JP4652449B2 - Refrigeration equipment - Google Patents

Description

  The present invention relates to a refrigeration apparatus, and more particularly to a refrigeration apparatus including an expander that recovers expansion energy of a refrigerant.

  In recent years, a power recovery type refrigeration cycle has been proposed in order to further improve the efficiency of the refrigeration cycle. According to Patent Document 1, the input of the compressor is reduced by using the expander to recover the expansion work of the refrigerant. An expander used for a power recovery type refrigeration cycle is disclosed in Patent Document 2, for example.

  FIG. 4 shows a conventional refrigeration apparatus described in Patent Document 1, which includes a compressor 1, a gas cooler (or radiator) 2, an expander (or expansion device) 3, and an evaporator 5. These are connected in series to form a refrigeration cycle. The expander 3 is connected to the generator 4. The compressor 1 is driven by driving means (not shown) such as a rotary electric motor or a traveling engine. The refrigerant is compressed from room temperature low pressure to high temperature high pressure in the compressor 1 and then cooled to room temperature high pressure in the gas cooler 2. Thereafter, the refrigerant expands to a low temperature and a low pressure in the expander 3, is then heated to normal temperature by the evaporator 4, and returns to the compressor 1 again. In the expander 3, the expansion work of the refrigerant is collected and the generator 4 is driven to generate electric power.

  FIG. 5 shows a Mollier diagram of a conventional refrigeration apparatus. In the expander 3, since the refrigerant expands in a short time of 10 ms to 20 ms, it can be regarded as adiabatic expansion, and the refrigerant decreases the enthalpy along the isentropic line (c → d). Therefore, the specific enthalpy difference in the evaporator 5 is increased by an amount corresponding to the expansion work Δiexp, and the refrigerating capacity can be increased, as compared with the case where the expansion valve is used to simply change the isenthalpy without causing expansion work. It becomes. Further, the expander 3 can reduce the electric power necessary for driving the compressor 1 by causing the generator 4 to generate electric power from the expansion work Δiexp of the refrigerant and supplying the electric power to the compressor 1. As described above, the COP (coefficient of performance) of the refrigeration apparatus can be improved by increasing the refrigerating capacity of the evaporator 5 and reducing the driving power of the compressor 1.

  As is clear from FIG. 5, in the expander 3 used in the refrigeration apparatus, the inlet c is a single-phase refrigerant and the outlet d is a two-phase (gas-liquid) refrigerant, so that a phase change occurs during the expansion process.

  FIG. 6 is a graph showing the relationship between the working chamber volume and pressure of the expander used in the conventional refrigeration apparatus described in FIG. In the first half of the expansion process, the supercritical phase or liquid refrigerant (single-phase refrigerant) close to the incompressible fluid expands, so the pressure drop with respect to the volume change is large, but in the second half of the expansion process, the refrigerant Larger expansion is caused by causing a phase change from the liquid phase to the gas phase while lowering, so the pressure drop with respect to the volume change is small.

JP 2000-329416 A JP 2004-257303 A

  Regarding the phase change of the refrigerant, the phase change occurs from the heat transfer surface in the nucleate boiling inside the refrigerant tube provided in the evaporator 5 of the refrigeration apparatus in FIG. 4, the surface shape of the heat transfer surface and the heat flux. It is generally known that affects phase change. However, since the phase change of the refrigerant in the expander 3 occurs in the process of adiabatic expansion along the isentropic line in FIG. 5, there is no heat flux from the wall surface, and the wall surface of the working chamber has fluid loss and sliding loss. Since it is formed smoothly for reduction, the phase change occurs from the inside of the refrigerant as well as from the wall surface. In order to generate bubble nuclei inside the fluid, a superheated liquid that stores energy by becoming a temperature higher than the saturation temperature is required, and a phase change delay occurs in the process of generating the superheated liquid. When the phase change is delayed, the expansion coefficient of the refrigerant accompanying the phase change is reduced, and thus the problem that the expansion work of the refrigerant recovered by the expander 3 is reduced occurs.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a highly efficient refrigeration apparatus capable of preventing a phase change delay.

