Characterization of Fouled Flat Sheet Membranes by Infrared Thermography

An Infrared thermography (IRT) technique for characterization of fouling on membrane surface has been developed. The emitted spectral power from the fouled membrane is a function of emissivity and surface morphology. In this work, a FLIR A320 IR camera was used to measure surface temperature and emissivity. The surface temperature and the corresponding emissivity value of various areas on the fouled membrane surface is measured by the infrared camera and recorded alongside its thermogram. Different fouling experiments were performed using different concentrations of aluminum oxide nanoparticle mixed with deionized water as feed solution (333 ppm, 1833 ppm and 3333 ppm) so as to investigate the effect of feed concentration on the degree of fouling and thus its effect on the emissivity values measured on the membrane surfaces. Surface plots in 3D and Line plots are obtained for the measured emissivity values and thickness of the fouling deposit on the membrane surface respectively. The results indicate that the IRT technique is sensitive to changes that occur on the membrane surface due to deposition of contaminants on the membrane surface and that emissivity is a function of temperature, surface roughness and thickness of the specimen under investigation.

Electrical Resistance and Natural Convection Heat Transfer Modeling of Shape Memory Alloy Wires

Shape memory alloy (SMA) actuators are becoming increasingly popular in recent years due to their properties such as large recovery strain, silent actuation and low weight. Actuation in SMA wires depends strongly on temperature which is difficult to measure directly. Therefore, a reliable model is required to predict wire temperature, in order to control the transformation, and hence the actuation, and to avoid potential degradation due to overheating. The purpose of this investigation is to develop resistance and natural convection heat transfer models to predict temperature of current-carrying SMA wires using indirect temperature measurement methods. Experiments are performed on electrically heated 0.5 mm diameter NiTi SMA wire during phase transformation. Convection heat transfer experiments are performed in an environment of air that allows for control of the ambient pressure and in turn the thermofluid properties, such as density and viscosity. By measuring convective heat loss at a range of pressures, an empirical natural convection heat transfer correlation is determined for inclination angles from horizontal to vertical, in the Rayleigh number range of 2.6 × 10−8 ≤ RaD ≤ 6.0 × 10−1. Later, effect of temperature changes on electrical resistance and other control parameters such as applied external stress, wire inclination angle, wire length and ambient pressure is investigated. Based on experimental results a resistance model is developed for SMA wires that combined with the heat transfer correlation previously derived can be used to predict temperature and natural convection heat transfer coefficient of NiTi SMA wires during phase transformation for different wire lengths and inclination angles under various applied external stresses.

Innovative Realizations of High Heat-Flux Boiling and Condensing Flows for Milli-Meter and Micro-Meter Scale Applications

For shear driven mm-scale flows, the traditional boiler and condenser operations pose serious problems of degraded performance (low heat-flux values, high pressure drops, and device-and-system level instabilities). The innovative devices are introduced for functionality and high heat load capabilities needed for shear dominated electronic cooling situations that arise in milli-meter scale operations, certain gravity-insensitive avionics-cooling and zero-gravity applications.

Measurement of Thermal Conductivity of a Flexible Substrate

A number of past papers have described experimental techniques for measurement of thermal conductivity of substrates and thin films of technological interest. Nearly all substrates measured in the past are rigid. There is a lack of papers that report measurements on a flexible substrate such as thin plastic. The paper presents an experimental methodology to deposit a thin film microheater device on a plastic substrate. This device, comprising a microheater line and a temperature sensor line is used to measure the thermal conductivity of the plastic substrate using the transient thermal response of the plastic substrate to a heating current. An analytical model describing this thermal response is presented. Thermal conductivity of the plastic substrate is determined by comparison of experimental data with the analytical model. Results described in this paper may aid in development of an understanding of thermal transport in flexible substrates.

A Computational Model for Performance Prediction of a Hybrid PV/T Module

In this paper we investigate the performance of an integrated solar photovoltaic and thermal (PV/T) liquid (water) collector using a computational simulation program. A detailed time-dependent thermal model was formulated to calculate and correlate the thermal parameters in a standard PV/T collector, including solar cell temperature, back surface temperature, and outlet water temperature. Based on the energy balance of each component of the system, an analytical expression for the temperature of the PV module and the water was derived. In addition, an analytical expression for the instantaneous energy efficiency of the PV/T collector was also derived in terms of thermal, design and climatic parameters. Built on previously published model, a new computer simulation program was developed and validated. The thermal simulation results obtained are more precise than those previously reported in the literature.

Development of Lift-Off Diameter Model of Bubbles Generated on Horizontal Tube

In this study, the theoretical correlation for the lift-off diameter of bubbles generated on a horizontal tube is proposed. A force balance analysis in the direction normal to the heated surface at the moment of the bubble lift-off was performed to develop the model. According to the developed model, the bubble lift-off diameter depends strongly on the azimuthal position of the horizontal tube, the relative velocity between a bubble and surrounding liquid, the properties of the bubble, and the liquid. The developed model can be applicable to define the sub-model of wall heat flux partitioning for natural and forced convective boiling.

