Experimental study on a two-stage rotary desiccant cooling system

The objectives of this study were to evaluate the performance of a novel two-stage rotary desiccant cooling (TSRDC) system and to obtain useful data and experiences for practical application. Newly developed compound desiccant (silica gel–haloids) was adopted in the system. An experimental set-up was built and used to test the system performance under three typical environmental conditions. System performances were evaluated in terms of moisture removal D and thermal coefficient of performance COP_th. It has found that the required regeneration temperature of TSRDC system is low and COP_th of the system is high. Regeneration temperatures from 65 °C to 80 °C, 65 °C to 75 °C and 80 °C to 90 °C were recommended for each environmental condition. In addition, the effects of some important operating parameters, such as inlet temperature and humidity ratio of process and regeneration air, on system performance were also investigated in this study.     

Characterization of desiccant wheels with alternative materials at low regeneration temperatures

A number of new desiccant materials have been proposed which have the potential to improve the performance of desiccant wheels being regenerated at low temperature. Desiccant wheels containing two such desiccant materials (zeolite and superadsorbent polymer) were compared with a conventional silica gel desiccant wheel. The superadsorbent polymer desiccant wheel achieved greater dehumidification than the silica gel wheel when dehumidifying high relative humidity air with low temperature (50 °C) regeneration air. The temperature of dehumidified air exiting the polymer wheel was also lower. The zeolite desiccant wheel was generally less effective at dehumidifying air and had a higher pressure drop.     

Elevated temperature low cycle fatigue of grey cast iron used for automotive brake discs

This paper evaluates the fatigue life properties of low carbon grey cast iron (EN-GJL-250), which is widely used for automotive brake discs. Although several authors have examined mechanical and fatigue properties at room temperatures, there has been a lack of such data regarding brake discs operating temperatures. The tension, compression and low cycle fatigue properties were examined at room temperature (RT) and at brake discs’ working temperatures: 500 °C, 600 °C and 700 °C. The microstructure of the material was documented and analysed. Tensile stress–strain curves, cyclic hardening/softening curves, stress–strain hysteresis loops, and fatigue life curves were obtained for all the above-mentioned temperatures. It was concluded, that Young’s modulus is comparable with both tension and compression, but yield its strength and ultimate strength are approximately twice as great in compression than in tension. All the mechanical properties remained quite stable until 500 °C, where at 700 °C all deteriorated drastically. During fatigue testing, the samples endured at 500 °C on average at around 50% of cycles at room temperature. Similar to other materials’ properties, the cycles to failure have dropped significantly at 700 °C.     

Failure and formability studies in warm deep drawing of Ti–6Al–4V alloy

Deep drawing experiments have been performed in order to study formability of Ti–6Al–4V alloy sheet at temperature ranging from room temperature to 400 °C. It is found that below 150 °C, formability of the material is very poor and above 150 °C till 400 °C, limiting drawing ratio (LDR) is found to be 1.8 which is substantially lesser than other structural alloys. For better understanding of failures in failed cups, failure regions have been identified in neck and wall which are validated using finite element (FE) simulations. Fractured surface has been examined with scanning electron microscope (SEM) which reveals different types of shallow dimples indicating predominantly ductile failure. Additionally, in the properly drawn cups, thickness distribution has been studied over a temperature range of 150–400 °C and blank diameter 50–54 mm. In order to optimize blank diameter and temperature to obtain uniform thickness distribution of drawn cups, artificial neural network (ANN) and genetic algorithm (GA) have been employed. Thickness distribution for optimized parameters is validated using FE simulation.     

Analytical modeling of a desiccant wheel

A simple integral model is presented for a desiccant wheel. The original governing equations for a desiccant wheel were simplified to a set of linear ordinary differential equations and an analytical solution was obtained. A brief analysis is given about the solution regarding the non-dimensional numbers that decide the behavior of a desiccant wheel. From the solution, algebraic expressions were obtained for time-averaged heat and mass transfer rates and the results were compared with a numerical model and a set of experimental data in the literature. In comparison with the numerical model, relative error was found less than 12% at 120 °C regeneration temperature and 10% standard deviation was observed with the experimental data. The analytical model is considered capable of describing a symmetric desiccant wheel realistically.     

An investigation to the hot deformation characteristics of AZ31 alloy through continuous cooling compression testing method

The design and control of thermomechanical processing (TMP) schedule are substantially facilitated by a thorough understanding of the dominant deformation mechanisms and phase transformations which occur in the alloy system under consideration. In this regards due to the effects of deformation history, the results of conventional methods such as dilatometry and thermal analysis are insufficient. In the present work, the hot deformation characteristics of AZ31 magnesium alloy has been studied through applying a series of continuous cooling compression (CCC) tests. The compression tests were conducted as the temperature was continuously reduced from 500 °C to 100 °C. The variations of true stress with true strain (or temperature) were extracted and the critical temperatures were determined. The derived true stress-true strain curves revealed five deviations at 440 ± 5 °C, 350 ± 5 °C, 300 ± 5 °C, 215 ± 5 °C and 150 ± 5 °C, which were properly addressed considering the related microstructural evolutions.     

