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Abstract The thermo-hydraulic and exergy characteristics of a new design called a triple tube helical coil with an inner triangular twisted tube, TTHCITTT, were explored experimentally. The structure of the new design involved a modified inner twisted fluid path for the inner tube of a triple tube helical coil with an inner triangular twisted tube. The study involved the impact of various designing parameters such as twisted pitch ratio, coil torsion, coil inclination angle, Dean number, and double tube helical coil with an inner triangular twisted tube, as a particular reference. The experimental runs were carried out at a wide range of inner annulus Reynolds numbers from 3000 to 26,900 corresponding to velocities of 0.05 to 2.05 m s−1. The main remarks show that the triple tube helical coil with an inner triangular twisted tube presents superior thermo-hydraulic and exergetic characteristics compared to the double tube helical coil with an inner triangular twisted tube by 73.68%. While the twisted pitch ratio increased from ∞ (smooth) to 4.69, the Nusselt number was enhanced by 24.7% at the expense of increasing the friction factor by 36.4%. The coil torsion presents a noticeable impact on increasing the Nusselt number by 18.8% while the increase in f h is approximately 12%. The coil inclination angles of 0° and 90° present a higher Nusselt number compared to that of 45° by 9.3%. The maximum thermal performance factor reached 2.12 for a twisted pitch ratio of 4.69 and coil torsion of 0.068 and at a coil inclination angle of 90°. The smooth tube predicts a higher exergy destruction rate and dimensionless exergy loss than the corrugated tube by 25% and 26.9%, respectively. New correlations to predict the Nusselt number and the friction factor were correlated. Graphical Abstract

Abstract This paper discusses the oil retention characteristics in the evaporator and suction line in a vapor compression system. Oil retention in the components can lead to reduced compressor efficiency and potential breakdowns. Lubricant in the evaporator reduces heat transfer efficiency and increases pressure drop, particularly under high-quality conditions. However, lubricant can also have a beneficial effect by making refrigerant distribution in the evaporator better. Experimental studies on the critical mass flux for oil recovery and the measurement of oil retention in the suction line are presented, highlighting key findings. Additionally, prediction models for oil retention in both the evaporator and suction line are suggested and organized. Most of the refrigerants discussed in this paper have a high global warming potential (GWP), except for R1234yf and R32. Given the global focus on transitioning to low-GWP refrigerants, future research should target the oil retention characteristics in next-generation refrigerants.

Abstract The model for predicting thermal comfort conditions established by Fanger remains widely used in scientific work, as a default means of in situ measurements. However, the use of Fanger data leads to dissatisfaction among users of air-conditioned buildings in humid tropical areas. This conclusion emerges from the work of Kemajou and al. (Cameroon) and Olissan and al. (Benin) in 2012, after survey studies on the judgments of thermal sensations of people occupying various air-conditioned spaces. This article develops a correction model for the Fanger model, by coupling the latter to models for predicting skin temperature and heat loss by evaporation of sweat through the skin, as well as to the skin thermal sensitivity of people active in a humid tropical climate. The model thus determined shows that the predicted optimal comfort temperatures are located in the range of 26.1 °C to 27.5 °C and better meets the expectations of the populations in this region. The respective differences with the investigations of Kemajou and al. and those of Olissan and al. are 0.40 °C and 0.55 °C. It also appears that the comfort humidity range is 30% to 80%, apart from any other safety measures.

