This paper presents a study on the effects of transient and steady-state vehicle operation on fuel economy and emissions trends of an in-use Euro 2 Asian utility vehicle in the Philippines, with a normally aspirated direct-injection engine, and fueled with different CME-diesel blends designated as B1, B2, B3, B5, B10, B20, B50, & B100 corresponding to increasing CME percentage blends. The vehicle was driven on a chassis dynamometer following the Japanese 10-15 Mode drive cycle and at steady speeds of 40, 60, & 80 kph for fuel consumption and CO, NOx, and THC measurements. PM measurements were not undertaken. Drive cycle results showed that adding CME up to 20% by volume (B20) has a small effect on the heating values, specific fuel consumption (SFC), fuel economy (FE), and maximum power. Relative to neat diesel, the increase in SFC, lower FE and power beyond B20 were attributed to lower heating values at higher blends. CO was practically constant while THC and NOx generally decreased with increasing CME blends. The CO and THC trends were ascribed to overall lean mixtures and increased amount of oxygenated fuel at higher CME blends. B20 yielded the most emissions reduction without performance loss. Steady speed results indicated for all blends, SFC increased with vehicle speed due to higher road load. Above B10, SFC went beyond 5% higher than that for neat diesel and is attributed to lowered heating values of higher blends. The SFC of blends up to B10 approached that of neat diesel as speed increased suggesting more diesel-like combustion characteristics. The blend fuel economy showed an inverse relationship to SFC as expected. Both CO and NOx exhibited slightly decreasing trends with higher blends at all speeds. For a given blend, CO decreased while NOx increased as speed went higher. THC followed bowl-shaped trendlines with blend ratio. THC was high for neat diesel going lowest at B5-B10 and upwards again beyond B10. For a given blend, THC emissions decreased with increasing vehicle speed.

The use of solid particles as a heat-transfer fluid and thermal storage media for concentrating solar power is a promising candidate for meeting levelized cost of electricity (LCOE) targets for next-generation CSP concepts. Meeting these cost targets for a given system concept will require optimization of the particle heat-transfer fluid with simultaneous consideration of all system components and operating conditions. This paper explores the trade-offs in system operating conditions and particle thermophysical properties on the levelized cost of electricity through parametric analysis. A steady-state modeling methodology for design point simulations dispatched against typical meteorological year (TMY) data is presented, which includes computationally efficient submodels of a falling particle receiver, moving packed-bed heat exchanger, storage bin, particle lift, and recompression supercritical CO 2 (sCO 2 ) cycle. The components selected for the baseline system configuration presents the most near-term realization of a particle-based CSP system that has been developed to date. However, the methodology could be extended to consider alternative particle receiver and heat exchanger concepts. The detailed system-level model coupled to component cost models is capable of propagating component design and performance information directly into the plant performance and economics. The system-level model is used to investigate how the levelized cost of electricity varies with changes in particle absorptivity, hot storage bin temperature, heat exchanger approach temperature, and sCO 2 cycle operating parameters. Trade-offs in system capital cost and solar-to-electric efficiency due to changes in the size of the heliostat field, storage bins, primary heat exchanger, and receiver efficiency are observed. Optimal system operating conditions are reported, which approach levelized costs of electricity of $0.06 kW e −1 hr −1 .

Efficient hydrogen flow control is of great importance to ensure the reliable operation of an automotive fuel cell system because it is closely associated with the safety and the economic efficiency. In this study, an effective hydrogen flow control algorithm for hydrogen excess ratio control is addressed by pointing out the recovery speed and overshoot response. Unlike previous studies on the hydrogen management systems of an automotive fuel cell, this study presents an analytic hydrogen tank model which can present the characteristics of the discharge and charge of hydrogen from a type 4 hydrogen tank. To this end, a mode reference adaptive control (MRAC) based on proportional-integral (PI) control is introduced, to ensure robust hydrogen flow during the dynamic operation of fuel cell system. The MRAC was compared with the nominal PI control and PWM control in the hydrogen management system of an automotive fuel cell operating within normal conditions, under steady-state responses and transient. Based on these result, it can further demonstrate that the MRAC algorithm shows better recovery speed and tracking performance than the nominal PI, and PWM control algorithm with respect to the transient behaviors.

