Effects of Evaporator and Condenser in the Analysis of Adsorption Chillers

Abstract

In a survey of the literature from the last 20 years, 20% of the numerical models used to analyze the performance of adsorption chillers assumed the evaporator and condenser were ideal, with a fixed evaporation temperature and condenser temperature, and ignored interactions between the adsorption bed and evaporator/condenser. Even when the interaction with the evaporator and condenser was included, the other 80% of studies modeled the adsorption bed based on the LPM (lumped parameter method), which ignores the geometry effect and contact resistance of the bed, and thus reduces the accuracy of the analysis. As a consequence, these earlier numerical studies overestimated the system performance of the adsorption chiller. In this study, we conducted a refined numerical approach which avoids these limitations, producing estimates in close agreement with experimental results. Compared with our approach, the models with ideal treatment of evaporator and condenser overestimated COP (coefficient of performance) and SCP (specific cooling power) by as much as 16.12% and 24.64%, respectively. The models based on LPM overestimated COP and SCP by 22.82% and 11.28%, compared to our approach.

Testing of a Falling-Film Evaporator for Adsorption Chillers

“…The convective internal thermal resistance depends on the chilled water properties and flow rate, while the conductive thermal resistance depends on the geometry of the evaporator tubes and the thermal conductivity of the metal they are made of; therefore, they are easily calculable from the input data of the systems. Knowing the UA coefficient from Equation (2), Equation ( 4) can be used to calculate the external heat transfer conductance: (7) The heat-transfer external coefficient (h ext ) cannot be separated from the h ext A ext parameter obtained by Equation ( 7) because the actual wetted area contributing to the falling-film evaporation process is unknown. Since the direct measurement of the mass flow rate of the evaporating refrigerant is challenging to implement without interfering with the system and the evaporation process, this quantity is derived from .…”

“…This increase is not negligible at the typical operating conditions of adsorption chillers; thus, nucleate boiling at low pressure occurs with exchanger wall temperature fluctuations and at high superheat [6]. However, high superheat is inefficient and increases the evaporator temperature and leads to a consequent performance reduction [7]. To avoid such a phenomenon, different types of evaporation processes can be adopted in the evaporators of adsorption devices.…”

Modelling of a falling-film evaporator for adsorption chillers

“…An important component of this heat pump is the evaporator, and its proper functioning can represent a bottleneck situation for the entire system (Lee et al (2020)). As previously mentioned, water can be used as refrigerant for adsorption heat pumps, forcing the evaporator to work in sub-atmospheric conditions (pressures that can be in the range 0.5 -5 kPa (Thimmaiah et al (2017))).…”

Evaporator Performance for Water Refrigerant Adsorption Cooling System

“…Water is well known as the heat transfer fluid and refrigerant due to its properties which have higher heat capacity [26]. Extensive studies of water evaporation have been studied in the literature but the scope is for atmospheric pressure conditions and data on the vacuum condition is still limited [27,28]. Previously in our study, a low pressure flooded type evaporator performance was also evaluated but the focus was on the optimization of adsorption/desorption cycle time and the effects were measured based on evaporator cooling power and SCP [29].…”