Thermal Performance Of System Research Articles

Study on Thermal Performance of Electric Heating System with Salt Hydrate-PCM Storage

An electric radiator combined with salt hydrate-phase change material (PCM) storage was developed to replace the existing scattered coal burning systems for clean heating applications. It was designed to have an average heat output of 400 W and a thermal storage efficiency of 65.6% for reducing the electricity peak load. The thermal performance was investigated experimentally and numerically by using various radiator configurations and electric heating powers, as well as three PCMs with a melting point of 58 °C (PCMI 58), 78 °C (PCMI 78) and 90 °C (PCMI 90). It was found that the radiator combined with PCMI 78 had an average heat output of 412 W, and the PCMI 78 could be completely charged within 8 off-peak hours at an electric heating power of 1270 W, in the case of the radiator external dimension L × B × H of 796 × 106 × 656 mm and the L/B ratio of 7.5. The experiment results indicated that the average room temperature could be maintained at 20.0 °C at an outdoor temperature of 5.2 °C when applying the electric radiator developed.

The Effect of Different Configurations of Copper Structures on the Melting Flow in a Latent Heat Thermal Energy Semi-Cylindrical Unit

Utilizing latent heat thermal energy storage (LHTES) units shows promise as a potential solution for bridging the gap between energy supply and demand. While an LHTES unit benefits from the latent heat of the high-capacity phase change material (PCM) and experiences only minor temperature variations, the low thermal conductivity of PCMs hinders the rapid adoption of LHTES units by the market. In this regard, the current work aims to investigate the thermal behavior of a semi-cylindrical LHTES unit with various copper fin configurations (including horizontal, inclined, and vertical fins) on the melting flow. The novelty of this research lies in the fact that no prior studies have delved into the impact of various fin structures on the thermal performance of a semi-cylindrical LHTES system. The nano-enhanced phase change material (NePCM) fills the void within the unit. The warm water enters the semicircular channel and transfers a portion of its thermal energy to the solid NePCM through the copper separators. It is found that the system experiences the highest charging capability when the fins are mounted horizontally and close to the adiabatic upper wall. Moreover, the presence of dispersed graphite nanoplatelets (GNPs) inside the pure PCM increases the charging power and temperature of the LHTES unit.

Performance analysis of a new ORC-VCC system with mechanical overheating and correlation fitting of most important system parameter

Abstract This paper proposes a new ORC-VCC(Organic Rankine Cycle+Vapor compression cycle) system(with mechanical overheating refrigeration cycle), and this system can not only reduce the heat absorption of the ORC evaporator, but also increase the refrigeration capacity of the system. Simulations were conducted to analyze the thermal efficiency and performance of the new system, and compare it with the system of ORC-VCC(with regenerator). The results show that the ηth, ηsys and COPsys(coefficient of performance) of new system are higher than the system of ORC-VCC(with regenerator), ηth, ηsys and COPsys of new system increased by up to 31.6%, 6.48%, 10.63% respectively. And the influence of superheat on both systems is stronger than other factors, the influence of superheat on the new system is obviously stronger than those of the system of ORC-VCC(with regenerator), and the influence of superheat on R245fa and Butane is stronger than those of other working fluids. In addition, ηth, ηsys, COPsys and ηex of system increase with the increase of Te-mech and decrease with the increase of Tg-mech. Finally, the correlation of δTmax with the change of ηexp and Te-orc is fitted, the results will provide some reference for the development of the ORC-VCC system in the future.

Optimization of entropy generation and thermal mechanism of MHD hybrid nanoliquid flow in a sinusoidally heated porous cylindrical chamber

