Intertube Falling-Film Heat Transfer Behavior of Multiwall Carbon Nanotube Suspensions (MWCNT Nanofluids)

2011 ◽  
Author(s):  
Binglu Ruan ◽  
Anthony M. Jacobi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Ethylene Glycol ◽  
Multiwall Carbon Nanotube ◽  
Falling Film ◽  
Water Based ◽  
Film Heat Transfer ◽  
The Heat Transfer Coefficient ◽  
Multiwall Carbon

The thermal conductivity and viscosity of water-based and ethylene-glycol-based multiwall carbon nanotube (MWCNT) suspensions are measured for MWCNT volume concentrations up to 0.24%. The thermal conductivity is found to increase up to 8.6% and 9.3% for water-based and ethylene-glycol-based nanofluids, respectively. The viscosity of the nanofluids increases compared to that of their base fluids, with larger increases for the ethylene-glycol-based nanofluids. Intertube falling-film heat transfer characteristics of these nanofluids are measured and compared to data for the base fluids. The heat transfer coefficient of the water-based nanofluids decreases at low MWCNT concentrations but increases as the concentration increases. The heat transfer coefficient of the ethylene-glycol-based nanofluids decreases with an increase in MWCNT concentration, with a maximum deviation of 30%.

Physiochemical studies of functionalized MWCNT/transformer oil nanofluid utilized in a double pipe heat exchanger

2021 ◽  
Author(s):  
Sajjad Porgar ◽  
Leila Vafajoo ◽  
Nader Nikkam ◽  
Gholamreza Vakili-Nezhaad
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Carbon Nanotube ◽  
Sodium Dodecyl ◽  
Transformer Oil ◽  
Multiwall Carbon Nanotube ◽  
Double Pipe ◽  
Multiwall Carbon ◽  
Pipe Heat

The transformer-oil based (TOB) nanofluid suspensions were prepared through adding 0.05 to 0.80 wt% multiwall carbon nanotube (MWCNTs) functionalized with a -COOH group. The sodium dodecyl sulfate was used to stabilize the suspensions. The resulting material was used as a coolant in a double pipe heat exchanger operated under co- and counter-current flow conditions. The nanofluid thermo-physical features such as the thermal conductivity, viscosity, and density were determined at various temperatures and mass fractions. Then pertinent semi-empirical relations were developed. To verify any multiwall carbon nanotube’s (MWCNT’s) and sodium dodecyl sulfate’s (SDS) interactions with the transformer-oil based (TOB) material, the Fourier-transform infrared (FTIR) analysis was performed. Moreover, the stability of the nanofluid suspension was understudied through the UV-Visible and thermogravimetric analysis (TGA) techniques. In addition, the maximum heat transfer coefficient improvement was determined to be 86.7% at a multiwall carbon nanotube (MWCNT) mass fraction of 0.8 wt%. Meanwhile, average increments of the overall heat transfer coefficient and thermal conductivity of the prepared nanofluid were revealed about 37.2% and 138%, respectively in comparison with that of the base fluid. Furthermore, the optimum thermal conductivity of 0.388 W/m.K was obtained at 45 °C and 0.8 wt% of the multiwall carbon nanotube (MWCNT). Ultimately, a sensitivity analysis emphasized that, the understudied system’s behaviors were within an accuracy limit of ±97%.

Investigation of Ethylene Glycol Heat Transfer Coefficient Trough Double Pipe and Coil Heat Exchanger

2021 ◽  
Vol 874 ◽  
pp. 165-170
Author(s):  
Sri Wuryanti ◽  
Tina Mulya Gantina ◽  
Indriyani
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Ethylene Glycol ◽  
Transfer Coefficient ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Test System ◽  
Double Pipe ◽  
The Heat Transfer Coefficient ◽  
Outer Pipe

