Tube Passes Research Articles

Energy-economic analysis and optimization of a shell and tube heat exchanger using a multi-objective heat transfer search algorithm

This study presents the energy-economic analysis and optimization of a shell and tube heat exchanger. A water-water, segmental baffled shell and tube heat exchanger was designed using the Kern method and analysed by performing energy and economic modelling. The analysis is carried out considering the design variables on the shell side i.e. baffle cut, baffle spacing, shell diameter and tube side variables i.e. tube layout, tube outside diameter, number of tube passes and number of tubes. The multi-objective heat transfer search algorithm was used to optimize the heat exchanger for minimum total cost and maximum heat exchanger efficiency. Multiple optimal solutions were presented using the Pareto optimal curve. TOPSIS selection criteria was used to identify the optimum operating condition. Within the given bounds of the variables, the shell and tube heat exchanger can be operated at a minimum cost of 72,000 $/year resulting in 16.4 % efficiency, or, it can be operated at a maximum efficiency of 81.6 % with a total cost of 275,000 $/year. The scattered distribution of shell diameter, baffle spacing, number of tube passes and number of tubes between the lower and upper bound represent their substantial role in optimizing the heat exchanger performance. The number of tubes and tube passes showed the maximum variation in efficiency, while significantly less impact was observed when the tube layout was altered.

Evaluating and enhancing heat storage in a Ca(OH)2/CaO shell-tube reactor: A numerical study on key factors and performance optimization

Thermochemical energy storage offers a promising solution to addressing the challenges such as the discontinuous operation of concentrating solar power plants. This study develops a comprehensive model to simulate the Ca(OH)2 heat storage process within a shell-tube reactor system by integrating the fluid dynamics, chemical reactions and thermal processes. The influence of operating conditions and geometric characteristics on the reactor's performance is systematically analyzed. Key performance evaluations are evaluated using an orthogonal experimental design. The results reveal that the reactor's reaction time is 11,305 s under baseline conditions. Increasing the HTF temperature from 825 K to 875 K can reduce the reaction time by 47.9 %, while decreasing the reactant porosity from 0.8 to 0.6 leads to an increase of 100 % in energy storage capacity and extends the heat storage duration by 183 %. Additionally, optimizing the tube arrangement by adding 22 tube passes can increase the energy storage efficiency except causing a marginal increase in reaction time. Among the factors analyzed, reactant porosity has the most significant impact on the heat storage time, while the HTF temperature determinates the heat exchange rate and energy storage efficiency.

Thermodynamic performance of air-cooled seasonal cold energy storage for space cooling: A case study

With the improvement in people's living standards, there is a growing demand for cooling, making it urgent to develop a low-carbon and energy-efficient refrigeration system. Therefore, this paper proposes an air-cooled seasonal energy storage (ACSES) system. The heat transfer model of the system is constructed. The impact of relevant parameters on the system's cold storage performance was analyzed. The results show that larger glycol flow rates, windward velocity, number of tube passes and tube rows, and the volume ratio of ethylene glycol to water (VR) are beneficial for improving cold storage performance. However, excessively large parameters do not significantly enhance cold storage performance. The influence of ambient temperature on cold storage performance is greater than that of ice thickness. When VR is 0.02, the cold storage performance is relatively superior. To demonstrate the energy-saving performance of the system, the energy consumption saving rate (ECSR) indicator was proposed. The ECSR of the ACSES system is 72.75 %. The system can significantly conserve resources and reduce energy consumption.

Comparative evaluation of C-MAC and McGrath MAC videolaryngoscopes with Macintosh direct laryngoscope for endotracheal intubation in adult patients undergoing elective surgeries.

