AU600560B2 - System for solar energy transfer to a liquid contained in a vessel - Google Patents

Description

COMMONWEALTH OF AUST I Patent Act 1952 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number Lodged Complete Specification Lodged Accepted Published This document contains the amendments made und :r Section 49 and is correct for printing Priority :11 March 1987 Related Art Name of Applicant Address of Applicant Actual Inventor/s Address for Service :KERNFORSCHUNGSZENTRUM KARLSRUHE

GMBH

:Postfach 3640, D-7500 Karlsruhe 1, Federal Republic of Germany H;:r Dr. Volker Heinzel Jurgen Holzinger RICE CO., Patent Attorneys, 28A Montague Street, BALMAIN 2041.

Complete Specification for the invention entitled: SYSTEM FOR SOLAR ENERGY TRANSFER TO A LIQUID CONTAINED IN A

VESSEL

The following statement is a full description of this invention including the best method of performing it known to us/At:a; -2 The present invention relates to a system for solar energy transfer to a liquid contained in a vessel falling under the generic description of claim I.

A familiar system of this type comprises directly evaporating collectors and a pot making up the inner part of a double walled vessel, a cooking pot. The steam hits the vessel on its outer face, the condensate produced is evacuated downward due to gravity. On account of the very good heat m transfer during condensation a steam temperature higher by less than 100 will suffice to make boil the water in the pot.

However, this familiar system calls for special vessels; conventional cooking pots cannot be used. Moreover, the loop i is associated with the danger that uncleaned external faces J" of the pots will contaminate the collector loop.

I i i Starting from this status of the art, the present invention i aims at providing a system and a loop, respectively, falling under the generic term of claim 1 which allow to heat liquid in a conventional vessel without requiring external energy i in addition to solar energy in order to overcome delivery i heights and without necessitating any modifications to be made of the vessel.

In order to solve this task the features enumerated in claim 1 are proposed in the present invention. Further, particularly advantageous variants of the invention result from the features enumerated in the subclaims. j According to the present invention the heating surface in the form of a condenser can be directly dipped into the liquid to be heated and into the charge of the pot, respectively. By -3 this, direct heat transfer is established which allows to further use in an advantageous manner existing and conventional, respectively, as well as already available vessels.

Moreover, the collector loop remains completely closed and has not to be reopened when the heating vessel is withdrawn. This is achieved according to the present invention by placing the i heat source directly into the liquid to be heated so that the external losses can be kept low.

Moreover, with water as the heat transfer agent, no more problems of exclusive heating occur on the heating surface.

j The heat transfer to the liquid is determinant of the rate of i condensation and hence of the heat flow. The maximum temperature achievable can be controlled by the system pressure and thus be kept within limits of about It is a particularly advantageous feature of the present invention that the heat transfer agent from the condenser can be j lifted over the edge of the vessel for reflow to the collecto' Sso that a permanently operating circulating pump can be dispensed with. The loop according to the present invention thus works without energy supplied from outside. This is achieved in the present invention through the interplay of an air volume enclosed in the direction of flow downstream of the condenser and the steam space in the steam line and in the condenser. The condensate is conveyed in this way from the condenser over the edge of the vessel.

Further details of the present invention will be explained in Smore detail by Figs. 1 to 4.

Figure 1 shows the loop in the cold condition.

Figure 2 shows steady state operation in the loop.

Figure 3 shows the end of the condensate rising phase in the condenser.

|A

4- Figure 4 shows the end of the condensate return phase with the water, being the liquid contained in the loop, represented as hatches, the steam as dots and the air with no symbols at all.

Figures 1 to 4 show the solar collector 1 as the heat source which, essentially, consists of the transparent boiling tube 2 as the receiver and the condensate reflow tube 3 in this case placed in a coaxial arrangement in the boiling tube. The steam line 4 runs from the boiling tube upward to the fully closed casing 6 of the condenser 5 as the heat sink which condenser is immersed from top over the edge 8 of a vessel 7 into the liquid 9 contained in it which must be heated. The steam line 4 enters on top the casing 6 at the steam inlet port 28 in order not to interfere with immersion. Two immersion tubes 10 and 11 penetrate through the wall of the casing 6 of the condenser 5 with sealings provided and with the end and outlet port 14, respectively, of the first immersion tube extending to the deepest point 16 of the casing inner space 17, '--hereas the outlet port 15 of the second immersion tube 11 is placed at a slightly higher geodetic level than the first port.

