Showing papers in "International Journal of Heat and Technology in 2016"

A review of electrochromic windows for residential applications

Abstract: Electrochromic windows can play an important role for energy saving as well as for controlling the visual and thermal conditions inside a room. This paper starts with a critical review and the state-of-art regarding the products today commercially available as well as the studies conducted on full scale electrochromic windows. The analysis allows to define the main parameters characterizing the electrochromic windows with particular regard to their optical, thermal and electrical characteristics, while assuming that the physical quantities, generally used to evaluate the behaviour of standard glasses, are not sufficient to evaluate the performances of the smart windows. In addition the experimental studies conducted on full scale electrochromic windows are analysed highlighting the measured physical quantities and the applied measurement methodologies considering both field and laboratory tests. Taking into account the need to accurately predict the operating characteristics and optimum design of electrochromic windows, a review of the theoretical studies available in the scientific literature as well as the developed theoretical models are presented. Finally, an experimental station for evaluating the on-site performances of different types of full scale smart windows and the layout of sensors used for the acquisition of internal and external physical quantities was described.

Three-Dimensional CFD Simulation of Fluid Flow inside a Vortex Tube on Basis of an Experimental Model- The Optimization of Vortex Chamber Radius

Abstract: Vortex-chamber is a main part of vortex tube which the pressured gas is injected into this part tangentially. An appropriate design of vortex-chamber geometry leads to better efficiency and good vortex tube performance. In this study, the computational fluid dynamics (CFD) model is created on basis of an experimental model and is a three-dimensional (3D) steady compressible model that utilizes the k-e turbulent model. In this paper the effect of changing radius of vortex-chamber (R*) on vortex tube performance has been studied for different value of R* and the optimized radius of vortex-chamber has been determined. According to numerical results the cold temperature difference has increased when we take into account the effect of the radius of vortex-chamber in range of 5.7-11 mm and when the radius of vortex chamber has located in range of 11-13 mm, the cold temperature difference has decreased. The highest ΔTc is 46.77 K for R*=11 mm at a cold mass fraction of 0.3, higher than basic model around 6.3% at the same cold flow fraction. Finally, the results obtained, particularly the temperature values, are compared with some available experimental data, which show good agreement.

Hypothermia Risk, Monitoring and Environment Control in Operating Rooms

Abstract: The air-conditioning systems in operating rooms must be able to ensure at the patients at the surgical team a high level of comfort indoor. There is many factors to consider and analyze in order to prevent the occurrence of problems such as hypothermia of the patient, the thermal discomfort for the medical team, and not least, pollution by anesthetic gases. The thermal comfort conditions within the operating rooms can be obtained by controlling microclimatic parameters such as: temperature, relative humidity and air velocity. In an environment maintained in the condition of health and thermal comfort are minimized risks related to the onset of post-operative complications. In this paper we present some studies reported in the literature on the methods used for environmental monitoring and control of operating rooms and HVAC systems; they are treated in the methodologies actually used to obtain a hospital environment in conditions of healthiness and thermal comfort. Are reported the result some simulations, obtained with the use of a model of the operating room in real scale, in them are analyzed ventilation rates suitable to obtain the chemical dilution of anesthetic gases and contaminants physical-biological. In the simulations we have determined the microclimatic parameters (air humidity and temperature) for prevent risks for patients such as hypothermia, and to ensure the comfort of the surgical team.

Experimental Investigations on Conventional Solar Still with Sand Heat Energy Storage

Abstract: In the present investigation, a detailed experimental study is carried out on a conventional single slope solar still with sand heat energy storage for improving the yield of fresh water. Yield of the solar still depends on the type of energy storage material used in the basin. Yield of the present study is compared with the solar still without any storage medium. Similarly, mathematically correlations of yield as a function of water and basin temperature were depicted. The results show that the use of sand as energy storage in cuboidal boxes the yield of solar still has improved by 145% than that of conventional single slope solar still. The total yield from the solar still with and without energy storage materials was found to be 5.1 and 1.9 kg/m2day respectively.

