Parallel Flow Heat Exchanger Research Articles

Numerical Study on Novel Design for Compact Parallel-Flow Heat Exchanger with Manifolds to Improve Flow Characteristics

Parallel flow heat exchangers with manifolds are widely used in various industries owing to their compact size and ease of application. Research has been conducted to understand their flow characteristics and improve flow distribution and pressure drop performance; however, it is difficult to derive generalized improvements under different conditions for each application. This study proposes a novel design to improve the flow characteristics of a compact heat exchanger with a sudden expansion area of a dividing manifold and uses computational fluid dynamics simulation to verify it. The abrupt cross-sectional area change in the dividing manifold induces a jet flow near the entry region, which causes the flow maldistribution of the first few parallel tubes. To improve the efficiency of the dividing manifold, simple and novel designs with a converging-diverging area in the manifold header have been proposed. Parametric studies on the novel designs show improvements of up to 37.5% and 52.0% flow uniformity and 2.65% and 0.74% pressure drop performance for U- and Z-types, respectively, compared to the base model. Thus, the simple and easily fabricated quadrilateral shape can improve the flow maldistribution and pressure drop caused by a dividing manifold with a sudden area expansion.

Indirect Evaporative Cooling: An Efficient and Convenient Energy System

Evaporative cooling is now an alternative method for the conventional air cooling method. This method does not only save energy but also protect the environment from global warming and hazardous gases. Thus this system is highly efficient and eco-friendly. Evaporative cooling system is further divided into two categories that are direct evaporative cooling system and an indirect evaporative cooling system. The direct evaporative cooling system is not much efficient due to high wet bulb temperature and moisture thus rather than using the direct evaporative cooling system the indirect evaporative cooling system is preferred. This paper discusses comparative studies of performance, working principles, material selection criteria’s and various methods. It also explains the performance under different weather conditions, hybrid structure to reduce the load on the further system. It summarises various aspects like wick attained aluminium sheet is the best material for IEC or counter-flow heat exchanger is effective than parallel-flow heat exchanger. It finally results that indirect evaporative cooling system is moisture free, very effective and environment savings. That can be used in various residential and commercial sectors effectively as an alternative for conventional energy-consuming system.

Numerical modelling of a parallel flow heat exchanger with two-phase heat transfer process

In this analysis a 1-D steady state heat transfer was accomplished for tube and shell type heat exchanger with parallel flow configuration. Molten salt was regarded as a secondary flow that runs in the shell part of the heat exchanger whereas the saturated water was regarded as the primary flow that flows in the tube part of heat exchanger. The analysis is done for 0.1 kg/s mass flow rate of the primary flow and for various mass flow rate of the secondary flow ranging from 0.1 kg/s to 0.6 kg/s. The heat exchanger's thermal characteristics, such as, variation in steam quality and two-phase convective coefficient of the saturated water alongside the length of the tube are collected from the analysis. In addition, temperature profiles for primary and secondary flows are presented in this article. It is found that for the considered geometry of the heat exchanger and the boundary conditions, a 0.376 kg/s mass flow rate of molten salt is required to convert the 0.1 kg/s mass flow rate of primary flow into saturated steam. As a result, a mass flow rate of molten salt which is greater than 0.376 kg/s is required to super heat the primary fluid (water).

Heat transfer intensification in MEMS two-fluid parallel flow heat exchangers by embedding pin fins in microchannels

This work proposes implementation of a passive heat transfer enhancement technique in MEMS two-fluid parallel flow heat exchangers as well as model based investigation of the same; the technique involves embedding square in-line pin-fins in the microchannels of the heat exchanger. Model based study is conducted using MEMS two-fluid heat exchangers, with and without pin fins, for a wide range of Reynolds number and two heat capacity ratios. With increase in Reynolds number, the effectiveness of heat exchangers with pin fins increases in comparison with those without pin fins for all heat capacity ratios; moreover, at low Reynolds number the effectiveness of both types of heat exchangers are equal. The power consumption in heat exchangers with pin-fins is higher than in those without pin-fins; the difference in the power consumption increases with increase in Reynolds number irrespective of the heat capacity ratio. This enhancement technique allows MEMS two-fluid parallel flow heat exchangers operate at higher throughput without compromising the effectiveness. For purposes of simulation, microchannel dimensions are kept at 150 μm (width) by 150 μm (height) by 2 cm (length) and pin fin dimensions are held at 75 μm (width) by 500 μm (pitch) while the Reynolds number is varied between 50 and 1500 for heat capacity ratios of unity and 0.5. For the cases considered for simulation, the maximum increase in effectiveness, relative to the baseline case, achieved is 84% and 66% for balanced and unbalanced flow conditions, respectively. • Square pin-fins embedded in microchannels for heat transfer enhancement of MEMS heat exchangers. • Simulations conducted for Reynolds number from 50 to 1500 and heat capacity ratios of 1 and 0.5. • High effectiveness possible without compromising flow rate and size and weight of heat exchanger. • Penalty of approach is increased pumping power.

