GB2597095A

GB2597095A - A new thermal buoyancy engine and its control method

Info

Publication number: GB2597095A
Application number: GB2010890.8A
Authority: GB
Inventors: Shi Weichao; Hou Hongbo; Xu Yunxin; Altar Mehmet
Original assignee: University of Strathclyde
Current assignee: University of Strathclyde
Priority date: 2020-07-15
Filing date: 2020-07-15
Publication date: 2022-01-19
Also published as: GB202010890D0

Abstract

The thermal buoyancy engine system includes a pressure vessel 18, a high-low hydraulic pressure conversion unit in the pressure vessel, a heat exchanger 1 connected to the high-low hydraulic pressure conversion unit, outer oil bladder 4, inner oil bladder 17, and accumulator 11. There may be phase change material (PCM) in the heat exchanger and hydraulic oil in the phase change material. The high-low hydraulic pressure conversion unit may include a single-acting low-pressure cylinder 7 and a double-acting high-pressure cylinder 10 with fixed relative positions, a hydraulic rod 8 between the cylinders and a carrying bracket 19 for fixing the cylinders. The double-acting high-pressure cylinder may be connected with the inner oil bladder and the accumulator, which may contain high-pressure nitrogen. The design of the high-low hydraulic pressure conversion unit of the invention can effectively achieve the conversion of the hydraulic oil from high pressure to low pressure, so as to achieve the increase of the buoyancy change capability. A method of operating the system is also disclosed.

Description

A New Thermal Buoyancy Engine and its Control Method

Field

The invention relates to the field of an underwater glider, in particular to a novel thermal buoyancy engine and its control method of hydraulic oil system.

Background

It is generally acknowledged that the ocean will play an increasingly important role in the world economy, ocean observation and monitoring is crucial to expanding the ocean knowledge of human beings and their wealth. For centuries, oceanographers have relied on the ships to gather data and perform observation work during their trips. And so far the research contributed to the early understanding about the ocean circulation, the climate change, etc. However, the limitations are obvious. The first limitation is the running cost, as operating ships for observation is expensive and it is also less efficient and sustainable. Ship surveys typically cannot last more than one or two months, which limits long duration and continuous monitoring to understand the constantly changing ocean.

Therefore, a self-sustainable monitoring platform is urgently needed. The underwater glider with thermal buoyancy engine is becoming more and more attractive in the long-term ocean observation as it is highly cost effective and requires less man hours to operate. It is often equipped with a thermal buoyancy engine that can harvest thermal energy from seawater and controls the buoyancy to drive itself up and down. The wings on the glider will transfer this vertical velocity into a latitude velocity, so that a glider can move in a saw tooth pattern. The glider with a thermal buoyancy engine can work theoretically forever, although the endurance is limited to 6-24 months which is mainly due to the payload.

The new thermal buoyancy engine in this invention make use of the motion driven by the thermal buoyancy engine to drive a turbine behind so that to covert the kinetic energy to electric energy. With the same amount of Phase Changing Material (PCM), the new buoyancy engine equipped with the buoyancy amplifier can amplify the buoyancy change, therefore to increase the electricity output to sustain this glider operation.

Summary

According to a first aspect there is provided a thermal buoyancy engine system with high-low hydraulic pressure conversion unit (buoyancy amplifier) configured to increase the buoyancy change of the buoyancy engine, the system comprising: a pressure vessel.

a high-low hydraulic pressure conversion unit in the pressure vessel; a heat exchanger connected to the high-low hydraulic pressure conversion unit; an outer oil bladder; an inner oil bladder; and an accumulator.

The heat exchanger may comprise phase change material (PCM) and hydraulic oil.

The high-low hydraulic pressure conversion unit may include: a single-acting low-pressure cylinder and a double-acting high-pressure cylinder with fixed relative positions, and a hydraulic rod between the single-acting low-pressure cylinder and the double-acting high-pressure cylinder.

The high-low hydraulic pressure conversion unit may further include a carrying bracket for fixing single-acting low-pressure cylinder and double-acting high-pressure cylinder. The carrying bracket may be omitted when the single-acting low-pressure cylinder and the double-acting high-pressure cylinder are made into a whole or as a unitary component.

