CFD Heat and Mass Transfer Studies in a R134a-DMF Bubble Absorber with Swirl Flow Entry of R134a Vapour

Study of absorber for heat and mass transfer analysis is essential to improve the performance of Vapour absorption refrigeration system(VARS). Tangential injection of refrigerant gas to liquid solution  in a bubble absorber increase the heat and mass transfer characteristics by following rotary and translation path. In this study, a vertical absorber is considered for heat and mass transfer study with refrigerant, R134a (1,1,1,2 –Tetrafluoroethane) and absorbent, DMF(dimethyl formamide). R134a vapour will be injected into the absorber using two injectors of 4.8 mm inner diameter at an injection angle of 30° to the vertical axis and parallel to the azimuthal axis of the absorber which mix well with liquid to increase the heat and mass transfer.            Finite volume method is used for the steady state with 3D cylindrical co-ordinates. Simulation is carried out for studying the heat and mass transfer behavior in laminar flow, using CFD.  For the numerical study, Mixture multiphase model is considered. A user defined function (UDF) is written for creating liquid solution mixture and refrigerant vapour to define the working fluid and its various properties like density, thermal conductivity, viscosity, etc. Grid  independent studies were carried out for the absorber geometry. Mass inlet boundary condition for solution inlet, and  vapour inlet, pressure outlet at the absorber and no-slip at wall boundary condition are used. In the absorber interface, wall constant heat flux boundary condition is defined. Evaporation and condensation model is used as phase and mass transfer interface mechanism between liquid and vapour. SIMPLER(Semi-Implicit Method for Pressure-Linked Equations) scheme is used for pressure- velocity coupling, PRESTO(Pressure Staggered Option) scheme is used for pressure and first order implicit upwind scheme is used for solving momentum equations. Converging criteria are achieved for momentum, energy and species equation by varying under relaxation factors.        Effect of solution pressure, solution flow rate, gas mass flow rate on heat and mass transfer rate, heat and mass transfer coefficients are computed. Numerical results are compared and validated with the co-axial entry of R134a in the R134a-DMF bubble absorber which show good agreement. Heat and mass transfer characteristic will be presented in this paper in terms of operational parameters

Experimental Study On Bubble Absorber With Multiple Tangential Nozzles

Vapour absorption refrigeration (VAR) system is one of the better system compared to other high grade energy utilized refrigeration system from thermodynamics point of view. For the successful operation of this system, the components are required to be designed and developed effectively and efficiently. Absorber is one of the crucial component of such a refrigeration system and bubble absorber is one type of absorber among different types of absorber. Bubble characteristics are studied experimentally with tangential nozzles, which may enhance the heat and mass transfer characteristics by following a swirling motion. Based on the inference drawn from these studies, experiments are planned with R134a and DMF combination for performance improvement of the VAR system. Visualization study of bubble growth with multiple tangential nozzles is investigated in a bubble absorber. Bubble behavior is studied with different flowing condition like still, co-current and counter-current flow of water. Bubble diameter during detachment increases with increase in gas flow rate in the above flow conditions. Effect of air flow rate, water flow rate, nozzle diameters, number of nozzles and nozzle angle with reference to vertical plane on bubble diameter is also studied. Results are compared with the available correlation in the literature which is found to be in good agreement. Comparison of performance between single and double nozzle also presented in this paper. Based on this study correlations are proposed. References: [1] M. Suresh, A. Mani, Heat and mass transfer studies on R134a bubble absorber in 134a/DMF based on phenomenological theory, International Journal of Heat and Mass Transfer 53 (2010) 2813–2825. [2] S. Ramakrishnan, R. Kumar, R.Kuloor, Studies in bubble formation-I Bubble formation under constant flow conditions, Chemical Engineering Science, 24 (1969) 731-747. [3] M. Jamialahmadi, M. R. Zehtaban , H. Muller-Steinhagen, A. Sarrafi A, J. M. Smith, Study of bubble formation under constant flow conditions, Trans IChemE, 79 (2001) Part A 523. [4] E.S. Gaddis, A. Vogelpohl, Bubble formation in quiescent liquids under constant flow conditions, Chemical Engineering Science, 41 (1986) 97-105

Performance Evaluation Of Bubble Absorber Using R134a/DMF In Vapour Absorption Refrigeration System With Swirl Injector

