Investigation of the launch time of NH₃-H₂O absorption chiller under different working condition

Abstract

This study deals with the launch time of main characteristic of NH3-H 2O absorption chiller under different working condition. The aim of this work was about to scrutinize a lumped-parameter dynamic simulation of aqua-ammonia absorption chiller in addition to investigating the effect of subcooled liquid at condenser/absorber outlet on absorption chiller’s key parameters launch time. Also, the effect of ambient temperature on absorption chiller’s key parameters’ launch time is studied. In order to determine the thermodynamic properties of the working fluid, the Engineering Equation Solver software is applied. By making a link between Engineering Equation Solver and MATLAB software, the differential equations are solved in the MATLAB software environment by fourth-order Rung–Kutta method. According to the result, increase of the sub-cool liquid temperature at condenser outlet has no effect on absorption chiller’s key parameters’ launch time. Besides, 10 ℃-increase in subcooled liquid temperature at the absorber outlet leads to decreasing the launch time of the coefficient of performance to 19.35%. The result shows that if cooling tower temperature goes from 22 ℃ to 30 ℃, launch time of the coefficient of performance rises by 10.43%, while evaporator heat transfer rate falls by 30%. To validate the dynamic model, the results deduced from numerical simulation are compared with peer steady–state results.

Comparison the start-up time of the key parameters of aqua-ammonia and water–lithium bromide absorption chiller (AC) under different heat exchanger configurations

“…The following assumptions are made to simplify the simulation were clearly stated in the literature: • There is no pressure loss in the pipes [9,11].…”

“…1, M i (t) corresponds to the mass within component i, and ṁ i (t) indicates the mass flow rate between components. Subsequently, the overall mass balances for each component are formed by [9,11]:…”

“…For aqua-ammonia absorption cycle, X i (t) is the mass fraction of the ammonia in the component. Subsequently, we have the following absorbent mass balances in the absorber and generator [8,11]:…”

“…[22][23][24][25], studied the effect of refrigerant and solution heat exchangers and heat exchanger's efficiency on the performance of the absorption cycle in the steady state mode while dynamic mode still needs to be investigated. In our previous study, we investigated the effect of subcool liquid at condenser/absorber outlet and also, effect of ambient temperature on AC's key parameters launch time [11]. The general structure and some of input data and initial values of the previous and current research are similar, but the subject that, investigated in this article is different.…”

“…Dynamic behavior of the model was described by mass storage terms in the absorber and generator, thermal heat storage terms in all vessels and a time-delay in the solution cycle. Many researchers conducted dynamic model of the absorption cycle by using the mass and energy conservation and momentum equations [7][8][9][10][11]. Investigation the behavior of the absorption cycle in dynamic mode by applying the step change in the cycle [5,6,8,12,13] and during start-up [7,14,15] have been already carried out.…”