In industries cooling and heating of the process streams takes place in heat exchange equipments. To maintain a specified temperature of a fluid in the system continues heat transfer has to take place that overcomes the loss to the surroundings. In some situations, fluids are to be cooled or heated without changing their phase state.
Heat transfer conditions under which an industrial process takes place
The phase of fluids depends on the degree of freedom and to maintain it we need control temperature and pressure in process plant rather than flow rate or mass rate. The thumb rule of heat transfer to fluids and phase change is if temperature fixed for the liquid to change its phase to vapour, pressure has to be decreased. Similarly, if pressure is fixed in the streamline then temperature should be increased for above condition to take place.Fluid flow in heat exchanger undergoes heat transfer by forced or natural convection. Download some important data about HEAT TRANSFER TO FLUIDS WITHOUT PHASE CHANGE in the heat exchanger
Heat transfer of Nanofluids without phase change:
Size of nanoparticles would be less than 100 nm, they are designed to easily suspend in the fluids used for heat transfer in heat exchange systems. Whether the heat transfer is natural or forced convection nanofluids can sustain and perform outstandingly.
Application of these nanofluids in heat transfer of fluids without phase change.
- They change the properties of the fluid in which they are suspended transforming the fluid into nanofluid.
- To get efficient heat exchange the fluid thermal and transport properties should to excellent and they can be altered by using nano-particles.
- Nanoparticles can be developed by any material may be metal or nonmetal substance.
The effect of using nanoparticles in the heat transfer fluids is that they alter important thermal-physical properties without disturbing the chemical structure of fluid.
- Thermal conductivity of the fluid
- Viscosity of the base fluid
- Specific heat
- Improves the density
- Cooling efficiency
- Increase surface-to-volume ratio
Varieties of nanofluids used as a three-phase system:
- TiO2 suspended in water
- Al2O3 dispersed in water
- Similarly CuO in oil
- Titanate nanotube/water
- Al2O3–Cu/water hybrid
The general heat transfer fluids used in industries are water, ethylene or propylene glycol and oil these can be converted to nanofluids without phase change, by mixing with nanoparticles of
- Metals, e.g. Copper, Nickel, Aluminium
- Metal oxides, e.g. Aluminium oxide, Tungsten oxide, Copper oxide, Silicon oxide, Ferrous oxide
- Nano compounds, e.g. Carbon nanotubes, Silicon carbide, Calcium carbonate, Graphene)
Heat transfer in a heat exchanger depends on the length of pipe when nanofluid flow along its surface as boundaries are the main parameter that affects its flow process. Due to the high thermal conductivity of nanoparticles like Al2O3 and SiO2, high heat transfer rate is achieved even by natural convection for low Rayleigh number. Numerical studies are done on the topic of nanofluid flow and pure fluid flow without phase change have improved the technologies in solar thermal applications and extended surface heat exchanger designs.