Total Heat Transfer Area Research Articles

Plate-fin heat exchanger optimal design for industry employing both single and multi-objective chaotic opposition based Kho-Kho algorithm

Manufacturers of heat exchangers are constantly looking for new and better designs because it is essential to the preparation of any engineering gadget, like a Plate-fin heat exchanger (PFHE). To find an optimal design of a plate-fin heat exchanger, both hydraulic and economic issues are considered by proposing an optimization technique. The proposed technique minimizes both single and multi-objective functions like total heat transfer area, total pressure loss function, and the total annual cost of a PFHE. This work proposes a Chaotic Opposition-based Kho-Kho optimization technique to deal with single and multi-objective functions. Various benchmark functions have been assessed to evaluate the capabilities of the proposed techniques, including the Wilcoxon signed-rank test. Finally, the outputs such as total heat transfer area, total pressure loss function, and total annual cost are minimized by the proposed optimization technique, resulting in values of 78.50 m2, 0.051, and 834.64$, respectively.

Basic design optimization of power and desalinated water for hybrid cycle ocean thermal energy conversion system integrated with desalination plant

AbstractOcean thermal energy conversion (OTEC) is a heat engine application that utilizes the Rankine cycle to extract energy from the thermal gradient between surface seawater and deep seawater. Hybrid cycle OTEC (H-OTEC) is a combination of an open cycle desalination system and a closed-cycle power generation system that leverages the features of both cycles. Unlike other desalination technologies that require extensive energy to operate, H-OTEC relies entirely on renewable energy. In addition, a desalination plant can be coupled with the H-OTEC system (H-OTEC + D) to improve its performance. Conventionally, the total heat transfer area of heat exchangers per net power is used as an objective function to achieve optimal performance with the lowest capital expenditure cost. The proposed objective function, unlike the conventional one, considers both power and water. In this study, the optimization of H-OTEC + D and H-OTEC is carried out by minimizing the proposed objective function, considering several independent variables. The performance of both systems is evaluated in terms of the objective function, power consumption, seawater flow rates, and desalination ratio. The findings also indicate the effectiveness of the proposed objective function over the conventional one as an effective tool for maximizing power and desalinated water generation.

Heat transfer area optimization of intermediate heat-exchange cycle system for aero engines

The present study constructs an intermediate heat-exchange cycle system for aero engines. To explore the impact of circulation parameters on the cycle, a mathematical model has been developed. Based on the mathematical model, a novel and convenient approach to determining intermediate working fluid (IWF) mass flow rate and temperature, achieving the minimum total system heat transfer area, has been proposed. A two-stage heat exchanger combined intermediate heat-exchange cycle system with Chinese aviation kerosene RP-3, high-pressure water, and air as working fluids is taken as an example to verify the analytical results through numerical calculations. The deviation between the analytical and numerical results is relatively small, below 0.03%. For the situation of a given higher intermediate temperature, a wide range of IWF mass flow rates can be selected as the design point without significantly affecting the total heat transfer area. For the situation where both intermediate temperature and IWF mass flow rate are variable, an optimal area exists where the total heat transfer area is very low and does not differ much with each point. Overall, the present findings can serve as reasonably accurate preliminary guidelines for designing and optimizing the intermediate heat-exchange cycle system.

Fast two-layer nonlinear economic predictive control using machine learning for ORC systems with non-Gaussian disturbances

This study proposes a machine learning-based generalized correntropy two-layer nonlinear economic model predictive control (ML-GC-TL-NEMPC) algorithm to improve the computational speed for Organic Rankine Cycle (ORC) systems with non-Gaussian disturbances. In the upper layer, the ratio of the net output power to the total heat transfer area is used as the economic performance index to optimize the optimal reference trajectory. In the lower layer, the generalized correntropy-based MPC (GC-MPC) is used to track the optimal trajectory. To quickly obtain an optimal solution, a Deep Neural Network (DNN) neural network controller is combined with kernel support vector machine (SVM). It learns the possible optimal solution via off-line training. Then it can be quickly implemented on on-line applications, so it can save the optimal calculation time. The proposed ML-GC-TL-NEMPC is applied to ORC. Its computation and performance are faster and better than the traditional two-layer EMPC and single-layer EMPC.