Vapour absorption refrigeration systems (VARS) importance has increased due to utilization of solar energy, waste heat, etc. To improve the efficiency of this system, it is necessary to increase the heat and mass transfer in the absorber with tangential injectors. Experiments were carried out to analyze a tubular heat exchanger used as an absorber with tangential injector. In this study, a vertical bubble absorber is considered for heat and mass transfer studies with refrigerant, R134a (1,1,1,2 –Tetrafluoroethane) and absorbent, DMF(dimethyl formamide). R134a vapour is injected into the absorber using two injectors of 4.8 mm inner diameter at an injection angle of 30° to the vertical axis and parallel to the azimuthal axis of the absorber, which enhances mixing of R134a with liquid R134a-DMF solution to increase the heat and mass transfer. Experiments were carried out by varying the operational parameters by varying refrigerant flow rate from 5 lph to 15 lph and liquid solution flow rate in the range of 20 lph to 50 lph. Chilled water is used to load the refrigeration system evaporator with flow rate 100 lph and temperature in the range of 5 to 20oC. Hot water is supplied to the generator in the range of 60 to 91oC with flow rate of 80 to 200 lph. Cold water is used as coolant to the condenser and absorber in the temperature range of 11 to 25 oC with the flow rate of 80 to 160 lph. Effects of operational parameters viz., gas flow rate, solution initial concentration, and solution pressure and solution temperature and number of injector on absorber performance are varied and analysed. Mass transfer effectiveness, heat transfer effectiveness, overall heat transfer coefficient, volumetric mass transfer coefficient, absorption rate and heat rejected from the absorber have been evaluated for the absorber. Heat and mass transfer coefficients evaluated from the experiments are compared with numerical model and it is found to be in good agreement. REFERENCE Suresh M., Mani A. (2012), Experimental studies on heat and mass transfer characteristics for R134a-DMF bubble absorber, International Journal of refrigeration 35 pp. 1104-1114. Santosh Kumar Panda, Mani A. (2014), Bubble dynamics study with tangential nozzles in a bubble absorber, International Sorption Heat Pump Conference at Maryland University, Maryland,USA

Finite element method: some modelling issues

This paper presents a meaningful discretization scheme for asymmetric object, such as rail section for central loading. Finite element (FE) plane stress analysis of the problem is carried out. The results from FE analysis are post processed to simulate the photoelastic experiment and check the discretization scheme. Issues related to experimental limitation of desired loading and their specification as boundary condition in finite element modeling are discusse

Assessment of benefits of employing natural refrigerants in seafood cold chain in India

In this paper we present a comprehensive assessment of benefits from adoption of suitable natural refrigerants at various stages of seafood cold chain in Indian scenario. This includes cooling demands during fish harvesting, transport of fresh catch, sorting and processing, and long-time storage. For each stage, the cooling demands are estimated and simple refrigeration cycle configurations are simulated to estimate the annual energy consumption and total equivalent warming impact for suitable natural refrigerants from among NH3, CO2, and hydrocarbons such as R170, R290, and R1270. The same is compared with synthetic refrigerants presently used for such application like R22, R134a and R404A etc. Field data from a surimi supply chain in west coastal region and shrimp supply chain in east coastal region of India are used for the study. The results highlight the potential benefits from use of natural refrigerants in seafood sector. Further, the various barriers in terms of technological, economic and policy related are highlighted.acceptedVersio

Comparative study of Exergetic and Economic analysis of Multi-evaporator NH3 and NH3-CO2 CRS for a Seafood Processing Plant

In a seafood processing plant, refrigeration is a vital and energy intensive process. In India, NH3 is predominately used to cater to such refrigeration demands. These industrial refrigeration systems have the multi-evaporator configuration with high pressure ratios necessitating adoption of multistage compression. In recent years, owing to excellent and favorable thermo-physical properties of CO2 in low temperature, adoption of NH3-CO2 cascade refrigeration system (CRS) with NH3 in high temperature cycle is gaining worldwide acceptance. In the present work, performance of a conventional NH3 multistage industrial refrigeration system is compared with a proposed NH3-CO2 CRS system in terms of energy, exergy and economic perspectives. Investigation is focused to thermodynamically evaluate and optimize the performance of the proposed cascade configuration with respect to operating parameters. A sensitivity analysis has been performed as well to study the effects of climatic conditions on system performance. The proposed NH3-CO2 CRS showed a maximum benefit of 13.3% in COP, 14% in exergy efficiency and 9% less TEWI compared to the baseline system. The estimated payback period is 25 months

