Liquid Fill Research Articles

Performance of Graphite Foam Evaporator for Use in Thermal Management

This paper presents the results of an investigation of the thermal performance of a graphite foam thermosyphon evaporator and discusses the foam’s potential for use in the thermal management of electronics. The graphitized carbon foam used in this study is an open-cell porous material that consists of a network of interconnected graphite ligaments whose thermal conductivities are up to five times higher than copper. While the bulk graphite foam has a thermal conductivity similar to aluminum, it has one-fifth the density, making it an excellent thermal management material. Furthermore, using the graphite foam as the evaporator in a thermosyphon enables the transfer of large amounts of energy with relatively low temperature difference and without the need for external pumping. Performance of the system with FC-72 and FC-87 was examined, and the effects of liquid fill level, condenser temperature, and foam height, width, and density were studied. Performance with FC-72 and FC-87 was found to be similar, while the liquid fill level, condenser temperature, geometry, and density of the graphite foam were found to significantly affect the thermal performance. The boiling was found to be surface tension dominated, and a simple model based on heat transfer from the outer surface is proposed. As much as 149W were dissipated from a 1cm2 heated area.

Some analytical tools for fluids management in space: Isothermal capillary flows along interior corners

Recent advances in the analysis of a class of capillary-driven flows relevant to materials processing and general fluids management in space have been made. The class of flows addressed concern spontaneous capillary flows in complex containers with interior comers. Such flows are commonplace in space-based fluid systems and arise from the particular container geometry and wetting properties of the system. Important applications for this work involve low-g liquid fill and drain operations where the container geometry is complex, possessing interior corners, and where quantitative information of fluid location, transients, flow rates, and stability is critical. Examples include the storage and handling of liquid propellants and cryogens, water conditioning for life support, fluid phase-change thermal systems for temperature control and power production, materials processing in the liquid state, and on-orbit biofluids processing. For several important problems, closed-form expressions to transient three-dimensional flows are possible that, as design tools, compliment if not replace difficult, time-consuming, and rarely performed numerical calculations. The theory is readily extended to address more complex flows. An overview of a selection of solutions in-hand is presented. Drop tower and low-g aircraft experimental results are cited to support the theoretical findings.

FREE VIBRATION ANALYSIS OF BAFFLED LIQUID-STORAGE TANKS BY THE STRUCTURAL-ACOUSTIC FINITE ELEMENT FORMULATION

In fluid–structure interaction systems, baffles as a dynamic damping device are being widely used to suppress the fluid sloshing motion. Meanwhile, natural and dynamic behaviors of such systems are significantly influenced by the baffle parameters, such as the baffle number, the installation location, the inner-hole diameter and the liquid fill height. This paper intends to numerically investigate the parametric eigen characteristics, by the coupled structural-acoustic finite element method (FEM), of baffled cylindrical liquid-storage tank. According to the symmetric two-field formulation, a test FEM program is developed, in which the reduced integration for avoiding the shear and membrane locking and the modified shear correction factor as well as degenerated 8- and 6-node shell elements and 3-D trilinear acoustic elements are used. Through the comparison with the available analytic solutions of no-baffled axisymmetric tank, the validity of the test program and theoretical work is verified. Next, with the verified test FEM program, various combinations of major baffle parameters are intensively examined, in order for the parametric baffle effects on the natural frequency of baffled tanks.

A study on the improvement of heat transfer performance in low temperature closed Thermosyphon

The study focuses on the heat transfer performance of two-phase closed thermosyphons with plain copper tube and tubes having 50, 60, 70, 80, 90 internal grooves. Three different working fluids (distilled water, methanol, ethanol) are used with various volumetric liquid fill charge ratio from 10 to 40%. Additional experimental parameters such as operating temperature and inclination angle of zero to 90 degrees are used for the comparison of heat transfer performance of the thermosyphon. Condensation and boiling heat transfer coefficients, heat flux are obtained using experimental data for each case of specific parameter. The experimental results are assessed and compared with existing correlations. The results show that working fluids, liquid fill charge ratio, number of grooves and inclination angle are very important factors for the operation of thermosyphons. The relatively high rate of heat transfer is achieved when the thermosyphon with internal grooves is used compared to that with plain tube. The optimum liquid fill charge ratio for the best heat transfer performance lies between 25% and 30%. The range of the optimum inclination angle for this study is 20°-30° from the horizontal position.

