Andrey Gunawan

Small particles, big impacts: A review of the diverse applications of nanofluids

Nanofluids—a simple product of the emerging world of nanotechnology—are suspensions of nanoparticles (nominally 1–100 nm in size) in conventional base fluids such as water, oils, or glycols. Nanofluids have seen enormous growth in popularity since they were proposed by Choi in 1995. In the year 2011 alone, there were nearly 700 research articles where the term nanofluid was used in the title, showing rapid growth from 2006 (175) and 2001 (10). The first decade of nanofluid research was primarily focused on measuring and modeling fundamental thermophysical properties of nanofluids (thermal conductivity, density, viscosity, heat transfer coefficient). Recent research, however, explores the performance of nanofluids in a wide variety of other applications. Analyzing the available body of research to date, this article presents recent trends and future possibilities for nanofluids research and suggests which applications will see the most significant improvement from employing nanofluids.

Liquid Thermoelectrics: Review of Recent And Limited New Data of Thermogalvanic Cell Experiments

Experimental studies on thermogalvanic cells (or thermo-electrochemical cells or simply thermocells) have shown promising results in the past two decades since being introduced in 1825. Recent literature on this topic ranging from aqueous redox couple cells to nonaqueous and molten salt thermogalvanic cells is reviewed and compared. Some limited new experimental data on power generation for the underdeveloped Cu-CuSO4 system are also reported. The Seebeck coefficient values of these experiments fit with a characteristic model extracted from a 1959 paper by deBethune et al. (Journal of the Electrochemical Society, Vol. 106, 1959). The power generation results are compared with the few previously reported values of the Cu-CuSO4 system by Holeschovsky (Analysis of Flooded Flow Fuel Cells and Thermogalvanic Generators, 1994) and Tester et al. (Evaluation of Thermogalvanic Cells for the Conversion of Heat to Electricity, 1992), including those published by Kuzminskii et al. (Journal of Power Sources, Vol. 52, 1994) and Quickenden and Mua (Journal of the Electrochemical Society, Vol. 142, 1995). Condensing the recently published literature, this article presents recent trends and identifies future possibilities or directions for realizing this attractive concept, which has been around for a long time.

Experimental investigation of the latent heat of vaporization in aqueous nanofluids

This paper reports an experimental investigation of the latent heat of vaporization (hfg) in nanofluids. Two different types of nanoparticles, graphite and silver, suspended in deionized water were exposed to a continuous laser beam (130 mW, 532 nm) to generate boiling. The latent heat of vaporization in the nanofluids was determined by the measured vapor mass generation and the heat input. To ensure that the measured hfg values are independent of heating method, the experiments were repeated with an electrically heated hot wire as a primary heat input. These experiments show considerable variation in the hfg of nanofluids. That is, graphite nanofluid exhibits an increased hfg and silver nanofluid shows a decrease in hfg compared to the value for pure water. As such, these results indicate that relatively low mass fractions of nanoparticles can apparently create large changes in hfg.

CRITICAL REVIEW OF THE NOVEL APPLICATIONS AND USES OF NANOFLUIDS

Nanofluids — one simple product of the emerging world nanotechnology — where nanoparticles (nominally 1–100 nm in size) are mixed with conventional base fluids (water, oils, glycols, etc.). Nanofluids have seen enormous growth in popularity since they were proposed by Choi in 1995 [1]. In the year 2010 alone there were nearly 500 research articles where the term nanofluid was used in the title, showing rapid growth from 2000 (12) and 2005 (78). Much of the first decade of nanofluid research was focused on measuring and modeling fundamental thermophysical properties of nanofluids (thermal conductivity, density, viscosity, convection coefficients). Recent research, however, has started to highlight how nanofluids might perform in a wide variety of other applications. These applications range from their use in nanomedicine [2] to their use as solar energy harvesting media [3]. By analyzing the available body of research to date, this article presents trends of where nanofluid research is headed and suggests which applications may benefit the most from employing nanofluids. Overall, this review summarizes the novel applications and uses of nanofluids while setting the stage for future nanofluid use in industry.Copyright

