Energy from Waste: Reuse of Compost Heat as a Source of Renewable Energy

Table 5

Inlet temperatures	𝑇𝑐,𝑖	0	°C
	𝑇ℎ,𝑖	65	°C
Cold fluid flow rate (water pump)	Flow rate	3	L min^-1
		0.00005	m^3 s^-1
	Density water	999	kg m^3
	Flow rate	0.04995	kg s^-1
	𝑚 dot 𝑐	0.04995	kg s^-1
Hot fluid flow rate (blower at average capacity)	𝑚 dot ℎ	2000	m^3 hr^-1
	Density air	1.2	kg m^3
		2400	kg hr^-1
	𝑚 dot ℎ	0.66667	kg s^-1
Specific heat capacities	𝑐𝑝,𝑐	4.19	kJ kg^-1K^-1
	𝑐𝑝,ℎ	1.004	kJ kg^-1K^-1
Pipe properties (stainless steel)	𝑑𝑖	0.02465	m
	𝑑𝑜	0.02667	m
	Thickness	0.00202	m
	𝑘𝑤	16.3	W m^-1K^-1
Heat transfer coefficients      ℎ=Δ𝑄𝐴×Δ𝑇×Δ𝑡	ℎ𝑐	1200	W m^-2K^-1
	ℎℎ	50	W m^-2K^-1
Heat capacity rates         𝐶=𝑚^•𝑐𝑝	𝐶𝑐	209.2905	W K^-1
	𝐶ℎ	669.3333	W K^-1
Heat capacity ratio         𝐶^∗=𝐶min𝐶max	𝐶min	209.2905	W K^-1
	𝐶^∗	0.31269
Fouling capacity (standard)	𝑅𝑤,𝑓	0.002	m^2K W^-1
Overall heat transfer coefficient 1𝑈=1ℎ𝑜+1ℎ𝑜,𝑓+𝑑𝑜ln(𝑑𝑜/𝑑𝑖)2𝑘𝑤+𝑑𝑜ℎ𝑖,𝑓𝑑𝑖+𝑑𝑜ℎ𝑖𝑑𝑖	1/ℎℎ	0.02
	𝑑𝑜/ℎ𝑐𝑑𝑖	0.0009015
	Wall	0.0000644
	Fouling inside	0.0021637
	Fouling outside	0.002
	𝑈	39.7936	W m^2K^-1
Pipe total surface area	𝐴	7.96	M^2
NTU              NTU=UA𝐶min	NTU	1.5135
𝐸             𝜀=1−exp[−NTU(1−𝐶^∗)]1−𝐶^∗exp[−NTU(1−𝐶^∗)]	eqn top line	0.6466
	eqn bottom line	0.8895
	𝐸	0.7270
Outlet temperatures      𝐶𝜀=^ℎ(𝑇ℎ,𝑖−𝑇ℎ,𝑜)𝐶min(𝑇ℎ,𝑖−𝑇𝑐,𝑖)=𝐶𝑐(𝑇𝑐,𝑜−𝑇𝑐,𝑖)𝐶min(𝑇ℎ,𝑖−𝑇𝑐,𝑖)	𝑇ℎ,𝑖−𝑇ℎ,𝑜	14.7750
	𝑇ℎ,𝑜	50.2250	°C
	𝑇𝑐,𝑜−𝑇𝑐,𝑖	47.2520
	𝑇𝑐,𝑜	47.2520	°C
Energy balance check	𝑞	9889.3897	kW
	𝑇ℎ,𝑜	50.2250	ºC
Pipe length needed	Surface area	0.0838	m^2 m^-1
	Pipe length	95.0036	m