Numerical evaluation of the heat transfer in a shell and corrugated coil tube heat exchanger with three various water-based nanofluids

In this paper, turbulence heat transfer and nanofluid flow in a shell and corrugated coil tube heat exchanger are evaluated numerically. The three-dimensional numerical simulations have been done by finite volume method using a commercial computational fluid dynamics code. The spatial discretization of mass, momentum, turbulence dissipation rate, and turbulence kinetic energy equations has been achieved by a second-order upwind scheme. A SIMPLE algorithm has been used for velocity–pressure coupling. To calculate gradients, Green-Gauss cell-based method has been utilized. The cross-section of the coil tube is lobe shaped. First, the impact of corrugated tube cross-section type and then, the impact of utilizing different types of nanofluid on thermal performance are investigated. The outcomes indicate that at high Reynolds number, utilizing a five-lobe cross-section causes augmentation in Nusselt number and pressure drop by about 4.8% and 3.7%, respectively. However, the three-lobe type shows the highest thermal performance. Moreover, water/CuO has the most thermal performance. As the volume concentration of the nanofluid increases, the thermal performance declines.     

Heat transfer characteristics in double tube helical heat exchangers using nanofluids

In the present work a three-dimensional analysis is used to study the heat transfer characteristics of a double-tube helical heat exchangers using nanofluids under laminar flow conditions. CuO and TiO₂ nanoparticles with diameters of 24 nm dispersed in water with volume concentrations of 0.5–3 vol.% are used as the working fluid. The mass flow rate of the nanofluid from the inner tube was kept and the mass flow rate of the water from the annulus was set at either half, full, or double the value. The variations of the nanofluids and water temperatures, heat transfer rates and heat transfer coefficients along inner and outer tubes are shown in the paper. Effects of nanoparticles concentration level and of the Dean number on the heat transfer rates and heat transfer coefficients are presented. The results show that for 2% CuO nanoparticles in water and same mass flow rate in inner tube and annulus, the heat transfer rate of the nanofluid was approximately 14% greater than of pure water and the heat transfer rate of water from annulus than through the inner tube flowing nanofluids was approximately 19% greater than for the case which through the inner and outer tubes flow water. The results also show that the convective heat transfer coefficients of the nanofluids and water increased with increasing of the mass flow rate and with the Dean number. The results have been validated by comparison of simulations with the data computed by empirical equations.     

Heat transfer enhancement of nanofluids in a double pipe heat exchanger with louvered strip inserts

The effect of using louvered strip inserts placed in a circular double pipe heat exchanger on the thermal and flow fields utilizing various types of nanofluids is studied numerically. The continuity, momentum and energy equations are solved by means of a finite volume method (FVM). The top and the bottom walls of the pipe are heated with a uniform heat flux boundary condition. Two different louvered strip insert arrangements (forward and backward) are used in this study with a Reynolds number range of 10,000 to 50,000. The effects of various louvered strip slant angles and pitches are also investigated. Four different types of nanoparticles, Al₂O₃, CuO, SiO₂, and ZnO with different volume fractions in the range of 1% to 4% and different nanoparticle diameters in the range of 20 nm to 50 nm, dispersed in a base fluid (water) are used. The numerical results indicate that the forward louvered strip arrangement can promote the heat transfer by approximately 367% to 411% at the highest slant angle of α = 30° and lowest pitch of S = 30 mm. The maximal skin friction coefficient of the enhanced tube is around 10 times than that of the smooth tube and the value of performance evaluation criterion (PEC) lies in the range of 1.28–1.56. It is found that SiO₂ nanofluid has the highest Nusselt number value, followed by Al₂O₃, ZnO, and CuO while pure water has the lowest Nusselt number. The results show that the Nusselt number increases with decreasing the nanoparticle diameter and it increases slightly with increasing the volume fraction of nanoparticles. The results reveal that there is a slight change in the skin friction coefficient when nanoparticle diameters of SiO₂ nanofluid are varied.     

