Comparison of efficiency between liquefied petroleum gas (LPG) and electric hot air dryer: case study of dried pork slice

Figures & data

Figure 1. Schematic diagram of LPG hot air dryer (a) and actual image of LPG hot air dryer (b).

Table 1. The mathematical models of sliced pork.

Model name	Model equation
Lewis	MR = exp (−kt)
Logarithmic	MR = a exp(−kt)+b
Henderson and Pabis	MR = a exp(−kt)
Avhad and Marchetti	MR = a exp(-kt^n)
Diffusion	MR = a exp(−kt)+(1-a)exp(−kbt)

Note: t is the drying time in min; a, b and n are the drying constants; k is the drying rate constant (min⁻¹).

Figure 2. The moisture ratio of sliced pork dried using LPG hot air dryer at different temperatures (50°C (a), 55°C (b), and 60°C (c)) and different air velocities (1, 1.5, 2 m/s). The moisture ratio of sliced pork dried using electric hot air dryer at different temperatures (50°C (d), 55°C (e), and 60°C (f)) and different air velocities (1, 1.5, 2 m/s).

Table 2. Statistical results from different models for LPG hot air dryer.

Model name	Air velocity	Temperature	Parameters			SSE	R^2	RMSE
Lewis	1	50	k = 0.000			0.015	0.995	0.017
		55	k = 0.006			0.032	0.979	0.033
		60	k = 0.010			0.027	0.980	0.039
	1.5	50	k = 0.007			0.095	0.967	0.053
		55	k = 0.006			0.018	0.990	0.024
		60	k = 0.007			0.042	0.980	0.039
	2	50	k = 0.006			0.033	0.973	0.034
		55	k = 0.006			0.026	0.981	0.030
		60	k = 0.007			0.027	0.980	0.031
Logarithmic	1	50	a = 0.923	b = 0.085	k = 0.005	0.002	0.999	0.008
		55	a = 0.963	b = 0.078	k = 0.007	0.004	0.998	0.998
		60	a = 1.092	b =−0.074	k = 0.007	0.003	0.998	0.011
	1.5	50	a = 0.958	b = 0.065	k = 0.005	0.002	0.999	0.008
		55	a = 0.942	b = 0.058	k = 0.007	0.001	0.999	0.007
		60	a = 1.097	b =−0.079	k = 0.008	0.002	0.999	0.010
	2	50	a = 0.828	b = 0.186	k = 0.009	0.003	0.998	0.010
		55	a = 1.051	b =−0.054	k = 0.006	0.001	0.999	0.008
		60	a = 1.024	b =−0.027	k = 0.011	0.001	0.999	0.005
Henderson and Pabis	1	50	k = 0.004	a = 1.009		0.015	0.995	0.017
		55	k = 0.006	a = 1.001		0.032	0.979	0.033
		60	k = 0.012	a = 1.128		0.001	0.999	0.006
	1.5	50	k = 0.008	a = 1.167		0.017	0.994	0.022
		55	k = 0.006	a = 1.042		0.012	0.993	0.021
		60	k = 0.008	a = 1.117		0.007	0.997	0.016
	2	50	k = 0.005	a = 0.939		0.021	0.982	0.028
		55	k = 0.006	a = 0.956		0.020	0.985	0.027
		60	k = 0.006	a = 0.931		0.014	0.990	0.022
Avhad and Marchetti	1	50	a = 3.758e^−6	k=−13.31	n=−0.025	0.825	0.733	0.129
		55	a = 1.201	k = 0.032	n = 0.703	0.010	0.993	0.019
		60	a = 1.104	k = 1.042	n=−0.009	0.001	0.999	0.005
	1.5	50	a = 1.126	k = 0.005	n = 1.075	0.015	0.995	0.021
		55	a = 1.121	k = 0.013	n = 0.855	0.007	0.996	0.016
		60	a = 1.052	k = 0.004	n = 1.138	0.003	0.999	0.011
	2	50	a = 1.159	k = 0.038	n = 1.159	0.000	0.998	0.004
		55	a = 3.815e^−6	k =−13.04	n =−0.023	0.317	0.768	0.108
		60	a = 1.102	k = 0.029	n = 0.730	0.000	0.999	0.004
Diffusion	1	50	a = 0.981	k = 0.004	n = 0.111	0.010	0.997	0.014
		55	a = 0.852	b = 1.119	k = 0.006	0.032	0.979	0.034
		60	a = 1.001	b = 0.010	k = 0.608	0.027	0.980	0.041
	1.5	50	a=−0.225	b = 0.103	k = 0.079	0.009	0.997	0.016
		55	a = 0.822	b = 0.916	k = 0.006	0.018	0.990	0.025
		60	a = 1.908	b = 0.845	k = 0.006	0.036	0.982	0.038
	2	50	a = 0.546	b = 0.220	k = 0.011	0.003	0.998	0.010
		55	a = 1.008	b = 0.756	k = 0.007	0.004	0.998	0.012
		60	a = 0.001	b = 0.291	k = 0.040	0.001	0.999	0.007

Table 3. Statistical results from different models for electrical hot air dryer.

