JPH04309762A - Operation method of heat utilization system using hydrogen storage alloy - Google Patents

Abstract

PURPOSE:To enhance the efficiency by achieving coincidence of head generating/ absorbing speed between the sides of generating and discharging a hydrogen occlusion heat of a heat utilizing device using a hydrogen storage alloy. CONSTITUTION:In a cooling cycle, MH-heat medium temperature difference is large on the side of generating a stored heat and small on the side of discharging or absorbing heat. To improve this, a strong vibration is applied on the side of generating a stored heat and the vibration applied is weak on the side of discharging and absorbing heat. As a result, a heat transfer coefficient between the MH and a heat exchanger tube is improved and the rate of the coefficient changes depending on the degree of vibration. The vibration is made stronger at a part with a larger temperature difference and weaker at the part with a smaller temperature difference to make a heating value equal between the sides of generating and discharging the stored heat so that the resulting generation of hydrogen can be made equal therebetween. Thus, the storing time and the discharge time of the heat utilizing apparatus can be equal eventually thereby achieving an operation with higher efficiency.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This technology is applied to the industrial field where the phenomenon of heat absorption or heat generation during exchange of hydrogen with a hydrogen storage alloy is used as a heat utilization device such as an air conditioner or a heat pump.

0002

[Prior Art] The most widely used conventional cooling system uses fluorocarbons as a heat medium [compression] - [heat dissipation]
The cycle of - [expansion] - [heat absorption from the outside] was repeated, and cooling was performed during the [heat absorption from the outside]. This method requires external power for compression, and recent global environmental issues have imposed restrictions on the use of fluorocarbons, so this method is an air conditioner that does not have these problems. The era has come when refrigeration equipment is required.

[0003] One of the technologies that satisfies this requirement is a cooling device or a heat pump that utilizes a hydrogen storage alloy (hereinafter abbreviated as MH). This system has high expectations because the MH-hydrogen reaction speed is extremely high and there is a possibility of miniaturization. However, the problem with this technology is that M
Since H is used as a powder, the thermal conductivity of the powder layer is poor, and large equipment is required to increase the amount of heat exchange, making it less economical than conventional methods using CFCs. Ta. The present inventor has filed Japanese Patent Application No. 2-282955.
proposed an improvement in this point by significantly increasing the amount of heat exchange by applying vibration to the MH container from the outside.

0004

[Problems to be Solved by the Invention] To give an example of a cooling system using MH, the operating diagram of MH has the reciprocal of temperature on the horizontal axis and the hydrogen pressure indicated by MH on the vertical axis. It is expressed as follows. Also, the high temperature alloy MH used here
FIG. 2 shows an example of the temperature change between MH1 and the low temperature alloy MH2. The progress of both the high-temperature MH and the low-temperature MH will be explained below.

(1) In a high-temperature MH, the MH temperature merely fluctuates between the high-temperature heat medium temperature and the heat radiation heat medium temperature during the cycle. The amount of heat Qh transferred at time Th here is expressed as follows. Qh=Hh×Ah×Δth×Th ……………(
a) Hh: Overall heat transfer coefficient between the heating medium and MH, Ah: Heat transfer area, Δth: Logarithmic average temperature difference between the heating medium and MH.

(2) On the other hand, in a low-temperature MH, during hydrogen storage, the MH temperature gradually rises from the low temperature, once exceeding the temperature of the heat dissipating heat medium, and then being cooled by this heat medium. When hydrogen is released, the MH cools itself due to the released heat, becomes below the temperature of the heat medium for obtaining cold heat, and is warmed by this heat medium (the heat medium is cooled). Ql=Hl×Al×Δtl×Tl …………
(b) Hl: Overall heat transfer area between the heating medium and MH, Al: Heat transfer area, Δtl: Logarithmic average temperature difference between the heating medium and MH.

[0007] As described above, the temperature difference between the high temperature MH1 and the low temperature MH2 with respect to the heat medium is different, and since a relatively large temperature difference can be obtained for the high temperature MH1, the Δth expressed by equation (a) is large, and the amount of heat exchanged Qh is large. growing. On the other hand, in the case of MH2 for low temperature, the complex changes shown in FIG. 2 occur, so that Δtl in equation (b) cannot be made large, so Ql also tends to become small. Therefore, Figure 3
When an air conditioner is assembled as shown in FIG. 1 and the cycle shown in FIG. 1 is performed, there is a problem that an imbalance of Qh>Ql occurs. In other words, more hydrogen than necessary is generated on the MH1 side,
A problem arises in that the MH2 side cannot absorb all the hydrogen. Specifically, excess hydrogen that does not participate in the reaction remains in the container, causing problems such as excessive pressure rise and an imbalance in the amount of heat generated.

