The demand for more powerful engines in smaller hood spaces has created a problem of insufficient rates of heat dissipation in automotive radiators. Upwards of 33% of the energy generated by the engine through combustion is lost in heat. Insufficient heat dissipation can result in the overheating of the engine, which leads to the breakdown of lubricating oil, metal weakening of engine parts, and significant wear between engine parts. To minimize the stress on the engine as a result of heat generation, automotive radiators must be redesigned to be more compact while still maintaining high levels of heat transfer performance.

Most four-cylinder automobiles, depending on their size, have radiator cores that vary from   to . We believe that we can greatly reduce the size of automotive radiators while maintaining the current levels of heat transfer performance expected.  Moreover, this can be done without significant modification to the existing internal radiator structure. There are several different approaches that one can take to optimize the heat transfer performance of a smaller radiator design. These include: 1) changing the fin design, 2) increasing the core depth, 3) changing the tube type, 4) changing the flow arrangement, 5) changing the fin material, and 6) increasing the surface area to coolant ratio. The latter method was chosen for our proposed design.

To prove this hypothesis, we conducted tests on our current radiator assembly, which measures , to determine the heat transfer performance under typical operating conditions. We found our current radiator assembly to be capable of dissipating heat at a rate of . Next, using the ε-Ntu (effectiveness-Ntu), we calculated the heat transfer performance of our new radiator assembly, which has a radiator length 30% smaller than the length of the current design (). As expected, the heat transfer performance decreased. However, by increasing the metal-to-air surface area from 384 fins per row to 437 fins per row, we increased the heat transfer performance of our proposed design to the same level as the current design under the same operating conditions.

Figure 1: Componets within an automotive cooling system

In an automobile, fuel and air produce power within the engine through combustion. Only a portion of the total generated power actually supplies the automobile with power -- the rest is wasted in the form of exhaust and heat. If this excess heat is not removed, the engine temperature becomes too high which results in overheating and viscosity breakdown of the lubricating oil, metal weakening of the overheated engine parts, and stress between engine parts resulting in quicker wear, among other things.

A cooling system is used to remove this excess heat. Most automotive cooling systems consists of the following components: radiator, water pump, electric cooling fan, radiator pressure cap, and thermostat. Of these components, the radiator is the most prominent part of the system because it transfers heat.

As coolant travels through the engine's cylinder block, it accumulates heat. Once the coolant temperature increases above a certain threshold value, the vehicle's thermostat triggers a valve which forces the coolant to flow through the radiator.

As the coolant flows through the tubes of the radiator, heat is transferred through the fins and tube walls to the air by conduction and convection.

From the laws of thermodynamics, we know that heat transfer increases as we increase the surface area of the radiator assembly. That said, the demand for more powerful engines in smaller hood spaces has created a problem of insufficient rates of heat dissipation in automotive radiators. As a result, many radiators must be redesigned to be more compact while still having sufficient cooling power capabilities.

This application proposes a new design for a smaller radiator assembly. The new design is capable of dissipating the same heat as the original, given a set of operating conditions.

The dimensions of our original radiator design can be extracted from the SolidWorks® drawing file (CurrentRadiatorDrawing.SDPR). The drawing is a scaled down version of the full radiator assembly which measures .  For the purpose of our analysis, the dimensions obtained from CAD are scaled up to reflect the radiator's actual dimensions.

Note: This application uses a SolidWorks design diagram to extract the dimensions of the original radiator. This design file can be found in the zip file this document came in. If you have SolidWorks version 8.0 or above, save the design file, and then click the radio button below to tell Maple™ where to find the file. If you do not have SolidWorks installed on your computer, the values will be pre-populated.

Figure 2: CAD rendering of current Radiator Model

We expect the heat transfer performance of our proposed radiator assembly to be smaller than that of the original model because we are reducing the surface area to coolant ratio. The question that we answer in this section is "How much smaller is the heat transfer performance?" If the heat transfer performance is only marginally smaller, we can take other approaches to increase the performance, for example, increase the number of fins per row, change the fin material, or change the flow arrangement.  

The ε-Ntu (effectiveness-Ntu) method is used to predict the heat transfer performance of our new system.

The more common equations that are typically used in heat exchange design are listed below.

We must first calculate the overall heat transfer coefficient  of the smaller radiator before we can determine it's heat transfer performance, .

We can create a CAD rendering of our smaller radiator assembly. The design parameters of our new design are the same as the original, except it is smaller in length and has more fins per row.

The parameters of our new radiator model are listed in the table below. It is important to note that the number of fins per row is actually a measure of the distance between the fins (that is, how the fins are spread out within a row).

* Note: For consistency, we are creating a scaled CAD rendering model of the new optimized radiator assembly similar to that of the original CAD rendering

In this worksheet, we proposed the design of a new smaller radiator assembly that is capable of the same heat dissipation as the current design.

Using the effectivness-Ntu method, we calculated the heat transfer performance of the proposed design. As expected, decreasing the radiator length by 30% caused the heat transfer performance to decrease; the heat transfer performance decreased by ~14%. That said, by increasing the number of fins per row, from 384 to 437, we increased the heat transfer performance back to its original level of .