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In this paper, the mixed refrigeration cycle of Skikda APCI (Air Products and Chemicals Inc.) process in Algeria was studied thermodynamically in order to determine the optimal operating conditions. The energy and exergy balance equations for each process component were established. The distribution of the exergy destruction of the basic cycle equipment revealed that the compressors had the highest exergy destruction rate. The effects of operating conditions on performance coefficient of the cycle (COP) and exergy efficiency of the APCI process were evaluated; mainly the inlet temperature of the compressors, natural gas (NG) temperature after cooling in the main cryogenic heat exchanger (MCHE) and inlet temperature of the mixed refrigerant (MR) expansion valve. The results of the numerical simulation validated using Aspen HYSYS software indicate that the COP and exergy efficiency of the basic cycle are 2.66 and 59.99% respectively. These results can be improved by reducing the inlet temperature of the compressor and the expander as well as that of the NG after cooling in the MCHE. Finally, the results of the optimization performed using the genetic algorithms (GA) are in agreement with those of the literature. They show signs of improvement in the COP and exergy efficiency of the APCI process by 1.48% and 3.64% respectively compared to the basic cycle. [ABSTRACT FROM AUTHOR]

In this work, user friendly software is described for the easy design of the GEHE. There are different procedures for designing the geothermal heat exchanger. Based on the different ways to extract the energy and the configurations of the GEHE system several methods are used for the design of the system. The software developed is based on two of such methods which are explained along with their applications in this paper. Results of the software along with some images of the software is also presented in this work which is compared by the help of a system which is installed in the library building of Deenbandhu Chhotu Ram University of Science and technology, Murthal along with the results of the software are compared with various scholarly articles published by different researchers based on different experimental setups or the simulation results for both the horizontal and vertical systems. A proposed system for the vertical type GEHE which can be installed in DCRUST Murthal is also presented in this paper. The results show that the methods used in the designing of the GEHE in the software gives very close values, i.e., the percentage average deviations are in the range of 0.5 to 6% to the actual system for the cases considered in this work. [ABSTRACT FROM AUTHOR]

This paper describes experimental investigations on convective heat transfer in counter flow double pipe heat exchanger under transverse vibration for single-phase flow with twisted tape insert in the inner tube. Experiments were conducted on twisted tape inserted counter flow double pipe heat exchanger under vibration for twist ratio from 7 to 17, amplitude from 23 to 69 mm, frequency from 20 to 100 Hz and Reynolds number (Re) changing from 10710 to 21420. A maximum gain of 91% in Nusselt number (Nu) was obtained at 40 Hz frequency and 69 mm amplitude for twist ratio of 7 and Re of 10710. The maximum value of performance evaluation criteria with compound enhancement technique on double pipe heat exchanger reached 1.38 in turbulent flow conditions. Empirical correlations for Nu were developed and predicted values were found to be within ± 9% of experimental values for both frequency ranges. [ABSTRACT FROM AUTHOR]

Energy-saving and heat transfer enhancement considerations are more crucial due to nearly running out energy resources and ensuring the sustainability of nature. The heat exchangers are one of the main components and directly affect the thermal efficiency of the systems. To enhance the heat transfer rate, the fin and plate structure is widely used. Various vortex generators may be involved generally on the surface of fins, like ribs, baffles, delta winglets, and perforations. Turbulators make the heat transfer performance better significantly but increase the friction of the fluid on the contacting surfaces and cause the pressure drop-down which depends on thermal properties of the fluid characteristics. This paper presents general protrusion vortex generators overview to heat transfer augmentation with pressure loss as an extensive literature review. The correlations are derived in terms of some parameters of turbulators like; angle, pitch, shape and combinations of an array. The target of this study is consolidating the verified outputs of the literature and support the increasing thermal performance of the heat exchangers. In conclusion, two tables are made for the first time and summarizing the crucial features of solid, perforated baffles/blockages and winglet turbulators, mentioned in the literature are presented. Obstacles such as winglets and vortex generators are used commonly to increase the heat transfer rate per unit volume for finned to tube exchangers with various types. In order to augment the heat transfer, the design parameters of important consideration are attack of angles, height and array structure in both laminar and turbulated fluid characteristics. Involving perforation forms on the surface may be used for winglets with variable angles both decrease the pressure loss and increase the heat transfer performance. [ABSTRACT FROM AUTHOR]

The paper investigates the heat transfer characteristics of the heat exchanger under two different configurations namely taper helical tube and spiral tube type heat exchanger. The working fluid is water which flows in tubes kept horizontally and the mass flow rate ranges from 0.04 kg/s to 0.16 kg/s. The effect of tube configuration parameters and Reynolds number on heat transfer coefficient and Nusselt number were studied. Regression equations have been developed for both the configurations under horizontal orientation using various process parameters and regression tools available in Minitab Software. A comparison has been made between the theoretical results and the results obtained from simulation gives an error of 15% which is well within the permissible limit. The result indicates that the highest value of Nusselt number is greater by 21% than taper helical tube heat exchanger which is attributed to better heat transfer characteristics of spiral tube heat exchanger and hence the former is thermally superior over the latter. In this study, temperature and velocity contour have been developed for both the configurations which clearly indicates that, when heat transfer is considered, spiral configuration should be preferred over taper helical configuration. [ABSTRACT FROM AUTHOR]

