CN107982948B - Method for reducing or increasing saturated vapor pressure by using electrostatic field - Google Patents

Method for reducing or increasing saturated vapor pressure by using electrostatic field Download PDF

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CN107982948B
CN107982948B CN201711273902.2A CN201711273902A CN107982948B CN 107982948 B CN107982948 B CN 107982948B CN 201711273902 A CN201711273902 A CN 201711273902A CN 107982948 B CN107982948 B CN 107982948B
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vapor pressure
electrostatic field
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CN107982948A (en
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韩光泽
蒙健佳
王琳
陈明东
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South China University of Technology SCUT
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
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Abstract

The invention discloses a method for reducing or increasing saturated vapor pressure by using an electrostatic field, which is characterized in that under the condition of unchanging temperature, when the saturated vapor pressure of a gas-liquid two-phase balance system needs to be reduced, the electrostatic field is applied to a phase interface of the gas-liquid two-phase balance system in parallel, or the electrostatic field is only applied to a liquid phase area of the gas-liquid two-phase balance system; when the saturated vapor pressure of the gas-liquid two-phase balance system needs to be improved, an electrostatic field is vertically applied to a phase interface of the gas-liquid two-phase balance system. The invention achieves the purpose of reducing or increasing vapor pressure under the condition of constant temperature by changing the action direction of the electrostatic field, improves the distillation efficiency and strengthens the heat and mass transfer process.

Description

Method for reducing or increasing saturated vapor pressure by using electrostatic field
Technical Field
The invention relates to a method for changing saturated vapor pressure of a gas-liquid two-phase system by an electrostatic field, in particular to a heat and mass transfer process for strengthening gas-liquid phase change by the electrostatic field, which can be applied to the industries of materials, chemical engineering, energy, pharmacy, food and the like.
Background
The phase change process involves both mass and energy transfer, such as phase change heat transfer characterized by boiling and condensation, phase change mass transfer characterized by evaporation and distillation, and the like. The phenomenon of gas-liquid phase transition widely exists in the fields of nature and engineering fields such as materials, energy, chemical industry, food, pharmacy and the like, and the concentration and drying of food and medicines, the distillation separation of chemical industry and the like all relate to the process of gas-liquid phase transition. Distillation separation is a typical gas-liquid phase change process, and is the most common method for separating mixtures in chemical industry and food. The greatest disadvantage of distillation is, however, the high energy consumption, since the distillation operation requires the vaporization and condensation of the liquid mixture to establish a gas-liquid two-phase system; in order to establish a gas-liquid two-phase system, conditions such as high pressure, high temperature, low pressure, and low temperature are sometimes required, which are not easily realized.
Temperature and pressure are two basic macroscopic physical quantities involved in the phase change process, and the traditional method for strengthening the phase change process of gas and liquid is to change the temperature or pressure of a system, which is closely related to equipment investment and energy consumption and is often limited by technology and equipment. In addition, the time and temperature of concentration and drying of foods, medicines and the like are closely related to the quality of products, and some heat-sensitive substances have special requirements on temperature. Therefore, the development of new enhanced technologies to improve the efficiency of the gas-liquid phase transition process and reduce energy consumption is a subject of general interest.
The electric field can effectively change the gas-liquid phase change process, improve the distillation efficiency and strengthen the heat and mass transfer process. The saturated vapor pressure is an important expression of pressure intensity in the gas-liquid phase change process, is one of the most basic physical parameters of the liquid working medium, is important basic data in the chemical production, scientific research and design processes, and the process design of a plurality of engineering processes is closely related to the vapor pressure of the working medium applied by the engineering processes. The influence of the electric field on the pressure in the dielectric system is of great significance for improving the intensified transmission efficiency of the electric field.
Disclosure of Invention
In order to solve the problems of the prior art for strengthening the gas-liquid phase change process, the invention provides a method for reducing or increasing saturated vapor pressure by using an electrostatic field, so that the distillation efficiency is improved, and the purpose of strengthening the heat and mass transfer process is achieved.
