Heat Exchange Section Research Articles

Numerical Simulation of Shell and Tube Heat Exchanger using Ansys Fluent

From the current situation, the Heat Exchangers uses extreme commonly are tube and Shell heat exchangers. The most usual uses of Shell and tube heat exchangers are electricity creation, cooling system of hydraulic fluid, oil in motors, transmissions, and hydraulic power packs. Shell and tube heat exchangers are made of the casing using a bunch of tubes with inside. The desirable outcome of the paper is to figure out the speed of heat transport using hot water as the hot liquid. The target of this paper is to mimic a tube and shell heat exchanger and also to assess blood flow and temperatures from the tubes and shell by employing applications tool Ansys. The simulation is composed of modeling and meshing cross section of tube and shell heat exchanger utilizing computational fluid dynamics (CFD).

A Model of Heat Transfer in Counter-Current Heat Exchanger with a Thermoelectric Cooling Element

In disregard of conductive transfer in heat-transfer agents and using the Newton- Richman law, a model of heat transfer in a counter-current exchanger with a thermoelectric cooling element. The heat transfer coefficient of the thermoelement branch, the average temperature of the heat-transfer agents at the entrance to the heat exchanger, as well as the average length of heat transfer between the coolant and the thermoelement are chosen as the conversion scales to dimensionless variables. The model is converted to a form containing only coolant temperatures, and the General solution of the model is obtained. The study of the model found that the cooling capacity of the heat exchanger varies along the flow of the coolant and with an increase in the density of the electric current becomes negative at the initial heat exchange section.

Analysis of a hybrid (topping/bottoming) ORC based CHP configuration integrating a new evaporator design concept for residential applications

The recommended design principles for the development of evaporators for ORC based micro-CHP systems attempting to retrofit the current combi-boilers are presented and discussed in this paper. From those principles, among which is the need of organic fluid direct vaporization, emerged a hybrid (topping/bottoming) CHP configuration in which the thermal energy is produced stepwise: firstly in the ORC-condenser and then in a post-heater, that is integrated on the ORC-evaporator, directly with the combustion gases. A model of this configuration was developed to determine the fraction of the CHP water heating process performed in the post-heater that maximizes the primary energy savings and ORC net power output for a wide range of CHP operating conditions. When compared to a standard CHP configuration, this solution show benefits for the greater part of those conditions. Besides solving the safety issue posed by the ORC-evaporator requirements and the performance benefits shown, this configuration has an additional positive side effect: the decrease of the combustion gases’ temperature before they reach the organic working fluid heat-exchanger section in the ORC-evaporator that leads to a reduction of the risk of the working fluid thermal degradation.

Thermal and Aerodynamic Researches of Staggered Bundles for Choice of an Effective Spacing of Round-Finned Tubes

The results of an experimental study of local modeling of convective heat transfer and aerodynamic resistance of staggered six-row bundles of bimetallic tubes with spiral knurled aluminum fins under transverse air flow in the range of its velocity alteration in a compressed bundle section of 1.9−11.0 m/s are presented. The velocity range covers the possible modes of operation of industrial air coolers (AVO). The fins with a diameter of approximately 57 mm are rolled on a steel supporting tube with an outer diameter of 25 mm. Tube finning ratio j = 19.26. Such tubes are widely used in the heat exchange sections of AVO of natural gas, in particular, at “Gribanovskii Engineering Plant” JSC (Russia). To measure the reduced heat transfer coefficients, an electric calorimeter had been developed by the authors with a power input of 600−1300 W. The temperature of the wall surface at the base of the fins did not exceed the range of 77–92 °C. The transverse tube spacing in bundles S1was 64.0 or 68.0 mm, while the longitudinal spacing S2 was 54.4 or 50.0 mm. The heat transfer of each transverse row of six-row bundles was measured, as well as the average heat transfer and aerodynamic drag, which are summarized by the similarity equation of a power type. The heat transfer rate of the last transverse row in the direction of air movement is 0–5 % lower than the heat transfer rate of the stabilized rows, and here new features of heat transfer variations in the insufficiently studied area of spacing changes S1 and S2 have been found. The thermal contact resistance (TCR) was measured in the range of the average temperature of the contact surfaces tк = (79–95) оС, and no dependence of the value of TCR on tк for the specified interval was found. The numerical average value of TCR was Rк = 2,13 × 10–4 m2×K/W, which is typical for reliable mechanical connection of the finned aluminum shell with the supporting steel tube made of carbon steel. The results of variant thermal and aerodynamic calculations with the use of the obtained data established the technical and economic feasibility of placing tubes at the vertices of an isosceles triangle with spacing S1 = 68–69 mm and S2 = 55 mm with failure to use the location of the tubes along an equilateral triangle with S1 = S2' = 64 mm (where S2' – is diagonal spacing). With Q = idem and other conditions being equal, the number of tubes on AVO decreases by 5.7 % with a decrease in power consumption to 4.0 %.