This paper presents a numerical simulation to determine the air-side heat transfer and the pressure drop characteristics of a flat tube heat exchanger with offset strip fin. The effects of the fin bending ratio such as 29%, 36%, 44%, 50%, and the fin spacing such as 2.10 mm, 2.35 mm, 2.60 mm on the performance of the heat exchanger are studied by using a commercial CFD software. The air having constant viscosity, thermal conductivity, and density enters the heat exchanger at 298 K and the wall temperature of the strip fins is considered as constant at 314 K. Variations of the heat transfer coefficient and the pressure drop in the airside are presented with respect to the frontal air velocity while Colburn j-factor and the friction factor f are presented with respect to the airside Reynolds number ranging from 200 to 1200. Finally, the thermal-hydraulic performance of all investigated cases is compared by using the volume goodness factor, j/f1/3. The results show that the air-side heat transfer coefficient and the pressure drop increase when the frontal air velocity ascends. The air-side heat transfer coefficient decreases with the increase of fin spacing. The fin bending ratio does not have a significant effect on the pressure drop in the considered fin spacing. Both the Colburn j-factor and friction factor reduce with the increment of Reynolds number and fin spacing [ABSTRACT FROM AUTHOR]

Earth to air heat exchanger EAHE is a renewable technique based on a geothermal source. Arid regions are characterised by hard winter and summer weather conditions, which lead to a large thermal discomfort for the big part of the year. In this paper, we study by experiments the performance of stand-alone earth-to-air heat exchanger without external devices (fans, etc.), but only with the local climatic conditions of the region of Bechar (located in the Southwest of Algeria). The EAHE contains a PVC pipe with 66 meters of length and 110 mm of diameter, and it is buried at a depth of 1.5 m in an agriculture zone, where the annual undisturbed subsoil at 1.5 m is 28°C. The stand-alone EAHE has the capacity to raise the air temperature by 10°C in the heating regime and reduce it by 11.9°C in the cooling regime. Furthermore, the relative humidity is raised by19% in the humidification regime and reduced by 27% in the dehumidification regime. The daily working regime was: 62.5% of heating (from 00h to 08h and from 18h to 23h) and 37.5% of cooling (from 09h to 17h) for the thermal regime, 62.5% of dehumidification (from 00h to 09h and from 18h to 23h) and 37.5% of humidification (from 10h to 17h) for the hygrometric regime. The stand-alone EAHE technique presents a great potential for the pre-heating, pre-cooling, and natural ventilation of dwellings and buildings in arid regions. [ABSTRACT FROM AUTHOR]

The decade has witnessed great importance of numerical techniques for scientists and researchers in deciding the correctness, stability, and reliability of new designs. In the present study a numerical technique has been implemented to investigate the thermo-hydraulic performance of the Louvered winglet tape inside the tube section of the double pipe heat exchanger. The Louvered winglet tape has been examined with the slope angle of 50, 100, 150 and 210 to study their thermal characteristics. The Reynolds number 4000-30000 was examined on slope angle of 50, 100, 150 and 210 to study their flow characteristics in the turbulent domain. A smooth pipe was examined to evaluate heat transfer characteristics in terms of Nusselt number and friction coefficient over augmented tube with Louvered winglet tape. The results show a satisfactory performance of Louvered winglet tape over the smooth tube with a similar trend of friction factor, Nusselt number, and thermo-hydraulic performance index (THPI). The percentage of increment of the Nusselt number of the results is found to be 237.04%, 258.4%, 275.11%, and 289.72% when compared to smooth pipe with respect to slope angle of 50, 100, 150 and 210, respectively. The amount of increase in the friction factor in comparison with plain tube is 5.13, 6.73, 8.33, and 11.73 times of that of smooth pipe with respect to slope angle of 50, 100, 150 and 210, respectively. The Louvered winglet tape with slope angle 150 has shown to be promising with respect to higher THPI when considering with other slope angle of 50, 100, and 210. The maximum THPI of 1.85 was obtained for slope angle 150 at Re 12000. Similarly, the THPI values for other slope angle 50, 100, and 210 are 1.71, 1.78 and 1.69. In addition to better performance the Louvered winglet tape can be easily fabricated and adapted for a wide variety of heat transfer industries. [ABSTRACT FROM AUTHOR]

