Experiments on an absorption refrigeration system powered by a solar pond

A heat source at temperatures not higher than 80°C was used to simulate the heat input to an absorption refrigerator from a solar pond. A laboratory model of an absorption refrigerator, using an ammonia-water solution at 52% concentration by weight, was operated intermittently using this heat source. Generation temperatures as high as 73°C and evaporation temperatures as low as −2°C were obtained. Tap water was used to remove the heat generated from the condensation of the ammonia vapour and the absorption of the refrigerant in the water. The temperature of the tap water was near the ambient laboratory temperature of 28°C. The COP for this unit working under such conditions was in the range 0.24–0.28.     

Thermodynamic cycle,correlations and nomograph for NH3NaSCN absorption refrigeration systems

The detailed thermodynamic cycle of the NH₃NaSCN absorption refrigeration unit is presented, based on the thermodynamic properties of the working media. Correlations are developed, which express the coefficient of performance and the cooling capacity in terms of the required evaporation temperature, T_ev, and the available ambient temperature, T_amb. A nomograph is also presented, which shows in a compact form the behaviour of the NH₃NaSCN system and allows direct estimation of its main characteristics. It is concluded that if (T_amb − T_ev) varies from 0 to 40°C, the theoretical coefficient of performance decreases linearly from 95 to 77%. For the same range of (T_amb − T_ev) the theoretical cooling capacity varies from 1150 to 1300 kJ/kg NH₃ if T_ev varies from 0 to −15°C. Under the conditions examined, for T_amb − T_ev > 23°C, the coefficient of performance of the NH₃NaSCN system becomes higher than that of the NH₃LiNO₃ system. The observed increase reached 4% at T_amb − T_ev = 40°C.     

Decomposition of the solid solution and the formation of a high-coercivity state in Fe<Subscript>2</Subscript>NiAl alloy upon cooling at the critical rate

Transmission electron microscopy and magnetic measurements are used to study the formation of the microstructure and magnetic properties of Fe₂NiAl (alni) alloy upon cooling at the critical rate (V ～ 2°/min) from the region of single-phase solid solution (1240°C). Cooling is interrupted by water quenching caused by temperatures Т_quench. The periodical modulated structure formed during sample cooling at the critical rate guarantees the strongest possible coercive force (Н_с = 670 Oe). The decomposition of the solid solution below 900°C includes a stage of primary modulated structural failure upon continuous cooling to temperature Т_quench ～ 850°C, which corresponds to the weakest coercive force on the Н_с(Т_quench) curve. The periodical modulated structure is recovered when the temperature falls further; this is accompanied by an increase in the coercive force (up to Н_с = 670 Oe) after cooling to 20°C.     

Absorption panel cooling using a TFE-NMP mixture

A panel system for cooling buildings is proposed, working with an absorption-refrigeration unit, the evaporator of which is the panel itself. Trifluoroethanol (TFE) and N-methylpyrrolidinone (NMP) are proposed as refrigerant and absorbent, respectively. Use of the TFE-NMP mixture seems to offer advantages over the usual H₂OLiBr or NH₃H₂O mixtures, and suits well the modest refrigeration temperatures needed in panel cooling. Analytical expressions are presented for the properties of the TFE-NMP mixture and a calculation procedure for NH₃H₂O units is used after suitable modifications to simulate the operation of the TFE-NMP absorption-refrigeration unit. Under the conditions considered, the lowest evaporation temperature varies from 3 to 16°C, and the theoretical coefficient of performance from 60% to 68.4%, with its maximum value obtained at 9°C. Under the above conditions, for panel cooling power 50–150 W/m², a refrigerant mass flow rate through the panel from 400 g/m² h to 1600 g/m² h is needed with a driving thermal power from 80 W/m² to 220 W/m².     

