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In order to explore the thermodynamic characteristics of the gradual cooling and liquefaction process of hydrogen, a small-scale open hydrogen liquefaction system with stepwise cooling is proposed, designed and experimentally tested. The fabrication and practical cooling operation of the hydrogen liquefaction system are conducted under the premise of pre-test of neon and safety precautions. The cooling capacity required for hydrogen cooling is continuously provided by two Gifford-Mcmahon (G-M) refrigerators and the returned cold hydrogen. The hydrogen gas is gradually cooled to about 21 K through two pre-cooling heat exchangers (PHEX) and three counter-flow heat exchangers (CHEX) and then throttled to about 120 kPa. Hydrogen gas with a mass flow rate of 0.2 kg/h can be liquefied to meet the design requirements in this system and the experimental results are compared with the Hysys simulation. The comparative analysis reveals that the measured data of key nodes are in good agreement with the simulation results, and the maximum deviation is around 8.70%, which proves the effectiveness of the experimental system and provides validation for the simulation. In addition, the design of the heat transfer module including the structure of the PHEX and the cold shield is reasonable and feasible. In conclusion, the designed experimental system and results can provide a technical reference for the corresponding equipment selection and operating experience in hydrogen liquefaction experiments. • A small-scale open hydrogen liquefaction system with stepwise cooling is proposed. • The temperature is divided into three zones and the throttling process is retained. • A heat transfer module is designed to enhance the heat transfer performance. • Standard operation procedures and safety precautions are conducted to ensure safety. • The experiment data and simulation results are compared to verify the feasibility. [ABSTRACT FROM AUTHOR]

Gravity-assisted separation heat pipes (GSHPs) are extensively utilized in telecommunications base stations and data centers. To ensure year-round cooling, integrating GSHPs directly with a vapor compression refrigeration system is a viable solution. It is unavoidable that the refrigeration system's lubricant will infiltrate the heat pipe loop, thereby affecting its thermal performance. This paper examines the performance of a GSHP, which features a water-cooled plate heat exchanger as the condenser and a finned-tube heat exchanger as the evaporator, when the working fluid (R134a) is contaminated with a lubricant (POE, Emkarate RL-46H). The findings are compared with those from a system free of lubricant. The experimental outcomes indicate that the presence of lubricant degrades the heat transfer efficiency, particularly when the filling ratio is adequate and no significant superheat is observed at the evaporator's outlet. This results in a 3.86% increase in heat transfer resistance. When the charge of the working fluid is suboptimal, the average heat transfer resistance remains relatively constant at a 3% lubricant concentration yet increases to approximately 5.27% at a 4–6% lubricant concentration, and further to 12.32% at a 9% lubricant concentration. Concurrently, as the lubricant concentration fluctuates between 3% and 9%, the oil circulation ratio (OCR) varies from 0.02% to 0.11%. [ABSTRACT FROM AUTHOR]

In industrial processes involving both heat and mass transfer, the enthalpy or total energy difference, not the temperature difference, is a more comprehensive driving-force potential for the design of heat exchanger systems, such as cooling towers. However, current enthalpy methods based on the Merkel integral require numerical integration with implied linear distributions of water temperature. If the cooling range of the cooling tower is relatively small, the outcome of the integration may carry little error. However, for a large cooling range and a substantially increased temperature, the error involved may be significant. Like log-mean temperature difference, a log-mean enthalpy difference method may require only the inlet and outlet conditions without prior knowledge of the enthalpy distributions of the fluids within the heat exchanger. The known Berman's enthalpy difference method requires correction factors and was derived based on the linearization of the interfacial enthalpy and the enthalpy difference between the interfacial moist air and the bulk moist air without underlying interpretation to demonstrate that the method could be broadly used. In this paper, an equivalent enthalpy model is proposed, and the log-mean enthalpy difference is derived without retaining model assumptions. The derived method is compared with some results of Merkel's method from literature with excellent agreement. Thus, the work in this paper would open up the possibility for broad uses of the log-mean enthalpy difference method for many industrial processes involving both heat and mass transfer. [ABSTRACT FROM AUTHOR]

To effectively reduce building energy consumption, a novel full fresh air system with a heat source tower (HST) and a borehole heat exchanger (BHE) was proposed for space cooling and dehumidification in this paper. The cooling system only adopts geothermal energy to produce dry and cold fresh air for space cooling and dehumidification through the BHE and HST, which has the advantage of non-condensate water compared to BHE systems integrated with a fan coil or chilled beam. Based on the established mathematical model of the cooling system, this paper analyzed the system characteristics, feasibility, operation strategy, energy performance, and cost-effectiveness of the proposed model in detail. The results show that the mathematical model has less than 10% error in estimating the system performance compared to the practical HST–BHE experimental set up. Under the specific boundary conditions, the cooling and dehumidification capacity of this system increases with the decrease in the air temperature, air moisture content, and inlet water temperature of the HST. The optimal cooling capacity and the system COP can be achieved when the air–water flow ratio is at 4:3. A case study was conducted in a residential building in Shenyang with an area of about 1800 m2. It was found that this system can fully meet the cooling and dehumidification demand in such a residential building. The operation strategy of the cooling system can be optimized by adjusting the air–water flow ratio from 4:3 to 3:2 during the early cooling season (7 June–1 July) and end cooling season (3 August–1 September). As a result, the average COP of the cooling system during the whole cooling season can be improved from 6.1 to 8.7. Compared with the air source heat pump (ASHP) and the ground source heat pump (GSHP) for space cooling, the proposed cooling system can achieve an energy saving rate of 123% and 26%, respectively. Considering that the BHE of the GSHP can be part of the proposed HST–BHE cooling system, the integration of the HST and GHSP for space cooling (and heating) is strongly recommended in actual applications. [ABSTRACT FROM AUTHOR]

Kuwait stands as one of the hottest locations globally, experiencing scorching temperatures that can soar to 50 °C during the summer months. Conversely, in the winter months of December and January, temperatures may plummet to less than 10 °C. Maintaining a comfortable temperature indoors necessitates a substantial amount of energy, particularly during the scorching summer seasons. In Kuwait, most of the electrical energy required for functions such as air conditioning and lighting is derived from fossil fuel resources, contributing to escalating air pollution and global warming. To reduce dependence on conventional energy sources for heating and cooling, this article presents a case study to explore the potential of using geothermal energy for space heating and cooling in Kuwait. The case study involves utilizing a geothermal heat pump (water-sourced heat pump) in conjunction with a vertical-borehole ground heat exchanger (VBGHE). The mentioned system is deployed to regulate the climate in a six-floor apartment block comprising a small two-bedroom apartment on each level, each with a total floor area of 57 m2. Two geothermal heat pumps, each with a cooling capacity of 2.58 kW and a heating capacity of 2.90 kW, connected to two vertical-borehole heat exchangers, were deployed for each apartment to maintain temperatures at 22 °C in winter and 26 °C in summer. The findings indicate that the estimated annual energy loads for cooling and heating for the apartment block are 42,758 kWh and 113 kWh, respectively. The corresponding electrical energy consumption amounted to 9294 kWh for space cooling and 113 kWh for space heating. The observed peak cooling load was approximately 9300 kJ/h (2.58 kW) per apartment, resulting in a power density of 45 W/m2. Moreover, the HP system achieved a 22% reduction in annual electric energy consumption compared to conventional air conditioning systems. This reduction in electric energy usage led to an annual CO2 reduction of 6.6 kg/m2. [ABSTRACT FROM AUTHOR]

