Counter-flow Heat Exchanger Research Articles

Design and Simulation of Counter Flow Heat Exchanger with Fins and Internal Ribs

A Heat Exchanger is a device to transfer heat from fluid at higher temperature to fluid at lower temperature with highest efficiency. Designed for various applications such as preheating the water before sending it into boiler for generation of steam. This work is carried out with the primary objective of increasing the thermal efficiency of the procedure heat transfer process. There are different types of heat exchangers from which shell and tube heat exchanger is considered for this present work. High temperature water passes through the copper tubes and low temperature water flows outside the copper tubes. To enhance the rate of heat, transfer the modified design is implemented. The design consists of fins outside the copper tubes to increase the surface area in contact with outside fluid. Also, ribs are provided inside the copper tubes for increasing the turbulence along with more area of contact. This paper mainly deals with design, modelling and CFD analysis of the heat exchanger. Overall heat transfer coefficient of the fins and internal ribs of heat exchanger is based on the results of effectiveness-NTU approach and LMTD approach. Modelling of various components are presented with the help of standard modelling software, solid works. Simulation of the process is done using ANSYS. The simulated results obtained in the software are compared with the published experimental results which are very close to our modified design heat exchanger and it is found that the results are very close to experimental results.

CFD simulation of bubbly flow in a long coaxial heat exchanger

The numerical investigation of a two-phase bubbly flow inside a long vertical counterflow heat exchanger has been performed in this study. The heat transfer was running from the steam moving inside the tubing to the two-phase bubbly water in the annulus. A two-dimensional steady-state heat transfer and fluid flow model are based on the coupling of a probability density function (PDF) coupled with a k-epsilon turbulence model is determined to be the best computation technique in this large-scale case. The k-epsilon model was used to analyze the carrier fluid (water or steam) and the PDF model to calculate bubble flow. The authors desired to receive practical results of the heat transfer process rather than paying attention to the formation of bubbles, their coalescence, tracking flow regimes, and other turbulence-related features that are useless in industrial applications. The article explored two cases: short (800 m) and long heat exchanger (8000 m). Several thermodynamic parameters were on track: flow velocities, pressure, temperature, and concentration of the bubbles in the radial direction. Einstein's correction equation adjusted the viscosity of the bubbles. Solution converged with non-uniform grid spacing in the longitudinal and radial directions. The results gave satisfactory conclusions about the validity of the obtained data with theoretical and experimental results. This article opens a new way on computational fluid dynamics (CFD) application to a large-scale simulation of long vertical or horizontal pipelines and coaxial heat exchangers with the coupled bubbly flow and heat transfer applicable to geothermal and petroleum industry problems.

Hexagonal and mixed arrays of flow channel design in counterflow heat exchanger

Heat exchanging is one of the critical process in a thermal system and requires in depth optimization of equipment configuration. In this study, the advantage of morphing the flow channel design to more complicated configuration is shown for the purpose of enhancing the flow and thermal characteristics of counterflow heat exchanger. The free pursuit for the optimal geometry of flow channel cross-sections will be investigated toward meeting two objectives simultaneously: lower longitudinal (along the flow direction) flow resistances and lower perpendicular (channel to channel) thermal resistance. For hexagonal, square, and triangular ducts, an analytical model is used to evaluate the fluid flow and heat transfer relative performances. The hexagonal array can be packed tightly without leaving spaces in between, such as in packing circular tubes. However, having inactive channels within the hexagonal bundle is one of the main challenges that reduce the thermal performance of counterflow heat exchanger. Thus, a hybrid packing of mixed configurations is considered in this paper for which a 3D numerical model (CFD) is used to analyze its thermal and fluid flow features. The findings reveal that the triangular array offers higher thermal performance as compared to that of the competitive arrays. However, when heating and flow effects are considered simultaneously, the hybrid array provides the improved performance among the other configurations considered.

