Sharif Digital Repository

One of the different methods of heat transfer, is pool boiling process. In this method, the operating fluid starts to boil on a hot surface whose temperature is more than boiling point of the fluid. Based on difference between between surface temperature and fluid boiling point, amount of heat flux from hot surface to fluid and fluid behavior will be different. In recent years, many researchers have tried to improve the amount of heat transfer in the boiling process by using various methods such as nanoparticle addition or using magnetic field.Latent heat is thermal energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process, usually a first-order... 

These days, the heat transfer phenomena is an important issue in internal combustion engines design because of direct effects on the performance, efficiency and emission of engine. One of the main parts is cylinder head which contacts with hot gases in combustion chamber and expose high heat flux. In this thesis, cylinder head of Tiba engine modeled by three dimensional and transient thermal analysis. In this modeling in order to consideration the effect of fluid flow, different domain of cylinder head (water jacket, intake/exhaust ports) has been simulated and appended to the model. Also combustion phenomena modeled separately, and then the heat transfer coefficient in the surface of... 

This project related to gas purification according to difference in the deposition point in the fludized bed.The main reason for choosing fluidized bed is increasing overall heat transfer coefficient compare in to other heat exchangers. Separation process, by cooling the wall causes the self- deposition gas phase shifts to solid phase. Solid formed on the wall, act as an insulating layer and greatly reduces the heat transfer. To solve this problem, the fluidized bed system is offered because fluid particles in addition to remove the insulating layer, improving convection heat transfer coefficient . Laboratory tests show the feasibility of preventing the formation of insulating layer by... 

Modern microelectronic systems generate a large amount of heat which must be transferred out of the system without excessive temperature rise. Conventional forced air convection and microchannel cooling plates have reached their performance limits Nanofiuids are proposed as an innovative way to solve the problem. A nanofiuid is nanoscale solid particles dispersed in a traditional heat transfer liquid. Some studies show an anomalous increase in the thermal conductivity for stationary nanofiuids. However, there are only few previous studies on the convection heat transfer rate and viscosity of nanofiuids. Both convection and stationary measurements of the thermal conductivity are widely... 

Mold/metal interfacial heat transfer coefficient (IHTC) is the most important parameter that influences the solidification and the mechanical properties of a solidified product. The present work focuses on the determination and evaluation of pressure effect on interfacial heat transfer coefficient from the experimental cooling curves during unidirectional solidification of A356 alloy against water cooled Gray iron mold (chill). For this purpose, inverse heat conduction method is used. The results showed that IHTC is not constant, but varies with time, temperature and pressure during solidification. IHTC variation is related to coherency and critical solid fraction during... 

The computer simulation of freezing patterns in castings has done much to broaden our understanding of casting and mold system design. The structural integrity of shaped castings is closely related to the time–temperature history during solidification, and the use of casting simulation could do much to increase this knowledge in the foundry industry. However, some uncertainties must be eradicated, particularly heat transfer at the metal/mold interface. The accurate knowledge of interfacial heat transfer coefficients is necessary for accurate modeling of castings. The present work focuses on the determination of transient mold–environment and metal–mold heat transfer coefficients during... 

As a result of fission reaction in a nuclear reactor, the produced high neutron flux would affect the material of Reactor Pressure Vessel (RPV). This neutron radiation has a detrimental impact on the mechanical properties of the RPV material such as hardening (or embrittlement) while neutrons are absorbed by the material. A major concern in embrittled RPVs is propagation of critical flaw causing through-wall cracks. Some transients leading to overcooling of RPV intensify the propagation of theses cracks and result in thermal load on RPV, known as Pressurized Thermal Shock (PTS). Such situation could be created in case of Emergency Core Cooling System (ECCS) actuation which leads to injection... 

The major features of batch sublimation were investigated in an experimental-theoretical study. An experimental setup with real-time displays, sublimated dry ice blocks of different sizes, with circular or rectangular geometries. When temperature of hotplate was changed from -30 to 200 oC, heat transfer coefficient “hsub” decreased from 126 to 70 W/m2K, while thermal flux increased, linearly. Weight and area of the block had a positive/negative effects on “hsub”, respectively. In theoretical part, at first, two “linear-gradient” and “cubic” models were developed by a combined mass-momentum-energy balance. The latter used Von Karman temperature profile, and in cases of circular and... 

Increasing energy consumption and limited energy resources are instances of the concerns of human societies and environmentalists today. The condensation process, as one of the most important processes in the industry, plays an important role in saving and regeneration the existing energy. Nowdays, surface optimization is one of the modern ways to improve condensation.In this research, two methods have been used to construct surfaces useful for enhancement of droplet condensation, including hybrid surfaces and solid infused surfaces. In the construction of hybrid surfaces, superhydrophobic coating with silica nanoparticles based on hydroxyl acrylic resin was used. The superhydrophilic parts... 

Creating sustainable development in today's society is essential, and one of the most important elements to achieve this is the phenomenon of recycling. Lead-acid batteries are one of the sources of environmental pollution, and their separators contain 50% recyclable silica nanoparticles. In this research, impurities in these separators were removed using two methods: washing with water and sandblasting. The purity of recycled nanoparticles was 85.5% in the first method and 98% in the second method. In addition to the importance of recycling, finding a suitable use for recycled materials is also critical. FDM 3D printing is a new method of producing parts, but polypropylene is not commonly... 

Electrospray is a process in which the charged liquid is subjected to the effect of an electric field and after passing through an emitter, it will propagate in the form of jets or small droplets. This process is used in applications such as electric thrusters, cooling or mass spectrometry. In the electronics industry, cooling high-temperature microprocessors is a challenge. In this regard, air-based cooling systems are not well able to discharge heat from electrical and electronic components. Electrospray cooling technology is one of the new and promising methods. In this research, the two-dimensional simulation of electrospray cooling is performed by using COMSOL commercial software as a...