Videolaryngoscopes have an undisputed role in difficult airway management, but their role in routine intubation scenarios remains underappreciated. McGrath MAC is a lightweight laryngoscope with a disposable blade. It remains to be proven if it performs as efficiently as the reusable videolaryngoscopes like C-MAC and whether it has an advantage over standard Macintosh laryngoscope in predicted normal airways. We recruited 180 adult patients and randomly divided them into three groups for intubation with either Macintosh laryngoscope (Group-A), C-MAC (Group-B), and McGrath (Group-C). The primary objective was to compare the first attempt success rate. Secondary objectives included Cormack-Lehane (CL) grades, laryngoscopy time, intubation time, ease of intubation, need for optimization manoeuver, and the number of passes to place the endotracheal tube. The two videolaryngoscopes provided a superior first attempt success rate as compared to Macintosh laryngoscope (P = 0.027). The CL grade-I was 100% in group B, 41.7% in group-A and 90% in group-C (B vs C; P = 0.037). Laryngoscopy time was 9.9 ± 2.5 s, 12.6 ± 0.8 s, and 13.1 ± 0.8 s for groups A, B, and C, respectively (B vs C; P = 0.001). Intubation time was 24.4 ± 12 s, 28.3 ± 1.9 s, and 37.3 ± 5.8 s for groups A, B, and C, respectively (P < 0.0001). The number of tube passes was highest in group C. Videolaryngoscopes provided a superior glottic view and resulted in a superior first attempt success rate as compared to Macintosh laryngoscope. When comparing the two videolaryngoscopes, C-MAC resulted in better intubation characteristics (shorter intubation time, better glottic views, and higher first-attempt success rates) and should be preferred over McGrath for intubation in adult patients with normal airways.

THE EFFECT OF ADAPTIVE LIQUID-VAPOR SEPARATORS FOR ENHANCING CONDENSATION HEAT TRANSFER IN A CONDENSER

In this paper, an adaptive liquid separation structure for enhancing condenser heat transfer is proposed. Performances of two stage adaptive liquid-vapor separation condenser (ALSC) and two stage U-type liquid-vapor separation condenser (ULSC) with R134a as working fluid are studied and compared under different air speeds. Moreover, thermodynamic characteristics of the condenser with adaptive liquid-vapor separators are studied. The results show that the adaptive separator further improves the heat transfer performance of related tube passes, thus improving the thermodynamic characteristics of the entire ALSC. The heat transfer coefficient (HTC) of the ALSC is 14.0&amp;#37; &amp;#126; 18.3&amp;#37; higher than that of the ULSC. Compared with the ULSC, the ALSC has lower pressure drop and higher unit coefficient of performance. The differences of HTC of the first three tube passes of the ALSC are no more than 9.8&amp;#37; under different heat loads, which proves that the ALSC has good adaptability.

Multipass hollow fiber membrane modules for membrane distillation

Membrane distillation (MD) is an interesting process for desalination; however high thermal energy consumption remains one of the main obstacles in its widespread adoption. The current study presents multipass hollow fiber membrane modules to improve thermal efficiency of MD process. Fundamentally three module designs are considered: conventional one shell and one tube (fiber) pass (A), 1 shell and multiple tube passes (B/C) and equal but multiple shell and tube passes (D). The performance of the proposed designs is analyzed as a function of length of each pass, number of passes and operating conditions by using Aspen Plus simulator. The results demonstrate that the traditional design A yields the highest flux — up to 92 % higher than the multipass design D. On the other hand, the multipass design D is the most energy efficiency and shows up to 35 % less thermal energy consumption than the conventional single pass design of the same length. Single shell and multiple tube pass designs (B/C) show higher flux than D; however, their specific thermal energy consumption remains the highest among all the designs investigated. The pressure drop in multipass modules was marginally (1.5 %) higher than the conventional single pass modules.

A Comparison of Tracheal Intubation with Ambu® AuraGainTM, Fastrach® and BlockBuster® Laryngeal Mask Airway: A Randomised Clinical Trial

