HFC Systems Research Articles

Halal food supply chain practices

Halal is a dietary guideline practised by Muslims. Halal is viewed as a seal of approval for food quality that cannot be easily verified by consumers prior to, during, or after eating. As a result, Halal certification serves as a useful tool for consumers to make educated purchasing decisions. Halal food and beverage supply chains relate to the process of managing halal food and beverage items from manufacturing to consumption, involving multiple partners in the SC networks. This study examines the significance of Halal Food Supply Chain features in the UAE market, as well as consumer trust and satisfaction. This study examined the supply chain in the United Arab Emirates, with an eye toward the future impact of HFC systems on customer perceptions of halal food practices.

A new correlation for carbon dioxide boiling heat transfer coefficient outside evaporating tubes

The Kigali Amendment to the Montreal Protocol encourages replacing hydrofluorocarbons or HFCs with natural refrigerants such as carbon dioxide. Since current CO2 transcritical systems have lower efficiency as compared to HFC systems, this study is proposed to carry out theoretical and experimental investigations of CO2 pool boiling heat transfer performance for efficiency improvements. The theoretical and experimental investigations are carried out for a smooth and three mechanically enhanced tubes under heat flux values ranging from 10 to 50 kW m−2 and evaporating pressures ranging from 2 to 4 MPa. The special structures of enhanced tube surface are favorable for the formation and maintenance of vaporization cores and for expelling the gas bubbles in the evaporation tubes. Results from the experimental investigations suggest that the heat transfer coefficient can be improved by a factor of 1.50–1.70, 1.58–1.82, and 1.94–2.23 respectively when using the three mechanically enhanced as compared to using the smooth tube. Such improvements in heat transfer coefficient can translate to an energy efficiency improvement of approximately 15.2%, 18.6% and 24.8% respectively. Based on the experimental data, a robust and simplified model for computing heat transfer coefficient is further proposed as a correlation of evaporating pressure and heat flux. The maximum deviation of the calculated and tested heat transfer coefficient is within ±8.73% for smooth tube and within ±15% for mechanically enhanced tubes. Findings from this study can provide a fundamental basis for improving the heat transfer performance of CO2 systems from the perspective of engineering design.

The Structure, Morphology, and Mechanical Properties of Ta-Hf-C Coatings Deposited by Pulsed Direct Current Reactive Magnetron Sputtering

Ta, Hf, TaCx, HfCx, and TaxHf1-xCy coatings were deposited by reactive pulsed Direct Current (DC) magnetron sputtering of Ta or Hf pure metallic targets in Ar plus CH4 gas mixtures. The properties have been investigated as a function of the carbon content, which is tuned via the CH4 flow rate. The discharge was characterized by means of Optical Emission Spectroscopy and, in our conditions, both Ta-C and Hf-C systems seem to be weakly reactive. The structure of the as-deposited pure tantalum film is metastable tetragonal β-Ta. The fcc-MeCx carbide phases (Me = Ta or Hf) are {111} textured at low carbon concentrations and then lose their preferred orientation for higher carbon concentrations. Transmission Electron Microscopy (TEM) analysis has highlighted the presence of an amorphous phase at higher carbon concentrations. When the carbon content increases, the coating’s morphology is first compact-columnar and becomes glassy because of the nano-sized grains and then returns to an open columnar morphology for the higher carbon concentrations. The hardness and Young’s modulus of TaCx coatings reach 36 and 405 GPa, respectively. For HfCx coatings, these values are 29 and 318 GPa. The MeCx coating residual stresses increase with the addition of carbon (from one-hundredth of 1 MPa to 1.5 GPa approximately). Nevertheless, the columnar morphology at a high carbon content allows the residual stresses to decrease. Concerning TaxHf1-xCy coatings, the structure and the microstructure analyses have revealed the creation of a nanostructured coating, with the formation of an fcc superlattice. The hardness is relatively constant independently of the chemical composition (22 GPa). The residual stress was strongly reduced compared to that of binary carbides coatings, due to the rotation of substrates.

