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snow_tiger [21]
3 years ago
8

A flat-plate solar collector is used to heat water by having water flow through tubes attached at the back of the thin solar abs

orber plate. The absorber plate has a surface area of 2 m2 with emissivity and absorptivity of 0.9. The surface temperature of the absorber is 35°C, and solar radiation is incident on the absorber at 500 W/m2 with a surrounding temperature of 0°C. Convection heat transfer coefficient at the absorber surface is 5 W/m2 ∙K, while the ambient temperature is 25°C. Net heat rate absorbed by the solar collector heats the water from an inlet temperature (Tin) to an outlet temperature (Tout). If the water flow rate is 5 g/s with a specific heat of 4.2 kJ/kg∙K, determine the temperature rise of the water.
Engineering
1 answer:
-BARSIC- [3]3 years ago
3 0

Answer:

dT = 21.35 C

Explanation:

Given:

- Area of the absorber plate A = 2 m^2

- e= a = 0.9

- T_s = 35 C

- q''_solar = 500 W/m^2

- T_surr = 0 C

- h = 5 W/m^2 K

- T_amb = 25 C

- flow(m) = 5 g/s

- c_p = 4.2 KJ/kgK

Find:

- The temperature rise of water.

Solution:

- Using Energy balance on the plate:

                                   E_in - E_out = q_in

- Find E_in and E_out:

                                   E_in = a*q''_solar

                            E_out = q"_convec + q"_rad

                   E_out = h*(T_s - T_amb) + e*σ*(T_s^4 - T_surr^4)

- Compute E_in and E_out:

                            E_in = 0.9*(500) = 450 W/m^2

         E_out = 5*(35 - 25) + 0.9*5.67*10^-8*(308^4 - 273^4)

                                E_out = 225.778 W/m^2

- Hence,

                                  E_in - E_out = q_in

                                 450 - 225.778 = q_in

                                  q_in = 224 W/m^2

- Assuming thickness of plate and pipe through which water flows as negligible, then:

                                flow(m)*c_p*(dT) = q_in*A

                                dT = q_in*A / flow(m)*c_p

- plug values in:

                                    dT = 224*2 / 5*4.2

                                    dT = 21.35 C

                     

                 

                             

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8 0
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We can find voltage across the load, again by using voltage-divider principle:  

V_o = A_voc*V_i*(R_o/R_l+R_o)

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Now we can determine delivered power:  

P_l = V_o^2/R_l

     = 125*10^-9 W

Delivered power to the load is significantly higher in case when we used amplifier, so a unity gain amplifier can be useful in situation when we want to deliver more power to the load. It is the same case with the voltage, no matter that we used amplifier with voltage open-circuit gain of unity.  

4 0
3 years ago
A tensile test was operated to test some important mechanical properties. The specimen has a gage length = 1.8 in and diameter =
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ts = 56050 / 0.5 = 112000 psi

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100 * (1 - A / A0)

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5 0
3 years ago
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