**4.2 Modeling the generator**

476 Solar Radiation

of asphaltic concrete. Too much asphalt cement results in mixture stability problems, while too little asphalt cement results in a mixture that is not durable, (Robert *et al.,* 1996; Gordon

**Thermocouple**: Type E thermocouple has good stability, highest sensitivity among the common metals and thus has high emf output. Based on ASTM set recommended upper temperature limits for various wire sizes, selected diameter for the E type thermocouple is AWG24, 0.51mm diameter. Upper temperature limits for E type is 427oC. Type E has the highest thermopower of 6.317mV/oC in the temperature range (0 -100) oC among any of the

**(Constantan)** 

**Copper – Nickel (Chromel)** 

standardized types. The thermocouple properties are as shown in Table 2.

Electrical conductivity 58.14 x106 m-1 -1 - Useful temperature range -200 to 980 -

Total thermal conductivity 5.4 x10-4 W/ m2 oC Diameter 0.51mm ( 0.00051m)

Length 15mm (0.015m)

Thermopower at (31-80)oC 3.116 mV/oC

Figure of merit 1.0 x 10-6

Table 2. Thermocouple Material Properties

**4.1.5 Extension wire** 

emf produced.

**4.1.6 Heat source** 

radiation from the absorber surface.

**Property Nickel- Chromium** 

Composition 90% Ni, 10% Cr 60% Cu, 40% Ni Thermal conductivity, *k* 22.7-w/m2 oC 17.1-w/m2 oC Thermal diffusivity, 61.2 x104 m2/s 44.4x104 m2/s Density, 8922 kg/ m2 8666kg/ m2

Thermocouple alloy wire is recommended to be used always to connect a thermocouple sensor to the instrumentation to ensure accurate measurements. Due to the high cost of thermocouple wire, a copper wire was used with assurance of no significant change in the

The mixture is compressed into small pallets (0.5cm) with thermocouple junctions cascaded and embedded into it. A glass screen is to be provided to prevent escape of long wave

1997).

**4.1.4 Thermocouple material** 

The following assumptions are used in determining the open circuit voltage: The heat source is a flat plate collector, thus an assumption of maximum temperature of 80oC is considered for the heat source, a black body absorber. An ambient temperature of 31oC was considered for the isothermal block because ice baths are often inconvenient to maintain at 0 oC and not always practical.