Abstract With the aim of saving a portion of the high-quality energy consumed in mechanical vapor compression systems for air conditioning applications, the present work focuses on utilization of low-quality energy conversion processes due to fluid evaporation. The conventional indirect evaporative cooler is selected based on its preference for further modification compared to a regenerative indirect evaporative cooler. It is configured to be operated with two identical stages in series. This task is achieved by developing a thermodynamic model to analyze the performance of the cooling unit and to indicate the extent of its development compared to the cooler in one stage. Preliminary results show that the best operating condition is when the ratio of primary air to secondary air is 1. The cooling unit produces fairly comfortable air within limited climatic conditions. It delivers air at 26 °C and lower even at climatic temperatures as high as 48 °C, but within a very low relative humidity range. The relative humidity range extends to less than 58% as the outdoor air temperature decreases. At high humidity levels (64 to 80% depending on climate temperature), cool air cannot be obtained at 26 °C, and the cooling unit performance is limited only by what the first stage produces. The average performance of the cooling unit exceeds that of the first stage by 42.6%. Increasing air flow rate leads to an increase in cooling capacity, but it also has a negative impact on supply temperature and effectiveness.

Abstract This study presented a numerical simulation of heat transfer characteristics in a microchannel evaporator for a transcritical CO2 air conditioning system, and the simulated results have been validated by the experimental data. The evaporator consists of 6 passes with 29 flat tubes. Each flat tube has 10 microchannels having a 1.2 × 0.6 mm cross-section. The two-phase flow was simulated in the range of evaporation temperatures from 5 to 15 °C; the mass flow rates of 24.16, 30, and 34.96 g/s; and inlet vapor qualities of 0.5, 0.61, and 0.75, respectively. The results show that the two-phase flow with the evaporative temperature at the inlet of 5, 10, and 15 °C became superheated at the 3rd, the 4th, and the 5th pass, respectively. At the evaporation temperature of 15 °C, the heat transfer coefficient decreases from 8.1 to 3.6 kW/m2 K as the vapor quality increases from 0.75 to 1. With the mass flow rate of 30 g/s, in the tube length range from 0 to 1.1 m, the heat flux achieved around 1.55 kW/m2. The numerical cooling capacity gets the maximum value of 2.85 kW at the evaporative temperature of 10 °C. The numerical results are in good agreement with those obtained from the experimental results and the other published results, with a deviation of less than 10%.

Abstract In this paper, a neuro-adaptive PI control strategy for a water-cooled centrifugal chiller system is developed, and its control performance is examined. The system model consists of a flooded evaporator, a flooded condenser, a centrifugal compressor, and an electronic expansion valve. The overall system consists of three control loops: a compressor speed control loop, an inlet guide vane (IGV) control loop, and a condenser liquid level control loop. A neuro-adaptive control strategy for compressor speed control was designed. The control performance of the chiller was tested by carrying out simulation runs using an integrated building and HVAC (IB-HVAC) system model. The major details of the IB-HVAC model are described in this paper. Results show that the neuro-adaptive controller can adapt to new system dynamics of the IB-HVAC system and give good setpoint tracking responses under a wide range of operating conditions. The results show that the neuro-adaptive controller performs better than the constant gain PI controller in terms of speed of response and setpoint tracking properties.

Abstract This study involves the collection of data from 10 different articles to develop experimental-based models for predicting the condensation heat transfer and the frictional pressure drop. The dataset comprises a total of 1168 condensation heat transfer coefficients and 792 frictional pressure drop data. The applied operating range considered is within the reduced pressure of 0.1–0.95, mass flux ranging from 75 to 700 kg/m2s, and an inner diameter between 3.4 and 12.5 mm. We developed the models for the condensation heat transfer coefficient based on Akers et al.’s model, whose parameters are the Prandtl number, density ratio, vapor quality, and mass flux. The total error for the condensation heat transfer coefficient is ± 22.6%. The data is further categorized into two groups of the reduced pressure: P r 0.5 with an error of ± 18.9%. The frictional pressure drop models were developed based on the three different ranges of the reduced pressure. The utilized non-dimensionless parameters were the two-phase multiplier (Φlo 2), the Bond number (Bo), the Weber number (We), and the Martinelli parameter (Xtt), along with the regression coefficients. Regarding the frictional pressure drop correlation, the total error is ± 32.7%, and the data is divided into three segments: P r

