Method of producing ice by using fluorinated pentane

An ice making refrigerant mainly consists of at least one compound selected from the group of normal perfluoropentane, cycloperfluoropentane, isoperfluoropentane, and fluorohydropentane. The refrigerant may also consists of pentane mixed with a sufficient amount of one or more of the above compounds for making the refrigerant substantially incombustible. The refrigerant is highly resistant to combustion and free from destroying the stratospheric ozone layer. Ice is produced by mixing the refrigerant in liquid phase with water at a pressure higher than the saturation pressure P.sub.0 of the refrigerant for 0.degree. C. and then ejecting the water-refrigerant mixture into a tank at a pressure below the above saturation pressure P.sub.0, so as to evaporate the refrigerant and let the water freeze by the latent heat of evaporation of the refrigerant. It is particularly suitable for air conditioning systems with heat storage in ice, direct contact type ice making plants, direct contact type water chillers, and the like.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a refrigerant for producing ice. In particular, 
the invention relates to a hardly-water-soluble refrigerant for heat 
storage in ice (ice heat storage) of direct contact type, i.e., freezing 
water by bringing the refrigerant into direct contact with water and 
evaporating the refrigerant, which refrigerant is highly resistant to 
combustion and has a high chemical stability. 
2. Description of the Prior Art 
Recently, annual peak demand of electric power in utility systems depends 
on cooling load. To lower the height of such peak demand, attention has 
been paid to cooling system with ice heat storage by using off-peak night 
power, and construction of actual ice heat storage systems has been 
started for the purpose of cooling of buildings and industrial processes. 
However, the use of such ice heat storage system has not spread so 
extensively, because of the present level of its cost and performance. To 
expand its applications, the so-called direct-contact-ice-making system 
has been proposed; i.e., an ice making system using such a refrigerating 
cycle in which a refrigerant is brought into direct contact with water to 
make ice. Thus, one can expect not only improvement in operational 
efficiency due to more efficient heat exchange through direct contact of 
the refrigerant with water but also cost reduction due to elimination of 
heat exchanger for ice making. 
Various types of direct-contact-ice-making systems have been proposed, but 
the following conditions are commonly required to refrigerant regardless 
of the difference in the type of system. 
(a) Insoluble to water (hardly-water-soluble) 
(b) Free from hydrolysis and chemical stability even after prolonged use 
(c) Free from clathration (not to form clathrate compound of refrigerant in 
water, or hydrate of refrigerant) 
The above condition (a) is necessary to evaporate the refrigerant for 
fulfilling the function of the refrigerant, and if dissolved in water, it 
becomes difficult for the refrigerant to evaporate. The above condition 
(b) is necessary to use the refrigerant over a long period of time as 
sealed in the ice making vessel including a series of devices for 
refrigerating cycle. The above condition (c) is necessary, because if 
transformed into clathrate, refrigerant molecules lose their activity due 
to their inclusion in cavities of the crystal lattice of water, and hence, 
in order to maintain sufficient amount of active refrigerant molecules in 
an ice making vessel for ensuring the desired ice making ability, the 
amount of the refrigerant to be sealed in the ice making vessel becomes 
very large (10 to 30 weight percent of water therein). 
Most conventional direct-contact-ice-making systems use either one of the 
following compounds as refrigerants satisfying the above conditions. 
(1) R114 (Dichlorotetrafluoroethane) 
(2) RC318 (Octafluorocyclobutane) 
(3) Pentane 
However, the above (1) R114 has a shortcoming in that it slightly 
hydrolyzes and produces hydrochloric acid and the like, so that the ice 
making vessel is required to be made of stainless steel, resulting in a 
cost increase. Further, it has a risk of destroying the stratospheric 
ozone layer, and hence it cannot be used at the present from the 
standpoint of environmental protection. 
