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Experiments are conducted under laminar flow conditions. The sol-gel method is used for preparations of copper (Cu) and nickel (Ni) nanoparticle. The prepared Cu-Ni nanoparticles are surface treated to lower the sedimentation after suspending these nanoparticles in pure water. The impact of pitch (0.032, 0.042 and 0.052m), massflow rate, coil material Aluminium (Al) and Copper (Cu), and volume concentration (0.02, 0.04 and 0.06) on heat transfer rate is computed. Reynolds number (Re), Nusselt number (Nu) are computed to evaluate thermal performance of counter flow helical coil heat exchanger. The overall heat transfer coefficient in case of a 12 turn copper coil is increased by 43.71, 52.196 and 60.782% for 0.02, 0.04 and 0.06 % vol respectively compared to distilled water at reynolds number equals to 2224. In this study the best optimal condition to operate shell and helical coil heat exchanger is 0.006% vol at Re=2224. This is due to mass flow rate and reduction in sedimentation of Cu-Ni nanoparticles in distilled water. This is due to flow ate and thermal conductivity of coil material. [ABSTRACT FROM AUTHOR]

This paper introduces a novel empirical correlation designed to predict the overall heat transfer coefficient (U) in concentric tube heat exchangers. The study utilizes a comprehensive dataset of 2700 data points from CFD simulations, examining the impact of critical variables including hot and cold fluid Reynolds numbers (Reh, Rec), Prandtl numbers (Prh, Prc), and heat exchanger dimensions (tube hydraulic diameter Dh, annular space hydraulic diameter Dc, and overall length L). The analysis incorporates a range of fluid combinations in the tube and annular sections – air–air, air–water, water-air, and water–water – across Reynolds number ranges from 1000 to 20000, covering both laminar and turbulent flow regimes. The correlation was developed using the Adam optimizer to minimize the Weighted Mean Squared Error (WMSE), achieving an impressive convergence to an average prediction error of 6.7% compared to actual U values. The model categorizes flow into four distinct categories, each corresponding to a combination of flow patterns in the tube and annular spaces regimes – Laminar–Laminar, Laminar–Turbulent, Turbulent–Laminar, and Turbulent–Turbulent – integrating both hydrodynamic and thermal entry effects to enhance prediction accuracy. Rigorous error analysis revealed a median error of 5.18%, substantially outperforming existing models. Notably, 10% of the predictions deviate by less than 1%, with 90th percentile errors staying below 15%. Parameters were finely tuned through extensive numerical simulations, ensuring accurate application of the correlation across diverse operational conditions. The study concludes by highlighting the model’s potential to significantly enhance the design and efficiency of heat exchangers and proposes future enhancements to further improve its predictive accuracy.

A full understanding of the fluid flow and heat transfer behaviors within a single fracture is important for geothermal heat extraction. In this study, models of single fractures with varying aperture and inner surface roughness (characterized by fractal dimension) are constructed, and a compound fracture aperture (CFA) is proposed to describe the coupled effect of fracture aperture and inner surface roughness. The effect of the fluid flow Reynolds number on heat transfer was investigated as it ranged from 4.84 to 145.63. The results show that the overall heat transfer coefficient (OHTC) in a single fracture significantly increases with the rise in fluid velocity and the compound fracture aperture. Particularly, the OHTC in a single fracture with an inner surface fractal dimension of 2.09 can be up to 1.215 times that of a parallel flat fracture when the flow velocity reaches 0.18 m/s. Moreover, for a fracture with a smaller CFA, enhancing the fracture aperture plays a decisive role in increasing the OHTC. Aperture emerges as a more sensitive optimization parameter for efficient heat extraction compared to the flow velocity. Meanwhile, based on simulation results, a convective heat transfer correlation equation is derived to provide more accurate estimates of the OHTC in rock fractures with different geometries and morphological features. [ABSTRACT FROM AUTHOR]

In order to reduce the impact of outdoor extreme weather events on crop production in winter, energy saving in greenhouses that are regularly heated is of great importance in reducing production costs and carbon footprints. For this purpose, the variations in indoor temperature, relative humidity and dew point temperature in the vertical direction (2 m, 4 m, 5.7 m) of thermal curtains in greenhouses were determined. In addition, depending on the fuel used, the curtains' effects on heat energy consumption, heat transfer coefficient, carbon dioxide equivalents released to the atmosphere and fuel cost were investigated. To reach this goal, two greenhouses with the same structural features were designed with and without thermal curtains. As a result of the study, the indoor temperature and relative humidity values in the greenhouse with a thermal curtain increased by 1.3 °C and 10% compared to the greenhouse without a thermal curtain. Thermal curtains in the greenhouse significantly reduced fuel use (59.14–74.11 m3·night−1). Considering the heat energy consumption, the average heat energy consumption was 453.7 kWh·night−1 in the greenhouse with a curtain, while it was 568.6 kWh·night−1 in the greenhouse without a curtain. The average heat transfer coefficient (U) values were calculated at 2.87 W·m−2 °C with a thermal curtain and 3.63 W·m−2 °C without a thermal curtain greenhouse. In the greenhouse, closing the thermal curtain at night resulted in heat energy savings of about 21%, related to the decrease in U values. The use of a thermal curtain in the greenhouse reduced the amount of CO2 released to the atmosphere (116.6–146.1 kg·night−1) and fuel cost (USD 21.3–26.7·night−1). To conclude, extreme weather events in the outdoor environment adversely affect the plants grown in greenhouses where cultivation is performed out of season. A thermal curtain, used to reduce these adverse effects and the amount of energy consumed, is essential in improving indoor climate conditions, providing more economical greenhouse management and reducing the CO2 released into the atmosphere due to fuel use. [ABSTRACT FROM AUTHOR]

Nanoparticles attracted many researchers because of their significant heat transfer enhancement properties in various applications. The nanoparticles have variable properties and a high specific surface (Cp) area, which enhance heat exchange between fluids and their particles at different volume concentrations. This article provides the outcomes of an experimental study on the overall heat transfer coefficient (Uo) and effectiveness (ε) of the shell and tube heat exchanger (STHE) with a 25% baffle cut using Al2O3 nanofluid consisting of base fluid distilled water (DW) and Al2O3 nanoparticles at 0.05%, 0.1%, and 0.2% of volume concentrations. Using a two-step method and adding a weight fraction of 0.1% sodium dodecylbenzene sulfonate (SDBS) as a surface active agent to each volume concentration of nanofluid provides better stability. The thermophysical properties like density (ρ), thermal conductivity (k), and dynamic viscosity (μ) of the Al2O3-DW nanofluid increased, but Cp of the same was reduced by increasing the volume fraction. Al2O3-DW nanofluid at different concentrations in parallel and counter flow variations of the STHE enhances the Uo and ε when compared with water. However, counterflow provides higher effectiveness. At 0.6 LPM of the nanofluid flow and hot fluid at T = 80°C temperature, the difference in the heat exchanger's effectiveness enhancement is 4.24% for parallel flow and 4.16% for counterflow at 0.2% concentration of Al2O3-DW nanofluid compared to water. [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]

