Logarithmic Mean Temperature Difference Research Articles

Experimental and Comparative Heat Transfer Analysis of Heat Exchanger with Surface Modification

This research aims to enhance the heat exchanger performance by a surface modification approach. The shot peening effect on the heat transfer performance of shell and tube heat exchanger (STHE) is experimentally studied with different surface modifications of stainless steel (SS) tube-like plain SS tube, grinded surface and blast with copper, sand & iron surface. The effect of shot peening on the surface morphology of the SS outer surface is analyzed by scanning electron microscope, and it was found that the iron blast surface has a coarse grain structure. The optimum flow rate for STHE was experimentally studied by base SS tube, and its values are compared with analytical results of computational fluid dynamics and heat transfer research. The underwater medium maintained the higher and lower temperatures of 80 °C and 30 °C, respectively. Based on the logarithmic mean temperature difference, number of transfer units (NTU), overall heat transfer coefficient, effectiveness and exergy efficiency of SS and its modified surface are experimentally evaluated, and iron blasted surface offered maximum heat exchanger performance like 100% for Stanton number, 89% for Nusselt number, 89% for overall heat transfer coefficient, 89% for an NTU, 57% for effectiveness, and 148% for exergy efficiency, while compared to SS surface without modification.

Experimental thermal performance intensification of gravitational water vortex heat exchanger using hexagonal boron nitride-water nanofluid

One of the main concerns presently is the rapid improvement of thermal technology for widespread heat exchanger applications involving energy conservation and intensification of heat transfer process. For the enhancement of heat exchange processes, nanofluids have been considered as a potential substitute for conventional fluids, which in general have subpar thermal characteristics. Therefore, the present study focusses on the heat transfer enhancement and the intensification of overall thermal performance of the developed gravitational water vortex heat exchanger (GWVHE). The experimental investigation first involves the preparation and characterization of water-based hexagonal-boron nitrides (h-BN) nanofluids as well as the computation of thermophysical properties of different volume fractions of h-BN nanofluids. Subsequently, a comparative analysis evaluating the thermal energy exchange capabilities of water-to-water and water-to-h-BN nanofluids combination of two fluids has been conducted to investigate the intensification in thermal performance of the developed GWVHE. The experimental investigation is primarily based on calculating the thermal energy balance, overall heat transfer coefficient, log-mean temperature difference (LMTD) and the effectiveness of the developed GWVHE using effectiveness-NTU method. The experimental results reported that 0.02 % volume fraction of water-based h-BN nanofluids is more suitable for further testing of the developed GWVHE to mitigate the stability concerns at higher concentrations. The minimal thermal losses, that lie within the 10 % confirms the thermal energy balance and by using the h-BN nanofluids −to-water strategy for two fluids. The maximum value of heat exchange rate significantly increased from 8490 W to 9998 W with the utilization of h-BN nanofluids-to-water as compared to water-to-water combination. Furthermore, the maximum values of LMTD employing h-BN nanofluids are found to be reduced from 21.15 K to 17.53 K compared to the water-to-water combination confirming the intensification in thermal performance of GWVHE. The overall heat transfer coefficient values are also found higher when h-BN nanofluids are substituted instead of water. The maximum value of overall heat transfer coefficient for h-BN nanofluids-to-water combination is improved from 874 W/m2K to 1142 W/m2K compared to water-to-water combination. Moreover, by utilizing the h-BN nanofluids-to-water combination, the values of effectiveness are intensified by an average of 13.5 % and 9 % in both sets of testing parameters, respectively. All these maximum improvement in findings for heat exchange, overall heat transfer coefficient, effectiveness, and reduction in LMTD values are obtained by maintaining the inlet mass flow rate of cold fluid at 0.142 kg/s, while the inlet mass flow rate of hot fluid was varied in the range from 0.092 kg/s to 0.133 kg/s. Additionally, the inlet temperatures of hot and cold fluids are kept at 330 K and 296 K, respectively. Hence, the utilization of h-BN nanofluids is proven to be highly effective for boosting thermal energy exchange and enhancing the overall thermal performance of the developed GWVHE.

