Cold Storage Tank Research Articles

The role of the saver in a HPLCs heat transfer process: a transient analysis

This work describes the experimental validation of a mathematical model implemented in Matlab/Simulink®, which is used to investigate energy consumption in the production process of high-pressure laminate composites (HPLCs). First, experimental onsite temperature measurements are used to determine parameters for the core component, i.e. the package, consisting of several layers of different materials. These otherwise hard to assess quantities are the generated power due to exothermal reactions in the cross-linking phase, and the piecewise approximation for the variable heat capacity of the impregnated paper over the heating phase of the process. The capability of the whole model (including the hot and cold water storage tanks) to replicate the behaviour of the actual production process has been verified. The validated model has been employed to investigate the influence of a saver tank for the spent hot water to be employed in the early stage of the heating phase of the process, with the load and discharge phases lasting three or five minutes each. Computations demonstrate that significant savings in energy (up to 34) can be obtained.

Design optimization of a residential scale solar driven adsorption cooling system in upper Egypt based

This study provides a decision support approach for selecting the best size of the main components of a small scale solar assisted, silica gel-water, adsorption cooling system in arid areas located in Assiut, Egypt. To achieve the objective of this work, an optimization based on a computer simulation has been performed on the design variables, which are: solar collector area, the volume of the hot storage tank, the volume of the cold storage tank, and thermostat set point of the auxiliary heating element. Economic and environmental evaluations of the proposed systems have been performed as well. A validation of the model results is performed with the experimental results of solar driven silica gel-water adsorption cooling system at Assiut University Campus which has worked since 2012. The results show that the tilt angle of 5° for the surface of the solar collectors achieved the best absorbed solar radiation by the collector filed. For all proposed systems, the solar fraction did not affect the volume of the cold water storage tank while it has a significant effect on the area of the solar collector field and as well as the volume of the hot water storage tank. The initial cost of the proposed systems ranges from 2897€/kWc to 4808€/kWc and this can be considered as a hindrance to spreading at the commercial level. Meanwhile, the running cost over a year achieves low values, and it ranges from 13.9€/kWc to 99.11€/kWc.The proposed systems of lower solar fraction give lower carbon dioxide emissions. The carbon dioxide emissions range from193kg of CO2eq./kWc per year for the fully solar driven cooling system to 1062kg of CO2eq./kWc per year for the cooling system fully driven by natural gas. Based on the solar saving approach the proposed system of 24m2 solar collector area, 0.6m3 hot storage tank, and 1m3 cold storage tank with 94°C auxiliary heater set-point temperature can be considered as the most economically feasible solution.

Design considerations and construction of an experimental prototype of concentrating solar power tower system in Saudi Arabia

A prototype of a solar power tower system was designed and constructed to produce electricity from solar energy. This prototype of a solar power tower system was constructed and installed at King Abdulaziz University in Saudi Arabia where solar intensity is excessive. Heliostats were implemented to capture the solar rays during daylight. These mirrors are used to direct the solar energy to a solar receiver that is made of alloy steel so that thermal energy is conveyed to a thermal fluid inside the receiver. Based on a detailed selection procedure presented in this article, a final number of ten heliostats were chosen to direct the solar energy to the solar receiver. In addition; two motors were used to control the heliostat rotational and elevation movements. The thermal fluid is a molten salt mixture (which consists of 60% NaNO3 and 40% KNO3). Cold and hot storage tanks were manufactured from steel and they were insulated with calcium silicate from all sides. A one-meter high and one and a half-meter cylindrical vessel was adopted for each of the cold and hot tanks. In this article, a detailed design analysis of each component is presented. The thermal power transferred to the water in the heat exchanger as it is heated by the molten salt was measured and found to be 11.26kW. The thermal power given by the molten salt in the heat exchanger was also measured and found to be 12.31kW. The design thermal power was 13kW. The percentage error in the thermal power obtained is about 5.3%.

