Abstract
M.Ing.
Heat pump water heaters (HPWHs) have been identified as a viable replacement for electrical resistance heaters due to their high efficiency and reliability. Heat exchangers are a crucial part of HPWHs, and play a vital role in improving the system's coefficient of performance (COP). Experimentally analysing a heat exchanger is usually a slow and highly labour intensive practice since vast amounts of data have to be logged and mathematically manipulated to obtain results. A lot of time and money could be saved, if this process were to be automated. The first objective of this study was to develop a software program capable of calculating the heat transfer correlation constants of a tube-in-tube heat exchanger using the modified Wilson plot technique from data obtained through water-to-water experimentation at different flow rates and temperatures. The data was to be captured by using data acquisition equipment capable of measuring temperature from several Ptl 00-type temperature sensors, pressure transducers as well as Coriolis flow meters, all within a few seconds, thus giving virtually steady-state measurements. The second objective of this study was to develop a software package, capable of capturing and manipulating data from a HPWH system using the same tube-in-tube heat exchanger and using R-22 as refrigerant. The software package had to be capable of capturing all the required experimental data from the system and calculate the local and average heat transfer coefficients on-line and display it to the user. It also had to capture it in the form of a spreadsheet data file for further manipulation. The success of the software package would depend on the results achieved, as well as the time saved with its implementation. To verify the results, the output of the program was compared with the findings of various other researchers. It was found that the output of the program compared well with the results obtained by other researchers, both for the average heat transfer coefficient as well as the local heat transfer coefficients. The time taken for a full set of data was as little as 30 minutes, compared to many hours previously needed to achieve stable results. The software package has thus succeeded in fulfilling its objective to reduce the time taken to achieve accurate results during heat transfer experimentation.