R744 booster integrated system for full heating supply to supermarkets

In warm climates carbon dioxide (R744) refrigeration systems are known to perform worse because of the transcritical operation which occurs for a large part of the year, increasing substantially their energy use. On the other hand, the high discharge temperature potentially allows recovering a large amount of heat at various temperature levels. This paper investigates the energy performance of a R744 refrigeration system which provides a medium-sized supermarket with DHW and space heating, besides satisfying the cooling load required by the chilled and frozen food storage and display equipment. The system is controlled to meet the full heating demand of the building and is equipped with an additional air-cooled evaporator, which can be used as a supplemental heat source. Dynamic simulations of the refrigeration system, including mutual interactions with the building and the HVAC, are carried out at three climate conditions. The results are compared to alternative refrigeration systems not controlled by the heating demand, such as the R744 booster system itself, a R404A direct expansion system and a R134a/R744 cascade system, where heat pumps are employed for heating. Energy saving was predicted both when compared to the CO2 system (up to 4.5%), and to the HFC systems (up to 16%). Furthermore, the heating COP of the integrated system appears to be always higher than that of standalone heat pumps.The comparison shows that heat recovery can fully supply refrigeration and heating needs of the supermarket with reduced running and possibly investment costs when compared to separate systems.

Review of phase stability in the group IVB and VB transition‐metal carbides

AbstractThis review summarizes the phase stability in the group IVB (Ti‐C; Zr‐C; Hf‐C) and group VB (V‐C; Nb‐C; Ta‐C) transition‐metal carbides. The order parameter functional (OPF) method and density functional theory (DFT) method have been used to predict phase equilibria in these systems. Extensive experimental investigations have attempted to determine both phase stability as a function of composition as well the crystal structures present using X‐ray diffraction, neutron diffraction, electron backscatter detection, and selected area electron diffraction. These investigations have demonstrated that the structures that form are based on the close‐packing of the metal atoms and the arrangement of the carbon atoms in the octahedral interstices. In general, the rocksalt B1 phase is stable for all of the transition‐metal carbides, with their substoichiometry tolerance increasing with temperature; vanadium carbide is the exception due to its negative vacancy formation energy. Vacancy‐ordered M6C5 phases have been predicted and experimentally confirmed in both groups of carbides; however, kinetic limitations often inhibit the formation of vacancy‐ordered phases, which has contributed to controversy in phase identification. The vacancy‐ordered M4C3 phase has been predicted for select carbides and has only been observed in zirconium carbide. In contrast, the stacking fault phase ζ‐M4C3−x has been readily reported in the group VB carbides (but not in the group IVB carbides). The vacancy‐ordered M3C2 has been predicted by DFT for the group IVB carbides but not in the group VB carbides, whereas OPF predicts its stability in both carbides. Vacancy‐ordered M3C2 phases have been experimentally observed in the Ti‐C and Hf‐C systems. Finally, the M2C phase has been predicted in both group carbides, except for hafnium carbide, with an order‐disorder transition with temperature. These factors result in phase diagrams that are similar among all the carbides, but each phase diagram is unique due to subtle differences in bonding that result in slight differences in thermodynamically stable phases.

Field measurements of supermarket refrigeration systems. Part II: Analysis of HFC refrigeration systems and comparison to CO2 trans-critical

This part of the study investigates the performance of HFC refrigeration systems for supermarkets and compares the performance with alternative CO2 trans-critical solutions. The investigated HFC system solutions are typical in supermarkets in Sweden. The analysis in this study is based on field measurements which were carried out in three supermarkets in Sweden. The results are compared to the findings from Part I of this study where five CO2 trans-critical systems were analyzed.Using the field measurements, low and medium temperature level cooling demands and COP’s are calculated for five-minute intervals, filtered and averaged to monthly values. The different refrigeration systems are made comparable by looking at the different COP’s versus condensing temperatures. The field measurement analysis is combined with theoretical modelling where the annual energy use of the HFC and CO2 trans-critical refrigeration systems is calculated.Comparing the field measurement and modelling results of COP’s for HFC and CO2 systems, the new CO2 systems have higher total COP than HFC systems for outdoor temperatures lower than about 24°C. The modelling is used to calculate the annual energy use of HFC and new CO2 system in an average size supermarket in Stockholm, new CO2 systems use about 20% less energy than a typical HFC system.The detailed analysis done in this study (Part I and Part II) proves that new CO2 trans-critical refrigeration systems are more energy efficient solutions for supermarkets than typical HFC systems in Sweden.

