Design and optimisation of a combination solar collector–thermal engine operating on Mars

A “dynamic” solar power plant (which consists of a solar collector–thermal engine combination) is proposed as an alternative for the more usual photovoltaic cells. A model for heat losses in a selective flat-plate solar collector operating on Mars is developed. An endoreversible Carnot cycle is used to describe heat engine operation. This provides upper limits for real performances. The output power is maximized. Meteorological and actinometric data provided by Viking Landers are used as inputs. Two strategies of collecting solar energy were considered: (i) horizontal collector; (ii) collector tilt and orientation are continuously adjusted to keep the receiving surface perpendicular on the Sun’s rays. The influences of climate and of various design parameters on solar collector heat losses, on engine output power and on the optimum sun-to-user efficiency are discussed.     

Thermodynamic analysis of thermal efficiency and power of Minto engine

Minto engine is a kind of liquid piston heat engine that operates on a small temperature gradient. But there is no power formula for it yet. And its thermal efficiency is low and formula sometimes is misused. In this paper, deriving the power formula and simplifying the thermal efficiency formula of Minto engine based on energy distribution analysis will be discussed. To improve the original Minto engine, a new design of improved Minto engine is proposed and thermal efficiency formula and power formula are also given. A computer program was developed to analyze thermal efficiency and power of original and improved Minto engines operating between low and high-temperature heat sources. The simulation results show that thermal efficiency of improved Minto engine can reach over 7% between 293.15 K and 353.15 K which is much higher than that of original one; the temperature difference between upper and lower containers is lower than half of that between low and high temperature of heat sources when the original Minto engines output the maximum power; on the contrary, it is higher in the improved Minto engines.     

Health and safety issues for microwave power transmission

A general public perception that microwaves are hazardous has been a key obstacle for acceptance of microwave power transmission (MPT). This perception will eventually dissipate and then attention will focus on a real technical problem, that of interference (RFI). This can range from perceptible through annoying to hazardous. A program of actions is proposed to accelerate the goal of public acceptance of MPT.In this paper, a historical review shows that the solar power satellite (SPS) was reviewed a number of times relative to potential microwave exposure hazards. In all cases, no “show-stopper” was found but often the shibboleth “more research is needed” was aired. It is shown that standards for safe exposure to microwaves are the most important asset in convincing an audience that microwave exposure associated with MPT or SPS is safe. Standard-setting, world-wide, is shown to converge towards rational limits that are supportive of the MPT/SPS concepts. In recent times there has been the proposed substitute of “risk communication” (“prudent avoidance”). This is an unwise substitute for standards.Other aspects of microwave exposure standards are the new interface with RFI—hence the need for a rational division of responsibility between the radiators and the victim devices, like medical electronics—using both radiation limits and susceptibility limits. Beneficial applications of microwave exposure are being developed.Several studies are recommended which could put into perspective the likelihood of improbable events that represent “catastrophe”—e.g. the inadvertent focusing of a great amount of energy into inhabited areas.     

An experimental investigation on DI diesel engine with hydrogen fuel

The internal combustion engines have already become an indispensable and integral part of our present day life style, particularly in the transportation and agricultural sectors [Nagalingam B. Properties of hydrogen. In: Proceedings of the summer school of hydrogen energy, IIT Madras, 1984]. Unfortunately the survival of these engines has, of late, been threatened due to the problems of fuel crisis and environmental pollution. Therefore, to sustain the present growth rate of civilization, a nondepletable, clean fuel must be expeditiously sought. Hydrogen exactly caters to the specified needs. Hydrogen, even though “renewable” and “clean burning”, does give rise to some undesirable combustion problems in an engine operation, such as backfire, pre-ignition, knocking and rapid rate of pressure rise [Srinivasa Rao P. Utilization of hydrogen in a dual fueled engine. In: Proceedings of the summer school of hydrogen energy, IIT Madras, 1984; Siebers DL. Hydrogen combustion under diesel engine conditions. Hydrogen Energy 1998;23:363–71]. The present investigation compares the performance and emission characteristics of a DI diesel engine with gaseous hydrogen as a fuel inducted by means of carburation technique and timed port injection technique (TPI) along with diesel as a source of ignition [Swain N, Design and testing of dedicated hydrogen-fueled engine. SAE 961077, 1996]. In the present study the specific energy consumption, NO_x emission and the exhaust gas temperature increased by 6%, 8% and 14%, respectively, and brake thermal efficiency and smoke level reduced by 5% and 8%, respectively, using carburation technique compared to baseline diesel. But in the TPI technique, the specific energy consumption, exhaust gas temperature and smoke level reduced by 15%, 45% and 18%, respectively. The brake thermal efficiency and NO_x increased by 17% and 34%, respectively, compared to baseline diesel. The emissions such as HC, CO, and CO₂ is very low in both carburation and TPI techniques compared baseline diesel.     

