Search

This study introduces innovative turbulators with unique geometries, namely the Conical Simple Wire Turbulator (CSWT) and Conical Braided Wire Turbulator (CBWT), designed to enhance heat transfer in a constant temperature tube. These turbulators resemble a conical shape in appearance but are constructed by interconnecting multiple wires, enabling fluid flow to pass through. The distinct geometry of these turbulators not only disrupts the thermal boundary layer for improved heat transfer and Thermal Enhancement Factor (TEF), and results in a favorable pressure drop. The study explored various geometrical parameters of the turbulator, including wire diameters (a) ranging from 0.5 to 1.5 mm and turbulator gaps (TG) ranging from −10 to 30 mm. Using the RNG k–ε model, the finite-volume scheme is utilized to discretize the turbulence flow equations. A numerical investigation was conducted across Reynolds numbers ranging from 5500 to 12375. The results show that increasing the wire diameter and reducing the turbulator gaps simultaneously enhanced heat transfer, pressure drop, and TEF. The highest heat transfer and TEF were achieved with the CBWT featuring a 1.5 mm wire diameter and a −10 mm TG. In this configuration, Nusselt was 2.84 times greater than a plain tube, with a maximum TEF recorded at 1.4.

This research reports on the combined effects of heat and mass transfer (HMT) under the influences of the Soret and Dufour in natural convection steady 2D magnetohydrodynamic flow through the boundary layer in a porous vertical tube or duct. The current study is motivated by the significant applications of HMT in engineering processes such as casting and welding. The goal of this framework is to explore the assisting and opposing movements with HMT above a vertical porous channel under the influence of invariant suction and fluid dissipation which have not been reported in the earlier studies. The governing flow equations in terms of partial differential equations (PDEs) are altered to dimensionless ordinary differential equations (ODEs) by using dimensionless variables. Employing the BVP4C approach, the leading equations are solved numerically. The dual nature of solutions has been observed due to suction. Stability exploration has been provided to confirm a stable solution. A comparison between published and current studies shows outstanding agreement. Key parameter effects on flow characteristics are visually offered using graphs as well as tables. It is noteworthy that the influence of Soret effects becomes apparent in a suspended mixture of particles and fluids. These phenomena can be attributed to temperature differences, whereby the motion of fluid particles in the warmest region with the maximum energy level causes the particles to migrate towards the coldest region. Notably, the flow speed rate at the left plate is initially high and slowly diminishes near the right plate.

In recent years, the rise of machine learning (ML) has prompted researchers to expand the datasets required for optimizing and designing thermal systems. Also, the development and widespread use of electric vehicles (EVs) have surged significantly. However, one of the major challenges associated with EVs is the efficient cooling of Lithium-ion batteries (LIBs). Therefore, the exploration of innovative cooling methods can contribute greatly to the rapidly growing electric vehicle industry. This study focused on investigating the impact of embedding a nickel porous medium around a single 38,120 LiFeO4 cell. To conduct the study, the LIB, along with the nickel porous medium, was placed inside a duct that received a flow of water and Nano-encapsulated phase change materials (NEPCMs). The results obtained from the study indicate that embedding nickel porous media around the LIB led to a significant decrease in the maximum temperature of LIB, more than 40 C, and a remarkable increase in pressure drop more than 100 times. Additionally, it was observed that the decrease in porosity from 1 to 0.97 had a more pronounced effect on pressure drop and the maximum temperature of the LIB's surface, compared to the decrease from 0.97 to 0.95.