Introduction: Airway management has been a key to quality, efficacy and safety of anaesthesia. The Ambu® AuraGain™ is an anatomically curved Supraglottic Airway Device (SAD), which has gastric access port and is used for both ventilation and endotracheal intubation. Fastrach® Intubating Laryngeal Mask Airway (FT-LMA) serves as a conduit for intubation and ventilation for difficult airway situation. It has an epiglottic elevating bar designed to lift the epiglottis as endotracheal tube passes. BlockBuster® LMA is latest generation LMA used for ventilation and intubation. It has a short airway tube which has &gt; 95° angulation to match the oropharyngeal curve and thus makes the insertion easy and less traumatic. Aim: To compare first attempt success rate of tracheal intubation using Ambu® AuraGain™, Fastrach® and BlockBuster® LMA in adult patients. Materials and Methods: The present randomised clinical trial was conducted in the Department of Anaesthesiology, Ravindra Nath Tagore Medical College, Udaipur, Rajasthan, India from February 2021 to February 2022. The study comprised of 135 ASA physical status I and II patients of both sex, aged 18-60 years who were admitted and scheduled for elective surgery requiring general anaesthesia and tracheal intubation. The patients were randomly assigned into three groups (45 in each) - group A (Ambu® AuraGain™ group), group F (Fastrach® group), and group B (BlockBuster® group). Tracheal intubation was performed using appropriate size endotracheal tube after LMA placement. The outcome measures were first attempt successful intubation, time taken for intubation, glottis visualisation, and incidence of complications (blood stained LMA, nausea/vomiting). Results: The mean age of the group A, group B and group F were 35.8±15.0, 32.71±12.59, and 38.7.0±14 respectively which was statistically not significant. Group B had a significantly greater success rate of first attempt intubation (93.3%) in comparison with group F (64.4%), and group A (22.2%). LMA insertion score of 1 was found in 53.3% patients in group B, 42.2% patients in group F and 15.5% patients in group A. A Brimacombe score of 4 was found in 46.6% patients in group B as compared to 13.3% patients in group F and (33.3%) patients in group A, (p-value=0.020). Blood stained LMA was found in 1 patient in group B, 9 in group F and 7 in group A (p-value=0.030). Conclusion: BlockBuster® LMA is a better conduit for tracheal intubation than Fastrach® LMA and Ambu® AuraGain™ in adult patients with no anticipated airway difficulties.

The efficiency of number of tube passes of MSF heat exchanger materials for water desalination

Many parts of the globe need large amounts of water for agricultural, industrial, and residential purposes. The global scarcity of fresh water is becoming more apparent. For saltwater desalination, a variety of methods are employed, some of which use energy and others which utilise mechanical energy. Multistage Flash Evaporation (MSF) techniques are commonly used. Essentially, the process involves gradually heating saline water to a maximum working temperature of (90 °C) to (130 °C), then flashing it in a series of phases under increasingly decreasing pressure. Each stage's vapour is condensed with entering feed water through a heat exchanger. The impact of the number of tube passes in a heat exchanger on the efficiency of a (MSF) plant was investigated, and the findings were compared to those of a (MSF) plant (Sirte City MSF plant in Libya).

A trust region framework for heat exchanger network synthesis with detailed individual heat exchanger designs

We develop a trust region filter strategy for simultaneous optimal design of heat exchanger networks that includes detailed design of shell-and-tube heat exchangers. The strategy first solves a mixed-integer nonlinear programming (MINLP) formulation with shortcut models to generate candidate network topologies, which are then used in a non-isothermal mixing nonlinear programming (NLP) suboptimization with detailed optimal exchanger design models embedded using a modified trust region filter (TRF) algorithm. An integer cut based strategy is used to bound the solutions from MINLP and the NLP which aids in convergence to the solution of the overall simultaneous design problem. Under assumptions, the TRF based strategy can guarantee convergence to near optimal solutions of the overall design problem. The presented solution strategy is thus able to find optimal heat exchanger network designs based on the simultaneous optimization of the network topology and mass and energy balances, together with detailed shell-and-tube heat exchanger optimization, including the number of shell and tube passes, pressure drops, and tubes, tube lengths, etc. The proposed strategy is tested on three literature based case studies and their results are compared with previous studies to showcase its performance.

Globally optimal design of kettle vaporizers

This article addresses the globally optimal design of kettle vaporizers. Established procedures are heuristics-based trial and verification as well as optimization-based that do not guarantee global optimality. The proposed optimization formulation aims at minimizing heat transfer area; the optimal set of the design variables are the tube length and diameter, number of tube passes, tube layout and pitch, and shell diameter. The problem is solved using Set Trimming, an optimization technique that employs the inequality constraints to gradually reduce the search space until only the feasible candidates remain. After the Set Trimming is performed, the globally optimal solution can be readily found through a simple inspection along the set of remaining viable candidate solutions. This approach has important advantages: it attains the global optimum solution without the need of initial values, there is no convergence drawbacks and it is fast. The performance of the proposed approach is illustrated by its comparison with four different stochastic methods.

