Chand K. Jotshi

Techno-Economic Analysis of Solar Detoxification Systems

Solar detoxification technology has shown great promise for treatment of toxic compounds in the ground water and wastewater. However, detailed analysis of the impact of techno-economic parameters on the treatment cost for the detoxification process is lacking in the literature. In this paper, the impact of different process parameters on the treatment cost has been presented and various strategies for reducing the cost of treatment have been discussed. For the processes with the reaction rate constants less than 0.1 min{sup {minus}1}, the system economics is very sensitive to the reaction rate constant and the unit reactor cost. However, for the reaction rate constant over 0.1 min{sup {minus}1} the general treatment costs can be reduced mainly by reducing the unit catalyst costs.

Thermal Storage in Ammonium Alum/Ammonium Nitrate Eutectic for Solar Space Heating Applications

Ammonium alum and ammonium nitrate in the weight ratio of 1:1 forms a eutectic that melts at 53 C and crystallizes at 48 C. The latent heat of fusion of this eutectic was found to be 215 kJ/kg. Its enthalpy as measured by drop calorimetry was found to be 287 kJ/kg in the temperature range of 24--65 C, which is 1.67 times greater than water (172.2 kJ/kg) and 8.75 times greater than rock (32.8 kJ/kg). Upon several heating/cooling cycles, phase separation was observed. However, by adding 5% attapulgite clay to this eutectic mixture, phase separation was prevented. This eutectic was encapsulated in 0.0254m diameter HDPE hollow balls and subjected to about 1,100 heating/cooling cycles in the temperature range between 25 and 65 C. At the end of these cycles, the decrease in enthalpy was found to be 5%. A scale model of the heat storage unit was fabricated to investigate the heat transfer characteristics of this eutectic encapsulated in HDPE balls. The thermal extraction efficiency of the system was measured with the recirculation of hot air during charging and was found to be in the range of 85--98%.

Investigation of a High-Temperature Packed-Bed Sensible Heat Thermal Energy Storage System With Large-Sized Elements

A high temperature sensible heat thermal energy storage (TES) system is designed for use in a central receiver concentrating solar power plant. Air is used as the heat transfer fluid and solid bricks made out of a high storage density material are used for storage. Experiments were performed using a laboratory scale TES prototype system and the results are presented. The air inlet temperature was varied between 300C to 600C and the flow rate was varied from 50 CFM to 90 CFM. It was found that the charging time decreases with increase in mass flow rate. A 1D packed bed model was used to simulate the thermal performance of the system and was validated with the experimental results. Unsteady 1D energy conservation equations were formulated for combined convection and conduction heat transfer, and solved numerically for charging/discharging cycles. Appropriate heat transfer and pressure drop correlations from prior literature were identified. A parametric study was done by varying the bed dimensions, fluid flow rate, particle diameter and porosity to evaluate the charging/discharging characteristics, overall thermal efficiency and capacity ratio of the system. INTRODUCTION The use of renewable energy sources has become important in view of growing energy demands and continuous depletion of conventional sources of energy. Among renewable energy sources, solar energy is considered a feasible means of generating electricity. Concentrating solar power (CSP) plants can be easily coupled with thermal energy storage (TES) and back-up heat sources making them highly dispatchable. The stored energy can be utilized in the absence of solar radiation or under peak load conditions. Two-tank systems, thermocline systems and packed bed systems using either sensible heat, latent heat, or thermochemical reactions have been used or analyzed for use in CSP plants. When incorporated in a power plant, TES system level efficiency and performance is very important in determining the performance and cost of the plant. Hence, as with any other application, an efficient TES system design that can reduce the levelized cost of energy (LCOE) of the power plant is desirable. Packed Bed Storage Systems A packed bed energy storage system consists of solid storage materials such as rocks or encapsulated phase change materials (PCMs), packed into a storage tank, and a heat transfer fluid that is circulated through voids in the bed. Hot fluid flows from solar collectors into the bed from top to bottom, where thermal energy is transferred from hot fluid to storage material during the charging phase. For heat retrieval, cold fluid flows from bottom to top during the discharging phase. A sensible heat storage system in a packed bed of rocks is especially suitable when air is used as the heat transfer fluid (HTF) in the solar receiver [1]. The advantages of a packed bed system with air as the HTF are: 1) Operating temperature

Effect of refrigerant charge on the performance of air-conditioning systems

An air-conditioning system operates in an optimal condition if the system is fully charged with a specified amount of refrigerant. Poor field maintenance or refrigerant leakage causes a low level of charge resulting in a lower thermal performance and higher operating cost. An experimental investigation was conducted to study the effect of low charge level of R-22 on the performance of a 3-ton residential air-conditioning system. The experimental results show that if a system is undercharged to 90%, the effect is small, 3.5% reduction in cooling capacity and 2% increase in COP. However. The system performance suffers serious degradation if the level of charge drops below 80%. An ice layer formed on the outer cooling coil surface impedes the heat transfer between the warm air and cold refrigerant vapor. An economic analysis shows that the cost of properly charging a system which has otherwise gone down to 85% charge level can pay for itself in savings in a short period of 3 to 4 months.

