Effect of Saw Type Corrugated Pipe on Laminar Convective Heat Transfer by Using SiC-Water Nanofluid: A Numerical Study

Enhancing the heat transfer rate is highly required to remove excessive heat load from the heat transfer apparatus, which may cause massive damage to the equipment. Thus, increment of heat transfer area is one of the prime solutions for this issue. The increment of heat transfer area can be done by enhancing the pipe wall and incorporating nanoparticles with working fluids because nanoparticles showed much faster heat dispersion due to a vast surface area for heat transfer and increased thermal conductivity. Also, small molecules of nanoparticles are allowed for free movement and thus micro-convection, promoting high thermal conductivity. Higher thermal conductivity is mainly the result of a higher heat transfer rate. Therefore, in this study, a saw-type corrugated tube was considered along with the SiC-water nanofluid as the working fluid to determine the improvement of laminar convective heat transfer in terms of the Nusselt number, heat transfer coefficient, and pressure loss. The result demonstrated that by increasing the Reynolds number, the Nusselt number, heat transfer coefficient, and pressure loss were increased significantly with the enhancement of SiC-water concentration. At a Reynolds number of 1200, the maximum increment of Nusselt number in comparison to the base fluid was 9.15% when the corrugated pipe was considered. Meanwhile, the maximum improvement of heat transfer coefficient for SiC-water nanofluid in comparison to the base fluid was 37.66%.

Techno-economic analysis of nitrogen-doped graphene/water nanofluid in various heat exchangers (A unified analysis)

Nitrogen-doped graphene (NDG)/water nanofluid is one of the emerging working fluids toward achieving high heating rates in heat transfer devices. In the present study, thermal performance improvement and techno-economic analysis of a double pipe, shell and tube, and plate heat exchangers are presented while incorporating NDG/water nanofluid as a working fluid. The variable properties of NDG nanofluid are incorporated and the influence of nanoparticle concentrations and mass flow rates on the device thermal performance and related costs are evaluated. The findings demonstrate that device heat transfer area and costs are adversely affected by using NDG/water nanofluid in all types of heat exchanging devices considered. An increase in heat transfer area is associated with the decrease of the specific heat capacity of the working fluid. The increase of heat transfer area can be as high as 58.5%, 45.1%, and 67.0% for double pipe, shell and tube, and plate heat exchangers, respectively. In addition, area increase becomes persistent with other types of nanoparticles used in the carrier fluid.

Measuring the Thermal Contact Resistance Between Cu Foams and Substrates for On-Chip Cooling Applications in Data Centers

Data centers housing high performance computing equipment have large and growing rack densities, which pushes the limits of traditional air cooling technologies because of limited heat transfer coefficients. Therefore, on-chip cooling using so-called cold plates is emerging as a necessary cooling option for high-density electronics. The use of mini-channels or pins fins to enhance internal heat transfer area inside cold plates requires extensive micro-machining that is relatively time consuming and expensive for mass production. As an alternative approach, inserting and bonding pre-manufactured metal foams into hollow bodies are explored as a potentially inexpensive means to enhance the interior heat transfer area of cold plates. One key aspect of the performance of metal foams in cold plates is the thermal contact resistance in the bonding between the foam and the substrate. This project predicts the contact resistance using measurements of different foam types (pure Cu and Cu with oxide), porosities (63%, 80%, 93%, and 95%) and thicknesses (4 mm, 8 mm, and 10 mm). These measurements are carried out with and without the use of thermal interface material (TIM) pads. A theory is proposed and implemented to estimate the contact and foam thermal resistances, but further work is needed to gain confidence in the results. Observations suggest that different thermal behavior is seen for the Cu foams compared to the Cu with oxide foams, and that the use of TIM pads can achieve 10x to 40x reduction in overall thermal resistance for highly porous foams bonded on Cu substrates.

Investigation into the Distribution of Erosion-Corrosion in the Furnace Tubes of Oil Refineries

Crude oil is one of the most important sources of energy in the world. To extract its multiple components, we need oil refineries. Refineries consist of multiple parts, including heat exchangers, furnaces, and others. It is known that one of the initial operations in the refineries is the process of gradually raising the temperature of crude oil to 370 degrees centigrade or higher. Hence, in this investigation the focus is on the furnaces and the corrosion in their tubes. The investigation was accomplished by reading the thickness of the tubes for the period from 2008 to 2020 with a test in every two year, had passed from their introduction into the work. Where the thickness of more than one point was measured on each tube in the same row and the corrosion rate was extracted for three furnaces, starting from the area of ​​heat transfer by radiation to the heat transfer area of ​​the convection in three different operating units. It was found that the highest percentage corrosion value between the standard tube thickness and the thickness of conduction position was 37% with the conduction zone, and 31% with radiation zone. There, the tubes specification was tested. Five percent Cr-0.5 Moly and the temperature of radiation zone was 578 °C to 613 °C and the stack temperature was 410 °C to 450 °C. So, the results show that the maximum erosion occur at the convection zone.

