Recently exploiting the methane in comparison with the hydrogen as a coolant fluid in launch vehicles captured the interest of space propulsion research community. A few of the main advantages are: it is denser and lower-cost, and it has a lower storage cost. Recognition and analyzing the thermal behavior of coolant flow in regenerative cooling paths are of great importance in the optimum design and performance enhancement of air vehicle engines. In the present study, near-critical fluids heat transfer under supercritical pressure and close to pseudo-critical temperature conditions are investigated. Thermal behavior of cryogenic coolant fluids in the regenerative cooling channels is also analyzed. Solving equations and simulations of fluid flow are conducted with a commercial CFD package, which contains applications and utilities for finite volume solvers. This software gives the possibility to use the self-developed object-oriented C++ programming for applying the boundary conditions, the state equation, and transport properties. Furthermore, coolant flows of methane and hydrogen in the transcritical and supercritical regimes inside the three-dimensional cooling channels are studied. Solver validation is performed through simulation of hydrogen in the uniformly heated circular channel. Further, real gas equations of state and transport property relations in transcritical and supercritical regimes have been explored. Also due to the significance of the near-wall phenomena inside coolant channels, the accuracy of Spalart-Allmaras and k-u{03c9} family turbulence models are compared with each other and numerical results are validated with experimental data. In the cooling channels with high heat fluxes, heat transfer from the hot wall to the coolant fluid suffers in some areas and thus the wall-temperature increases. One observes that the transcritical regime and heat transfer deterioration regions through the behavior of specific heat at constant pressure, transport property and thermodynamic parameters of coolant fluid could be identified.

Design and optimization of various thermodynamic processes that are used in chemical industries such as low-temperature refrigeration and cryogenic cycles, requires computer software to simulate the thermodynamic cycle and examine the effect of various parameters on the performance of the cycle. So the existence of an equation of state to predict thermodynamic properties of working fluids in a wide range of temperatures and pressures is essential. Despite the greater complexity than the other equations, the fundamental equations of state have higher accuracy in the calculation of the thermodynamic properties and the main advantage of them is that other thermodynamic properties can be obtained with high accuracy by differentiating them. In this study, the thermodynamic properties of Helium and Neon as working fluids in cryogenic processes including density, internal energy, enthalpy, entropy, isobaric specific heat capacity, and isochoric heat capacity, have been calculated based on fundamental equations of state using a developed computer code in MATLAB software. By comparing the results with the valid reference data, a range of temperature and pressure in which the fundamental equations of state can be used with high accuracy, have been presented. In this high accuracy region, the maximum error is related to the isobaric heat capacity that is 3. 37 % and 1. 1 % respectively for Helium and Neon.

Introduction: Many efforts have been made to improve Ni-Ti alloy for endodontic use and it has been shown that surface properties and thus cutting efficiency of the rotary files can be improved by processes such as electro-polishing, ion implantation and surface coating. The aim of this study was to evaluate the effect of cryogenic treatment on cutting efficiency of Ni-Ti rotary files.Materials and Methods: In this in vitro study, 60 Ni-Ti rotary instruments (Hero 642, #25, 0.04 taper) were selected and divided into 3 groups of 20. In group I no treatment was used. In group II the instruments were subjected to a deep cryogenic treatment in liquid nitrogen pool (-196oC) for 24 hours and after treatment were immediately tested for cutting efficiency. In group III after cryogenic treatment the temperature of the samples was raised slowly to room temperature for 24 hours. A new piece of test equipment was designed and used. The instruments were attached to the testing machine and rotated in Plexiglas samples for 10 seconds in a working length of 16 mm. The depth of grooves and weight loss of Plexiglas were measured after instrumentation. One-way and two-way ANOVA were used to compare the means of cutting efficacy between the three groups at 95% confidence interval.Results: The instruments which were immediately tested for cutting efficiency had significantly more weight loss and deeper grooves (pweight<0.001; pgroove=0.022), indicating better cutting efficiency. However, there was no significant differences between group I and group III in cutting efficacy (p weight=0.23; p groove=0.61).Conclusion: The results of this study showed that the surface properties of Ni-Ti alloy could be improved by the cryogenic treatment for a limited period of time after treatment, increasing the cutting efficiency of Ni-Ti rotary instruments.

This paper introduces an effective parameter for optimum design of integrated cryogenic NGL recovery plants. The process fluid pressure is an important factor which can affect the plant characteristics. A cryogenic liquid recovery plant was selected as a case study. The influence of different values of pressure drop in various equipments on the quality and quantity of the process outputs were analyzed. The results show that the product specification, quantity and operating costs of the plant are important parameters which a balance between them will determine the optimum pressure distribution in the process. The plant wide net profit can be used as an objective for obtaining the optimum pressure distribution. The products’ price and operating costs change due to economical and political situations. So the optimum pressure distribution in a process can be changed based on the plant wide net profit in various situations.