Model name	Air velocity	Temperature	Parameters			SSE	R^2	RMSE
Lewis	1	50	k = 0.005			0.017	0.989	0.024
		55	k = 0.006			0.013	0.991	0.021
		60	k = 0.006			0.022	0.985	0.028
	1.5	50	k = 0.005			0.030	0.980	0.032
		55	k = 0.007			0.010	0.993	0.019
		60	k = 0.007			0.015	0.990	0.023
	2	50	k = 0.006			0.033	0.978	0.033
		55	k = 0.007			0.017	0.989	0.024
		60	k = 0.008			0.022	0.984	0.028
Logarithmic	1	50	a = 0.858	b = 0.175	k = 0.008	0.003	0.998	0.010
		55	a = 0.929	b = 0.132	k = 0.008	0.002	0.999	0.008
		60	a = 0.905	b = 0.151	k = 0.009	0.002	0.999	0.009
	1.5	50	a = 0.870	b = 0.148	k = 0.009	0.003	0.998	0.011
		55	a = 0.932	b = 0.102	k = 0.008	0.002	0.999	0.009
		60	a = 0.923	b = 0.100	k = 0.009	0.003	0.998	0.011
	2	50	a = 0.879	b = 0.126	k = 0.009	0.005	0.997	0.013
		55	a = 0.923	b = 0.096	k = 0.009	0.005	0.997	0.014
		60	a = 0.894	b = 0.073	k = 0.009	0.003	0.998	0.011
Henderson and Pabis	1	50	k = 0.005	a = 0.980		0.015	0.990	0.023
		55	k = 0.006	a = 1.007		0.012	0.992	0.021
		60	k = 0.006	a = 0.981		0.021	0.986	0.027
	1.5	50	k = 0.006	a = 0.957		0.016	0.988	0.024
		55	k = 0.006	a = 0.988		0.010	0.994	0.019
		60	k = 0.007	a = 0.971		0.013	0.991	0.022
	2	50	k = 0.006	a = 0.946		0.017	0.988	0.024
		55	k = 0.007	a = 0.968		0.015	0.990	0.023
		60	k = 0.007	a = 0.927		0.009	0.994	0.018
Avhad and Marchetti	1	50	a = 1.141	k = 0.025	n = 0.712	0.001	0.999	0.006
		55	a = 1.191	k = 0.037	n = 0.660	0.002	0.999	0.008
		60	a = 1.147	k = 0.024	n = 0.762	0.001	0.999	0.005
	1.5	50	a = 1.140	k = 0.031	n = 0.718	0.001	0.999	0.005
		55	a = 1.920	k = 0.034	n = 0.700	0.002	0.999	0.007
		60	a = 1.147	k = 0.029	n = 0.737	0.001	0.999	0.007
	2	50	a = 1.126	k = 0.031	n = 0.721	0.002	0.999	0.007
		55	a = 1.125	k = 0.027	n = 0.762	0.003	0.998	0.010
		60	a = 1.059	k = 0.024	n = 0.788	0.001	0.999	0.006
Diffusion	1	50	a = 0.515	b = 0.963	k = 0.005	0.017	0.986	0.025
		55	a = 0.759	b = 0.118	k = 0.008	0.007	0.994	0.017
		60	a = 0.971	b =−0.39	k = 0.007	0.006	0.996	0.015
	1.5	50	a = 0.684	b = 0.238	k = 0.010	0.003	0.998	0.010
		55	a = 0.948	b =−0.28	k = 0.008	0.007	0.994	0.017
		60	a = 25.55	b = 0.999	k = 0.007	0.018	0.988	0.026
	2	50	a = 0.396	b = 0.209	k = 0.015	0.003	0.998	0.011
		55	a = 0.504	b = 0.358	k = 0.012	0.005	0.997	0.014
		60	a = 0.240	b = 0.246	k = 0.026	0.001	0.999	0.006

Figure 3. Specific energy consumption (SEC) of sliced pork drying process using LPG hot air dryer (a) and electric hot air dryer (b) under different temperatures (50°C, 55°C, and 60°C) and air velocities (1, 1.5, 2 m/s).

