Single and Competitive Removal of Pb(II) in the Presence of Ni(II) using Polyacrylamide Grafted Rice Husk

In a quest to find efficient adsorbents for metal ions, studies on various adsorbents for metals have been of interest since the past several decades. The present study is focused on the removal of Pb (II) ions from aqueous solution using poly acrylamide grafted rice husk by batch studies. Industrial waste waters generally contain metals present as mixtures, therefore the effect of Ni (II) on the removal of Pb(II) from mixtures of Pb(II)+Ni(II) ions has also been investigated. The adsorbent has been prepared by the treatment of rice husk with acrylamide in the presence of N,N-methylene bis acrylamide and potassium persulphate. The adsorbent has been characterised by infrared spectral studies. Maximum adsorption obtained is 93% at pH 5, metal ion concentration 300mg/L in 180mins at 298K. Isotherm analyses show that both Langmuir and Freundlich isotherm models are best obeyed. The process is endothermic and spontaneous in nature and follows pseudo first order kinetics. Intraparticle diffusion also occurs but is not the rate determining step. Application of Langmuir competitive model for the binary system shows that  adsorption of Pb(II) has been supressed by presence of Ni(II) ions. Studies suggest that the adsorbent is effective and can find industrial applicability

Analysis and Improvement of the Hot Disk Transient Plane Source Method for Low Thermal Conductivity Materials

The hot disk transient plane source (TPS) method is a widely used standard technique (ISO 22007-2) for the characterization of thermal properties of materials, especially the thermal conductivity, k. Despite its well-established reliability for a wide variety of common materials, the hot disk TPS method is also known to suffer from a substantial systematic errors when applied to low-k thermal insulation materials. Here, we present a combined numerical and experimental study on the influence of the geometry of hot disk sensor on measured value of low-k materials. We demonstrate that the error is strongly affected by the finite thickness and thermal mass of the sensor's insulation layer was well as the corresponding increase of the effective heater size beyond the radius of the embedded metal heater itself. We also numerically investigate the dependence of the error on the sample thermal properties, confirming that the errors are worse in low-k samples. A simple correction function is also provided, which converts the apparent (erroneous) result from a standard hot disk TPS measurement to a more accurate value. A standard polyimide sensor was also optimized using both wet and dry etching to provide more accurate measurement directly. Experimentally corrected value of k for Airloy x56 aerogel and a commercial silica aerogel using the numerical correction factor derived based on the standard TPS sensor is in excellent agreement with the directly measured value from the TPS sensor using the optimized polyimide sensor. Both of these methods can reduce the errors to less than 4% as compared to around 40% error of overestimation from raw values measured with the pristine sensor. Such results show that both the numerical correction to a pristine senor or an optimized sensor are capable of providing highly accurate value of thermal conductivity for such materials.Comment: 76 pages, 11 figure

Growth, yield and nutrient uptake of guava (Psidium Guavaja L.) affected by soil matric potential, fertigation and mulching under drip irrigation

Our objective was to examine the effect of plastic mulching, three soil matric potentials (SMP) treatments    {I1(-20 kPa), I2(-40 kPa), and I3(-60 kPa)} and three fertigation levels {F1(100%), F2(80%), and F3(60%) recommended dose of fertilizer} under drip irrigation conditions for nutrient uptake, growth parameters and yield in guava plants.  The experiments were set up in factorial randomized block design with eighteen treatment combinations.  The experiments were conducted during the year 2012-13.  The investigation indicated that the plant canopy spread in (N/S and E/W) directions was greatly affected by different treatments.  However, non-significant effects of interaction parameters were found on plant height, crop volume and plant girth.  The maximum yield was obtained in MI2F2 (68.66 kg per plant and 22.86 t ha-1) followed by NMI2F2 (66.50 kg per plant and 22.14 t ha-1) treatments.  The maximum percentage of high quality (fruit levels A and B) were 48.2% and 50.1% in -40 kPa  irrigation treatment for mulch and no mulch conditions under 100% application of recommended dose of fertilizers.  The varying range of leaf nutrients observed for different treatments of irrigation, fertigation and mulch is  1.26-1.74% N, 0.14-0.26% P, 0.44-0.88% K, 36.33-74.23 ppm Zn, 11.33-32.76 ppm Cu, 415.6- 557.3 ppm Fe, 26.80- 39.06 ppm Mn, 0.533-0.762 % Mg and 3.42-5.06% Ca.  Based on the results above, it is recommended that controlling SMP between -40 kPa to -45 kPa at 0.2 m depth immediately under the drip emitter and fertilizer dose of 80% recommended dose of fertilizer can be used as an indicator for drip irrigation scheduling in semi-arid region of northwest India.   Keywords: fertilizer application, irrigation strategies, pressure head, tensiometer, leaf uptak

Water Freezes at Near-Zero Temperatures Using Carbon Nanotube-Based Electrodes under Static Electric Fields.

