This is not necessarily true. Each manufacturer's hole diameter and spacing are different. Please point out that of a regular manufacturer for your reference: The normal hole spacing of the inner tank of the 47 tube water tank is 70mm. the inner diameter of the tank is 360mm and the capacity of 18 tubes is 0.18m*0.18m*3.14*(18*0.07m+0.2m)=0.148 cubic meters , or 148 liters. 20 bottles make 162 liters. The normal inner hole spacing of the 58 tube water tank is 85mm, and there are also 80mm holes. Small plants generally have 75mm, and the inner diameter of the tank is generally 360mm. Calculated based on 85mm hole spacing. The 16-tube water tank is 0.18m*0.18m*3.14*(16*0.085m+0.2m)=0.158 cubic meters, which is 158 liters, which is larger than the capacity of 47 tubes with 18 tubes and slightly smaller. than the capacity of 47 tubes with 20 tubes
V=200 liters=0.2 cubic meters, T1=20 degrees Celsius, T2=45 degrees Celsius, C water=4.2*10^3 Joules/(kilogram degrees Celsius )
P=2000 watts, t=3.5 hours=12600 seconds
Analysis:
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(1) The mass of water in the water tank is M=ρwater*V=1*10^3 * 0.2=200 kilograms
Once the tap water enters the water tank, the absorbed heat is Q= C water*M* (T2-T1)
That is to say Q=4.2*10^3 * 200* (45-20)=2.1 *10^7 Joules
(2) If the heat absorbed by the water is supplied by the water heater, the electrical energy consumed is
E＝P* t＝ 2000*12600＝2.52*10^7 Joules
Then this electric water heater The efficiency is
η=Q/E=(2.1*10^7)/ (2.52*10^7)*100%=83.3%
Note: The second question in the question The goal should be efficiency, not power.