WO2015143590A1

WO2015143590A1 - Solar radiation energy heat engine

Info

Publication number: WO2015143590A1
Application number: PCT/CN2014/000798
Authority: WO
Inventors: 邱纪林
Original assignee: 邱纪林
Priority date: 2014-03-26
Filing date: 2014-08-26
Publication date: 2015-10-01
Also published as: CN104949382A

Abstract

A solar radiation energy heat engine recovers, by means of expansion of an expander, expansion work by using carbon dioxide as a working medium. An evaporation end of the heat engine is serially connected to a condenser by means of a heat pipe sleeve type heat exchanger. A low temperature generated by the working medium on the evaporation end by absorbing heat from an environmental heat source is transferred to the condenser, and as a low-temperature heat source of the heat engine, is subjected to heat exchange with the expanded working medium, so that condensation latent heat of the expanded working medium is released. The condensed low-temperature and low-pressure working medium enters an evaporator through a working medium pump, is subjected to heat exchange with the environment to recover heat energy, and enters a next cycle.

Description

Solar radiant heat engine

Technical field

The invention relates to a method for effectively utilizing solar radiation energy by using carbon dioxide as a working medium, expanding through an expander, and recovering expansion work, and the working fluid after work is replenished by internal heat exchange with the ambient temperature to enter the next cycle.

Background technique

The solar radiant energy is huge, and the total annual energy consumption of human beings is only equivalent to 60 minutes of solar energy that the sun shines on the earth. At present, solar energy has two methods of photovoltaic, photothermal, and they all use sunlight. The former uses the photoelectric effect to directly convert part of the spectrum of sunlight into electricity. In the latter case, the high-temperature heat generated by focusing the sunlight by a heat engine is converted into mechanical motion, and the generator generates electricity. These two methods are limited by photoelectric conversion efficiency, illumination time, solar current density, etc., and there are insurmountable hard constraints, that is, it is necessary to increase the lighting area to obtain more solar energy.

In fact, in addition to atmospheric scattering and absorption of airborne clouds, nearly 70% of solar radiation is received by shallow soils, water systems, and the atmosphere, and the reserves are huge. In the absence of sunlight, these stored solar energy still exists in the form of heat. However, solar radiant energy - ambient temperature is low grade heat, and it is necessary to find effective and economical methods of utilization.

Summary of the invention

According to the second law of thermodynamics "it is impossible to transfer heat from a low temperature object to a high temperature object without any other influence". “It is impossible to take heat from a single heat source to completely convert it into useful work without other effects”. The heat engine must use the ambient temperature to do work and must have a low temperature environment to form an effective temperature difference with the ambient temperature. Under the effect of temperature difference, the ambient temperature spontaneously releases energy into the low temperature environment. Manufacturing low temperatures requires heat absorption from the object until its temperature is below ambient temperature. The phase change process of matter, such as solid melting, liquid gasification, and solid sublimation, requires absorption of heat and low temperature. In addition, throttling, eddy current, thermoelectric effects, etc. can also produce low temperatures.

Throttle expansion refers to the process of moving a fluid (gas, liquid or two phases) at a higher pressure to a lower pressure direction through a throttle valve, and causing a large pressure drop due to local resistance. The throttling expansion consumes the internal energy of the working medium and outputs the work externally, causing the working medium pressure, the temperature to decrease, and the enthalpy value to decrease. The heat absorption capacity of the working medium to reduce the energy increase is called the expansion cooling capacity. The amount of expansion refrigeration is equal to the enthalpy of the decrease in the expansion process of the working fluid.

According to the first law of thermodynamics - energy conservation, energy is required to produce low temperatures. In theory, if a working fluid, its critical point is in the ambient temperature range, the ambient temperature can be used as the working temperature, and the temperature difference and pressure difference before and after expansion are sufficiently large, then we can obtain the ambient temperature from the working temperature. Energy, instead of artificially input compression work, achieves endothermic---exothermic---the thermodynamic cycle of endothermic.