Mathematical model and numerical calculation of the movement of oil products in helicoidal heat exchangers

Heating of oil and oil products is widely used to reduce energy losses during transportation. An approach is developed to determine the effective length of the heat exchanger and the temperature of the cold coolant (oil) at its outlet in the case of a strong dependence of oil viscosity on temperature. The method of the log-mean temperature difference, modified for the case of variable viscosity, and the methods of computational fluid dynamics (CFD) are used for calculations. The results of numerical calculations are compared with the data obtained on the basis of a theoretical approach at a constant viscosity. When using a theoretical approach with a constant or variable viscosity, the heat transfer coefficients to cold and hot coolants are found using criterion dependencies. The Reynolds-averaged Navier-Stokes (RANS) and a turbulence model that takes into account the laminar-turbulent transition are applied. In the case of variable oil viscosity, a transition from the laminar flow regime to the turbulent one is manifested, which has a significant effect on the effective length of the heat exchanger. The obtained results of CFD calculations are of interest for the design of heat exchangers of a new type, for example, helicoidal ones.

Design and performance comparison of large-scale hydrogen liquefaction processes based on mixed refrigerant cycle

Liquid hydrogen (LH2) is an efficient carrier for storage and transportation of hydrogen energy. To investigate the effect of mixed refrigerant cycle (MRC) on the performance of large-scale hydrogen liquefiers, three processes with a capacity of 50 TPD LH2 are designed in a relatively achievable way. Process I utilizes a dual-pressure hydrogen Claude cycle with nitrogen precooling as a reference. Process II incorporates a five-component mixed refrigerant cycle in place of the nitrogen cycle. Process III advances further by replacing the hydrogen cycle in Process II with an additional MRC composed of Ne, He and H2. Sensitivity analysis is applied to optimize the parameters of the three processes prior to the comparison of their heat exchangers performance and the energy and exergy analyses. Due to the synergistic effect of smaller temperature difference and higher refrigeration temperature, the employment of MRC for precooling yields a SEC of 1.350 kWh/kg LH2, 57.1% and 66.3% lower than those of nitrogen cycle and liquid nitrogen, respectively. The sensible heat of the Ne/He/H2 mixture shows a better temperature matching than the latent heat of the refrigerant hydrogen when cooling the product hydrogen, reducing energy consumption by 28.4%. The utilization of MRC for precooling generates more exergy loss in the separators, mixers and throttle valves, but the absence of nitrogen expanders and much lower flow rate of refrigerant save more exergy in total. The essential reason for the progressiveness of Process III is that the integrated heat exchanger in the cryostat achieves the logarithmic mean temperature difference (LMTD) of 2.11 K, effectively reducing the exergy loss of the refrigerant compressors, thereby diminishing the thermodynamic irreversibility.

Equivalent Enthalpy Model and Log-Mean Enthalpy Difference Method for Heat-Mass Transfer in Cooling Towers

Abstract In industrial processes involving both heat and mass transfer, the enthalpy or total energy difference, not the temperature difference, is a more comprehensive driving-force potential for heat exchanger systems, such as a cooling tower. However, the common practice of current enthalpy methods based on Merkel integral requires numerical integration with implied linear distributions of air enthalpy and water temperature. If the cooling range is relatively small, the outcome of the integration may carry little error. But for a large cooling range and a substantially increased temperature, the error involved may be significant. Like log-mean temperature difference, a log-mean enthalpy difference method may require only the inlet and outlet conditions without prior knowledge of the enthalpy distributions of the fluids within the heat exchanger. The known Berman's enthalpy difference method requires correction factors, which was derived based on the linearization of the interfacial enthalpy and the enthalpy difference between the interfacial moist-air enthalpy and the bulk air enthalpy without underlying interpretation to demonstrate that the method could be broadly used. In this paper, an equivalent enthalpy model is proposed, and the log-mean enthalpy difference is derived without any constraints for broad uses. The derived method is compared with the results of Merkel's method from literature with excellent agreement. Thus, the work in this paper would open the possibility for broad uses of the log-mean enthalpy difference method for many industrial processes involving mass transfer.

