An experimental optimization study on a tube-in-shell latent heat storage

Thermal energy storage (TES) using phase change materials (PCMs) has recently received considerable attention in the literature, due to its high storage capacity and isothermal behaviour during the storage (melting or charging) and removal (discharging or solidification). In this study, a novel modification on a tube-in-shell-type storage geometry is suggested. In the proposed geometry, the outer surface of the shell is inclined and it is the objective of this study to determine the optimum range for the inclination angle of the shell surface. Paraffin with a melting temperature of 58.06°C, which is supplied by the Merck Company, is used as the PCM. The PCM is stored in the vertical annular space between an inner tube through which the heat transfer fluid (HTF), hot water, is flowing and a concentrically placed outer shell. At first, the thermophysical properties of this paraffin are determined through the differential scanning calorimeter (DSC) analysis. Temporal behaviour of the PCM undergoing a non-isothermal solid–liquid phase change during its melting or charging by the HTF are determined for different values of the inlet temperature and the mass flow rate of the HTF. The new geometry is shown to respond well with the melting characteristics of the PCM and to enhance heat transfer inside the PCM for a specific range of the shell inclination angle. Copyright © 2006 John Wiley & Sons, Ltd.     

Screening of free radical scavenging capacity and antioxidant activities of Rosmarinus officinalis extracts with focus on location and harvesting times

Methanolic extracts from the leaves of Rosmarinus officinalis (rosemary) harvested from different locations of Turkey at four different times of the year were analyzed by HPLC, and their radical scavenging capacities and antioxidant activities were studied by various assays. The amounts of carnosol, carnosic acid and rosmarinic acid, active constituents of rosemary, varied in different geographical regions of growth, and also showed a seasonal variation. The levels of the constituents were higher in the warm months of June 2004 and September 2004. The antioxidant activities of 12 extracts were determined by in vitro DPPH radical scavenging activity, by Trolox equivalent antioxidant capacity (TEAC), and by reversing H₂O₂-induced erythrocyte membrane lipid peroxidation (EMLP). The two antioxidant enzyme activities of human erythrocyte, namely superoxide dismutase (SOD) and catalase (CAT), after in vitro incubation with the extracts, were also examined in order to see whether the observed effects are related to altered enzymatic efficiency. The resulting values were correlated with active metabolite and total phenol contents of the extracts. The results indicated that the plants harvested in September possessing higher levels of active constituent had superior antioxidant capacities compared to the ones collected at other times. With respect to the location, plants harvested from the Izmir region had lower total phenol and active constituent levels resulting in poorer antioxidant activity.     

Investigation of cylinder pressure for H2/CH4 mixtures at different loads

The purpose of this study is to experimentally analyze the performance and the pollutant emissions of a four-stroke spark-ignition engine operating on natural gas–hydrogen blends of 0%, 10%, 20% and 30% at full load and 65% load for different excess air ratios. This present work was carried out on a Ford engine. This is a four-stroke cycle four-cylinder spark-ignition engine with a bore × stroke of 80.6 × 88 mm and a compression ratio of 10:1. Experiments were made at a constant engine speed of 2000 rpm. CO, CO₂ and HC emission values and cylinder pressures were measured. The results showed that while the excess air ratio increases, CO and CO₂ emission values decrease.     

The Effect of Surface Treatments on Tensile Bond Strength between a Silicone Soft Liner and a Heat-Cured Denture Base Resin

This study evaluated tensile bond strength of a denture soft lining material to a poly (methylmethacrylate) (PMMA) denture base resin subjected to different surface treatment modalities and thermocycling. The materials tested were a silicone-based liner, Molloplast B®, and a heat-cured denture base resin, Meliodent^TM. The denture soft lining material was packed against cured PMMA base resin, which was smoothed; sandblasted with 250-μm Al₂O₃ particles; or lased with a KTP laser; or against uncured PMMA dough (n = 10). In each group, five specimens were thermocycled in a water bath (5–55°C; 3000 cycles) before testing, whereas the other five were directly tested after 24 h. A tensile test was performed using a universal testing machine. Data showed that different treatment modalities of resin surfaces affected adhesion between these two materials and the highest bond values were recorded for cured/smoothed samples under each condition tested. Thermocycling of specimens had no significant reducing effect on measured bond strength values.     

