Side Heat Transfer Research Articles

Development of improved correlations for shell side heat transfer co-efficient in multi-tubular reactors network heat exchanger

The multi-tubular reactor takes the form of a shell and tube heat exchanger. The baffles that became of interest were the disk and doughnut baffles as they provided a 15 % greater effectiveness than the commonly used segmental baffle. The shell side heat transfer coefficient is usually predicted by correlations developed by Donohue (1949) and Goyal & Gupta (1984) for disk and doughnut baffles. However, these correlations result in inaccuracies due to the complexity of the configuration. Therefore, Slipcevic (1978), had developed a new method to calculate the shell side heat transfer coefficient. The Slipcevic method takes into consideration the annular flow, the crossflow and the doughnut flow. However, certain portions were gone unconsidered by this method. Therefore, the aim of this study was to modify the Slipcevic method to generate a more accurate shell side heat transfer coefficient. The heat transfer coefficient calculated using the original Slipcevic method was determined to be 58.6 W/m^2. K. The modified method resulted in a coefficient of 49.9 W/m^2. K. The modification resulted in a coefficient 14.8 % less than the original method. Since the simulated value for the propylene process was 15.8 % lower than the Slipcevic procedure, this revealed that the modification was slightly more accurate. The difference of 6.5 % between the two percent differences may be due to inaccuracies resulting from the assumptions of triangular gaps and that the wall viscosities were equivalent to the bulk viscosities.

Multi-energies assisted and all-weather recovery of crude oil by superhydrophobic melamine sponge.

Efficient and safe recovery of high-viscosity marine crude oil spills is still a worldwide challenge. High-viscosity crude oil is difficult to be removed by traditional adsorbent materials. Although some recent developments in photothermal or electric-thermal oil-absorbing materials, the vertical heat transfer inside and the potential hazard of electrical leakage are difficult to be guaranteed. In order to overcome these problems, we polymerized dopamine (DA) in situ on the skeleton surface of the commercial melamine sponge (MS), and further coated the full-wavelength light-absorbing Fe3O4 NPs-Graphene (HF-G) on it to obtain the superhydrophobic sponge with excellent photothermal conversion effect, heat conductivity and magnetic heating capabilities (HF-G/PDA@MS). When the thickness of sponge is 5mm, the HF-G/PDA@MS shows excellent vertical heat conductivity ability, and can absorb about 80g/g. It also can be combined with an extra electric-heating device to achieve continuous heating to reduce the viscosity and recover crude oil at night or extreme weather. In addition, the temperature of HF-G/PDA@MS can reach about 40°C by electromagnetic induction heater, indicating that we can use multiple energies-assisted modes to heat the HF-G/PDA@MS to. This work provides a promising solution and theoretical support for all-weather solving offshore crude oil spills pollution and recovery.

NUMERICAL STUDY ON THE EFFECT OF THE NUMBER OF SPIRAL COIL LAYERS ON SHELL SIDE FLOW AND HEAT TRANSFER

NUMERICAL STUDY ON THE EFFECT OF THE NUMBER OF SPIRAL COIL LAYERS ON SHELL SIDE FLOW AND HEAT TRANSFER

Heat management system of electric vehicle based on heat pump and energy recovery of removable battery

In order to manage the air-conditioning thermal system, battery thermal system and motor thermal system in a unified manner, the author proposes a self-developed integrated thermal management system for electric vehicles to recover battery energy. Firstly, the problems in the development of electric vehicles and the importance of thermal management system are introduced, secondly, the self-developed thermal management system scheme and the principle of each part are analyzed, the experimental results of thermal system in enthalpy difference chamber are also introduced. The experimental results show that: Under the double evaporation system, when the compressor speed is 4500 rpm, the maximum COP is 2.46, and the maximum COP charge is 1180 g, the maximum heat transfer capacity is 4819 W (wind side heat transfer + water side heat transfer), the evaporation temperature is 5.35?C, the evaporation superheat is 9.5?C, the condensation temperature is 59.3?C, the undercooling degree is 10.4?C, the suction pressure is 280 kPa, and the exhaust pressure is 1694 kPa. In conclusion, the thermal management system has great energy saving effect, which ensures that the electric vehicle range will not be greatly attenuated under winter heating conditions, and meets the requirements of comfort.

