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COVID-19 Pandemic: Stock Markets Situation in European Ex-Communist Countries

- Żebrowska-Suchodolska, Dorota, Karpio, Andrzej, Kompa, Krzysztof

  • Authors: Żebrowska-Suchodolska, Dorota , Karpio, Andrzej , Kompa, Krzysztof
  • Date: 2021
  • Subjects: Stock index , Market situation , Regression
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/487048 , uj:44322 , Citation: Żebrowska-Suchodolska, D., Karpio, A. & Kompa, K.. (2021). COVID-19 Pandemic: Stock Markets Situation in European Ex-Communist Countries. EUROPEAN RESEARCH STUDIES JOURNAL. XXIV. 1106-1128. 10.35808/ersj/2408.
  • Description: Abstract: Purpose: The aim of this article is to present the impact of the COVID-19 pandemic on the capital markets of post-communist economies and, whether these markets are reacting in the same way. The research concerns indices of stock exchanges in Poland, Hungary, Latvia, Lithuania, Bulgaria, Czech Republic, Romania, Estonia, Croatia, and Slovenia. Methodology: The investigation covers the period from 30 SEP 2019 to 31 DEC 2020 divided into three sub-periods - pre-pandemic, pandemic shock, and pandemic stabilization. A trend analysis of the indices studied and a volatility analysis of the returns of the indices were conducted. Econometric trend models and GARCH-class models were applied. Findings: As a main finding it can be concluded that the capital markets of the post-communist economies responded to the pandemic in an analogous way, as well as that the scale and level of development of stock markets does not affect their response to the pandemic and stock market prosperity during the pandemic period. Practical Implications: The work focuses on the analysis of major stock market indices in countries with very different levels of capital market development. The course of the pandemic varies from country to country in terms of freezing the economy. As a consequence, it allows answering the fundamental question from the economic point of view: To what extent does a crisis of a non-economic nature affect the stock exchange situation in countries at the stage of capital market development? Originality/Value: The analysis of the level of capital markets development in post-communist countries has been the subject of many works, including by authors. However, the emergence of a pandemic creates a unique (hopefully) opportunity for research under extreme conditions such as the pandemic. As a consequence, information is obtained about the economic resilience, or lack thereof, of post-communist countries to crisis situations of a non-economic nature.
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How do family supportive supervisors affect nurses’ thriving: A research before and during COVID-19 pandemic

- Şahin, Safiye, Adegbite, Waliu Mulero, Şen, Hanife Tiryaki

  • Authors: Şahin, Safiye , Adegbite, Waliu Mulero , Şen, Hanife Tiryaki
  • Date: 2021
  • Subjects: Family supportive supervisor behaviors , Work-to-family conflict , Psychological well-being
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/489571 , uj:44643 , Citation: Şahin, S., Adegbite, W.M. and Şen, H.T., 2021. How do family supportive supervisors affect nurses' thriving: A research before and during COVID-19 pandemic. Archives of Psychiatric Nursing, 35(6), pp.602-609.
  • Description: Abstract: Nurses need psychological resources (supervisor support), as well as formal support from their organizations, which help them combat the demands from work and home and be more thrive at work. Family supportive supervisor behaviors have been demonstrated above and beyond general levels of supervisor support in reducing work–family conflict and improving well-being. In line with this, first aim is to examine the effects of Covid-19 pandemic on nurses’ perceived family supportive supervisor behaviors, work-to-family conflict, psychological well-being, and thriving. Second the aim of this study is to test the effects of nurses’ perceived family supportive supervisor behaviors on their thriving through work-to-family conflict and psychological well-being. The study was designed as cross-sectional and analytical. A total of 511 nurses from Nigeria and Turkey participated in the study. Parametric tests and Structural Equation Analysis were employed to analyze the data. The scores of nurses’ perceived family supportive supervisor behaviors and thriving decreased during Covid-19 pandemic, while the scores of their work-to-family conflict increased significantly. Results confirmed the negative effects of Covid-19 pandemic on nurses. Furthermore, results showed that family supportive supervisor behaviors had positive effects on thriving by decreasing work-to-family conflict and increasing psychological well-being. This study is one of the very first study examining the effects of family supportive supervisor behaviors on nurses’ work-to-family conflict, psychological well-being and thriving. Results of this study indicate that nurses need family supportive supervisors to be more thrive at work. Therefore, formal family friendly policies and implications improving family supportive supervisor behaviors are recommended in organizations.
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Positive interaction between work and home, and psychological availability on women’s work engagemen t: a ‘shortitudinal’ study

