Performance analysis of humid air turbine cycle with solar energy for methanol decomposition

According to the physical and chemical energy cascade utilization and concept of synthesis integration of variety cycle systems, a new humid air turbine (HAT) cycle with solar energy for methanol decomposition has been proposed in this paper. The solar energy is utilized for methanol decomposing as a heat source in the HAT cycle. The low energy level of solar energy is supposed to convert the high energy level of chemical energy through methanol absorption, realizing the combination of clean energy and normal chemical fuels as compared to the normal chemical recuperative cycle. As a result, the performance of normal chemical fuel thermal cycle can be improved to some extent. Though the energy level of decomposed syngas from methanol is decreased, the cascade utilization of methanol is upgraded. The energy level and exergy losses in the system are graphically displayed with the energy utilization diagrams (EUD). The results show that the cycle’s exergy efficiency is higher than that of the conventional HAT cycle by at least 5 percentage points under the same operating conditions. In addition, the cycle’s thermal efficiency, exergy efficiency and solar thermal efficiency respond to an optimal methanol conversion.     

Thermal performance of solar air heaters—Experimental correlation

A mathematical model and a solution procedure for predicting the thermal performance of four types of single-pass flat-plate solar air collectors were presented in an earlier paper by Ong (1995). Instead of resorting to complicated algebraic manipulations to solve the energy equations a matrix-inversion technique was employed. In this paper, theoretical predictions of surface and air temperatures were obtained for the Types II, III and IV collector designs. In addition, the Type II collector was considered with and without bottom insulation. Experimental data from previous studies were obtained and compared with the present theoretical predictions. Satisfactory qualitative and quantitative agreement was obtained between theoretical predictions and experimental data.     

Experiments in a solar simulator on solid desiccant regeneration and air dehumidification for air conditioning in a tropical humid climate

This paper presents an indoor and analytical study to evaluate the performance of a desiccant cooling system that uses silica gel as desiccant, electric light bulbs to simulate solar radiation, and forced flow of air through an IDC (integrated Desiccant/Collector). In the regeneration process, the rate at which water is removed from the desiccant increases with irradiation and decreases with air flowrate. In the air dehumidification process, the adsorption rate decreases with irradiation and increases slightly with flowrate. Comparisons between analytical calculations and experimental data show good agreement, and the calculations show that it should be possible to operate this system in tropical humid climates using the regeneration process in the day and the air dehumidification in the night time.     

Effect of internal partitioning on room air quality with mixing ventilation—statistical analysis

In designing modern office buildings, building spaces are frequently zoned by introducing internal partitioning, which may have a significant influence on the room air environment. This internal partitioning was studied by means of model test, numerical simulation, and statistical analysis as the final stage. In this paper, the results produced from the statistical analysis are summarized and presented.     

Thermodynamic investigation and comparison of selected production processes for hydrogen and hydrogen-derived fuels

The results are reported of comparisons based on energy and exergy analyses of a wide range of production processes for hydrogen and hydrogen-derived fuels (HDFs). A commercial process-simulation computer code, previously enhanced by the author for exergy analysis, is used in the analyses. Depending on the process and the efficiency definition used, overall efficiencies are determined to range widely, from 21 to 92% for energy efficiencies and from 19 to 83% for exergy efficiencies. The losses for all processes are found to exhibit many common factors. Energy losses associated with emissions account for 100% of the total energy losses, while exergy losses associated with emissions account for 4 to 11% of the total exergy losses. The remaining exergy losses are associated with internal consumptions. It is anticipated that the results will prove useful to those involved in the improvement of existing and design of future production processes for hydrogen and HDFs.     

A thermodynamic analysis of a novel high efficiency reciprocating internal combustion engine—the isoengine

A novel concept for a high efficiency reciprocating internal combustion engine (the isoengine) is described and its cycle is analysed. The highly turbocharged engine configuration, which is intended primarily for on-site and distributed power generation, has a predicted electrical output of 7.3 MW. It has the option for co-generation of up to 3.2 MW of hot water at 95 °C supply temperature. The maximum net electrical plant efficiency is predicted to be about 60% on diesel fuel and 58% on natural gas. The key to the high electrical efficiency is the quasi-isothermal compression of the combustion air in cylinders, which are separate from the power cylinders. This achieves a significant saving in compression work and allows the recovery of waste heat back into the cycle, mainly from the exhaust gas by means of a recuperator. The construction of a first 3 MW_e prototype isoengine has been completed and its testing has begun. Relevant test results are expected in the near future.     

