Articles

Articles

Solar Cooling By Viuna Absorption Chiller in University of Technology of Sydney

This thesis aims to develop simple and accurate steady-state models of small capacity absorption machines based on experimental data obtained from a solar, single-effect, hot-water absorption machine, installed at UTS. These models are further used in a simulation tool for energy optimisation of this absorption machine. The thesis encompasses components of testing, modelling and energy optimisation of small capacity absorption machines. The first task is obtaining highly reliable data from our installation. This part involves several steps: test planning, data modelling, uncertainty estimation and analysis of results.

Velocity Distributions in (r,θ) Directions for Laminar Flow of a Film around
Horizontal Circular Tube

Velocity distributions in (r,θ) directions are evaluated by solving simultaneous simplified Navier-Stokes equations (NSE) and continuity equation (CE) in polar coordinate. The analysis is based on steady state laminar flow of thin falling liquid film on a horizontal circular tube, for cases in which traction on the film surface is considered negligible. It is a common geometry for part of engineering problems such as evaporator, condenser, absorber, generator of absorption chillers and other similar units in mechanical and chemical engineering. Knowledge of the velocity profiles is usually needed for: 1- solving governing energy and species equations 2- estimating the average and film surface velocity, and 3- evaluating film thickness distribution and its gradient. Two models of velocity distributions are considered, namely actual model and simplified model. Models are compared not only with each other but also with semi actual model in (x,y) coordinate given in the literatures. The average and film surface velocity profiles and film thickness distribution for these models have been shown in various conditions. The results clearly show that the larger flow rates and / or smaller tube diameter increases the calculation error.

SIMULATION OF DIRECT FIRED DOUBLE EFFECT LIBR-H2O ABSORPTION CHILLERS

Three model choices of actual parallel cycle of direct fired double effect “LiBr-H2O” absorption chillers (DEAC) are simulated. Our aim is to estimate the influence of different variables on the cycle performance with the final goal of optimum cycle components. The simulation algorithm of the cycle and its components are presented. These three choices are compared according to their cycle “LiBr-H2O” (P- T-X) equilibrium chart, considering fabricating efforts, operating costs and maintenance. The selected optimum cycle with the optimum input and output data is investigated. The output data for three choices are shown and compared at similar design conditions.

Laminar Falling Film Flow of Aqueous Li Br Solution on a Horizontal Elliptical Tube

Flow hydrodynamics of laminar falling film of aqueous Li Br solution (Li Br − H2O) on a horizontal elliptical tube has been investigated in this research. The film velocity distribution and film thickness, namely, the flow characteristics are determined by solving analytically simultaneous simplified Navier – Stokes equations and continuity equation in polar and Cartesian coordinates. The analy- sis is based on steady state laminar flow of falling liquid film of Li Br − H2O on a horizontal elliptical tube in polar model and Cartesian model (CM), for cases in which traction on the film surface is considered negligible. Models are compared with each other in three cases of aspect ratios (Ar), tube diameters, flow rate, mass concentration and temperature of solution. The flow characteristics values in Cartesian model are over predicted with respect to polar model. The results show that the error in Cartesian model with smaller tube diameter is increased as mass flow rate increases. In Cartesian model, the aspect ratio and tube diameter show no effect on flow characteristics values around the elliptical tube. Therefore, as the eccentricity of ellipse (the ratio of the ellipse focal separation to the major axis) in the elliptical tube increases, the error increases as well. Finally the flow characteristics around horizontal elliptical tube with Ar > 1 are showing better performance with respect to flow characteristics around horizontal elliptical tube with Ar < 1.

Experimental investigation of aqueous LiBr solution absorber bundle with horizontal elliptical tubes

This article reports on the results of experimental studies on combined heat and mass transfer in the absorption of water vapor by aqueous LiBr solution under laminar falling film flow on the horizontal elliptical tube (HET) bundle. The performance of the absorber with HET has been calculated based on the measured parameters. The outputs are shown with respect to absorbent inlet mass concentration and Reynolds Number (Re), coolant inlet temperature and flow rate, and absorber vapor pressure. The results are compared with the published experimental results on absorber bundle with horizontal circular tubes (HCT). The results show that the heat and mass transfer coefficients enhanced on HET at aspect ratio (Ar) > 1 with respect to HCT and improve with the increase of absorbent mass flow rate, absorber vapor pressure, coolant flow rate, and also with the decrease of absorbent concentration and coolant inlet temperature. Because of film thickness increasing and droplet flying off from the tube bundle, the maximum heat transfer coefficient is attained in an optimum absorbent mass flow rate around Re = 45. Finally, the empirical correlations for outside Sherwood number (Sh) and Nusselt number (Nu) are found to depend on the Re, Schmidt number (Sc), mass concentration and absorber vapor pressure