The environmental advantages of hydrogen as a clean energy carrier are more prominent when it is produced utilizing renewable resources. In this regard, a novel geothermal energy driven electricity generation system integrated to hydrogen production plant is developed and investigated in this research. In the developed plant, a PEM electrolyzer is employed for hydrogen generation such that its required electricity is provided by an improved double-flash geothermal cycle. A self-superheater is applied for superheating the vapor at the steam turbine inlet using the geothermal resource to enhance the hydrogen production capacity. To evaluate feasibility of such superheating process and to examine its effects on hydrogen production, thermodynamic models are developed based on first and second laws. Also, environmental considerations are considered in evaluation of the proposed plant performance based on exergo-environmental indices. The influences of first and second flashing pressure, geothermal source temperature and current density of water electrolyzer on energy and exergy efficiency, hydrogen production rate, and environmental damage index are investigated. After carrying out a parametric study, the optimum operation point of the plant is determined via a two-objective optimization based on the hydrogen rate and environmental damage index (EDI). It is found that, under optimum operation, the system can produce 25.48 kg/h of hydrogen, while its environmental damage index is calculated to be as 0.00645.

Entropy generation and convection heat transfer in a partially porous chamber with different side wall temperatures using CuO–H2O have been investigated. The importance of this issue is wide application of the results in solar collectors, thermal extrusion systems, heat exchangers, bio-medicine, nuclear waste disposal, etc. The innovation of the present work is related to the investigation of fluid and heat fields and entropy generation by using a matrix with subordination of porosity to the vertical axis and permeability, thermal conductivity, and viscosity with subordination of porosity. To obtain accurate results, the two-phase mixture model was used, and thermal conductivity and viscosity of nanofluid were simulated by experimental models by temperature and volume fraction dependence. Governing equations are solved by the FVM. The main findings indicate that the best and worst optimization factor will occur in the porous matrix ε = ε(y2) and ε = -ε(y2), respectively, which is 113 % and 86 % of NH of the homogeneous matrix, respectively. Also increasing the filling of the cavity, highly improves NH, so that the NH will reach from 1.19 to 1.82 with the increase of S from 0.25 to 1.

In the modern era, Artificial Intelligence (AI) has emerged as a powerful tool that can rapidly generate highly accurate data, offering tremendous potential for optimizing system performance. This study focuses on harnessing the capabilities of an artificial neural network (ANN) to determine optimal parameter values for heat transfer in a mixed convection mechanism. The first step of this research involved conducting CFD simulations to investigate the impact of varying Grashof numbers (102,103,and104), Reynolds numbers (1,10,and100), and MWCNT volume fractions (0, 0.01, 0.02, and 0.03) on the Nusselt number within an elliptical enclosure containing a centrally located rotational cylinder. A total of 48 simulations were performed, generating a comprehensive dataset for training the ANN-Multilayer Perceptron (MLP). In the second step, the trained ANN was utilized to generate an additional 700 data points with remarkable accuracy. This enabled efficient exploration of the parameter space, providing valuable insights into the system behavior and facilitating optimization efforts. The findings of this study revealed a 0.03 vol fraction of MWCNT into the water in Grashof numbers of 102,103,and104, the average Nusselt number increased by approximately 46%, 31%, and 12%, respectively. The ANN-based approach successfully identified optimal values for the variables that maximize the Nusselt number.

This study represents a pioneering investigation into the impact of a punched twisted tape turbulator on the hydrothermal parameters of a pipe operating under constant surface temperature conditions. The punched turbulator was specifically designed by incorporating cuts with diverse geometries, including semicircular, square, and triangular shapes, into the basic twisted tape turbulator. To evaluate the performance of the punched twisted tape, a comparative analysis was conducted with both a smooth tube and a tube equipped with a basic turbulator. The criterion for selecting the optimal cut geometry was the thermal enhancement factor. Subsequently, the influence of the cut area on the hydrothermal parameters was thoroughly elucidated. The enhancement factor was again utilized to identify the most optimal area. Based on the comprehensive evaluations, it was observed that the turbulator with a semicircular cut geometry and a diameter of 5 mm exhibited superior thermal performance compared to all other geometries. By employing this specific turbulator design, a remarkable enhancement in heat transfer and pressure drop within the heat exchanger was achieved, offering improvements of up to 1.63 and 3.65 times, respectively, when contrasted with the plain tube. The maximum enhancement factor value recorded during the investigation reached 1.09.