Axisymmetric modal analysis of liquid‐storage tanks considering compressibility effects

AbstractIn this paper, we address analytical and numerical studies on the free vibration of fluid–structure interaction problems considering the fluid compressibility. According to the separation of variables together with the boundary condition enforcement, we first derive a compressible‐fluid velocity potential function. Next, we split the structure region into the wet and dry parts, for which we apply the Novozhilov thin shell theory. Combining two dynamic displacement fields, for two split structure parts, using the displacement compatibility conditions, we finally obtain a simultaneous equation system for computing natural frequencies and modes. According to the derived analytical formulae, we compute natural frequencies and modes, stress resultants, together with the comparison with the FEM analysis and the incompressible case. Numerical results show, compared to the incompressible case, that the compressible case produces lower natural frequencies and, furthermore, the relative difference is influenced by the slenderness of tanks and the relative liquid fill height. Copyright © 2002 John Wiley & Sons, Ltd.

Single chamber compact two-phase heat spreaders with microfabricated boiling enhancement structures

Presents the thermal performance evaluation of a compact single-chamber two-phase heat spreader. The heat spreader setup has a central evaporator section with integrated fins for cooling along the edges. The evaporator employs a micro-fabricated three-dimensional (3-D) copper structure for enhancing boiling heat transfer. The thermal performance of the system was characterized at various power levels and condenser cooling conditions. The size of the boiling enhancement structure and effects of liquid fill volumes on performance were also investigated. Incorporation of the enhancement structure resulted in an improvement in the spreader thermal performance by decreasing the wall temperature at the evaporator by 8/spl deg/C, for a power dissipation of 36 W/cm/sup 2/ at an air speed of 1 m/s. The maximum heat flux obtained based on a maximum evaporator temperature of 75/spl deg/C for an air speed of 1 m/s was 42.5 W/cm/sup 2/. Variation in the liquid fill volume showed negligible effect on the maximum temperature at the evaporator, as long as the enhanced structure was fully flooded.

Analytical and numerical simulation of the thermal performance of `mini' gravitational and `micro' gravitational heat pipes

An analytical model has been developed to investigate the performance of a `mini' gravitational heat pipe and two `micro' gravitational heat pipes of different sizes, using water as the refrigerant. The model has been used to determine the limits of heat transport capacity, which expresses the thermal performance of heat pipes. The model is defined in terms of the physical shape of the heat pipes and evaluates the limits of heat transport capacity as functions of the properties of the working fluid used, the inclination angle and liquid fill level. A numerical model has also been developed and used to investigate the operating characteristics of the heat pipes. The results are presented in terms of the cross-sectional areas, pressures, temperatures and mass flow rates of the liquid and vapour within the heat pipes. In general, the modelling results indicate `micro' gravitational heat pipes have higher heat transport limits than `mini' heat pipes of the same cross-sectional area.

Fuzzy flow estimation for ultrasound-based liquid level measurement

Under current operational conditions, the control of liquid fill levels within bottling plant does not provide the accuracy or sensitivity to improve the process to meet waste reduction targets. This paper describes an intelligent fuzzy controller based on the use of ultrasound as a primary measurement tool for fill level and flow rate determination. A Kalman filter has also been used to provide a robust measurement environment on which the strategy can be implemented. Simulation results of a multiple-valve filling machine are presented, demonstrating the potential of the system for reducing waste in the bottling industry.

Structure optimisation and performance simulation of a novel thin membrane heat pipe solar collector using a mathematical model

SYNOPSIS A novel thin membrane heat pipe solar collector was designed to be a compact, efficient and low cost heat generator capable of achieving temperatures up to 250°C and suitable for generating electricity and hot water for domestic and industrial use. Two variations of this, “normal” and “thermosyphon”, were indicated and their performance was investigated. The mathematical theory and simulation approach used for efficiency and solar irradiation calculation, geometry and size optimisation as well as numerical analysis were summarised. Influences of geometry, liquid fill level, inclination and working temperature on collector performance were analysed, and the thermal behaviours of the collector under given conditions, including liquid and vapour cross-sectional areas, liquid and vapour pressures, liquid, vapour and wall temperatures, mass flow rate and start-up process, were described in detail. A number of conclusions regarding the aspects above were given.

Heat Pipe Augmented Passive Solar System for Heating of Buildings

A passive solar heating system was built using heat pipes bonded to the absorbing surface of a solar collector mounted on the south wall of a building. The heat pipes provided one-way heat transfer from the absorber through the insulated wall of the building to water tanks placed inside the space to be heated. The space was then heated by means of natural convection from the surfaces of the tank. The evaporator and condenser ends of the heat pipe were designed to be connected by means of a flexible hose so that the system could be retrofit to an existing building. Simulations were carried out to match the experimental and simulated results. The conductance values obtained as a result of matching showed good agreement with theoretically calculated values. Potential performance improvements were identified, including increased liquid fill fraction in the heat pipes and increasing the heat transfer surface area of the water tanks at the condenser end of the pipe.

