• Transactions of the Korean hydrogen and new energy society
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• v.35 no.4
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• pp.428-436
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• 2024

Liquid hydrogen, which operates in cryogenic environments has a density 800 times greater than gaseous hydrogen, making it advantageous for large-scale storage and transportation. However, continuous evaporation due to external heat intrusion and internal heat generation poses challenges. To mitigate heat conduction, various insulation materials are used. In pipe systems, viscous heating effects from turbulence and viscosity, especially in bends, cause heat generation. This study employs computational fluid dynamics (CFD) to analyze the impact of fluid velocity, pressure drop, inner diameter, and curvature radius of pipe bends on viscous heating. Using liquid nitrogen at 77 K as a working fluid, the CFD results showed that increased velocity and pressure drop along with smaller inner diameter and curvature radius enhanced viscous heating, raising fluid temperature.

• Korea-Australia Rheology Journal
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• v.19 no.4
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• pp.201-209
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• 2007

The present paper is concerned with non-isothermal spherical Couette flow of Oldroyd-B fluid in the annular region between two concentric spheres. The inner sphere rotates with a uniform angular velocity while the outer sphere is kept at rest. Moreover, the two spherical boundaries are maintained at fixed temperature values. Hence, the fluid is effect by two heat sources; namely, the viscous heating and the temperature gradient between the two spheres. The viscoelasticity of the fluid is assumed to dominate the inertia such that the latter can be neglected. An approximate analytical solution of the energy and momentum equations is obtained through the expansion of the dynamical fields in power series of Nahme number. The analysis show that, the temperature variation due to the external source appears in the zero order solution and its effect extends to the fluid velocity distribution up to present second order. Viscous heating contributes in the first and second order solutions. In contrast to isothermal case, a first order axial velocity and a second order stream function fields has been appeared. Moreover, at higher orders the temperature distribution depends on the gap width between the two spheres. Finally, there exist a thermal distribution of positive and negative values depend on their positions in the domain region between the two spheres.

• Korean Journal of Food Science and Technology
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• v.47 no.4
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• pp.474-479
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• 2015

In this study, five different Gochujang (a traditional Korean sauce prepared using fermented red pepper paste) sauces were heated at $100^{\circ}C$ for 5 min using a continuous ohmic heating system. Ohmic heating yielded greater reduction in microbial counts (90-95% reduction) than did conventional heating (65-75% reduction). The sterilization effect of the continuous ohmic heater increased with increasing sample flow rate and decreasing Reynolds number inside the pipe. Low-viscosity samples had higher electrical conductivity and were better suited for ohmic heating than were high-viscosity samples. The color and texture were also satisfactorily maintained after ohmic heating. Compared with conventional heating, ohmic heating provided rapid and uniform heating, which is more suitable for aseptic thermal processing of viscous foods.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.311-318
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• 2001

A three-dimensional numerical analysis of the flow and heat transfer characteristic of wood-flour-filled polypropylene melt in an extrusion die was carried out Used for this analysis were Finite Concept Method based on FVM, unstructured grid and non-Newtonian fluid viscosity model. Temperature and flow fields are closely coupled through temperature dependent viscosity and viscous dissipation. With large Peclet, Nahme, Brinkman numbers, viscous heating caused high temperature belt near die housing, Changing taper plate thickness and examining some predefined parameters at die exit investigated the effect of taper plate on velocity and temperature uniformities. In the presence of taper plate, uniformity at die exit could be improved and there existed an optimum thickness to maximize it.

• Journal of Drive and Control
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• v.11 no.1
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• pp.8-13
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• 2014

Hydraulic servo valves are widely used in various fluid power systems because of their fast response and precision control. In this paper, we studied the effect of metering notch shapes and amount of their openings on the flow characteristics within the spool valve using a computational fluid dynamic (CFD) code, FLUENT. To obtain the results for more realistic operating conditions, viscous heating due to the jet flow and viscosity variation of the hydraulic fluid with temperature were considered. For two types of notch shape, streamlines, oil temperature and viscosity distributions, and variations of flow and friction forces acting on spool were showed. The flow and friction forces affected by the metering notch shapes and their openings, and oil temperature rise near metering notch was significant enough to results in the jamming phenomenon. A thermohydrodynamic (THD) flow analysis adopted in this paper can be used in optimum design of hydraulic servo valves.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.2
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• pp.147-154
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• 2003