Dynamic response of a packed bed thermal storage system—a model for solar air heating

A mathematical model for simulating the dynamic temperature response of a packed column to an arbitrary time-dependent inlet air temperature is developed. The model includes axial thermal dispersion as well as intra-particle conduction, features that have usually been neglected but can be important in solar energy applications. Solutions, presented in terms of moments of the temperature response to an impulse of heat at the inlet, can be evaluated by simple numerical quadrature. Results of the model compare favorably with experimental data found in the literature. The model is used to optimize heat storage in a rock bin system subject to a realistic transient inlet temperature.     

Thermal comfort standards for air conditioned buildings in hot and humid Thailand considering additional factors of acclimatization and education level

This paper presents the result of a large thermal comfort survey conducted using 1520 Thai volunteers from different climatic regions of Thailand. The survey was conducted using different types of air-conditioned buildings from the private and public sectors.Apart from common thermal comfort factors such as air dry bulb temperature, relative humidity and air velocity, two non-quantifiable factors were considered. These are the acclimatization to the use of air conditioner at home and the education level, i.e., post graduate, graduate and scholar. A general database for thermal comfort studies in Thailand was created, and different thermal comfort standards were developed for the three climatic regions of Thailand. Twenty six degree Celsius and 50–60% relative humidity could be used as a comfortable environment condition for the whole country. The data was then used to generalize an earlier concept we developed for setting thermal comfort standard using data from non air-conditioned buildings.     

Energy and economic assessment of desiccant cooling systems coupled with single glazed air and hybrid PV/thermal solar collectors for applications in hot and humid climate

This paper presents a detailed analysis of the energy and economic performance of desiccant cooling systems (DEC) equipped with both single glazed standard air and hybrid photovoltaic/thermal (PV/t) collectors for applications in hot and humid climates. The use of ‘solar cogeneration’ by means of PV/t hybrid collectors enables the simultaneous production of electricity and heat, which can be directly used by desiccant air handling units, thereby making it possible to achieve very energy savings. The present work shows the results of detailed simulations conducted for a set of desiccant cooling systems operating without any heat storage.System performance was investigated through hourly simulations for different systems and load combinations. Three configurations of DEC systems were considered: standard DEC, DEC with an integrated heat pump and DEC with an enthalpy wheel. Two kinds of building occupations were considered: office and lecture room. Moreover, three configurations of solar-assisted air handling units (AHU) equipped with desiccant wheels were considered and compared with standard AHUs, focusing on achievable primary energy savings.The relationship between the solar collector’s area and the specific primary energy consumption for different system configurations and building occupation patterns is described. For both occupation patterns, sensitivity analysis on system performance was performed for different solar collector areas. Also, this work presents an economic assessment of the systems. The cost of conserved energy and the payback time were calculated, with and without public incentives for solar cooling systems. It is worth noting that the use of photovoltaics, and thus the exploitation of related available incentives in many European countries, could positively influence the spread of solar air cooling technologies (SAC). An outcome of this work is that SAC systems equipped with PV/t collectors are shown to have better performance in terms of primary energy saving than conventional systems fed by vapour compression chillers and coupled with PV cells.All SAC systems present good figures for primary energy consumption. The best performances are seen in systems with integrated heat pumps and small solar collector areas. The economics of these SAC systems at current equipment costs and energy prices are acceptable. They become more interesting in the case of public incentives of up to 30% of the investment cost (Simple Payback Time from 5 to 10 years) and doubled energy prices.     