Numerical study on the thermal-hydraulic characteristic of an automotive parallel-flow condenser under non-uniform airflow

The performance of an automotive parallel-flow condenser was numerically investigated considering both airside and refrigerant-side flow mal-distributions, the thermal-hydraulic characteristic of the condenser under the air-side blockage of each tube pass was first studied, then the influence of the form and degree of uneven airflow that may be revealed in vehicles on the performance of the condenser was analyzed. At last, using the simulation model combined with the measurements of the vehicle in the climatic wind tunnel, the thermal-hydraulic features of the condenser as well as the performance of the A/C system under various front-end status and vehicle conditions was evaluated. It was found that the performance degradation of the condenser resulting from the air-side blockage of the first pass exceeds that caused by the obstruction of all the other three passes together. According to the performance deterioration sequence of the condenser from high to low, the order of the four possible non-uniform airflow patterns in vehicles is low on the top and high at the bottom (LTHB), low in the middle (LM), high in the middle (HM), and high on the top and low at the bottom (HTLB), and the last two forms could even enhance the performance of the condenser under certain working conditions. The rule of cooling airflow optimization is to arrange large/small air velocity on the area with intrinsically large/small refrigerant side heat transfer coefficient of the condenser. The possible direction of cooling airflow design in vehicles is inferred.

Modeling and Optimization of a Micro-Channel Gas Cooler for a Transcritical CO2 Mobile Air-Conditioning System

This study focuses on developing and optimizing of a microchannel gas cooler model for evaluating the performance of a transcritical CO2 mobile air-conditioning system. A simulation model is developed with the aid of MATLAB R2022a. A segment-by-segment modeling approach is utilized by applying the effectiveness-NTU method. State-of-the-art heat transfer and pressure drop correlations are used to obtain air and refrigerant side heat transfer coefficients and friction factors. The developed model is validated through a wide range of available experimental data and is able to predict a gas cooler capacity and pressure drop within an acceptable range of accuracy. The average errors for a gas cooler capacity and pressure drop are 3.79% and 10.24%, respectively. Furthermore, a parametric optimization method is applied to obtain optimal microchannel heat exchanger dimensions, including the number of tubes, microchannel ports, and passes. Different combinations were selected within the practical range to obtain optimal dimensions while keeping the total core volume constant. The simultaneous effect of the number of tubes, the number of ports in each tube, and the number of passes is determined. The objective of the current optimization technique is to minimize the pressure drop for the specific design capacity under different operating conditions without changing the overall volume of the gas cooler. The average pressure drop reduction for the optimal geometry as compared with the baseline geometry under all operating conditions is about 15%. The results from this study can be used to select an optimal geometric design for the required design capacity with a minimal pressure drop without the need for expensive prototype development and testing.

Experimental and theoretical study on the onset of nucleate boiling in non-uniform heating tube bundle channel

The transverse non-uniform heating tube bundle exists in steam generator and will affect the heat transfer and flow conditions in the shell side. It is important for the operational performance of the steam generator. In this study, a non-uniform heating tube bundle channel experimental device was set up. The channel consisted of two groups of heating tube bundles which were non-uniform heating in the transverse direction and uniform heating in the axial direction. Experiments and theoretical analysis were conducted to evaluate the influence of transverse non-uniform heating on the Onset of Nucleate Boiling (ONB). The locations of ONB during the experiments were determined from the heat transfer coefficient variations and the tube wall temperature variations. Experimental results at ONB were compared with existing well-known correlations under uniform heating conditions. And then under non-uniform heating conditions, the experimental wall superheat at ONB were furthermore compared with results predicted by the verified existing correlation. It was found that the correlation can’t predict the experimental wall superheats well under transverse non-uniform heating conditions. Therefore, the influence of transverse non-uniform heating on ONB was theoretically analyzed. Correction factors were theoretically introduced and a new correlation was proposed. This new correlation was examined with experimental data and the result showed the correction factors need to be further studied.

