1st Example: Combustion heater

A heater warms up water using butane, with a heating value of pc=MJ/kg, and it has an efficiency of η=%, providing a flow rate of q=L/min while causing an increase in its temperature of Δt=℃. Butane is obtained from gas cylinders holding mb=kg, which cost cb=€. Water's specific heat is of cp=J/(g K). Under these conditions, determine:

• b)qcomb, fuel consumption in grams per second.
• c)c, cost in €, and mcomb mass of the fuel consumed during a time frame of t=min.
Feeling curious, Mr.Holmes?

Solutions

• a)$P=\frac{E}{t}=\frac{Cp*m*Δt}{t}=Cp*q*ρ*Δt$
P=W

Note:ρ represents water's density, which is ρ=1kg/L
• b) $q_{comb}=\frac{m_{b}}{t_{b}}=\frac{m_{b}*P_{b}}{E_{b}}=\frac{m_{b}*P_{b}}{p_{c}*m_{b}}=\frac{P}{p_{c}*η}=\frac{Cp*q*ρ*Δt}{p_{c}*η}$
$q_{comb}=$g/s

Note:ρ represents water's density, which is ρ=1kg/L
• c) $c=\frac{m_{comb}*c_{b}}{m_{b}}→m_{comb}=?→m_{comb}=q_{comb}*t=\frac{Cp*q*ρ*Δt*t}{p_{c}*η}$
$m_{comb}=$kg

$c=\frac{m_{comb}*c_{b}}{m_{b}}$
$c=$

Note:ρ represents water's density, which is ρ=1kg/L