Defects in boiler evaporator tubes—A detailed case study concerning defect initiation and extension processes

The present report attempts to describe a detailed failure analysis that was conducted on a series of full and partial through-thickness tube wall defects. Essentially two different defects were observed. One was a full through-thickness defect, the shape of which strongly suggests that it was driven by an active corrosion-dominated process. The second type of defect was partial through-thickness in nature and exhibited a common development route inasmuch as it extended through the evaporator tube wall by at least four discrete events or defect extension processes, viz.

1. (i) semi-elliptical pit formation, 0·3 mm deep;

2. (ii) thick porous-like magnetite growth (up to 400 μm thick) at the base of the pit;

3. (iii) heavy or active corrosion tunnelling, 1.3 mm in diameter; and

4. (iv) an environmentally assisted crack (EAC) fatigue crack propagation region which varied between 0.5 and 1.4 mm in size.

In some instances, a fifth defect extension event, which was corrosion dominated, was observed at the end of the fatigue-dominated event (iv). This event was similar to event (iii). Detailed fractography demonstrated that pit formation was the result of a mixed transgranular and intergranular corrosion process while the corrosion tunnelling was caused by a predominantly intergranular corrosion activity. The fatigue-dominated (event (iv)) fracture surface region contained a mixture of flat, cleavage-like facets which are indicative of an EAC growth process, and a fissured, ductile striated, failure mode which is commonplace in the case of pure, mechanically driven, fatigue processes. In the case of the full through-thickness defect, only an intense intergranular corrosion process was evidenced. The likelihood of these discrete events being caused by on-load or off-load process is discussed, while the presence of localised concentrations of sulphur and chlorine were detected on the corrosion-tunnelled and EAC fatigue growth surface regions.     

Experimental study of free convection heat transfer and condensation of vapor of humid air over an inclined cold tube

In this study condensation heat transfer on a cold inclined circular cylinder due to natural convection for various conditions is investigated experimentally. The cylinder is placed in an isolated test room to permit pure natural circulation of ambient air. Ambient temperature and humidity of the test room are controlled by a refrigeration cycle and humidifying. The ambient relative air humidity changed in the range of 30 to 50% and temperature from 25 to 35 °C. The ethylene‐glycol/water solution is used as a refrigerant to control and keep the temperature of the test section at a constant value. The cold surface temperature is varied from 2 to 6 °C. The condensation rate and heat flux are found to depend mainly on time, temperature difference between ambient air and cold surface, ambient relative humidity, and tube inclination. Results are plotted for various conditions with respect to time. The experimental results are used to propose a correlation to predict the condensate mass flow rate for free convection heat transfer. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21015     

Analysis of heat transfer and frost layer formation on a cryogenic tank wall exposed to the humid atmospheric air

In this paper heat transfer characteristics and frost layer formation are investigated numerically on the surface of a cryogenic oxidizer tank for a liquid propulsion rocket, where a frost layer could be a significant factor in maintaining oxidizer temperature within a required range. Frost formation is modeled by considering mass diffusion of water vapor in the air into the frost layer and various heat transfer modes such as natural and forced convection, latent heat, solar radiation of short wavelength, and ambient radiation of long wavelength. Computational results are first compared with the available measurements and show favorable agreement on thickness and effective thermal conductivity of the frost layer. In the case of the cryogenic tank, a series of parametric studies is presented in order to examine the effects of important parameters such as temperature and wind speed of ambient air, air humidity, and tank wall temperature on the frost layer formation and the amount of heat transfer into the tank. It is found that the heat transfer by solar radiation is significant and also that heat transfer strongly depends on air humidity, ambient air temperature, and wind speed but not tank wall temperature.     

Cost benefits analysis and emission reductions of optimum thickness and air gaps for selected insulation materials for building walls in Maldives

The demand for electricity in the Maldives continues to increase by more than 11% in recent years. This is mainly due to the growing number of high-rise air-conditioned buildings and the increasing use of electrical appliances in the residential and commercial sector. This paper investigates potential cost savings and emission reductions achieved by installing different insulation materials of optimum thickness in building's walls. The paper also investigates the effect when air gaps are introduced in the wall. The optimum insulation thickness is based on the cost benefits of each insulation material over its lifetime. This study found that by introducing optimal thickness of different insulation materials and by having air gaps of 2 cm, 4 cm and 6 cm, energy consumption and emissions can be reduced by 65–77%, in comparison to a wall without insulation or air gaps. And, hence have considerable cost savings.     