A numerical study of temperature distribution in the cylinder liner of biodiesel-powered compression ignition engine is presented. The mathematical model equations developed were based on heat transfers in the cylinder liner and subsequently transformed using the finite difference method. Numerical solutions were obtained from computer codes written in MATLAB programming language. A biodiesel produced from Nigerian physic nut oil was used in the study. The result was compared with that obtained for conventional diesel fuel. The results revealed that the cylinder head section of the liner material presented higher temperature distribution compared to the oil sump section of the liner. Over a twelve-minute time range, the liner attained steady state with Jatropha-based biodiesel, recording a maximum temperature of 873.1°C. Conventional diesel recorded the lower temperature of 784.3°C. Results also showed that the cylinder head section of the liner material closest to the combustion chamber experienced the greatest temperature rise in comparison to other parts of the liner. These results show that though there are lots of publications confirming that a compression ignition engine previously running on diesel fuel can run on biodiesel fuel or its blend with diesel, there is a need for a further critical study on the development of engine parts like the cylinder liner.

To investigate the performance of photovoltaic/thermal (PV/T) collectors, the steady-state model is not sufficient. Therefore, a dynamic model of the PV/T collector is required to capture the PV/T electrical and thermal output variation throughout the day. This article presents a dynamic model of a water type flat-plate PV/T collector. The model can be used to carry out in depth analysis of the PV/T transient thermal and electrical performance. It is developed based on the energy analysis of each component of the PV/T collector. The energy balance equations are solved by employing an explicit Runge-Kutta method using MATLAB program. The model is then validated with an experimental work. The thermal and electrical performance of a certain PV/T collector on a typical summer day is investigated under the hot and humid weather conditions of Abu Dhabi, the United Arab Emirates. A parametric study is also performed in order to study the effect of various parameters, namely: the inclination angle of the PV/T collector, the thermal conductance of the adhesive layer between the PV cells and the absorber plate, and the water mass flow rate.

The Philippine Department of Environment and Natural Resources (DENR) has issued Department Order 2015-04 (DAO 2015-04) or the “The Implementation of Vehicle Emission Limits for EURO 4/IV, and In-Use Vehicle Emission Standards”. This policy, coupled with the Philippine Biofuels Act of 2016 (RA 9367) should greatly reduce the environmental impact of local automobile emissions. Commercial fuel is a mix of local coconut methyl ester (CME) and neat diesel blend. However, commercial diesel fuel is still at 2% v/v as of 2016 in contrast to the 5% v/v set by the policy, part due to the fact that only few local studies are done to show the effects of higher percentage of CME, with most recent studies showing results against increased CME usage. The study shows the effects of the usage of higher CME percentage in accordance to the set schedule of RA 9367. Five fuel blends with varying CME percentages v/v (2%, 5%, 10%, 15%, and 20%) are used in a heavy duty turbocharged common rail direct injection (CRDI) engine. The engine is run on an eddy current dynamometer with steady state measurements at 50 to 500Nm with 50Nm intervals. Each fuel is tested at three pedal positions, alpha, (25%, 50%, and 60%) controlled directly from the engine control unit (ECU). Results show that higher CME usage does not result in reduction of power and achieved torque. There is, however, a significant increase in brake specific fuel consumption at higher percentages of CME. No significant change in carbon monoxide (CO) and unburned hydrocarbons of diesel (HCD) is observed but there is a significant increase in Nitrous Oxides (NOx) concentration as CME percentage is increased. However, brake specific CO and HCD were found to be out of standard for near no load and near full load operations. A similar trend is observed for brake specific. Brake specific NOx is particularly more problematic since all measurements were observed to be out of standard with maximum values of 1350% of the set EURO 4/IV standard. However, it is also seen that the performance of each blend does not significantly differ from each other. Nevertheless, there is still some potential in the usage of CME due to the fact that power and torque requirements are still met at the expense of higher fuel consumption; but with the opportunity of being self-sufficient as coconut-producing country.