The present computational investigation explores the fluid and thermal characteristics along with entropy generation due to buoyancy-driven magnetohydrodynamic (MHD) convective flow of aqueous hybrid nanoliquid filled in a nonuniformly heated porous cylindrical chamber. The fluid motion in the enclosure is modeled by Brinkman — extended Darcy model. The modeled equations are resolved by finite difference approach. The computations are conducted for Rayleigh number (103–105), Hartmann number (0–50), Darcy number (10−5–10−1), different nanoparticle shapes and nanoparticle volume fraction (Ag/MgO: 0–0.05) to understand the characteristic of flow, thermal and irreversibility distribution. With vast numerical simulations, the outcomes reveal that though the buoyancy force is greater, the fluidity cannot be enhanced unless the permeability and magnetic field strength are optimally maintained. As Ra,Ha and Da is varied respectively from 103 to 105, 50 to 0 and 10−5 to 10−1, the fluidity has been enhanced by 99.39%,83.26% and 99.79%. Among all considered parametric combinations, it has been noticed that the choice of Ha=0,Ra=105,Da=10−1 with proper ratio of nanoparticles enhance the system efficiency. However, minimal entropy generation can be achieved with greater Hartmann and lower Darcy numbers. Furthermore, it has been found that blade shaped nanoparticles lead to increase the performance of thermal system.

An in-depth study on melting performance of latent heat thermal energy storage system under rotation mechanism by fluctuating heat source

The Organic Rankine Cycle (ORC) is a reliable and efficient means of converting solar energy into electricity. The challenges brought about by the unpredictable nature of solar energy can be effectively mitigated by utilizing latent heat thermal energy storage (LHTES) technology, specifically by implementing heat source pretreatment. This paper investigates the thermal storage properties of a rotating triplex-tube LHTES unit under different sinusoidal fluctuating heat sources. A transient numerical model is built to analyze the effects of sinusoidal wall temperature amplitude and angular velocity on the melting characteristics of the unit, including melting time, heat storage rate, and temperature response. The design is further analyzed using the Taguchi method. The results show that the angular velocity of the sinusoidal wall temperature has a greater effect on the average heat storage rate and melting time than the amplitude. When the amplitude is set to 10 and the angular velocity to 0.02, the melting time is decreased by 8.7%, while the average heat absorption rate and average temperature response increase by 10.21% and 12.27%, respectively. Additionally, the sensible and total heat energy absorption increase by 2.23% and 0.62%, compared to the initial heat source condition. Furthermore, the heat transfer is enhanced through the introduction of Al2O3 nanoparticles at varying percentages. The unit heat storage rate improves significantly with an increasing percentage of nanoparticles. Specifically, when 2.5% and 5% Al2O3 nanoparticles are added, the melting time of the unit is reduced by 3.77% and 15.07%, respectively, while the average heat absorption rate increases by 2.43% and 10.39%.

Effects of shape and ratio of copper foam on thermal storage properties of the heat storage system with phase change materials

Latent heat storage technology can be used to overcome the instability of solar-powered equipment. However, the poor thermal conductivity of phase change materials markedly weakens the thermal storage efficiency of the heat storage system. Filling copper foam is a valid method to improve the thermal conductivity of phase change materials. To explore the synergistic effect of copper foam filling shape and ratio on the thermal storage performance of the heat storage system, the present study researched the thermal storage performance of the heat storage system with different copper foam filling ratios under two types filling shapes using myristic acid and copper foam as feedstocks. The mechanism of the influence of the ratio and shape of copper foam on the heat storage performance was discussed from Rayleigh number and natural convection velocity. The results show that there is a linear relationship between the ratio of copper foam and the thermal storage performance for the compact stacking shape. The melting time is shortened by 32.8 % and the heat storage efficiency is increased by 45.1 % when the content of copper foam increases from 10 % to 50 %. For the spaced stacking shape, the ratio of copper foam has a non-linear relationship with the thermal storage performance, reaching a maximum at 40 % copper foam filling ratio. Compared with the control group, the full melting time is shortened by 38.53 % and the heat storage efficiency is increased by 64 %. As the ratio of copper foam increases from 10 % to 50 %, the Rayleigh number increases from 208 × 103 to 188 × 103 and the convection velocity decreases by 47.8 % to 66 %. The average convective velocity of spaced stacking shape is 2 % to 38 % lower than that of compact stacking shape under the same ratio of copper foam.