Thermophysical Properties of Nanofluids

: Nanofluids, consist of base liquid and nano-sized conductive particles, are widely acclaimed as a new generation liquid for heat transfer applications. Since it possesses a variety of conductive particles, it can be efficiently utilized in the heat exchanger. These nano-sized conductive particles can increase the surface area, thus the heat transfer area, and change the thermophysical features of nanofluids. Density, thermal conductivity, viscosity, and heat capacity are crucial parameters and cannot be underestimated in heat transfer. These properties can be manipulated by the particle and base-liquid, and significantly influence the performance of nanofluids. For the last decade, several models, equations, and investigations were performed to examine the parameters that promote the properties. The review is necessary for terms of classifying the studies both compatible, and contradictory on the effects of density, thermal conductivity, viscosity, and heat capacity on the performance of nanofluids.

HEAT TRANSFER ENHANCEMENT IN A RECTANGULAR COOLING CHANNEL WITH AIRFOIL SHAPED FINS

This paper experimentally investigates heat transfer in a cooling passage with airfoil shaped fins for channel Reynolds numbers 10,000 to 40,000. This study uses airfoil shaped fins, instead of circular or oblong-shaped pins, for heat transfer augmentation. The airfoil shaped fins have more surface area than traditional pins. Assuming they both provide similar internal surface heat transfer coefficients, airfoil shaped fins will perform better than circular or oblong fins due to increased surface area. There is a need to obtain the heat transfer enhancement and pressure drop penalty in this cooling passage with airfoil shaped fins. Results are compared to the same rectangular cooling channel with smooth surfaces. The heat transfer can be enhanced 6 to 8 times while pressure drop is increased 70 to 90 times, as compared with the same channel with a smooth surface. With the fins significantly increasing the heat transfer area, three different methods are proposed for analyzing the heat transfer enhancement: (a) using the smooth channel area with the endwall temperature, (b) combining the total heat transfer area with the endwall temperature, and (c) coupling the total heat transfer area with the area weighted, average temperature including both the endwall and fin temperatures. Finally, compared directly to round pins, the airfoil shaped fins incur similar pressure penalties while providing slightly less heat transfer. The airfoil shaped fins benefit from a significant increase in the heat transfer area, a characteristic similar to more narrow strip fins.

Heat Transfer Enhancement Through Array Jet Impingement on Strategically Placed High Porosity High Pore-Density Thin Copper Foams

High porosity, high pore-density (pores per inch: PPI) metal foams are a popular choice in high heat flux cooling applications as they offer large heat transfer area over a given volume, however, accompanied by a concomitant increase in pumping power requirements. Present experimental study aims towards developing a novel metal-foam based cooling configuration featuring thin copper foams (3 mm) subjected to orthogonal air jet array impingement. The foam configurations allowed strategic and selective placement of high pore-density (90 PPI) and high porosity (~ 96%) copper foam on the heated surface with respect to the jet array in the form of foam stripes aiming to enhance heat transfer and reduce pressure drop penalty. The thermal-hydraulic performance was evaluated over range of Reynolds numbers, jet-to-jet (x/dj ,y/dj) and jet-to-target (z/dj) spacings and compared with a baseline smooth surface. The effect of pore-density was further analyzed by studying 40 PPI copper foam and compared with corresponding 90 PPI foam arrangement. The thermal-hydraulic performance was found to be governed by combinational interaction of three major factors: heat transfer area, ease of jet penetration and foam volume usage. Strategic placement of metal foam stripes allowed better utilization of the foam heat transfer area and available foam volume by aiding penetration of coolant fluid through available foam thickness. Thus, performing better than the case where entire heat transfer area was covered with foam. For a fixed pumping power of 10 W, the optimal metal foam-jet configuration showed ~50% higher heat transfer with negligible increase in pumping power requirements.

Nanorefrigerants: A Review on Thermophysical Properties and Their Heat Transfer Performance

The last decade has seen the rapid enhancement of nanofluid in several ways. Nanofluid with refrigerant base have been introduced as nanorefrigerant in recent years due to their significant effects on the efficiency of heat transfer. A brief review of past studies on nanorefrigerants and their performance in thermodynamics and heat transfer area are reported in this paper. Some current challenges and future prospect of nanorefrigerant will also be highlighted.