In order to achieve the above object, a refrigeration apparatus according to the present invention forms a refrigeration cycle by sequentially connecting a compressor, a gas cooler, an expander that recovers refrigerant expansion energy, and an evaporator in series. The refrigerating apparatus is provided with a mesh-like or rod-like fluid stirring member at the inlet of the expander, and the refrigerant is carbon dioxide and the refrigerant is mixed with nitrogen as 1% by weight or less as a non-condensable gas. It is characterized by that.

  With this configuration, the non-condensable gas mixed in the refrigerant becomes a bubble nucleus for causing a phase change from the inside of the refrigerant of the expander, and a phase change delay can be prevented, thereby providing a highly efficient refrigeration apparatus. be able to.

  The boiling point of the non-condensable gas is preferably −40 ° C. or lower. Even when the refrigeration apparatus according to the present invention is used for hot water supply and heating applications in cold regions, the non-condensable gas can be used with a sufficient margin, so that the effect of preventing phase change delay can be increased. .

  The non-condensable gas should be nitrogen. Nitrogen is relatively inexpensive and readily available.

  The concentration of the non-condensable gas is preferably 1% by weight or less.

  The refrigeration apparatus can be provided with a fluid stirring member at the inlet of the expander. The fluid stirring member acts to increase the number of bubble nuclei for phase change by decomposing non-condensable gas bubbles mixed in the refrigerant into small bubbles, thereby increasing the effect of preventing phase change delay.

  The refrigerant is preferably carbon dioxide. When carbon dioxide is used, the differential pressure between the high and low pressures of the refrigeration system can be increased, and by using a non-condensable gas, phase changes that have occurred in conventional refrigeration systems that use only carbon dioxide as a refrigerant. Delay can be prevented.

  First, although the refrigeration apparatus of FIG. 4 is described as a conventional one, this can also be applied to the present invention. That is, in the refrigeration apparatus according to the present invention, the compressor 1, the gas cooler or the radiator 2, the expander or the expansion apparatus 3, and the evaporator 5 are sequentially connected in series to form a refrigeration cycle. . The refrigeration apparatus according to the present invention also includes a generator 4 connected to the expander 3. The refrigeration apparatus according to the present invention is different from the conventional refrigeration apparatus in that a refrigerant mixed with a non-condensable gas is used.

  The non-condensable gas always maintains a gas state regardless of the refrigerant state (pressure and temperature). Here, the non-condensable gas is defined as a substance whose condensation temperature is equal to or lower than the lowest temperature that can be taken by the refrigerant during operation of the refrigeration apparatus. Since the non-condensable gas is always a gas even when the refrigerant is in a liquid state, in the expander 3, the non-condensable gas becomes a bubble nucleus for causing a phase change from the inside of the refrigerant, and prevents the above-described phase change delay from occurring. be able to. As other requirements for non-condensable gases, it is desirable that both the reactivity with the refrigerant and the solubility in the refrigerant are very small and there is no influence on the refrigerant. In addition, the amount of non-condensable gas mixed in the refrigerant is excessive when the amount of the non-condensable gas is deteriorated. The number of bubble nuclei is reduced, and the effect of preventing phase change delay is reduced. Therefore, the amount of noncondensable gas needs to be an appropriate amount.

<Example>
An experiment was conducted in the case where carbon dioxide was used as the refrigerant circulating in the refrigeration cycle and 1.0% by weight of nitrogen was mixed as a non-condensable gas.

  The boiling point of nitrogen at atmospheric pressure is −195.8 ° C., the critical point at 3.4 MPa is −147.0 ° C., and the temperature of −40 ° C. or higher that carbon dioxide in a general refrigeration cycle can take is nitrogen. Is always a gas. In addition, the reactivity and solubility of nitrogen to carbon dioxide are very small.

  The experiment was performed using the refrigeration cycle of FIG. 4 in a state where 100 g of nitrogen was first sealed in a vacuum-evacuated cycle and then 10 kg of carbon dioxide as a refrigerant was sealed. As the expander 3, a swing type expander having a suction volume of 11.8 cc was used.

