Enhancement Of Heat Exchanger Performance Research Articles

Enhancement of heat exchanger performance using additive manufacturing of gyroid lattice structures

Enhancement of heat exchanger performance using additive manufacturing of gyroid lattice structures

Experimental investigation of the effect of air bubbles injection on the performance of a plate heat exchanger

• Air is injected in cold water to enhance the performance of plate heat exchanger . • A first PHEX performance test at various air and hot water flow rates is reported. • NTU and effectiveness are enhanced by up to 12.4 and 14.6 %, respectively. • Entropy generation rate increases up to 4.1 W/K with air bubble injection. • Witte-Shamsundar efficiency reaches a maximum of 96.9% for lowest water flow rate. Injection of sub-millimeter scale air bubbles into liquid flows has been recognized recently as an effective method for thermal performance enhancement of heat exchangers. However, no studies have been reported so far on air injection into the cold liquid stream of plate heat exchangers (PHEX). This approach is investigated experimentally in the present study for the first time in PHEXs to map the energetic and exergetic performance characteristics of a typical PHEXs in terms of the number of transfer units (NTU), effectiveness, entropy generation number, augmentation entropy generation number, rational effectiveness, and Witte-Shamsundar efficiency. Air (150–840 L/h) and hot water (280–880 L/h) streams are mixed in a T-junction mixing chamber before entering the PHEX as a two-phase flow. The results show a remarkable increase in NTU by up to 12.4% due to injected air bubbles, whereas the effectiveness increases by up to 14.6%. On the other hand, considerable increments in entropy generation rate are noticed, reaching a maximum of 4.1 W/K, but this increment was less than 3 folds for most examined cases. Overall, the Witte-Shamsundar efficiency, representing the combined energetic-exergetic performance, reached a maximum of 96.9% at air and hot water flow rates of 350 and 280 L/h, respectively.

Effect of graphene on the performance of heat exchangers and related simulation studies

Industrial growth depends on the availability of energy sources and energy utilization. For various applications which require effective heat transfer between cold fluid and hot fluid (CF and HF), the heat exchangers (HEs) are widely used. The phenomenon related to quicker heat flow can enhance the thermal performance of HEs, resulting in considerable savings in energy. Hence, various methods are employed to improve heat flow characteristics of HEs. The solid particles having higher thermal conductivity can be used to enhance the heat transfer between CF and HFs. The graphene-based nanoparticles (NPs) possess higher thermal conductivity and have better properties such as low erosion, corrosion, higher stability, and hence it is preferred in various HEs. With the advancement in technology, graphene-based NPs can help to reduce the size of the HEs. In this paper, performance enhancement of HEs due to graphene addition in HEs is summarized. Further, simulated studies were carried out to analyze the performance characteristics of HEs by exploring it by using different boundary conditions. The simulation studies can also be extended to other types of exchangers of different designs. In the present studies, the simulated results are compared with experimental values for HF (Water at 40°C) and CF (Water at 21°C) for various flow rates of CF. After a good agreement, simulation studies are extended to Graphene-Water nanofluid (NF), and the results are presented. The simulation studies have proven their capability in predicting parameters related to performance evaluation of HEs.

Energetic and exergetic performance enhancement of heat exchangers via simultaneous use of nanofluid and magnetic swirling flow: A two-phase approach

A high-efficient method has been considered for simultaneously improving the hydrothermal and exergetic performance of heat exchangers. Two-phase Eulerian model is employed in a 3-D numerical study to precisely study the hydrothermal and entropic behaviors of Fe3O4/water ferrofluid, under the effect of a magnetic field inducer. The findings reveal that employing the magnetic field can improve the energetic and exergetic performance by generating a swirling flow in the heat exchanger. The pressure drop and entropy generation minimization are also achieved by the induced flow in comparison with other passive techniques due to the lack of any additional obstacle in the flow path. Results show that in the presence of the magnetic field the thermal and exergy efficiencies increase up to 90% and 33%, respectively. Regarding that, the proposed method for boosting energy and exergy efficiencies of similar applications (like other heat exchangers) can be highly efficient.

Enhancement of Heat Exchanger Performance by Using Dimpled Tube

The enhancement of heat exchanger performance was investigated using dimpled tubes tested at different Reynolds numbers, in the present work four types of dimpled tubes with a specified configuration manufactured, tested and then compared performance with the smooth tube and other passive techniques performance. Two dimpled arrangements along the tube were investigated, these are inline and staggered at constant pitch ratio X/d=4, the test results showed that Nusselts number (heat transfer) of the staggered array is higher than the inline array by 13%. The effect of different depths of the dimple (14.5 mm and 18.5 mm) has been also investigated; a tube with large dimple diameter enhanced the Nusselts number by about 25% for the range of Reynolds number between 4000- 20000. The overall enhancement ratio was used to differentiate the passive technique and comparison of different configurations for the technique itself, the result depicted that the 10 mm dimple diameter with a pitch ratio of X/d= 4 gives better performance than the static mixer and twisted tape techniques. The overall enhancement ratio of the 10 mm dimple diameter is varied from (1.21 to 1.65) that means good performance for a range of Reynolds numbers (4000-20000). This indicates that 21- 65 % of heat transfer area can be saved at the same pumping power compared with the smooth tube heat exchanger.