Abstract This study investigates the utilization of Al2O3 nanofluids in an Active Magnetic Regenerative (AMR) system, focusing on varying nanoparticle concentrations from 0.01 to 1.0%. Numerical modelling is used to analyze the effects of nanoparticle incorporation on system efficiency and cooling performance. Al2O3 nanoparticles are found to significantly increase the thermal conductivity, density, and viscosity of the base fluid while reducing specific heat capacity. Comparative analysis reveals that Al2O3 nanofluids outperform pure water in terms of cooling performance, achieving a lower final temperature and a higher temperature span after 60 min of operation. Moreover, the study highlights that cooling capacity and pumping work increase with higher nanoparticle concentrations, with a notable improvement of 64.95% in cooling capacity and 39.31% in pumping work for the 1.0% Al2O3 nanofluid compared to water. The Coefficient of Performance (COP) of the AMR system peaks at an optimal nanoparticle concentration of 0.2%, reaching 3.88, before declining due to increased pumping power requirements.

Abstract Thermoacoustic air-to-water air source heat pumps (TAWASHP) are the eco-friendly, simple, compressor less, low cost and likely looking future substitute for the existing compressor-based heat pumps. In this work, the design optimization of the 1-kW TAWASHP with helium for the temperature difference of 15 to 70 K for pumping heat from the atmospheric air to water using the linear thermoacoustic concepts was discussed. The optimized design can fit for both cooling and water heating applications without wasting the heat rejection to the surrounding atmosphere, rather supplied to the insulated hot water tank. The optimized one-fourth wavelength resonator TAWASHP shows the coefficient of performance of 1.1 to 2.34. The theoretical results are validated with the DeltaEC software results, and the results are in concurrence with each other. The DeltaEC predicts the TAWASHP can supply 1.55 to 3.35 kW of heat to water, which is equivalent to 37.3 to 80.3 kWh of heat energy per day.

Abstract The main focus of this study is the transmission of SARS-CoV-2 through virus-laden aerosols in enclosed spaces that utilize ceiling fans. The impact of an air circulation of ceiling fans on virus transmission is not clear. Computational modeling is employed to investigate aerosol transmission within an enclosed space that features ceiling fans. The aerosol concentration is modeled using a transport equation, and the probability of infection distribution across individuals’ breathing zones is assessed. The particle removal efficiency for two ceiling fan speeds of 10 and 35 rad/s is calculated to evaluate the effect of the ceiling fan’s shear flows on the spread of breathing aerosols. The simulated breathing aerosol considers various environmental situations, including thermal gradients, thermally active surface interaction, and deformability. The results indicate that increasing the ceiling fan speed within an enclosed space causes the aerosol cloud to circulate within the room rather than exiting it. Therefore, ceiling fans may not effectively suppress breathing aerosols and could increase transmissibility. Understanding aerosol behavior is essential in reducing the risk of SARS-CoV-2 transmission in enclosed spaces.

Abstract Hydrogen emerges as a promising alternative energy source, particularly in fuel cell applications, necessitating efficient and safe charging and storage systems. This paper presents the design and development of a specialized regulator tailored for high-pressure hydrogen environments. Focusing on precision control, the regulator ensures optimal performance and safety during charging and storage phases. In order to improve the unstable response characteristics of the existing commercial hydrogen regulator, which has the same differential pressure generation site and pressure control site, a regulator operating at an ultra-high pressure of 105 MPa was designed by separating the differential pressure site and the control site. And structural safety and performance of the regulator were predicted through structural and flow analysis. The results of structural and flow analysis of a 105 MPa high-pressure regulator that can be used for high-pressure hydrogen charging and storage systems were compared with the experimentally measured values.

