Cold storage condensation heat recovery system with a novel composite phase change material

© 2016 Elsevier Ltd. Using condensation heat from cold storage refrigeration systems to provide heat for domestic hot water preparation and industrial hot water supply promotes energy conservation. However, few studies have investigated cold storage condensation heat recovery using phase change materials (PCMs). In this study, a cold storage condensation heat recovery system that uses PCMs has been designed and analysed. According to the principle of energy cascade recycling, different operation modes could be effectively switched to recycle condensation heat. Furthermore, a novel and suitable phase change composite material is developed for cold storage condensation heat recovery, which has a relatively large latent heat, high thermal conductivity, and an appropriate phase change temperature (i.e. 80 °C). With carnauba wax (CW) as the PCM and expanded graphite (EG) as the additive, a composite was developed with an optimal mass ratio of CW:EG = 10:1. The thermal and physical properties and the interior structure of the composite were then investigated using a scanning electron microscope (SEM), thermal constants analyser (Hot Disk), differential scanning calorimeter (DSC), and Fourier transform infrared spectrometer (FT-IR). Furthermore, experiments on the melting and solidification processes and accelerated thermal cycling were also conducted. It was found that at the optimal mass ratio of 10:1, the temperatures of the CW/EG composite in the melting and solidification processes were 81.98 °C and 80.43 °C, respectively, while the corresponding latent heats were 150.9 J/g and 142.6 J/g, respectively. During both processes, CW could retain its original worm-like structure after being completely adsorbed by EG. Compared to only CW, the melting and solidification time of the CW/EG composite were reduced by 81.7% and 55.3%, respectively, while its thermal conductivity was 16.4 times higher. After 1000 runs of accelerated thermal cycling, the endothermic/exothermic phase change temperatures of CW and the CW/EG composite increased by only 0.42%/0.42% and 0.23%/0.27%, respectively, while their endothermic/exothermic latent heats decreased by 4.96%/4.78% and 2.05%/3.44%, respectively. These results indicate that both CW and the CW/EG composite have excellent thermal reliability, while the CW/EG composite exhibits a slightly better performance. Finally, the experiments show that the CW/EG composite has desirable thermal and physical properties such as high thermal conductivity and reliability; Hence, it has good potenti al as a material for facilitating condensation heat recovery from cold storage refrigeration systems

Thermal storage/management system with phase change materials for building

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Coupled Cooling Method and Application of Latent Heat Thermal Energy Storage Combined with Pre-cooling of Envelope: Optimization of Pre-cooling with Intermittent Mode

This document is the Accepted Manuscript version of the following article: Xiangkui Gao, Yanping Yuan, Hongwei Wu, Xiaoling Cao, and Xudong Zhao, ‘Coupled cooling method and application of latent heat thermal energy storage combined with pre-cooling of envelope: Optimization of pre-cooling with intermittent mode’, Sustainable Cities and Society, Vol. 38: 370-381, April 2018. Under embargo until 10 January 2019. The final, definitive version of this paper is available online via: https://doi.org/10.1016/j.scs.2018.01.014The coupled cooling method combining latent heat thermal energy storage and pre-cooling of the envelope (PE) is a new free-cooling method that is suitable for exposure to high temperatures and other types of harsh environments. PE plays the most critical role in the coupled cooling method. Long-term, continuous PE cannot only reduce energy storage capacity, but it also causes numerous energy waste. Thus, an intermittent operational mode is firstly proposed to improve the heat transfer performance and reduce energy consumption. A simplified numerical model of intermittent thermal storage is established, and the subsequent effects of intermittent ratio (IR) and intermittent period (IP) on cold storage performance have been systematically investigated. Furthermore, the operational period is divided into a cold storage period (CSP) and a cold preservation period (CPP), each with their own respective evaluation indices. Long-term intermittent PE is optimized, and an interchanging continuous/intermittent cold storage strategy is proposed. Under the current operating conditions, as compared with the conventional continuous mode, the duration of CSP is extended by 0–26%, yielding an annual cold storage energy consumption reduction of 68–78%. Thus, the current study demonstrates the significant potential of intermittent operational mode application in underground thermal energy storage systems.Peer reviewedFinal Accepted Versio

Risk Factors of HIV and Other Sexually Transmitted Infections in China: A Systematic Review of Reviews.

BACKGROUND: Sexually Transmitted Infections (STIs) are a global challenge. China, once said to have eradicated STIs, is now facing a rapid rise in the prevalence of HIV/STIs. This review of reviews aims to map HIV/STI risk factors among the Chinese population, with the objective of identifying risk factors to inform the formulation of effective prevention strategies. METHODS: A systematic search using key terms related to HIV/STIs, risk factors and the Chinese population in both English and Chinese databases (PubMed, PsycINFO, the Cochrane Library; Wanfang data, CNKI, VIP and SINOMED) was conducted, and peer-reviewed systematic reviews on the topic from 1991 to 2014 were selected. Identified risk factors were grouped into different level determinants based on the HIV Social Epidemiology Model, and then evaluated and reported based on the PRISMA checklist. FINDINGS: Of the twenty-eight reviews included, the majority were focused on well-established, individual level risk factors within key populations, with some highlighting the complexity of interacting factors (e.g., alcohol use and higher income in male migrants). While twenty-two reviews covered individual factors, only ten mentioned social factors and five had contents on structural factors. There are gaps in the evidence on social and structural level impacts of HIV/STIs, such as on stigma, discrimination, health policy, access to care, and illicit drug control policies. Migration and social expectation appear to pose a significant threat in aggravating the HIV/STI situation in China; for example, incarceration patterns indicated a significant risk of HIV/STIs for female sex workers. CONCLUSIONS: Since international guidelines recommend an integrated and multi-level approach to HIV/STI prevention, a comprehensive approach targeting interventions at all levels along the continuum of care is needed to effectively curtail HIV/STI transmission in China. More research is needed to better understand the impact of socio-political interventions within a Chinese context