Local room‐side heat transfer of an office room with different heating strategies

AbstractThe room‐side heat transfer of a building is essential for calculating and simulating heat loss through radiation and convection in interior spaces, and also for preventing mould growth and condensation. By means of Computational Fluid Dynamics (CFD) simulations, this study investigates the effect of floor heating, mixing ventilation, furniture, room geometry, and their combinations on the interior heat transfer coefficient (HTC) of a typical office room. The results show an inhomogeneous distribution of the HTC on the exterior walls. HTC values are generally below the German standardised value for thermal protection, which means an overestimation of the heat loss when the standardised value is applied. However, compared to the standardised value for preventing mould growth, the minimum surface‐averaged HTC behind closets is 63 % lower, potentially leading to mould growth and condensation.

Opportunities for improved space heating energy efficiency from fluid property modifications

Unsteady behaviour of hydronic heating systems causes higher mean room temperatures than are required for comfort. Peak room temperatures depend on interactions between thermostats, heat emitters and the room. The importance of fluid properties on such unsteady heating is often misunderstood meaning potential energy savings are overlooked. This paper demonstrates the influence of fluid modifications and indicates a plausible magnitude of the energy saving opportunity. The results showed that fluid side heat transfer coefficient in isolation had negligible effect. Specific heat capacity of the fluid and flow rates were important, as they altered the amount of embedded energy in the heat emitter when thermostat conditions were met. Reductions in mean heating power for steady demand conditions were between 0 and 7% for plausible changes to fluid properties, depending on heat emitter size, room insulation and external temperature. Reductions in individual cycle energy were between 5 and 25%. When considered in the context of intermittent finite duration heating events, those that contained a small number of thermostat cycles demonstrated energy savings that tended towards the reductions in individual cycle energy. Heating events with larger numbers of cycles showed energy savings tending towards the reduction in mean heating power.

Integration of hydrogen storage and heat storage in thermochemical reactors enhanced with optimized topological structures: Charging process

The low density for hydrogen storage can be solved by metal hydrides, and the energy loss for hydrogen storage with metal hydrides can be recovered by the combination of metal hydrides (Mg/MgH2) with thermochemical heat storage materials (MgO/Mg(OH)2) under the different reaction temperatures. However, the poor heat conduction of thermochemical materials limits the heat transfer rate and the implementation of this technology. In this study, an accurate theoretical model of hydrogen charging process in the hydrogen storage reactor assisted with heat storage was developed to accommodate the operating pressure. A novel method to overcome the poor heat transfer problem was proposed by topology optimization of high thermal conductivity fins for matching the heat transfer and reaction rate in the hydrogen storage side with those in the heat storage side. Increasing the average temperature of MgO/Mg(OH)2 was considered for the formulation of the topology optimization problem, and a density-based approach was used. The influence of the conductivity of materials on the topology optimization was discussed. The outcomes displayed that higher thermal conductivity accommodated more heat transfer directions, resulting in a distinct branch structure. Furthermore, the obtained topologies were geometrically reconstructed and evaluated during the hydrogen charging process. Results revealed that the topology optimized geometry had outstanding heat transfer performance, with an obvious improvement in terms of hydrogen charging time over the reactor without fins. This work can provide the theoretical basis for thermochemical conversion processes of hydrogen storage and heat storage, the implementation procedure for topology optimization, and the design guidance of thermochemical reactors for hydrogen storage assisted with heat storage.

Mathematical Model of Air Dryer Heat Pump Exchangers

This paper presents a mathematical model of heat pump exchangers and their thermal interaction with a fan for an air dryer. The calculation algorithm developed for the finned heat exchangers is based on the ε-NTU method, allowing the determination of air side and refrigerant side heat transfer coefficients, evaporator and condenser heat capacity and air parameters at the dehumidifier outlet with known exchanger geometries, initial air parameters and mass flow rate. The model was verified on an industrial dehumidifier test bench. This enabled the heat transfer coefficients for the exchanger to be calculated as a function of the speed and, therefore, the power of the fan’s drive motor. An increase in fan performance on the one hand results in an increase in the heat transfer rate, but, on the other hand, it causes an increase in the total energy consumption of the motor. Thus, while it causes an increase in drying capacity, it also causes an increase in the energy consumption of the dehumidifier. In order to optimise the unit in terms of energy consumption, it is therefore necessary to determine a function that relates the amount of heat exchanged to the efficiency of the fan.