For the purpose of enhancing the thermal efficiency of double-tube heat exchangers, a new technique has been implemented. By integrating a vibrating turbulator and bubble injection technique, this innovative method produces an added turbulence effect. This research aims to experimentally assess the thermal efficiency of employing two active methods concurrently. Different parameters were analyzed, including water flow rates ranging from 0.5 to 4 kg/min and bubble injection flow rates varying from 2 to 6 l/min, to investigate the effects on heat transfer and pressure drop with and without the magnetic turbulator. The results suggest that by incorporating bubble injection, adopting the magnetic turbulator, and simultaneously utilizing both methods, there is a significant improvement in heat transfer. In optimal scenarios, the heat transfer coefficient is amplified by 150.3% through the injection of bubbles, 328.8% through the implementation of magnetic turbulator, and 586.2% when both techniques are employed in tandem. In comparison to the smooth tube, the friction factor ratios were 6.7, 1.6, and 7.8 times higher in the specified cases. The findings indicated that the concurrent utilization of both techniques can yield an added impact on heat transfer. Ultimately, the integrated approach demonstrated a noteworthy thermal enhancement factor value of 3.49.

The fluctuating nature of wind energy and shortage of biomass resources, as two types of renewables, can be fulfilled via their hybridization. In this respect, present research proposes a hybrid biomass/wind energy driven power generation framework based on combined gas turbine-Rankine cycle scheme. The gas turbine includes a reheat stage where the produced hydrogen is added to the combustion chamber for increasing flue gas temperature to enhance output power. The injected hydrogen is generated via a water electrolyzer which is powered by electricity from the wind turbines. The proposed scheme of biomass/wind powered system leads to a reduction in biomass consumption and will fulfill the fluctuations and non-continuous availability of wind energy. To appraise the feasibility of developed hybrid scheme, thermodynamic first and second law-based analyses were performed. Also, the exergo-environmental evaluation of the hybrid plant is conduced using three exergo-environmental indices. Finally, optimum operation conditions of the proposed hybrid plant is determined based on the minimization of environmental damage index. The results under optimum operation indicate that, the proposed hybrid power generation plant yields exergy efficiency of 47.35 % with environmental damage index of 0.0104.

The reliable supply of electricity and potable water has crucial importance on achieving higher level of human welfare, where the primary energy source to provide these requirements is fossil fuels at present. Since the combustion of fossil fuels has irreparable environmental impacts, thus utilization of clean and renewable energy resources is a promising alternative to overcome the energy-related environmental issues. In this regard, present research aims at development of an effective co-generation of electricity and freshwater plant driven by hybrid geothermal and biomass renewable energy sources. To make a comprehensive system assessment, thermodynamic, exergy, environmental and economic aspects are considered and appraised in detail and multi-objective optimization is used to detect the best performance of the plant. The results indicated feasibility of hybridization of biomass and geothermal resources for efficient co-production of potable water and electricity. Under optimized operation, the plant exergetic efficiency, unit product cost, exergo-environmental index, and CO2 emission are found to be 44.12 %, 66.97 $/MWh, 0.5114 and 0.7105 kg/kWh, respectively. The second law analysis revealed that, from 18302 kW of input exergy, a value of 9357 kW is destructed within the components, where the gasifier owns the largest portion with 3569 kW.

In this study, flow visualization, pressure drop and thermal characteristics of the corrugated tube with non-boiling air–water two-phase flow were experimentally studied. Glass tubes were used to visualize the flow patterns of two-phase flow. Furthermore, the thermal behavior of two phase flow was studied in the copper made tubes which was under constant heat flux. The total of 740 W thermal energy was applied on tubes. Superficial velocity of liquid was within the range of 0.42 m/s to 1.69 m/s. Also, the superficial velocity of air was within the range of 0.21 m/s to 1.06 m/s. The results revealed that the corrugations significantly affect the flow patterns which results in earlier transition. The flow patterns of bubbly, churn, wavy slug, wavy plug, wavy stratified and mist flow were observed inside corrugated tube. Also, it was found that the maximum Nusselt number increment in corrugated tube was 3%. Besides, formation of the mist flow in corrugated tube reduced the Nusselt number. Also, the pressure drop was significantly affected by the air–water two-phase flow presenting around 165 % in the pressure drop compared to the single phase flow.