A molten carbonate electrolysis cell (MCEC) is capable of separating carbon dioxide from methane reformate while simultaneously electrolyzing water. Methane reformate, for this study, primarily consists of carbon dioxide, hydrogen, methane, and a high percentage of water. Carbon dioxide is required for the operation of a MCEC since a carbonate ion is formed and travels from the reformate channel to the sweep gas channel. In this study, a spatially resolved physical model was developed to simulate an MCEC in a novel hybrid reformer electrolyzer purifier (REP) configuration for high purity hydrogen production from methane and water. REP effectively acts as an electrochemical CO 2 purifier of hydrogen. In order to evaluate the performance of REP, a dynamic MCEC stack model was developed based upon previous high temperature molten carbonate fuel cell modeling studies carried out at the National Fuel Cell Research Center at the University of California, Irvine. The current model is capable of capturing both steady state performance and transient behavior of an MCEC stack using established physical models originating from first principals. The model was first verified with REP experimental data at steady state which included spatial temperature profiles. Preliminary results show good agreement with experimental data in terms of spatial distribution of temperature, current density, voltage, and power. The combined effect of steam methane reformation (SMR) and water electrolysis with electrochemical CO 2 removal results in 96% dry-basis hydrogen at the cathode outlet of the MCEC. Experimental measurements reported 98% dry-basis hydrogen at the cathode outlet.

There has been a global search for alternative fuels that are environmentally friendly to replace and or compliment the conventional fossil fuels used in running engines. This is in line with the global action to reduce CO 2 emissions hence ameliorating the effect of climate change. Biodiesel fuels have been adjudged to be clean energy with minimal environmental pollution during combustion. Hence, biodiesel fuels for running compression ignition engines have been developed from various feedstocks such as vegetable oils, animal fat, and waste or used cooking oils. The properties of these biodiesels have been reported to be dependent on the feedstock type and therefore vary according to the source feedstock. In carrying out this present study on the effects of utilising biodiesel fuel on the compression ignition engine, a numerical study of temperature distribution in the cylinder liner of biodiesel-powered compression ignition engine is presented. Biodiesel produced from palm kernel oil is used. Eight nodes in the cylinder liner spanning the top section of the liner, midpoint and the interface between the liner and the block were used as data source as it is established that sharp-edged points are most likely regions for thermal stress. Of the eight nodes selected, four were edge nodes and the other four were nodes at the interface with varying conditions. Model equations used for the study were developed and subsequently transformed using the finite difference method. Numerical solutions were obtained from computer codes written in MATLAB programming language. The obtained results from this code were compared to results obtained from commercial software (ANSYS FLUENT) for same geometry and boundary conditions. Results on the cylinder liner showed steady state temperatures were reached in about five minutes using both the MATLAB code and ANSYS FLUENT and both results showed a similar trend of temperature distribution in the radial direction. However, the MATLAB code showed higher temperatures at the upper section of the liner material as compared to the midpoint of the liner whereas ANSYS FLUENT showed the midpoint section to possess maximum temperatures as compared to the cylinder head section. Both results agree with the lower section having least temperature distribution. Further analyses were carried out on the midpoint of the cylinder and the cylinder head section and factors responsible for the discrepancies discussed. The outcome of this study presents palm kernel based biodiesel as an alternative fuel in cylinder engines while highlighting sections of the engine that require design attention in terms of heat flux and engine stability.

Supercritical carbon dioxide (sCO 2 ) Brayton cycle is an emerging technology to be used as a power block with concentrated solar power (CSP) systems, tower type, sCO 2 Brayton cycle has the potential to be competitive with traditional Rankine steam cycle. Most of the studies have been focused on the steady state analysis of this technology. This research has developed numerical models for five configurations of sCO 2 Brayton cycles operating under quasi steady state conditions. The studied cycles are connected directly to the solar central receiver tower, which is used to provide heat input to the cycles; consequently, the heat addition is changing over time as a function of solar radiation. During the off load operation, the mass flow rate of the cycle is changing with the goal of keeping the turbine inlet temperature at 700°C. The compressor and turbine use a partial load model to adjust velocities according to the new mass flow rate. Also, the heat exchangers effectiveness are adjusted as they present off-design operation. In the recompression cycle, the model permits to explore the relationship between recompression fraction and the ambient temperature. It is demonstrated that the power generated by the cycle may be improved more than 6 % if the recompression fraction is continuously changed and controlled as a function of the ambient temperature.