Thermolysis of waste plastics to liquid fuel: A suitable method for plastic waste management and manufacture of value added products—A world prospective

The present rate of economic growth is unsustainable without saving of fossil energy like crude oil, natural gas or coal. Thus mankind has to rely on the alternate/renewable energy sources like biomass, hydropower, geothermal energy, wind energy, solar energy, nuclear energy, etc. On the other hand, suitable waste management strategy is another important aspect of sustainable development. The growth of welfare levels in modern society during the past decades has brought about a huge increase in the production of all kinds of commodities, which indirectly generate waste. Plastics have been one of the materials with the fastest growth because of their wide range of applications due to versatility and relatively low cost. Since the duration of life of plastic products is relatively small, there is a vast plastics waste stream that reaches each year to the final recipients creating a serious environmental problem. Again, because disposal of post consumer plastics is increasingly being constrained by legislation and escalating costs, there is considerable demand for alternatives to disposal or land filling. Advanced research in the field of green chemistry could yield biodegradable/green polymers but is too limited at this point of time to substitute the non-biodegradable plastics in different applications. Once standards are developed for degradable plastics they can be used to evaluate the specific formulations of materials which will find best application in this state as regards their performance and use characteristics. Among the alternatives available are source reduction, reuse, recycling, and recovery of the inherent energy value through waste-to-energy incineration and processed fuel applications. Production of liquid fuel would be a better alternative as the calorific value of the plastics is comparable to that of fuels, around 40 MJ/kg. Each of these options potentially reduces waste and conserves natural resources. Plastics recycling, continues to progress with a wide range of old and new technologies. Many research projects have been undertaken on chemical recycling of waste plastics to fuel and monomer. This is also reflected by a number of pilot, demonstration, and commercial plants processing various types of plastic wastes in Germany, Japan, USA, India, and elsewhere. Further investigations are required to enhance the generation of value added products (fuel) with low investments without affecting the environment. The paper reviews the available literature in this field of active research and identifies the gaps that need further attention.     

Desiccant solar air conditioning in tropical climates: I—Dynamic experimental and numerical studies of silicagel and activated alumina

This paper presents a dynamic study of moist air dehumidification in view of its use in an air conditioning process by evaporative cooling in tropical climates. A special device has been built to study dehumidification of tropical-like inlet air, through a fixed compact bed of silicagel and activated alumina. The compact desiccant storage is composed of two parallel beds to reduce the pressure drop. A good agreement is obtained for our experiment, and the computed amount of cycled water from the numerical model in the adiabatic process. This analytical model is used to simulate a complete air conditioning open cycle operating with hot and humid air.     

Interactive processes in gasification and combustion—Part III: Coal/char particle arrays, streams and clouds

A comprehensive review is presented on the interactive transport processes in the gasification and combustion of a cloud of drops and solid particles. The review is divided into three parts. Part I is concerned with the interactive processes for arrays, streams and clouds of drops, Part II presents a review of isolated coal, carbon and porous char particles pertaining to interactive processes, and finally Part III deals with the interactive processes for solid particle arrays, streams and clouds. Isolated particle gasification (pyrolysis and heterogeneous) and combustion were briefly reviewed in Part II. Because of strong analogy of the group ignition and combustion, to porous char ignition and combustion, the literature on porous char combustion was also included in Part II and new results were presented on the internal ignition of porous char particle using Frank-Kamanetsky type of analysis. Part III presents an integrated approach starting from arrays to clouds and gasification to combustion. The interactions occur through processes ranging from pure diffusive to convective transport processes. Approximate criteria for interactive processes are given.

As opposed to liquid drop arrays and clouds, there is no systematic study for arrays of char or coal particles. Due to the similarity between droplet evaporation and char combustion, new results are presented for the combustion of char arrays in quiescent atmosphere. Convective effects are also briefly discussed. Expanding the Frank-Kamenetsky analysis to ignition of clouds, simple solutions are presented for cloud ignition temperatures. A comparison of results between different techniques and between theory and experiment is given.

