Heat Transfer Duty Research Articles

Heat integration analysis based on recycle split vapor ethane recovery process

AbstractRecovering ethane from natural gas involves significant energy consumption. Globally, the recycle split vapor process (RSV) is widely adopted as an efficient method for ethane recovery. Nonetheless, one major challenge faced by the RSV process is the lack of adequate heat integration, despite its overall effectiveness. In this article, we investigate the heat integration of the RSV process and propose two novel ethane recovery processes: the recycle split vapor process with direct heat integration of the feed gas (RSV‐DTI) and the recycle split vapor process with split heat integration of the feed gas (RSV‐SHI). A comparative analysis is conducted among these three processes, focusing on integrated energy consumption, exergy efficiency, and economic investment. The study's findings reveal the following: (1) The RSV‐DTI process distinguishes itself with its reduced energy consumption, enhanced stability, and minimized refrigerant usage. In comparison to the RSV process, the RSV‐DTI process achieves a reduction of over 15% in total compression duty and a remarkable decrease of 68% in propane usage. (2) Electricity emerges as the predominant energy consumed in the ethane recovery process, and the RSV‐DTI process significantly improves upon this aspect. Notably, the RSV‐DTI process incurs the lowest investment cost, yielding a swift payback period of approximately 1 year for the plant. The characteristics of the RSV‐DTI process are investigated, and the effect of changes in feed gas conditions on the heat integration of the RSV‐DTI process is analyzed. The characteristics of the RSV‐DTI process show the following: (1) Different pressures of feed gas existing in the main cold box have different minimum heat integration temperatures (MHIT). When the feed gas temperature is lower than the MHIT, heat integration becomes difficult, and the heat energy can be supplied by hot liquid propane at 48°C. When the feed gas temperature is higher than the MHIT, changes in feed gas temperature have little effect on the process, only affecting the external gas temperature. (2) The heat transfer duty of the demethanizer sideline outlet stream is affected by the feed gas pressure. To enhance heat integration, it is recommended to set the heat transfer duty of the low‐temperature sideline outlet stream (DLTSS) between 40% and 90% of the reboiler duty and the heat transfer duty of the high‐temperature sideline outlet stream (DHTSS) between 40% and 75% of the reboiler duty.

Theoretical and experimental study on a novel evaluation criteria of heat exchangers applied in aero engines

For the application of heat exchangers in the aeronautic field, an effective evaluation method is required to support the satisfaction of the multi-aspect design restrictions including the thermal and hydraulic performance, occupied volume, total weight, etc. To weigh the benefit and cost for both heat transfer units and heat exchangers, this study thus proposes three evaluation indexes Rp, RV, and Rm defined by the product of heat transfer coefficient and heat transfer area of unit windward area times pressure drop (hA/(AfrontΔp)), that of unit volume (hA/V) and that of unit weight (hA/m). Considering the factors h and A comprehensively and excluding the influence of mean differential temperature, the three indexes can reflect the low flow resistance, compactness, and lightness characteristics under fixed operating conditions and heat transfer duty requirement accordingly. A validation experiment is carried out and the deviation between the evaluation and experiment results is less than 10.88% for the three indexes. To show the applicability, a detailed evaluation of six different heat transfer units and five types of heat exchangers is conducted. A heat transfer unit selection method based on the new indexes is provided finally for heat exchanger design.

Analytical model for extremum analysis of moistened fins involving all nonlinear energy exchange processes

Dehumidification on a fin surface happens when the thermal interface state maintains an undervalue corresponding to saturation condition, and a temperature boundary layer develops during heat transmission. The local thickness of the temperature boundary layer changes, and consequently, sensible and latent heat transfer coefficients become highly non-uniform. In this study, a new mathematical procedure depending on the Adomian decomposition method (ADM) is established to predict the heat transfer duty from a moistened fin where all heat transfer modes involved are functions of temperature. A cubic algebraic equation for connecting the specific humidity of air and the thermal state level of a fin is closer to the actual relation determined based on the regression analysis, which converts the governing equation into a highly nonlinear character. The present model has no restriction using the fractional power factor of temperature-dependent convection coefficients. The current results highlight that the variable convection coefficients decrease both the fin performance index and heat load rate, and this influence becomes significant at the optimum design condition. Therefore, establishing the optimum state of a fin adopting all the variability events in the practical design system is essential for the correct analysis. As the equipment implementation analysis always requires an extremum study, the proposed research will help to predict the optimum information in the practical design with the highest accurate prediction of results.