Carbon dioxide can meet the above requirements. Carbon dioxide is environmentally friendly and is the most environmentally friendly refrigerant in addition to water and air. Its ozone depletion potential is zero and its global warming potential is 1. The critical temperature is low, 31.1 ° C, and the critical pressure is high, 7.3 MPa. The three-phase point is -56.6 ° C, the pressure is 0.518 MPa, the boiling point is -78.5 ° C, and the melting point is -56.6 ° C. At an atmospheric pressure, the temperature drops to -78.5 ° C, and the gas is not liquefied to form dry ice (the gaseous state is directly converted into a solid state). Temperature -78 ° C, dry ice sublimation (solid state directly converted to gaseous). In addition, the expansion process of carbon dioxide is different from the usual high pressure gas expansion work. The high-pressure gas relies on the volume expansion to output the shaft work. Although the gas-liquid phase change occurs during the CO2 expansion process, the volume change is not large. The CO2 expansion ratio is small, only 2-4, which is 10% of the conventional working fluid. The expansion power is three times that of conventional working fluid. The evaporation pressure is 10 times that of the conventional working fluid, and the transcritical cycle efficiency is much higher than that of the conventional working fluid.

The solar radiant heat engine cycle includes four processes of evaporation, expansion, condensation, and compression:

Evaporation: The low temperature, low pressure and high liquid pumped into the evaporator by the working fluid pump are compared with the two-phase working medium and the ambient temperature to evaporate and vaporize, increase the volume, increase the pressure, obtain and store the phase change energy, and become the normal temperature and high pressure. High gas compared to working fluid. The heat absorption of the working fluid is refrigeration for the external environment of the evaporator. Gasification of CO2 at one atmosphere can result in desublimation of the outer wall of the evaporator.

Expansion: The working fluid compared with the normal temperature, high pressure and high gas after heat exchange with the ambient temperature expands through the expander and performs work externally. Expansion of the expander is an adiabatic process. Since it cannot absorb heat from the outside, it can only consume the internal energy of the working medium, resulting in a decrease in the pressure and temperature of the working medium and a decrease in the enthalpy. After the work is done, the low temperature, low pressure and high gas are discharged from the expander outlet.

Condensation: low temperature, low pressure, high gas compared to the working medium entering the condenser and the low temperature heat exchange formed by the dry ice sublimation generated by the working medium evaporation process, condensing into low temperature, low pressure, high liquid compared to the working medium.

Compression: low temperature, low pressure, high liquid compared to the working fluid through the screw pump into the heat exchanger and the environment heat exchange, start the next cycle.

The evaporator of the solar radiant heat engine is a three-casing heat exchanger with external insulation, and the heat exchanger is connected in series with the condenser. When the carbon dioxide working medium enters the heat exchanger, the casing can evaporate to form solid carbon dioxide between the outer wall of the inner casing and the inner wall of the intermediate casing, that is, dry ice, -78.5 °C. The outer casing of the built-in fan introduces an ambient heat source to exchange heat with the solid carbon dioxide in the intermediate casing, and the solid carbon dioxide is sublimated by heat (-78 ° C), and the low temperature generated by sublimation cools the heat source of the outer casing. The low temperature heat source of the outer casing is condensed by the heat exchange of the low temperature, low pressure and high gas which are discharged from the condenser and the expander is higher than the triple point. In this way, the heat engine can achieve the ambient temperature of T1, and the low temperature generated by the negative heat of the working medium to absorb heat is T2.