Increasing production of poultry litter, and its associated problems, stimulates the need for generating useful energy in an environmentally friendly and efficient energy system, such as the use of shell-and-tube heat exchangers (STHE) in a fluidized-bed combustion (FBC) system. A holistic approach which involves the integration of the First Law of Thermodynamics (FLT) and Second Law of Thermodynamics (SLT) is required for conducting effective assessment of an energy system. In this study, the STHE designed by the CAESECT research group, which was integrated into the lab-scale FBC, was investigated to determine the maximum available work performed by the system and account for the exergy loss due to irreversibility. The effects of varying operating parameters and configuration of the space heaters connected to the STHE for space heating purposes were investigated in order to improve the thermal efficiency of the poultry litter-to-energy conversion process. Exergy and energy analysis performed on the STHE using flue gas and water media showed higher efficiency (75–92%) obtained via energy analysis, but much lower efficiency (12–25%) was obtained when the ambient conditions were factored into the exergy analysis, thus indicating huge exergy loss to the surroundings. From the obtained experimental data coupled with the simulation on parallel arrangement of air heaters, it was observed that exergy loss increased with increasing flue gas flow rate from 46.8–57.6 kg/h and with increasing ambient temperature from 8.8 °C to 25 °C. To lower the cost of STHE during final design, a larger temperature difference between the hot and cold flue gas is needed throughout the exchanger, which further increases the exergetic loss while maintaining an energy balance. In addition, this study also found the optimal conditions to reduce exergy loss and improve energy efficiency of the designed STHE. This study shows the possibility to evaluate energy systems using integration of exergy and energy analysis. [ABSTRACT FROM AUTHOR]

Introduction. The new Rules for the perishable freight conveyance have changed the structure of freight flows towards higher volumes of transportation in special isothermal vehicles. When choosing them, the shipper should know the estimated period of transportation of perishable food, where the temperature of the latter would remain within the range of established transportation and storage temperatures.Materials and methods. The calculation of the permissible transportation period uses the overall heat transfer coefficient of the body of a special vehicle determined by thermal tests using internal heating or cooling methods with mathematical dependencies that factor in the calculated change in the heat transfer coefficient during movement in train set.Results. The authors calculated the permissible transportation period of bottled beer in a special isothermal vehicle in summer for permissible storage temperatures of perishable food from 0 to 10 °C in the range of average train speeds from 0 to 120 km/h. The calculation results show that the permissible transportation time with the heat transfer coefficient obtained in thermal tests amounted to 69.4 hours, and the calculation using external factors showed 57.1 hours, i. e. decreased by 12.3 hours, or approximately 18 %.Discussion and conclusion. The permissible period of perishable freight conveyance in special isothermal vehicles depends on the average transportation speed and the infiltration of outside air and solar radiation into the vehicle. The shipper should consider these circumstances while selecting the parameters of special vehicles in order to prevent food fromdeterioration or spoilage.

Upgrading the thermal efficiency of the cooling system of liquid rocket engines is one of the most significant and intricate problems in designing modern rocket engines in the missile industry. The present study employed the Bees algorithm (BA) to attempt a single-objective optimization of the cooling system of the combustion chamber and nozzle of an LH2/LOX rocket engine considering the overall heat transfer coefficient objective function and four parameters, including the diameter and thickness of the cooling tubes, the radius of the throat, and the mass flow rate of liquid hydrogen (cooling fluid). The optimization was examined by the heat transfer analysis of combustion gases with the chamber walls, the use of the BA optimization algorithm, and the consideration of the sensitivity of the design parameters regarded for the overall heat transfer coefficient objective function. In this respect, these parameters were considered constant in the design ranges, while other parameters were variable. The results show that the overall heat transfer coefficient can increase almost by 17.78% during the optimization process of the cooling system of this rocket engine through the parametric analysis of the four mentioned design parameters.

In this work, an experimental system was established to measure the heat transfer characteristics, including the heat transfer coefficient, overall heat transfer, Nusselt number, and thermal conductivity. The investigation focused on spring water and tap water-based nanofluids containing Fe2O3 and ZnO nanoparticles with particle sizes of 50 nm and 70 nm, respectively. The experiments were conducted inside an automobile engine, studying the effects of varying nanoparticle volume fractions at a constant temperature. Fe2O3 and ZnO concentration in the respective based fluids was verified between 0.02 % and 0.08 % v/v and 0.01 and 0.07 %, respectively. The spring water is not so far used in the previous studies and is much more available in Kurdistan region. Reynolds numbers of nanofluids inside the engine were considered between 1000 to 8000 in a different range as that of the literature review. Reynolds analogy for heat and momentum has been employed in this study. It was observed that the thermo-physio-mechanical properties of nanofluids increased with increase in the concentration of nanoparticles and Reynolds number. However, the friction factor decreased with increasing Reynolds number but increased with an increasing volume concentration of nanoparticles. Generally, the results showed that the enhancement of the effective heat transfer of the nanofluids reached 46%, the overall heat transfer coefficient reached 39%, thermal conductivity reached 21.35% and Nusselt number reached to 38%. at 0.08% volume fraction of Fe2O3/spring water nanofluid. Based on all previous parameters estimated, the designed nanofluids in this study could be classified as a workable nanofluid in many industry applications

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Sandwich composites are materials that have superior properties including low weight, high impact energy absorption and high thermal insulation features, compared to conventional materials. In this study, four different sandwich samples were explored for use in cold storage chambers. The composites were created using an injection molding process with polyurethane foam as the core and different materials (glass fiber reinforced polyester, galvanized steel, aluminum sheets and crimped aluminum) as face materials. Morphological, physical and mechanical properties were evaluated. An inexpensive and nondestructive method was used to determine the thermal behavior of the sandwich panels, and the surface temperature evolution was thermally monitored during the tests. In general, results showed that polyurethane had a homogeneous distribution of size and shape with closed cells, which can improve the retention of the insulating gas. Additionally, the compressive strength of polyurethane within the composites exhibited typical values to be used in specific applications. Thus, the sandwich with galvanized steel exhibited lower flexural strength, which provides more freedom in panel design. The overall heat transfer coefficient of the panels in the form of cubes presented values below the maximum limit requested by ABNT NBR-15457. Finally, the composite galvanized steel/polyurethane/galvanized steel achieved the best performance for use as a thermal insulation material in a cold storage chamber. [ABSTRACT FROM AUTHOR]

