Xiao Ming's house installed a solar water heater

1.

80L=80dm?=0.08 m?

m=ρv=1000kg/m?×0.08m?=80kg

2.

Q suction=cm△t=4200j/ (kg·℃)×80kg×50℃=1.68×10^7 j

m=Q/q=(1.68 ×10 ^7 j)/(4.2×10^7)= 0.4 kg

Answer: The mass in the water heater is 80 kg and the heat that must be absorbed to increase the water temperature of 50 degrees is 1.68×10^7 j

To generate this heat, 0.4 kg of gas is completely burned.

The Solar water heater is a device that directly uses solar energy to heat water. The following table contains the relevant information about Xiao Ming's solar water heater exposed to the sun on a certain day (1) According to ρ= Obtainable, the mass of water:

m=ρV=1.0 ×103kg/m3×80×10-3m3=80kg;

(2) Heat absorbed by water:< /p>

Absorption Q=cm△t=4.2×103J/(kg?℃ ）

Quality of gaz required:

m′=

m

V

< /tr>

Q put

q×60%

=

1.68×107J

4.2×107J/kg×60%< /td>

≈0.67 kg.

Answer: (1) The mass of water in the water heater is 80 kg

(2) When the water temperature increases by 50°C, it must absorb 1.68×107J; of heat;

(3) The generated heat is assumed to be released by the combustion of gas in a gas stove with 60% efficiency, and 0.67 kg of gas should be completely burned.

Known: The mass of water m=100kg, the increasing temperature of water Δt=50℃, the specific heat of water c=4.2×103J/(kg?℃) and the solar radiation power P=1.68 ×106J/(m2?h), time t=10h, the calorific value of natural gas is q=8.4×107J/m3 and the area of ​​the heat absorption plate is S=2.5m2 .

Find: (1) The amount of heat absorbed by water in 10 hours Q = ? ; (2) The volume of completely burned natural gas V =? ; (3) The total amount of solar energy absorbed by the heat absorbing plate Q total = ? ;The energy conversion efficiency of the solar water heater η=?

Solution: (1) Heat absorbed by water (useful energy):

Absorption Q=cm△t=4.2×103J/(kg?℃)×100kg ×50℃=2.1×107J;

(2) From the question, Q release = vq = Q suction = 2.1×107J,

The volume of natural gas required:

v =

Q put

q

=

2.1×107J

8.4×107J/kg

=0.25m3;

< p> (3) Solar energy absorbed by the solar water heater for 10 hours (energy total):

Q total=1.68×106J/(m2?h)×2.5m2×10h=4.2×107J,

η=

Q sucks

Q total

×100%=

2.1×107J

4.2×107J

×100%= 50%

Answer: (1) The heat absorbed by water in 10 hours is 2.1 × 107J

; (2) If the heat absorbed by water is provided by natural gas, 0.25 m3 must be completely burned Gas n;natural;

(3) The heat absorption plate absorbs a total of 4.2 × 107 J of solar energy; the energy conversion efficiency of solar water heater is 50%;