Demonstration of a multi-channel fluidized bed particle–supercritical carbon dioxide heat exchanger for concentrating solar applications

High-temperature thermal energy storage in oxide particles at temperatures above 600°C can couple concentrated solar energy with high-efficiency thermal power cycles to provide dispatchable solar-driven electricity. Challenges remain in developing cost-effective primary heat exchangers, which require expensive alloys, to extract the high-temperature thermal energy from the particles to power cycle fluids, such as supercritical CO2 (sCO2) in recuperated Brayton cycles. To explore one pathway for cost-effective, high-temperature particle heat exchangers, the current study demonstrates a shell-and-plate, particle–sCO2 heat exchanger with narrow-channel fluidized beds coupled with micro-channel sCO2 flows in the heat exchanger walls. This study evaluates the feasibility of multiple parallel, narrow-channel fluidized beds in shell-and-plate particle–sCO2 HXs, to achieve high bed-wall heat fluxes at elevated temperatures. A reduced-order model simulates the narrow-channel, fluidized-bed particle–sCO2 heat exchanger to design the fluidized bed geometry, in terms of depth, height, and number of channels,for a nominal 40-kWth heat exchanger at particle and sCO2 inlet temperatures up to 600°C and 400°C respectively. The resulting shell-and-plate heat exchanger design operates with bubbling fluidization of the downward-flowing oxide particles to enhance bed-wall heat transfer. The heat exchanger core is fabricated with etched sCO2 micro-channels in thin wall plates that are diffusion bonded to spacer frames to form the shell-and-plate structure with 12 parallel, fluidized bed channels, 10.4 mm deep. The heat exchanger is tested at the National Solar Thermal Test Facility at Sandia National Laboratories with CARBOBEAD HSP particles at design particle flow rates of 0.20 kg s−1 and inlet temperatures up to 525°C. Results show that fluidization across multiple parallel channel beds can maintain uniform particle inventory with a common freeboard zone above the heat exchanger core. Bubbling fluidization improves particle–wall heat transfer coefficients but also increases axial dispersion of particle thermal energy, which lowers the log-mean temperature difference such that total heat transfer remains relatively constant to within ±10% over a broad range of fluidization gas velocities. The axial dispersion required particle and sCO2 flow rates to be increased by 25% over model-designed conditions to achieve the targeted 40 kWth, which indicates the importance of incorporating axial dispersion into heat exchanger design models and of deploying bed structures to suppress it. This study demonstrates the feasibility and preferred fluidizing gas conditions for particle heat exchangers for releasing high-temperature thermal energy storage systems.

Airside heat transfer analysis using Wilson plot method of three analogous serpentine tube heat exchangers for aero-engine cooling

This research investigates the design, manufacture and heat transfer characteristic evaluation of three types of heat exchangers (HXs) serving for modern aero-engines. In the field of heat transfer system, previous research has concentrated on large-diameter tubes, whereas estimation for heat transfer in small-diameter tubes commonly relies on correction factors. However, small-diameter heat exchangers offer extensive applicaiton prospects in aero-engines utilizing cooled cooling air (CCA) technology, benefiting from their high heat transfer efficiency and lightweight. Hence, directly investigating compact small-diameter HXs is significant. In this paper, three analogous serpentine tube bundle HXs with different tube diameters (OD: 2.2/1.8/1.4 mm with 0.2 mm thickness) were designed by the Logarithmic Mean Temperature Difference method (LMTD). A series of comparative experiments were conducted to explore the effects of the tube diameter and flow rates on the airside heat transfer under different fuel flow conditions. The results indicate that in the case of turbulent fuel flow, decreasing the tube diameter assists in enhancing total heat transfer, whereas the trend is opposite in laminar fuel flow. In addition, during turbulent fuel flow, heat transfer capacity rises with the increase of flow rates on both sides, while variations in air flow rate have minimal impact on airside heat transfer in laminar fuel flow. Finally, the calculated heat transfer rate exceeds the experimentally measured value by no more than 15%, with this deviation escalating as the reduction of tube diameter. Subsequently, an airside Nu-Re correlation suitable for small-diameter HXs is fitted based on experimental data, with 94.1% of the data points locate in the 5% error band, providing guidance for the design and validation of aero-engine HXs in future.