Fixed-Point Theorems for Nonlinear Contraction in Fuzzy-Controlled Bipolar Metric Spaces

In this paper, we introduce the concept of fuzzy-controlled bipolar metric space and prove some fixed-point theorems in this space. Our results generalize and expand some of the literature’s well-known results. We also provide some applications of our main results to integral equations.The authors thank the Basque Government for its support of this study through grant IT1555-22

Effect of Ferroelectric Nanopowder on Electrical and Acoustical Properties of Cholesteric Liquid Crystal

Ferroelectric nano-materials are very sensitive to several external stimuli and have attracted great deal of attention due to their property of improving various properties such as photoluminescence, higher polarization, fast response time, low operating voltage and improved conductivity. For enhancing the physical properties, a proper selection of nano-materials for liquid crystals depends upon various factors such as size, shape, preparation methods, surfactant concentration and amount of doping materials. In the present study an attempt is made to study  electrical and acoustical properties of cholesteric liquid crystal after dispersing ferroelectric nano-powder of Barium Titanate (BaTiO3). In addition with this particle size and surface area of pure and nono-particle dispersed liquid crystal were also measured. Our investigation shows increase in Rao’s constant or molar sound velocity, which indicates increase in molecular density indicating a close packing of the material. The measurement of dielectric relaxation at different frequencies gives information about the dynamics of polar groups and molecular motion

Histidylated lipid-modified sendai viral envelopes mediate enhanced membrane fusion and potentiate targeted gene delivery

Recent studies have demonstrated that covalent grafting of a single histidine residue into a twin-chain aliphatic hydrocarbon compound enhances its endosome-disrupting properties and thereby generates an excellent DNA transfection system. Significant increase in gene delivery efficiencies has thus been obtained by using endosome-disrupting multiple histidine functionalities in the molecular architecture of various cationic polymers. To take advantage of this unique feature, we have incorporated L-histidine (N,N-di-n-hexadecylamine) ethylamide (L(H)) in the membrane of hepatocyte-specific Sendai virosomes containing only the fusion protein (F-virosomes (Process for Producing a Targeted Gene (Sarkar, D. P., Ramani, K., Bora, R. S., Kumar, M., and Tyagi, S. K. (November 4, 1997) U. S. Patent 5,683,866))). Such L(H)-modified virosomal envelopes were four times more (p <0.001) active in terms of fusion with its target cell membrane. On the other hand, the presence of L(H) in reconstituted influenza and vesicular stomatitis virus envelopes failed to enhance spike glycoprotein-induced membrane fusion with host cell membrane. Circular dichroism and limited proteolysis experiments with F-virosomes indicated that the presence of L(H) leads to conformational changes in the F protein. The molecular mechanism associated with the increased membrane fusion induced by L(H) has been addressed in the light of fusion-competent conformational change in F protein. Such enhancement of fusion resulted in a highly efficient gene delivery system specific for liver cells in culture and in whole animals

Population Genetics and Structure of a Global Foxtail Millet Germplasm Collection

Foxtail millet is one among the most ancient crops of dryland agriculture. It is the second most important crop among millets, grown for grains or forage. Foxtail millet germplasm resources provide reservoirs of novel alleles and genes for crop improvement that have remained mostly unexplored. We genotyped a set of 190 foxtail millet germplasm accessions (including 155 accessions of the foxtail millet core collection) using genotyping-by-sequencing (GBS) for rapid single nucleotide polymorphisms (SNP) characterization to study population genetics and structure, which enable allele mining through association mapping approaches. After filtering a total 350,000 raw SNPs identified across 190 germplasm accessions for Minor Allele Frequency (MAF), coverage for samples and coverage for sites, we retained 181 accessions with 17,714 high quality SNPs with ≥ 5% MAF. Genetic structure analyses revealed that foxtail millet germplasm accessions are structured along both on the basis of races and geographic origin, and the maximum proportion of variation was due to among individuals within populations. Accessions of race indica were less diverse and are highly differentiated from those of maxima and moharia. Genome-wide linkage disequilibrium (LD) analysis showed on an average LD extends up to ~150 kbp, and varied with individual chromosomes. The utility of these data for performing genome-wide association studies was tested with plant pigmentation and days to flowering, and identified significant marker-trait associations. This SNP data provides a foundation for exploration of foxtail millet diversity and for mining novel alleles and mapping genes for economically important traits