Base Working Fluid Research Articles

Steady flow properties and spectral absorption potential of supercritical carbon dioxide nanofluids: Experimental comparison and machine learning optimization

To improve the performance of the power cycle and accelerate the realization of the carbon neutrality goal, the development and application of nanofluids are imminent. In this research, we established a supercritical nanofluid spectral absorbance prototype and prepared seven supercritical carbon dioxide nanofluids for various valuable works. The experiments indicated that titanium carbide/supercritical carbon dioxide had the most outstanding stability with the shortest stabilization time (3.2 min) and the smallest fluctuation amplitude in spectral irradiance (±6.33%). Graphene/supercritical carbon dioxide emerged as the most competitive choice in terms of deposition characteristics and spectral absorption capacity, boasting a deposition density and spectral absorbance of 8.146% and 86.39%. Titanium was the most suitable raw material for constructing the prototype. Then, a performance factor was introduced to quantify the contribution of stability and deposition characteristics, and hydroxylated multi-walled carbon nanotube/supercritical carbon dioxide was found to have the most outstanding comprehensive performance with promising applications. Finally, we combined particle swarm optimization and artificial neural networks to develop an improved machine learning optimization model. Compared to the original prediction model, the root mean square error and mean absolute error of this model were reduced by 64.02% and 66.8%. Significantly, the spectral irradiance through the supercritical carbon dioxide nanofluid was reduced by 68.21% compared to the base working fluid, providing guidelines for improving the performance of the power cycle.

Critical operating parameters of solar flat plate collectors using CuO nanoparticles of different volume fractions subjected to natural convection

AbstractA flat plate solar water heater is investigated for its efficiency when water and the copper oxide (CuO) of 20 nm size nanoparticles of varying volume fractions and their performance are studied. A solar water heater with a flat plate collector of dimensions 1 × 0.45 m2 with 25 liter per day storage tank capacity, which works on the thermo‐syphon principle, is fabricated. The collector is run with a base working fluid of deionized water and then with CuO nanoparticles for different volume fractions of 0.2% and 0.4% with a surfactant to study the collector's efficiency. The surfactant used in cetyltrimethylammonium bromide of 1% in working fluid. The rise in temperature and the collector efficiency is compared for different volume fractions of CuO nanoparticles in the collector. The mixing of nanoparticles thus improves the efficiency of the collector. The experimental result shows that the collector with a 0.4% volume fraction of CuO with water as a working fluid has the maximum rise in temperature and efficiency compared with that of 0.2% and water. During the test, CuO without surfactant showed a slight decrement in heat transfer due to the agglomeration. The collector efficiency for 0.4% volume fraction achieves 63.28%, for 0.2% is 61.58%, and for water 54.15%. The overall efficiency was increased by up to 9.1% compared with base conventional fluid water for lower volume fractions of CuO nanoparticles for a smaller collector area.

A novel design for solar collector used for water heating application having nanofluid as working medium: CFD modeling and simulation.

A solar collector is a simple and cheap device that converts solar radiation into valuable heat energy. The thermal performance of the solar collectors can be enhanced significantly with the suspension of nanoparticles in the base fluid. A novel design for a solar-assisted water heater (SWH) is proposed in the current study, and the effect of nanofluid has been investigated on the thermal efficiency of the SWH. The use of nanofluid is one of the prominent methods in comparison to other techniques for improving the performance of solar collectors. Therefore, the base working fluid, i.e., water is mixed with the alumina nanoparticles of average particle size of 30nm, and they are assumed to be spherical. The flow and thermal characteristics of nanofluid through the solar water heater are simulated numerically with the help of the Eulerian-Eulerian two-phase model using the finite volume method (FVM). The commercial package ANSYS Fluent, is used for modeling the problem under transient conditions with a pressure-based solver. In comparison to a conventional flat plate collector, the proposed solar water heater consists of a corrugated absorber-plate and the effect of the radius of curvature has been investigated on the heat transfer and collector efficiency. With the proposed design, the heat transfer area available with the riser tubes increases remarkably and it leads to a 43% and 14% increase in heat transfer augmentation and collector efficiency, in comparison to the conventional solar water heater.