The double-acting high-pressure cylinder may be connected with an inner oil bladder, a heat transfer, and an accumulator which may contain high-pressure nitrogen.

There may be provided high-pressure resistance tubes to connect one or more of the following: the heat exchanger and the double-acting high-pressure cylinder; the accumulator and the double-acting high-pressure cylinder; the inner oil bladder and the double-acting high-pressure cylinder; the outer oil bladder and the single-acting low-pressure cylinder; the heat exchanger and the inner oil bladder.

Valves, e.g. check valves, may be provided on the tube between the heat exchanger and double-acting high-pressure cylinder, and/or between inner oil bladder and heat exchanger. It will be appreciated that check valves in this disclosure can be replaced by other kinds of valves.

Valves, e.g. magnetic valves, may be provided on the tube between the accumulator and double-acting high-pressure cylinder, between inner oil bladder and double-acting high-pressure cylinder, and/or between outer oil bladder and single-acting low-pressure cylinder. The magnetic valve between the accumulator and the double-acting high-pressure cylinder can be omitted, only using a high-pressure resistance tube to connect the accumulator and the double-acting high-pressure cylinder. It will be appreciated that magnetic valves in this disclosure can also be replaced by other kinds of valves.

The accumulator, high-low hydraulic pressure conversion unit and/or inner oil bladder may be provided inside the pressure vessel. The outer oil bladder may be located outside the pressure vessel.

Single-acting low-pressure cylinder and double-acting high-pressure cylinder may be fixed in relative positions inside the pressure vessel. The piston in double-acting high-pressure cylinder and the piston in single-acting low-pressure cylinder may be connected by a hydraulic rod.

The hydraulic rod may be complete (as shown for example in Figure 1-a), or may be a rod that is divided into two parts and connected by a spring (as shown in figure l-b).

Compared to the existing technology, the new thermal buoyancy engine in this invention has the following advantages: Buoyancy change of thermal buoyancy engine can be enlarged by the high-low hydraulic pressure conversion unit (buoyancy amplifier).

When the buoyancy change of the thermal buoyancy engine is amplified, the glider with the engine can move faster and have a bigger load capacity.

According to another aspect there is provided a hydraulic system control method of the thermal buoyancy engine according to the first aspect.

When the phase change material in the heat exchanger is melting on the sea surface, the hydraulic oil in the heat transfer may be squeezed out. The tube between the outer oil bladder and the single-acting low-pressure cylinder and the tube between the double-acting high-pressure cylinder and accumulator may be opened. The tube between the double-acting high-pressure cylinder and the inner oil bladder may be closed.

Then the piston in the double-acting high-pressure cylinder may be moved to push the piston in the single-acting low-pressure cylinder to such the oil in from the outer bladder.

At the same time, the oil at the accumulator side of the double-acting high-pressure cylinder may be pushed into the accumulator.

When phase change material is nearly halfway melted and the buoyancy is close to the gravity. The tube between the outer oil bladder and the single-acting low-pressure cylinder may be closed so that to present the glider from descending and to keep melting the phase change material.

If the hydraulic rod between the double-acting high-pressure cylinder and the single-acting low-pressure cylinder is complete (as shown in figure 1-a), the piston in the single-acting low-pressure cylinder may be pulled by the hydraulic rod to move and vacuum may appear in the single-acting low-pressure cylinder. If the hydraulic rod between the double-acting high-pressure cylinder and the single-acting low-pressure cylinder is divided into two parts (as shown in figure 1-b), the two hydraulic rods in contact may be separated and connected by a spring. No vacuum appears in the single-acting low-pressure cylinder.

When all the phase change material melts, the tube between the single-acting low-pressure cylinder and outer oil bladder may be opened. If the hydraulic rod between the double-acting high-pressure cylinder and the single-acting low-pressure cylinder is complete (as shown in figure 1-a), the oil in outer oil bladder may be pushed into the single-acting low-pressure cylinder by ambient static pressure, and the buoyancy may decrease. The thermal buoyancy engine may start to descend.