The above refrigerant (2) RC318 does not contain any chlorine and free from 
the risk of destroying the stratospheric ozone layer. Its saturation 
pressure for room temperature is, however, higher than that of R114, and 
it requires a stronger heat storage tank as compared with R114, resulting 
in a cost increase. More specifically, its saturation pressure for 
0.degree. C., when co-existing with ice, is 1.3 kg/cm.sup.2 (128 kPa) in 
terms of absolute pressure, but its saturation pressure for room 
temperature, e.g., 25.degree. C., increases to 3.2 kg/cm.sup.2 (314 kPa) 
in terms of absolute pressure. Thus, it becomes necessary to provide 
various reinforcements in the heat storage tank, both during construction 
and during operation, so as to meet safety requirements of various laws 
and regulations, such as "Safety Code for Pressure Tank". Since the heat 
storage tank must have a volume proportional to the desired magnitude of 
heat storage, such tank is one of the major factors affecting or 
increasing the cost of direct-contact-ice-making system. Hence, 
consideration for reducing the cost of heat storage tank is extremely 
important from the view point of expanding the use of 
direct-contact-ice-making system. 
Pentane of the above refrigerant (3) is free from the risk of destroying 
the ozone layer, does not hydrolyze, has a low saturation pressure (below 
atmospheric pressure or negative relative thereto) for room temperature, 
and has a boiling point of 36.degree. C. for atmospheric pressure. Thus, 
the cost of heat storage tank in case pentane refrigerant is low. However, 
pentane is highly combustible and safety precaution must be taken. 
Besides, pentane can be subject to biological activation and may be 
decomposed by such activation; e.g., it can become food of microorganism 
such as anaerobic bacteria and the like. 
An object of the invention is to provide a hardly-water-soluble refrigerant 
for producing ice, which is substantially incombustible and free from risk 
of destroying the stratospheric ozone layer and evaporates while in 
contact with water. 
SUMMARY OF THE INVENTION 
The physical and chemical properties which are required for refrigerant to 
be used in direct-contact-ice-making system can be summarized as follows. 
(a) Hardly-water-soluble 
(b) Free from hydrolysis and chemically stable even after prolonged use 
(c) Free from clathrate formation 
(d) Free from destruction of stratospheric ozone layer 
(e) Low saturation pressure for room temperature (preferably, saturation 
pressure of below atmospheric pressure for room temperature) and 
not-very-low saturation pressure for ice forming temperature (preferably, 
saturation pressure of below atmospheric pressure but not lower than 100 
Torr (13 kPa) for 0.degree. C.) If the saturation pressure for the ice 
forming temperature is below 100 Torr, it is technically difficult to form 
a vapor-compression type refrigeration cycle of high efficiency. 
(f) Substantially incombustible 
(g) Free from decomposition by microorganism 
(h) Free from poisonousness 
As to the chemical stability and incombustibility of refrigerant, the 
inventor noted fluorocarbon. More specifically, the bond energy between 
fluorine and carbon in fluorocarbon (116 Kcal/mol) is larger than the bond 
energy between hydrogen and carbon in hydrocarbon (99.5 Kcal/mol), and 
hydrocarbon has its carbon chain in most reduced state while fluorocarbon 
has its carbon chain in most oxidized state. Thus, fluorocarbon has a high 
oxidation resistance and it is incombustible. The inventor also noted the 
fact that various kinds of fluoropentane can be used, because even when 
all hydrogen atoms of the normal pentane are substituted by fluorine atoms 
to produce normal perfluoropentane, change in their boiling points is 
small; namely, boiling point of normal pentane is 36.1.degree. C. and 
boiling point of normal perfluoropentane is 29.5.degree. C. 
The inventor has succeeded in developing a new refrigerant for producing 
ice by testing compounds resulting from replacement of hydrogen atoms of 
pentane with fluorine atoms, based on the outcome of prior studies 
concerning conventional direct-contact-ice-making system and the outcome 
of the inventor's own research and development concerning the 
above-mentioned properties of fluorocarbon. 
The refrigerant for producing ice according to the invention evaporates 
while being in direct contact with water so as to cool and freeze the 
water into ice by its latent heat of evaporation. Examples of the 
composition of such refrigerant are as follows. 