A Numerical Study of Swirl Effects on the Flow and Flame Dynamics in a Lean Premixed Combustor

Abstract: This paper reports a numerical investigation of an atmospheric lean-premixed swirl-stabilized burner. The focus on the flow behavior and flame stability is done at various swirl intensity to better understand the propane turbulent premixed flames. The numerical simulation is carried out using RANS technique with three turbulence closer models Standard k-ε, Realizable k-ε and SST k-ω. This in order to evaluate the performance of these models in the prediction of confined turbulent swirling flows. The turbulence-chemistry interaction scheme is modelled using Finite Rate-Eddy Dissipation model with three step global reaction mechanism. The combustor is operated with air and propane mixture under an atmospheric pressure at a global equivalence ratio of Φ = 0.5. The investigation is done using five different swirl numbers Sn = (0, 0.35, 0.75, 1.05, 1.4), including a validation with the available experimental data. Good agreement is found between RANS results and experimental data, in particular axial and radial velocity profiles, temperature and propane concentration profiles. Results indicate the presence of outer recirculation zone (ORZ) in the inlet burner corner, irrespective of the swirl number. When the swirl number reaches a critical value Sn = 0.75, an inner recirculation zone (IRZ) appears in the center of the burner inlet as a result of vortex-breakdown. Increasing swirl number to an excessive value leads to the propagation of the IRZ upstream the combustion chamber, and consequently the appearance of the flame flashback.

The Applications of the New Technologies "E-Sensing" in Hospitals

Abstract: The technologies or techniques “e-sensing”, in the past decade have had significant developments from the technical and commercial point of view. The term “e-sensing”, refers to the ability to reproduce human senses by means of sensors and recognition systems. The proposed work has been developed within the doctoral thesis and is part of a larger research project about sensors underway at the Faculty of Engineering of Messina. The research, combining the knowledge of engineering methods and tools with medical and chemical competence, is oriented to the development of a system able of monitoring the exhaled air for diagnostic purposes, for the realization of electronic systems at a low cost, for the diagnostics in medicine. It was built an artificial olfactory system, known as “electronic nose”, which allows monitoring the exhaled air components of patients undergoing a dialysis treatment. This diagnostic non-invasive method is able to provide at low cost, through the specific control of the markers of the exhaled air, some useful information to assess health of dialyzed patients. The realized device, was tested for biomedical applications and mainly for the specific monitoring of volatile biomarkers in the exhaled air, associated with certain medical conditions (eg. NH3 for nephrological diseases). It will allow to obtain an effective early diagnosis of the disease reducing care times and, at the same time, reducing the invasiveness of diagnostic treatments.

Heat and Mass Transfer on MHD Viscoelastic Fluid Flow in the Presence of Thermal Diffusion and Chemical Reaction

Abstract: The paper carries out an analysis on the momentum, heat and mass transfer characteristics in an incompressible magnetohydrodynamic non-Newtonian boundary flow of a viscoelastic fluid over a stretching sheet in the presence of thermal diffusion and chemical reaction. The partial differential equations governing the flow as well as heat and mass transfer features are converted into highly non-linear coupled ordinary differential equations by similarity transformations. The resulting differential equations are solved by using a shooting technique with fifth-order Runge-Kutta-Fehlberg integration scheme. The influence of magnetic interaction, variable thermal conductivity, viscoelastic, variable fluid viscosity, heat source/sink rate of chemical reaction, themal radiation and thermal diffusion parameters as well as Prandtl and Schmidt numbers are analyzed for velocity, temperature and concentration profiles. The wall shear stress, wall temperature and concentration gradients are also investigated for the problem. The fluid viscosity varies as an inverse function of velocity while the thermal conductivity assumes a linear and an inverse function of temperature and concentration respectively. The study shows that the thermal diffusion and thermal radiation parameters have opposite effects on the skin friction coefficient and wall concentration gradient. However, the rate of chemical reaction has similar influence on the skin friction coefficient and wall temperature gradient.