An Experimental Investigation on the Heat Transfer Characteristics of Pulsating Heat Pipe with Adaptive Structured Channels

In recent years, the development of electronic chips has focused on achieving high integration and lightweight designs. As a result, pulsating heat pipes (PHPs) have gained widespread use as passive cooling devices due to their exceptional heat transfer capacity. Nevertheless, the erratic pulsations observed in slug flow across multiple channels constitute a significant challenge, hindering the advancement of start-up and heat dissipation capabilities in traditional PHP systems. In this paper, we introduce a flat plate pulsating heat pipe (PHP) featuring adaptive structured channels, denoted as ASCPHP. The aim is to enhance the thermal performance of PHP systems. These adaptive structured channels are specifically engineered to dynamically accommodate volume changes during phase transitions, resulting in the formation of a predictable and controllable two-phase flow. This innovation is pivotal in achieving a breakthrough in the thermal performance of PHPs. We experimentally verified the heat transfer performance of the ASCPHP across a range of heating loads from 10 to 75 W and various orientations spanning 0 to 90 degrees, while maintaining a constant filling ratio (FR) of 40%. In comparison to traditional PHP systems, the ASCPHP design, as proposed in this study, offers the advantage of achieving a lower evaporation temperature and a more uniform temperature distribution across the PHP surface. The thermal resistances are reduced by a maximum of 37.5% when FR is 40%. The experimental results for start-up characteristics, conducted at a heating power of 70 W, demonstrate that the ASCPHP exhibits the quickest start-up response and the lowest start-up temperature among the tested configurations. Furthermore, thanks to the guiding influence of adaptive structured channels on two-phase flow, liquid replenishment in the ASCPHP exhibits minimal dependence on gravity. This means that the ASCPHP can initiate the start-up process promptly, even when placed horizontally.

Advanced design, parameter optimization, and thermodynamic analysis of integrated air-blown IGCC power plants

With the increasing energy demand, it is essential to improve the utilization of traditional energy sources. Coal is still the mainstay of the Chinese energy market, especially in power generation. The IGCC offers significant advantages in terms of power efficiency and environmental protection. However, conventional IGCC uses oxygen as the gasification medium, posing serious economic challenges. To address this challenge, in this study, the overall system process for the IGCC systems using air-blown gasification is constructed by Aspen Plus. To explore the potential of the thermal performance of the air-blown gasification IGCC system, the operating parameters and process flows are improved. The energy and exergy analysis of the whole system using the advanced process is carried out and compared with the oxygen gasification IGCC. Optimal operating parameters and technical parameters are determined, and the gasifier is optimized. The results show that the system efficiency increased by 3.17%, and the exergy efficiency increased by 3.09%. Although the integrated gas turbine process does not offer obvious advantages, it is more compatible with the current gas turbine in terms of flow rate. The utilization of a high-pressure reheat gas turbine results in a 2.52% increase in system efficiency. The implementation of high-pressure reheat gas turbines and hot gas desulfurization can improve the thermal performance of the system. The air-blown gasification IGCC with this process has the highest power supply efficiency of 52.80%. It presents an improvement of 3.69% compared with oxygen gasification. The exergy loss in the cooling and cleaning module and the gas turbine module is significantly reduced. The heat efficiency of the air-blown gasification IGCC is 3.60% higher, and the effective energy in the system is fully utilized. It provides some heuristic ideas for the clean and efficient utilization of coal resources.

Experimental study on thermal performance of a closed heat pump drying system

The compressor speed, expansion valve opening and drying temperature are critical to the thermal performance improvement and control logic optimization of the closed heat pump drying (CHPD) system. This paper investigates the effects of the three parameters on the thermal performance of the CHPD system by the single factor experiment method. According to the experimental findings, as the compressor speed of the system increased, the heating capacity grew by 11.4%, but the coefficient of performance (COP) declined by 41.3%. As the expansion valve opening of the system increased, the heating capacity and COP grew by 73.5% and 82.9%, respectively. As the drying temperature of the system rose, the heating capacity grew by 3.1%, but the COP dropped by 25.3%. It can be concluded that reducing the compressor speed and drying temperature, and increasing the expansion valve opening could effectively enhance the thermal performance of the CHPD system.

