Applications and technological challenges for heat recovery, storage and utilisation with latent thermal energy storage

Thermal energy storage (TES) technology is considered to have the greatest potential to balance the demand and supply overcoming the intermittency and fluctuation nature of real-world heat sources, making a more flexible, highly efficient and reliable thermal energy system. This article provides a comprehensive state-of-the-art review of latent thermal energy storage (LTES) technology with a particular focus on medium-high temperature phase change materials for heat recovery, storage and utilisation. This review aims to identify potential methods to design and optimise LTES heat exchangers for heat recovery and storage, bridging the knowledge gap between the present studies and future technological developments. The key focuses of current work can be described as follows: (1) Insight into moderate-high temperature phase change materials and thermal conductivity enhancement methods. (2) Various configurations of latent thermal energy storage heat exchangers and relevant heat transfer enhancement techniques (3) Applications of latent thermal energy storage heat exchangers with different thermal sources, including solar energy, industrial waste heat and engine waste heat, are discussed in detail

Investigation on thermal and electrical performance of late-model plate-and-tube in water-based PVT-PCM collectors

A large amount of redundant energy gained from incident solar energy is dissipated into the environment in the form of low-grade heat, which significantly reduces and limits the performance of photovoltaic cells, so removing or storing redundant heat and converting it back into available thermal energy is a promising way to improve the utilization of solar energy. A new combined water-based solar photovoltaic-thermophotovoltaic system embedded in the phase change material (PCM) mainly is proposed and designed. The effects of the water flow rate, cell operating temperature, the presence of PCM, and the thickness of the PCM factor on the overall module performance are explored comprehensively. The maximum thermal power output and the corresponding efficiency of the combined-system-embedded PCM are calculated numerically, The results obtained are compared with those of the PV (photovoltaic) and PVT(photovoltaic-thermal) cells with the same solar operating conditions. In addition, the PVT-PCM system possesses a higher power output and overall efficiency in comparison with the PVT and PV system, and the maximum cell temperature reduction of 12.54 °C and 42.28 °C is observed compared with PVT and PV systems. Moreover, an increased average power of 1.13 W and 4.59 in PVT-PCM systems is obtained compared with the PVT system and the PV system. Numerical calculation results illustrate that the maximum power output density and efficiency of the PVT-PCM are 3.06% and 16.15% greater than those of a single PVT system and PV system in the working time range, respectively. The obtained findings show the effectiveness of using PCM to improve power output and overall efficiency

Investigation of organic Rankine cycle integrated with double latent thermal energy storage for engine waste heat recovery

In this work, organic Rankine cycle (ORC) integrated with Latent Thermal Energy Storage (LTES) system for engine waste heat recovery has been proposed and investigated to potentially overcome the intermittent and fluctuating operational conditions for vehicle applications. A melting-solidification model has been established to investigate and compare the performance of twelve Phase Change Materials (PCMs) under different heat source conditions. Among the twelve PCMs, LiNO3-KCl-NaNO3 is identified as the optimal PCM for engine exhaust heat recovery. The performance of the ORC system integrating with different volume of LTES using LiNO3-KCl-NaNO3 under dynamic heat source simulating vehicle conditions is studied. Results illustrate the fluctuation of engine exhaust heat can be potentially overcome by using the proposed solution. The condition of 100 L LTES provides 30.4% larger total output work than that of 50 L LTES, while it is merely 1.5% larger than that of 90 L LTES. The performance of three different LTES-ORC scenarios are compared and results show ORC combining with double LTES delivers 17.2% larger total power output than that of single LTES (100 L) under the same operational conditions

Investigation of an innovative cascade cycle combining a trilateral cycle and an organic Rankine cycle (TLC-ORC) for industry or transport application

An innovative cascade cycle combining a trilateral cycle and an organic Rankine cycle (TLC-ORC) system is proposed in this paper. The proposed TLC-ORC system aims at obtaining better performance of temperature matching between working fluid and heat source, leading to better overall system performance than that of the conventional dual-loop ORC system. The proposed cascade cycle adopts TLC to replace the High-Temperature (HT) cycle of the conventional dual-loop ORC system. The comprehensive comparisons between the conventional dual-loop ORC and the proposed TLC-ORC system have been conducted using the first and second law analysis. Effects of evaporating temperature for HT and Low-Temperature (LT) cycle, as well as different HT and LT working fluids, are systematically investigated. The comparisons of exergy destruction and exergy efficiency of each component in the two systems have been studied. Results illustrate that the maximum net power output, thermal efficiency, and exergy efficiency of a conventional dual-loop ORC are 8.8 kW, 18.7%, and 50.0%, respectively, obtained by the system using cyclohexane as HT working fluid at THT,evap = 470 K and TLT,evap = 343 K. While for the TLC-ORC, the corresponding values are 11.8 kW, 25.0%, and 65.6%, obtained by the system using toluene as a HT working fluid at THT,evap = 470 K and TLT,evap = 343 K, which are 34.1%, 33.7%, and 31.2% higher than that of a conventional dual-loop ORC

Comparative evaluation of the efficiency of the BG-Sentinel trap, CDC light trap and Mosquito-oviposition trap for the surveillance of vector mosquitoes

Distribution of the traps in the third week of each month. A. Liangtian (suburban area), B. Tonghe (urban area). Twelve each of BGS Traps, CDC Light Traps and MOTs were used to survey the mosquito density in Tonghe and Liangtian. (PDF 639 kb