If the hydraulic rod between the double-acting high-pressure cylinder and single-acting low-pressure cylinder is divided into two parts which are connected by a spring (as shown in figure 1-b), the oil in outer bladder may be drawn into single-acting low-pressure cylinder by the spring and the ambient static pressure, and the buoyancy may decrease. The thermal buoyancy engine may start to descend.

As the thermal buoyancy engine keeps descending, the water temperature decreases, and the phase change material may start to solidify and shrink. The oil in the inner oil bladder may be drawn into the heat exchanger.

When the new thermal buoyancy engine reaches the preprogrammed depth, the tube between the outer oil bladder and the single-acting low-pressure cylinder, the tube between double-acting high-pressure cylinder and accumulator and the tube between the double-acting high-pressure cylinder and inner oil bladder may be opened. The oil in the accumulator may be pushed out into the double-acting high-pressure cylinder. The piston in the double-acting high-pressure cylinder may be pushed and may move, the piston in the single-acting low-pressure cylinder may also move and the hydraulic oil in the single-acting low-pressure cylinder may be pushed into outer bladder.

The hydraulic oil at the left side of the piston in the double-acting high-pressure cylinder may be pushed into the inner oil bladder. At this moment, the buoyancy of the thermal engine may be greater than its gravity. The thermal engine may start to ascend. When the glider reaches the sea surface, the next cycle may start.

For the avoidance of doubt, any feature described in respect of any aspect of the invention may be applied to any other aspect of the invention, in any appropriate combination. For example, method features may be applied to apparatus features and vice versa.

Brief Description of the Drawings

The present invention will now be further described in detail and with reference to the figures in which: Figure 1-a is the structure diagram of a thermal buoyancy engine according to a first embodiment; Figure 1-b is the structure diagram of a thermal buoyancy engine according to a second embodiment; Figure 1-c is the structure diagram of a thermal buoyancy engine according to a third embodiment; Figure 1-d is the structure diagram of a thermal buoyancy engine according to a fourth embodiment; Figures from 2 to 7 show the working stages of the thermal buoyancy engine of figure 1-a (The arrow indicates the movement direction of hydraulic oil flow in the high-pressure resistance tube, the dotted line indicates the high-pressure resistance tube where is no hydraulic oil flow); Figures from 8 to 12 show the working stages of the thermal buoyancy engine of figure 1-b (The arrow indicates the movement direction of hydraulic oil flow in the high-pressure resistance tube, the dotted line indicates the high-pressure resistance tube where is no hydraulic oil flow); Figure 13 shows a 3D structure diagram of Figure 1-c.

Detailed Description of the Drawings

A description of the various parts shown in the drawings is shown in Table 1 below: heat exchanger 1 phase change material 2 (PCM) hydraulic oil 3 outer oil bladder 4 magnetic valve 5, 14, 16 single-acting low- 6 pressure cylinder Piston in single-acting low- 7 hydraulic rod 8 pressure cylinder check valve 9, 13 double-acting high- 10 pressure cylinder accumulator 11 piston in accumulator 12 piston in double-acting high-pressure cylinder 15 inner oil bladder 17 pressure vessel 18 carrying bracket 19 spring 20 air hole 21

Table 1

The buoyancy change of the traditional thermal buoyancy engine is very limited, which limits the speed and the payload capacity of the glider with the thermal buoyancy engine. It is unreasonable to increase the buoyancy change by increasing the size of the heat exchanger 1 and the mass of phase change material 2. There are two reasons, the first is that the big heat exchanger 1 will increase the total resistance of the glider, the second is that too much phase change material 2 can dramatically increase the melt time of itself and reduce the working efficiency of the whole system because the thermal conductivity of phase change material 2 is very low.

This invention can fully use the extremely high pressure generated by phase change material 2 without increasing the mass of PCM 2 (the phase change material 2 can achieve a respectable expansion rate when the background pressure is 100 Mpa). The efficiency of the whole system will be increased. Unlike the traditional thermal engine, the air pressure in the pressure vessel 18 can be set higher than atmospheric pressure to reduce the porous phenomenon of PCM 2 caused by low air pressure, cycle efficiency can be further increased, the glider will have higher efficiency of ocean exploration and have better environment suitability and load capacity.

