Experimental and analytical study of cryogenic propellant boiloff to develop and verify alternate pressurization concepts for Space Shuttle external tank using a scaled down tank

Self pressurization by propellant boiloff is experimentally studied as an alternate pressurization concept for the Space Shuttle external tank (ET). The experimental setup used in the study is an open flow system which is composed of a variable area test tank and a recovery tank. The vacuum jacketed test tank is geometrically similar to the external LOx tank for the Space Shuttle. It is equipped with instrumentation to measure the temperature and pressure histories within the liquid and vapor, and viewports to accommodate visual observations and Laser-Doppler Anemometry measurements of fluid velocities. A set of experiments were conducted using liquid Nitrogen to determine the temperature stratification in the liquid and vapor, and pressure histories of the vapor during sudden and continuous depressurization for various different boundary and initial conditions. The study also includes the development and calibration of a computer model to simulate the experiments. This model is a one-dimensional, multi-node type which assumes the liquid and the vapor to be under non-equilibrium conditions during the depressurization. It has been tested for a limited number of cases. The preliminary results indicate that the accuracy of the simulations is determined by the accuracy of the heat transfer coefficients for the vapor and the liquid at the interface which are taken to be the calibration parameters in the present model

IMECE2012-86903 A PARAMETRIC STUDY OF LAMINAR MIXED CONVECTION IN A SQUARE CAVITY USING NUMERICAL SIMULATION TECHNIQUES

ABSTRACT A parametric study is conducted using numerical experimentation to construct an empirical Nusselt number correlation in terms of Richardson and Prandtl numbers for laminar mixed convection in a square cavity. The square cavity under study is assumed to be filled with a compressible fluid. The bottom of the cavity is insulated and stationary where as the top of the cavity (the lid) is pulled at constant speed. The vertical walls of the cavity are kept at constant but unequal temperatures. A two-dimensional, mathematical model is adopted to predict the momentum and heat transfer inside this rectangular cavity. This physics based mathematical model consists of conservation of mass, momentum (two-dimensional, unsteady Navier-Stokes equations for compressible flows) and energy equations for the enclosed fluid subjected to appropriate boundary and initial conditions. The compressibility of the working fluid is represented by an ideal gas relation. The thermodynamic and transport properties of the working fluid are assumed to be constant. The governing equations are discretized using second order accurate central differencing for spatial derivatives and second order finite differencing (based on Taylor expansion) for the time derivatives. The resulting nonlinear equations are then linearized using Newton's linearization method. The set of algebraic equations that result from this process are then put into a matrix form and solved using a Coupled Modified Strongly Implicit Procedure (CMSIP) for the unknowns of the problem. Grid independence and time convergence studies were carried to determine the accuracy of the square mesh adopted for the present study. Two benchmark cases (driven cavity and rectangular channel flows) were studied to verify the accuracy of the CMSIP. Numerical experiments were then carried out to simulate the heat transfer characteristics of mixed convection flow for different Richardson numbers in the range of 0.036<Ri<1.00 where the Reynolds number is kept less than 2000 to ensure laminar flow conditions inside the cavity. The velocity vector field maps (circulation patterns) and temperature contours, and temperature profiles along the † Author to whom the correspondence should be addressed. horizontal axes were generated for different Prandtl numbers ranging from 0.3 to 1. Wall heat fluxes and Nusselt numbers were determined for each parametric study. The collected data from the numerical experiments were then used to construct an empirical Nusselt number correlation in terms of Richardson and Prandtl numbers

Identification and recognition of animals from biometric markers using computer vision approaches: a review

Although classic methods (such as ear tagging, marking, etc.) are generally used for animal identification and recognition, biometric methods have gained popularity in recent years due to the advantages they offer. Systems utilizing biometric markers have been developed for various purposes in animal management, including more effective and accurate tracking of animals, vaccination, disease management, and prevention of theft and fraud. Animals" irises, retinas, faces, muzzle, and body patterns contain unique biometric markers. The use of these markers in computer vision approaches for animal identification and tracking systems has become a highly effective and promising research area in recent years. This review aims to provide a general overview of the latest developments in image processing approaches for animal identification and recognition applications. In this review, we examined in detail all relevant studies we could access from different electronic databases for each biometric method. Afterward, the opportunities and challenges of classical and biometric methods were compared. We anticipate that this study, which conducts a literature review on animal identification and recognition based on computer vision approaches, will shed light on future research towards developing automated systems with biometric methods

Influence of variable viscosity and thermal conductivity, hydrodynamic and thermal slips on magnetohydrodynamic micropolar flow: a numerical study

Thermophysical and wall slip effects arise in many areas of nuclear technology. Motivated by such applications, in this article the collective influence ofvariable viscosity, thermal conductivity, velocity and thermal slipseffects on a steady two-dimensional magnetohydrodynamic microplar fluid over a stretching sheet are analyzednumerically. The governing nonlinear partial differential equations have been converted into a system of non-linear ordinary differential equations using suitable coordinate transformations. The numerical solutions of the problem are expressed in the form of non-dimensional velocityand temperature profiles and discussed from their graphical representations. Nachtsheim-Swigert shooting iteration technique together withthesixth order Runge-Kutta integration scheme has been applied for the numerical solution.A comparison with the existing results has been done and an excellent agreement is found.Further validation with adomian decomposition method is included for the general model. Interesting features in the heat and momentum characteristics are explored. It is found that greater thermal slip and thermal conductivity elevate thermal boundary layer thickness. Increasing Prandtl number enhances Nusselt number at the wall but reduces wall couple stress (micro-rotation gradient). Temperatures are enhanced with both magnetic field and viscosity parameter. Increasing momentum (hydrodynamic) slip is found to accelerate the flow and elevate temperatures

Mathematical Modelling Of Two-Phase Flow Oscillations

A mathematical model is developed to study the stability characteristics of a single channel, electrically heated, forced convection upflow system. The model is based on the assumptions of homogeneous two-phase flow and thermodynamic equilibrium of the phases. The effects of the two-phase viscosity and heat transfer, gravitational forces, and the compressibility of the two-phase region are included in the formulation. The model consists of a set of non-linear hyperbolic partial differential equations. These equations are solved by explicit finite-difference techniques on a high speed digital computer. Comparison with experiments showed that the model is satisfactory in simulating the density-wave type oscillations. The model is found to be sufficiently accurate to predict the stability-instability boundaries at various flow conditions. With further simplification the model is also used to simulate, successfully, the low frequency oscillations, i.e., pressure-drop type oscillations.The model is applied at various inlet conditions and power inputs. The variations in heat transfer characteristics are also simulated; it is concluded that it has an important role in sustaining the oscillations. The theoretical analysis has verified that the compressible air-vapor mixture located at the upstream side of the system is equally important in sustaining the pressure-drop type oscillations. In the case of density-wave oscillations, the compressibility of the two-phase mixture at the downstream side is found to be an important factor in sustaining the oscillations