- Łaba, Karolina, Geldenhuys, Madelyn

  • Authors: Łaba, Karolina , Geldenhuys, Madelyn
  • Date: 2018
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/278401 , uj:29874 , Citation: Łaba, K., & Geldenhuys, M. (2018). Positive interaction between work and home, and psychological availability on women’s work engagement: A ‘shortitudinal’ study. SA Journal of Industrial Psychology/SA Tydskrif vir Bedryfsielkunde, 44(0), a1538. https://doi.org/ 10.4102/sajip.v44i0.1538 , ISSN: (Online) 2071-0763
  • Description: Abstract: Orientation: Women’s work engagement is affected by how well they balance their work and personal life, and their level of confidence in their capability at work. Research purpose: Determine whether women’s daily psychological availability mediates daily positive work-home interaction and daily positive home-work interaction on daily work engagement. Motivation for the study: Research into negative work–home and home–work interaction is in abundance. Limited studies focus on the positive effects on women’s experiences at work (i.e. work engagement). Little is known about women’s psychological availability and how it affects their work. Furthermore, little research provides us insights into the day-level experiences of women at work. Research approach/design and method: A quantitative, shortitudinal design was used. Data analyses accounted for multilevel structure in the data (within-person vs. between-person differences). Female employees (n = 60) from various industries in Gauteng, completed electronic diaries in the form of a survey for 10 consecutive working days. Main findings: Daily psychological availability mediates between daily positive work-home interaction and daily work engagement. Daily positive home-work interaction did not predict daily work engagement, but had a significant effect on daily psychological availability. Practical/managerial implications: Examining systems and structures that promote opportunities for women to become more psychologically available at work impacts their sustainable retention. Contribution/value-add: This study found significant relationships between day-level uses of personal resources and spillover effects of home-work and work-home on day-level work engagement. The study further contributes to the literature on positive work–home and home–work interaction.
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Dissecting the ‘Decolonisation Movement’ at South African Universities

- Zwane, Duduzile

The role of neuroleadership in work engagement

- Zwaan, Leigh A., Viljoen, Rica, Aiken, Dorrian

Indigenisation, politics of exclusion, and problematics of autochthony in Zimbabwe’s redistribution agenda

- Zvoushe, Hardlife, Uwizeyimana, Dominique E., Auriacombe, C. J.

  • Authors: Zvoushe, Hardlife , Uwizeyimana, Dominique E. , Auriacombe, C. J.
  • Date: 2017
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/254617 , uj:26661 , Citation: Zvoushe, H., Uwizeyimana, D.E. & Auriacombe, C.J. 2017. Indigenisation, politics of exclusion, and problematics of autochthony in Zimbabwe’s redistribution agenda.
  • Description: Abstract: Zimbabwe’s public policy trajectory has courted global attention specifically through its redistributive policies that include the land reform programme – which was implemented in the first decade of independence; and the black economic empowerment programme, which was implemented in the 1990s through affirmative action initiatives until the enactment of the comprehensive Indigenisation and Economic Empowerment Act in 2007. Notably, indigenisation has been the rallying ideology undergirding the state’s redistribution agenda since the 1980s. Over time, the understanding and application of the concept have raised serious questions on aspects of autochthony, nativity, belonging, and citizenship. Evidence on the ground suggests that the concept has been deliberately twisted, highly politicised, and manipulated as an instrument of exclusionary politics played at racial, political, class, and nationality levels, with the effect of calculatively side-lining potential beneficiaries, as well as facilitating the expropriation and dispossession of critical resources and assets from perceived “foreigners” in the country. Politicisation of indigenisation, economic empowerment, and autochthony has thrust clientelism, cronyism, loyalty, and political correctness as major criteria for accessing benefits of ownership and control of key strategic resources such as land and minerals, as well as shareholding in economic empowerment deals.
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The effects of natural and artificial UV exposure on the physical properties of synthetic turf used for various sports fields