Abstract In this paper, the performance of a parallel two-stage compression (PTC) cycle on the domestic refrigerator-freezer in a laboratory according to the IEC 62552–2015 standard is investigated. The relatively large temperature difference between the fresh food compartment (FFC) and the refrigerant in the fresh food compartment evaporator (FFCE) leads to high compression and irreversible losses in the refrigeration circuit. To avoid the mentioned problems and reduce energy consumption, a PTC cycle is used. The innovation of this article is the 4E analyses (energy, exergy, exergoeconomic, exergoenvironmental) for the PTC cycle using the results obtained from the laboratory. Ultimately, the multi-objective optimization of the PTC cycle is conducted. For optimizing the PTC cycle, the total cost rate and the exergy efficiency are set as targets and the evaporator pressure and condenser pressure as variables. MATLAB and REFPROP 9.1 are used to model the system. Results showed that the highest exergy destruction rate is associated with the FFCE (0.349 kW) and compressor (0.183 kW). The highest exergy efficiency among the equipment is evaporators. The maximum exergoeconomic factor is related to the freezer compartment evaporator (FZCE) (98.70%) and then the compressor (98.62%). FZCE has the highest environmental impact (99.9%).

Abstract The objective of this study is to design a heat-recovery boiler for a 1 MW-class gas engine-based cogeneration system intended to recover heat from engine exhaust gas. To accommodate high-pressure applications, a water tube-type boiler is selected. For ensuring effective water circulation within the boiler, an innovative modular-type boiler based on the mini-boiler concept is developed. This boiler comprises finned tube-type risers, and their heat-transfer characteristics are measured and compared with the conventional correlation used in the design process. Additionally, an inlet guide vane is developed to address the temperature nonuniformity resulting from the shape mismatch between the gas engine outlet and heat-recovery boiler inlet. The performance of the proposed boiler was evaluated by integrating it into an experimental rig. The diamond-shaped inlet guide vane, which was designed by computational fluid dynamics, facilitated a uniform temperature distribution. However, the temperature became nonuniform downstream owing to the influence of a downcomer. Although the modular heat-recovery boiler effectively produced steam from gas engine exhaust gasses, its heat-transfer performance in the downstream section was lower than expected, necessitating additional heat-transfer area.

Abstract Virtual product design (VPD) of the refrigeration cycle has long been a major subject of many engineers and manufacturers. Issues should be the question of how simulation gets close to the real world in virtual ways. It is especially true when we consider variable refrigerant flow (VRF) heat pumps, having various types of indoor unit combinations, long and complicated piping configurations, and simultaneous cooling and heating functions under extreme weather conditions. In this regard, model-based systems engineering (MBSE) or model-based design (MBD) guides a methodology to make a virtual model easily. Now, there are plenty of engineering platforms and tools to make a strong simulation model, which provides interfacing technology among multiple physics, different dimensions, and codes in different languages. In the study, the authors share their experience in the virtual design for a VRF heat pump system including the architecture, multiple physics, and the connection with the control SW. Modelica, an acausal and object-oriented modeling language, constructs the backbone of the model to describe the dynamic behavior of refrigerants and to combine external components in the form of functional mock-up units (FMUs). The developed virtual model is validated against measured data, showing it can reproduce all the essential physics of interest both in qualitative and quantitative ways.

Abstract The performance of an ejector-assisted condenser outlet split dual-evaporator cycle is compared with a conventional dual-evaporator cycle albeit consisting a pressure reducing valve. The cycles do not employ any separator due to its inability to efficiently separate the liquid and the vapor phases. The comparison of both the cycles has been made for the same cooling capacity in low-temperature evaporator and unit flow rate of R134a and R1234yf as refrigerants. The impacts of changing the operating temperatures of evaporator and condenser have been examined in the current investigation. The study reveals that with the increase in temperature of the high-temperature evaporator, the cooling capacity of the high-temperature evaporator yields, while that of the low-temperature evaporator plummets in both the cycles. Further, the compressor work is allayed in the ejector-assisted cycle; thus, the COP is enhanced considerably. The percentage COP improvement over the basic cycle is obtained from 14.7 to 17.53% for the refrigerant R1234yf and from 14.45 to 17.32% for R134a; however, the COP of both the cycles with R12134yf is slightly lower than with R134a. The ejector has been modeled assuming a constant pressure theory. The observed trend indicates that the entrainment ratio is improved with the rise in the temperature of low-temperature evaporator, whereas it is decreased with the rise in the temperature of high-temperature evaporator.

