 Okay, ladies and gentlemen, my name is Massoud Irod, and I will talk about modeling of turbulent flow through the ejector of a two-stage ejector refrigeration system. First I should say some introduction about the work. The energy requirements from low-cost resources direct us toward using refrigeration cycles instead of conventional systems because in ejector and absorption cycles it's possible to use solar energy, geothermal energy, and also dissipative energies from combustions, for example, systems. And ejector cycles have lower coefficient of performance. Actually, we denote it by COP during the presentation. Yeah, the COP are less than common stream compression cycles, but they need less equipments. It's very important and no lubrication. It's required and also they have low cost of maintenance. So these are the advantages of ejector refrigeration cycles. Here we can see the components of a conventional ejector refrigeration cycle denoted by CERC, a generator, an evaporator, an ejector, a pump, and an expansion valve. So about the ejector, first I should say that ejector is the heart of this system and it's a substitution for mechanical compressors in compression refrigeration systems. It has two essential tasks, the ejector. First, making the vacuum and discharging the fluids. And the other task is to mix the fluids we will see in the next slide. That's how does it work. Actually, it's a simple model of a vacuum pump or compressor, I mean the ejector, without moving parts. It uses the kinetic energy of high pressure fluid before it exists from the generator here and move low pressure fluid and taint, exit from the evaporator and taint it and mix them together. About the generator as mentioned before, using the dissipative energies or solar energy or geothermal energy, we can prepare the heat for the generator. In a refrigeration cycle with solar energy generator, actually solar collectors are used in a closed cycle, another cycle to warm up the operating fluid and then it exchange its heat using a heat exchanger with the refrigerant, which works through the cycle. About the condenser, I can say that as you know, the heat of vaporized refrigerant is exchanged with the condensation fluid, which is water on air, for example, and about the expansion valve, the expansion valve has two tasks. First, to close the liquid refrigerant from condenser to evaporator with the same rate of evaporation and then to make a pressure difference between them, that both of them can work properly. Here is a schematic of an ejector and we can see different parts consist of a nozzle, a constant diameter part section and also a diffuser. Initial fluids, initial fluids, number one flows through the nozzle and expand isentropic holy to pressure P2, we will see in the next slide and move. And this flow moves the intained fluid with pressure PE and TE from the evaporator. This with number two comes from the evaporator and this flow from the nozzle intains is another one with itself. So then the flows are mixed after the chock region of the nozzle, they will mix here and before constant diameter parts, they will mix, they will be mixed. Then supersonic mixed flow of fluid flows through the constant diameter pipe, this section and a normal shock will occur at this section which increase the pressure from supersonic to subsonic. It's better to see it in the next slide. Here is the diagram of pressure and also the velocity. Before this is the isentropic part through the nozzle, then here is a normal shock wave where the pressure increases and the velocity decreases to subsonic from supersonic. This one, this dashed line is the sonic velocity line. Okay, the location of shock wave depends on you know that it depends on the back pressure in the condenser. Finally, the subsonic flow inserts the diffuser and compressed isentropic to pressure P index by C between generator and evaporator. This is how an ejector operates. But the idea here is to use a two-stage ejector for the refrigeration cycle. A two-stage ejector despite the common models doesn't, it doesn't mean to separate the ejectors, to use two separate ejectors in parallel or series. But we use an unconventional model in which the ejectors are measured into a structure. So what happened in a two-stage ejector is that the first stage ejector has no diffuser and it is connected from constant diameter part, its constant diameter part to the second one. So the first one has no diffuser just connected directly from its constant section part to the next ejector. And it consists of a generator but the generator is a two-circuit generator, a condenser again, an expansion valve, circulation pump, circulation pump and a two-stage ejector which can be seen here. And the working fluid is water. So here is a schematic of a two-stage ejector and this is the geometry we modeled and the information of dimensions, the length and the radius, heights can be seen in this table. Also we can see the connection parts between different parts of two-stage ejectors in this figure. So the objectives are using CFD to model and investigate the performance of the ejector based on the cycle operating conditions. Then comparing one stage with two-stage ejector refrigeration cycle using EES software which help us to, the software, the EES software can help us to obtain the transport and thermodynamic properties of working fluid. And then studying the effect