(1) Composition consisting of perfluoropentane as a major component, 
(2) The above composition (1) wherein the perfluoropentane is normal 
perfluoropentane (nC.sub.5 F.sub.12), 
(3) The above composition (1) wherein the perfluoropentane is 
cycloperfluoropentane or isoperfluoropentane (C.sub.5 F.sub.12), 
(4) Composition consisting of fluorohydropentane (C.sub.5 F.sub.n 
H.sub.12-n, 1.ltoreq.n.ltoreq.11) as a major component, 
(5) Composition consisting of a major component including 
fluorohydropentane (C.sub.5 F.sub.n H.sub.12-n, 1.ltoreq.n.ltoreq.11) and 
perfluoropentane, or 
(6) Composition consisting of pentane and such amount of fluorohydropentane 
(C.sub.5 F.sub.n H.sub.12-n, 1.ltoreq.n.ltoreq.11) and/or perfluoropentane 
which amount is sufficient to make the refrigerant substantially 
incombustible. 
Perfluoropentane in the above composition (1) satisfies all of the 
above-mentioned properties (a) through (h) required for the refrigerant of 
direct-contact-ice-making system. As to the configuration of carbon atoms 
in perfluoropentane, normal perfluoropentane (nC.sub.5 F.sub.12) of the 
above composition (2) has a straight chain form, cycloperfluoropentane of 
the above composition (3) has a cyclic form, and isoperfluoropentane 
(C.sub.5 F.sub.12) of the above composition (3) has a branched chain form. 
At the present, normal perfluoropentane is the easiest to obtain among the 
above three types of perfluoropentane. As far as properties relating to 
refrigerant for ice heat storage by direct-contact-ice-making are 
concerned, there seems to be no significant difference between 
cycloperfluoropentane and isoperfluoropentane, as their boiling points are 
nearly equal to each other. 
Fluorohydropentane of the above composition (4) is a compound whose 
molecule has five carbon atoms, which compound is formed by partially 
substituting the hydrogen atoms of pentane of chain, cyclic, or branched 
chain configuration with fluorine atoms. The reason for substituting one 
to eleven hydrogen atoms of pentane molecule with fluorine atoms is in 
that, compound derived by substitution of at least one hydrogen atom with 
fluorine atom is expected to have improved level of the above properties 
required for the refrigerant of direct-contact-ice-making, especially 
incombustibility and biological non-activity. It is also expected that, 
with the increase of the number of fluorine atoms substituting the 
hydrogen atoms, the above properties required for the refrigerant are 
further improved. However, as to the thermodynamic characteristics of the 
refrigerant, such as latent heat of evaporation and the like, the more the 
number of hydrogen atoms is the better such thermodynamic characteristics 
is. It is noted that if a fairly large amount of fluorohydropentane is 
produced, its cost may become lower than that of perfluoropentane. 
The mixture of fluorohydropentane and perfluoropentane in the above 
composition (5) can also be used, of course, as a refrigerant for heat 
storage by direct-contact-ice-making. 
If a refrigerant is prepared by mixing combustible pentane with sufficient 
amount of fluorohydropentane and/or perfluoropentane for making the 
refrigerant substantially incombustible, as in the case of the above 
composition (6), such refrigerant can be safely used in ice heat storage 
by direct-contact-ice-making. The problem of decomposition of refrigerant 
by anaerobic bacteria can be solved by using a suitable germicide and the 
like. 
Perfluoropentane and fluorohydropentane are derivatives of hydrocarbon 
having five carbon atoms in each molecule thereof, i.e., pentane. The 
reason why such derivatives of hydrocarbons having six or more carbon 
atoms are not used is in that, if one dares to use perfluorocarbon having 
six or more carbon atoms as refrigerant for ice heat storage by 
direct-contact-ice-making including change of phase, saturation pressure 
for water freezing point 0.degree. C. becomes very low, for example, 80 
Torr (8 kPa) or less, and the compressor in refrigeration cycle has to 
suck a large volume of gaseous refrigerant, so that the compressor becomes 
large in size, and hence both intake and discharge gas pipes of the 
compressor must be large, resulting in an increase of equipment cost. 