Thermal performance of self-rewetting gold nanofluids: Application to two-phase heat transfer devices

This paper presents an experimental analysis of the phenomenon of phase change inside a porous medium using different types of working fluids. It represents the impact of these fluids on improving the characteristics of heat and mass transfer in a Capillary Heat Pipe (CHP). In this study, gold nanoparticles (5 nm in diameter with 1% Cv), a self-rewetting binary solution (butanol with 3% Cv), and a mixture of self-rewetting butanol and gold nanofluid are considered to be the operating fluids within the CHP. The experiments are carried out after designing and developing the capillary heat pipe section. It consists of a water tank with a pump, an evaporator attached to a copper porous medium on which thermocouples and power supplies are placed. The experimental results showed the positive influence of gold nanoparticles on the thermal system's performance by reducing the thermal resistance by 13% compared to pure water as the base working fluid. In addition, a self-rewetting butanol solution showed improvement in the performance of the capillary evaporator by decreasing its casing temperature. While a mixture of self-rewetting butanol solution (3 % Cv) and gold nanofluid (1% Cv) exhibited the best performance of heat and mass transfer performance by reducing the thermal resistance of the system by approximately 22 %. To explain the mechanism for improving heat transfer, the phase change phenomenon was visualized by an infrared camera for the three working fluids. It is shown that as the applied power increases, the shape of the vapor pocket developed in the wick also increases, for pure water, until it reaches a stable form. Whereas, with respect to nanofluid and self-rewetting fluid, the shape of the vapor pockets was smaller than that of pure water allowing more efficient mass and heat transfer. The thermophysical properties of these fluids such as thermal conductivity, stability, surface tension, Marangoni, wettability, and capillary forces were presented to ensure and validate the decrease in the vapor pocket as well as the enhancement of the CHP thermal system.

Thermal performance evaluation of various nanofluids with non-uniform heating for parabolic trough collectors

Nanoparticles when used even in relatively low concentrations, can significantly alter the thermal properties of a base working fluid, thereby substantially enhancing the thermal performance of a power generation system. In the present study, numerical simulations were performed for a solar collector to test the effectiveness of six non-metallic nanoparticles, namely aluminum oxide (Al2O3), cerium oxide (CeO2), copper oxide (CuO), ferric oxide (Fe2O3), titanium dioxide (TiO2) and Silicon dioxide (SiO2). These nanoparticles were dispersed individually in three different base working fluids; therminol VP-1 (at 400 K), water (at 400 K) and molten salt (at 600 K) to form different nanofluids. Each of these nanofluids were then examined with three different volume fractions (2%, 4% and 6%) in addition to the pure base working fluid case for a range of Reynolds number (Re=104-105). For the simulation the Monte Carlo Ray Tracing (MCRT) model was used to represent the non-uniform heat flux around the absorber tube of the Parabolic Trough Collector (PTC). The results show that the enhancement of the thermal and the hydraulic performances depended upon the combination of the nanoparticles and the base working fluid. Silicon dioxide, SiO2, however, was found to be the most efficient nanoparticle regardless of the choice of the base working fluid for all the tested volume fractions. For example, for typical operating conditions for SiO2 with a volume fraction (VF) of 6%, the average Nusselt number of the water-based mixture was enhanced by 32.4%, with a thermal efficiency improvement of 5.11% and performance evaluation criterion (PEC) of 1.313. On the other hand, for a molten salt-based SiO2 mixture, the average Nusselt number was improved by 21.36% and thermal efficiency by 9.92% with a PEC of 1.155. Finally, the corresponding improvements with therminol VP-1-base fluid were 15.6%, 9.18% and 1.21 for the average Nusselt number, thermal efficiency and PEC respectively.

Experimental investigation on lowering the environmental hazards and improving the performance patterns of solar flat plate collectors by employing the internal longitudinal fins and nano additives.

The main objective of this study is to lower the greenhouse gases by developing and optimizing a solar flat plate collector. The rifled tube is integrated into the collector to increase the thermal heat transfer thereby improving its performance. Two flat plate collectors, one with in-housed longitudinal fins and another without fins of 0.5m2 collector area, have been intended and fabricated with provisions for K-type thermocouples to examine the temperature variations inside the collector for different working fluids. This current study reveals using CuO and Al2O3 nanoparticles in varying weight fractions in incremental order to study the effect of weight fractions on the efficiency of the collector. The simulation was done using computational fluid dynamics both for the finned and without finned tube collectors separately and the outcome of the results for the collector outlet temperatures is compared with the experimental one and results show a valuable outcome for the intended collectors. Initially, the test was conducted with pure distilled water as working fluid and further nanoparticles were opted and doped inside the collector side for varying weight fractions of 0.2% and 0.4% and their results are compared. The experimental results showed an improved heat transfer was pragmatic in the collector side for using nanoparticles. Mixing the nanofluids exhibited superior efficiency on the collector side. The results showed after successful trials of experimentation, doping of CuO nanoparticles by varying weight fractions of 0.2% and 0.4%, augmentation of the collector (unfinned) efficiency is 2.1% and 4.05%, and similarly for finned tube collector, it is 3.02% and 5.5% for same weight fractions. In order to improve the thermal efficiency of collector, CuO is replaced by Al2O3 nanoparticles; for dissimilar weight fractions, the efficiency is enhanced nearly by 3.7% and 6.54% for unfinned tube collector, and for the finned tube, the collector is 4.8% and 7.8% respectively, compared with the base working fluid (water). Experimentation of the collectors with finned tube type achieved a superior efficiency compared with that of unfinned tube collectors which is proved to be higher when used for nanofluids to that of the base working fluid water.