Heat Transfer Performance Analysis of an E-Vehicle Cooling System Using a Hybrid Peltier System

Abstract: This research investigates the heat transfer performance of an electric vehicle (EV) cooling system utilising a hybrid Peltier as integrated system with advancements in EV battery technology, the demand for efficient cooling systems has become crucial for ensuring battery safety, longevity, and overall performance. Present research focus on the application of ethylene glycol as a coolant, exploring the thermal parameters, heat transfer rates, and overall effectiveness of the hybrid cooling system. A literature review highlights the significance of heat transfer enhancement techniques, emphasising the need for energyefficient methods in the automotive industry. The research methodology involves experimental work, analytical calculations, and the preparation of coolant samples to evaluate thermo-physical parameters. The results demonstrate the temperature drop, Overall heat transfer for different flow rates, Logarithmic Mean Temperature difference, and Comparative Power Consumption of different setup. The result showed that presence of ethylene glycol in water enhances the desirable temperature drop of the heat transfer fluid. The Overall heat transfer rate is increased by 58% for EG-100 sample as compared to pure water. Further an ANN model is also developed for prediction of temperature drop, the result showed 2 layer model with 8, 8 neurons as optimum model for prediction.

Parametric design optimization and thermodynamic analysis of plate fin heat exchanger for helium liquefaction system

The plate-fin heat exchanger is one of the most important components of helium liquefaction system as it recovers cold energy from helium gas in the cold box. Because of larger heat transfer surface area and compact geometrical configuration, plate-fin heat exchangers are widely used. The design of heat exchanger using helium as a cryogenic fluid needs high thermodynamic performance with minimum pressure drop which particularly requires the optimization of dimensional array and its geometrical configurations. In this regard, a parametric investigation was performed to compute the effective geometrical parameters and its effect on thermodynamic (effectiveness and log-mean temperature difference) performance has been discussed in detail. The present study aims to design optimization and thermodynamic performance evaluation of plate-fin type heat exchangers used in helium liquefaction systems. The developed helium liquefaction model has been simulated for the most critical liquefier with and without liquid nitrogen precooling, mixed mode, and refrigeration mode. Each component of the liquefaction model has been technically and thermodynamically analyzed and, in particular, four plate-fin heat exchangers have been considered and designed accurately using Aspen EDR®. Initially, the sensitivity analysis was carried out to characterize the most significant geometrical parameters (fin thickness, height, number and arrangement of layers, frequency, and fin type) and their effect on thermodynamic performance and pressure drop. After that, the artificial intelligence model was used to determine the optimal range of such geometrical variables in which the heat exchanger has maximum effectiveness and log mean temperature difference. Finally, the operating conditions obtained from cycle modeling and optimized geometrical datasets have been applied in commercial simulation software Aspen EDR® for plate-fin heat exchangers design. Finally, a comparative thermodynamic analysis has been carried out to determine the performance of all the designed heat exchangers operating at four different modes (boundary conditions).

Dynamic Modeling of Heat Exchangers Based on Mechanism and Reinforcement Learning Synergy

The current lack of a high-precision, real-time model applicable to the control optimization process of heat exchange systems, especially the difficulty in determining the overall heat transfer coefficient K of heat exchanger operating parameters in real time, is a prominent issue. This paper mainly unfolds the following work: 1. We propose a dynamic model for the control and optimization of the heat exchanger operation. By constructing a system to collect real-time operating data on the flow rates and temperatures on both sides of the heat exchanger, the parameter identification of the overall heat transfer coefficient K is performed. Subsequently, by combining this with mechanistic equations, a novel heat exchanger model is established based on the fusion of mechanistic principles and reinforcement learning. 2. We validate the new model, where the average relative error between the model’s temperature output values and the actual measured values is below 5%, indicating the high identification accuracy of the model. Moreover, under variations in the temperature and flow rate, the overall heat transfer coefficient K demonstrates the correct patterns of change. 3. To further enhance the model’s identification accuracy, a study on the reward functions in reinforcement learning is conducted. A model with the Logarithmic Mean Temperature Difference (LMTD) as the reward function exhibits a high identification accuracy. However, upon comparison, a model using the Arithmetic Mean Temperature Difference (AMTD) for relative error as the reward function shows an even higher identification accuracy. The model is validated under various operating conditions, such as changes in the flow rate on the hot side, demonstrating good scalability and applicability. This research contributes to providing a high-precision dynamic parameter basis for the precise control of heat exchange systems, offering significant guidance for the control optimization of actual heat exchange system operations.

