Effect Of Specific Heat Ratio Research Articles

Specific-heat ratio effects on the interaction between shock wave and heavy-cylindrical bubble: Based on discrete Boltzmann method

Specific-heat ratio effects on the interaction between a planar shock wave and a two-dimensional heavy-cylindrical bubble are studied by the discrete Boltzmann method. Snapshots of schlieren images and evolutions of characteristic scales, being consistent with experiments, are obtained. The specific-heat ratio effects on some relevant dynamic behaviors such as the bubble shape, deformation process, average motion, vortex motion, mixing degree of the fluid system are carefully studied, as well as the related Thermodynamic Non-Equilibriums (TNE) behaviors including the TNE strength, entropy production rate of the system. Specifically, it is found that the influence of specific-heat ratio on the entropy production contributed by non-organized energy flux (NOEF) is more significant than that caused by non-organized momentum flux (NOMF). Effects of specific-heat ratio on entropy production caused by NOMF and NOEF are contrary. The effects of specific-heat ratio on various TNE quantities show interesting differences. These differences consistently show the complexity of TNE flows which is still far from clear understanding.

Experimental and numerical investigation on heat transfer in the vertical upward flow water wall of a 660 MW ultra-supercritical CFB boiler

Heat transfer in the vertical upward water wall of a 660 MW ultra-supercritical circulating fluidized bed (CFB) boiler was experimentally and numerically studied. A new variable turbulent Prandtl (Prt) model was used in the numerical simulation. The effects of specific heat ratio, buoyancy parameter, and acceleration parameter on the heat transfer of supercritical water were investigated through experimental data. Results show that the independence between the heat transfer coefficient and these dimensionless parameters was weak with the majority of them, only buoyancy parameter proposed by Jackson showed a strong independence. Additional parameters are required if specific heat ratio and acceleration parameter are used to predict the supercritical water heat transfer. A new variable Prt model was proposed as a function of the turbulent viscosity ratio and the molecular Prandtl number on the basis of the analyses of the effect of Prt on the supercritical water heat transfer. Experimental data of supercritical water were used to validate the accuracy of this Prt model. The results indicated that this Prt model provided accurate heat transfer predictions, especially for the heat transfer deterioration (HTD) cases. The variable Prt model demonstrated a significant effect on the radial velocity distribution, thereby leading to an ‘‘M” shape velocity profile. The zero velocity gradients limit the turbulent mixing, thereby leading to a significant reduction in the turbulent kinetic energy and HTD. The safe heat transfer characteristics of a 660 MW ultra-supercritical CFB boiler water wall were analyzed on the basis of the experimental research and simulation with the new Prt model. The results show that the water wall adopts a smooth tube can ensure the nonexistence of film boiling and overtemperature, and the water wall heat transfer is safe.

Experimental and numerical investigation on heat transfer of ultra-supercritical water in vertical upward tube under uniform and non-uniform heating

Heat transfer of ultra-supercritical water in vertical upward tube under uniform heating was investigated experimentally and numerically. For comparison, similar studies under non-uniform heating were also simulated. The effects of specific heat ratio, buoyancy and acceleration on the heat transfer of ultra-supercritical water were discussed according to the experimental data. Results show that these dimensionless parameters have no single relationship of independence with the heat transfer coefficient which indicates that using them directly to predict heat transfer is inaccurate. The shear stress transport k-ω model was used in the numerical simulation. Results concur with the experimental data to a high degree, which proves that the model has strong applicability in predicting heat transfer. The mechanisms of heat transfer enhancement and deterioration were analyzed through simulation results, and the integral of specific heat in the boundary layer and the buoyancy effect were confirmed to be their main factors, respectively. Furthermore, the differences between the uniform and non-uniform heating were also revealed. The wall temperature of smooth tube under non-uniform heating shows a parabola distribution, and the peak value occurs at the midpoint of the heated side. Moreover, the peak value of the wall temperature is higher under non-uniform heating than that under uniform heating; however, the heat flux is higher when heat transfer deterioration occurs.

