WO1983000358A1 - HEAT-ENGINE FOR THE EFFECTIVE UTILIZATION OF LOW TEMPERATURE DIFFERENCES OF 10oC-12oC - Google Patents

Abstract

A heat-engine, to operate by means of a heat source liquid of low thermal gradient (10-12<o>C) contained within the tank (1) providing the input energy needed to increase the temperature of a specific working fluid, contained within clusters (4) of the rotating copperpipe system (2), to its critical point. Optimum expansion at that temperature causes some of the working fluid to be expelled from the clusters and directed onto the turbine (9), via the governing cylinder (5), the directional valves (6), and through the tubular axle compartment (3), thereby converting the given heat energy into usable mechanical energy. The descending clusters emit the previously absorbed heat to the upper layers of the source liquid, whilst the expelled working fluid returns to the bottom cluster from the turbine housing.

Description

Heat-engine for the effective utilization of low temperature differences of 10°C-12°C

This invention relates to the design of a new heat-engine cycle, whereby any available heat source that can provide as low a temperature differences as 10-12ºC may be effectively harnessed for power production, by using the expansion properties of liquid substances in the immediate vicinity of their critical point as the vehicle for heat conversion into mechanical energy.

A modern thermoelectric power plant, considered as the ultimate advancement made in conventional heat engine design technology, operates on the principle that a certain quantity of heat must be added to every kilogramme of water, in order to vapourise it. The vapour is then put to work by expansion at high pressure, thereby causing cooling, but still retaining the latent heat of vapourisation previously added to effect the desired change of state. This latent heat has to be removed by the process of condensation before a new cycle may commence, which once again requires additional heat input. Through the essential condensation phase a large quantity of heat is wasted, resulting at best in an efficiency ratio of around 36%.

If due regard is given to the phenomenon that the thermal capacity of fluids is fairly constant up to within a few degrees of their critical point, where it increases ten to twentyfold, it will become evident that as a consequence, the expansion properties of such fluids are at their highest within that region, even surpassing that found beyond the critical point in their gaseous state. Experiments have in fact shown that the expansion of a fluid very near its critical point is about double that found 50-60°C below, whilst in the gaseous state above the critical point the expansion rate once again becomes constant at a 1/273-th increase for every 1°C rise in its temperature.

Given these facts, it is evident that any design able to employ such phenomenon, would have far reaching implications in substantially improving the harnessing capabilities of any apparatus currently operating.

This is exactly the objective of my invention, achieved by designing a closed cycle, wherein a heat source providing a temperature gradient of 10-12°C is established, with the driving force being provided by a specific fluid selected entirely on the basis of having a critical temperature corresponding to that of the heat source.

According to the invention there is provided a water tank (1) of a length to correspond to the length of copper pipes that will form what shall henceforth be referred to as the copper-pipe cluster system (2), as shown in Figure 1. This water tank will serve the function of being the container for the heat source, with the top and bottom layers providing the essential 10-12°C temperature difference; at the same time also acting as the housing for most of the other components of the apparatus.

A relatively small diameter steel pipe (3) is placed along the horizontal axis of this tank in a manner to extend beyond both ends, thereby acting as the axle for the copper-pipe cluster system 2 that is affixed to the wheels connected to that axle. The copper-pipe system is made up of clusters of copper pipes running parallel to the axle, with each cluster (4) consisting of a number of individual pipes, each sealed at one end, and all interconnected at the other end by leading into a single central pipe. This pipe is connected to an enclosed steel cylinder (5). One of these cylinders is positioned between each cluster of the copper-pipe system and the central axle pipe, along the length of the axle in a way to achieve the best rotational balance of the whole unit within the tank.

The steel pipe axle itself is divided into two separate sealed compartments. Both compartments are interconnected with each and every one of the steel cylinders (5) by means of special one way valves, in such a manner as to permit the high pressure working fluid being transferred from the copper-pipe cluster system into one compartment of the steel axle pipe (6), and from the other compartment back to the steel cylinder at a reduced pressure (7).

The primary function of these steel cylinders is to maintain the position of the hottest part of the working fluid near the copper-pipe cluster system, at the same time permitting the completion of a full cycle by enabling the cooler working fluid to flow from the low pressure axle compartment into the steel cylinders, thereby re-filling them.