SIMULASI PERUBAHAN BEBAN PEMBANGKIT LISTRIK TENAGA UAP: STUDI KASUS DI GORONTALO UTARA

Conceptual and design studies on 25 MW Northen Gorontalo steam based power plant are carried out under the existing comissioning data at four different load. The urgency of this study is related with supporting the prevention of greenhouse gass emission and completing indonesian power plant energy map. This observation conducted by simulating those condition in Gatecycle software and analyzing the output parameter to determine the power plant performance specifically heat rate, heat transfer duty, efficiency, power generated and fuel consumption.The study outcomes shows that heat rate at 50% TMCR was increased as much as 50 kcal/kwh as the load ramped down indicating power plant requires more energy to generate similar amount of power. While the fuel consumption, power, and efficiency proportionally werer increased as the power plant load ramping up. Comparing thirteen equipments heat transfer, condenser was conducting the highest heat transfer duty followed by boiler and first stage of superheater.

Study of nuclear reactor external vessel passive cooling using computational fluid dynamics

Nuclear energy has recently re-gained support as a reliable source of carbon-free electricity. However, the safety of nuclear plants is still questioned, particularly in the wake of the tragic events in Fukushima. In response to this, the adoption of passive safety systems, providing cooling to the plant even in the absence of any active power, has been accelerated. However, the confident assessment of their effectiveness is still constrained by the large spatial scales involved, which makes experimental validation difficult and expensive. Additionally, the many complexities intrinsic to the prediction of natural convection makes the mathematical modelling of such systems problematic. In this paper, the development of computational fluid dynamics (CFD) as a reliable method to ultimately prove, and eventually improve, the passive safety features of reactors is described. The focus of the paper is external reactor vessel cooling. In the case of a reactor core melting, the core is kept inside the reactor vessel, which is cooled from the outside by natural convection after flooding the region of the containment that houses the vessel. More specifically, a recent experiment that simulates, at a reduced scale, cooling of the horizontal calandria vessel of a pressurized heavy water reactor, submerged in a water pool, is modelled using CFD. For this situation, of major relevance is the correct prediction of boiling on the external surface of the reactor vessel, and thermal stratification in the water pool, which could prevent lower regions of the pool from performing any heat transfer duty. Results from standard Reynolds-averaged Navier-Stokes based turbulent flow simulations demonstrate that more advanced models are needed for accurate simulation, specifically in view of the excessive mixing predicted by such approaches. In contrast, the development of a more advanced tool based on large eddy simulation (LES) is started from the prediction of thermal stratification in the water pool, for which good accuracy is demonstrated through comparisons with available data. Although further improvements are needed, and discussed, it is demonstrated that LES can provide a reliable tool for the analysis and design of passive safety systems and strategies, and the assessment of passive cooling effectiveness and reactor safety. Although computational effort remains the main constraint in using LES, computation times are not prohibitive, particularly given the continual increase in available computing resources.

Thermohydraulic characteristics of a micro plate heat exchanger operated with nanofluid considering different nanoparticle shapes

Improvement in thermal performance of plate heat exchangers is crucial, and nanoparticle shape can have significant effects on their efficiency in the case of using nanofluids as working fluid. In the current contribution, the thermal and hydraulic attributes of a microchannel plate heat exchanger, using the boehmite alumina nanofluid in the hot fluid side and the pure water in the cold fluid side, are analyzed. The finite volume method is employed in the simulations. This investigation is performed for five particle shapes (i.e., platelet, brick, cylinder, blade, and oblate spheroid) at inlet temperature of 90 °C and Reynolds number of 500 for the hot fluid side. In the cold fluid side, three inlet temperatures (i.e., 10, 20, and 30 °C) and three Reynolds numbers (i.e., 500, 1000, and 1500) are considered. The nanoparticle concentration is considered constant (φ = 1%) for all the particle shapes. The nanofluid having the platelet-shaped particles results in the maximum overall heat transfer coefficient (U) and heat transfer duty (q), followed by the suspensions containing the cylinder-, blade-, brick-, and Os-shaped particles, respectively. Moreover, the nanofluid having the Os-shaped particles leads to the highest effectiveness, followed by the suspensions with the brick-, blade-, cylinder-, and platelet-shaped nanoparticles, respectively. Additionally, by diminishing the inlet temperature of the cold water, the performance index and q enhance for all the nanoparticle shapes. Besides, by elevating the Reynolds number, the pressure loss, effectiveness, heat transfer rate, and U increase. The main novelty of this investigation is to evaluate the effects of nanoparticle shape on the thermohydraulic performance of nanofluids in the micro plate heat exchanger.