Efficiency amplified: Enhancing energy performance in biodiesel vacuum thermal water removal system

Thermal vacuum is a common method for removing water from biodiesel, where water content is one of the biggest challenges in the implementation of biodiesel as a fuel. This process has been confirmed through performance testing in this study and has successfully reduced the water content of biodiesel by 65.8 %. There is potential to improve the energy performance of this process by using heat exchangers. Accordingly, this study presents both experimental and economic evaluations to find the efficacy of shell-tube heat exchangers and plate heat exchangers in biodiesel vacuum thermal water removal system. The heat exchangers were designed with a capacity of 300 L/hour to facilitate the heat transfer between a 35 °C and a 105 °C fluids. This experiment included performance tests analyzed by the effectiveness-Number of Transfer Units (Ɛ-NTU) method and economic analysis. The shell-tube heat exchangers employed 189 tubes and three shells with a total heat transfer area of 18.5 m2, whereas the plate heat exchangers consisted of two U-type units with a total heat transfer area of 4.41 m2. The effectiveness and NTU provided by plate heat exchangers are 86.33 % and 6.02, while by shell-tube heat exchangers are 70.64 % and 2,81 respectively. From the economic analysis, plate heat exchangers and shell-tube heat exchangers were able to reduce annual process costs by IDR 76,818,565 and IDR 76,818,565 respectively. These findings indicate that implementing plate heat exchangers in the biodiesel vacuum thermal water removal system is more advantageous than utilizing shell-tube heat exchangers.

CFD-Based Approach to Propose a Zigzag-Shaped Tube Heat Exchanger without Fins

This study explores the application of zigzag-shaped, finless tubes in enhancing heat transfer performance within heat exchangers. Using three-dimensional numerical simulations, we examined the heat transfer per unit area and the volume of the pressure drop, comparing these findings with a traditional parallel tube heat exchanger. This innovative design strategy involved arranging zigzag-shaped tubes at varying distances, and the thermal transfer and frictional characteristics were tested at different air speeds. This research suggests that the introduction of zigzag heat exchangers, as opposed to traditional fin-and-tube designs, led to a significant improvement in heat transfer. This enhancement is attributed to the swirling flow created around the zigzag tubes, which increased the total heat transfer area. Furthermore, we found that the heat transfer area increased by 14.2%, 32.1%, and 63.9% for tube zigzag angles of 30°, 45°, and 60°, respectively, when compared to a parallel tube heat exchanger. Consequently, the zigzag-shaped tube heat exchanger demonstrated not only superior heat transfer, but also a reduction in frictional pressure loss.

Experimental and Numerical Optimization Study on an Airfoil-Shaped Heat Exchanger

Heat exchanger design is a laborious and time-consuming task that often relies on a trial-and-error process. In light of this, our study proposes a design method for optimizing airfoil-shaped heat exchangers using the improved stochastic ranking evolutionary strategy (ISRES) algorithm. The ISRES algorithm provides significant advantages in identifying the global optimum, surpassing genetic algorithms (GAs). In the present study, the thermal model of the heat exchanger protype was validated using experimental techniques. Additionally, the ISRES algorithm was employed for the optimization of a plate-fin heat exchanger with airfoil-shaped fins by minimizing the total heat transfer area and pressure drops, while considering the main geometrical parameters of the exchanger as the design variables. The corresponding computer code was developed, and two case studies were conducted. In case study 1, the total heat transfer area was saved up to 25.7%, while in case study 2, the objective function value reached its minimum value of 0.0738. The numerical results demonstrate that the ISRES algorithm can be successfully applied in optimizing heat exchangers. Finally, a parametric analysis was conducted to evaluate the sensitivity of the proposed method to the heat transfer area.