Investigation of Counterflow Microchannel Heat Exchanger with Hybrid Nanoparticles and PCM Suspension as a Coolant

The effect of the hybrid suspension on the intrinsic characteristics of microencapsulated phase change material (MEPCM) slurry used as a coolant in counterflow microchannel heat exchanger (CFMCHE) with different velocities is investigated numerically. The working fluid used in this paper is a hybrid suspension consisting of nanoparticles and MEPCM particles, in which the particles are suspended in pure water as a base fluid. Two types of hybrid suspension are used (Al2O3 + MEPCM and Cu + MEPCM), and the hydrodynamic and thermal characteristics of these suspensions flowing in a CFMCHE are numerically investigated. The results indicated that using hybrid suspension with high flow velocities improves the performance of the microchannel heat exchanger while resulting in a noticeable increase in pressure drop. Thereupon, it causes a decrease in the performance index. Moreover, it was found that the increment of the nanoparticles’ concentration can rise the low thermal conductivity of the MEPCM slurry, but it also leads to a noticeable increase in pressure drop. Furthermore, it was found that as the thermal conductivity of Cu is higher than that for Al2O3, the enhancement in heat transfer is higher in case of adding Cu particles compared with Al2O3 particles. Therefore, the effectiveness of these materials depends strongly on the application at which CFMCHE is employed.

Effect of shot peening on augmenting the thermo-fluid characteristic of a concentric tube water-to-air counter flow heat exchanger

The current work focuses on heat transfer and pressure drop performance and determines the thermal enhancement factor in a concentric tube heat exchanger (HEX), whereby the external profile of the copper inner tube is modified via shot peening. The Reynolds number of the water-side varied from 6000 to 12,000 and the water temperature varied from 60 to 80 °C. The cold air mass flow rate was maintained at approximately 0.01 kg/s. The Nusselt number of a shot-peened surface HEX was improved by nearly 25.78%, compared with the normal copper tube HEX, where the water inlet temperature and Re were 80 °C and 10,000, respectively. The test outcomes displayed that the increase in surface roughness induces the rise in HTFs turbulence and, successively, an augmentation of Nusselt number. The shot peening process breaks the thickness of the viscid sublayer and it creates the local wall turbulence owing to flow separation and reattachment between the grain particles, which enhances the heat transfer to a considerable amount. The friction factor increased up to 26.82% when Re was 6000 and reduced as Re increased. The thermal enhancement factors were in the range 1.007–1.19 for surface roughness of 6.41 μm.

Influence Of Coiled Wire Presence On The Convective Heat Transfer Coefficients In R-600 Condensers

An experimental investigation has been performed to examine the heat transfer enhancement achieved by helically coiled wire inserts during forced convective condensation of R-600 vapor inside horizontal tubes. The experimental setup is a vapor-compression refrigeration cycle. This system includes a main condenser which is a coaxial double-pipe counter-flow heat exchanger with water as a coolant. To reach the favorable vapor qualities, pre-condenser and after-condenser systems were invoked. Experiments were carried out for plain tube and five different coiled wire inserted tubes. At each test, various parameters were measured like refrigerant mass flow rate, inlet and outlet water temperature of the condenser, refrigerant pressure, etc. Using the acquired data, heat transfer coefficients were calculated for different tubes. Investigation of the results showed that increasing the thickness of the wires can augment the heat transfer rate. Also, it is seen that reducing the coil pitch can enhance the heat transfer rate as high as 31.6%. Also, it was seen that employing coiled wire inserts inside the tube, increases the average heat transfer coefficient up to approximately 80% regarding the plain tube results.

Design and performance analysis of an ejector-equipped Joule–Thomson cryocooler

Ejectors can be used in Joule–Thomson (JT) cooling systems to create sub-atmospheric pressures and to recover expansion work, and thus achieve lower temperatures and higher system efficiencies. As the key components of ejector-equipped JT cryocoolers, ejectors and counter flow heat exchangers (CFHXs) have significant effects on the cryocooler performance. In order to optimize the cryocooler performance, a 1-D ejector model, a 1-D finite-element model of CFHXs and a cryocooler model are developed. Results show that the variation of the ejector entrainment ratio with the primary flow inlet temperature depends on the ejector operation modes. Two tubes-in-tube CFHXs are designed to realize heat recovery with a relatively low pressure drop along the low-pressure channel of the CFHXs. The performance of CFHX I determines the operating conditions of the ejector, and there is an optimal CFHX I length corresponding to the maximum system COP. Differing from CFHX I, the COP increases with the length of CFHX II. For the designed cryocooler with nitrogen as the working fluid, a cooling capacity of 10.89 W at 71.8 K and COP of 0.042 can be obtained, and the COP increases by 13.1% compared to the basic ideal JT cooling cycle with the same cold-end temperature.