In order to reduce the impact of outdoor extreme weather events on crop production in winter, energy saving in greenhouses that are regularly heated is of great importance in reducing production costs and carbon footprints. For this purpose, the variations in indoor temperature, relative humidity and dew point temperature in the vertical direction (2 m, 4 m, 5.7 m) of thermal curtains in greenhouses were determined. In addition, depending on the fuel used, the curtains’ effects on heat energy consumption, heat transfer coefficient, carbon dioxide equivalents released to the atmosphere and fuel cost were investigated. To reach this goal, two greenhouses with the same structural features were designed with and without thermal curtains. As a result of the study, the indoor temperature and relative humidity values in the greenhouse with a thermal curtain increased by 1.3 °C and 10% compared to the greenhouse without a thermal curtain. Thermal curtains in the greenhouse significantly reduced fuel use (59.14–74.11 m3·night−1). Considering the heat energy consumption, the average heat energy consumption was 453.7 kWh·night−1 in the greenhouse with a curtain, while it was 568.6 kWh·night−1 in the greenhouse without a curtain. The average heat transfer coefficient (U) values were calculated at 2.87 W·m−2 °C with a thermal curtain and 3.63 W·m−2 °C without a thermal curtain greenhouse. In the greenhouse, closing the thermal curtain at night resulted in heat energy savings of about 21%, related to the decrease in U values. The use of a thermal curtain in the greenhouse reduced the amount of CO2 released to the atmosphere (116.6–146.1 kg·night−1) and fuel cost (USD 21.3–26.7·night−1). To conclude, extreme weather events in the outdoor environment adversely affect the plants grown in greenhouses where cultivation is performed out of season. A thermal curtain, used to reduce these adverse effects and the amount of energy consumed, is essential in improving indoor climate conditions, providing more economical greenhouse management and reducing the CO2 released into the atmosphere due to fuel use.

A microplate heat exchanger is one of the most compact types of heat exchanger used for cooling systems, and not much research was carried out to study the performance of this type of heat exchanger with hybrid nanofluids. In this regard, the performance analysis of the microplate heat exchanger is carried out by estimating the convective heat transfer coefficient in terms of Nusselt number using a hybrid nanofluid. In current research work, Microplate heat exchangers tested using TiO2/ethylene glycol, ZnO/ethylene glycol nanofluids, and a hybrid nanofluid with varied nanoparticle volume fractions. Based on the results, it was found that the thermal conductivity of hybrid nanofluids and the overall heat transfer coefficient by applying hybrid nanofluids show better enhancement than nanofluids. The maximum thermal conductivity ratio between the hybrid nanofluid and the base fluid is 2.10. The maximum Nusselt number of 35.8 was observed for hybrid (TiO2–ZnO/ethylene glycol) at 50 °C and a volume fraction of 4%.

The helical coil heat exchanger (HCHX) is one of the most popular heat transfer devices in heat pump water heaters. In this study, the Computational Fluid Dynamics (CFD) software, ANSYS FLUENT, was employed to predict the thermohydraulic performance of an HCHX, including the overall heat transfer coefficient and Fanning friction factor. Using different sizes of the HCHX, comparing the CFD results with experimental data or correlations available in the literature revealed that both results on thermohydraulic performance agreed well. The objective of this study was to choose the Taguchi method coupled with grey relational analysis (GRA) to optimize the HCHX design with the improvement of thermohydraulic performance. Among the selected three factors in the optimization process, it was found that the coil pitch and coil diameter were the two most important factors in influencing the thermohydraulic performance of HCHXs, while the outer diameter of the helical tube had little impact. Consequently, the optimal design of the HCHX increased the overall heat transfer coefficient by 131% and decreased the friction fanning factor by 6%, resulting in the increase of heat transfer rate by 47% and the reduction of pumping work by 72%. Moreover, the predicted optimal thermohydraulic performance was verified by the predictive formula of the Taguchi method.

In this paper, heat transfer performance is investigated for plain and nanoparticle coated tube-in-tube heat exchangers. Four types of tubes, i.e. bare copper tube, bare aluminium tube, Cu-Al2O3 nanoparticle coated tube and anodized aluminium tubes are used for performing the experimental investigation. The coating thickness of Cu-Al2O3 nanocomposite surface and anodized aluminium tube varies from 10, 25 and 30 micrometres to 15, 20 and 30 micrometres respectively. The surface is found to be hydrophilic in nature as the contact angle changes from 79.82° to 55.47°. The prepared surfaces are characterized by FESEM, EDS and FTIR. By adjusting the hot and cold fluids relative mass flow rates, one may calculate not only the overall heat transfer coefficient but also the efficiency of the tube-in-tube heat exchanger. The Cu-Al2O3 nanocomposite coated surface has the highest overall heat transfer coefficient and efficiency, followed by an anodized aluminium surface, bare copper surface and bare aluminium surface. The aluminium anodic oxide (AAO) surface also exhibits an increased heat transfer coefficient, but to a lesser extent than the nanocomposite coating. [ABSTRACT FROM AUTHOR]

The present paper, for the first time, examines the influences of utilizing oil-ZnO nanofluid with different volume fractions φ = 0.5 %, 1 %, and 2 % in alternating flattened tubes (AFTs) with different alternating pitch angles of 30°, 45°, 60°, and 90° on the performance of a dual-tube heat exchanger (DTHE). This work is conducted experimentally and numerically for the Reynolds number (Re) range of 300 < Re < 1900 for oil-ZnO nanofluid and Re = 2000 for water. Based on the experimental results, the optimal case is selected for the numerical simulations of AFTs. The performance evaluation criterion (PEC) is defined for the simultaneous evaluation of pressure drop (Δp) and heat transfer coefficient (HTC). The results demonstrate that the overall heat transfer coefficient (U) and Δp are augmented with the inlet flow rate and the alternating angle between the pitches. Therefore, the maximum heat transfer (HT) and Δp correspond to the AFTs with the angle of 90° (AF4) at Re = 1900. The PEC amount of AF4 shows a 56 % enhancement compared to the circular tube. It is also observed that using copper oxide nanoparticles inside the oil improves the HT rate and Δp in the heat exchanger. Besides, an increment in φ increases U and Δp; however, the values of PEC show that the positive effects of the nanofluid are larger than their negative impacts in such a way that the PEC is improved by 64 % when the nanofluid with φ = 2 % is utilized in AFTs compared to the circular tube. [ABSTRACT FROM AUTHOR]