Economic optimization of heat exchanger networks based on geometric parameters using hybrid genetic-particle swarm algorithm technique

PurposeThe purpose of this study is to provide a method for designing the shell and tube heat exchangers and examine the total annual cost of heat exchanger networks from the economic view based on the careful design of equipment.Design/methodology/approachAccurate evaluation of heat exchanger networks performance depends on detailed models of heat exchangers design. The simulations variables include nine design variables such as flow direction determination of each of the two fluids, number of tubes, number of tube passes, length of tubes, the arrangement of tubes, size and percentage of baffle cut, tube diameter and tube pitch. The optimal designing of the heat exchangers is based on geometrical and hydraulic modeling and using a hybrid genetic particle swarm optimization algorithm (PSO-GA) technique. In this paper, optimization and minimization of the total annual cost of heat exchanger networks are considered as the objective function.FindingsIn this study, a fast and reliable method is used to simulate, optimize design parameters and evaluate heat transfer enhancement. PSO-GA algorithms have been used to minimize the total annual cost, which includes investment costs of heat exchangers and pumps, operating costs (pumping) and energy costs for utilities. Three case studies of four, six and nine streams are selected to demonstrate the accuracy of the method. Reductions of 0.55%, 23.5% and 14.78% are obtained in total annual cost for the selected streams, respectively.Originality/valueIn the present study, a reliable method is used to simulate and optimize design parameters and the economic optimization of the heat exchanger networks. Taking into account the importance of shell and tube heat exchangers in industrial applications and the complexity in their geometry, the PSO-GA methodology is adopted to obtain an optimal geometric configuration. The total annual cost is chosen as the objective function. Applying this technique to case studies demonstrates its ability to accurately design heat exchangers to optimize the objective function of the heat exchanger networks by giving the detail of design.

CFD analysis of an economizer for heat transfer enhancement using serrated finned tube equipped with variable fin segments

Due to the extensive use of heat exchangers in various daily and industrial applications, the improvement of their performances is of great importance. It is evident from the literature that very limited work has been done in serrated finned tube economizer for heat transfer enhancement and pressure drop performance. This paper deals with the heat transfer improvement and pressure drop performance of helical serrated finned tube bundles in inline bare tube counter cross-flow water tube boiler Economizer, which has larger heat transfer area and higher heat exchange efficiency. Numerical simulation on heat transfer performance is carried out on 116.3 TPH of MCR boiler unit, one tube row with three-row finned tube passes; helically wound fin geometries of partially serrated finned tubes are investigated. A steady-state approach, with two-equation, a k-ε turbulence model is employed to examine the effect of Reynolds number in the range of 8000 to 20000. In this study the conjugate heat transfer is considered for the calculation of the conduction in a solid region is coupled with the calculation of the temperature distribution in the working fluid flowing over or through this solid region. The effect of a number of serrated segmented finned tubes per period on the performance of heat transfer enhancement is also investigated. The computational results fall within the range of values predicted by empirical correlation. The results show that the heat transfer is enhanced by up to 3.53% to 5.14% if the number of segments per period varied from 20 to 50.

Polymer based phase change material for photo-thermal utilization

Phase change materials are widely used as thermal capacitors in solar thermal systems. The phase change materials with carbon materials could directly absorb the solar energy and transfer to water for building heating, while are rarely reported. In this work, an Ethylene-Propylene-Diene Monomer based phase change material with expanded graphite is prepared. The photo-thermal performance of the phase change material is investigated with combined experimental and numerical method. The SiO2 aerogel is first used as the thermal insulator in the solar thermal systems with the high transmittance and low thermal conductivity. The effect of the phase change material height and tube passes number on the photo-thermal performance of the phase change materials are calculated. The results show that the new material has a tensile strength of 3.6 MPa, enthalpy of 126.8 J g−1，and thermal conductivity of 1.106 W m−1 K−1. The phase change material with SiO2 aerogel could resist heat lost on the surface. The phase change material has good photo-thermal performance in solar thermal systems, could heat more than 200 L of hot water at daytime.