Direct solar power receivers consist of tubular arrays, or panels, which are typically tubes arranged side by side and connected to an inlet and outlet manifold. The tubes absorb the heat incident on the surface and transfer it to the fluid contained inside them. To increase the solar absorptance, high temperature black paint or a solar selective coating is applied to the surface of the tubes. However, current solar selective coatings degrade over the lifetime of the receiver and must be reapplied, which reduces the receiver thermal efficiency and increases the maintenance costs. This work presents an evaluation of several novel receiver shapes which have been denominated as fractal like geometries (FLGs). The FLGs are geometries that create a light-trapping effect, thus, increasing the effective solar absorptance and potentially increasing the thermal efficiency of the receiver. Five FLG prototypes were fabricated out of Inconel 718 and tested in Sandia’s solar furnace at two irradiance levels of ∼15 and 30 W/cm 2 and two fluid flow rates. Photographic methods were used to capture the irradiance distribution on the receiver surfaces and compared to results from ray-tracing models. This methods provided the irradiance distribution and the thermal input on the FLGs. Air at nearly atmospheric pressure was used as heat transfer fluid. The air inlet and outlet temperatures were recorded, using a data acquisition system, until steady state was achieved. Computational fluid dynamics (CFD) models, using the Discrete Ordinates (DO) radiation and the k-ω Shear Stress Transport (SST) equations, were developed and calibrated, using the test data, to predict the performance of the five FLGs at different air flow rates and irradiance levels. The results showed that relative to a flat plate (base case), the new FLGs exhibited an increase in the effective solar absorptance from 0.86 to 0.92 for an intrinsic material absorptance of 0.86. Peak surface temperatures of ∼1000°C and maximum air temperature increases of ∼200°C were observed. Compared to the base case, the new FLGs showed a clear air outlet temperature increase. Thermal efficiency increases of ∼15%, with respect to the base case, were observed. Several tests, in different days, were performed to assess the repeatability of the results. The results obtained, so far, are very encouraging and display a very strong potential for incorporation in future solar power receivers.

An ammonia thermochemical energy storage system consists of an endothermic reaction that disassociates ammonia into hydrogen using the solar energy, which can be stored for future use. The reverse reaction is carried out in the energy recovery process; the ammonia synthesis reaction is used to heat supercritical steam to temperatures on the order of 650 degrees Celsius as required for a supercritical steam Rankine cycle. The goal of this paper is to investigate the transient response in a synthesis reactor-heat-exchanger. It is desired to predict the time the system takes to reach steady state and the effect a perturbation has on the temperature response of the system. A numerical model has been developed to investigate the transient behavior of an ammonia synthesis reactor-heat exchanger. The model consists of a transient one dimensional concentric tube counter-flow reactor-heat exchanger. The effect of gas mass flow rate and initial gas temperature was investigated. Results show that as gas mass flow rate increases, the time for the outlet steam temperature to reach steady state decreases. For low gas mass flow rates, the required outlet steam temperature is not achieved.