The research objective is to assemble a convection test system which acts as a heat exchanger (HE) and test its applicability using ethylene glycol. A Double Pipe (DP)-type HE consists of an inner pipe surrounded by an outer pipe (annulus) whereas a Coil-type HE composed of a coil surrounded by an outer pipe. Water flows through the outer pipe in both types of HE, while ethylene glycol flows through the inner piper or coil. HE in combination with other components (such as) forms a convection test system. The applicability of the system was tested to determine the heat transfer coefficient of ethylene glycol in a DP-type and Coil-type HEs. After that, the heat transfer rate was calculated and compared. The results show that the heat transfer coefficient in the DP-type HE is the lowest at 12.2 W/m2 oC and the highest at 26.8 W/m2 oC; and the corresponding heat transfer rate is the lowest at 8.3 W and the highest is 56.3 W. In comparison, for Coil-type HE, the lowest heat transfer coefficient is 38.9 W/m2 oC and the highest is 66.2 W/m2 oC which correspond to the heat transfer rate 19.9 W at the lowest and 225 W at the highest.

Heat Transfer and Fouling Performance During Falling Film Evaporation in Vertical Porous Tubes

2020 ◽  
Author(s):  
Lei Wang ◽  
Weiyu Tang ◽  
Limin Zhao ◽  
Wei Li
Keyword(s):  
Heat Transfer ◽  
Stainless Steel ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Smooth Tube ◽  
Outer Diameter ◽  
Falling Film ◽  
Film Evaporation ◽  
Falling Film Evaporation ◽  
The Heat Transfer Coefficient

Abstract An experimental investigation was conducted on falling film evaporation along two porous tubes, which were sintered by stainless-steel powder with a diameter of 0.45 and 1 um, respectively. The test section is a 2 m long sintered tube with an outer diameter of 25 mm and a wall thickness of 2 mm. During the experiment, the pressure inside the tube was maintained at 1 atm, the inlet temperature was 373 K, and mass flux ranged from 0.51 to 1.36 kg/ (m s). Conditions of the steam outside the pipe, which was the heat source, were fixed, while the fouling tests were carried out at a constant mass flow of 0.74 kg/ (m s) using high-concentration brine as work fluid. The overall heat transfer coefficient under different working conditions was tested and compared with the stainless steel smooth tube of the same dimensions. The heat transfer coefficient of the two porous stainless tubes are about 35% and 20% lower than that of the smooth one, showing an inferior effect because the steam in the pores of the pipe wall during the infiltration process will reduce the heat conductivity. The heat transfer coefficient of the smooth tube deteriorated severely due to the deposition of calcium carbonate, which had little effect on the sintered tubes. Besides, the fouling weight of porous tubes is 2.01 g and 0 g compared with 5.52 g of the smooth tube.

A Parameter for Selection of Nano-Dispersoids in Nanofluids for Thermal Applications

2012 ◽  
Vol 736 ◽  
pp. 223-228
Author(s):  
M.M. Ghosh ◽  
S. Ghosh ◽  
S.K. Pabi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Elastic Modulus ◽  
Heat Source ◽  
Ethylene Glycol ◽  
Preliminary Identification ◽  
Water Based ◽  
Selection Of ◽  
Poissons Ratio

A model reported by the present investigators has earlier shown that the extent of heat pick up by a nanoparticle during its collision with the heat source in a given nanofluid would depend on the thermal conductivity (kp, unit W/m.K), density (ρ, unit kg/m3), elastic modulus (E, unit GPa) and Poissons ratio (μ) of the nanoparticle and heat source. Considering the expression for collision period and thermal conductivity of nanoparticle, a factor χ =kp(ρ/E)0.4 is proposed here and examined for the preliminary identification of the potential of a dispersoid in enhancing the thermal conductivity of a nanofluid. The χ-factor for Ag, Cu, CuO, Al2O3 and SiO2 are 2960, 2247, 116, 14.1 and 5.5, respectively. The higher χ-factor of CuO compared to that of Al2O3 can explain why water and ethylene glycol (EG) based CuO-nanofluid is reported to show higher enhancement in the thermal conductivity, when compared to similar Al2O3-nanofluid. The χ for SiO2 is much smaller than that for Ag, which also corroborates well with the marginal enhancement in thermal conductivity of water based nanofluid containing SiO2 nanoparticles. Therefore, a high value of χ of the nanodispersoid can serve as a parameter for the design of nanofluids for heat transfer applications.

