4. FINDINGS AND INTERPRETATIONS
4.1 Recommendations
After comparing the theoretical calculations to the testing results, there are a couple recommendations that should be made for future designs. These alternate design features have the potential to offer rather large increases in both performance and
efficiency in return for relatively small increases in cost and mild design alterations. Any of these suggested alterations, if attempted, should be tested to verify their effectiveness.
The first issue relates to one of the problems mentioned near the end of the description of the experiments. The coolant line routed to the heat exchanger from the vehicle coolant system must be larger in diameter than what was used in the experiments in order to increase the coolant flow rate through the shower system heat exchanger.
Additionally, this line must be spliced to a larger vehicle coolant line instead of the 5/8”
line that is tapped off of the main line and runs up to the heater core on the inside of the vehicle as done in the tests. The solution to this would be to locate a splice in between the main coolant line, which is two inches in diameter. Coolant would be diverted to the shower system heat exchanger, pass through, and then be routed back into the vehicle‟s cooling system. In order to perform these tasks, larger fittings with incorporated valves must be used, which is significantly more expensive than the original design. This solution adds to the cost of the system as well as increases the difficulty with the initial system installation. Although the testing of the shower system was performed by using a
rather simple set-up, the simplicity must be reduced in order to accomplish the desired results.
Another recommendation for future heat exchanger designs is to alter the size of the tube coiled inside the shell. The maximum flow rate through the 3/8” O.D. tube, despite having been misshapen due to the coiling procedure, greatly surpassed the design criteria for this particular project. It would be possible to use a smaller diameter tube, such as one measuring 1/4" O.D. This would still allow a sufficient amount of fresh water to flow through the system while allowing the tube to keep its circular shape.
Using a smaller diameter tube will make it possible to increase the length of tube used inside the heat exchanger, thus increasing the length of time the fresh water is exposed to the heating process. Although the surface area per unit length of tube will be reduced when using a smaller diameter tube, the actual amount of heat transfer may increase due to the added length of tubing that is made possible to fit inside the shell of the heat exchanger. However, this solution would require more testing, as any change will affect the heat transfer rates inside the system.
One other physical design modification that can be applied to a future heat exchanger was actually utilized for the second attempt of this project‟s trial experiments (the first attempt at construction of the heat exchanger failed due to inadequate materials).
Instead of simply soldering a reducer at the end of the shell, a coupler was soldered in its place. The reducer was soldered at the other end of this coupling. The addition of the coupling allowed for a wall thickness at these soldering points double that for which the system was originally designed. This change provided a much more sufficient amount of
material to which the inlet and outlet fittings of the fresh water tube could be soldered.
This greatly improved ease of construction of the shower system heat exchanger.
Another recommendation that would improve the performance of the shower system would be to wrap the inner tube around the exhaust pipe of the vehicle before it enters the heat exchanger. Although this would require a significantly additional amount of copper tubing, it could prove to be an overall benefit to the system. More analysis would be required in order to validate this modification.
The final recommendation also stems from a problem mentioned at the end of the description of the experiments. As previously mentioned, the shower system heat
exchanger is tapped into the coolant system of the vehicle at the point immediately before the coolant flows into the heater core on the interior of the vehicle. The coolant system of the vehicle is designed so that by this point, coolant has already flowed through the main radiator in front of the engine. The vast majority of heat energy is dissipated through this primary radiator, greatly reducing the temperature of the coolant. After heat exchanger temperatures were recorded from the coolant inlet side, it was found that the assumed temperatures used in the theoretical calculations were much greater than the actual temperatures measured. This is a problem because the performance of the entire shower system is based, among other factors, on the temperature difference between the two working fluids.
The solution to this issue would be to not only use larger fittings as described above, but to locate those fittings directly after the thermostat housing mounted at the top of the engine. A thermostat in a vehicle is a simply a mechanical valve that is operated
via a temperature-dependent spring. Its location at the top of the engine is vital to the performance and efficiency of the engine. It is here where the coolant, which has been flowing through the engine‟s water passages and providing a heat sink for the engine, exits and flows back into the radiator to be cooled. Thus, it is at this point where the temperature of the coolant will be at its highest level. Locating the splice point for the shower system‟s heat exchanger directly aft of this point will allow for the coolant at a much higher temperature to flow through the heat exchanger. This temperature may be as much as thirty degrees Fahrenheit hotter than the temperatures measured during the original experiments.
It is obvious that this solution will increase the performance of the shower system.
The temperature difference between the two working fluids will be much larger, thus greatly increasing the energy exchange inside the heat exchanger. While this outcome would be the desired result of this recommended design change, another less-obvious result stems from this alteration. After the coolant is routed through the shower system heat exchanger, it is then looped back into the vehicle coolant system and continues on to the primary radiator at the front of the vehicle. If the insulation around the shower system heat exchanger is removed, allowing heat to be radiated out, the coolant will have already undergone a substantial decrease in temperature. In this case, the heat exchanger is operating as a simple fluid-to-air radiator. Even more energy will be pulled from the vehicle coolant system as it passes through the main radiator. The extra energy pulled out of the system will help keep the vehicle‟s engine temperature lower than it would be if there was no shower system.