Particle Heating Receivers (PHR) offer a range of advantages for concentrator solar power (CSP). PHRs can facilitate higher operating temperatures (>700°C), they can allow for inexpensive direct storage, and they can be integrated into cavity receiver designs for high collection efficiency. In operation, PHRs use solid particles that are irradiated and heated directly as they fall through a region exposed to concentrated sunlight. The heated particles can subsequently be stored in insulated bins, with the stored thermal energy reclaimed via heat exchanger to secondary working fluid for the power cycle in CSP. In this field Georgia Tech has over five years’ experience developing PHR technology through the support of the DOE SunShot program and similar research efforts. Georgia Tech has dealt with the crucial challenges in particle receiver technology: particulate flow behavior, particulate handling, and particulate heat transfer. In particular, Georgia Tech has specialized in innovative advances in the utilization and design of discrete structures in PHRs (DS-PHR) to prolong particulate residence time in the irradiated zone. This paper describes the development and results of lab-scale testing for DS-PHRs especially in the Georgia Tech high flux solar simulator (GTHFSS). The GTHFSS is a bank of high intensity xenon lamps with elliptical reflectors designed to replicate a concentrated solar source. Two series of tests have been undertaken: batch and continuous operation. Initially the DS-PHR has been tested in a batch apparatus in which a substantial but still limited quantity of preheated particulate flows through from an elevated bin through the irradiated PHR into a weighing box collecting bin. The use of a weighing box is advantageous since the flow rate of particulate is otherwise especially hard to measure. Temperature rise measurements and mass flow rate measurements allow calculation of energy collection rates. Calorimetry measurements, also described in the paper, are used to verify the incident concentrated radiation allowing the calculation of the collection efficiency. This preliminary series of experiments have been completed using the batch apparatus, with the efficiencies of the lab-scale DS-PHR being determined for a range of temperatures. Efficiencies above 90% have been measured at low temperatures roughly corresponding to the so-called optical efficiency, which is the rate of energy collection at low temperature and minimal heat loss. Batch experiment data indicates a collection efficiency of approximately 81–85% at an average particle operating temperature of 500°C. Lab-scale batch results at 700°C in proved to be unstable, and as such a rework employing a continuous recirculation loop is underway. While the batch apparatus is convenient for preliminary work, it is challenging to reach steady state operation in the mixing and measurement section below the DS-PHR, which limits this apparatus in higher temperature experiments. Consequently, the experiment is being reconfigured for continuous flow, in which the particulate will be heated and recirculated by a high temperature air conveyor. The advantage of the high temperature conveyor has already been proved by its successful integration as a heater and mixer in the hot bin of the batch apparatus. Such a compact device was also quite advantageous in the limited confines of a typical laboratory simulator such as the GTHFSS. While continuous flow prevents the exceedingly desirable use of an uninterrupted mass measurement device, highly accurate mass flow data is still expected based on the use of a perforated plate flow control station. This device relies on the Berverloo effect to maintain a constant flow of particulate through an array of orifices, for which the flow is largely independent of upstream conditions. A weighing box will be used to calibrate and verify the mass flow. This paper will report on efficiency measurements with the batch flow experiments and present the preliminary steps taken to conduct the recirculation experiment. The bulk the research reported in the paper is sponsored by and done in support of the DoE Sun Shot initiative.

Quite a few computer programs have been developed to model power plant performance. These software codes are geared towards modeling steady state operations which is usually sufficient for conventional power plants. Solar thermal power plants undergo lengthy transient start–up and shut–down operations due to the sporadic nature of solar radiation; therefore, valid modeling of their performance must address those unsteady state operations. A novel scheme has been developed to fine–tune steady state solar power generation models to accurately take account of the impact of those transient operations. The suggested new scheme is implemented by adjusting solar radiation input data and has been shown to significantly improve modeling accuracy by moving modeled results closer to matching real operating data.

Small scale solar thermal systems are increasingly investigated in the context of decentralized energy supply, due to favorable costs of thermal energy storage (TES) in comparison with battery storage for otherwise economical PV generation. The present study provides the computational framework and results of a one year simulation of a low-cost pilot 3kW el micro-Concentrated Solar Power (micro-CSP) plant with TES. The modeling approach is based on a dynamic representation of the solar thermal loop and a steady state model of the Organic Rankine Cycle (ORC), and is validated to experimental data from a test site (Eckerd College, St. Petersburg, Florida). The simulation results predict an annual net electricity generation of 4.08 MWh/a . Based on the simulation, optimization studies focusing on the Organic Rankine Cycle (ORC) converter of the system are presented, including a control strategy allowing for a variable pinch point in the condenser that offers an annual improvement of 14.0% in comparison to a constant condensation pinch point. Absolute electricity output is increased to 4.65 MWh/a . Improvements are due to better matching to expander performance and lower condenser fan power because of higher pinch points. A method, incorporating this control strategy, is developed to economically optimize the ORC components. The process allows for optimization of the ORC subsystem in an arbitrary environment, e.g. as part of a micro-grid to minimize Levelized electricity costs (LEC). The air-cooled condenser is identified as the driving component for the ORC optimization as its influence on overall costs and performance is of major significance. Application of the optimization process to various locations in Africa illustrates economic benefits of the system in comparison to diesel generation.

