Performance of a solar liquid desiccant air conditioner – An experimental and theoretical approach

In this paper the results of testing a solar liquid desiccant air conditioner (LDAC) in the tropical climate of Queensland, Australia have been presented. The system uses polymer plate heat exchanger (PPHE) for dehumidification/indirect evaporative cooling, and a cooling pad as the direct evaporative cooler for the dry air leaving the PPHE. Lithium chloride, which is an effective desiccant in air dehumidification, was used in the experiments and a scavenger air regenerator concentrates the dilute solution from the dehumidifier using hot water from flat plate solar collectors. The data obtained from performance monitoring of the solar LDAC operating on a commercial site in Brisbane was compared with a previously developed model for the PPHE. The comparison reveals that good agreement exists between the experiments and model predictions. The inaccuracies are well within the measuring errors of the temperature, humidity and the air and solution flow rates. The above tests further indicate a satisfactory performance of the unit by independently controlling the air temperature and humidity inside the conditioned space.

In order to prevent carryover of the solution particles into the environment, eliminators are used at outlet of the absorber unit and the regenerator. An alternative method in preventing the carryover is the use of indirect cooling, in which the supply air does not contact the solution. The method can be used to produce potable water from the atmospheric air in remote areas.

The liquid desiccant system can be used in the HVAC industry, either as a packaged roof-top air conditioner, or as an air handler unit for commercial applications. The system could also be used for space heating in winter due to the property of desiccants to provide heat when wetted.     

A novel ratiometric fluorescent Yb3+ sensor based on a N′-(1-oxoacenaphthylen-2(1H)-ylidene)furan-2-carbohydrazide as a suitable fluorophore

N′-(1-oxoacenaphthylen-2(1H)-ylidene)furan-2-carbohydrazide (L) was synthesized for the first time and used as a ratiometric fluorescent chemosensor for high selective recognition of Yb³⁺ ions in acetonitrile (MeCN) solution. The L–Yb³⁺ complexation quench the fluorescence of L at 420 nm and induces new fluorescent enhancement at 516 nm. Due to the formation of a 2:1 metal ligand complex in acetonitrile solution, the red shift of fluorescent emission spectrum occurred. The sensor shows a linear response toward Yb³⁺ ion concentration in the range of 3.3 × 10^? 7 M to 1.0 × 10^? 4 M with detection limit of 1.2 × 10^? 7 M. The fluorescent probe exhibits high selectivity for Yb³⁺ ion over the other common mono-, di-, and trivalent cations.     

Viscoelastic nature of calcium silicate hydrate

The origin of the time-dependent response of cement-based materials to applied stress has not been clearly resolved. The role of interlayer water in the mechanical behavior of calcium silicate hydrate (C–S–H) is still debated. In order to better understand the pertinent mechanisms, the stress relaxation tests were conducted on thin rectangular beams of compacted synthetic C–S–H powder and hydrated Portland cement subjected to three-point bending. C–S–H specimens of variable composition (C/S = 0.8, 1.2 and 1.5) were prepared at various moisture content levels from saturation to the dry state. A special drying procedure was applied in order to remove the adsorbed and interlayer water incrementally from C–S–H conditioned at 11%RH. It was shown that a significant part of the relaxation at saturation is attributed to the hydrodynamic component associated with the pore water. It was demonstrated that the viscoelastic performance of C–S–H depends considerably on the presence of interlayer water. It was argued that the results support the validity of the theory of sliding of C–S–H sheets as a time-dependent deformation mechanism responsible for the creep and stress relaxation of cement-based materials. This concept was illustrated in a proposed model for the viscoelastic response of C–S–H.     

Multi-pressure absorption cycles in solar refrigeration:: A technical and economical study

A technical and economical study of regenerative absorption chillers with multi-pressure cycle has been undertaken as solar operated refrigeration systems. Referred to as advanced absorption chillers they represent one of the new technology options that are under development. Advanced absorption cooling technology offers the possibility of chillers with thermal COPs of 1.5 or greater at driving temperatures of 140°C, which reduces the collector area and the heat rejection requirements compared to current absorption cooling technology. Two different absorption systems have been considered. The first is an advanced, double-effect regenerative absorption cooling system, driven at 140°C, whose efficiency is about 55% of the Carnot efficiency. The second is an ideal, single-effect regenerative absorption system that achieves 70% of the Carnot efficiency driven at 140°C or 200°C. To evaluate the solar performance of a thermally driven chiller requires a separate analysis of the solar availability for a given location compared to the required monthly average solar input. In this analysis different systems, including the vapour compression chillers, have been compared in terms of the thermal and electrical energy input. An effective electrical COP may be computed assuming that the ratio of electrical energy cost to thermal energy cost is four, which is typical of today’s fossil fuel costs. The effective electrical COPs of different technical options can then be compared. Those systems with higher electrical COPs will have lower energy costs. If solar is to be competitive, then the cost of delivered solar thermal energy should be less than the cost of delivered fossil thermal energy.     

Low-cost synthesis of nano-hydroxyapatite from carp bone waste: Effect of calcination time and temperature

The aim of this study was to synthesize Hydroxyapatite (HA) from carp bone waste by calcination treatment. The effects of calcination temperature and time on crystallite size, crystallinity%, powder size and morphology, formed phases, and Ca/P ratio were analyzed. The XRD analyses indicated that for 1 h calcination time, HA was the only phase produced at all temperatures. However, for 5 h calcination time, temperatures other than 700ºC resulted in formation of TCP+HA. The HA obtained at 700ºC at both times had less crystallinity compared to other temperatures. Crystallite size increased by increase in temperature at 1 h calcination time. The smallest and largest particulate sizes were obtained at 800ºC for 1 h and 900ºC for 5 h, respectively. The Ca/P ratio close to theoretical value (1.67) was obtained for 5 h calcination time. Finally, the results showed the usefulness of the methodology used in natural HA production that can be used in orthopedics and dentistry.     

Study of bulk crystallization in MgO-CaO-SiO2-Na2O glasses in the presence of CaF2 and MoO3 nucleant

The crystallization process of MgO-CaO-SiO₂-Na₂O glasses in the presence of CaF₂ and MoO₃ nucleating agents was investigated by DTA, XRD and SEM. The effect of compositional changes on bulk crystallization and growth morphology has been studied. After a two-stage heat treatment, the phases such as wollastonite, diopside and cristobalite, were identified. The ability of CaF₂ and MoO₃ pair as nucleating agents in inducing bulk nucleation in these glasses was attributed to the surface tension and viscosity reductions. The observed pore formation phenomenon upon the increase of MgO content in these glass-ceramics was related to the difference in density between the residual glass and diopside as the main crystalline phase.     

Physical mapping of chromosomes: A combinatorial problem in molecular biology

This paper is concerned wth the physical mapping of DNA molecules using data about the hybridization of oligonucleotide probes to a library of clones. In mathematical terms, the DNA molecule corresponds to an interval on the real line, each clone to a subinterval, and each probe occurs at a finite set of points within the interval. A stochastic model for the occurrences of the probes and the locations of the clones is assumed. Given a matrix of incidences between probes and clones, the task is to reconstruct the most likely interleaving of the clones. Combinatorial algorithms are presented for solving approximations to this problem, and computational results are presented.Research supported in part by NSF Grant No. CDA-9211106.Research supported in part by NSF Grant No. CCR-9005448.