Further, mechanical loss of compressor and the like also increases, and it 
becomes difficult to work out an efficient refrigeration cycle of gas 
compression type. 
On the other hand, the reason why perfluorocarbons and fluorohydrocarbons 
derived from hydrocarbons having four or less carbon atoms are not used is 
in that, in the case of such fluorocarbons having four or less carbon 
atoms, the saturation pressure for room temperature is high, and building 
cost of heat storage tank becomes high as explained above. Therefore, 
among derivatives of various hydrocarbons, fluorocarbon having five carbon 
atoms, i.e., fluoropentane, is most suitable for the refrigerant of 
direct-contact-ice-making. 
It is noted that perfluorocarbon having five carbon atoms can be used as a 
refrigerant for refrigerating machines of centrifugal (turbo) type as a 
substitute of Freon R11. However, the refrigerant of the invention is to 
be brought into direct contact with water so as to improve the efficiency 
of ice heat storage by direct-contact-ice-making, and it is not a mere 
substitute refrigerant for refrigerating machines using Freon. 
It has been known that perfluorocarbon having six or more carbon atoms can 
be used as an antifreeze solution or high-boiling-point heat carrier 
(under Registered Trademark "Fluorinert" owned by The 3M Corporation of 
the U.S.A. An ice heat storage system may be formed by using Fluorinert; 
namely, liquid Fluorinert may be cooled to about -6.degree. C. by a 
regular refrigerating machine (refrigerating machine using Freon) and the 
cooled Fluorinert may be circulated as an insoluble brine (antifreeze 
liquid) while being brought into direct contact with water so as to freeze 
the water into ice for storing energy therein. However, such ice heat 
storage system uses the refrigerant only as a heat carrier for 
transferring sensible heat alone, and no phase transition (between gas and 
liquid) of the refrigerant is caused when it is in contact with water. 
Hence, the above ice heat storage system using Fluorinert cannot achieve 
the high efficiency which is available only by the use of the latent heat 
of evaporation of the refrigerant according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
Before entering the details of preferred embodiment, the operating 
principle of the invention will be described with reference to FIG. 1. 
Deaired water and deaired refrigerant are fed into evacuated space at the 
top portion 3 of a water tank 1, and the refrigerant in the water tank 1 
is extracted and compressed by a compressor 7 so as to be discharged to a 
condenser 9. After liquefied at the condenser 9, the liquid phase 
refrigerant is mixed with water in a mixer 30 or the nozzle 32 at a 
pressure sufficiently higher than saturation pressure P.sub.0 of the 
refrigerant for 0.degree. C. (in order to prevent water from freezing 
upstream of a nozzle). The resultant mixed liquid is jetted from the 
nozzle 32 into the space within the water tank 1 at a pressure equal to or 
less than the above saturation pressure P.sub.0, and the refrigerant 
evaporates and the water is cooled and frozen by the latent heat of 
evaporation of the refrigerant. Thus, ice heat storage by 
direct-contact-ice-making is effected. 
The refrigerant according to the invention is perfluoropentane with or 
without fluorohydropentane (C.sub.5 F.sub.n H.sub.12-n, 
1.ltoreq.n.ltoreq.11), or a mixture of pentane and such amount of 
fluorohydropentane (C.sub.5 F.sub.n H.sub.12-n, 1.ltoreq.n.ltoreq.11) 
and/or perfluoropentane which amount is sufficient for making the mixture 
substantially incombustible. Thus, with the refrigerant of the invention, 
possibility of combustion is small and the risk of destroying the 
stratospheric ozone layer is scarce. 
Thus, the object of the invention, i.e, to provide an ice producing 
refrigerant which is evaporated without possibility of destruction of the 
stratospheric ozone layer, is fulfilled. 
FIG. 1 shows an embodiment of ice heat storing system by 
direct-contact-ice-making which uses a refrigerant according to the 
invention. A heat storage tank, or a water tank 1 is made of steel which 
withstands vacuum. Since the refrigerant of the invention does not 
hydrolyze and does not produce acid, anti-corrosion treatment is not 
necessarily required and the water tank 1 can be built at a low cost. 