The world is facing the problems of the energy crisis. Thermal analysis and energy conservation of the engineering devices help to improve their performance. This paper conducted an experimental investigation for the performance analysis and exergy assessment of an Inertance Pulse Tube Cryocooler (IPTC) that uses working fluid - helium operated between 80 K cold end side temperature and room temperature. The variation of the different performance parameters like the effect of charge pressure, pulse tube volume, pulse tube length, etc., and its effect on the refrigerating effect is described graphically. Exergy analysis involves the use and concepts of energy and exergy balances, enthalpy, entropy, and exergy calculations at various stages in the system. Exergy analysis identifies the zones of key exergy destruction that occurs inside the system, which afterward can be subjected to its minimization to amend the system performance. The actual exergy efficiency value calculated for the overall system is 21.30 %. The decreasing order of exergy efficiency among the different components is a compressor (38.79 %), a hot end heat exchanger (6.19 %), regenerator, pulse tube and inertance tube (6 %), and cold end heat exchanger (2.70 %). [ABSTRACT FROM AUTHOR]

Energy is a key aspect of any country's economic development. Improving heat transfer performance leads to saving energy. Nanotechnology has a key role to play in optimizing heat exchangers. Fluids containing nanosized particles are called nanofluids. Nanofluids have higher thermal conductivity than typical liquids. This paper outlines current research on convective heat transfer performance, thermophysical properties, particle size, and volume concentration effects in nanofluid studies. Measurement methods for thermal conductivity and correlations used by earlier researchers to determine thermal conductivity are also encompassed. The main applications of nanofluids as lubricants and radiator systems to improve the efficiency of heat removal from vehicle engines have also been emphasized. Results suggest that by using a larger size of particle some drawbacks include particle sedimentation, clogging, erosion, stability, and increasing pressure drop. Enhancing thermal conductivity with optimum volume concentration. Improving the efficiency of heat exchange systems is one of the possible ways to reduce energy consumption. The need for optimum concentration of nanofluids is required. The Problem of stability, corrosion, and erosion arrived by increasing the volume concentration of nanoparticles in a nanofluid. [ABSTRACT FROM AUTHOR]

The objective of this paper is to study the effect of nanofluid on the performance of the heat exchanger, as well as the heat transfer rate, coefficient of total heat transfer, friction influence and average Nusselt number, and thermal efficiency factor and has been investigated and discussed. In this work, the output heat transfer of Fe3O4/water nanofluid through shell and tube heat exchanger has been numerically investigated under laminar flow. CFD simulations with ANSYS FLUENT 2020R1 were used adopting finite volume approach to solve the governing equations. Numerical calculations were carried out for Reynolds numbers ranging from 200 to 1400, with nanoparticles as the volume fraction (0.2% and 0.35%). The results show that the augmentation in increase Nusselt number and amount of heat transfer rate and the efficiency of nanofluid at the concentration of 0.35% are approximately 19%, 25% and 12% respectively. It was observed through the results that the friction decreases as the Reynolds number increase. [ABSTRACT FROM AUTHOR]

A study investigated how a new swirl airflow design could impact the heat transfer rate in a tubular heat exchanger with axial flow. A perforated conical baffle plate with rectangular air deflectors of different inclination angles was created to generate a swirl flow. The tubes in the heat exchanger were aligned longitudinally, and the heat flux across their surface was kept constant. Each plate had four deflectors with equal deflector angles and adjustable pitch ratios, which created a swirling airflow inside the circular duct containing the heated tubes. This increased turbulence and the rate of heat transfer across the tube surface. The Reynolds number stayed within the range of 93,500 to 160,500. The result indicates that the inclination angle and Pitch ratio profoundly impact the Nusselt number, while the pitch ratio has a greater effect on the friction factor. Furthermore, the conical baffle plate design resulted in an average improvement of 2.51 in thermal efficiency compared to a segmental baffle design with a deflector angle of 30° and a pitch ratio of 1, all under similar Reynolds number, pitch ratio, and blockage ratio conditions. [ABSTRACT FROM AUTHOR]

In this paper, the numerical results of the study on geothermal-air heat exchanger in dry areas of Algeria (Ghardaia region) were presented. Computational fluid dynamics equations were solved using our specific code compilated with Fortran. The outputs of the numerical calculations were compared and validated with the experimental results and the outputs of a commercial CFD code. In these conditions, our results present good agreements with an error not exceeding 2%. By using our numerical model, we have calculated the optimum length, the internal diameter, the air velocity of the pipe in winter and summer periods and have determined the optimum depth at different depths. The comparison of two types of pipes making material (PVC and PEHD) has taken into account the characteristics of the Ghardaia-Algeria region (specific heat capacity, density, thermal conductivity and temperature) of the soil. The obtained results proved that the chosen model gives a satisfactory agreement in all the studied variables. [ABSTRACT FROM AUTHOR]

