Parallel Flow Heat Exchanger Research Articles

EXERGY TRANSFER CHARACTERISTICS ON LOW TEMPERATURE HEAT EXCHANGERS

By analyzing exergy transfer process of the low temperature heat exchangers operating below the surrounding temperature, the concept of exergy transfer coefficient is put forward and the expressions which involving relevant variables for the exergy transfer coefficient, the heat transfer units number and the ratio of cold to hot fluids heat capacity rate, etc. are derived. Taking the parallel flow, counter flow and cross flow low temperature heat exchangers as examples, the numerical results of exergy transfer coefficient are given and the comparison of exergy transfer coefficient with heat transfer coefficient is analyzed.

Exergy transfer effectiveness on heat exchanger for finite pressure drop

In this paper, exergy transfer effectiveness is defined to describe the performance of heat exchangers operating above/below the surrounding temperature with/without finite pressure drop. It is discussed systemically that the effects of heat transfer units number, the ratio of the heat capacity of cold fluids to that of hot fluids and flow patterns on exergy transfer effectiveness of heat exchangers. Furthermore, the results of exergy transfer effectiveness with a finite pressure drop are compared with those without pressure drop when different objective media, such as ideal gas and incompressible liquid, etc. are applied. The detailed comparisons of the exergy transfer effectiveness with heat transfer effectiveness are also performed for the parallel flow, counter flow and cross flow heat exchangers operating above/below the surrounding temperature.

Observability and reachability for parallel-flow heat exchanger equations

Observability and reachability for parallel-flow heat exchanger equations

On reachability of parallel-flow heat exchanger equations with boundary inputs

This paper is concerned with the problem of reachability of parallel-flow heat exchanger equations with boundary inputs. It is shown that the system with boundary inputs is formulated as a boundary control system which is well-defined in the sense of Curtain and Zwart (1995), and further that it is reachable through a concrete expression of the solution. In addition, the reachable subspace is given for the case where only one boundary input is added to the system.

Two-phase flow distribution of air–water annular flow in a parallel flow heat exchanger

The air and water flow distribution are experimentally studied for a round header – flat tube geometry simulating a parallel flow heat exchanger. The number of branch flat tube is 30. The effects of tube outlet direction, tube protrusion depth as well as mass flux, and quality are investigated. The flow at the header inlet is identified as annular. For the downward flow configuration, the water flow distribution is significantly affected by the tube protrusion depth. For flush-mounted configuration, most of the water flows through frontal part of the header. As the protrusion depth increases, more water is forced to the rear part of the header. The effect of mass flux or quality is qualitatively the same as that of the protrusion depth. Increase of the mass flux or quality forces the water to rear part of the header. For the upward flow configuration, however, most of the water flows through rear part of the header. The protrusion depth, mass flux, or quality does not significantly alter the flow pattern. Possible explanations are provided based on the flow visualization results. Negligible difference on the water flow distribution was observed between the parallel and the reverse flow configuration.

Optimal Design of a Parallel-Flow Heat Exchanger Using a Response Surface Methodology

ABSTRACT The heat and flow characteristics in a single-phase parallel-flow heat exchanger were examined numerically to obtain its optimal shape. A response surface methodology was introduced to predict the performance of the heat exchanger with respect to selected design parameters over the design domain. The design parameters were the inflow and outflow angles of the working fluid and the horizontal and vertical locations of the inlet and outlet. The relative priority of the design parameters was evaluated to identify the most important parameters, and these were then optimized using a response surface methodology. The JF factor was chosen as the evaluation characteristic value since it can consider the heat transfer and pressure drop simultaneously. The JF factor of the optimum model was 5.3% greater than that of the reference model.

Constructal tree-shaped parallel flow heat exchangers

The paper reports the performance of balanced two-stream parallel flow heat exchangers, in which each stream flows as a tree network through its allotted space. The two trees are in parallel flow, and are arranged like two palms pressed against each other. The relationships between effectiveness and number of heat transfer units are developed for several parallel tree flow configurations: (i) constructal dichotomous trees covering uniformly a rectangular area, (ii) trees on a disk-shaped area, and (iii) trees on a square-shaped area. In configurations (ii) and (iii) each stream flows between the center and the periphery of the area. Configurations (i) and (ii) are trees with minimal resistance to fluid flow. Configuration (iii) is designed by minimizing the length of each duct in the network. The performance of the parallel flow configurations is compared with the performance of counterflow configurations. The future use of dendritic heat exchangers in devices with maximal heat transport density is proposed.

