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GB2102550A - Refrigerating - Google Patents

Refrigerating Download PDF

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Publication number
GB2102550A
GB2102550A GB08204789A GB8204789A GB2102550A GB 2102550 A GB2102550 A GB 2102550A GB 08204789 A GB08204789 A GB 08204789A GB 8204789 A GB8204789 A GB 8204789A GB 2102550 A GB2102550 A GB 2102550A
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GB
United Kingdom
Prior art keywords
duct
reabsorption
degassing
heat exchanger
solution
Prior art date
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Granted
Application number
GB08204789A
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GB2102550B (en
Inventor
Dr Helmut Lotz
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BSH Hausgeraete GmbH
Original Assignee
Bosch Siemens Hausgerate GmbH
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Publication of GB2102550A publication Critical patent/GB2102550A/en
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Publication of GB2102550B publication Critical patent/GB2102550B/en
Expired legal-status Critical Current

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Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25BREFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B25/00Machines, plants or systems, using a combination of modes of operation covered by two or more of the groups F25B1/00 - F25B23/00
    • F25B25/02Compression-sorption machines, plants, or systems

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Sorption Type Refrigeration Machines (AREA)
  • Compression-Type Refrigeration Machines With Reversible Cycles (AREA)

Abstract

A refrigerating machine, for operation as a heat pump, comprises a degasser (E) from which weak solution is impelled by means of a pump (P) through a heat exchanger (T) into a reabsorber (R), where it reabsorbs refrigerant- rich vapour extracted from the degasser (E) and compressed by a compressor (V), and thence is returned as a strong solution back through the heat exchanger (T) to the degasser (E). A connecting line between the lines for the weak and the strong solution connected to the degasser (E) serves to enable partial streams of these solutions to be transferred into each other. <IMAGE>