The solar radiant heat engine simulates the operating conditions; the ambient temperature is set to 20 ° C for T1 (expander inlet), the expander outlet is -55 ° C (higher than the triple point), and the working fluid circulates in the two-phase region. The expander (two-stage) expansion ratio is 11, and the inlet-exhaust pressure difference is 5 MPa. The low-temperature, low-pressure, high-liquid compared with the working medium in the heat exchanger and the 20 ° C ambient heat source evaporation vaporization, the pressure rose to 5.7 MPa. After the expansion of the expander releases the internal energy, the pressure at the outlet of the expander drops to 0.52 MPa and the temperature is -55 °C. The low-temperature, low-pressure, high-liquid, which has been condensed and released latent heat, is returned to the heat exchanger via the working fluid pump and then exchanges heat with the environment. The temperature rises from -55 °C to 20 °C, and the pressure rises from 0.52 MPa to 5.7 MPa. The energy that causes the temperature and pressure of the working fluid to rise back comes from the ambient heat source, which means that the compression work of the heat machine is mainly from the ambient temperature, not the compressor.

The working fluid absorbs heat and cooling in the evaporation end, and expands with the expander and expands the expander. This means that the amount of refrigeration at the evaporation end is equal to the amount of expansion (latent heat) of the expander. The latent heat of CO2 solid sublimation is 540KJ/KG, which is greater than the latent heat of vaporization 350KJ/KG, and the solid-gas temperature is -78 °C, which is lower than -56 °C of gas-liquid phase change, which makes the cooling capacity of working fluid evaporative cooling possible as T2. Pressure and latent heat are negatively correlated. In order to achieve effective condensation, the steam can be properly pressurized, for example, from 0.52 MPa to 0.8 MPa, and the liquefaction temperature of carbon dioxide is -42 ° C. If pressurized to 1.6 MPa, carbon dioxide. The corresponding liquefaction temperature is -25 °C.

At present, the carbon dioxide expansion chiller for industrial applications can recover up to 40% of the work of compression (three times that of conventional work), exceeding the heat pump, fan and possible energy input for spent steam pressurization. Part of the energy comes from the ambient heat source. This is not difficult to understand, because the working fluid absorbs heat from the ambient heat source, and the net pressure is increased by nearly 5 MPa, which is greater than the compressor input of 0.28 MPa (0.8 MPa-0.52 MPa) and the energy of the working pump and fan. Sum. The efficiency of the heat engine is not important because the ambient heat source used by the heat engine - solar radiant energy resources is almost infinite and the cost is zero. Obtain more expansion work (power generation) as long as the working fluid flow rate is increased. The solar radiant heat engine is not limited by the lighting area and the illumination time, and can efficiently acquire and utilize solar energy at any time and place.

DRAWINGS

Figure 1. Schematic diagram of the solar radiant heat engine cycle

Figure 2, schematic diagram of a three-casing heat exchanger for solar radiant heat engine

Detailed ways

The solar radiant energy heat machine uses the ambient temperature as the high temperature heat source T1, adopts a low boiling point working fluid including carbon dioxide, and replaces the expansion valve with an expander in the circulation process to recover the expansion work. The heat exchanger is connected in series with a condenser to transfer the working medium at a low temperature generated by vaporization endotherm at the evaporation end to the condenser as a low temperature heat source T2. The heat engine adopts a volumetric, full-flow machine-screw expander and a screw compressor adapted to two-phase flow. In order to maintain the thermal and pressure balance in all aspects of the cycle, the heat engine is operated intermittently.

Claims

The utility model relates to an environment temperature as a high temperature heat source, adopts a low boiling point working medium, expands through an expander, recovers expansion work, and the low temperature and low pressure working medium after work is absorbed from the ambient temperature to recover the internal energy, and enters the heat engine of the next cycle.
According to claim 1, the low boiling point working fluid used includes, but is not limited to, carbon dioxide.
According to claim 2, a tube-and-tube heat exchanger is connected between the evaporator and the condenser, and the low temperature generated by the gasification endothermic at the evaporation end (for the outside of the evaporator) is transmitted to the condenser as a low-temperature heat source. To make the steam condense.
According to claim 3, both the expansion and the compression are carried out by a screw machine.