GATE AG 2017 • Q34 NAT • 1 Mark

Section 3: Farm Power

Sources of Power

Subtopic: Sources of power on the farm – human, animal, mechanical, electrical, wind, solar and biomass

Question Statement:

A cylindrical parabolic solar collector is designed to heat a fluid that enters the absorber at 140 °C at a flow rate of 5 kg min⁻¹. The specific heat capacity of the fluid is 1.5 kJ kg⁻¹ °C⁻¹ and its outlet temperature is 180 °C. If the incident beam radiation on the plane of aperture is 3000 kJ h⁻¹ m⁻² and useful projected area of the reflector is 2 m × 10 m, the efficiency of the collector in percentage will be __________.

Official Answer Key:

30 to 30

Step-by-Step Solution & Explanation

• Useful heat gain, Qu = ṁ Cp ΔT = (5 kg/min × 60) × 1.5 kJ/kg°C × (180–140)°C = 300 kg/h × 1.5 × 40 = 18,000 kJ/h. • Incident solar energy = Ib × A = 3000 kJ/h·m² × (2×10) m² = 3000 × 20 = 60,000 kJ/h. • Collector efficiency = Qu/Incident = 18,000/60,000 = 0.30 = 30%.

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