MAE 441 Design of a Finned Radiator Assembly Heat Exchanger Design Project Thin Van Trans Chris Longwinded Eric Papacies Olivia Aching 4/3/2012 Scope of the Project The objective of the project was to design an effective radiator assembly to accommodate the Diesel-Engine Generator Set 1500-EXCITED by incorporating the use of tubes with inner fins in various geometries in order to meet the heat rejection requirements specified. This was done with consideration for minimizing cost, size, and complexity.
Initial Parameters The initial parameters were the operating requirements of the Diesel-Engine Generator Set 1500-EXCITED are as follows: Coolant capacity – The coolant chosen for our radiator is ethylene glycol (50/50 % by volume) Its maximum operating temperature of OFF Air flow rate – Since the generator is stationary as opposed to that used in an automobile application, a fan will be needed to provide the necessary flow rate. The required air flow rate specified by the engine is 9. 383 Is in order to dissipate the heat generated Coolant flow rate – The coolant flow rate is 17. 14 keg/s through the radiator The initial coolant temperature is assumed to be OFF, which is slightly below the operating temperature of the engine. The initial coolant temperature is taken as the ethylene glycol entering the radiator immediately after leaving the engine. Pressure drop allowance – The The total heat rejected to the coolant is skew The outlet temperature of the coolant leaving the radiator was calculated to be OFF Assumptions In order to design a radiator for a specific operating condition, we assume the ambient temperature is OFF, which was the highest average temperature in Miami, Florida last year.
This is accounting for the worst case scenario. We also assume that the ambient air density is constant throughout operation. We also assumed that there was no significant fouling on the inside of the tubes, so the heat transfer coefficient of the materials remains constant. Design Methodology Identification of Problem The heat rejection requirements were specified by the diesel-engine generator’s operating conditions. Our objective was to reduce construct a radiator that would provide better performance while functioning at a higher efficiency by reducing size and cost.
Selection of an Appropriate Heat Exchanger Classification The conventional and most effective form for a radiator in this application is the late-fin and tube heat exchanger operating in cross-flow conditions. Rather than attempting to create a more innovative heat exchanger assembly while sacrificing simplicity, the present work aimed to improve and maximize the performance of the current heat exchanger type. Material Selection The materials of each specific component were chosen based primarily on thermal conductivity as compared to price.
The estimated manufacturing cost Manufacturing Hours $/her Cost Design Time 8 30 $240. 00 Machining Time 2 12 $24. 00 Assembly Time 10 15 $150. 00 Miscellaneous $100. 00 $514. 00 $530. 24 The working fluid selected for the radiator was ethylene glycol (50% by mass), due o its prominent use in convective heat transfer applications, particularly in automobiles. Selection of Provisional Dimensional Parameters In order to design an ideal heat exchanger with minimal cost and size, preliminary measurements were chosen and initial calculations were run to provide a scope of the required parameters.
The radiator core’s dimensions were determined by comparing the conventional radiator specified by the Diesel-Engine Generator. Its size was slightly reduced, since an increase in heat transfer in the tubes was anticipated in our design. The initial dimensions considered are listed in Table 3 low. Table 3. The initial dimensions chosen to gauge heat rejection rates Width (m) 2. 2098 Height (m) 2. 4384 Depth (m) 0. 12065 Number of Fins 1140 XSL (m) 0. 0254 Ext (m) 0. 0001 ODD (m) 0. 0127 The use of previously derived correlations for the inner-finned tubes was the primary means of determining heat rejection requirements.
The pitch for the ribs was calculated using, where 0 represents the angle of each rib’s alignment with respect to the axial direction of the tube. The Reynolds number was derived by, where the mass flow rate is that of the ethylene glycol. The friction factor for flow inside the tubes can be determined using the following equation. This correlation is valid for turbulent flows within tubes, and relates the pressure loss due to friction in the tubes to wall shear stress. This pressure drop can be determined using the preceding equation.
This pressure drop in turn governs the pumping power required for the coolant mass flow rate. The Mussels number required to find the heat transfer coefficient needed to determine heat transferred from the engine to the coolant to the air is given by the following correlation for turbulent flow. The local heat transfer coefficient for finned tube as compared to the coefficient for plane tubes is illustrated by the following equation. The friction factor for the finned tubes can be determined using the original friction factor through the following correlation. 7) Design Optimization For the preliminary design of our radiator, some optimization was performed for the heat transfer in the coolant tubes, fins, inner ribs, as well as other surface areas. Local heat transfer coefficient was calculated and compared for various cases of inside tube diameters, rib angles, and rib heights, as well as the number of ribs. These results can be observed in figures 4 and 5. Figure 4. Local heat transfer as a function of rib number Figure 5.