Design of a Combined Proportional Integral Derivative Controller to Regulate the Temperature Inside a High-Temperature Tubular Solar Reactor

Abstract Solar fuels are proven to be promising candidates for thermochemical energy storage. However, the transient nature of solar radiation is an obstacle to maintaining a stable operational temperature inside a solar reactor. To overcome this challenge, the temperature of a solar reactor can be regulated by controlling the incoming solar radiation or the feedstock flowrate inside the reactor. In this work, a combined proportional integral derivative (PID) controller is implemented to regulate the temperature inside a high-temperature tubular solar reactor with counter-current flowing gas/particles. The control model incorporates two control systems to regulate incoming solar radiation and gas flow simultaneously. The design of the controller is based on a reduced-order numerical model of a high-temperature tubular solar reactor that is vertically oriented with an upward gas flow and downward particle flow. The reactor receives heat circumferentially through its wall over a finite segment of its length. Formulation of the heat transfer model is presented by applying the energy balance for the reactor tube and considering heat and mass transfer inside. A set of governing differential equations are solved numerically by using the finite volume method to obtain reactor wall, particles, and gas temperatures along the reactor length with various boundary conditions. Simulation results are used to tune the PID controller parameters by utilizing the Ziegler–Nichols tuning method. Both the simulation results and the controller performance are visualized on the labview platform. The controller is challenged to track different temperature setpoints with different scenarios of transient solar radiation. The performance of the PID controller was compared to experimental results obtained from an industrial PID controller embedded in a 7 kW electric furnace. Results show that the combined PID controller is successful in maintaining a stable temperature inside the reactor by regulating the incoming solar radiation and the flowrate via small steady-state error and reasonable settling time and overshoot.

Heat transfer and exergy efficiency analysis of 60% water and 40% ethylene glycol mixture diamond nanofluids flow through a shell and helical coil heat exchanger

The thermodynamic, heat transfer and thermal performance factor were analyzed experimentally at different particle volume loadings of water + ethylene glycol mixture based nanodiamond (ND) nanofluids flow in a shell and helical coiled tube heat exchanger. Chemical treatment was used to make ND nanoparticles with an average size of 5.42 nm. The stable ND nanofluids were prepared by considering 60:40% water + ethylene glycol (weight percentage) mixture as base fluid and the experiments were performed at particle loadings ranging from 0.2% to 1.0% and the Reynolds number ranging from 900 to 4800, respectively. In the heat exchanger, the hot fluid passes through the shell side and the cold fluid (nanofluid) passes through the helical coil side. The Wilson plot method is used to analyze the helical coil side heat transfer coefficients. The hot fluid volume flow rate was fixed to 1 lit/min, whereas, the cold fluid (nanofluid) volume flow rate was varied from 2 to 6 lit/min. Results show, at 1.0 vol% and the Reynolds number of 2702, the heat transfer coefficient and Nusselt number is increased by 36.05%, and 27.47%, respectively, over the base fluid. However, the penalty in friction factor and pressure drop is 17.28% and 14.24% under the same Reynolds number and 1.0 vol% nanofluid over the base fluid. Similarly, at 1.0 vol% and Reynolds number of 2702, the thermal entropy generation is dropped by 38.12%, frictional entropy generation is raised by 12.86%, exergy efficiency is enhanced by 36.48% and thermal performance factor is augmented by 1.2094 times over the base fluid.

Investigations on the effect of spacer in direct contact and air gap membrane distillation using computational fluid dynamics

Direct contact membrane distillation (DCMD) and air gap membrane distillation (AGMD) have emerged as potential technologies for water and wastewater treatment. This investigation developed a comprehensive two-dimensional computational fluid dynamics model to describe and simulate heat transfer, mass transfer, and fluid flow in DCMD and AGMD processes. The effect of Reynolds number, inlet feed temperature, and distance between two successive spacer filaments on the performance parameters such as mass flux, temperature polarisation, concentration polarisation, and thermal efficiency was investigated in this work. The feed and permeate side heat transfer coefficient increased with Re in the DCMD and AGMD models. The thickness of the velocity boundary layers reduced upon introducing spacers in the feed and permeate channels. The mass flux on the introduction of spacers increased in DCMD and AGMD models because the boundary layer resistance was reduced. The models with spacer showed a lower oncentration polarisation. DCMD model demonstrated a loweroncentration polarisation than the AGMD model as the former has higher mass flux than the latter leading to a higher solute concentration on the membrane surface. The thermal boundary layer was smaller in the spacer-filled channel because of the fluid mixing. In the AGMD model, the permeate side thermal boundary layer was unaffected because of the poor conductivity of air than water.