Developments in geothermal energy in Mexico—Part twenty six: Experimental assessment of an ammonia/water absorption cooler operating on low enthalpy geothermal energy

Mexico possesses large amounts of geothermal brine at temperatures which are too low to enable electricity to be generated efficiently and economically. Most of the geothermal fields in Mexico are located near important agricultural areas. Perishable food losses in Mexico, resulting from inadequate handling and cold storage facilities, vary from 35 to 50%. In order to prove the technical feasibility of operating heat-driven absorption cooling systems on low enthalpy geothermal energy, a prototype ammonia/water absorption cooler was installed in the Cerro Prieto geothermal field, where the ambient temperatures exceed 40°C and the cooling water temperatures reach 30°C. The unit has operated successfully with evaporative cooling loads exceeding the design value. The experimental data obtained will provide an excellent basis for the design of large scale heat-driven absorption refrigeration systems.     

Experimental investigation of liquid drop evaporation on a heated solid surface

Evaporation of a water drop was studied experimentally at a temperature difference between the solid surface and surrounding atmosphere from 30 to 60 °C. The studies were performed on the substrates with micro- and nanocoatings with different wettability. The features of evaporation were studied for the pinned, partially pinned, and depinned three-phase contact line (solid-liquid?gas interface). It is shown that with a decrease in the water drop volume, the specific evaporation rate (mass flow per unit of surface area) increases, particularly at the last stage of evaporation.     

Performance prediction of an absorption heat pump for utilization in industry

Recently, an absorption heat pump has been put on the market for industrial utilization. It is a H₂O-LiBr absorption machine which heats up water to 90°C with a cold source at 40°C. The capacity and COP of the machine have been studied by a computer program as a function of cold source temperature and heated fluid temperature. Also, a comparison with a compression heat pump is reported.     

Application of TiO2 nanofluid-based coolant for jet impingement quenching of a hot steel plate

Cooling rate in Run Out Table (ROT) in steel industries tailors microstructure which lead to improved mechanical properties. The current work aims to increase cooling performance of steel using TiO₂ nanofluid as coolant in jet impingement. Different concentrations of TiO₂ nanofluid have been used to study effect on jet cooling of a steel plate from 900°C. Thermal conductivity of nanofluid is found to significantly enhance at optimum concentration and this plays major role in increasing cooling rate of the steel plate. 19% enhancement in cooling rate is observed by using 40 ppm of TiO₂ nanofluid compared to water.     

Some dielectric properties of monoclinic lysozyme crystals

The frequency dependences of the dielectric loss tangent and the magnitude of the impedance for monoclinic lysozyme single crystals and the solution used for preparing the crystals were investigated. The measurements were performed in the frequency range 1–10⁷ Hz under exposure of the crystals at a temperature of 25°C, cooling to ?20°C, and subsequent heating. The analysis of the experimental dielectric properties of the crystals demonstrated that drying of the crystals at room temperature in air initially led to the removal of “free” water with the content approximately equal to 65% of the total content. Further drying resulted in the removal of “bound” water. The solvent contained in the crystals (～26 wt %) was frozen at a constant temperature of approximately ?6.5°C. The permittivity of the dehydrated crystal at high frequencies was considerably higher than that of ice.     

Enhancement of Cooling Rate for a Hot Steel Plate using Air-Atomized Spray with Surfactant-Added Water

The objective of the current research deals with the experimental study of an air-atomized spray with surfactant-added water, cooling a 12-mm-thick AISI-1020 stationary steel plate at three different initial surface temperatures (400°C, 600°C, and 900°C). Furthermore, the effects of surfactant concentration and airflow rate on the cooling rate have been investigated. The surface heat flux and surface temperature show a significant improvement in cooling for all three cases of initial surface temperatures when the air-atomized spray was used with surfactant-added water.     

Structural and optical characterization of Sb-doped CuInS2 thin films grown by vacuum evaporation method

Structural, electrical and optical properties of Sb-doped CuInS₂ thin films grown by single source thermal evaporation method were studied. The films were annealed from 100 to 500 °C in air after the evaporation. The X-ray diffraction spectra indicated that polycrystalline CuInS₂ films were successfully obtained by annealing above 200 °C. This temperature was lower than that of non-doped CuInS₂ films. Furthermore, We found that the Sb-doped CuInS₂ thin films became close to stoichiometry in comparison with non-doped CuInS₂ thin films. The Sb-doped samples annealed above 200 °C has bandgap energy of 1.43–1.50 eV.     