Experimental and numerical analysis on using CuO-Al2O3/water hybrid nanofluid in a U-type tubular heat exchanger

PurposeHeat exchangers (HEXs) are extensively used in many applications such as heating and cooling systems. To increase the thermal performance of HEXs, nano-sized particles could be added to the base working fluid which can improve the thermophysical properties of the fluid. In addition, further improvement in the thermal performance of nanofluids can be obtained by using two or more different nanoparticles which are known as hybrid nanofluids. This paper aims to improve the thermal efficiency of U-type tubular HEX (THEX) by using CuO-Al2O3/water hybrid nanofluid.Design/methodology/approachNumerical simulation has been used to model THEX with various configurations. Also, CuO-Al2O3/water hybrid nanofluid has been experimented in THEX in two various modes including parallel (PTHEX) and counter flow (CTHEX) regarding to the numerical findings. Hybrid nanofluids have been prepared in two particle concentrations and compared with CuO/water nanofluid at the same concentrations and also with water.FindingsThe numerical simulation results showed that adding fins and also using hybrid nanofluid can increase heat transfer rate in HEX. However, adding fins cannot be a good option in U-type THEX with lower diameter because it increases pressure drop notably. Experimental results of this work illustrated that using Al2O3-CuO/water hybrid nanofluid in the THEX improved thermal performance significantly. Maximum enhancement in overall heat transfer coefficient of THEX by using CuO-Al2O3/water nanofluid in 0.5% and 1% concentrations achieved as 9.5% and 12%, respectively.Originality/valueThe obtained findings of the study showed the positive effects of using hybrid type nanofluid in comparison with single type nanofluid. In this study, numerical and experimental analysis have been conducted to investigate the effect of using hybrid type nanofluid in U-type HEX. The obtained results exhibited successful utilization of CuO-Al2O3/water hybrid type nanofluid in HEX. Moreover, it was observed that thermal performance analysis of the nanofluids without any experiment can be done by using numerical method.

Performance analysis of internally helically v-grooved absorber tubes using nanofluid

With the depletion of fossil fuel effective utilization and efficient collection of solar energy has gained popularity in the recent days. In the present study an attempt is made for the performance improvement of parabolic trough collector (PTC) by modifying absorber tube with internally helically groove. Further, base working fluid of water is replaced with Aluminium oxide (Al2O3) nanofluid (3–8% by volume) for better thermal performance. Tests are performed considering 600, 800, and 1000 W/m2 heat flux at the tube outer surface. ANSYS Fluent 14.0 is used to simulate the problem considering two distinct Reynolds number (Re) of 4000 and 6000. Results indicate that with the increase in concentration of Al2O3 from 3% to 8%, pressure drop is increased by 14.5%. Heat transfer coefficient is enhanced by as high as 13.8% with the nanofluid compared to base fluid working at heat flux of 1000 W/m2 and Re = 4000. Further, increase in the value of Re from 4000 to 6000 heat transfer coefficient with nanofluid is increased by as high as 41.3%.

Effect of Surface Tension Variation of the Working Fluid on the Performance of a Closed Loop Pulsating Heat Pipe

ABSTRACTIn this article, the effect of surface tension variation of the working fluid on the thermal performance of a pulsating heat pipe (PHP) is presented. A two-turn closed loop PHP is fabricated with a combination of copper and quartz tubes having 2 mm inner diameter. Three filling ratios are considered in the present study. A common surfactant namely sodium dodecyl sulfate is used to vary the surface tension of the distilled water which is the base working fluid tested in the PHP. Visualization as well as heat transfer studies is performed in the PHP. Thermal resistances of working fluids with different surface tension are estimated for each filling ratio. Further, the effect of surfactant concentration on the hydrodynamics of the PHP is also discussed. Addition of surfactant induces formation of foam after the filling process and in some phase of PHP operation. It changes the flow regime boundaries and lowers the evaporator temperature under specific operating conditions. A flow regime map is also constructed for the present PHP. The working fluid with a lower surface tension gives a minimum evaporator temperature in the vertical orientation and thus, lowest thermal resistance has been obtained. However, surface tension does not influence the performance in the horizontal position appreciably.