Diagnosis methodology for the turbocharger groups installed on a 1 MW internal combustion engine

The issue of internal combustion engine (ICE) diagnosis attracts great interest because modern engines need continual control of the operational status, in order to obtain high efficiency in energy conversion and accurate control of the polluting emissions. In particular, in reference to an alternative ICE of 1 MW, the present study relates the development, through the design of neural simulators, of the turbocharger maps to reproduce the operational states characterized by new&clean conditions and allowing the evaluation of particular “health state” indices of such a module. In detail, after an experimental campaign, turbocharger fundamental characteristics referred to new&clean conditions, such as the compressor isoentropic efficiency and the mass flow elaborated by the turbine, were evaluated at different operation conditions of the alternative ICE Subsequently, the neural simulators were developed through the training and test of different neural architectures.     

An analytical method for reflected flux density calculations

Conception, evaluation and real time control of solar “power tower” systems require the use of fast and accurate computer programs for calculating the flux density distributions on the receiver. Since the classical methods of “cone optics” and “hermite polynomial expansion” have some limitations of speed and accuracy, we have built an analytical model for calculating the convolution of the solar brightness distribution with the principal image of a heliostat (i.e. the fictive image for a “point sun”). We first characterize a principal image of a focusing heliostat by its shape and its geometrical concentration factor. Then this image is projected back onto the central plane (which passes through the center of the mirror), and considered as a flat reflecting surface. And the problem is reduced to density calculation for a flat heliostat. For each point of the receiver, the density of flux reflected by a heliostat is obtained by direct resolution of a convolution integral. The different formulations used to express the density function correspond to the various types of intersections between the image of the solar disk for the considered point and the principal image of the heliostat. Confrontation of this method with a program based on “cone optics” shows a good concordance of results and a strong decrease of computation time. We want to apply this method to the existing “THEMIS” solar plant built in France and to compare our results with real observations. Our density calculation programs will help conceiving fields of focusing heliostats for a new generation of power systems (gaz turbine systems).     

Variance analysis of estimates and measurements of terrestrial heat flow

A components-of-variance-analysis is applied to compare heat flow estimates with heat flow measurements. Three types of heat flow data are analysed; they are: “between depth interval within well” variances, “between well site-within region” variances and “between region” variances. “Between depth interval-within well” heat flow variances are typically greater for estimates than for measurements, implying a greater unsystematic uncertainty with the interval heat flow estimates as compared to the interval measurements. “Between well site-within region” variances of heat flow are about the same, or in some cases less, for groups of estimated data as compared with groups of measured data. Therefore unsystematic uncertainties for good heat flow estimates at sites within a region should compare favourably with similar uncertainties for heat flow measurements at sites within a region. Both the “F” test and the “between region” heat flow variances suggest that estimates and measurements of heat flow can reasonably differentiate between regions of different heat flow.Some of the estimated and measured data groups are from the same region. The very limited number of heat flow estimates and measurements available indicate that the mean of estimates and the mean of deep measurements in the northern Colorado Plateau are in close agreement. While this suggests the possibility that a number of carefully calculated heat flow estimates may reasonably define the mean heat flow for a region, more data in other regions will be needed to support the concept.     

