Heat exchanger

heat Exchanger analHeat Exchanger Analysis

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Table of Contents

Principle Objective Goals Background a) Experimental approach Overall efficiency Temperature efficiencies Overall heat transfer coefficient (U) b) a) b) c) Analytical approach Tubular Heat Exchanger Technical Data Plate Heat Exchanger Technical Data Shell & tube heat exchanger TechnicalData Procedure Report Tasks Experimental Setup

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University of Puerto Rico Mayagüez Campus Department of Mechanical Engineering

Experiment 3: Heat Exchanger Analysis
Principle
This experiment is designed to acquire experience on heat exchangers. The most common of these components found in industrialapplications are: Tubular, Plate (or Compact), and Shell & Tube heat exchangers. Through this experiment, we will understand the factors and parameters affecting the heat transfer rates and performance in heat exchangers.

Objective
To acquire experience on the basic process parameters affecting the performance in heat exchangers. Three basic heat exchanger configurations (Tubular, Plate and Shell &Tube) will be used to understand the factors and parameters affecting the rates of heat transfer.

Goals
The heat exchangers available in our laboratory will be operated in parallel and counterflow operation while varying the flowrate of the hot and cold fluids to determine the following: a) The heat lost to the surroundings. b) The overall efficiency. c) The temperature efficiency for the hot andcold fluids. d) The overall heat transfer coefficient U determined experimentally. e) The overall heat transfer coefficient U determined theoretically. Compare with the experimental one.

Background
The process of heat exchange between two fluids that are at different temperatures and separated by a solid wall occurs in many engineering applications. The device used to implement this exchangeis called a heat exchanger, and specific applications may be found in space heating and airconditioning, power production, waste heat recovery and chemical processing. Heat exchangers are typically classified according to flow arrangement and type of construction. In the first classification, flow

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INME 4032 / 4236

can be cocurrent (also called parallel) or counterflowas shown in Figure 1. According to their geometrical configuration, heat exchangers can be labeled as tubular, plate, and shell & tube heat exchangers.

Figure 1: Counterflow and parallel operation for a shell and tube heat exchanger

a) Experimental approach Overall efficiency
To design or predict the performance of a heat exchanger, it is essential to determine the heat lost to thesurrounding for the proposed configuration. To quantify the percentage of heat losses or gains in the equipment, we must perform energy balances for both the hot and cold fluids. If Qh is the heat transfer rate from the hot fluid while Q c is the heat transfer rate absorbed by the cold fluid and neglecting potential and kinetic energy changes, we can express these heat transfer rates as follows,

  Qh = m h (hh,i − h h,o ) = m h c p,h (Th,i − Th,o )   Qc = m c (hc,i − h c,o ) = m c c p ,c (Tc,i − Tc,o )
where,

  m h , m c : mass flow rate of hot and cold fluid, respectively.
hh,i , hh,o : inlet and outlet enthalpies of hot fluid, respectively. hc,i , hc,o : inlet and outlet enthalpies of cold fluid, respectively. Th,i , Th,o : inlet and outlet temperatures of hot fluid, respectively.Tc,i , Tc,o : inlet and outlet temperatures of cold fluid, respectively. cp,h , cp,c: specific heats of hot and cold fluid, respectively.

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Heat power lost (or gained): Qh − Qc Percentage of losses or gains P =

Qc Qh

× 100

If the heat exchanger is well insulated, Qh and Qc should be equal. In practice there is a difference due to heat losses...