At the extremity outside the water tank of that part of the axle pipe into which the high pressure working fluid flows, a spherical or double convex shaped vessel (8) is fixed, to provide the housing for a special low speed turbine (9). From this axle compartment the high pressure fluid is directed on to the turbine by jet nozzles, thereby transforming the pressure energy of the fluid into rotating mechanical energy. As a consequence, the pressure of the working fluid decreases (although it is still equal to its critical pressure), and is transferred by means of a small diameter tube into the other axle compartment, from where it enters into that steel cylinder which has reached the bottom of the tank.

To complete the apparatus, a spherical or double convex shaped vessel (similar to the one housing the turbine (10) is added to each side of the divided steel axle pipe, also preferably outside the water tank for ease of maintenance. Both of these vessels are connected to their respective axle compartments by apertures and 2/3 filled with the same working fluid, with the remainder of their volume being filled by some high pressure gas, such as nitrogen. These will serve the function of regulating the two differing pressures within the apparatus.

As the copper-pipe cluster system rotates at a very slow speed within the tank, the working fluid (which must be at a higher than critical pre-ssure) enters each cluster at the bottom dead centre. During the ascending phase of the filled cluster, the working fluid within heats up and, since its volume does not change, there is a resultant increase in its pressure.

When the desired pressure increase is reached (which would probably be in the region of double the critical pressure, although the ideal point would need to be determined by experimentation, giving regard to the higher pressures causing some decrease in the volume of the working fluid but at the same time increasing the resultant energy due to the larger pressure difference). part of the working fluid starts leaving the copper pipe cluster to flow into the interconnecting steel cylinder, and from there through the special one way valve into the axle compartment, and finally onto the turbine via the jet nozzles, resulting in work being done. This process of the working fluid being ejected from each of the copper-pipe clusters and directed on to the turbine, is maintained right up to when heating ceases at the top of the cycle near the surface of the water tank.

After leaving the turbine, the working fluid flows into the low pressure axle compartment, from where it enters the steel cylinder, and through the other one way valve into the copper-pipe cluster that has reach ed the bottom. Thus, a complete cycle is established, which operates constantly as long as the 10-12°C temperature difference between the top and bottom layer of the water tank is maintained.

Due to the rotation of the copper-pipe cluster system however, a gradual downward heat transfer will obviously occur, despite the counter-acting effect caused by natural convection. A passive way to reduce such a heat transfer is to allow the water to leave the tank at a level where the temperature is about 7°C below that of the surface temperature, thereby preventing any further descent below that level.

To further assist this natural automatic convection cycle to counter-balance the downward heat transfer, a component device has been designed to actively transfer the descending heat to the surface, based on the principle that the main heat exchange occurs within a few degrees of a substances' critical point, where its thermal capacity is at its greatest. Thus, it is essential to have the water at the surface of the tank around 99°C. One or more highly conductive large diameter pipes (1) of Figure 3 are placed horizontally in the tank at the 90-92°C temperature level, and half filled with water. The upper half of the pipe is to be fitted to a. compressor (2), to function as the water vapour extractor. The other end of the compressor is connected to another set of pipes (3) placed directly under the water surface of the tank.

By adjusting the compressor to provide a pressure of 0.72 kg/cm² in the lower pipes, evaporation occurs, with the resultant water vapour being compressed to 1 kg/cm² and forced into the upper pipes. At that pressure and temperature of 99°C, condensation takes place, with its attendant release of heat.

Given that 1 kg of water vapour occupies a volume of 2350 litres at 90°C and 1750 litres at 99°C, the difference of 600 litres at a mean pressure of 0.15 kg/cm² provides work of 6000 m multiplied by 0.15 kg/cm² eαuals 900 kgm. The 1750 litres is multiplied by 0.3 kg/cm², since the maximum density of the vapour already exists, the only requirement being to force it up into the upper pipes to condense. Therefore, 1750 multiplied by 10 equals 17500, which multiplied by 0.3 equals 5250 kgm. Adding to it the previously calculated 900 kgm, one arrives at the energy required to evaporate 1 kg of water vapour at 90°C and condense the same quantity at 99°C (more is needed in reality, since machines never reach 100% efficiency).

One kg of water vapour at a temperature of 90°C and a pressure of 0.72 kg/cm² contains 635 kilocalories of heat, whilst the same quantity contains 639 kilocalories at a temperature of 99°C and a pressure of 1 kg/cm². The 4 kilocalories heat increase may be attributed to the investment of mechanical energy necessary for the compressor operation. As a consequence, this external addition of the 4 kilocalorie heat quantity being released by every kilogramme of water vapour into the water mass at the surface upon condensation may be sufficient to replenish the heat that gradually descends within the tank.