Heat exchanger network synthesis with detailed exchanger designs: Part 1. A discretized differential algebraic equation model for shell and tube heat exchanger design

AbstractA new method for the detailed design of shell and tube heat exchangers is presented through the formulation of coupled differential heat equations, along with algebraic equations for design variables. Heat exchanger design components (tube passes, baffles, and shells) are used to discretize the differential equations and are solved simultaneously with the algebraic design equations. The coupled differential algebraic equation (DAE) system is suitable for numerical optimization as it replaces the nonsmooth log mean temperature difference (LMTD) term. Discrete decisions regarding the number of shells, fluid allocation, tube sizes, and number of baffles are determined by solving an LMTD‐based method iteratively. The resulting heat exchanger topology is then used to discretize the detailed DAE model, which is solved as a nonlinear programming model to obtain the detailed exchanger design by minimizing an economic objective function through varying the tube length. The DAE model also provides the stream temperature profiles inside the exchanger simultaneously with the detailed design. It is observed that the DAE model results are almost equal to the LMTD‐based design model for one‐shell heat exchangers with constant stream properties but shows significant differences when streams properties are allowed to vary with temperature or the number of shells are increased. The accuracy of the solutions and the required computational costs show that the model is well suited for solving heat exchanger network synthesis problems combined with detailed exchanger designs, which is demonstrated in Part 2 of the paper.

Solar-driven melting dynamics in a shell and tube thermal energy store: An experimental analysis

The integration of an array of two evacuated-tube solar collectors with a latent thermal energy storage system has been accomplished, in order to study the heat transfer characteristics during solar-driven melting. A shell-and-tube heat exchanger is employed for energy storage purposes, using 30 kg of paraffin RT70HC in the shell side. A tube bundle uniformly distributed accommodates 12 tube passes, allowing a total mass flow of 100–1000 kg/h of water for inducing turbulent-flow in the tube side. A Coriolis flowmeter is employed for measuring the mass flow through the tubes, and PT100 temperature sensors are used for measuring the inlet and exit temperature of the heat transfer fluid. Outside wall temperature is measured in different cross-sections of the tubes using T-type thermocouples, which capture the buoyancy plume of the PCM induced over the tubes during phase change. Vertical and horizontal temperature probe arrays in the shell characterize the thermal stratification that occurs during melting. Liquid fraction and energy storage during three different scenarios of solar irradiance are computed. The relation between the primary energy source and the heat transfer dynamics of the LTES are described, considering the constraints in terms of maximum PCM operating temperature and achievable liquid fraction.

Heat exchanger optimization of a domestic refrigerator with separate cooling circuits

In this study, the effects of evaporator type and geometry, capillary tube diameter and capillary length on the cooling system performance and energy consumption in the bypass two-circuit cycle have been examined experimentally. In the experiments, wire on tube and finned tube evaporators were used in the fresh food compartment of a 500 L top mount freezer refrigerator. 0.66 mm and 0.8 mm capillary tube diameters and 3000 mm and 3500 mm capillary tube lengths were selected as other design parameters. Experiments were performed according to IEC 62552 household refrigerating appliances standard at 25 °C ambient temperature when the average temperature of the fresh food compartment is set to 5 °C and the warmest temperature of the freezer compartment is −18 °C. The Design of Experiments (DOE) technique which is a six sigma method has been used to determine simultaneously the individual and combined effects of parameters on the refrigerator performance. General linear model method, which is a useful framework for comparing how several variables affect different continuous variables, was chosen to identify the effectiveness of the parameters. According to the experimental results, it was found that the most effective parameter of the system is the evaporator type. Finned tube evaporator with 12 tube passes were found the best option for the bypass two-circuit refrigeration cycle among the 8 different options. The optimum cooling performance and the lowest energy consumption were provided with 0.66 mm capillary tube diameter and 3500 mm capillary tube length in the experiments.

