Heat transfer prediction for radiant floor heating/cooling systems using artificial neural network (ANN)

Radiant floor cooling and heating systems (RHC) are gaining popularity as compared with conventional space conditioning systems. An understanding of the heat transfer capacity of the radiant system is desirable to design a space conditioning system using RHC technology. In the present work, a simplified heat flux model for RHC is developed for both cooling and heating modes of operation. The Artificial Neural Network (ANN) technique is used for the development of the simplified model. Experimental data from literature covering a wide operating range of the RHC is considered for model development and validation. Operating parameters such as mass flow rate (m_f), heat resistance (R_s), mean temperature of water flowing through the pipe (T_m), and operative temperature (T_op) are considered independent variables influencing the heat flux (q_t). The neural network consists of four input layers, one output layer, and one hidden layer with a feed-forward-back-propagation algorithm. A study on the selection of the optimum number of neurons in the range of 1–9 for the hidden layer is also performed. On the basis of the performance parameters, namely, average-absolute-relative-deviation (AARD = 0.11283) percentage, mean-square-error (MSE = 0.00055), and the coefficient of determination (R² = 0.9984), a hidden layer is modeled with five neurons.     

Photocatalytic hydrogen production from aqueous methanol solution with CuO/Al2O3/TiO2 nanocomposite

The photocatalytic hydrogen production from aqueous methanol solution was investigated with ZnO/TiO₂, SnO/TiO₂, CuO/TiO₂, Al₂O₃/TiO₂ and CuO/Al₂O₃/TiO₂ nanocomposites. A mechanical mixing method, followed by the solid-state reaction at elevated temperature, was used for the preparation of nanocomposite photocatalyst. Among these nanocomposite photocatalysts, the maximal photocatalytic hydrogen production was observed with CuO/Al₂O₃/TiO₂ nanocomposites. A variety of components of CuO/Al₂O₃/TiO₂ photocatalysts were tested for the enhancement of H₂ formation. The optimal component was 0.2 wt% CuO/0.3 wt% Al₂O₃/TiO₂. The activity exhibited approximately tenfold enhancement at the optimum loading, compared with that with pure P-25 TiO₂. Nano-sized TiO₂ photocatalytic hydrogen technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy.     

Electrochemical and mechanical behavior of carbon composite bipolar plate for fuel cell

Composite bipolar plates for fuel cells were prepared by a compression molding technique using novolac type phenol formaldehyde resin as a binder and natural graphite, carbon black and carbon fiber as reinforcements. The plates were characterized for electrical conductivity, mechanical strength and corrosion resistance. The flexural strength of the bipolar plate for optimum composition (PF:30%; NG:60%; CB:5%; CF:5%) was 55.28 MPa, with a deflection of 5.2% at mid-span, while the in-plane and through-plane electrical conductivities were 286 and 92 S cm⁻¹, respectively. Corrosion analyses were conducted in normal and rigorous simulated polymer electrolyte membrane fuel cell and alkaline fuel cell environments. The corrosion current density was close to the limit set by the USA Department of Energy. The corrosion current density at the optimum composition was found to be 0.99 μA cm⁻² for polymer electrolyte membrane fuel cell and 17.62 μA cm⁻² for alkaline fuel cell environments.     

First‐principles spectroscopic screening of hybrid perovskite (CH3CH2NH3PbI3) with fundamental physical properties: A potential photovoltaic absorber