Temperature setpoint-ramp control structure for batch reactors

Batch reactors can present challenging dynamic control problems because of the large nonlinear changes in process parameters during the batch cycle. Large reactant concentrations at the beginning of the batch produce fast reaction rates and large heat-transfer duties if the reactor temperature is increased too rapidly from its low initial temperature. Exothermic reactions can lead to reactor runaways that exceed maximum temperature/pressure safety constraints. Several papers have studied sophisticated techniques for detecting the potential of an impending runaway and taking corrective action. A complex stability criterion embedded in a model predictive control structure is a recent suggestion for handling the problem.This paper discusses a simple practical technique that has been used in industry for decades. The setpoint of a temperature/pressure controller is ramped up at a reasonable rate, but if the demand for coolant increases too much, the ramp is stopped until the demand for control effort drops down to a normal level.

Design of plate-fin surfaces for multi-fluid heat exchanger applications

Amidst the various design approaches available for the design of plate-fin heat exchangers for multi-fluid applications, are those based on the segmentation of the exchanger length into blocks that correspond to the enthalpy intervals in the Composite Curves. Such methods are characterized by three main features: identification of exchanger sections, surface selection from among the available types, and reconciliation of dimensions by pressure drop relaxation. The work presented in this paper introduces new concepts and removes some limitations in earlier approaches. In the first place, it reduces the number of block sections when the space between them is too short to fit intermediate headers along the length of the exchanger. Additionally, it introduces the concept of surface design as an aid to fulfil the heat transfer duties. Finally, it allows the design to meet fixed dimensions as design objective together with the heat duty within the limitations imposed by the pressure drop. The approach is demonstrated using a case study solved by different authors in the open literature. It is shown that the number of block sections is reduced from 3 to 2.

Self-cleaning compact heat exchangers: The role of two-phase flow patterns in design and optimization

Fouling on heat exchanger surfaces significantly impedes heat recovery from exhaust gases in many industrial applications. An introduction of the process of self-cleaning possibly represents an efficient solution to this well-known problem. Even if special treatments of the surfaces can help to protect them from fouling, it is still not well understood how to properly design heat exchangers in order to promote the self-cleaning process. In the present study, we investigate by means of Lattice-Boltzmann-based simulations the pivotal role of two-phase flow patterns and condensation-related phenomena in understanding the mechanisms that promote the self-cleaning, and, consequently, a stable heat recovery. In particular, we identify optimal flow conditions and two-phase flow characteristics that allow a clean and efficient operation of compact heat exchangers. Our results indicate that low heat duties and flow rates, which induce the condensation of small and motile droplets able to collect gas impurities, are beneficial for provoking and sustaining self-cleaning mechanisms. We therefore suggest that an effective design of self-cleaning heat exchangers should primarily be governed by principles of two-phase flow, rather than by the heat transfer duty. This work thus represents a step forward in identifying and proposing a procedure for an optimal design of heat exchangers to facilitate an effective heat recovery process from a wider range of exhaust gas mixtures.