Experimental investigation of a novel desiccant cooling system

Desiccant based air conditioning systems are a suitable way to improve indoor air quality due to its superior humidity control. In this study, a novel desiccant based air conditioning system is designed and tested experimentally to improve the indoor air quality and reduce energy consumption. In the system studied, a heat exchanger, which is not used in this type of systems, for pre-heating the regeneration air with exhaust air is used. This paper reports results of initial operation and operational procedures. The performance of the system and its components is discussed.     

Hydrodynamics of a turbulent slot jet flow impinging on a concave surface

This study investigates hydrodynamic characteristics of a slot jet flow impinging on a concave surface experimentally and numerically. Six different concave plates with varying surface curvature and a flat plate are used. Air is used as the impinging coolant. In the experimental work, the slot nozzle used was specially designed with a sixth degree polynomial in order to provide a uniform velocity profile at its exit. The experiments were carried out for the jet Reynolds numbers in the range of 3000 < Re < 12500, the dimensionless nozzle-to-surface distance range of 1 ≤ H/W ≤ 14 for dimensionless value of the curvature of impinging surfaces in the range of R/L = 0.5, 0.5125, 0.566, 0.725, and 1.3. The pressure coefficient, C_p, for each test case was obtained across dimensionless arc length, s/W. Numerical computations were performed by using the k-ε turbulence model with enhanced wall functions for the concave plate with R/L = 0.725 and for the flat plate. The numerical results showed a reasonable agreement with the experimental data.     

Traces of Defects in the Electronic Structure of Porous Ni--Ti Alloys

The electronic structures of Ni—Ti shape-memory alloy samples were investigated by X-ray absorption fine structure(XAFS) spectroscopy both experimentally and theoretically.In the experimental section,the samples were measured at low temperature to determine the persistent traces of both preheating process and atomic concentration effects on the crystal and electronic structure by X-ray absorption near-edge structure(XANES) spectroscopy.As a second step,the extended-X-ray absorption fine structure(EXAFS) calculations,which are based on different choices of one electron potentials according to Ti coordinations by using the real space multiple scattering method FEFF 8.2 code,were performed.The crystallographic and electronic structures of the porous Ni-Ti alloys were tested at various temperatures ranging from 5 to 1323 K.     

Joint analysis of transient flux behaviors via membrane fouling in hybrid PAC/MF processes using neural network

The main purpose of this study is to understand the transient flux behaviors via membrane fouling in hybrid powdered activated carbon/microfiltration (PAC/MF) processes. Experiments were carried out for nickel solution at various surfactant adsorbent and membrane types and membrane pore sizes. Transient fluxes were modeled together using neural network (NN). A good agreement was obtained with correlation value of 0.986 and mean absolute error of 0.366 m³/m² h respectively. In hybrid processes three discriminable phase behaviors for the flux were determined as fast [0-40s] slow [40-1000s] and low stable [1000-4500s]. Considerable losses in the flux were determined during the first and the second phases while the flux reached a partial steady-state in the third phase. In the first and the third phases participation of surfactant-adsorbed PACs to the cake layer and/or interaction of surfactants and PACs in the cake with each other were found to be predominant ways for the fouling. Whereas in the second phase the interaction of surfactants with both membrane and cake layer was appeared more influential on transient flux behavior.     

Poly(ethylene glycol)/poly(methyl methacrylate) blends as novel form‐stable phase‐change materials for thermal energy storage

In this study, we focused on the preparation and characterization of poly(ethylene glycol) (PEG)/poly(methyl methacrylate) (PMMA) blends as novel form‐stable phase‐change materials (PCMs) for latent‐heat thermal energy storage (LHTES) applications. In the blends, PEG acted as a PCM when PMMA was operated as supporting material. We subjected the prepared blends at different mass fractions of PEG (50, 60, 70, 80, and 90% w/w) to leakage tests by heating the blends over the melting temperature of the PCM to determine the maximum encapsulation ratio without leakage. The prepared 70/30 w/w % PEG/PMMA blend as a form‐stable PCM was characterized with optical microscopy and Fourier transform infrared spectroscopy. The thermal properties of the form‐stable PCM were measured with differential scanning calorimetry (DSC). DSC analysis indicated that the form‐stable PEG/PMMA blend melted at 58.07°C and crystallized at 39.28°C and that it had latent heats of 121.24 and 108.36 J/g for melting and crystallization, respectively. These thermal properties give the PCMs potential LHTES purposes, such as for solar space heating and ventilating applications in buildings. Accelerated thermal cycling tests also showed that the form‐stable PEG/PMMA blend as PCMs had good thermal reliability and chemical stability. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010