Scott K. Thomas

Experimental analysis and flow visualization of a thin liquid film on a stationary and rotating disk

The mean thickness of a thin liquid film of deionized water with a free surface on a stationary and rotating horizontal disk has been measured with a nonobtrusive capacitance technique. The measurements were taken when the rotational speed ranged from 0-300 rpm and the flow rate varied from 7.0-15.0 lpm. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. When the disk was stationary, a circular hydraulic jump was present on the disk. Upstream from the jump, the film thickness was determined by the inertial and frictional forces on the fluid, and the radial spreading of the film. The surface tension at the edge of the disk affected the film thickness downstream from the jump. For the rotating disk, the film thickness was dependent upon the inertial and frictional forces near the center of the disk and the centrifugal forces near the edge of the disk.

One-dimensional analysis of the hydrodynamic and thermal characteristics of thin film flows including the hydraulic jump and rotation

The flow of a thin liquid film with a free surface along a horizontal plate that emanates from a pressurized vessel is examined numerically. In one g, a hydraulic jump was predicted in both plane and radial flow, which could be forced away from the inlet by increasing the inlet Froude number or Reynolds number. In zero g, the hydraulic jump was not predicted. The effect of solid-body rotation for radial flow in one g was to wash out the hydraulic jump and to decrease the film height on the disk. The liquid film heights under one g and zero g were equal under solid-body rotation because the effect of centrifugal force was much greater than that of the gravitational force. The heat transfer to a film on a rotating disk was predicted to be greater than that of a stationary disk because the liquid film is extremely thin and is moving with a very high velocity.

Fully developed laminar flow in trapezoidal grooves with shear stress at the liquid–vapor interface

Abstract This paper discusses the behavior of liquid flowing in a groove with a trapezoidal cross-section. For fully developed laminar flow, the conservation of mass and momentum equations reduce to the classic Poisson equation in terms of the liquid velocity. A finite difference solution was employed to determine the mean velocity, volumetric flow rate, and Poiseuille number ( Po = fRe ) as functions of the groove aspect ratio, groove-half angle, meniscus contact angle and imposed shear stress at the liquid–vapor interface. Comparisons with existing solutions for fully developed flow in rectangular ducts and rectangular and triangular grooves are provided. The volumetric flow rate in a groove in which the fill amount varies is discussed. A semi-analytical solution and a two-point numerical solution for the mean velocity in a groove are presented and used to determine the capillary limit for a revolving helically grooved heat pipe. The effects of interfacial shear stress and groove fill ratio on heat pipe performance are investigated.

Vapor flow analysis of an axially rotating heat pipe

Abstract The vapor flow in an axially rotating heat pipe has been numerically analyzed using a two-dimensional axisymmetric model in cylindrical coordinates. A parametric study was conducted for radial Reynolds numbers of 0.01, 4.0, and 20.0. and rotational speeds ranging from 0 to 2800 r.p.m. The numerical results indicate that the pressure and the axial, radial, and tangential velocities are significantly affected by the rotational speed and the radial Reynolds number. In comparison to non-rotating heat pipes, the radial pressure distribution is no longer uniform. Also, above a certain rotational speed, flow reversal occurs near the centerline of the heat pipe. The shear stress components in the axial and tangential directions at the inner pipe wall increase with the evaporation rale and the rotational speed. The magnitude of the shear stress components are highest in the condenser section. The results of this study will be beneficial in the prediction of the performance of axially rotating heat pipes.

Conjugate Heat Transfer From a Heated Disk to a Thin Liquid Film Formed by a Controlled Impinging Jet

An experimental and numerical study of the heat transfer from a heated horizontal disk to a thin film of liquid is described. The liquid was delivered to the disk by a collar arrangement such that the film thickness and radial velocity were known at the outer radius of the collar. This method of delivery is termed as a controlled impinging jet. Flow visualization tests were performed and heat transfer data were collected along the radius of the disk for different volumetric flow rates and inlet temperatures in the supercritical and subcritical regions. The heat transfer coefficient was found to increase with flow rate when both supercritical and subcritical regions were present on the heated surface. A numerical simulation of this free surface problem was performed, which included the effects of conjugate heat transfer within the heated disk and the liquid. The numerical predictions agree with the experimental results and show that conjugate heat transfer has a significant effect on the local wail temperature and heat transfer coefficient.