Description

SPECIFICATION Refrigerating means The present invention relates to refrigerating means, and has particular reference to a compression refrigerating machine with solution circuit intended especially for operation as heat pump, comprising a degasser, from which weak solution is impelled by means of a pump via a heat exchanger into a reabsorber, where it reabsorbs refrigerant-rich vapour drawn from the degasser and compressed by a compressor, and returns it thence as rich solution via the heat exchanger into the degasser.
Reabsorption refrigerating machines additionally equipped with a compressor have been named according to a proposal by E. Altenkirch as compression refrigerating machines with solution circuit. The compression refrigerating machine with solution circuit described by Altenkirch, amongst other places, in volume 10,11 and 12/1950 of the periodical "Kältetchnik" ("Refrigeration Engineering") possesses the advantage over the usual compression refrigerating machines of providing a significant energy saving. This is particularly so when it is used as a heat pump. Since, however, it is more complicated in its engineering than a normal compression refrigerating machine, the compression refrigerating machine with solution circuit has not achieved commercial importance.
There is accordingly a need for improvement of compression refrigerating machines of the initially described type, especially by reducing energy consumption to compensate for the disadvantage of the more complicated construction as compared with normal compression refrigerating machines and thereby to render possible their use on a wider basis.
According to the present invention, there is provided refrigerating means comprising degassing means for separating refrigerant-rich vapour from a refrigerant solution, reabsorption means for causing reabsorption of the vapour by the solution, a compressor for extracting and compressing the separated vapour from the degassing means and delivering the compressed vapour to the reabsorption means, a pump for pumping the solution from the degassing means to the reabsorption means by way of first duct means after vapour separation in the degassing means and from the reabsorption means back to the degassing means by way of second duct means after reabsorption of the compressed vapour in the reabsorption means, a heat exchanger for effecting heat exchange with the solutions in the first and second duct means during feed to and from the reabsorption means, and transfer duct means interconnecting the first and second duct means between the degassing means and the heat exchanger for effecting a transfer of a proportion of the solution between the flows in the first and second duct means.
In a preferred embodiment, a connecting line between the lines for the weak and the rich solution connected to the degasser enables partial streams of these solutions to be transferred into each other. This permits a flexible adaptation to different temperature bands of heating medium and cooling agent and thus contributes to a considerable increase in the efficiency and economy of the refrigerating means.
The purpose of such a flow transfer is based on the knowledge that, in heat engineering, flows of substances (water or air) always have to be heated up or cooled down in a temperature band AT. Due to the sliding temperatures, it is not the Carnot cycle with its constant temperatures that should be aimed at as ideal reference cycle, but the Lorenz cycle, which in its internal performance promises a higher theoretical energy saving than the Carnot cycle, the greater the temperature band is. It has been found that, in the external performance which is extremely important for use as a heat pump, the Lorenz cycle is still more favourable and thus produces an additional energy saving.
As an especially advantageous arrangement, the connecting or transfer line is disposed behind the degasser, through which line a feedback of a partial stream of the weak solution into the rich solution flowing back to the degasser takes place. For preference, the connecting line is connected on the one hand to the line for the weak solution between the pump and the heat exchanger and on the other hand to the line for the strong solution between the heat exchanger and the degasser. By the feedback of a partial stream branched off between the pump and the heat exchanger, behind the heat exchanger, it becomes possible to adapt the temperature band of the heating medium as accurately as desired to the temperature band of the cooling agent which is different therefrom.
Expediently, a regulating valve is arranged in the connecting line to regulate the feedback of the partial stream according to the current operating state of the refrigerating means.
An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Figure 1 is a simplified flow diagram of a compression refrigerating machine with solution circuit according to the said embodiment, Figure 2 is a pressure-temperature diagram (1 g p:: 1TT) of a solvent cooling mixture, Figure 3 is a diagrammatic temperature graph in the internal and external cycle respectively (heating medium and cooling agent) plotted against the heat exchanger length L of the refrigerating machine, Figure 4 is a diagram showing the thermal efficiency of a Carnot cycle Ec and Lorenz cycle EL, as a function of external cycle conditions, Figure 5 is a diagram showing the thermal efficiency of the refrigerating machine as a function of the partial stream flow rate and of the suction pressure p,, and Figure 6 is a diagram showing the ratio of the volumetric heat outputs of the refrigerating machine with solution circuit to that of a normal compression refrigerating machine with single-substance refrigerant as a function of the suction pressure pO.
Referring now to the drawings, there is shown in Figure 1 a compression refrigerating machine with solution circuit, which basically comprises a degasser E, a solvent pump P, a heat exchanger T, a reabsorber R, a throttling device X and a compressor V. According to the 1 g p - T diagram of Figure 2, the compressor V draws from the degasser E coolant-rich vapour (for example NH3 out of the solvent H20) having the state Q.