This is a very useful feature of the shower system that was originally overlooked, as it was not one of the desired outcomes. A common problem plaguing drivers and their vehicles when four-wheeling is an overheating engine. This is caused by the fact that in most cases, driving on an off-road trail is done at extremely low speeds. The vehicles are driven over rather large boulders and fallen trees, and this must be done very slowly so as not to damage the vehicle as well as create a semi-comfortable ride for the driver and any passengers. These slow speeds cause airflow through the fins of the primary radiator due to the velocity of the vehicle to become practically negligible.
In most cases, slow vehicle speeds translate to low vehicle engine RPMs. Most vehicles, especially those that are typically used on off-road excursions, originally come equipped with mechanically operated fans from the manufacturer, which are driven by the accessory drive system of the engine. Some people have remedied engine
overheating issues by replacing the stock manufacturer‟s mechanically operated fan with an electrically driven fan. While effective, this is sometimes a rather expensive solution to an overheating engine in an off-road vehicle. Once the new design features are incorporated into this shower system, increasing its heat transfer efficiency, it may prove to be a viable alternative to an electric fan. The added benefit over an electrically
operated fan will be the ability to use the shower as designed in order to obtain heated water.
The parametric study has proven to be a valuable resource for the design of this vehicle shower system. Although the desired results based on the parametric study were not achieved, it highlights the areas where the actual test system is inferior to the ideal
case. Changes can now be implemented on the original test set-up, which can then be re-evaluated. It is expected that the modified system will show improvements in
efficiencies and effectiveness over the original design.
APPENDIX A Parametric Study Figures
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow = 0.1321 GPM; T,in(Coolant) = 190 Deg. F; H2O Flow Rate = 1.5 GPM
y = 9.0196x - 278.29
115 120 125 130 135 140 145
Working Fluid Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow = 4.623 GPM; T,in(coolant) = 200 Deg. F; H2O Flow Rate = 1.5 GPM
115 120 125 130 135 140 145
Temperature Difference, Deg. F
Heat Transferred, (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids
125 130 135 140 145 150 155
Working Fluid Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 0.1231; T,in (Coolant) = 190 Deg. F; H2O Flow Rate = 2.0 GPM
y = 9.0719x - 282.03
115 120 125 130 135 140 145
Temperature Difference (Deg. F)
Heat Transferred (W)
Pipe Length = 6.096 m Pipe Length = 6.858 m Pipe Length = 7.620 m Pipe Length = 8.382 m Pipe Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 4.623; T,in (Coolant) = 200 Deg. F; H2O Flow Rate = 2.0 GPM
y = 112.88x - 1860.2
115 120 125 130 135 140 145
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.868 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 7.925; T,in (Coolant) = 210 Deg. F; H2O Flow Rate = 2.0 GPM
y = 147.33x - 364.42
125 130 135 140 145 150 155
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 0.1321; T,in (Coolant) = 190 Deg. F; H2O Flow Rate = 2.5 GPM
y = 3.0118x - 94.396
115 120 125 130 135 140 145
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 4.623; T,in (Coolant) = 200 Deg. F; H2O Flow Rate = 2.5 GPM
y = 118.93x - 2246.6
115 120 125 130 135 140 145
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 7.925; T,in (Coolant) = 210 Deg. F; H2O Flow Rate = 2.5 GPM
y = 56.599x - 633.31
125 130 135 140 145 150 155
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 0.1321; T,in (Coolant) = 190 Deg. F; H2O Flow Rate = 3.0 GPM
y = 3.0185x - 94.873
115 120 125 130 135 140 145
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 4.623; T,in (Coolant) = 200 Deg. F; H2O Flow Rate = 3.0 GPM
y = 42.124x - 931.22
115 120 125 130 135 140 145
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 7.925; T,in (Coolant) = 210 Deg. F; H2O Flow Rate = 3.0 GPM
y = 58.551x - 767.57
125 130 135 140 145 150 155
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Convective Heat Transfer Coefficient vs. Fresh Water Inlet Temperature
Fresh Water Inlet Temperature, Deg. F
Convective Heat Transfer Coefficient (W/m^2-K)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Convective Heat Transfer Coefficient vs. Fresh Water Inlet Temperature H2O Flow Rate = 2.0 GPM