Optimal design and application of a compound cold storage system combining seasonal ice storage and chilled water storage

Seasonal cold storage using natural cold sources for cooling is a sustainable cooling technique. However, this technique suffers from limitations such as large storage space and poor reliability. Combining seasonal storage with short-term storage might be a promising solution while it is not explored sufficiently. This paper presents a compound cold storage system that combines a heat pipe-based seasonal ice storage system with a chilled water storage system. The seasonal ice storage system automatically charges winter cold energy in the form of ice. In summer, the stored ice is extracted for cooling, and then the melting ice is used as a chilling medium for chilled water storage. Design optimization of the seasonal ice storage system and the compound storage system is addressed, including the sizes of heat pipes, the configuration and volume of the cold storage tank and the chiller capacity. A case study is conducted to demonstrate the design and the application of the proposed system in a real building in Beijing. Results show that the appropriate combination of the two types of cold storage can greatly improve the applicability of the seasonal cold storage and reduce the life-cycle cost of a building cooling system by 40%.

Energy Storage Start-up Strategies for Concentrated Solar Power Plants With a Dual-Media Thermal Storage System

A concentrated solar power (CSP) plant typically has thermal energy storage (TES), which offers advantages of extended operation and power dispatch. Using dual-media, TES can be cost-effective because of the reduced use of heat transfer fluid (HTF), usually an expensive material. The focus of this paper is on the effect of a start-up period thermal storage strategy to the cumulative electrical energy output of a CSP plant. Two strategies—starting with a cold storage tank (referred to as “cold start”) and starting with a fully charged storage tank (referred to as “hot start”)—were investigated with regards to their effects on electrical energy production in the same period of operation. An enthalpy-based 1D transient model for energy storage and temperature variation in solid filler material and HTF was applied for both the sensible heat storage system (SHSS) and the latent heat storage system (LHSS). The analysis was conducted for a CSP plant with an electrical power output of 60 MWe. It was found that the cold start is beneficial for both the SHSS and LHSS systems due to the overall larger electrical energy output over the same number of days compared to that of the hot start. The results are expected to be helpful for planning the start-up operation of a CSP plant with a dual-media thermal storage system.

Transient analysis of the cooling process of molten salt thermal storage tanks due to standby heat loss

Molten salts consisting of 60% sodium nitrate and 40% potassium nitrate have been used successfully as a thermal energy collection and storage fluid in different solar thermal plants. However, the relatively high melting point of this mixture (221°C) represents an important risk of local solidification in the operation of the solar power plants during standby periods. In this work, a computational fluid dynamics (CFD) model is developed to analyze the cooling process of representative state-of-the-art molten salt thermal storage tanks during these standby periods. A comprehensive set of operating conditions is analyzed, covering both hot and cold storage tanks, charging levels, and heat losses. Results show that the onset of local crystallization is highly influenced by the tank charging level. While the risk is relatively high in the case of the minimum charging level, in the case of maximum charging level the risk is minimal as it would require a very long standby period. To summarize the results, this work presents a safe charging level calculation, as a function of the operation temperature and the expected standby duration, which could be used as part of an appropriate operational strategy to avoid the risk of freezing for long standby periods. The model assumptions, the different configurations studied and their results are presented and discussed in detail.

Experimental investigation of a novel phase change cold storage used for a solar air-conditioning system

Solar energy systems in combination with thermal driven sorption chillers for air conditioning are gaining increasing attention. Since solar energy is available only during daytime and solar cooling systems are usually intermittent and susceptible to the weather, applying cold storage methods to solar air-conditioning systems is favorable to utilize renewable energy and enhance the system stability. A self-developed phase change material (PCM) providing a suitable phase change temperature of 14.97°C and a reasonable phase transition latent heat of 115.1 kJ/kg is used to fabricate a cold storage tank. The aim of this article is to experimentally investigate the performance of the cold storage tank for solar air-conditioning application. The experiment includes a small-scale steady-state testing of a single spherical capsule and a solar air-conditioning system integrated with the PCM cold storage tank. The temperature distribution and phase change interface movement of the capsule are theoretically predicted. Main parameters of the cold storage tank, namely the inlet and outlet water temperature, internal temperature variation of capsules, charging/discharging capacity and charging/discharging rate are analyzed. The experimental results show that the charging and discharging process completed in 230 min and 220 min under steady states. While under unsteady states of a solar air-conditioning system, the charging and discharging process of the phase change cold storage tank completed within 320 min and 110 min with the total amount of charging and discharging capacity of 1016.1 kJ and 942.8 kJ, respectively. The phase change cold storage tank manifests good feasibility and stability for solar air-conditioning application.