The Effects of Transverse Acceleration-Induced Body Forces on the Capillary Limit of Helically Grooved Heat Pipes

A helically grooved copper heat pipe with ethanol as the working fluid has been fabricated and tested on a centrifuge table. The heat pipe was bent to match the radius of curvature of the table so that uniform transverse (perpendicular to the axis of the heat pipe) body force fields could be applied along the entire length of the pipe. By varying the heat input (Q in = 25 to 250 W) and centrifuge table velocity (radial acceleration |a, = 0 to 10g), information on dryout phenomena, circumferential temperature uniformity, heat lost to the environment, thermal resistance, and the capillary limit to heat transport was obtained. Due to the geometry of the helical grooves, the capillary limit increased by a factor of five when the radial acceleration increased from |a r | = 0 to 6.0g. This important result was verified by a mathematical model of the heat pipe system, wherein the capillary limit to heat transport of each groove was calculated in terms of centrifuge table angular velocity, the geometry of the heat pipe and the grooves (including helix pitch), and temperature-dependent working fluid properties. In addition, a qualitative study was executed with a copper-ethanol heat pipe with straight axial grooves. This experimental study showed that the performance of the heat pipe with straight grooves was not improved when the radial acceleration was increased from |a r | = 0 to 10.0g.

Fluid Flow in Axial Reentrant Grooves with Application to Heat Pipes

The fully developed laminar flow within a reentrant groove has been analyzed using a finite element model. A parametric analysis was carried out to determine the Poiseuille number Po = fRe, the dimensionless mean velocity v ∗ , and the dimensionless volumetric flow rate ˙ V ∗ as functions of the geometry of the reentrant groove (groove height 1.0 < ‐ H ∗ < 4.0, slot half-width 0.05 < W ∗ /2 < 0.9, and fillet radius 0.0 < R ∗ < ‐ 1.0), and the liquid‐vapor shear stress (0.0 < −τ ∗ lv < 2.5). The case in which the meniscus recedes into the reentrant groove was examined and could be a result of evaporator dryout or insufficient liquid fill amount. The cross-sectional area of the liquid in the groove, A ∗ , the meniscus radius R ∗, and the aforementioned flow variables were calculated as functions of the meniscus contact angle (0 < ‐ φ < ‐ 40 deg) and the meniscus attachment point (0.0 < H∗ l < ‐ 2.75). Finally, the results of the numerical model were used to determine the capillary limit of a low-temperature heat pipe with two different working fluids, water and ethanol, for a range of meniscus contact angles.

Performance characteristics of a stainless steel/ammonia loop heat pipe

The purpose is to experimentally determine the operating characteristics of a stainless steel/ ammonia loop heat pipe for vapor line temperatures of 40 and 50°C. The thermal resistance, temperature distribution, evaporative heat transfer coefficient for an inverted meniscus evaporator, and the capillary limit were determined as functions of the vapor temperature for a horizontal orientation. A two-dimensional numerical model of the evaporator section was developed and verified using the experimental results. The evaporative heat transfer coefficient for an inverted meniscus evaporator determined from the experimental results was used in the numerical model as a convective boundary condition

Fully-Developed Laminar Flow in Sinusoidal Grooves

The flow of a constant property fluid through a sinusoidal groove has been analyzed. A numerical solution of the conservation of mass and momentum equations for fully developed flow is presented. The mean velocity, volumetric flow rate, and Poiseuille number are presented as functions of the groove geometry, meniscus contact angle, and shear stress at the liquid-vapor interface

The Effect of Working Fluid Inventory on the Performance of Revolving Helically Grooved Heat Pipes

The results of a recently completed experimental and analytical study showed that the capillary limit of a helically-grooved heat pipe (HGHP) was increased significantly when the transverse body force field was increased. This was due to the geometry of the helical groove wick structure. The objective of the present research was to experimentally determine the performance of revolving helically-grooved heat pipes when the working fluid inventory was varied. This report describes the measurement of the geometry of the heat pipe wick structure and the construction and testing of a heat pipe filling station. In addition, an extensive analysis of the uncertainty involved in the filling procedure and working fluid inventory has been outlined. Experimental measurements include the maximum heat transport, thermal resistance and evaporative heat transfer coefficient of the revolving helically grooved heat pipe for radial accelerations of |a r | =0.0, 2.0, 4.0, 6.0, 8.0, and 10.0-g and working fluid fills of G=0.5, 1.0, and 1.5. An existing capillary limit model was updated and comparisons were made to the present experimental data.