Assessment of Pilot Direct Contact Membrane Distillation Regeneration of Lithium Chloride Solution in Liquid Desiccant Air-conditioning Systems Using Computer Simulation

Membrane distillation (MD) has been increasingly explored for treatment of various hyper saline waters, including lithium chloride (LiCl) solutions used in liquid desiccant air-conditioning (LDAC) systems. In this study, the regeneration of liquid desiccant LiCl solution by a pilot direct contact membrane distillation (DCMD) process is assessed using computer simulation. Unlike previous experimental investigations, the simulation allows to incorporate both temperature and concentration polarisation effects in the analysis of heat and mass transfer through the membrane, thus enabling the systematic assessment of the pilot DCMD regeneration of the LiCl solution. The simulation results demonstrate distinctive profiles of water flux, thermal efficiency, and LiCl concentration along the membrane under co-current and counter-current flow modes, and the pilot DCMD process under counter-current flow is superior to that under co-current flow regarding the process thermal efficiency and LiCl concentration enrichment. Moreover, for the pilot DCMD regeneration of LiCl solution under the counter-current flow, the feed inlet temperature, LiCl concentration, and especially the membrane leaf length exert profound impacts on the process performance: the process water flux halves from 12 to 6 L/(m2×h) while thermal efficiency decreases by 20% from 0.46 to 0.37 when the membrane leaf length increases from 0.5 to 1.5 m.

Detailed Design Optimisation of Three-Fluid Parallel-Flow Plate-Fin Heat Exchanger Using Second Law Analysis

Three-fluid compact heat exchanger of plate-fin type with parallel-flow configuration is optimised for the entropy generation. Four different types of plate fins (plain rectangular, offset strip, corrugated louvered and wavy fin) are embodied within heat exchanger for both co-current and counter-current flow arrangements have been selected for the study. Genetic algorithm is selected as an optimisation tool having apt in handling various continuous variables and discrete variables and the problems with complexities in the objective function as well as in constraints. Validation of the optimization model is carried out by comparing the results with that from experimental results, Particle swarm optimization (without heat duty constraint) and from graphical method (with heat duty constraint). It is observed that for a specified heat duty and given operating conditions corrugated louvered fin with counter-current flow arrangement offers the minimum entropy generation amongst all.

FENOMENA ALIRAN UDARA-AIR BERLAWANAN ARAH PADA PIPA HORIZONTAL PADA L/D = 25 DAN L/D = 50

Fenomena aliran sangat penting dalam rangka untuk mengetahui lebih lanjut tentang mekanisme Counter-Current Flow Limitation (CCFL) atau transisi dari aliran berlawanan arah menjadi aliran searah. Pola aliran stratified menjadi karakter yang awal dalam fenomena selanjutnya. Peningkatan kecepatan udara yang kecil akan sangat mempengaruhi pola aliran berubah. Gangguan antar muka akan selalu besar seiring dengan peningkatan kecepatan udara. Alat yang digunakan untuk penelitian ini sama dengan salah satu komponen pada Pressurized Water Reactor (PWR) yang disebut hot leg dengan perbandingan 1/30. Hot leg adalah bagian pipa yang diamati dalam penelitian ini. Dimensi dari hotleg berupa pipa mendatar, pipa miring dan belokan yang terpasang menjadi satu dalam suatu saluran pokok PWR. Pada penelitian ini simulator hot leg dibuat dengan L/D = 50 dan L/D = 25. Simulator ini terdiri dari pipa horizontal, belokan dan miring dengan sudut kemiringan 50o. Visual yang dapat diamati dalam saluran hotleg, sehingga fenomena-fenomena yang terjadi dapat diamati secara rinci. Pengamatan visual dilakukan dengan menggunakan kamera berkecepatan tinggi. Sehingga data yang didapat dan diolah didapatkan secara valid. Hasil pengamatan yang diperoleh adalah pola aliran yang terjadi pada pipa horizontal. Penambahan kecepatan udara menyebabkan cepat terjadinya perubahan pola aliran pada L/D = 50. Sedangkan, pada L/D = 25 perubahan pola aliran dapat terjadi dengan kecepatan udara yang besar.