Numerical model evaluation of a PCM cold storage tank and uncertainty analysis of the parameters

Thermal energy storage (TES) tanks for cold storage can be used for peak load shaving. This paper presents and evaluates a mathematical model where a TES tank is filled with commercial phase change material (PCM) flat slabs. The 2D model is used for simulating the outlet temperature of the heat transfer fluid, and also the heat transfer rate during the discharging process. The study includes the use of an approximation of the PCM specific heat (cPCM;old) which corresponds to the parameter calculated in the previous iteration of the implicit finite difference method. Thus, an evaluation of the different model parameters is performed, based on the comparison between the computational time and accuracy of the different simulations. Moreover, the uncertainties in different input variables are also analysed in order to find out which variable should be known more accurately. The results show that using the approximated parameter cPCM;old is a good solution for reducing the computational time despite a slight error increase in the case of using small time step in the simulation. Moreover, the inlet HTF temperature, and melting temperature, density and specific heat of the PCM are the main parameters to take into account in terms of uncertainty variables evaluation.

Integration of industrial solar and gaseous waste heat into heat recovery loops using constant and variable temperature storage

Solar is a renewable energy that can be used to provide process heat to industrial sites but require thermal storage. HRLs (heat recovery loops) are an indirect method for transferring heat from one process to another using an intermediate fluid. With HRL's thermal storage is also necessary to effectively meet the stop/start time dependent nature of the multiple source and sink streams. Combining solar heating with HRL's is a cost effective way to share common storage and piping infrastructure. The conventional HRL design method based on a CTS (constant temperature storage) and a new HRL design method using VTS (variable temperature storage) are applied to demonstrate the potential benefits of inter-plant heat integration and installing solar heating. The dairy case study had available 12 source streams including four spray dryer exhausts and six sink streams. The addition of the dryer exhausts as heat sources was a critical factor in gaining a heat recovery of 10.8 MW for the variable temperature storage design, of which 5.1 MW was contributed from exhaust heat recovery. For the same minimum approach temperature the VTS approach achieved 37% more heat recovery compared to the CTS approach. Solar heating also proved to be a valuable source to be integrated into an HRL with a pinch around the cold storage tank with the maximum addition of 0.9 MW of heating on average for the CTS approach and 1.0 MW of heating on average for the VTS approach.

Exergo-economic analysis of a solar driven hybrid storage absorption refrigeration cycle

This paper presents the exergo-economic analysis of a 5kW refrigeration cycle with hybrid storage system. The novel hybrid storage comprises a cold (ice) storage tank, an ammonia storage tank, a weak solution tank and a strong solution tank to suffice the nighttime cooling load. The exergo-economic analysis is performed to compare the components of the refrigeration cycle based on the costs of initial capital investment and the costs of irreversibilities. The components of the refrigeration cycle are evaluated and compared using exergo-economic variables such as the relative cost difference, exergy destruction cost rate and exergo-economic factor. The effect of generator temperature, condenser temperature and evaporator temperature on the exergetic efficiency of the system is also studied. The paper also presents a quasi-steady exergy and exergo-economic analysis for a representative summer day of Dhahran region. This study can be further used in the optimization of design variables of the studied refrigeration cycle.