Analysis on the Influence of Nanoparticles of Alumina, Copper Oxide, and Zirconium Oxide on the Performance of a Flat-Plate Solar Water Heater

In this work, a solar flat-plate collector integrated with four riser tubes having 0.5 m2 area is designed and fabricated. Experiments were conducted using three working nanofluids, namely, alumina, copper oxide, and zirconium oxide, along with the base working fluid water of different weight fractions. The efficiency of collector and storage tank is calculated using the ASHRAE method, and the obtained results were compared. The experimental result shows that alumina nanofluid influences the collector efficiency nearly about 17% for the collector and 13.5% for the storage tank compared to the base working fluid water. The efficiency of the solar collector by appending 0.4% Al2O3, CuO, ZrO2, and water is found to be 55, 51.3, 47, and 38%, respectively. Experimental results raveled that the addition of nanoparticles to water as heat transfer fluid enhances the heat transfer, thereby increasing the efficiency of the collector.

Theoretical investigation of the efficiency of a U-tube solar collector using various nanofluids

Using thermal energy balance, this paper analyzes and investigates the thermal performance of a U-tube solar collector whose temperature thermal energy is high due to solar radiation. A working fluid of 20% PG (propylene glycol)–water is used. Solar collector efficiency was calculated and energy savings predicted for various nanofluids, such as MWCNT, Al2O3, CuO, SiO2, and TiO2. As a result, thermal conductivity increased as the concentration of nanofluid increased. Solar collector efficiency increased in the following order from greatest to least: MWCNT, CuO, Al2O3, TiO2, and SiO2 nanofluids. When the thermal loss value ((Ti−Ta)/G) was equal to 0, the solar collector using 0.2vol% MWCNT nanofluid showed the greatest efficiency (62.8%, a 10.5% improvement compared to 20% PG–water). By dispersing nanoparticles in the working fluid, the coal usage could be further reduced by approximately 39.5–131.3 kg per year when 50 solar collectors are used. Therefore, CO2 generation could be reduced by 103.8–345.3 kg and SO2 generation by 0.4–1.1 kg per year, compared to solar collectors using a base working fluid of 20% PG–water. These findings contribute to knowledge of solar energy technology, which has the potential to reduce electricity and energy consumption world-wide.

Experimental analysis on the influence of internal finning on the efficiency of a solar flat plate collector using Al 2 O 3 nanoparticles

Abstract Two collectors with the same area of 945 × 420 $945\times 420$ mm have been designed and fabricated: one flat plate collector with internally grooved fins inserted inside the riser tubes and the other one with plain riser tubes. Provisions were made for inserting the T-type thermocouples at six different locations to monitor temperature variations inside the riser tubes of the collector. The two identical systems of collectors (finned and unfinned tube) were initially run with base working fluid (water) and then with Al 2 O 3 nanoparticles with a size of 40 nm for different weight fractions of 0 . 2 $0.2$ % and 0 . 4 $0.4$ % in incremental order to study the effect on the efficiency of collectors. Mixing of nanoparticles in water thus improves the efficiency of the collector. Results show the efficiency of finned tube collector using the nanoparticles and water is substantially higher when compared to that of unfinned riser tubes collector.

Experimental investigation on the effect of nanofluid on the thermal performance of symmetric sintered U shaped heat pipe

In this study, the impact of Entrance Power and Silver nanofluid concentration (with base fluid ethanol and DI-water) on heat pipe thermal performance are considered. In order to reach the aim a U-shaped sintered heat pipe is utilized which causes occupied space to decline. The length of the heat pipe is 135 mm in each branch. On account of recognition the effect of working fluid on heat pipe thermal performance, thermal resistance and overall heat transfer coefficient in base working fluid and nano-colloidal silver are measured in the shape of thermosyphon. The working fluid is with volume percentages of 70 ethanol and 30 distilled water. The average size pertaining to the nanoparticle applied is 40 nm. In addition, the influences of nanofluid concentrations are measured by comparing three concentrations 0.001, 0.005, 0.1 vol%. The range of entrance power is from 10 to 40 W and the temperature of coolant has been changed from 20 to 40 °C. The results of the experiment indicate that by increasing entrance power, the temperatures of the condenser, evaporator and working temperature experience a rise. Furthermore, this causes a decrease of thermal resistance and an increase of overall heat transfer coefficient. A comparison of three concentrations reveals that in concentration of 50 ppm, thermal resistance compared to the base fluid has decreased to 42.26 % and overall heat transfer coefficient has gone up to 1883 (W/m2·°K) . Also, due to unexpected changes in concentration of 1000 ppm, the existence of an optimized concentration for the silver nanofluid in this heat pipe with this geometry has been clear.