• Thermo-hydraulic performance of minichannel heat exchanger is presented. • Analytical model for entire heat exchanger is included. • The minichannel heat exchanger has overall heat transfer coefficient of up to 3000 W/(m2K). The paper presents an experimental investigation of the thermo-hydraulic performance of a prototype single-plate minichannel heat exchanger. The symmetric heat exchanger plate made of aluminum alloy consists of square cross section channels with a hydraulic diameter of 1000 µm and a length of 100 mm and rectangular inlet and outlet plenums. The heat exchanger operates in a counterflow configuration and the working fluids are hot and cold deionized water, respectively. The flow in minichannels is considered laminar due to its maximum Reynolds number limited to approximate value of 2200. Experimental measurements were carried out for various combinations of hot and cold side Reynolds numbers for the purpose of seeking optimal thermo-hydraulic performance. The minichannel geometry and operating conditions were chosen to operate in the laminar thermal entry length in order to achieve higher average Nusselt number along the minichannel length compared to the Nusselt number in the fully developed laminar flow. The general analytical model for prediction of the heat transfer performance of these types of heat exchangers is presented and includes the heat transfer process in the inlet plenum, the parallel configuration of the minichannels, and the outlet plenum. A comparison of the overall heat transfer coefficient resulting from the experiment and the analytical model is presented. The thermo-hydraulic performance of the investigated minichannel heat exchanger and exemplary microchannel heat exchangers is also presented. The main advantage of the presented minichannel heat exchanger is a very high overall heat transfer coefficient up to 3000 W/(m2K) and relatively low pressure drop on the one side of the heat exchanger up to 6.5 kPa, while still maintaining the high compactness and ease of manufacturing compared to microchannel heat exchangers. The comparison of minichannel heat exchanger considered in this paper and exemplary microchannel heat exchangers reflected slight decrease of the overall heat transfer coefficient, while still being approximately of the same order, together with incomparably lower pressure drop, on average of two orders of magnitude. [ABSTRACT FROM AUTHOR]

To efficiently recover waste heat from mine water, this study numerically investigates the flow and heat transfer performance of a tube-shell coupled helical coil heat exchanger (HCHE), under high Reynolds number conditions. The effects of inlet water temperature, mass flow rate (m), tube diameter (d), and helix pitch (P) on the tube side, shell side, and overall performance are analyzed. Performance metrics include friction factor (f), Nusselt number (Nu), overall heat transfer coefficient (U), heat transfer rate, and the Performance Evaluation Criteria (PEC) number. Specifically, this study focuses on detailed observation and analysis of the shell-side flow and temperature fields. Findings reveal that enlarging d from 30 mm to 50 mm results in a 32.55% decrease in U , whereas increasing P from 50 mm to 200 mm boosts U by 8.02%. The highest PEC number of HCHE is 2.43, observed in conditions of P = 50 mm, d = 30 mm, and m c = 4 × 103 kg/h. Correlations for f c , Nu c , and Nu sh are proposed based on simulation results. This study provides a theoretical basis for the design and structural optimization of HCHE in the mine water waste heat recovery applications. [ABSTRACT FROM AUTHOR]

This study aims to improve the performance of the vehicle’s cooling system called the radiator, which is part of increasing energy efficiency. Research has been done to investigate the convective heat transfer of hybrid nanofluid, using CuO and TiO2 nanoparticles and water-ethylene glycol (RC) as base fluids on a radiator. The mass concentration of the hybrid nanoparticles varied from 0.25 %, 0.30 %, and 0.35 %. For the preparation of the hybrid nanofluid through a two-step method, by mixing dry samples of CuO and TiO2 nanoparticles (50:50) and then the mixture of radiator coolant, RC (60 % water and 40 % ethylene glycol). The fluid flow varies from 20 liters per minute to 28 liters per minute. Temperature variations range from 70 °C to 90 °C by using controlled heating. Four thermocouples measure the inlet and outlet hot fluid flow and the airflow before and after the radiator. The experiment showed that the overall heat transfer coefficient increases remarkably with the increase of the hybrid nanoparticle concentration under various flow rate values. The maximum overall heat transfer coefficient increases by about 83 % compared to pure radiator coolant under 0.35 % mass concentration at a flow rate of 22 liters per minute and a temperature of 70 °C. It has also been found that the heat transfer rate is highly dependent on the radiator’s mass fraction and flow rate. Increasing the mass concentration shows maximum enhancement in heat transfer rate. Inlet temperature also enhances the heat transfer rate, but its effect is small compared to nanofluid’s mass concentration and flow rate. This study reveals that hybrid nanofluids can be suitable as a working fluid, especially in small-scale heat transfer devices. [ABSTRACT FROM AUTHOR]

In this study, the effect of adding zinc oxide nanoparticles to the reversible effect double tube heat exchanger with a length of 1.5 meters, an outer diameter of 19.0 mm, is made of copper material that is used by Nano water as a cold liquid. Zinc solid nanoparticles with a volume concentration of 3% were used with water as the base liquid. The cold nanoscale water flows into the real tube with a volume of 4 L/min which enters into the heat exchanger at 16°C, where the hot water flows into the separator of the heat exchanger representing a blank volume of 6 L/min. The Reynolds number range and flowrate ranges are 10000 to 20000 and 5 to 15 respectively. The heat exchanger was introduced at a temperature of 65°C. An improvement in the performance of the exchanger was shown in the case of using water with the addition of nanoparticles. [ABSTRACT FROM AUTHOR]

A heat pipe (HP) is a device transferring large quantities of heat through a small area of the cross‐section with very small deviations in temperature. The thermal impedance of HP is lower while thermal conductance is higher. HPs are designed for controlling temperature, amplification of heat flux, and diminution. HPs are being used in the cooling of aircraft and electronics, solar energy, systems of heat recovery, and nuclear reactors. Complex mathematical formulation demands experimentation to acquire the physical phenomena. Performing experiments is a tedious task with increasing the working parameters and their assigned levels. In such situations, a systematic statistical approach (viz., the Taguchi method) has to be adopted to minimize the number of experiments and to provide the information for the full factorial design of experiments. This paper adopts the modified Taguchi method and applies a simple and reliable multiobjective optimization concept to determine the optimal HP working parameters (viz., heat input, inclination angle, and flow rate). In the optimization process, efficiency, thermal resistance, and overall heat transfer coefficient are the performance indicators (PIs). Empirical relations are developed and validated for the PIs in terms of the HP working parameters. The recommended Taguchi's orthogonal array to perform a few tests may not have the set of optimal working parameters. Additional tests are to be performed to confirm the estimates of the PIs for the optimal working parameters. Confirmation test results in the present study indicate close‐to/within the estimated range. [ABSTRACT FROM AUTHOR]