Experimental investigation of volumetric exergy transfer coefficient in vertical moving bed for sinter waste heat recovery

The volumetric exergy transfer coefficient of sinter bed layers in vertical tank for sinter waste heat recovery has been presented. Correlations involving relevant variables to predict the local and mean volumetric exergy transfer coefficient, Nusselt number and the non-dimensional exergy flux have been deduced by using the second law of thermodynamics and non-equilibrium thermodynamics theory. The relationships of the local and mean volumetric exergy Nusselt number with the local and mean volumetric heat transfer Nusselt number and Reynolds number are analyzed. The experimental results of exergy transfer characteristics in sinter moving bed with different cooling air flow rate and different sinter mass flow rate are obtained from a homemade moving bed set up, and the influences of the height of gas-solid heat exchange section, Reynolds number and gas-solid water equivalent ratio on exergy transfer characteristics are graphically and analyzed. The research results indicates that air-sinter exergy transfer process is mainly determined by the exergy transfer caused by temperature difference, and the impact of exergy transfer due to internal pressure loss is relatively small for given vertical tank and sinter particles. There is an ideal range of gas-solid water equivalent ratio, which makes exergy transfer more efficient.

Prediction of the Ash Deposition Characteristics of Blended Coals in a 500 MWe Tangentially Fired Boiler

A computational simulation was performed to predict ash deposition in an industrial scale coal-fired boiler. The single-rate model and the improved nth order model were employed for devolatilization and char reaction with the model constants obtained from PC Coal LAB.(1) Ash particles were deposited on the wall by inertial impaction with the capture efficiency in terms of the estimated viscosity. The models for char combustion and ash deposition were implemented as new user defined functions in ANSYS-FLUENT.(2) The results showed that the deposition of blended coals was in good agreement with measurements under the influence of the surrounding flow field in a pilot scale furnace. The same combustion and ash deposition models were applied to the 500 MWe tangentially fired boiler burning blended coals. Ash deposition results for the boiler showed the same tendency as the measured data in terms of the wall fouling resistance. A larger deposition was predicted at the heat exchangers for sub-bituminous coal than for bituminous coal. However, there was no significant influence of the coal types in the furnace region. A parametric investigation was performed on ash deposition with respect to injection location and tilt angle of the burners. Deposition in the ash hopper was affected by the injection location but not by the coal types. The results showed a maximum ash deposition at the heat exchanger section for sub-bituminous coal from the lower burner set. Ash deposition increased in the ash hopper for the downward tilt angle of burners, whereas the maximum deposition occurred at the heat exchangers for the upward tilt angle.

Study on reasonable selection of insulation depth of the outlet section of vertical deep-buried U-bend tube heat exchanger

Around the scientific prediction of insulation depth of the outlet section of vertical deep-buried U-bend tube heat exchanger (THE) in geothermal heating, in this study, a full-scale numerical calculation model combining the heat transfer processes inside and outside the tube was established. This model was further validated through in-situ experiment for a vertical deep-buried U-bend THE system with a depth of 2505 m in Xi'an. Four constant heat conditions with different magnitudes were selected and the highest average outlet temperature of the circulating water within the tube in the entire heating season corresponded to the optimum insulation depth. Furthermore, the effect of insulation depth at the outlet section of the buried tube on the heat transfer performance was analyzed by numerical calculation. The results showed that the critical exothermic depth of the outlet tube without insulation in a heating season was exactly the optimum insulation depth. Moreover, the linear fitting relationship between the initial temperature of the soil at the optimum insulation depth and the average water temperature at the outlet in the entire heating season of the insulated vertical deep-buried U-bend tube was obtained by numerical method under the determinant conditions of rock structure, temperature distribution, and geometrical parameters of the buried tube system, which can provide the optimum insulation depth of deep-buried THE projects under the geological conditions in the construction plan phase.

