On the development of high temperature ammonia–water hybrid absorption–compression heat pumps

Ammonia–water hybrid absorption–compression heat pumps (HACHP) are a promising technology for development of efficient high temperature industrial heat pumps. Using 28 bar components HACHPs up to 100 °C are commercially available. Components developed for 50 bar and 140 bar show that these pressure limits may be possible to exceed if needed for actual applications. Feasible heat supply temperatures using these component limits are investigated. A feasible solution is defined as one that satisfies constraints on the COP, low and high pressure, compressor discharge temperature, vapour water content and volumetric heat capacity. The ammonia mass fraction and the liquid circulation ratio both influence these constraining parameters. The paper investigates feasible combinations of these parameters through the use of a numerical model. 28 bar components allow temperatures up to 111 °C, 50 bar up to 129 °C, and 140 bar up to 147 °C. If the compressor discharge temperature limit is increased to 250 °C and the vapour water content constraint is removed, this becomes: 182 °C, 193 °C and 223 °C.     

Numerical and experimental investigations of the effects of the breakup of oil droplets on the performance of oil–gas cyclone separators in oil-injected compressor systems

A numerical simulation was conducted of the dynamic trajectories and the separation performance of oil droplets, with a focus on the breakup of oil droplets in an oil–gas cyclone separator. The separation efficiency was also studied experimentally, and the oil droplets' diameter distributions before and after the separator were measured with a Malvern particle size analyser to verify the simulation model. Both the experimental and simulation results showed that the breakup of oil droplets occurred in the separation process, clearly influencing the separation efficiency. In addition, the results indicated that inlet velocity played an important role in separation efficiency, as it not only significantly affected the tangential velocity inside the separator, but also determined the possibility and degree of the breakup of oil droplets.     

Studies on the performance of a small reciprocating compressor with different nitrogen–hydrocarbon mixtures

The performance of Joule–Thomson refrigerators operating with mixed refrigerants depends on the composition of mixtures as well as the hardware employed. The role of mixture composition on the overall performance of the system has been well addressed in the open literature. What is not well known is the role of mixture composition on the performance of individual components such as the compressor, heat exchanger, etc. The adiabatic efficiency of a single stage Joule–Thomson refrigerator compressor was measured with thirty different nitrogen–hydrocarbon and neon–nitrogen–hydrocarbon mixtures. Our results show that the adiabatic efficiency of the compressor is independent of the mixture composition in the range of pressure ratios tested.     

Role of nickel in the oxidation of Fe–Cr–Ni alloys in air–water vapour atmospheres

Abstract

A series of experimental austenitic alloys has been produced in which the nickel content ranges from 14 to 43%, with constant levels of 20%Cr, 1%Mn and 0.5%Si. A combination of isothermal, discontinuous and cyclic oxidation testing has been used to elucidate the performance in dry air and in air with 10%, 45% or 62% water vapour at 700°C and 1000°C. Evaluation was by means of thermogravimetry, surface analysis with glow discharge optical emission spectroscopy and scanning electron microscopy.

Nickel is shown to have several roles: it accelerates the kinetics of chromia formation yet suppresses chromia spallation at 700°C. At 1000°C, it strongly decreases the breakaway oxidation and spalling associated with iron oxide formation. This effect is particularly marked in environments containing water vapour, where the material loss may be decreased 10-fold by an increase in the nickel content. Results correlate to thermodynamic and kinetic data which show nickel to increase the chromium activity and diffusivity in the alloy.     

Maldistribution in air–water heat pump evaporators. Part 1: Effects on evaporator,heat pump and system level

This paper presents an approach to quantify the effect of evaporator maldistribution on operating costs of air–water heat pumps. In the proposed simulation model maldistribution is induced by two parameters describing refrigerant phase and air flow distribution. Annual operating costs are calculated based on heat pump performance at distinct operating conditions. Results show that percentage increase of operating costs is similar for the three considered climate zones, even though the effect of maldistribution on heat pump performance varies with operating conditions. Differences in terms of absolute cost increase for the climate zones arise mainly due to a varying number of operating hours. Absolute cost increase is considerable in the average and especially colder climate zone and can only partly be reduced by enlarging the evaporator.     

