Showing papers in "International journal of ambient energy in 2009"
TL;DR: In this article, the authors examined the theoretical aspects of choosing a tilt angle for the solar flat-plate collectors used at New Delhi and made recommendations on how the collected energy can be increased by varying the tilt angle.
Abstract: SYNOPSIS Flat-plate solar collectors are widely used at New Delhi in India for water heating purposes. The roofs of many residential premises in the capital city are fitted with such collectors. This article examines the theoretical aspects of choosing a tilt angle for the solar flat-plate collectors used at New Delhi and makes recommendations on how the collected energy can be increased by varying the tilt angle. In this paper, the collector surface is assumed to be facing South and the calculations are based upon the measured values of hourly global and diffuse solar radiation on a horizontal surface in the capital city. The beam component of the horizontal global radiation is estimated as the difference between the global and diffuse solar radiation. The solar radiation on a tilted surface is calculated as the angle of tilt is varied from 0° to 90°. It is shown that very nearly optimal energy can be collected if the angle of tilt is varied seasonally, four times a year.
22 citations
TL;DR: In this article, the effect of a complex generalised heat transfer law on the ecological performance of an endoreversible Carnot heat pump is derived by taking as the objective function an ecological optimisation criterion representing the best compromise between the exergy output rate and exergy loss rate (entropy production rate).
Abstract: SYNOPSIS The effect of a complex generalised heat transfer law q ∝ (ΔTn)m on the ecological performance of an endoreversible Carnot heat pump is derived by taking as the objective function an ecological optimisation criterion representing the best compromise between the exergy output rate and exergy loss rate (entropy production rate) of the heat pump. The results obtained include the optimal ecological performance of an endoreversible heat pump with various heat transfer laws, as obtained in existing literature.
20 citations
TL;DR: In this paper, the authors investigated the exergoeconomic performance of an endoreversible simple gas turbine cycle cogeneration plant coupled to constant temperature heat reservoirs using finite time thermodynamics.
Abstract: SYNOPSIS The exergoeconomic performance of an endoreversible simple gas turbine cycle cogeneration plant coupled to constant temperature heat reservoirs is investigated using finite time thermodynamics. The analytical formulae for profit rate and exergy efficiency of the cogeneration plant are deduced. By means of numerical calculations, the heat conductance allocation and pressure ratio are optimised by taking the maximum profit rate as the objective. The characteristic of optimal dimensionless profit rate versus exergy efficiency is investigated and the effects of design parameters on optimal performance of the cogeneration plant are also analysed. The results show that there exist a sole group of optimal heat conductance allocations among hot-, cold- and consumer-side heat exchangers and an optimal pressure ratio which lead to the maximum dimensionless profit rate, and there exists an optimal consumer-side temperature which leads to a double-maximum dimensionless profit rate.
18 citations
TL;DR: In this article, a model of a new type thermoelectric heat pump driven by a generator is built and the performance of the device is analyzed and optimized based on non-equilibrium thermodynamics.
Abstract: SYNOPSIS A model of a new-type thermoelectric heat pump driven by a thermoelectric generator is built and the performance of the device is analysed and optimised based on non-equilibrium thermodynamics. The analytical formulae concerning heating load, non-dimensional heating load and coefficient of performance (COP) of the device versus the working electric current (or the distribution ratio of thermoelectric element numbers between the thermoelectric generator and the thermoelectric heat pump) are derived. The optimum non-dimensional working electric current and the optimum distribution ratio of thermoelectric element numbers are obtained. Moreover, the effects of temperature of the two heat reservoirs on the performance of the device are analysed and the COP versus non-dimensional heating load characteristic is obtained.
17 citations
TL;DR: In this paper, the authors present the analysis and results of a pilot survey regarding energy consumption patterns for major end-uses in the residential sector of the Kashmir valley in the Indian province of Jammu and Kashmir.
Abstract: SYNOPSIS This study presents the analysis and results of a pilot survey regarding energy consumption patterns for major end-uses in the residential sector of the Kashmir valley in the Indian province of Jammu and Kashmir. The major energy consuming end-uses are space heating, water heating, cooking and lighting. A questionnaire was designed to collect the responses. A total of 120 households were interviewed regarding their energy consumption and purchase patterns, energy source usage for different end-uses, types of energy sources and systems for different end-uses in rural and urban households and reasons for their choice. The survey covered different income group families in rural and urban areas. Space heating was found to be the major energy consuming end-use in the residential sector of the valley.