Although static electric fields have been effective in controlling ice nucleation, the highest freezing temperature (Tf) of water that can be achieved in an electric field (E) is still uncertain. We performed a systematic study of the effect of an electric field on water freezing by varying the thickness of a dielectric layer and the voltage across it in an electrowetting system. Results show that Tf first increases sharply with E and then reaches saturation at -3.5 °C after a critical value E of 6 × 106 V/m. Using classical heterogeneous nucleation theory, it is revealed that this behavior is due to saturation in the contact angle of the ice embryo with the underlying substrate. Finally, we show that it is possible to overcome this freezing saturation by controlling the uniformity of the electric field using carbon nanotubes. We achieve a Tf of -0.6 °C using carbon nanotube-based electrodes with an E of 3 × 107 V/m. This work sheds new light on the control of ice nucleation and has the potential to impact many applications ranging from food freezing to ice production

Particle Size Optimization of Thermochemical Salt Hydrates for High Energy Density Thermal Storage

Thermal energy storage (TES) solutions offer opportunities to reduce energy consumption, greenhouse gas emissions and cost. Specifically, they can help reduce the peak load and address the intermittency of renewable energy sources by time shifting the load which are critical towards zero energy buildings. Thermochemical materials (TCMs) as a class of TES undergo a solid-gas reversible chemical reaction with water vapor to store and release energy with high storage capacities (600 kWh/m3) and negligible self-discharge that makes them uniquely suited as compact, stand-alone units for daily or seasonal storage. However, TCMs suffer from instabilities at the material (salt particles) and reactor level (packed beds of salt), resulting in poor multi-cycle efficiency and high-levelized cost of storage. In this study, a model is developed to predict the pulverization limit or Rcrit of various salt hydrates during thermal cycling. This is critical as it provides design rules to make mechanically stable TCM composites as well as enables the use of more energy efficient manufacturing process (solid-state mixing) to make the composites. The model is experimentally validated on multiple TCM salt hydrates with different water content and effect of Rcrit on hydration and dehydration kinetics is also investigated

A non-volatile thermal switch for building energy savings

Compared with traditional static insulation, a thermally switchable building envelope could reduce annual heating and cooling loads by intermittently coupling to the outside environment when beneficial. Here, we demonstrate a voltage-actuated, contact/non-contact thermal switch that meets the unique challenges of this application. The switch is non-volatile, consuming electricity only briefly while switching and none to hold steady state. The switch ratio is 12, the off state has a low effective thermal conductivity of 0.045Wm-1K-1, comparable to fiberglass insulation, and the performance is stable over 1,000 switching cycles. Numerical simulations using real-world climate data show that combining this thermal switch with a thermal storage layer in a building envelope can yield annual energy savings of 9%–55% (heating) and 17%–76% (air conditioning), depending on the climate zone. The greatest benefits are realized when the exterior temperature crosses well above and below the desired interior temperature within a single 24 h period

Predicting supercooling of phase change materials in arbitrarily varying conditions

Phase change materials are promising for thermal energy storage; however, one major bottleneck for their practical implementation is their unclear supercooling behaviors. In this work, we introduce a framework to predict the degree of supercooling for a phase change material subject to arbitrary geometrical and thermal conditions by analyzing the phase change material's intrinsic nucleation characteristics with a statistical model. The prediction capability of our framework is successfully validated with experiments using magnesium chloride hexahydrate as a phase change material. For a system with a uniform temperature distribution, our framework can predict the average degree of supercooling. For a general case such as phase change materials embedded in a heat sink, the framework can accurately predict the expected time, with less than 8% deviation, for nucleation under given conditions. This work provides important insights in understanding and predicting supercooling behavior, thereby providing guidelines for the optimal design of phase change material-based thermal energy storage applications

Distributed Desalination using Solar Energy: A Techno-economic Framework to Decarbonize Nontraditional Water Treatment

Desalination of nontraditional waters (e.g., agricultural drainage, brackish groundwater, industrial discharges, etc.) using renewable energy sources offers a possible route to transform our incumbent linear consumption model (discharge after use) to a circular one (beneficial reuse). This transition will also shift desalination from large-scale centralized coastal facilities towards modular distributed treatment plants (~1000 m3/day) in inland locations. This new scale of desalination can be satisfied using solar energy to decarbonize water production, but additional considerations, such as storage to address intermittency and inland brine management to address high disposal costs, become important. In this work, we evaluate the levelized cost of water or LCOW for 16 solar desalination technologies (with different generation–storage-desalination–brine management subsystems) at 2 different salinities corresponding to nontraditional sources. For fossil fuel-driven desalination plants at the distributed scale, we find that zero liquid discharge is economically favorable to inland brine disposal. For renewable desalination, we discover that (i) solar-thermal energy is better suited to both membrane and thermal desalination plants compared to photovoltaics largely due to the low cost of thermal storage, and that (ii) energy storage, despite its higher cost, outperforms water storage on a levelized basis as the latter has a low utilization factor with intermittently operated desalination plants. The analysis also yields a promising outlook for the LCOW of solar desalination by 2030 as the costs of solar generation and energy storage decrease to meet the U.S. Department of Energy targets. Finally, we highlight subsystem cost and performance targets for solar desalination to achieve cost parity with fossil fuel-driven water treatment

Distributed desalination using solar energy: A technoeconomic framework to decarbonize nontraditional water treatment.

Desalination using renewable energy offers a route to transform our incumbent linear consumption model to a circular one. This transition will also shift desalination from large-scale centralized coastal facilities toward modular distributed inland plants. This new scale of desalination can be satisfied using solar energy to decarbonize water production, but additional considerations, such as storage and inland brine management, become important. Here, we evaluate the levelized cost of water for 16 solar desalination system configurations at 2 different salinities. For fossil fuel-driven plants, we find that zero-liquid discharge is economically favorable to inland brine disposal. For renewable desalination, we discover that solar-thermal energy is superior to photovoltaics due to low thermal storage cost and that energy storage, despite being expensive, outperforms water storage as the latter has a low utilization factor. The analysis also yields a promising outlook for solar desalination by 2030 as solar generation and storage costs decrease