Theoretical and numerical study of a shell and tube heat exchanger using 22% cut segmental baffle

AbstractIn this present study, the three‐dimensional geometry of shell and tube heat exchanger with conventional segmental baffle is considered. A numerical and theoretical study is carried out for shell side heat transfer characteristics under the same mass flow rates with shell side mass flow rates ranging from 0.23 to 0.43 kg/s. The Colburn factor is decreasing with an increase in mass flow rate. The tube side Nusselt number obtained is in good agreement with the correlations available. The Colburn factor (js) for the present geometry was compared with Kern's equation. Tube side Nusselt number for the present study, Dittus–Boelter equations, Notter Rouse equation, Syam Sundar et al. equation, and Gnielinski equation have shown good agreement with each other. The present study is further extended with 1%, 3%, and 5% volume concentrations of Al2O3, graphene oxide, TiO2, single‐wall carbon nanotube, and MXene nanofluids. The author notices that the 5% volume concentration of each nanofluid has shown the highest heat transfer coefficients when compared to other concentrations of nanofluids.

The numerical investigation of the finned double-pipe phase change material heat storage system equipped with internal vortex generator

Energy storage is among the factors that could reduce the use of fossil fuels. Having a large heat storage capacity, phase change materials found their wide applications in energy storage applications. The present study investigates the effect of using phase change materials on the performance of a double pipe heat storage system. The three-dimensional simulation was developed to model the transient flow and heat transfer via the finite volume method. To enhance the heat transfer, fins with the varying cross-sectional area are employed over the surface of the inner tube. Furthermore, to enhance the water side heat transfer, the vortex generator is employed there. The sensitivity analysis was performed to unveil the effect of inlet hot water temperature on the change and discharge processes. The results show that the fins inside the phase change material reduce the melting time up to 100 min and increase the outlet hot water temperature. Also, using the vortex generator in the water path had the reverse effect on the charging process and increases the charging time. For hot water temperature of 75 °C, the temperature of phase change material archives to its maximum value after 189 min. In the case of 70 °C hot water temperature, the phase change process begins 41 min later than in the case of temperature 75 °C and reaches its maximum temperature within 229 min.

Thermal energy storage system with a high-temperature nanoparticle enhanced phase change material: Charging and discharging characteristics upon integration with process preheating

Nanoparticle enhanced Phase Change Materials (NePCMs) are modified forms of phase change materials containing nanoparticles such that the thermophysical properties are improved. Solar salt, a phase change material comprising a eutectic mixture of sodium nitrate and potassium nitrate has a thermal conductivity in the range of 0.5–1 W/m K and the addition of nanoparticles to solar salt (nanoparticle enhanced solar salt) has been demonstrated to improve its thermophysical properties. This work evaluates the charging and discharging characteristics of solar salt and nanoparticle enhanced solar salt, with copper nanoparticles (at 0.5 wt%) and reduced Graphene Oxide nanostructures (at 0.5 wt%) individually as additives. Experiments were performed simulating a thermal energy storage system (TES) for process preheating. Silicone oil and Therminol® 55 were used as heat transfer fluids during charging and discharging cycles respectively. The overall heat transfer coefficients of TES containing copper nanoparticle enhanced solar salt and reduced Graphene Oxide nanostructure enhanced solar salt as an energy storage medium were greater than that containing solar salt during both charging and discharging cycles. The enhancements in overall heat transfer coefficients were due to respective enhancements in PCM side heat transfer coefficients caused by thermal conductivity and specific heat increase brought about by the addition of copper nanoparticles/reduced Graphene Oxide nanostructures to solar salt. Considering >10 % enhancements in overall heat transfer coefficient in both charging and discharging cycles with these two NePCMs, latent heat thermal energy storage systems employing them as phase change material will be suitable for integration with a process preheating application.