Experimental study on a channel-embedded sensible thermal energy storage unit with the heat storage body immersed in heat-conducting oil

ABSTRACT In order to study the feasibility of a liquid working medium working in a solid heat storage body, this paper experimentally studied a novel pilot-scale sensible thermal energy storage unit (STESU) with a channel-embedded solid thermal energy storage body (STESB). The material of the body with fluid channels is corundum castable, and the heat-conducting oil works as a heat-transfer medium. While working, the heat-conducting oil flows through the fluid channels of the solid thermal energy storage body, and the oil submerges the body for convection heat exchange in the unit. The charging experiments under different flow rates were carried out to evaluate the thermal performance of the heat storage unit, including temperature, power, and efficiency. The results indicate that the unit’s thermal energy storage capacity is about 1.054 × 106 kJ. When the flow rate increases from 2.0 kg · s−1 to 2.8 kg · s−1, the heat storage power increases from 71.90 kW to 90.58 kW, the total heat transfer area and heat transfer coefficient increases from 3.29 to 3.60 W/K, and the working efficiency of the charge-discharge cycle is 95.6%, which indicates that the thermal performance of the unit is better than that of heat storage unit which uses air as the heat transfer working medium.

Simulation of Compression Heat Pump Cycles Using NH3/H2O Mixtures to Estimate Their Working Domains

AbstractA computer‐aided process design methodology is used to determine the limits of NH3/H2O mixtures in different heat pump cycles from 20 °C to 150 °C. The evaluation is based on a defined parameter set consisting of the coefficient of performance, total heat transfer area and volumetric heat capacity. Simple cycles with two heat flows were chosen to meet good process integration capabilities. The results are shown in a sink outlet/temperature lift matrix considering current technical limits. R1366mzz(Z) in a standard compression cycle with internal heat exchanger serves as a benchmark. To provide temperatures up to 150 °C the lift of the heat pump has to increase to about 80 K of which only the wet compressions cycle with NH3/H2O is capable of. The working domains of NH3/H2O and R1366mzz(Z) are similar, when a two‐stage compression for NH3/H2O is applied.

Thermodynamic, Exergoeconomic and Multi-Objective Analyses of Supercritical N2O-He Recompression Brayton Cycle for a Nuclear Spacecraft Application

Detailed thermodynamic, exergoeconomic, and multi-objective analysis are performed for a supercritical recompression Brayton cycle in which the advanced working medium mixture of nitrous oxide and helium (N2O–He) is utilized for power generation. The thermodynamic and exergoeconomic models are propitious based on the standard components’ mass and energy conservation, exergy balance equation, and exergy cost calculation equation. An investigation of the sensitivity parametric is considered for judging the impact of crucial decision variable parameters on the performance of the proposed Brayton cycle. The proposed cycle’s performance is evaluated by systematic analysis of the thermal efficiency (ηth), exergy efficiency (ηex), total cost rate (C.total), levelized cost of electricity (LCOE), and the total heat transfer area (Atotal). Furthermore, multi-objective optimization is adopted from the viewpoint of the first and second laws of exergoeconomics to find the optimum operating parameters and to improve the circular’s exergoeconomic performance. The final results illustrate that the optimization calculation is based on the fact of the exergoeconomics method; the whole system produces electrical power of 0.277 MW with C.total of USD 18.37/h, while the ηth, ηex, Atotal, and LCOE are 49.14%, 67.29%, 165.55 m2 and USD 0.0196/kWh, respectively. It is concluded that the work exergy destruction for the reactor and turbine is higher than that of other components; then, after the multi-objective optimization analysis, the ηth and ηex improved by 2.08% and 5.07%, respectively, and the C.total, Atotal, and LCOE decreased by 13.99%, 0.01%, and 5.13%, respectively.

