Guillermo Soriano

Experimental Characterization of Single and Multiple Droplet Impingement on Surfaces Subject to Constant Heat Flux Conditions

Spray cooling is one of the most promising technologies in applications which require large heat removal capacity in very small areas. Previous experimental studies have suggested that one of the main mechanisms of heat removal in spray cooling is forced convection with strong mixing due to droplet impingement. These mechanisms have not been completely understood mainly due to the large number of physical variables, and the inability to modulate and control variables such as droplet frequency and size. Our approach consists of minimizing the number of experimental variables by controlling variables such as droplet direction, velocity and diameter. An experimental study of single and multiple droplet impingements using HFE 7100 as the cooling fluid under constant heat flux conditions is presented. A monosized droplet train is produced using a piezoelectric droplet generator with the ability to adjust droplet frequency, diameter and velocity. In this study, heaters consisting of a layer of Indium Tin Oxide (ITO) as heating element, and silicon substrates are used. Film morphology was characterized using a Laser Induced Fluorescence (LIF) technique with a focus on the droplet impact zone by measuring variables such as film thickness and diameter of the impact zone. Infrared thermography was used to measure surface temperature at the liquid-solid interface. The IR thermography technique was also used to characterize temperature gradients at the droplet impact zone. The results and effects of droplet frequency, fluid flow rate, and fluid temperature on heat flux are also presented.Copyright

Characterization of Thermal Properties and Heat Transfer Behavior of Microencapsulated Phase Change Material Slurry and Multiwall Carbon Nanotubes in Aqueous Suspension

In the last decade, microencapsulated phase change material (MPCM) slurries have been proposed and studied as novel coolants for heat transfer applications. Such applications include electronics cooling, and secondary coolants in air conditioning systems among others. Experiments have shown that MPCM’s increase the overall thermal capacity of thermal systems by taking advantage of the phase change material’s latent heat of fusion. However, research has also shown that the overall heat transfer coefficient is diminished due to a reduction in the effective thermal conductivity and increased viscosity of the slurry. For this reason, there is an urgent need to modify the content of microcapsules containing phase change material to increase their effective thermal conductivity and the overall heat transport process. Our solution consists of increasing the thermal conductivity of MPCM by adding carbon nanotubes to the shell and core of the microcapsules. Carbon nanotubes have shown to increase the thermal conductivity of liquids by 40% or more in recent experiments. In this paper, MPCM slurry containing octadecane as phase change material and multi-wall carbon nanotubes (MWCNTs) embedded in the capsule material and core are compared with pure water as heat transfer fluid. Thermal and physical properties of MPCM slurry containing carbon nanotubes were determined using a differential scanning calorimeter and concentric viscometer, respectively. Experimental convective heat transfer coefficient data for MWCNT aqueous suspensions under laminar flow and constant heat flux were determined using a bench-top heat transfer loop. Experimental heat transfer results are presented.Copyright

Film dynamics relevant to spray cooling

For a number of years spray cooling has shown to be a viable alternative for thermal management of high-density electronics. Nevertheless, the key fundamental physical processes are to a large degree poorly understood due mostly to the complicated fluid dynamics resulting from nucleate boiling coupled with spray drop impingement. In this combined experimental and modeling effort, a representative configuration consisting of a liquid film resting on a solid silicon-based substrate with an imposed constant heat flux and an impinging train of droplets has been studied. This configuration mimics to a great degree the physics of spray cooling, while simultaneously simplifying the experimental and computational analysis to a manageable level. It is shown that a number of statistically quasi-stationary states are possible by carefully coordinating the heat flux and drop impingement rates. Studies were both performed for water and FC-72. Due in part to its lower surface tension, the quasi-stationary states for FC-72 were instantaneously much more chaotic than the corresponding water cases. The OpenFoam (open source computational fluid dynamics) code has been supplemented with an energy equation within the existing Volume-of-Fluid infrastructure. This was used to analyze the dynamics in the impingement region. It is shown that the temperature in this region is approximately equal to the temperature of incident droplets. For all water and FC-72 films, it was found that each droplet impact penetrated the entire thickness of the film bringing a significant cooling effect on the heated substrate. This was the case even for film thickness-to-impact droplet diameter ratios far exceeding one.