Abstract Four hot-gas bypass defrosting configurations for CO2-NH3 cascade blast freezer for application in fish processing firm are numerically investigated. Due to the high moisture content of fish, defrosting is necessary after every 4 to 5 h of batch operation. A thermodynamic model for the cascade system and defrosting was developed to study various defrosting configurations formulated by rearranging the existing compressor to operate as a defrosting compressor and with the addition of an external defrosting compressor. From the simulation findings, it can be summarized that the conventional hot-gas bypass defrosting without defrost compressor is suitable for a high-capacity cascade refrigeration system with more than three evaporators. For low cooling capacity refrigeration systems, a defrosting compressor is necessary to elevate the temperature above the cascade condensing temperature. A dedicated defrosting compressor with a power consumption of 3.1 kW and a modified refrigeration/defrosting compressor with a power consumption of 6.8 kW can deliver 33.3 kW of heating at a temperature of +10 °C (45 bar). Incorporating a desuperheater between the main and defrosting compressors reduces compressor temperature and maintains the lubricating oil stability, without change in defrosting energy consumption and less exergy loss. The defrosting efficiency is obtained in the range of 39.7–42% which is in agreement with published literature.

Abstract Air conditioner (AC) systems are important for maintaining indoor thermal comfort, but discrepancies can exist between setpoints and the actual room temperature. In the present study conducted in a typical Korean office during summer, we identified differences of up to 2.77 °C between the AC setpoint and the average room temperature. This variation may have originated from the oscillatory cooling pattern, leading to moments of discomfort even though the overall thermal balance was maintained. While consistent initial cooling rates were observed for various setpoints, oscillations at 20 °C lowered the efficiency of the AC system. A bi-exponential model applied to the cooling pattern confirmed a two-phase cooling process. Interestingly, the coefficient of performance was highest at the lowest temperature setpoint, even though this led to greater energy consumption and possible overcooling. The weather strongly affected AC performance, with rainy conditions requiring less power than sunny conditions at the same setpoint. Furthermore, our experiment comparing the predicted mean vote (PMV) with actual human comfort revealed that the PMV often recommends a cooler ambient temperature than what occupants actually prefer.

Abstract In the current era, national and international energy strategies are increasingly focused on promoting the adoption of clean and sustainable energy sources. In this perspective, thermal energy storage (TES) is essential in developing sustainable energy systems. Researchers examined thermochemical heat storage because of its benefits over sensible and latent heat storage systems, such as higher energy density and decreased heat loss. Solar energy is a promising alternative among the numerous renewable energy sources. As a result, this study provides an overview of thermochemical heat storage materials, focusing on materials utilized by solar energy systems in buildings. The research examines the storage materials used in relevant studies and the models used to predict and enhance system performance.

Abstract In this work, a two-dimensional computational fluid dynamic (CFD) model is developed to describe the drying process of a packed bed made of spherical particles. The volumetrical evaporation rate inside the bed is computed from the pressure difference between the particle surface and the airflow. By using the thermal equilibrium assumption, the heat conservation equation is derived. The CFD model is solved in the COMSOL Multiphysics environment. The obtained results indicate remarkable maldistributions of temperature and moisture content. These maldistributions can be explained by the impact of lateral edges on thermo-hydraulic behavior. Additionally, the impact of particle diameter, air velocity, and bed width on the spatial-temporal moisture content and temperature distribution is investigated. It shows that the CFD model can be simplified to the receding front drying model for a bed made of small particles. Furthermore, by changing the thermal boundary conditions at the lateral edges, the influence of the heating mode at the lateral edges on the drying behavior is explored. The results indicate that contact heating at the bed wall can help to accelerate the drying process significantly.