Experimental characterization of a spiral heat exchanger for waste water heat recovery from partially filled sewage pipes

This paper focuses on the experimental characterization of horizontal, spiral heat exchangers used for heat recovery from sewage pipes. Such non-intrusive heat exchanger configurations are appealing for this application, but they often exhibit reduced heat exchange performances compared to more compact designs. To compare the performance of this configuration with that of an ideal counter-flow heat exchanger, a representative test setup was constructed. As the sewer pipes are generally not completely filled, tests were conducted using three different fillings (100%, 50%, 33%) and a filling parameter z was introduced in the heat transfer equations. Correction factors to be applied in the Logarithmic Mean Temperature Difference (LMTD) design method for this specific spiral configuration were derived from the test results. It was found that the filling of the sewer pipe has minimal impact on the correction factor, which ranges between 0.78 and 0.83. The average value of 0.81 is recommended for design purposes.

Shell and tube heat exchange comparison with gravitational water vortex flow configuration

As a recent addition to the heat exchanger family, gravitational water vortex heat exchangers may be considered a potential alternative to shell-and-tube heat exchangers in the process industry. Their shared reliance on the turbulent fluid flow for heat transfer and comparable sizes indicates the need to compare the two thermal systems in terms of input energy requirement, heat exchange effectiveness, temperature distribution, log-mean temperature difference and overall heat transfer coefficient. The present study reports an experimental comparison of the performance of a shell-and-tube heat exchanger with a gravitational water vortex heat exchanger for the same heat exchange area, mass flowrates and reference temperatures. The validation of the experiments is supported by the analytical results for both heat exchangers. The experimental findings highlight the importance of the presence of air core in the gravitational water vortex heat exchanger, which performs 40 % better than in the absence of air core. Moreover, the same air core provides support in outperforming the shell-and-tube configuration by a margin of 22 % and 24 % more heat transfer rate for the same hot-side inlet temperatures of 313 K and 323 K, respectively. The study concludes that the gravitational water vortex heat exchanger performs better than the shell-and-tube heat exchanger at high inlet flow rates, whereas the latter is more effective in terms of log-mean temperature difference with better heat loss counter measures.

Operation Parameters Variation of Air Source Heat Pump According to the Outdoor Temperature

Air source heat pumps (ASHP), known as energy efficient systems, emerge as environmentally friendly and economical solutions for building heating. Unfortunately, the operating parameters of ASHPs and accordingly their performance are directly affected by the daily and seasonal temperature changes of the outside air. In this study, change in operation parameters of a selected ASHP with 3.4kW nominal heating capacity is investigated with a calculation method based on the logarithmic mean temperature difference, between -10°C to 18°C outdoor temperature range with 2°C steps, at constant compressor power. The study is verified with published COP data of the manufacturer. Results are shared with graphs that give the variation of refrigerant evaporation and condensation temperature and pressure, COP, and condenser heating load according to outdoor air temperature. A raise from -10°C to 18°C in outdoor temperature, increases the COP value from 3.38 to 5.49. Detection of the increase in evaporation pressure in parallel with the outdoor temperature may allow easy control of the refrigerant charge level with a manometer. This study can be a useful guide for researchers who aim to determine the outdoor temperature dependent operating parameters of an ASHP and for technical personnel who need this information in fields.

Novel approach for modeling a full-sized air-cooled heat exchanger using porous media and iterative processes

Air-Cooled Heat Exchangers (ACHE) have gained importance through their extensive use in the oil and gas industry. Many researchers studied ACHE extensively and proposed analysis methods. Most of them investigate part of the ACHE in their modeling. Others consider only pressure drop in their calculations in simulating the porous media (fins and surrounding air). These assumptions lead to unprecise modeling results. In contrast to existing literature, by incorporating computational fluid dynamics (CFD) with real geometry design, this paper includes a study of a full-size ACHE with precise geometric measurements, commencing at the hot water's input and going all the way to the ACHE's exit through a U-path tube. By incorporating the complete geometry dimensions of the U-path tube length from the hot water inlet to the outlet, this methodology has the potential to produce more accurate predictions of temperature distribution, heat flow rate, logarithmic mean temperature difference (LMTD), and fin efficiency for each tube along the entire length of the ACHE. Further, unlike other works of literature, the porous media in this research includes calculations for pressure drops and heat transmission in place of real geometry design which gives more sensible and accurate modeling results. Moreover, a novel verification method is proposed by presenting an iterative process for verification of entire geometry design calculations by comparison with the Real Geometric Design. The incorporation of Real Geometry Design and Computational Fluid Dynamics (CFD) Code programs can lead to more precise and efficient methodologies for modeling air-cooled exchangers, offering valuable insights that can ultimately enhance their design and performance. In this work, the convergence with the actual geometrical design is less than 1%, demonstrating the superiority of the suggested strategy.

