6.2.1 Water bath
The water bath (Polystat R6L) designed by Cole Parmer was used to pump the water at the required temperature to the thermal store. The bath is proportional-intergral - derivative (PID) controlled, it uses a programmable controller. It allows for a set point temperature to be set as it heats or cools. An image of the water bath is shown in Figure 6:1.
Figure 6:1: Hot water bath (Cole Palmer Polystat R6L).
The device possesses an ability to heat or cool the fluid,however the system does not provide cooling over the full range of temperatures. The cooling system commences for set points less than 35°C ColePalmer (2016). Thus a drain valve had to be provided to release hot fluid as cold water is poured into the bath to aid cooling. This is because experiments in this research were all above the set point temperature that allows for cooling. Table 6.1 shows the specification of the Polystat R6L hot water bath or circulating bath. More information on the bath is available in Appendix D.
Table 6:1: Specification of circulating Bath(Polystat R6L). ColePalmer (2016) Technical Data
Bath volume 6litres
Temperature range -20 to 200 °C
Heating power 1 kW
Cooling power @20 °C 0.29 kW Pump delivery 15 l/min
Electrical requirement 230VAC, 50Hz, 10 Amps. Overall dimension 0.25 x 0.55 x 0.4m
Refrigerant R134A
6.2.2 Data acquisition (DAQ)
Temperature data were logged using TC-08 Thermocouple data logger. This device has a USB interface. It is an eight (8) channel temperature logger; as shown in Figure 6.2.
Key attributes of the TC08
Measure from 1 to 8 thermocouples
Measures from -270 to +1820 °C
Automatic cold junction compensation
High resolution- 20 bits
Temperature accuracy- Sum of ±0.2% of reading and ±0.5 °C
Fast sampling rate — up to 10 measurements per second
USB interface
Figure 6:2: Pico temperature logger TC-08. Picotech (2014).
Appendix B has a description of the specification of the USB TC-08 used for the plate heat exchanger experiment to record and save temeprature records.
6.2.3 Thermocouples
Thermocouples were used for measuring the temperatures. K-type thermocouples were used for the experiment to take temperature at different locations. They are connected to the temperature logger; TC-08. Two types of type K thermocouples were used, and they are shown in Figure 6:3.
(a)Type K Stainless Steel Shim Labfacility leaf thermocouple (b)Type K Probe Thermocouple; 1mm diameter.
Appendix C shows the locations where the Type K Stainless Steel Shim Labfacility leaf and Type K Probe thermocouple were placed on the PP (polypropylene) sheet to monitor the temperature of the PCM , HTF(heat transfer fluid) and room temperature during the experiment.
6.2.4 Polypropylene/Acrylic
The polypropylene (PP) sheet used was procured from Twinplast Company. The sheet has a layout of channels that could be used as a heat exchanger for this chosen application; thermal energy storage. Figure 6:4 shows the channels on the PP sheet. Efforts were made to weld the PP sheet, but it was not possible to find anyone capable of welding it. There were concerns about the thickness of the sheet being too thin to weld; however, it can be bonded using adhesives. Several adhesives were tested, to confirm which was well suited to bond the sheet to the PVC pipe required for inlet and outlet flow of water on the rig. The following adhesives were used in the final design.
1. DP 8005, procured from 3M Products
2. Ultimate instant grab: this is used on the inner part of the wood in contact with the hot surface.
3. All in one sealant, adhesive and filler MS polymer. Used on the exterior part of the wood.
4. Araldite.
Further experiment involved the replacement of the wooden frame with PVC strips of 30cm width. DP 8005 was used to bond the PVC strips on to the polypropylene surface. It was discovered that this bonding was better than using wood strips.
Figure 6:4: Polypropylene sheet with channels.
6.2.5 Electric wax heater:
The wax heater was used to melt the solid PCM on to the thermal store. It has a temperature range up to 200°C. It has a control switch which is used to set the desired temperature to heat the material or sample. This device is only used for heating; it is not designed for cooling the material. Figure 6:5 shows the electric wax heater unit and an image of paraffin wax melting in it.
Figure 6:5: Electric wax heater.
6.2.6 Coriolis mass flow meter
The mass flow rate of the fluid flow for the experiment was monitored by a Coriolis flow meter manufactured by Emerson (Micro Motion Inc.). The flow meter can measure fluid flow up to a temperature of 200°C. The Coriolis mass flow meter has a flow range of 2g/s to 100g/s. It comprises of a flow transmitter and mass flow sensor; shown in Figure 6.6.
(a)Flow transmitter (b) Mass flow sensor Figure 6:6: Coriolis mass flow meter. Emerson (2017)
The flow meter operates based on the “Coriolis principle” where the change in frequency or amplitude as a result of the fluid flowing through the vibrating tubes is produces a linear flow signal. When there is no fluid flow, the tubes within the unit oscillate at the same frequency. However as flow passes through the unit, there is a phase difference in the frequency. The signal from the sensors mounted on the tube at the inlet, middle and outlet of the unit with the aid of the transmitter gives the mass flow of the fluid travelling through it Emerson (2017). This device can also determine the density of the fluid passing through it. Coriolis meter accuracies for mass flow is ± 0.10% of the flow rate. Emerson (2018)