- Zuzarte, Adriano Coutinho, Deon, KRUGER

  • Authors: Zuzarte, Adriano Coutinho , Deon, KRUGER
  • Date: 2014
  • Subjects: Ultraviolet radiation , Sports facilities
  • Type: Article
  • Identifier: uj:5061 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13624
  • Description: Since its induction at the Astrodome, in 1965 synthetic turf has been improved and adapted to now be accepted as a playing surface for a variety of sports. These sports include Rugby, Soccer and Field hockey. As synthetic turf is most likely destined for outdoor use it will be subject to Ultra Violet (UV) degradation in the form of Ultra Violet light band A (UVA), Ultra Violet light band B (UVB) or a combination of both. Synthetic turf is a polymer based material, specifically polyethylene for this study. For this reason it is useful to investigate how polyethylene degrades due to UV. Absorbed UV causes a break in the intermolecular bonds of the polyethylene, which leads to cracking, inhibiting the material to perform as initially intended. Colour change is also a consequence of extended exposure to UV. Various UV stabilizers are used, by manufacturers, in order to slow this process down. These however are largely dependent on the type of UV being exposed. Natural UV testing of new materials is time consuming, thus accelerated weathering testers such as the QUV/spray machines are used to simulate artificial UV and accelerate this process. A correlation between natural and artificial UV is sometimes difficult to achieve. For this reason both natural and artificial UV exposures were performed in this study. Through these various exposures to the samples, it was possible to indeed confirm that UV degrades synthetic turf as well as the processes leading to it. It was also confirmed that the samples would meet the sporting standards set out by the Internaltional Rugby Board (IRB), Fédération Internationale de Football Association (FIFA) and International Hockey Federation (FIH), for use as a playing surface. A correlation between natural and artificial UV in terms of colour change was achieved with UVA being found as thepredominant type of natural UV exposure in Johannesburg, during the winter months. Solutions were also provided to mitigate the degrading effects of UV on synthetic turf, these solutions would however need further investigation.
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Waste vegetable oils to biodiesel over Al₂O₃ –supported SnO₂ catalyst : effect of support pore size

- Zulu, Vusumuzi C., Vunain, Ephraim, Meijboom, Reinout, Jalama, Kalala

  • Authors: Zulu, Vusumuzi C. , Vunain, Ephraim , Meijboom, Reinout , Jalama, Kalala
  • Date: 2015-07-01
  • Subjects: Biodiesel , Waste vegetable oils
  • Type: Article
  • Identifier: uj:5132 , ISBN 9789881404701 , http://hdl.handle.net/10210/14098
  • Description: The main aim of this study was to investigate the catalytic properties of Al₂O₃-supported SnO₂ for the conversion of waste vegetable oil into biodiesel. The effect of support pore size on waste oil conversion was investigated at 100 and 200 °C by using α-alumina (with larger pore size) and γ-alumina (with smaller pore size) respectively as support for SnO₂. The effect of pore-size on conversion was found to depend on the operating temperature. At low temperature, i.e. 100 °C, higher conversion for waste vegetable oil was measured on SnO₂ catalyst supported on α-Al₂O₃ than the catalyst supported by γ-Al₂O₃. This effect became less significant at 200 °C. It was also observed that the oil conversion increased with an increase in reaction temperature and reaction time.
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Classification of defect formation during rotary friction welding of titanium alloy

- Zulu, M. C., Mashinini, P. M.