Parabolic trough collectors are economically and technically attractive options for process heat applications that require temperatures in excess of 200 °C. One of the reasons is that low-cost non-evacuated receivers are used in this type of application. However, at higher temperatures, the performance of non-evacuated receivers deteriorates considerably due to excessive radiation and natural convection losses. A new idea had been preliminarily investigated by the authors both numerically and experimentally. The idea was to introduce a thermally insulating layer to the part of the receiver’s annular gap that does not receive concentrated sunlight from the parabolic mirrors, and the results had been quite promising. This paper presents additional, more extensive experiments on this concept. In these experiments, a cartridge heater is inserted along the axis of the receiver tube of a non-evacuated receiver. The heater is surrounded by a conductive material to ensure uniform heating of the receiver tube. A number of thermocouples are affixed near the inner surface of the receiver as well as on the outer surface of the glass envelope to monitor temperature uniformity. Two sets of experiments are then conducted, one with the insulating layer, and the other without. In each set, the power input is set to a certain level and the receiver temperature is measured once steady state conditions are attained. The power level is then increased, and the measurements are repeated. The heat loss values from each set are compared to determine whether adding the insulating layer enhances receiver performance. Results show that a reduction in heat loss of as much as 15% can be achieved using this design, and collector efficiency can increase by up to about 6%. However, it was also found that the extent of improvement in collector efficiency depends on the operating temperature and direct normal irradiance, with the improvement being more significant at higher temperature applications and at low direct normal irradiance.

This paper presents a solar Organic Rankine Cycle (ORC) for electricity generation; where a regression based approach is used for the working fluid. Models of the unit’s sub-components (pump, evaporator, expander and condenser) are also presented. Heat supplied by the solar field can heat the water up to 80–95 °C at mass flow rates of 2–12 kg/s and deliver energy to the ORC’s heat exchanger unit. Simulation results of steady state operation using the developed model shows a maximum power output of around 40 kWe. Both refrigerant and hot water mass flow rates in the system are identified as critical parameters to optimize the power production and the cycle efficiency.

In this study, an analytical quasi-steady state thermodynamic cycle of an adsorption cooling system (ACS) for automotive applications is presented which allows evaluating impact of different parameters on the ACS performance as well as effects of various working pairs: zeolite 13X/water, zeolite 4A/water and activated carbon-35/methanol. A comprehensive parametric study has been performed to investigate effects of temperature variation of the evaporator and condenser as well as the ICE exhaust gas temperature on the COP, cooling load produced by the evaporator and entropy generation of ACS with (or without) the heat recovery cycle (HRC). The results show that using the heat recovery cycle in the ACS can increase the COP of system up to 41% for zeolite 13X/water pair at the base-line condition. In addition, the parametric study shows that increasing regeneration and evaporation temperature increase the COP and entropy generation of ACS while increasing condensation temperature has negative effect on the COP and entropy generation. Finally, based on our modeling results, the ACS with the heat recovery cycle (HRC) and zeolite 13X/water pair are proposed for the automotive A/C applications.

