Georgios A. Florides

Design and construction of a LiBr–water absorption machine

Abstract The objective of this paper is to present a method to evaluate the characteristics and performance of a single stage lithium bromide (LiBr)–water absorption machine. The necessary heat and mass transfer equations and appropriate equations describing the properties of the working fluids are specified. These equations are employed in a computer program, and a sensitivity analysis is performed. The difference between the absorber LiBr inlet and outlet percentage ratio, the coefficient of performance of the unit in relation to the generator temperature, the efficiency of the unit in relation to the solution heat exchanger area and the solution strength effectiveness in relation to the absorber solution outlet temperature are examined. Information on designing the heat exchangers of the LiBr–water absorption unit are also presented. Single pass, vertical tube heat exchangers have been used for the absorber and for the evaporator. The solution heat exchanger was designed as a single pass annular heat exchanger. The condenser and the generator were designed using horizontal tube heat exchangers. The calculated theoretical values are compared to experimental results derived for a small unit with a nominal capacity of 1 kW. Finally, a cost analysis for a domestic size absorber cooler is presented.

Modelling and simulation of an absorption solar cooling system for Cyprus

Abstract In this paper a modelling and simulation of an absorption solar cooling system is presented. The system is modelled with the TRNSYS simulation program and the typical meteorological year file containing the weather parameters of Nicosia, Cyprus. Initially a system optimisation is carried out in order to select the appropriate type of collector, the optimum size of storage tank, the optimum collector slope and area, and the optimum thermostat setting of the auxiliary boiler. The final optimised system consists of a 15-m2 compound parabolic collector tilted 30° from the horizontal and a 600-l hot water storage tank. The collector area is determined by performing the life cycle analysis of the system. The optimum solar system selected gives life cycle savings of C£1376 when a nonsubsidized fuel cost is considered. The system operates with maximum performance when the auxiliary boiler thermostat is set at 87°C. The system long-term integrated performance shows that 84,240 MJ required for cooling and 41,263 MJ for hot water production are supplied with solar energy.

Methods for Improving the Lifetime Performance of Organic Photovoltaics with Low‐Costing Encapsulation

Recent years have seen considerable advances in organic photovoltaics (OPVs), most notably a significant increase in their efficiency, from around 4 % to over 10 %. The stability of these devices, however, continues to remain an issue that needs to be resolved to enable their commercialization. This review discusses the main degradation processes of OPVs and recent methods that help to increase device stability and lifetime. One of the most effective steps that can be taken to increase the lifetime of OPVs is their encapsulation, which protects them from atmospheric degradation. Efficient encapsulation is essential for long-term device performance, but it is equally important for the commercialization of OPVs to strike a balance between achieving the maximum device protection possible and using low-cost processing for their encapsulation. Various encapsulation techniques are discussed herein, with emphasis on their cost effectiveness and their overall suitability for commercial applications.

A THERMAL MODEL FOR REPTILES AND PELYCOSAURS

Abstract This paper deals with the thermal analysis of reptiles and pelycosaurs. The energy budgets affecting the body temperature of the reptile are presented. In the analysis the behaviour of the reptile, energy gains and losses due to metabolism, evaporation, solar heat, convection, and radiation are considered. The effect of the sail of pelycosaurs is also examined. Finite difference equations are derived and a computer program is written which allows also evaluation of the effect of the reptile blood flow rate. It is shown that the sail of pelycosaurs provided an advantage to the reptile by warming it up quicker in the morning in cold environments.

Global Warming: CO2 vs Sun

It is an undoubted fact, within the scientific community, that the global temperature has increased by about 0.7°C over the last century, a figure that is considered disproportionally large. With the whole world being alarmed, the scientific community has assumed the task to explain this warming phenomenon. This has resulted in the formation of basically two schools of thought with two opposing theories. The first theory (the most popular one) claims that the prime guilty for the recent temperature increase is the release of greenhouse gases – mainly Carbon Dioxide (CO2) – coming mostly from the burning of fossil fuels, the clearing of land and the manufacture of cement. Due to these anthropogenic activities the concentration of CO2 has increased by about 35% from its ‘pre-industrial’ values, with all the resulting consequences. There are though other factors – besides the greenhouse gases – that affect the global temperature, like changes in solar activity, cloud cover, ocean circulation and others. Therefore, the ‘second’ theory claims that it is the Sun’s activity that has caused the recent warming that, incidentally in this theory, is considered to be in the generally expected limits of the physical temperature variation throughout the aeons. One assumption on how the Sun is affecting the climate is that the magnetic field and the solar wind modulate the amount of high energy cosmic radiation that the earth receives. This in turn affects the low altitude cloud cover and the amount of water vapor in the atmosphere and thus regulates the climate. (It must be noted that water vapor is considered as the main greenhouse gas.) In the sequel both of the above-mentioned theories are examined and conclusions about their soundness are drawn. Firstly (section 2), an analysis in past time of the temperature of the Earth is presented, showing that today’s temperatures are not in any way extraordinary, unnatural or exceptional, contrary to what many scientists claim. In fact, on large time scale today’s temperatures agree with what was expected for this geologic period, while on a small time scale the higher temperatures observed are the result of a natural recovery of the planet from the global coldness of the Little Ice age. In section 3, the view of the Intergovernmental Panel on Climate Change (IPCC) on the effect of the accumulation of the CO2 in the atmosphere is presented. Then, in section 4 the CO2 accumulation effect during the past is examined on large and small time scales. Note that Florides & Christodoulides (2009) using three independent sets of data (collected from ice-cores and Chemistry) presented a specific regression analysis and concluded that forecasts about the correlation between CO2-concentration and temperature rely heavily on the choice of data used, making it very doubtful if such a correlation exists or even, if