The figure 1-a shows the first embodiment. The thermal buoyancy engine in figure 1-a includes pressure vessel 18, the high-low hydraulic pressure conversion unit in the pressure vessel 18, inner oil bladder 17, accumulator 11 and the heat exchanger 1, outer oil bladder 4. The inside and the outside of pressure vessel 18 are connected with high-pressure resistance tubes. There is PCM 2 in heat exchanger 1, there is hydraulic oil 3 in PCM 2. The high-low hydraulic pressure conversion unit includes: carrying bracket 19, the single-acting low-pressure cylinder 6 and double-acting high-pressure cylinder 10, the hydraulic rod 8 between the single-acting low-pressure cylinder 6 and double-acting high-pressure cylinder 10. The double-acting high-pressure cylinder 10 is connected with inner oil bladder 17, heat exchanger 1, and accumulator 11. There is high-pressure nitrogen in accumulator 11.

In the first embodiment, there are high-pressure resistance tubes to connect heat exchanger 1 and double-acting high-pressure cylinder 10, accumulator 11 and double-acting high-pressure cylinder 10, inner oil bladder 17 and double-acting high-pressure cylinder 10, outer oil bladder 4 and single-acting low-pressure cylinder 6, heat exchanger 1 and inner oil bladder 17.

In the first embodiment, there is a check valve 9 between heat exchanger 1 and double-acting high-pressure cylinder 10. There is a check valve 13 between the heat exchanger 11 and inner oil bladder 17. There is a magnetic valve 5 between outer oil bladder 4 and single-acting low-pressure cylinder 6. There is a magnetic valve 14 between accumulator 11 and double-acting high-pressure cylinder 10. There is a magnetic valve 16 between inner oil bladder 17 and double-acting high-pressure cylinder 10.

In the first embodiment, the accumulator 11, high-low hydraulic pressure conversion unit and inner oil bladder 17 are inside the pressure vessel 18. The outer oil bladder 4 is outside the pressure vessel 18.

In the first embodiment, the single-acting low-pressure cylinder 6 and double-acting high-pressure cylinder 10 are fixed in relative positions inside/by the carrying bracket 19, the piston 15 in double-acting high-pressure cylinder 10 and the piston 7 in single-acting low-pressure cylinder 6 are connected by a hydraulic rod 8.

Specifically, the specific implementation steps of this embodiment include the following steps: (1) See figure 2, the thermal buoyancy engine is on the surface of the ocean. The PCM 2 melts, hydraulic oil 3 is pushed out from heat exchanger 1. The magnetic valve 5 and magnetic valve 14 is opened and the magnetic valve 16 is closed. The hydraulic oil 3 from the heat exchanger 1 pushed the piston 15 in double-acting high-pressure cylinder 10 to move right, the oil in the right side of piston 15 is pushed into accumulator 11. Because the piston 15 is connected with piston 7 in single-acting low-pressure cylinder 6 by a rod 8, the piston 7 also moves in the same way. The oil in the outer oil bladder 4 is pushed into single-acting low-pressure cylinder 6 by surrounding pressure; (2) See figure 3, the PCM 2 melts nearly in half, at this moment, the buoyancy is slightly higher than gravity. The magnetic valve 5 is closed, magnetic valve 16 keeps close. The buoyancy does not change anymore; (3) See figure 4, the PCM 2 keeps melting, the piston 15 and the piston 7 is pushed and move, vacuum appears in single-acting low-pressure cylinder 6 because the piston 7 is sealed. (After vacuum appears, there will be a force to the left acting on piston 7 which is generated by inner air pressure, it will cause some energy loss. However, this energy loss is negligible compared to the work done by the buoyancy engine in the operating water depth); (4) See figure 5, when all the PCM 2 melts, magnetic valve 14 is closed, magnetic valve 16 is closed, magnetic valve 5 is opened. The oil in outer oil bladder 4 is pushed into single-acting low-pressure cylinder 6, the buoyancy is smaller than gravity, the thermal buoyancy engine starts to descend; (5) See figure 6, the new thermal engine keeps descending, the water temperature drops rapidly. The PCM 2 starts to solidify and shrink. The oil in inner oil bladder 17 is pushed into the heat exchanger 1 by the air pressure in the pressure vessel 18; (6) see figure 7, the thermal buoyancy engine reaches the preprogrammed depth (about 1000 meters). The magnetic valve 5, magnetic valve 14 and the magnetic valve 5 are opened at the same time, the hydraulic oil in the accumulator 11 is pushed into double-acting high-pressure cylinder 10, the piston 15 in cylinder 10 is pushed and move to the left. Because the piston 15 and the piston 7 are connected by a hydraulic rod 8, the piston 7 also move to the left and the oil in the single-acting low-pressure cylinder is pushed into outer oil bladder 4, and the oil on the left side of the piston 15 in double-acting high-pressure cylinder is pushed into inner oil bladder 17. At this moment, the buoyancy is bigger than the gravity, the thermal engine starts to ascend. After arriving at the sea surface, PCM 2 starts to melt again, the next cycle starts.