Rational Transfer Function Model for a Double-Pipe Parallel-Flow Heat Exchanger

Transfer functions of typical heat exchangers, resulting from their partial differential equations, usually contain irrational functions which quite accurately describe the spatio-temporal nature of the processes occurring therein. However, such an accurate but complex mathematical representation is often not convenient from the practical point of view, and some approximation of the original model would be more useful. This paper discusses approximate rational transfer functions for a typical thick-walled double-pipe heat exchanger working in the parallel-flow configuration. Using the method of lines with the backward difference scheme, the original symmetric hyperbolic partial differential equations describing the heat transfer phenomena are transformed into a set of ordinary differential equations and expressed in the form of N subsystems representing spatial sections of the exchanger. Each section is described by a rational transfer function matrix and their cascade interconnection results in the overall approximation model expressed by a matrix of rational transfer functions of high order. Based on the rational transfer function representation, the frequency and steady-state responses of the approximate model are evaluated and compared with those resulting from its original irrational transfer function model. The presented results show better approximation quality for the “crossover” input–output channels where the in-domain heat conduction effects prevail as compared to the “straightforward” channels, where the transport delay associated with the heat convection dominates.

Effect of non-uniform airflow on the performance of a parallel-flow heat exchanger considering internal fluid distribution—Simulation studies and its experimental validation

A series of tests under uniform and non-uniform airflow conditions were conducted to study the influence of airflow form on the heat transfer capacity of a parallel-flow heat exchanger (PFHX) used as a vehicle radiator. A numerical model of the heat exchanger (HX) based on the principle of internal pressure balance (PIPB) and the method of effectiveness-NTU was proposed, which included the coupled relation between internal fluid distribution and outside airflow distribution. A movable multi-propeller-based device was used to measure the air velocity distribution of the HX in bench test as well as in vehicle wind tunnel test to validate the numerical model. Besides the mean air velocity and the non-uniformity of airflow distribution, the matching degree of the fluid distributions of the two sides (M) was first taken into consideration to investigate the thermal performance of the HX in uneven airflow. It was found that, under the same mean air velocity and non-uniformity, better matching degree of the two side fluid distribution resulted in smaller performance deterioration. Airflow with low mass flow rate and better matching degree of flow distributions could even improve the heat exchanger performance, especially for the HX with small aspect ratios. The results of vehicle wind tunnel test further proved the effectiveness of the method in this work to predict the performance of the HX under realistic uneven airflow.

Role of viscous heating in entransy analyses of convective heat transfer

The entransy theory is widely used and found to be effective in thermal analyses and optimizations. Some researchers considered the entransy variation due to viscous heating as part of entransy dissipation and analyzed convective heat transfer based on the differential relationship between entropy and entransy. However, it has been pointed out that the derivation of the differential relationship between entropy and entransy is incorrect. In this paper, the convective heat transfer processes with viscous heating is reconsidered and analyzed from the viewpoint of the energy conservation and the entransy balance equation. It is shown that the influence of the viscous heating is equivalent to that of an inner heat source. Therefore, the contribution of viscous heating to system entransy should not be treated as part of entransy dissipation, but entransy flow into the system. Two-stream parallel and counter flow heat exchangers with viscous heating and a thermal insulation transportation problem of heavy oil are taken as examples to verify the theoretical analyses intuitively. In the examples, the numerical results show that the entransy dissipation rates could be negative when the influence of the viscous heating on the system entransy is treated as part of the entransy dissipation. This is obviously unreasonable. Meanwhile, when the entransy contribution from the viscous heating to the system entransy is treated as entransy flow into the system, it is shown that the entransy dissipation rate is always positive, and the heat transfer processes can be well explained with the entransy theory.

