Numerical Analysis on a Latent Thermal Energy Storage System with Phase Change Materials and Aluminum Foam

Abstract

A latent heat thermal energy storage system with phase change material (PCM) is numerically studied. To enhance the heat transfer inside the system, a highly conductive metal foam is employed with ceramic nanoparticles. The latter method of enhancement leads to a new class of material called Nano-PCM. The system under investigation is a 70-L tank filled up with pure PCM or Nano-PCM and several pipes are situated where the heat transfer fluid (HTF) flows. The pipe surfaces are assumed at constant temperature above the PCM melting temperature to simulate the heat transfer from the HTF. The enthalpy-porosity theory is applied to simulate the PCM phase change, while the porous media formulation is assumed to describe the metal foam behavior. The nano-PCM is modeled with single-phase model where the properties are the weighted-average between the fluid base and the nanoparticles. The simulations are accomplished for charging-discharging process at different porosities and nanoparticle concentration. The results are given in term of average melting fraction evolution, average temperature as function of time, average stored energy. The metal foam significantly improves the heat transfer between PCM and HTF respect to the addition of nanoparticles, reducing the charging and discharging time more than one order of magnitude.     

Exploring a Bayesian hierarchical approach for developing safety performance functions for a mountainous freeway

While rural freeways generally have lower crash rates, interactions between driver behavior, traffic and geometric characteristics, and adverse weather conditions may increase the crash risk along some freeway sections. This paper examines the safety effects of roadway geometrics on crash occurrence along a freeway section that features mountainous terrain and adverse weather. Starting from preliminary exploration using Poisson models, Bayesian hierarchical models with spatial and random effects were developed to efficiently model the crash frequencies on road segments on the 20-mile freeway section of study. Crash data for 6 years (2000–2005), roadway geometry, traffic characteristics and weather information in addition to the effect of steep slopes and adverse weather of snow and dry seasons, were used in the investigation. Estimation of the model coefficients indicates that roadway geometry is significantly associated with crash risk; segments with steep downgrades were found to drastically increase the crash risk. Moreover, this crash risk could be significantly increased during snow season compared to dry season as a confounding effect between grades and pavement condition. Moreover, sites with higher degree of curvature, wider medians and an increase of the number of lanes appear to be associated with lower crash rate. Finally, a Bayesian ranking technique was implemented to rank the hazard levels of the roadway segments; the results confirmed that segments with steep downgrades are more crash prone along the study section.     

Bubbles and Market Crashes

We present a dynamical theory of asset price bubbles that exhibits the appearance of bubbles and their subsequent crashes. We show that when speculative trends dominate over fundamental beliefs, bubbles form, leading to the growth of asset prices away from their fundamental value. This growth makes the system increasingly susceptible to any exogenous shock, thus eventually precipitating a crash. We also present computer experiments which in their aggregate behavior confirm the predictions of the theory.     

A performance evaluation approach for GSM-based information services

The ever increasing diffusion of mobile communications will lead to massive mobile access to the Internet. The paper focuses on the wireless application protocol (WAP) for providing mobile information services, as envisaged by the personalized access to local information and services for tourists (PALIO) project within the fifth research framework of the European Commission. In particular, we consider a global system for mobile communications (GSM) network where WAP traffic is transported by the short message service (SMS) on specific GSM signaling channels. We develop suitable traffic models for both the WAP downlink traffic and the signaling traffic. An analytical approach is described that allows evaluation of the mean transmission delay of a WAP page. Finally, a downlink traffic scheduling policy is proposed in order to reduce the delay variance so that users experience a more regular traffic behavior (service usability requirement). The theoretical derivations for the GSM-SMS scenario are general and can also be tailored for other mobile communication systems. The study allows dimensioning of both the service and the downlink signaling traffic capacity in order to fulfill quality-of-service requirements for users.     

Macro- and micro-cellular porous ceramics from preceramic polymers

Macrocellular and microcellular SiOC open cell ceramic foams were fabricated from a preceramic polymer. Macrocellular foams, with a cell size ranging from about 100–600 μm and a bulk density ranging from about 0.25–0.58 g/cm³, depending on the processing parameters, were fabricated using a direct foaming approach. Microcellular foams, with a cell size of about 8 μm, were fabricated using poly(methyl methacrylate)microbeads as sacrificial templates. The bulk density ranged from about 0.31–0.48 g/cm³, depending on the amount of microbeads in the starting material. The compression strength of the foams increased with increasing relative density, and microcellular foams possessed a 2–5 times higher crushing strength than macrocellular foams of similar density.     

