Thermal Engineering & Tribology

Thermal Interface Materials (TIM)

Heat transfer in LED lighting solutions is generally enabled by employing thermal tapes to join the components. However, these tapes are very expensive. In this age of high competition, a thermo-adhesive material would be best suited to minimize this cost. The research team at the lab is developing novel materials for this application by using MWCN based thermal pastes. Experimental results have demonstrated improved heat transfer characteristics. Further study is on with respect to their adhesive properties.

Heat Sinks

All heat sinks are provided with fins to dissipate heat from the heat source. With limitations on their shape, size and operating environment, fins may not be efficient enough to remove heat generated. The lab is currently developing and testing novel designs for heat sinks used in LED lighting applications that seek to improve heat transfer, given existing constraints.

Numerical Simulations (CFD)

• The natural convection flow phenomena inside an enclosed space, is an interesting example of very complex fluid systems that may yield to analytical, empirical and numerical solutions. Natural convection in enclosures is always created by the complex interaction between the fluid and heat with all the walls. Internal interactions will cause a diversity of flows that can appear inside the enclosures. In many engineering applications and naturally occurring processes, natural convection plays an important role as a dominating mechanism. Natural convection in a differentially heated enclosed space is often encountered in various engineering applications such as solar energy collection, cooling of microelectronic equipments, growing of single crystal from fluid phase, energy storage devices, furnace design and many others. A CFD studies were carried out to investigate the effect of Rayleigh number with rotation on the flow and heat transfer characteristics in a differentially heated enclosure. An in-house Code was developed based on FVM to discretize governing equations. Upwind difference scheme for convective terms and fully implicit scheme for transient terms were used. The SIMPLE algorithm was employed to couple pressure and velocities on staggered grid arrangement.

• To reveal the hydrodynamics of the different flow field designs for Redox flow batteries, CFD analysis were conducted using FVM code with 2^nd order upwind differencing method for treating convective terms. The SIMPLE algorithm is used to couple the pressure and velocities on staggered grid arrangement with pressure being descriterised using 2^nd order scheme. The porous substrate is modeled by the addition of source term to the momentum equation. This comprises of two components, a viscous loss term and an inertial loss term were solved with relevant boundary conditions are solved using in-house developed code to ensure the convergence. Modified serpentine flow field – 2 (MSFF2) design provided least pressure drop across the channel and maximum velocity penetration across the porous substrate when compared to the other designs. This increases its wetting ability that is very important in terms of mass transfer over potential for electrochemical reaction happening in the porous substrate to achieve effective electrochemical cell performance.

• Pulsating heat pipes (PHPs) are passive heat transfer devices where the heat transfer is much higher as compared to the general heat transfer devices such as metal fins. The main reason for this is the two phase phenomenon happening inside PHPs with the oscillatory motion of the bubbles. It can be used in various applications, space satellites, laptops or any other place where you want heat transfer to be very high in a small temperature drop. The CFD studies were carried to model the two phase flow using a single fluid formulation based on VOF method were used for modelling the slug flow in capillaries. The hydrodynamics were described by the equations for the conservation of mass, momentum and energy together with an additional advection equation to determine the gas-liquid interface. The performance parameters such as temperature difference between evaporator and condenser, thermal resistance evaluated. The obtained simulation results are compared with the experimental trials under the same condition.

Experimental studies

• Pulsating heat pipes (PHPs) are passive heat transfer devices where the heat transfer is much higher as compared to the general heat transfer devices such as metal fins. The main reason for this is the two phase phenomenon happening inside PHPs with the oscillatory motion of the bubbles. It can be used in various applications, space satellites, laptops etc where high heat transfer is required with small drop in small temperature. Experimental studies on the development of flat plate pulsating heat pipe (FPPHP) for space application is in progress

Tribology

Tribology is the science and technology of relative motion between interacting surfaces. The domain of tribology includes the study of friction, lubrication and wear. Relative motion between two mating surfaces in machine members requires special attention to friction. Improper lubrication results in loss of precision in manufacturing and, hence, loss of productivity; this, further, leads to serious economic losses to the industry. Lubrication minimizes the stick-slip phenomena between the interacting surfaces. As machines consist of a number of moving parts, there is a huge demand for lubricants to meet the needs of a number of industrial applications. Recognizing this high-felt demand, the Centre is actively involved in the design and characterization of specific industrial additive-based lubricants that can enhance the life of machine members.

