Refrigeration – Refrigeration producer – Sorbent type
Reexamination Certificate
2001-12-05
2003-10-21
Jones, Melvin (Department: 3744)
Refrigeration
Refrigeration producer
Sorbent type
C062S480000, C062S324100
Reexamination Certificate
active
06634183
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a chemical heat pump.
BACKGROUND
The principle of the operation of the chemical heat pump is well-known, see for example U.S. Pat. Nos. 5,440,889, 5,056,591, 4,993,239, 4,754,805 and the published International patent application WO 94/21973. In a chemical heat pump an active substance, the absorbent, is used which performs the very process of the heat pump and which works together with a volatile medium, the absorbate or sorbate, which usually is a dipolar liquid, in most cases water. As the working active substance, according to the known technology, either a solid substance or a liquid substance can be used. A solid substance has the advantages that the vapor pressure remains constant during the whole discharging process for a constant cooling temperature and a relatively large capacity of storing heat. A typical value of the storage capacity for a solid substance having water as the sorbate, counted as cooling energy, is about 0.3 kWh/1 substance. A further advantage associated with a solid substance is that no movable components are required in the system. Heat is transferred to or conducted away from the substance through a lamellar heat exchanger or a plate heat exchanger in a homogenous contact with the substance. The disadvantage associated with a solid substance is the limited power which can be obtained, due to the bad thermal conductivity of solid substances. For systems the charging time of which corresponds to for example six hours of daytime charging using solar energy and the discharging time of which corresponds to a period of twelve hours of cooling for example a building, this provides no major problem. However, a disadvantage is that for continuous cooling at day and night and based on solar energy two installations working in parallel with each other are required.
A liquid substance has the advantage of a high power since the substance can be spread over the heat exchanger both in charging and in discharging and thereby be efficiently cooled or heated respectively. The disadvantage of a liquid substance is that the cooling capacity decreases as a function of the dilution of the sorbate. This actually strongly limits the operational interval within which the substance can be used, what in turn reduces the storage capacity, counted as above as cooling energy per liter substance. Most liquid substances or absorbent used in chemical heat pumps comprise solutions of strongly hygroscopical inorganic salts in preferably water together with which water is used as the volatile liquid, the sorbate. Then another limitation is obtained by the fact that the dissolved substance cannot be allowed to crystallize. Crystallization creates problems in spray nozzles and pumps. Thus, the use of a liquid substance is limited to converting heat energy to cooling without any storing of heat and systems therefor are generally known and utilized. In such a process e.g. a lithium bromide solution can be used which when heated is evaporated to pass from a diluted solution to a more concentrated solution. This can be made in a chemical heat pump at a low pressure or at atmospheric pressure using air flows. The amount of working substance is relatively small, since no storing of “charged” concentrated solution is made. The hot concentrated solution is then cooled and is then again made to absorb the sorbate which is evaporated from a heat exchanger, the heat of which is taken from for example the rooms to be cooled. Disadvantages of this known system can be that the hot concentrated solution has to be continuously cooled what practically can result in energy losses and that no cooling can be obtained during the time period when there is no supply of heat. Thus, such a system cannot perform air-conditioning at night.
In U.S. Pat. No. 925,039 for William W. Seay a process of refrigeration is disclosed. Ammonia is in an absorber/generator tank absorbed by a solid salt, a thiocyanate of ammonium or of an alkali metal, to form a solution, the tank being cooled by cold water passing through a heat exchanger. In the absorbtion the dissolving of ammonia is an endothermal process, requiring or consuming energy, for which all of the latent heat of evaporation/condensation of the ammonia gas is used. This reduces the external cooling power required in the absorption process compared to processes in which the dissolving instead liberates energy, the latter case being advantageous when the process is also intended for heat generation. The solution is then heated by passing hot water through the heat exchanger. The ammonia is liberated from the solution, passes through another heat exchanger to be cooled thereby and condenses in a receiver tank. After most of the ammonia has condensed, valves are opened to let it expand and pass through a third heat exchanger or refrigerator element from which heat is drawn by the ammonia gas when it expands. The expanded gas then passes to the absorber/generator tank to start a new cycle.
SUMMARY
It is an object of the invention to provide a chemical heat pump which can be driven by solar energy.
It is another object of the invention to provide a chemical heat pump in which advantages associated with a solid substance system are combined with advantages of a liquid substance system.
It is another object of the invention to provide a chemical heat pump in which efficient exchanging of heat between a liquid phase and a heat exchanger is obtained.
In a system using a solid substance which also after absorbing the volatile liquid remains solid a constant reaction pressure of the volatile liquid is maintained for a constant temperature of the substance when is absorbs vapor of the volatile liquid. The reaction pressure remains constant until all of the substance has been transferred from the first solid phase to the second solid phase. For a system, as suggested in the cited U.S. patent, which has a substance selected so that when in the discharging process vapor is absorbed by the substance the first phase is solid and the second phase is liquid, a solution phase, similarly a constant reaction pressure of the sorbate is maintained for a constant reaction temperature. The substance is then successively converted from a solid state to a liquid state. The process continues at a constant reaction pressure until all of the substance has been transferred to a liquid state. In the same way the reaction pressure in the last portion of the charging process is constant for a constant temperature when the substance is being converted from a liquid to a solid shape and vapor is liberated from the solution. In the first portion of the charging process the solution phase is only heated and no vapor is liberated. Thus, for such a heat pump using a phase transition between solid and liquid states advantages of a solid substance system can be combined with advantages of a liquid substance system.
When discharging the substance, i.e. when it absorbs the volatile liquid, the substance is made to be more and more dissolved in a somewhat diluted solution of the substance in the volatile liquid which exists in its vapor state around the solid and liquid phases. Thus, the produced solution is made to trickle over and through the remaining solid substance and is then passed through a filter or net to be separated from the solid substance. The solution which now becomes saturated then liberates heat produced both in the condensation of the vapor and in dissolving the vapor in the substance to a heat exchanger which is cooled by e.g. the outdoor air. This can be achieved by having a pump make the solution pass over a heat exchanger. The solution is then spread or distributed on some surface enlarging means in order to again participate in the absorbtion of vapor. The surface enlarging means can comprise balls, rods, nets, fibers made from some suitable material. The heat exchanger and the surface enlarging means can be combined in one unit.
Thus, in the process a three-phase system is used, in which vapor, a solid active substance and the satura
Jonsson Staffan
Karebring-Olsson Mona
Olsson Ray
Jones Melvin
Solsam Sunergy AB
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