This study utilized four distinct shell and helical tube heat exchanger layouts to numerically evaluate the thermal and hydraulic efficiency of each arrangement. The numerical research was conducted using ANSYS FLUENT 2022R1. Currently, there has been no research conducted on the investigation of multiple helical coiled tubes enclosed by multiple shell heat exchangers. This study aimed to optimize various tasks using the Grey Relational Analysis approach in combination with the Taguchi method to maximize thermal efficiency and minimize pressure drop. A parallel configuration was used to connect two to three concentric helical tubes, with each helical tube being enclosed by a shell to control the flow of fluid. The P–P-2M − 36 design, consisting of two helical tubes, has the highest enhancement ratio of Uo = 26.75 %, when compared to the P–P-3M − 36 configuration. Similarly, the P–P-2M − 42 configuration enhances Uo by 38.42 % in comparison to the P–P-3M − 42 configuration. These findings demonstrate that a configuration consisting of two helical tubes exhibits a higher enhancement ratio of Uo compared to a configuration consisting of three helical tubes. The P–P-3M − 36 design, which consists of three helical tubes, exhibits a minimum pressure drop of 39.19 % compared to the P–P-2M − 36 configuration. Similarly, the P–P-3M − 42 configuration reduces pressure drop by 37.76 % compared to the P–P-2M − 42 configuration. The P–P-3M − 36 configuration is designed to simultaneously reduce pressure drop and boost heat transfer rate. The model achieves the optimal values for heat transfer rate and pressure drop at a Reynolds number of 55,000. • Multi helical coiled tubes each enclosed by a shell is modeled as an innovative configuration. • Two and more helical coiled tubes are connected in parallel to enhance the hydraulic performance. • Two and more shell is connected in series to guide the flow over the helical tube and enhance heat transfer rate. • Different annular space, numbers of tubes/numbers of shells, and flow rate used as a design factor. [ABSTRACT FROM AUTHOR]

Heat exchangers are widely used for cooling and heating in every process industry. Here, a laboratory-scale experimental setup is used to investigate the thermal performance of inserted helical tube three-fluid heat exchanger using three different concentrations of graphene/water nanofluid (viz. 2, 4, and 6 volume percentage) as a working fluid. The influence of fluid flow in parallel configuration (viz. the flow of hot water, nanofluid, and air) is examined on the overall heat transfer coefficient, effectiveness and Nusselt number. The overall heat transfer coefficient increases with increasing all fluid flow rates. Significant improvements of the heat transfer coefficient between hot water and nanofluid and between nanofluid and air are found for the cases of nanofluids at the hot water flow or air flow rates, while a negligible effect of nanofluids between hot water and nanofluid is observed with increasing nanofluid fluid flow. Additionally, effectiveness decreases up to a minimum, after that it increases with increasing flow of hot water or nanofluid, while the effectiveness increases with increasing air flow and an improvement is found for the case of high concentration of nanofluid. A comparison between Nusselt numbers and correlations of a double-pipe helical tube heat exchanger shows a significant variation in results. Therefore, we proposed semiempirical correlations to estimate the Nusselt number and friction factor for the triple-fluid helical tube heat exchanger, and the correlations agree well with the experimental results. The semiempirical correlations would be useful for the flow of multiple fluids and several thermal communications in heat exchangers. [ABSTRACT FROM AUTHOR]

Sugar is one of the most important commodities of the world, this high production makes the sugar factories have a complex energy integration of the process. One point of energy consumption is the heating of sugarcane juice in heat exchangers. To analyze this point, the thermal design of five boxes of the shell and tube exchangers of a sugar plant was evaluated in terms of the outlet temperature of sugarcane juice, overall heat transfer coefficient, fouling resistance and pressure drop. It was considered actual process conditions and service requirements, as well as equipment characteristics. In combinations of the exchangers was reached the operation minimum temperature of the sugarcane juice (105 °C). It was estimated that production could be increased by 24% if the outlet juice temperature was reduced to 101 °C. The clean and dirty overall coefficient varied between 2364 and 3462 kcal/hm2 °C and 114 and 158 kcal/hm2 °C, respectively. Fouling resistance ranged between 0.0061 and 0.0084 hm2 °C/kcal, about 10 times more than the recommendations. Despite the fouling resistance, the pressure drops of the exchangers are within the limits of the specifications, but it can still be increased in order to improve the heat exchange. The results are discussed and commented, and possible immediate solutions for improvement are recommended. The data obtained serve as a reference for comparative purposes and future simulations of the process. [ABSTRACT FROM AUTHOR]

The pipeline efficiency factor (E‐value) and the overall heat transfer coefficient (K‐value) are, respectively, the characteristic parameters that describe the flow and heat transfer behavior of gas pipe sections. These parameters have a significant impact on the accuracy of the thermo‐hydraulic calculations of the gas flow processing. Hence, they should be investigated thoroughly. Due to various complex factors affecting the E‐value and the K‐value in operating the in‐service gas pipe sections, it is often difficult to calculate the two characteristic parameters accurately using physics‐based formulae. Based on quasi‐steady‐state historical operational data sets of the in‐service gas pipe section, the characteristic parameters are identified with the maximum likelihood method and the least square method, respectively. Besides, the characteristic parameters of the gas pipe section are derived from solving the inverse problem of the steady‐state thermo‐hydraulic calculations. Both methods are applied to an in‐service pipeline, and the two parameters are obtained from 144 historical operational data sets. By introducing the two parameters into the thermo‐hydraulic calculations for certain quasi‐steady‐state historical conditions in the same gas pipe section, the maximum relative errors occurred between the calculated results and the measured data are 2.91% and 2.66%, respectively. Additionally, the difference between the two methods is small, with a gap of 0.0037 W/(m2 K) in K‐value and 0.0206 in E‐value. The proposed identification methods are extendable to provide adequate technical support for large‐scale gas pipeline networks. [ABSTRACT FROM AUTHOR]

Controlling heat transfer and managing heat flows in a building has become very important in recent years and is essential to ensure the thermal comfort of occupants, increase energy efficiency, and sustainable development. These measures reduce energy consumption in buildings, save resources and money and at the same time reduce pollution and CO2 emissions into the atmosphere, as the severity of the climate increases. The paper describes the analytical method used to analyse the one-dimensional, steady-state heat transfer through homogeneous walls and composite walls of buildings (wall structure may contain different construction materials, air spaces, insulation, etc.). The web application allows users to analyse one-dimensional and steady-state heat transfer through the building walls and calculate the heat flux density, total heat flux, overall heat transfer coefficient of the building wall, thermal resistance, temperature profile through the wall, the specific thermal resistances and the temperatures at the interface between wall layers. The user can analyse the one-dimensional, steady-state heat transfer through homogeneous and multilayer walls of buildings, being able to analyse a wall composed of a single layer, or one with a maximum of seven layers. The application allows the user, after defining the cross section’s geometry, materials properties, and boundary conditions, to determine the optimal insulation thickness, depending on its placement, on the inner or outer wall surface.

Abstract The pipeline efficiency factor (E‐value) and the overall heat transfer coefficient (K‐value) are, respectively, the characteristic parameters that describe the flow and heat transfer behavior of gas pipe sections. These parameters have a significant impact on the accuracy of the thermo‐hydraulic calculations of the gas flow processing. Hence, they should be investigated thoroughly. Due to various complex factors affecting the E‐value and the K‐value in operating the in‐service gas pipe sections, it is often difficult to calculate the two characteristic parameters accurately using physics‐based formulae. Based on quasi‐steady‐state historical operational data sets of the in‐service gas pipe section, the characteristic parameters are identified with the maximum likelihood method and the least square method, respectively. Besides, the characteristic parameters of the gas pipe section are derived from solving the inverse problem of the steady‐state thermo‐hydraulic calculations. Both methods are applied to an in‐service pipeline, and the two parameters are obtained from 144 historical operational data sets. By introducing the two parameters into the thermo‐hydraulic calculations for certain quasi‐steady‐state historical conditions in the same gas pipe section, the maximum relative errors occurred between the calculated results and the measured data are 2.91% and 2.66%, respectively. Additionally, the difference between the two methods is small, with a gap of 0.0037 W/(m2 K) in K‐value and 0.0206 in E‐value. The proposed identification methods are extendable to provide adequate technical support for large‐scale gas pipeline networks.

