Page 61 - MASHRAE 35th Anniversary

relative humidity of ambient air and drying air were measured using hygrometer. The air speed at the outlet of the drying cabinet was measured using anemometer. In order to ensure that all experiments are performed correctly, we use the ASHRAE Standard 108 as the guiding principle for measurement and experiment setup guidelines.
Figure 3: Diagram of measuring point
Performance of TSDS
The overall efficiency of TSDS is defined as the heat energy gained by the drying air to the solar energy input on the solar collector, as given by Eq. (1).
􏰉 The door must be facing north, so that direct sunlight cannot fall on the sensor when the door is opened.
􏰉 Tilt angle of the collector during testing shall be between 30° to 60° unless specified by manufacturer of the collector.
RESULTS AND DISCUSSION
30.00 27.60 25.00
20.00 16.28 15.00 10.19
10.00 5.00 0.00
Water
25.20
14.42
Efficiency of Collector
24.23
12.26
6.75
1.88 1.77
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Quantity of collector
Ethanol R134a R600a
23.81
7.84 2.40 2.05
11.32 6.17
Figure 4 Efficiency of Collector
m􏰅 c 􏰀T 􏰃T 􏰁 􏰂 􏰄 a p,a a,o a,i
s IAc
􏰀􏰇􏰁
From Fig. 4, the most efficient fluid for the two collectors is R600a, and the value of efficiency is 27.6%. The reason for the high efficiency of R600a is lower density (517.37kg / m3 at 50 ° C) and specific heat (2.615kJ / kg. K at 50 ° C). Density, specific heat and the working pressure of fluid can affect to the value of mass flow rate. The efficiency of collector is proportional to mass flow rate of fluids. All the fluids shown that the highest efficiency of solar collector was occurring in two collectors because of lowest surface area of two collectors compare with other set of collectors. Meanwhile, the results shown R600a has better efficiency with two collectors at 27.6%, water at 16.28%, ethanol at 10.19% and R134a at 2.4% .
Where Ta,i and Ta,o are the inlet and outlet temperature of drying air respectively. I is the instantaneous solar radiation and Ac is the aperture area of solar collector, where is an area of cylinder, Ac = [2􏰈r2 + h(2􏰈r)] x (quantity of collector). In this experiment, the performance of parallel U- pipe flows as well as the performance of water, ethanol, R134a and R600a would be evaluated based on the overall thermal efficiency of TSDS.
ASHRAE Standards
In order to ensure that all experiments are performed correctly, we use the ASHRAE Standard 108 as the guiding principle for measurement and experiment setup guidelines. The guidelines as below:
1) Measurement guidelines:
􏰉 Ambient temperature must in range -20 °C to 40
°C.
􏰉 Time constant of pyranometer must less than 5
seconds.
􏰉 Sensor ambient temperature must above 1.25
meter from the ground.
􏰉 Measurements shall be taken as closely as
possible to the collector inlet and outlet.
􏰉 Wind velocity across the collector shall be less
than 4.5 m/s.
2) Experiment setup guidelines:
Figure 5
Water
Ethanol
R134a
R600a
110
100
90
80
70 60 50
93.8
81.7 68.2
54.7
85.7 74.7 64.7
95.4 90.2
Temperature Outlet Collector
106.2 100.4
110.2
80.82 71.3
77.3
2468
Quantity of collector
3
Temperature at outlet of collector
Tout collector , °C 􏰊C, %