The two immersion tubes 10 and 11 each form one of the legs of two inverted siphons 12 and 13 whose other downward running legs are termed siphon tube 18 and siphon breaker tube 19. The second siphon 13 is termed siphon breaker tube to describe its function. The two tubes 18 and 19 run downwards geodetically :i and end in the gas space 20 of a preferably tubular air collector 21 in an almost vertical or inclined position which contains a specified air volume VA. The air collector 21 is connected via a downcomer 22 with the return line 23 through which the condensate and the water, respectively, are returned to the boiling pipe 2 of the solar colle'ctor 1 via the condensate return pipe 3. The collector 1, the condenser 5, the air collector 21 together with their connection lines 4, 12, 13, 22 and 23 make up a closed system which is protected against exceeding of the maximum pressure by a safety device not represented in detail here.

As already mentioned, the siphon tube 18 and the other leg, respectively, of the first siphon 12 penetrate into the gas space 20 of the air collector 21 and are routed downward in it until the outlet port 24 reaches a point below the outlet S 10 port 14 of the first immersion tube from the first siphon 12 a, so that the siphon difference A S 1 is established. The siphon a breaker tube 19 and the other leg, respectively, of the second siphon 13 are connected to the top end 24 of the air collector 21 so that its outlet port 26 ends above the outlet port of the second immersion tube and the siphon difference A S 2 is established. The siphon breaker tube 19 should be as short as possible whereas the outlet port 26 must be positioned at a geodetic level above the outlet port 15. The first siphon 12 serves to evacuate the condensate 27 from the casing 6, the second siphon 13 serves as an additional pressure equalization through air reflow in non-steady-state operation.

Functioning of the system and of the loop, respectively, will be described below by the four diagrams and process stages, respectively, represented in Figs. 1 through 4.

Figure 1 shows the closed system with the collector 1 and the condenser 5. A filled up vessel 7 acting as the heat sink will surround the condenser S. In the cold condition the boiling Spipe 2 of the collector 1 and the return line 23 are completely filled with water while the riser of the collector 1 and the downcomer 22 are partly water-filled. The rest of loop components inclusive of the condenser 5 contain air at atmospheric pressure.

-6 When heat is supplied to tie collector 1 and the boiling temperature is attained steam will flow through the riser to the condenser 5. Since the loop is closed, the air originally present in line 4 and in the condenser 5 is displaced by the condenser 5 and the siphons 12 and 13 into the downstream air collector 21 (Fig. The steam condenses in the condenser; the siphon 12 during steady-state operation conveys the condensate 27 to the air collector 22 and to the downcomer 22 and the return line 23, respectively.

However, as the conveyance capacity of the first siphon 12 cannot be adapted to the quick variations of the condensate volumes in the inner space 17 of the condenser 5 which result from the variations in the heat flow withdrawn and, on the other hand, the siphon 12 has to be designed to accommodate the maximum volume, the siphon effect and conveyance would be frequently interrupted. After interruption the condensate accumulates in the inner space 17 and replenishes it from the 1 bottom (see Fig. However, this means a limitation on the heat transfer surface in the condenser 5 on the steam side which implies inadequate condensation for the pressure to rise in the system. Consequently, the air volume available is reduced while the steam generated does not only compensate steam compression but also replenishes the space emptied by reduction in the air volume. For the condensate 27 which, on account of the immersion tube 10 of the siphon 12 pulled down in the condenser 5, acts as the barrier between the steam and Ui a:r spaces, this implies a' displacement into the air collector 21 so that in the steam line 4 and in the condenser inner space 17 an overpressure builds up which lifts the condensate in the condenser 5 over the siphon 12 by an amount corresponding to the height of the condenser.

:-3 -7 On the other hand, the first siphon 12 interferes with the pressure equalization under conditions of fluctuating heat evacuation, in case of cold water supply or drop in performance in collector 1 due to the high water column in the siphon tube 18. To avoid resulting fluctuations in the water level going beyond the marked maxima in the collector system, the second siphon and the siphon breaker tube 13, respectively, have been provided in addition. They ensure pressure equalization by reflow of air from the air collector 21 to the condenser 5 while the first siphon 12 can continue the process of conveyance.