Numerical prediction of compressible heat flow with complex wall temperature in supersonic rocket nozzles

Wall heat transfer coefficients and static wall pressures are determined over wide ranges of stagnation pressures and stagnation temperatures under large pressure gradients in a cooled convergent-divergent nozzle. The effects of specific heat ratio, turbulent Prandtl number and wall temperature value on the heat transfer and on the position of separation flow are not yet dis- cussed accurately. Computing correct boundary layer under adverse pres- sures gradients is of a particular importance to the accurate modeling of separated flow. This numerical investigation is conducted to assess the accu- racy of the SST-V turbulence model when computing boundary layer separa- tion in supersonic nozzle with heat transfer. It is concluded that the wall heat transfer coefficients and the position of separation point are influenced by the variation of many parameters as heat specific ratio, wall temperature and turbulent Prandtl number.

Effect of Reynolds number on supercritical helium axial compressor rotors performance in closed Brayton cycle

Supercritical helium has been considered as an ideal working fluid in a number of design studies for closed Brayton cycle due to its thermal properties. But the low density level of supercritical helium, the characteristics of the small flow channel in the turbomachine and the variable working condition method of the system determine that the compressor may run at low Reynolds number. In this paper, the influence of Reynolds number on supercritical helium compressor rotor is investigated under different conditions by numerical simulation program. Effects of specific heat ratio on Reynolds number sensitivity of supercritical helium compressor rotor are also investigated by comparing the calculated results of different working fluids. Special attention is paid to the relationship between properties of working fluids and efficiency. Then, the equations of efficiency and total pressure ratio for different working fluids are established. The results show that the Reynolds number sensitivity of supercritical helium compressor rotor decreases with the increase of tip clearance and increases with the increase of the specific heat ratio.

The Effect of Specific Heat Ratio on Neutron Yield

It is known that the radius ratio of a plasma pinch depends on the specific heat ratio γ of the pinch plasma, where radius pinch ratio is defined as: radius of plasma pinch column/radius of anode. The lower the specific heat ratio the lower would be the pinch radius ratio with corresponding increased compression and pinch density. The deuterium plasma focus pinch is invariably fully ionized and has a specific heat ratio of practically the highest possible value of 5/3. If the deuterium plasma focus could have its specific heat ratio reduced below 5/3 we might expect its radius ratio to be correspondingly reduced, increasing the pinch density, thus improving the D-D fusion neutron yield. To demonstrate this effect we run the Lee model code in deuterium but hypothetically fix the specific heat ratio, reducing it at each run. The results show that indeed the radius ratio is reduced, increasing the compression, and the neutron yield is substantially increased. The effect is used to explain the observed neutron yield enhancement when a deuterium plasma focus doped with a small amount of krypton.

Alternative Equations to Compute the Network and the Thermal Efficiency of the Irreversible Diesel Cycle Using Genetic Algorithm

In the current study, the effect of specific heat ratio, compression ratio, and the maximum to minimum temperature ratio of cycle on the thermal efficiency and the Network of irreversible Diesel cycle have been investigated. For this purpose, numerical solution and multi-objective genetic algorithms with a Pareto optimization method are used to determine the optimum values of specific heat ratio, compression ratio, and the maximum to minimum temperature ratio of cycle. The optimized values of the objective functions (namely Network and thermal efficiency) are then determined by using these vales. The numerical solution shows that the maximum Network and thermal efficiency is obtained simultaneously when the values of specific heat ratio, compression ratio, and the maximum to minimum temperature ratio of cycle are 1.3, 17.7, and 6.0, respectively, and these parameters are obtained by multi-objective genetic algorithms with a Pareto optimization method as 1.3, 17.57, and 6.0. The results obtained from current work are presented in the form of optimal equations for Network thermal efficiency in term of compression efficiency, expansion efficiency and compression ratio of the cycle. The results of current research work can provide a significant insight for optimal design of internal combustion engines including irreversibility.