Maldistribution in air–water heat pump evaporators. Part 2: Economic analysis of counteracting technologies

In this study a methodology is applied to quantify the effect of evaporator maldistribution on operating costs of air–water heat pumps. The approach is used to investigate the cost-effectiveness of two technologies enabling to counteract maldistribution: a flash gas bypass setup and the individual superheat control in parallel evaporator channels. In the total cost of ownership analysis, different scenarios for climatic conditions, severity of maldistribution, and economic framework are considered. Results show that the flash gas bypass system is cost-effective only in a few conditions, namely severe maldistribution, high electricity prices, and colder climate. Investment in the individual superheat control technology, however, can be quickly amortized in many scenarios. For the warmer climate zone with a small number of operating hours counteracting of maldistribution does not pay off under the used economic assumptions.     

The effects of water aging on the interphase region and interlaminar fracture toughness in polymer–glass composites

Three different unidirectional polymer–glass composite systems involving phenolic and polyester resins were aged for 6 and 11 weeks in tap water and tested in the mode I double cantilever beam (DCB) test. The results showed a dramatic increase in water absorption and a decrease in fracture toughness for phenolic/glass systems. Fractographic analysis revealed interfacial debonding to be dominant failure mechanism, indicating a strong influence of water degradation on fracture toughness results. The interphase region of each system was investigated using the nano-indentation and the nano-scratch techniques before and after aging in water. The nano-indentation test produced a series of indents as small as 30 nm in depth, to detect water degradation of the material properties at the interphase region between the fibre and the matrix. The nano-hardness results indicated interdiffusion in water aged interphase regions. The nano-scratch test was used in conjuction with the nano-indentation test, in order to detect the width of the interphase regions before and after water degradation. It was shown, from the coefficient of friction and the scratch profile depth, that the interphase region width increased and the material properties degraded during water aging. Qualitative links between water degradation of the glass–polymer interphase on a nanometer level and interlaminar fracture toughness are discussed.     

Effect of load and reciprocating velocity on the transition from mild to severe wear behavior of Al–Si–SiCp composites in reciprocating conditions

In the present paper, the effect of normal load and reciprocating velocity on transition from mild to severe wear of A319/15%SiC_p, A336/15%SiC_p, and A390/15%SiC_p composites have been reported. Composites were produced through liquid metal metallurgy route. Adhesive wear behavior of composites was studied under dry reciprocating conditions using indigenously developed reciprocating friction wear test rig conforming to ASTM Standard G133-05. It was found that increase in normal load increases wear rate and depending upon the reciprocating velocity and type of composites, mode of wear changes from mild oxidative to severe metallic wear was noticed. The load corresponding to the transition from mild to severe wear usually termed as transition load was found to decrease with increase in reciprocating velocity and reduction in silicon content in the alloys used for the development of Al–Si–SiC_p composites. At 1 m/s reciprocating velocity, the transition load for A319/15%SiC_p, A336/15%SiC_p and A390/15%SiC_p composites were found to be in the range of 60–90 N, 60–105 N and 60–120 N respectively. Scanning electron microscope (SEM) study of wear surface and wear debris were conducted to analyze the mode of wear and operating wear mechanism. Severe wear was characterized by massive plastic deformation and gross material removal while the mild wear was found to be associated with delamination and scoring as main wear mechanisms responsible for material loss. Wear mechanism maps for different Al–(6–18)%Si–15%SiC_p composites were proposed in reciprocating contacts.     

Hydraulic design and operation of variable-speed pumps as the water–energy saving strategies in pressurized irrigation systems

Clean Technologies and Environmental Policy - Low efficiencies of irrigation pumping stations usually stem from their improper designing, operation, and maintenance of such systems. In the present...     

An investigation on effects of heat treatment on corrosion properties of Ni–P electroless nano-coatings

Electroless Ni–P coatings are recognized for their excellent properties. In the present investigation electroless Ni–P nano-crystalline coatings were prepared. X-ray diffraction technique (XRD), scanning electron microscopy (SEM), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were utilized to study prior and post-deposition vacuum heat treatment effects on corrosion resistance together with the physical properties of the applied coatings.     

