Pressure Drop In Heat Exchanger Research Articles

Numerical modeling and optimization of beta-type Stirling engine

Numerical modelling can significantly contribute to the performance enhancement and technological advancement of Stirling engines. In this paper, a practically feasible thermodynamic model was developed for beta type of Stirling engines with rhombic-drive mechanism. Quasi-steady flow approach was adopted to analyze the heat transfer and flow friction effects of the heater, cooler, and regenerator on the performance of engine. The numerical model predicts the output power and thermal efficiency while considering the pressure drop in heat exchangers and numerous power and thermal losses. A parametric study is utilized to investigate the impact of operating and geometric parameters on the power output and efficiency of the Stirling engine. A combination of optimized temperature ratio, swept volume, regenerator matrix porosity, phase angle, pressure and engine frequency are assessed. The optimized model is then compared and validated against the experimental data obtained from the General Motor’s prototype of GPU-3 Stirling engine. Substantial improvement on the performance of the engine is achieved by optimizing the operating and geometric parameters of the engine.

Experimental study on optimum concentration of polyacrylamide for drag reduction and heat transfer performance in a compact heat exchanger

The effects of adding polyacrylamide (PAM) to pure water on pressure drop and heat transfer in a compact heat exchanger was experimentally investigated. Laminar flow was studied to transfer heat between water and air. By adding PAM to water, the pressure drop has continuously decreased until the concentrations of 100 ppm. After this optimum concentration, the pressure drop began to increase. The maximum percentage of drag reduction (%DR) was 14%. On the other hand, the overall heat transfer coefficient decreased with the increase in PAM concentration. In this condition, the overall heat transfer coefficient had reduced by 28%.

Experimental investigation on condensation heat transfer and pressure drop of a low GWP refrigerant R-1233zd(E) in a plate heat exchanger

In this study, condensation heat transfer performance and frictional pressure drop in plate heat exchanger using a low GWP refrigerant R-1233zd(E) as a working fluid are experimentally analyzed. Experiments on single phase water-to-water are also conducted in the tested plate heat exchanger, and the heat transfer coefficient correlation of the cooling water side is derived by applying the modified Wilson plot technique. In the refrigerant-to-water experiments, the influences of heat flux, refrigerant mass flux, and saturation pressure on the heat transfer and pressure drop in the tested plate heat exchanger are analyzed with varying the mean vapor quality. Experimental results show that the heat transfer coefficient increases with increasing the heat flux, mean vapor quality, and the mass flux while it decreases with increasing the saturation pressure. On the other hand, the frictional pressure drop increases with increasing the mass flux and mean vapor quality while it decreases with increasing the saturation pressure. Experimental correlations for predicting Nusselt number and friction factor of R-1233zd(E) in plate heat exchanger are developed and compared against other correlations from literature.

Characterization of a triple concentric-tube heat exchanger with corrugated tubes using Artificial Neural Networks (ANN)

This work presents a model of Artificial Neural Networks (ANNs) capable of accurately predicting the heat transfer rate and pressure drop in a triple concentric-tube heat exchanger (TTHX) with corrugated and non-corrugated inner tubes and involving a fluid typically used in the food industry. Pitch and depth are varied in the case of corrugated tubes. The ANN model was developed and validated using a huge databank including 181 experimental datasets. The best training algorithm is the Bayesian regulation. A back-propagation algorithm, which is considered to be the most common learning method for ANNs, is used in the training and testing of the network. Different network configurations were tested, and the optimum ANN configuration consisted of a network with two hidden layers with 15 and 21 nodes in the first and second layer, respectively. The ANNs results were found to be in good agreement with the experimental data, with the absolute average relative deviation (AARD) being below 1.91% for the heat transfer coefficient and below 3.82% for the pressure drop, respectively. The simplicity of the developed ANN model and its low levels of error for a huge experimental databank are some of the key features of the model.

