The Ericsson cycle is named after inventor John Ericsson who designed and built many unique heat engines based on various thermodynamic cycles. He is credited with inventing two unique heat engine cycles and developing practical engines based on these cycles. His first cycle is now known as the closed Brayton cycle , while his second cycle is what is now called the Ericsson cycle. Ericsson is one of the few who built open-cycle engines,  but he also built closed-cycle ones. The following is a list of the four processes that occur between the four stages of the ideal Ericsson cycle:. The aforementioned irreversibility renders the thermal efficiency of these cycles less than that of a Carnot engine operating within the same limits of temperature.
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Stirling cycle and Rankine cycle heat engines are used to transform the heat energy of solar concentrators to mechanical and electrical energy. The Rankine cycle is used for large-scale solar power plants. The Stirling cycle can be used for small-scale solar power plants. The Stirling cycle heat engine has many advantages such as high efficiencyand long service life. However, the Stirling cycle is good for high-temperature difference. It demands the use of expensive materials.
Its efficiency depends on the efficiency of the heat regenerator. The design and manufacture of a heat regenerator are not a trivial problem because the regenerator has to be placed in the internal space of the engine.
It is possible to avoid this problem if we place the regenerator out of the internal engine space. To realize this idea it is necessary to develop the Ericsson cycle heat engine. We propose theoretical model and design of this engine. There are many different sources of sustainable energy. There are different types of solar energy plants. STES consists of a solar concentrator, a heat engine, and a generator of electric current.
Sometimes it also includes an energy storage system. The solar concentrator permits us to obtain the high temperature needed for heat engines. In our previous work we described a low-cost solar concentrator based on multiple triangular flat facets [ 1 — 3 ]. Two prototypes of the solar concentrators are presented in Figures 1 a and 1 b.
Two types of heat engines are usually used now in STES: steam turbines and Stirling engines [ 4 — 7 ]. Steam turbines are good for large power plants, and Stirling engines are proposed for distributed installations.
The Stirling engine in general has high efficiency, long service life, and many other useful properties, but in existing versions it demands high-temperature difference [ 8 ] and for this reason demands expensive materials. This leads to elevated cost of this engine. The Ericsson Cycle Heat Engine at present is investigated not so good as the Stirling Engine, but it has many promising properties and can be considered as a good candidate for STES [ 9 — 11 ]. The scheme of Stirling engine is shown in Figure 2 , it contains a hot cylinder, a heater, a regenerator, a cooler, a cold cylinder, and 2 crankshafts that drive the pistons of the hot cylinder and the cold cylinder.
This displacement ensures the compression of the working liquid in the cold cylinder. After compression the working liquid is displaced from the cold cylinder to the hot cylinder.
During this displacement the working liquid is heated to the temperature of the hot cylinder. In the hot cylinder the working liquid is expanded and produces more work than that was spent during its compression in the cold cylinder. Thereafter the working liquid is moved from the hot cylinder to the cold cylinder. The Stirling engine has a simple structure without valves. But the simple structure of the Stirling engine generates many problems. In theory the Stirling cycle consists of the following processes: i isothermal compression, ii heating at constant volume, iii isothermal expansion, iv cooling at constant volume.
Real Stirling engines at present have no isothermal processes. To approximate the compression and expansion of the working fluid to the isothermal processes it is necessary to increase the thermal conductivity of working fluid, to decrease the rotation speed of the engine or to decrease the size of the cylinders.
To increase the thermal conductivity modern Stirling engines use Hydrogen or Helium instead of air. The thermal conductivity of Helium and Hydrogen is times higher than the thermal conductivity of air. However, it is not sufficient to obtain the compression and expansion processes close to the isothermal process.
Practically it is impossible to decrease the speed of rotation of the engine to obtain isothermal compression and expansion because in this case the specific power the relation of the power to the engine weight drastically decreases.
In principle it is possible to obtain isothermal processes if we decrease the sizes and increase the number of the cylinders. At present we have no technology to produce such engines. At present existing Stirling engines have compression and expansion processes that are closer to adiabatic processes than to isothermal processes.
The difference between these processes is small if the compression and expansion rate is low. For example, if the coefficient of compression is 1. Normal engines with small coefficient of compression have low power. To preserve acceptable power the pressure in all the space of the engine is made high e. These conditions demand the development of a regenerator of very high efficiency.
Real regenerators do not permit us to obtain Carnot efficiency efficiency of an engine divided by efficiency of Carnot cycle of Stirling engines more than 0. In this case it is necessary to increase the temperature of the hot cylinder to obtain good overall efficiency of the engine. High temperature of the hot cylinder demands the use of special materials that increase the cost of the engine. It is possible to propose another method to obtain approximately isothermal processes of compression and expansion.
