Thermal Efficiency of LPG and PNG-fired burners: Experimental and numerical studies

In the present work, the thermal efficiency of a conventional domestic burner is studied both experimentally and numerically for liquefied petroleum gas (LPG) and piped natural gas (PNG) fuels. Three-dimensional computational fluid dynamic (CFD) modeling of the steady-state flow, combustion and heat transfer to the vessel is reported for the first time in such burners. Based on the insights from the CFD model concerning the flow and heat transfer, design modifications in the form of a circular insert and a radiant sheet are proposed which are observed to increase thermal efficiency for LPG. For PNG, predictions showed that loading height was a much more important factor affecting efficiency than these design modifications and an optimal loading height could be identified. Experiments confirm these trends by showing an improvement in burner thermal efficiency of 2.5% for LPG with the modified design, and 10% for PNG with the optimal loading height, demonstrating that the CFD modeling approach developed in the present work is a useful tool to study domestic burners. (C) 2013 Elsevier Ltd. All rights reserved.

NOx emission and thermal efficiency of a 300 MWe utility boiler retrofitted by air staging

Full-scale experiments were performed on a 300 MWe utility boiler retrofitted with air staging. In order to improve boiler thermal efficiency and to reduce NOx emission, the influencing factors including the overall excessive air ratio, the secondary air distribution pattern, the damper openings of CCOFA and SOFA, and pulverized coal fineness were investigated. Through comprehensive combustion adjustment, NOx emission decreased 182 ppm (NOx reduction efficiency was 44%), and boiler heat efficiency merely decreased 0.21%. After combustion improvement, high efficiency and low NOx emission was achieved in the utility coal-fired boiler retrofitted with air staging, and the unburned carbon in ash can maintain at a desired level where the utilization of fly-ash as byproducts was not influenced.

The effect of melt viscosity on thermal efficiency for single screw extrusion of HDPE

In this work, a highly instrumented single screw extruder has been used to study the effect of polymer rheology on the thermal efficiency of the extrusion process. Three different molecular weight grades of high density polyethylene (HDPE) were extruded at a range of conditions. Three geometries of extruder screws were used at several set temperatures and screw rotation speeds. The extruder was equipped with real-time quantification of energy consumption; thermal dynamics of the process were examined using thermocouple grid sensors at the entrance to the die. Results showed that polymer rheology had a significant effect on process energy consumption and thermal homogeneity of the melt. Highest specific energy consumption and poorest homogeneity was observed for the highest viscosity grade of HDPE. Extruder screw geometry, set extrusion temperature and screw rotation speed were also found to have a direct effect on energy consumption and melt consistency. In particular, specific energy consumption was lower using a barrier flighted screw compared to single flighted screws at the same set conditions. These results highlight the complex nature of extrusion thermal dynamics and provide evidence that rheological properties of the polymer can significantly influence the thermal efficiency of the process.

Analisys of thermal efficiency of a modified solar collector type evacuated tube

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Thermal efficiency of fiber cement corrugated sheets applied to individual housing for calves exposed to sun and shade

This research presents a study of roof thermal efficiency in individual housing for calves exposed to sun and shade through infrared thermography, internal temperature and thermal comfort indexes. Four different individual housing for calves covered with asbestos-free fiber-cement corrugated sheets were evaluated. Three of them were directly exposed to the sun: (i) corrugated sheets painted white in the external surface, (ii) corrugated sheets without painting and (iii) with screen shade fabric installed 0.10m under de internal surface of the corrugated sheet. The fourth individual housing was installed in the shade area and covered with unpainted corrugated fiber-cement sheets. The analysis was taken for 21 days at 11h00min, 14h00min and 17h00min. The results indicate significant variations in the roofing surface temperature and thermal comfort indexes among the treatments exposed to the sun and shade, for all the evaluations during the day. The infrared thermography images were effective for better understanding the heat transfer processes from the roof to the internal environment of the housing.