A novel particle-to-fluid direct-contact counter-flow heat exchanger for CSP power generation applications: Design features and experimental testing

A novel particle-to-fluid direct-contact counter-flow heat exchanger (PFDCHX) is introduced and investigated. The proposed heat exchanger offers efficient integration with an air-breathing power cycle. A proposed particle-based power tower integrated system using the PFDCHX is presented. The PFDCHX system comprises two main parts: the particle handling unit (PHU) and the direct-contact heat exchanger (DCHX). The PHU delivers solid particles to the pressurized DCHX, a manifold assembly was deployed to separate particles into several separate streams to be injected at the upper end of the DCHX via several distributor pipes. Several enhancement features were considered to prevent particle carryover, including a tangential inlet for the pressurized air (at the bottom end of the DCHX), particle–air disengagement zone (at the top end of the DCHX), and a tapered-shaped heat exchange chamber. Results showed that, for tests with excessive particle flow rate, more than 80% of the temperature rise was achieved within 0.35 m above the air inlet, attributed to the tangential inlet’s swirl flow pattern. The overall temperature rise along the heat exchanger was not significantly influenced by a change in operating air pressure from one barg to three barg.

Catalyst filled heat exchanger for hydrogen liquefaction

Cryogenic hydrogen liquefaction plants have a uniquely designed plate fin heat exchanger (PFHE) in which the fin channels are filled with an ortho-para hydrogen conversion catalyst (O-P catalyst). This PFHE can save liquefaction energy by reducing the heat of liquefaction. Despite the unique heat exchanger design, there are few studies on the thermohydraulic performance of the PFHE for the hydrogen liquefaction process. In this study, the thermohydraulic performance of a PHFE filled with an O-P catalyst is investigated in two steps. In the first step, pressure drop experiments are performed using a cylinder filled with commercial O-P catalyst. The pressure drop is approximately five times lower than that of the Ergun's equation. Therefore, we propose a new correlation for the porous channel filled with the O-P catalyst and apply it in the numerical research, which is the second step. According to the results, the difference in Nu/f1/3 between the new empirical correlation and the Ergun's equation is up to 1.6 times, and the exergy efficiency of the CPFHE is underestimated by Ergun's equation. Furthermore, we report the impact of the design parameters on the heat transfer and pressure drop on a PFHE filled with catalyst. This CPFHE is a counter-flow heat exchanger and includes a porous hot laminar stream and two cold laminar streams through the plain-fin channel. The design parameters are selected based on the fin height and fin spacing. Among the various fin channel designs, the most effective one involves a fin height of 4 mm and a fin spacing of 0.7 mm. Interestingly, at the same Re number, the variation in Nu/f1/3 is almost twice the variation in the fin spacing. Based on these results, we discuss the impact of the design parameters on the PFHE performance, using the performance evaluation plot. Therefore, this study is expected to provide insights and guidance for designing PFHEs in hydrogen liquefaction plants.

Comparative evaluation of flow-through and counter-flow indirect-evaporative air coolers and their influence on the heat balance of transformer underground substations

In order to optimize the air environment temperature of the underground engineering equipment premises, it is necessary to conduct a comparative assessment of the operation of flow-through and counter-flow indirect-evaporative air coolers. Based on the previous mathematical models that describe the thermophysical processes in the channels of indirect evaporative coolers, an analysis of the structural and standard parameters of their operation is carried out. The most rational ratios of flows through the “wet” and “dry channels” are revealed and they ensure the maximum station cooling capacity. The transformer substation of the underground illustrates the effectiveness of their use. According to a result of the studies, it has been proved that the most rational ratio of air flows through wet and dry channels for flow-through indirect-evaporative coolers is 2.1-2.2, for counter-flow heat exchangers it is 3.0. The advantage of recuperation coolers is established by such indicators as: cooling capacity - 53.5%, air cooling range - 41%.