Interesting results for the ignition characteristics of coal dispersions are obtained in that the particles with relatively small or low volatile matter which ignite heterogeneously when isolated are found to ignite homogeneously under cloud conditions. The minimum ignition temperature is found to increase with decrease in size under isolated mode while the opposite is true under interactions. The problems of the gasification, ignition, and combustion of clouds in confined and unconfined volumes are reviewed.

Experiments conducted with streams (laminar flow reactors, LFR) and clouds (TGA, heated grids, shock tubes, batch of particles in LFR, Hertzberg Ignition apparatus) are reviewed. Following the drop literature, the relation between array and group combustion is presented. Finally, the relevance of the reviewed literature to pollutants' formation and destruction and spray combustion modeling is briefly discussed.     

SOLCHIPS—A fast predesign and optimization tool for solar heating with seasonal storage

A new version of the SOLCHIPS predesign and optimization tool for solar heating systems with seasonal storage is described. The tool is based on analytical solution of the energy balance equations describing the system performance. It comprises a user-friendly interface with a minimum input requirement and is intended for preliminary system sizing and optimization purposes. The tool is here applied to the redesign of an existing solar heating installation and to the predesign of a completely new solar plant. The evaluation and dimensioning of one CSHPSS configuration can now be done in 10–20 s thus enabling fast optimization in respect to several parameters. A case study of an existing CSHPSS plant shows a 50% decrease in the annual energy price when the system is redesigned using the SOLCHIPS tool.     

Toward a better understanding of energy consumption—I. The distribution of per capita energy consumption in the world

This paper deals with the inputs that are necessary for investigating future energy demands in various countries.With the view of providing inputs that are indispensable for writing scenarios, we have investigated how energy is linked to the state of the economy and how the life styles of individuals relate to the state of technology achieved, to name two important issues.The information will be presented in three parts. This Part I deals with the distribution of energy consumption in the world. The simple distribution curve of the world's per capita consumption provides considerable insight into the importance of energy for different life styles. In Part II, factor analysis will be used to compare energy consumption with other economic indices and to relate it to the structure of energy consumption. Part III will be devoted to energy analysis, the concept and its applicability. Energy analysis will also be discussed from the points of view of engineering and statistics.The quantitative information presented here provides a crude picture as to how energy is used today, by whom and what for. The figures, which were mainly derived from statistical data, are largely self-explanatory and should be generally useful.     

A combustion concept for oxyfuel processes with low recirculation rate – Experimental validation

Oxyfuel combustion is a technology for Carbon Capture & Storage from coal fired power plants. One drawback is the large necessary amount of recirculation of cold flue gases into the combustion chamber to avoid inadmissible high flame temperatures. The new concept of Controlled Staging with Non-stoichiometric Burners (CSNB) makes a reduction of the recirculation rate possible without inadmissible high flame temperatures. This reduction promises more compact boiler designs. We present in this paper experiments with the new combustion concept in a 3 × 70 kW natural gas combustion test rig with dry flue gas recirculation of 50% of the cold flue gases. The new concept was compared to a reference air combustion case and a reference oxyfuel combustion case with recirculation of 70% of the cold flue gases. FTIR emission spectroscopy measurements allowed the estimation of spectral radiative heat fluxes in the 2–5.5 μm range. The mixing of the gases in the furnace was good as the burnout and the emissions were comparable to the reference cases. The flame temperatures of the CSNB case could be controlled by the burner operation stoichiometry and were also similar to the reference cases. The heat flux in the furnace through radiation to the wall was higher compared to the oxyfuel reference case. This is an effect of the lowered recirculation rate as the mass flow out of the furnace and therefore the sensible heat leaving the furnace decreases. The higher oxygen consumption with lower recirculation rate could be compensated by a lower furnace stoichiometry. This was possible due to better burnout with increased oxygen concentrations in the burner. The results prove that a reduction of the flue gas recirculation rate in oxyfuel natural gas combustion from 70% down to 50% is possible while avoiding inadmissible high flame temperatures with the concept of Controlled Staging with Non-stoichiometric Burners.