The present research has analyzed the energy and exergy of a combined system of simultaneous power generation and cooling. To provide a comprehensive data sheet of this system, the system has been investigated in the temperature range of 300–800 °C, and 6 working fluids, including air, carbon dioxide, nitrogen, argon, xenon, and helium, have been investigated. The parameters affecting the performance of the system, namely the compressor inlet pressure, the compressor pressure ratio, and the intermediation pressure ratio were investigated. The power produced by the Brayton cycle at a pressure ratio of 5.2 is the highest due to the increase in compressor power consumption and turbine power generation. The results of the parametric study showed that the exergy efficiency of the system has the maximum value at the pressure ratio of 4.73. The results of the parametric study showed that increasing the pressure of the compressor does not have a significant effect on the electricity consumption and the temperature of the working fluid due to the constant pressure ratio. The input energy to the heat exchanger of the absorption chiller decreases with the increase in the Brayton cycle pressure ratio, and as a result, the cooling created by the chiller also decreases. In this method, three objective functions of exergy efficiency, energy efficiency, and total production power are considered as objective functions. The most optimal value of intermediation pressure ratio was obtained after the optimization process of 1.389. Also, the most optimal value of the pressure ratio of high-pressure and low-pressure turbines was reported as 2.563 and 1.845, respectively. [ABSTRACT FROM AUTHOR]

Adsorption refrigerators are a compelling ecological alternative to compressor refrigerators; global warming forces us to constantly look for alternative sources of energy and cold. Cold production in adsorption chillers is based on the use of heat generated by other processes running in the company. Waste heat from production processes, which has, until now, been irretrievably lost, is a potential source of energy for generating cold via an adsorption unit producing chilled water. Cooling optimizes the use of the heating network in summer and can lead to increased electricity production while reducing heat supply losses. Thus far, attempts to implement adsorption refrigerators for widespread use have not been successful as a result of the low efficiency of these devices; this is directly related to the poor heat and mass transfer conditions in the beds and heat exchangers of adsorption refrigerators. The solutions used so far, such as new working pairs, glued beds or modifications to the structure or cycle length, are still not strong enough for these devices. Therefore, it is necessary to look for new solutions. Using micro- and nanobubbles as media to increase mass and heat transfer in refrigerators is an innovative and pioneering solution. Thus, this document describes the most important features of micro- and nanobubble technology applications in adsorption refrigerators. This article is an introduction and a basis for the implementation of further research, consolidating the existing literature as a review. [ABSTRACT FROM AUTHOR]

This study investigates a low-temperature three-circuit cooling system for a 55 kW industrial electric motor. The cooling system provides an increase of the power-to-dimension ratio by 63%, together with an improvement in motor performance. The three-circuit cooling system includes water cooling of the housing and stator and air-cooling of the motor's interior. The test results show that the motor efficiency was maintained in the range between 92.5 and 94.5%, with respect to the motor's power. With power increases up to 90 kW, a winding temperature of 67 °C was observed during three hours of operation. This advancement is particularly valuable for vehicles, ships, and aircraft applications, where maximizing power within limited space is crucial. An analysis of the experimental data showed that the cooling system operates at an average efficiency of 79.2%, indicating that roughly 20% of heat was accumulated in the rotor. This leads to a gradual temperature rise, particularly in the rotor, posing a risk of overheating and failure during motor overloads above 90 kW. Enhancing the cooling efficiency within the motor's interior can be achieved by incorporating extra heat exchangers, implementing evaporative heat transfer, and employing water-cooling circuits at lower temperatures. This, in turn, can boost the electric motor's power-to-dimension ratio. [ABSTRACT FROM AUTHOR]

Earth–air heat exchangers (EAHX) use the soil thermal capacity to dampen the amplitude of outdoor air temperature oscillations. This effect can be used in hot and dry climates for room cooling, and depending on the EAHX design, this cooling can be achieved with very few resources other than those used during EAHX construction. This is an obvious advantage compared to the significant energy consumption and operational costs of refrigeration machines traditionally used in room cooling. Despite the large number of papers on EAHXs available in the scientific literature, very few deal with large-diameter EAHXs (with pipe diameters larger than 0.30 m), and even fewer present monitoring data gathered from a built and functional large-diameter EAHX. The present paper uses monitoring data and provides a detailed quantitative analysis of the performance of a large-diameter EAHX built for standalone cooling of an existing office building. The field monitoring was carried out during a characteristic hot and dry summer period of the south of Portugal. Results show that outdoor air to EAHX exit air temperature gradients reach 9 K and cooling capacities exceed 27 kW. Moreover, the studied EAHX is capable of standalone cooling for outdoor air temperatures up to 33 °C and meets more than 50% of the room design cooling demand for outdoor air temperatures as high as 37 °C. This evidences that large-diameter EAHXs have the potential to achieve significant reductions in CO 2 emissions and in energy consumption associated with building cooling in hot and dry climates. [ABSTRACT FROM AUTHOR]

In this paper, earth–air heat exchanger is examined to achieve better system operation to cool a building in the arid climate of Ouargla city (Algeria). A higher cooling power requires a big pipe size which increases the pressure losses. Based on fluid dynamics, a new approach is carried out to evaluate the air flow pressure losses that contribute to the determination of the required blower power. The mathematical model of governing equations set is presented, and its numerical solution is calculated using a Matlab program. The multi-objectives optimization between two opposite targets is adopted for achieving the compromise solutions between maximal efficiency and minimal system size. For a given cooling power, the resolution of the earth–air heat exchanger model is carried out using the weighting method to perform the bi-objective optimization. At each cooling power, Pareto curves are generated for plotting the optimal points of efficiency and lateral pipe area. Obtained results show that for a chosen cooling power range, the system operation must reach at least an efficiency of 35% but less than 90% to cover all the size-efficiency compromises. Also, the lateral pipe area must be at least 6.025 m2/kW to start with acceptable efficiency. On the hottest summer day, for 3.5 kW as cooling power, the pipe outlet temperature reaches about 26 °C at a relatively high pipe length of about 95 m. [ABSTRACT FROM AUTHOR]

Common phase change materials (PCMs) have serious shortages, and the most important one is the low thermal conductivity. This issue makes the phase change process a time-consuming period that decreases the performance of thermal storage units. This paper concentrated on improving energy and exergy performance with the aid of an air–PCM heat exchanger, which could be employed for free cooling of buildings. For the heat exchanger, the PCM of Rubitherm 22 °C high capacity (RT22HC) and the nanoparticles of multi-wall carbon nanotube were employed. The initial charging and discharging experiments showed that due to thermal conductivity enhancement, melting and solidification periods decreased using nano-PCM with three concentrations of 0.1, 0.2, and 0.5 mass% compared to the PCM without nanoparticles. Moreover, the highest exergy and energy efficiencies were obtained for the case of nano-PCM 0.5 mass% during the charging process and the values were 11.03 and 21.33%, respectively. Experiments with nano-PCM 0.5 mass% were accomplished during three continuous days. The results demonstrated that the heat obtained from nano-PCM 0.5 mass% encapsulations varied with weather conditions. In addition, the output energy and exergy rose with sunrise and fell with sunset. Finally, an economic analysis was carried out for cold climate conditions. The results indicated that the whole invested capital expenditures will return in the ninth year of exploitation. [ABSTRACT FROM AUTHOR]