Thermal and FTIR spectral characterisation of diammonium tetrachlorocobaltate(II) monohydrate crystals

Single crystals of a novel compound, diammonium tetrachlorocobaltate(II) monohydrate, were grown by slow evaporation method at room temperature. The crystals belong to a class of compounds that show interesting properties like ferroelectricity at low temperatures. The grown crystals were characterised through powder XRD, thermogravimetric (TG-DTA), low temperature differential scanning calorimetric (DSC) analyses and FTIR spectroscopy. While the powder XRD pattern of the compound confirms its crystallinity, the TG-DTA studies confirm the stoichiometry of the compound. The thermal anomalies observed in DSC curve at −4°C and −39.1°C in the cooling cycle indicate a first order phase transition. The FTIR spectrum of the compound characterizes the various chemical bonding and water of crystallization. Further investigation of the low temperature properties of the compound is under progress.     

A theoretical analysis of a solar-fuel assisted absorption power cycle (SFAPC)

This study presents a novel power generating cycle suitable for solar energy applications. A modified version of the conventional LiBr-H₂O absorption refrigerating machine is used for the proposed cycle. The condenser, expansion valve and evaporator are replaced by a superheater and a steam turbine, while a flashing tank replaces the generator. The cycle is powered by medium concentrators with a solar collecting temperature of 165°C. Steam generated in the flashing tank (100 kPa) is superheated (using fuel) to 600°C before it expands in the turbine down to 1.25 kPa. This is maintained by the equilibrium conditions in a water cooled absorber, LiBr-H₂O solution is directly circulated in the solar collectors and the non-solar energy input to the system is 23% of its total requirements.Results showed that using a 710 ton refrigeration absorption machine, the SFAPC would generate 960 kW shaft power at a system thermal efficiency of 25% which is 44% higher than the available systems. Moreover, when the SFAPC is combined with a vapour compression refrigerator, an overall COP of 1.4 is obtained. This is 72% higher than that of the absorption machine alone at the expense of 23% non-solar energy supply.     

Gas turbine waste heat recovery distillation system

This article presents a method for improving the gas turbine's performance through an efficient utilization of the waste heat in a distillation system with a special arrangement. This consists of two trains of VTE/MEB connected to increase the fresh water produced. Exhaust gases from the gas turbine are used in a multi-temperature level heat recovery system with five feed heaters, and gases are released to ambient at 130°C. Distillation top train has nine effects and evaporation range from 130 to 82°C while the bottom train has six effects with evaporation range from 76 to 46°C and is supplied with the steam leaves the last effect in the top train.Thermal analysis using a 32.67 MW gas turbine showed that the present arrangement can produce 3.2 million gallons per day (mgd) of fresh water with more than 4 g/kWh at a performance ratio (PR) of 8.8. This is 34% more than that produced in an existing gas-turbine distillation combination and 14% more than that expected from a reverse osmosis plant driven by a bottoming Rankine power cycle.     

Synthesis and magnetic properties of Cu0.5Ni0.5Fe2O4 nanoparticles produced by glycothermal and hydrothermal processes

Cu_0.5Ni_0.5Fe₂O₄ nanoparticles have been synthesized in ethylene glycol solution and in deionised water. The glycothermal reaction was carried at 200°C under gauge pressure of 100 psi. The hydrothermal treatment was done at 100°C under zero pressure. Complete single-phase cubic spinel structure in the samples made by glycothermal (sample G) and hydrothermal (sample H) processes formed after annealing at 600°C and 900°C respectively. The coercive field of sample H increases from 72 Oe to 133 Oe after sintering at 700°C and then decrease to 11 Oe on sintering at 1000°C. This variation is attributed to surface effects and crossover from single to multidomain behavior due to increasing particle size.     