CFD simulation for evaluation of optimum heat transfer rate in a heat exchanger of an internal combustion engine

Heat exchanger is an essential component of an engine cooling system. Radiators are compact heat exchangers used to transfer the heat absorbed from engine to the cooling media. The jacket cooling water gets cooled and re-circulated into system after exchanging the heat with cooling water in a heat exchanger. Conventional fluids like water, oil, ethylene glycol, etc. possess less heat transfer performance; therefore, it is essential to have a compact and effective heat transfer system to obtain the required heat transfer. A reduction in energy consumption is possible by improving the performance of heat exchanging systems and incorporating various heat transfer enhancement techniques. In this paper, the heat transfer rate using nano-sized ferrofluid with and without magnetization is analysed using CFD simulation and compared with the experimental values obtained from a heat exchanger using water as base fluid. The heat transfer rate is measured using different combinations by varying the percentage of nano particles and by introduction of different magnetic intensity (gauss) on to the ferrofluid. The optimum heat transfer rate and efficiency of heat exchanger is calculated with the different combinations and the values are compared with the values of CFD simulation. CFD simulation was undertaken for water alone as cooling media and for water with ferro particle addition from 2% to 5%. The difference in temperature observed to be similar with experimental values. The deviation is within the acceptable limit and therefore the experimental findings are validated. The experiment was conducted on a parallel flow heat exchanger with water alone as cooling media, water with varying percentage of ferro fluid and water with varying magnetic intensity on ferrofluid. Percentage of ferro particles added up to where the optimum temperature difference could be obtained and the magnetic intensity also varied up to the optimum value.

Characteristics of flow distribution in central-type compact parallel flow heat exchangers with modified inlet and header

This study numerically investigated the effect of the application of modified methods in a central-type parallel central-type heat exchanger on the flow distribution. For the flow maldistribution in the heat exchanger, it can greatly reduce the device performance. Therefore, It is significant to apply methods to the modification of the heat exchanger geometry for a better flow distribution. Except for the reducing the flow maldistribution, the reduction of the pressure drop in the heat exchanger should also be taken into account especially in the passive system such as passive containment cooling system and passive core cooling system etc., which are driven by natural circulation flow. Taken both flow maldistribution and pressure drop into consideration, four different methods have been applied in this study for a better flow distribution and less pressure drop. The methods include modifications of double-inlet and header. Besides, the inlet diameter and the insert angle and inlet have been investigated. The simulation results show that the modified double-inlet can reduce the flow maldistribution by 66.36% at most and pressure drop by 29.62% at the mean time. The modified header is able to reduce flow maldistribution by 53.16% at most and pressure drop by 36.03% meanwhile.

Enumeration of Parallel Flow Heat Exchanger using RK-4 Numerical Method

This paper presents the details of theoretical and numerical investigation of parallel flow heat exchanger. Theoretical or Empirical Formulae are used only for simpler geometry object but numerical technique can be used for complex geometry. Runge-Kutta fourth order numerical method is used here for high accuracy. Accuracy is also increased by increasing the number of elements. The numerical results had high degree of consistency and showed a perfect match with the theoretical readings. Using the parallel flow arrangement, the temperature difference between the hot and cold fluid dropped from 70 oC at the entry side to 40 oC at the exit of the heat exchanger

Experimental study on Al2O3 /H2O nanofluid with conical sectional insert in concentric tube heat exchanger

ABSTRACT A parallel flow heat exchanger containing conical sectional inserts with three different pitch ratio (i.e., 1, 2, and 3) in a different orientation to the flow direction of the working fluid had been fabricated. Al2O3 with different volume concentration, i.e., 0%, 2%, and 4% nanoparticles (90 nm size) were added to De-ionized water as the working fluid. The combined effect of the Nanofluid and the inserts in different orientations was studied. It was concluded that the insert, flow direction, and Nanofluid volume concentration provided most augmented heat transfer and enhanced the thermal properties.