수소생산을 위한 수증기-메탄-개질 반응기의 성능 분석 및 설계

This study is to design a steam methane reforming (SMR) reactor that can produce hydrogen from methane, the main component of LNG, by extracting a portion of the gas (BOG) generated from the fuel tank to use a fuel cell as an auxiliary power source for an LNG propulsion ships. Prior to the design, performance was analyzed using several parameters. As the pressure in the reforming reactor increased, the methane conversion rate decreased. The yield to hydrogen is maximal at a temperature of 750 to 800℃, with almost 40% being reduced to hydrogen. At a low temperature, the methane conversion rate was low, and the concentrations of other compositions were also low. At a temperature above 700℃, the concentration of carbon monoxide continued to increase, while the concentration of carbon dioxide decreased. It can be seen that the water gas conversion reaction does not occur smoothly at high temperatures. The reactor design was carried out in the temperature range of 700 to 900℃, and it was found that for each 50℃ increase, the total heat transfer area required increased in the range of about 17~25%.

Thermo-hydraulic rating of a shell and tube heat exchanger for methanol condensation

Shell and tube heat exchangers are the most common type of heat exchangers, and are applicable for a wide range of operating temperatures and pressures. In the present work the thermo-hydraulic rating of a shell and tube heat exchanger was carried out, in order to perform the condensation of a methanol stream using water as coolant. The overall heat transfer coefficient for both the sensible-heat and latent-heat zone had values of 166.41 W/m2.K and 1,198.39 W/m2.K, respectively; while the required total heat transfer area and percent excess area had values of 38.08 m2 and 3.05 %, respectively. The pressure drops of methanol and water streams reached the values of 51,490.84 Pa and 2,890.50 Pa, respectively. The proposed shell and tube heat exchanger can be employed satisfactorily for the demanded heat transfer service, since the calculated percent excess area does not exceed 25%, and the pressure drop of the water stream does not exceed the value of 80,000 Pa.

Modeling and parametric study for a two-phase loop passive containment cooling system

In this study, an optimization method is developed for the structure of the two-phase loop passive containment cooling system. The total heat transfer area of the passive containment cooling system is minimized. At the same time, a new mathematical model is developed with the considerations of the filling ratio and the noncondensable gas inside the loop. On the basis of the mathematical model, the performances of the passive containment cooling system with different filling ratios and noncondensable gas contents are evaluated. Parametric studies are further performed for the key parameters including the operating pressure in the containment, the filling ratio and the noncondensable gas content. The results indicate that the loop heat transfer rate is significantly influenced by these parameters. The effect of the filling ratio on the loop performance is highly related to the optimal filling ratio. The loop heat transfer rate can increase as the filling ratio increases, until the filling ratio reaches the optimal. In addition, the loop heat transfer rate drops by 34% as the noncondensable gas content increases from 0 to 10 kPa, while the corresponding optimal filling ratio increases. As the filling ratio is fixed at 0.56, the difference between the filling ratio and the optimal filling ratio can aggravate the inhibition of noncondensable gas on the loop performance. The reduction of the loop heat transfer rate increases to 37.5% as the noncondensable gas content reaches 10 kPa.

Improvement of the critical heat flux correlation in a thermal-hydraulic system code for a downward-flow narrow rectangular channel

Several critical heat flux (CHF) correlations including the look-up table in the MARS code have been assessed for the prediction of CHF in a downward-flow narrow rectangular channel. For the assessment, we built an experiment database that covers pressures between 1.01 and 39.0 bar, gap sizes between 1.09 and 6.53 mm, mass fluxes up to 25,772 kg/m2s, and under one-sided and two-sided heating conditions. The results of the assessment showed that the Kaminaga correlation has the best overall prediction compared to others. However, because the correlation uses global variables, such as inlet and outlet subcooling and total heat transfer area, it is difficult to use in a system code. A new CHF correlation is then proposed by replacing the global variables in the Kaminaga correlation with local ones and adding correction factors to consider the effect of gap size, mass flux, and the number of heating walls. Additional correction factor is added to consider the effect of inlet subcooling. It is shown that the new one is better than the Kaminaga correlation and it is easy to implement to any system code.

