RU2148722C1 - Energy cycle with use of mixture - Google Patents

Abstract

FIELD: power engineering; mechanical engineering; engine operating in cyclic process. SUBSTANCE: gas-liquid mixture featuring inverse solubility to temperature. During first working phase, volume of chamber increases, pressure drops and mechanical work is carried out. At increase in volume and drop of pressure liberation of gas phase takes place, accompanied by liberation of heat, so amount of supplied heat can be reduced. During compression gas dissolves in liquid, absorbing the heat, thus reducing compression work. EFFECT: enhanced thermodynamic efficiency of cycle. 2 cl, 5 dwg

Description

 The invention relates to the field of energy and can be used in engine building, in particular in engines operating in a circular process.

 A known method of operating a heat engine in which the working cycle is carried out by introducing the working substance into the space closed by the working wall at the temperature of the boiler, the volume of which in the first working phase is expanded by moving the moving wall from internal dead center to external dead center, and in the second working phase through the movement inside the movable wall is compressed to the initial volume to the internal dead point, while the working substance is brought to the temperature of the boiler through heat transfer. As a working substance, a gas-liquid solution is used (see Russian patent application 94009482/06 (009394), 1994).

 The disadvantage of this method is the low efficiency and difficulties in the implementation of the isothermal cycle.

 A known method of operation of a heat engine using a gas-liquid solution having inverse temperature solubility as a working substance. In the first working phase, the solution expands to complete work with subsequent heat transfer, and in the second working phase it is compressed to its original volume, after which it is brought to its original temperature by heat exchange (see U.S. Patent No. 4,779,424, F 01 K 25/06, 12/27/83.

 The disadvantage of this method is that in the field of reverse solubility, the cycle can be carried out at high pressures, which leads to an increase in the weight of the power plant.

 The aim of the present invention is to increase thermodynamic efficiency.

This goal is achieved by the fact that in the energy cycle, using as a working fluid a mixture of substances in the form of a gas-liquid solution, in which in the first phase at the initial temperature the working fluid expands to complete work with subsequent heat transfer, and in the second phase it is compressed, after which the heat transfer is brought to its initial temperature, a mixture consisting of several components in the liquid and gas phases is used as a working fluid, while the proportions of the components in the mixture, d apazone pressures and temperatures of the working fluid is selected so that
- in the process of isothermal expansion while simultaneously registering the input heat, the ratio is satisfied:
V ₂ (P ₁ -P ₂ ) ≥Q,
where Q is the summed heat
P ₁ - initial pressure
P ₂ - final pressure
V ₂ is the final volume.

FIG. 1 shows a cycle consisting of expansion isotherms, cooling isobars and compression adiabats in which volumes under isobaric cooling relate to the temperatures of the beginning and end of cooling V ₂ / V ₃ = T ₂ / T ₃ .

FIG. 2 shows the experimental dependences of the heat input and the isotherm at a temperature of 30 ^° C. of a nitrogen-butane mixture at a gas component concentration of 0.3; from a pressure of 100 kg / cm ² to a pressure of 30 kg / cm ² .

FIG. 3 depicts a PV diagram of a thermodynamic cycle,
FIG. 4 shows curves of constant efficiency of cycles when the temperature of isothermal expansion changes from -30 ^o C to 70 ^o C and isothermal compression at -30 ^o C in the range of pressures from 100 to 20 kg / cm ² , counting the upper pressure of 100 kg / cm ² .

FIG. 5 depicts a PV diagram of a reversible thermodynamic cycle built on the experimental dependences of adiabatic expansion and compression, mixes nitrogen - butane at a gas component concentration of 0.2 from a pressure of 250 kg / cm ² to a pressure of 50 kg / cm ² in a temperature range from 30 ^o C to - 29 ^o C.

 In the energy cycle, the working fluid is a mixture of substances consisting of several components that are in equilibrium in the liquid and gas phases. When pressure and temperature change, equilibrium processes of changes in the quantity and concentration of phases occur that occur with thermal processes, the values of which depend on the choice of pressure and temperature. The use of such a mixture as a working fluid in a closed cycle due to the presence of internal processes for measuring the concentration of phases that occur with thermal effects makes it possible to accumulate part of the heat during compression, and to release heat during expansion, which can significantly increase the thermodynamic efficiency of the cycle.

Consider the cycle depicted in FIG. 1, consisting of expansion isotherms 1-2, cooling isobars 2-3 and compression adiabats 3-1. We choose the cycle mode in which the volumes during isobaric cooling relate as the temperatures of the beginning and end of cooling V ₂ / V ₃ = T ₂ / T ₃ . During isothermal expansion, heat Q is supplied.

Максимальный теоретический КПД составит

так как температура отвода тепла (T₂+T₃)/2 при теплоемкости C_p2 = C_p3, что для выбранных условий справедливо.The initial pressure P ₁ and the final pressure P ₂ are chosen so that the area of the cycle is equal to the area of the triangle with the base (V ₂ -V ₃ ) and height (P ₁ -P ₂ ). This is practically carried out at P ₁ ≤2P ₂ . The efficiency of such a cycle will be:

The maximum theoretical efficiency will be

since the temperature of heat removal (T ₂ + T ₃ ) / 2 at a specific heat of C _p2 = C _p3 , which is true for the selected conditions.

Equating η = η _max, we obtain the condition under which the efficiency of our cycle is maximum.

или
V₂(P₁-P₂)=Q.

or
V ₂ (P ₁ -P ₂ ) = Q.

 This condition is a search criterion for the working fluid.