Analytical and experimental study of hybrid photovoltaic–thermal–thermoelectric systems in sustainable energy generation

A new hybrid system, known as photovoltaic–thermal–thermoelectric (PVT-TE), has been proposed to enhance the conversion efficiency of PV cells by incorporating an intelligent thermal management system, which leverages the dual functions of thermoelectric (TE). This study aims to explore the potential for creating a hybrid system that is more efficient and offers improved performance than standalone photovoltaic thermal (PVT) systems. The key parameters for the creation of a hybrid system were analysed, and the theoretical and experimental results were compared to validate the model. The performance of the PVT-TE collector was evaluated through a steady-state analysis using a one dimensional (1D) mathematical model. Energy balance equations were solved using Microsoft Excel and inverse matrix method. Experiments on PVT and PVT-TE collectors were examined at a solar radiation intensity of 593.16 W/m2. The air mass flow rate was set at 0.009, 0.021, 0.039, 0.069 and 0.095 kg/s for specific radiation intensity. The thermal and electrical performance of the hybrid system was higher than that of the conventional PVT system. The PVT-TE system combines photovoltaic and thermoelectric components, including a thermoelectric module and an air collector. The integration improves system efficiency and performance, surpassing previous research efforts. The PVT-TE system with an air collector has innovative features including efficient thermal-electric conversion, integrated component utilisation, and air collector integration. The overall efficiency of the hybrid system was 7.05%–31.13% higher than the theoretical values and 9.64%–34.83% higher than the experimental values. The increase in the output power of the hybrid system was also higher by 32.59%–55.93%. The findings indicate that the integration thermoelectric (TE) with PV cells has the potential to enhance solar thermal systems' performance. This study provides the basis for further analysis and optimisation of PVT-TE hybrid systems.

Heat transfer and thermal performance investigation on a visualized latent heat storage system in pilot-scale: Scalable medium-temperature thermal energy storage system

Large-capacity medium-temperature (100–300 °C) and high-temperature (>300 °C) latent heat storage (LHS) systems can enhance the reliability and performance of solar thermal utilization systems due to their characteristics of balancing the gap between energy supply and demand. In this study, a pilot-scale LHS system was developed and investigated, incorporating a mass of 270 kg of phase change material (PCM), specifically a commercial nitrate mixture. Moreover, the thermal energy storage unit featured a rectangular aperture at its center, covered by a quartz visualization window to facilitate the observation of the melting and solidification behavior of the PCM. The charging process lasted 111 min, with a mean average power, accumulated energy and efficiency of 11.90 kW, 79.33 MJ, and 77.67%, while those of the discharging process were 56.5 min, 12.99 kW, 44.11 MJ, and 71.41%, respectively. Furthermore, a comparative analysis was conducted concerning heat transfer performance and mechanisms during the charging and discharging processes. The heat transfer coefficients and average thermal resistances of the LHS system during charging and discharging were 613.08 W/(m2·K), 295.28 W/(m2·K), and 0.001984 (m2·K)/W, 0.005285 (m2·K)/W, respectively. The average thermal resistance observed during the charging process was notably lower than that observed during the discharging process, attributable to the variance in the predominant heat transfer mechanism. For a substantial portion of the charging process duration, heat transfer was dominantly governed by natural convection, whereas throughout a significant duration of the discharging process, heat transfer was primarily driven by thermal conduction.

Thermodynamic performance of CaCl2 absorption heat pump thermal energy storage system with triple storage tanks

Renewable energy source is playing an increasingly important role in district heating based on cogeneration units. Absorption thermal energy storage has the characteristics of high thermal energy storage density and low heat loss in long-term storage. In this paper, an absorption heat pump thermal energy storage system with CaCl2-water solution as the working fluid is proposed for solving the problem of insufficient wind power accommodations due to coal-fired cogeneration heat-power coupling. A steady-state thermodynamic model of the system is constructed in the Aspen Plus software. Under the considered design conditions, the volume of the tank required for one hour of operation of the system, thermal energy storage density, thermal energy storage ratio, and heating ratio are 464.61 m3, 29.81 kW h/m3, 46.50%, and 53.54%, respectively. The thermal energy storage density is 1.43 times and 1.25 times, and the tank volume is 0.7 times and 0.8 times, of those of a dual tank thermal energy storage system with H2O and CaCl2-water solution as the working fluids respectively. The effects of the system parameters on the thermal energy storage performance are simulated to obtain the optimal performance. At the optimum system performance, the tank volume required to operate the system for one hour, thermal energy storage density, heating ratio, and thermal energy storage ratio are found to be 439.56 m3, 37.39 kW h/m3, 44.83%, and 55.17%, respectively. Accordingly, the thermal energy storage performance of this system is also found to be superior to that of the traditional thermal energy storage system, which will be beneficial for reducing the volume of storage tanks in cogeneration units and increasing the thermal storage temperature.