Thermal–hydraulic performance of the circular-slice-shaped-winglet for tube bank heat exchanger

In this study, heat transfer performance of circular-slice-shaped-winglet (CSSW) for tube bank heat exchanger (TBHE) was numerically investigated. Circular-slice angle (α = 5°, 10° and 20°), layer gap (h/d = 0.08, 0.14, and 0.20) and winglet diameter (D/d = 1.60, 1.76 and 1.92) were analyzed as geometric parameters to obtain optimal design. Comprehensive numerical simulations were conducted under both laminar and turbulent flow (1100 ≤ Re ≤ 8500) conditions. Navier Stokes Equations were solved by using RNG k-ε turbulence model (with enhanced wall treatment). Colburn-j factor (j), friction factor (f), modified London area goodness factor (j/f1/3) and performance evaluation criterion (PEC) were investigated quantitatively. Flow characteristics were also analyzed to elucidate the underlying physics of the effects of CSSW on thermal-hydraulic performance for TBHE. Results were compared with the data related to bare tube heat exchanger, and showed that the highest modified London area goodness factor is 26.34% with α = 10°, h/d = 0.20 and D/d = 1.92 CSSW winglet design. Additionally, numerical calculations revealed that PEC increased to 1.356 with these CSSW design parameters, which corresponds to reduction of the required total heat transfer area by 36.60% compared to the bare tube heat exchanger for the same heat duty at a fixed pumping power.

Enhanced Heat Transfer Performance of Multiple Triangular Air Flow Passages in Parallel With Inclined Fins for Flat Plate Solar Air Heater

Abstract This paper presents results of a study of heat transfer performance of multiple equilateral triangular parallel air flow passages below a uniformly heated flat plate having inclined fins of different thickness, length, and material covering a part of the side walls of the duct for transition to early turbulent regimes using appropriate experimental heat transfer coefficient and friction factor correlations from the literature. The heat transfer performance enhancement at equal pumping power has been measured in terms of a performance parameter (hA/hsAs), where hA is the product of heat transfer coefficient and total heat transfer area for the finned triangular duct, and hsAs is the product for the triangular duct with heated flat plate without fins and adiabatic side walls. The values of the performance parameter for steel fins integral with the heated plate are found to be 1.71–1.78 for 1.0 mm thick fins of 15 mm length and 1.94–2.04 for 1.5 mm thick fins of 20 mm length. For aluminum fins, the performance parameter is 2.36–2.54 for 30 mm long fins of 1–1.5 mm thickness. The results of the presented novel scheme of the finned heated plate can be utilized for the development of enhanced performance solar air heater with the finned absorber plate. Since the presented scheme enhances heat transfer without increased pumping power penalty, the existing smooth rectangular duct solar collectors can be modified for enhanced performance.

A new indicator for minimizing size of an ORC power plant based on heat exchanger and turbine design parameters

• System size index SSI – a novel indicator for minimizing size of the ORC is proposed. • SSI is defined based on heat exchanger area and turbine rotor diameter. • By using heat transfer indicators, the turbine may be oversized by up to 70%. • With the use of turbine indices, the heat exchanger may be oversized by up to 40% . • By applying the SSI index, the ORC components are sized optimally. The increasing interest in mobile applications and modular structures of an organic Rankine cycle (ORC) has resulted in growing importance of the optimal sizing of the ORC installation. Most of the existing works were focused on reducing dimensions of the ORC by applying indicators estimating size of a single type of the ORC component. This study aims to define an indicator which comprehensively evaluates the size of the ORC power plant. The proposed indicator, specified as System Size Index SSI , is formulated based on two key ORC design parameters, namely the total heat transfer area of the heat exchangers and the rotor diameter of the turbine. To examine the versatility of SSI , the analysis was conducted considering different ORC applications scenarios, including modular geothermal power plants and mobile waste heat recovery units. The findings of single-objective optimization procedures have shown that by applying indicators evaluating size of the heat exchangers, the turbine rotor diameter may deviate from its smallest possible dimension by up to 70%. Similarly, by utilizing indices evaluating size of the turbine, the heat exchangers area may differ from its optimal size by up to 40%. Meanwhile, by using the SSI indicator, both the total heat transfer area and turbine rotor diameter did not differ from their smallest possible dimensions by more than 1% for each scenario considered. Finally, based on a bi-objective analysis with SSI and net power output as the criteria, it was concluded that by applying such indicators as APR parameter or performance factor PF , the designer is left with a single design solution, while the adoption of the bi-objective approach gives much more flexibility in finding a compromise between the system size and power output of the installation.