  • Authors: Zulu, M. C. , Mashinini, P. M.
  • Date: 2021
  • Subjects: Weld joint , Process parameters , Rotary friction welding
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/488315 , uj:44482 , Citation: Zulu, M.C. Mashinini, P.M.2021. Classification of defect formation during rotary friction welding of titanium alloy.
  • Description: Abstract: The weld defects are a constant problem to mechanical components of various applications. Defects may be the root cause of constant failure to critical components and may further create unsafe work environment in industries. Although friction welding process is a solid state welding technique, it is also susceptible to weld defects. The rotary friction welding of titanium alloy Ti-6Al-4V was conducted to investigate the formation of weld defects and their types. The microstructure analysis and visual inspection of weld joints was done to identify defects present in the welds of different welding parameters. Mechanical tests were also conducted to investigate the effect of defects in the properties of the weld joints. The common defects in rotary friction welding were observed. Flaws such as voids, excessive flash and discolouration were identified during the study and were linked to the unsuitable welding conditions. The tests conducted revealed that defects have a negative impact on the properties and quality of the weld joint. The relationship between defect and weld condition was studied. The study revealed that majority of the defects exist due to unsuitable combination of welding parameters utilised. Therefore, this paper presents the study of defects formation in the friction welding process of titanium alloy Ti-6Al-4V.
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Identity experiences of black people in the Netherlands

- Zonneveld, Renée, Brand, Susanne B.E., Adams, Byron G.

  • Authors: Zonneveld, Renée , Brand, Susanne B.E. , Adams, Byron G.
  • Date: 2017
  • Subjects: Identity , Identity experiences , Acculturation
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/260306 , uj:27406 , Citation: Renée Zonneveld, Susanne B. E. Brand & Byron G. Adams (2017) Identity experiences of black people in the Netherlands, Journal of Psychology in Africa, 27:2, 141-149. , DOI: https://doi.org/10.1080/14330237.2017.1301709
  • Description: Abstract: In this study, we used the tri-dimensional model of identity and acculturation strategies to explore how black people living in the Netherlands define themselves We used a qualitative survey design in which 14 participants (females = 8; age range 21 to 58) completed open-ended questions about their experiences of being black in the Netherlands Data was analysed using hermeneutic phenomenology in three steps: naive understanding, structural analysis, and comprehensive understanding We derived several main themes: Acceptance; Inclusion; Stereotypes; Social membership; Personspecific characteristics; Separation (Contributors); and Social Status We associated the themes Acceptance, Inclusion, and Separation (Contributors) with acculturation and acculturative strategies The other themes can be connected to the tri-dimensional identity model Social membership and Social status are related to the social and relational aspects of identity, while Person-specific characteristics can be linked to personal identity Lastly, the theme Stereotypes can be related to both acculturation and racism, but also personal identity as it shows how the participants perceive their self-concept to contradict the beliefs that mainstream Dutch society holds about them We conclude that identity construction among the black respondents was reliant on both their ethnic community membership and their membership of the mainstream Dutch community.
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A case study of induced current unbalance as a result of capacitor failure

- Zondi, S., Bokoro, P., Paul, B.

  • Authors: Zondi, S. , Bokoro, P. , Paul, B.
  • Date: 2015-01-28
  • Subjects: Point on wave switching , Transient voltage , Capacitor banks , Current unbalance
  • Type: Article
  • Identifier: uj:5143 , ISBN 978-0-86970-786-9 , http://hdl.handle.net/10210/14124
  • Description: Capacitor banks rated 132 kV/ 72 MVAr are installed at the Durban North Substation of Ethekwini municipality to compensate for inductive power losses. The POW or synchronous switching technique is used for on-line switching of these banks, in a bid to minimise high magnitude induced transient voltage and current. in this study, the voltage waveform records and the percentage current unbalance, measured on and six months post commissioning of the capacitor banks are analysed in order to test the effectiveness of POW switching method, when implemented with mechanically linked 3-phase, 3-pole SF6 circuit breakers. The results obtained indicate that within 6 months of commissioning, capacitive impedance of the banks failed, as result of high magnitude induced transient current and voltage, and the percentage unbalance level observed in the neutral current grew from 2.3% to 5.7%.
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In vitro and in vivo antiestrogenic effects of dichloromethane-methanol extract of Crateva adansonii DC

