Thermal Storage Cycle Research Articles

Chemical Characterization and Genesis of Thermal Reservoir Water in the Southern Part of the Jizhong Depression

The Jizhong Depression is a typical Mesozoic and Cenozoic fault basin located in the northwestern part of the Bohai Bay Basin that has abundant hydrothermal and geothermal resources and enormous development potential. In this study, hydrochemical and isotopic analyses were conducted on water samples from the southern region of the Jizhong Depression. The formation and evolution processes of the deep geothermal water were analyzed, the circulation process of the deep geothermal water was determined, and the genetic mechanism of the geothermal systems was elucidated. The hydrochemical types of the geothermal fluids in the sandstone reservoirs in the research area are mainly Cl·HCO3−Na type, while the geothermal fluids in the carbonate reservoirs are mainly Cl-Na type and Cl·HCO3−Na type. The ion components in the geothermal water are mainly controlled by the dissolution of the carbonate rocks and the alternate adsorption of cations. The elevation of the geothermal water supply area is 763–1063 m, and the main source is precipitation from the mountainous areas in the western Taihang Mountains. The Na-K-Ca temperature scale and multi-mineral equilibrium method have relatively small errors and are suitable for the southern region of the Jizhong Depression, with average errors of 21.44 °C and 32.64 °C, respectively. The depth of the Jxw thermal storage cycle in the research area is 3033–5187 m, and the depth of the Ng thermal storage cycle is 1360–2862 m. The content of the main ions (Na+, K+, and Cl−) in the water samples of the study area is greater in the Jxw thermal storage than in the Ng thermal storage; the Jxw thermal storage water samples have lower γNa+/γCl− values than the Ng thermal storage; and the γSO42−/γCl− and γCl−/(γHCO3− + CO32−) values are greater than those of the Ng thermal storage, indicating that the Jxw thermal storage is located in a geological environment with better sealing, longer flow, slower water circulation, more complete leaching, and higher salinity than the Ng thermal storage. Part of the deep thermal storage is transmitted upwards through the rocks via thermal conduction, and part is transmitted upwards along fault channels via thermal convection, forming a convection–conduction-type geothermal system.

Effects of time and temperature of storage on chemical and nutritional characteristics of raw milk for Provolone Valpadana PDO cheesemaking: a multivariate approach.

We evaluated the possibility of increasing the storage temperature of raw milk for Provolone Valpadana cheesemaking, to identify the most suitable conditions of time and temperature for a pre-maturation process. We used Principal Component Analysis (PCA) to analyze the overall effects of different storage conditions on chemical, nutritional and technological characteristics of the raw milk. Four different thermal storage cycles, two at fixed temperature/time (6 and 12°C for 60 h) and two with two-phase thermal cycle (10 and 12°C for 15 h, followed by refrigeration at 4°C for 45 h) were studied. Although a moderate heterogeneity among raw milks from the 11 producers of Provolone Valpadana cheese was observed, PCA revealed the critical aspects of the extreme storage conditions (60 h of refrigeration). Some samples resulted in anomalous behaviors, probably related to unexpected fermentation phenomena occurring with increasing storage temperature. The acidification and the increase in the contents of lactic acid, soluble calcium, and degree of retinol isomerization observed in the anomalous samples can compromise the technological functionality of milk. Conversely, the storage with a two-phase thermal cycle did not lead to variations in any measured characteristic, suggesting that mild refrigeration conditions (10 or 12°C for 15 h followed by 4°C for 45 h) could be a good compromise in favoring milk pre-maturation without altering its quality characteristics.

Thermodynamic evaluation of three-phase absorption thermal storage in humid air with energy storage density over 600 kWh/m3

Thermal energy storage based on the sorption process is promising for long-term solar energy and waste heat storage. Aiming at higher ESD (energy storage density), the three-phase absorption process combining vapor absorption and solution crystallization is gaining increasing attention. However, the crystals blocking and long-term vacuum maintenance make the system design challenging. To address these issues, an open three-phase absorption thermal storage cycle is proposed in this paper, which is suitable for the complete crystallization process without vacuum operation. A comprehensive thermodynamic analysis of the proposed cycle for heating was carried out with different working pairs. To understand the thermodynamic processes in solution and humid air simultaneously, combined psychrometric diagram is adopted. Under operating conditions of 80 °C charging temperature, 80% charging humidity and 10 °C temperature lift, the proposed cycle with LiCl-H2O was the best choice with ESD of 670 kWh/m3, which is higher than that of LiBr-H2O (273 kWh/m3) and CaCl2-H2O (590 kWh/m3) cycles. Cycle comparison showed that the ESD of the proposed cycle is 2.0 and 3.3 times higher than that of the closed cycle and conventional open cycle, respectively. Besides, with a lower discharging relative humidity of 60% and higher temperature lift of 18 °C, comparable high ESDs of 639–657 kWh/m3 could still be maintained. With high energy storage density and easy operation, the proposed cycle is promising for future practical applications.