1 The overpressure prevailing in the condenser 5 would cause the accumulated condensate to be transferred also in the absence of the siphon effect, through the siphon breaker tube 13.

i However, condensate evacuation into the air collector 21 gives i rise to a high rate of condensation in the condenser 5. Making i use of a siphon effect also the condensate initially produced can be transferred thanks to the differences in geodetic levels of the ports 14 and 15 so that the frequency of repeti- I tion of the filling and evacuation cycles described before is reduced by the response of the first siphon (see Fig. 4)j.

The ratio VA of the air volume in the collector 21 to that of the air volume Vto t in the whole loop should at least attain the same value as the ratio of the atmospheric pressure Patm to the operating pressure Poper" For this to be possible, VA i must at least be so large that at a pressure corresponding to the geodetic delivery height the siphon 10 is compressible by the volumes of both siphons 11 and 12.

Another important feature is that a type of sump constitutes the deepest point 16 in the casing 6 of'the condenser 5 where the ports 14 and 15 of the immersion tubes 10 and 11 end. This point 16 should be as far distant as possible from the steam inlet port 28.

-8 Experiments have confirmed the performance of the loop; the powers conveyed were in the range of 100 1500 Watts at Sa maximum steam temperature of 1050. This corresponds to a saturation range of 1, 2, 3 bar.

a

Claims (4)

1. A system for solar energy derived heat transfer to a liquid contained in a vessel, the system comprising: a) a closed volume loop for steam generation by direct evaporation of a heat transfer agent in a solar collector defining a heat source; b) circulation by natural convection of the heat transfer agent in the loop; c) a heat exchanger provided in the loop for heat transfer from the agent to liquid contained in the vessel, the heat exchanger being at a higher geodetical level than the heat source; and S: d) a pipe network connecting the heat exchanger inlet to the heat source outlet and the heat source inlet to 0 the heat exchanger outlet forming in part said closed loop; and wherein e) the heat exchanger acts as a steam condenser adapted to be immersed from a top of the vessel into liquid therein; and f) steam feed and condensate evacuation lines of the condenser forming part of the pipe network and routed upwards from the condenser over an uppermost edge of the vessel.

2. A system as claimed in claim I further including: g) the condenser including a closed casing; h) the steam feed line exfending from an upper region of the solar collector to an inner space of the casing; oa ga S i) an immersion tube penetrating a wall of the casing from its top and a lower end thereof forming an outlet port extends to the lowest point of the inner space; j) the immersion tube further forming a first leg of a siphon tube routed over the edge of the vessel; r 10 k) a second leg of the siphon tube continuous with the first leg, entering on top of an air space of an air collector whose volume defines part of the loop volume; 1) an outlet port of the second leg of the siphon tube being at a lower geodetic level than that of the immersion tube; m) the air collector connected at its lower end by a downcomer to the condensate return line leading to the solar collector as part of the pipe network.

3. A system as claimed in claim 2 further including: 0o 0o 0 n) a second immersion tube entering the top of the inner J space of the condenser and its casing, having an end defining an outlet port being at a higher geodetic O9 uo 00o level than that of the outlet port of the other immersion tube; o o) the second immersion tube forming a first leg of a second siphon being a siphon breaker; p) a second leg of the second siphon entering on top of the air space of the air collector; S q) the point of entrance of the siphon breaker tube into the air collector being at a higher geodetic level than the point of entrance of the other siphon tube into the air collector.

4. A system as claimed in claim 3 further including: r) the ratio of the air volume VA in the air collector AB to the total volume Vto t in the cold condition being equal to the ratio of the atmospheric pressure and atm to the operating pressure Poper; and s) VA being sufficient to allow compression of the air therein by the volume amount of both siphons under a pressure condition corresponding to the geodetic height of delivery of the immersion tube so that the siphon effect can be started. i. L i; 4 11 A heat transfer system substantially as described herein with reference to the drawings. DATED this 29 day of May 1990 KERNFORSCHUNGSZENTRUM KARLSRUHE GmbH Patent Attorneys for the Applicant: F.B. RICE CO. L. i t c