This paper makes attempt to optimize a high-temperature differential Ericsson engine with several conditions. A mathematical approach based on the finite-time thermodynamic was proposed with the purpose of gaining thermal efficiency, the output power and the entropy generation rate throughout the Ericsson system with regenerative heat loss, finite rate of heat transfer, finite regeneration process time and conductive thermal bridging loss. In this study, an irreversible Ericsson engine is analyzed thermodynamically in order to optimize its performance. In addition, three Scenarios in multi-objective optimization are presented and the results of them are assessed individually. The first strategy is proposed to maximize the Ecological function, the thermal efficiency and the Exergetic performance criteria. Furthermore, the second strategy is suggested to maximize the Ecological function, the thermal efficiency and Ecological coefficient of performance. The third strategy is proposed to maximize the Ecological function and the thermal efficiency and Dimensionless ecological based thermo-environmental function. Multi-objective evolutionary algorithms based on NSGA-II algorithm was applied to the aforementioned system for calculating the optimum values of decision variables. Decision variables considered in this paper including the regenerator's effectiveness, the high-temperature heat exchanger's effectiveness, the low-temperature heat exchanger's effectiveness, the working fluid temperature in the low-temperature isothermal process and the working fluid temperature in the high-temperature isothermal process. Moreover, Pareto optimal frontier was achieved and an ultimate optimum answer was chosen via three competent decision makers comprising LINMAP, fuzzy Bellman-Zadeh, and TOPSIS approaches. The results from scenarios shown that third scenario is the best scenario. [ABSTRACT FROM AUTHOR]

In this paper, the hot and cold utilities of a complex natural gas refinery containing multiple heat exchanger networks (HENs) were properly selected. Following using pinch analysis for designing the HENs of the natural gas refinery, this selection could be done by considering available utilities in the plant under consideration. The plant network was divided into the five heat exchanger networks for better and precise estimation of utility requirements in each smaller network. By comparing the type and temperature level of the utility required in each network, the best utility could be selected, in order to use as the heating and cooling media in the plant network with a considerable reduced operating cost of the system. The results show that in the new network design, there was about 38 and 100% reduction in cooling air and BFW respectively, but 45% increase in cooling water, as cold utilities and almost 64.4, 30.0, 90.9 and 100% reduction in HP steam, LP steam, hot flue gas and electric heater as hot utilities, respectively relative to the existing network. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the cubical fins and the thermal-hydraulic characteristics in a Printed Circuit Heat Exchanger (PCHE). The working fluid is considered a supercritical LNG. The outcomes show that the thermalhydraulic performance is enhanced using the cubical fins comparing it to the straight channel. The maximum and minimum difference of Nu/Eu between the cubical fins channel and the straight channel were 71.7 % and 64.8 % respectively. It is noticed that the pressure drop and Heat Transfer coefficient are increasedsimultaneously with increasing the mass flux.Using Ansys Fluent 15.0, numerical optimization isperformed to examine and analyzethe influence of the sparser staggered arrangement. The computed results show that this type of arrangement improves the thermal-hydraulic efficiency of the cubical fins in a PCHE. A comparison between the straight fins arrangement and the staggered fins arrangement is reported.It has been noticed that the velocity of the LNG flow in the cubical fins channel is increased along the length of the PCHE,and decreased byincreasing the vertical separationLV. The side effect of the vertical separation LV on the PCHE’s efficiency was more evident than that of the staggered arrangementLS. Finally, afeasibility study is performed to inspect the power consumption of the new design. [ABSTRACT FROM AUTHOR]

This paper investigates numerically the influence of detached square vortex generator (VGs) on the heat transfer and pressure drop inside a square duct. Reynolds number is fixed at 5000. The geometrical parameters in this investigation are: i) The blocking ratios are 0.1, 0.15 and 0.2), ii) Vortex generator numbers are 1, 2, and 3), iii) Attack angles are 0, 30, and 45, iv) The aspect ratios are 1, 1.5 and 2. The numerical simulation is carried out using ANSYS FLUENT 15. The results show that the rectangular vortex generators have a positive influence on heat transfer as a result of the augmentation in turbulence level. The maximum enhancement in average heat transfer could reach 40%. The heat transfer is found to increase with the blocking ratio. The heat transfer enhanced by 17% for one VG and 28% for 3 VGs for blocking ratio = 0.2. The VGs at angle value of 45° produce the highest heat transfer enhancement. The aspect ratio is found to have an adverse effect on heat transfer rate. [ABSTRACT FROM AUTHOR]

Heat exchanger networks (HENs) play a significant role in the energy conservation of any process industry. The HENs are used to maximize heat recovery by exchanging heat between hot and cold process streams. Therefore, the optimum design of HENs is extremely important to reach the maximum efficiency of energy systems. Many graphical methods have been developed during the last four decades for synthesizing of heat exchanger networks (HENs). However, most of these methods have only been evaluated for retrofitting design of HENs. In the grassroots design situation, these methods are often complicated and tedious. This paper introduces a new and simple graphical approach for HEN grassroots design. The new approach based on a single graph called Supply-Target Diagram (STD). The ST-D is formulated by plotting supply temperatures versus target temperatures of streams. Streams matching can easily be applied in the ST-D and splitting of streams is clearly visualized and evaluated. A case study is used to illustrate the application of the new graphical method for grassroots design of HENs. [ABSTRACT FROM AUTHOR]