Inverted Brayton Cycle With Exhaust Gas Condensation

Approximately 30% of the energy from an internal combustion engine is rejected as heat in the exhaust gases. An inverted Brayton cycle (IBC) is one potential means of recovering some of this energy. When a fuel is burnt, water and CO2 are produced and expelled as part of the exhaust gases. In an IBC, in order to reduce compression work, the exhaust gases are cooled before compression up to ambient pressure. If coolant with a low enough temperature is available, it is possible to condense some of the water out of the exhaust gases, further reducing compressor work. In this study, the condensation of exhaust gas water is studied. The results show that the IBC installed in series on a turbocharged engine can produce an improvement of approximately 5% in brake-specific fuel consumption at the baseline conditions chosen and for a compressor inlet temperature of 310 K. The main factors that influence the work output are heat exchanger pressure drop, turbine expansion ratio, coolant temperature, and turbine inlet temperature. For conditions when condensation is possible, the water content of the exhaust gas has a significant influence on work output. The hydrogen to carbon ratio of the fuel has the most potential to vary the water content and hence the work generated by the system. Finally, a number of uses for the water generated have been presented such as to reduce the additional heat rejection required by the cycle. It can also potentially be used for engine water injection to reduce emissions.

Experimental Investigation of Forced Convective Heat Transfer Coefficient & Pressure Drop in Bi-metallic Plate Heat Exchanger

Experimental Investigation of Forced Convective Heat Transfer Coefficient & Pressure Drop in Bi-metallic Plate Heat Exchanger

Thermohydraulic characteristics of a multi-string direct-contact heat exchanger

Direct-contact heat exchangers that involve energy exchange between gas and liquid streams have a variety of applications, including waste heat recovery, thermoelectric power plant cooling, and thermal desalination. Direct-contact heat exchangers are appealing as they may help mitigate potential corrosion, fouling, and scaling of solid surfaces and enhance heat transfer effectiveness. In this study, we experimentally investigate the thermohydraulic characteristics of an economic light-weight direct-contact heat exchanger that incorporates an array of strings of diameter of the order of 0.1–1 mm to sustain flows of thin liquid films. We constructed a 1.6 m-tall prototype heat exchanger with an array of as many as 112 vertically aligned strings. Thin films of a non-evaporating liquid are flown down the strings by gravity and exchange thermal energy with a counterflowing gas stream. We obtained axial liquid temperature profiles and frictional loss in the gas stream for different combinations of liquid and gas flow rates and two different string pitches. Numerical simulation is also performed to help interpret and indirectly validate our experimental results. The overall, gas-side, and liquid-side heat transfer coefficients extracted from the experimentally measured temperature profiles are examined to evaluate the impact of instability in liquid film flows and inter-bead spacing. The applicability of the Reynolds analogy is also assessed using the measured gas-stream pressure drops and air-side heat transfer coefficients. The present study helps improve our understanding of heat transfer and gas-stream pressure drop in string-based direct-contact heat exchangers and provides an experimental database to help systematically optimize their design.

Influence of wet-particle deposition on air-side heat transfer and pressure drop of fin-and-tube heat exchangers

Wet particles have higher propensity to deposit on fin surfaces than dry particles, and may cause a more serious deterioration of the air-side performance of fin-and-tube heat exchanger. The purpose of this paper is to experimentally investigate the influence of deposited wet particles on the air-side heat transfer and pressure drop of heat exchangers. Test samples cover three types of fins, i.e., plate fin, wavy fin and louver fin. Experimental conditions cover the inlet air relative humidity of 50–90%, the inlet air velocity of 1.0–3.0 m s−1, and the particle concentration of 2.1–10.8 g m−3. The results show that wet particles mostly deposit on the leading edge of fins as well as the front part of tubes, and the louver fin is almost completely blocked by the wet particulate fouling. Moreover, the increase of inlet air relative humidity, particle concentration and the decrease of fin pitch reduce the air-side heat transfer and increase the air-side pressure drop after wet particle deposition; the increase of inlet air velocity firstly deteriorates and then enhances the air-side performance; and louver fin is the most conducive to the deterioration of air-side performance.