Abstract The resonator is one of the key components of thermoacoustic machines and the choice of its geometry is of course of crucial importance, as it determines the way the machine operates. The resonator must be designed so that the quality factor of the resonance is as high as possible and must satisfy the technological production constraints related to the high pressurization of the working fluid and the presence of temperature non-uniformities. The shape of the resonator can be modified to reduce certain loss phenomena, particularly on the walls, and to limit the formation of harmonics in the high-level acoustic field. In this work, an acoustic power losses analysis and a numerical study of a standing-wave TAE with air working gas, considering changes in resonator shape, are performed to investigate the effect of resonator geometry on the thermoacoustic energy conversion. The acoustic power dissipation in the resonator is analyzed based on the simplified thermoacoustic theory and the numerical study is conducted based on a 2D numerical model based on a CFD analysis. Results show that the shape of the resonator significantly affects the frequency, the temperature along the stack, and the acoustic pressure produced on the TAE. In addition, it is shown that the resonator composed of two different diameters showed its ability to produce a high acoustic pressure amplitude (20.5% than the iso-diameter resonator) and minimize the viscous and thermal losses.

Abstract We report a numerical evaluation of the impact of continuous helical baffle on the heat recovery efficiency of counterflow tube bundle heat exchangers. The baffle inclination angle has been varied from $$11^{\circ }$$ 11 ∘ to $$22^{\circ }$$ 22 ∘ . Since the fluid flows over the tube bundle at an angle due to helical flow inside the shell, the heat exchanger operates in cross counter mode. Fluent simulations with the k- $$\omega$$ ω transition shear stress transport turbulence model have been performed to investigate the thermal-hydraulic parameters of the system in terms of heat recovery efficiency, pressure loss, and overall heat transfer rate. Outside air temperature has been varied to mimic cold and warm weather. Pressure loss has been constrained to be less than 250 Pa, conforming to EU guidelines for energy labeling of residential ventilation units. At the maximum volume flow rate of 40 m $$^3$$ 3 /h, the device performed with over $$80\%$$ 80 % heat recovery efficiency for the considered temperature difference. Continuous helical baffles helped to improve convective heat transfer by reducing cross flow area and increasing velocity. Smaller angles result in greater pressure loss while having no discernible effect on heat recovery efficiency for the considered geometry. The analysis demonstrates the potential of a compact counterflowing recuperative heat exchanger with continuous helical baffles for decentralized ventilation systems and serves as a basis for further optimization.

Abstract This work attempted to conduct an experimental study which demonstrates the effect of the initial concentration of solute on the apparent viscosity of ice slurry in a horizontal circular pipe. The study was conducted on ice slurry based on propylene glycol, varying from 5 to 24% with different ice mass fractions varying from 5 to 25%. During the experiments, the initial concentration of the propylene glycol, ice concentration, and flow rate was modified as parameters. The flow tests were performed on laminar flows. The results of the investigation revealed that the ice slurry behaved like a non-Newtonian fluid, while it sometimes behaved like a Newtonian fluid. The rheological behavior of the ice slurry is reflected by its viscosity. For the shear-thickening behavior, the apparent viscosity increases with increasing the shear rate, and for the shear-thinning behavior, the viscosity decreases with increasing the shear rate, while for the Newtonian behavior, the viscosity remains almost constant. Then it was revealed that the viscosity of the mixture became too high for low shear rates at high ice mass fractions by increasing the concentration of the solute. The power law was used to establish a relationship between the apparent viscosity and the indexes of flow and consistency of ice slurry.