The 635 kilocalorie heat quantity does not cause release of additional heat to the water tank as such, only serving to reposition the heat from the 90°C temperature level to the 99°C level. In fact, not all that heat quantity is used for increasing the temperature of the tank water at the surface, because the condensed water retains 99 kilocalories of heat, which leaves 540 kilocalories specifically for the purpose of heating the tank water near its surface.

This device therefore provides for the automatic maintenance of the heat gradient, which is essentially the central driving force for the effective functioning of the total concept, with the only external energy input required being that expended in the operation of the compressor. Naturally, interconnection of the individual tanks along the lines illustrated in Figure 3 will enable the continuous use of the water heat gradient source, whilst still providing the necessary heat difference required within each tank. Figure 3 shows some variation in the heat difference within individual tanks, dictated by the physical characteristics of each available working substance within that temperature range.

Such interconnection may extend right down the temperature scale, subject only to the availability of suitable working substances with their critical temperatures corresponding to the surface temperature of the additional tanks. The optimum heat gradient appears to be 10-12°C, as indicated by the following comparison. Given that at a heat gradient of 24°C the expansion factor is only 30& higher than exists at a gradient of 12°C, yet twice the time unit is required to achieve that heat exchange, it then becomes apparent that the resultant work done by the larger heat transfer means is only 62..5% efficient, compared to the 12°C gradient.

Employing the ideal means however is not always possible, due to problems in finding working substances with physical characteristics to match those needed at each respective level within the interconnected enclosed system referred to above.

The copper-pipe cluster system rotating within an enclosed tank containing the source heat gradient as described above, is one of the ways to create a cycle by which means a heat source of low temperature gradientis to be converted to work through the process of expansion of liquid substances near their critical point. Another way is to have the copper-pipe system remain stationary, with the liquid working substance within it moving. This variation however differs from the 10-12°C temperature gradient criteria in that it resembles the operation of the conventional heat-engine, with one essential difference being that the working substapce retains its liquid state throughout the entire cycle.

The major components of this type of apparatus are two sets of vertically placed copper-pipe cluster systems to function as heat exchangers, also to be immersed in an appropriately shaped water tank. Both extremities of each cluster system are to converge into a single pipe. The appropriate working fluid is to be placed into the cluster system, with the pressure of one unit being equal to the critical pressure, whilst the pressure of the other unit being 20-30 or more atmospheres higher. Within the latter cluster system the working fluid ascends gradually and absorbs heat from the surrounding water. At the top, its temperature reaches the critical temperature, thereby causing a substantial expansion, with the expanding working substance being forced into a cylinder and providing work by moving the piston therein. This cylinder is connected to the lower pressure cluster system. The working substance enters this pipe cluster, and as it gradually descends, the heat previously absorbed during the ascending cycle is transferred by emission to the surrounding upper water layer and to the high pressure copper-pipe cluster system. Reaching the bottom in a denser and cooler condition, the working substance flows into a smaller piston-cylinder, which provides an increase in pressure as the substance returns into the higher pressure cluster, to repeat another cycle.

The essential difference between this operational method, compared with the rotating pipe cluster principle, is the need to invest substantially more external energy for the purpose of returning the cooler descending working substance from the lower into the high pressure pipe cluster, in order to maintain a continuous cycle. To conserve this invested energy however, the object is to establish the highest possible volume reduction. This in turn requires a substantially greater temperature gradient of the order of between 30-40°C or even perhaps 50°C, instead of the previously adequate 10-12°C. There is no further advantage provided in reducing the gradient beyond 50°C, since the volume changes achieved thereafter are quite negligible and do not compensate for any additional energy expenditure. Even with a 50°C temperature reduction, there is only about a half decrease in the volume, and considering the wastage caused by friction, more than half of the resulting energy has to be expended to force the cooler working substance into the higher pressure cluster. Compensating for the reduced efficiency are the advantages of only that part of the working substance undergoing the necessary heating which passes from one pipe cluster to the other, rather than the whole amount contained within both of the pipe cluster systems, and its markedly more compact size in comparison to that of the rotating pipe cluster system type. Hence, this design unit would be better suited to small scale application, such as at individual farms or commercial operations not connected to the main power grid network.