 Polymer Tribology

Polymers, by virtue of their ease of processing and low cost of production, have become the most sought-after materials for industrial applications, replacing traditional metals and materials. Their scope in industrial and structural applications has been ever increasing. In this context, the Centre is involved in developing polymer composites materials for machine parts. These composites have a polymer matrix filled with varying volume percentage of reinforcements to improve the mechanical and tribological properties of the composites. Such composites have the potential to replace a monolithic material.

 Lubricant Tribology

Linear motion guideways are one of the most critical parts of machine tools. The main factor affecting the performance of guideways is friction. In sliding contact guideways, the relative motion between the elements is sliding, thus giving rise to sliding friction. Reduction of friction, either through improved design, or through the use of more suitable contacting materials, or again through the application of better lubricating substances, is thus an extremely important problem of modern technology.

Lubricants and coolants, being the mainstay of the automotive and machine tool industry for reducing friction and wear, become important from both the operational and manufacturing points of view. Generally, the smoothness of movement is improved by reducing friction. Though frictional force is reduced by the application of lubricant, it is also important to keep the frictional force steady. Unsteady or variation in frictional force leads to jerky motion or stick slip in machine tool slideways. Thus, stick slip, in tribology, is a cyclic fluctuation in the magnitudes of friction force and relative velocity between two elements in sliding contact, usually associated with a decrease of the coefficient of friction with onset of sliding or with increase of sliding velocity. In most practical sliding systems, these fluctuations of the sliding velocity are considered a serious nuisance, and measures are taken to eliminate or reduce the amplitude of these fluctuations.

The requirements of linear guideways and industrial lubricants are rising, especially for machine tools which have to meet various demands such as high positioning exactness, good compatibility with coolants, stick slip free with low coefficient of friction over a wide speed range and good demulsifying behaviour on metallic slideways. These requirements can be achieved by employing different slideway materials and design of lubricants by the addition of different additives like Boron Nitride, etc. The tribological efficiency of these lubricants with regard to linear guideways is tested using a reciprocating tribometer or a four ball tester. Research at the lab investigates of tribological efficiency of lubricant (oils and greases) or coolant governed by a number of parameters. These include the sliding speed of the mating members, physical and chemical properties of the lubricant, demulsification behaviour of the lubricant/coolant, oil groove design and geometry and the material of the sliding members involved. It is also proposed to investigate some of the tribological issues by replacing the liquid with a solid lubricant such as Molybdenum di-sulphide or Boron Nitride or Graphite impregnated into a polymer. The other aspects of study include possible oil and wear particle analysis.

Additive Manufacturing (AM)

CIIRC^® has 3D printing lab facility for prototyping products to be used by various industries for different applications. AM at Centre offers the advantages of mid-sized, thematically focused, scientific groupings within the larger, more diverse academic environment in additive manufacturing.

3D Printing

3D printing is the process of manufacturing physical objects/prototypes of designed geometry directly from their CAD models without any human intervention and without the use of any tools, dies or fixtures. As the object is built in a layer by layer manner in this process, 3D printing is known more appropriately as the Layered Manufacturing (LM) process or rapid prototyping. 3D printing, utilizing the extrusion of thermoplastic material, is easily the most common and recognizable 3DP process. The most popular name for the process is Fused Deposition modeling (FDM). The process works by melting plastic filament that is deposited, via a heated extruder, a layer at a time, onto a build platform according to the 3D data supplied to the printer. Each layer hardens as it is deposited and bonds to the previous layer. The most common material for FDM 3D printers is ABS.

Researchers at the lab have also worked with other 3D printing methods in developing micro products for mechanical and other applications. Figure shows some of the prototypes developed at the Centre using micro stereolithography.

Plating of RP Components

Other topic of interest is plating of rapid prototyped components, optimization of build features, metal coating (Ni & Ag), which provides structural integrity and enhancement in strength and evaluating thermo-mechanical properties. The primary objective includes identification of potential applications in aerospace, medical devices and automobiles.

^{Plating Methodology of Rapid Prototyped Components}

 Rapid Prototyped Components Coated with Ag and AU for Space Applications