Fresh Water Inlet Temperature (Deg. F)
Convective Heat Transfer Coefficient (W/K)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Convective Heat Transfer Coefficient vs. Fresh Water Inlet Temperature
Fresh Water Inlet Temperature (Deg. F)
Convective Heat Transfer Coefficient (W/K)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Convective Heat Transfer Coefficient vs. Fresh Water Inlet Temperature H2O Flow Rate = 3.0 GPM
Fresh Water Inlet Temperature (Deg. F)
Convective Heat Transfer Coefficient (W/K)
Tube Length = 6.096 m Tube Length = 6.858 Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Coolant Convective H.T. Coefficient vs. Coolant Outlet Temperature
135 145 155 165 175 185 195 205 215
T,out (Deg. F)
Convective Heat Transfer Coefficient (W/m^2 - K)
Flow = 0.1321 GPM, T,in = 190 Deg. F Flow = 4.623 GPM, T,in = 200 Deg. F Flow = 7.925 GPM, T,in = 210 Deg. F
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow = 0.1321 GPM; T,in(Coolant) = 190 Deg. F; H2O Flow Rate = 1.5 GPM
y = 9.0196x - 278.29
115 120 125 130 135 140 145
Working Fluid Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids
115 120 125 130 135 140 145
Temperature Difference, Deg. F
Heat Transferred, (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow = 7.925 GPM; T,in (Coolant) = 210 Deg. F; H2O Flow = 1.5 GPM
125 130 135 140 145 150 155
Working Fluid Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 0.1231; T,in (Coolant) = 190 Deg. F; H2O Flow Rate = 2.0 GPM
y = 9.0719x - 282.03
115 120 125 130 135 140 145
Temperature Difference (Deg. F)
Heat Transferred (W)
Pipe Length = 6.096 m Pipe Length = 6.858 m Pipe Length = 7.620 m Pipe Length = 8.382 m Pipe Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 4.623; T,in (Coolant) = 200 Deg. F; H2O Flow Rate = 2.0 GPM
y = 112.88x - 1860.2
115 120 125 130 135 140 145
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.868 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 7.925; T,in (Coolant) = 210 Deg. F; H2O Flow Rate = 2.0 GPM
y = 147.33x - 364.42
125 130 135 140 145 150 155
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 0.1321; T,in (Coolant) = 190 Deg. F; H2O Flow Rate = 2.5 GPM
y = 3.0118x - 94.396
115 120 125 130 135 140 145
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 4.623; T,in (Coolant) = 200 Deg. F; H2O Flow Rate = 2.5 GPM
y = 118.93x - 2246.6
115 120 125 130 135 140 145
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 7.925; T,in (Coolant) = 210 Deg. F; H2O Flow Rate = 2.5 GPM
y = 56.599x - 633.31
125 130 135 140 145 150 155
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 0.1321; T,in (Coolant) = 190 Deg. F; H2O Flow Rate = 3.0 GPM
y = 3.0185x - 94.873
115 120 125 130 135 140 145
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 4.623; T,in (Coolant) = 200 Deg. F; H2O Flow Rate = 3.0 GPM
y = 42.124x - 931.22
115 120 125 130 135 140 145
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Overall Heat Transferred vs. Temperature Difference between Working Fluids Coolant Flow Rate = 7.925; T,in (Coolant) = 210 Deg. F; H2O Flow Rate = 3.0 GPM
y = 58.551x - 767.57
125 130 135 140 145 150 155
Temperature Difference (Deg. F)
Heat Transferred (W)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Convective Heat Transfer Coefficient vs. Fresh Water Inlet Temperature H2O Flow Rate = 1.5 GPM
Fresh Water Inlet Temperature, Deg. F
Convective Heat Transfer Coefficient (W/m^2-K)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Convective Heat Transfer Coefficient vs. Fresh Water Inlet Temperature
Fresh Water Inlet Temperature (Deg. F)
Convective Heat Transfer Coefficient (W/K)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Convective Heat Transfer Coefficient vs. Fresh Water Inlet Temperature H2O Flow Rate = 2.5 GPM
Fresh Water Inlet Temperature (Deg. F)
Convective Heat Transfer Coefficient (W/K)
Tube Length = 6.096 m Tube Length = 6.858 m Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Convective Heat Transfer Coefficient vs. Fresh Water Inlet Temperature
Fresh Water Inlet Temperature (Deg. F)
Convective Heat Transfer Coefficient (W/K)
Tube Length = 6.096 m Tube Length = 6.858 Tube Length = 7.620 m Tube Length = 8.382 m Tube Length = 9.144 m
Coolant Convective H.T. Coefficient vs. Coolant Outlet Temperature
y = -0.9171x2 + 367.7x - 34695
135 145 155 165 175 185 195 205 215
T,out (Deg. F)
Convective Heat Transfer Coefficient (W/m^2 - K)
Flow = 0.1321 GPM, T,in = 190 Deg. F Flow = 4.623 GPM, T,in = 200 Deg. F Flow = 7.925 GPM, T,in = 210 Deg. F
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