Numerical Analysis of Time Required for De-stratification in Warehouses

A significant source of energy consumption comes from maintaining desired indoor environment conditions in warehouses and other industrial facilities. To combat the raising energy costs, studies into more efficient heating and cooling strategies has been a topic of consideration for a number of years. One of the areas of investigation is the implications of a thermally stratified environment. In heating, removing the stratification phenomena has been linked to savings in the cost of fuel to heat an environment. Whereas in cooling a highly stratified environment is desired. The primary method of de-stratification is the utilization of ceiling fans. The use of fans reduces the overall savings of de-stratification for heating purposes. A solution to offset the reliance on grid power is the use of solar powered ceiling fans. The challenge with utilizing solar power during heating seasons is a reduction in the time the sun is available to charge and store energy to run the fans. While there are studies on the impact of thermal stratification, with air as a medium in an indoor environment, there is a lack of information on the frequency at which the ceiling fans need to operate to maintain a de-stratified environment. The determination of a fan operation frequency, to maintain a de-stratified environment, informs potential designers on the viability of installing solar powered fans as an alternative to grid powered fans. In the event that solar powered fans were not a viable option, it also provides information on the frequency that a grid powered fan would need to run to maintain de-stratification. To determine a fan operating frequency, a numerical analysis will be performed. This numerical analysis will assess the time required to de-stratify an environment based on inputs such as flow rate and spatial considerations. In order to establish the quality of the numerical analysis, two experiments have been conducted to observe the impact of de-stratification. One experiment is located at a large retail warehouse distribution center, the other is a small classroom. The data collected from these experiments will be compared to the models developed to predict the change in stratification with time

Conceptual Design of a Manufacturing Process for an Automotive Microchannel Heat Exchanger

Calls for higher fuel efficiency in the United States and Europe are driving the need for waste heat recovery in automotive markets. While conventional heat exchangers can be designed to meet the heat duty requirement, the resulting volume, weight, and thermal mass are too large for rapid transient response and packaging of the device. The lightweight, compact form factor of microchannel heat exchangers with submillimeter flow passages is attractive for automotive applications. However, the industrial use of microchannel heat exchangers continues to be inhibited by high manufacturing costs. The objective of this paper is to develop a microchannel heat exchanger concept capable of meeting the cost and performance goals for an automotive application. So-called printed-circuit microchannel heat exchangers are produced using a stacked-lamina approach in which individual metal laminae are photochemically machined and diffusion bonded. Here, the conceptual design of a microchannel heat exchanger produced using more conventional stamping and joining technologies is discussed for an automotive application. The device is sized to provide waste heat recovery from an exhaust stream to engine coolant for a representative passenger vehicle with acceptable pressure loss. Using the specified design, a process-based cost model is presented showing cost modeling efforts to date including the capital investment and cost-of-goods-sold as a function of annual production volume. The initial results show a pathway for the cost effective integration of compact microchannel heat exchangers into advanced vehicle thermal management systems

Two-phase flow regimes of condensing R-134a at low mass flux in rectangular microchannels

Qualitative two-phase flow regime data are obtained from high-speed visualization of condensing flows of R-134a at mass fluxes from 75 to 150 kg m−2 s−1 and quality from 0.1 to 0.8 in square microchannels (DH = 0.84 mm) cooled from a single side. Superheated R-134a is distributed into multiple parallel microchannels and then partially condensed, using a counterflow water loop, to the desired quality prior to the inlet of a visualization section. This experimental arrangement mitigates the potential for flow maldistribution. Despite very small heat duties, a low uncertainty in the quality in the visualization section is maintained by enforcing a large temperature difference on the water-side (ΔT > 10 K). For all conditions, annular or annular/wavy type flow were observed, with no distinct intermittent flow. Data are compared with flow macro and mini/microchannel maps, which are shown to over predict the occurrence of intermittent or wavy flow

Tuning the magneto-optical response of TbPc2 single molecule magnets by the choice of the substrate

In this work, we investigated the magneto-optical response of thin films of TbPc2 on substrates which are relevant for (spin) organic field effect transistors (SiO2) or vertical spin valves (Co) in order to explore the possibility of implementing TbPc2 in magneto-electronic devices, the functionality of which includes optical reading. The optical and magneto-optical properties of TbPc2 thin films prepared by organic molecular beam deposition (OMBD) on silicon substrates covered with native oxide were investigated by variable angle spectroscopic ellipsometry (VASE) and magneto-optical Kerr effect (MOKE) spectroscopy at room temperature. The magneto-optical activity of the TbPc2 films can be significantly enhanced by one to two orders of magnitude upon changing the molecular orientation (from nearly standing molecules on SiO2/Si substrates to nearly lying molecules on perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) templated SiO2/Si substrates) or by using metallic ferromagnetic substrates (Co)

Optical properties and electrical transport of thin films of terbium(III) bis(phthalocyanine) on cobalt

The optical and electrical properties of terbium(III) bis(phthalocyanine) (TbPc2) films on cobalt substrates were studied using variable angle spectroscopic ellipsometry (VASE) and current sensing atomic force microscopy (cs-AFM). Thin films of TbPc2 with a thickness between 18 nm and 87 nm were prepared by organic molecular beam deposition onto a cobalt layer grown by electron beam evaporation. The molecular orientation of the molecules on the metallic film was estimated from the analysis of the spectroscopic ellipsometry data. A detailed analysis of the AFM topography shows that the TbPc2 films consist of islands which increase in size with the thickness of the organic film. Furthermore, the cs-AFM technique allows local variations of the organic film topography to be correlated with electrical transport properties. Local current mapping as well as local I-V spectroscopy shows that despite the granular structure of the films, the electrical transport is uniform through the organic films on the microscale. The AFM-based electrical measurements allow the local charge carrier mobility of the TbPc2 thin films to be quantified with nanoscale resolution