A COMPARATIVE ENTHALPY APPROACH FOR CO- AND COUNTERCURRENT FLOW IN CONCENTRIC TUBE HEAT EXCHANGER

ABSTRACT

The comparison Evaluation of a heat transfer coefficient between the countercurrent and cocurrent flow arrangement was carried out on heat trainer, fabricated in Nigeria. The experiments carried out are of two different arrangement; countercurrent flow arrangement and co-current flow arrangement of which countercurrent flow firstly consist of countercurrent flow with cold phase variation, hot phase constancy. Countercurrent flow with hot phase variation and cold phase constancy. Secondly the arrangement is co-current flow arrangement which also consist of two different conditions, which are co-current flow with cold phase variation and hot phase constancy; co-current flow with hot phase variation and cold phase constancy. The equipment involves also liking reading of temperature at different flow rate, having completed the experiment and getting result a critical analysis and evaluation was carried out to get the best arrangement of the experiment. Using the graph plotted i.e. a graph of heat transfer rate per unit area against the log mean temperature difference, A result showing the heat transfer coefficient was observed, This helped to get a conclusion of recommended flow arrangement.

CHAPTER ONE

1.O INTRODUCTION

BACKGROUND OF THE STUDY

According to the modern or dynamical Theory of heat: Heat a form of energy. The molecules of a substance are in parallel motion. The mean Kinetic energy per molecules of the substance is proportional to its absolute temperature. In description of heat, a molecule may consist of one or two or many atom depending upon the nature of the gas. The force of attraction between the molecules of a perfect gas is negligible. The atom in a molecules vibrate with respect to one another, consequently a molecules has vibration energy. The whole molecules may rotate about one or more axes, so it can have “notational energy”. A molecule has “translational energy” due to its motion, thus kinetic energy of a molecule is “the sum of its translational, rotational and vibrational energies. Summarily heat energy given to a substance e is used in increasing its internal energy. Increase in internal energy cause increase in Kinetic energy or potential energy or increase in both the energies. Due to increase in Kinetic energy of a molecules, its translational, vibrational or rotational energy may increase. In a nut shell “heat transfer is the science which deal with the rate of bodies called the Source aims receiver KERN, [2006:1]

MECHANISM OF HEAT

Heat transfer is of three distinct way in which heat may pass from a source to a receiver, although most engineering application are combination of two or three method, which are conduction convection and radiation

Conduction: Conduction heat Transfer is energy transport due to molecular motion and interaction. Conduction heat transfer through solids is due to molecular vibration. Fourier determined that Q/A, the heat transfer per unit area (W/m2) is proportional to the temperature gradient ∂t/∂x. The constant of proportionality is called the material thermal conductivity K. Fourier equation according to Colostate [2014:4] Q/A = -K ∂t/∂x …(1-1) The thermal conductivity K depends on the material and also some what on the temperature of the materials.

Convection: Convection heat transfer is energy transfer due to bulk fluid motion. Convection heat transfer through gases and liquids form a solid boundary results from the fluid motion along the surface.

Newton determined that the heat transfer/area Q/A, is proportional to the fluid sold temperature difference T2. if the temperature difference normally occurs across a thin layer of fluid adjacent to the solid surface. This thin fluid, layer is called a boundary layer. The constant of proportion is called the heat transfer coefficient, h. Newton’s equation: According to Colostate [2014:4] Q/A = h ( Ts – Tf) …(1-2) The heat transfer coefficient depends on the type of fluid and the fluid velocity. The heat flux) depending on the area of interest, is the local or area averaged. The various types of convective heat transfer are usually categorized into the following

CONVECTIVE HEAT TRANSFER COEFFICIENT CONVECTION

Types & Description

Natural Convection: Fluid motion induced by density difference.

Forced Convection: Fluid motion induced by pressure differences from a fan or pump.

Boiling: Fluid motion induced by a change of phase from liquid to vapour

Condensation: Fluid motion induced by a change of phase from vapor to liquid.

Source: Colostate [2014:4]