This study reports on experimentally enhancing the performance of a concentric double pipe heat exchanger using nanofluid and refrigerant vapor under constant wall temperature conditions. Ferro-nanoparticles with diameters of 80 nm are distributed in distilled water with volume concentrations of 0.1-0.7 % (nanofluid), which is used as hot fluid flowing turbulently inside the inner tube with Reynolds numbers ranging from 3900 to 11800, while refrigerant vapor produced from the refrigeration unit is used as cold fluid with counterflow through the annular tube. The results show that the convection heat transfer coefficient and Nusselt number in the inner tube increase proportionally with a rise in the mass flow rate of nanofluid and the ratio of nanoparticles in the fluid (concentration). Under Reynolds number 11900, the maximum enhancement for convection heat transfer coefficient and Nusselt number in the inner tube was 13.4% and 10.7%, respectively, when using the iron oxide nanofluid with volume concentration of 0.7% compared to pure water. The results of the test were also compared with an almost similar study that used water in the annular tube, and it was found that the use of refrigerant vapor in the annular tube gives better performance compared to water. [ABSTRACT FROM AUTHOR]

In the current work, a substantial research and cost-effective strategy has been conducted to enhance the thermal efficiency of shell and coil heat exchangers, and geometrical modification is one technique to improve the exchange of thermal energy between two or more fluids. Therefore, experimental and numerical analysis across a shell and single/double coil heat exchanger at constant temperatures of 36 °C for cold water and 65 °C for hot water are studied. Various coil pitches (baseline pitch, P-2P-P and 2P-P-2P) and mass flow rates (1 L/min for hot water and 2, 4, 6, and 8 L / min for cold water) were studied. The present experimental results for single and double coil heat exchangers were in good agreement with previous research's numerical study, with an error rate of 9% and 5%, respectively. Moreover, the numerical findings revealed that modifying the double coil pitch improves the heat transfer rate by 10% compared to a baseline case. Following the encouraging simulation findings, improving the heat exchanger's performance by utilizing more than one pitch for the same coil is a novel method that has not yet been reported. Therefore, when comparing the modified pitch of a double coil heat exchanger to a conventional coil under the same conditions (400

In this research paper, energy and exergy analyses of water lithium bromide half effect vapour absorption refrigeration system has been carried out. Based on energy and exergy analysis the optimum intermediate pressure is computed corresponding to maximum values of coefficient of performance and exergetic efficiency under various operating conditions. It is found that the optimum intermediate pressure corresponding to maximum values of coefficient of performance and exergetic efficiency is same. The effects of low and high pressure generator temperatures, evaporator temperature, effectiveness of solution heat exchangers and difference between low and high pressure generator temperatures have been considered in computing optimum intermediate pressure. The maximum COP varies between 0.415 - 0.438 and maximum exergetic efficiency varies between 6.96-13.74%. [ABSTRACT FROM AUTHOR]

This paper focuses on the effect of inlet temperature of the cold fluid on the thermal performance of two mini channel flat-tube with multi-louvered fin compact heat exchangers experimentally. Two louvered fin heat exchangers in the same sizes with different number of fin rows are tested in a constant temperature test room by a wind-tunnel. The cold fluid flowing on the external side of the heat exchanger is air. The hot fluid flowing through the mini channels is water. The inlet temperature of the water passes through the mini channel flat-tube is predetermined and supplied at a temperature of 42°C. Mass flow rate of the water is regulated by a water circulator at a rate of 0.025 kg/s. The mass flow rate of the air is measured 0.0472 kg/s. It is found that the model which has two fin rows is more effective in terms of overall thermal conductance, number of transfer units and effectiveness at all values of inlet temperature of the air. In addition, both of the heat exchangers have the highest thermal performance at an air inlet temperature of 24°C. [ABSTRACT FROM AUTHOR]

This paper investigated optimization of two objectives function include the total amount of heat transfer between two mediums and the total cost of shell and tube heat exchanger. The study was carried out for k-type heat exchanger of the cryogenic unit of gas condensates by multiple objective particle swarm optimization. Six decision variables including pipe pitch ratio, pipe diameter, pipe number, pipe length, baffle cut ratio, and baffle distance ratio were taking into account to conduct this simulation-based research. The results of mathematical modeling confirmed the actual results (data collected from the evaporator unit of the Tehran refinery's absorption chiller). The optimization results revealed that the two objective functions of heat transfer rate and the total cost were in contradiction with each other. The results of the sensitivity analysis showed that with change in the pitch ratio from 1.25 to 2, the amount of heat transfer was reduced from 420 to 390 kW about 7.8%. Moreover, these variations caused reduction in cost function from 24,500 to 23,500 $, less than 1%. On the other hand, an increase in pipe length from 3 to 12 meters, the heat transfer rate raised from 365 to 415 kW by 13.7%, while the cost increased from 20,000$ to 24500$ about 22%. [ABSTRACT FROM AUTHOR]