Finite element modelling of sling-supported pressure vessels

A novel sling design for the support of horizontal pressure vessels is modelled by finite element methods. Each component is initially considered some distance apart and then brought together by using three-dimensional contact surfaces. Thereafter, external loads, such as self-weight, liquid fill and internal surcharge pressure, are applied to the combined model. Several numerical difficulties arising because of the different flexibilities of the vessel shell and the sling support, which has the form of a cloth material, are overcome. The vessel strains and contact interface pressures are evaluated and plotted and show good agreement with experimental work. The magnitude of the strains at the location of the traditional saddle horn is significantly reduced. The maximum strain, however, is found to have moved to a new location well within the sling contact angle.

Rheology and Filling Characteristics of Particulate Dispersions in Polymer Melt Formulations for Liquid Fill Hard Gelatin Capsules

The rheology and capsule filling properties of molten excipients, Dynafill, Dynasan-114, Lutrol-F68, and polyethylene glycols (PEG) 6000, 8000, 10,000, and 20,000 have been investigated. Lactose (α-monohydrate) was selected as a model particulate solid with low solubility in PEG in order to investigate the effects of disperse phase particle size, concentration, and PEG molecular weight on rheology and capsule filling properties of these systems. All excipients behaved as Newtonian fluids between 65 and 90°C, which was chosen as a possible temperature range for liquid filling of hard gelatin capsules. The excipients, apart from Dynasan-114 and PEG 20,000, showed satisfactory capsule filling properties at 70°C using a semiautomatic filling machine. Dynasan-114 (viscosity = 0.012 Pass at 70°C) leaked from the seals between the hopper and pump of the filling machine, whereas PEG 20,000 (viscosity = 24 Pas at 70⪚C) showed bridging of the molten polymer between successive capsule bodies during the filling process. The effect of disperse phase (lactose) particle size and concentration, and continuous phase (PEG) molecular weight on the apparent viscosity and filling properties of the non-Newtonian dispersions were investigated at 70°C. Satisfactory filling of the dispersions was achieved at 70°C up to a limiting concentration of disperse phase which was dependent upon disperse phase particle size and continuous phase molecular weight, and corresponded to a pronounced increase in apparent viscosity of the dispersion.

Steady-State Performance of a Rotating Miniature Heat Pipe

The operating principle of a rotating miniature heat pipe (RMHP) with a grooved inner wall surface is addressed. A mathematical model of the hydrodynamic performance of RMHPs is developed. A simple correlation for the friction coefficient of axial liquid flow including a vapor drag effect is proposed, based on the numerical analysis of two-dimensional laminar liquid now in a groove. With the present model, the maximum performance and optimum liquid fill amount of RMHPs are predicted under various operating conditions. Influences of operating temperature, rotational speed, and liquid-vapor interfacial shear stress on the maximum performance and optimum liquid fill amount are discussed. Pressure drops of the axial liquid flow and vapor flow are demonstrated.

Experimental investigation of geyser boiling in an annular two-phase closed thermosyphon

Geyser boiling in a vertical annular two-phase closed thermosyphon was experimentally studied. The effects of the heat load, condenser temperature, degree of liquid fill and length of the evaporator on the characteristics of the geyser boiling were investigated in detail for both water and ethanol as working fluids. Flow visualization at light heat load clearly illustrates the process of geyser boiling. It also indicates that it occurs more frequently and irregularly at high heat load. The wall temperature measurement dictates that the period of geyser boiling is shorter at a higher heat load, a shorter evaporator length and a smaller liquid fill. Additionally, the heat transfer coefficient is found to increase approximately linearly with the heat load on a logarithmic scale. An empirical equation was proposed to correlate the data for the heat transfer coefficient. A criterion was suggested for the occurrence of geyser boiling based on the present data.

Transmission Properties of A Plane Fault

Continuity conditions are derived for a fault modelled as a plane with isolated areas of slip. These slip areas are, for simplicity, taken to be such that their overall effect is that of a distribution of circular cracks; discontinuities in both normal and tangential components of displacement are allowed, depending on the internal conditions. Dry (gas-filled), partial or saturated liquid fill, or a fill of a weak visco-elastic solid are possible within the theory. the results are given in terms of the mean wave, which, at wavelengths long compared with the scale-lengths of the fault structure, is an accurate approximation to the displacement field. the continuity conditions that arise under this scheme are identical to those for a thin layer of visco-elastic material. However, unlike earlier, more empirical models of an ‘averaged’ fault, the parameters involved are directly related to the fault structure and include crack-crack interactions. It is clear from earlier work that a fault of this type is capable of supporting Stoneley waves.