This method is used in some multistage gas turbines where the gas is cooled during the compression stages and is heated during the expansion stages. The method can also be used in piston engines including relatively low-power engine but in piston engines it demands the use of valves and cannot be realized in Stirling engine, but can be realized in Ericsson engine.
An example of Ericsson engine is described in [ 11 ]. The engine power is It is based on the open cycle; that is, the air from atmosphere enters to the two stage compressor with intermediate cooling. At this temperature the air goes to the atmosphere. The theoretical Ericsson cycle is made up of two isothermal processes and two isobaric processes. As it was mentioned in [ 11 ] this theoretical cycle is not appropriate to study Ericsson engine. To improve real Ericsson cycle it is necessary to decrease compression and expansion rate from 6 in the mentioned engine to 1.
With this compression ratio the adiabatic process has small difference from the isothermal process, but in this case the power of the engine will decrease. To restore the engine power it is possible to make a multistage compression with the intermediate cooling and a multistage expansion with intermediate heating [ 12 , 13 ].
This type of engine is shown in Figure 3. It is possible to increase additionally the engine power if we will use the closed thermal cycle instead of open cycle used in [ 11 ]. The closed cycle permits us to increase the total pressure in the engine space.
The engine presented in Figure 3 consists of 3 compressors, 3 coolers, 3 expanders, 3 heaters, and recuperator. The number of the compressors, expanders, coolers, and heaters can be more than 3.
The coolers are placed at the input of each compressor, and the heaters are placed at the input of each expander. The Ericsson engine uses a recuperator instead of the regenerator that is used in the Stirling engine. The recuperator has two areas: the first area contains high-pressure gas obtained from the compressors and the second area contains low-pressure gas obtained from the expanders. The heat exchanger of the recuperator permits heating of the compressed gas using the heat energy of the expanded gas.
The Ericsson engine works as follows: the working gas that is cooled in the recuperator and in the first cooler is compressed in the first compressor.
The compression rate at this stage is as low as in the Stirling engine. The temperature of the gas at the compressor output is slightly higher than the temperature at the compressor input. After the first compressor the gas flows to the cooler that decreases its temperature.
After that gas flows to the second compressor, where its pressure and temperature increase, but the temperature is returned to its previous value in the third cooler. In principle many stages of compression and cooling may be used to obtain a quasi-isothermal process of compression with high compression rate. A similar process occurs at the expansion of the gas.
The difference is that we use expanders instead of compressors and heaters instead of coolers. The proposed design of the engine permits us to obtain acceptable approximation of isothermal processes preserving high compression and expansion rates and acceptable specific power of the engine.
In this case the influence of the recuperator parameters on the overall performance will be lower than in the Stirling engine, and that is why the Ericsson engine can have higher Carnot efficiency than the Stirling engine. In this engine means the pressure, means the absolute temperature, and means specific volume of the gas in different points shown in Figure 3. The results are presented in Table 1 for different engine versions. This temperature permits us to use synthetic lubrication oils in all parts of Ericsson engine.
Using of lubrication increases the service life and mechanical efficiency of the engine. To create the Ericsson heat engine it is necessary to implement compressors, expanders, coolers, heaters, and recuperator.
In this paper we describe the design of compressors, expanders, and recuperator. The intake piston and exhaust piston periodically open and close the intake windows and exhaust windows.
The compressor takes the gas from the intake port, slightly compresses it, and pushes the gas through the exhaust port. The expander receives the compressed hot gas from the intake port, allows the gas to expand, and pushes it through exhaust port. Low compression and expansion rate in each main cylinder permits us to consider the process as an isotermal one. The main element of microchannel recuperator is its base plate. The base plate is circular plate from the metal with high thermal conductivity e.
This plate contains several circles of holes that form microchannels for compressed and expanded air. Each circle for compressed air excluding external circle is located between two circles for expanded air, and each circle for expanded air excluding internal circle is located between two circles for compressed air. In Figure 5 only two circles are presented. The micro channel recuperator contains many base plates separated by sealing rings Figure 6 in the manner that each zone of compressed and expanded air is hermetically sealed.
In Figure 7 we present the fragment of micro channel recuperator. In this figure stands for the radial distance between the hole circles, is the tangential distance between the holes, is the diameter of micro channel, is the thickness of the disk, and is the step of the disks in the recuperator. The calculations of recuperator parameters are presented in appendix.
Design of Ericsson Heat Engine with Micro Channel Recuperator