The limitation of hot spot cooling in microchips represents an important hurdle for the electronics industry to overcome with coolers yet to exceed the efficiencies required. Nanotechnology-enabled heat sinks that can be magnetophoretically formed onto the hot spots within a microfluidic environment are presented. CrO2 nanoparticles, which are dynamically chained and docked onto the hot spots, establish tuneable high-aspect-ratio nanofins for the heat exchange between these hot spots and the liquid coolant. These nanofins can also be grown and released on demand, absorbing and releasing the heat from the hot spots into the microfluidic system. It is shown that both high aspect ratio and flexibility of the fins have a dramatic effect on increasing the heat sinking efficiency. The system has the potential to offer a practical cooling solution for future electronics.

Dynamic nanofin heat sinks

Particle swarm optimization (PSO) is a heuristic global optimization method, proposed originally by Kennedy and Eberhart in 1995. It is now one of the most commonly used optimization techniques. This survey presented a comprehensive investigation of PSO. On one hand, we provided advances with PSO, including its modifications (including quantum-behaved PSO, bare-bones PSO, chaotic PSO, and fuzzy PSO), population topology (as fully connected, von Neumann, ring, star, random, etc.), hybridization (with genetic algorithm, simulated annealing, Tabu search, artificial immune system, ant colony algorithm, artificial bee colony, differential evolution, harmonic search, and biogeography-based optimization), extensions (to multiobjective, constrained, discrete, and binary optimization), theoretical analysis (parameter selection and tuning, and convergence analysis), and parallel implementation (in multicore, multiprocessor, GPU, and cloud computing forms). On the other hand, we offered a survey on applications of PSO to the following eight fields: electrical and electronic engineering, automation control systems, communication theory, operations research, mechanical engineering, fuel and energy, medicine, chemistry, and biology. It is hoped that this survey would be beneficial for the researchers studying PSO algorithms.

/pdf/a-comprehensive-survey-on-particle-swarm-optimization-1d380v5xx1.pdf

A Comprehensive Survey on Particle Swarm Optimization Algorithm and Its Applications

Experimental thermodynamic evaluation for a single stage heat transformer prototype build with commercial PHEs

A state-of-the-art review is presented of the different technologies that are available to deliver refrigeration from solar energy. The review covers solar electric, solar thermal and some new emerging technologies. The solar thermal systems include thermo-mechanical, absorption, adsorption and desiccant solutions. A comparison is made between the different solutions both from the point of view of energy efficiency and economic feasibility. Solar electric and thermo-mechanical systems appear to be more expensive than thermal sorption systems. Absorption and adsorption are comparable in terms of performance but adsorption chillers are more expensive and bulkier than absorption chillers. The total cost of a single-effect LiBr–water absorption system is estimated to be the lowest.

/pdf/solar-refrigeration-options-a-state-of-the-art-review-201j2z3ixb.pdf

Solar refrigeration options – a state-of-the-art review

Modeling of solar energy systems using artificial neural network: A comprehensive review

This study presents the environmental impact assessment of an absorption heat transformer designed to recover 1 kW of thermal energy from each 2 kW of waste heat supplies. The net contribution of the heat transformer is a load avoided of 0.665 kg CO2 equivalents; the recovery process avoids 0.729 kg CO2 equivalents and the major contribution to the environment impacts is the pumping process with 0.0437 kg CO2 equivalents for each 1 kWh recovered. The study results show that absorption heat transformer is a good environmental option because it produces useful energy from waste heat and the final result is an environmental impact diminution.

/pdf/environmental-impact-assessment-for-an-absorption-heat-2rpy92xycg.pdf

Environmental Impact Assessment for an Absorption Heat Transformer

this paper shows the values of Flow ratio (FR) for control of an absorption double stage heat transformer The main parameters for the heat pump system are defined as COP, FR and GTL The control of the entire system is based in a new definition of FR The heat balance of the Double Stage Heat Transformer (DSHT) is used for the control The mass flow is calculated for a HPVEE program and a second program control the mass flow The mass flow is controlled by gear pumps connected to LabView program The results show an increment in the fraction of the recovery energy An example of oil distillation is used for the calculation The waste heat energy is added at the system at 70 °C Water ™ - Carrol mixture is used in the DSHT The recover energy is obtained in a second absorber at 128 °C with two scenarios

Double Stage Heat Transformer Controlled by Flow Ratio

In this paper we present and evaluate the spectral response of uniform gratings written in different tapered core sections of single mode fibre. This combination of uniform gratings and tapers leads to three, types of Chirped Fibre Bragg Gratings with different reflection spectra and different mechanical properties. These devices are characterized in function of the applied strain, showing interesting chirp tunability.

Spectral response evaluation of fibre Bragg gratings written in tapered single mode optical fibres

In absorption systems using the aqueous lithium bromide mixture, the Coefficient of Performance is affected by the desorber. The main function of this component is to separate the refrigerant fluid from the working mixture. In conventional boiling desorbers, constant heat flux and vacuum pressure conditions are necessary to carry out the desorption process, and usually, the absorbers are heavy and bulky; thus, they are not suitable in compact systems. In this study, a membrane desorber was evaluated, operating at atmospheric pressure conditions with a water/lithium bromide solution with a concentration of 49.6% w/w. The effects of the solution temperature, solution mass flow, and condensation temperature on the desorption rate were analyzed. The maximum desorption rate value was 6.1 kg/m2h with the following operation conditions: the solution temperature at 95.2 °C, the solution mass flow at 4.00 × 10−2 kg/s, and the cooling water temperature at 30.1 °C. On the other hand, the minimum value was 1.1 kg/m2h with the solution temperature at 80.2 °C, the solution mass flow at 2.50 × 10−2 kg/s, and the cooling water temperature at 45.1 °C. The thermal energy efficiency, defined as the ratio between the thermal energy used to evaporate the refrigerant fluid with respect to the total thermal energy entering the membrane desorber, varied from 0.08 to 0.30. According to the results, a high solution mass flow, a high solution temperature, and a low condensation temperature lead to an increase in the desorption rate; however, a low solution mass flow enhanced the thermal energy efficiency. The proposed membrane desorber could replace a conventional boiling desorber, especially in absorption cooling systems that operate at high condensation temperatures as in warm weather regions.

Experimental Performance of a Membrane Desorber Operating under Simulated Warm Weather Condensation Temperatures.

Differential group delay (DGD) generation by inducing birefringence in uniform fiber Bragg gratings (FBG) is studied. Applying a transverse load, a birefringence is induced on a uniform FBG creating a tunable differential group delay. A theoretical behavior of this phenomenon is presented being in good agreement with the experimental results obtained. A maximum experimental tunable DGD of ∼60 ps was obtained with this induced birefringent process in the uniform FBG. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2451–2454, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22729

Rosenberg J. Romero

Papers

Environmental Impact Assessment for an Absorption Heat Transformer

Double Stage Heat Transformer Controlled by Flow Ratio

Spectral response evaluation of fibre Bragg gratings written in tapered single mode optical fibres

Experimental Performance of a Membrane Desorber Operating under Simulated Warm Weather Condensation Temperatures.

Tunable first-order differential group delay generation using a uniform fiber Bragg grating