The invention is realized by adopting the following technical scheme: a method for reducing or increasing the saturated vapor pressure using an electrostatic field comprising the steps of:
s1, under the condition of unchanged temperature, when the saturated vapor pressure of the gas-liquid two-phase balance system needs to be reduced, an electrostatic field is applied to the phase interface of the gas-liquid two-phase balance system in parallel, or the electrostatic field is applied to the liquid phase region of the gas-liquid two-phase balance system only;
and S2, under the condition of constant temperature, when the saturated vapor pressure of the gas-liquid two-phase balance system needs to be increased, vertically applying an electrostatic field to the phase interface of the gas-liquid two-phase balance system.
Preferably, the gas-liquid two-phase substance of the gas-liquid two-phase equilibrium system is a dielectric substance, such as water, ethanol, benzene, carbon tetrachloride or the like, but is not limited to these four substances.
Compared with the prior art, the invention has the following beneficial effects: the electrostatic field can change the equilibrium pressure of the dielectric system, the pressure decrease or increase is related to the action direction of the electric field, and the pressure change is related to the electric field intensity and the dielectric constant of the substance. For a two-phase system with a planar phase interface, when the direction of the electrostatic field is parallel to the phase interface, the pressure of the phase with a larger dielectric constant is larger; when the direction of the electric field is perpendicular to the phase interface, the pressure of the phase with the larger dielectric constant is smaller. For a gas-liquid two-phase equilibrium system, when the action direction of the electrostatic field is parallel to the phase interface, the vapor pressure is reduced; when the action direction of the electrostatic field is vertical to the phase interface, the vapor pressure rises; when the electrostatic field acts only on the liquid phase portion, the vapor pressure decreases. The vapor pressure of the same substance is reduced by a value far larger than the rising value at the same temperature. The invention achieves the purpose of reducing or increasing vapor pressure by changing the action direction and the action area of the electrostatic field, improves the distillation efficiency and strengthens the heat and mass transfer process.
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FIG. 1 is a schematic diagram of the action direction of an applied electrostatic field parallel to a gas-liquid two-phase interface;
FIG. 2 is a schematic diagram of the action direction of an applied electrostatic field perpendicular to a gas-liquid two-phase interface;
fig. 3 is a schematic diagram of an applied electrostatic field acting only on the liquid phase.
Detailed Description
For a better understanding of the present invention, reference is made to the following description taken in conjunction with the accompanying drawings and examples, which are set forth, however, not to limit the scope of the invention as claimed.
Based on the theoretical basis of the present invention, the method for reducing or increasing the saturated vapor pressure by using an electrostatic field comprises the following steps:
s1, when the saturated vapor pressure of the gas-liquid two-phase balance system needs to be reduced, applying an electrostatic field to a phase interface of the gas-liquid two-phase balance system in parallel;
as shown in figure 1, the container is provided with a gas-liquid two-phase balance system, when the two phases reach balance, the pressure p of the liquid phase isLWith pressure p in the gas phaseGHave a relation between
Figure BDA0001496129170000021
In the formula (1), the reaction mixture is,Etis the electric field strength, epsilon, directed along the two-phase boundaryLIs the dielectric constant, epsilon, of the liquid phase materialGIs the dielectric constant of the gas phase substance, the dielectric constant in vacuum ∈0＝8.854×10-12F/m. The saturated vapor pressure without the action of an electrostatic field at the same temperature is p0Since the liquid phase is nearly incompressible compared to the gas phase, the pressure within the liquid phase is still p under the influence of the electrostatic field0Then the saturated vapor pressure at this time is:
Figure BDA0001496129170000022
the dielectric constant of a liquid phase material is generally greater than the dielectric constant, ε, of a gas phase materialL>εGTherefore has p<p0. That is, the saturated vapor pressure of the two-phase equilibrium system is lowered by the electrostatic field parallel to the phase interface.