Falling Film and Spray Evaporation Enhancement Using an Applied Electric Field

2000 ◽  
Vol 122 (4) ◽  
pp. 741-748 ◽  
Author(s):  
J. Darabi ◽  
M. M. Ohadi ◽  
S. V. Desiatoun
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Electric Field ◽  
Transfer Coefficient ◽  
Test Section ◽  
Applied Electric Field ◽  
Falling Film ◽  
Electrode Gap ◽  
Maximum Enhancement ◽  
The Heat Transfer Coefficient

The effect of an electric field on the falling-film evaporation of refrigerant R-134a on a vertical plate and three commercially available tubes was investigated experimentally. The plate test section was 25.4 mm wide and 76.2 mm long, and each tube test section was 19 mm in diameter and 140 mm long. Experiments were conducted in both falling film and spray evaporation modes. The effects of various parameters such as heat flux, refrigerant flow rate, electrode gap, and applied voltage were investigated. It was found that in the presence of an applied electric field, the maximum enhancement in the heat transfer coefficient for both falling film and spray evaporation modes on a plate was nearly the same. A maximum enhancement of fourfold in the heat transfer coefficient with the plate, 90 percent with the smooth tube, 110 percent with the Turbo BIII, and 30 percent with 19 fpi tube were obtained. The electrohydrodynamic power consumption in all cases was less than 0.12 percent of the total energy exchange rate in the test section. [S0022-1481(00)03003-6]

Performances of falling film evaporators on whole milk and a comparison with performance on skim milk

1997 ◽  
Vol 64 (1) ◽  
pp. 57-67 ◽  
Author(s):  
R. SELWYN JEBSON ◽  
HONG CHEN
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Skim Milk ◽  
Falling Film ◽  
Transfer Coefficients ◽  
Liquid Loading ◽  
Heat Transfer Coefficients ◽  
Whole Milk ◽  
The Heat Transfer Coefficient

The performances of falling film evaporators used in the New Zealand dairy industry for concentrating whole milk were evaluated by determining kg steam used/kg water evaporated, and the heat transfer coefficient of each pass in the evaporators. A specially written computer program was used to calculate the results. The heat transfer coefficients varied from 0·3 to 3·0 kW/m2K, and the steam consumption from 0·10 to 0·39 kg steam/kg evaporation, depending on the number of effects. The steam consumptions for whole and skim milk were similar. The momentum of the vapours passing down the tubes, the temperature difference across the tubes, the viscosity of the feed and the liquid loading were found to be the main factors controlling the heat transfer coefficient. A correlation between the heat transfer coefficient and these factors is presented, and other factors likely to have an influence on the performance are discussed. The correlation is compared with that obtained for skim milk.

Inverse analysis for the determination of heat transfer coefficient

2013 ◽  
Vol 91 (12) ◽  
pp. 1034-1043 ◽  
Author(s):  
Ali Fguiri ◽  
Naouel Daouas ◽  
M-Sassi Radhouani ◽  
Habib Ben Aissia
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Source Strength ◽  
Hot Wire ◽  
Source Power ◽  
Heating Source ◽  
The Heat Transfer Coefficient

The parallel hot wire technique is considered an effective and accurate means of experimental measurement of thermal conductivity. However, the assumptions of infinite medium and ideal infinitely thin and long heat source lead to some restrictions in the applicability of this technique. To make an effective experiment design, a numerical analysis should be carried out a priori, which requires a precise specification of the heating source strength and the heat transfer coefficient on the external surface. In this work, a more accurate physical and mathematical modeling of an experimental setup based on the parallel hot wire method is considered to estimate the two above-mentioned parameters from noisy temperature histories measured inside the material. Based on a sensitivity analysis, the heating source strength is estimated first using early time measurements. With such estimated value, determination of the heat transfer coefficient using temperatures measured at later times is then considered. The Levenberg–Marquardt (LM) method is successfully applied using a single experiment for the inverse solution of the two present parameter estimation problems. Estimates of this gradient-based deterministic method are validated with a stochastic method (Kalman filter). The effects of the measurement location, the heating duration, the measurement time step, and the LM parameter on the estimates and their associated confidence bounds are investigated. Used in the traditional fitting procedure of the parallel hot wire technique, the estimated heating source power provides a reasonable agreement between fitted and exact values of the thermal conductivity and the thermal diffusivity.

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