The following complementary comments apply to the first embodiment: 1 The reason why this new kind of thermal buoyancy engine does not use a small diameter high-pressure single-acting cylinder and a big diameter low-pressure single-acting cylinder to achieve the transition of hydraulic oil from high-pressure to low-pressure. Some single action cylinders do not need springs to finish the return trip of the hydraulic rod, in those cases, the gravity of the hydraulic rod and the load can be used to offset the friction of the piston seal ring to complete the return trip. However, if a small diameter single oil cylinder and a big diameter single oil cylinder are used to achieve the transition of oil pressure in the thermal engine, a spring is needed. Because the thermal buoyancy engine uses the pressure difference between outside and inside of the pressure vessel to achieve the return trip. The pressure difference between the outside and inside of the pressure vessel is about 0.1Mpa, which is not enough for offsetting the fraction between pistons and cylinders. So, two springs in the single cylinders are needed. These two springs, however, pose an uncertainty. A high-quality hydraulic cylinder has a very reliable seal, but spring is not as reliable as the seal.

Because it is easy to wear and corrode. Finally, the restoring force of spring will decrease, which will cause the piston to be stuck in the return trip. Actually, it is one of the most common failures of the single-acting cylinder that the piston is stuck in the return trip, which can reduce the reliability of the thermal engine. And because of the two springs, the whole system is hard to keep compact, the length of the glider will increase, the total resistance of the gliders will be high. In this embodiment, the force for pushing the oil in the outer oil bladder 4 into pressure vessel 18 comes from the heat exchanger 1, it can reach several tons, the piston in cylinders is unlikely to be stuck. Because there is no spring, the length of the two cylinders decreases when they are connected in series. This feature allows for flexible design and arrangement of glider's internal equipment. Compared to the single-acting cylinder, the double-acting cylinder also has the following advantages: (1) Lower cost. (2) Easy to get, almost all standard cylinders are double-acting cylinders. (3) Higher sealing effect. (4) Piston won't be stuck. (5) Resistant to corrosion.

2 The advantage of the new buoyancy engine to reduce the porous phenomenon. When the PCM is solidifying and shrinking, the PCM will become porous more or less, this property will reduce the cycle efficiency of the thermal engine. The porous phenomenon will reduce with the increase of the pressure in the pressure vessel. However, the inner pressure of the pressure vessel has to be less than 0.1 Mpa in traditional thermal buoyancy engine. It is because the oil in the outer bladder can not be sucked into a pressure vessel if the inner pressure of the pressure vessel is higher than the atmospheric pressure. However, in this new thermal buoyancy engine, the recovery of the oil in the outer bladder is finished by the force from the heat exchanger directly which can reach several tons. The optimized inner air pressure which can improve the cycle efficiency of the thermal engine can be selected according to the relationship between the pressure and the porosity of phase change material.

3 The magnetic valve 14 in this embodiment can be omitted. The installation of magnetic valve 14 is just for avoiding keeping the piston in high-pressure cylinder under high-pressure for a long time and making the system more reliable.

