Experimental study on a coiled tube solar receiver under variable solar radiation condition

Manipulation of the catalyst surface coverage for improved conversion and selectivity substantially requires more frequent flow reversals than the classical reverse flow operation for energy saving does (Chapter 1). 2.A reverse flow reactor should be operated at comparable switching time and residence time in order to manipulate the reactor's selectivity (Chapter 3).3. The concept of reverse flow operation with concentration programming provides an engineering tool to control conversion and selectivity, with three benefits: ammonia feedstock savings, increased ammonia conversion, and increased selectivity to NO; a drawback is the decrease of production rate (Chapter 4).4. The concept of reverse flow operation with reactor side feeding shows a fourfold superior performance: higher conversion of ammonia, higher selectivity to NO, no dead gas volume, and high production rate (Chapter 5).5. Intensification of a university study program must assure that the students' residence time distribution for completing their study follows a plug flow model.6.The concept of periodic reactor operation is natural.7. So called relaxation oscillation occurs when the cycling time period is much less than the system's time constant.However, this is not the case during reverse flow operation when operating the reactor at extremely short cycling time.8. The porosity of a fixed bed can be determined elegantly by a combination of reverse flow operation and cycling of the feed concentration.9. Joint bachelor-master-doctor programs improve the selectivity to master and doctor degrees as well as the productivity of a university.10. Assalamu'alaikum is a time-independent greeting.

An advanced modeling and experimental study to improve temperature uniformity of a solar receiver

This computational study investigates design of microchannel based solar receiver for use in concentrated solar power. A design consisting of a planar array of channels with solar flux incident on one side and using supercritical carbon dioxide as the working fluid is sought. Use of microchannels is investigated as they offer enhanced heat transfer in solar receivers and have the potential to dramatically reduce the size and increase the performance. Designs are investigated for an incident heat flux of 1 MW/m2, up to 3.3 times that of current solar receivers [1], resulting in significant reduction of size and cost. The goal is to design a microchannel receiver with inlet and outlet temperatures of the working fluid of 500°C and 650°C, operating pressure of 100 bar, pressure drop less than 0.35 bar and surface efficiency greater than 90% defined by radiation and convection losses to the environment. Three micro-channel designs are considered: rectangular cross section with high and low aspect ratio (designs A and B) and rectangular cross section with an array of micro pin-fins of various shape spanning the height of the channel (design C). Numerical simulations are performed on individual channels and on a unit cell of the pin-fin design. Structural analysis is performed to ensure that the design can withstand the operating pressure and thermal stresses. The effects of flow maldistribution and header system in an array of channels are also investigated. Preliminary results show that all three designs are capable of meeting the requirements, with the pin-fin design having the lowest pressure drop and highest efficiency.

Evaluation of hydrogen production with iron-based chemical looping fed by different biomass

Design and performance of a new type of boiler using concentrated solar flux

Recuperated solar-dish Brayton cycle using turbocharger and short-term thermal storage

Semiconductor materials for thermoelectric power generation up to 700°C

Biological oxidation of hydrogen sulfide under steady and transient state conditions in an immobilized cell biofilter

The commercial sector in Europe consumes a lot of energy and has one of the highest rates of energy consumption in supermarkets. Thus, supermarkets are an important part for the purposes of meeting the targets for reducing greenhouse gases which Europe has set as 10% by 2020. This article discusses the potential of economic and energy consumption savings in addition to the reduction in greenhouse gases that a high energy efficiency air conditioning installation can have in supermarkets. An analysis of the air conditioning installation is carried out in a commercial infrastructure considered as a model. Exploring the way energy is used at different times of the year and comparing the results obtained from a traditional duct installation and a high energy efficiency installation. High energy efficiency installation uses inverter technology and energetically takes advantage of the residual heat from industrial cooling processes. When high energy efficiency system is used for supermarket air conditioning, the savings in electricity consumption vary between 56 and 62%, reducing CO2 emissions to less than half with a payback period in high energy efficiency installation of three-to-four years and this reduces the ecological footprint of the products sold in supermarkets.

This paper evaluates cost and performance tradeoffs of alternative supercritical carbon dioxide (s-CO2) closed-loop Brayton cycle configurations with a concentrated solar heat source. Alternative s-CO2 power cycle configurations include simple, recompression, cascaded, and partial cooling cycles. Results show that the simple closed-loop Brayton cycle yielded the lowest power-block component costs while allowing variable temperature differentials across the s-CO2 heating source, depending on the level of recuperation. Lower temperature differentials led to higher sensible storage costs, but cycle configurations with lower temperature differentials (higher recuperation) yielded higher cycle efficiencies and lower solar collector and receiver costs. The cycles with higher efficiencies (simple recuperated, recompression, and partial cooling) yielded the lowest overall solar and power-block component costs for a prescribed power output.