Nanoparticle-Assisted Heating Utilizing a Low-Cost White Light Source

In this experimental study, a filtered white light is used to induce heating in water-based dispersions of 20 nm diameter gold nanospheres (GNSs)—enabling a low-cost form of plasmonic photothermal heating. The resulting temperature fields were measured using an infrared (IR) camera. The effect of incident radiative flux (ranging from 0.38 to 0.77 W·cm−2) and particle concentration (ranging from 0.25–1.0 × 1013 particles per mL) on the solutions temperature were investigated. The experimental results indicate that surface heat treatments via GNSs can be achieved through complementary tuning of GNS solutions and filtered light.

Optimization of Cell Configuration for Maximizing Performance of a Cu/Cu2+ Aqueous Thermogalvanic Cell

This paper presents experimental results and analysis of a new high-power Cu/Cu2+ thermogalvanic cell and its comparison with previous results. Past researches were mostly focused on finding the best redox couples and electrode materials [1, 2], however, they generally lacked a comparison of power conversion efficiency (η) dependence on cell geometry. This inspired our interest in exploring the relation of η, internal resistance, maximum power, and cell geometry. Based on previous results [3], a low internal resistance, variable orientation thermogalvanic cell was designed to achieve the highest power output. Experimental results of the Seebeck coefficient (α = ∂E/∂T), power density, and η of Cu/Cu2+ electrolytes in various molar concentrations showed that 0.7M CuSO4 electrolyte has maximum α and power output of 0.7196 mV/°C and 3.17 μW/cm2, respectively. Power output of the new cell has significant improvement which is 219 times greater than previous research. This paper also presents economical aspects of Cu/Cu2+ thermogalvanic cells relative to ferri/ferrocyanide cells.Copyright

Thermogalvanic Waste Heat Recovery System in Automobiles

Recovering waste heat from automobiles remains an inviting subject for research. Solid-state thermoelectric generators (TEGs) have been widely investigated for this purpose, but their practical application remains challenging. An alternative to TEGs are thermogalvanic cells. Temperature difference between hot and cold electrodes creates a potential difference. Once connected to a load, electrical current and power are delivered, converting heat into electricity. In this work, we investigate the feasibility of incorporating such systems into automobiles. We carry out the experiments under real-world conditions. A climate-controlled wind tunnel is built to provide equivalent conditions to the ambient air stream under the car. The demonstrated system achieved a power density on the order of mW m−2. We compare the power generated to those of TEGs currently tested by GM, Honda, BMW and Ford. Further, a simple economic estimation is calculated to assess the

New directions in thermoelectric and thermal-electric cooling

per Watt cost of future practical thermogalvanic waste heat recovery system.Copyright

Electrode Separation and Operating Orientation: Mechanisms for Maximizing Performance of Cu/Cu2+ Aqueous Thermogalvanic Cells

Conventional thermoelectric coolers have been widely used for cooling of electronic devices. Utilizing bismuth telluride materials, these Peltier modules are typically categorized as high heat flux devices that can achieve modest temperature differences in a compact architecture. Breaking from convention of typical bismuth telluride thermoelectric devices, an alternative method of providing thermal-electric cooling will be discussed providing inspiration for new cooling directions and materials challenges. While this approach has application in electric cooling of solids, there are also wider applications including space cooling and heat pumping.

CHARACTERIZATION OF LIGHT-INDUCED, VOLUMETRIC STEAM GENERATION IN NANOFLUIDS

Aqueous thermogalvanic cells have been studied since 1825, and have largely been explored in the past two decades because of their potential to convert low-temperature waste heat to electricity [1, 2]. However, even though these cells have long been known in the electrochemistry community, they have not received much attention from the thermal transport community. This is surprising given that their performance is highly dependent on controlling both thermal and mass (ionic) transport.Copyright