4 The design of the high-low hydraulic pressure conversion unit of the invention can effectively achieve the conversion of the hydraulic oil from high-pressure to low-pressure, so as to achieve the increase of the oil discharge quantity of the new thermal buoyancy engine in the deep sea. The cruising speed and information collection efficiency of glider with this new kind of thermal engine will increase. The environmental suitability of glider with thermal buoyancy engine will be improved.

Figure 1-b shows a structure diagram according to a second embodiment of the thermal buoyancy engine. The structure of the second embodiment of the new thermal buoyancy engine is very similar to the first embodiment, the only difference is that the hydraulic rod 8 between single-acting low-pressure cylinder 6 and the double-acting high-pressure cylinder 10 are divided into two parts which are connected with a spring 20. And the outer oil bladder 4 is made of high elastic material. The elastic force of spring and outer oil bladder 4 can push more than half of the oil in outer oil bladder 4 into the single-acting low-pressure cylinder 6. The two separated parts of the rod 8 are fixed on the piston 7 and piston 15 respectively.

Specifically, the specific implementation steps of this embodiment include the following steps: (1) See figure 1-b and figure 8, phase change material 2 is melting, magnetic valve 14 is opened, magnetic valve 5 and magnetic valve 16 are closed. The hydraulic oil 3 pushed the piston 15 in cylinder 10 to move, the two parts of hydraulic rod 8 no longer contact. At this moment, the hydraulic oil on the right side of the piston 15 is pushed into accumulator 11.

(2) See figure 9, all the phase change material 2 melts, the magnetic valve 14 is closed, the magnetic valve 16 is closed, the magnetic valve 5 is opened. The elastic force from spring 20 and outer oil bladder 4 will push some of the oil in outer bladder 4 into pressure vessel 18. At this moment, the gravity of the glider will be slightly bigger than its buoyancy. Glider starts to descend. The remaining oil will be pushed into single-acting low-pressure cylinder 6 by the pressure of water. Because the difference between gravity and buoyancy is small, the gliding speed of glider is slow in this stage.

(3) See figure 10, in this stage, all the oil in outer oil bladder 4 is pushed into single-acting low-pressure cylinder 6 by water pressure. Two parts of the rod 8 start to contact with each other, the glider with the thermal engine starts to glide in full speed.

(4) See figure 11, phase change material 2 starts to solidify and shrink. The oil in inner oil bladder 17 is pushed into the heat exchanger 1 by the inner air pressure.

(5) See figure 12, the glider reaches the preprogrammed depth, magnetic valve 5, magnetic valve 14 and magnetic valve 16 are opened, the high-pressure nitrogen pushes hydraulic oil in accumulator 11 into double-acting cylinder 10, the piston 15 in double-acting cylinder 10 is pushed and moves to the left side. At this moment, the two parts of the rod 8 contacts with each other, the whole rod 8 and the piston 7 are pushed to the left side. The oil in single-acting cylinder 6 is pushed into outer oil bladder 4. At the same time, the oil at the left side of piston 15 of double-acting high-pressure cylinder 10 is pushed into inner oil bladder 17. The buoyancy becomes bigger, the thermal engine starts to ascend. After arriving at the sea surface, PCM 2 starts to melt again, the next cycle starts.

The following complementary comments apply to the second embodiment: 1. Compared to the first embodiment, this embodiment does not need to create a vacuum which is about half the volume of the oil in the outer bladder. This feature can reduce energy loss and can reduce the sealing requirements of single-acting low-pressure cylinder6.

2. In this embodiment, nearly half of the oil in the outer bladder is pushed into pressure vessel 18. This oil recovery method has two advantages. The first advantage is that it can reduce the quality requirement of outer oil bladder 4 and spring 20 and make the system more reliable, and it can reduce the weight of the spring. The second advantage is that the inner air pressure of pressure vessel can be higher than the traditional thermal engine (inner air pressure of pressure vessel of traditional thermal buoyancy engine is 0.1 Mpa at most when the phase change material is solidifying, but inner air pressure of this embodiment can be higher than 0.1 Mpa). As mentioned before, higher inner air pressure in the pressure vessel can reduce the porous phenomenon of PCM and increase the cycle efficiency.