The simulation and free‐cooling economic optimization of a phase change material (PCM)‐air heat exchanger (PAHX), including containers filled with fictitious SiO2 nano‐enhanced PCM (NEPCM), are investigated. The airside, PCM side and heat balance governing equations are solved numerically by employing analytical solutions during the 3‐month summer from June 22 to September 22. Two climate zones of Tehran and Mashhad have been selected due to temperature contrast, especially at off‐peak times. Particle swarm optimization is employed to determine indoor setpoint temperatures (SPTs) and phase change temperatures (PCTs) to optimize the total cooling energy cost of a residential building. The effects of local climate, airflow rate, nanoparticle concentrations, and SPT range on optimization variables are studied. Two SPTs for day and night and two PCTs for melting and solidifying are between 22°C and 26°C. The mass percentage of nanoparticles is considered to be from 0% to 14%. Based on optimization analysis, Toff‐peak = 22°C, and Tpeak = 26°C are considered the best SPTs for both cities, for Mashhad Ts = 24.05°C, Tl = 18.97°C while for Tehran Ts = 24.83°C, Tl = 25.35°C are considered as the best PCTs. The optimum electrical cost increases significantly with increasing airflow rate and SPT range, while nanoparticle concentration has a low influence of up to about 3% for all desired days. [ABSTRACT FROM AUTHOR]

The current study proposed an innovative combined power and cooling solar Organic Rankine Cycle (ORC) with bottoming vapour absorption (VAS) and vapour compression refrigeration (VCP) cycles using ammonia-water as the working fluid. The advantage of these cycles is the integration of two cooling evaporators, producing equivalent refrigerating effects from the VCP condensate. The power generation sub-system, the topping cycle, employed a solar-driven ORC. At operating conditions, the energy and exergy efficiencies stood at 38.63 and 42.09%, respectively, with overall refrigerating effect, power output, and COP calculated at 1358 kW, 26.65 kW, and 2.34 in that order. The parametric results indicated a 40% and 55% increase in energy and exergy efficiencies at high turbine inlet temperatures, with a 1.73% increase in refrigerating effect and a 1.56% decrease in the exergy of cooling. Similarly, at an elevated generator pressure of 4.75 bar, an overall COP of 3.046 was reached. The total exergy of products and fuel was calculated at 1347.91 and 786.38 kW, respectively, with an exergy destruction ratio of 0.997. The results showed a total improvement potential (IP) of 426.768 kW, with the evaporators, absorber, and heat exchanger having the highest IP of 66. 32, 119.4, and 68.08 kW respectively. The study showed enhancement in performance when compared with previous studies and recommended system optimization and sustainability analysis as future considerations for system practical application. [ABSTRACT FROM AUTHOR]

In the present research paper, the thermal performance of helical ground air heat exchanger (HGAHE) has been experimentally analyzed under Saharan climate conditions during summer season. A flexible PVC pipe with a diameter of 0.06 m and a length of 30 m has been arranged as a helical-coil layout to design the HGAHE, and it is inserted into a borehole of 5 m depth. The study acknowledges that a drop as high as 11.0 °C in air temperature can be achieved with an air velocity of 10 m s−1 and an inlet air temperature of 38 °C. The study also revealed that, by incrementing the air velocity from 10 to 20 m s−1, the heat exchange rate of the HGAHE system increases by 158% after 3 h of operation time; however, the efficiency of the HGAHE decreases by 21.51%. Moreover, thermal performance derating factor (TPDF) increments with increasing the operation time and air velocity. After 3 h of operation time, the highest TPDF is attained as 0.27 with a velocity of 20 m s−1, whereas the lowest TPDF is observed as 0.14 for a velocity of 10 m s−1. [ABSTRACT FROM AUTHOR]

The joint processes of bubble boiling and refrigerant movement in heat pump tubes are considered. A coil located on the back side of the photovoltaic panel (PVP) is used as an additional heating surface. A mathematical model of the theoretical determination of the temperature on the front surface of the PVP cooled by freon in the coil from the back side has been created. A feature of the numerical simulation of bubble boiling of refrigerant in a coil was the insufficiently detailed study of the process and the lack of references to the results obtained in earlier work. The authors have clarified the boundary conditions and assumptions for numerical simulation of the bubble boiling process of refrigerant R407C. The results were compared with the theoretically found values, and later used in the design of an energy complex consisting of a heat pump and a photovoltaic panel. The mathematical model of theoretical calculation of the PVP temperature and the methodology for constructing a numerical model of bubble boiling of refrigerant as part of the methodology for designing energy technology complexes based on the authors' plan to present a unified methodology for energy technology complexes for desalination of seawater based on other types of renewable energy sources. [ABSTRACT FROM AUTHOR]

Heat exchangers in absorption chillers are usually made of copper material. However, problems of corrosion are usually encountered, especially in the solution heat exchanger. In this study a numerical investigation of the heat transfer effectiveness in a double pipe helical heat exchanger made from a thermally enhanced polymer material was conducted. The material consists of a Liquid crystal polymer (LCP), (Vectra A950) as the matrix material, while carbon fibre is the filler material. The resulting composite has a carbon fibre weight fraction of 74%. The heat exchanger was modelled as a counter flow solution heat exchanger to be used in a lithium bromide -- water absorption chiller of 3 kW capacity. The numerical software ANSYS fluent (version 14.5) was used for the modelling and simulation. Thermal and mechanical properties of the thermally enhanced polymer were used in the modelling and simulation. The viscous laminar model was used, while employing a second order upwind solution method. Results indicate that the heat exchanger was able to perform the required duty by reducing the strong solution temperature from 90°C at inlet to 57°C at outlet, while increasing the weak solution temperature from 40°C at inlet to 67°C at outlet. The effectiveness of the heat exchanger was 77.4%. Results were numerically compared to a corresponding heat exchanger of same geometry and flow conditions, made of copper. It was observed that the polymer heat exchanger attained 89.2% effectiveness of the copper heat exchanger. [ABSTRACT FROM AUTHOR]