Experimental investigation on TiO2 nanoparticle migration from refrigerant–oil mixture to lubricating oil during refrigerant dryout

The application of nanorefrigerant–oil mixture in refrigeration system requires continuous circulation of nanoparticles; however, only a small part of nanoparticles circulate by migration from the mixture to vapor within refrigerant dryout process. This study points out a more important nanoparticle circulation way by migration from bulk refrigerant–oil mixture to oil excess layer, and quantitatively evaluate the mixture-to-oil migration ratio affected by oil mass fraction, nanoparticle mass fraction and heat flux. The nanorefrigerant–oil mixture is TiO₂/R141b/NM56; experimental conditions cover oil mass fraction of 5%–20%, nanoparticle mass fraction of 0.2%–1.0%, and heat flux of 10–100 kW m⁻²; the mixture-to-oil migration ratio is measured by absorbance method. The results show that mixture-to-oil migration ratio ranges within 0.388–0.969, and increases averagely by 51.8%, 28.3% and 8.0% with increasing oil mass fraction, reducing nanoparticle mass fraction and lowering heat flux over the whole range of present conditions, respectively.     

Experimental investigation on the performance of a solar powered lithium bromide–water absorption cooling system

The performance of solar cooling absorption system needs further research, due to its poor coefficient of performance (COP). Therefore, this study investigated the performance of a 23 kW solar powered single-effect lithium bromide–water (LiBr–H₂O) absorption cooling system. Furthermore, the space heating mode was also investigated and the improvement methods were analyzed and discussed. The cooling system was driven by a parabolic trough collector of 56 m² aperture area and used for cooling a 102 m² meeting room. Research results revealed that the chiller's maximum instantaneous refrigeration coefficient (chiller efficiency) could be up to 0.6. Most of the time, in sunny and clear sky days the daily solar heat fraction ranged from 0.33 to 0.41 and the collectors field efficiency ranged from 0.35 to 0.45. At the same time, chiller efficiency was varied from 0.25 to 0.7 and the daily cooling COP was varied from 0.11 to 0.27, respectively.     

Effects of heat treatments on the serrated flow in a Ni–Co–Cr-base superalloy

Serrated flow in a Ni–Co–Cr-base superalloy was studied in three microstructural conditions (SUB, SUBA, and SUPER) from 25 to 750 °C by tensile test at initial strain rates ranging from 8 × 10⁻⁵ to 3 × 10⁻³ s⁻¹. The results showed that the SUB and SUBA samples had fine grain size of about 9 μm, whereas the SUPER samples had coarse grain size of about 600 μm. The tertiary γ′ fraction was about 0 in the SUB, 5% in the SUBA, and 15% in the SUPER samples, respectively. The types and temperature ranges of serration were different in the alloy with SUB, SUBA, and SUPER microstructures. It is proposed that the tertiary γ′ fraction and size had great effects on the serrated flow of the alloy with different microstructures.     

Monolayer studies of sugar- and nucleoside-terminated dendrimers at the air–water interface

Sugar- and adenosine-terminated dendrimers, [1,2-o-Isopropylideneribosyl-(G₁-12acid), -(G₂-36acid)] and [Adenosyl-(G₁-12acid), -(G₂-36acid)], were synthesized using Newkome's dendrimer synthetic method. Langmuir and Langmuir–Blodgett (LB) monolayers of these dendrimers have been constructed and characterized at the air–water interface and on solid substrates by measuring surface pressure–molecular area (Π–A) isotherms, atomic force microscopy (AFM), ellipsometry and contact angle measurement. Π–A isotherms and AFM images showed that these dendrimers formed stable and homogeneous monolayers without aggregation on pure water surface. The first and second generation of sugar-terminated dendrimers show molecular areas of 647 and 1359 Ų, respectively. Ellipsometry measurement indicates that the thickness of both the first and the second generation of sugar-terminated dendrimers were about 10 Å. This reflects a flat orientation of both molecules at the air–water interface. On the other hand, the first generation of adenosine-terminated dendrimer shows an area of 105.6 Ų per molecule with a thickness of 16 Å, and for the second generation, the area was 738.4 Ų with a thickness of 27 Å. These results suggested that adenosine-terminated dendrimers maintain a spherical form at the air–water interface. It was found that small difference in the structure of thymine and uracil in the subphase critically affects the interaction of the molecules and conformation of the dendrimers at the interface.     