Experimental investigation on PCM cold storage integrated with ejector cooling system

An experimental investigation on the operating characteristics of cold storage ejector cooling system with finned tube inside a cylindrical PCM tank was presented in this paper. The PCM cold storage tank was coupled with the evaporator to store the excess cooling capacity of ejector cooling system and provide cooling effect when the ejector did not operate. Medium temperature source (from solar collector or industrial waste) at temperature of 120 °C was the main driving force for ejector cooling system. The performance parameters, such as temperature inside the PCM tank, inlet and outlet temperature of heat transfer fluid, cold storage rate and cold storage capacity were measured at various mass flow rates, at the evaporator temperature of 3–5 °C. The same testing parameters were measured for discharging process at the heat source temperature of 25 °C. The experimental results demonstrated that the PCM cold storage integrated with ejector could help to maintain a more stable COP for ejector cooling system. The effectiveness-NTU method was applied for characterizing the tube-in tank PCM storage system. The correlation of effectiveness as the function of mass flow rate was derived from experimental data, and was used as a design parameter for the PCM cold storage system.

Experimental analysis of a paraffin-based cold storage tank

The aim of this study is to characterize a paraffin-based cold storage tank. Novel experimental results are presented for this system which combines a significant amount of paraffin (1450 kg) immersed around 18 spiral-shaped coils disposed in counter-current flow. The paraffin has a phase-change temperature in the range 4–8 °C as measured by a 3-layer calorimeter. Different tests have been carried out with a constant mass flow rate and supply temperature. Around 31% of the paraffin has hardly any contact with the coils and hereby acts as a dead mass. The results show the importance of natural convection within the phase-change-material, particularly during the melting process. The highest efficiency has been achieved for the lowest supply temperatures and mass flow rates of the heat transfer fluid.

A feasibility integrated approach in the promotion of solar house design

SUMMARY In many countries, although solar energy is plentiful, due to technical and economic issues, micro-scale solar energy technologies have not properly found their places in the market. The present work demonstrates the convenience of employing economic feasibility assessments together with engineering analyses before applying solar strategies during the design stages, in order to convince house owners that these solar technologies can be economically viable. In a case study, this approach is tested for a real house project developed in North Cyprus (NC) in which solar energy applications for electricity generation, hot water preparation, space heating and passive cooling are investigated. It is reported that grid-connected photovoltaic (PV) systems would be economically feasible with savings-to-investment ratio (SIR) values of 2.9 to 3.4. A thermal performance analysis is carried out for a thermal storage wall (TSW) together with a direct solar gain (DSG) window in the living room. It is discovered that the temperature range of the living room was within 18–22 °C throughout the majority of winter days. This application is also proved to be economically feasible with an SIR of 1.3, compared to installing an 18,000 Btu/h heat pump. It is determined that both locally produced solar water heaters and imported solar water heaters (ISWHs) are economically viable compared to using a 3-kW storage-type electric water heater. Their SIR values are estimated to be 7.5 and 3.7, respectively. A solar-assisted stack-effect ventilation (SEV) system is verified to have techno-economic feasibility and is also useful in concealing the unattractive cold and hot water storage tanks on the roof. The prospective house owner decides to invest 3840 EUR in installing a grid-connected PV system of 1 kWp, an ISWH, a DSG window, building a TSW for space heating and a SEV system with an overall SIR value of 3.2. This procedure can be developed into a government policy where all these assessments are made mandatory to increase the awareness of the home builders before they make their decisions about the final designs of their houses. The present work demonstrates the convenience of employing economic feasibility assessments together with engineering analyses before applying solar strategies during the design stages, in order to convince house owners that these solar technologies can be economically viable. In a case study, this approach is tested for a real house project developed in NC in which solar energy applications for electricity generation, hot water preparation, space heating and passive cooling are investigated. Copyright © 2013 John Wiley & Sons, Ltd.