THERMAL ENERGY STORAGE FOR CONCENTRATING SOLAR POWER PLANTS

Thermal energy storage for concentrating solar thermal power (CSP) plants can help in overcoming the intermittency of the solar resource and also reduce the levelized cost of energy (LCOE) by utilizing the power block for extended periods of time. In general, heat can be stored in the form of sensible heat, latent heat, and thermochemical reactions. This article describes the development of a costeffective latent heat storage TES at the University of South Florida (USF). Latent heat storage systems have higher energy density compared to sensible heat storage systems. However, most phase change materials (PCMs) have low thermal conductivity that leads to slow charging and discharging rates. The effective thermal conductivity of PCMs can be improved by forming small macrocapsules of PCM and enhancing convective heat transfer by submerging them in a liquid. A novel encapsulation procedure for high-temperature PCMs that can be used for thermal energy storage (TES) systems in CSP plants is being developed at USF. When incorporated in a TES system, these PCMs can reduce the system costs to much lower rates than currently used systems. Economical encapsulation is achieved by using a novel electroless deposition technique. Preliminary results are presented and the factors that are being considered for process optimization are discussed.

Investigation of Polyaniline Nanocomposites and Cross-Linked Polyaniline for Hydrogen Storage

One of the biggest challenges for the commercial application of existing hydrogen storage materials is to meet the desired high volumetric and gravimetric hydrogen storage capacity and the ability to refuel quickly and repetitively as a safe transportation system at moderate temperature and pressure. In this work, we have synthesized polyaniline nanocomposites (PANI-NC) and hypercrosslinked polyaniline (PANI-HYP) materials to provide structure and composition which could meet the specific demands of a practical hydrogen storage system. Hydrogen sorption measurements showed that high surface area porous structure enhanced the storage capacity significantly at 77.3K and 1atm (i.e., 0.8wt% for PANI-HYP). However at 298K, storage capacity of all samples is less than 0.5wt% at 70 bar. Hydrogen sorption results along with the surface area measurements confirmed that hydrogen storage mechanism predominantly based on physisorption for polyaniline.

Heat transfer characteristics of a high temperature sensible heat storage water heater using cast iron as a storage material

This paper describes the heat transfer characteristics of high temperature sensible heat storage in cast iron for water heating applications. An experimental setup consisting of a cast iron cylinder and a tube running through its center was fabricated and tested. The experimental data were compared with the theoretical model. It was observed that the contact resistance between the cast iron and the tube plays a dominant role in extracting the heat. An approximate contact resistance prediction was obtained by assuming the resistance due to the air gap modulated by a correction factor, which accounts for the contacting surface area. Based on the results from the experimental setup and theoretical modeling a prototype storage water heater using cast iron blocks as the storage material was designed, fabricated and tested.

Macroencapsulation of Sodium Nitrate for Thermal Energy Storage in Solar Thermal Power

Storage systems based on latent heat storage have high-energy storage density, which reduces the footprint of the system and the cost. However, phase change materials (PCMs) have very low thermal conductivities making them unsuitable for large-scale use without enhancing the effective thermal conductivity. In order to address the low thermal conductivity of the PCMs, macroencapsulation of PCMs is adopted as an effective technique. The macro encapsulation not only provides a self-supporting structure but also enhances the heat transfer rate.In this research, Sodium nitrate (NaNO3), a low cost PCM, was selected for thermal storage in a temperature range of 300–500°C. The PCM was encapsulated in a metal oxide cell using self-assembly reactions, hydrolysis, and simultaneous chemical oxidation at various temperatures. The metal oxide encapsulated PCM capsule was characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The cyclic stability and thermal performance of the capsules were also studied.Copyright

Investigation of a High Temperature Packed Bed Sensible Heat Thermal Energy Storage System With Large Sized Elements

A high temperature sensible heat thermal energy storage (TES) system is designed for use in a central receiver concentrating solar power plant. Air is used as the heat transfer fluid and solid bricks made out of a high storage density material are used for storage. Experiments were performed using a laboratory scale TES prototype system and the results are presented. The air inlet temperature was varied between 300°C to 600°C and the flow rate was varied from 50 CFM to 90 CFM. It was found that the charging time decreases with increase in mass flow rate. A 1D packed bed model was used to simulate the thermal performance of the system and was validated with the experimental results. Unsteady 1D energy conservation equations were formulated for combined convection and conduction heat transfer, and solved numerically for charging/discharging cycles. Appropriate heat transfer and pressure drop correlations from prior literature were identified. A parametric study was done by varying the bed dimensions, fluid flow rate, particle diameter and porosity to evaluate the charging/discharging characteristics, overall thermal efficiency and capacity ratio of the system.Copyright