- Zingue, Stéphane, Fogang, Robinson Charly Mbe, Njuh, Amstrong Nang, Tchuidjou, Daniel, Tueche, Alain Brice, Ndinteh, Derek Tantoh, Njamen, Dieudonné

  • Authors: Zingue, Stéphane , Fogang, Robinson Charly Mbe , Njuh, Amstrong Nang , Tchuidjou, Daniel , Tueche, Alain Brice , Ndinteh, Derek Tantoh , Njamen, Dieudonné
  • Date: 2018
  • Subjects: Antiestrogenic , Crateva adansonii , E-screen assay
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/288124 , uj:31222 , Citation: Zingue, S. et al. 2018. In vitro and in vivo antiestrogenic effects of dichloromethane-methanol extract of Crateva adansonii DC. Indian Journal of Experimental Biology, 56:795-802.
  • Description: Abstract: Despite significant developments occurring in the treatment of cancer, it still remains the second deadly disease, responsible for 8.2 million deaths every year. Various natural substances have been studied for active molecules of tumor suppression in the past and the tropical flora, by its diversity, continues to provide new antitumor drugs. Crateva adansonii dichloromethane-methanol (DCM/MeOH) extract was previously reported to prevent breast tumors in Wistar rats. However, it exhibited weak cytotoxic effect in human MCF-7 cells. The present study, therefore, deals with the investigation of its estrogenic and antiestrogenic effects. In vitro estrogenicity and antiestrogenicity of C. adansonii DCM/MeOH extract were performed by E-screen assay. In vivo, the investigation was carried out using the 3 days uterotrophic assay in ovariectomized rats, a classical tool for the prediction of estrogenicity of chemicals. As a result, C. adansonii extract did not induce MCF-7 cells proliferation, which is an estrogenic hallmark. However, C. adansonii extract induced a significant (P <0.05) decrease in a concentration-dependent manner of the MCF-7 proliferation when co-administered with E2B. In vivo, no estrogen-like effect was observed following a 3-day treatment with C. adansonii extract in estrogen target organs. However, the co-administration of C. adansonii extract with E2V lead to decreased uterine wet weight (P <0.05), total protein levels in uteri (P <0.01) as well as uterine and vaginal epithelial heights (P <0.05) as compared to animals treated with E2V only. These results suggest that C. adansonii has antiestrogenic effects but not estrogenic effects, which might account for its previously observed antimammary tumour effects in rats.
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The influence of human investment on the performance of SMEs in the manufacturing sector, Harare, Zimbabwe

- Zindiye, S., Roberts-Lombard, M.

Zimbabwean female principals’ promotion of children’s rights in disadvantaged school contexts

- Zikhali, Joyce T., Perumal, Juliet Christine

  • Authors: Zikhali, Joyce T. , Perumal, Juliet Christine
  • Date: 2014
  • Subjects: Children’s rights , Child labour , Child abuse , Exploitation of children
  • Type: Article
  • Identifier: uj:6143 , ISBN 978-84-617-2484-0 , http://hdl.handle.net/10210/13186
  • Description: This is qualitative multiple case study explored the extent to which children’s rights are observed in five disadvantaged school contexts in Masvingo District in Zimbabwe. Data were collected through one-hour individual in-depth interviews. The participants comprised five school heads, four deputy school heads and three teachers-in-charge (TICs). Content analysis was used to analyse the data. The data revealed that a number of children’s rights were being flouted. The children’s families were generally poor as a result children did not have adequate time to rest and play as they helped to augment family income through working in the fields and vending. The schools lacked adequate facilities and furniture exposing children to discomfort and harsh weather conditions. Some guardians exploited resources meant for orphans for their personal use. Older boys at times sexually abused younger girls. Some teachers applied corporal punishment to school children. The study recommends that government set up programmes that educate the populace on children’s rights and the need to respect them. It should invest more resources and improve the conditions in disadvantaged schools. Needy children should be on payroll and should be placed in homes where the government working with other stakeholders could take care of them.
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Semantiese meerduidigheid in motiveringsnavorsing.