Influence of leaf removal on berry thermal efficiency for anthocyanin accumulation

The aim of this work was to analyse the effects of leaf removal on Touriga Nacional berry temperature and consequent thermal efficiency for anthocyanins biosynthesis. The field experiment was located at Dão Wine Research Station, Nelas, Portugal in an adult vineyard planted with North-South oriented rows, with the red grape variety Touriga Nacional grafted on 110R rootstock. The vines were trained on a vertical shoot positioning, spur-pruned on a bilateral Royat cordon system and deficit irrigated (50% ETc). The experimental design was a randomized complete block design with four replications of twelve vines per elemental plot, and the following two treatments: basal leaf removal (LR) and a control non-defoliated (ND). Berry temperature (Tb) was measured continuously during the second half (3rd to 19th September) of the 2009 ripening period using two-junction, fine-wires copper-constantan thermocouples manually inserted into the berries and connected to a data logger. A sample of clusters located in different canopy positions (exposed and internal; facing East and West) of 4 vines per treatment were used. To quantify the effect of Tb on anthocyanins biosynthesis, the berry hourly mean temperatures were converted into normal heat hours (NHH) and accumulated per day (NHHd) and per monitoring period (NHHc). For quantification of thermal requirements for anthocyanins synthesis and accumulation, a minimum of 10°C, a maximum of 35°C, and an optimum of 26°C were used. Meteorological variables were measured at an automatic weather station installed within the experimental plot. For all days of the monitoring period, daily average berry temperature (dTb) of all monitored berries was lower in ND treatment than in LR, being the maximum differences between treatments registered on 11th September. The highest dTb differences between treatments were registered on the clusters located at the west side of the canopy on 7th September while dTb of the clusters located in the centre of the canopy was less affected by leaf removal. The control non-defoliated treatment (ND) presented a significantly higher NHHc than that of LR being the higher differences presented by the clusters located in the west side. The lowest differences in NHHc were obtained in the clusters located in the centre of the canopy. Our results show that the thermal efficiency for berry anthocyanins accumulation was significantly affected by leaf removal and that this effect was dependent of the meteorological conditions, time of the day and berry/cluster location into the vine canopy.

THERMAL EFFICIENCY OF INDIVIDUAL SHELTERS FOR GIROLANDO CALVES IN BRAZILIAN SEMI-ARID REGIONS

The objective of this research was to evaluate the thermal efficiency of roofs used on individual shelters during milk-feeding stage of Girolando calves. The research was conducted at a farm located in a dry region of Pernambuco state, Brazil. The experimental design was completely randomized, with 27 Holstein × Gir dairy crossbred calves housed in shelters with three roofing materials (fibre cement tile, recycled tile, and thatched roofs). The recycled tiles and thatched roofs provided reductions of 18.7 and 14.6% in radiant thermal load, respectively. Regardless the roofing material, all animals increased their respiratory rate to maintain thermal equilibrium.

A trade-off between maxima in efficiency and specific work output of super- and trans-critical CO2 Brayton cycles

Several operational aspects for thermal power plants in general are non-intuitive and involve simultaneous optimization of a number of operational parameters. In the case of solar operated power plants, it is even more difficult due to varying heat source temperatures induced by variability in insolation levels. This paper introduces a quantitative methodology for load regulation of a CO2 based Brayton cycle power plant using the `thermal efficiency and specific work output' coordinate system. The analysis shows that a transcritical CO2 cycle offers more flexibility under part load performance than the supercritical cycle in case of non-solar power plants. However, for concentrated solar power, where efficiency is important, supercritical CO2 cycle fares better than transcritical CO2 cycle. A number of empirical equations relating heat source temperature, high side pressure with efficiency and specific work output are proposed which could assist in generating control algorithms. (C) 2015 Elsevier B.V. All rights reserved.

