Chakraborty, Prodyut Ranjan

The present study focuses on the thermodynamic analysis of zeolite–water and activated carbon–ethanol based adsorption cooling systems. The performance of the system depends critically on four operating temperatures namely maximum desorption temperature, minimum adsorption temperature, condensing temperature, and evaporating temperature and also on the ratio of specific heat of structural material and the specific heat of adsorbent. Dubinin–Astakhov equation is used to estimate the equilibrium uptake of working pairs. A comparative study is made between these working pairs for the air-conditioning applications.

The PCM based heat source and heat sink devices can be effectively used for various heating and cooling applications and can store and release heat in the form of latent heat. This latent heat can be utilized for maintaining body temperature within comfort range of 33 ± 2°C. The present work focuses on developing a 2-D numerical model to evaluate the performance of PCM cool pack configuration in terms of the evolution of average skin temperature with respect to time. The numerical model is first validated with a 1-D semi-analytical for a simple PCM pack configuration. Once the model is validated, the next level of studies involves the comparison of performance analysis for different PCMs with more realistic cooling pack configuration. Optimal thermal conductivity (which can be engineered by introducing PCM-Graphite composites) is also predicted for different PCMs in order to obtain thermal comfort for a prolonged duration of 3 hrs. The studies do not include the perspiration model; however, incorporation of the skin layer within the model domain took the approach closer to the real condition.

In this experimental study, a comprehensive analysis of the flash evaporation of a static liquid pool is conducted. The study investigates the impact of different parameters on the process, including the initial temperature of the water pool ranging from 50 to 85 ◦C and primary pressure between 5 to 50 kPa (abs.) with corresponding superheat levels ranging from 7 to 38 ◦C. The research highlights that superheat is the primary driving force behind flash evaporation operation, and its impact reduces over time. Initially, a high superheat value is present, which affects the temperature drop and evaporated mass evolution throughout the process, along with the initial water pool temperature.

The present work focuses on developing a 2-D axisymmetric numerical model to study the dynamic behaviour of charging and discharging cycle for an elementary latent heat storage unit with simple geometry. The domain under consideration consists of a pipe of negligible thickness carrying heat transfer fluid (HTF), while being surrounded by latent heat storage medium or the phase change material (PCM). The PCM domain is considered to be 2-D axisymmetric and heat transfer mechanism is diffusion dominated. On the other hand, 1-D model is considered for the flow of HTF through the pipe. The heat transfer models in the PCM and HTF is coupled through the energy balance at the pipe wall. A fully implicit Finite Volume model is developed to obtain the evolution of temperature in PCM and HTF domain along with extent of melting/solidification in the PCM domain. Simulations are performed for charging and discharging of PCM domain considering pure PCM and PCM-Graphite composite with enhanced thermal conductivity.

Solar energy-based technologies have seen remarkable development in the last decades. This is observed all across the world. The concerns related to cost and availability of fossil fuels, effects of climate change due to use of fossil fuels are the primary drivers behind the usages of these technologies. With such motivation, several research groups around the world are working in the field of solar energy. Since this field is quite diverse, it includes academicians of diverse background such as physics, chemistry, materials science, mechanical engineering, electrical engineering etc. This monograph is an effort to present the collection of such effort with an aim to present the developments at the system-level as well as the challenges and opportunities that are present at the technical level. It includes chapters covering the following themes—overview of energy usage in developing countries, solar thermal systems (heating and cooling), energy storage, and solar cells.

