Despite their potential as a sustainable energy technology, the operation of proton exchange membrane fuel cells (PEMFCs) in sub-freezing conditions remains a critical challenge due to the risk of ice formation and performance degradation. This study introduces a new passive thermal management technique using strategically arranged multi-layer phase change materials (PCMs) to address this challenge. A numerical model was developed to evaluate the thermal behavior across various PCM configurations, incorporating one, two, and three layers arranged both in parallel and series with distinct melting points ranging from 55 to 65 ◦C. The results show that multi-layer PCM configurations provide significant improvements over the single-layer baseline. The parallel three-layer arrangement extended the thermal management duration by 48.8 % compared to the single-layer system, maintaining PEMFC temperatures above 55 ◦C for over 12 h in an ambient at − 20 ◦C. This configuration also demonstrated superior temperature stability, with a temperature differential of only 3 ◦C. The series three-layer design achieved a 39 % increase in duration but maintained the same 3 ◦C temperature differential. The novelty of this work lies in the systematic analysis of parallel and series PCM layer configurations, each designed for specific operating conditions. These passive solutions can effectively manage the energy demand of PEMFCs during cold startup, overcoming the limitations of conventional methods.
The present investigation deals with experimental study of three-phase direct-contact heat exchanger, for water-Freon R11 system, where water is the continuous phase (liquid) and Freon R11 (liquid-gas) is the dispersed phase. The test section consisted of a cylindrical Perspex column with inner diameter 8cm and 1.2m long, in which, water was to be confined. Liquid Freon R11 drops were injected into the hot water filled column, through a special design of distributors at the bottom of the column. The liquid Freon R11 drops rose on their way up and evaporated into two-phase bubbles at atmospheric pressure. The study was devoted to express the effect of process variables such as c
... Show MoreGas hydrate formation poses a significant threat to the production, processing, and transportation of natural gas. Accurate predictions of gas hydrate equilibrium conditions are essential for designing the gas production systems at safe operating conditions and mitigating the problems caused by hydrates formation. A new hydrate correlation for predicting gas hydrate equilibrium conditions was obtained for different gas mixtures containing methane, nitrogen and carbon dioxide. The new correlation is proposed for a pressure range of 1.7-330 MPa, a temperature range of 273-320 K, and for gas mixtures with specific gravity range of 0.553 to 1. The nonlinear regression technique was applie
This research describes the design & implementation of frequency synthesizer using single loop Phase lock loop with the following specifications: Frequency range (1.5 – 2.75) GHz,Step size (1 MHz), Switching time 36.4 µs, & phase noise @10 kHz = -92dBc & spurious -100 dBc
The development in I.C. technology provide the simplicity in the design of frequency synthesizer because it implements the phase frequency detector(PFD) , prescalar & reference divider in single chip. Therefore our system consists of a single chip contains (low phase noise PFD, charge pump, prescalar & reference divider), voltage controlled oscillator , loop filter & reference oscillator. The single chip
... Show MoreThe research aims to identify the risks faced by projects and work on the administration, such as those risks by using professional Project Management System (Project Management Professional) by identifying those risks and their impact on the objectives of the project, if they occur and to provide appropriate responses to Ha.autam search application on the draft Law Faculty port by the General Mansour Construction Contracting company has been using a method personal interview with the heads of departments and project managers in the Al-Mansour and tools descriptive and quantitative analysis as was used (likelihood and impact of risk analysis, Ai_kaoa scheme Sbb- effect, analysis of probability and impact, risk matrix (probability
... Show MoreInelastic transverse magnetic dipole electron scattering form
factors in 48Ca have been investigated through nuclear shell model
in an excited state energy Ex= 10.23 MeV which is so called
"mystery case" with different optional choices like effective
interaction, restricted occupation and core polarization interaction.
40Ca as an inert core will be adopted and four orbits with eight
particles distributed mainly in 2p1f model space and in some extend
restricted to make sure about the major accuse about this type of
transition. Theoretical results have been constituted mainly with
experimental data and compared with some important theoretical
results of the same transition.
Taken the word the word God itself the task when the Muslim calligraphers because of its holiness and majesty and altitude, so take Calligraphers innovate in their design, which represents the images and forms experiencing them prolific artistic output to highlight the aesthetic value through the use of Kufic script which is one of the most prominent lines his susceptibility diversity decorative Add the possibility of extending the letters in different directions because of the vision calligrapher aesthetic and an investigation is required for the word of the design, so the researcher examined by dividing into four chapters,Was the first research problem and the importance and goals and identify the term, while the second chapter was div
... Show MoreThe rotor dynamics generally deals with vibration of rotating structures. For designing rotors of a high speeds, basically its important to take into account the rotor dynamics characteristics. The modeling features for rotor and bearings support flexibility are described in this paper, by taking these characteristics of rotor dynamics features into standard Finite Element Approach (FEA) model. Transient and harmonic analysis procedures have been found by ANSYS, the idea has been presented to deal with critical speed calculation. This papers shows how elements BEAM188 and COMBI214 are used to represent the shaft and bearings, the dynamic stiffness and damping coefficients of journal bearings as a matrices have been found
... Show MoreThe goal of the study is to discover the best model for forecasting the exchange rate of the US dollar against the Iraqi dinar by analyzing time series using the Box Jenkis approach, which is one of the most significant subjects in the statistical sciences employed in the analysis. The exchange rate of the dollar is considered one of the most important determinants of the relative level of the health of the country's economy. It is considered the most watched, analyzed and manipulated measure by the government. There are factors affecting in determining the exchange rate, the most important of which are the amount of money, interest rate and local inflation global balance of payments. The data for the research that represents the exchange r
... Show MoreSince the nineties of the last century, Iraqi youth have been exposed to Mexican soap operas dubbed into classical Arabic, and the stories and ideas presented by these series were almost new to all the minds of the youth at that time, a culture completely different from the culture we have of social relations, and since the number of episodes was more than Of the 100 episodes, exposure to these series has left young people confused by the addiction to all their ideas and stories. They differ from the foreign films (mostly American) that we used to watch, and they only take two hours (at most). These films contain diverse stories and may be forgotten. Memory includes events and characters in their entirety at times, and you may remember th
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