One of the performance enhancement strategies in thermoelectric technology is application of two-stage leg instead of normal single stage leg structure. However, for a thin-film solar thermoelectric generator applying this strategy requires many in-depth considerations including economic -cost and reliability aspects. In this research, attempts are made to identify the economic and performance characteristics of a two-stage thin-film solar thermoelectric generator under various geometrical conditions and then compare with normal single stage configuration. Generally, in addition to being cost-effective compared to the single-stage design, the double-stage design can produce more power if the appropriate material is selected. The results of numerical simulations show that the use of bismuth tellurides in single stage thermoelectric generator (SATEG) legs improves the performance of the system in terms of power generation. But the use of skutterudites in the lower layer and bismuth tellurides in the upper layer of the two-stage case, in addition to increasing the output power, significantly reduces the dollar/watt value. Furthermore, the highest output power and exergy efficiency are obtained in the lower layer angle ratio of 0.8–1 and in the upper layer angle ratio of 2. Among the geometrical parameters, the radius of heated area (Rh) has the greatest effect on the performance of double-stage solar annular thermoelectric generator (DSATEG). The highest power output is obtained at Rh = 1.5, which is equal to 1.323W.

Increasing heat transfer rate in heat exchangers is one of the topics interested by researchers which leads to economic savings. Various methods have been proposed in this field which are categorized into two main groups of active and passive techniques. Despite numerous investigations were conducted in this regards, very rare investigations have probed these methods from the economic viewpoints. Present study was carried out to investigate the effect of volume fraction (VF) of air bubbles on exergo-economic performance of horizontal shell and helically coiled tube exchanger (HSHTE). The air bubbles were injected into shell side via especial method. Holes with certain properties were fabricated on a plastic pipe with diameter of 3 mm for injecting air bubbles. Both counter flow and parallel flow were considered in this investigation. Present study showed that air injection has significant effect on thermal efficiency, exergy destruction and economic performance of the HSHTE. It was found that increment of VF increases number of thermal units, first law efficiently and exergy destruction increase by 4.5, 2.4 and 12.5 times, respectably. Furthermore, best values of Net profit per unit transferred heat load (դp) was about 9.3 × 10−5 ($/J) which presented up to 13% better financial performance in comparison with parallel flow.

Latent heat thermal energy storage (LHTES) systems are widely used due to their ability to store a lot of heat energy as latent, and few studies have directly or indirectly investigated on the heat exchange methods with LHTES systems. In the present study, the free convection of a mixture of water and Nano-encapsulated phase change material (NEPCM) with a porous medium was used to exchange heat energy between a cold-water stream and a hot tank filled phase change material (PCM). NEPCM are nanostructures consisted of a solid shell and a PCM core, and the addition of these nanostructures to water has remarkable effects on the heat transfer parameters. In this research, a number of cases were simulated using computational fluid dynamic (CFD) to observe the impacts of injecting NEPCM to water, the porosity of the porous media and the location of the phase change zone on the average heat flux of the PCM tank. The results showed that increment of porosity number from 0.85 to 0.95 decreased the average heat flux of the PCM tank by 13.8%. Moreover, adding 3% NEPCM to water enhanced the average heat flux of the PCM tank by 22.2% and 18.4% when porosity numbers were 0.85 and 0.95, respectively.

This study probes the effect of connection angle of “L” shaped fin on the melting and discharge process of a vertical PCM unit. The PCM enclosure had dimensions of 50 ×50 mm and the L shaped fin was located at middle of enclosure. The enclosure was heated and cooled by considering constant temperature at the vertical wall. The Lauric acid was considered as the phase change material. Seven different coincidence angles of 0°, 30 °, 60 °, 90 °, −30 °, −60 ° and −90 ° were considered in present investigation. Results indicated that L shaped fin with Teta = −30 ° could provide 14% reduction in the melting process. Furthermore, the case with Teta = 0° provided 45% enhancement in solidification time. The outcomes revealed that maximum charging rate was associated with case with Teta = −30 ° which had the value of 103.41 J/S and provided a 32% enhancement in comparison with the base case. Also, the best discharge rate for the solidification process was about 34.184 J/s which was related to case with Teta = 0° and presented a 2.23 times improvement in the average solidification rate.