Fluid force activated spacecraft dynamics driven by gravity gradient and jitter accelerations

Using as an example the liquid helium dewar of the Gravity Probe-B spacecraft, the dynamics of liquid motions in a slowly rotating, partially liquid fill tank are investigated under the combined action of gravity gradients and £-jitter accelerations. The equilibrium configuration of the liquid interface, which is controlled by centripetal acceleration and surface tension, is a torus. Three different cases of liquid responses are examined: 1) when gravity gradient is the dominant driving acceleration, 2) wheng jitter is the dominant acceleration, and 3) wheng-jitter and gravity gradient accelerations are comparable. For case 1, the vapor bubble responds in an asymmetric oscillation in which the part of the bubble on one side of the centerline rises while the other side sinks (one-up, one-down oscillation). For case 2, the bubble responds in a combined up-and-down and side-to-side oscillation. The response for case 3 is a combination of the responses for cases 1 and 2. The motion-induced forces and torques are also computed for these cases to quantify the effects on spacecraft control.

Charge optimization for a triangular-shaped etched micro heat pipe

An analytical model considered to be the first analytical micro heat pipe model to predict the capillary limit of operation as well as the radius of curvature in the evaporator section and the optimal value of liquid charge was developed for a triangular-shaped, etched micro heat pipe. This model predicted optimal liquid prime values between 16-25% for various power levels and also indicated an optimal charge value which would not exceed 25%. Micro heat pipe arrays with liquid prime values ranging from 10 to 50% were used. The model was validated by comparing the predicted values of maximum heat transport capacity with experimental data at various liquid fill ratios. Although the model correctly predicted the trends associated with the variations in the fill ratio, significant differences were evident in the predicted and measured dryout level. 8 refs.

Experimental investigation of geyser boiling in an annular two-phase closed thermosyphon

Geyser boiling in a vertical annular two-phase closed thermosyphon was experimentally studied. The effects of the heat load, condenser temperature, degree of liquid fill and length of the evaporator on the characteristics of the geyser boiling were investigated in detail for both water and ethanol as working fluids. Flow visualization at light heat load clearly illustrates the process of geyser boiling. It also indicates that it occurs more frequently and irregularly at high heat load. The wall temperature measurement dictates that the period of geyser boiling is shorter at a higher heat load, a shorter evaporator length and a smaller liquid fill. Additionally, the heat transfer coefficient is found to increase approximately linearly with the heat load on a logarithmic scale. An empirical equation was proposed to correlate the data for the heat transfer coefficient. A criterion was suggested for the occurrence of geyser boiling based on the present data.

Thermal Analysis of a Micro Heat Pipe

A detailed mathematical model is developed in which the heat and mass transfer processes in a micro heat pipe (MHP) are examined. The model describes the distribution of the liquid in a MHP and its thermal characteristics depending upon the liquid charge and the applied heat load. The liquid flow in the triangular-shaped corners of a MHP with polygonal cross section is considered by accounting for the variation of the curvature of the free liquid surface and the interfacial shear stresses due to a liquid-vapor frictional interaction. The predicted results obtained are compared to existing experimental data. The importance of the liquid fill, minimum wetting contact angle, and the shear stresses at the liquid-vapor interface in predicting the maximum heat transfer capacity and thermal resistance of the MHP is demonstrated.

Performance of a Wickless Heat Pipe Solar Collector

Abstract The wickless heat pipe solar collector has the advantage of high effective thermal conductance due to its exploitation of phase-change phenomena, and the advantage of solving the problems of flat-plate solar water heaters suck as scale formation (corrosion), cycle reversing (during the night), and freezing. The use of the heat pipe technology in solar collectors will not only solve these problems but also eliminate the effect of the daily and seasonal variation of the solar radiation on the collector performance. The purpose of this article is to obtain a comprehensive understanding of the thermal performance of a wickless heat pipe solar collector on the basis of heat-transfer analysis using R-11, acetone, or water as a working fluid at different charging pressures. Also the effect of angle of inclination and the effect of liquid fill on the performance of the wickless heat pipe solar collector were studied. The experimental results show that the maximum efficiency occurs at 45° tilt angle. The ...