The solution degasses from the state 4 to 5 in a temperature range, to which the temperatures of the cooling agent (for example air) can be adapted by counterflow conducting. The weak solution ma is raised by the pump P to a higher pressure p and delivered to the reabsorber R after being preheated in the heat exchanger T. In the reabsorber R, it meets the compressed refrigerant gas rh of state (2), coming from the compressor V, and.reabsorbs the gas in the temperature range of the change of state from ( to (ss) . The reabsorption heat 0 is given up to the heating medium (e.g. water) which is to be heated up, flowing in counterflow.The solution rhrthus enriched to the state finally flows through the heat excbanger T and the throttling device X back to the degasser E, where it can again absorb the reabsorption heat Qo.
When the illustrated and described compression refrigerating machine with solution circuit is used as a heat pump, a considerable energy saving can be achieved on the basis of the fact that, in heat engineering, flows of substances (water or air) always have to be heated up or cooled down in a temperature band AT. On account of the sliding temperatures, it is not the Carnot cycle with its constant temperatures that should be aimed at as ideal reference cycle, but the Lorenz cycle.
The fact that the Lorenz cycle promises in its internal performance a theoretical energy saving which becomes higher, the wider the temperature band is, has already been demonstrated (see "rationelle Energienutzung in Kälteanlagen" ("rational energy utilization in refrigerating plants"), H. Lotz, Kongress Expoclima 76, pages 57/85). As will be shown below, the Lorenz cycle also leads to a further energy saving in the important external performance.
The thermal efficiency EC of the Carnot cycle can be represented, using the symbols of Figure 3, as
and the thermal efficiency L of the Lorenz cycle, on the assumption that ATwa = Tw - Ta = a + b.Tw and the "local" #LX = TwxIATwa can be expressed by:
with the abbreviations: b Ts/ATW ri = (1 - b) (T2 + T",) - (tea? > a) For ATa = ATw, equation (2a) simplifies to::
The values plotted in Figure 4 for Cc and EL against the driving temperature difference e in the condenser and evaporator (or from the k.A value of the heat exchanger divided by the k. A value when e = 1 K, derived therefrom) show that, especially at fairly low temperature differences less than 4 K (or relative k.A values above 0.3) the Lorenz cycle provides clearly better values than the Carnot cycle. The higher the temperature band AT is, the higher will these values be.
With the described compression refrigerating machine with solution circuit according to Altenkirch, it was already possible to realise such a Lorenz cycle. This machine was accompanied by the drawback, however, that the improvement shown in Figure 4 was only fully achieved if the temperature bands AT in the reabsorber and the degasser are equal, that is to say the heating medium is heated up by the same amount as the refrigerant is cooled down. Such a condition, however, is very unusual and usually these states are different, with the result that the possible energy saving is appreciably reduced.
This defect is overcome by the compression refrigerating machine with solution circuit in accordance with the said embodiment of the invention. In particuiar, by feeding back a partial stream rhx behind the degasser E, it becomes possible to adapt a temperature band ATs of the cooling agent, which differs from the temperature band ATw of the heating medium, as accurately as desired to each other, by changing the partial flow rate mx. This represents a marked advantage over the compression refrigerating machine with non-azeotropic refrigerants, in which, as is well known, the temperature bands in the condenser and evaporator are dependent only upon the filling concentration and thus are fixed and have approximately equal values.
By the help of heat and flow balances and on the assumption that, in the heat exchanger T, at full heat exchange t = t3 is achievable, that in the degasser E and in the reabsorber R the temperature difference e can be kept constant by appropriate counterflow guiding along the heat exchanger length and that the energy consumption of the solution pump is negligible, there can be obtained from the thermal efficiency, using the terminology of Figure 1::
Here, the concentrations t1 and 5 are established by the initially freely selectable pressure p0 and the temperature tsi - 5, whereas the enthalpy h5a is determined by the temperature t,l + Ew. The partial stream f which is to be adjusted according to equation (4) determines the concentration of the strong solution t3:: f - fs 4 - (4) - - - g (4) where t4a iS determined by p0 and t52 Furthermore the enthalpy h2 after compression with X as the isentropic coefficient and cpm as the specific thermal capacity of the gas mixture and also i, as the efficiency factor referred to isentropic compression, is given by:
All the following calculations for the compression refrigerating machine with solution circuit are carried out from the solution refrigerant mixture NH3/H20, since on account of its predominating use in absorption plants, its use in the compression refrigerating machine with solvent circuit appears logical.Other mixtures are, however, equally conceivable, but they would have to more closely investigated having regard to the special requirements of the compression refrigerating machine with solution circuit.
In the attached table, various thermal efficiencies are given for comparison both for a heat exchange temperature difference of 1K and also for one of 5K. The external conditions "heating up of heating medium from 45"C by 10K and cooling down of cooling agent from 5"C by 5K" were chosen because they represent a frequently encountered operating state, and these different temperature bands ATw and AT5 clearly show the advantage of the partial stream regulation.