Table 4. Moisture content and a_w of sliced pork dried using LPG and electric hot air dryers under different temperatures (50°C, 55°C, and 60°C) and air velocities (1, 1.5, 2 m/s).

Drying condition		Moisture content (%)			aw
Temperature (°C)	Air velocity (m/s)	LPG	Electric	Sig	LPG	Electric	Sig
50	1	24.71 ± 1.42	24.62 ± 1.71	ns	0.667 ± 0.015	0.678 ± 0.019	ns
	1.5	24.42 ± 0.99	24.57 ± 1.62	ns	0.684 ± 0.018	0.676 ± 0.025	ns
	2	24.41 ± 0.34	24.01 ± 1.44	ns	0.695 ± 0.019	0.674 ± 0.022	ns
55	1	24.31 ± 1.08	24.25 ± 1.04	ns	0.697 ± 0.06	0.714 ± 0.034	ns
	1.5	23.96 ± 1.81	23.96 ± 1.60	ns	0.784 ± 0.017	0.694 ± 0.028	ns
	2	23.66 ± 1.00	23.33 ± 1.08	ns	0.712 ± 0.025	0.685 ± 0.025	ns
60	1	23.02 ± 1.25	23.18 ± 1.26	ns	0.689 ± 0.032	0.694 ± 0.018	ns
	1.5	22.62 ± 0.84	23.10 ± 1.35	ns	0.673 ± 0.023	0.689 ± 0.028	ns
	2	22.15 ± 1.01	22.89 ± 1.57	ns	0.658 ± 0.018	0.673 ± 0.024	ns

The data was presented as mean ± standard error of five replications.

Sig means significantly different whereas ns means not significantly different at 95% confidence (p < 0.05).

Table 5. Colour of sliced pork dried using LPG and electric hot air dryers under different temperatures (50°C, 55°C, and 60°C) and air velocities (1, 1.5, 2 m/s).

Colour	Drying condition		Colour value		Sig
	Temperature (°C)	Air velocity (m/s)	LPG	Electrical
L*	50	1	16.53 ± 0.33	16.20 ± 0.54	ns
		1.5	16.61 ± 0.77	16.94 ± 0.98	ns
		2	17.61 ± 0.66	18.27 ± 0.56	ns
	55	1	29.31 ± 1.25	29.98 ± 1.37	ns
		1.5	30.06 ± 1.10	30.26 ± 0.91	ns
		2	31.20 ± 2.11	31.87 ± 1.78	ns
	60	1	30.48 ± 0.42	31.75 ± 0.05	ns
		1.5	30.75 ± 0.60	32.14 ± 0.12	*
		2	32.11 ± 1.14	33.11 ± 1.01	ns
a*	50	1	26.27 ± 5.38	26.61 ± 4.21	ns
		1.5	25.86 ± 1.21	25.86 ± 0.32	ns
		2	22.78 ± 0.32	23.12 ± 1.10	ns
	55	1	20.25 ± 0.23	19.59 ± 0.32	ns
		1.5	17.57 ± 1.19	17.24 ± 1.62	ns
		2	16.38 ± 1.36	16.38 ± 2.13	ns
	60	1	16.94 ± 0.40	17.60 ± 0.72	ns
		1.5	15.60 ± 0.50	15.26 ± 0.43	ns
		2	14.68 ± 0.33	15.01 ± 0.10	ns
b*	50	1	3.35 ± 0.52	4.02 ± 0.24	ns
		1.5	3.47 ± 0.52	4.30 ± 0.13	ns
		2	3.63 ± 0.29	4.47 ± 0.27	ns
	55	1	4.40 ± 0.53	4.73 ± 0.56	ns
		1.5	5.66 ± 0.44	5.66 ± 0.51	ns
		2	6.15 ± 0.85	5.82 ± 0.49	ns
	60	1	8.25 ± 0.64	7.99 ± 0.98	ns
		1.5	8.32 ± 0.86	8.91 ± 0.75	ns
		2	8.53 ± 0.70	9.19 ± 0.87	ns

The data was presented as mean ± standard error of five replications.

Sig means significantly different whereas ns means not significantly different at 95% confidence (p < 0.05).