Multi-Objective Optimization with PCM integration and delayed cooling strategy for high-rate discharge applications

The thermal safety of lithium-ion batteries has been a significant concern in the industry, prompting a pressing need for research to ensure efficient and energy-saving operation of energy storage battery's thermal management system. This study focuses on addressing the multi-objective optimization problem of heat dissipation coupling energy consumption in battery packs under high discharge rate with a maximum temperature (Tmax), a maximum temperature difference (ΔT) and the pump energy consumption (P) as objectives. The Kriging interpolation and CRITIC weighting method are used for multi-objective optimization to determine the optimum solution objectively. The results indicate that increasing the diameter of the liquid cooling pipe (X) and the coolant inlet velocity (vin) both contribute to reducing the maximum temperature of system. However, these changes have negative impacts on temperature uniformity within the battery pack and the energy consumption of the water pump. The above rule is reversed when considering the impact of initiation time of coolant flow (T), which in addition can lead to exhaustion of latent heat of CPCM and insufficient cooling capacity and thus potential overheating of the battery pack. According to the CRITIC weighting method analysis, the index weights of Tmax, ΔT and P are 40.21%, 32.01% and 27.79%, respectively. Further analysis reveals that the optimal comprehensive performance of the battery pack thermal management system is achieved when X = 3.875 mm, vin = 0.4 m/s, and T = 537.5 s, corresponding the P of 2.53 J, Tmax of 309.32 K and ΔT of 2.41 K, both falling within the specified technical requirements at a discharge of 4 C . The latent heat of the phase change material in the battery pack has been recovered at this stage, providing sufficient cooling capacity for the next cycle of charging and discharging.

Thermodynamic analysis of combined heating and power system with In-Situ resource utilization for lunar base

With the growing interest in lunar exploration around the world, the construction of lunar base has naturally become a focus for researchers seeking sustainable exploration. The extreme temperature variations on the lunar surface and the 14-day lunar night pose great challenges to the stable output of electricity and heat energy from the lunar base energy system. In addition, the launch cost of constructing lunar base has emerged as an urgent research focus. In-Situ Resource Utilization (ISRU) has the potential to be a feasible and effective way. With the aim of reducing launch mass, this study proposes a combined heating and power system (CHP) with ISRU for lunar base. With specific power and net output being the primary research objectives, the system design and thermal performance analysis are conducted. The results show that the proposed system can achieve a net output of 101.25 kW and a specific power of 13.00 W/kg by optimizing working fluid and parameters to satisfy the heating demand of 15 kW. Compared with the solar photovoltaic cell system of 0.86 W/kg and the nuclear reactor power system of 6.88 W/kg, the proposed system with ISRU can significantly reduce launch costs while ensuring sufficient power and heat output.

A comprehensive optimization study of personal cooling radiant desks integrated to HVAC system for energy efficiency and thermal comfort in office buildings

Personal comfort systems (PCS) maintain the occupant's preferred thermal environment and expand his thermal comfort experience under varying environmental conditions. Among PCSs, radiant-based systems are popular due to their comfort and energy efficiency. A personal cooling radiant desk (PCRD) in conjunction with conventional heating, ventilation, and air conditioning (HVAC) has proven to reduce energy costs. A system's energy and thermal performance, however, depends on various factors making it important to identify the optimal design parameters of a PCRD coupled with HVAC system in an office space. To optimize the energy and thermal performance of the PCRD-HVAC system, a numerical/mathematical model is developed simulating different design parameters. The model uses an artificial neural network (ANN), combined with a multi-objective genetic algorithm (MOGA) to identify the optimal design parameters. The decision variables include the supply temperature, the temperature, and the flow rate of chilled water flowing inside the desk. The study's findings show that the optimal design parameters achieved a balance between thermal comfort and energy efficiency. The recommended design parameters result in an annual energy consumption of 3880 kWh and a predicted percentage of dissatisfied individuals (PPD) of 6 %. The experiment is carried out to validate the model showed a maximum relative error of only 12.54 %. The results of this study have important implications for designing sustainable cooling solutions for office spaces in hot climates. The successful optimization of the PCRD system highlights the importance of balancing energy efficiency and thermal comfort in designing sustainable cooling solutions.