Enhancement of heat transport in oscillating heat pipe with ternary fluid

The thermo-physical properties of working fluids play an important role in the heat transport performance of an oscillating heat pipe (OHP). In the present study, the heat transport performance of the OHP is investigated using two types of binary fluids and a type of ternary fluid as the working fluids. The working fluids include a nanofluid, self-rewetting fluid, and a mixed solution of self-rewetting fluid and a nanofluid called self-rewetting nanofluid. The tilt angle of the OHP is 90° with a charge ratio of 50%. In contrast to de-ionized water used as a base working fluid in the OHP, all working fluids can enhance the heat transport performance of the OHP. However, through an analysis of the enhancement ratios, it is found that nanofluids can only enhance the performance of an OHP within a heat load range of 30–70W. The maximal enhancement ratio is about 11% as the heat load is 60W. If the heat load exceeds 70W, the heat transport performance of the OHP degrades. For a self-rewetting fluid, the maximum of enhancement ratio is only 6% as the heat load is less than 30W, and then, as the heat load increases, the enhancement ratio decreases gradually. The OHP that uses self-rewetting nanofluids shows excellent heat transport performance over the entire heat load range. The maximal enhancement ratio is approximately 15%. Therefore, self-rewetting nanofluids are considered to be appropriate working fluids for use in the OHPs.

Metal-organic heat carrier nanofluids

Nanofluids, dispersions of metal or oxide nanoparticles in a base working fluid, are being intensively studied due to improvements they offer in thermal properties of the working fluid. However, these benefits have been erratically demonstrated and proven impacts on thermal conductivity are modest and well described from long-established effective medium theory. In this paper, we describe a new class of metal-organic heat carrier (MOHC) nanofluid that offers potential for a larger performance boost in thermal vapor–liquid compression cycles. MOHCs are nanophase porous coordination solids designed to reversibly uptake the working fluid molecules in which the MOHCs are suspended. Additional heat can be extracted in a heat exchanger or solar collector from the endothermic enthalpy of desorption, which is then released as the nanofluid transits through a power generating device such as a turboexpander. Calculations for an R123 MOHC nanofluid indicated potential for up to 15% increase in power output. Capillary tube experiments show that liquid–vapor transitions occur without nanoparticle deposition on the tube walls provided entrance Reynolds number exceeds approximately 100.

EXPERIMENTAL STUDY OF SILVER NANOFLUID ON FLAT HEAT PIPE THERMAL PERFORMANCE

This study utilizes silver nano-fluid filled flat heat pipe. It is aimed at effect of various concentrations on flat heat pipe thermal performance by air-cooling testing equipment. The particles used in these experiments were silver particles 35 nm in size. The base working fluid was pure-water. Nano-fluids were prepared using a two-step method. In the experiment, the thickness and length of the heat pipe are 3 mm and 200 cm, respectively. An experimental system was set up to measure the temperature distribution of heat pipes and calculate the thermal resistance by equation R = ∆T/Q. At a same charge volume, the thermal resistance of heat pipe filled nano-fluid was lower than DI water.

Heat pipe efficiency enhancement with refrigerant–nanoparticles mixtures

In the present study, the enhancement of heat pipe efficiency with refrigerant–nanoparticles mixtures is presented. The heat pipe is fabricated from the straight copper tube with the outer diameter and length of 15, 600 mm, respectively. The refrigerant (R11) is used as a base working fluid while the nanoparticles used in the present study are the titanium nanoparticles with diameter of 21 nm. The mixtures of refrigerant and nanoparticles are prepared using an ultrasonic homogenizer. Effects of the charge amount of working fluid, heat pipe tilt angle on the efficiency of heat pipe are considered. For the used pure refrigerant as working fluid, the heat pipe at the tilt angle of 60°, working fluid charge amount of 50% gives the highest efficiency. At the optimum condition for the pure refrigerant, the heat pipe with 0.1% nanoparticles concentration gives efficiency 1.40 times higher than that with pure refrigerant.