COUPLED OPTICAL-THERMAL-FLUID MODELING OF A DIRECTLY HEATED TUBULAR SOLAR RECEIVER FOR SUPERCRITICAL CO2 BRAYTON CYCLE

Recent studies have evaluated closed-loop supercritical carbon dioxide (s-CO2) Brayton cycles to be a higher energy density system in comparison to conventional superheated steam Rankine systems. At turbine inlet conditions of 923K and 25 MPa, high thermal efficiency (similar to 50%) can be achieved. Achieving these high efficiencies will make concentrating solar power (CSP) technologies a competitive alternative to current power generation methods. To incorporate a s-CO2 Brayton power cycle in a solar power tower system, the development of a solar receiver capable of providing an outlet temperature of 923 K (at 25 MPa) is necessary. The s-CO2 will need to increase in temperature by similar to 200 K as it passes through the solar receiver to satisfy the temperature requirements of a s-CO2 Brayton cycle with recuperation and recompression. In this study, an optical-thermal-fluid model was developed to design and evaluate a tubular receiver that will receive a heat input similar to 2 MWth from a heliostat field. The ray-tracing tool SolTrace was used to obtain the heat-flux distribution on the surfaces of the receiver. Computational fluid dynamics (CFD) modeling using the Discrete Ordinates (DO) radiation model was used to predict the temperature distribution and the resulting receiver efficiency. The effect of flow parameters, receiver geometry and radiation absorption by s-CO2 were studied. The receiver surface temperatures were found to be within the safe operational limit while exhibiting a receiver efficiency of similar to 85%.

Electricity Storage Using a Thermal Storage Scheme

The increasing use of renewable energy technologies for electricity generation, many of which have an unpredictably intermittent nature, will inevitably lead to a greater demand for large-scale electricity storage schemes. For example, the expanding fraction of electricity produced by wind turbines will require either backup or storage capacity to cover extended periods of wind lull. This paper describes a recently proposed storage scheme, referred to here as Pumped Thermal Storage (PTS), and which is based on "sensible heat" storage in large thermal reservoirs. During the charging phase, the system effectively operates as a high temperature-ratio heat pump, extracting heat from a cold reservoir and delivering heat to a hot one. In the discharge phase the processes are reversed and it operates as a heat engine. The round- trip efficiency is limited only by process irreversibilities (as opposed to Second Law limitations on the coefficient of performance and the thermal efficiency of the heat pump and heat engine respectively). PTS is currently being developed in both France and England. In both cases, the schemes operate on the Joule-Brayton (gas turbine) cycle, using argon as the working fluid. However, the French scheme proposes the use of turbomachinery for compression and expansion, whereas for that being developed in England reciprocating devices are proposed. The current paper focuses on the impact of the various process irreversibilities on the thermodynamic round-trip efficiency of the scheme. Consideration is given to compression and expansion losses and pressure losses (in pipe-work, valves and thermal reservoirs); heat transfer related irreversibility in the thermal reservoirs is discussed but not included in the analysis. Results are presented demonstrating how the various loss parameters and operating conditions influence the overall performance.

Thermal Evaluation of a Solarus PV-T collector

Low concentrator PV-T hybrid systems produce both electricity and thermal energy; this fact increases the overall efficiency of the system and reduces the cost of solar electricity. These systems use concentrators which are optical devices that concentrate sunlight on to solar cells and reduce expensive solar cell area. This thesis work deals with the thermal evaluation of a PV-T collector from Solarus.Firstly the thermal efficiency of the low concentrator collector was characterized for the thermal-collector without PV cells on the absorber. Only two types of paint were on the absorber, one for each trough of the collector. Both paints are black one is glossy and the other is dull,. The thermal efficiency at no temperature difference between collector and ambient for these two types of paint was 0.65 and 0.64 respectively; the U-value was 8.4 W/m2°C for the trough with the glossy type of paint and 8.6 W/m2°C for the trough with dull type of paint. The annual thermal output of these two paints was calculated for two different geographic locations, Casablanca, Morocco and Älvkarleby, Sweden.Secondly the thermal efficiency was defined for the PV-T collector with PV cells on the absorber. The PV cells cover 85% of the absorber, without any paint on the rest of the absorber area. We also tested how the electrical power output influences the thermal power output of the PV-T collector. The thermal and total performances for the PV-T collector were only characterized with reflector sides, because of the lack of time we could not characterize them with transparent sides also.