The efficiency of heat transfer in air-cooled heat exchangers of various industrial facilities depends on the flow rate of the coolant, its inlet temperature and ambient temperature. These parameters are transient and depend both on the features of the technological process and on weather conditions. One option for a compact design of heat exchangers is the use of close-packed coils with a small bending radius. In this case, heat transfer in the complex geometry of the annular space cannot be described by simple one-dimensional dependencies. To solve this problem, it is necessary to consider the three-dimensional spatial structure of the heat exchange surface. Since the size of the grid elements will be several orders of magnitude less than the size of the facility, the size of the computational grids for CFD modeling full-scale heat exchangers will be billions of finite volumes, and even on powerful supercomputers, the solution time will be about a month. One way to reduce computational costs is to use reduced order models, in which the computational domain is not modeled directly; instead, simplified models, such as a porous medium model, are used to describe it. However, such models require additional closing relations and coefficients that characterize the actual channel geometry. This paper presents a technique for creating a digital twin of a heat exchanger with small bend radius coils based on a porous medium model. The values of heat transfer coefficients and hydraulic resistance depend on the speed of air movement in the space between the coils. The calculated value of the thermal power obtained using the strengthened model was 529 kW, which corresponds to the passport data of 500 kW, with less than 6% deviation for the heat exchanger under study. This confirms the correctness of the calculation with accepted simplifications. The calculation time in this case was only a few minutes when using a personal computer. The developed numerical model allows for the resolution of performance characteristics based on the temperature of the cooled medium at the inlet, air temperature, and fan speed. Analyzing the different modes of turning on the cooling fans made it possible to determine the values of the thermal power when turning off the fans or reducing the number of revolutions. [ABSTRACT FROM AUTHOR]

Microchannel heat sinks and heat exchangers are widely used in the cooling of electronic systems. However, it is still important to enhance the heat transfer in the microchannel so that the intense heat generated can be removed. Vortex generators (VGs) create secondary flow structures in the flow, in creasing the fluid mix ing, thi nning the the rmal bou ndary layer, and ultimately boosting heat transfer. Here, we have controlled the flow structure and improved the heat transfer with the lowest possible pressure loss by placing VGs of different sizes, numbers, and angles of attack in a microchannel. The improvement in heat transfer is accelerated as vortex intensity increases. The angle of attack has a significant impact on vortex formation lengths, which reach high dimensions around 90°. Furthermore, increasing the VG length significantly increases the vortex formation lengths. The number of VG pairs has a significant impact on heat transfer and pressure losses. As the number of VG pairs increases, so does the area occupied by the secondary flow regions in the microchannel, increasing the fluid mixture and boosting heat transfer. The highest enhancement in heat transfer using VGs is obtained at around 230%, while the corresponding increase in pressure loss is 950%. According to the JF factor which we consider a performance evaluation criteria, the best result is around 1.38. The G enetic A ggregation R esponse S urface Methodology has been applied to numerical results. The related method is realized to produce results that are consistent with the numerical results within a ±5% error interval. All the input parameters considered in the sensitivity analysis have an impact of at least 10% on the output parameters. [ABSTRACT FROM AUTHOR]

In this paper, a new R744 heat pump system is studied. The gas cooler, evaporator, indoor heat core, and indoor gas cooler are all micro-channel heat exchangers. The R744 high pressure system adopts a combination of an accumulator and internal heat exchanger (ACCU/IHX). In addition, an electronic reversible regulating valve is added before the outdoor gas cooler, making the outdoor heat exchanger able to be used as a gas cooler or evaporator. The water-cooled condenser can improve the performance in the cooling or heating mode. The research contents contain the performance and optimal pressure under extreme conditions as a result of the experiments. The results show that the cooling capacity can reach 8.2 kW with a COP of 1.87, under a 40 °C external circulation intake. The cooling capacity on the battery side can reach 11 kW under an ambient temperature of 40 °C, which can provide a sufficient cooling capacity. Under an ambient temperature of −20 °C, the maximum heating capacity can reach 6.86 kW with a COP of 1.67. Under an ambient temperature of −15 °C, the heating capacity reaches 5.07 kW with a COP of 1.78, when the indoor air volume flow rate is 200 m3/h. Obviously, R744 heat pumps show a huge advantage, compared with the traditional PTC heating or R134a heat pumps at extremely low temperatures. [ABSTRACT FROM AUTHOR]

The work examines the heat exchange characteristics of a condenser in which heat removal of the refrigerant condensation occurs due to natural convection and radiation cooling. The heat exchanger is designed to reduce energy costs for the removal of condensation heat. Unlike traditional air cooling condensers, it uses radiation cooling, a method of heat removal based on its transmission in the form of infrared radiation through the planet’s atmosphere into the surrounding outer space. A method for calculating the thickness of the radiating plate has been developed. To minimize material consumption and cost, the distance between the tubes is reduced to 40 mm, and the thickness of the aluminum radiating plate is reduced to 0.32 mm. The inner diameter of the coolant channels is 1 mm. For the experimental study of the condenser, an experimental stand working on R134a refrigerant was developed. Theoretical and experimental studies of heat transfer have been carried out. The heat transfer coefficient of the heat exchanger, reduced to the area of the radiating surface, was from 10.3 ± 1.36 to 18.7 ± 2.47 W·m–2·°C–1, when the condensation temperature was 12.8...21.9 °С higher than the temperature of atmospheric air. The operability of the condenser is shown both during the day and at night, in the presence of precipitation in the form of rain and snow, and a high level of cloudiness. The material capacity and filling of the refrigerant in the condenser are comparable to the characteristics of air-cooled condensers with forced air circulation. At the same time, it does not consume electricity. It can be used in stationary refrigeration systems (in data processing centers, commercial refrigeration equipment, air conditioners) to increase their energy efficiency. [ABSTRACT FROM AUTHOR]

In this article, energy optimization of the cooling system of IKEA Budaörs is carried out. The cooling system is served by a centrifugal water chiller and includes a large-volume cooling buffer tank. The facility operates the hydraulic system of the buffer storage tank only during the transitional period. The main goal is to reduce energy consumption by changing the operating strategy of the existing system. To test the operating strategies, the operation and the thermal load of the shopping center during the summer season had to be simulated to find the best operation strategy. A hybrid method (real data and calculated values) was used in the simulation. The three operating scenarios examined show that the annual energy consumption and the number of operating hours of the chiller can be reduced by using the buffer tank with the right strategy. In the examined scenarios, a 30% energy improvement was achieved. The possibility of using a buffer tank is significantly limited by the fact that the heat exchangers were sized for low forward water temperatures. By re-sizing the heat exchangers, the utilization of the buffer tank could be considerably improved in conditions close to peak heat load. [ABSTRACT FROM AUTHOR]

Heat reduces the performance of machine tool spindles. In particular, the heating of the shaft leads to numerous undesirable effects. Fluid-based shaft cooling systems exist but are expensive and energy-intensive. For this reason, a novel, liquid-free shaft cooling concept is researched. Heat is transferred from a rotating heat exchanger to a non-rotating and cooled structure through a narrow air gap. In this paper, the cooling potential of this concept is identified simulatively and experimentally by quantifying the heat transfer coefficients as well as the generated air friction. For the first time, a suitable simulation setup for the modelling of such heat exchangers is presented, providing a fundamental contribution to the design of liquid-free cooling systems. [ABSTRACT FROM AUTHOR]

