Heat exchanger Lab Report Authors: Sijin He DOCX

Title	Heat exchanger Lab Report Authors: Sijin He
Author	Sijin He
Pages	5
File Size	52.5 KB
File Type	DOCX
Total Downloads	72
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Summary

The Effectiveness, ε, of a heat exchanger is a Heat exchanger Lab Report function of the number of transfer units NTU Authors: Sijin He, Xihao Huang, George and the capacity ratio c, that is, ε= F（NTU, c）. Wright and Joseph Wookey Our object is to study how the effectiveness varies with capacity rat...

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Heat exchanger Lab Report Authors: Sijin He, Xihao Huang, George Wright and Joseph Wookey 1. Introduction 1.1 Heat exchanger A heat exchanger is a thermodynamic device which concerns the rate and extent of heat exchange between two surfaces, or fluids. The function of a heat exchanger is to either remove heat from a hot fluid or to add heat to the cold fluid. There are normally three categories of flow arrangement corresponding to the direction of fluid motion inside the heat exchanger: parallel flow, counter flow and cross flow. In parallel flow, both the hot and cold fluids enter the heat exchanger at the same end and move in the same direction. In counter flow, the hot and cold fluids enter the heat exchanger at opposite ends and flow in opposite directions. This experiment concerned the counter flow. Reduce the theory part? Add the graph "Flow through a plate heat exchanger" in lab sheet? 1.2 The Effectiveness-NTU Method The ε-NTU method is used to evaluate the performance of heat exchangers. This method is based on a dimensionless parameter called the heat transfer effectiveness ε, defined as ε= ´ Q/ ´ Qmax(1) NTU, the number of transfer units is expressed as(those r in nest page) NTU = U As ( ´ m Cp)min ; (2) When ´ m= ´ V ·ρ; (3) Another dimensionless quantity called the capacity ratio c is defined as; c= ( ´ m·Cp)min ( ´ m·Cp)max ; (3) The Effectiveness, ε, of a heat exchanger is a function of the number of transfer units NTU and the capacity ratio c, that is, ε= F （NTU, c （ . Our object is to study how the effectiveness varies with capacity ratio for a constant NTU. This will be done on a plate heat exchanger which has a flow arrangement of counter flow. 2. Procedure & Data Analysis 2.1 Procedure Ensure the thermostat is set to 50 . Set both the hot and cold water flow rates to 1 l min-1 . Take all six pieces of data once the system has stabilized. Repeat increasing the hot flow rate in 0.5 l min-1 increments. The maximum flow rate the instrument can achieve is 4 l min-1 . 2.2 Data T1/ ) T2/ T3/ T4/ Vh/L min^- 1 Vc/L min^- 1) 48.3 35.5 15.6 20.7 1 1 49.1 42.6 15.6 21.9 1.5 1 48.3 43.9 15.7 22.8 2 1 48.5 44.9 15.6 23.7 2.5 1 48.7 45.6 15.7 24.7 3 1 Table 1: Measured & Known parameters Use cp = 4.18 KJ Kg-1 K-1 and the density of water to be 998 kg m-3 . Use As =0.05m2 , F=0.95 (In additon to the 3 page report, on a third page I would like you to put the name of each member of the group and briefy say what they did. I will use this informaton to scale back the marks of anyone who has not engaged with the labs presentaton and report.) Notice that the specific heat of a fluid in general changes with temperature. But in a specified temperature range, it can be treated as a constant at some average value with little loss in accuracy. Table 2: Calculated values from data given in Table 1. (table 2 maybe useless, all the results are shown in appendix) 2.3 Analysis Applying effectiveness-NTU method, ε is defined as ε = ´ Q/ ´ Qmax ;(1) NTU, the number of transfer units is expressed as ´ Qhot (KJ) ´ Qcold (KJ) ε Tm ( ) U (W/m² （ NTU mc mh 0.89 0.35 0.4 23.54 0.32 0.23 1 0.68 0.44 0.65 27.1 0.34 0.24 0.67 0.61 0.49 0.81 26.83 0.39 0.28 0.5 0.63 0.56 0.9 26.99 0.44 0.32 0.4 0.65 0.63 1.0 26.84 0.49 0.35 0.33...