Experimental study on the heat transfer enhancement of MWNT-water nanofluid in a shell and tube heat exchanger

Heat transfer enhancement of multi-walled carbon natube(MWNT)/water nanofluid in a horizontal shell and tube heat exchanger has been studied experimentally. Carbon nanotubes were synthesized by the use of catalytic chemical vapor deposition (CCVD) method over Co–Mo/MgO nanocatalyst. Obtained MWNTs were purified using a three stage method. COOH functional groups were inserted for making the nanotubes hydrophilic and increasing the stability of the nanofluid. The results indicate that heat transfer enhances in the presence of multi-walled nanotubes in comparison with the base fluid.     

Fluid flow and heat transfer in fluidized bed vertical shell and tube type heat exchanger

Measurements were made on the effects of circulating solid particles on the characteristics of fluid flow and heat transfer in the fluidized bed vertical shell and tube type heat exchanger with counterflow. The present work showed that the flow velocity range for collision of particles to the tube wall was higher with heavier density solid particles, and the increase in heat transfer was in the order of sand, copper, steel, aluminum, and glass.     

Heat transfer performance and exergy analyses of a corrugated plate heat exchanger using metal oxide nanofluids

Heat exchangers have been widely used for efficient heat transfer from one medium to another. Nanofluids are potential coolants, which can afford excellent thermal performance in heat exchangers. This study examined the effects of water and CuO/water nanofluids (as coolants) on heat transfer coefficient, heat transfer rate, frictional loss, pressure drop, pumping power and exergy destruction in the corrugated plate heat exchanger. The heat transfer coefficient of CuO/water nanofluids increased about 18.50 to 27.20% with the enhancement of nanoparticles volume concentration from 0.50 to 1.50% compared to water. Moreover, improvement in heat transfer rate was observed for nanofluids. On the other hand, exergy loss was reduced by 24% employing nanofluids as a heat transfer medium with comparing to conventional fluid. Besides, 34% higher exergetic heat transfer effectiveness was found for 1.5 vol.% of nanoparticles. It has a small penalty in the pumping power. Hence, the plate heat exchanger performance can be improved by adapting the working fluid with CuO/water nanofluids.     

Heat transfer characteristics of a temperature-dependent-property fluid in shell and coiled tube heat exchangers

An experimental investigation was performed to study the heat transfer characteristics of temperature-dependent-property engine-oil inside shell and coiled tube heat exchangers. For this purpose, a well-instrumented set-up was designed and constructed. Three heat exchangers with different coil pitches were selected as the test section for counter-flow configuration. Engine-oil was circulated inside the inner coiled tube, while coolant water flowed in the shell. All the required parameters like inlet and outlet temperatures of tube-side and shell-side fluids, flow rate of fluids, etc were measured using appropriate instruments. An empirical correlation existed in the previous literature for evaluating the shell-side Nusselt number was invoked to calculate the heat transfer coefficients of the temperature-dependent-property fluid flowing in the tube-side of the heat exchangers. Using the data of the present study, an empirical correlation was developed to predict the heat transfer coefficients of the temperature-dependent-property fluid flowing inside the shell and coiled tube heat exchangers.     

Effect of nanoparticle shape on the heat transfer and thermodynamic performance of a shell and tube heat exchanger

Nanofluid is a heat transfer fluid that can improve the performance of heat exchanger systems. Different parameters such as particle size, shape, and volume concentration affect the performance of these systems. The objective of this paper is to study the effect of different nanoparticle shapes (such as cylindrical, bricks, blades, platelets, and spherical) on the performance of a shell and tube heat exchanger operating with nanofluid analytically. Boehmite alumina (γ-AlOOH) nanoparticles of different shapes were dispersed in a mixture of water/ethylene glycol as the nanofluid. The thermodynamic performance of the shell and tube heat exchanger that is used in a waste heat recovery system was analysed in terms of heat transfer rate and entropy generation. Established correlations were used to measure the thermal conductivity, heat transfer coefficient and rate and entropy generation of nanofluid. The results show an increase in both the heat transfer and thermodynamic performance of the system. However, among the five nanoparticle shapes, cylindrical shape exhibited better heat transfer characteristics and heat transfer rate. On the other hand, entropy generation for nanofluids containing cylindrical shaped nanoparticles was higher in comparison with the other nanoparticle shapes. However, the increased percentage of entropy was below 1%. Therefore, this greater entropy generation could be deemed negligible and cylindrical shaped nanoparticles are recommended to be utilized in heat exchanger systems working with nanofluids.     