Herein, we have discussed the ethyl‐ammonium based hybrid perovskite (viz. CH₃CH₂NH₃PbI₃ or EAPbI₃) as the potential candidate material for the development of photovoltaic devices having low processing cost and high power conversion efficiency (PCE). To address the stability and environmental issues due to leaching of lead from MAPbI₃, we urge to replace cation CH₃NH₃⁺ (MA⁺) with an appropriate cation CH₃CH₂NH₃⁺ (EA⁺) and hope that the EAPbI₃ perovskite would prove to be a stable and eco‐friendly photovoltaic absorber (PVA) material yielding high PCE. We have investigated physical properties like energy bandgap, electron density distribution and optical coefficients by FP‐LAPW+lo and density functional theory (DFT). The present study reveals that EAPbI₃ has a direct energy bandgap of 1.55 eV with absorption coefficient exceeding 2 × 10⁴ per cm, which confirms its suitability as PVA material. The dependence of thermoelectric (TE) coefficients on chemical potential and carrier concentration at various temperatures has also been discussed. We have also carried out the calculations of spectroscopic limited maximum efficiency (SLME) parameter (30.5%), and the thermodynamic (TD) properties in the realm of quasi‐harmonic approximation. A detailed investigation on some of the properties of EAPbI₃ perovskite relevant to PVA material is being done for the first time, the present study may motivate researchers for more comprehensive theoretical and experimental investigations in search of stable and economically and environmentally viable PVA materials.     

Flexible polypyrrole activated micro-porous paper-based photoanode for photoelectrochemical water splitting

We herein demonstrate polypyrrole decorated micro-porous laboratory filter paper (PFP) as photoanode (PA) for efficient and stable water splitting. The straddling band position with water redox and the measured band gap of ~1.98 eV, make these PFP-PAs effective for water splitting reactions. The results manifest excellent photo-anodic PEC activity of these PFP-PAs, yielding a photocurrent density of ~9.5 mA/cm² (at 1.23 V vs. RHE) in a three-electrode configuration. The incident photon-to-current efficiency (IPCE) and applied bias photon-to-current efficiency (ABPE) was measured to be 43.19% and ~1%, respectively. Moreover, the robustness of these flexible PFP-PAs was visualized by the provided stability for more than ~160 min in alkaline conditions. The current study provides a proof-of-concept for the realization of a cost-effective, flexible, and efficient paper-based artificial catalyst (like a natural leaf) for solar-driven water splitting.     

Kinetics of N2O formation/destruction from coal combustion at low temperatures

Emission of nitrous oxide (N₂O) from coal combustion at low temperatures has recently become a subject of intense research and debate, because of its increasing concentrations in the atmosphere and its known ability to deplete the Ozone layer and also to contribute to the Greenhouse effect. In the present study, the nonlinear, first‐order differential equations, which describe the time behaviour of chemical systems, are solved using the analytical form of the first derivative of the species concentration, in order to calculate the time‐dependent composition of various chemical species that evolve from the coal combustion. These studies are made under the low‐temperature combustion conditions to determine the factors influencing the N₂O formation/destruction and a comparison with experimental findings has been done. Copyright © 2001 John Wiley & Sons, Ltd.     

Application of the error propagation theory in estimates of static formation temperatures in geothermal and petroleum boreholes

We used the error propagation theory to calculate uncertainties in static formation temperature estimates in geothermal and petroleum wells from three widely used methods (line-source or Horner method; spherical and radial heat flow method; and cylindrical heat source method). Although these methods commonly use an ordinary least-squares linear regression model considered in this study, we also evaluated two variants of a weighted least-squares linear regression model for the actual relationship between the bottom-hole temperature and the corresponding time functions. Equations based on the error propagation theory were derived for estimating uncertainties in the time function of each analytical method. These uncertainties in conjunction with those on bottom-hole temperatures were used to estimate individual weighting factors required for applying the two variants of the weighted least-squares regression model. Standard deviations and 95% confidence limits of intercept were calculated for both types of linear regressions. Applications showed that static formation temperatures computed with the spherical and radial heat flow method were generally greater (at the 95% confidence level) than those from the other two methods under study. When typical measurement errors of 0.25 h in time and 5 °C in bottom-hole temperature were assumed for the weighted least-squares model, the uncertainties in the estimated static formation temperatures were greater than those for the ordinary least-squares model. However, if these errors were smaller (about 1% in time and 0.5% in temperature measurements), the weighted least-squares linear regression model would generally provide smaller uncertainties for the estimated temperatures than the ordinary least-squares linear regression model. Therefore, the weighted model would be statistically correct and more appropriate for such applications. We also suggest that at least 30 precise and accurate BHT and time measurements along with the respective errors should be obtained for a reliable application of the proposed regression procedure.     