Overheating of solar cells under normal operational conditions highly reduces their energy harvesting efficiency and produces additional problems related to thermal cycling and performance degradation of the modules. In this paper, a novel cooling system for solar photovoltaics, using the underground as a heat sink, is proposed, theoretically described and experimentally validated. A prototype of the technology (including a single-axis sun tracking mechanism) has been designed, manufactured, and rigorously tested in outdoor conditions during summer 2021 in Spain, under different environmental conditions. The excess heat is removed from the backside of the solar module by a close-loop and single-phase cooling system and then dissipated in the underground, which is at a constant temperature of about 16 °C at relatively low depths at the location where tests were performed. A single U-shaped copper tube, 18 mm in diameter, immersed in a 15.5-m-deep borehole naturally filled with water, is used as an underground heat exchanger. As a consequence of the reduction of the cooled module temperature, its net power generation is significantly increased. A promising improvement of the net power generation of the cooled solar module up to 12.4% has been measured for a coolant flowrate of 1.84 l/min per square meter of solar module, proving the technical feasibility of the approach. In addition, a dependency of the power gain with the pump efficiency, the global radiation, and ambient temperature has been observed. [ABSTRACT FROM AUTHOR]

The heat of combustion of converter gas periodically generated in oxygen-converter steelmaking of a metallurgical combine can be used for alternate heating of the ceramic checkers of two or more regenerators (such as Cowper stoves of blast furnaces) and alternate cooling of them by a continuous air flow heated to a high temperature. The air heated to a temperature of about 1200–1300°C can be used as an air blast for a blast furnace, or in a heat-recovery steam generator. A configuration for combustion of converter gas in regenerators and recovery of its heat of combustion is proposed, and a mathematical model is developed to analyze the thermal state of the ceramic checker of regenerative heat exchangers and the temperature of heating gases and heated air during heating and cooling of regenerators with variable flow of heating gases. When using this method of recovery of the heat of combustion of converter gas at the Severstal Company, where two or three converters with a capacity of 410 tons alternately operate, it is possible to save gaseous fuel in an amount of about 200 thousand tons of standard fuel per year and to significantly reduce the carbon dioxide emissions into the atmosphere. [ABSTRACT FROM AUTHOR]

The demand for resource circulation of heat exchangers in air conditioners is expected to grow rapidly; however, the market stocking time is relatively long. Therefore, this scenario was used as a case study for sustainable products design. A material flow analysis was conducted to estimate the balance between global relative resource consumption for shipment, waste, and installed stock from publicly available information up to 2050. Based on the projected demand through 2050, the shipment volume for each year was calculated on a cooling capacity basis. From this analysis, the waste volume was calculated. Using the shipment volume on the basis of yearly cooling capacity, the shipment volume on a resource basis was calculated considering the heat transfer coefficient. The balance between the waste volume and the installed stock was estimated. The resource circulation was simulated by defining variables such as the ratio of units that can be converted from waste to shipment and the ratio of heat exchangers using circulated resources in the total number of shipments. The results indicate that the shipment, waste, and installed stock of resources projected for 2050 were greater than those at the 2021 levels by factors of 2.2, 2.8, and 2.9, respectively. In addition, they were greater than those of the 2021 levels in the scenarios by factors of 1.8, 2.2, and 2.8 accounting for the increase of heat transfer coefficient into account, indicating the importance of improvement of heat transfer. The simulation of circulation showed that a fully closed loop in 2050 would be difficult to achieve owing to the shortage of heat exchangers for waste-to-shipment. Sensitivity analysis also indicated that even under conditions where there is no predicted shortage of circulated resources for 2050, achieving the target in a short period of time may cause a rapid increase in demand for circulating resources. This would subsequently, lead to a shortage of supply compared to demand. Thus, it is important to account for these dynamics relating resource circulation and strategy planning during analysis. [ABSTRACT FROM AUTHOR]

The standard photovoltaic solar panels are characterized by their low efficiency, especially at high ambient temperatures. Cooling with water and nanofluid has been one of the most promising cooling strategies used to minimize the temperature of the PV module and improve the performance of the system. The main objective of this paper is to compare the performance of a PV panel located in the Gabes region in different cases: standalone PV panel, PV/T system with water-cooling, and PV/T system with nanofluid cooling. The tested fluids flow in a rectangular heat exchanger to maximize the contact area between the cooling fluid and the back wall of the solar panel. The influence of mass flow rate, nanofluid mass fraction, and nanofluid type on PV cell temperature, thermal, and electrical efficiency are investigated. The simulation results show that MgO is the best nanofluid in our working conditions and the electrical energy produced by MgO is 77.04 W/m² . In addition, the thermal energy produced by MgO-water nanofluids is higher than that of other nanofluids. To highlight the benefits of using a rectangular heat exchanger mounted on the back of the panel, we compared its performance with that of a standalone photovoltaic panel. The results show that using a PV/T system with a flowing nanofluid inside improves the electrical power by 26.28 W/m 2 compared to a standalone PV panel. [ABSTRACT FROM AUTHOR]

A heat exchanger was integrated to increase the efficiency of a geothermal double flash cycle and decrease the liquid content at a low-pressure turbine outlet. The liquid cooling (LC) and liquid splitting technologies have three different configurations: i.) steam superheating (SH), ii.) steam reheating (RH) and iii.) mixture heating (MH) was implemented. An exergoeconomic analysis was applied to the systems and analyzed using geothermal power plant operation parameters. An increase in the net power of the double flash cycle of 418.6 kW was achieved with LC-SH configuration, 5008.6 kW with LC-RH, 5248.6 kW with LC-MH, 3758.61 kW with LS-RH and 3958.61 with LS-MH. The power of the low-pressure turbine also increased compared to the double flash design in a 0.5236% (SH), 5.48%(RH), and 5.72%(MH), and the produced electricity cost were 5.9963 $ USD/GJ, 5.9976 $ USD/GJ, 6.0089 $ USD/GJ, 6.0086 $ USD/GJ, 5.9336 $ USD/GJ, 5.9482 $ USD/GJ and 5.9481 $ USD/GJ for the double flash, DF-LC-SH, DF-LC-RH, DF-LC-MH, DF-LS-SH, DF-LS-RH, and DF-LS-MH designs, respectively. The DF-LS-SH design is the most feasible because the cost of electricity produced is reduced while the steam quality of the low-pressure turbine and the net power of the geothermal plant increases. • Six modifications to a double flash cycle were analyzed from an exergoeconomic point of view. • The design of liquid splitting and superheating reduced the exergy cost to 5.9336 $ USD/GJ compared to the double-flash base case. • The liquid cooling technology with mixture heating improved the net power by 5331.61 kW. • The liquid content at the outlet of the low-pressure turbine was reduced by 5.54%. [ABSTRACT FROM AUTHOR]

Miniature Joule-Thomson (J-T) cryocoolers are widely used in the cryogenic field due to their advantages of small size, and fast cooling. Selecting the appropriate refrigerant is a crucial task in designing a J-T cryocooler, as it significantly affects its cooling performance. To study the refrigerant-dependent influencing on the cryocooler's performance, an improved one-dimensional model for a conical double layer J-T cryocooler was developed. The model has been verified to have higher accuracy, faster computing speed, and applicability across a wider range of operating conditions. Nitrogen and argon, commonly used refrigerants with similar saturation temperatures, were investigated. Both simulation and experimental results indicate that argon exhibits a faster cooling rate, while nitrogen achieves a lower cooling temperature under the working conditions. The numerical studies suggest that argon's higher density and lower J-T coefficient contribute to its faster cooling characteristic, resulting in a higher heat transfer quantity in the double layer heat exchanger. However, increasing the vessel pressure can quickly reduce the difference in cooling rates between nitrogen and argon, and it may even make nitrogen more optimal. Moreover, it was observed that a significant portion of the cooling capacity is utilized to cool the cryocooler itself for both nitrogen and argon. • The simulation model has been optimized to increase computational speed by over five times. • Experimental verification was conducted on the model containing various working conditions. • A high density of refrigerant is expected to improve the Joule-Thomson cryocooler's performance. [ABSTRACT FROM AUTHOR]