Formal Performance Modelling and Evaluation of an Adaptive Mechanism for Packetised Audio over the Internet

A case study is presented which concerns the design of an adaptive mechanism for packetised audio for use over the Internet. During the design process, the audio mechanism was modelled with the stochastically timed process algebra EMPA and analysed via simulation by the EMPA based software tool TwoTowers in order to predict the percentage of packets that are received in time for being played out. The predicted performance figures obtained from the algebraic model illustrated in advance the adequacy of the approach adopted in the design of the audio playout delay control mechanism. Based on these performance figures, it was possible to implement and develop the complete mechanism without incurring additional costs due to the late discovery of unexpected errors or inefficiency. Performance results obtained from experiments conducted on the field confirmed the predictive simulative results. Received March 1997 / Accepted in revised form July 1998     

Treatment of the regional lymph nodes in squamous carcinoma of the penis

OBJECTIVES: We evaluated the management of the regional lymph nodes to determine the appropriate treatment for carcinoma of the penis. METHODS: The records of 36 patients with carcinoma of the penis were reviewed. Lymphadenectomy was performed in 18 patients, 17 were managed conservatively (watchful waiting) and 1 patient had a biopsy and received radiotherapy. RESULTS: Positive nodes were found in 2 of 2 pT4, 2 of 3 pT3, 8 of 13 pT2 and 2 of 12 pT1 patients submitted to lymphadenectomy. Concerning the histological grade, positive nodes were found in all of the 4 G3, 5 of 12 G2 and 3 of 20 G1 patients. The survival rate was 100% for the patients with negative lymph nodes (pNO = 6) or a single positive inguinal lymph node (pN1 = 5). A correlation was found between the T and the histological grade and the likelihood of lymph node invasion. CONCLUSIONS: The T and the histological grade of the primary lesion must be considered when deciding the approach in the management of the lymph nodes as unnecessary lymphadenectomy can be avoided and those at high risk of lymph node invasion can be treated radically and timely.     

Molecular characterization of Italian rice cultivars

Random amplified polymorphic DNA (RAPD) is an efficient tool to detect DNA polymorphisms and to distinguish different clones and cultivars. We have applied the RAPD technique to distinguish, starting from a single rice seed, among some Italian rice cultivars from market and from National Institute for research on food and nutrition, Italy. We also estimated the genomic similarity among the rice cultivars object of this study taking advantage of the amplification patterns. Despite the low genomic variability among Italian rice cultivars, RAPD technique allowed us to distinguish among them. This indicates that RAPD can be used routinely to verify the identity of Italian rice cultivars in order to prevent fraudulent commercial activity.     

Stochastic analysis of crude oil procurement and processing under uncertain demand for bunker fuel oil

Bunker fuel oil (ifo), one of the products of petroleum refining, has a strong impact in the production process because it drives the availability of heavy residues that depend on the crude quality. A simplified stochastic model for the Administración Nacional de Combustibles Alcohol y Portland refinery, based on the uncertainty of the demand for ifo, is proposed for comparison with the current approach of deterministic demand. In this model, the benefits of the production process are maximized, taking decisions on the more suitable raw material, intermediate products and final blends in order to fulfill quality and demand requirements of final products. A specific case is analyzed where the maximum benefit is achieved when the most expensive crude quality is purchased, due to a lack of incentive to produce extra amounts of heavy fuel oil that must be exported at a non‐attractive price. Results are compared with the solution of a deterministic model with mean demand. In addition, the stochastic model solution depicts how the refinery should operate for each scenario of ifo demand.     

Mixing logics and rewards for the component-oriented specification of performance measures

Formal notations for system performance modeling need to be equipped with suitable notations for specifying performance measures. These companion notations have been traditionally based on reward structures and, more recently, on temporal logics. In this paper we propose an approach that combines logics and rewards, together with a definition mechanism that allows performance measures to be specified in a component-oriented way, thus facilitating the task for non-experts. The resulting Measure Specification Language (MSL) is interpreted both on action-labeled continuous-time Markov chains and on stochastic process algebras. The latter interpretation provides a compositional framework for performance-sensitive model manipulations and emphasizes the increased expressiveness with respect to traditional reward structures for implicit-state modeling notations.