- Zietsman, S.H., Raubenheimer, I. van W.

  • Authors: Zietsman, S.H. , Raubenheimer, I. van W.
  • Date: 1979
  • Subjects: Semantic ambiquity , Pottas Need Questionnaire
  • Type: Article
  • Identifier: uj:6533 , http://hdl.handle.net/10210/2732
  • Description: The premise is made that semantic ambiguity, which is manifested in measuring instruments, could lead to controversial and divergent research results often reported in studies on work motivation. Researchers, the literature indicates, are largely unaware of this phenomenon. In this investigation no studies were found in which semantic ambiguity in questionnaires had been controlled. In order to demonstrate the existence of semantic ambiguity as a phenomenon, a semantic differential was administered to 38 Industrial Psychology students in order to measure the meaning of the items on the Pottas Need Questionnaire. The results indicated that six of the 13 questionnaire items differed significantly from the need categories they purported to measure, which confirmed the notion that semantic ambiguity is a source of variance that should be controlled.
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Achieving high-efficiency conversion and poly-generation of cooling, heating, and power based on biomass-fueled SOFC hybrid system : performance assessment and multi-objective optimization

- Zhu, Pengfei, Yao, Jing, Guo, Leilei, Dai, Min, Ren, Jianwei, Kurko, Sandra, Wu, Zhen, Yang, Fusheng, Zhang, Zaoxiao

  • Authors: Zhu, Pengfei , Yao, Jing , Guo, Leilei , Dai, Min , Ren, Jianwei , Kurko, Sandra , Wu, Zhen , Yang, Fusheng , Zhang, Zaoxiao
  • Date: 2021
  • Subjects: Biomass energy , SOFC hybrid system , Thermodynamic analysis
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/481290 , uj:43605 , Citation: Zhu, P. et al. 2021. Achieving high-efficiency conversion and poly-generation of cooling, heating, and power based on biomass-fueled SOFC hybrid system : performance assessment and multi-objective optimization.
  • Description: Abstract: In order to develop clean and efficient energy conversion technology, a novel combined cooling, heating and power (CCHP) system using biomass as fuel is proposed in this work. The proposed CCHP system consists of biomass gasification unit, solid oxide fuel cell (SOFC) and engine power generation unit and absorption refrigeration unit. Thermodynamic model of the CCHP system is developed for the parametric and exergy analyses to evaluate the performance. The parametric analysis shows that increasing the steam to biomass ratio or the SOFC fuel utilization factor helps to improve the electrical efficiency, while the increase of air equivalent ratio has a negative effect. The exergy analysis shows that the two units of biomass gasification and engine power generation have the largest exergy destruction ratio, which is 46.9% and 16.8% under the biomass flux of 500 kg·h -1 . This is because these two units involve in high-temperature thermochemical reaction process, resulting in relatively large exergy destruction. Besides, the tradeoff between maximum exergy efficiency, CCHP efficiency and minimum total annual cost is conducted by multi-objective optimization. Through optimization, the system could reach the high CCHP efficiency of 75 % and net electrical efficiency of 52%, as well as the low total annual cost of 410 k$ simultaneously. This work could provide the basic design idea, and high-efficiency and low-cost operation strategy for the practical application of the proposed novel biomassfueled CCHP poly-generation system.
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Numerical investigation of a silicon six-wafer microcombustor under the effect of heat loss through the outer walls

- Zhu, Lin, Jen, Tien-Chien, Kong, Xiao-Ling

Feasibility and effectiveness of heat pipe cooling in end milling operations : thermal, structural static, and dynamic analyses : a new approach

