An analysis of material selection when designing liquefied natural gas heat ex changersFull description
Tugas Laporan Tetap Praktikum Satuan Opersai II Politeknik Negeri Sriwijaya
HE Problems SolvingFull description
Full description
Plate heat Exchanger
Abstract: In this experiment we heated a rod on a furnace until reaching a specific temperature and leave it to cool naturally and forced Then we measured the heat transfer coefficient for air in these three cases: 1) Natural convection 2) Forced convection on top of the tube bank 3) Forced convection on the bottom of the tube bank The method we used called the lumped body analysis
Introduction: The cross flow heat exchanger is a common component in many engineering applications. The normal configuration involves heat transfer between one fluid flowing through a bundle of tubes and another flowing transversely over the outside of the tubes. The tubes may have extended surfaces internally and/or externally in order to enhance heat transfer between the two fluids. Typical application includes internal combustion engine radiators, air heaters, refrigeration evaporators and condensers.
Square air duct Bank of rods assembly Rod heater and temperature control unit Thermocouples unit
Procedure: 1) Heat the rod in the heater until it reaches 45 degrees 2) Put the rod in the heat exchanger and let it cool down 3) Take readings of the time and the temperature every 10 sec until it reaches 35 degrees 4) Repeat the experiment again but put the rod on top then at bottom of the assembly with the fan on.
Discussion: We used the Fourier and Biot number to get (h) by drawing the relation between logarithm of the temperature difference and the Fourier number The lumped body analysis depends on: 1) No temperature gradient from center to surface in the copper 2) Huge cooling medium so that its temperature stay constant We assumed that there is no temperature gradient in the copper rod since it has a large thermal conductivity. Staggered tubes make the flow more turbulent as it moves through the rows This makes the temperature drop takes more time when the tube is in the bottom In-line tubes do not affect the flow as much as the staggered.
Conclusion: We see that the forced transfer has a higher heat transfer coefficient than the free transfer Heat transfer coefficient in staggered will be higher than the in-line tubes. At the bottom of the tubes heat transfer take more time in compassion with tubes at the top As we go through the rows of the tubes as (h) increase, but it is eventually useless due to small h difference, so we must know when to stop adding rows. If the velocity of the air increases h will increase.