Solar Space Heating and Cooling Systems

This chapter examines solar space heating and cooling systems. Initially, the basic system configurations are presented which include active solar systems in which direct circulation systems, indirect water-heating systems, and air water-heating systems are presented; space heating and service hot water systems which include air and water systems, issues concerning the location of auxiliary and heat pump systems; and solar cooling, which includes adsorption units, absorption units, lithium--water absorption systems, ammonia--water absorption systems, and solar cooling with absorption refrigeration. Subsequently, heat storage systems are examined which include air and liquid systems thermal storage. Finally, details of various aspects of system design are presented which include module and array design, heat exchangers, and differential temperature controllers.

Classification of Buildings in Cyprus Based on Their Energy Performance

This paper describes the work that will be done in a research project, which will facilitate the implementation of the EPBD through the calculation of the existing Cyprus Building Stock energy behaviour. This will be achieved through the selection of a representative sample of 500 housing units and the collection of data through questionnaires, followed by statistical analysis of the data and the interpretation of the results. The key parameters that will form the different clusters are climatological zone, type, age and size of each housing unit. The statistical interpretation of the collected dataset will provide insights with regards to the energy behaviour of the building stock for each class. The ultimate goal is to suggest the number of classes for the Energy Performance Certificate and the upper and lower energy consumption limits for each class. Moreover, the formulation of an energy behaviour map, the consideration of the historical development of the buildings behaviour and the improvement of the insulating materials and solutions, will lead to the readjustment of the values, particularly for the best two classes, so as not only to reflect today’s reality, but also to show the intent of the state to improve the level of the construction industry. In this study, the various types and quantities of thermal insulating materials utilized in Cyprus, for the time interval 01/01/08–30/09/08, are also reported. The data were extracted from applications made by individuals who claimed financial subsidy. A random specimen of 400 applications was evaluated: 55% refer to existing housing, and 45% to new buildings. The different kinds of materials used for insulating floorings, walls and roofs, in different regions of the island were evaluated. The principal observation made is the extensive use of double glazing for doors and windows.

Assessment and Comparison of Soil Thermal Characteristics by Laboratory Measurements

Soil thermal characterization is an important aspect affecting the performance of Ground Heat Exchangers (GHE) in a Shallow Geothermal Energy (SGE) system application. Thermal conductivity and specific heat capacity are the sole requirements in designing such systems and can be obtained using empirical prediction models, laboratory tests and in situ tests. Laboratory thermal tests can be performed under steady-state or transient conditions. Transient tests have the advantage of being fast and of requiring a small volume of soil. This has led to recent developments and types of heat probes commercially available, but for which there is limited comparative assessment of results. This paper focuses on the evaluation of thermal properties, namely the ground thermal conductivity, specific heat capacity and thermal diffusivity by means of two different probes; a needle probe and a surface probe, and on comparing and testing their accuracy. Comparison of the different samples was also performed using two different transient needle probes, from two commercially available equipment, Isomet-2104 and Hukseflux-TPSY02. The laboratory measurements are supported by numerical modelling using the COMSOL Multiphysics software which applies a finite-element analysis method on the convection-diffusion equation for heat transfer.

Experimental Investigation of the Effect of Solar Collector’s Inclination Angle on the Generation of Thermosiphonic Flow

Cyprus is currently the leading country in the world with respect to the application of solar water heaters for domestic applications, with more than 93 % of the houses equipped with such a system. The great majority of these solar water heaters are of the thermosiphonic type. Currently, the knowledge about the parameters affecting the ‘thermosiphonic phenomenon’ is rather poor while on an international level (International Organization for Standardization, ISO, and Comite Europeen de Normalisation CEN committees) there is no standard available to test thermosiphon solar collectors. The deeper understanding of the ‘thermosiphonic phenomenon’ and the identification of the key parameters affecting it is the main aim of a research project currently in process in Cyprus.

Microfluidic flow and heat transfer and their influence upon optical modes in microstructure fibres

Using finite element analysis (FEA), a model has been constructed to predict the thermo-fluidic and optical properties of a microstructure optical fibre (MOF). The properties under study include external temperature, input water velocity and optical fibre geometry. Under laminar flow the steady-state temperature is dependent on the water channel radius while independent of the input velocity. A critical channel radius is observed below which the steady-state temperature of the water channel is constant, while above, the temperature decreases. The MOF has been found capable of supporting multiple modes whose response to temperature was dominated by the thermo-optic coefficient of glass, despite the larger thermo-optic coefficient of water. This is attributed to the majority of the light being confined within the glass, which increased with increasing external temperature due to a larger difference in the refractive index between the glass core and the water channel.