The present study modifies the structural design of a shell-and-tube heat exchanger by considering two key parameters such as the maximization of the overall heat transfer coefficient and minimization of the total pressure drop. Five geometric design variables which include the tube inside diameter, tube outside diameter, pitch size, baffle spacing, and the tube length are investigated for optimization. The governing equations for design and optimization of the shelland-tube heat exchanger are evaluated and the optimum design parameters are obtained by bees algorithm. The selection of the important design parameters to achieve the proper design is evaluated by fixing each of these parameters, while the other the design parameters are selected as variable to optimize the effectiveness. Compared with the original shell-and-tube heat exchanger, the overall heat transfer coefficient is increased by 22.78% with the minimum increase in the total pressure drop by 1.8%. [ABSTRACT FROM AUTHOR]

Nanoparticles enhances the heat transfer between particles and the fluids due to their high specific surface area and adjustable properties, including thermal conductivity and surface wettability, by varying particle volume concentrations in the base fluid to suit different applications. This article is an experimental study on the effectiveness and overall heat transfer coefficient in STHE (shell and tube heat exchanger), comprising baffle cut 25% with a nanofluid at 0.05, 0.1, and 0.2 percentage concentrations of CuO nanoparticles in the DW (distilled water) base-fluid. The inclusion of 0.15% SDBS (Sodium dodecyl-benzene sulphonate) by a two-step method as a surfactant improves the stability of dispersed CuO nanoparticles. The CuO/DW nanofluid thermo-physical properties such as thermal conductivity (k), density (ρ), and dynamic viscosity (μ), have increased. However, the nanofluid's specific heat (Cp) reduces as the nanoparticles proportion rises in the DW base fluid. There is an enhancement of the overall heat transfer coefficient and effectiveness compared to water during parallel flow variation. The maximum heat exchanger effectiveness was 3.01%, 4.01%, and 5.94% higher than water at 0.6 lpm mass flow rate and temperature T = 80 °C for volume fractions of 0.05, 0.1, and 0.2 percentage of CuO/DW nanofluid respectively during parallel flow. [ABSTRACT FROM AUTHOR]

Prediction of heat exchangers performance is primordial in the world of machine design especially when the industrial environment becomes demanding in terms of size reducing or price lowering. The most common adopted procedure for this kind of investigation is defining the exchanger's overall heat transfer coefficient with a purely empiric way using interpolations and mathematical operations missing physical senses in the modeling. The present work offers a first step in theoretically modeling the heat transfer coefficient and presents a semi-empirical method which allows expressing the latter in function of the Reynolds' numbers of the fluids' flows when the variations of the Prandtl numbers of the two fluids are small. The method consists in an iterative technique based on a single test approach and allows the prediction of the heat exchanger performance for a large range of flowrates. Experimental validation of the method is performed for a cross-flow heat exchanger with water and air as working fluids, showing a relative error less than 1.6%. The relative error of the mathematical methods applied is less than 1.7%.

The paper discusses the combined methods of increasing heat transfer, effects of adding nanofluids and ultrasonic vibration in the radiator using radiator coolant (RC) as a base fluid. The aim of the study is to determine the effect of nanoparticles in fluids (nanofluid) and ultrasonic vibration on the overall heat transfer coefficient in the radiator. Aluminum oxide nanoparticles of 20–50 nm in size produced by Zhejiang Ultrafine powder & Chemical Co, Ltd China were used, and the volume concentration of the nanoparticles varied from 0.25 %, 0.30 % and 0.35 %. By adjusting the fluid flow temperature of the radiator from 60°C to 80°C, the fluid flow rate varies from 7 to 11 lpm. The results showed that the addition of nanoparticles and ultrasonic vibration to the radiator coolant increases the overall heat transfer coefficient by 62.7 % at a flow rate of 10 liter per minute and temperature of 80°C for 0.30% particles volume concentration compared to pure RC without vibration. The effect of ultrasonic vibration on pure radiator coolant without vibration increases the overall heat transfer coefficient by 9.8 % from 385.3 W/m²·°C to 423.3 W/m²·°C at a flow rate of 9 liter per minute at a temperature of 70°C. The presence of particles in the cooling fluid improves the overall heat transfer coefficient due to the effect of ultrasonic vibrations, nanofluids with a volume concentration of 0.25 % and 0.30 % increased about 10.1 % and 15.7 %, respectively, compared to no vibration. While, the effect of nanoparticles on pure radiator coolant at 70°C enhanced the overall heat transfer coefficient by about 39.6 % at a particle volume concentration of 0.35 % compared to RC, which is 390.4 W/m²·°C to 545.1 W/m²·°C at 70°C at a flow rate of 10 liter per minute [ABSTRACT FROM AUTHOR]

This work presents a case study of thermodynamic performance of a condenser used in a 210 MW thermal power station at Mejia in West Bengal, India. The analysis involves an improvement of actual overall heat transfer coefficient by varying tube materials and fouling resistance. Exergy Destruction Factor (EDF) is introduced to quantify the percentage of exergy loss from the condenser wall. From this study, it is revealed that the second law performance of the condenser increases with the increase in thermal conductivity of the tube materials, decreases with the increase in fouling resistance and decreases with the increase in condenser pressure at the turbine outlet. The actual overall heat transfer coefficient can be increased up to 6% by selecting better conducting tube materials. While the EDF decreases with the increase in cooling water temperature rise and increases with the increase in cooling water inlet temperature, EDF is found to decrease with the increased cooling water mass flow rate.

The spatiotemporal temperature distributions of NIR irradiated polypyrrole nanoparticles (PPN) were evaluated by varying PPN concentrations and the pH of suspensions. The PPN were synthesized by oxidative chemical polymerization, resulting in a hydrodynamic diameter of 98 ± 2 nm, which is maintained in the pH range of 4.2–10; while the zeta potential is significantly affected, decreasing from 20 ± 2 mV to −5 ± 1 mV at the same pH range. The temperature profiles of PPN suspensions were obtained using a NIR laser beam (1.5 W centered at 808 nm). These results were analyzed with a three-dimensional predictive unsteady-state heat transfer model that considers heat conduction, photothermal heating from laser irradiation, and heat generation due to the water absorption. The temperature profiles of PPN under laser irradiation are concentration-dependent, while the pH increase only induces a slight reduction in the temperature profiles. The model predicts a value of photothermal transduction efficiency (η) of 0.68 for the PPN. Furthermore, a linear dependency was found for the overall heat transfer coefficient (U) and η with the suspension temperature and pH, respectively. Finally, the model developed in this work could help identify the exposure time and concentration doses for different tissues and cells (pH-dependent) in photothermal applications.