3. The magnetic valve 14 in this embodiment can be omitted. The installation of magnetic valve 14 is just for avoiding keeping the piston of the high-pressure cylinder under high pressure for a long time and making the system more reliable.

Figure 1-c shows the structure diagram of a third embodiment of the thermal buoyancy engine. The structure of the second embodiment of the new thermal buoyancy engine is very similar to the first embodiment, the implementation steps are exactly the same. The only difference is that double-acting high-pressure cylinder 10 and single-acting low-pressure cylinder 6 are made into a whole in this case. The carrying bracket 19 is omitted. There is an air hole 21 on the single-acting low-pressure cylinder. Its 3D diagram is shown in figure 13, and its implementation steps are exactly the same as the first embodiment.

The following complementary comments apply to the third embodiment: 1. Compared with the first embodiment, this embodiment omits the carrying bracket 19 to reduce the total weight of the thermal buoyancy engine.

Figure 1-d shows the structure diagram of a fourth embodiment of the thermal buoyancy engine. The only difference between this embodiment and the first embodiments is that the magnetic valve 14 between double-acting high-pressure cylinder 15 and accumulator 11 is omitted. There is only a high-pressure resistance tube between cylinder 15 and accumulator 11.

The following complementary comments apply to the fourth embodiment: 1. This embodiment can prevent the system damage caused by failing to open the electronic control valve 14 in time when the phase change material melts.

2. Compared to other embodiments, this embodiment can reduce the total number of valves and make the system lighter and more compact The above embodiments describe the technical principle of the invention. These descriptions are only intended to explain the principles of the invention and shall not in any way be construed as limiting the scope of protection of the invention. Based on the interpretation herein, other specific implementation methods of the invention which personnel in this technical field do not need to pay creative labor to be associated with will fall within the protection scope of the invention.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as described herein without departing from the scope of the present invention. The present embodiments are therefore to be considered for illustrative purposes and are not restrictive, and are not limited to the extent of that described in the embodiment.

