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Design and construction

This document explores effective design methodologies for heat exchangers, specifically focusing on air-water and water-water systems. It emphasizes the need for compact and efficient designs that satisfy project goals. Key aspects covered include types of heat exchangers, design calculations involving cooling/heating loads, overall heat transfer coefficients, and the logarithmic mean temperature. A detailed analysis of condenser design using trial-and-error methods is provided, alongside necessary equations for mass and energy balance, flow evaluations, and Nusselt number calculations.

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Design and construction

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  1. Design and construction • We need to seek a design that Achieve the goal of the project • which should be : compact effective • So we need to know types of heat exchangers

  2. Heat exchangers type There are two type of heat exchanger Air water heat exchanger cross flow Water- water system counter flow

  3. Air-water system design • This type depend on water as refrigerant air as cooling agent • To design the cycle need to know : • cooling and heating load • Over all heat transfer coefficient • Logarithmic mean temperature • So we find the surface area of different componaent

  4. As we saw from the previous slide we have to calculate U to get the surface area to construct the design for the components • As all the design is proceeded in the same method we will present the design of a sample which will be condenser

  5. Condenser design Air-water system • This design is constructed by trial and error method • So we need to assume the initial values for U, and the temperature to be calculated • U is assumed based on reference

  6. Assumptions Assume U = 35 W/m2 .C° An initial value for the surface area is obtained

  7. Equations • Mass and energy balance equation • To find velocity • Then find Reynolds number

  8. After we find Reynolds number we decide whether its laminar or turbulent flow • If Re < 500000 (Laminar)

  9. As the mass flow rate was for water we just calculate inside heat transfer coefficient • So repeating the previous steps for air we will find outside heat transfer coefficient • But :

  10. Sd The Nusslets number for outside heat transfer coefficient= Substitute in over all heat transfer coefficient and with trial and error method the resulted surface area was 28.25 meter square

  11. The resulted surface area was unsuitable for the construction so another design is proposed Water -Water system • This design based on empirical equations • All of the values related to temperature • Same principle of the previous system but not the same evaluation

  12. Cycle

  13. Equations

  14. Q for the condenser = m`*(hf-hg) =2.4 kw

  15. for 104<Red<5×106 and 0.5<Pr<2000

  16. Sizing

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