Numerous investigations were conducted to enhance heat transfer in smooth tubes. They have used both active and passive methods. However, very rare investigations have reported the simultaneous usage of active and passive methods. Furthermore, the investigations on entropic behaviors are very rare too. Through present paper, effect of air bubble injection (as active method) together with spring wire turbulator (as the passive method) is probed. The pipe was subjected to a constant heat flux. Spring pitch and fluids flow rates were variable parameters of this study. Four flow levels of 2, 3, 4, and 5 were intended for water and air. The studied parameters were Nusselt number, cost-performance coefficient, and dimensionless exergy destruction. The flow patterns were also assessed. To calculate the Nusselt number and exergy destruction, ambient temperature, pipe surface temperature, water inlet, and outlet temperatures were measured. Results showed that reducing the induced rotational flow by the pitch, affects two-phase flow and leads significant changes flow pattern and two-phase flow motion model. Air bubble injection increased Nu by 40% and dimensionless exergy destruction by 36%.

MHD natural convection of Fe3O4-water suspension in the presence of magnetic field of solenoid inside a porous enclosure was numerically simulated. Computational fluid dynamic based on finite volume method were exerted to break and solve the PDEs equations. A solenoid was embedded around the cavity for generating a non-uniform magnetic field. The vertical walls of enclosure were maintained at uniform temperatures of Th and Tc and horizontal walls were insulated. Many cases have been simulated to understand the impacts of porous Rayleigh numbers of 10–1000, volume fractions of 0–4%, porosities of 0.5–0.9, and Hartmann numbers 0 to 120. Findings indicate that the presence of magnetic field had a positive effect on heat transfer in low porous Rayleigh number and high Hartmann number, for all porosities. In highest porosity and 4% volume fraction, Nusselt number increased 140%; whereas at high Rap, the presence of a weak magnetic field decreased the heat transfer rate.

This paper presents a multi-objective experimental study, to enhance the thermal performance of the helically coiled pipe. The main objective of this study is the hydrothermal evaluation of single-phase (water) flow and two-phase flow (air-water) transition through a helically coiled tube at the presence and absence of helically coiled wire. Water flow rate was varied from 2 l/min to 8 l/min and air flow rate was varied from 1 l/min to 5 l/min which makes the volume fraction (VF) range of 0.110–0.714. Thermal-frictional and exergetic behavior of two-phase flow for a helically coiled tube with a helical wire insert have been studied. Results show that in exergy efficiency inside helical tube without turbulator for single-phase flow is 87% higher than when the turbulator is inserted. The second law analysis demonstrated that the exergetic efficiency decreases by the increment of VF and water flow rate. Generally, when pressure drop increment is less important than heat transfer augmentation, simultaneous use of two-phase flow and turbulator is recommended. Conversely, single-phase flow with turbulator is recommended when the desired pressure drop is low.

In the present study, the natural convection flow of water with Nano-encapsulated phase change material (NPCM) was simulated inside an insulated chamber, which a pair of pipes were considered as a heater and cooler sources with the boundary condition of uniform temperature. The NPCM's core was made of n-nonadecane with melting temperature of 30.44°C. This core has ability to change the liquid-solid phase to transfer heat between the heater and the cooler sources. Current simulation was steady state and was solved by SIMPLE algorithm based on FVM to investigate the effects of Rayleigh number, volume fraction and location of phase change zone on the convective heat transfer coefficient. Observations showed that, phase change of NPCM occurs at low Rayleigh numbers but had no effect on the convective heat transfer coefficient, but it was directly related to the thermal conductivity of mixture. Moreover, adding volume fraction of NPCM 0.02 into water increased the convective heat transfer coefficient by 10.43%, 19.1% and 18.3% compared to pure water for Rayleigh numbers 102,104,and106, respectively.