Claims

CLAIMS: A thermal buoyancy engine system, wherein the system includes: a pressure vessel; a high-low hydraulic pressure conversion unit in the pressure vessel; a heat exchanger connected to the high-low hydraulic pressure conversion unit; an outer oil bladder; an inner oil bladder; and an accumulator.
2. The thermal buoyancy engine system of claim 1, wherein the heat exchanger comprises a phase change material (PCM), and wherein there is hydraulic oil in the phase change material.
3. The thermal buoyancy engine system of any preceding claim, wherein the high-low hydraulic pressure conversion unit includes a single-acting low-pressure cylinder and a double-acting high-pressure cylinder with fixed relative positions, a hydraulic rod between a single-acting low-pressure cylinder and a double-acting high-pressure cylinder.
4. The thermal buoyancy engine system of any preceding claim, wherein the high-low hydraulic pressure conversion unit includes a carrying bracket for fixing single-acting low-pressure cylinder and double-acting high-pressure cylinder.
5. The thermal buoyancy engine system of any preceding claim, wherein the double-acting high-pressure cylinder is connected with an inner oil bladder, the heat exchanger and an accumulator, which contains high-pressure nitrogen.
6. The thermal buoyancy engine system of any preceding claim, wherein there are high-pressure resistance tubes to connect heat exchanger and double-acting high-pressure cylinder, accumulator and double-acting high-pressure cylinder, inner oil bladder and double-acting high-pressure cylinder, outer oil bladder and single-acting low-pressure cylinder, and heat exchanger and inner oil bladder.
7. The thermal buoyancy engine system of any preceding claim, wherein one or more valves are equipped on the tube between the heat exchanger and double-acting high-pressure cylinder, and between inner oil bladder and heat exchanger.
8. The thermal buoyancy engine system of any preceding claim, wherein one or more valves are equipped on the tube between the accumulator and double-acting high-pressure cylinder, between inner oil bladder and double-acting high-pressure cylinder, and between outer oil bladder and single-acting low-pressure cylinder.
9. The thermal buoyancy engine system of any preceding claim, wherein the accumulator, high-low hydraulic pressure conversion unit and inner oil bladder are inside the pressure vessel.
10. The thermal buoyancy engine system of any preceding claim, wherein the outer oil bladder is outside the pressure vessel.
11. The thermal buoyancy engine system of any preceding claim, wherein the single-acting low-pressure cylinder and double-acting high-pressure cylinder are fixed in relative positions inside the pressure vessel.
12. The thermal buoyancy engine system of any preceding claim, wherein the piston in the double-acting high-pressure cylinder and the piston in the single-acting low-pressure cylinder are connected by a hydraulic rod.
13. The thermal buoyancy engine system of any preceding claim, wherein the hydraulic rod is a complete rod or a separated rod which is divided into two parts and connected by a spring.
14. A method for controlling the thermal buoyancy engine system of claim 1, the method comprising: when the phase change material in the heat exchanger is melting on the sea surface, pushing out the hydraulic oil in the heat transfer; opening the tube between the outer oil bladder and the single-acting low-pressure cylinder and the tube between the double-acting high-pressure cylinder and accumulator; closing the tube between the double-acting high-pressure cylinder and the inner oil bladder; pushing and moving the piston in the double-acting high-pressure cylinder to a right side.
15. The method according to claim 14, wherein if the hydraulic rod between the double-acting high-pressure cylinder and the single-acting low-pressure cylinder is complete, the piston in the single-acting low-pressure cylinder also moves to the right side, and the oil in the outer bladder is sucked into the single-acting low-pressure cylinder.
16. The method according to any of claims 14 to 15, wherein the oil at the right side of the piston of the double-acting high-pressure cylinder is pushed into the accumulator.
17. The method according to any of claims 14 to 16, wherein when phase change material is nearly halfway melted, the buoyancy of the engine is a greater than its gravity.
18. The method according to any of claims 14 to 17, comprising closing the tube between the outer oil bladder and the single-acting low-pressure cylinder, and wherein the phase change material continues melting.
19. The method according to any of claims 14 to 18, wherein when all the phase change material melts, the method comprises opening the tube between the single-acting low-pressure cylinder and outer oil bladder.
20. The method according to claim 19, wherein if the hydraulic rod between the double-acting high-pressure cylinder and the single-acting low-pressure cylinder is not divided into two parts, the oil in outer oil bladder is pushed into the single-acting low-pressure cylinder by atmospheric pressure, causing the buoyancy to decrease, and the thermal buoyancy engine to descend.
21. The method according to claim 19, wherein if the hydraulic rod between the double-acting high-pressure cylinder and the single-acting low-pressure cylinder is divided into two parts which are connected by a spring, the oil in the outer bladder is pushed into the single-acting low-pressure cylinder by the spring, the high-elastic oil bladder and the atmospheric pressure, causing the buoyancy to decreases, and the thermal buoyancy engine to descend.(the part of oil which is pushed into single acting cylinder by water pressure?)
22. The method according to any of claims 14 to 21, wherein as the thermal buoyancy engine descends, the water temperature decreases, causing the phase change material to solidify and/or shrink.
23. The method according to claim 22, wherein the oil in the inner oil bladder is pushed into the heat exchanger by the air pressure inside the pressure vessel.
24. The method according to any of claims 14 to 23, wherein when the new thermal buoyancy engine reaches the preprogrammed depth, the tube between the outer oil bladder and the single-acting low-pressure cylinder, the tube between double-acting high-pressure cylinder and accumulator and the tube between the double-acting high-pressure cylinder and inner oil bladder are opened, and wherein the oil in the accumulator is pushed into the double-acting high-pressure cylinder.
25. The method according to any of claims 14 to 24, wherein when the piston in the double-acting high-pressure cylinder is pushed and moves, the piston in the single-acting low-pressure cylinder also moves and the hydraulic oil in the single-acting low-pressure cylinder is pushed into the outer bladder and the hydraulic oil at the left side of the piston in the double-acting high-pressure cylinder is pushed into the inner oil bladder, and wherein, as the thermal engine ascends, the phase change material melts when the temperature increases.