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

Numerical Simulation of Tidal Currents in an Island Basin with Variational Boundaries

In this paper, we describe a numerical model that is called “the crevice method” using a triangular mesh difference to simulate tidal currents in an island basin with a large area of beach ; the land boundaries move with the shift of the tide, and with geometrically complex boundaries. This model is based on shallow water momentum and continuity equations. For simulating variational boundaries, crevices which are artificially imagined are erected all over the shallows where the bed elevations are not lower than the lowest tidal level and where the water depth in the crevices changes with the ascent and descent of the tidal levels. For simulating a flow field within geometrically complex island boundaries, especially in flow circumstances near the islands, the triangular mesh difference is adopted in this model. The second derivative of u, ν and ζ with respect to time and the semi-implicit scheme are used in the triangular mesh difference for the purpose of increasing stability and accuracy, Practical calculation of tidal currents shows that this model has the advantages of better stability, higher accuracy, shorter calculation time, and it saves computer memory. The calculated results coincide reasonably with the measured ones

Kropina metrics with isotropic scalar curvature

In this paper, we study Kropina metrics with isotropic scalar curvature. First, we obtain the expressions of Ricci curvature tensor and scalar curvature. Then, we characterize the Kropina metrics with isotropic scalar curvature on by tensor analysis

Analysis of Nursing Care of Acute Myocardial Infarction

Objective: To investigate and improve the clinical nursing care method of acute myocardial infarction. Methods: Make a retrospective analysis of the clinical data for 69 cases of acute myocardial infarction from January 2009 to December 2012 in our hospital and summarize the clinical nursing method. Results: 63 from 69 patients are improved after being rescued and nursed through the above-mentioned method, and improvement rate was 92.0%. 5 patients were died (all of them were died from the heart failure), which the mortality is 8.0%. Wherein the complicated arrhythmia cases were 24, the complicated cardiogenic shock cases were 12, hospitalization time: 4‒17 days, and the average hospitalization time is 9.2 days. Conclusion: The strengthened nursing cooperation of acute myocardial infarction for patients may enhance clinical improvement rate and improve the prognosis

Modeling spatial-temporal change of Poyang Lake marshland based on an uncertainty theory - random sets

AbstractUncertainty modeling now engages the attention of researchers in spatial temporal change analysis in remote sensing. Some studies proposed to use random sets for modeling the spatial uncertainty of image objects with uncertain boundaries, but none have considered the parameter determination problem for large datasets. In this paper we refined the random set models for monitoring monthly changes in wetland vegetation areas from series of images. Twelve cloud-free HJ-1A/1B images from April 2009 to March 2010 were used for monitoring spatial-temporal changes of Poyang Lake wetlands. We applied random sets to represent spatial uncertainty of wetland vegetation that were extracted from normalized difference vegetation index (NDVI) maps. Time series of random sets reflect the seasonal differences of location and extents of the wetlands, whereas degree of uncertainties indicated by SD and CV indices reflect the gradual change of the wetland vegetation in space. Results show that the uncertain extents of wetland vegetation change through the year, achieving the largest range and uncertainty degree in autumn. This coincides with the highly heterogeneous vegetation status in autumn, since the wetland recovers gradually after flooding and young vegetation emerges at gradually changing densities, thus providing forage in different ecological zones for different types of migratory birds. We conclude that the random set model enriches spatial-temporal modeling of phenomena which are uncertain in space and dynamic in time

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

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