Tankless water heaters present an opportunity to dramatically reduce water heating energy use. These impacts are possible because of their dramatic reduction of environmental losses through lower heat transfer areas and not keeping the heat exchanger at operating temperature between draws. The potential for energy savings has caused a lot of interest in the scientific community. However, the scientific community has not yet gained an understanding of these devices and several questions regarding their behavior remain. The areas of uncertainty include the following: 1) how these heaters behave around the minimum flow rate, 2) how well they adapt to changes in water flow rate, 3) how they behave in situations with preheated water (i.e. when used with solar water heaters) and 4) whether or not draw characteristics impact the steady state efficiency. Tests have been performed on a Rinnai R75Lsi to determine the answers to these questions for a specific heater. Tests were performed with 1) gradually changing flow rate to identify the minimum flow rate, 2) rapidly adjusting the flow rate to observe how the heater responded to suddenly changing draws, 3) temperature-flow combinations such that the minimum heat rate exceeded the required heat rate, and 4) draws under steady state conditions with varying flow rates and set temperatures. Minimum flow rate results indicate that the heater will not fire unless the flow rate surpasses 2.8 L/min and will cease firing if the flow rate decreases below 2.15 L/min while the owners manual states that the minimum flow rate is 2.3 L/min. Rapidly changing flow rate results indicate that there can be temperature fluctuations up to 9 °C and unsteady operation for up to 1 minute depending on the magnitude of the flow rate change. Tests with preheated inlet water showed that the heater uses feedback controls to avoid unstable operation at low heat rates. Steady state efficiency tests did not identify any variables which impact efficiency. Future work should include testing additional units to determine how other heaters, particularly those not manufactured by Rinnai, behave in similar situations.

Concentrating solar energy systems can use either refractive or reflective approaches to achieve the desired concentration ratio. However this is done, there is always a question about what the flux might actually be incident on the target of interest after the concentration process. Assessing the losses due to the concentration process is quite important in understanding the overall performance of the solar concentrating system. An issue that impacts this measurement is the type of system being evaluated, as the total flux at the focal point could be quite large. We have been working with concentrating PV units that utilize acrylic Fresnel lenses to achieve the necessary concentration on a single multi-junction cell. The magnitude of the losses associated with these types of lenses was desired. We developed two calorimeters for the purpose of evaluating the optical efficiency of Fresnel lenses utilized in various point focus concentrating systems. The first calorimeter developed utilizes a transient technique whereby a time-measured pulse of the beam is directed to a mass of material in a cavity form. The material has a high conductivity, so the lumped mass approximation can be used for the analysis of the energy absorbed if the temperature rise of the material is measured. The other calorimeter developed was a steady-state type that employs a technique commonly known as flow calorimetry. In this approach, the concentrated flux is beamed into the core of the calorimeter which is cooled to some steady-state value of temperature with a liquid (water near the ambient temperature was used in our tests). Knowing the liquid flow rate and temperature rise of the fluid allows the total heat input to be assessed. This paper discusses the development, testing, and comparison of the two calorimeters. Results are given for the evaluation of several types of commercial acrylic Fresnel lenses having different characteristics such as groove density and focal length.

The United States spends over 700 billion dollars on foreign oil every year. A promising method to reduce this dependence, and be carbon-neutral as well, is concentrated solar thermochemical technology. Concentrated solar thermochemical technology has the potential to directly convert sunlight into a useable, carbon-neutral fuel that can be easily stored and integrated into our existing forms of energy demand such as transportation and heating fuels. Research is being performed by several groups at Sandia National Laboratories to fundamentally understand the complex physics and chemistry occurring within a solar thermochemical reactor prototype named the CR5 [counter-rotating-ring receiver/reactor/recuperator]. The objective of the work presented in this paper is to understand recuperative heat transfer within the CR5 as a function of reactor geometry and operational conditions. The CR5 vessel utilizes counter-rotating disks to provide for thermal energy recuperation, which is a necessity for an efficient reactor. Initially a simplified steady-state two-dimensional recuperation analysis was made to evaluate the relationship between the reactive material fin height and recuperation. The results from the simplified two-dimensional model indicate that recuperation is a strong function of fin height. Next, a more detailed, but still simplified, transient, three-dimensional model was developed. The initial three-dimensional simulations presented in this paper were performed to determine recuperator effectiveness and mesh density requirements for a generic case that had 2.5 kW energy input, fin height to gap ratio of 0.9, and finned reactor disks rotating at 1 rpm. A recuperator effectiveness of 88% and 85% was calculated from the finer and coarser meshes, suggesting that the coarser mesh (lumped in the fin thickness direction) is adequate for future parametric analysis simulations. This analysis will lead to a better understanding of recuperation as a function of reactor geometry, energy input, rotational speed, and thermophysical properties.