Improvement of two-phase refrigerant distribution for upward flow of a parallel flow minichannel heat exchanger using insertion devices

In a parallel flow heat exchanger, significant mal-distribution of flow occurs due to phase separation. In this study, various insert devices (perforated tube, perforated tube with perforated plate, orifice and perforated tube, concentric perforated tube) were investigated to obtain an improved flow distribution in a 36 channel parallel flow heat exchanger. The test section was made to closely simulate an actual heat exchanger. Tests were conducted for upward flow for the mass flux from 57 to 241 kg m−2 s−1 and quality from 0.2 to 0.4 using R-410A. Of the investigated insert devices, concentric perforated tube yielded the best flow distribution. Insertion of the concentric perforated tube reduced the thermal degradation from 61% to 14%. Furthermore, the preferred number of holes of the concentric perforated tube was dependent on the mass flux. At a low mass flux, an insert having small number of holes was preferred, whereas the reverse was true at a high mass flux. At a low mass flux, the effect of inlet vapor quality on flow distribution was significant. At a high mass flux, however, the effect of vapor quality on flow distribution was minimal. Possible explanations on the flow distribution behavior were provided through flow visualization in the header.

Design and Analysis of Parallel Flow Heat Exchanger with Baffles

Design and Analysis of Parallel Flow Heat Exchanger with Baffles

Thermal performance of an active thermoelectric ventilation system applied for built space cooling: Network model and finite time thermodynamic optimization

An active thermoelectric ventilated (ATEV) system coupling with multiple thermoelectric coolers and heat sinks was proposed in the present work. Depending on global energy balance and finite time thermodynamics, performance parameters were firstly presented, including cooling capacity, entropy generation and coefficient of performance (COP). Subsequently, two analytical sub-models respectively for parallel flow heat exchangers and counter flow ones were developed. Input current of thermoelectric coolers, quantitative numbers of thermoelectric coolers and two heat exchanger types (parallel and counter flows) were sensitively varied to optimize overall performance of this system. In a representative residential space, demo case comparisons between traditional thermoelectric cooling units and present ATEV system have been conducted. When the number of thermoelectric coolers exceeded eight, cooling capacity of this new system decreased remarkably. For parallel flow heat exchangers, the entropy generation rate (Sg) firstly dropped and then started to increase; for counter flow heat exchangers, whereas, it continuously decreased with increasing unit cell numbers. Overall, present ATEV system integrating built envelope wall and thermoelectric modules simultaneously could be a promising technology to enhance space cooling, whatever for built residents or electronic facilities.

Numerical investigation of swirl flow effect on heat exchanger efficiency according to different inlet position and Reynolds number

The aim of this investigation is to determine the configuration that will enable a micro heat exchanger system to function more efficiently. Heat exchangers are devices that can be used for exchanging energy between flows, which can have a wide variety of uses and different configurations; therefore, studies are carried out in order to increase the efficiency of heat exchangers. In this study, heat transfer capacity and system efficiency of the swirl flow were investigated using CFD as compared to the parallel flow heat exchanger, which is another configuration. The air drawn by the fan is sucked into the holes and enters the system, thereby air entering the system impinges on the heat exchanger tube. The flow character has a major role on the Nusselt number and heat transfer coefficient. The main flow variables are Reynolds number and the orientation of the inlet holes. The boundary conditions were determined according to the fan capabilities and power of resistance. The positions and types of the holes were adjusted to allow for axial and tangential impact onto the heat exchanger tube, and the holes were also located in order to obtain the best impingement angle. CFD simulations were carried out with ANSYS Fluent and k-epsilon turbulent model was used with coupled algorithm. The effect of laminar flow on the heat transfer were observed at different Reynolds numbers. Also the effect of swirl flow characteristics on system efficiency is clearly observed as compared to parallel flow.

Parameters optimization of a parallel-flow heat exchanger with a new type of anti-vibration baffle and coiled wire using Taguchi method

This study presents the thermal-hydraulic optimization of the design parameters of a parallel-flow shell-and-tube heat exchanger with a new type of anti-vibration hexagon clamping baffle and equilateral triangle cross-sectioned coiled wire. A periodic flow unit duct with non-staggered tube layout is adopted as the numerical analysis model by Fluent. The Taguchi method is used to explore the influence of five geometric parameters including baffle distance (A), baffle width (B), coil diameter (C), coil pitch (D), and the side length of the equilateral triangle (E). An L18 (35) orthogonal array is chosen to carry out the numerical simulation. The comprehensive thermal-hydraulic performance evaluation criterion (PEC) is set as the optimization goal. The results show that the order of the factor effectiveness for the Nusselt number is E>C>A>D>B, for the flow friction is C>E>A>B>D and for the PEC is C>E>A>B>D. This means that the coil pitch has a great influence while the baffle width and the coil diameter have a trifling effect. Finally, the optimal factor combination for PEC is obtained. The PEC of the optimal combination is 0.19%–1.92% higher than the model with better comprehensive performance among 18 cases for Reynolds number in the range from 14 465 to 32 547.

