Discharging performance of a forced-circulation ice thermal storage system for a permanent refuge chamber in an underground mine

doi:10.1016/j.applthermaleng.2016.08.192

Applied Thermal Engineering

Volume 110, 5 January 2017, Pages 703-709

https://doi.org/10.1016/j.applthermaleng.2016.08.192 Get rights and content

Highlights

•
Thermal analysis of an ice thermal storage system for a permanent refuge chamber.
•
Experimental measurements used to provide and validate a correction factor.
•
Correlation developed between transient discharging power and remaining ice fraction.
•
Minimum cooling requirement satisfied via automatic control through correlation.
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Operational duration of system maximized via automatic control.

Abstract

This study aimed to develop a proper control strategy for a forced-circulation ice thermal storage system (ITSS) designed for a permanent refuge chamber with an accommodation capacity of 50 persons. The heat transfer characteristics of the ITSS were investigated through theoretical and experimental approaches. A quasi-steady one-dimensional mathematical model for predicting the transient discharging power was proposed. On this basis, a control strategy was proposed to fulfill the minimum cooling requirement in consideration of both effective discharging time and human comfort. The minimum required velocity of the ITSS was analyzed; from this, the effective working time of the ITSS was determined to be 64.57 h. Additionally, the heat load inside the chamber was found to be the main factor that affected the effective temperature control duration and the utilization ratio of the ice. Thus, a reserve factor, which is defined as a function of rated heat load and determined by the discharging performance model, is suggested for consideration during optimization.

Introduction

Refuge alternatives, which provide a well-sealed environment for isolating miners from a potentially toxic or high-temperature environment during a mine emergency, facilitate escape for miners trapped underground by fire, explosion, or rock collapse. Recently, two types of refuge alternatives, mainly classified by accommodation capacity—portable shelters/chambers and permanent chambers/stations—have been used in underground mines. A reliable environmental control and life support system (ECLSS), which contains sufficient breathable oxygen, reasonable air scrubbing, adequate food and water, and a temperature control system, is needed to sustain miners’ lives while they await rescue. Considering the specifics of underground emergencies, technologies with low energy consumption are preferred [1], [2].

For temperature control within the refuge space, there are generally two kinds of strategies. In one strategy, fresh air is supplied from the ground through compressed air lines or boreholes; this method can aptly control both air quality and temperature, but air lines may be destroyed in an emergency [3]. Alternatively, refrigeration equipment that uses phase-changing materials, such as the ice thermal storage system (ITSS), have widely been applied [4].

ITSSs, which utilize the latent heat of fusion of water, have been extensively researched by predecessors in the context of energy saving buildings both for charging and discharging processes, with the ultimate aim of a more efficient, stable, and economic system [5], [6], [7], [8], [9]. Several configurations, such as ice-on-coil or encapsulated ice, have been developed and continually optimized in recent years. To utilize the stored energy of an ITSS, there are generally two typical methods: external melt or internal melt. Jia et al. [4] studied and developed an ice storage capsule that utilizes natural convection; it was an application of the external melt method in a refuge chamber. The experimental results demonstrated that the capsule is sufficient for eliminating the additional heat generated by four persons inside a refuge chamber.

This work focused on the discharging performance of an internal-melt-type ITSS operating under forced circulation, which is more applicable for high heat-load scenarios in permanent stations. Several studies have observed and reported that the cooling discharge rate decreases with the melting process over time [10]. Thus, it is important to determine the heat transfer characteristics of ITSSs, as they are fundamental for further optimal design. Various heat transfer models considering particular conditions have been proposed, and Oró et al. [11] summarized them well. However, these models, which are composed of basic parts that come from classical empirical formulas and correctional parts for particular configurations or application conditions, are not universal.

In this study, with the final aim of developing a proper control strategy for an ITSS for a permanent refuge station, the heat transfer characteristics of an ITSS were theoretically and experimentally studied. Then a quasi-steady one-dimensional mathematical model was developed to reveal the evolution of the instantaneous discharging performance of the system. On this basis, a control strategy for the ITSS is proposed to fulfill the minimum cooling requirement in consideration of both effective discharging time and human comfort. The method used in the study is also applicable for discharging performance determination and control strategy development for forced-circulation ITSSs with different configurations in refuge chamber applications.

Section snippets

Theoretical model for discharging performance

The ITSS targeted in this study is a stainless steel structure (shell material: SUS304; 4-mm thickness), with external dimensions of 2.5 m (Length) × 1.5 m (Width) × 2.0 m (Height), and isolated by thermal insulation with a wall thickness of 50 mm. Thus, the heat leak through the wall is neglected. The total ice storage capacity (V_s) is 5.345 m³. An annular rectangular air duct was designed with a cross-section dimension of 300 mm (Width) × 250 mm (Height) and an approximate total length (L_d) of 7.778 m, as

Materials and methods

Experiments were performed using the system shown in Fig. 1 to evaluate the discharging performance under two outlet speeds (5.97 m/s ± 0.114 m/s, and 7.89 m/s ± 0.146 m/s as measured) and modify the model derived in the previous section. A supervisory control and data acquisition (SCADA) system, which consisted of a temperature inspecting instrument (Type: STI-AS; measurement accuracy: 0.2% F.S), platinum resistance temperature detectors (PRTD) (Type: WZP–Pt100; range: −50 °C to 200 °C; error: ±0.15 °C),

Application and discussion

The heat load (Q_hl) inside the refuge chamber was composed of two parts: human metabolic heat output and heat output of chemical reactions in the air scrubbing system [30]. Simply considering the cooling demand, the following inequality should be satisfied within the operating duration of the ITSS: $Q ⩾ Q_{hl} .$

From the above experimental and theoretical analysis, it is known that the instantaneous Q, which varied with η and T_in, is much higher at the initial stage and dropped significantly during the

Conclusion

Through experiment and theoretical analysis, the following conclusions were drawn:

(1)
A discharging performance model was developed for the ice thermal storage system of a refuge chamber and verified by good agreement between experimental and predicted output temperatures.
(2)
The discharging power of the ITSS achieved its peak at the very beginning of operation and decreased sharply within approximately the first two hours; then, its variation subsided with the ongoing melting of ice. A significant

Acknowledgements

This work was supported by the Ministry of Science and Technology of China through Project No. 2011BAK09B04 and No. 2012BAK09B07 under the National Key Technology Research and Development Program during the 12th Five–year Plan Period.

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Research PaperDischarging performance of a forced-circulation ice thermal storage system for a permanent refuge chamber in an underground mine

Highlights

Abstract

Introduction

Section snippets

Theoretical model for discharging performance

Materials and methods

Application and discussion

Conclusion

Acknowledgements

Saf. Sci.

Saf. Sci.

Appl. Therm. Eng.

Prog. Energy Combust. Sci.

Renew. Sustain. Energy Rev.

Renew. Sustain. Energy Rev.

Renew. Sustain. Energy Rev.

Energy Build.

Exp. Therm. Fluid Sci.

Appl. Energy

Renew. Sustain. Energy Rev.

Appl. Therm. Eng.

Energy Build.

Int. J. Heat Mass Transf.

Renew. Energy

Appl. Therm. Eng.

Research Paper
Discharging performance of a forced-circulation ice thermal storage system for a permanent refuge chamber in an underground mine