This grid network would of course be supplied by substantially larger dimensional rotating pipe cluster power plant units, either in the format of the simple apparatus placed around the coast line using the natural temperature gradient source of the sea, or the interconnected composite form being connected to existing conventional power plants or using the natural and abundant solar energy obtained by solar ponds etcetera. Apart from connection to the existing power plants, which will eventually be phased out anyway through conservation considerations, the size of the rotating pipe-cluster type plants will be governed in the main by the size of the recipient community, as there is no sense in the construction of huge plants with. the resultant power production being wasted through the distant transportation of the output electricity, as is the case with power plant/power grid transmission methods currently in use.

Of course, this is not to suggest that the stationary method is less practical or desirable, the choice being dictated simply by circumstances relating to the particular output requirement, nature of the source energy input, size of the unit etcetera. In fact, the stationary type can be interconnected as readily as the previously outlined rotating type plant, with the only modification being to effect a number of interconnections between each tank at every 5-10°C level, necessitated by the higher gradient of up to 50°C within each tank. The objective in mentioning these alternative operational processes is to emphasize that the overall concept of the effective use of the sudden multiple expansion characteristics of fluids near their critical point is the principal invention, with the differing cycles being the means by which to put into practical effect that concept.

On this very point, another alternative operational method comes to mind, in which the variation relates to the active energy input in fact being opposite to the previously described methods in that it involves cooling of the bottom layer of the temperature gradient fluid substance. Based on the previously mentioned fact that the thermal capacity of a fluid near its critical point is ten to twentyfold its normal, it conversely follows that much less energy input is required to effect the necessary cooling of the fluid at its bottom layer. Therefore, given a naturally available heat source such as ground-water, a temperature gradient (even 6-8°C may suffice) is established by artificially cooling the bottom layer of that water. Now, by using etheline (C₂H₄) with a critical temperature of 9.9°C as the working fluid within the pipe-cluster system, a plant may be successfully placed into operation with very little external energy to run.

Of course, subject to finding further suitable fluids for the other pipe-cluster systems, a composite plant may be established with interconnection of the individual tanks being into the negative temperature range, thereby increasing the efficiency of the apparatus even further. Apart from the limitations imposed on the establishment of such a composite plant due to lack of suitable working fluids with corresponding critical temperatures though, the other drawback in going into the negative temperature range is the tendency of metal components to become brittle, with consequential deterioration in their tolerances to the high pressures subjected to. However, with substantial improvements made in the field of materials science, it is quite feasible that such problems will in due course be eliminated.

Reverting to the subject of transforming the high pressure energy of the working fluid within the rotating pipe-cluster system into mechanical energy by means of a turbine attached to the axle outside of the tank, it has occurred that such a turbine would be rather inefficient under the force of a dense, high pressure, low velocity fluid. Efficiency would be greatly enhanced by substitution of the turbine with a pistoncylinder. Transfer of the working fluid thereto is achieved via a well sealed transmission apparatus housing, of any existing design type, whereby one section is able to rotate with the axle with the outer section remaining stationary for attachment to the pistoncylinder unit.

Claims

The claims defining the invention are as follows:

Claim 1. Design of a new heat engine cycle, to operate on the basis of the driving force being provided by a specific working fluid absorbing heat from an available source in order to raise its temperature to within its critical point, at which point the optimum rate of expansion occurs, thereby maximizing efficiency. The cycle is maintained by the emission of heat from the expanded fluid back to the source, before once again re-using the same heat in a new cycle. The essential element in this design concept is the provision of any available heat source from which a temperature gradient of between 10-12°C can be maintained within some liquid, and the necessity of having some specific fluid possess ing a critical temperature to correspond to the surface temperature of the chosen liquid gradient source.

Claim 2. The cycle referred to in Claim 1 can take the form of a copper-pipe cluster system rotating on a horizontal axle, enclosed within a tank containing water or some other liquid as the medium for the heat source temperature gradient. A working fluid possessing a critical temperature corresponding to that of the surface layer of the tank liquid is inserted into the pipe-cluster system, with substantial expansion occurring through heating of the ascending clusters. This tremendous expansion forces some of the fluid from the pipe-clusters through their individual steel cylinders to one side of the enclosed divided axle compartment via a one way valve, and thence along this compartment to an externally mounted, slow speed turbine or preferably a piston-cylinder affixed to the end of the axle. Upon conversion of the considerable force provided by the expanding fluid by means of either the turbine or the piston-cylinder, the fluid is returned to the other enclosed compartmental half of the axle, and from there through another one way valve via the steel cylinder back into the cluster which has descended to the bottom. The purpose of having the steel cylinders incorporated into the cycle is to enable the hottest part of the working fluid to be maintained near the copper-pipe cluster system. Two spherical vessels are also attached to both external parts of the axle, interconnected with their respective axle compartments and 2/3 filled with the same working fluid and the remainder with some high pressure gas, such as nitrogen; to function as pressure regulators within the apparatus.