Evaluation of ideal double-tank hybrid pneumatic engine system under different compression cycle scenarios

A double-tank hybrid pneumatic engine system, with one low pressure tank and one high pressure tank has been proposed to improve the energy conversion efficiency and auxiliary braking power output of regenerative braking of vehicles. The performance of three ideal compression cycle scenarios for the double-tank system has been investigated and the results are compared with that of ideal one-tank scenario in order to identify the optimal compression cycle under different primary performance requirements. Results indicate the maximum brake mean effective pressure can be improved to not over 0.2 MPa less than the HP tank pressure and the highest improvement of total air mass recovered can reach over 40% utilising the double-tank scenarios. Scenario 3 performs the best at the braking power output ability, while scenario 4 shows the greatest high pressure compressed air recovery potential. Considering about the LP tank air sources, scenario 2 is the only one that can operate independently without other air complements, which also performs the best at the energy conversion efficiency among the three double-tank scenarios

Conceptual study of scroll-type rotary gasoline Internal Combustion Engine

This paper reports the study of a conceptual gasoline Internal Combustion Engine (ICE) using scroll type rotary device rather than conventional piston as the main engine component. The proposed innovate engine adopts Humphrey Cycle to maximize the power performance of ICE. A performance comparison of the Humphrey Cycle, Otto cycle and Brayton cycle has firstly been conducted and studied. The effects of using different designed compression ratio under variable expansion ratio have been investigated, which identify the optimal operational conditions under different compression/expansion ratio of the engine. A case study has been conducted to study the performance of small scale scroll-type rotary ICE. Results pointed out under designed compression ratio from 2:1 to 10:,1 the effective energy efficiency of the scroll-type rotary ICE ranges from 0.41 to 0.55 and the effective power from the system ranges from 2.88 to 15.82 kW

Simulation study of Ferricyanide/Ferrocyanide concentric annulus thermocell with different electrode spacing and cell direction

Thermogalvanic cell also named as thermocell is a new type of technology converting low-grade thermal energy to electricity. In this study, we establish an one-dimensional model of a Fe(CN)63-/4- concentric annulus thermocell and evaluate the influence of electrode spacing and cell direction on the cell performance. Results indicate the ratio of electrolyte thermal resistance to total thermal resistance plays a crucial role in cell performance while electric resistance has relatively less influence. The power of thermocell rises significantly as the electrode spacing increases, from about 0.75mW in both directions to 1.75 mW in horizontal direction and 2.75 mW in vertical direction. Convection of electrolyte is unfavorable to cell performance and the critical electrode spacing where convection begins to affect heat transfer is predicted to be the optimized spacing. At all values of electrode spacing in this study, thermocell in vertical direction performs better than that of horizontal direction

Numerical study of using different Organic Rankine cycle working fluids for engine coolant energy recovery

Engine waste heat recovery technology especially Organic Rankine cycle (ORC) has been widely studied in order to achieve higher overall thermal efficiency, reduce the engine emissions and improve the fuel economy. The coolant energy occupies around 30% of the fuel energy can be used as the heat source for ORC system. This paper studies thermal status of the engine heated components when using different ORC working fluids as engine coolant to avoid the heat loos using heat exchanger to transfer coolant to the ORC fluid. A Solid-Liquid Conjugated Heat Transfer (SLCHT) calculation method is developed to calculate the heat transfer inside the engine, which can solve the temperature field of both solid zone and fluid zone. The simulation results have been validated by the experimental data from a 6-cylinder medium duty diesel engine, when water is the coolant in the system. The simulation model is then used to predict the temperature profile using different ORC working fluids and investigate the influence of different ORC working fluids on the cooling effects of the engine heated parts. The maximum temperature of the heated components has been selected as the evaluation parameters. The results reveals that applying selected ORC working fluids in engine as coolant is not practical under the designed conditions, which will make the engine overheated. Further investigation showed that increasing mass flow rate of the coolant can decrease the thermal status of the heated components but still cannot meet the cooling demands even under 200% of the original mass flow rate. The variations of the coolant outlet temperature and exergy were also analysed

Comparison study of trilateral Rankine cycle, organic flash cycle and basic organic Rankine cycle for low grade heat recovery

Organic Rankine Cycle (ORC) has been widely used for the recovery of low-grade heat into power such as solar energy and industrial waste heat. The overall thermal efficiency of ORC is affected by large exergy destruction in the evaporator due to the temperature mismatching between the heat source and working fluid. Trilateral Cycle (TLC) and Organic Flash Cycle (OFC) have been recognized as potential solutions because of their better performance on temperature matching between the heat source and working fluid at the evaporator. In this study, thermodynamic models of above three cycles are established in MATLAB/REFPROP. Results indicate that TLC obtains the largest net power output, thermal efficiency and exergy efficiency of 13.6 kW, 14.8% and 40.8% respectively at the evaporation temperature of 152℃, which is 37% higher than that of BORC (9.9 kW) and 58% higher than that of OFC (8.6 kW). BORC is more suitable under the conditions low evaporation temperature is relatively low due to the achieved maximum net power output, thermal efficiency and exergy efficiency. OFC has the minimum net power output, thermal efficiency and exergy efficiency under all the conditions of evaporation temperature compared to TLC and BORC. As for the UA value, TLC has the largest one ranging from 7.9 kW/℃ to 8.8 kW/℃ under all conditions while OFC gains the minimum UA value at low evaporation temperature and BORC gains the minimum UA value at high evaporation temperature