Performance Investigations of the Charging and Discharging Processes in a 3-Tank Thermal Energy Storage System

The paper presents a 3 tank thermal energy storage system. The system consists of cold oil reservoir, heat storage tank, and a residual drainage tank. Cold oil flows by gravity into a heating chamber and after being heated to the required temperature, a mechanical thermostat opens allowing the hot oil to flow into a heat storage tank. The storage tank was discharged through the cooking unit by boiling 0.5 litres of water. The used oil flowed by gravity to the drainage tank. The discharge flow rates of 0.5, 2.1, 2.8 and 6.5 g/s were considered. A charging efficiency of 51.3% and overall discharging efficiency range of 15.3 34.7% were achieved. Charging efficiency increased when the source was embedded in the storage tank. The instantaneous discharge power had a peak value for each flow rate. The adopted cooking unit had a thermal transfer efficiency range of 34.7 57.6%. A method for sizing oil based TES systems was proposed and illustrated based on the obtained discharge results. Keywords:     3-tank, sizing, discharging, efficiency, thermal energ

Steam-based charging-discharging of a PCM heat storage

Latent heat storage and efficient heat transport technology helps to utilize the intermittent solar energy for continuous and near isothermal  applications. However, many latent heat storages face challenges of storage charging, heat retaining, and discharging the stored heat. This paper tries to address the challenges of heat transportation and storage charging-discharging issues. The heat transportation from the receiver over some distance, from outside to the kitchen, is carried out with a stainless pipeline and water as heat transfer fluids. However, the  charging-discharging process is carried by conduction method with the help of fins. In addition, the stored heat is retained for about one-two days by using aerogel insulation. The latent heat is stored in a phase change material (PCM), nitrate salt (mixture of 60% NaNO3 and 40% KNO3), which melts at 222ºC and has 109 J/g specific heat of fusion. The storage has the capacity of storing up to 250ºC heat and supply this heat isothermally during baking in the liquid-solid phase transition. However, the sensible heat stored in the solid and liquid form of the PCM is used to perform additional applications that do not require uniform heat which includes bread baking, kita (large pancake) baking and water boiling. The low thermal conductivity of PCM is enhanced by using extended aluminum fins that are attached to the baking plate and extruded inward to the storage. In this paper, two-phase loop thermosyphon of steam is used to manage the long distance heat transportation required between the receiver (outside) and the storage (inside a house). The steam in the thermosyphon flow has restricted to a maximum working temperature of 250ºC. Steam is selected for its highest heat capacity, availability and stable nature. It carries heat from the collector focus point and condenses in a coiled pipe imbedded in aluminum plate placed on top of the storage. Many fins are solidly attached to this plate to conduct the heat down to the PCM inside the storage during charging. This design configuration avoids pressure development inside the PCM storage and the charging-discharging temperature is recorded in three zones (top, middle and bottom) of the storage. The experimental and numerical results show that the heat transportation, retention and charging-discharging methods are effective.Keywords: Solar energy, PCM storage, Latent heat storage, Two-phase thermosyphon

Numerical and experimental Analysis of Solar Injera Baking with a PCM Heat Storage

Today, many developing countries are using biomass as their primary energy supply. However, this energy affects the environment, health and safety of women and children. In addition, utilization of this energy using traditional cooking stoves is causing indoor air pollution and in turn health problems to millions of people. To overcome such problems, efforts are being made by researchers globally and are suggesting alternative safe energy sources. This paper demonstrates solar cooker with an integrated PCM thermal storage and heat transportation loop system suitable for high temperature applications. The system has designed to address Injera baking application. Injera, a fermented flat bread type, is the most common food type served three to four times a day in Ethiopia. Other countries like Eritrea, Somalia, Sudan and Yemen also use this food. The storage system has storing capacity of heat up to 2500C and it can retain this heat for about two days. The storage has coupled to a polar mounted concentrator, fixed receiver and used steam heat transfer fluid. The steam circulates naturally between the evaporator and condenser in a closed loop. The paper focuses on indirect charging, simultaneous charging-discharging and discharging of the stored heat for the purpose of Injera baking. The frying pan is a custom-made aluminum plate casted by embedding a 10mm coiled stainless steel steam pipe as heating element. The pan is 500mm in diameter and 30mm thick; and the fins are 20mm in diameter and 140mm long. The fins have immersed into a 20kg PCM, which is coupled to a 1.8m diameter parabolic dish collector. The solar fryer demonstrates Injera baking for average family size. Baking is tested from the stored heat, while storage is charging. A fully charged storage has supplied enough heat to baked average household Injera demands about 19Injeras and additional breads with the remaining heat.Keywords: Solar Injera baking; PCM charging; PCM storage; Solar Injera stove design; Solar cooking; Ethiopia

