Masanori Kiyota

EFFECT OF INCLINATION ON DISTRIBUTION OF ENTRAINMENT FLOW RATE IN AN INCLINED UPWARD ANNULAR FLOW

The droplet entrainment in an annular flow plays an important role in heat and mass transfer. owever the fundamental experimental data such as film thickness, entrainment flow rate and disturbance wave velocity in the case of an inclined upward annular flow are very few compared with similar data in the case of two-phase flow in vertical and horizontal pipelines. In this paper, experimental data on the distribution of entrainment flow rate and the onset of liquid entrainment in an inclined upward annular flow are presented and the effects of the inclination angle are examined. In this experiment, the isokinetic sampling probe technique was used for the measurement of the entrained droplet flow rate and the ranges of inclination angle examined were 0, 30, 45, 60°and 75°from horizontal. As a result, it was clarified that the difference in droplet mass flux between the upper and lower tubes becomes small as pipe inclination increases, the entrainment fraction increases as both the flow rate and the inclination increase and the critical gas velocity for the onset of entrainment becomes small as the liquid film Reynolds number and the inclination increase. Furthermore, Ishii & Mishimas correlation for the entrainment fraction was modified for application to the inclined upward annular flow.

Absorption of water vapor into a lithium bromide water solution film falling along a vertical plate.

An experimental study of the absorption process of water vapor into a lithium bromide solution film was performed. The lithium bromide solution is circulated between the absorber and the generator vessel. The absorber is a chrome-plated brass tube of 84 mm outer diameter and 400 mm length. The solution is fed from the annular slit at the top of the pipe. After absorbing water vapor, the weak solution is fed to the genetor for the recovery of concentration. The generated vapor is provided to the absorber vessel, and the enriched solution is then returned to the absorber. The absorbed water, which is measured as the vapor flow rate by a rotameter is plotted against cooling water temperature while keeping film thickness, inlet temperature and concentration constant. They are compared with the theoretical results by the method proposed previously. Although the experimental values are somewhat lower at 5 Torr, they showed good agreement with the theoretical ones.

STEAM ABSORPTION INTO FILMS OF LITHIUM BROMIDE SOLUTION FALLING OVER HORIZONTAL PIPES ARRANGED IN VERTICAL COLUMN

Absorber of water/LiBr absorption chiller is made up of horizontal tube banks, and its improvement is needed to get higher COP. To clarify the absorption process in these tube banks, a single row of horizontal pipe column is studied experimentally and analytically. The analytical model proposed in previous paper is further changed to conservative form according to the method of Shyy. It is confirmed that the mass balance of water is kept exactly by the present procedure. As for total absorption rate for the pipe column, agreement between experiment and numerical calculations are fairly good except the cases of 8 to 10 pipes at lower flow rate. The roughed pipes with different knurls on their surface were also tested in the experiment and it was found that knurl height of 0.5 mm was the most effective in absorption enhancement.

Steam absorption into films of aqueous solution of LiBr flowing over multiple horizontal pipes

The absorbers of absorption chillers consist of horizontal tube banks, over the outer surfaces of which absorbent flows and inside of which cooling water runs. The dependence of the distribution of absorption rate on the position of the pipes is important but has not been studied previously. In this paper, the cases of one to three pipes are studied experimentally in the range of film Reynolds numbers between 5 and 40. Three different surfaces are tested to study the effect of wettability. Numerical calculations are also performed using the method proposed in our previous paper. The highest absorption rates are obtained for the pipes with higher knurls, and their distributions agree with the numerical predictions. The pipe position which shows the maximum absorption rate varies with flow rate but the maximum absorption rate does not vary greatly with flow rate. The heat transfer coefficient is minimum and almost constant with flow rate at the top pipe. At lower pipes it becomes larger, but tends to decrease with increasing flow rate.

Numerical Calculation of Liquid Film Flowing down Flat Plates with Protrusions

Vertical plates or vertical tubes are used as absorber surface in certain type of absorption chiller. Regularly spaced protrusions would be necessary on their surface to cause mixing within the liquid film flowing over them to promote absorption. To determine the most suitable form of the protrusions experimentally takes much time due to so many possible combinations of parameters. It is convenient from the point of designing to replace them by computer simulations. So numerical calculations are tried using CIP method for the most part and Level set method for the treatment of film surface. Parameters concerning rectangular protrusions such as height h, width w and interval s are varied to study their effect on the flow patterns. Flow rates are also varied between 1 000 and 2 000 in film Reynolds number. It was found that for s/h=3 a single circulation vortex is formed between fins and for s/h=6 two completely separate vortex is formed for all Reynolds numbers studied.