Abstract The approach that could reduce the energy consumption of water-cooled chillers in office buildings was investigated through experimental and simulation methods. The chiller was modelled in TRNSYS and validated using physical measurements from an operational water-cooled water chiller and fan coil system. The validated model was used to analyse the energy consumption of the water chiller-fan coil system under a high chilled water temperature setpoint (CWTS) in a representative commercial office building. Subsequently, indoor thermal comfort was evaluated using the PMV-PPD model. Finally, the design of experiment (DOE) was employed using a statistical two-level non-randomized factorial design in Minitab to study the effects of high CWTS, number of rows, and tube diameter on the heat and mass transfer performance of the fan coil unit. The results showed that the CWTS can be increased by various degrees from 10 up to 18 °C for energy efficiency for a commercial office building in the tropics. This increase in CWTS would result in a daily energy saving potential of about 5% of the chiller as compared to the existing operational settings without any extra cost. Conversely, the daily energy consumption by the fan coil would increase by about 5.5% by this increment in the CWTS. It was determined that the chiller system can provide comfort even when the CWTS is increased to 14 °C. The DOE analysis showed that under the condition of high CWTS (14 °C), energy consumption that is less than the current energy consumption may be expected from the fan coil system when the number of rows increased from 3 to 6 and the tube diameter increased from 7 to 9 mm.

Abstract One of the most important parts of direct evaporative cooling systems is the cooling pad. Pads vary in materials and construction features. The parameters studied in the performance of the pads are air speed, pad thickness, geometrical characteristics, and its configuration and the provided water flow rate. The performance of the pads is usually determined through saturation efficiency, pressure drop, temperature drop and humidity increase in the treated air, evaporation and water consumption, cooling capacity, coefficient of performance, and heat and mass transfer coefficients. Since the geometry and how to place the pad in the evaporative cooling system is one of the most important issues related to the performance of such systems, the present work experimentally investigates the amount of cooling and evaporation of the direct evaporative cooling system under 5 different angles of placement of the cellulose pad in relation to the vertical position. It includes angles of $$0^\circ$$ 0 ∘ , $$5^\circ$$ 5 ∘ , $$10^\circ$$ 10 ∘ , $$15^\circ$$ 15 ∘ , and $$20^\circ$$ 20 ∘ in 5 different air speeds, 2 different inlet water flow rates, 2 inlet air temperatures, and 2 different inlet water temperatures. Results show that the lowest output temperature, highest air relative humidity, highest coefficient of performance (about 12% more than $$0^\circ$$ 0 ∘ ), highest saturation efficiency, and highest evaporation rate are obtained in the case of a $$15^\circ$$ 15 ∘ of cooling pad placement angle.

Abstract The primary focus of this study is on the energy, exergy, and environmental (3E) analysis of a dedicated mechanical subcooled vapor compression refrigeration (DMS-VCR) system for applications involving commercially available water chillers that employ R134a (in both subcooler and main cycle). For a cooling capacity of 100-kW water chillers, the mathematical model of the DMS-VCR system is built to determine the performance parameter of the system. The DMS-VCR system reduces electricity usage by 15.52% and increase in COP by 9.5%, which results in a significant reduction in CO2 emissions of about 15.55%. When compared to equivalent vapor compression refrigeration system (VCRS), the system’s exergetic efficiency is also increased by 8%. Since the computer simulation results will undoubtedly give design engineers a better option, the subcooling and superheating of the vapor compression refrigeration system become alluring in this study. Consequently, the DMS-VCR system performs better as per the combined 3E study.

Abstract Responding to climate change and adapting to global warming requires creative solutions. In Iraq, the most reliable and popular tool to have buildings cooled is airconditioning units (AC). While an evaporative cooler is not enough to achieve thermal comfort in a very hot climate, AC units consume a lot of energy which causes a significant load on the grid in Iraq resulting in increasing the emissions of CO2. This paper investigates the potential energy-saving associated with adopting a new arrangement of heat recovery ventilation (HRV) unit and evaporative cooler to achieve thermal comfort with far less energy. Two sets of efficiencies of both HRV and the evaporative cooler have been considered, and two different envelope performances are also investigated. To properly size the proposed system, an iterative process has been used until the smallest size of the proposed system enough to cool the building is determined. The proposed system has achieved considerable energy savings comprising a reduction of up to 66% in the cooling load energy consumption and a reduction of up to 44% in the overall energy consumption.