The thermal efficiencies of the reference cycles according to Carnot Ec and Lorenz CL have been established by means of equations (1 ) and (2). The practical values for the compression refrigerating machine with R22 and with the non-azeotropic refrigerant mixture of R22/R 114 have been obtained from measured values for the internal performance according to Jakobs (5). The thermal efficiency for the compression refrigerating machine with solvent has been calculated for the proposed partial flow arrangement by equation (3).
The table clearly shows that, as a result of the flexible adaptation by partial flow regulation of the compression refrigerating machine with solution circuit to the different temperature bands of heating medium and cooling agent, the machine clearly permits higher thermal efficiencies to be achieved than a compression refrigerating machine with non-azeotropic refrigerants, for an adapted temperature band in at least one heat exchanger (AT = 10 K at t = 0.79).With a poor adaptation af the compression refrigerating machine with non-azeotropic refrigerants to the external temperature bands (in this case for example AT = 16.5 K, with 5 = 0.56, which imply the maximum E for the internal performance), this indeed lies around the values for the compression refrigerating machine with single-substance refrigerant. The lowest values are, of course, exhibited by the single-substance compression refrigerating machine with R 22, and this is particularly so in the case of heat exchangers of large design (i.e. small temperature differences 0).
In Figure 5, the thermal efficiency of the compression refrigerating machine with solution circuit in the construction hereinbefore is plotted as a function of the partial stream f according to equation (4) and of the suction pressure pO. The upper part of Figure 5 shows that CKML increases gradually from partial stream f = 0 until the maximum valuefmax is reached.This results in the circuit in a concentration t3 = t3max according to equation (4), which corresponds to the saturation concentration at point (g (Figure 1), determined by the pressure p and the temperature tW2 = hw. In the lower part of Figure 5 it can be seen that, with fmax as parameter, the thermal efficiencies exhibit, as a function of the suction pressure p,, an optimum which is situated at comparatively low pressures. These maximum values are entered in the table.
A recalculation shows that it is permissible to ignore the solvent pump output when determining CKML, since even with a pump efficiency to 25% this reaches only approximately 0.25% of the compressor output.
The partial stream branching "my" indicated by dot-and-dash lines in Figure 1, in which by contrast to the partial stream branching "my" a portion of the strong solution from the heat exchanger T is fed into the line for the weak solution from the degasser E, results, as a further possibility, in relatively high irreversible mixing losses and is therefore less favourable than the regulation "mx" illustrated in Figure 1 in solid lines. It provides thermal efficiencies which, for example for the calculated case according to the table with e = 5 K, are only approximately 85% of those for the partial stream regulation "my".
The comparatively low suction pressures are characteristic for the compression refrigerating machine with solution circuit. This results, as illustrated in Figure 6, in a low volumetric heat output qv by comparison with the compression refrigerating machine with single-substance refrigerant. In Figure 6, the ratio vq of the volumetric heat output of the compression refrigerating machine with solution circuit to that of the R 22, or single-substance, compression refrigerating machine is plotted for two different heat exchanger tempera ture differences h. The volumetric heat output increases rapidly with increasing suction pressure.These comparatively low volumetric heat outputs do not, however, substantially influence the size of the heat exchangers, since liquid solutions are circulating and the degassing and reabsorption processes can be carried out favourably, i.e. with relatively low heat exchange surface area, at the large volume of the circulating gas quantity and on account of the availability of pressure gradient due to compression. It is basically only the size of the compressor which is affected.
In these conditions it is especially advantageous to use flow compressors, such as screw or spiral lobe-type compressors, which are not sensitive to a possible wet gas mixture.
The described and illustrated compression refrigerating machine with solution circuit renders possible, by exact adjustment of the variable partial stream mx to different temperature bands in the degasserl reabsorber, for operations to be carried out at all times at maximum thermal efficiency. Control devices which are appropriate here are microprocessors, which can process the various operating states for controlling the partial stream mx so that the operation can always be carried out with the optimum partial stream fraction fmax.
TABLE - Heating up of heating medium from twi = 45 to tW2 = 55 C (Tw = 10K) - Cooling down of cooling agent from tsi = 5 tots2 = OOC (T5 = 5K) - Mean temperature difference in the heat exchangers Es = Ew = 1,5K respectively - Efficiency factor is referred to the isentropic compression output, for the KKM with R 22 and with NA R 2/R 114 according to measurements from [5] andforthecalculationofthe KML is = 0.726.
Heat exchanger temperature difference * K 1 5 Carnot - thermal efficiency Ec - 5.96 5.54 Lorenz - thermal efficiency EL - 6.55 5.71 Thermal efficiencies of: - KKM with R 22 according to [5] - 3.36 3.12 - KKM with NA R 22/R 114 acc. to [5] for u = 0.79 (AT = 10 K) - 3.61 3.20 for u = 0.56 (AT = 16.5K) - 3.29 3.11 - KMLacc.tothisworkfor maximum p0 according to Figure 5 - 4.22 3.77 KKM = Compression refrigerating machine KML = Compression refrigerating machine with solution circuit NA = Non-azeotropic refrigerant mixture [5] "Contribution on the use of non-azeotropic two-substance refrigerants in heat pumps", R.M. Jakobs, discussion at University of Hanover 1980