Design and evaluation of an additively manufactured aircraft heat exchanger

Additive manufacturing (AM) technology has significant potential to improve heat exchanger (HX) performance through incorporation of novel geometries and materials, but there is limited understanding of AM HX functionality relative to conventionally manufactured components. This study compares the performance of conventionally-built plate-fin air–liquid crossflow heat exchangers (i.e., aircraft oil coolers) to additively manufactured heat exchangers of similar geometry. To replicate internal features, three dimensional X-ray computed tomography scans were performed on the conventionally-built heat exchanger. A baseline AM model of the conventional design was designed, as well as an AM model with additional enhancement features on the air side. The two AM heat exchanger geometries were constructed using a laser-based powder bed fusion process with AlSi10Mg aluminum-alloy powder. Visual inspection of the as-built AM HX indicated significant surface roughness and some cracks in the fin-tube joint, but only at the edges of the heat exchanger. Overall heat transfer was increased by about 10 percent for the baseline AM and by 14 percent for the enhanced AM heat exchanger when compared to the conventionally built baseline heat exchanger. Measured air-side pressure drop for the AM heat exchangers was double that of the conventionally built baseline heat exchanger. Overall, this study indicates potential for improved heat transfer and demonstrated functionality of AM HX in realistic applications.

Basic Heat Exchanger Performance Evaluation Method on OTEC

Ocean thermal energy conversion (OTEC) harvests the power from the thermal energy in the ocean, which is reserved in the ocean as the temperature difference between warm surface and cold deep seawaters. In the energy conversion, the heat exchangers transfer the thermal energy to the heat engine, which converts it into power. The pressure drops yielded by piping, valve and heat exchangers cause pump loads, which show significant negative power with respect to net power in OTEC. The heat transfer performance and the pressure drop in heat exchanger depend on the types and shapes of each heat transfer area. Generally, heat exchangers with higher friction factors yield higher heat transfer performance and vice versa. However, heat transfer performance and pressure drop are separately evaluated and there is no comprehensive performance evaluation index for OTEC power take-off. Therefore, this research proposes a new simplified overall performance evaluation method for heat exchangers, which can be comprehensively and easily applied and takes into consideration the heat transfer performance and the pressure drop. The evaluation results on plate-type heat exchangers show that the overall performance in each heat exchanger are elucidated and are quantitatively compared.

A novel method for combined entropy generation and economic optimization of counter-current and co-current heat exchangers

In this paperwork, a novel methodology of entropy generation minimization (EGM) for counter-current and co-current heat exchangers is developed. The methodology can be applied in general case for all types of the heat exchangers with the counter-current and co-current flow configuration. A number of entropy generation units (NEGU) function, along with its pressure drop and temperature difference components, are presented. Additionally, evaluated EGM can be easily incorporated into some optimization algorithms for industrial practice. Beside of the theoretical background, on an example and case study were proved that the EGM analysis could be useful in practical applications of heat exchanger optimization. Furthermore, the correlation between the minimum value of NEGU and minimum of total annual costs (operational and investment costs) have been shown. Based on the EGM methodology, on a case study was presented that pressure drop of the plate counter-current heat exchangers in series should be 36 kPa, in order to achieve minimal annual costs of the 456 EUR/year. The result corresponds to the heat exchangers in series with 2 sections and 46 plates per section.

Discrete phase numerical model and experimental study of hybrid nanofluid heat transfer and pressure drop in plate heat exchanger

In the present study, numerical as well as experimental investigations have been done on the plate heat exchanger using hybrid nanofluid (Al2O3+MWCNT/water) at different concentration to investigate its effect on heat transfer and pressure drop characteristics. Discrete phase model has been used for the investigation using CFD software and results have been compared with the experimental result as well as result of the homogenous model. Effects of different operating parameters (nanofluid inlet temperature, flow rate and volume concentration) have been studied on coolant outlet temperature, heat transfer rate, convective and overall heat transfer coefficients, Nusselt number, friction factor, pressure drop, pumping power, effectiveness and performance index. Velocity and temperature profiles have been also studied for base fluid, nanofluid and hybrid nanofluid. By using hybrid nanofluid, heat transfer coefficient enhances by 39.16% (merit) with negligible increase in pumping power of 1.23% (demerit). An enhancement in heat transfer and pressure drop characteristics; and hence on the effectiveness of plate heat exchanger has been observed while using hybrid nanofluids instead of base fluid.

