Search

The paper presents a review of publications dedicated to the gas-dynamic temperature stratification device (the Leontief tube) and shows main factors affecting its efficiency. Describes an experimental installation, which is used to obtain data on the value of energy separation in the air to prove this device the operability.The assumption that there is an optimal relationship between the flow velocities in the subsonic and supersonic channels of the gas-dynamic temperature stratification device is experimentally confirmed.The paper conducts analysis of possible ways to raise the efficiency of power plants of various (including space) basing, and shows that, currently, a mainstream of increasing efficiency of their operation is to complicate design solutions.A scheme of the closed gas-turbine space-based plant using a mixture of inert gases (helium-xenon one) for operation is proposed. What differs it from the simplest variants is a lack of the cooler-radiator and integration into gas-dynamic temperature stratification device and heat compressor.Based on the equations of one-dimensional gas dynamics, it is shown that the total pressure restorability when removing heat in a thermal compressor determines operating capability of this scheme. The exploratory study of creating a heat compressor is performed, and it is shown that when operating on gases with a Prandtl number close to 1, the total pressure does not increase.The operating capability conditions of the heat compressor are operation on gases with a low value of the Prandtl number (helium-xenon mixture) at high supersonic velocities and with a longitudinal pressure gradient available.It is shown that there is a region of the low values of the Prandtl number (Pr

The paper analyses a technique to calculate the Leontiev tube and shows that there are several ways to increase operating efficiency of this device of gas-dynamic energy separation. Application of regular relief (dimples and protrusions) on the wall between supersonic and subsonic channels is one of them.Analyses the results available in publications of experimentally numerically investigated influence of semi-spherical protrusions in the slot channels on the enhancement of heat transfer and drag coefficients at various Reynolds numbers.Shows that at the laminar flow owing to semi-spherical protrusions in the slot channel a heat transfer coefficient can be 1.1‑2.6 times increased with simultaneous 1.7‑4.8 times growth of drag coefficient (as compared to the smooth channel).At transition and turbulent flows the heat transfer enhancement, because of shallow dimples (depth-to-print diameter ratio is from 0.1 to 0.25), can reach 1.1‑2.4 times, with simultaneous 1.2‑7.9 times growth of the drag coefficient (as compared to smooth channel).Using the higher protrusions can provide up to 3.0‑3.5 times heat transfer intensification, but in this case there is an outrunning growth of the drag coefficient.It is shown that the staggered array of the shallow spherical protrusions is advisable to use for heat transfer enhancement in the subsonic channel of the Leontiev tube. The shallow spherical dimples correspond to them and operate as heat transfer intensifiers in the supersonic channel.The paper proposes a mechanism that enables taking into consideration an impact of the protrusions in the slot channel on the intensification of the heat transfer and momentum processes when calculating the gas-dynamic energy separation device (Leontiev tube) using the known (earlier published) technique.The study has been implemented under supporting Grant no. 15-08-08428 of the Russian Foundation for Basic Research.

The paper considers numerical simulation of a non-machine energy separation device with a porous inner tube. The results obtained show that with a flow rate variation up to 30% of general rate the channel efficiency of gas-dynamic non-machine device for energy separation falls by 3-5%. Hence, a heat efficiency loss due to the colder air injection prevails over the increase of heat flow resulting from a recovery factor decrease when the temperature difference between supersonic and subsonic flows rises. So, the use of gas injection (porous inner tube) to improve the efficiency of the non-machine device for energy separation is beside the purpose.The effect when the temperature changes its sign in the non-machine device for energy separation and supersonic flow becomes cooler while a subsonic one is heated has been also simulated. This effect was previously obtained experimentally.The numerical simulation has shown good coincidence with analytical solution in case of the laminar flow regime. The research has shown that with the laminar flow the efficiency of the non-machine device for energy separation can be significantly higher than with the turbulent flow, but its implementation is quite difficult.

The paper presents possible application fields of the binary noble gas mixtures with low Prandtl numbers. It shows that it is expedient to select these mixtures as the working fluids for closed Brayton cycle gas-turbine installations, thermo-acoustic engines and for the gas dynamic energy separation device (Leontiev tube). As follows from the analysis, He-Ar, He-Kr, and HeXe mixtures have proven to be the most attractive choice. The paper has analyzed the calculation results for coefficient of dynamic viscosity, coefficient of thermal conductivity, and for heat capacity at constant pressure for the given mixtures in terms of mixture molecular weights at pressures of 2MPa and 7MPa and temperatures of 400 and 1200°K. According to data of experiments and calculations available in public sources published by another authors, the results are verified. It was found that at constant pressure within the examined range of parameters (i.e. pressure, temperature, mixture molecular weight) the obtained heat capacity values are in good agreement with the values of the verification data. In calculating dynamic viscosity coefficient for any pressure and temperature the utilized technique provides results for He-Ar and He-Kr mixtures within the entire range of the molecular weights, which are, essentially, as good as shown by international verification techniques. However, at high pressures and low temperatures for He-Xe mixture with molecular weights close to the pure Xe the divergence was found to be as high as 25 % while for other parameter intervals under consideration and with the same mixture the difference does not exceed 10 %. A good agreement with the verification data is observed for the values of a thermal conductivity coefficient of He-Ar and He-Kr mixtures for any value of parameters, while for He-Xe mixture with molecular weights close to 60 g/mole independently of pressure the divergence can reach 30 % for 1200°K and 20 % for 400°K. It is shown that for a He-Xe mixture, with increasing temperature for all molecular masses, the underestimation of the thermal conductivity coefficient values may partially compensate for underestimation of the dynamic viscosity coefficient values, thereby leading to the net inaccuracy in Prandtl number calculations at most 15 % for any value of parameters under consideration.