S2, when the saturated vapor pressure of the gas-liquid two-phase balance system needs to be improved, an electrostatic field is vertically applied to a phase interface of the gas-liquid two-phase balance system;
as shown in figure 2, under the action of the electrostatic field vertical to the gas-liquid two-phase interface, when the system reaches equilibrium, the pressure p of the liquid phaseLPressure p with gas phaseGThe following relations exist between the following components:
Figure BDA0001496129170000031
the vapor pressure in the absence of an electrostatic field is p0The pressure in the liquid phase under the action of the electrostatic field is still p0The pressure of the gas phase is:
Figure BDA0001496129170000032
since the dielectric constant of liquids is greater than that of gases and is all greater than 1, i.e.. epsilonL>εG>1, therefore, has p>p0(ii) a That is, under the action of an electrostatic field perpendicular to the phase interface,the vapor pressure of the equilibrium system increases.
In this embodiment, the step S1 can be implemented by the following steps: s3, when the saturated vapor pressure of the gas-liquid two-phase balance system needs to be reduced, applying an electrostatic field to the liquid phase region of the gas-liquid two-phase balance system;
as shown in fig. 3, the electrostatic field is only applied to the liquid phase region, and after the system reaches the equilibrium:
Figure BDA0001496129170000033
this is the pressure difference caused when the electrostatic field acts on the liquid phase region of the gas-liquid two-phase equilibrium system. Description of the formula pL＞pGThat is, the pressure intensity of the region with the action of the electrostatic field is larger than that of the region without the action of the electrostatic field. The pressure of the liquid phase before and after the action of the electrostatic field is p0The vapor pressure under the action of the electrostatic field is then:
Figure BDA0001496129170000034
that is, when the electrostatic field acts only on the liquid phase, the vapor pressure decreases.
In the present invention, the liquid phase substance of the gas-liquid two-phase equilibrium system can be any dielectric substance, such as water, ethanol, benzene or carbon tetrachloride, etc., which will be further described below by way of example.
Example 1
In this example, water was selected for explanation, and the saturated vapor pressure of water was 10.10kPa at a temperature of 46 ℃. In a size of 106Under the action of a V/m electrostatic field, when the direction of the electric field is parallel to a gas-liquid interface, the vapor pressure is 2.83kPa, which is reduced by 7.27kPa and 72.0%; when the direction of the electric field is vertical to the gas-liquid interface, the vapor pressure is increased by 2.87Pa and increased by 0.028%; when the electric field was applied to the liquid phase portion only, the vapor was reduced by 7.58kPa, 75.05%.
The saturated vapor pressure of water at 100 ℃ was 101.42 kPa. In a size of 106When the direction of the electric field is parallel to the gas-liquid interface under the action of the V/m electrostatic fieldWhen the vapor pressure is 96.99kPa, the vapor pressure is reduced by 4.43kPa and 4.37%; when the direction of the electric field is vertical to the gas-liquid interface, the vapor pressure is increased by 2.85Pa and is increased by 0.0028 percent; when the electric field was applied to the liquid phase portion only, the vapor was reduced by 4.67kPa, 4.6%.
Example 2
Ethanol is used for illustration in this example.
The saturated vapor pressure of ethanol was 10kPa at a temperature of 27.5 ℃. In a size of 106Under the action of a V/m electrostatic field, when the direction of the electric field is parallel to a gas-liquid interface, the vapor pressure is 9.18kPa, which is reduced by 0.82kPa and 8.2%; when the direction of the electric field is vertical to the gas-liquid interface, the vapor pressure is increased by 2.72Pa and increased by 0.027%; when the electric field is applied to the liquid phase part only, the steam is reduced by 0.923kPa, and the steam is reduced by 9.23%.
The saturated vapor pressure of ethanol at a temperature of 78.0 ℃ was 100 kPa. In a size of 106Under the action of a V/m electrostatic field, when the direction of the electric field is parallel to a gas-liquid interface, the vapor pressure is 99.47kPa, which is reduced by 0.53kPa and 0.53 percent; when the direction of the electric field is vertical to the gas-liquid interface, the vapor pressure is increased by 2.66Pa and increased by 0.0027 percent; when the electric field was applied to the liquid phase portion only, the vapor was reduced by 0.62kPa, 0.62%.
Example 3
Carbon tetrachloride is used for illustration in this example.
