Chance Linarez
Heat Exchanger System
Testing
Introduction
The heat exchanger will be tested on how well it cools off hot water in a given amount of time.
The heat exchanger must keep 2000 gallons of water below 100 degrees Fahrenheit, maintain cooling in 40 to 100-degree Fahrenheit environments, be able to operate 12 hours a day. The main parameter of interest is to find the heat transfer rate of the heat exchanger. Calculations predict that it will have a heat transfer rate of 11.76 kW. Data will be collected with thermocouples and various other equipment. Tests on other aspects of the heat exchanger will be done as well like withstanding pressure, being deemed portable, and testing the stand construction to see if it can withstand continuous weight and use. Testing the heat exchanger will take an estimated 20.5 hours. The testing schedule can be seen in the Gantt chart at the end of this report.
Tests to be conducted include:
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Rate of Heat Transfer
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Pressure Test
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Trans-portability
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Stand Deflection
Method and Approach
Data will be collected using built in thermometers in the manifolds of the heat exchanger and a thermocouple will be used to measure air temperature leaving surface of heat exchanger, water temperature and ambient air temperature.
The heat exchanger will be tested by placing a temperature probe in the water intake manifold and a temperature probe in the water outtake manifold. This will show how much heat is being taken out of the water by the heat exchanger. The hot water source will be a tank of water that is heated to 120-150 degrees Fahrenheit and the cooled water will be returned to the tank so a rate can be determined of how long it took the heat exchanger to cool X amount gallons of water to a desired temperature. To heat the water to a much higher temperature, the tank will sit on a propane burner. The goal will be to have the water enter the heat exchanger at a temperature higher than 120 degrees Fahrenheit. Data described in the next section will be collected to determine the rating of the heat exchanger in kW or Btu/hr.
Results
Predictions of test 1 were the heat exchanger should have a heat transfer rate of 24kW in the given conditions. The actual heat transfer rate that was calculated from raw data was a maximum of 18.7kW. This is close to 20kW but failed to meet the required heat transfer rate. The heat exchanger failed to meet the required heat transfer rate because all calculations and design choices were assuming an ideal heat exchanger and this heat exchanger has construction flaws that impact its performance and reduce its rating.
Test Accuracy
The test was not accurate in that the water tank was only 100 gallons vs. 2000 gallons where it will be used. Also in the test, the energy input into the tank water was different than what the energy input into the water would be on the water jet. The requirement was to have a 20kW heat transfer rate but the heat transfer rate was 18.7kW. Accuracy is off by 1.3kW, precision of the test and calculations was +/- 0.25kW. The test results do not fall within the required target.
Test Validity
The above test for heat transfer rate was was valid for operating conditions and representative of the conditions the unit would operate in. The requirement was to be able to be able to maintain cooling in ambient air temperatures of 40-100 degrees Fahrenheit, although the test was conducted in 68 degree air temperature which is on the lower end of the operating conditions requirement.
Although the test proved that the heat exchanger will not meet heating requirements, results are relevant to calculations in estimating results. Being 1.3kW under the required rate at a air temperature of 68 degrees Fahrenheit matters. At this temperature the heat transfer rate should be much higher. If the unit was operating in a 98 degree Fahrenheit environment, the heat transfer rate would be much slower and it would more than likely fail to meet the requirement of keeping water under 100 degrees.