Combining suspended radiant ceiling with diffuse ventilation – Numerical performance analysis of low-energy office space in a temperate climate

The development of low energy buildings present new opportunities to develop HVAC products that works well with renewable energy sources. In this paper, we present a novel comfort system that combines a full radiant ceiling with diffuse ventilation into one flexible ceiling solution, HVACeiling. The purpose of the paper is to investigate how the combination changes heating and cooling performance and how the thermal storage cycle of the exposed slab in the closed plenum affects energy consumption and thermal comfort. The heating and cooling performance was investigated numerically in IDA ICE with daily based occurrence temperatures and compared to a reference with a radiant ceiling and mixing ventilation. The HVACeiling was a perforated gypsum board with pipes embedded that is used for diffuse ventilation and acoustical absorption as well as a radiant ceiling. Water was circulated day and night at fixed supply temperatures of 20–22 °C without any other controls. The convective surface heat transfer coefficients of the plenum was modelled in a preliminary CFD study and compared to literature and experiments. It was found that for daily based occurrence scenarios, with outdoor temperature in the range 23–28 °C, the heat exchange from the ceiling was increased 5–16% compared to the reference. The studies also disclosed improved thermal comfort, up to 1.5 °C lower peak operative temperature in the occupied zone down from 27.2 °C. This implies that thermal comfort is easier achievable with the HVACeiling, even with a small temperature offset that is well suited for renewable sources.

Conceptualization and analysis of a novel combined sorption and phase-change material thermal storage system

Abstract A new sorption-based thermal storage cycle is proposed. Energy is stored chemically by separating the constituents of highly non-ideal solutions, yielding much lower stand-by losses than in conventional approaches. The cycle avoids limitations of previously proposed sorption-based storage cycles by using a liquid-liquid mixer, and does not require a thermal source during discharge. A criterion based on a second law analysis is developed to evaluate potential working fluids for the cycle. Different cycle configurations are analyzed. An enhanced combined sorption and phase-change material (PCM) cycle is also investigated and compared with conventional thermal storage systems. For delivering 100 GJ of energy after 8 months, the combined cycle has an efficiency of 11% and lower storage volumes (down to 0.1 ×) than conventional thermal storage technologies. The energy density of the combined sorption-PCM system is 30 kWh m − 3.

Absorption seasonal thermal storage cycle with high energy storage density through multi-stage output

Absorption thermal storage is attractive due its small thermal loss during long term storage, which is advantageous for seasonal solar thermal storage. For the long term storage, high energy storage density is favorable to ensure a compact system. In this paper, the novel absorption seasonal thermal storage cycles with multi-stage output processes are proposed. Comparing to the conventional cycle with single stage output, larger concentration glide could be achieved by the proposed cycles under the same condition, resulting in high energy storage density. Performances of the water-LiBr absorption thermal storage cycles with double stage output and triple stage output are calculated and compared with that of the conventional single stage cycle. Energy flows, effects of temperature parameters, and working pair comparison are analyzed. For typical condition of solar thermal charging in summer and heat output in winter with output temperature of 50 °C, the proposed cycles with double stage output and triple stage output have 75.4% and 82.3% less heat losses, and achieve 7.32 times and 6.78 times higher energy storage densities than the single stage cycle. The proposed absorption thermal storage cycle with multi-stage output could be a good option for seasonal solar thermal energy storage.

Experimental and numerical investigation of combined sensible–latent heat for thermal energy storage at 575 °C and above

The design, testing, and modelling of a high-temperature thermocline-type thermal energy storage (TES) are presented. The TES concept uses air as the heat-transfer fluid and combines sensible and latent heat for stabilizing the discharging outflow air temperature. A 42kWhth lab-scale prototype of 40cm diameter was fabricated, containing a 9cm high layer of encapsulated phase change material (AlSi12) on top of a 127cm high packed bed of sedimentary rocks with a mean diameter of about 3cm. A two-phase transient heat transfer model of the thermal storage cycle was numerically formulated and experimentally validated with measured thermoclines during charging and discharging obtained with the lab-scale prototype. The thermal inertia of the experimental setup and the radial variation of void fraction due to the small tank-to-particle diameter ratio affected the validation process. The outflow air temperature during discharging was stabilized around the melting temperature of AlSi12 of 575°C. The thermal losses stayed below 3.5% of the input energy for all the experimental runs.

Heat Flow through Soils and Effects on Thermal Storage Cycle in High-Mass Structures

The solar radiation absorbed in massive building components is stored and later emitted as long-wave thermal radiation into the interior space. Heat storage capacity is directly related to the mass of the building envelope surrounding this space and particularly that of high-mass, homogeneous earthen or cementitious material. A thermal storage cycle is created by the time-lag effect if sufficient mass is available. A similar strategy applied to the lunar and/or Martian regolith would provide a surface structure with micrometeorite and radiation protection, thermal insulation, and natural supplemental heat energy that would significantly reduce the energy requirements met by mechanical equipment. HEAT2 is an energy simulation program that solves heat transfer problems using the partial differential heat conduction equation in two dimensions with the method of explicit finite differences. HEAT2 simulation data suggests that, although thermal mass is most suitable for climates where desired indoor temperatur...