of cycle parameters such as evaporator and generator temperatures on the cycle general performance and the system coefficient of performance. Here are the governing equations. I'm not going to explain more about the equations because we use a solver, flange solver. So it's just to say that we use the standard K-epsilon model to compute the turbulent viscosity applying coupled implicit solver. And for near wall treatment we use the standard wall function which gives reasonably accurate results for the wall-bounded high Reynolds flows. Here is the grid network. We use simply structured tetrahedral grids. It's fine mesh near the nazes and some other areas like, such as the walls, near the walls. The solution algorithm is to solve the governing equations by camera calls CFD package flue and ends. They are discretized using the console volume technique. We use the second order of wind discretization scheme for the momentum turbulent kinetic energy and turbulent energy dissipation rate. And also a quick scheme was used for volume fraction. A reduction factor of 0.2 was used for the pressure momentum while it was 0.1 for the slip velocity volume fraction and K-epsilon. We use also experimental data of gas phase holdup to determine the outlet boundary condition for our CFD modeling. The process of solving multi-phase systems now that's inherently it's difficult. So to improve the convergence we have here the initial solution calculation is recommended. It is obtained the initial solution I mean by solving the volume fraction and slip velocity equations only once a converged initial solution was obtained then we enable the volume fraction and the slip velocity equations and also and then the mixture model is computed. The solution is iterated until the convergence is achieved such that the residual of each equation falls below 10 powered by minus 3. Okay there are many several results from the contours, different contours for the mark pressure and so on. And also we have some validation with some analytical and experimental results but here I just present just one contour. Here you can see the counter of Mach number through the ejector of first stage. At the inflow of the ejector yeah we can see that the velocity is very low at the nozzle throat of the first ejector the Mach number reaches unity here and then it increases to supersonic state at the exit the velocity increases significantly and hence the pressure is reduced and the required vacuum is obtained here and this vacuum is required for the suction of the flow from the evaporator. The next slide we can see some good results from cycle coefficient of performance versus evaporator temperature in different generator temperatures. As we can see here as the generator temperature increases in a constant at a constant evaporator temperature we can see that the coefficient of performance decrease since the work of the pump and also the heat of the generator both increase and also the heat of the evaporator slightly decrease as the generator temperature increases. Also the mass ratio of the first and second stage ejector both increase and the ejector exit temperature also increase. All of these results in decrease in the coefficient of performance by increasing the generator temperature. The next slide also we can see that here is the mass ratio of the ejector of the first stage versus evaporator temperature as I mentioned when the evaporator temperature increase the mass ratio decreases and also the ejector exit temperature exhaust temperature also decreases. These happen at constant generator and compressor temperatures when also the evaporator temperature increases the heat of evaporator increase and while the heat of generator and the work of the pump remain constant so the coefficient of performance increase in this case. Here is also the mass ratio for the second stage ejector of second stage versus evaporator temperature the same behavior can be seen here for the second stage. So we see we saw that increasing the generator temperature while the evaporator and condenser temperatures are constant leads to increase in mass ratio at the first and second stage as well as the exhaust temperature of the ejector. Also we showed that at the generator temperature as the generator temperature increases the heat of generator and the work of the pump also increase while the heat of evaporator slightly decreases. Hence the COP of the cycle is reduced this means that it is possible to use different generator temperatures according to the application. Increasing the evaporator temperature causes the mass ratio and ejector outlet temperature to decrease hence depending on the application and the ambient temperature also is possible to use higher evaporator pressures. Also we observed that as Q of evaporator ascends but Q of generator and work of the pump do not change as the evaporator temperature descends therefore the coefficient of performance is increased. Finally it would be worth to say that although R20, R245FA refrigerant which we used here in some parts as working fluid has no damaging effects on the ozone layer and also has a high mass ratio however it's high cost very high greenhouse effect and low cycle COP with this working fluid are the limitations. Thank you very much for your attention. But the next presentation is also for me. Yeah this is the name of the first author I'm the second third author I will present