Fabrication of optimized oil–water separation devices through the targeted treatment of silica meshes

Abstract

Efficient oil–water separation is achieved using an optimized superhydrophobic material, generated by the zeolitic roughening and subsequent hydrophobic surface treatment of silica filter membranes. The material is both highly rough and intrinsically hydrophobic, resulting in superhydrophobic membranes which show a substantial affinity for hydrophobic solvents and oils. The membranes are syringe-mounted, suction pressure is applied and the selective collection of oil is achieved. The membranes are extremely robust, which is a result of the zeolitic roughening process, they possess small pores (0.7 μm), as a result these devices can perform complete separation and operate at a range of suction pressures. The devices could be readily used in a range of real-world applications, including oil spill clean-up and industrial filters.     

Fabrication of optimized oil–water separation devices through the targeted treatment of silica meshes

Efficient oil–water separation is achieved using an optimized superhydrophobic material, generated by the zeolitic roughening and subsequent hydrophobic surface treatment of silica filter membranes. The material is both highly rough and intrinsically hydrophobic, resulting in superhydrophobic membranes which show a substantial affinity for hydrophobic solvents and oils. The membranes are syringe-mounted, suction pressure is applied and the selective collection of oil is achieved. The membranes are extremely robust, which is a result of the zeolitic roughening process, they possess small pores (0.7 μm), as a result these devices can perform complete separation and operate at a range of suction pressures. The devices could be readily used in a range of real-world applications, including oil spill clean-up and industrial filters.     

Driving factors of external funding and funding effects on academic innovation performance in university–industry–government linkages

This study focuses on analyzing the driving factors of government and industry funding and the effects of such funding on academic innovation performance in the Taiwan’s university–industry–government (UIG) collaboration system. This research defines the relationships of the triple helix in the UIG collaboration system as a complex intertwined combination that covers demography, financial support, and innovation performance. These relationships are simultaneously modeled by a multivariate technique, structural equation modeling, to investigate the causal-effect relationship among the antecedent factors on the subsequent ones. This model will enable us to investigate three questions: (1) Is government funding or industry funding tied to university demography, to university innovation performance, or to both? (2) Does government funding lead industry funding? (3) Is government funding or industry funding conducive to more university innovation performance? In addition to verifying the model against all participating universities in the UIG collaboration, we also categorize them into two tiers in terms of whether or not universities have been selected for the incentive programs of UIG collaboration so as to explore groups’ differences.     

Some effects of trace elements in reducing creep performance of high–strength superalloys

Abstract

In the high–strength superalloys used for ‘hot-end’ components in gas turbine engines, small amounts of elements with low melting points can have a seriously detrimental effect on high–temperature performance. Some of the more recent work carried out to define harmful levels of trace element content and to develop an understanding of the mechanisms involved is briefly reviewed in this paper. The emphasis is on results available for cast alloys; the problem of gaseous impurities in recycled material is also considered. The implications for the specification and control of trace element content are briefly discussed.

MST/161     

The effect of Ca on the in vitro corrosion performance of biodegradable Mg–Nd–Y–Zr alloy

The effect of 0.4% Ca on the in vitro corrosion behavior of Mg–1.2% Nd–0.5% Y–0.5% Zr was evaluated in a simulated physiological environment in the form of 0.9% NaCl solution saturated with Mg(OH)₂ at ambient temperature and at 37 °C. The microstructure examination was carried out using optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. The corrosion behavior was evaluated by immersion test, salt spray testing, and potentiodynamic polarization analysis. The stress corrosion behavior was examined using slow strain rate testing analysis in different strain rates. The results obtained have shown that the addition of 0.4% Ca has a beneficial effect on the corrosion resistance of the tested alloy. This was mainly attributed to the effect of calcium, which reduces oxidation in the molten condition and consequently improves the soundness of the obtained casting. Hence, it is believed that the reduction in the extent of inherent casting defects in the alloy containing calcium overcomes the detrimental micro-galvanic effect of the Mg₂Ca phase that was formed in the tested alloy. Contrary to the beneficial effect of calcium on the corrosion performance, the addition of calcium has a damaging effect on the stress corrosion behavior in terms of reduced ultimate tensile strength and ductility. This was mainly due to the embrittlement effect of calcium that was generated by the formation and distribution of Mg₂Ca phase at grain boundaries.