Effect of specific heat ratio on heat release analysis in a spark ignition engine

The specific heat ratio used in heat release calculations plays a crucial role in the determination of combustion parameters. In this study, the effects of assumed specific heat ratio on the heat release analysis of engine pressure data are studied in a spark ignition engine, using natural gas and gasoline fuels. The experiments were carried out with the spark timing adjusted to the maximum brake torque timing, at an equivalence ratio of ϕ=1 and a speed engine of N=3300rpm. The combustion parameters are obtained from the heat release rate, which obtained from the first law of thermodynamics during a cycle. The results show that the combustion parameters have high sensitivity to the variation and first derivative of the specific heat ratio. The results also show that the influence of the first derivative of the specific heat ratio on the combustion parameters for natural gas operation is higher than that for gasoline operation. Moreover, the first derivative of the specific heat ratio for determination of combustion parameters should not be ignored.

Increased efficiency in SI engine with air replaced by oxygen in argon mixture

Basic engine thermodynamics predicts that spark ignited engine efficiency is a function of both the compression ratio of the engine and the specific heat ratio of the working fluid. In practice the compression ratio of the engine is often limited due to knock. Both higher specific heat ratio and higher compression ratio lead to higher end gas temperatures and increase the likelihood of knock. When the knock limit is not reached, increased heat transfer losses at higher compression ratios can limit efficiency. In this paper, we investigate the role of both the compression ratio and the specific heat ratio on engine efficiency by conducting experiments comparing operation of a single-cylinder variable-compression ratio engine with both hydrogen–air and hydrogen–oxygen–argon mixtures. For low load operation, it is found that the hydrogen–oxygen–argon mixtures result in higher indicated thermal efficiencies. Peak efficiency for the hydrogen–oxygen–argon mixtures is found at compression ratio 5.5, whereas for the hydrogen–air mixture with an equivalence ratio of 0.24 the peak efficiency is found at compression ratio 13. The spark timing when operating the engine with hydrogen–oxygen–argon was found to be knock limited for compression ratios above 4.5. However, for operation with hydrogen–air the spark timing was not limited by knock. We apply a three-zone model to help explain the effects of specific heat ratio and compression ratio on efficiency. Operation with hydrogen–oxygen–argon mixtures at low loads is more efficient because the lower compression ratio results in a substantially larger portion of the gas residing in the adiabatic core rather than in the boundary layer and crevices, leading to less heat transfer and more complete combustion.

The Affects of Molecular Properties of Motive Gas on Supersonic Ejection

The motive gas of a supersonic ejector is supplied from different sources depending on the application. The performance of an ejector that is represented by the secondary flow pressure, starting and unstarting pressures heavily depends on the molecular properties of the motive gas. The effects of specific heat ratio of the motive gas were investigated experimentally for an axi-symmetric annular injection type supersonic ejector. Both the starting pressure and unstarting pressure, however, decreased with the increase of the specific heat ratio of the motive gas. It was discovered that the secondary flow pressure increased as the specific heat ratio of the motive gas decreased even if the stagnation pressure of the motive flow was invariant. However, when the motive gas flow nozzle area ratio is large enough for the motive gas to be condensed, different tendency was observed.

Lie-group theoretic method for analyzing interaction of discontinuous waves in a relaxing gas

A Lie group of transformations method is used to establish self-similar solutions to the problem of shock wave propagation through a relaxing gas and its interaction with the weak discontinuity wave. The forms of the equilibrium value of the vibrational energy and the relaxation time, varying with the density and pressure are determined for which the system admits self-similar solutions. A particular solution to the problem has been found out and used to study the effects of specific heat ratio and ambient density exponent on the flow parameters. The coefficients of amplitudes of reflected and transmitted waves after the interaction are determined.

Theoretical discharge coefficient of a critical circular-arc nozzle with laminar boundary layer and its verification by measurements using super-accurate nozzles

The discharge coefficient of a circular-arc critical Venturi nozzle is derived theoretically by combining theories to calculate mass flow defects caused by the core flow distribution and the laminar boundary layer. The equation obtained is verified by measurements using a constant volume tank system and nozzles of similar shape machined by super accurate lathes, which achieved mirror finish without polishing thus resulting in a machining error of less than 1 μm. The agreement of the theoretical and measured discharge coefficients is better than 0.04% at Reynolds numbers larger than 8×10 4, the minimum used. The equation derived is in an analytical form, which enables an estimation of the effects of specific heat ratio as well as nozzle shape.