Solid fraction determination in cold storage by tetra-n-butyl ammonium bromide clathrate hydrate slurry

Thermal or cold storage by phase change material slurry attracted many attentions in recent years, in which solid fraction distribution in the storage tank is an important issue due to different densities of the solid particle and carrier fluid. Tetra-n-butyl ammonium bromide (TBAB) clathrate hydrate slurry (CHS) has recently been intensively investigated for the purpose of the cold storage. In the present study, solid fraction distribution of TBAB CHS in a cold storage tank was both experimentally and numerically investigated. The different sedimentation characteristics of type A and type B TBAB CHS were identified. It was shown that high-capacity cold storage can be achieved by taking advantage of the sedimentation of type A TBAB CHS, based on which a procedure to realize it was also proposed.

Characterization of Contaminants from a Sanitized Milk Processing Plant

Milk processing lines offer a wide variety of microenvironments where a diversity of microorganisms can proliferate. We sampled crevices and junctions where, due to deficient reach by typical sanitizing procedures, bacteria can survive and establish biofilms. The sampling sites were the holding cell, cold storage tank, pasteurizer and storage tank - transfer pump junction. The culturable bacteria that were isolated after the sanitation procedure were predominantly Pseudomonas spp., Serratia spp, Staphylococcus sciuri and Stenotrophomonas maltophilia. We assayed several phenotypic characteristics such as the ability to secrete enzymes and siderophores, as well as the capacity of the strains to form biofilms that might contribute to their survival in a mixed species environment. The Pseudomonas spp. isolates were found to either produce proteases or lecithinases at high levels. Interestingly, protease production showed an inverse correlation with siderophore production. Furthermore, all of the Serratia spp. isolates were strong biofilm formers and spoilage enzymes producers. The organisms identified were not mere contaminants, but also producers of proteins with the potential to lower the quality and shelf-life of milk. In addition, we found that a considerable number of the Serratia and Pseudomonas spp. isolated from the pasteurizer were capable of secreting compounds with antimicrobial properties.

Investigation of four geometrical parameters on thermal stratification of cold water tanks by exergy analysis

In this paper, effects of four geometrical parameters of tanks on the thermal stratification within a cold storage tank are analysed. Nine two–dimensional models have been numerically simulated by using the Computational Fluid Dynamics (CFD) program, fluent. Realistic boundary and initial conditions are applied. The level of thermal stratification in each model has been quantified by means of exergy analyses. The results obtained show increasing the tanks Aspect Ratio (AR) of height to width, decreasing inlet/outlet diameter, moving the inlet/outlet position to the outer extremities of the tank, and increasing input angle towards top of the tank all lead in increasing levels of thermal stratification.

A Solar-Driven Ejector Refrigeration System for Mediterranean Climate: Experience Improvement and New Results Performed

The need for air-conditioning in the Mediterranean countries is higher and higher due to the effects of global warming. This paper deals with an investigation of a high performance, solar-driven air-conditioning system, the project entitled “Mediterranean AIRCOND”, is funded by the European Community under the „Community Activities in the Field of the specific program for RTD and demonstration on “Energy, Environment and Sustainable Development”. “AIRCOND” aims to study and investigate performances of advanced solar driven air conditioning system; the field system is composed of three sub systems: the heating loop, the ejector cycle and the cold storage-air handling units: The heating loop is composed of a solar array of 60 square meters evacuated tube solar collectors; installed at a tilt angle of 45o and facing to south, a 3000 L tank which is used as hot water storage in order to cover the required energy by the ejector cycle. The cold water produced by the ejector cycle will be then transferred in a 900L cold storage tank filled with 800L micro-encapsulated phase change material (MEPCM) for cold storage. It is designed to meet the dynamic cooling load. The ejector was tested at the School of the Built Environment in the University of Nottingham in UK and then transferred to Tunisia for field evaluation. Many previous theory studies have been fulfilled on this technology but never been performed experimentally at this level. This paper presents the research effort made and the experience gained during the implementation of the whole system: Different operation strategies were followed during more than one year to make the ejector cycle functional. The whole procedure has turned out to be very difficult; it was particularly difficult to obtain a deep vacuum and to ensure a good vacuum quality; this is a necessary working condition for the ejector cycle. Successful ejector tests were obtained during 8min, 15min and 40min, after many investigations; later experiments led to 3hours of continuous working. Results are very promising; the installation is still under tests in order to obtain a whole day permanent working of the ejector cycle and so of all the solar installation.