Enhancing energy efficiency in supermarket refrigeration systems through a robust energy performance indicator

Supermarket chains require benchmarking and analysing refrigeration performance in order to manage their energy efficiency investments. This paper contributes in robustly assessing refrigeration system energy and carbon performance in which commonly believed drivers are used to conduct correlations. Based on this, refrigeration connected load, store opening hours and external temperature were found to construct a more representative energy performance indicator (EPI) than other metrics. By using such an indicator, it is possible to identify poor performing systems from an estate portfolio and thus select sites suitable for energy saving measures. Furthermore, energy impact from introducing natural refrigerants is examined using empirical data from a UK supermarket chain. It was found that CO2 systems have different seasonal performance than HFC systems, nonetheless on an annual basis no system has a clear edge over another. Lastly, other initiatives such as cabinet night blinds and suction pressure optimisation achieved 10% and 7% energy reduction respectively.

A refrigeration system for supermarkets using natural refrigerant CO2

This paper describes a refrigeration system using a natural refrigerant that has been developed to reduce significantly both direct and indirect greenhouse gas emissions. The new system uses both R-404A and CO 2 (R-744) as refrigerants. The new system has very low global warming potential compared with conventional HFC systems which reduces significantly direct emissions. Indirect emissions are also much reduced as the system efficiency is much greater than achieved using conventional HFC refrigeration. Copyright , Manchester University Press.

Thermodynamic evaluation of the C−Co−W−Hf−Zr system for cemented carbides applications

Cemented carbides consist of hard carbide particles of hexagonal WC and often also of cubic carbides cemented together in a binder consisting of mainly cobalt (Co). A thermodynamic evaluation of the cubic carbide formers hafnium (Hf) and zirconium (Zr) in cemented carbides has been done. Both thermodynamic evaluations of lower-order systems and experimental investigations have been performed. The new experimental information was necessary for a satisfactory thermodynamic description because there is a lack of earlier experiments of this alloy system. The assessment work with the C-Co-W-Hf-Zr system has resulted in a satisfactory description of the thermodynamic properties compared with the experimental values. This work has been done by combining a new assessment of the CoHf and CoZr systems with already assessed investigations of the Hf-C and Zr-C systems. New experimental information in higher-order systems has been used to improve the thermodynamic descriptions and to verify the reliability of the assessments. The main results of the experimental work are measurements of the composition of the cubic carbide in selected equilibria; measurements of the temperatures of the L+fcc+WC+graphite and L+fcc+WC+M6C equilibria in the C-Co-Hf, C-Co-Zr, and C-Co-W-X (X=Hf and Zr) systems; and measurements of the solubility of Hf and Zr in liquid cobalt. Detailed comparisons between calculated and experimental data are presented.

Diffusion Interaction in Fiber-Reinforced Composites of the Chromium Alloy – Silicon Carbide System

Diffusion interaction in the Cr – ZrC and Cr – HfC systems has been studied in the temperature range 1200-1400°C. The impurities contained in chromium or carbides were found to affect the interaction in the systems. Almost no interaction was observed when the systems were held at temperatures up to 1300°C for 100 h. At higher temperatures the carbides were reduced to ZrO2, HfO2, and Cr23C6 because of the presence of a slight amount of oxygen. Thermodynamic calculations indicated no interaction in these systems at temperatures up to 1600°C. A study of the interaction in the systems SiC – ZrC and SiC – HfC showed that a transition zone formed already in the stage of sample preparation by diffusion welding in vacuum (1300°C, vacuum of 10_3 Pa, with a load applied for 20 min). During annealing (1300°C, 50 h) the transition zone stratified, forming a solid solution of silicon in Zr(Hf)C and SiC inclusions in the SiC – Zr(Hf)C solid solution. A transition zone formed on the zirconium carbide side when SiC interacted with Zr(Hf)C. The interaction in SiC – Zr(Hf)C casts doubt on the use of them as a barrier without antidiffusion layers.