A compressor 7 of an oil free type is used to extract refrigerant from top 
space 3 of the water tank 1 through a refrigerant gas suction pipe 6. The 
reason why the oil free type compressor 7 is used is in that, if a 
compressor using oil for cylinder lubrication is used, such oil is 
discharged from the compressor 7 to its discharge refrigerant pipe 8, and 
such discharged oil is likely to reach the water tank 1 and remain there, 
resulting in accumulation of oil in the water tank 1. Once accumulated in 
the water tank 1, it is difficult to return such oil to the compressor 7. 
As the oil free compressor, recipro (reciprocating) type and screw type 
are available for small size, and turbo (centrifugal) type is available 
for large size. 
A condenser 9, which receives compressed refrigerant from the compressor 7 
through its discharge refrigerant gas pipe 8 for condensation thereof, can 
be of water cooling type using cooling water from a cooling tower or of 
air cooling type using fan-driven forced ventilation for heat radiation. 
A gas trap 10 interrupts passage of non-condensed gaseous refrigerant and 
allows passage of only condensed or liquefied refrigerant. In the 
illustrated example, partial pressure reduction is effected here. The 
circulating refrigerant may contain water (small amount), and to prevent 
such water from freezing at the partial pressure reduction, the extent of 
the partial pressure reduction is limited so as to maintain the saturation 
temperature of the refrigerant higher than 0.degree. C. (for instance, in 
case of perfluoropentane, pressure reduction to about 450 Torr). The 
refrigerant is then mixed with cold water from cold water return pipe 17, 
and the water-refrigerant mixture is jetted from a nozzle 32 into the top 
space 3 of the water tank 1, and depressurized to, for example, about 200 
Torr in case of perfluoropentane. As a result, the saturation temperature 
of the refrigerant is reduced to 0.degree. C. or lower, thereby ice is 
formed. The symbol 2c in the drawing indicates mixture of ice (or water) 
droplets and refrigerant droplets and gas produced by the jetting of 
water-refrigerant mixture. When the temperature of water in the water tank 
1 is high, the jetted return water may not freeze immediately, and 
sometimes it may just cool water in the water tank 1. 
A part of the jetted liquid refrigerant may not evaporate and fall into 
water in the water tank 1. If the refrigerant has a large number of 
fluorine atoms in its molecule and its specific gravity is larger than 
that of water, it sediments on a bottom of the water tank 1. The 
sedimented refrigerant is extracted from the bottom of water tank 1 
together with cold water by a cold water circulating pump 15, and is 
delivered again to the nozzle 32 so as to be jetted together with the 
water, whereby the refrigerant evaporates in the top space 3 or evaporates 
from the surface of floating ice or from the surface or inside of water in 
the water tank 1. If the refrigerant has a small number of fluorine atoms 
in its molecule and its specific gravity is smaller than that of water, it 
evaporates from the floating ice or from the surface or inside of water in 
the water tank 1. 
Cold water 2b in the bottom of the water tank 1 is extracted to a cooling 
water outlet pipe 14 by the cold water circulating pump 15 and sent to a 
cold water heat exchanger 16 and then to a cold water return pipe 17. At 
the end of the return pipe 17, the return cold water is mixed with the 
liquid refrigerant (including refrigerant gas if remained) from the gas 
trap 10. To ensure thorough mixing of cold water and liquid refrigerant, a 
mixer 30 of static type (with guide vanes and the like) or dynamic type 
(with rotating vanes and the like) may be used as shown in the drawing. 
The nozzle 32 for jetting the mixture of the refrigerant and cold water 
should scatter or distribute the jetted particles over a wide area, and 
preferably, it is of multi-nozzle (multi-hole) type or rotating nozzle 
type. 
The ice thus produced floats at first on the top surface of water in the 
water tank 1, and then on top of the preceding ice layer so as to be piled 
thereon and form piled layers of ice. The piled layers of ice fill the 
water tank 1 to its bottom in a time period, depending on the size of 
water tank 1 and the capacity of direct-contact-ice-making system, for 
example, in about ten hours. The symbol 2a of the drawing indicates 
water-ice mixture in the intermediate portion of the water tank 1. When 
the water tank 1 is filled with such ice, it may be detected by a suitable 
means (not shown) so as to generate a signal for stopping the compressor 
7. 