Natural convection heat transfer in a power-law fluid from a heated rotating cylinder in a square duct

Laminar natural convection heat transfer in a power-law fluid from an isothermal rotating cylinder placed coaxially in a square duct has been studied numerically over the following ranges of conditions: Grashof number (10⩽Gr⩽103); Prandtl number (0.72⩽Pr⩽100); power-law index (0.2⩽n⩽1.5) and non-dimensional rotational velocity (0⩽S⩽4). The spatial variation of the velocity and temperature fields are visualised in terms of the streamline and isotherm patterns, and temperature and vertical velocity at a few locations, respectively. Indeed, a range of flow patterns including twin-celled and single-celled recirculating regions can be observed depending upon the relative strengths of the buoyancy-induced and forced flow. The rate of heat transfer is described in terms of the distribution of the local Nusselt number over the surface of the cylinder together with its surface averaged value. As expected, the mean Nusselt number shows a positive dependence on the both Grashof and Prandtl numbers irrespective of the values of the power-law index and rotational velocity. For a non-rotating cylinder (S = 0), shear-thinning fluid behaviour promotes heat transfer, whereas shear-thickening viscosity impedes it with reference to that in Newtonian fluids otherwise under identical conditions. For the case of a rotating cylinder (S≠0), the rotation has positive influence on the rate of heat transfer at low values of the Grashof or Rayleigh number (Ra<500) irrespective of the type of fluid behaviour, i.e., shear-thinning or shear-thickening or Newtonian. However, at high values of the Grashof or Rayleigh numbers, the gradual increase of rotation of the cylinder first lowers the rate of heat transfer, and then increases it for shear-thickening (n > 1) and Newtonian fluids (n = 1). On the other hand, a reverse trend is seen for shear-thinning fluids. These non-monotonous trends in the overall heat transfer stem from the interactions between the rate of variation of the fluid viscosity and the temperature gradient on the surface of the cylinder. Therefore, a prudent choice of the operating conditions and the fluid behaviour can be used to regulate the rate of heating or cooling from a rotating cylinder. Finally, the present values of the average Nusselt number are correlated in order to facilitate the interpolation of the present results for the intermediate values of Gr, Pr, S and n and/or the estimation of heat transfer duty in a new application.

A collaborative optimization method for heat transfer systems based on the heat current method and entransy dissipation extremum principle

Optimization of the heat transfer system (HTS) plays an important role in energy utilization fields. However, two aspects of HTS optimization: local optimization for components and system global optimization, are generally performed independently, thus a combination of them is required. This contribution proposes a collaborative optimization strategy for HTS and minimizes the total pumping power consumption for a typical HTS. The global optimization employs the heat current method to derive global optimum results without redundant intermediate variables, and the local optimization applies the CFD-based simulation and the entransy dissipation extremum principle which obtains the optimum flow field directly. Besides, these two parts are integrated by the iteration and updating strategy with an optimization platform. Results present local optimization of components and global optimization of the HTS influence each other. As the heat transfer duty of the HTS increases, the minimum pumping power consumption, optimal frequencies of pumps and mass flow rates increase simultaneously. However, due to the performance improvement of the convective heat transfer process in the evaporator, it requires less increment of mass flow rate. That is, the global optimization of the HTS not only requires system and component optimization but also requires an efficient collaborative optimization strategy.

Troubleshooting a Thermosiphon Reboiler – Why New Is Not Always Better than Old

During an ethylene plant turn-around, a 38-year-old tube bundle of a vertical thermosiphon reboiler was replaced with a new, seemingly identical one. However, when the plant returned to full operation after the turn-around, the reboiler was not able to reach the same duty as the old tube bundle.Systematic troubleshooting using detailed column and thermosiphon simulation, neutron backscatter, plant data reconciliation and flow regime analysis ruled out possible reasons such as thermosiphon inlet line plugging, or lowered heat transfer due to steam superheat, or the presence of non-condensables in the steam, leaving reduced heat transfer on the tube side as the strongest suspect.To avoid plant shut-down, the issue was temporarily solved by switching from low pressure (1.6 barg) to medium pressure (7.2 barg) steam as heating medium. With the higher steam pressure and increased ?T across the exchanger the original duty was successfully recovered.To investigate the reduced heat transfer, light, laser and electron microscopy studies revealed that the surfaces of old and new reboiler tubes were very different in roughness and cleanliness, causing differing heat transfer characteristics. The gradual degradation of the tube surface, which occurred over the years, is believed to have increased the maximum heat transfer duty of the old reboiler. This theory is supported by a report from the old tube bundle’s first year of operation when similar capacity problems occurred.