- Zhu, Lin, Jen, Tien-Chien, Yen, Yi-Hsin, Kong, Xiao-Ling

  • Authors: Zhu, Lin , Jen, Tien-Chien , Yen, Yi-Hsin , Kong, Xiao-Ling
  • Date: 2011
  • Subjects: Heat pipes , Heat pipe cooling
  • Type: Article
  • Identifier: http://ujcontent.uj.ac.za8080/10210/384755 , uj:5288 , http://hdl.handle.net/10210/14957
  • Description: In this paper, the feasibility and effectiveness of heat pipe cooling in end milling operations are investigated. A new embedded heat pipe technology was utilized to remove the heat generated at the tool-interface in end milling processes. Numerical studies involved four cases, including dry milling, fluid cooling, heat pipe cooling, and heat pipe cooling with cutting fluid supplied. The thermal, structural static, and dynamic characteristics of the endmill were investigated using a numerical calculation with fast finite element plus solvers based on explicit finite element analysis software. The results demonstrate that the heat pipe end-mill is most feasible and effective in the actual end milling processes
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Structural design of a silicon six-wafer micro-combustor under the effect of heat transfer boundary condition at the outer walls

- Zhu, Lin, Jen, Tien-Chien, Zhu, Mei, Yin, Cheng-Long, Kong, Xiao-Ling

  • Authors: Zhu, Lin , Jen, Tien-Chien , Zhu, Mei , Yin, Cheng-Long , Kong, Xiao-Ling
  • Date: 2010
  • Subjects: Micro-combustors , Heat transfer
  • Type: Article
  • Identifier: uj:5281 , http://hdl.handle.net/10210/14950
  • Description: The aim of this investigation was to establish a methodology for designing highly stressed micro fabricated structures by studying the structural design issues associated with a silicon six–wafer micro combustor under the effect of heat transfer boundary condition at the outer walls. Some experimental and numerical simulation results have indicated that the flame can not be sustained in the micro combustor if the poor heat transfer coefficients at the outer wall are present. This could cause the combustor wall temperature higher than the auto ignition temperature of reactants and results in the upstream burning. Since silicon has relatively poor high temperature strength and creep resistance when the temperature is above the brittle to ductile transition temperature (BDTT), e.g. 900K, the combustion in the recirculation jacket could possibly damage the micro combustor due to the high wall temperature.
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Experimental analyses to investigate the feasibility and effectiveness in using heat pipe-embedded drills

- Zhu, Lin, Jen, Tien-Chien, Yin, Cheng-Long, Kong, Xiao-Ling, Yen, Yi-Hsin

  • Authors: Zhu, Lin , Jen, Tien-Chien , Yin, Cheng-Long , Kong, Xiao-Ling , Yen, Yi-Hsin
  • Date: 2012
  • Subjects: Heat pipe cooling , Drilling , Heat pipes
  • Type: Article
  • Identifier: uj:5289 , http://hdl.handle.net/10210/14958
  • Description: This paper presents an experimental investigation to verify the feasibility and effectiveness of heat pipe cooling in drilling operations. The basic idea is to insert a heat pipe at the center of the drill tool with the evaporator close to the drill tip and the condenser at the end of the drill. Consequently, the heat generated at the tool–chip interface can be removed by convection heat transfer. Experimental studies were involved in three cases, including solid drill without coolant, solid drill with coolant, and heat pipe drill. Drilling tests were conducted on a CNC machining center with full immersion cutting. The cast iron square block was used as the workpiece, and the high-speed steel was chosen for the drill tool material. Flank wear is considered as the criterion for tool failure, and the wear was measured using a Hisomet II Toolmaker’s microscope. The tests were conducted until the drill was rejected when an average flank wear greater than 0.10 mm was recorded. The results demonstrate that using a heat pipe in the drilling process can effectively perform thermal management comparable to the flooding coolant cooling used pervasively in the manufacturing industry, extending the tool life of the drill.
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