Performance enhancement of heat exchangers using eccentric tape inserts and nanofluids

Optimizing the performance of solar collectors and photovoltaic thermal systems that are used for heating/cooling of building as well as electricity generation will efficiently help to approach zero-energy buildings. For this purpose, improving the efficiency of heat exchangers as the main part of solar collectors and photovoltaic thermal systems is necessary. In this paper, two passive methods are employed to ameliorate the efficiency of heat exchangers. To do this, the effect of using Al2O3/water nanofluid in a heat exchanger tube with a swirling flow turbulator was studied. A numerical simulation was carried out to obtain thermal–hydraulic performance in the tube with eccentric helical screw-tape turbulators. The influences of different parameters including nanoparticles volume fraction and eccentricity of tube insert on the performance of heat exchanger are investigated. The results reveal that the coefficient of heat transfer enhances approximately 4.5 times by using nanofluid at nanoparticles volume fraction of 4% with helical turbulator compared to the plain tube at nanoparticles volume fraction of 0%. It was also found that the value of Performance Evaluation Criterion ameliorates as the nanoparticle loading increases. The maximum value of Performance Evaluation Criterion reached 2.2 at nanoparticles volume fraction of 4%, Reynolds number of 4000 and eccentricity of 3. The results of this study reveal the potential of the suggested technique to enhance various thermal systems including solar collectors.

Study of mineral fouling mitigation on heat exchanger surface

Investigation on fouling behaviour of calcium carbonate on heat exchanger surfaces as well as mitigation of fouling are presented in this paper. By varying parameters such as concentration of the fouling solution, temperature of the heating surface, type of materials and use of additives, the fouling rate on the test specimens were observed. A set of experiments were performed by using calcium carbonate solution. Fouling rate, fouling resistances and the rate of heat transfers were determined for different heat exchanger material surfaces. Fouling resistance is enhanced by the thermal conductivity and temperature of the heat exchanging surfaces and also by the concentration of the foulant in the solution. The addition of gum arabic additive (benign to the environment) to the solution retarded the rate of deposition. The results of these investigations could be design aid for economic and enhancement of heat exchanger performance.

Experimental Characterization of Heat Transfer and Pressure Drop Inside a Tubular Evaporator Utilizing Advanced Microgrooved Surfaces

Performance enhancement of heat exchangers with a focus in optimum weight/volume and the amount of working fluid in circulation is of significance to a diverse range of industries. This paper presents heat transfer and pressure drop characteristics of a compact tubular evaporator which utilizes a manifold force-fed microchannel design. A microgrooved structure with an aspect ratio of 3:1 (channel width of 100 μm and channel height of 300 μm) forms the channels used on the refrigerant side and minichannels of 1 mm depth were used on the water side. The system was tested using R134a as the refrigerant with a refrigerant flow rate of 6 to 22 g/s and water flow rate of 150 to 640 ml/s. Overall heat transfer coefficients of more than 10,000 W/m2 K were obtained with modest values of pressure drop. The present results indicate a significant enhancement in thermal performance when compared to the state-of-the-art technologies in the same application area.

96/06454 Enhancement of heat exchanger performance using combined electrohydrodynamic and passive methods

Gelled electrolytes prepared from fumed silica for use in absorptive glass mat valve-regulated lead-acid (AGM VRLA) batteries and the effect of veratraldehyde addition on the electrochemical behavior and performance of AGM VRLA batteries are investigated. Cyclic voltammetry is used to investigate differences in the electrochemical behaviors of nongelled and gelled electrolytes and between gelled electrolytes with and without veratraldehyde. Battery performance is tested under 100% depth of discharge (100% DoD) conditions at both low- (0.1 C) and high- (1 C) rate discharges. The addition of silica or veratraldehyde does not affect the main reaction of the lead-acid batteries but tends to suppress the hydrogen evolution reaction. AGM VRLA batteries with gelled electrolytes have a higher discharge capacity and longer cycle life than the conventional nongel AGM VRLA batteries. The addition of 0.005% (w/v) veratraldehyde further improves battery performance, but higher (0.01%, w/v) veratraldehyde concentrations reduce it and correlate with the enhanced growth of lead sulfate crystals. The AGM VRLA battery prepared from a gelled electrolyte containing 0.005% (w/v) veratraldehyde provides the best battery performance in every operating temperature studied (0–60 °C).

Enhancement of heat exchanger performance using combined electrohydrodynamic and passive methods

Improvements are shown in the performance of heat exchangers fitted with passive enhanced tube surfaces by applying up to 30 kV between those surfaces and a surrounding electrode. In this context, enhancement means the addition of corrugations or more complicated surface irregularities, leading to increased surface area and modified bubble contact angles. Although it is now banned, R114 was used as the working fluid, so comparison could be made with previous published work. Equations are derived showing that a local electric field gradient will enhance nucleation rate and decrease critical bubble radius, both leading to improved heat transfer rate. Computational analysis has been used to show that the shapes of passive enhanced surfaces potentially create considerable increases in local field gradient to produce such favourable conditions. An additional by-product is that at far-field strengths of above some 1 kV/mm, boiling hysteresis seems to be eliminated.

Electrostatic effects on pressure drop in tube flows

Electrohydrodynamic effects on forced convection in tubes may have significant implications for enhancement of heat exchanger performance in heat pumps and other devices. Of particular concern in such applications is the possibility of increased pressure drop associated with electrostatic discharge. Large frictional losses could substantially increase the required pumping power, offsetting performance gains associated with improved heat transfer rates. This articles describes a series of experiments designed to determine the effects of corona discharge on pressure fields for air flow in cylindrical tubes. Experiments were performed with a single concentric electrode in the tube and with two nonconcentric electrodes. Measurements were performed at potentials from the onset of measurable current to near the spark-over point and at Reynolds numbers from 10 3 to 2 × 10 4. Friction factors were seen to increase as much as 250 percent over the values obtained in the absence of an applied electric field. Results suggest that the electrostatic effect on pressure drop is very sensitive to current density, Reynolds number, and electrode configuration.