Claims (8)

1. Refrigerating means comprising degassing means for separating refrigerant-rich vapour from a refrigerant solution, reabsorption means for causing reabsorption of the vapour by the solution, a compressor for extracting and compressing the separated vapour from the degassing means and delivering the compressed vapour to the reabsorption means, a pump for pumping the solution from the degassing means to the reabsorption means by way of first duct means after vapour separation in the degassing means and from the reabsorption means back to the degassing means by way of second duct means after reabsorption of the compressed vapour in the reabsorption means, a heat exchanger for effecting heat exchange with the solutions in the first and second duct means during feed to and from the reabsorption means, and transfer duct means interconnecting the first and second duct means between the degassing means and the heat exchanger for effecting a transfer of a proportion of the solution between the flows in the first and second duct means.
2. Refrigerating means as claimed in claim 1, the transfer duct means comprising a transfer duct so arranged with respect to the degassing means as to in use conduct a solution flow from the first duct means to the second duct means.
3. Refrigerating means as claimed in claim 2, wherein the pump is arranged in the first duct means between the degassing means and the heat exchanger and the transfer duct is connected to the first duct means between the pump and the heat exchanger and to the second duct means between the heat exchanger and the degassing means.
4. Refrigerating means as claimed in either claim 2 or claim 3, comprising a regulating valve arranged in the transfer duct to regulate the rate of flow therethrough in dependence on the operating state of the refrigerating means.
5. Refrigerating means as claimed in claim 1, wherein the pump is arranged in the first duct means between the degassing means and the heat exchanger, the transfer duct means comprising a transfer duct so arranged as to in use conduct a solution flow from the second duct means to the first duct means upstream of the pump.
6. Refrigerating means as claimed in any one of the preceding claims, wherein the compressor is a flow compressor.
7. Refrigerating means as claimed in claim 6, wherein the compressor is a screw compressor.
8. Refrigerating means substantially as hereinbefore described with reference to the accompanying drawings.
GB08204789A 1981-04-29 1982-02-18 Refrigerating Expired GB2102550B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE19813117019 DE3117019A1 (en) 1981-04-29 1981-04-29 IN PARTICULAR, COMPRESSION REFRIGERATOR WITH SOLUTION CIRCUIT DETERMINED FOR OPERATION AS A HEAT PUMP

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GB2102550A true GB2102550A (en) 1983-02-02
GB2102550B GB2102550B (en) 1984-12-05

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GB08204789A Expired GB2102550B (en) 1981-04-29 1982-02-18 Refrigerating

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JP (1) JPS57182059A (en)
DE (1) DE3117019A1 (en)
FR (1) FR2505034A1 (en)
GB (1) GB2102550B (en)
SE (1) SE8202619L (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4780967A (en) * 1986-04-17 1988-11-01 Tch Thermo-Consulting-Heidelberg Gmbh Apparatus for the recovery of waste heat contained in the exhaust from dryers of paper machines
WO1998029701A1 (en) * 1997-01-02 1998-07-09 Sjoeblom Hans Heat transport apparatus

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102733243B (en) * 2011-04-08 2015-05-20 上海东冠纸业有限公司 Hot-air drying system of paper machine

Family Cites Families (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE278076C (en) * 1911-08-11
US1713934A (en) * 1925-10-09 1929-05-21 Burchard M Thoens Refrigerating apparatus
US2307380A (en) * 1939-12-26 1943-01-05 Carroll W Baker Refrigeration
DE867122C (en) * 1950-08-29 1953-02-16 Edmund Dr-Ing E H Altenkirch Method and device for raising the amount of heat withdrawn from a heat carrier at a lower temperature to a higher temperature
DE953378C (en) * 1950-08-29 1956-11-29 Margarete Altenkirch Geb Schae Method and device for operating a heat pump
US3122002A (en) * 1961-02-09 1964-02-25 Trane Co Absorption refrigerating system
SE419479B (en) * 1975-04-28 1981-08-03 Sten Olof Zeilon REFRIGERATION PROCEDURE AND APPARATUS FOR EXTENDING THE PROCEDURE
IL51603A (en) * 1977-03-07 1981-12-31 Univ Ramot Method and apparatus for air conditioning motor vehicles
DE2850403A1 (en) * 1978-11-21 1980-05-29 Luft U Kaeltetechnik Veb K Lubrication system for refrigerator compressor - uses refrigerant depleted solvent liquid for lubrication of screw compressor

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4780967A (en) * 1986-04-17 1988-11-01 Tch Thermo-Consulting-Heidelberg Gmbh Apparatus for the recovery of waste heat contained in the exhaust from dryers of paper machines
WO1998029701A1 (en) * 1997-01-02 1998-07-09 Sjoeblom Hans Heat transport apparatus
US6220040B1 (en) 1997-01-02 2001-04-24 Sjoeblom Hans Heat transport apparatus

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Publication number Publication date
DE3117019A1 (en) 1982-11-18
FR2505034A1 (en) 1982-11-05
GB2102550B (en) 1984-12-05
JPS57182059A (en) 1982-11-09
SE8202619L (en) 1982-10-30

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