Performance of Calcium Chloride- Ammonia Adsorption Refrigeration System

An experimental study on the performance of calcium chloride-ammonia adsorption system is described. A single bed water cooled condenser adsorption refrigerator prototype, which utilises calcium chloride-ammonia pair has been developed and tested in the laboratory. Experiments have been conducted for desorption temperatures of 100 °C with desorption time varying from 1 to 4 hours. An electric tape heater and a timer were used to perform the experiments. The adsorption temperature profile, adsorption rate and prototype performance have been analysed and discussed. The tested heating and desorption temperature of 100 °C and heating and desorption time of 1 to 4 hours was able to create a cooling effect of the cold chamber of the prototype of between -0.8 to 8.3 °C, which is adequate for vaccine storage requirement of 2 to 8 °C. The estimated Coefficient of Performance of the system ranges between 0.025 and 0. 076

Dynamic model of a small scale concentrating solar cooker with rock bed heat storage

This study presents a dynamic model for a concentrating solar energy collector with an integrated rock bed heat storage system. The model is based on numerical integration of a set of conservation equations for mass, momentum and energy of the heat carrier, the rock pebbles and the walls. The heat carrier is compressible air. Numerical solutions are implemented based on implicit time integration without iterations. Stability problems at large time steps do not occur but the accuracy is reduced. The model predicts pressure, velocity, density and temperatures of the fluid, rock bed and wall in time and along the bed. The model is validated with experimental results in a laboratory setting on temperature profiles during charging and discharging of rock bed heat storage. The intention is that the model shall serve as a computational tool for upscaling of air based concentrating solar energy systems with rock bed heat storage units

Vitenskapelig (u)redelighet

Since the 1980’s, there has been a marked increase in disclosures of fraud in research. Cases of scientific fraud and misconduct do not only damage society’s confidence in research, they also contribute to reduce the trustworthiness in research in itself. Research ethics, however, involve much more than investigations of misconduct. How can we encourage good scientific practice? What does honest research entail? Which gray areas exist, and when is the limit to misconduct crossed? How should allegations of misconduct be handled? What are the consequences of fraud, and what sanctions should follow? In this anthology, Norwegian researches contribute to the discussion of various perspectives on scientific integrity and misconduct. The purpose of this book is not to give unequivocal or definitive answers to what scientific misconduct is, but to convey a diversity of positions and perspectives. Some of these are overlapping, others contradictory - which also reflects the field internationally. This anthology is an important resource for students and researchers, particularly in education and training. In addition, it will also provide insights for others involved in the prevention of misconduct and the promotion of good scientific practice

Experimental investigation on heat extraction from a rock bed heat storage system for high temperature applications

Solar energy is available in an intermittent way, and integrating an energy storage system with solar energy collection devices may promote uninterrupted supply of energy in the absence of the availability of solar energy. It has been shown that heat can be stored using rocks packed in a bed, but limited work has been reported on heat extraction from a charged rockbed. This paper reports on the heat extraction from a charged rock bed. Discharging tests were performed under different air flow conditions and initial bed temperatures. Without the blower, the discharging rate is very slow. The discharging rate can be increased, and the cooking time controlled by adjusting the air speed through the rock-bed system

Vitenskapelig (u)redelighet

Since the 1980’s, there has been a marked increase in disclosures of fraud in research. Cases of scientific fraud and misconduct do not only damage society’s confidence in research, they also contribute to reduce the trustworthiness in research in itself. Research ethics, however, involve much more than investigations of misconduct. How can we encourage good scientific practice? What does honest research entail? Which gray areas exist, and when is the limit to misconduct crossed? How should allegations of misconduct be handled? What are the consequences of fraud, and what sanctions should follow? In this anthology, Norwegian researches contribute to the discussion of various perspectives on scientific integrity and misconduct. The purpose of this book is not to give unequivocal or definitive answers to what scientific misconduct is, but to convey a diversity of positions and perspectives. Some of these are overlapping, others contradictory - which also reflects the field internationally. This anthology is an important resource for students and researchers, particularly in education and training. In addition, it will also provide insights for others involved in the prevention of misconduct and the promotion of good scientific practice