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.

The time that an absorption chiller needs to reach the designed working condition is called start-up. During this time, energy is consumed through the system while efficient refrigeration is not available. So, it's too important to consider the influencing parameters on this period of time so that reduction in energy consumption is achieved. Also, dynamic analysis is used to reduce the startup time and increase system performance in addition to strategic control purposes. Optimizing an absorption cycle during transient operations, such as start up or shut down is very important. The aim of this study is to investigate and compare the effect of employing refrigerant and solution heat exchangers (RHX and SHX) on dynamic performance of both NH 3-H 2 O and H 2 O-LiBr absorption chillers (ACs). Also, the effect of solution heat exchanger's efficiency on the start-up time of the key parameters of both ACs is investigated. To diminish the effect of approximate relations on the results, thermodynamic properties of NH 3-H 2 O and H 2 O-LiBr solutions are extracted from the EES software. By making a link between MATLAB and EES software, a set of differential equations is solved in MATLAB software. The fourth order Runge-Kutta method is employed to solve the differential equations system. This process is continued until convergence criteria are satisfied. The results show that removing SHX from the cycle increases the start-up time of both NH 3-H 2 O and H 2 O-LiBr AC's COPs by 11.76% and 45.16% respectively. The start-up time of the COP of H 2 O-LiBr absorption chiller is highly affected in comparison with the NH 3-H 2 O absorption cycle, by removing SHX or increasing the SHX efficiency. Also, utilizing the RHX does not affect the dynamic response of the key parameters of the both absorption chillers.

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In this study, the effect of fin number and size on the solidification output of a double‐tube container filled with phase change material (PCM) was analyzed numerically. By altering the fins' dimensions, the PCM's heat transfer performance is examined and compared to finless scenarios. To attain optimal performance, multiple inline configurations are explored. In addition, the initial conditions of the heat transfer fluid (HTF), including temperature and Reynolds number, are considered in the analysis. The research results show a significant impact of longer fins with higher numbers on improving the solidification rate of PCM. The solidification rate increases by 67%, 170%, 308%, and 370% for cases with 4, 9, 15, and 19 fins, respectively, all with the same fin length and initial HTF boundary condition. The best case results in a solidification time that is 4.45 times shorter compared to other fin number and dimension scenarios. The study also found that moving from Reynolds numbers 500 to 1000 and 2000 reduced discharging times by 12.9% and 22%, respectively, and increased heat recovery rates by 14.4% and 27.9%. When the HTF entrance temperature was 10°C and 15°C, the coolant temperature showed that the entire discharging time decreased by 37.5% and 23.1% relative to the solidification time when the initial temperature was 20°C. Generally, this work highlights that increasing the length and number of fins enhances thermal efficiency and the phase change process.