Heat transfer and pressure drop performance of twisted oval tube heat exchanger

Twisted oval tube heat exchanger is a type of heat exchanger that aims at improving the heat transfer coefficient of the tube side and also decreasing the pressure drop of the shell side. In the present work, tube side and shell side heat transfer and pressure drop performances of a twisted oval tube heat exchanger has been experimentally studied. The tube side study shows that the tube side heat transfer coefficient and pressure drop in a twisted oval tube are both higher than in a smooth round tube. The shell side study shows that the lower the modified Froude number Fr_M, the higher the shell side heat transfer coefficient and pressure drop. In order to comparatively analyze its shell side performance of the heat exchanger, a rod baffle heat exchanger with similar size of the twisted oval tube heat exchanger is designed and its performance is calculated with Gentry's method. The comparative study shows that the heat transfer coefficient of the twisted oval tube heat exchanger is higher and the pressure drop is lower than the rod baffle heat exchanger. In order to evaluate the overall performance of the twisted oval tube heat exchanger, a performance evaluation criterion considering both the tube side and shell side performance of a heat exchanger is proposed and applied. The analyze of the overall performance of the twisted oval tube shows that the twisted oval tube heat exchangers works more effective at low tube side flow rate and high shell side flow rate.     

Heat transfer intensification in horizontal shell and tube latent heat storage unit

Employment of latent heat storage unit (LHSU) utilizing phase change material (PCM) in a substantial scale is constrained by the poor thermal conductivity of PCMs. Future utilization of LHSU will therefore to a great extent rely on the heat transfer intensification techniques. Present research is on enhancement techniques in which heat transfer mechanism is altered without altering the mass of PCM and heat transfer surface area. The intensification mechanisms considered in the present research include imparting eccentricity to heat transfer fluid (HTF) pipe, imparting rotation to the LHSU and providing multi HTF tube. Numerical investigations are reported here towards comparative evaluation of the thermal characteristics associated with such intensification mechanisms for horizontal LHSU. In the present study stearic acid (melting point 55.7–56.6?°C) is used as PCM and water is used as HTF. Results infer that all the three mechanisms offer quicker melting rate. For the geometric configuration of LHSU considered in the present research, a reduction in melting time of 47.75% is evaluated for rotating LHSU. The rate of energy storage is higher for both eccentric and rotating LHSU. Solidification process is however not accelerated by such techniques. On the contrary, eccentric and multi HTF tube LHSU takes more time for solidification.     

Finite element analysis of shell and tube heat exchanger

A finite element model to predict temperature distribution in heat exchangers is reported. The model can be effectively used to analyse and design the heat exchangers with complex flow arrangements for which no regular design procedure is available. Illustrations are provided to explain the application of the method for the analysis of shell and tube heat exchangers.     

Heat and mass transfer from a single horizontal tube of an evaporative tubular heat exchanger

In this investigation, water side heat transfer coefficients without air flow from a single horizontal tubes are determined. Mass transfer coefficients are determined with water and air flow from the same tube. The total energy dissipated by inside hot fluid when only water is falling is compared with that when both the air and water flow past the tube. The water side heat transfer coefficient and mass transfer coefficient are given by empirical relations h_w = 6.0(Re_p)^0.18(Re_w)^0.87 and K = 3.5(Re_p)^0.18(Re_a)^0.28 (Re_w)^0.54, respectively. The ratio of energies dissipated with water and air flow and with only water flow increases with Re_w and Re_a and its maximum value is 1.72 in the range of variables used.     