Numerical simulation of heat transfer enhancement in a plate-fin heat exchanger using a new type of vortex generators

In this work, the effect of different vortex generators on fin-plate heat exchanger performance with a triangular channel cross-section is examined. The analysis is done using finite volume method. The effects of vortex generators in a channel are investigated by consideration of channel temperature and heat transfer coefficient. Six different vortex generators including a simple rectangular vortex generator (SRW), rectangular trapezius vortex generator (RTW), angular rectangular vortex generator (ARW), Wishbone vortex generators (WW), intended vortex generator (IVG) and wavy vortex generator (WVG) have been investigated. The observations suggest that simple rectangular vortex generator increases the heat transfer of fin-plate heat exchanger more than other models. This vortex generator increases heat transfer in the heat exchanger by 7%. However, vortex generators increase the pressure drop in heat exchanger. In addition, by increasing the height of the vortex generators the heat transfer rate is increased and the best angle of attack for the installation of vortex generator is 45°.

Airside heat transfer and pressure drop of louver-finned parallel flow heat exchanger having a drainage channel

Airside heat transfer and pressure drop of louver-finned parallel flow heat exchanger having a drainage channel

Study of Shell and Tube Heat Exchanger with the Effect of Types of Baffles

For evaluation of shell and tube heat exchanger, thermal performance and pressure drop are considered as major factors. Both, thermal performance and pressure drop are dependent on the path of fluid flow and types of baffles in different orientations respectively. Increasing the complexity of baffles enhances heat transfer which also results in higher pressure drop which means higher pumping power is required. This reduces the system efficiency. This paper presents the numerical simulations carried out on different baffles i.e. single segmental, double segmental and helical baffles. This shows the effect of baffles on pressure drop in shell and tube heat exchanger. Single segmental baffles show the formation of dead zones where heat transfer cannot take place effectively. Double segmental baffles reduce the vibrational damage as compared to single segmental baffles. The use of helical baffles shows a decrease in pressure drop due to the elimination of dead zones. The less dead zones result in better heat transfer. The lower pressure drop results in lower pumping power, which in turn increases the overall system efficiency. The comparative results show that helical baffles are more advantageous than other two baffles.

Horizontal distribution of two-phase refrigerant in parallel flat mini-channels

A literature survey revealed that no prior investigation has been conducted on the horizontal distribution of a two-phase refrigerant in mini-channel tubes, which may be of importance for the cooling of heat-generating objects. In this study, we investigated R-134a distribution into four flat tubes inside a horizontal plane. In order to simulate the battery of an electric vehicle, a 600-W power supply was used during our tests. Tests were conducted with mass fluxes ranging from 280 to 480 kg m−2s−1 and an inlet quality of 0.2. The effects of inlet port orientation and heat exchanger inclination on flow distribution were investigated. Results indicated that the effects of heat exchanger inclination on flow distribution were more prevalent than those of inlet port orientation. However, these effects are weakened as mass flux increases. Flow distribution deteriorated as the inclination of the heat exchanger increased. Header pressure drop constituted a significant portion of heat exchanger pressure drop and became more pronounced as mass flux increased.

Prediction of fouling tendency in PHE by data of on-site monitoring. Case study at sugar factory

The fouling deposition on heat transfer surfaces can have significant detrimental effect on heat recuperation and jeopardise the efficiency of energy usage, increasing fossil fuels consumption and harmful environmental effects. The data of plate heat exchanger (PHE) thermal performance monitoring in fouling conditions are presented. PHE is installed at sugar factory for preheating purified thin juice before evaporation. The character of deposits on plate heat transfer surface is examined by opening PHE after the tests. It reviled the scaling and particulate fouling mechanism. Mathematical model for prediction of fouling deposition development in time is proposed, which accounts for shear stress at the channel walls and surface temperature. The model parameters are determined according to industrial tests data. The ways of fouling mitigation in PHE are discussed using the model predictions. It is shown that fouling mitigation in PHE is possible by increasing wall shear stress at the same pressure drop in heat exchanger. It requires to eliminate additional pressure loss in connections and to optimize the number of plates and their arrangement adding some plates with higher corrugation angle. These recommendations are discussed and some are implemented at the factory conditions. That allowed increase the operation time between stops for PHE cleaning maintenance. The proposed model can be directly used for design and maintenance scheduling at the specific factory. It can also be used asa preliminary guidance for energy saving reconstructions in other sugar factories. But the direct model application requires data of fouling formation monitoring to identify its parameters for work with specific media streams prone to fouling.