14 citations
TL;DR: In this article, an ecological criterion is introduced into the performance analysis and optimisation of an endoreversible four-heat-reservoir absorption refrigerator cycle with Newtonian heat transfer law.
Abstract: SYNOPSIS An ecological criterion is introduced into the performance analysis and optimisation of an endoreversible four-heat-reservoir absorption refrigerator cycle with Newtonian heat transfer law. The ecological optimisation criterion is set up based on the viewpoint of energy analysis. The optimal relationship between the ecological criterion and the (COP) coefficient of performance, the optimal relationship between the entropy generation rate and the COP, and the maximum ecological criterion and the corresponding COP, cooling load and entropy generation rate are derived by using finite-time thermodynamics. Moreover, the ecological criterion is compared with the cooling load criterion by numerical example. The results show that the ecological criterion is a significant one for the optimal design of absorption refrigerators.
13 citations
TL;DR: In this article, an irreversible closed intercooled regenerated Brayton cycle coupled to variable-temperature heat reservoirs is analyzed and optimised for an arbitrary number of variables, defined as the ratio of power output to maximum specific volume in the cycle.
Abstract: SYNOPSIS In this paper, power density, defined as the ratio of power output to maximum specific volume in the cycle, is analysed and optimised for an irreversible closed intercooled regenerated Brayton cycle coupled to variable-temperature heat reservoirs, according to the theory of finite-time thermodynamics. The analytical formulae for dimensionless power density and efficiency, as functions of the total pressure ratio, the inter-cooling pressure ratio, the component (i.e. regenerator, intercooler, and hot- and cold-side heat exchangers) effectivenesses, the compressor and turbine efficiencies, the thermal capacity rates of the working fluid and the heat reservoirs, the pressure recovery coefficients, the heat reservoir inlet temperature ratio, and the inlet temperature ratio of cooling fluid in the intercooler and the cold-side heat reservoir, are derived. The optimum dimensionless power density is obtained by optimising the intercooling pressure ratio. The maximum dimensionless power density is obtain...
11 citations
TL;DR: In this article, performance analysis and parametric study for combined Brayton and two parallel inverse Brayton cycles using second law analysis was carried out and the analytical formulae of exergy balance, exergy and work output, and exergy efficiency were derived.
Abstract: SYNOPSIS Performance analysis and parametric study has been carried out for combined Brayton and two parallel inverse Brayton cycles using second law analysis. The analytical formulae of exergy balance, exergy and work output, and exergy efficiency are derived. The largest exergy loss location is determined. The influences of various parameters on the exergy efficiency and other performances are analysed and the optimizations of the expansion pressure of the first inverse Brayton cycle are carried out by numerical examples.
10 citations
TL;DR: In this paper, the effect of helical tape inserts of two different twist ratios (23 and 11) on the friction factor and heat transfer coefficient for a flow in a circular tube maintained at uniform heat flux conditions was investigated.
Abstract: SYNOPSIS The thermal performance of a solar air heater may be enhanced by means of twisted tapes, inserted inside the fluid flow tubes, which induce swirl flow acting as turbulence promoters. Experiments were carried out to investigate the effect of helical tape inserts of two different twist ratios (23 and 11) on the friction factor and heat transfer coefficient for a flow in a circular tube maintained at uniform heat flux conditions. The data were recorded at low Reynolds numbers, well in the turbulent region, for a wide range, 8.05 × 103 − 1.36 × 104. The results confirm that this system with helical tape inserts could enhance heat transfer by about 1. 15 to 1.7 times compared to that of plain tube. Also, the study shows that higher heat transfer rates were recorded for lower twist ratios.
10 citations
TL;DR: In this article, an analysis of the application of ground source heat pump (GSHP) systems to different temperature zones in China is presented, and the results show that a GSHP system can be applied to the first four temperature zones above, but not the cold temperate zone and the Qinghai-Tibet Plateau vertical temperature zone.
Abstract: SYNOPSIS An analysis of the application of ground source heat pump (GSHP) systems to different temperature zones in China is presented in this paper. According to the climate characteristics, China is divided into six different temperature zones: the tropical zone, the subtropical zone, the warm temperate zone, the mid temperate zone, the cold temperate zone, and Qinghai-Tibet Plateau vertical temperature zone. Six representative cities corresponding to the six temperature zones are chosen and their different climate and soil characteristics are studied. The results show that a GSHP system can be applied to the first four temperature zones above, but not the cold temperate zone and the Qinghai-Tibet Plateau vertical temperature zone. However, in different temperature zones, different GSHP systems should be designed and built.