Background and Aim: Surgical treatment of some renal neoplasia is partial nephrectomy; but in some cases subsequent injuries lead to complete nephrectomy. cryogenic surgery as a minimally invasive procedure can be helpful in avoiding complete nephrectomy. The aim of the study is determination of the effect of cryosurgery on macroscopic and microscopic injury and healing of kidney tissue, along with determination of the speed and quality of healing compared with other current procedures. Materials and methods: cryogenic Partial nephrectomy was performed on posterior pole of left kidney of 6 male Dutch rabbit using contacting probe. After 1, 6 and 24 hours, and after 3, 7 and 14 days nephrectomy was done via laparatomy. After recording macroscopic properties of kidneys, they were processed for histopathologic studies. Results: The freezed area in 1 to 24 hours’ samples showed filling of renal tubes by RBCs, hemorrhage in glumerols, fibrinous deposition in capillaries and some interlobular venuls and arteries, along with initiation of cell necrosis. On 3, 7, 14 day samples, injured and non injured areas were separated by a transitional zone. Gradually, necrotic tissues were reabsorbed which resulted in involution of injured area that makes kidney smaller in size. Conclusion: It seems that cryosurgery is effective in healing. cryogenic partial nephrectomy can be done easily and causes only limited injury during operation. This study showed that contacting probe has less invasive effect than needle probes and its healing process is faster and works through reabsorbtion of necrotic tissue.

In this paper try with use of cryogenic cooling by liquid nitrogen damage such as surface roughness, micro cracks, surface oxidation and burns, as well as control the grinding force in grinding titanium alloy to get their minimum. In addition to the latest statistical techniques appropriate to the nature and effect of each of the grinding parameters (cutting speed, work speed and depth of cut) and the interaction effect of surface roughness on the output power of vertical and tangential force put to their optimal levels has identified. This paper demonstrates the use of liquid nitrogen as a coolant has a positive effect on reducing surface roughness and grinding forces, the surface also reduces the damages of the work piece and the titanium alloy surface oxidation during grinding to prevent. In addition, each of the parameters including, cutting speed, work speed and depth of the outputs of the paper, to be effective, for example by increasing shear rate increases the surface roughness and grinding forces are reduced, as well as increased depth of cut increases the surface roughness and forces.

Composites are combined with at least two materials,one is considered as the base material and later is used to improve the material properties. This study is also about one of the widely used composites so-called aluminium metal matrix composites (Al-MMC) and additional reinforcing particles, including silicon carbide (SiC). The main features of such composite are high hardness and strength, as well as lightweight. The main disadvantages are low machinability and high wear in cutting tools. Several studies have been conducted to improve the machinability of MMCs. The literature review in this domain denotes that limited studies have yet been conducted on the effects of different cooling methods, especially cryogenic cooling and related strategies, on the wear and tool life in the machining of MMCs. Therefore, in this study, the effects of cutting parameters and cryogenic cooling on the tool wear in the machining of A356-10%SiC were studied. Based on the statistical analysis, it was observed that the effects of cutting parameters and cryogenic cooling parameters on the tool wear was significant (R2=0. 97, and a robust mathematical relationship exists between tool wear and the studied parameters. Moreover, compared with previous studies, it was observed that tool life under cryogenic conditions was increased by around 26% compared to readings made under dry conditions.

This investigation explores the mixing dynamics of transcritical and supercritical jets under excitation in cryogenic bi-shear coaxial injector. The study identifies dominant frequencies in the flow field and oscillates the inlet velocity of propellants, LN2 and GN2. Utilizing a 35-degree sector and applying Large Eddy Simulation (LES) alongside the Peng-Robinson equation of state and Chung method, enables the assessment of evaluate the thermodynamic and transport properties in real cryogenic fluids. Results show that oscillations enlarge Kelvin-Helmholtz instability-induced vortex structures, particularly in the supercritical gas jet, enhancing turbulent mixing and, the thermal-shield undergoes localized distortions, improving heat transfer, enhancing mixing, and shortening the jet core. .

The present experimental study reports on enhancement of heat transfer by addition of nanoparticles to the working fluid of commercial swimming pool heat exchangers under laminar flow condition. Three different concentrations of Titanium dioxide nanoparticles were added to the water as working fluid of a typical forced convective heat exchanger used to transfer heat to public swimming pools. The experimental setup is capable of measuring velocity, heat transfer rate, and temperature at different points. TiO2 nanoparticles with mean diameter of 20 nm were used. The effects of suspended nanoparticles concentration and that of Peclet number on forced convective heat transfer were investigated. It is observed that at 0.1%, 0.5% and 1% weight concentration of suspended TiO2 nanoparticles, the average convective heat transfer coefficient improved by 1.1%, 15.9% and 31.6% respectively. The coefficient is further increased at higher Peclet numbers. The efficiency of heat exchanger is evaluated for different scenarios.