In FIG. 2, PV calibration shows the experimentally obtained isotherm of 30 ^° C with an expansion of 100 kg / cm ² to 30 kg / cm ^{2 of a} mixture consisting of two components - nitrogen in the gas phase and butane in the liquid phase at a gas component concentration of 0.3 and supply my heat is in the QV calibration. To obtain maximum efficiency at P ₁ = 60 kg / cm ² and P ₂ = 30 kg / cm ^{2 the} supplied heat must be:
Q = V ₂ (P ₁ -P ₂ ) = 28 kJ / kg,
and experimental data give a value of Q = 13 kJ / kg, that is, the real efficiency is greater than the maximum. Thus, the criterion for choosing the proportion of components in the mixture, the range of pressures and temperatures of the working fluid is the expression:
V ₂ (P ₁ -P ₂ ) ≥Q,
In FIG. Figure 3 shows the energy cycle consisting of two isotherms and two isobars.

Compression 1 - 2 causes an increase in the fraction of the liquid phase, an increase in the concentration of the liquid phase and an increase in the concentration of the gas phase, then we heat it at a constant pressure of 2 - 3, at which an increase in the proportion of the gas phase, an increase in the concentration of the liquid phase and a decrease in the concentration of the gas phase. Then, the working fluid 3–4 is compressed, in which there is an increase in the fraction of the gas phase with a decrease in the concentration of the liquid phase and an increase in the concentration of the gas phase. Then, 4-1 is cooled to the initial temperature with an increase in the fraction of the liquid phase and an increase in the concentration of the gas phase. During compression, the amount of heat Q ₂ is removed, during the heating process, the amount of heat Q ₃ is supplied, during the expansion process, the amount of heat Q _{1 is} supplied and during the cooling process, the amount of heat Q ₄ is removed. The cycle does the job L. In the processes of expansion and contraction, when the concentration in the liquid and gas phases changes, thermal effects occur that depend on pressure and temperature. This is a specific property of a given working fluid. Using these properties, it is possible to find modes, for example, of isothermal expansion, when the heat supply to ensure a constant temperature is minimal, since heat is released during internal processes.

Based on the experimental data on the expansion isotherms of the nitrogen-butane mixture in various modes according to the criterion V ₂ (P ₁ -P ₂ ) ≥Q, a working fluid with a nitrogen concentration of 0.3 was selected and an analysis of energy cycles consisting of two isotherms and two isobars at constant compression temperature - 30 ^o C, constant upper pressure of 100 kg / cm ² and variable lower pressure and expansion temperature for the working fluid of the same composition.

In FIG. 4 shows the efficiency curves when changing the expansion temperature from -30 ^o C to 70 ^o C and lower pressure from 100 to 20 kg / cm ² . As can be seen from the graph, the efficiency of the cycle can be changed by choosing the operating mode, which allows you to find the most efficient cycle for the heat engine.

 Thus, choosing the composition of the composite working fluid, we provide the necessary characteristics of the isotherms, which are characterized by the efficiency shown in FIG. 4.

 A characteristic feature of the cycle resulting from the data of FIG. 4, is the dependence of efficiency on pressure at constant upper and lower temperatures.

The real cycle is limited by two adiabats and two isobars. In FIG. Figure 5 shows a cycle within the pressure range from 250 to 50 kg / cm ² for a nitrogen-butane mixture at a nitrogen concentration of 0.2. The adiabatic compression 1 - 2 starts at a temperature of -29 ^o C at a pressure of 50 kg / cm ² and ends with a pressure of 250 kg / cm ² with a temperature of the mixture -21 ^o C. The adiabatic expansion 3 - 4 begins with a pressure of 250 kg / cm ² and ends a pressure of 50 kg / cm ² with an initial temperature of 30 ^o C and a final temperature of 20 ^o C. Heated at a constant pressure of 2 - 5 is carried out by regeneration during the selection of heat 4 - 6 with isobaric cooling 4 - 1. The temperature of the car 6 is -21 ^o C, the temperature of point 5 is 20 ^o C.

Максимальный теоретический КПД приведенного цикла при средней температуре подвода тепла 25^oC и средней температуре отвода тепла -25^oC должен составлять

то есть меньше полученного при таких же перепадах температур.In the cycle, heat is supplied in the process 5 - 3, is removed in the process 6 - 1 and partially 4 - 6, since the heat 2 - 5 is less than the heat 4 - 6. In this cycle, the supplied heat is Q _5-3 = 27.2 kJ / kg , and the work of the cycle is L = 9.7 kJ / kg, the efficiency of the cycle will be

The maximum theoretical efficiency of the reduced cycle at an average heat supply temperature of 25 ^o C and an average heat removal temperature of -25 ^o C should be

that is, less than that obtained at the same temperature differences.

Thus, applying the condition V ₂ (P ₁ -P ₂ ) ≥Q, when choosing the components of the mixture of the working fluid, the characteristics of heat engines can be significantly improved.

Claims (1)

The energy cycle, in which a mixture of substances in the form of a gas-liquid solution is used as a working fluid, in which in the first phase at the initial temperature the working fluid expands to complete work with subsequent heat transfer, and in the second phase it is compressed, after which it is brought to the initial temperature through heat exchange , characterized in that as the working fluid use a mixture consisting of several components in the liquid and gas phases, with the proportions of the components in the mixture, the range is yes the phenomena and temperatures of the working fluid are chosen so that in the process of isothermal expansion while registering the input heat, the relation
V ₂ (P ₁ - P ₂ ) ≥ Q,
where Q is the supplied heat;
P ₁ - initial pressure;
P ₂ is the final pressure;
V ₂ is the final volume.

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