The aim of this study is numerically to investigate the effects of local thermal non-equilibrium porous media on the melting process of paraffin with the melting temperature33°C. The geometry consists of a half-cylinder containing paraffin with a uniform constant temperature and an insulating wall. Also, Darcy model and buoyant force due to density changes are considered in this simulation. The effects of the presence of aluminum foam with porosity ε=0.8,and0.95 and difference temperature ΔT=5,10,and15 have been studied on the melting fraction of PCM, temperature and streamlines contours and heat flux of cylinder's surface. The observations show that enhancement of porosity 0.8 to 0.9 increases the volume of PCM 11.7%, and reduces time of melting process 30.8% for ΔT=15. Moreover, increment of ΔT=5to15 leads to decrease time of melting process 71.8% when porosity is 0.95.

A two-stage ORC (Organic Rankine Cycle) is being proposed for the recovery and utilization of low-grade heat from single flash geothermal power plant exhaust flue fluids. The working fluids for two-stage the recovery system are R227ea and R116. The impact of essential design parameters such as inlet temperature of the cycle, ambient temperature, geothermal turbine inlet pressure, geothermal condensation temperature on system performance are investigated using thermodynamic mathematical models regarding energy and exergy efficiencies as the objective function. The addition of the recovery section to the base cycle improves the thermal efficiency from 0.2023 to 0.2178, a 7.66% improvement in this critical metric. Furthermore, the exergy efficiency rises from 0.55044 to 0.5803, representing a 15.04% boost in exergy efficiency. Furthermore, the system's overall output rises from 7690 kW to 9898 kW, representing a substantial gain of 28.71%. The suggested recovery system's cycle has a lower LEC than a single flash geothermal cycle from an economic standpoint. LEC Reduced from $ 0.125 per kilowatt to $ 0.108 per kw, a cost savings. As a result, including a recovery section in the basic single flash geothermal cycle will significantly improve system performance.

In the current research, the natural convection of water-Al2O3 nanofluid has been simulated inside a cold semi-annulus chamber with a hot block at the its bottom. Also, an oblique magnetic field (MHD) has been implemented to improve and control the flow. The unstructured triangular mesh and FVM with SIMPLE algorithm have been employed for discretization and coupling of pressure and velocity equations. In this simulation, the parameters of Hartmann, Rayleigh numbers and volume fraction of nanoparticles have been investigated on temperature contours, flow pattern, and hot wall Nusselt number. The observations show that, increasing the volume fraction increases the Nusselt number at low Rayleigh numbers. Moreover, the Nusselt number is inversely related to the Hartmann number for high Rayleigh numbers.

Increasing use of fossil fuels has led to serious consequences on the environment including global warming, pollution, and increased costs of heating systems. This indicates the importance of improving the efficiency of devices used in heating and air conditioning systems such as heat exchangers. In this study, it was tried to enhance the performance of the heat exchanger by simultaneous use of a flat tube as a central tube of the heat exchanger and dual conic turbulator. In addition to plain conical turbulator, the influence of the conical turbulator with aerodynamic geometry was investigated on the heat transfer and pressure drop. Finally, economic evaluation of the studied cases was done based on the thermal performance enhancement factor (TEF) and the net profit of unit transferred heat load (ηp). Tests were conducted in the hot water flow rate ranging 0.033–0.0678 L/s while cold water flow rate was kept constant at 0.166 L/s. The results indicated that the heat transfers and exergy loss of the flat tube heat exchanger with a dual modified conical turbulator was up to 33% and 30% higher than the plain tube heat exchanger, respectively. Also, a heat exchanger with a modified dual turbulator with convergent embellishment (case B) selected as the economic case and has the highest TEF and ηp . It was revealed that the application of enhanced conical turbulator would lead in the increment of ηp up to 1.26 times.