A three-dimensional numerical analysis of the flow and heat transfer characteristic of wood-flour-filled polypropylene melt in an extrusion die was carried out. Used for this analysis were Finite Concept Method based on FVM, unstructured grid and non-Newtonian fluid viscosity model. Temperature and flow fields are closely coupled through temperature dependent viscosity and viscous dissipation. With large Peclet, Nahme, Brinkman numbers, viscous heating caused high temperature belt near die housing. Changing taper plate thickness and examining some predefined parameters at die exit investigated the effect of taper plate on velocity and temperature uniformities. In the presence of taper plate, uniformity at die exit could be improved and there existed an optimum thickness to maximize it.

• Journal of computational fluids engineering
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• v.8 no.4
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• pp.34-40
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• 2003

The effect of nose radius on aerodynamic heating is investigated by using the Navier-Stokes code extended to thermochemical nonequilibrium airflow, Spherical blunt bodies, whose nose radius varies from 0.O03048 m to 0.6096 m, flying at Mach 25 at an altitude of 53.34 km are considered. Comparison of heat flux at stagnation point with the solution of Viscous Shock Layer and Fay-Riddell are made. Results show that the flow for very small radius is in a nearly frozen state, and therefore the heat flux due to diffusion is smaller than that due to translational energy. As the radius becomes larger, the portion of heat flux by diffusion becomes greater than that of heat flux by translational temperature and approaches to a constant value.

• Journal of the Korean Ceramic Society
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• v.35 no.3
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• pp.264-272
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• 1998

The effect of catalytic condition on the properties of SiO2 aerogels has been investigated and then the dri-ed aerogels were partially densified to induce mechanical strength by heat treatment in order to prepare Type-VI silica by Sol-Gel method. Aerogel made by 1-step base process had the highest skeletal density lowest shrinkage and the smallest particle size. But in case of using acid catalyst in both 1st and 2nd step had the lowest skeletal density highest shrinkage and the largest particle size The aerogel synthesized by 1-step base process was most transparent because of its homogeneous microstructure. During heat treatments cracks occurred below 200$^{\circ}C$ for aerogel with the skeletal density lower than 1.9 g/cm3 but the with the higher skeletal density did not cracked up to 800$^{\circ}C$ shrinkage and skeletal density increased as heating temperature increased due to condensation and viscous sintering mechanism.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1326-1331
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• 2009

Drying process in the cylindrical thin film layer of sludge with the thickness less than a few millimeters has been investigated. Thin film drying is specially designed and used to dry the viscous materials like sewage sludge. The thin film layer of sludge is dried on the metallic cylindrical surface through which thermal energy is supplied to the layer during drying. The wall temperature is assumed to be constant during drying in the present study for the simplification. In order to solve the equations, the mass transfer rate on the drying surface should be determined. The mass flux of evaporated water vapor on the surface is estimated with the formulation given in the literature. The effect of some physical parameters on drying has been examined to figure out the drying characteristics of the sludge layer.

• International Journal of Aeronautical and Space Sciences
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• v.2 no.1
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• pp.1-11
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• 2001

The time implicit point SGS scheme is applied to compute hypersonic viscous flows in thermochemical nonequilibrium. The performance of the point SGS scheme is then compared with those of the line SGS and the LU-SGS schemes. Comparison of convergence histories with the effect of multiple forward and backward sweeps are made for the flow over a 2D cylinder experimentally studied by Hornung and the flow over a hemisphere at conditions corresponding to the peak heating condition during the reentry flight of an SSTO vehicle. Results indicate that the point SGS scheme with multiple sweeps is as robust and efficient as the line SGS scheme. For the point SGS and the LU-SGS scheme, the rate of improvement in convergence is largest with two sweep cycles. However, for the line SGS scheme, it is found that more than one sweep cycle deteriorates the convergence rate.