The growing demand for new and eco-friendly energy resources has raised the need of sustainable sources or renewable energy for use in present era. A vapor absorption refrigeration system (VARS or VAS) is a closed loop refrigeration system which requires low heat for its functioning and, it is therefore, considered an eco-friendly solution. Since, generator is the main component of VAS which can significantly influence the efficacy of overall system, the current paper involves modeling and thermal analysis of generator using Computational Fluid Dynamics (CFD). The objective of this study is to optimize the heat transfer by changing baffle spacing of generator heat exchanger, running on a single effect LiBr/water absorption cycle. For this purpose, hot water driven generator of 1ton capacity is taken. The simulation results of CFD were validated by comparing them with theoretical results. The overall design estimation and design technique that follows Birmingham Wire Gauge (BWG) and Tubular Exchangers Manufacturers Association (TEMA) standard are considered in this study. It was found from the analysis that the design model with smallest baffle spacing has the highest heat transfer coefficient. On reducing the baffle spacing from 137mm to 101mm, an increment of 48% in overall heat transfer coefficient was observed. Likewise, an increase in velocity by 36% and drop in static pressure by 27% were seen. Similar trend was observed in the theoretical results. [ABSTRACT FROM AUTHOR]

In this study, a triple concentric tube heat exchanger (TCTHE) was designed. It had three copper concentric tubes. Their thicknesses were 0.762 mm, 1.143 mm, and 1.27 mm. The diameters were 9.525 mm, 22.25 mm, and 34.925 mm, respectively. The tube's length was 670 mm. The cooling medium used was the ionic-liquid (IL) 1-Ethyl-3-methylimidazoliumtetra-flouraborate [EMIM][BF4] and the ionanofluid (INF) prepared of 0.5% Multi walled carbon nanotubes (MWCNT) in [EMIM][BF4], while oil forty stock was the hot fluid, to investigate TCTHE performance. The volumetric flow rate (VFR) of the cooling medium was 20-55 l/hr, with a 25-27 °C temperature (temp). VFR of the hot fluid was constant and equal 20 l/hr. The inlet oil temp was 50, 60, and 70 °C, respectively. The type of flow was countercurrent. The heat transfer was investigated by calculating different parameters for the cooling medium. There was an improvement in the Nusselt number (NU) of INF of 5% compared to the IL. A 75% increase in the friction factor of INF was found compared to that of IL. A 95% increase in the pressure drop was calculated in the inner tube using INF compared with that of IL. The overall heat transfer coefficient (U) was enhanced by 3% using INF in comparison with IL. Fi- nally, U showed some improvement, resulting in increased heat transfer. In conclusion, using the prepared INF lead to improve the heat transfer in the TCTHE. [ABSTRACT FROM AUTHOR]

A wide variety of heating and cooling applications use heat exchangers. The increase in energy prices, the requirement for size reduction, and restriction on greenhouse gas emissions has led to the need for finding ways to develop efficient heat exchangers. A cost-efficient way to enhance the model of a heat exchanger by visualizing the effects of the design parameters is using Computational Fluid Dynamics (CFD). The reason for this exploration was to lead an examination of the varieties/changes in the general intensity move process for a Finned-Tube Heat Exchanger (FTHE), also known as Air Coil Heat Exchanger (ACHE) with a variety of plan boundaries like the quantity of tubes, course of action of tubes, and the material utilized for the intensity exchanger. The widely used heat exchanger that uses refrigerant R314a and air as the working fluids was simulated with different design modifications. The simulated results exhibited as to how the number of tubes, arrangement of coils/tubes, material of tubes, and density / spacing of fins, effects the pressure drop, temperature and velocities profiles, and heat exchangers' transfer of a heat. The use of copper coils improved the heat transfer by approximately 61% as compared to aluminium coils. [ABSTRACT FROM AUTHOR]

This study aims to present a novel experimental method for studying the performance of water source heat pumps which have not received sufficient attention, although this is particularly important for hot regions with great potential of hot water sources. The experimental model has special characteristics as it allows to investigate the performance of heat pumps under different operating conditions and allows a comparison between different types of heat pumps without the need to install a ground heat exchanger. The ground heat exchanger is known to be the most expensive part of any experimental model. In addition to that, it only allows to study the performance under specific conditions. The ground heat exchanger was replaced by a secondary heat pump that allows to provide an environment that simulates the different operating conditions of different types of heat pumps. It was found that water source heat pumps are more efficient than air source heat pumps with efficiency that increases with increasing water source temperature. It was found that increasing the water source temperature from 5 to 20 oC, improved the rate of heat extracted from the water source by 11.3% and the coefficient of performance by 2.8% for each degree. Another important feature of water source heat pumps is the stability of the energy flow rates, which is a guarantee of higher seasonal performance coefficients. It can be concluded that hot regions with high potential of hot water sources has valuable opportunities to invest in the field of water source heat pumps with the consequent significant energy savings. [ABSTRACT FROM AUTHOR]