Chemical process systems analysis using thermodynamic balance equations with entropy generation. Revaluation and extension

Modeling inconsistencies exhibited in previous work (O'Connell, 2017) associated with post-combustion methanolamine (MEA) and ammonia (NH3) absorption processes have been revealed. The origin of the problem was that entropies for ionic reactions were not evaluated from input model equilibrium constants regressed from data. Revised calculations have been made using only properties of formation. Positive and consistent entropy generation rates (S˙gen) are now found for all units and sections, and process convergence was achieved for multiple sections rather than for only single sections as before. Only minor changes in material, energy and overall S˙gen appeared in the new simulations. Results for S˙gen values show that the greatest irreversibilities for the MEA process are in the stripping section, though significant effects appear in the chiller, heat exchanger, and stripper flash. For the NH3 process, roughly equal and large contributions to S˙gen are in the absorption, heat exchange, and stripping sections. Process improvements should focus on these sections. Applying the methodology to proposed changes would quantitatively reveal the amounts of increased efficiency.

Determination of the Heat-Exchange Characteristics of Low-Pressure Heat-Exchangers for Lead and Lead-Bismuth Cooled Loops

Heat removal during transient processes in nuclear power installations and bench loops cooled by lead and lead-bismuth coolant is studied. It is shown that low-pressure heat-exchange equipment is effective. The studies were conducted in a non-isothermal loop with circulating of lead coolant at 450–500°C, average speed in the narrow section of the gap in longitudinal flow over the heat-exchange surface 0.1–1.05 m/sec, Peclet number 300–3300, and the oxygen thermodynamic activity in lead 1–10–3. The processes occurring in a non-isothermal liquid-metal loop with an experimental heat-exchange section model the dependence of the heat-exchange characteristics on impurity mass transfer in the loop.

Performance evaluation of a novel flat-plate solar air collector with micro-heat pipe arrays (MHPA)

This paper proposes a new type of a flat-plate solar air collector (SAC) with micro-heat pipe arrays (MHPA), which consist of a heat collection and transfer section and an air ventilation and heat exchange section. In the unique structure, the heat exchange of air is separated from heat collection and transmission. This work experimentally and theoretically investigates the heat transfer and friction factor characteristics of the proposed MHPA-flat plate solar air collector. Numerical simulation and experimental results are compared to show the instantaneous performance of the collector under quasi-steady state conditions. Efficiency, time constant, inlet temperature, outlet temperature, absorber temperature, and glass cover temperature are obtained. The effects of weather condition, and operational parameters are evaluated on the basis of thermal efficiency, outlet temperature, heat loss, and heat transfer. Results reveal that the average efficiency is approximately 69% at a flow rate of 290m3/h. In the testing range of the air flow rate, the frictional coefficient varies from 0.05 to 0.18.

Thermal diffusivity measurement of erythritol and numerical analysis of heat storage performance on a fin-type heat exchanger

Abstract Temperature dependency of thermal diffusivity of erythritol was measured by temperature wave analysis (TWA) method. This modulating technique allowed measuring thermal diffusivity continuously, even during the phase transition solid-liquid. Together with specific heat capacity and specific enthalpy measured by differential scanning calorimetry, the values of measured properties were utilized in a bi-dimensional numerical model for analysis of heat transfer and heat storage performance. The geometry of the model is representative of a cross section of a fin-type heat exchanger, in which erythritol is filling the interspaces between fins. Time-dependent temperature change and heat storage performance were analyzed by considering the variation of thermophysical properties as a function of temperature. The numerical method can be utilized for a fast parametric analysis of heat transfer and heat storage performance into heat storage systems of phase-change materials and composites.

Aerodynamic numerical calculations of air-cooled condensers and dry cooling towers at different wind velocities and multilevel configuration of sections

Multilevel configuration of heat exchange sections of air-cooled condensers and dry cooling towers with a multi-row arrangement are offered. Results of a research of the combined operation of fans and V-shaped heat exchangers by methods of numerical model operation at wind and without it for three-row sections are given. It is shown that in the presence of wind multilevel configuration of heat exchange sections has advantages over single-level configuration.

