Showing papers on "Heat transfer published in 2016"

Numerical Heat Transfer And Fluid Flow

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A review on preparation, characterization, properties and applications of nanofluids

Abstract: Selection of suitable heat transfer fluid for heat dissipation is an important consideration in the design of heat exchanging systems. Nanofluid, a colloidal mixture made of a base fluid and a nanoparticle, is a new generation of heat transfer fluids becoming a high potential fluid in heat transfer applications due to enhanced thermal conductivity. Research studies about nanofluids are on the rise owing to the mounting interest and demand for nanofluids as heat transfer fluids in a wide variety of applications. Recently, nanofluid technology has a new dimension of impregnating two or more nanoparticles in base fluids, namely hybrid or composite nanofluids. This paper reviews the preparation of metal and metal oxides nanofluids and hybrid nanofluids and the various techniques used to study the physical and chemical characteristics of nanofluids. Thermo-physical and heat transfer properties of nanofluids including the improved thermal conductivity, viscosity and specific heat models for nanofluids are presented. Finally, various application areas of nanofluids, such as transportation, electronic cooling, energy storage, mechanical applications etc. are discussed.

Heat exchanger design handbook

Abstract: Heat exchanger design handbook , Heat exchanger design handbook , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Vertically Aligned and Interconnected Graphene Networks for High Thermal Conductivity of Epoxy Composites with Ultralow Loading

Abstract: Efficient removal of heat via thermal interface materials has become one of the most critical challenges in the development of modern microelectronic devices. However, traditional polymer composites present limited thermal conductivity even when highly loaded with highly thermally conductive fillers due to the lack of efficient heat transfer channels. In this work, vertically aligned and interconnected graphene networks are first used as the filler, which is prepared by a controlled three-step procedure: formation of graphene oxide liquid crystals, oriented freeze casting, and high-temperature annealing reduction under Ar. The obtained composite, at an ultralow graphene loading of 0.92 vol %, exhibits a high thermal conductivity (2.13 W m–1 K–1) that is equivalent to a dramatic enhancement of 1231% compared to the pure matrix. Furthermore, the composite also presents a much reduced coefficient of thermal expansion (∼37.4 ppm K–1) and increased glass transition temperature (135.4 °C). This strategy provide...

Nanofluid convective heat transfer using semi analytical and numerical approaches: A review

Abstract: The use of additives in the base fluid like water or ethylene glycol is one of the techniques applied to augment the heat transfer. Newly an innovative nanometer sized particles have been dispersed in the base fluid in heat transfer fluids. The fluids containing the solid nanometer size particle dispersion are called ‘nanofluids’. Two main categories were discussed in detail as the single-phase modeling which the combination of nanoparticle and base fluid is considered as a single-phase mixture with steady properties and the two-phase modeling in which the nanoparticle properties and behaviors are considered separately from the base fluid properties and behaviors. Both single phase and two phase models have been presented in this paper. This paper intends to provide a brief review of researches on nanofluid flow and heat transfer via semi analytical and numerical methods. It was also found that Nusselt number is an increasing function of nanoparticle volume fraction, Rayleigh number and Reynolds number, while it is a decreasing function of Hartmann number.

Principles Of Heat Transfer In Porous Media

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Constructing Black Titania with Unique Nanocage Structure for Solar Desalination.

Abstract: Solar desalination driven by solar radiation as heat source is freely available, however, hindered by low efficiency. Herein, we first design and synthesize black titania with a unique nanocage structure simultaneously with light trapping effect to enhance light harvesting, well-crystallized interconnected nanograins to accelerate the heat transfer from titania to water and with opening mesopores (4–10 nm) to facilitate the permeation of water vapor. Furthermore, the coated self-floating black titania nanocages film localizes the temperature increase at the water–air interface rather than uniformly heating the bulk of the water, which ultimately results in a solar–thermal conversion efficiency as high as 70.9% under a simulated solar light with an intensity of 1 kW m–2 (1 sun). This finding should inspire new black materials with rationally designed structure for superior solar desalination performance.

Directional transport of high-temperature Janus droplets mediated by structural topography

Abstract: Directed motion of liquid droplets is of considerable importance in various water and thermal management technologies. Although various methods to generate such motion have been developed at low temperature, they become rather ineffective at high temperature, where the droplet transits to a Leidenfrost state. In this state, it becomes challenging to control and direct the motion of the highly mobile droplets towards specific locations on the surface without compromising the effective heat transfer. Here we report that the wetting symmetry of a droplet can be broken at high temperature by creating two concurrent thermal states (Leidenfrost and contact-boiling) on a topographically patterned surface, thus engendering a preferential motion of a droplet towards the region with a higher heat transfer coefficient. The fundamental understanding and the ability to control the droplet dynamics at high temperature have promising applications in various systems requiring high thermal efficiency, operational security and fidelity. Controlled motion of a droplet on a hot surface is hampered by the formation of an evaporation layer below the droplet (Leidenfrost effect). But a cleverly patterned surface induces a Leidenfrost–contact-boiling state, directing the droplet’s motion.

The Enhancement of Effective Thermal Conductivity and Effective Dynamic Viscosity of Nanofluids – A Review

Abstract: The determination of thermo-physical properties and especially thermal conductivity and viscosity were important for evaluating heat transfer coefficients either for single or two phase flow. The thermo-physical properties measurements and heat transfer observations were mostly obtained with nanoparticles above 10 nm. Various researchers measured and modelled for the determination of thermal conductivity and viscosity of nanofluids. Most of the investigators developed equations for the estimation of thermal conductivity and viscosity as a function of percentage volume concentration, temperature and sometimes with the consideration of particle size valid in their experimental range. Nanofluids are considered to have great potential for heat transfer enhancement and are applied in heat transfer processes. Many studies were carried out to investigate this phenomenon. The main aim of this study is to give a comprehensive review on the research progress on the enhancement of effective thermal conductivity and effective dynamic viscosity of nanofluids.

Sensible heat thermal storage energy and exergy performance evaluations

Abstract: Sensible heat thermal energy storage has been drawing increasing attention for various applications for many years, which is an important technology for solving the time-discrepancy problem of waste or renewable energy utilization. This paper reviews available technologies for sensible heat storage under various operating conditions and storage tank geometries. Several aspects from sensible storage material, water stratification phenomenon, heat storage heat transfer modes, and various influencing factors, have been detailed for introduction. The influencing factors for energy and exergy performance were investigated and summarized from the fluid mass flow rate, storage tank geometrical structure, fluid properties, fluid inlet temperature, etc. The performance comparison with the latent thermal storage system was also briefly studied. The paper is beneficial for the researchers and engineers to design more efficient and optimized sensible storage systems.

Phase change material based cold thermal energy storage: Materials, techniques and applications – A review

Abstract: This paper gives a comprehensive review on recent developments and the previous research studies on cold thermal energy storage using phase change materials (PCM). Such commercially available PCMs having the potential to be used as material for cold energy storage are categorised and listed with their melting point and latent heat of fusion. Also techniques for improving the thermo-physical properties of PCM such as heat transfer enhancement, encapsulation, inclusion of nanostructures and shape stabilization are reviewed. The effect of stability due to the corrosion of construction materials is also reported. Finally, different applications where the PCM can be employed for cold energy storage such as free cooling of building, air-conditioning, refrigerated trucks and cold packing are discussed.