Performance assessment of an internal combustion engine at varying dead (reference) state temperatures

This study deals with investigating the effect of varying dead state temperatures on exergy efficiency of a high-oleic methyl ester (HOME) fueled internal combustion engine (ICE). This engine is a 4.5L, four-stroke, four-cylinder, turbocharged, 66.5 kW maximum power capacity John Deere 4045T diesel engine run with HOME, which is genetically modified with a high-oleic soybean oil methyl ester. The test speed is 1400 min⁻¹ at a full load. In the analysis, actual operational data obtained from a study conducted by one of the co-authors at Iowa State University, USA are used. Exergy efficiency values at various dead state temperatures are calculated for comparison purposes since these types of engines may be operated under different outdoor air conditions. The results obtained are discussed from the exergetic point of view. It was found that exergetic efficiency increased as dead state temperature decreased. As a result, exergy efficiency values ranged from 29.78% to 34.93% based on dead state temperatures between −5 °C and 30 °C.     

Pinch analysis for cooling towers

Optimizing the operation of a power plant with respect to the so-called “cold end” allows for a higher overall efficiency. Among other methods it also requires the proper adaptation of the mass flow rate of the cooling water. In this paper a pinch analysis with respect to heat and mass transfer has been applied to find the optimum mass flow rate for the cooling tower.     

The use of waste heat in a solar still

There are instances in remote areas where heat is being wasted, e.g., in internal combustion, engines, etc. Some of this heat can be recovered to produce distilled water in solar stills.

The solar still replaces the cooling tower, ponds, or radiators normally used to control the engine temperature. The diesel cooling water in such a system remains separate from the saline water in the solar still.

The advantages of using such a system compared with a conventional solar still are:

1. (a) water costs are very much reduced

2. (b) the area occupied is much less, i.e., about 1/5th

3. (c) production has much less seasonal variation

4. (d) the efficiency of the solar still is improved due to the higher operating temperatures.

From experiments conducted at Highett using a Mk VI solar still fitted with a simple heat exchanger and a separate electrically-heated source of hot water to simulate the waste heat, design data are not available for application to working systems. The information required to match a solar still to a diesel's cooling requirement is:

1. (a) engine efficiency

2. (b) hourly fuel consumption

3. (c) hourly solar radiation

4. (d) hourly ambient temperatures.

A by-product of this work has been the production of a “solar water heater” which costs less than that of the cheapest conventional system. This “solar” hot water system uses a heat exchanger similar to what is used to transfer the waste heat to the saline water. It is envisaged to have hot water productions approximately the same as the distilled water productions. The influence of hot water production on the output of the waste heat solar still is discussed.     

CAFE compliance by light trucks: economic impacts of clean diesel engine

With the popularity of light trucks increasing in the United States, their share of the US light vehicle market had doubled between 1980 and 1996, climbing from 20 to 40%. By 1996, annual energy consumption for light trucks had risen to 5.97×10¹⁵ Btu [5.97 quadrillion Btu, or “quad,” or 6.30×10¹⁸ joule (J)], compared to 7.94 quad (8.38×10¹⁸ J) for cars. In recent years (since 1995), the fuel economy of US - manufactured light trucks (almost 99% of which use gasoline engines) has been below the Corporate Average Fuel Economy (CAFE) standards. This paper analyzes a strategy to reduce the CAFE shortfalls by adopting the new, highly energy-efficient clean diesel engine. Research on such engines has been funded by the US Department of Energy, Office of Heavy Vehicle Technologies, under its Light Truck Clean Diesel Engine Program. A clean diesel engine market penetration trajectory is developed, representing an industry response to meet the CAFE standards. Whether the engine will be produced inside the country or imported remains uncertain, so two cases are defined. Values of exports/imports of clean diesel engines/trucks under these cases are estimated. The macroeconomic benefits are estimated by using a model of the US economy developed by Standard & Poor's Data Resources, Inc. On the basis of gains in the gross domestic product projected under the alternative cases, domestic production of the clean diesel engine is favored over importing it.     

