Design sensitivity analysis of using various in-tube condensation correlations for an air cooled condenser for ORCS

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.The study is related to the evaluation of using 19 condensation heat transfer correlations in an annular finned horizontal round tube V-shaped air-cooled condenser design problem for a representative low-temperature waste heat recovery Organic Rankine Cycle (ORC) case. The condensation is realized through cold air provided by the fan suction at a mass flow rate of 90,35 kg/s, whereas the working fluid mass flow rate is 7,8 kg/s. The considered condensation temperature is 40°C which corresponds to a saturation pressure of 1,17 bar. The ambient air is considered to be 15°C. The investigated working fluid is SES36. For a given set of geometrical constraints, an iterative condenser design model is implemented. All considered correlations are applied separately for the same boundary conditions. The design sensitivity on the overall heat transfer coefficient, total transferred heat, required fan power, air- and refrigerant-side pressure drops is assessed. By those means, the engineering error margin of using different calculation tools in designing air-cooled condensers for ORC is reported.am201

Performance analysis of internally reformed MCFC/IT-SOFC combined cycle

Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.High temperature fuel cells such as the solid oxide fuel cell (SOFC) and molten carbonate fuel cell (MCFC) are considered extremely suitable for electrical power plant application. The intermediate temperature (IT) SOFC and MCFC performances are calculated using numerical models which are built in Aspen customer modeler for the internally reformed (IR) fuel cells. These models are integrated in Aspen PlusTM. In this article, a new combined cycle is proposed: this combined cycle consisting of two-staged of MCFC and IT-SOFC. The MCFC&IT-SOFC combined cycle and single-staged cycle with MCFC only are simulated in order to evaluate and compare their performances. The simulations results indicate that the net efficiency of MCFC&IT-SOFC combined cycle is 64.6 % under standard operation conditions. On the other hand, the net efficiency of single-staged MCC cycle is 51.6%. In other words, the cycle with two-staged MCFC and IT-SOFC gives much better net efficiency than the cycle with single-staged MCFC.vk201

Selection of prospective working fluid candidates for subcritical OR evaporators

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.The trade-off between lower grade waste heat sources and thermal efficiencies of evaporators using refrigerants is an important in subcritical organic Rankine cycles (ORCs). Although the heat transfer performances of many refrigerants have been reported in various studies, there are relatively low amount of studies focusing on temperature and pressure ranges relevant to evaporators for subcritical ORCs. Therefore there is a necessity for new studies that would meet the current needs and fill the gaps in literature. For this purpose, the present study aims to contribute to the revealing and concretizing the lack of information about working fluids for ORC evaporators operating under subcritical conditions. An extensive literature survey is made for deducing the proper working fluids, by means of including both the older and new generation refrigerants. The thermo-hydraulic, environmental, safety and physical properties of 10 refrigerants with zero Ozone Depletion Potentials (ODP) and low Global Warming Potentials (GWP) such as R134a, R245fa, R365mfc, R245ca, R1234ze, R1233zd, Solkatherm® SES36, R1234yf, DR-2 and HDR-14 are discussed, where R134a was taken as reference for evaluation. The best candidates for future research for evaporators for subcritical ORC are proposed, by taking the two-phase heat transfer coefficients and pressure drops into consideration.cf201

Supercritical heat transfer and heat exchanger design for organic rankine application

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.Supercritical Organic Rankine Cycle is introduced as promising technology for low grade waste heat recovery. The advantage of this supercritical cycle is a better thermal match between the heat source and the working fluid temperature profiles in the supercritical heat exchanger. Heat exchangers have a vital part of this cycle, in manner of cycle efficiency and for the economic feasibility of one ORC installation. There are many challenges in the design process of these components suitable to operate at relatively high pressure and temperature. The reason for that is strong properties variation of the organic working fluid at supercritical state. Since, the value of the heat transfer coefficient depends on these thermophysical properties of the working fluid, it is important to study and understand the behavior of the properties of the fluid going from subcritical to supercritical state. The supercritical heat exchanger was first modeled in EES software, and then designed and built. For the designing procedure of the heat exchanger several different correlations available from literature were selected. These correlations have been previously validated at supercritical state, but for working fluids such as H2O, CO2 and refrigerants blends R404a and R410a. However, the diameters tested and the applications differ from this research. In order to ensure proper operation of the heat exchanger, this component was oversized by 20%. From the first set of measurements it can be concluded that the size of this component can be lowered by 10% and will result in reduced cost of an ORC installation.am201

Performance evaluation of CHP with heat storage in buildings

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.Combined heat and power (CHP) production gains more and more attention. Offices and public buildings often have a large thermal power demand in combination with a fairly large electrical power demand. On the other hand they are seldom occupied by night and in weekends, reducing the actual operational time of the heating system. This in turn brings down the financial benefits of investing in CHP. A second problem is that electrical and thermal demands are often shifted in time. The running time of the engine is again limited this way, as it is often not allowed to deliver electricity to the power grid. A possible solution is using heat storage. This way the CHP-engine can run when the electricity demand is high. In the paper a simulation model of CHP with gas engine and heat storage by means of a hot water vessel is developed. The model is validated through experiments on an engine and a vessel. This model is used to analyze the design, control and performance of cogeneration plants. It is shown that storage is marginal beneficial and the design has to be done with great care.cs201