A comparison of solar absorption system configurations

Abstract Solar thermal driven cooling systems for residential applications are a promising alternative to electric compression chillers, although its market introduction still represents a challenge, mainly due to the higher investment costs. The most common system configuration is an absorption chiller driven by a solar thermal system, backed up by a secondary heating source, normally a gas boiler. Heat storage in the primary (solar) circuit is mandatory to stabilize and extend the operation of the chiller, whereas a cold storage tank is not so common. This paper deals with the selection of the most suitable configuration for residential cooling systems with solar energy. In Spain, where cooling needs are usually higher than heating needs, the interest of a reversible heat pump as auxiliary system and a secondary cooling storage are analyzed. A complete TRNSYS model has been developed to compare a configuration with just hot storage (of typical capacity 40 L/m 2 of solar collector surface) and a configuration with both, hot and cool storages. The most suitable configuration is very sensible to the solar collector area. As the collector area increases, the advantages of a cool storage vanish. Increasing the collector area tends to increase the temperature of the hot storage, leading to higher thermal losses in both the collector and the tank. When the storage volume is concentrated in one tank, these effects are mitigated. The effect of other variables on the optimal configuration are also analyzed: collector efficiency curve, COP of the absorption chiller, storage size, and temperature set-points of the chillers.

Performance study of solar-assisted air-conditioning system provided with storage tanks using artificial neural networks

This study presents the performance of solar-assisted air-conditioning system provided with two storage tanks installed in the Solar Energy Research Center (CIESOL) building. The system consists mainly of solar collectors’ array, a hot-water driven absorption chiller, a cooling tower, two hot storage tanks, an auxiliary heater as well as two cold storage tanks. The hot storage tank circuit was further investigated. In first step, we have carried out the study about the necessity of the integration of hot water storage tanks to solar system. Subsequently, the unique Artificial Neural Network (ANN) model with the lowest number of input variables has been proposed with the main purpose to predict the coefficient of performance and the cooling capacity of the absorption chiller. The configuration 5-9-2 (5 inputs, 9 hidden and 2 output neurons) was found to be the optimal topology. The results demonstrate proper ANN’s predictions with a Root Mean Square Error (RMSE) of less than 0.70% and practically null deviation, which can be considered very satisfactory.

Concentrated solar power on demand

Abstract A concentrating solar power system is presented which uses hillside mounted heliostats to direct sunlight into a volumetric absorption molten salt receiver with integral storage. The concentrated sunlight penetrates and is absorbed by molten salt in the receiver through a depth of 4–5 m, making the system insensitive to the passage of clouds. The receiver volume also acts as the thermal storage volume eliminating the need for secondary hot and cold salt storage tanks. A small aperture and refractory-lined domed roof reduce losses to the environment and reflect thermal radiation back into the pond. Hot salt is pumped from the top of the tank through a steam generator and then returned to the bottom of the tank. An insulated barrier plate is positioned within the tank to provide a physical and thermal barrier between the thermally stratified layers, maintaining hot and cold salt volumes required for continuous operation. As a result, high temperature thermal energy can be provided 24/7 or at any desired time. The amount of storage required depends on local needs and economic conditions. About 2500 m3 of nitrate salt is needed to operate a 4 MWe steam turbine 24/7 (7 h sunshine, 17 h storage), and with modest heliostat field oversizing to accumulate energy, the system could operate for an additional 24 h (1 cloudy day). Alternatively, this same storage volume can supply a 50 MWe turbine for 3.25 h without additional solar input. Cosine effect losses associated with hillside heliostats beaming light downwards to the receiver are offset by the elimination of a tower and separate hot and cold storage tanks and their associated pumping systems. Reduced system complexity also reduces variable costs. Using the NREL Solar Advisor program, the system is estimated to realize cost-competitive levelized production costs of electricity.