Study of overall heat transfer coefficients of adsorption bed under adsorption-desorption operating conditions

• Main Author: Mohamed Jiyaudin Sultanul Ariff
• Other Authors: Anutosh Chakraborty
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Mechanical engineering::Alternative, renewable energy sources; Engineering::Mechanical engineering::Energy conservation
• Online Access: https://hdl.handle.net/10356/150509
• Institution: Nanyang Technological University

The major demands for human civilisation are power, heating, cooling, and freshwater, which are conventionally generated by the burning of fossil fuels at power stations. Moreover, energy efficient boilers, chillers, and desalination plants are used to meet the needs for heating, cooling, and freshwater. The combustion of fossil fuels is used to meet these major needs, which not only emits CO2 but also pollutes the atmosphere substantially. If the energy is fully recovered from the exhaust flue gases of power/co-generation plants, a major part of thermal, cooling and water demands can be solved. Adsorption assisted heat transformation (AHT) provides an important role due to the use of low-grade waste heat / renewable energy as driving sources to produce cooling, heating, and desalinated water. The performances of AHT system mainly depend on the quality of adsorbent materials and the efficiency of adsorption bed. Adsorption bed is a helical tube heat exchanger in which porous adsorbents are housed. The adsorption characteristics of adsorbent-adsorbate systems are required to design the adsorption heat exchanger. The experimental study of an adsorption cooling device is the focus of this project. The temporal history within each adsorption chiller element is shown. The overall heat transfer coefficient (U in W/m2K) is determined using the temperature difference between the bed and the heat transfer fluid at the inlet and outlet of the heat exchanger. In this experiment, a mixture of type A silica gel and zeolite system is tested with water adsorption. In the literature, there is no comprehensive study on the U values of silica gel - water based systems. Therefore, the adsorption bed comprising silica gel which are meshed with steal wire is focused is this project. The experiments are conducted for the hot water inlet temperatures of 50-70 ℃ whilst the cooling water is maintained 25-30 ℃, and the chilled water is obtained between 10 and 15 ℃. During experiments, the bed pressures are controlled by maintaining the transfer of water vapour from the evaporator to bed (adsorption) and from the bed to the condenser (desorption). Hence, a simulation study is performed to calculate the average heat transfer coefficient of adsorption bed. It is found that the U values are varied from 400 to 1200 W/m2‧K from transient to cyclic steady state for both adsorption and desorption conditions.