• Three fast cooling J-T cryocoolers with different structures were designed and experimentally studied. • The evaporator temperature is measured to distinct analysis the energy recovery and jet impingement in fast cooling J-T cryocoolers. • The enhanced heat transfer treatment of cold plates can notably boost the cryocooler's cooling performance. • A larger cone angle of the heat exchanger is advantageous and the optimal length depends on the refrigerant type. Compared to other Joule-Thomson (J-T) refrigeration systems, open-cycle miniature J-T cryocoolers offer exceptional rapid cooling capabilities, making them ideal for applications such as infrared guidance in missiles. The energy recovery in the heat exchanger enables the refrigerant reach saturation temperature quickly and improve the jet liquefaction rate. The heat transfer intensity of the impinging jet determines the cooling rate of the target. Hence, heat recovery and the impact jet process are the primary factors behind this rapid cooling, with distinct roles that require separate consideration. The structural differences will directly affect the energy recovery and jet impact process. To investigate these affects, an experimental system for rapid cooling J-T cryocoolers was established and three distinct cryocoolers with substantial structural variations were designed. The important structures, including jet height, orifice diameter, enhanced heat transfer treatment of the cold plate, heat exchanger height, and heat exchanger cone angle, were closely studied. In the range of our experiments, it was found that larger heat exchanger cone angle leading better energy recovery performance, while the length of the heat exchanger is limited by the type of refrigerant. Longer heat exchanger actually introduce too much thermal mass for the refrigerant with better energy recovery performance. In the aspect of jet impingement, enhanced heat transfer treatment and larger jet height will improve the jet heat transfer intensity. [ABSTRACT FROM AUTHOR]

Solution electrospinning is a facile method for the production of nanofibrous meshes. Here, we present a syringe‐jacket heat exchanger as a simple add‐on for solution electrospinning, which enables spinning from various solvents by a direct and precise solution temperature control between −20 °C and 100 °C. An effective manipulation of the solvent evaporation rate is enabled by adjusting the temperature. Exemplarily, we investigated the spinning of poly(vinylidene fluoride)‐co‐hexafluoropropylene (PVDF‐HFP) in pure dimethylacetamide (DMAc) or acetone as representatives of low and highly volatile solvents. Electrospinning of these solutions is not possible at ambient conditions, either due to a too low or too high evaporation rate. However, we find that PVDF‐HFP nanofibers can be successfully electrospun from DMAc at a solution temperature of 75 °C and from acetone at −19 °C. We show for the first time the use of an active solution cooling for electrospinning from a highly volatile solvent such as acetone. The ability to precisely adjust the solution temperature during electrospinning offers an improved process control and broadens the spectrum of spinnable solution compositions. Especially the prospect of replacing highly toxic solvents with less‐toxic solvents such as acetone opens up a wide field of application for the produced fibers. [ABSTRACT FROM AUTHOR]

Just as the double-pipe heat exchanger is being utilized in an increasing number of applications, its research content is also deepening. For this paper, based on the air-conditioning cold and heat source project of a building in Handan, Hebei Province, a 300-meter medium-shallow well double-pipe heat exchanger was used for heating and cooling, and a corresponding heat transfer model was established. The changes of parameters such as the inlet and outlet temperature, heat exchange (with and without a temperature gradient), and borehole wall temperature distribution between a single borehole, double boreholes, and four boreholes over one year in medium-shallow wells were simulated and analyzed. By comparing the obtained experimental data and the simulation data, the accuracy of the heat transfer model was verified. This provides a theoretical basis for the further advancement of the project and lays the foundation for an in-depth study of multi-borehole double-pipe heat exchangers. [ABSTRACT FROM AUTHOR]

Solid desiccant dehumidification systems are an alternative to vapor-compression-based air dehumidification systems. They use solid desiccant materials to adsorb air moisture in space cooling. DCHE can integrate the cooling component in the heat exchanger to achieve higher dehumidification capacity. Comprehensive numeric modeling would be necessary to assist in the design and operation of the DCHE under development to achieve maximum performance. This paper provides the details of a heat and mass transfer model developed for this purpose. The model aims to cover a gap in existing models by independently modeling heat transfer on the solid desiccant, fin, and tube. The model results were compared with an experimental reference for validation. The air outlet humidity and temperature results for dehumidification and regeneration showed a deviation lower than 15% from the experiment. The validated model was used to perform a parametric study for a series of design and operating conditions. The parametric analysis showed that an increase of 25% in desiccant layer thickness and thermal contact resistance between solid elements reduces moisture removal by 9.1% and 1%, respectively. These results indicate the need to independently model the desiccant layer. [ABSTRACT FROM AUTHOR]

Pinch analysis approach of the heat exchanger network in the hydrocracking unit was carried out to save energy consumption and reduce gas emissions simultaneously. This method based on mathematical model of the hydrocracking unit for a heat exchanger network using LINGO program to achieve the minimization of environmental impacts and the reduction of energy cost. The presented energy demands for the heat exchanger network are 20.38 MMBtu/hr and 26.52 MMBtu/hr for heating and cooling loads, respectively. The current analysis shows a huge opportunity in order to decrease the energy consumption of the hydrocracking process at a minimum temperature difference of 60°F. The final results display the save of energy is about 44% for heating utility in the furnace, while the save for cooling utility is around 34%. All these savings of the energy will lead to saving in the energy costs of about 1,415,078 USD$/yr. Similarly, reducing gas emissions in the hydrocracking unit from 12,301.67 to 6,854.77 metric tons/year equates to a reduction of 44.3%. [ABSTRACT FROM AUTHOR]

Motivated by the search for sharp bounds on turbulent heat transfer as well as the design of optimal heat exchangers, we consider incompressible flows that most efficiently cool an internally heated disc. Heat enters via a distributed source, is passively advected and diffused, and exits through the boundary at a fixed temperature. We seek an advecting flow to optimize this exchange. Previous work on energy-constrained cooling with a constant source has conjectured that global optimizers should resemble convection rolls; we prove one-sided bounds on energy-constrained cooling corresponding to, but not resolving, this conjecture. In the case of an enstrophy constraint, our results are more complete: we construct a family of self-similar, tree-like 'branching flows' whose cooling we prove is within a logarithm of globally optimal. These results hold for general space- and time-dependent source–sink distributions that add more heat than they remove. Our main technical tool is a non-local Dirichlet-like variational principle for bounding solutions of the inhomogeneous advection–diffusion equation with a divergence-free velocity. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 1)'. [ABSTRACT FROM AUTHOR]