Hydro-fluorocarbons (HFCs) that are not harmful to ozone layer and are used in many applications, including as refrigerants, aerosols, solvents and blowing agents for insulating foams replace chlorofluorocarbons and hydro chlorofluorocarbons (HCFCs). However, some HFCs have a high GWP, which stands for "Global Warming Potential(GWP)." Because of the growing concern over global climate change, researchers are paying closer attention for alternatives to these HFCs. The main focus of this work was on the theoretical analysis of the refrigerant mixtures namely AC5, R430A, and R440A as direct replacements for HFC-134a in a refrigerator. The performance of the refrigerator may be enhanced using heat exchanger. The compressor discharge temperature, COP, VCC, refrigerant mass flow rate, power consumption of a compressor and pressure ratio were used to measure the performance of a home refrigerator. The typical COP of R440A and R430A was about 2.5% and 1.4% higher than that of HFC-134, while the average COP of AC5 was 6.1% lesser than that of HFC-134a. R430A almost has the same VCC (Volumetric Cooling Capacity) as HFC-134a. The results also show that HFC-134a uses more power than AC5, R440A, and R430A. R440A and AC5 have higher compressor outlet temperatures than HFC-134a, which affects the life span of the compressor. In comparison with all the above refrigerants, R430A gives the best overall performance and used as replacement to HFC-134a in a VCR. [ABSTRACT FROM AUTHOR]

The present work deals with the deployment of an air bottoming cycle as a technology for thermal energy valorization. This solution is integrated within the preheater tower on an Algerian cement plant. A combined MATLAB-Coolprop optimization tool has been developed to carry out a thermo-economic calculation allowing to design and optimize the air bottoming cycle and also check its economic returns. The developed code employs the genetic algorithm through a multi-objective function aiming to maximize the cycle's net power output as a priority objective, then minimize the heat exchanger's area of exchange, and also maximize the cycle's net present value. through the implemented models on it, the code gives the ability to confirm the applicability of this technology through the Algerian market which is characterized by one of the cheapest prices of electricity in the world that doesn't exceed 0.040 $ kWh-1. The obtained results highlight that the implementation of such technology for energy valorization purposes from the preheater tower of the selected cement plant can be a profitable and attractive solution, particularly in scenarios of water scarcity. Since the implementation of this technology presented a power capacity of 1.2 MW covering then around 7.8% of the electricity demand of the investigated cement plant. The economic analysis of the proposed ABC cycle pointed out a net present value of 6.59 M$, and a payback time less than 3.6 years, besides a Levelized cost of energy less than 0.017 $ kWh-1 which is a comparable value to the subsidized prices of electricity in the Algerian market. [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]

Sewage wastewater heat exchanger (SWHE) has a significant role in the performance of sewage wastewater sourced heat pump (SWSHP) system as it provides to transfer the energy of wastewater to intermediary fluid or working fluid. Thus, a theoretical analysis of the SWSHP system was carried out to investigate the effects of SWHE design parameters on the system's performance. For this purpose, a simulation program based on the proposed mathematical model of the SWSHP system was developed in MATLAB. Afterward, the indirect type SWSHP system that can meet 50 kW heating load was theoretically designed. The influences of SW temperature, its mass flow rate, the inner diameter of the heat exchanger tube, and intermediary fluid mass flow rate on the performance of the designed SWSHP system were analyzed. The results indicate that variation of SW temperature affects the COPsys more than the variation of SW mass flow rate. Considering the ranges of parameters investigated, the COPsys raises from 2.56 to 4.51 and 2.89 to 4.27 with the variations of SW temperature and SW flow rate, respectively. Moreover, an increase in the intermediary fluid mass flow rate provides an improvement on the COPsys and COPunit. However, SWSHP performance is adversely affected by the increasing value of the inner diameter of the tubes. As a result, small changes in the design parameters of the SWHE directly affect the system performance and system operating conditions. [ABSTRACT FROM AUTHOR]

The present study proposes a plate heat exchanger model that is capable of simulating the supercritical fluids like CO2. The plate heat exchanger is of U-type configuration, and the size of the plate is 600 mm wide and 218 mm in height. Simulations are carried out for both isothermal and nonisothermal cases with water-to-water and water-to-CO2 plate heat exchanger. The proposed model was first compared with some existing water-to-water plate heat exchanger data. Generally, the predicted water flow distributions are in line with the experimental data. Yet the simulation results of temperature distribution alongside the plate agree excellently with other predicted model. For the water side distribution within the plate heat exchanger, it is found that a detectable mal-distribution prevails and the flowrate shows a consistent decline from the first to the last plate. Basically, a larger mal-distribution is seen when the inlet flowrate is increased or when the plate number is increased. The simulation indicates that the inlet temperature of water casts negligible influence on the water flowrate distribution. By contrast, it is found that the inlet temperature difference for the CO2 side may raise significant changes of thermodynamics and transport property of CO2, and result in a great difference in flow distribution. Generally the maldistribution of the CO2 is much less severe due to more even pressure difference between the intake and exhaust manifold. The effect of pressure on heating capacity for the water-CO2 plate heat exchanger also depends on the ratio of heat capacity flow. [ABSTRACT FROM AUTHOR]