Experimental comparison and CFD analysis of conventional shell and tube heat exchanger with new design geometry at different baffle intervals

Basically, in the working principle, the transition from high temperature to low temperature is achieved, while the temperature value of the one with the lower temperature rises, this process can continue until the temperature value of the other decreases and reaches equilibrium. Therefore, heat exchangers are highly preferred in the industry where heat transfer is possible, in mass production facilities where nonstop production takes place such as the pharmaceutical and paper industry, and in sectors where energy efficiency is of utmost importance. In the analyses, it is aimed to investigate the changes in the fluid behavior of the conventional one-piece type baffle plate shell and tube heat exchanger at different baffle plate intervals by keeping it constant at different flow rates. Here, water was used as the working fluid to examine the changes in fluid behavior, the direction in which the heat transfer rate per pressure drop changes, the pressure drop and the effects on the body side heat transfer coefficient. As a result, it has been determined that the distance between the baffle plates used in the conventional one-piece type shell and tube heat exchanger varies and the values compared at different flow ranges differ.

Evaluation of Thermal Performance of Conically Shaped Micro Helical Tubes Using Non-Newtonian Nanofluids–A Numerical Study

Abstract Nowadays, the cooling and heating of micro-thermal devices have received a growing interest. To improve the thermal management of these micro-thermal devices, various efforts are being made by the researchers. In the present study, conically shaped micro helical tubes are used to investigate the coil side heat transfer rate and friction factor of non-Newtonian nanofluids under laminar flow conditions. For the numerical analysis, single-phase approach with commercial software ansys-fluent-19 has been utilized. Investigations encompass generalized Reynold numbers ranging from 306 to 2159 and four different curvature ratios (0.066, 0.076, 0.088, and 0.1) of conically shaped micro helical tubes. The inner diameter of the helical tube is 2 mm and contains 20 turns. Al2O3-based non-Newtonian nanofluids with volume concentrations of 0.0%, 0.1%, and 0.2% having base fluid of aqueous solution of carboxymethyl-cellulose (CMC) are used as the working fluid (hot) for the coil side, while in the shell side cold water is used. The results from numerical investigation are validated and found in good agreement with earlier experimental results. The results show that with the increase in the curvature ratio of conically coiled tubes both heat transfer rate and friction factor increase by 46% and 98% respectively, for base fluid at a curvature ratio of 0.1. Also, the present study reveals that adding nanoparticles to the base fluid enhances the heat transfer rate to a maximum value of 40%. Moreover, the maximum value of thermal performance factor (TPF) is found to be 1.52.

Comparison of Numerical Methods for Thermal Performance Evaluation of Circuit Protection Devices in EV Application

With the growing demand of electric vehicles, design of circuit protection devices is now an important consideration in automobile industry. Modern day circuit protection devices have been constantly undergoing miniaturization due to requirement of minimizing the foot print for use in electrical vehicles and aerospace applications. This size reduction makes thermal management one of the most important aspects of their design. Use of numerical model to predict heat transfer can significantly reduce the cost and time required in testing physical prototypes. In this paper, three different approaches for numerically predicting temperature rise of circuit breakers are discussed and compared from the point of view of accuracy and computational effort. The three methods are 1) Finite volume based analysis in which conjugate heat transfer inside and outside the breaker is modelled by solving Navier-Stokes equations 2) Finite element based heat conduction model in which convection is modelled as boundary condition instead of solving for fluid motion, and 3) Thermal network based model which uses electrical analogy of heat transfer to solve a thermal resistance network. In the first two iterative models mentioned above, heat generation from current-carrying parts is calculated by solving Maxwell’s equations of electromagnetics by Finite element method. Eddy current losses and temperature dependence of electrical conductivity is considered in the calculation of heat loss. In all three methods, electrical and thermal contact resistances are added at appropriate locations based on analytical calculations. All three methods have been validated with temperature rise test results. In this paper, the heat loss and temperature of a molded case circuit breaker have been predicted by all three methods discussed above. It is observed that the Finite volume-based method is the most accurate amongst the three methods. It can computationally predict air motion and air temperature at critical locations. However, this additional accuracy comes at the cost of added effort in terms of additional mesh count and computation. The Finite elementbased method gives good accuracy but does not predict air temperature. The analytical network-based model is less accurate compared to other methods and relies on product expertise and experience. Based on the study, the following recommendations are made:1) The finite element-based method is best suited to evaluate designs which do not alter flow pattern significantly 2) The finite volume method is recommended to evaluate effect of flow altering design changes 3) The network-based model is recommended for initial evaluation of correct cross sections of current carrying members.