Low pressure vaporization (LPV) is considered a promising method for rapid cooling and a significant rate of water vaporization. This article presents an experimental investigation for the detailed heat and mass characterization of a static water pool exposed to low pressure conditions. An LPV experimental setup has been fabricated in the lab to investigate the effect of process parameters like initial temperature (Tw,0), initial vacuum tank pressure (Pv,0), and the water pool height (Hw,0) on the non-equilibrium fraction (NEF) and heat transfer coefficient (hv). Results shows that NEF initially increased to a high value and then tediously dropped. The final value of NEF decreased with decreasing the initial vacuum tank pressure and initial water pool height inside the flash chamber. A maximum value of the hv existed with the rise of the degree of superheat (ΔT) of liquid. It is found that with an increase of the degree of superheat by 13.44 °C, the value of hv is enhanced by 67%, and the NEF decreased by 46.7%, respectively.

Abstract: A numerical visualization study of wetlands is detailed in this article using finite volume methods. The aim of this study is to model treatment efficiency of the wetlands in terms of the residence time distribution function. Shape and depth of wetlands are critically analysed to find the optimal flow requirement for effective treatment. Laminar three-dimensional flow dynamics is used to simulate the slow water flows that occur in treatment wetlands. Slow inlet flows are assumed. Dye is used as the tracer to characterize the hydrodynamics within the wetlands. Three different geometrical configurations, namely square, square with two islands, and triangle, respectively, are simulated. The variation in the tracer concentration is studied as a function of recirculation volumes, flow rates, time and depth of the wetland for each of the wetland shapes. The change in the variation of tracer concentration at inlet and exit helps to assess treatment effectiveness. In another case, glycerine is used to simulate sewage flow. Plug flow is prominent in sewage-laden wetlands. The results obtained from the above-illustrated case studies are compared with each other to assess the reproducibility of the optimal flow model. Multi-parameter regression models for residence time distribution functions are derived to characterize flow through constructed wetlands of different shapes.

Solar thermal resources can be effectively utilized to meet the refrigeration and air-conditioning demands for both household and industrial purposes. Considerable fraction of total available electricity is consumed by the conventional vapor compression refrigeration systems (VCRS) during the summer season in countries with tropical climate. The leakage of VCRS refrigerants in the atmosphere has also been identified as one of the major contributors toward ozone layer depletion and hence global warming. The utilization of solar thermal energy for obtaining refrigeration and air-conditioning is the key to address these issues concerning high electricity demand as well as the environmental pollution. Solar thermal energy, being one of the leading resources of green energy, can reduce the carbon footprint considerably, when used for sorption cooling process. The advantages of using sorption cooling systems powered by solar thermal energy over VCRS are twofold when we consider environmental issues. Sorption-based solar thermal cooling reduces the electricity demand for cooling to a large extent, which in turn reduces usage of fossil fuels to produce this electricity, and thus leads to low-carbon footprint. Also, the refrigerants used for sorption cooling are less prone to cause ozone layer depletion. Although sorption-based refrigeration systems driven by solar thermal energy are mature technologies, wide acceptability of such cooling system is yet to be achieved. Two major limitations of sorption-based solar thermal cooling are relatively low coefficient of performance (COP), and large volume requirement. Other than these two limitations, the intermittent nature of solar thermal resource and heat exchanger and control mechanism design complicacies also pose considerable challenge. Sorption cooling technology can be broadly classified base on absorption and adsorption processes. Absorption is a volumetric phenomenon where a substance of one state gets absorbed in another substance in a different state with or without having chemical reaction, such as liquid being absorbed by solid or gas being absorbed by liquid. On the other hand, adsorption is a surface phenomenon due to physical bonding forces such as Van der walls forces between a solid surface and adjacent fluid or due to chemical bonding between the two. The discussion in this chapter is attributed to Water–Lithium Bromide-based absorption cooling systems. The discussion emphasizes on fundamental concepts of absorption refrigeration cycle, starting with simplest intermittent vapor absorption refrigeration system and gradually elaborating toward the operating principles of commercially used chillers at the end. Cycle analysis of most commonly used single-effect absorption chillers is discussed in a detailed manner along with the background knowledge of how to determine pertinent thermodynamic properties at the inlet and outlet of individual components. Finally, methods and design criteria that can improve the system performance are discussed.