The heat loads on electronic systems of an unmanned air vehicle are a significant problem. So enhancing heat transfer is a critical key to solve these thermal problems. This study is focused on increasing heat transfer rate in a crossflow heat exchanger by using nanofluids numerically. Effects of different Reynolds number of hot fluid (Re = 6000, 8000, 10000, 12000), different inlet velocity (Vair,inlet = 30, 45, 60, 90 m/s) of cooling fluid, temperature of cooling air at different altitude (Tair,inlet = 15, 10, 4, -17°C) and different types of nanofluids (Cu-H2O, CuO-H2O, TiO2-H2O, H2O) on heat transfer were studied numerically. Realizable k-e turbulence model of ANSYS FLUENT computational fluid dynamics code was used for numerical analysis. It was obtained that increasing Reynolds number from Re = 6000 to 12000 causes an increase of 44.65% on average Nusselt Number. Increasing inlet velocity of cooling air from 30 m/s to 90 m/s causes an increase of 6.96% on average Nusselt number. Increasing or decreasing air inlet temperature at different attitude does not cause any significant change on average Nusselt number. Using Cu-H2O nanofluid, which shows the best performance, causes an increase of 6.63% on average Nusselt number according H2O. Numerical results were also compared with experimental results at literature. It was obtained that numerical model can represent experimental results in a good level. [ABSTRACT FROM AUTHOR]

Heat transfer improvement plays a vital role in several industrial applications as well as in the transportation sector such as gas turbines, heat exchangers, various cooling devices, and combustor liners. The extensive research to enhance the heat transfer rate in various sectors has been carried out to achieve the objectives such as (i) to increase the system efficiency, (ii) to reduce thermal load, (ii) to reduce consumption of non-renewable energy, (iii) to reduce the production of emission, (iv) to develop new green technologies, (v) to lower energy prices for the consumer. The heat transfer in various sectors has been carried out by adopting three different ways (i) increasing the surface area of the heat transfer systems, (ii) enhancing the fluid properties, (iii) by adding extra surface on the heat transferring surface. This article aims to deliver a comprehensive review of the current research on heat transfer enhancement techniques by using artificial roughness elements such as rib tarbulator, fin, and dimple. It includes various types of rib tarbulators, fins, and dimples used for heat transfer enhancement of gas turbine blades of the power plant, combustion liners as well as solar air heaters. The physical mechanism responsible for heat transfer enhancement in various artificial roughness elements has been discussed and compared. The challenges and difficulties associated with the heat transfer techniques have been discussed. The parameters such as dimple depth, channel height to dimple imprint diameter, pitch, the density of artificial roughness element, arrangement of artificial roughness, relative roughness pitch, relative roughness height, angle of attack on flow, mass flow rate, Reynolds number on thermal performance, thermohydraulic performance, flow structure, friction characteristics have been studied and compared. From the comprehensive review, it may be recommended that the teardrop shape dimple can be used for further enhancement of heat transfer as compared to other artificial roughness elements. In the future, this teardrop may be used to enhance the heat transfer in the solar thermal system and some other relevant thermal systems. [ABSTRACT FROM AUTHOR]

Diversity in living standards and population growth leads to increased global energy consumption. Human comfort always plays a vital role in using different means to reduce the effects of weather conditions. The building sector captures approximately 40% of the global energy and it is most commonly used for cooling and for heating of the space occupied due to the use of appliances such as room heaters or air coolers, air conditioners, etc. The use of these appliances contributes significantly to global warming, which is a very serious environmental problem. Passive energy sources are used widely to reduce the consumption of energy due to heating and cooling of the building. Earth air pipe heat exchanger is one of the passive cooling/heating technology used for the indoor thermal comfort of the occupants. In this review article, various discussion has been done on the use of passive energy explained by the earth air pipe heat exchanger and various investigations conducted by authors under different conditions and parameters like air velocity, pipe depth, pipe length, etc. that the thermal conductivity of the soil is the key point to the efficient operation of the earth air pipe heat exchanger system and it is also necessary to maintain the thermal conductivity of the soil in the vicinity of the pipe in order to achieve better performance in operation. [ABSTRACT FROM AUTHOR]

The exergy loss and performance optimization of a cross flow heat exchanger (CFHE) with air and hot water as working fluid have been experimentally investigated. Experiments are performed on various mass flow rates of hot water and air over a ranges of 0.015 kg.s-1- 0.04 kg.s-1 and 0.117 kg.s-1 - 0.763 kg.s-1 respectively. To validate the results of the present study, they are compared with available data in literature through which a reasonably a good agreement is obtained between them. This study demonstrates the successful application of Taguchi approach for optimal design of the (CFHE). The effects of design parameters and two different operating conditions such as the fin pitch, the inside tube diameter and the mass flow rate of water and air on exergy loss are investigated. In the Taguchi experimental design method, exergy loss is considered as performance parameter and it is revealed that parameter combinations such as ṁh=0.0163 kg.s-1, ṁa=0.1175 kg.s- 1, di=0.0199 m and Fp=0.00259 m resulted optimum performance. Contribution ratios of each parameter on exergy loss are assessed. Mass flow rate of air is determined to be the most effective parameter on exergy loss with a contribution ratio of 51.26 % followed by mass flow rate of hot water, fin pitch, and diameter contribution ratios of 35.91 %, 7.02 %, 5.79 % respectively. [ABSTRACT FROM AUTHOR]