Finite element analysis for co‐current and counter‐current parallel flow three‐fluid heat exchanger

PurposeTo study the thermal performance of both co‐current and counter‐current parallel flow heat exchangers. The hot stream is assumed to flow in the middle of two cold streams and exchange heat with them.Design/methodology/approachThe dimensionless governing equations are derived based on the conservation of energy principle and solved using FEM based on subdomain collocation method and Galerkin's method. The results show that the subdomain collocation method is more accurate than the Galerkin's method, as observed when the results obtained are compared with the analytical results for the classical two‐fluid heat exchangers.FindingsThe results are presented in terms of effectiveness and number of transfer units (Ntu) for different values of the governing parameters. The governing parameters are the Ntu, the heat capacity ratios, the overall heat transfer coefficient ratio, and the inlet temperatures parameter. The results show that the effectiveness of the three‐fluid heat exchanger is always higher than that of classical two‐fluid flow heat exchanger for fixed values of the governing parameters. The results also show that for fixed values of the governing parameters, the effectiveness of the counter‐current is higher than the co‐current parallel flow three‐fluid heat exchangers.Research limitations/implicationsOne‐dimensional governing equations are derived based on the conservation of energy principle. The ranges of the governing parameters are: Ntu (0:5), the heat capacity ratios (0:1,000), the overall heat transfer coefficient ratio (0:2), and the inlet temperatures parameter (0:1).Practical implicationsBoth co‐current and counter‐current parallel flow heat exchangers are used in the thermal engineering applications. The design and performance analysis of these heat exchangers are of practical importance.Originality/valueThis paper provides the details of the performance analysis of co‐current and counter‐current parallel flow heat exchangers, which can be used in thermal design.

1101 並行流熱交換器における共役グレツ問題の解析解(OS5-1,オーガナイズドセッション:5 熱と流体の複合現象)

1101 並行流熱交換器における共役グレツ問題の解析解(OS5-1,オーガナイズドセッション:5 熱と流体の複合現象)

Numerical simulation of heat transfer in simultaneously developing flows in parallel rectangular ducts

The F correction factor charts and the ε–NTU relations assume the overall heat transfer coefficient to be constant across the heat exchanger. In microchannel heat exchangers, the short lengths and the comparatively thick walls through which heat is conducted preclude the existence of thermally fully developed flow over a large portion of the heat exchanger. In this study, a parallel flow heat exchanger is numerically simulated to determine the impact of different parameters on the performance and the accuracy of constant heat transfer coefficient assumption. It is shown that there is significant change in the overall heat transfer coefficient in the developing region and that the three-dimensional heat transfer in the heat exchanger wall must be included in the analysis.

境界フィードバックを伴う並流型熱交換方程式の指数安定性について

This paper is concerned with stability analysis of parallel-flow heat exchanger equations with boundary feedback. The parallel-flow heat exchanger equation is super-stable when the boundary inputs are identically zero. However, when a pole assignment problem is considered, a suitable output feedback law needs to be added to the equation in order to produce finite poles. In this paper, it is shown that a C0-semigroup generated by the closed-loop operator, which consists of the parallel-flow heat exchanger equation and an output feedback law, satisfies the spectrum determined growth assumption.

Optimal strategies for steady state heat exchanger operation

Two procedures for deriving the optimal steady state operation of heat exchangers are presented. The first procedure, which is based on calculus of variations, can be used in case the optimization criterion is minimum entropy generation. The second procedure can be used in principle for any optimization criterion. Here the minimum entropy generation and the minimum lost available work are envisaged as examples. Both procedures show that, whatever the optimization criterion, parallel flow heat exchangers cannot be optimal but counter-flow devices can be. The empirical wisdom embodied in conventional counter-flow heat exchangers is examined. The usual ‘equilibrated’ operation is in many cases rather close to the optimum.

Development of gas–solid direct contact heat exchanger by use of axial flow cyclone

A heat exchanger between particulate or granular materials and gas is developed. It makes use of a swirling gas flow similar to the usual cyclone separators but the difference from them is that the swirl making gas is issued into the cyclone chamber with downward axial velocity component. After it turns the flow direction near the bottom of the chamber, the low temperature gas receives heat from high temperature particles supplied from above at the chamber's center. Through this configuration, a direct contact and quasi counter-flow heat exchange pattern is realized so that the effective recovery of heat carried by particles is achieved. A model heat exchanger was manufactured via several numerical experiments and its performances of heat exchange as well as particle recovery were examined. Attaching a small particle diffuser below the particle-feeding nozzle brought about a drastic improvement of the heat exchange performance without deteriorating the particle recovery efficiency. The outlet gas temperature much higher than the particle outlet temperature was finally obtained, which is never realized in the parallel flow heat exchanger.

반응표면법을 이용한 평행류 열교환기의 형상 최적화

The heat and flow characteristics in a single-phase parallel-flow heat exchanger was examined numerically to obtain its optimal shape. A response surface method was introduced to approximately predict its performance with respect to the design parameters over the design domain. The inflow/outflow angle of the working fluid, the location of inlet/outlet, the protruding height of flat tube and the height of header were chosen as a design parameter The evaluation of the relative importance of the design parameters was performed based on a sensitivity analysis. An efficiency index was used as an evaluation characteristics value to simultaneously consider both the heat transfer and the pressure drop. The efficiency index of the optimum model, compared to that of the base model, was increased by 9.3%.