9 citations
TL;DR: In this article, the energy efficiency of a low cost, locally fabricated, natural convection type solar crop dryer in India has been studied, and the energy payback period has been evaluated when displacing different conventional fuels and found to be 1.1 0, 1.55, 1.32 and 1.77 years.
Abstract: SYNOPSIS The energetics of a low cost, locally fabricated, natural convection type solar crop dryer in India has been studied. Other types of dryers are available commercially in the market, but they are costly and their total energy input is high. This analysis may be helpful to manufacturers who wish to know the energy requirement of the different components of the systems, and to reduce GHG emissions. Locally grown chilli has been dried to evaluate the energetics of the dryer. Energy payback period has been evaluated when displacing different conventional fuels and found to be 1.1 0, 1.55, 1.32 and 1.77 years in the case of fuelwood, light diesel oil (LDO), coal and natural gas respectively. The energetics of such a simple and affordable dryer should be further analysed to reduce national and global energy demand.
TL;DR: In this paper, the optimal configuration of a class of endoreversible heat engines with generalised radiative heat transfer law [q ∝ Δ(Tn)] has been determined by using optimal-control theory and the differential equations are solved by Taylor series expansion.
Abstract: SYNOPSIS The optimal configuration of a class of endoreversible heat engines with generalised radiative heat transfer law [q ∝ Δ(Tn)] has been determined by this paper. The optimal cycle that maximises the power output of the engine has been obtained using optimal-control theory and the differential equations are solved by Taylor series expansion. It is shown that the optimal cycle for maximum power output has six branches including two isothermal branches and four maximum-power branches, without adiabatic branches. The interval of each branch has been obtained, as well as the solutions of the temperatures of heat reservoirs and working fluid. Numerical examples for the optimal configurations with n = −1, n = 1, n = 2, n = 3 and n = 4 respectively, are given. The results obtained are compared with each other and with those results obtained with a fixed compression ratio constraint for maximum power output.
TL;DR: In this article, an exergy-based ecological optimisation criterion, which consists of maximising a function representing the best compromise between the exergy output rate and exergy loss rate (entropy generation rate and environment temperature product), is taken as the objective function.
Abstract: SYNOPSIS On the basis of exergetic analysis, ecological performance analysis and optimisation of an endoreversible simple air heat pump cycle with constant-temperature heat reservoirs is carried out in this paper. An exergy-based ecological optimisation criterion, which consists of maximising a function representing the best compromise between the exergy output rate and exergy loss rate (entropy generation rate and environment temperature product) of the heat pump cycle, is taken as the objective function. The analytical formulae concerning the relationship between the exergy-based ecological function and pressure ratio is derived with heat resistance losses in the hot- and cold-side heat exchangers. The effects of the effectivenesses of the heat exchangers, the ratio of hot-side heat reservoir temperature to ambient temperature and the heat reservoir temperature ratio on the exergy-based ecological function are analysed. The cycle performance optimisations are performed by identifying the optimum pressur...
TL;DR: In this paper, a continent-wide supergrid is proposed to enable the huge renewable resources on the periphery of the EU to be tapped and would also help limit the supply-and demand-matching problems caused by the local variability of some renewable sources.
Abstract: SYNOPSIS A continent-wide supergrid would enable the huge renewable resources on the periphery of the EU to be tapped and would also help limit the supply-and demand-matching problems caused by the local variability of some renewable sources.
TL;DR: In this article, two alternative novel retrofit solutions have been identified and their advantages over current installation practice presented, and both systems have been shown to offer a substantial improvement over the conventional installation practice.
Abstract: SYNOPSIS The retrofit solar water heating market represents the greatest single area in the UK where significant application of solar energy capture can be achieved. However, many barriers exist to wide-scale implementation. Cost-effectiveness is by far the greatest single factor, created by high installation cost and reduced solar collection due to the typical prevailing solar conditions in a Northern Maritime Climate. The installation of a solar water heating system typically requires disruption to the existing domestic hot water system, quite often including disruption to the auxiliary space heating system as well. Finally, the typical installation produces a certain amount of waste arising from the removal of existing components that have been, prior to the solar water heating installation, in perfectly good working order. Two alternative novel retrofit solutions have been identified and their advantages over current installation practice presented. Both systems have been shown to offer a substantial ...