Thermal Performance of a Borehole Heat Exchanger Located in Guayaquil-Ecuador Using Novel Heat Transfer Fluids

An analysis of thermal performance of a vertical Borehole Heat Exchanger (BHE) from a close loop Ground Source Heat Pump (GSHP) located in Guayaquil-Ecuador is presented. The project aims to assess the influence of using novels heat transfer fluids such as nanofluids, slurries with microencapsulated phase change materials and a mixture of both. The BHEs sensitive evaluation is performed by a mathematical model in a finite element analysis by using computational tools; where, the piping array is studied in one dimension scenario meanwhile its surroundings grout and ground volumes are presented as a three dimensional scheme. Therefore, an optimized model design can be achieved which would allow to study the feasibility of GSHP in buildings and industries in Guayaquil-Ecuador.Copyright

Coaxial borehole heat exchanger simulation with power generation potential for Chachimbiro, Ecuador

This work presents a virtual coaxial Borehole Heat Exchanger (BHE) energy balance simulation in Chachimbiro, Ecuador. The purpose of this study was to estimate the power generation and optimize the engineering parameters from a virtual coaxial BHE of 1500 meters depth on the mentioned site. The methodology used was the modeling simulation based on mass and energy balance through AMEsim software, and the parameters employed in the model considered the previous location surveys besides a sensitivity analysis of geometry, pipe materials, and BHE insulation depth. The results showed that a single coaxial BHE on Chachimbiro would have a thermal power potential between 3–4 MW, and its efficiency would mainly depend on the thermal conductivity of the pipes plus the insulation casing depth.Copyright

Energy Consumption Modeling of a Heat Pump System for Combined Space Conditioning and Residential Water Heating in a Typical Household in Quito, Ecuador

This research develops a detailed model for a Water to Water Heat Pump Water Heater (HPWH), operating for heating and cooling simultaneously, using two water storage tanks as thermal deposits. The primary function of the system is to produce useful heat for domestic hot water services according to the thermal requirements for an average household (two adults and one child) in the city of Quito, Ecuador. The purpose of the project is to analyze the technical and economic feasibility of implementing thermal storage and heat pump technology to provide efficient thermal services and reduce energy consumption; as well as environmental impacts associated with conventional systems for residential water heating. An energy simulation using TRNSYS 17 is carried to evaluate model operation for one year. The purpose of the simulation is to assess and quantifies the performance, energy consumption and potential savings of integrating heat pump systems with thermal energy storage technology, as well as determines the main parameter affecting the efficiency of the system.Finally, a comparative analysis based on annual energy consumption for different ways to produce hot water is conducted. Five alternatives were examined: (1) electric storage water heater; (2) gas fired water heater; (3) solar water heater; (4) air source heat pump water heater; and (5) a heat pump water heater integrated with thermal storage.Copyright

Entropy Generation AnalysisOf Engineered Heat Transfer FluidsUnder A Constant Surface Temperature

An assessment of the use of engineered heat transfer fluids working under constant wall temperature conditions in the turbulent regime is presented. An analysis of entropy generation and pumping power on the system working with different engineered heat transfer fluids is performed. Three types of fluids are considered: multiwalled carbon nanotube (MWCNT) based nanofluids, slurries with microencapsulated phase change materials (MPCM) and a mixture of both fluids. Specific heat, thermal conductivity and viscosity of the fluids are included in the analysis using theoretical and experimental results available in literature. Nanofluids in the system result on greater entropy generation and pumping power consumption when compared with base fluid. MPCMs slurries produce the minimum entropy generation and pumping power consumption. Mixtures are affected by the content of nanofluids resulting in a performance below of MPCMs slurries. The improvement on the heat capacity of the fluid produced by the Microencapsulated phase change material is the main factor in reducing entropy generation and pumping power consumption for the system. Under the conditions assessed, the increase in viscosity offsets the increase in thermal conductivity on the MWCNT based nanofluids. On the other hand in the case of MPCM slurries, the increase in heat capacity outweighs the reduction in thermal conductivity and increase in viscosity.