Optimal synthesis of compression refrigeration system using a novel MINLP approach

Abstract The optimal design of a compression refrigeration system (CRS) with multiple temperature levels is very important to chemical process industries and also represents considerable challenges in process systems engineering. In this paper, a general methodology for the optimal synthesis of the CRS, which simultaneously integrates CRS and Heat Exchanger Networks (HEN) to minimize the total compressor shaft work consumption based on an MINLP model, has been proposed. The major contribution of this method is in addressing the optimal design of refrigeration cycle with variable refrigeration temperature levels. The method can be used to make major decisions in the CRS design, such as the number of levels, temperature levels, and heat transfer duties. The performance of the developed methodology has been illustrated with a case study of an ethylene CRS in an industrial ethylene plant, and the optimal solution has been examined by rigorous simulations in Aspen Plus to verify its feasibility and consistency.

Modeling and simulation of an integrated steam reforming and nuclear heat system

In this study, a dynamic and two-dimensional model for a steam methane reforming process integrated with nuclear heat production is developed. The model is based on first principles and considers the conservation of mass, momentum and energy within the system. The model is multi-scale, considering both bulk gas effects as well as spatial differences within the catalyst particles. Very few model parameters need to be fit based on the design specifications reported in the literature. The resulting model fits the reported design conditions of two separate pilot-scale studies (ranging from 0.4 to 10 MW heat transfer duty). A sensitivity analysis indicated that disturbances in the helium feed conditions significantly affect the system, but the overall system performance only changes slightly even for the large changes in the value of the most uncertain parameters.

Design of A Single Tube Fuel Oil Preheater

ABSTRACTThis article presents design analysis of a fuel oil preheater. The preheater is a concentric tube heat exchanger where the fuel oil is on the tube-side and the heating medium flows in the annular space. Two situations were addressed in this study. In the first case, an analytical model was developed where the required heat exchanger length, diameter and the fluid velocity were determined for a given heat transfer duty and for an allowable pressure loss. A detailed study was conducted by individually varying parameters such as pressure loss, preheater discharge temperature, and mass flow rate of the fuel oil. In each instance their influence on the predicted design of the heat exchanger was investigated. In the second case, an optimization strategy was proposed for a certain heat transfer duty. The heat exchanger dimensions and the fluid flow rate were selected such that the annual operating cost of the heat exchanger was minimized. In addition, a detailed study was conducted to understand the total annual operating cost as a function of the fuel oil outlet temperature and the fuel oil mass flow rate.

Pilot plant study for effective heat transfer area of coiled flow inverter

Three new coiled flow inverter (CFI) heat exchangers with heat transfer area (At) of 0.88m2 (4-banks), 0.44m2 (2-banks) and 0.22m2 (1-bank) were designed, fabricated and commissioned to develop a more compact heat exchanger. More than 800 experiments were carried-out in counter-flow configuration. The hot and cold fluids were used in the tube and shell side of CFI heat exchanger, respectively. Tube side flow rates were varied from 50–300kg/h for water and 30–100kg/h for compressed air, respectively. The shell side flow rates were varied from 100–2000kg/h for water and 400–750kg/h for air, respectively. The overall heat transfer coefficients of present CFI heat exchangers were found in good agreement with the results reported for the CFI heat exchangers of At=1.76m2. The proposed CFI heat exchanger with At=0.22m2 provides 2.2–4.5 and 2–3.6 times higher overall heat transfer coefficient as compared to SHE and PHE of At=1.76m2, respectively. The present study offers a small footprint CFI heat exchanger to meet the same heat transfer duty as compared to previously reported study.

Effects of psychrometric properties on fin performances of minimum envelope shape of wet fins

A method based on the variational principle is used to determine a minimum shape of wet fins for effective transfer of heat in fins. In many air-cooling applications, fin surface becomes wet as the surface is lower than the dewpoint temperature of the surrounding air. On the wet surface, both the sensible and latent heat transfer take place due to an existence of respective driving forces. The fin temperature is also dependent upon the latent heat released on its surface from the condensed moisture. The humidity ratio of air adjacent to the fin surface for the latent heat transfer is a psychrometric function with temperature. Due to this, the analysis of wet fins is always difficult as the governing fin equation is complex in nature. A simple model based on a linearity function between humidity ratio and temperature has been an alternative approximate model. The present analysis is attempted to estimate an envelope shape of wet fins by minimising fin volume for a constraint heat transfer rate for an actual variation of humidity ratio with temperature. The effect of psychrometric properties of air on the minimum shape of wet fins has been studied in the present work. The fin performance for the least envelope shape of wet fins is proposed with the variation of thermo-psychrometric parameters. A comparison of results for the variation of linear and nonlinear humidity ratio with temperature on the analysis of the minimum envelope shape has been systematically investigated. This study is also highlighted errors in connection with the linear model to determine the least fin shape for efficient heat transfer. This analysis may be extremely important in those augmentation heat transfer apparatuses where a gain in weight creates always an excessive overburden. Due to this, the selection of the function of humidity ratio as a fin surface temperature may be extremely important for calculating minimum weight of a fin for the same heat transfer duty.