Research on heat treatment of TiBw/Ti6Al4V composites tubes

Heat treatment with different parameters were performed on the hot-hydrostatically extruded and swaged 3.5 vol.% TiBw/Ti6Al4V composites tubes. The results indicate that the primary α phase volume fraction decreases and transformed β phase correspondingly increases with increasing solution temperatures. The α + β phases will grow into coarse α phases when the aging temperature is higher than 600 °C. The hardness and ultimate tensile strength of the as-swaged TiBw/Ti6Al4V composite tubes increase with increasing quenching temperatures from 900 to 990 °C, while they decrease with increasing aging temperatures from 550 to 650 °C. A superior combination of ultimate tensile strength (1388 MPa) and elongation (6.1%) has been obtained by quenching at 960 °C and aging at 550 °C for 6 h. High temperature tensile tests at 400–600 °C show that the dominant failure modes at high temperatures also differ from those at room temperature.     

An experimental investigation into the warm deep-drawing process on laminated sheets under various grain sizes

It has been proved by many researchers that increasing the temperature in warm deep-drawing process of single layer sheets decreases the forming load, however, this phenomenon is not necessarily the case in warm deep-drawing process of laminate sheet. The objective of the present paper is to carry out a comprehensive investigation on warm deep-drawing process on laminated sheets experimentally. Based on the results of this study, it can be observed that by raising the temperature, variation of forming load more depends on blank holder force (BHF). In this study, thinning and wrinkling in Al 1050/St 304 and Al 5052/St 304 samples for each layer in warm deep-drawing process are evaluated individually. In addition, the effects of various grain sizes, blank temperatures and sequence layer on forming load are investigated. In order to carry out a comprehensive survey of warm deep-drawing; three blank temperatures namely, 25 °C, 100 °C and 160 °C are examined. Furthermore, to achieve various grain sizes, the aluminum sheets are annealed at 350 °C, 400 °C and 450 °C for 1 h. Finally, several tests are conducted to obtain the influences of grain size on some material characteristics such as stress, elongation and friction coefficient.     

Ultrasonic fatigue of a single crystal Ni-base superalloy at 1000 °C

An ultrasonic fatigue testing system capable of operating at temperatures up to 1000 °C has been developed and utilized to study the fatigue behavior of a single crystal superalloy (PWA 1484) at a temperature of 1000 °C and loading frequency of approximately 20 kHz. The stress-life data generated from the ultrasonic testing system were comparable to those from conventional servo-hydraulic fatigue tests for similar single crystal alloys. Interior Ta-rich carbides were the major microstructural feature responsible for crack initiation in the alloy. Crack growth under ultrasonic loading frequency at 1000 °C for PWA 1484 occurred in a crystallographic manner on {1 1 1} octahedral slip planes, in contrast to the normal Mode-I growth mode typically observed for single crystal superalloys at high temperature (>850 °C) with conventional servo-hydraulic loading frequencies (<100 Hz).     

Mechanical properties of hot pressed CoCrMo alloy compacts for biomedical applications

This study aimed at investigating the influence of the processing conditions on the mechanical properties of hot pressed compacts of a CoCrMo biomedical alloy.Several hot pressed CoCrMo compacts were processed in vacuum (10⁻² mbar), at a pressure of 60 MPa with different temperatures (900 °C, 1000 °C and 1100 °C) and different times (10 min, 30 min and 60 min). Compacts were examined by SEM/EDS. The transverse rupture strength, Young’s Moduli and hardness were determined. The fracture surface of compacts were also examined.The compacts hot pressed at 900 °C exhibited lower TRS than those processed at 1000 °C and 1100 °C, which showed similar strength values, regardless the sintering time. The 900 °C compacts showed also lower YM and higher porosity. Lower hardness values were registered for 900 °C compacts while 1000 °C compacts exhibited the highest values. The fracture surface analyses revealed fragile fracture for 900 °C compacts (10 min and 30 min) and 1000 °C (10 min). The remaining compacts exhibited ductile fracture.A full characterization of the mechanical properties of hot pressed CoCrMo compacts has been made and the selection of the processing parameters according to the desired mechanical properties is now possible.     