Assessment of analytical and numerical models on experimental data for the study of single-phase natural circulation dynamics in a vertical loop

In this paper, semi-analytical and numerical models developed in our previous works to study the dynamic behaviour of natural convection are assessed against the experimental data obtained by means of the L2 Natural Circulation Loop (NCL) of DIME-Tec Labs (University of Genoa). As for the experimental campaign, reference is made to a set of nine experiments performed using water as working fluid and providing a thermal power of 2kW. This set of data is firstly adopted for the validation of a semi-analytical linear analysis tool aimed at studying the asymptotic behaviour of NCLs through the definition of dimensionless stability maps. Then, two different numerical models (adopted in our previous work to confirm the linear analysis) are assessed, namely an Object-Oriented (O-O) one-dimensional model and a three-dimensional Computational Fluid Dynamics (CFD) model. In this regard, the O-O model represents a fast tool for the evaluation of the most important quantities, such as the velocity and the temperature fields in the loop along the axial coordinate. On the other hand, the CFD tool, which is intended as a support to the 1D analysis, is characterised by a high computational burden, but allows highlighting interesting 3D spatial effects. The validation of these tools is not secondary with respect to that of the stability maps. Actually, the numerical approach is fundamental to study the time-dependent behaviour of both stable and unstable natural circulation regimes, for which the stability maps do not provide information. As for the achieved results, the developed models are able to catch the behaviour of the experimental data. In particular, this outcome is possible if an accurate modelling of both the heat-exchanger section and the piping thermal inertia is considered.

The Effect of Fuel Mass Fraction on the Combustion and Fluid Flow in a Sulfur Recovery Unit Thermal Reactor

Sulfur recovery unit (SRU) thermal reactors are negatively affected by high temperature operation. In this paper, the effect of the fuel mass fraction on the combustion and fluid flow in a SRU thermal reactor is investigated numerically. Practical operating conditions for a petrochemical corporation in Taiwan are used as the design conditions for the discussion. The simulation results show that the present design condition is a fuel-rich (or air-lean) condition and gives acceptable sulfur recovery, hydrogen sulfide (H2S) destruction, sulfur dioxide (SO2) emissions and thermal reactor temperature for an oxygen-normal operation. However, for an oxygen-rich operation, the local maximum temperature exceeds the suggested maximum service temperature, although the average temperature is acceptable. The high temperature region must be inspected very carefully during the annual maintenance period if there are oxygen-rich operations. If the fuel mass fraction to the zone ahead of the choke ring (zone 1) is 0.0625 or 0.125, the average temperature in the zone behind the choke ring (zone 2) is higher than the zone 1 average temperature, which can damage the downstream heat exchanger tubes. If the zone 1 fuel mass fraction is reduced to ensure a lower zone 1 temperature, the temperature in zone 2 and the heat exchanger section must be monitored closely and the zone 2 wall and heat exchanger tubes must be inspected very carefully during the annual maintenance period. To determine a suitable fuel mass fraction for operation, a detailed numerical simulation should be performed first to find the stoichiometric fuel mass fraction which produces the most complete combustion and the highest temperature. This stoichiometric fuel mass fraction should be avoided because the high temperature could damage the zone 1 corner or the choke ring. A higher fuel mass fraction (i.e., fuel-rich or air-lean condition) is more suitable because it can avoid deteriorations of both zone 1 and heat exchanger tubes. Although a lower fuel mass fraction (i.e., fuel-lean or air-rich condition) can avoid deterioration of zone 1, the heat exchanger tubes may be damaged. This paper provides a guideline for adjusting the fuel mass fraction to reduce the high temperature inside the thermal reactor and to ensure an acceptable sulfur recovery.

Effect of inclination angle on the performance of a shell and tube heat storage unit – An experimental study

This study includes experimental investigation on the performance of a shell and tube heat exchanger subjected to inclination angle variation. Paraffin RT35 is used as phase change material (PCM). The investigation was performed for modified Stefan numbers of 0.47, 0.53 and 0.59 and inclination angle rang from 0° to 90°. The Reynolds number is about 770 and the Grashof number is in the range of 4.6×104–5.8×104 which indicated that the flow is laminar. Results show that as the inlet temperature increases melting process accelerates and complete melting time reduces. Results also indicated that the rate of melting process in the first half of the process is more in the horizontal system with respect to the other inclinations. It is also revealed that the angle’s variation doesn’t affect the rate of heat transfer and the temperature during solidification which is due to the domination of conduction in this process. Results also clarified that during melting, the rate of heat transfer of the horizontal system is more than that of vertical, however the reverse is true for the solidification. It is also concluded that the average temperature of the horizontal heat exchanger sections closer to the inlet is more than the section nearer to outlet. However, when the 30°, 60° and 90° cases are considered, the PCM average temperatures of the sections nearer to the outlet are more.