Thermal performance investigation of SWCNT and graphene quantum dots nanofluids in a shell and tube heat exchanger by using fin blade tubes

The experimental study, thermal performance, and pressure drop of single-walled carbon nanotube (SWCNT) and graphene quantum dot (GQD) nanofluids in shell and tube heat exchanger with fin blade tubes are evaluated. The effects of the working fluid (water) volume flow rates ($\dot{V}=$ 2.5–10 L/min), volume concentration of nanoparticles ($\omega =$ 0.0%, 1%, 3%, and 5%), Reynolds number of working fluid (Re = 850–3300), and tube building (heat exchanger with fin blade tubes and without fin blade tube) have been analyzed. Results represent that with augmentation of volume concentration of SWCNT nanoparticle up to 1%, heat transfer rate increases by ∼5% and then up to 5% volume concentration of SWCNT nanoparticle decreased about 17%, also this calculation for GQD nanoparticle conducted and results represented decreasing 6% and approximately unchanged heat transfer rate, respectively. With regard to obtained results, heat transfer rate of heat exchanger can be improved by using the fin blades by 188%, compered without fin blade heat exchanger also most related increase for pressure drop of heat exchanger was recorded about 80% for 5% SWCNT of nanofluid. At the end, the mean enhancement in effectiveness of heat exchanger with various concentrations of SWCNT and GQD nanofluids and using the fin blades is about over 100% and 85%, respectively. In fact, the present study shows that applying the new finned tubes in the heat exchanger has more impact, related to the mentioned nanoparticles on the thermal properties of heat exchanger.     

Optimisation of heat transfer enhancement devices in a bayonet tube heat exchanger

This paper considers the assessment and analysis of heat transfer enhancement devices which can be considered for a bayonet tube heat exchanger. Due to restraining conditions, such as material selection, manufacturing complexity, etc., simple rib roughened surfaces in the form of rings were used on the air side flow, in the annulus. Analysis of the effect of the rings were studied, starting from cited geometries, using computational fluid dynamics. Validation was carried out using laser diagnostics. For the range of Reynolds numbers (Re_ave=160,000) considered the optimal ring configuration was a ring to annulus height ratio of 0.37 with a pitch to ring height ratio of 10. This provided the optimal heat flux to pressure drop for the given conditions.     

Turbulent heat transfer enhancement in a heat exchanger using helically corrugated tube

The augmentation of convective heat transfer in a single-phase turbulent flow by using helically corrugated tubes has been experimentally investigated. Effects of pitch-to-diameter ratio (P/D_H = 0.18, 0.22 and 0.27) and rib-height to diameter ratio (e/D_H = 0.02, 0.04 and 0.06) of helically corrugated tubes on the heat transfer enhancement, isothermal friction and thermal performance factor in a concentric tube heat exchanger are examined. The experiments were conducted over a wide range of turbulent fluid flow of Reynolds number from 5500 to 60,000 by employing water as the test fluid. Experimental results show that the heat transfer and thermal performance of the corrugated tube are considerably increased compared to those of the smooth tube. The mean increase in heat transfer rate is between 123% and 232% at the test range, depending on the rib height/pitch ratios and Reynolds number while the maximum thermal performance is found to be about 2.3 for using the corrugated tube with P/D_H = 0.27 and e/D_H = 0.06 at low Reynolds number. Also, the pressure loss result reveals that the average friction factor of the corrugated tube is in a range between 1.46 and 1.93 times over the smooth tube. In addition, correlations of the Nusselt number, friction factor and thermal performance factor in terms of pitch ratio (P/D_H), rib-height ratio (e/D_H), Reynolds number (Re), and Prandtl number (Pr) for the corrugated tube are determined, based on the curve fitting of the experimental data.     

