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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.

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

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.

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.

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%.

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.

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 %.

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.

In this paper, overall heat transfer coefficient and friction factor of water based γ-Al2O3 nanofluid in a double tube counter flow heat exchanger have been measured experimentally under turbulent flow condition. For better dispersion of γ-Al2O3 nanoparticles in distilled water, magnetic stirrer and ultrasonic vibrator (with a power of 240 kW and frequency of 35 kHz) were implemented. The stabilized γ-Al2O3 /water nanofluid have been examined at the concentrations of 0.05 and 0.15 vol. % with variation of flow rates in the range of 7–9 l/min. Nanofluid enters the inner tube of the heat exchanger at different temperatures including 45, 55,and 65 °C. Results demonstrated that increasing the nanofluid flow rate, concentration and inlet temperature can improve the overall heat transfer coefficient and heat transfer rate. Also, the ratio of the overall heat transfer coefficient of nanofluid to that of pure water decreased with increasing the nanofluid flow rate. Meanwhile, the maximum enhancements of the overall heat transfer coefficient and heat transfer rate and friction factor compared with those of base fluid (distilled water) are respectively equal to 19.3%, 10% and 25% which is occurred at the concentration of 0.15 vol. %.

The work carried out in this project is based on analytical study. The performance parameters of a natural circulation solar collector have been evaluated using the empirical relations formulated and discussed in the literature. The study emphasizes on the method of evaluation of optimum mass flow rate of water in a Solar Collector for a given inlet and outlet temperature of water flowing through the collector. The mass flow rate of water in the collector has been evaluated using an iteration method. An excel spreadsheet has been prepared to calculate the mass flow rate.

Chłodzenie jest niezbędne dla właściwego funkcjonowania i niezawodności różnorodnych produktów, jak urządzenia elektroniczne, komputery, samochody, systemy laserowe wielkiej mocy, itp. W sytuacji wzrostu obciążenia cieplnego i strumieni ciepła wytwarzanych przez urządzenia przemysłowe, chłodzenie jest jednym z najważniejszych wyzwań występujących w różnych gałęziach przemysłu, transporcie, mikroelektronice, itp. Płynami, które zwykle są używane do odprowadzania ciepła z tych urządzeń są woda, glikol etylenowy i oleje. Nanopłyny, opracowane w ostatnim czasie, wykazują generalnie lepsze charakterystyki przewodnictwa cieplnego niż woda. Przedstawiona praca stanowi podsumowanie badań doświadczalnych nad wymuszonym, konwekcyjnym odprowadzaniem ciepła i charakterystykami przepływu nanopłynu składającego się z wody i cząsteczek Al2O3 (w 1% stężeniu objętościowym) w warunkach laminarnego przepływu współprądowego i przeciwprądowego w płaszczowych i rurowych wymiennikach ciepła. W przedstawionych badaniach użyto cząstek Al2O3 o średnicy ok. 50 nm. Wybrano trzy różne prędkości przepływu masy, opisano wyniki eksperymentów. Wyniki te wskazują, że całkowity współczynnik odprowadzania ciepła i bezwymiarowa liczba Nusselta nanopłynu są, przy tej samej prędkości przepływu masy i temperaturze na wlocie, nieznacznie wyższe, niż dla samego płynu bazowego. Z wyników doświadczalnych wynika, że całkowity współczynnik odprowadzania ciepła wzrasta wraz z prędkością przepływu masy. Pokazano, że gdy wzrasta prędkość przepływu masy, całkowity współczynnik odprowadzania ciepła wraz z bezwymiarową liczbą Nusselta ostatecznie wzrastają, niezależnie od kierunku przepływu. Stwierdzono także, że ze wzrostem prędkości przepływu masy wartość LMTD (średniej logarytmicznej różnicy temperatur) ostatecznie maleje, niezależnie od kierunku przepływu.

Overall heat transfer coefficient, also known as the intrinsic performance measurement of the building, determines the amount of heat lost by a building due to temperature difference between indoor and outdoor. QUB (Quick U-value of Buildings) is a short-term method for measuring the overall heat transfer coefficient of buildings. The test involves heating and cooling the house with a power step and measuring the indoor temperature response in a single night. Ideally, the outdoor temperature during QUB experiment should remain constant. To compare the influence of variable outdoor temperature, the QUB experiments are simulated on a well-calibrated model with real weather conditions. The experiments at varying outdoor temperature and constant outdoor temperature during the night show that the results in both conditions are nearly similar. A ±2 °C increase or decrease in the outdoor temperature during the QUB experiment can change the results in the measured overall heat transfer coefficient by ±5%. QUB experiments simulated during the months of winter show that the majority of results are ±15% of the steady-state overall heat transfer coefficient. The QUB results during the months of summer show relatively large variation. The large errors coincide with the small temperature difference between indoor and outdoor temperatures before the start of QUB experiment. The median error of multiple QUB experiments during summer can be reduced by increasing the setpoint temperature before the start of QUB experiment.