Experimental and Analytical Study of Flow Diversion Beyond an Underexpanded Nozzle

A steady-state flow apparatus was used to investigate the process of gun gas diversion through a single hole perforated disk diverter. The amount of diverted flow was found to depend on the distance between the nozzle and the diverter disk and the ratio of nozzle pressure to diverter exit pressure. Experimental studies used nitrogen and carbon dioxide as the working fluids to show the effect of specific heat ratio. At ratios of nozzle pressure to ambient pressure ranging from 4 to 60 diversion efficiencies of 50 to 99 percent were produced. A one-dimensional analytic gas flow model was developed. Results of the analytic model paralleled the experimental data for pressure ratios over 10.

Effect of Specific Heat Ratio on Two-Dimensional Transonic Aerodynamics

HEAVY gases can be used to increase simulation Reynolds number. For this reason, and to test transonic modeling, interferograms were taken of 10% nonlifting biconvex airfoils in gases with specific heat ratios 7 of 1.101.67. The airfoils were mounted in Ludwieg/shock tubedriven solid-wall test sections and run at chord Reynolds number of O.SOxlO 6 to 5.5xl0 6 with nominal Mach numbers M of 0.70 to 0.80. No 7 effect was detected at subcritical M, and the data were in agreement with inviscid theory. A 13% systematic decrease in peak negative pressure coefficient and forward shock movement were observed as 7 increased in supercritical flow, contrary to the predictions of inviscid theory. A model incorporating a viscous displacement correction explained these results. Contents New simulation problems can arise from changing test gases.l For the present study, real gas effects are calculated to be unimportant compared with a change in the specific heat ratio 7. This parameter appears in the similarity rules obtained from the small-disturbance form of the inviscid equations of motion, but it persists to first order only in transonic flow. Recent experiments have shown that some correlation may be achieved at supercritical M through use of transonic similarity.2 However, the boundary-layer development depends on local properties, which change with 7. Thus the displacement thickness, transition point, separation point, and shock/boundary-layer interaction may also exhibit 7 dependence. This investigation primarily used a Ludwieg-tube-d riven staged nozzle with a 30x40 cm cross-section solid-wall test section.3 Biconvex airfoils 10% thick, with chords c of 9.8 and 7.3 cm, were pin mounted in windows centered 35 cm upstream of the choke. The airfoils had cross-sectional area blockages of 2.5 and 1.8%, tunnel half height H to c ratios of 2.0 and 2.7, and aspect ratios of 3 and 4, respectively. They were tested in unheated A, N 2, or CO 2 (7 = 1.67, 1.40, 1.31). In order to avoid condensation, a shock-tube-dri ven 7.5 x 10 cm solid-wall test section was used for the Freon - 12 and SF6 7=1.10 experiments. For these a 10% biconvex airfoil with c = 2.5 cm was pin mounted in windows centered 30 cm upstream of the choke, giving H/c and aspect ratio identical to

Experimental study of effect of specific heat ratio on gas pressure behind an annular step

There are practically no experimental data which permit establishing the effect of the specific heat ratio on the base pressure. The available theoretical data for a planar step [1], first, require experimental verification themselves and second, cannot be converted to an annular step.

Effect of specific heat ratio on surface pressure coefficient for lifting cones

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Effect of specific-heat ratio on mass flow for swirling nozzle flow.

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

TRAVEL SUMMATION AND TIME SUMMATION METHODS OF FREEOSCILLATION DATA ANALYSIS

Figure 4 presents comparison of the effects of specific heat ratio for a cone angle of 20°. Both approximations are close for shock angle and surface Mach number, but the approximation of Ref. 1 shows appreciable error in surface pressure coefficient, even for MM = 20. Approximations for shock wave angle and surface pressure coefficient, which can be used for all Mach numbers and for cone angles from zero to the detachment value, have been determined for the case of a cone at zero angle of attack in supersonic flow. Comparisons with exact results indicate that the precision is adequate for engineering purposes.