In cooling operation (causing the ice to melt), an air conditioner 18 runs 
its cold water pump 19 to feed cold water from the cold water heat 
exchanger 16 to its air conditioning coil 21 through load piping 20. The 
cold water heat exchanger 16 effects heat exchange between the cold water 
of the air conditioner 18 and that from the water tank 1. A blower 22 
blows air to the air conditioning coil 21 for cooling the air thus blown. 
The return water from the cold water heat exchanger 16, which is warmed by 
giving its cryogenic heat to the air conditioner 18, is sent to the nozzle 
32 and sprayed onto the surface of the ice in the water tank 1. The warmed 
return water melts the ice in the water tank 1, starting from the upper 
surface portion thereof. Thus, the piled ice layer gradually rises in a 
piston-like fashion, while allowing cold water to penetrate through gaps 
between ice particles toward the bottom of the water tank 1. A check valve 
11 in the illustrated embodiment is to prevent reverse water flow to the 
liquid refrigerant pipe 12 when the compressor 7 is at rest. Ice-melting 
operation and ice-making operation may be effected simultaneously. 
In the water tank 1, both the ice-making and ice-melting are effected in a 
layered manner by the liquid jetted from the nozzle 32 as described above. 
Thus, no ice fluidizer (e.g., propylene glycol, and the like) is not 
required in principle, but suitable fluidizer may be added depending on 
the circumstances. 
In the embodiment of the system for ice heat storing using perfluoropentane 
refrigerant, the pressure in the top space 3 of the water tank 1 under 
operation with ice therein is about 200 Torr. The intake pressure of the 
compressor 7 during operation is a little lower than the pressure in the 
top space 3. The discharge pressure of the compressor 7 and a condensing 
pressure for the refrigerant is about atmospheric pressure, although it 
depends on outdoor air temperature. Since most devices of the system are 
at low pressure (negative relative to the atmospheric pressure), it is 
preferable to provide an air extracting device 9a for removing air which 
has leaked therein from the outside. 
The refrigerant according to the invention is primarily for ice heat 
storage, but it may be also used in water chillers. More specifically, the 
evaporator of water chiller (water cooling means such as turbo 
refrigerating machine) can be replaced with the direct-contact-ice-making 
means using the refrigerant of the invention, and the conventional heat 
exchanger of multiple pipe type may be eliminated. Thus, cost is reduced, 
and in addition, an improvement of efficiency can be expected by the use 
of direct-contact-type heat exchange between refrigerant and water. Even 
if water chiller produces ice inadvertently, it causes no problem. The 
construction of water chiller is essentially the same as in FIG. 1, and 
its example is not illustrated. 
As hereinbefore fully described, the refrigerant according to the invention 
is for producing ice and particularly suitable for 
direct-contact-ice-making applicable to ice heat storage and the like, and 
uses perfluoropentane and/or fluorohydropentane which are derivatives of 
pentane by replacing its hydrogen atom(s) with fluorine atom(s). Thus, the 
following outstanding effects are achieved. 
(1) Risk of fire due to combustibility of the refrigerant can be eliminated 
from facilities using it, such as ice heat storage systems and the like. 
(2) Risk of destroying the stratospheric ozone layer by the use of 
refrigerant is eliminated, and it becomes possible to build ice heat 
storage facilities and the like which are free from such risk. 
(3) No acid due to hydrolysis of refrigerant. Thus, there is no need for 
anti-corrosion treatment and cost for it can be saved. 
(4) No need for ice fluidizer, at least in principle. 
(5) Problems impeding the spread of direct-contact-ice-making for ice heat 
storage or the like have been dissolved; for instance, combustibility, 
destruction of the stratospheric ozone layer, chemical stability, 
clathrate formation, pressure at room temperature, resistance to 
micro-organism, and no poisonousness to humanity and animals. Thereby, 
actual use of such direct-contact-ice-making is facilitated.