Background: Everyone in the world started using their home air conditioners as a result of the escalating global warming circumstances. However, the power output of the power plants is consistent throughout the day, therefore it cannot satisfy this enormous demand. Objectives: After several hours of research on conventional air conditioning systems, engineers created a new idea for an Earth to Air Heat Exchanging System that may be used for passive cooling of buildings. Methods: The changeable properties of a pipe include its buried depth, cross section, length, design, number, and inlet and outflow cross sections. Thermal inertia, chimney wall insulation, input and output parts and positions, direction, height, and upper and lower chimney components. The two identical, well-insulated structures are simulated numerically over the summer. The first building serves as a model because it has the mentioned passive cooling system, whereas the second has no passive elements. Conclusions: The outcomes confirmed about Reviewing numerical, experimental, parametric, and economic studies of an earth-to-air heat exchanger with an emphasis on its application in semi-arid and arid climates is the topic of the current study. [ABSTRACT FROM AUTHOR]

The surface of the Earth is a source of radiation of thermal energy, which, passing through the atmosphere, is partially absorbed while the bulk of the energy is released into the surrounding outer space. A cooling technique based on this physical phenomenon is known as radiative cooling (RC). It is possible to reduce the consumption of electricity for cooling, as well as to reduce capital costs, by integrating the unit with radiative cooling directly into the circulation circuit of the refrigerant of the refrigeration machine. An experimental refrigeration system has been designed, in which in the cold periods of the year the removal of heat from the cooled object is carried out due to the mode of natural circulation of the refrigerant from the evaporator to the heat exchanger, cooled by radiative cooling. A refrigeration system with natural circulation and radiative cooling of the refrigerant R134a was experimentally studied during the autumn period in Almaty. The experimental study established that the chamber is cooled with the help of the examined system while the temperature in the cooled volume is maintained by 5...7 K above ambient air temperature at night. The dependence of the air temperature in the refrigerating chamber on the temperature of the atmospheric air has been determined. A procedure for assessing the cooling capacity of the system has been devised. The study reported here demonstrated the possibility of using radiative cooling to remove heat under the mode of natural circulation of the refrigerant. The refrigeration system reduces energy consumption in the cold seasons by diverting heat to the environment without the compressor operating. [ABSTRACT FROM AUTHOR]

The well-known traditional vapor compression refrigeration cycle is considered to be the most effective technique used in the field of refrigeration and air-conditioning systems. It's used almost in every facility including industrials, homes and food storages. There are some environmental hazards concerning the use of vapor-compression cycles such as global warming and ozone layer depletion mainly due to refrigerant's leakages. However, it's still considered as a leading technology for its capability of producing high cooling and heating powers with great coefficient of performance. The present work represents an experimental investigation of the effect of the condenser's temperature on the thermal performance of a conventional vapor compression refrigeration cycle. The geothermal cooling technique was introduced and utilized for cooling the temperature of the condenser that operates in harsh climate conditions. The experiment was performed using two additional heat exchangers for enabling heat exchange with geothermal temperature. The first heat exchanger (primary HX1) was connected directly to the condenser while the other one (secondary HX2) was installed inside the geothermal hole intended for heat exchange with the geothermal temperature. These exchangers (HX1 and HX2) were thermally connected via two PVC tubes with straight water circulating inside them (using a DC water pump). The experimental results proved the success of the current utilized method in improving the thermal performance of the system. Cooling the condenser via geothermal cooling has led to a considerable reduction in the temperature of the refrigerant and improved the overall performance of the cycle. The experimental apparatus showed an increase in both cooling capacity and COP by 25% and 21.5%, respectively. In addition, a considerable enhancement in the temperature of the evaporator was accomplished to reach a minimum temperature of 14.5°C. [ABSTRACT FROM AUTHOR]

Heating capacity of an earth to air heat exchanger EAHE equipped with an exterior fan in the arid region like the Southwest of Algeria is investigated experimentally. In-situ measurement of annual undisturbed subsoil vertical temperature profile is shown that it was 28°C at a depth of 1.5 meters. The EAHE made of 66 meters of PVC tube is demonstrated a heating capacity of 13°C and a cooling capacity of 7°C and a big dependence on local climate conditions. Great potentials and thermal comfort with less energy consumption are represented by earth to air or air-ground heat exchanger in the arid regions like the South of Algeria. [ABSTRACT FROM AUTHOR]

• Different studies of greenhouse-earth air heat exchanger systems are reviewed. • The effects of geometrical parameters, configurations, and operation conditions are presented. • Using an earth air heat exchanger can effectively cover the greenhouse thermal loads. • Integrating the photovoltaic and photovoltaic/thermal modules can improve the performance of the SG-EAHE systems. In recent years, yearly climatic changes, continuous temperature increases, and the impact of global environmental change have seriously affected agricultural production. The solar greenhouse (SG) system is designed to maintain suitable temperatures and humidity levels for cultivating plants. For this purpose, an earth-to-air heat exchanger (EAHE) can be coupled with the SG to provide the necessary heating and cooling required to maintain suitable conditions for vegetation. This review presents a comprehensive literature survey on SG-EAHE systems. The thermal characteristics of heating and cooling modes are presented for SG-EAHE systems. Reports indicate that integrating EAHE with the SG can meet the heating and cooling needs of the SG while significantly reducing water consumption. The design parameters of EAHE, such as configuration, pipe diameter, pipe length, and buried depth, can affect the performance of SG-EAHE systems. Additionally, integrating photovoltaic (PV) and photovoltaic/thermal (PVT) systems with SG-EAHE systems was discussed. Moreover, the challenges and prospective aspects of SG-EAHE systems were identified. [ABSTRACT FROM AUTHOR]

Heating up of photovoltaic modules during operation results in a significant power output reduction. This effect is especially relevant in regions with the highest photovoltaic potential, where irradiance and ambient temperature are particularly high. In this paper, a novel low enthalpy geothermal cooling system that improves the efficiency of a commercial solar module is described and experimentally validated. Two heat exchangers, one attached to the backside of the module, and another introduced inside a 15 m deep borehole, are connected in a closed circuit. A water-based coolant is pumped through the system, evacuating the excess heat from the module, and dissipating it underground in a clean and efficient manner, without additional water consumption after filling the system. The performance of the cooling system was experimentally tested by implementing it, for the first time, in a single-axis solar tracking isolated photovoltaic facility. Extensive tests were carried out in Spain, between September 2021 and August 2022 under a wide variety of environmental conditions. The efficiency improvement system has demonstrated its technical feasibility over a one-year period, showing a peak net efficiency improvement up to 13.4 %. Moreover, a positive net efficiency improvement has been demonstrated all year long, even during the winter months. [ABSTRACT FROM AUTHOR]