Kinetics of thermal gradient chemical vapor infiltration of large-size carbon/carbon composites with vaporized kerosene

Large-size samples of carbon/carbon composites were prepared using thermal gradient chemical vapor infiltration with kerosene precursor at 950, 1020, 1100, 1180 and 1250 °C. The temperature gradient, kinetics and density distribution of these samples were studied and the microstructure of pyrolytic carbon was examined by polarized light microscopy. The results show that the initial infiltration rate increased from 5.81 to 21.32 g min^?1 by increasing deposition temperature from 950 to 1250 °C. The densification kinetics relied on deposition temperature and competition between reaction and diffusion, and the diffusion mechanism transformed from bulk to Knudsen diffusion regime. The calculated apparent activation energy is about 68.2 kJ mol^?1. The temperature range 1020–1100 °C is appropriate for fabricating composites with high final bulk density due to high degree of pore filling and the density of sample S3 infiltrated at 1100 °C is the highest among all investigated samples.     

Experimental study on critical breaking stress of float glass under elevated temperature

Cracking and subsequent fallout of glass may significantly affect fire dynamics in compartments. Moreover, the breaking tensile stress of glass, a crucial parameter for breakage occurrence, is the least well known among mechanical properties. In this work, a series of experiments were conducted, through mechanical tensile tests, to directly measure the breaking stress of float glass using Material Testing System 810 apparatus. Clear, ground and coated glass samples with a thickness of 6 mm were measured under ambient conditions, with a room temperature of 25 °C. The breaking stress of smooth glass samples was also measured at 75 °C, 100 °C, 125 °C, 150 °C, 200 °C, 300 °C and 400 °C, respectively. The results show that surface treatment may decrease the critical tensile stress of glass panes. The average breaking stress also fluctuates considerably, from 26.60 to 35.72 MPa with the temperature variations investigated here. At approximately 100 °C, critical stress reached the minimum value at which glass breakage occurs more easily. In addition, the thermal expansion coefficient was established using a thermal dilatometer, to obtain the maximum temperature difference float glass can withstand. It is intended that these results will provide some practical guidelines for fire safety engineers.     

Ni24.7Ti50.3Pd25.0 high temperature shape memory alloy with narrow thermal hysteresis and high thermal stability

High temperature shape memory alloys with operating temperatures above 100 °C are in demand for use as solid-state thermal actuators in aerospace, automobile and other engineering applications. The present study deals with transformation behaviour and thermal stability of Ni_24.7Ti_50.3Pd_25.0 (at.%) high temperature shape memory alloy, in cast and homogenized condition. The martensite finish temperature and transformation hysteresis of the alloy were determined to be 181.0 °C and ∼8.5 °C respectively. The alloy showed high stability upon stress-free thermal cycling, variation in transformation temperatures being ±1 °C. The narrow thermal hysteresis and high thermal stability of the alloy upon transformation cycling has been discussed and correlated with its microstructural features, activation energy and elastic strain energy of thermoelastic martensitic transformation. The alloy exhibited modulus of ∼82 GPa and hardness of ∼4.7 GPa in martensite phase.     

Intermediate temperature brittleness and directional coarsening behavior of nickel-based single-crystal superalloy DD6

The microstructure of the nickel-based single-crystal superalloy DD6 after tensile deformation has been studied by transmission electron microscopy (TEM) with an energy-dispersive X-ray spectroscopy (EDS). The samples were strained to fracture at room temperature, 650 °C, 850 °C and 1020 °C along the [001] orientation. The results indicate that the yield strength at 650 °C is superior to that at room temperature (20 °C), 850 °C and 1020 °C, but low ductility was observed at 650 °C. It is demonstrated that the intermediate temperature brittleness (ITB) behavior was caused by the change of the deformation mechanism at intermediate temperature. At high temperature, the γ′ precipitates coarsening directionally along the direction perpendicular to the stress axis. This can be attributed to the directional diffusion of the chemical elements.     

Hot workability of 00Cr13Ni5Mo2 supermartensitic stainless steel

The hot workability of 00Cr13Ni5Mo2 supermartensitic stainless steel was investigated by hot compression and hot tension tests conducted over the temperature range of 950–1200 °C and strain rates varying between 0.1 and 50 s^?1. The processing map technique was applied on the basis of dynamic materials model and Prasad instability criterion. Microstructure evolutions, Zener–Hollomon parameter as well as hot tensile ductility were examined. The results show that, as for the hot working of 00Cr13Ni5Mo2 supermartensitic stainless steel in the industrial production, the large strain deformation should be carried out in the temperature range 1140–1200 °C and strain rate range 0.1–50 s^?1, where the corresponding Zener–Hollomon parameters exhibit low values. Moreover, when deformed under high strain rate range (above 15 s^?1), the deformation temperature can be reduced reasonably.     