Flow and heat transfer enhancement in tube heat exchangers

The performance of heat exchangers can be improved to perform a certain heat-transfer duty by heat transfer enhancement techniques. Enhancement techniques can be divided into two categories: passive and active. Active methods require external power, such as electric or acoustic field, mechanical devices, or surface vibration, whereas passive methods do not require external power but make use of a special surface geometry or fluid additive which cause heat transfer enhancement. The majority of commercially interesting enhancement techniques are passive ones. This paper presents a review of published works on the characteristics of heat transfer and flow in finned tube heat exchangers of the existing patterns. The review considers plain, louvered, slit, wavy, annular, longitudinal, and serrated fins. This review can be indicated by the status of the research in this area which is important. The comparison of finned tubes heat exchangers shows that those with slit, plain, and wavy finned tubes have the highest values of area goodness factor while the heat exchanger with annular fin shows the lowest. A better heat transfer coefficient ha is found for a heat exchanger with louvered finned and thus should be regarded as the most efficient one, at fixed pumping power per heat transfer area. This study points out that although numerous studies have been conducted on the characteristics of flow and heat transfer in round, elliptical, and flat tubes, studies on some types of streamlined-tubes shapes are limited, especially on wing-shaped tubes (Sayed Ahmed et al. in Heat Mass Transf 50: 1091–1102, 2014; in Heat Mass Transf 51: 1001–1016, 2015). It is recommended that further detailed studies via numerical simulations and/or experimental investigations should be carried out, in the future, to put further insight to these fin designs.

Model demonstrates functional purpose of the nasal cycle.

BackgroundDespite the occurrence of the nasal cycle being well documented, the functional purpose of this phenomenon is not well understood. This investigation seeks to better understand the physiological objective of the nasal cycle in terms of airway health through the use of a computational nasal air-conditioning model.MethodA new state-variable heat and water mass transfer model is developed to predict airway surface liquid (ASL) hydration status within each nasal airway. Nasal geometry, based on in-vivo magnetic resonance imaging (MRI) data is used to apportion inter-nasal air flow.ResultsThe results demonstrate that the airway conducting the majority of the airflow also experiences a degree of ASL dehydration, as a consequence of undertaking the bulk of the heat and water mass transfer duties. In contrast, the reduced air conditioning demand within the other airway allows its ASL layer to remain sufficiently hydrated so as to support continuous mucociliary clearance.ConclusionsIt is quantitatively demonstrated in this work how the nasal cycle enables the upper airway to accommodate the contrasting roles of air conditioning and the removal of entrapped contaminants through fluctuation in airflow partitioning between each airway.

Modeling and experimental validation of a tube-in-tube refrigerant cooled absorber

A model for predicting heat and mass transfer and pressure drops occurring inside a tube-in-tube refrigerant cooled absorber (RCA) is developed. This heat exchanger is used as a low pressure absorber in a half-effect water-ammonia absorption chiller. The two-phase stream, resulting from the mixing at low pressure of the weak solution coming from the generator and the refrigerant leaving the evaporator, flows in the tube-in-tube annulus, while the stream of condensed refrigerant, throttled to a pressure level intermediate between condenser and evaporator pressures, flows counter-current in the internal tube. The RCA model is validated by comparing overall heat transfer duty, pressure drops on each stream and temperature axial profile in the annulus with experimental data. Results are in reasonable agreement with experiments in most of the analyzed cases, although some deviations exist in off-design operations. A sensitivity analysis of the model has shown that the measurement uncertainty of the inputs to the model does not affect the validity of the results.