Analysis of MPPT characteristics in photovoltaic power system

This paper describes characteristics evaluation of the power conditioner which has the function of Maximum Power Point Tracking (MPPT) by “mountain climbing method” through computer simulations. The generated power on the constant voltage control is compared to the one on MPPT with the load matching correction factor (Kpm). In this simulation, the following parameters are chosen, the rate of the voltage ΔV on changing the operating point and of the voltage ΔV_c on checking the maximum point.As a result, the influence of these parameters on Kpm is showed and it is made clear that we should decide the MPPT parameters with care.     

复杂热源下不可逆诺维科夫热机最大功率输出

考虑实际热机工作下的旁通热漏和内部耗散等不可逆因素,建立了包括连续均匀分布、三角形分布、二次分布和帕累托分布等四种不同的统计概率分布高温热源温度下的广义不可逆诺维科夫热机模型,导出了热机最大输出功率及相应的热效率和熵产率随高温热源温度、内部不可逆性等因素变化的关系式。结果表明：热漏和内部耗散分别对热机性能有着不同的影响,热漏使统计热源温度分布下最大功率输出对应的热效率减小,同时也增大了熵产率,但对热机的最大功率输出无影响;内部耗散不可逆性使热机的最大输出功率及相应热效率均明显减小,但使熵产率先增大后减小;熵产率随高温热源温度的标准差增大而减小。研究结果对太阳能发电厂性能提升具有一定理论指导意义。     

Recent developments in EHD Enhanced Heat Transfer

This paper considers that the case for using electrohydrodynamic (EHD) enhancement of heat transfer has been established, especially in thermodynamic renewable energy applications where temperature levels are relatively low. It goes on to establish the basis on which nucleate boiling heat transfer is enhanced by EHD forces at surfaces designed to improve condensation, giving experimental results for a six-tube, shell/tube heat exchanger boiling R12 at “Io-fin” surfaces as well as for single-tube tests using “Thermoexcel” and “Gewa-T” surfaces.     

Performance of low-temperature differential Stirling engines

In this paper, two single-acting, twin power piston and four power pistons, gamma-configuration, low-temperature differential Stirling engine are designed and constructed. The engine performance is tested with air at atmospheric pressure by using a gas burner as a heat source. The engine is tested with various heat inputs. Variations of engine torque, shaft power and brake thermal efficiency at various heat inputs with engine speed and engine performance are presented. The Beale number obtained from testing of the engines is also investigated. The results indicate that, for twin power piston engine, at a maximum actual heat input of 2355 J/s with a heater temperature of 589 K, the engine produces a maximum torque of 1.222 N m at 67.7 rpm, a maximum shaft power of 11.8 W at 133 rpm, and a maximum brake thermal efficiency of 0.494% at 133 rpm, approximately. For the four power pistons engine, the results indicate that at the maximum actual heat input of 4041 J/s with the heater temperature of 771 K, the engine produces a maximum torque of 10.55 N m at 28.5 rpm, a maximum shaft power of 32.7 W at 42.1 rpm, and a maximum brake thermal efficiency of 0.809% at 42.1 rpm, approximately.     

Numerical investigation of natural convection heat loss in modified cavity receiver for fuzzy focal solar dish concentrator

In the present work, a 2-D-model is used to investigate the approximate estimation of the natural convection heat loss from an actual geometry of the modified cavity receiver (hemisphere with aperture plate) of fuzzy focal solar dish concentrator. The analysis of the receiver has been carried out based on the assumption of the uniform and maximum solar flux distribution in the central plane of the receiver. The total heat loss from the receiver has been estimated for both the configurations “with insulation” (WI) and “without insulation” (WOI) at the protecting aperture plane of the receiver. The convection heat loss of the modified cavity receiver was estimated by varying the inclinations of the receiver from 0° (cavity aperture facing sideways) to 90° (cavity aperture facing down). The convection heat loss is maximum at 0° and decreases monotonically with increase in angle upto 90°. The effect of operating temperature on convection heat loss for different orientations of the receiver was studied. The results of the numerical analysis are presented for a modified cavity receiver “with insulation” (WI) and “without insulation” (WOI) in the form of Nusselt number correlation: and . The maximum convection heat loss occurs at 0° inclination for both cases of the receiver, which is 63.0% (WI) and 42.8% (WOI) of the total heat loss, though the heat loss in WI configuration is lower than that of WOI configuration. Upon increasing the inclination of the receiver, the convection heat loss reduces to a minimum of 12.5% (WI) and 24.9% (WOI) of the total heat loss at 90°. The result of the present numerical model of standard receiver configuration (modified cavity receiver with insulation at bottom) is comparable with other well-known models.     

