Fundementals of heat and mass transfer kotandaraman

[...]... influence the rate of heat transfer The aim of this text is to introduce the various rate equations and methods of determination of the rate of heat transfer across system boundaries under different situations 1.1 HEAT TRANSFER The study of heat transfer is directed to (i) the estimation of rate of flow of energy as heat through the boundary of a system both under steady and transient conditions, and (ii) the... product of volume density and specific heat ρcV and dT where the group ρcV is called the heat capacity of the system The basic analysis in heat transfer always has to start with one of these relations 1 Chapter 1 1 2 FUNDAMENTALS OF HEAT AND MASS TRANSFER 2 The second law of thermodynamics establishing the direction of energy transport as heat The law postulates that the flow of energy as heat through... thermal contact without the involvement of mass flow and mixing This is the mode of heat transfer through solid barriers and is encountered extensively in heat transfer equipment design as well as in heating and cooling of various materials as in the case of heat treatment The rate equation in this mode is based on Fourier’s law of heat conduction which states that the heat flow by conduction in any direction... the direction of lower temperature or along the negative temperature gradient 3 Newtons laws of motion used in the determination of fluid flow parameters 4 Law of conservation of mass, used in the determination of flow parameters 5 The rate equations as applicable to the particular mode of heat transfer 1.2 MODES OF HEAT TRANSFER 1.2.1 Conduction: This is the mode of energy transfer as heat due to temperature... design of all equipments involving heat transfer require the estimate of the rate of heat transfer There is no need to list the various equipments where heat transfer rate influences their operation The driving potential or the force which causes the transfer of energy as heat is the difference in temperature between systems Other such transport processes are the transfer of momentum, mass and electrical... density of 19000 kg/m3 and a specific heat of 0.118 kJ/kgK Determine the rate of change of temperature of the body at that instant in °C/s Solution: Refer equation 1.4 and Fig 1.8 (q – QR – QC) dτ = ρVC dT 10 FUNDAMENTALS OF HEAT AND MASS TRANSFER dT q − Q R − QC = ρVC dτ ∴ 0.3 m = 2πr2 + 2πrh The surface area 0.3 m = 2π × 0.152 + 2π × 0.15 × 0.3 = 0.4241m2 Heat capacity = Volume × density × sp heat =... receives heat by radiation over its surfaces at 4kW and the heat convection rate over the surface of the solid to the surroundings is 5.2 kW, and heat is generated at a rate of 1.7 kW over the volume of the solid, determine the heat capacity of the solid if the time rate of change of the average temperature of the solid is 0.5°C/s Solution: The energy balance yields: Heat received by radiation – heat convected... surface is at 200°C and is exposed to surroundings at 60°C and convects and radiates heat to the surroundings The convection coefficient is 80W/m2K The radiation factor is one If the heat is conducted to the surface through a solid of conductivity 12 W/mK, determine the temperature gradient at the surface in the solid Chapter 1 11 AN OVERVIEW OF HEAT TRANSFER 12 FUNDAMENTALS OF HEAT AND MASS TRANSFER Solution:... FUNDAMENTALS OF HEAT AND MASS TRANSFER In this chapter only simple cases will be dealt with and the determination of F will be taken up in the chapter on radiation The concept of hr is convenient, though difficult to arrive at if temperature is not specified The value also increases rapidly with temperature 1.3 COMBINED MODES OF HEAT TRANSFER Previous sections treated each mode of heat transfer separately... OVERVIEW OF HEAT TRANSFER 14 FUNDAMENTALS OF HEAT AND MASS TRANSFER Problem 5: A spherical reactor vessel of outside radius 0.48 m has its outside temperature as 123.4°C The heat flow out of the vessel by convection and radiation is 450 W Determine the surrounding temperature Solution: In this case Temp should be in K, Tµ = Ts Radiation Tµ 450 W 2 1.5 W/m K T2 = 123.4°C r2 = 0.48 m Fig 1.11 or, heat conducted . situations. 1.1 HEAT TRANSFER The study of heat transfer is directed to (i) the estimation of rate of flow of energy as heat through the boundary of a system both under steady and transient conditions, and. flow velocity also influence the rate of heat transfer. The aim of this text is to introduce the various rate equations and methods of determination of the rate of heat transfer across system boundaries. of mass flow and mixing. This is the mode of heat transfer through solid barriers and is encountered extensively in heat transfer equipment design as well as in heating and cooling of various materials