西太平洋蒸发波导的时空统计规律研究

海洋蒸发波导自然现象对近海面电磁波的传播有重要影响,获取大面积海域蒸发波导的长时间统计分布规律,对于海上雷达、通信、制导等电磁系统的设计与应用,具有重要意义.针对现有单点局部观测方法的缺点,建立了基于美国环境预报中心再分析数据的大面积海域蒸发波导统计特性计算方法,利用太平洋气象浮标数据、北部湾海岛气象观测数据对分析方法的正确性进行了验证.利用该分析方法和最近18年的美国环境预报中心再分析数据,重点研究了西太平洋蒸发波导的统计规律,获得了蒸发波导高度在不同海域、不同月份的分布特性,建立了空间分辨率约为18 关键词： 蒸发波导 再分析数据 电磁波 统计特性     

Morphology of poly(p-phenylene terephthalamide) precipitated from hexamethylphosphoric triamide/N-methylpyrrolidone-2/lithium chloride solutions

Morphology of poly(p-phenylene terephthalamide) (PPTA) precipitated from hexamethylphosphoric triamide (HMPA)/N-methylpyrrolidone(N-MP)/LiCl solution has been studied. Low molecular weight ([n] = 0.90) PPTA was dissolved in a mixture of HMPA and N-MP containing LiCl. The solution (5%) was solidified by cooling, dried under reduced pressure, and characterized by x-ray and differential scanning calorimetry. New diffraction peaks were observed at 2Θ = 9.4°, 15.4α, and 16.9α in the x-ray pattern, indicating the formation of a PPTA complex crystal having an expanded unit cell. The diffraction peaks could be indexed by assuming a monoclinic unit cell with dimensions a = 12.2Å, b = 11.0Å, 7 = 118α. The PPTA complex melted at 260°C. Negative spherulites of the PPTA complex were obtained; they were unstable in the presence of water. For electron microscopy, the PPTA complex spherulites were solvent-exchanged to acetone; they were found to consist of fibrous lamellae. The width of the lamellae (300400 A) corresponded to the extended chain length of the starting PPTA. The structure of PPTA formed under shear varied from stacked lamellar structures with many tie links to fibrillar structures depending on crystallization conditions.     

Effect of Coolant Temperature on the Condensation Heat Transfer in Air-Conditioning and Refrigeration Applications

This article directly investigates the effect of a cooling medium's coolant temperature on the condensation of the refrigerant R-134a. The study presents an experimental investigation into condensation heat transfer, vapor quality, and pressure drop of R-134a flowing through a commercial annular helicoidal pipe under the severe climatic conditions of a Kuwait summer. The quality of the refrigerant is calculated using the temperature and pressure obtained from the experiment. Measurements were performed for refrigerant mass fluxes ranging from 50 to 650 kg/m²s, with a cooling water flow Reynolds number range of 950 to 15,000 at a fixed gas saturation temperature of 42°C and cooling wall temperatures of 5°C, 10°C, and 20°C. The data shows that with an increase of refrigerant mass flux, the overall condensation heat transfer coefficients of R-134a increased, and the pressure drops also increased. However, with the increase of mass flux of cooling water, the refrigerant-side heat transfer coefficients decreased. Using low mass flux in a helicoidal tube improves the heat transfer coefficient. Furthermore, selecting low wall temperature for the cooling medium gives a higher refrigerant-side heat transfer coefficient.     

Acoustic emission upon spontaneous polarization in triglycine sulfate single crystals

We report on the results of analysis of acoustic emission (AE) under thermal action on a triglycine sulfate (NH₂CH₂COOH)₃ ? H₂SO₄ crystal. The triglycine sulfate single crystals grown from solution and not subjected to mechanical treatment are heated to a temperature above the Curie point (T_C = 49°C). During natural cooling of the crystal, a transition from the paraelectric to ferroelectric phase is accompanied by intense AE. In the temperature range ～28–30°C, an anomalous drop of the mean-square voltage in the AE signal is observed against the background of monotonic accumulation of AE events.     

Evidence for a new metastable crystalline phase of strontium nitrate

The undercooling of aqueous solutions of strontium nitrate a few mm³ in volume or microsized by dispersion within an emulsion is investigated. The experimental results are consistent with a succession of transformations in undercooled solutions of binaries. Following concentration, the undercoolings are from 14°C to 20°C for macrosamples or from 39°C to 60°C with emulsions. However it is observed that Sr(NO₃)₂ crystallizes into a metastable phase which can be preserved for a long time. The existence of this metastable crystalline phase has been evidenced by Differential Scanning Calorimetry and by an original evaporation method. The phase diagram, including the metastable phase, is presented.