Plate-fin heat exchanger network modeling, design and optimization – a novel and comprehensive algorithm

PurposeThe purpose of this paper is to present a novel and applied method for optimum designing of plate-finned heat exchanger network. Considering the total annual cost as the objective function, a network of plate-finned heat exchanger is designed and optimized.Design/methodology/approachAccurate evaluation of plate-finned heat exchanger networks depends on different fin types with 10 different geometrical parameters of heat exchangers. In this study, fin numbers are considered as the main decision variables and geometrical parameters of fins are considered as the secondary decision variables. The algorithm applies heat transfer and pressure drop coefficients correction method and differential evolution (DE) algorithm to obtain the optimum results. In this paper, optimization and minimization of the total annual cost of heat exchanger network is considered as the objective function.FindingsIn this study, a novel and applied method for optimum designing of plate-finned heat exchanger network is presented. The comprehensive algorithm is applied into a case study and the results are obtained for both counter-flow and cross-flow plate-finned heat exchangers. The total annual cost and total area of the network with counter-flow heat exchangers were 12.5% and 23.27%, respectively, smaller than the corresponding values of the network with cross-flow heat exchanger.Originality/valueIn this paper, a reliable method is used to design, optimize parameters and the economic optimization of heat exchanger network. Taking into account the importance of plate-finned heat exchangers in industrial applications and the complexity in their geometry, the DE methodology is adopted to obtain an optimal geometric configuration. The total annual cost is chosen as the objective function. Applying this technique to a case study illustrates its capability to accurate design plate-finned heat exchangers to improve the objective function of the heat exchanger network from the economic viewpoint with the design of details.

Non-linear filter design for a counter-flow heat exchanger: some investigations

This article presents a second-order non-linear filtering technique for a non-trivial state-dependent noise perturbation case of a counter-flow heat exchanger. The conditional mean and variance evolution equations are derived for the non-linear stochastic differential equations relating the dynamics of a counter-flow heat exchanger. The efficacy of the proposed filtering technique is adjudged through detailed parametric investigations for different flow, temperature and noise intensity conditions. These parametric investigation results and that obtained by employing Extended Kalman Filter are compared. The proposed filtering technique is validated using Computational Fluid Dynamics. Theoretical, as well as simulation results, demonstrate the superiority of the proposed filtering technique for estimating stochastically perturbed counter-flow heat exchanger.

Experimental Investigation on an Absorption Heat Transformer for Production of Hot Water or Steam Generation

The absorption heat transformer is widely used to utilize low-temperature waste heat in the field of distributed energy, industrial processing, and long-distance indoor heating, because it can upgrade energy level and deliver heat to heated medium. In this work, an experimental system of a vertical single-stage LiBr/H2O absorption heat transformer was established to study its performance in the case of producing high-temperature water or low-pressure steam generation under different heating water flow rates. The useful output heat, coefficient of performance, exergy coefficient of performance, and gross temperature lift of the single-stage heat transformer have all been tested. The results show that the absorber cannot directly generate low-pressure steam under the condition of counter-flow heat exchange but can obtain more useful output heat. The largest useful output heat is 20.3 kW, which is higher than that in the case of parallel-flow heat exchange. The generation of low-pressure steam has certain requirements on the mode of heat transfer. The largest internal gross temperature lift of 28.1°C corresponds to the smallest coefficient of performance of 0.22 when the heating water flow rate is 2.1 m3/h. The performance of the single-stage absorption heat transformer can be improved to some extent by increasing the heating water flow rate.

Development of MLP-ANN model to predict the Nusselt number of plain swirl tapes fixed in a counter flow heat exchanger

The plain swirl tapes augmentation technique is most commonly used in the area such as, air conditioning systems, chemical reactors, air refrigeration systems and heat recovery process. Experimental investigation were conducted to predict the Nusselt number of a counter flow concentric heat exchanger with Plain Swirl Tapes of different swirl ratios y = 2.0, y = 4.4 and y = 6.0. The proposed study concentrate on the most popular approach MLP-ANN with 3-layer feed forward neural network is adopted to obtain Nusselt number (Nu) based on the three inputs such as Prandtl number (Pr), twist ratios (y) and Reynolds number (Re) as input variables for heat exchanger with double tube which is attached with plain twisted tape. The experiment has been conducted and generated 33 experimental data which is utilized as training data. Simulation results convey that Nusselt number predicted by the proposed MLP-ANN model has the best correlated with experimental Nusselt number with the accuracy of 90% and error rate of 0.01.