The saturated vapor pressure of carbon tetrachloride was 10kPa at a temperature of 15.8 ℃. In a size of 106Under the action of a V/m electrostatic field, when the direction of the electric field is parallel to a gas-liquid interface, the Pa is reduced by 2.31 percent and is reduced by 0.023 percent; when the direction of the electric field is vertical to the gas-liquid interface, the vapor pressure is increased by 0.91Pa and increased by 0.0091%; when the electric field was applied to the liquid phase portion only, the vapor was reduced by 7.84Pa, 0.084%.
The saturated vapor pressure of carbon tetrachloride was 100kPa at a temperature of 76.2 ℃. In a size of 106Under the action of a V/m electrostatic field, when the direction of the electric field is parallel to a gas-liquid interface, the Pa is reduced by 1.88 percent and is reduced by 0.0019 percent; when the direction of the electric field is vertical to the gas-liquid interface, the vapor pressure is increased by 0.83Pa and increased by 0.00083%; when electricity is generatedWhen the field only acts on the liquid phase part, the steam is reduced by 6.89Pa and is reduced by 0.0069 percent.
Example 4
This example uses benzene for illustration.
The saturated vapor pressure of benzene was 10kPa at a temperature of 23.7 ℃. In a size of 106Under the action of a V/m electrostatic field, when the direction of the electric field is parallel to a gas-liquid interface, the Pa is reduced by 2.39Pa and is reduced by 0.024%; when the direction of the electric field is vertical to the gas-liquid interface, the vapor pressure is increased by 0.93Pa and increased by 0.0093%; when the electric field is applied to the liquid phase part only, the vapor is reduced by 8.03Pa and is reduced by 0.08%.
The saturated vapor pressure of benzene was 100kPa at a temperature of 79.7 ℃. In a size of 106Under the action of a V/m electrostatic field, when the direction of the electric field is parallel to a gas-liquid interface, the vapor pressure is reduced by 2.02Pa and is reduced by 0.002%; when the direction of the electric field is vertical to the gas-liquid interface, the vapor pressure is increased by 0.86Pa and increased by 0.00086%; when the electric field is applied to the liquid phase part only, the vapor is reduced by 7.20Pa and reduced by 0.0072%.
From the above examples, it is known that the decrease or increase of the vapor pressure is closely related to the action direction of the electrostatic field, and different action directions or action areas lead to different results; the magnitude of the decrease or increase in vapor pressure is determined by the electric field strength and the dielectric constant of the material; the vapor pressure decreases by a much greater amount than it increases under the same conditions. The above embodiments have the following rules:
(1) the larger the dielectric constant is, the more obvious the pressure variation is; i.e., the greater the dielectric constant of the liquid dielectric, the greater the decrease or increase in pressure;
(2) the lower the temperature, the more obvious the pressure change; i.e. the lower the equilibrium temperature of the substance, the greater the decrease or increase in pressure;
(3) the pressure intensity reduction value when the electric field is parallel to the phase interface is far larger than the pressure intensity increase value when the electric field is vertical to the phase interface;
(4) when the electric field only acts on the liquid phase part, the effect of reducing the pressure intensity is more obvious.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims (3)

1. A method for reducing or increasing the saturated vapor pressure using an electrostatic field, comprising the steps of:
s1, under the condition of unchanged temperature, when the saturated vapor pressure of the gas-liquid two-phase balance system needs to be reduced, an electrostatic field is applied to the phase interface of the gas-liquid two-phase balance system in parallel, or the electrostatic field is applied to the liquid phase region of the gas-liquid two-phase balance system only;
and S2, under the condition of constant temperature, when the saturated vapor pressure of the gas-liquid two-phase balance system needs to be increased, vertically applying an electrostatic field to the phase interface of the gas-liquid two-phase balance system.
2. The method for reducing or increasing the saturated vapor pressure by using electrostatic field according to claim 1, wherein the substance of the gas-liquid two-phase equilibrium system is dielectric.
3. The method of reducing or increasing the saturated vapor pressure using electrostatic field according to claim 2, wherein the dielectric is water, ethanol, benzene or carbon tetrachloride.
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