Enhanced bifunctional electrocatalysis of Co5.47N nanocrystals in porous carbon nanofibers for high-efficiency zinc-air batteries

<div class="section abstract"><div class="htmlview paragraph">Fundamental engine research is primarily conducted under steady-state conditions, in order to better describe boundary conditions which influence the studied phenomena. However, light-duty automobiles are operated, and tested, under heavily transient conditions. This mismatch between studied conditions and in-use conditions is deemed acceptable due to the fundamental knowledge gained from steady-state experiments. Nonetheless, it is useful to characterize the conditions encountered during transient operation and determine if the governing phenomena are unduly influenced by the differences between steady-state and transient operation, and further, whether transient behavior can be reasonably extrapolated from steady-state behavior.</div><div class="htmlview paragraph">The transient operation mode used in this study consists of 20 fired cycles followed by 80 motored cycles, operating on a continuous basis. The intention of the cycle is to provide a significant transient condition, namely the change from motored to knock-limited fired operation, while also maintaining a repeatable cycle that allows for the collection of statistics during quasi- steady-state operation.</div><div class="htmlview paragraph">This study investigates the effect of transient operation on Knock-Limited Combustion Phasing (KL-CA50) compared to steady-state operation. Three compositionally dissimilar matched Research Octane Number (RON) = 98 fuels are used in this study, allowing for the assessment of fuel-specific effects on differences between steady-state and transient operation.</div><div class="htmlview paragraph">This study first characterizes the 20/80 firing cycle described above, before comparing the transient KL-CA50 measurements to the steady-state KL-CA50 measurements. Analysis of both the steady-state and transient results are used to gain insights into the effects of transient operation on end-gas autoignition, relative to steady-state operation and as a function of fuel composition.</div><div class="htmlview paragraph">The results of this study indicate the significant effect that transient operation has on KL-CA50 behavior of a fuel. This is both universal, in that all fuels show responses to the differences in compression temperatures of the charge, as well as fuel specific, in that the fuel response varies based on the fuel’s sensitivity to temperature, [O2], and trace species. All fuels showed a significant load extension under transient operation, based on tolerance of higher intake pressures. However, transient operation moved operating conditions to “beyond RON” (Octane Index K < 0) conditions, which favored higher-sensitivity fuels. Based on the analysis of system time constants (e.g. cylinder head temperature dynamic response, exhaust gas temperature dynamic response), it is expected that transient operation, and the benefits for knock-limited operation, are highly influential on drive-cycle performance.</div></div>

Concentrated Solar Power (CSP) with Thermal Energy Storage (TES) has the potential to realize grid parity. This can be achieved by operating CSP systems at temperatures above 700 °C to reach high thermal efficiencies (> 50%). However, operating CSP systems at elevated temperatures poses several problems, among which the design of solar receivers to handle increased thermal loads is critical. To this end, this work explores and optimizes various swirl-inducing internal fin designs for improving heat transfer in solar receiver tubes. These fin designs, in addition to enhancing the thermal performance of receiver tubes, are also capable of reducing temperature unevenness caused by nonuniform solar loads. This work optimizes the geometric parameters such as height and helical pitch of these fin designs by maximizing the Nusselt number with a constraint on the friction factor. The fin design optimization, however, is computationally intensive, often requiring hundreds of simulation call to the Computational Fluid Dynamics (CFD) model. To circumvent this problem, this work employs surrogate models to approximate the simulation outputs needed during the optimization.

Design and evaluation of a lab-scale tungsten receiver for ultra-high-temperature solar energy harvesting

A conceptual design for a 10-MWe Heat Pipe Central Receiver Gas-Turbine Power Plant has been developed. The heat pipe central solar receiver uses heat pipes to transform the concentrated high solar heat flux at the receiver into a lower heat flux compatible with gas heat-transfer systems. Several Brayton cycles were studied to determine which cycles and operating conditions are technically and economically most viable for a central receiver power plant. A regenerative open-gas cycle with an inlet turbine temperature of 816/sup 0/C (1500/sup 0/F) was selected. The turbine-generator and receiver are located at the top of a steel tower, with a north field of 2-axis tracking heliostats. The system can be adapted for operation as a hybrid plant, providing a higher level of availability and a dependable generating capacity - important considertions from the utility point of view. The predicted cycle efficiency is 33 to 38 percent, and the overall solar-to-electric efficiency is 19.1 to 22.3 percent. Capital cost of the plant is estimated to be in the $1947 to $2002/kW range, depending on the assumed cost for the collector system. Compared with a water/steam solar system, estimated costs in mid-1978 dollars are lower and plant efficiency is superior.