Experimental Investigation on Heat Transfer Enhancement by Swirl Generators in a Solar Air Heater Duct

Abstract: Twisted tape is a widely used technique for heat transfer enhancement. In the present study, the influences of centre-trimmed twisted tapes (CTTT) on heat transfer rate, friction factor and thermal enhancement efficiency were numerically investigated. The centre-trimmed twisted tapes were used as swirl flow generators inside the circular duct. Investigations were performed in the Reynolds number range of 100 5,000 with four different centre-cleared twin twisted tapes at twist ratio (TR) of H/W = 1.0, 2.0, 3.0 and 4.0. The governing equations are solved with a finite-volume-based numerical method. A three-dimensional non uniform grid was generated, in order to critically examine the flow and heat transfer. Results show that the centre-cleared twin twisted tape causes considerable enhancement of heat transfer when compared with plain twisted tape (TT). The enhancement over standard twisted tape increases with the increase of Reynolds number. The improved parameter is observed in the range of Reynolds number below 800 and also above Re 4000 for all TR, though the best performance is found at TR = 1.0 and 3.0

Analysis of a Concentrating Solar Power Tower Operating with a Closed Joule Brayton Cycle and Thermal Storage

Abstract: In this paper, a solar tower power plant with a closed Joule-Brayton cycle, of 5 MW rate power, with molten salts thermal storage, located in Seville is presented. The peculiarity of the cycle, using air like fluid work, is to vary, by an auxiliary compressor and a vent valve, the pressure, so that fluid average density, at gas turbine inlet. An adjustment of the mass flow rate, in order to regulate the exit air temperature from the receiver of concentrating solar tower, is obtained. During energy surplus production, the thermal storage energy is loaded. Particular attention is placed to the energy thermal storage, which uses molten salt KCl-MgCl2, suitable for this application due to its high melting temperature, in double tank configuration. The thermodynamic model of the entire plant was implemented using Thermoflex® software, while, for the concentrating tower, WinDelsol software was used. Using time data relating to the locations, the performance of the entire plant, during a year, has been simulated. Preliminary results show that this plant can achieve relevant benefits in total energy production and equivalent operation hours per year, therefore it is competitive with conventional energy production systems. Furthermore, a performances estimation with a cost analysis, using a LCOE parametric analysis, has been performed.

CFD Analysis of a Pipe Equipped with Twisted Tape

Abstract: In this work, a pipe provided with twisted tape inserts is analyzed. This system allows a significant increase of convective heat transfer coefficient by introducing a swirl motion which determines greater heat removal from the solid surface, by improving the fluid mixing. The analysis performed in this paper focuses on the evaluation of the thermal and flow quantities for a pipe of a shell and tube heat exchanger, previously optimized through a design software widely used in the petrochemical industry. The thermo and fluid dynamics analysis were performed by using a commercial CFD software (FluentTM). After performing the necessary computational checks for the acceptance of the results provided by the solver, a pitch parameterization was performed through a finite volume simulation. In this way the behaviour of a highly viscous fluid was studied, whose thermo-physical characteristics are highly variable with temperature. Furthermore, using water as fluid, the behaviour of the pipe provided with inserts was investigated by varying the Reynolds number, through mass flow rate variation. To verify the correctness of the results, they were compared in both cases with correlations in the literature.

Sustainable Mobility: Environmental and Economic Analysis of a Cable Railway, Powered by Photovoltaic System

Abstract: Nowadays, the massive use of fossil fuels, required to satisfy the energy needs of modern society, has caused evident climate changes which are dangerously destabilizing the ecosystem. Currently, among the sectors responsible for the increased energy consumption are the building industry and the transportation systems. As regards the latter, in particular, the main issue consists in conjugating the growing demand for personal mobility with the safeguard of the environment, providing for policies aimed at discouraging the use of private cars and increasing the use of alternative low-impact energy sources. In this context, the paper aims to analyze the effectiveness of a collective transport system which, being powered by renewable sources and designed to reduce the private car flow directed to and coming from the Mediterranea University of Reggio Calabria, is an example of sustainable urban mobility action. To fulfill this purpose the expected outcome generated by the described measure has been evaluated by both the economic and environmental point of view.

Technical and economic evaluations about the integration of co-Trigeneration systems in the dairy industry

Abstract: The dairy industries are characterized by a high demand for electricity, and energy for heating and cooling, necessary for obtaining a finished quality product. The scope of this study is to evaluate the technical and economic feasibility of a proposed intervention in the integration of a cogeneration and trigeneration system fueled with natural gas in an existing factory service, located in the north of Italy. The proposed intervention is analyzed in order to allow for the reduction of the overall energy demand of primary energy optimizing the activity management cost. The energy demand of this activity is analyzed below. The design choice are made in terms of energy production and distribution, as well as the economic and financial assessments related to the energy integration of either the cogeneration system or by tri-generation.