Isothermal vapor–liquid equilibrium for the three binary systems 1,1,1,2,3,3-hexafluoropropane with dimethyl ether or propane, and 1,1,1,3,3,3-hexafluoropropane with dimethyl ether

Isothermal vapor–liquid equilibria (VLE) were measured for mixtures of dimethyl ether (RE170) or propane (R290) with 1,1,1,2,3,3-hexafluoropropane (R236ea) or 1,1,1,3,3,3-hexafluoropropane (R236fa), using a recirculation apparatus in which the vapor is forced through the liquid. The phase composition at equilibrium was measured by gas chromatography. The experimental data were regressed with the Carnahan–Starling–De Santis (CSD) equation of state (EOS). A good data fit was achieved and the excess Gibbs energy was calculated using the resulting coefficients. The R290+HFC systems (where HFC, in this case, is one of the isomers of hexafluoropropane) show strong positive deviations from Raoult’s law, whereas the RE170+HFC system shows strong negative deviations. The deviations from Raoult’s law observed for the RE170+HFC systems are attributed to hydrogen bonding and, on the basis of the homomorph concept, the gE of the H-bonding was estimated as the difference between the gE of respective pairs of systems. The behavior of the two HFC isomers is compared in mixtures with the non-polar R290 and the proton acceptor RE170.

An ATM-friendly MAC for traffic concentration in HFC systems

Proliferating deployment of amphidromic broadband services over commercial cable TV networks is bringing a taste of IBCN capabilities to vast numbers of domestic customers. The fluctuating and unpredictable traffic of the new services favours TDMA multiplexing of traffic from many customers inside each channel for flexible and dynamic bandwidth sharing on the basis of a medium access protocol. As penetration grows, traffic aggregations will exceed the capabilities of store-and-forward switching bringing more and more into prominence fast switching techniques and ATM networking. The first HFC systems designed primarily for LAN interconnection and Internet traffic are not optimised for ATM sources even when they employ ATM cells as a unit of transport. A novel contention approach designed to greatly reduce the distortions to traffic profiles characterising first generation HFC medium access protocols is the theme of this paper. The proposed method provides a high number of simultaneous orthogonal contention opportunities which allow quick identification of cell arrivals which is a key to preserving temporal relationships of contending traffic, vastly reducing cell delay variations in line with the traffic control philosophy of ATM.

A comparison between Anderko's model with composition-dependent physical interaction parameters and SRK-based hexamer model for HFC and HF systems

A new composition-dependent mixing rule in physical contribution term of AEOS by Anderko [A. Anderko, Phase equilibria in aqueous systems from an equation of state based on the chemical approach. Fluid Phase Equilibria, 1991, 65, 89.] was introduced to predict the phase behavior for HFC-134a+HF and HFC-32+HF binary systems. The approach developed in this work gives better results for systems containing strongly associating compounds in the vapor phase such as hydrogen fluoride than the SRK-based hexamer model developed by Twu et al. [C.H. Twu, J.E. Coon, J.R. Cunningham, A new cubic equation of state for hydrogen fluoride, Fluid Phase Equilibria 1993, 86, 47.] with fewer binary adjustable parameters. The equation of Peng and Robinson [D.Y. Peng, D.B. Robinson, A new two-constant equation of state. Ind. Eng. Chem. Fundam., 1976, 15, 59.] is used to describe the physical interactions. The van der Waals mixing rule was replaced by composition-dependent mixing rules to improve the predictability of this model. This study shows more accurate results for VLE phase behavior for HFC and HF systems than the SRK-based hexamer model or any other activity coefficient-based hexamer models developed so far.

Calculation of phase diagrams of interstitial compounds

The previously proposed order parameter functional method is considered for application to phase equilibria in ordering nonstoichiometric interstitial compounds MX y . Equations are derived for calculating the ranges of temperature and composition where a disordered phase and ordered phases exist. The ordering was taken into account for the first time to calculate the phase diagrams of the Zr-C, Hf-C, Nb-C and Ta-C systems, and the possible types of nonstoichiometric ordered carbide phases were determined. It is shown that superstructures of the M 4X 3 and M 8X 7 type cannot be formed in nonstoichiometric MX y compounds.