[0008]

[Means for solving the problem] Solve this problem and Qh=
As a means for determining Ql, the following method can be considered in equations (a) and (b). a. Add changes to cycle time. Since Q becomes large on the high temperature side MH1, it is conceivable to shorten the duration T by that amount. However, as shown in Figure 3, since two sets of devices are normally operated continuously, if the storage and release times do not match, there will be a period of time in the cycle during which cooling will not continue.
If this continues, it will not be possible to create a continuous cycle.

b. A difference is made between the heat exchanger heat transfer areas of MH1 and MH2. By designing Ah/Al=Δtl/Δth, the amount of heat exchanged can be made to match in calculation. However, operating conditions are subject to seasonal and hourly fluctuations.
It's not always constant. For example, the heat dissipation medium often dissipates heat into the outside air, but since the outside air temperature fluctuates over time, the amounts of Qh and Ql also change constantly, and the relationship shown in FIG. 1 also changes between day and night. In order to solve this problem, fixing equipment such as heat exchangers is not enough; it must be possible to flexibly respond to changes in external conditions.

c. The inventor has filed Japanese Patent Application No. 2-282955,
FIG. 4 shows the relationship between the vibration acceleration of the MH container and the amount of hydrogen generated. The reason why the amount of hydrogen generated changes depending on the strength of the vibration is that the amount of heat transfer changes and the amount of heat transferred from the heat medium to the MH increases, resulting in an increase in the amount of hydrogen generated. Therefore, by providing a difference in the amount of vibration given to MH1 and MH2, it is possible to set the amount of heat transfer inside to different values. Thereby, it becomes possible to cover the difference in heat transfer amount due to the heat medium-MH temperature difference in the MH1 and MH2 containers.

[0011]

[Effect] In Figure 4, the horizontal axis shows the vibration strength, and the vertical axis shows the MH.
and the apparent overall heat transfer coefficient of the heat medium tube, and the experimental results are displayed. When vibration is applied to the MH, the amount of heat transfer changes because the MH powder fluidizes and comes into contact with the heat transfer surface, which increases the heat transfer coefficient, and also because the MH powder is present in areas farther from the heat transfer surface and is heated or heated. This is due to two effects: MH, which is difficult to cool, flows and mixes like a liquid and approaches the heat transfer surface, so a large temperature difference Δt can be obtained.

As shown in FIGS. 1 and 2, in the MH1 in which the high-temperature side alloy is stored, the temperature difference between the heating medium and the MH is large even when the MH is at rest. On the other hand, in MH2, the temperature difference reverses halfway, and even after the reverse occurs, the temperature difference cannot be large. Therefore, by applying vibration weakly to MH1 and strongly to MH2, it is possible to make Hh < Hl, and since this temperature difference is canceled out, Qh and Ql can be made equal, and as a result, the amount of hydrogen exchange can be made equal. I can do it.

[0013] If there is a difference between the two MH containers (hydrogen generation amount>storage amount), the pressure increases because unoccluded hydrogen gas exists in the MH container space. Although there are factors that change dynamically, such as MH absorbing more hydrogen when the pressure increases, it has been pointed out that the problem is that the legal limit pressure of the container may be exceeded.

On the other hand, if the amount generated is smaller than the amount stored, the internal pressure of the container decreases, and the driving force for moving hydrogen between the two MHs decreases. As a result, there is a delay in the reaction itself, which causes problems in heat generation. By operating Qh and Ql equally, such a situation can be avoided and balanced operation becomes possible.

As a specific control method, a hydrogen flow meter is installed to control the amount of hydrogen transferred between MH containers, and MH1→M
Although it is possible to measure the value of H2 or MH2→MH1, hydrogen flowmeters are actually expensive, and installing a flowmeter for each hydrogen flow direction is problematic. In order to measure flow rates in two directions with one flowmeter, it is necessary to install piping and valves around the flowmeter, and to switch the valves each time the flow direction changes.

[0016] A simple method is to measure the temperature difference and flow rate of the heating medium in and out of the MH container in each MH container, calculate and compare the amount of heat absorbed by the MH and the amount of heat released. You can know the amount generated and the amount stored. In this case, the temperature inside the MH alloy is measured at the same time.
It is also necessary to take into account changes in the amount of sensible heat of H itself.