TL;DR: In this article, the theory of finite-time thermodynamics is used in the performance analysis of a class of endoreversible closed IFGT cycles coupled to variable temperature heat reservoirs, as functions of the total pressure ratio, component (HTHE, hot- and cold-side heat exchangers) effectivenesses, compressor and turbine efficiencies and the thermal capacity rates of the working fluid and the heat reservoirs.
Abstract: SYNOPSIS Indirectly or externally-fired gas-turbines (IFGT or EFGT) are interesting technologies under development for small and medium scale combined heat and power (CHP) supplies in combination with micro-gas-turbine technologies. The emphasis is primarily on the utilisation of the waste heat from the turbine in a recuperative process and the possibility of burning biomass (even “dirty” fuel) by employing a high temperature heat exchanger (HTHE) to avoid the combustion gases passing through the turbine. In this paper, the theory of finite time thermodynamics is used in the performance analysis of a class of endoreversible closed IFGT cycles coupled to variable temperature heat reservoirs. The analytical formulae for the dimensionless power output and efficiency, as functions of the total pressure ratio, component (HTHE, hot- and cold-side heat exchangers) effectivenesses, compressor and turbine efficiencies and the thermal capacity rates of the working fluid and the heat reservoirs, the pressure recover...
TL;DR: In this article, a new cyclic model of a four-reservoir endoreversible chemical potential transformer was proposed and the optimal relationship between the rate of energy pumping and the coefficient of performance was derived by using thermodynamic optimisation.
Abstract: SYNOPSIS A new cyclic model of a four-reservoir endoreversible chemical potential transformer is put forward. The optimal relationship between the rate of energy pumping and the coefficient of performance (COP) as well as the maximum rate of energy pumping and the corresponding COP are derived by using thermodynamic optimisation. The optimal times of the four mass transfer processes are also obtained. Moreover, the effects of the cyclic parameters on the optimal relationship and the limits of COP and the rate of energy pumping are studied by detailed numerical examples.
TL;DR: In this article, an energy loss model based on the loss of relative kinetic energy is presented and implemented to obtain realistic values of the expected power coefficient of a small wind turbine, which is compared to those of some wind turbines.
Abstract: SYNOPSIS Stagnation enthalpy is used to obtain the expression of the performance of a horizontal-axis wind turbine blade row. An energy loss model based on the loss of relative kinetic energy is then presented and implemented to obtain realistic values of the expected power coefficient of a small wind turbine. Values of the mean expected coefficient of performance from the present model are compared to those of some wind turbines.
TL;DR: In this article, a closed cycle gas turbine power plant with reheater was investigated on the basis of harmonic mean isentropic exponent and an analytical expression was derived for the pressure ratio corresponding to maximum power and maximum dimensionless net work output.
Abstract: SYNOPSIS A closed cycle gas turbine power plant with reheater is investigated on the basis of harmonic mean isentropic exponent. An analytical expression is derived for the pressure ratio corresponding to maximum power and maximum dimensionless net work output. It is found that the pressure ratio corresponding to maximum power and the maximum non-dimensional net work is high when the ratio of extreme temperatures of cycle (i.e. Tmax and Tmin) and isentropic efficiencies of compressor and turbine (i.e. ηc and ηt) are high. The theoretical results are also compared with the results obtained by considering practical reheat turbine data.
TL;DR: In this paper, the authors investigated the transverse temperature distribution inside the micro-channel of a thermoacoustic stack based on wave theory, and derived expressions of velocity and transversal temperature, which can be taken as complex due to the wave characteristics.
Abstract: SYNOPSIS The characteristics of a transverse temperature wave which was generated by diffusion and a wave inside the micro-channel of a thermoacoustic stack are investigated in this paper, by extending the application of the “relaxation-time” approximation to the description of the transverse heat exchange in the total temperature field. The purpose of this paper is to investigate the transverse temperature distribution inside the micro-channel of a thermoacoustic stack based on wave theory. The expressions of velocity and transverse temperature, which can be taken as complex due to the wave characteristics, are derived by solving the governing equations for the flow. Theoretical calculations show that the influence of the system construction and the penetration depth on both the real part and the imaginary part of the temperature field is significant. The irreversible model accounting for the relaxation-time established in the paper reveals the boundary layer effects of viscosity and thermal conduction. ...