Helical coil heat exchangers are widely used in industrial applications ranging fromcryogenic processes, air-conditioning, and nuclear reactors to waste heat recovery due totheir compact size and high heat transfer coefficient. In this kind of heat exchangers, flowand heat transfer are complicated. This paper reports a numerical investigation of theinfluence of different parameters such as coil radius, coil pitch and diameter of tubeon the characteristics of heat transfer in helical double tube heat exchangers usingthe well-known Fluent CFD software. Modeling of the study was implemented based onprinciples of heat transfer, fluid mechanics, and thermodynamics. By imposing boundaryconditions and selecting of an appropriate grid, whereby the results are independent ofmeshing, the obtained results were compared and validated with existing experimentalresults in the open literature. The results indicate that heat transfer augments by increasingof the inner Dean number, inner tube diameter, curvature ratio, and by the reduction of thepitch of the heat exchanger coil.

Pabrik Gula Gempolkrep mengoperasikan evaporator Robert secara quintuple-effect dengan variasi tekanan yakni 1,6 bar, 1,26 bar, 0,9 bar, 0,54 bar dan 0,18 bar. Tekanan yang rendah membuat titik didih nira semakin menurun sehingga didapatkan nira yang terkonsentrasi. Konsentrasi nira ditunjukkan dalam obrix. Dalam penelitian ini, overall heat transfer coefficient dihitung untuk mengetahui karakteristik perpindahan panas. Nilai ini dihitung berdasarkan metode Dessin dan koefisien konveksi perpindahan panas. Konveksi sisi dalam tube dihitung menggunakan Chen’s correlation sedangkan sisi luar tube dihitung menggunakan persamaan konveksi kondensasi film. Hasil yang didapat yaitu obrix semakin besar setiap keluar evaporator yakni 18 obrix, 25 obrix, 32 obrix, 43 obrix dan 68 obrix. Nilai U yang didapat untuk kelima evaporator berdasarkan metode Dessin adalah 3,46 kW/m2.K, 2,92 kW/m2.K, 2,35 kW/m2.K, 1,71 kW/m2.K, dan 0,86 kW/m2.K, sedangkan berdasarkan pendekatan koefisien konveksi didapat U 3,14 kW/m2.K , 2,92 kW/m2.K , 2,48 kW/m2.K , 2,21 kW/m2.K dan 1,57 kW/m2.K secara berurutan.

This study was carried out to study the effect of silver and oxide zirconium – oil nanofluids on enhancement heat transfer in a heat exchanger with and without fins by changing flow direction. This study was done by changing the parallel flow configuration into counter flow configuration under laminar flow regime. The properties of nanofluids (density, viscosity, thermal conductivity and specific heat) are practically measured. The two types of nanofluids at 1%, 2%, 3%, 4% and 5% particle volume concentration were prepared by two step method. The nanofluid was applied in a heat exchanger with and without fins to enhance heat transfer. The measured results show that silver with oil nanofluid gives maximum heat transfer enhancement compared with oxide zirconium nanofluid used. The presence of Ag and ZrO2 nanoparticles attributes to the generation of strong nanoconvection current and better mixing. The effect of different parameters such as flow Reynolds number, nanofluid temperature, concentration and type of nanoparticle on heat transfer coefficient and pressure drop of the flow are studied.

Superheater merupakan alat yang berfungsi untuk menghilangkan kadar air dalam uap dengan cara menaikkan temperatur uap jenuh sampai menjadi uap panas lanjut (superheated vapour). Kondisi uap panas lanjut yang memasuki turbin uap adalah uap yang tidak akan mengembun ketika digunakan untuk melakukan kerja dengan jalan ekspansi di dalam turbin uap. Hal tersebut bertujuan untuk mengurangi kemungkinan timbulnya bahaya yang disebabkan oleh terjadinya pukulan balik atau back stroke sehingga mengakibatkan penurunan kinerja peralatan pembangkitan khususnya pada turbin uap. Pada PLTGU, hasil dari data operasi secondary superheater menunjukkan adanya penurunan temperature uap keluar secondary superheater menuju steam turbine yang cukup signifikan jika dibandingkan dengan design point. Maka dari itu, dilakukan analisa performa secondary superheater dan mencari peluang peningkatan effectiveness dengan cara memvariasikan jarak, jumlah dan diameter tube. Analisa dilakukan dengan menggunakan metode LMTD dan NTU. Dari perhitungan didapatkan effectiveness secondary superheater eksisting adalah sebesar 0,649. Berdasarkan hasil perhitungan dipilih hasil redesign yang sesuai yaitu pada CF-9.05-3/4 (e) dengan kondisi mass flowrate 40 kg/s dengan temperature keluar superheated steam sebesar 767,8 K dengan effectiveness sebesar 0,86. Adapun detail dimensi redesign adalah dengan jumlah tube sebesar 2886, diameter tube 0,01965 m, diameter fins 0,0371 m, jumlah fins/meter 356, transverse pitch 0,05 m dan longitudinal pitch sebesar 0,034 m.