[0017]

[Example] Cooling device using MH (3000kcal
/h) was configured as follows. Two types of powdered MH (lanthanum-nickel as low-temperature side MH2, lanthanum-nickel-aluminum as high-temperature side MH1) 10 each
kg each was prepared and placed in a pressure vessel (reported pressure 9.9 kg/cm2) containing a fin-tube heat exchanger, and piping was installed as shown in Figure 3. Here, the fin tube heat exchanger has the same heat transfer area for all four MH containers. Hot water at 105°C is used as the driving heat source, and the heat generated during hydrogen storage is radiated to the atmosphere using water using a radiator installed outside. Also, since cold heat is generated from MH2, it is guided to a cooling radiator using an organic heat transfer liquid. An electric vibrator was installed in each MH container, and the amount of vibration of each was made variable by inverter control. A commercially available vibration device for concrete placement (motor 30W) was used.

The operating cycle of this device is basically the same as that shown in FIG. 1, but due to fluctuations in outside temperature,
■Heating medium temperature is affected. It was also found that the driving heat source temperature fluctuated irregularly from a maximum of 115°C to a minimum of 95°C. Therefore, the maximum and minimum differences between the driving heat source temperature and the radiating heat medium temperature in the cycle are shown in (1) and (2) in FIG. 5, and the cooling heat medium temperature ■ is also greatly affected.

In the operation shown in (1) of FIG. 5, the temperature difference between the heating medium and the alloy for MH1 is relatively large, whereas for MH2
The temperature difference between ■ and ■ could not be maintained, and hydrogen storage and desorption were slow as it was. Therefore, in MH1, the amount of vibration is 0.
I set it as low as 5G, and set it as high as 3.5G for MH2. The storage and release times were each 5 minutes, and the total cycle time was 10 minutes. The amount of cooling heat obtained by this operation was 3080 kcal/hr.

In the case of FIG. 5(2), the driving heat source temperature was lowered, and since it was daytime, cooling was performed under poor conditions in which the heat radiation temperature did not decrease. The difference between the driving heat medium temperature and the heat radiation heat medium temperature decreased to 95°-30°=65°, so MH
The vibration of 1 was increased to 1.0G. The vibration of MH2 is shown in Figure 5.
Same as (1), it was 3.5G. The storage and release times were 5 minutes each, and the total cycle time was 10 minutes. The amount of cooling heat obtained by this operation was 2300 kcal/hr.

[0021]

[Comparative example] Driving heat medium temperature: 115°C, heat dissipation heat medium temperature: 2
Under the same temperature conditions as 5° C. and FIG. 5(1), cooling operation was performed in the same apparatus with the vibrations of the four MH containers set equally at 1.0 G.

[0022]

Effects of the Invention According to the present invention, in an MH-based cooling device or heat pump, it is possible to control the amount of hydrogen generation and storage in the high-temperature side alloy and the low-temperature side alloy almost equally, thereby reducing the amount of hydrogen exchanged due to excessive pressure rise or pressure drop in the container. It became possible to prevent the decline in At the same time, it has become possible to change the amount of heat output due to changes in heat source temperature and heat radiation temperature by changing the vibration conditions of each MH container.

The significance of the present invention lies in the fact that it adds a new control method to the heat utilization system, which was conventionally determined based on the characteristics of the MH and the specifications of the heat exchanger, etc., and greatly expands the applications of the MH heat utilization system. It is.

[Brief explanation of the drawing]

Figure 1 is a diagram of temperature and pressure operation in a cooling system using a hydrogen storage alloy, Figure 2 is a diagram showing the temperature of each part during cooling operation, Figure 3 is a diagram showing the flow of hydrogen and heat in the cooling system, and Figure 4 is a diagram showing the flow of hydrogen and heat in the cooling system. FIG. 5 is a diagram showing an example of the relationship between vibration acceleration and the apparent overall heat transfer coefficient between the heating medium and the MH, and FIG. 5 is a temperature-pressure operation diagram in the cooling device of the embodiment.

Claims (1)

[Claims] Claim 1: When operating a heat pump or refrigerator using a hydrogen storage alloy, vibration is applied to the hydrogen storage alloy on the side where the temperature difference between the heating medium and the hydrogen storage alloy is small to increase the heat transfer coefficient and the temperature is increased. A method of operating a heat utilization system using a hydrogen storage alloy, characterized in that the product of the difference and the heat transfer coefficient is made to match on the high temperature side and the low temperature side.