Nucleate Boiling of Dielectric Liquids on Hydrophobic Patterned Surfaces

This study experimentally investigated the effect of hydrophobic patterned surfaces in nucleate boiling heat transfer. A dielectric liquid, HFE-7100, was used as the working fluid in the saturated boiling tests. Dielectric liquids are known to have highly-wetting characteristics. They tend to fill surface cavities that would normally trap vapor/gas, and serve as active nucleation sites during boiling. With the lack of these vapor filled cavities, boiling of a dielectric liquid leads to high incipience superheats and accompanying temperature overshoots. Heater samples in this study were prepared by applying a thin Teflon (AF400, Dupont) coating on 1-cm2 smooth copper surfaces following common photolithography techniques. Matching size thick film resistors, attached onto the copper samples, generated heat and simulated high heat flux electronic devices. Tests investigated the heater samples featuring circular pattern sizes between 40–100 μm, and corresponding pitch sizes between 80–200 μm. Additionally, a plain, smooth copper surface was tested to obtain reference data. Based on data, hydrophobic patterned surfaces effectively eliminated the temperature overshoot at boiling incipience, and considerably improved nucleate boiling performance in terms of heat transfer coefficient and critical heat flux over the reference surface. Hydrophobic patterned surfaces therefore demonstrated a practical surface modification method for heat transfer enhancement in immersion cooling applications.

Foam Insulation Behavior in Void Space Under Fire Conditions

A fire contained within a room can spread into void spaces in the walls and ceiling through penetrations in the material that lines the compartment. Few studies have looked at how a room and contents fire transitions to a structural fire. One of the active areas of fire research is the coupling of the fire to the structure. Lightweight wood frame construction represents the majority of residential construction in the U.S. The construction details and choice of materials will affect the overall fire resistance of the structure. Because of the relative lack of knowledge on the fire penetration into wall spaces, this research examined how fire might penetrate into the void spaces of wood framed structures. In the U.S.A., a critical barrier to the penetration of hot gas products into void spaces is provided by the gypsum-board skin of the compartment. For most compartments, there are many penetrations within the compartment’s gypsum-board skin. Common potential access points include security system wiring (e.q. smoke detectors and cameras), ventilation fixtures, light switches, and electrical outlets among others. A hole in the gypsum may create opportunities for void space ignition. One of the purposes of this work is to develop a small scale testing system to characterize fire driven flow and heat transfer into a void space. With such an apparatus, one can rapidly identify materials that are prone to igniting for a given leakage geometry and fire size. Common materials found in void spaces include wooden structural members, plywood/oriented strand board, a variety of insulation types, and vapor barriers. This study discusses the characteristics of the small scale experimental system and preliminary tests on a range of void space construction materials.

Numerical Investigation of the Onset of Steady Natural Convection in a Square Cavity Partially Filled With a Single Porous Block

The critical Rayleigh number at the onset of natural convection within a square cavity filled with a centralized porous block was investigated. The porous medium is modeled by using the heterogeneous model and the governing equations are solved for each phase separately. The thermal gradient is applied from the bottom to the top horizontal walls while the vertical walls are kept adiabatic. The amount of solid within the cavity was kept constant by fixing both external and internal porosity in 36% and 40%, respectively. The equations are solved using the Finite Volume Method and the interpolation scheme for the convective terms is the Hybrid Scheme. For the pressure-velocity coupling, the SIMPLEC method is used. The effects on the conductive-convective regime transition, reads critical Rayleigh Number, characterized by the average Nusselt number and the heatlines contour plot, was investigated by varying the Rayleigh number and the porous block permeability. The results show that the so called critical Rayleigh number is affected by the block permeability. As the permeability decreases, the flow tends to recirculate around the block being squeezed against the cavity walls and therefore, more susceptible to viscous effects. A correlation to the critical Rayleigh number is presented as a function of the agglomerate permeability showing that the higher the permeability the lower the amount of energy required to trigger the convection.

Higher Order Finite Elements for the Accurate Prediction of Temperature Gradients in Heat Conduction Problems

When the Finite Element Method (FEM) is used to solve heat conduction problems in solids, the domain is typically discretized using elements that only include the nodal values of the temperature as Degrees of Freedom (DOFs). If the values of the spatial temperature gradients are needed, they are typically computed by differentiating the functional representation for the temperature inside the elements. Unfortunately, this differentiation process usually leads to less accurate results for the temperature gradients as compared to the temperature values. For elliptic problems, like steady state heat conduction, with Neumann Boundary Conditions (BCs), recent research related to Adini’s element suggests that higher order elements that include spatial derivatives of the primary field variable as nodal DOFs are promising for obtaining accurate values for those quantities as well as providing a higher order of convergence than conventional elements. In this paper, steady state and transient heat conduction problems which involve Dirichlet BCs or both Dirichlet and Neumann BCs are studied and a new auxiliary BC is proposed to increase the accuracy of the FE solution when Dirichlet BCs are present. Examples are used to illustrate that Adini’s elements converge faster and are more computationally economical than the conventional Lagrange linear elements and Serendipity quadratic elements when auxiliary BCs are used.