Laminar Momentum and Heat Transfer in a Channel with a Built‐In Tapered Trapezoidal Bluff Body

Effects of wall confinements on the laminar flow and heat transfer around a heated tapered trapezoidal bluff body are investigated numerically in the confined domain (Reynolds number, Re = 1 to 40; blockage ratio = 0.125 to 0.5; and Prandtl number, Pr = 0.71). The onset of flow separation is found between Re = 4 and 5 for the blockage ratio of 0.125 and between Re = 5 and 6 for the blockage ratios of 0.25 and 0.5. If compared with a long circular obstacle on the basis of equal projected area, the total drag coefficient of the trapezoidal cylinder is found to be larger than the circular one, but an opposite trend is observed for the heat transfer. The augmentation in heat transfer for trapezoidal and circular cylinders is found to be approximately 46, 72, 74, and 65 percent for Re = 1, 5, 10, and 40, respectively for the blockage ratio of 0.25. The maximum enhancement in heat transfer for a tapered trapezoidal bluff body with respect to a square bluff body is found to be approximately 104 percent and 101 percent for blockage ratios of 0.25 and 0.5, respectively. Finally, simple correlations of wake length, drag, and average cylinder Nusselt number are established.     

Microcomputer based digital differential relaying for generator protection: Real time test results

The paper presents the development of a digital differential relaying scheme around a 16-bit microprocessor for generator winding protection. It uses a simple filter algorithm which is based on cross-correlation with a heptagonal wave for the extraction of fundamental frequency components of differential and sum currents. Application of this filter and use of the real parts alone, instead of both the real and imaginary parts, of the fundamental frequency components for the relaying reduces the computation requirement drastically, thus enabling implementation of a complete three-phase differential relay on a single microprocessor without requiring a coprocessor or multiplier. The relay has been tested in real time on simulated generator currents representing internal-, external- and no-fault conditions separately. The test results agree well with the results of off-line evaluation reported earlier and point to a successful implementation of the differential relaying algorithm on a microprocessor in real time.     

Application of Analytic Hierarchy Process in Water Resources Planning: A GIS Based Approach in the Identification of Suitable Site for Water Storage

One of the important objectives of water resources planning is to tap the maximum possible water available in the river basin that can be utilized particularly during the period of drought. This can be materialized by creating water storage structures. For this purpose initially, the first task could be the identification of suitable site for creating water storage sites. With the advent of Remote Sensing (RS) and Geographic Information System (GIS) techniques, it becomes easier for water resources planner to identify the suitable location of water storage structure within the basin. Present study demonstrates the identification of suitable location in the upper basin of Sheonath river in Chhattisgarh State, India. Based on the various physical characteristics of the basin, GIS based multi-criteria evaluation technique is being applied to determine the most suitable water storage sites. The suitable sites are assessed by considering the spatially varying parameters. These parameters include potential runoff, hydrologic soil group, land use, lineament, slope, stream order and settlement and basin area. Potential runoff is calculated from Soil Conservation Service Curve Number (SCS-CN) equation. Since, there is more than one parameter; it is significant to determine the importance of one layer over another layer. Analytic Hierarchy Process (AHP) is one of the multi-criteria decision making method resulting in the percentage relative importance. The AHP model consists of three levels objective i.e. suitable site for water storage, the parameter used and the alternatives. In the overlay process of GIS the relative importance determined by AHP is applied to produce suitable locations. Suitability is divided into three categories “suitability level 1”, “suitability level 2” and “suitability level 3” representing storage tank, stop dam and check dam respectively. This mapping helps in selecting potential site for water storage structures in the basin.