Thermal and structural response of a pavement solar collector prototype

Thermal and structural response of a pavement solar collector prototype

Thermal energy storage with tunnels in different subsurface conditions

Thermal energy storage with tunnels in different subsurface conditions

Experimental performance of a full-scale solar thermal system designed to meet residential heating demands with passive solar energy

This article presents the results of a 250 day study into a novel mechanical system (called PiSCES) that increases the proportion of residential heating demands that can be met with passive solar energy. PiSCES uses hydronic floor cooling to capture excess solar gains to avoid overheating in highly glazed spaces and this extracted energy is transferred to thermal energy storage (TES) systems via a heat pump. The stored energy can then be used to supply active space heating (SH) and domestic hot water (DHW) heating demands as needed. In the current experiment, active cooling removed 54% of the passive solar gains entering the test house and, of the gains left in the conditioned spaces, 93% were able to offset active heating demands without causing overheating. The excess daytime solar gains collected by PiSCES were used towards active heating demands and resulted in modest solar fractions between 51%–54% for SH and between 30%–39% for DHW demands. The utilization of passive solar gains towards heating demands was increased from 49% to around 70% with the addition of PiSCES to manage and distribute the incoming gains. Although PiSCES, as it is currently configured, was not seen to be a net energy benefit for the test house (the system consumed more electrical energy to operate than the solar energy it was able to resupply), it is suspected that improved TES efficiency, increased TES capacity, and a modified heat pump design could significantly improve performance in future studies.

An experimental investigation to optimise pebbles-based sensible heat storage system: An exploration to improve thermal efficiency of solar devices

The substantial energy loss from the thermal system is the most prevalent reason behind their deprived performance. The use of some energy storage systems is one of the most promising solutions to address this difficulty. The present study is associated with designing an efficient and cost-effective sensible energy storage system to improve the thermal performance of thermal systems with pebbles as sensible energy storage material. The present study examined 28 pebbles of various sizes (1–50 g) outdoors, in a water bath, and in a greenhouse. During this exploration, it was found that pebble temperatures were almost identical in experiments. Regardless of pebble mass, it varies from 46.9 °C to 43.5 °C. The pebbles released 77 % less energy after losing 98 % of their bulk mass. The highest and lowest sensible heat transfer was 0.0217 W (50 g pebble) and 0.0005 W (1 g pebble). The average charging and discharging efficiency were estimated as 19.1 % and 56.1 %, respectively. The remarkable impact of employing pebbles as sensible heat storage material is that they extend system operation time. Estimated regression equation: Total mass of stones needed (kg) = 2.45–0.1882 Mass of stone (gm) + 2.2885 Heat to be absorbed (W). Today, most surface water reservoirs are heavily polluted, making direct human consumption unsafe. Since pebbles are abundant around surface water, reservoirs like rivers, lakes, and ponds may be directly employed for heating and water decontamination.

Thermal and economical performances analyses of a desiccant wheels-assisted atmospheric water harvesting system used in humid climate regions

The thermal and economic performance of an atmospheric water harvesting system that uses four-stage desiccant wheels to pre-humidify processed air was analyzed. A vapor-compression refrigerator was used as the cold source. Two types of heat sources, i.e., heat pump and solar water heater, were considered, and their performance was evaluated. First, thermal performance of the system using different heat sources was analyzed under humid ambient conditions (relative humidity was 40–90 %, dry bulb temperature was 15–35 °C). The results showed that the water harvesting rate was 25.1–94.1 kg/h under these ambient conditions. When a heat pump was used, the water harvesting efficiency with heat recovery was 0.97–2.48 kg/kWh, and 2.41–4.59 kg/kWh when the solar water heater was used. The economic performance of the system was investigated by using diesel generators as the power source. To provide drinking water for 100 people, who consume 3–8 kg/day/person, as compared with bottled water sold in the market, the recovery period of the systems with heat recovery were 0.97–2.58 years and 0.34–0.91 years when the heat pump and solar water heater were used, respectively.