Enhancement of Heat Transfer for Plate Fin Heat Exchangers Considering the Effects of Fin Arrangements

ABSTRACTIn the present study, the potential of rectangular fins with different fin types of inner zigzag-flat-outer zigzag (B-type) and outer zigzag-flat-outer zigzag (C-type) and with different fin angles of 30° and 90° for 2 mm fin height and 10 mm offset from the horizontal direction for heat transfer enhancement with the use of a conjugated heat transfer approach and for pressure drop in a plate fin heat exchanger is numerically evaluated. The rectangular fins are located on a flat plate channel (A-type). The numerical computations are performed by solving a steady, three-dimensional Navier–Stokes equation and an energy equation by using FLUENT software program. Air is taken as working fluid. The study is carried out at Reynolds number of 400 and inlet temperatures, velocities of cold and hot air are fixed as 300 K, 600 K and 1.338 m.s−1, 0.69 m.s−1, respectively. This study presents new fin geometries which have not been researched in the literature for plate fin heat exchangers. The results show that while the heat transfer is increased by about 10% at the exit of a channel with the fin type of C, it is increased up to 8% for the fin angle of 90° when compared to a channel with A-type under the counter flow. The heat transfer enhancements for different values of Reynolds number and for varying fin heights, fin intervals and also temperature distributions of fluids are investigated for parallel and counter flow.

Computational fluid dynamics (CFD) technique to study the effects of helical wire inserts on heat transfer and pressure drop in a double pipe heat exchanger

In this communication, the computational fluid dynamics (CFD) technique has been employed to study the influence of coiled wire inserts on the Nusselt number, friction coefficient and overall efficiency in double pipe heat-exchangers. For this purpose, some wire coil inserts fitted inside heat-exchangers were meshed and simulated at various Reynolds numbers by using the CFD softwares of Gambit and Fluent. To fulfill reliable and validated results, a big effort was made to generate structural hexahedral meshes over all of the heat-exchanger geometries. The validated models, then, made clear the object and the conditions which could exactly facilitate heat transfer throughout double pipe heat-exchangers. The outcome of this work indicates that taking the advantage of proper wire coils could improve the Nusselt values to 1.77 times. Following the numerical simulation, proper friction coefficient and Nusselt number correlations for various coiled wire inserts with different geometry arrangements under the laminar flow were proposed. Unlike the preceding relations, the correlations of this work are based on the occupied spaces where helical wires take up inside tubes; therefore, the two modified correlations can both be used for non-uniform helical wire insert geometries.

Prospects of the use of nanofluids as working fluids for organic Rankine cycle power systems

The search of novel working fluids for organic Rankine cycle power systems is driven by the recent regulations imposing additional phase-out schedules for substances with adverse environmental characteristics. Recently, nanofluids (i.e. colloidal suspensions of nanoparticles in fluids) have been suggested as potential working fluids for organic Rankine cycle power systems due to their enhanced thermal properties, potentially giving advantages with respect to the design of the components and the cycle performance. Nevertheless, a number of challenges concerning the use of nanofluids must be investigated prior to their practical use. Among other things, the trade-off between enhanced heat transfer and increased pressure drop in heat exchangers, and the impact of the nanoparticles on the working fluid thermophysical properties, must be carefully analyzed. This paper is aimed at evaluating the prospects of using nanofluids as working fluids for organic Rankine cycle power systems. As a preliminary study, nanofluids consisting of a homogenous and stable mixture of different nanoparticles types and a selected organic fluid are simulated on a case study organic Rankine cycle unit for waste heat recovery. The impact of the nanoparticle type and concentration on the heat exchangers size, with respect to the reference case, is analyzed. The results indicate that the heat exchanger area requirements in the boiler decrease around 4 % for a nanoparticle volume concentration of 1 %, without significant differences among nanoparticle types. The pressure drop in the boiler increases up to 18 % for the same nanoparticle concentration, but this is not found to impact negatively the pump power consumption.