The effects of component dimensions on heat transfer and pressure loss in shell and tube heat exchangers

ABSTRACTIn this study, the effects of geometric properties such as baffle spacing, baffle cut, sealing strips, gaps between heat exchanger components, number of tubes and tube passes have been investigated for shell and tube heat exchangers (STHE). For this purpose, geometrical dimensions and data of a specific heat exchanger (HE) used in an industrial application have been obtained. The HTRI Xchanger Suite Educational software was utilized to analyze the reference HE, to verify the results of the software and the output temperatures of the fluids, the shell side heat transfer coefficient (HTC) and the pressure loss (PL) values were compared with the experimental data. After confirming that the results of the software were within the acceptable deviation values, the geometric dimensions of the reference design were changed and new analyzes were carried out to examine the effects of several dimension options on the performance of STHE. Results were discussed in a detailed and comprehensive manner via curves.

Dynamic and steady state performance model of fire tube boilers with different turn boxes

The market for fire tube boilers is increasingly demanding custom designs from the manufacturers. For these new designs, a comprehensive thermal model is needed. In this article, both a steady state and dynamic thermal model is developed based on the plug flow furnace model with general experimental correlations. The steady state model allows optimizing (i.e. safely downsizing) boiler designs. This model has been verified with measurement reports. The dynamic model is used to estimate the peak load capability of a boiler. In the presented case, the fire tube boiler can produce up to 2.5 times the nominal steam flow rate for a period of 10 min. Special attention has been paid to the turn boxes and their specific placement, which other models in literature neglect. The efficiency penalty of a non-submerged turn box can reach up to 12% but can be reduced significantly by insulation. Turn boxes also affect peak load capability. If the total length of the boiler is constant, submerging the turn box has a positive effect on the peak load capability. This effect is mostly attributed to the increased water volume. Finally, the article includes a comparison between the plug flow furnace model the ε-NTU method and the ε-NTU method with inclusion of radiation to model the tube passes. The ε-NTU method with inclusion of radiation allows to significantly reduce the necessary number of control volumes without reduction in the model accuracy.

Multi-objective optimization of the basic and single-stage Organic Rankine Cycles utilizing a low-grade heat source

This study deals with the multi-objective optimization of basic and single-stage Organic Rankine Cycles (ORC) utilizing a low-grade heat source. Twelve different isentropic and dry pure refrigerants are considered as the primary working fluid for two different ORC configurations. Specific Investment Cost (SIC) and second law efficiency of the thermodynamic cycle are considered for optimization objectives to be optimized seperately and concurrently. Sixteen and twenty two different decision variables are respectively taken into account for modeling of the basic and the single-stage ORC optimization problems. The optimization problem is solved by applying a swarm based metaheuristic optimizer called Artificial Cooperative Search (ACS) algorithm. A pareto curve comprised of non dominated optimal solutions is constructed for each refrigerant-cycle pair and the best answer among the set of non dominated solutions are chosen by means of TOPSIS decision making method. Thermodynamic performance of each refrigerant are evaluated with respect to numerical outcomes of the objective functions. Comparative analysis based on the efficiencies of problem objectives reveals that R236ea, R245fa and R600 are selected as the best performers of the basic ORC and R245ca, R245fa and R600 are selected as the best performers of the single-stage ORC. Finally, a sensitivity analysis is executed to observe the effect of the decision variables on the objectives. It is understood that the evaporator shell diameter, number of tube passes in the evaporator, evaporator pressure and mass flow rate of the refrigerant are the decision variables with the most influence on the design objectives.

Effect of Al2O3/water nanofluid on performance of parallel flow heat exchangers

A comprehensive experimental investigation is intended to survey consequence of nanofluid on performance of sundry parallel flow heat exchangers with the same heat transfer surface area. An experimental setup including one double-pipe heat exchanger, two shell-and-tube heat exchangers with different tube passes, and one plate heat exchanger is designed and built to carry out the experiments. The experiments are performed under turbulent flow conditions using distilled water and Al2O3/water nanofluid with 0.2, 0.5, and 1% particle volume concentrations. Based on the results from this study, the double-pipe heat exchanger reflected the best outcomes in the heat transfer coefficient with a maximum enhancement of 26%, while only a 7% increment in the heat transfer coefficient is observed for the plate heat exchanger. On the other hand, minimum punishment for pressure drop of the working fluids due to adding the nanoparticles is observed in the plate heat exchanger at 1% volume concentration with a maximum value of 10%.