that part
of the heat exchanger 3 located in the pile 4 of shingle
than for that part located freely in the water. By and
10 large, this is compensated for, however, when the pile 4 of
shin~le freezes and a large quantity of heat is taken from
the ice surface 13 on the pile 4. The quantitites in which
shingle is placed over the heat-exchanger tube 3 can be ad-
justed to prevent the heat-exchanger tube 3 frorn rising in
the water as a result of the buoyancy developed by the ice 6.
