iChemingeniare

  MODES OF HEAT TRANSFER Heat transfer occurs in different ways: Conduction, Convection, and Radiation. In real-time engineering problems, it can occur through 2 or 3 modes combined. 1. Conduction is the method through which heat is transferred in solids. It occurs due to the vibrational energy transfer between the molecules of the solid. Though conduction is majorly confined to solids, it also extends to some liquids and gases. Fourier's Law governs conduction.      Q = kA(-dT/dX) Which states that the rate of heat transferred (Q) is directly proportional to the heat transfer area (A) and the temperature (T) distribution across the length (X) of the solid, otherwise termed as the temperature gradient (dT/dX). The negative sign indicates the flow of heat from a region of higher temperature to a region of lower temperature. The proportionality constant (K) is called Thermal Conductivity. Thermal Conductivity indicates the ability of a solid to conduct heat. I...

  BASICS OF HEAT TRANSFER What is Heat transfer? We know through thermodynamics that energy can exist in many forms. One such form of energy is heat. The energy that is transferred between systems as a result of the temperature gradient is called heat. Heat transfer is the science that indicates the rate at which this heat is transferred between the systems. Imagine holding a bottle of water in a refrigerator. There is going to be energy transfer between the bottle and the cold air inside. The energy transfer takes place until the temperatures of the cold air and the water is the same. Therefore, we can conclude that heat transfer occurs until equilibrium is obtained. Heat is transferred from higher temperature to lower temperature. Here comes thermodynamics that can tell us about the amount of heat to be transferred to effect the change in the state according to the law of conservation of energy. But the amount is not everything that we need. Consider a scenario where we pur...

  BOILING Evaporation is one of the major heat transfer operations for concentrating solutions by boiling off the solvent. So, boiling can be considered as the backbone for evaporation. Boiling is a phenomenon where the liquid is transitioned to its vapor phase at its boiling point, the temperature at which the vapor pressure is equal to the pressure exerted on the liquid by the surrounding atmosphere. Boiling occurs at the solid-liquid interface where the liquid in contact with a surface whose temperature is greater than the saturation temperature of the liquid itself. The substantial amount of heat/energy that is required to vaporize 1kg of a liquid is called the latent heat of vaporization. When spoken of boiling, a simple household setup of water on a pan over a stove is what we generally live up to. This is a great example to understand pool boiling, where the heating surface is submerged in a pool of liquid. Considering the above setup, now the heat flux for boiling wil...