Thermal evaluation of a low cost wood burner

Small-scale producers of dried products in rural areas of developing countries must often rely on sun drying to dry their crops, but this can be unreliable and produce an inferior product. There is therefore a need for simple and inexpensive combustion devices that can be fabricated and used locally. A wood burner has been constructed from a "200 litre" steel drum and has then been evaluated experimentally. The thermal efficiency of the burner was found to be 31% in two trials. An energy balance, calculated for three trials, was within + 16%. Approximately one third of the energy available in the wood was lost in the flue gases, either as sensible heat or unburned volatile gases. Excess combustion air through the burner was calculated and measured to be approximately 400% of the stoichiometric requirements. A significant amount of energy was required to heat the thermal mass surrounding the burner, indicating that a lightweight insulated structure would be more suitable in most circumstances.

The effect of colour on the thermal performance of building integrated solar collectors

The use of solar collectors with coloured absorbers for water heating is an area of particular interest when considering their integration with buildings. By matching the absorber colour with that of the roof or façade of the building, it is possible to achieve an architecturally and visually pleasing result. Despite the potential for the use of coloured absorbers, very little work has been undertaken in the field.

In this study, the thermal performance of a series of coloured (ranging from white to black), building integrated solar collectors for water heating was examined both theoretically and experimentally. Subsequently, the annual solar fraction for typical water heating systems with coloured absorbers was calculated. The results showed that coloured solar collector absorbers can make noticeable contributions to heating loads. Furthermore, although their thermal efficiency is lower than highly developed selective coating absorbers, they offer the advantage of improved aesthetic integration with buildings.

Ecological efficiency in thermoelectric power plants

This work evaluates the environmental impact resulting from the natural gas and diesel combustion in thermoelectric power plants that utilize the combined cycle technology (CC), as regarding to Brazilian conditions according to Thermopower Priority Plan JPP). In the regions where there are not natural gas the option has been the utilization of diesel and consequentily there are more emission of pollutants. The ecological efficiency concept, which evaluates by and large the environmental impact, caused by CO2, SO2, NOx and particulate matter (PM) emissions. The combustion gases of the thermoelectric power plants working with natural gas (less pollutant) and diesel (more pollutant) cause problems to the environment, for their components harm the human being life, animals and directly the plants. The resulting pollution from natural gas and diesel combustion is analyzed, considering separately the CO2, SO2, NO2 and particulate matter gas emission and comparing them with the in use international standards regarding the air quality. It can be concluded that it is possible to calculate thermoelectric power plant quantitative and qualitative environment factor, and on the ecological standpoint, for plant with total power of 41441 kW, being 27 170 kW for the gas turbine and 14271 kW for the steam turbine. The natural gas used as fuel is better than the diesel, presenting ecological efficiency of 0.944 versus 0.914 for the latter, considering a thermal efficiency of 54% for the combined cycle. (c) 2006 Elsevier Ltd. All rights reserved.

Ecological efficiency in CHP: Biodiesel case

This paper evaluates and quantifies the environmental impact resulting from the combination of biodiesel fuel (pure or blended with diesel), and diesel combustion in thermoelectric power plants that utilize combined cycle technology (CC). In regions without natural gas, the option was to utilize diesel fuel; the consequence would be a greater emission of pollutants. Biodiesel is a renewable fuel which has been considerably interesting in Brazil power matrix in recent years. The concept of ecological efficiency, largely evaluates the environmental impact caused by CO(2), SO(2), NO(x) and particle matter (PM) emissions. The pollution resulting from biodiesel and diesel combustion is analyzed, separately considering CO(2), SO(2), NO(x) and particulate matter gas emissions, and comparing them international standards currently used regarding air quality. It can be concluded that it is possible to calculate the qualitative environmental factor, and the ecological effect, from a thermoelectric power plant utilizing central heat power (CHP) of combined cycle. The ecological efficiency for pure biodiesel fuel (B100) is 98.16%; for biodiesel blended with conventional diesel fuel, B20 (20% biodiesel and 80% diesel) is 93.19%. Finally, ecological efficiency for conventional diesel is 92.18%, as long as a thermal efficiency of 55% for thermoelectric power plants occurs. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.