The free convection of Cu-water nanofluid is simulated and investigated inside a square heat exchanger chamber in the presence of MHD magnetic field. The Buongiorno model with the effects of Brownian and thermophoresis motion is considered to nanoparticles distribution inside the chamber. The geometry consists of a square chamber with two cylinders on the right and left sides as heater and cooler in order to create the buoyancy force, respectively. These cylinders represent hot and cold pipes, and the walls of the chamber are heat and mass insulation. the FVM with SIMPLE algorithm are used for velocity and pressure coupling. In current two-phase simulation, the effects of Rayleigh number, Hartmann number, inclination angle of chamber and volume fraction on streamline contours, isothermal lines, Lorentz force lines, nanoparticle distribution and Nusselt number are investigated. By modeling the motion of nanoparticles and evaluating it, a nanoparticle transport zone was observed. The diffusion effects of thermophoresis were significant in this zone. The nanoparticles were thrown from the hot cylinder to the cold cylinder. The application of a magnetic field enlarged the nanoparticle transport zone. However, increasing the Rayleigh number and decreasing the inclination angle of the enclosure caused the nanoparticles to disperse evenly.

Through the present investigation, the thermal and power output of novel-shaped solar panels are evaluated. For the cooling of the mentioned forms, forced air flow was utilized. Three novel shapes, of Pyramid, Hexagonal, and Conical which had the equal lateral surface were considered. For the simulation, an open source CFD software was utilized. The lateral surfaces were put under identical amount of heat flux. Air as the coolant fluid was injected with constant inlet temperature from the trapdoors at the bottom of different shaped structures. Three different values of heat flux and air injection rate were evaluated for each shape. The outcomes presented that the conical shaped solar panel exhibits better thermal performance than other geometries. Furthermore, conical form finds the least temperature that was about 10.5 °C less than that of the pyramid-shaped panel. Furthermore, it was revealed that the corners of pyramid and hexagonal-shaped solar panels have higher temperature. Also, it was found that the efficiency of conical shaped panel was up to 8.4% more than that of pyramid-shaped panel.

Ground source heat pump, due to high coefficient of performance (COP) and use of low-temperature thermal energy source, is one of the best technologies to use renewable energy resources. In this work, at first, a geothermal heat pump for heating with an economizer is simulated, and then the effects of the variations in different parameters such as evaporator pressure, condensation pressure, and intermediate pressure on heat pump and total COP and exergy efficiency are analyzed. Initially, the thermodynamic simulation of the system is performed for different working fluids (R134a, R-12, R152a, R1234yf, and R1234ze(E)) in the EES software programming environment. The COP and exergy efficiency are calculated for different working fluids and obtained optimal values. The best overall coefficient of performance of the system is related to fluid R134a with a value of 3.663 and the best overall exergy efficiency of the system is related to fluid R1234ze(E) with a value of 0.5517. The lowest PCEU value is for fluid R152a with 0.01247$ per kilowatt. It can be concluded that by reducing the evaporator pressure of the cycle, the cost of producing an energy unit will be cheaper and by reducing the middle pressure of the cycle, the cost of producing an energy unit will be more expensive.

In this research, entropic analysis of a double helical tube heat exchanger including circular depressions on both inner tube and outer tube is provided. Experimentally validated 3D numerical simulation is employed to reach the aim of this study. Entropic characteristics of four cases are investigated and reported. In case “a” both inner tube and outer tube are smooth. In case “b”, circular depressions are created on only inner tube while in case “c” both tubes contain circular depression. Case “d” is the same as case “c” while the depression arrangement is different from case “c”. Dimensionless entropy generation and dimensionless Nu number are used to evaluate the proposed designs based on the first and second laws of thermodynamics. Moreover, heat transfer improvement (HTI) factor is adopted to consider the impacts of said two parameters simultaneously. Results demonstrate that, although creating circular depressions on both tubes significantly improves the heat transfer characteristics of the heat exchanger, it increases the entropy generation level of heat exchanger as well. Case “d” in which the location of any circular depression of the outer tube is placed between any two continuous depressions of the inner tube, gives the highest thermal performance and also entropy generation.