In the literature, numerical heat transfer analysis of supercritical carbon dioxide (sCO 2) is often conducted in idealized tubular geometries to better understand its fundamental properties. Its sensitivity to temperature and pressure variations at supercritical conditions indicates that, unlike traditional subcritical turbulent flows in tubes, the thermal boundary condition (TBC) will have a noticeable influence on heat transfer trends. Despite this, it has become standard practice to validate sCO 2 numerical models without considering the TBCs. In this work, local heat transfer and flow characteristics of sCO 2 in cooled horizontal tubes under all three TBCs were investigated numerically. Five configurations were considered: a conjugate tube-in-tube heat exchanger, a single tube with constant wall heat flux, a walled tube with constant wall heat flux, a single tube with constant wall temperature, and a walled tube with constant wall temperature. Heat transfer coefficients along the tube axis were analyzed using local temperature and heat flux. Circumferential distributions of temperature and heat flux were assessed. Temperature, density, and velocity profiles within the flow were also considered. Despite being the most commonly compared in the literature, the heat exchanger and single tube with a uniform wall heat flux materialized the largest heat transfer coefficient difference (10%–12%) between configurations. Furthermore, the single tube with constant heat flux exhibits variations in circumferential wall temperature of up to 9 K when contrasted with the heat exchanger, which demonstrates nearly uniform trends in circumferential wall temperature. The results holistically indicate that the TBC significantly influences heat transfer trends in supercritical fluids and that careful consideration must be taken when validating numerical models involving supercritical fluids. • Thermal boundary condition (TBC) type strongly impacts supercritical fluid heat transfer. • TBCs used in supercritical CO 2 models and experiments rarely match during validation. • Careful consideration of TBC is needed for supercritical fluid model validation [ABSTRACT FROM AUTHOR]

This article presents evaluation of alumina/water nanofluid (NF) in a glazed tube and sheet photovoltaic/thermal (PV/T) system with ground-coupled heat exchanger (GCHE) in semi-arid region of Pilani, Rajasthan (India). Conventionally in the literature, the cooling performance of NF is reported compared to the normal fluid cooling under equal Reynolds number (Re) comparison criterion. However, according to many researchers, equal pumping power-based evaluation is more pragmatic and is explored here. The first law of thermodynamics analysis is invoked to appropriately assess the replacement of water with NF in the PV/T system coupled with GCHE. Nanoparticle concentration is varied from 0.5% to 6% by volume fraction and the Re from 3000 to 9000. Temperature of PV panel, temperature difference in PV/T outlet and inlet, electrical efficiency, thermal efficiency and Bejan number in PV as well as in GCHE are computed using a validated mathematical model for both equal Re and equal pumping power evaluation criteria. The performance of PV/T system with NF is found superior under equal Re comparison. The improvement observed are reduction in PV panel temperature by 2 °C, reduction in temperature difference in PV/T outlet and inlet by 6 °C, rise in electrical efficiency by 0.1% and a rise in thermal efficiency by 4%. However, the performance of PV/T system with NF is found inferior under equal pumping power evaluation criterion. [ABSTRACT FROM AUTHOR]

This paper aims to study an earth-air heat exchanger system proposed to cover the living environment needs and reduce energy consumption and greenhouse gas emissions of an industrial poultry house in southern Algeria. For this purpose, a detailed mathematical model was used to determine the thermal needs of this industrial building. The soil temperature was studied to estimate the appropriate depth for installing the earth-air heat exchanger, followed by a parametric and economic study to determine its dimensions and cost. Finally, compare its performance with the systems currently used in this industrial farm. The study results, which were obtained in extreme working conditions, showed that the earth air heat exchanger could cover 45% and 38% of the heating and cooling demands, respectively. In summer, the proposed heat exchanger was able to reduce the temperature from 47°C to 27.1°C, while in winter, it was able to increase the temperature from 4.8°C to 22.9°C, and its performance was stable compared to the systems currently used, and, it recorded temperatures better under hot outside conditions. Furthermore, its use reduces CO2 emissions to 719 kgCO2/day in heating and 2531 kgCO2/day in cooling, making it a suitable solution for this type of industrial building. [ABSTRACT FROM AUTHOR]

• Thermodynamic, thermoeconomic, and greenhouse gas assessments were carried out. • The H&S and UFS methods are combined with Life Cycle Assessment for the first time. • The study object is a chilled water system for air conditioning purposes. • Thermoeconomic criteria correctly address dissipative components. • The framework developed can be applied to other refrigeration systems. This is the first study to apply a combination of two thermoeconomic approaches (UFS and H&S) with Life Cycle Assessment (LCA) to a chilled water system installed in a shopping mall. The objective is to obtain monetary and environmental costs for the thermal energy stored by developing both thermoeconomic and thermoenvironmental assessments. The thermoeconomic study determined internal flows, defined inputs and products, and described the productive structure to obtain exergy and monetary costs. The LCA methodology quantified the greenhouse gas emissions associated with equipment operation and energy flows. The results indicated efficient thermoeconomic behavior for the heat exchangers. The monetary and environmental costs of chilled water are, respectively, US$ 0.2267/MJ and 0.8186 kg CO 2 -eq/MJ. [ABSTRACT FROM AUTHOR]

This study investigates the performance of vehicle cabin supplemental cooling and heating systems equipped with a 1 kW thermoelectric module (TEM) heat exchanger. The TEM heat exchanger comprises 96 thermoelectric modules, the heat sink with a louver fin and water cooling jacket, attached on the thermoelectric modules both hot and cold side. The cooling and heating performance experiment was conducted under various conditions, considering parameters such as air flow volume, air inlet temperature, water inlet temperature, water flow rate, and intake voltage to the TEM heat exchanger. The calorimeter experimental results demonstrate that the cooling capacity and coefficient of performance (COP) were 1.63 kW and 1.6, while the heating capacity and COP are 4.44 kW and 4.4, respectively. An air-conditioning system level evaluation was then conducted using system bench apparatus, considering the environmental conditions when vehicles were in use; a rear air-handing unit (AHU) with a 1 kW TEM heat exchanger was employed to determine both cooling and heating performance. [ABSTRACT FROM AUTHOR]

In mining plants (underground and on the surface), high-power machines are used. Electric motors and the gears driven by them have a specific cooling system as a flow system with an internal heat exchanger. The role of the heat exchanger is to collect the thermal energy generated during the unit operation. The refrigerant with the received thermal energy must be led away from the motor and gear unit, where it will be cooled. In the drives used in underground hard coal mines, water is the cooling medium, supplied through a firefighting pipeline. The water used for cooling is often discharged directly to the floor or to sewers, and further it is transported to the surface. The article presents a solution that uses tanks for cooling liquid with highly efficient air-water coolers in surface and underground applications. [ABSTRACT FROM AUTHOR]

Direct cooling of the windings in a motor using oil offers more effective thermal management than conventional alternatives and can therefore increase the torque density of electric machines; however, this technique is limited by the thermophysical properties of the oil. The use of a direct winding heat exchanger allows a glycol-water coolant mixture to be used, which leads to a significant improvement in heat transfer and a reduction in the pumping losses compared to direct oil cooling. This article proposes ceramic 3-D printed direct winding heat exchangers (3D-DWHX), which can significantly improve the cooling of windings in electric machines due to the unique geometries enabled by 3-D printing. Ceramics are also capable of withstanding extremely high temperatures, which extends the application of the proposed 3D-DWHX. A closed-form analytical thermal model incorporating the temperature dependence of winding losses is proposed and used with empirical heat transfer correlations to design a microfeature enhanced 3D-DWHX. The ceramic 3D-DWHX was built and tested in a motorette that demonstrated a continuous current density of 35.7 ARMS/mm2, corresponding to a continuous specific power in the reference electric machine of at least 12.1 kW/kg while keeping the maximum winding temperature below 200 °C. [ABSTRACT FROM AUTHOR]