An investigation of the performance of a car radiator with CuO-MgO-TiO 2 aqueous ternary hybrid nanofluid has been presented to elucidate the effect of nanoparticle concentration, flow rate, and frontal air velocity. The volume concentration of nanoparticles ranges from 0.1% to 0.5%. The effect of fluid inlet temperature, the coolant flow rate and the frontal air velocity on a flat tube radiator were investigated. The effectiveness of the radiator increases with increasing volume concentration as well as coolant flow rate. The coolant side heat transfer coefficient of 0.5% hybrid nano-coolant was 46% higher than the base fluid. The overall heat transfer coefficient was 7.65% higher than the base fluid. The friction factor and the pumping power both decrease with increasing fluid inlet temperature. The pumping power required for nano-coolant is 1.71 times the base fluid. A correlation for the overall heat transfer coefficient is also presented. [Display omitted] • Water based ternary hybrid nanofluid with CuO-MgO-TiO2 for flat tube car radiator • 46.02% rise in the coolant side heat transfer coefficient • Radiator effectiveness increases with nanoparticle concentration • The pressure drop increases with nanoparticle concentration • A correlation for overall heat transfer coefficient is presented [ABSTRACT FROM AUTHOR]

Numerical and experimental analysis has been studied to estimate the overall heat transfer coefficient in the three zones along wire and tube condenser. The model is based on the empirical formulation of the refrigerant and air sides heat transfer coefficients in finite sections along condenser tube which is solved using EES software. To validate the obtained result from the numerical model, a test rig for a vapour compression refrigeration system with R-134a builds for this purpose. Investigating the temperature distribution and heat transfer coefficient along the length of condenser under different operating conditions have shown that, the de-superheated, two-phase and sub-cooled zones are approximately occupied 15 %, 80% and 5% of the total condenser length respectively. The ratio of Overall heat transfer coefficient to the saturated heat transfer coefficient was significantly affected by the variations of the ambient temperature. Comparison between experimental and numerical results has displayed maximum deviation of 5.5% which is reasonably acceptable. Finally, an acceptable relation has been made to summarize all the important parameter that’s effects directly on the heat transfer contributions of the de-superheating, saturated, and subcooling in one equation to simplex the boring calculations of overall heat transfer coefficient. Proposed correlation presents a mean square error about 3.1 %.

The wellbore injected with heating fluid requires temperature field prediction to formulate production strategy. The classical radial heat transfer calculation of wellbore takes into account the thermal conductivity resistance of casing, cement sheath and formation, ignoring the "Thermal Contact Resistance" caused by the micro-annulus at the cementing interface. In order to study the influence of micro-annulus on radial wellbore temperature field prediction, the calculation method of thermal contact resistance of micro-annulus at the cementing interface filled with gas was deduced. And then it was verified by the experimental equipment and specimens of casing, cement sheath and formation. Finally, the thermal contact resistance was introduced into the "overall heat transfer coefficient" to study the deviation of the classical method in predicting the wellbore temperature field. The results show that, if the interfacial thermal contact resistance isn't considered, under the conditions of the roughness of micro-annulus increases (0.01 mm ~ 1 mm), the time of steam injection increases (2 d ~ 40 d), the temperature of injected steam increases (500 K ~ 700 K), and the temperature of formation increases (300 K ~ 400 K), the calculated inner wall temperature of the cement sheath will be relatively high (1 K ~ 3 K), and the outer wall temperature will be relatively low (4 K ~ 9 K), while the inner wall temperature of the formation is relatively much high (28 K ~ 38 K). Moreover, the change of these conditions has little influence on the deviation. The research in this paper proves that the micro-annulus at the cementing interface has a great influence on the radial wellbore temperature prediction. The calculation method used can make the prediction more in line with the actual situation, thus making the production dynamic analysis and method optimization more effective. [ABSTRACT FROM AUTHOR]

Earth air tube heat exchanger (EATHE) is one of the passive technologies which utilize the earth stored heat (renewable energy) for heating/cooling the buildings. EATHE releases heat to earth for cooling space in summer, making the earth a heat sink and extracts earth-stored energy for heating space in winter and makes the earth a heat source. This paper optimizes the Length of the ground heat exchanger and overall heat transfer coefficient of earth air heat exchanger using the Taguchi technique for cooling application. For this purpose, we select six factors such as installation depth of Pipe (A), Pipe's inner diameter (B), Thermal conductivity of pipe material (C), Inlet air temperature (D), Outlet air temperature (E), Inlet air velocity (F). All these factors are taken at three levels, and we select an L27 orthogonal array for experimental runs. The ground heat exchanger's Length and the overall heat transfer coefficient were then calculated for each experimental run. In the Taguchi method, we find the signal to noise ratio for an optimal combination of all six factors and ANOVA to find the order of influencing parameters and their percentage contributions for both the objective parameters. According to our results, the best combination for all the six factors for ground heat exchanger length and overall heat transfer coefficient were A1B1C3D1E3F1 and A2B3C2D3E1F3, respectively. The highest and lowest influencing factors for ground heat exchanger length were the pipe's inner diameter and the pipe's installation depth with their contribution factors of 69.12 and 0.32%, respectively. In contrast, the highest and lowest influencing factors for the overall heat transfer coefficient were the pipe's inner diameter and thermal conductivity of pipe material with their contribution factors of 75.97and 0%, respectively. Hence the order of influence of all the six factors for both the objective parameters was BEFDCA. [ABSTRACT FROM AUTHOR]

In the present study the effects of the addition of four drag reducing agents (DRA), including carboxy methyl cellulose with high molecular weight (DRA1) and medium molecular weight (DRA2), polyacrylamide (DRA3) and the natural polymer, xanthan gum (DRA4), to water on the pressure drop and heat transfer performance in a finned tube-heat exchanger were compared. Laminar flow (Reynolds number (Re) <1400) was studied to transfer heat between water and air in the finned tube heat exchanger. The results showed that DRA1, with a maximum %DR of 26%, and DRA4, with a maximum %DR of 5%, were the highest and the lowest obtained results, respectively. In the case of heat transfer reduction percentage (%HTR), DRA4, having more than 34.5%, was the highest, and DRA1, with about 13.7%, was the lowest result for the concentration range of 0-100 ppm and temperature range of 40–65 °C. [ABSTRACT FROM AUTHOR]

Aimed at biggish prediction error of the overall heat transfer coefficient caused by running parameters fluctuations, analyze the correlations between various elements including outlet oil temperature, oil physical properties, flow rate, environmental temperature, wax deposition rate as well as running time after pigging and the overall heat transfer coefficient. And four dimensionless number determining the laws of overall heat transfer coefficient was put forward. Simplified model came in the use of collinearity diagnosis theory and dimensionless experimental analysis, followed by determining the optimal functional form of prediction model and physical meaning for each dimensionless numbers, then establish a new prediction model. Prediction of the overall heat transfer coefficient for several pipelines came after applying Ten-fold Cross Validation to solve the model. The results showed that, compared with back calculation, the error of overall heat transfer coefficient reduces by 3.62%, and average relative error of end-point temperature lowers by 2.88%. The model is of good steadiness and generalization, and better characterization on heat transfer mechanism of overall heat transfer coefficient, to some degree, solving the biggish prediction error led by running parameters fluctuations.