Thermal-economic optimization design of shell and tube heat exchanger using an improved sparrow search algorithm

Optimal design of heat exchangers is challenging, since complex non-linear relationship exists among the various design parameters. This study aims to construct a full-dimensional thermal-economic model for shell-and-tube heat exchanger using two commonly (i.e., Kern and Bell-Delaware) methods based on Logarithmic-Mean-Temperature-Difference (LMTD) or ε-Number-of-Transfer-Units (ε-NTU) method and proposes a novel solving mechanism based on improved sparrow search algorithm to achieve thermal-economic optimization design of heat exchanger. The improved method organically combines nonlinear gradient descent weight factor, elite reverse strategy, selection-mutation operator to maintain population diversity, enhance convergence speed and avoid being stuck in local optima. Firstly, the constructed model’s accuracy is verified by numerical analysis. Then, the improved sparrow search algorithm is applied to four examples after algorithm parameter tuning, and the results show that the area decreases by 15.62%∼49.30% and total annual cost is reduced by 27.93% compared to the literature. It can also identify feasible solutions at a lower total cost than the metaheuristic method, with reductions of 7.56%∼59.42%(Kern) and 6.26%∼60.19%(Bell-Delaware). Moreover, a multi-objective optimization algorithm is obtained by adding fast non-dominated sorting mechanism and archival gene pool, and the superiority is verified by standard test functions. Finally, a multi-objective optimization scheme with the higher effectiveness-economic benefit is conducted to achieve cost-effectiveness tradeoff for two real-world cases. The results show that total cost of the most economic-efficient scheme decreases by 53.73% and effectiveness increases by 2.33%, while the runtime decreases by 35%. Furthermore, sensitivity analysis of effectiveness and total cost varying with crucial variables is performed and discussed.

Numerical analysis of fluid type and flow mass rate on logarithmic temperature difference and heat transfer coefficient of double pipe heat exchanger

This CFD and statistical article aims to evaluate the impact of fluid type and flow mass rate on the log-mean temperature difference (ΔTLM) and the heat transfer coefficient (Ushell) in a double tube heat exchanger (DPHEX) using computational fluid dynamics (CFD) and statistical analysis. ANSYS Fluent software was utilized to conduct CFD calculations. CFD analyses were implemented using Taguchi L8 orthogonal array containing two variables such as the fluid types and the flow mass rates. The levels of fluid types were considered as water-liquid, ethylene-glycol, engine-oil, and benzene-liquid. The levels of fluid types were decided as 1.1 kg/s to 1.5 kg/s. To determine the optimal levels of variables and their impacts on the ΔTLM and Ushell in DPHEX, analysis of Signal to Noise (S/N) ratio was employed. Analysis of Variance (ANOVA) was also utilized to decide the effective variables and their percentage contribution rates on the outcomes. The CFD result obtained using the optimum levels of variables were compared with Taguchi estimation result. According to the study, the highest effects were obtained using ethylene-glycol, engine-oil, water-liquid, and benzene-liquid on the highest log-mean temperature difference values, respectively. In addition, the highest heat transfer coefficient values were found utilizing water-liquid, benzene-liquid, ethylene-glycol, and engine-oil, respectively. Increasing flow mass rate from 1.1 kg/s to 1.5 kg/s causes an increase in both outcomes. The study provides a reference for resolving issues that may arise in the production of experimental DPHEXs.

Using the Log Mean Temperature Difference (LMTD) and ε-NTU Methods to Analyze Heat and Mass Transfer in Direct Contact Membrane Distillation.

In direct contact membrane distillation (DCMD), heat and mass transfers occur through the porous membrane. Any model developed for the DCMD process should therefore be able to describe the mass transport mechanism through the membrane, the temperature and concentration effects on the surface of the membrane, the permeate flux, and the selectivity of the membrane. In the present study, we developed a predictive mathematical model based on a counter flow heat exchanger analogy for the DCMD process. Two methods were used to analyze the water permeate flux across one hydrophobic membrane layer, namely the log mean temperature difference (LMTD) and the effectiveness-NTU methods. The set of equations was derived in a manner analogous to that employed for heat exchanger systems. The obtained results showed that the permeate flux increases by a factor of approximately 220% when increasing the log mean temperature difference by a factor of 80% or increasing the number of transfer units by a factor of 3%. A good level of agreement between this theoretical model and the experimental data at various feed temperatures confirmed that the model accurately predicts the permeate flux values for the DCMD process.