Investigation on the performance of fluted tube-in-tube gas cooler in transcritical CO2 heat pump water heater

The utilization of fluted inner tube in tube-in-tube heat exchangers is an effective way to improve the heat transfer performance. Based on the segmented model, the performance of a fluted tube-in-tube gas cooler (FTGC) in the transcritical CO2 heat pump water heater was studied in this paper. The simulation model was validated and adopted to numerically investigate the effects of different parameters on the heat transfer performance of the gas cooler, which was compared to the smooth tube-in-tube gas cooler (STGC) with the same geometric parameters. The results showed that the FTGC had higher heat transfer capacity in most conditions. The heat transfer rate first increased and then decreased as the CO2 inlet pressure increased. The temperature difference at the pinch point in the FTGC was lower than that in the STGC. In the FTGC, the pinch point position was mainly influenced by the CO2 inlet pressure and water inlet and outlet temperatures. Regarding the system COP, the improvement of maximum COP could be up to 29.41% by using the FTGC compared to STGC when the water inlet temperature was 10 °C and the water outlet temperature was 80 °C. However, when the water inlet temperature was 40 °C, the improvement of COP could be impaired to 12.98%. Through changing the designs of the FTGC with the fixed total heat transfer area, when the water inlet and outlet temperatures were 10 °C and 60 °C, the highest maximum COP could be obtained with the design used in the experiments.

Thermal-hydraulic design of natural circulation integrated steam generator using design map

A natural circulation integrated steam generator (NCISG) is a new steam generator concept that prevents the sodium-water reaction, which is a major safety issue in sodium heat transfer systems using the water Rankine cycle. To estimate and enhance the heat transfer performance of NCISG according to the design parameters, a design parameter evaluation method using the design map is suggested for the natural circulation system. The design map evaluates the effect of the temperature distribution of the heat transfer system in advance, allowing a simpler evaluation of the design parameters of a natural circulation system. The design map of NCISG is presented, and the effects of the tube diameter and pitch-to-diameter ratio (P/D) on the heat transfer area and natural circulation flow rate were evaluated. The heat transfer area is mostly affected by the tube diameter and the natural circulation flow rate is mostly affected by the P/D. The tendency of the total heat transfer area to be small in a specific natural circulation mass flow rate, regardless of the tube diameter or P/D, was identified and analyzed as a trend of the total UA value according to the natural circulation flow rate and optimal temperature. Finally, the optimal design of the NCISG under the evaluated design variable conditions is presented.

Optimal Heat Exchanger Area Distribution and Low-Temperature Heat Sink Temperature for Power Optimization of an Endoreversible Space Carnot Cycle.

Using finite-time thermodynamics, a model of an endoreversible Carnot cycle for a space power plant is established in this paper. The expressions of the cycle power output and thermal efficiency are derived. Using numerical calculations and taking the cycle power output as the optimization objective, the surface area distributions of three heat exchangers are optimized, and the maximum power output is obtained when the total heat transfer area of the three heat exchangers of the whole plant is fixed. Furthermore, the double-maximum power output is obtained by optimizing the temperature of a low-temperature heat sink. Finally, the influences of fixed plant parameters on the maximum power output performance are analyzed. The results show that there is an optimal temperature of the low-temperature heat sink and a couple of optimal area distributions that allow one to obtain the double-maximum power output. The results obtained have some guidelines for the design and optimization of actual space power plants.