Analytical Entropy Analysis of Recuperative Heat Exchangers

The analytical solutions for the temperature variation of two streams in parallel flow, counter flow and cross-flow heat exchangers and related entropy generation due to heat exchange between the streams are presented. The analysis of limiting cases for the relative entropy generation is performed, and corresponding analytical expressions are given. The obtained results may be included in a more general procedure concerning optimal heat exchanger design.

A semi-analytical method for determining unsteady temperature field in a parallel-flow three-fluid heat exchanger

This paper presents a semi-analytical solution of a set of partial differential equations describing the transient temperature field in a parallel-flow three-fluid heat exchanger. The set of partial differential equations is Laplace-transformed and the resultant set of ordinary differential equations is solved analytically. The inverse of the solution is obtained numerically. Exemplary calculations are performed for the case of a step change in the inlet temperature of one fluid and steady state initial conditions.

Optimal shape of the multi-passage branching system in a single-phase parallel-flow heat exchanger

A numerical simulation is performed to examine the heat and fluid flow characteristics of the branching system in a single-phase parallel-flow heat exchanger (PFHE) and to obtain its optimal shape. The relative importance of the design parameters [injection angle of the working fluid (Θ), inlet shape and location (Yc), and height of the protruding flat tube (Yb)] is determined to decide the optimization sequence. The optimal geometric parameters are obtained as follows: Θ=−21°, Type A, Yc=0 and Yb=0. The heat transfer rate of the optimum model compared to that of the reference model is increased by about 55%. The optimal values of the parameters can be applicable to the Reynolds number ranging from 5000 to 20,000.

A heat exchanger model that includes axial conduction, parasitic heat loads, and property variations

High performance heat exchangers are a critical component in many cryogenic systems and the performance of these devices is typically very sensitive to axial conduction, property variations, and parasitic heat losses to the environment. This paper presents a numerical model of a heat exchanger in which these effects are explicitly modeled. The governing equations are derived, nondimensionalized, discretized, and solved on an exponentially distributed grid. The resulting numerical model is simple to implement and computationally efficient and can therefore easily be integrated into complex system models. The numerical model is validated against analytical solutions in the appropriate limits and then used to investigate the effect of heat exchanger end conditions (adiabatic vs fixed temperature) and radiation parasitics. The numerical model, which explicitly considers the combined effect of several loss mechanisms as they interact, is compared to simple models that consider these effects separately. Finally, the model is applied to an example heat exchanger core under a specific set of operating conditions in order to demonstrate its utility. This numerical model may also be used to examine the effect of property variations including temperature driven changes in specific heat capacity, metal conductivity, parasitic heat load, and heat transfer coefficients and is therefore useful in the design of a variety of cryogenic system components including counter- and parallel-flow heat exchangers for gas liquefaction, mixed-gas refrigeration, and reverse Brayton systems.

A transient experimental method to determine the overall heat transfer coefficient in a concentric tube heat exchanger

An experimental method to determine the overall heat transfer coefficient (U) in a concentric tube, parallel flow heat exchanger is presented. This method is based on transient analysis of such a heat exchanger subjected to an arbitrary temperature change at the inlet of one fluid stream. The transient method of measurement of U can be used for a speedy determination of the thermal performance of a smooth or augmented heat exchanger tube in comparison to a traditional steady-state method. Application of the transient method to a tubular heat exchanger with smooth inner tube is presented. The Nusselt number (Nu) and friction factor (f) obtained for the smooth inner tube over a range of Reynolds number (Re=12,000 - 50,000) are each within ± 5% of Gnielinski's and Filonenko's correlation respectively.

평행류 열교환기 내부의 열유동 해석

In the present study, the heat and flow characteristics of a parallel-flow heat exchanger are numerically analyzed by using three-dimensional turbulent modeling. Heat transfer rate and pressure drop are evaluated using the concept of the efficiency index by varying the locations, the shapes and angles of inlet/outlet, and the protrusion height of flat tube. It is found that negative angle of the inlet improves the heat transfer rate and pressure drop. Results show that the locations of the inlet and outlet should be toward the right side and the left side to the reference model, respectively, in order to enhance the heat transfer rate and pressure drop. Increasing the height of the lower header causes pressure drop to decrease and yields the good flow characteristics. The lower protrusion height of flat tube shows the improvement of the heat transfer rate and pressure drop. The heat transfer rate is greatly affected by the parameters of outlet side such as the location and angle of the outlet. However, the pressure drop is influenced by the parameters of inlet side such as the location and angle of inlet and the height of the header.