Reducing the demand of energy cooling in the CED, "centers of Processing Data", with use of free-cooling systems

Abstract: The data processing centers (CED) are defined today among the areas with the greatest demand for energy for specific use, and for the intrinsic operation of the technological equipment of processing and the data transmission. As a result of the high diffusion of today’s telecommunications systems, the CEDs are increasingly widely disseminated and characterized by logics of operation, such as to ensure a high level of reliability in terms of continuity of service. Objective of the proposed study is to evaluate the reduction of demand energy by cooling, through implementation of air conditioning technologies based on airconditioning systems of free-cooling type. The study compares different operating scenarios in relation to hypothetical operating conditions, in different regions of Italy characterized by different environmental thermo-hygrometric conditions, highlighting the limiting factors in terms of energy demand.

Study of Natural Convection in a Square Cavity Filled with Nanofluid and Subjected to a Magnetic Field

Abstract: This paper presents a numerical study of natural convection cooling of water-Al2O3 nanofluid by two heat sinks vertically attached to the horizontal walls of a cavity subjected to a magnetic field. The left wall is hot, the right and the horizontal walls are insulated. Lattice Boltzmann method (LBM) is applied to solve the coupled equations of flow and temperature fields. This study has been carried out for the pertinent parameters in the following ranges: Rayleigh number of the base fluid, Ra = 103 to 105, Hartmann number varied from Ha = 0 to 60 and the solid volume fraction of nanoparticles between  = 0 and 6%. In order to investigate the effect of heat sinks location, three different configurations of heat sinks are considered. Results show that the heat sinks positions greatly influence the heat transfer rate depending on the Hartmann number, Rayleigh number and solid volume fraction of nanoparticles.

Research on the Hydrate Formation in the process of Gas Phase CO2 Pipeline Transportation

Abstract: With the development of the third oil recovery in oil fields and CO2 capture, utilization and storage (CCUS) technology, CO2 injection has become an effective means to enhance oil recovery (EOR) and relieve the greenhouse gas effect. The CO2 pipeline transportation technology started relatively late in China, where the gas phase and liquid phase transportation are widely used methods. The CO2 hydrate formation in the process of transportation may reduce the valve, destroy the equipment and even cause pipeline ice blockage, but research in China on CO2 hydrate is not very extensive. In this paper, the CO2 hydrate formation conditions were simulated using HYSYS, and the simulation results were compared with the experimental results to verify the feasibility of the simulation method. Based on this, factors in the influence of gas impurities on CO2 hydrate formation are simulated, and the pipeline transportation process of CO2 hydrate formation are predicted. The results show that when there is a low amount of impurity content, the gaseous impurities such as CH4, N2, H2, O2, have little effect on CO2 hydrate formation in gaseous CO2 pipeline transport. Furthermore, environmental temperature has little effect on the changes in pipeline pressure along the transport route. However, with a change in environment temperature, temperature along the pipeline changes greatly. CO2 will change from a gas state to a liquid state in the pipeline when the ambient temperature is low. In the case of low ambient temperature, a thick insulation layer should be used, and heating of the pipeline may also be required. When the ambient temperature is higher than about 10°C , there will be no hydrates formed in the pipeline.

Thermodynamic optimization of three-thermal irreversible systems

Abstract: Multi-temperature-level systems enlarge the prospects and degrees of freedom for an effective design and an environment-friendly use of energy. Based on a general thermodynamic model of three-thermal cycles and finite thermal capacity of the heat sources, this paper aims at the analysis and the performance optimization of these systems by considering the influence of irreversibility. Suitable dimensionless parameters for an overall optimization are introduced and their influence on the cycle efficiency is investigated. This approach identifies the limitations imposed to the physical processes by accounting for the inevitable dissipation due to their constrained duration and intensity, and constitutes a general thermodynamic criterion for the optimization of three-thermal irreversible systems. Dependence on the main factors is highlighted in a way that shows how to change them in order to improve the overall efficiency. Under this point of view, the analysis evaluates COP improvements and can be used to perform plant diagnostics, besides predicting the system performance. The use of this criterion is exemplified for the absorption chiller application case.