Prediction of mold risk in cavity walls combining a coupled CFD/HAM-model and a 2D hygrothermal model: the influence of the outer cavity layer on the inner cavity layer

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Preventing mould risk in buildings is important to ensure a healthy environment for the people and to avoid material damage. A reliable prediction is especially important for ventilated cavity walls made of a moisture sensitive material such as wood. In this paper the influence of the outer cavity layer on the inner cavity layer has been analyzed. The cavity wall consists of a timber frame on the inside and a brick veneer on the outside separated by an air layer. For this hygrothermal evaluation of air cavities, coupled CFD/HAM-software and a commercial hygrothermal software package WUFI-2D® are used. First the coupled CFD/HAM-software is used to examine the heat and mass transfer coefficients at the surfaces between the air and the material layer and the applicability of the heat/mass-analogy. Afterwards, the effect of long-wave radiation in the cavity will be simulated with the coupled CFD/HAM-model. Finally the model developed in WUFI to simulate a ventilated cavity wall and the influence of different materials for the outer layer will be examined combining the coupled CFD/HAM-model and WUFI-2D.dc201

Modelling heat and moisture transport in porous materials with CFD for building applications

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.Heat and moisture transport in buildings have a large impact on the building envelope durability, the energy consumption in buildings and the indoor climate. Nowadays HAM (Heat, Air and Moisture) models are widely used to simulate and predict the effect of these transport phenomena in detail. Recently these HAM models are being coupled to CFD (Computational Fluid Dynamics) to study the moisture exchange between air and porous materials on a local scale (microclimates). A direct coupling approach between CFD and HAM is applied. The transport equations for heat and moisture in a porous material are directly implemented into an existing CFD package and the transport equations in the air and in the porous material are solved in one iteration by only one solver. In this paper a model for moisture transport in the hygroscopic range and over-hygroscopic range is developed. This way a broad range of problems can be tackled such as drying phenomena and interstitial condensation in building components. The model is verified and validated with data from literature.mp201

Short-term health effects in the general population following a major train accident with acrylonitrile in Belgium

Background: Following a train derailment, several tons of acrylonitrile (ACN) exploded, inflamed and part of the ACN ended up in the sewage system of the village of Wetteren. More than 2000 residents living in the close vicinity of the accident and along the sewage system were evacuated. A human biomonitoring study of the adduct N-2-cyanoethylvaline (CEV) was carried out days 14-21 after the accident. Objectives: (1) To describe the short-term health effects that were reported by the evacuated residents following the train accident, and (2) to explore the association between the CEV concentrations, extrapolated at the time of the accident, and the self-reported short-term health effects. Methods: Short-term health effects were reported in a questionnaire (n=191). An omnibus test of independence was used to investigate the association between the CEV concentrations and the symptoms. Dose-response relationships were quantified by Generalized Additive Models (GAMs). Results: The most frequently reported symptoms were local symptoms of irritation. In non-smokers, dose-dependency was observed between the CEV levels and the self-reporting of irritation (p=0.007) and nausea (p=0.007). Almost all non-smokers with CEV concentrations above 100 pmol/g globin reported irritation symptoms. Both absence and presence of symptoms was reported by non-smokers with CEV concentrations below the reference value and up to 10 times the reference value. Residents who visited the emergency services reported more symptoms. This trend was seen for the whole range of CEV concentrations, and thus independently of the dose. Discussion and conclusion: The present study is one of the first to relate exposure levels to a chemical released during a chemical incident to short-term (self-reported) health effects. A dose-response relation was observed between the CEV concentrations and the reporting of short-term health effects in the non-smokers. Overall, the value of self-reported symptoms to assess exposure showed to be limited. The results of this study confirm that a critical view should be taken when considering self-reported health complaints and that ideally biomarkers are monitored to allow an objective assessment of exposure

Heat transfer in horizontal tubes at supercritical pressures for organic Rankine Cycle applications

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.Today process industry has to deal with a lot of waste heat. Very often this waste heat is dumped to the environment, while it could be efficiently used. Low grade heat is also available in solar thermal systems, geothermal systems, biomass combustion and etc. This heat can be converted into electricity using an organic Rankine cycle (ORC). This thermodynamic cycle is similar to the well-known Rankine steam cycle, but it works with an organic working fluid instead of water/steam. As a consequence, the temperature of the heat source at the evaporator is typically lower compared to the steam cycles. To increase the cycle efficiency, supercritical cycles seem very promising. The advantage of supercritical ORCs is a better thermal match between the heat source and the working fluid temperature profiles in the supercritical heat exchanger. Consequently, the overall system efficiency improves. In the current literature, research work on heat transfer mechanisms under supercritical conditions in ORC is very limited. Therefore, it is an essence to study and investigate the relatively unknown heat transfer phenomena at supercritical working conditions for organic fluids in the temperature and pressure ranges relevant for ORCs. Heat exchanger design and heat transfer coefficients are factors that have great influence on the heat transfer and the overall cycle efficiency. Furthermore, special attention must be drawn to the choice of appropriate working fluid, which is a factor of great importance because the organic fluid properties also affect the overall efficiency of the cycle. In this paper, relevant researches are reviewed regarding Supercritical Organic Rankine Cycle applications, selection of working fluids and description of newly designed test facility is presented.dc201