Effect of nanofluids on reflood heat transfer in a long vertical tube

Experiments were conducted to investigate the effect of nanofluids on reflood heat transfer in a hot vertical tube. The nanofluids, which are produced by dispersing nano-sized particles in traditional base fluids such as water, ethylene glycol, and engine oil, are expected to have a reasonable potential to enhance a heat transfer. 0.1 volume fraction (%) Al₂O₃/water nanofluid was prepared by two-step method and 0.1 volume fraction (%) carbon nano colloid (CNC) was prepared by the process self-dispersing by carboxyl formed particle surface. Transmission electron microscopy (TEM) images are acquired to characterize the shape and size of Al₂O₃ and graphite nanoparticles. The dispersion behavior of nanofluids was investigated with zeta potential values. And then, the reflood tests have been performed using water and nanofluids. We have observed a more enhanced cooling performance in the case of the nanofluid reflood. Consequently, the cooling performance is enhanced more than 13 s and 20 s for Al₂O₃/water nanofluid and CNC.     

Flow-boiling heat transfer of R-134a-based nanofluids in a horizontal tube

The influence of nanoparticles on the flow-boiling of R-134a and R-134a/polyolester mixtures is quantified for flows of low vapor quality (x < 20%) over a range of mass fluxes (100 < G < 400 kg/m² s). With direct dispersion of SiO₂ nanoparticles in R-134a, the heat transfer coefficient decreases (as much as 55%) in comparison to pure R-134a. This degradation is, in part, due to difficulties in obtaining a stable dispersion. However, excellent dispersion is achieved for a mixture of R-134a and polyolester oil with CuO nanoparticles, and the heat transfer coefficient increases more than 100% over baseline R-134a/polyolester results. In the range of these experiments, nanoparticles have an insignificant effect on the flow pressure drop with the R-134a/POE/CuO nanofluid.     

Heat transfer coefficients under dry- and wet-surface conditions for a spirally coiled finned tube heat exchanger

In the present study, the average tube-side and air-side heat transfer coefficients in a spirally coiled finned tube heat exchanger under dry- and wet-surface conditions are experimentally investigated. The test section is a spiral-coil heat exchanger, which consists of six layers of concentric spirally coiled tube. Each tube is fabricated by bending a 9.6-mm outside diameter straight copper tube into a spiral coil of four turns. Aluminium fins with thickness 0.6 mm and outside diameter 28.4 mm are placed helically around the tube. The chilled water and the hot air are used as working fluids. The test runs are done at the air and water mass flow rates ranging between 0.02 and 0.2 kg/s and between 0.04 and 0.25 kg/s, respectively. The inlet-air and -water temperatures are between 35 and 60 °C and between 10 and 35 °C, respectively. The effects of the inlet conditions of both working fluids flowing through the heat exchanger on the heat transfer coefficients are discussed. New correlations based on the data gathered during this work for predicting the tube-side and air-side heat transfer coefficients for the spirally coiled finned tube heat exchanger are proposed.     

Heat transfer in rectangular microchannels heat sink using nanofluids

The effect of using nanofluids on heat transfer and fluid flow characteristics in rectangular shaped microchannel heat sink (MCHS) is numerically investigated for Reynolds number range of 100–1000. In this study, the MCHS performance using alumina–water (Al₂O₃-H₂O) nanofluid with volume fraction ranged from 1% to 5% was used as a coolant is examined. The three-dimensional steady, laminar flow and heat transfer governing equations are solved using finite volume method. The MCHS performance is evaluated in terms of temperature profile, heat transfer coefficient, pressure drop, friction factor, wall shear stress and thermal resistance. The results reveal that when the volume fraction of nanoparticles is increased under the extreme heat flux, both the heat transfer coefficient and wall shear stress are increased while the thermal resistance of the MCHS is decreased. However, nanofluid with volume fraction of 5% could not be able to enhance the heat transfer or performing almost the same result as pure water. Therefore, the presence of nanoparticles could enhance the cooling of MCHS under the extreme heat flux conditions with the optimum value of nanoparticles. Only a slight increase in the pressure drop across the MCHS is found compared with the pure water-cooled MCHS.