Computation of thermal properties of CMSP shell and tube heat exchanger using different types of helical baffles

AbstractThis paper investigates the flow and thermal properties of a combined multiple shell pass (CMSP)‐shell and tube heat exchanger (STHE) with the provision of unilateral ladder‐type helical baffle (ULHB) and continuous helical baffle (HB) in the outer shell pass of the heat exchanger. Two CMSP‐STHEs with ULHB and HB, respectively, are compared with the traditional STHE having segmental baffles (SG‐STHE) using the computational fluid dynamics method. The computational outcomes are validated with the empirical correlations of the Kern and Esso method. The Reynolds‐averaged Navier–Stokes‐based standard k–ω turbulence model accurately predicts the heat transfer (HT) rate and pressure drop. The computed results of HT rate, pressure drop, and logarithmic mean temperature difference corresponding to various mass flow rates (m) for three STHEs are presented. The results show that the overall HT rate of CMSP (ULHB)‐STHE and the CMSP (HB)‐STHE at the same mass flow rate are nearly 28.3% and 14.8% larger than that of traditional SG‐STHE, respectively. Furthermore, the overall area‐weighted average pressure drop (ΔP) of CMSP (HB)‐STHE is smaller than that of SG‐STHE by 26.5% at the same mass flow rate (m) and for CMSP (ULHB)‐STHE it is larger by 2% than that of traditional STHE. Based on the above results, it is concluded that the CMSP (ULHB)‐STHE is a suitable replacement for the conventional SG‐STHEs.

Fouling resistance study in industrial tubular reactor for low density polyethylene production

Fouling is the development and buildup of unwelcome elements on the surface of processing equipment. Fouling study in LDPE production via tubular reactor is very important with regard to safety, economic and productivity. However, the fouling study in LDPE production was rarely reported in the literature due to complex chemical reaction and reactor configuration. In this work, the overall heat transfer coefficient (U) computed by component’s physical properties (method 1) and log mean temperature difference of plant data (method 2) were studied. The U obtained from the correlation method is larger than plant data. The U variations obtained from industrial data were employed in this work to determine the maximum reactor fouling resistance Rfmax. The Rf reaction zone is significantly lesser than the Rf cooling zone.The fouling investigation utilized fouling resistance (Rf) as the fouling measurement. Rf is signified by the alteration of U dynamically over ten hours. The Rfmax achieved is 50.0 cm2.s.K/cal. The Rfmax value obtained were then applied as a constraint for the optimization study.

Thermal Performance and Turbulence Modeling of Combined Multiple Shell-Pass Shell and Tube Heat Exchanger

Abstract This paper investigates the adaptability of different Reynolds-averaged Navier-Stokes (RANS)-based turbulence models for flow behavior and thermal performance of combined multiple shell-pass shell and tube heat exchanger (CMSP-STHE) with unilateral ladder-type helical baffle (ULHB). The presence of ULHB in the outer shell pass of the heat exchanger leads to a complex flow configuration and makes it quite challenging to deal with its computational analysis. The computational fluid dynamic method compares the CMSP-STHE with ULHB with the traditional shell and tube heat exchanger with segmental baffles (SG-STHE). The performance of four turbulence models, namely, realizable k–ɛ, standard k–ɛ, standard k–ω and RNG k–ɛ models are compared with the correlation data. It is observed that the standard k–ω turbulence model more accurately predicts the heat transfer and pressure drop compared to other models. The logarithmic mean temperature difference (LMTD) results for various mass flowrates and thermal performance enhancement factor (TPEF) corresponding to various values of Re are also presented. It is concluded that the TPEF of CMSP (ULHB)-STHE is higher than that of the conventional STHE. The average enhancement is approximately 28% for ULHB STHE than the conventional one. Further, variations in velocity, turbulence kinetic energy, and local Nusselt number along the tube length are examined to understand the thermal performance behavior with CMSP (ULHB)-STHE. It is clear from the results that the CMSP (ULHB)-STHE is a better alternative to the traditional SG-STHEs.