  1 to 3 are graphs showing experimental results. In the figure, “with NC-1” means that 1.0% by weight of nitrogen is mixed in carbon dioxide, and “without NC-1” means that pure carbon dioxide is used as a refrigerant. Means. In FIG. 1, the horizontal axis indicates the load amount (W) connected to the expander 3, and the vertical axis indicates the rotational speed (rpm) of the expander 3. For example, when the rotation speed of the expander 3 is set to around 1800 rpm, “with NC-1” can increase the load from 200 W to 300 W. Further, even when the rotation speed of the expander 3 is set to around 900 rpm, “with NC-1” can improve the load from 900 W to 1000 W. That is, the graph of FIG. 1 shows that the generated power of the generator 4 connected to the expander 3 is improved by the addition of 1.0 wt% nitrogen.

  FIG. 2 is a graph showing the relationship between the temperature of carbon dioxide at the inlet of the expander 3 and the efficiency of the expander 3. This graph shows that the addition of 1.0 wt% nitrogen improves the efficiency of the expander 3 in the entire temperature range tested.

  FIG. 3 is a graph showing the relationship between the temperature of carbon dioxide at the inlet of the expander 3 and the COP of the refrigeration cycle. COP is a coefficient of performance defined by the ratio of the amount of heat obtained by the evaporator 5 and the power supplied to the compressor 1 after subtracting the power recovery in the expander 3, and the larger this value, the higher the efficiency of the refrigeration cycle. . FIG. 3 shows that the addition of 1.0 wt% nitrogen improves COP and improves the efficiency of the refrigeration cycle in the entire temperature range tested. According to another experiment, the addition of 1.0 wt% or less nitrogen to the refrigerant is preferred.

  As is apparent from the above, it is possible to improve the expander efficiency and improve the COP of the refrigeration cycle by mixing the non-condensable gas into the refrigerant.

  In the above-described embodiment, the expander 3 is connected to the generator 4. However, the shaft (not shown) of the expander 3 and the shaft (not shown) of the compressor 1 are axial. The structure connected so that it may correspond to may be sufficient.

  Further, a mesh-like or rod-like fluid stirring member may be inserted at the inlet of the expander 3. The fluid agitation member breaks the non-condensable gas bubbles mixed in the refrigerant into small bubbles, increasing the number of bubble nuclei for phase change, increasing the effect of preventing phase change delay, and highly efficient refrigeration An apparatus can be provided.

  In the above-described embodiment, a swing type expander is used as the expander 3, but other positive displacement expanders such as a scroll type, a rolling piston type, and a sliding vane type may be provided.

  The non-condensable gas is not limited to nitrogen, and a rare gas such as argon or neon may be used.

  Although the present invention has been sufficiently described based on specific examples with reference to the accompanying drawings, various modifications can be understood by those skilled in the art. Accordingly, unless such modifications depart from the spirit and scope of the present invention, they are intended to be included in the present invention.

  The refrigeration apparatus according to the present invention is not limited to a refrigeration apparatus or a refrigeration apparatus, and can be applied to a general air conditioner or a heat pump for a water heater.

A graph showing the relationship between the load applied to the expander and the rotation speed of the expander Graph showing the relationship between the carbon dioxide temperature at the inlet of the expander and the expander efficiency Graph showing the relationship between the temperature of carbon dioxide at the expander inlet and the COP of the refrigeration cycle Schematic of refrigeration apparatus according to the present invention and a conventional refrigeration apparatus Mollier diagram of conventional refrigeration equipment Graph showing the relationship between the working chamber volume and pressure of an expander used in a conventional refrigeration system

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Compressor 2 Gas cooler 3 Expander 4 Generator 5 Evaporator

Claims (1)

A compressor, a gas cooler, an expander that recovers expansion energy of a refrigerant, and an evaporator are sequentially connected in series to form a refrigeration cycle,
The inlet of the expander is provided with a mesh-like or rod-like fluid stirring member,
A refrigerating apparatus characterized in that the refrigerant is carbon dioxide and nitrogen is mixed in the refrigerant as a non-condensable gas in an amount of 1% by weight or less.

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