Second-Law Analysis of Micro-Fluidic Counter-Flow Parallel Plate Heat Exchangers: Maximum Effectiveness and its Relation to Minimal Wall Entropy Production

Second-Law Analysis of Micro-Fluidic Counter-Flow Parallel Plate Heat Exchangers: Maximum Effectiveness and its Relation to Minimal Wall Entropy Production

An exergy analysis of a concentric tube heat exchanger using hBN-water nanofluids

This study investigated the effects of using nanofluids prepared with hexagonal boron nitride (hBN) nanoparticles on the thermal performance and pressure drop of a concentric tube heat exchanger. Experiments were carried out with water-hBN nanofluids for stable, dispersed, 0.01%, 0.1% and 1% volume concentrations, at different flow rates and Reynolds numbers under parallel and counter-flow conditions. When the experimental results were examined, the exergy loss was higher in the parallel-flow heat exchanger compared to the counter-flow heat exchanger. The highest exergy loss value was obtained for distilled water at the highest Reynolds number (Re = 8,700) for parallel flow operation at 170 W. The exergy loss of water at the highest Reynolds number (Re = 8,700) for parallel flow operation increased by 15.7%, 24.8% and 49.8% for hBN-water concentrations of 0.01%, 0.1% and 1%, respectively. Exergy loss of water at the highest Reynold number (Re = 8,700) for counter flow operation increased by 11.3%, 17.3% and 29.2% for hBN-water concentrations of 0.01%, 0.1% and 1%, respectively. When evaluating the exergy analysis of the system, exergy losses due to pressure drops were negligible for both flows (parallel and counter).

An exergy analysis of a concentric tube heat exchanger using hBN-water nanofluids

This study investigated the effects of using nanofluids prepared with hexagonal boron nitride (hBN) nanoparticles on the thermal performance and pressure drop of a concentric tube heat exchanger. Experiments were carried out with water-hBN nanofluids for stable, dispersed, 0.01%, 0.1% and 1% volume concentrations, at different flow rates and Reynolds numbers under parallel and counter-flow conditions. When the experimental results were examined, the exergy loss was higher in the parallel-flow heat exchanger compared to the counter-flow heat exchanger. The highest exergy loss value was obtained for distilled water at the highest Reynolds number (Re = 8,700) for parallel flow operation at 170 W. The exergy loss of water at the highest Reynolds number (Re = 8,700) for parallel flow operation increased by 15.7%, 24.8% and 49.8% for hBN-water concentrations of 0.01%, 0.1% and 1%, respectively. Exergy loss of water at the highest Reynold number (Re = 8,700) for counter flow operation increased by 11.3%, 17.3% and 29.2% for hBN-water concentrations of 0.01%, 0.1% and 1%, respectively. When evaluating the exergy analysis of the system, exergy losses due to pressure drops were negligible for both flows (parallel and counter).

A comprehensive analysis for second law attributes of spiral heat exchanger operating with nanofluid using two-phase mixture model: Exergy destruction minimization attitude

The present article focuses on the second law attributes of a counter-flow spiral heat exchanger working with an Al2O3–H2O nanofluid with employing the two-phase mixture model. To improve the cogency of the simulations, the turbulence modeling is performed using four-equation transition Shear Stress Transport (SST) model. The simulations are conducted for different nanoparticle volume fractions and nanofluid flow rates. It is shown that by dispersing further nanoparticles in the common fluid, the total entropy generation of the hot nanofluid significantly diminishes, whereas the cold water and the heat exchanger body exhibit higher thermal entropy generation. The overall exergy destruction in the heat exchanger significantly decreases by the increase of the volume fraction, while it tends to increase by the flow rate increment. For instance, an about 9.2% reduction in the overall exergy destruction is observed as the volume fraction increases from 0.01 to 0.04. All the conditions exhibit great second law efficiency so that the minimum second law efficiency is larger than 0.84, and increases with the raise of either the volume fraction or flow rate.

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.

A low-order dynamic model of counterflow heat exchangers for the purpose of monitoring transient and steady-state operating phases

We present a model-based real-time method to monitor a counterflow heat exchanger’s thermal performance for all operating conditions. A first principle reference model that describes the reference counterflow process in an accurate manner is derived first. Real gas behavior is taken into account. Without simplifications, the respective equations must be solved in an iterative, computationally expensive manner, which prohibits their use for real-time monitoring purposes. Therefore, we propose one-step-solvable model equations, resulting in an approximate but quick model, which is able to track an important thermal property reliably. The monitoring, i.e., the online estimation of the thermal properties, is achieved via a nonlinear Kalman-Filter. Due to the low-order dynamic model formulation, the overall monitoring scheme is accompanied by an acceptable computational burden. Moreover, it is easy to deploy and to adapt in industrial practice. Monitoring results, where the reference model replaces a real process with supercritical carbon dioxide, are given and discussed herein.