最大功率密度输出时Atkinson热机的效率

有限时间热力学主要研究循环的最大功率及相应效率。本文则以功率密度——循环输出功率与最大比容之比——作为优化目标分析Ａｔｋｉｎｓｏｎ循环的性能，以兼顾发动机尺寸性能。计算表明最大功率密度输出时循环的效率总是大于最大功率输出时的效率，且前者相应的尺寸参数比后者要小。     

Numerical simulation of the He II/He I phase transition in superconducting magnets

In this paper we simulate a special type of Stefan problem in large-scale superconducting magnet systems in which superfluid helium (He II) is used as the coolant for the system. Liquid helium in a narrow channel called a “cable-in-conduit” conductor (CICC) is used to remove the heat load from the conductors. Liquid helium exhibits a phase change transition to normal helium (He I) when its temperature rises above the lambda point (2.716 K under saturated vapor pressure). A simple one-dimensional model is described to analyze this special He II/He I Stefan problem. A moving mesh technique is used to solve this model to improve the numerical efficiency compared with front-tracking methods. The results illustrate the simplicity and efficiency of this model.     

An array of directable mirrors as a photovoltaic solar concentrator

Calculations of the optics of heliostats for use in large thermal power towers have been carried out in considerable detail, chiefly by Vant-Hull et al.[1, 2]. This paper describes a simplified method for calculating the images generated by a special type of concentrator, i.e. an array of independently steered mirrors on a single frame, intended to direct the solar image onto a flat photovoltaic solar cell target. The case of interest is one in which the field of illumination on the target is as uniform as possible, and the emphasis is thus on small “rim angle” geometries (a configuration which also minimizes mirror interference effects). Calculations are presented for constructing the individual mirror target images in terms of three angles: (1) The angle between the photovoltaic target normal and the reflecting mirror (celled here the mirror position angle). (2) The angle between the target center and the sun as measured from the center of the reflecting mirror, and (3) The angle at which the plane defined by the center of the sun, the mirror center and the target center intersects the plane of the target.The overall system efficiency for various mirror configurations, charaterized by such parameters as the maximum mirror angle (i.e. “rim angle”), target-mirror plane separation, and mirror aiming accuracy is discussed in terms of the specifications desirable in an optical concentrator designed specifically to illuminate uniformly a photovoltaic solar cell target.     

Effect of finite heat input on the power performance of micro heat engines

Micro heat engines have attracted considerable interest in recent years for their potential exploitation as micro power sources in microsystems and portable devices. Thermodynamic modeling can predict the theoretical performance that can be potentially achieved by micro heat engine designs. An appropriate model can not only provide key information at the design stage but also indicate the potential room for improvement in existing micro heat engines. However, there are few models reported to date which are suitable for evaluating the power performance of micro heat engines. This paper presents a new thermodynamic model for determining the theoretical limit of power performance of micro heat engines with consideration to finite heat input and heat leakage. By matching the model components to those of a representative heat engine layout, the theoretical power, power density, and thermal efficiency achievable for a micro heat engine can be obtained for a given set of design parameters. The effects of key design parameters such as length and thermal conductivity of the engine material on these theoretical outputs are also investigated. Possible trade-offs among these performance objectives are discussed. Performance results derived from the developed model are compared with those of a working micro heat engine (P3) as an example.