Experimental Investigation of Heat Transfer Study on Plate Fin Heat Exchangers with Wavy Fins

Objectives: This study investigates the variation of heat transfer parameters using wavy fin located in the plate heat exchanger. Methods/Statistical Analysis: Velocity and temperature relations, fanning friction factor for iso-temperature and Colburn factor are evaluated for different flow rates of Reynolds Number from 200 to 2000 and its various fin pitches within 9 mm respectively. Similarities were found between this experimental data and semi empirical correlations of Plate Heat Exchanger. Findings: The various parameters are evaluated using this experimental setup and we obtained the optimum j/f for swirl flow regime with Reynolds Number of around 200 to 210. The general correlations for friction factor and Colburn factor were derived by multiple linear regression analysis. Application/Improvements: This studies show the periodic growth of parameters in the wall region of cross section of cross flow heat exchanger. Also we obtained the higher heat transfer co-efficient by using wavy fin with reasonable pressure fall.

EVOLUTION OF SCHEMES OF HEAT EXCHANGE IN A BLAST FURNACE

The development of schemes of heat exchange in a blast furnace was considered with the improvement of the blast furnace smelting technology. It was noted that for the estimation of the thermal state of blast furnace as a control object it is expedient to divide it into two thermal zones, upper and bottom. The interface between them is in the top of the mixed recovery between the level of the beginning of the carbon gasifi cation of coke and the horizon, below which iron oxides are directly reduced. Upper slow heat exchange section in terms of heat exchange is reserve height providing better thermal and regenerative operation of the furnace. The bottom section of slow heat exchange should not be used as a reserve for improvement of thermal and reduction work of the blast furnace. It is shown that the presence of two zones of intense heat exchange in the present conditions of smelting of various types of iron ore using the combined blowing of high parameters is a prerequisite for the stability of the course of the blast furnace process and effi ciency of smelting.

Testing of a 4 K to 2 K heat exchanger with an intermediate pressure drop

Most large sub-atmospheric helium refrigeration systems incorporate a heat exchanger at the load, or in the distribution system, to counter-flow the sub-atmospheric return with the super-critical or liquid supply. A significant process improvement is theoretically obtainable by handling the exergy loss across the Joule-Thompson throttling valve supplying the flow to the load in a simple but different manner. As briefly outlined in previous publications, the exergy loss can be minimized by allowing the supply flow pressure to decrease to a sub-atmospheric pressure concurrent with heat exchange flow from the load. One practical implementation is to sub-divide the supply flow pressure drop between two heat exchanger sections, incorporating an intermediate pressure drop. Such a test is being performed at Jefferson Lab's Cryogenic Test Facility (CTF). This paper will briefly discuss the theory, practical implementation and test results and analysis obtained to date.

Assessment of the performances of a heat exchanger in a light helicopter

This study has the aim to develop a numerical design regarding the position and the inner performances of a heat exchanger in a light helicopter. the problem was to find first of all the best position of the heat exchanger inside the engine vane in order to maximize the air flow rate capable to pass through the heat exchanger section. It is to be said that the only air contribution in the vane comes from the opening present in the roof under the main rotor. The design has been performed by means of the commercial code Fluent and using the well known grid generator ICEM CFD. Different positions are first investigated so to establish the best one. Subsequently, different areas of the opening on the roof have been considered in order to maximize even more the flow rate in the heat exchanger that was not sufficient based on the first guess of velocity, as aforementioned. At the end interesting design results are presented and discussed by contours of fields and values.

Influence of fin arrangement on fluid flow and heat transfer in the inlet of a plate-fin heat exchanger

Fin arrangement, which can cause temperature to be distributed non-uniformly and decrease heat exchange efficiency, can also affect fluid flow and distribution in different channels of a plate-fin heat exchanger. To reduce fluid maldistribution, the fluid flow and distribution should be investigated systematically. However, there is as yet no research reported on the fin ar- rangement effect. We investigated fluid flow and heat transfer at the inlet of a plate-fin heat exchanger by numerical calculation combined with simulation analysis. We simulated the fluid flow under seven kinds of fin arrangement, and analyzed the effects. The distribution of fluid parameters in four monitor positions among three sections was examined when the inlet flow velocity was 1 m/s with an inlet structure arranged with different numbers of fins. Denser fin arrangements among inlet, diversion, and heat exchange sections all intensify the turbulence at the outlet. With increase of arrangement density, the fluid flow direction will be changed and the fluid distribution inside the exchanger will be intensified to equalize the fluid temperature in different channels of the same layer. Furthermore, the effects of 18 combinations of fins in different sections on fluid flow were studied. Fin arrange- ments in different sections have more significant effect on turbulence than flow velocity and pressure; in comparison with the inlet and heat exchange sections, the diversion section has a significant effect on turbulence at the outlet of the heat exchanger.