Abstract Magnetic refrigeration utilizes the magnetocaloric effect of a magnetic material, whose temperature changes according to the change of magnetic field strength. It is regarded as an eco-friendly refrigeration technology in that it uses magnetic materials as refrigerants instead of CFC, HCFC, and HFC refrigerants used in vapor compression refrigeration. It is also regarded as an energy-efficient refrigeration technology in that it does not use noisy and power-consuming compressors. This paper presents thermodynamic analysis on a magnetic refrigeration system using experimental results obtained from a magnetic refrigeration apparatus. The magnetic refrigeration apparatus was built using two sets of concentric Halbach cylinders consisting of permanent magnet segments. Specifically the coefficient of performance (COP) of the magnetic refrigeration system was calculated using the energy removed from the working fluid across an AMR bed and the work input to run electric motors.

Abstract In this work the design and analysis of 1 kW thermo-acoustic refrigerators with hydrogen and helium for the temperature difference of 38 K is discussed. Helium is the best for thermoacoustic refrigerators compared to the other competent gases. But hydrogen is chosen since it is less expensive and better thermophysical properties compared to helium. The best parallel plates geometry with 15% blockage is chosen for the stack and heat exchangers. The effect of resonance frequency of hydrogen and helium varying from 400–600 Hz on the theoretical performance is discussed. The coefficient of performance and the power density of 1.65 and 40.3 kW/m3 for hydrogen, and 1.58 and 19.2 kW/m3 for helium is reported for the optimized designs, respectively. The theoretical results are compared with the DeltaEC software results, shows the cooling power and coefficient of performance of 590 W and 1.11 for hydrogen, and 687 W and 1.25 for helium, respectively.

Abstract The application of external stimuli such as the magnetic and electric field in magnetocaloric and electrocaloric materials, and stress and pressure in elastocaloric and barocaloric materials give rise to a new generation of a refrigeration technology based on caloric materials which are considered an emerging alternative to classical refrigeration. Active caloric regenerator (ACR) made in parallel plates is studied under a large number of materials with Comsol multiphysics for a 2D numerical model. In this work, we compare various types of caloric materials, in terms of their thermodynamic properties, working mechanisms, and potential applications as solid refrigerant on caloric refrigeration devices. For this purpose, the energy equation, Navier-Stocks equation, and continuity equation are considered to study the heat transfer phenomena in refrigerator. The water was used as a carrier fluid to transport the thermal energy from the solid refrigerants to heat exchanger. This study is performed at velocity 0.06 m/s and the frequency 2 Hz at room temperature. Among them, Gadolinium show the best results in term temperature span, coefficient of performance, and the cooling power, higher than every other caloric materials, conferring to magnetocaloric cooling globally the most promising system. Our analysis provides insights into the selection and optimization of caloric materials for caloric refrigeration, which can contribute to the development of sustainable energy systems.

This paper shows that the peak temperature of a nonuniformly heated region can be decreased by embedding highconductivity tree-shaped inserts which is in contact with a heat sink from its stem. The volume fraction of the high-conductivity material is fixed, and so is the volume of the solid region. The length scale of the solid domain is L. Inside there is a cubeshaped region with length scale of 0.1L and heat production 100 times greater than the rest of the domain. The location of this hot spot was varied to uncover how its location affects the peak temperature and the design of inverted fins, i.e. highconductivity tree-shaped inserts. The volume fraction of the high-conductivity tree was varied for number of bifurcation levels of 0, 1 and 2. This showed that increasing the number of the bifurcation levels decreases the peak temperature when the volume fraction decreases. The optimal diameter ratios and optimal bifurcation angles at the each junction level are also documented. Y-shaped trees promise smaller peak temperatures than T-shaped trees. The location of the vascular tree in the z direction also affects the peak temperature when the heat generation is non-uniform. In addition, the peak temperature is minimum when z = 0.65L even though the hot spot is located on z = 0.75L