RETRACTED: Production of Hydrogen by Methane Steam Reforming Coupled with Catalytic Combustion in Integrated Microchannel Reactors

This paper addresses the issues related to the rapid production of hydrogen from methane steam reforming by means of process intensification. Methane steam reforming coupled with catalytic combustion in thermally integrated microchannel reactors for the production of hydrogen was investigated numerically. The effect of the catalyst, flow arrangement, and reactor dimension was assessed to optimize the design of the system. The thermal interaction between reforming and combustion was investigated for the purpose of the rapid production of hydrogen. The importance of thermal management was discussed in detail, and a theoretical analysis was made on the transport phenomena during each of the reforming and combustion processes. The results indicated that the design of a thermally integrated system operated at millisecond contact times is feasible. The design benefits from the miniaturization of the reactors, but the improvement in catalyst performance is also required to ensure the rapid production of hydrogen, especially for the reforming process. The efficiency of heat exchange can be greatly improved by decreasing the gap distance. The flow rates should be well designed on both sides of the reactor to meet the requirements of both materials and combustion stability. The flow arrangement plays a vital role in the operation of the thermally integrated reactor, and the design in a parallel-flow heat exchanger is preferred to optimize the distribution of energy in the system. The catalyst loading is an important design parameter to optimize reactor performance and must be carefully designed. Finally, engineering maps were constructed to design thermally integrated devices with desired power, and operating windows were also determined.

Reducing the Flow Distribution in Central-Type Compact Parallel Flow Heat Exchangers Having Optimized Tube Structure

Compact parallel manifolds are widely applied in flow heat exchangers. However, the flow maldistribution exists in the parallel manifolds when the flow is distributed in the header, because of the pressure maldistribution. For a heat exchanger, the uniformity of the flow distribution greatly influence the performance of the heat exchanger. It is significantly important to modify the design of the heat exchanger for a uniform flow distribution. In present study, to reduce the maldistribution in the manifolds, the numerical analysis has been made and a method by varying the insert length of tubes inside the header has been pointed out to solve this problem of flow maldistribution. To illustrate the reliability of this method to reduce the maldistribution, three base cases with different header diameters have been applied to be solved with the method. The results indicates that, by using the method, the maldistribution for three base cases can be reduced by 82% for the case1, 72% for the case2 and 68% for the case3. However, the insert length of tubes inside the header increases more pressure loss. The pressure drop for base cases are respectively increased by 2.83%, 4.83% and 6.46%. This method is proved to be effective under all flow rates.

Heat exchanger dynamic analysis

• Energy balance model yielding the system governing, partial differential equations. • The multivariable, multi-dimensional, Laplace transformed formulation of heat exchanger representations. • A frequency domain description of the system model is derived enabling the recovery of rationality. • The system is irrational in terms of s for both parallel and counter flow heat exchanger models. The modeling and dynamic analysis of shell and tube heat exchangers will be considered in this contribution. Procedures which incorporate the heat transfer and the fluid flow system properties, for these processes, will be developed. An incremental, energy balance yielding the system, partial differential equations presents the governing process. The multivariable, multi-dimensional, Laplace transformed, distributed parameter formulation of heat exchanger representations, are provided. A frequency domain description of the system model is derived enabling the recovery of Laplace function rationality for both parallel and counter flow heat exchanger models. Suitable feedback control techniques are identified, as a prelude to closed loop design studies. The dynamics, for tubular heat exchangers are computed, for purposes of comparison with alternative response and regulation approaches. A typical application study is outlined.

Local Entropy Production of the Parallel Flow and Counterflow Heat Exchanger

Local Entropy Production of the Parallel Flow and Counterflow Heat Exchanger