Technological advancement in previous years has resulted in decrease in the size of microprocessors and thus, high heat generation. To address this problem, experiments were carried out to optimize the performance of nanofluid-cooled heat sinks at a power of 300 W for better thermal management. The optimization process involved varying both the concentration of the coolant (and by extension, its thermo-physical properties) and the fin spacing of the heat sink (to modify the convective and conductive heat transfer area) to achieve the lowest thermal resistance at different flow rates. Instead of an actual microprocessor, a copper block heated by a mica insulated clamp heater (rated at 285 W) was used to simulate the microprocessor. The evaluation of the heat sink performance was also based on the lowest base temperature achieved, the total heat rejected and the overall heat transfer coefficients for all iterations.

The effect of shell side and coil side volume flow rate on overall heat transfer coefficient, effectiveness, pressure drop and exergy loss of shell and helical coil heat exchanger were studied experimentally under steady state conditions. The working fluid, i.e., water was allowed to flow at three different flow rates of 1, 2, and 3 l/min on shell side (cold water) and at 1, 1.5, 2, 2.5, and 3 l/min on coil side (hot water) for each shell side flow rate at the temperatures of 298±0.4K and 323±0.4K, respectively. The results found that the overall heat transfer coefficient increased with increasing both shell side and coil side volume flow rates. The inner Nusselt number significantly increased with the coil side Dean number. [ABSTRACT FROM AUTHOR]

Heat exchanger networks (HENs) play an important role in the chemical industries. Unfortunately, fouling is inevitable in heat exchangers operation. Therefore, the optimal cleaning procedure is required to restore heat exchangers' performance periodically. A systematic cleaning scheduling strategy for the heat exchanger network in an oil refinery is proposed in this work. There are 11 operating heat exchangers in an oil refinery to be reviewed. Different cleaning decision scenarios based on the overall heat transfer coefficient are explored for optimal cleaning schedule performance. The daily number of exchangers available to be cleaned i.e., the unit cleanability, is investigated while minimizing the energy consumption and the additional heat requirement due to the offline heat exchanger under cleaning procedure. The HEN performance and the energy-saving from the cleaning procedures are benchmarked with the uncleaned HEN. The results indicate that the cleaning procedure significantly increases the HEN performance and simultaneously reduces the heat requirement if compared to the untreated HEN benchmark. The possible conflicting situation is discussed when some heat exchangers are waiting to be cleaned due to the unit cleanability restriction, which allows the overall heat transfer coefficient to be below the allowed limit. Therefore, nonconflicting cleaning scheduling is also addressed in this work by relaxing the unit cleanability limit. Furthermore, the optimal cleaning schedule is also suggested for user reference. In this work, the optimum cleaning schedule with minimum energy consumption and maximum energy saving could be achieved when cleaning decision limit is set at 40% decrease of overall heat transfer coefficient. In the contrast, the lowest number of cleaning procedures is associated with 90% decrease in the overall heat transfer coefficient as the cleaning decision limit. [ABSTRACT FROM AUTHOR]

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The modeling accuracy of artificial neural networks (ANN) was evaluated by using limited heat exchanger data acquired experimentally. The artificial neural networks were used for predicting the overall heat transfer coefficient of a concentric double pipe heat exchanger where oil flowed inside the inner tube while the water flowed in the outer tube. In the cases of parallel and counter flows, the experimental data were collected by testing heat exchanger in wide range of operating conditions. Curve fitting and artificial neural network combination was used for the estimation of the overall heat transfer coefficient to compensate the experimental errors in the data. The curve fitting was used to detect the trend and generate data points between the experimentally collected points. The artificial neural network was trained better from the generated data set. The feed forward type artificial neural network was trained by using the Levenberg-Marquardt algorithm. Two backpropagation network type artificial neural network algorithms were also used, and their performance were compared with the estimation of the Levenberg-Marquardt algorithm. The average estimation error between the predictions and the experimental data were in the range of 1.31e-4 to 4.35e-2%. The study confirmed that curve fitting and artificial neural network combination could be used effectively to estimate the overall heat transfer coefficient of heat exchanger . [ABSTRACT FROM AUTHOR]

A possible way to enhance the rate of heat transfer in the spiral plate heat exchanger (SPHE) is by employing hybrid nanofluids as its working medium. Hence, in the present work, effects of hybrid nanofluids on the thermal performance of SPHE has been investigated numerically. First, a countercurrent SPHE is designed and modeled. Later, simulation of SPHE has been carried out by employing conventional fluid (H2O), nanofluids (Al2O3)/H2O,CuO/H2O,TiO2/H2O), and hybrid nanofluids (Al2O3+CuO/H2O,Al2O3+TiO2/H2O) to investigate the heat transfer rates. Finally, the performance of SPHE using hybrid nanofluid is compared with that of using water and nanofluids. The heat transfer augmentation of approximately 16%‐27% with hybrid nanofluids of overall 4% nanoparticles volume concentration and 10%‐16% with 2% nanoparticles volume concentration is observed when compared with that of pure water. Therefore, it can be inferred that the application of hybrid nanofluids in SPHE seems to be one of the promising solutions for augmentation of its thermal performance. [ABSTRACT FROM AUTHOR]

Heat exchanger analysis is regarded to be challenging due to the numerous parameters influencing the overall heat transfer coefficient. Errors in estimating convective heat transfer coefficients often arise from the geometric complexity of heat exchangers and varying flow regimes. The current work proposes a novel iterative method for calculating the overall heat transfer coefficients of concentric tube heat exchangers based on the Reynolds number of the two fluid streams. The approach is validated using numerical simulations performed with ANSYS-FLUENT, focusing on Reynolds numbers ranging from 4000 to 8000 for both hot and cold streams. The proposed method yields a maximum percentage of error between the CFD results and the correlation of just 1.2% for all Reynolds number combinations studied. The mean squared error (MSE) decreases by approximately 9% when 25 data points are used for the correlation fitting process compared to using only 5 data points. A comparison with existing literature correlations reveals a strong agreement within ± 5 % difference, demonstrating the accuracy and reliability of the developed correlation in predicting the overall heat transfer coefficients in concentric tube heat exchangers over the investigated range of Reynolds numbers. [ABSTRACT FROM AUTHOR]