Claim 3. Another method by which to establish the cycle referred to in Claim 1 is to have the copper-pipe system remain stationary, and only have the working fluid undergo the necessary cyclic motion. This requires two sets of vertically positioned copper-pipe cluster systems enclosed in an appropriately shaped tank containing the heat source temperature gradient liquid. The two sets of clusters are interconnected at the surface by a piston-cylinder to function as the converter into mechanical energy of the expanded fluid force, and at the bottom by a small piston-cylinder to function as a pressure supplement device. A particular working fluid is placed into the cluster sets, and the pressure within one set is arranged to be equal to the critical pressure of the fluid, whilst in the other set it is about 20-30 atmospheres higher. Ascending within the latter cluster set, the fluid absorbs heat from the surrounding liquid heat source in the tank, and arriving at the top of the cluster, it reaches its critical temperature, which causes substantial expansion to occur, exerting work on the piston. Thence, the fluid gradually descends within the other cluster set, emitting heat to the surrounding tank liquid, thereby cooling down and becoming denser. Reaching the bottom, it is forced by the smaller piston- cylinder into the higher pressure cluster set, thus completing a cycle and commencing another one. Apart from the obvious difference between this operational method and the one referred to in Claim 2, there is an additional difference to the concept referred to in Claim 1, in that the temperature gradient necessary for effective functioning is around 30-50°C, rather than 10-12°C, in order to compensate for the greater energy input required for transferring the cool working fluid into the higher pressure cluster, with an attend ant decrease in efficiency.

Claim 4. Given regard to the phenomenon that the thermal capacity of any fluid substance is at its greatest within a few degrees of its critical point, and hence most of the heat exchange occurs in that region, a component device is designed to utilize this principle in effectively returning the gradually descending heat within the tank referred to in Claim 2 back to the surface layer. To achieve this however requires the tank liquid at its surface to be near the critical temperature. One or more highly conductive large diameter pipes are placed horizontally in the tank at a level some 8°C below the surface temperature and permitted to be half filled by the same liquid, with the top half connected to a compressor. The other side of the compressor is connected to another set of pipes located directly under the tank surface. By adjusting the compressor to provide the appropriate pressure in the lower pipes to enable evaporation taking place, the resultant vapour is forced up to the higher pipes, where it condenses, releasing the heat quantity absorbed during evaporation.

Claim 5. Converse to the phenomenon referred to in Claim 4, the least heat exchange occurs furthest from the critical temperature. Therefore, by reversing the practice of heat replenishment at the top of the temperature gradient as implied in Claim 2, and actively cooling the bottom layer to maintain that gradient, it follows that the input energy required is substantially reduced. Furthermore, a reduced gradient of the order of 6-8°C may be sufficient to maintain successful operation, thereby enabling natural sources of heat - such as groundwater for example - to provide the upper gradient, with artificial cooling of the bottom- layer of the same water, to establish the necessary gradient. In such a case, the working fluid used would be etheline (C₂H₄) possessing a critical temperature of 9.9°C. This alternative would prove the most efficient in terms of the ratio of input to resultant output energy, despite its lesser power production capability in comparison to a large scale plant designed along the lines referred to in Claim 2, with the possibility of interconnecting such a plant to establish a massive composite one in accordance with the description given in the main text, and as illustrated by Figure 3.

Claim 6. To provide for small scale/domestic power generation at a competitive price structure, a less sophisticated, more simplistic unit to the one referred to in Claim 2 is envisaged; whereby multi clusters are replaced by one single pipe-cluster system moving in a vertical up-down plane instead of rotating. Such a unit would eliminate most of the costly components, such as the special one way valves, steel cylinders, the axle and its two separate compartments, the transmission housing apparatus, the spherical vessels for pressure regulation etcetera, which are so essential and integral parts of the rotating type plant framework.