Localized Ridge Wrinkling of Stiff Films on Compliant Substrates

Wrinkling of thin stiff films on thick compliant elastomeric substrates subject to plane strain compression is considered for cases in which the substrate is pre-stretched prior to film attachment. Advanced wrinkling modes are investigated that evolve as the systems are compressed beyond the onset of the primary sinusoidal wrinkling mode. If the substrate pre-stretch is greater than about 40%, an advanced mode in the form of a series of well-spaced ridges separated by relatively flat film is observed in the simulations. Our experiments reveal a localization mode in the form of alternating packets of large and small amplitude wrinkles, but not ridges, while ridge formation has been observed in other recent experiments. Measurements of undulation amplitudes have been made for wrinkle fields of stiff films formed by oxidation of the surface of pre-stretched PDMS substrates. Simulations have been performed with a finite element model and an analytical film/substrate model. The formation of the ridge mode is a consequence of the altered nonlinearity of the substrate produced by the pre-stretch. The role of the tangential substrate stiffness in suppressing localization at the ridges is also highlighted. If there is no substrate pre-stretch, or if the substrate is pre-compressed, the primary sinusoidal mode gives way to an entirely different sequence of advanced modes usually entailing period doubling followed by folding. The nature of substrate nonlinearity that leads to ridges or folds is discussed.Engineering and Applied Science

Coupled Cooling Method and Application of Latent Heat Thermal Energy Storage Combined with Pre-cooling of Envelope: Sensitivity Analysis and Optimization

This document is the Accepted Manuscript version of the following article: Xiangkui gao, Yanping Yuan, Hongwei Wu, and Xudong Zhao, ‘Coupled Cooling Method and Application of Latent Het Thermal Energy Storage Combined with Pre-cooling of Envelope: Sensitivity Analysis and Optimization’, Process Safety and Environmental Protection, first published online 9 March 2017. Under embargo. Embargo end date: 9 March 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ The version of record is available online at doi: http://dx.doi.org/10.1016/j.psep.2017.03.005 © 2017 Elsevier Ltd. All rights reserved.Cooling system for mine refuge chamber provides comfortable environment for miners to avoid heat damage. The existing cooling systems have their own application scopes and limitations. The coupled cooling method of Latent Heat Thermal Energy Storage (LHTES) combined with Pre-cooling of Envelope (PE) is a new free cooling method which is suitable for high-temperature, passive, impact and other harsh environment. Then, to improve the thermal comfort and reduce energy consumption, the effect of the pre-cooling temperature, melting temperature of PCM, aspect ratio and amounts of PCM unit on the indoor temperature are investigated in a systematic manner. Furthermore, the system is optimized and the generalized results for the evaluation parameter are given. Analysis of the results may lead to following main conclusions: (i) the method really controls the indoor temperature and the saving amount of PCM is more than 50% compared to the traditional LHTES systems; (ii) the Temperature Control(TC) performance of PCM would drop significantly if it melts more than 80%; (iii) under current operating conditions, the optimal melting temperature is about 29 °C and the aspect ratio of PCM unit is 60:500; (iv) per 1 °C the pre-cooling temperature dropped, 19% the actual amount of PCM decreased for the case studied.Peer reviewedFinal Accepted Versio

Synergistic Effects of Serum Uric Acid and Cardiometabolic Risk Factors on Early Stage Atherosclerosis: The Cardiometabolic Risk in Chinese Study

Objective: To comprehensively examine the associations of serum uric acid (SUA) with central and peripheral arterial stiffness in Chinese adults, and particularly assess the interactions between SUA and other cardiometabolic risk factors. Methods: The study included 3,772 Chinese men and women with carotid radial pulse wave velocity (crPWV), carotid femoral PWV (cfPWV), carotid artery dorsalis pedis PWV (cdPWV) and SUA measured. Results: After adjustment for age, sex, and BMI, the levels of SUA were significantly associated with increasing trend of cfPWV, crPWV and cdPWV (P for trend <0.0001). Further adjustment for heart rate (HR), blood pressure (BP) and lipids attenuated the associations with crPWV and cdPWV to be non-significant (P = 0.1, P = 0.099 respectively), but the association between SUV and cfPWV remained significant (P = 0.004). We found significant interactions between SUA and HR or BP in relation to cfPWV (P for interaction = 0.03, 0.003 respectively). The associations between SUA and cfPWV were more evident among individuals with higher HR or normal BP than those with lower HR or hypertension. Conclusions: SUA was associated with elevated aortic arterial stiffness in Chinese adults, independent of conventional cardiovascular risk factors. BP and HR might modify the deleterious effects of SUA