Effect of heat treatment on microstructure,hardness and rollability of V55Ti30Ni15 alloy membranes

The effect of heat treatment on the microstructure, hardness and rollability of V₅₅Ti₃₀Ni₁₅ alloy membranes has been investigated in this study. The microstructure resulting from different heat treatment conditions has a great influence on hardness. Fine NiTi particles precipitate from the supersaturated V-matrix solid solution at temperatures above 600 °C, increase in quantity until 800 °C, then dissolve back into the V-matrix with a further increase in temperature up to 950 °C. The resultant hardness decreases with temperature until 800 °C, and then increases from 800 to 950 °C. In the present study, a comparison has been made between the rollability of the as-cast and the heat treated state selected for deformation at different rolling temperatures. The percent reduction in thickness of the heat-treated alloy (800 °C/18 h) has been found to be up to 30% higher than that of the as-cast alloy, even at room temperature (cold rolling).     

Effect of overheating temperature on the microstructure and creep behavior of HP40Nb alloy

HP40Nb alloy has been widely used as a high temperature material in petrochemical plants. However, overheating or local temperature excursion occurs occasionally in service and leads to serious damage on the material. Effect of temperature on the microstructure and creep performance of the HP40Nb alloy is investigated in the present work. Several specimens are cut from serviced components of the alloy and heat-treated at different temperatures from 900 °C to 1250 °C for its possible working conditions, in which the temperature of 1200 or 1250 °C is used to simulate the overheating condition of HP40Nb tubes. The microstructure of specimens is examined by scanning electron microscope (SEM) and transmission electron microscope (TEM). The creep behavior is evaluated through using impression creep tests with a flat-ended cylindrical indenter. The content of inter- and intra-dendritic carbides in the specimens is represented by the surface fraction of each phase, which has been estimated by image processing method. The results show that the total of the surface fraction of inter- and intra-dendritic carbides in the HP40Nb alloy does not significantly change at the temperature lower than 1100 °C. However, the surface fraction of inter-dendritic carbides reaches the maximum at 1100 °C. A maximal steady state impression rate is also observed at 1100 °C. The results suggest that the content of inter-dendritic carbides is the main influencing factor on the creep performance of HP40Nb alloys comparing with that of the intra-dendritic carbides.     

Modeling the forced-air cooling process of fresh strawberry packages,Part I: Numerical model

A numerical analysis of the forced-air cooling process of retail packages of strawberries was performed by solving the conservation equations of mass, momentum and energy within the system. The results showed that the heterogeneity of the cooling process is largely influenced by the structure and design of the packaging system (individual clamshell packages and trays). On average 75 ± 2% of the total airflow forced through the system bypassed the clamshells, and 46 ± 5% of the flow rate forced through clamshells bypassed the strawberries. After 1 h of cooling, the average-fruit-temperature per clamshell ranged from 2.4 °C to 8.3 °C between the first and last clamshells along the main flow direction. Within these clamshells, the maximum differences in the volume-average temperature of individual fruits reached 3.5 °C and 5.1 °C, respectively. The results show the potential use of this numerical approach as a design tool to optimize the forced-air cooling process of horticultural products.     

Combined influence of sulphate and temperature on the saturated hydraulic conductivity of hardened cemented paste backfill

This paper presents an experimental study that focuses on the investigation of the coupled effects of temperature and sulphate on the permeability of hardened cemented paste backfill (CPB). Hydraulic conductivity tests and a microstructural analysis are conducted on mature CPBs prepared with various amounts of sulphate (0, 5000, 15,000, and 25,000 ppm) and cured at various temperatures (2 °C, 20 °C, 35 °C, and 50 °C). Important findings and valuable results are gained. It is found that the coupled effects of sulphate and temperature can lead to decrease (i.e. improvement of the environmental performance of CPBs) or increase of the hydraulic conductivity of CPBs. There is competition between the permeability decreasing and increasing factors. The dominant influencing factors depend on the curing temperature and initial sulphate content.     

The effect of post-cure duration on the mode I interlaminar fracture toughness of glass-fibre reinforced vinylester

The effect of different post-cure conditions on the mode I fracture toughness of a vinylester resin and its glass-fibre reinforced composite counterpart has been studied. Two sets of parameters were investigated. The first was the post-cure duration at constant temperature; 90°C for 1, 4 and 24 h. The second, for resin toughness only, was a combination of post-cure temperature and duration; 90°C/4 h, 80°C/8 h and 70°C/16 h. The results show that the post-cure increases toughness. This trend is consistent between the pure resin and the fibre composite for all treatments, except at 90°C/24 h. It is believed that the prolonged post-cure duration of 24 h has weakened the bond strength at the fibre–matrix interface, thus reducing the effectiveness of toughness transfer from the matrix to the composite. The study concludes that the post-cure enhances the toughness of the glass-fibre/vinylester composite, mainly due to the increase of resin toughness.