The Transient Hot Wire Liquid Thermal Conductivity Meter (THW-L1) is a precision analytical instrument for directly measuring the thermal conductivity of liquids and low viscosity pastes, from (THW-L1) -50 °C / 10 °C to 200 °C and (THW-L1E) -50 °C to 300 °C.

Thermtest THW-L1 Liquid Thermal Conductivity Instrument

Figure 1. Thermtest THW-L1 Liquid Thermal Conductivity Meter

The Thermtest Transient Hot Wire (THW-L1) Liquid Thermal Conductivity Meter is an advanced measurement system for direct determination of the thermal conductivity liquids and pastes in accordance with ASTM D7896-19 – Standard Test Method for Thermal Conductivity of Engine Coolants and Related Fluids by Transient Hot Wire Liquid Thermal Conductivity Method.
The THW-L1 Meter was designed with speed and operational simplicity in mind. With a single measurement of 1 second in duration, small volumes of liquids and low viscosity pastes can be accurately and precisely measured for thermal conductivity, thermal diffusivity and specific heat. The THW-L1 Meter uses a non-stationary measurement approach and rapid test times limiting convective effects for samples with a wide range of viscosities (0.1 to 10,000,000 mPas).

 

Thermal Conductivity Results

 

The Engine oil Castrol Edge SAE 5W-30 measured with the THW-L1 device from 5 °C to 195 °C without any back pressure applied to the fluid. Three tests performed at each temperature step and the repeatability was better than 1 %.

 

In the picture below, the Engine oil samples can be seen. The left vial is a fresh sample, vial in the middle is after a full temperature run, and the right vial is a sample of used oil from a car engine after 6,000 km.

Samples of the Engine oil

Picture 1. Samples of the Engine oil. From the Left to the Right they are Fresh, after one temperature run and used sample.

Tables 1-3 show the thermal conductivity, thermal diffusivity and volumetric specific heat of both the fresh and the used oil samples, while these data are plotted in Figures 2-4.

 

It was noticed the thermal conductivity of the used oil is around 2 % lower than the thermal conductivity of the fresh oil sample, while the thermal diffusivity and the volumetric specific heat of the used oil sample was around 1 % lower than the properties of the fresh oil sample. The decrease in repeatability above 170°C is due to a little movement of the liquid and could be improved with use of back-pressure.

 

Table 1. Thermal Conductivity Measurements of the Fresh and the Used Engine Oil.

 

T (°C) λ (W/m·K)
Fresh
λ (W/m·K)
Used
5.1 0.139 0.136
10.0 0.138 0.135
14.9 0.137 0.135
19.8 0.137 0.134
24.6 0.136 0.133
29.5 0.136 0.133
34.4 0.135 0.132
39.3 0.135 0.132
44.2 0.134 0.131
49.2 0.133 0.131
54.1 0.133 0.130
59.1 0.132 0.130
64.0 0.131 0.129
69.9 0.131 0.128
74.9 0.130 0.127
79.8 0.129 0.127
84.7 0.129 0.126
89.6 0.128 0.126
94.5 0.127 0.125
99.5 0.127 0.125
T (°C) λ (W/m·K)
Fresh
λ (W/m·K)
Used
104.4 0.126 0.124
109.3 0.125 0.123
114.2 0.125 0.123
119.1 0.124 0.122
124.0 0.124 0.122
129.9 0.122 0.121
134.9 0.122 0.121
139.8 0.121 0.120
144.8 0.121 0.119
149.7 0.121 0.119
154.7 0.120 0.119
159.7 0.119 0.119
164.7 0.119 0.117
169.7 0.119 0.117
174.7 0.118 0.117
179.7 0.120 0.118
184.8 0.118 0.118
189.7 0.120 0.117
194.6 0.120 0.116
Table 2. Thermal Diffusivity Measurements of the Fresh and the Used Engine Oil.
T (°C) α (mm2/s)
Fresh
α (mm2/s)
Used
5.1 0.077 0.076
10.0 0.077 0.076
14.9 0.076 0.075
19.8 0.075 0.075
24.6 0.075 0.074
29.5 0.074 0.073
34.4 0.073 0.073
39.3 0.073 0.072
44.2 0.072 0.071
49.2 0.072 0.070
54.1 0.071 0.070
59.1 0.070 0.070
64.0 0.070 0.069
69.9 0.069 0.069
74.9 0.068 0.068
79.8 0.067 0.067
84.7 0.067 0.067
89.6 0.066 0.066
94.5 0.065 0.065
99.5 0.065 0.065
T (°C) α (mm2/s)
Fresh
α (mm2/s)
Used
104.4 0.064 0.064
109.3 0.064 0.063
114.2 0.063 0.063
119.1 0.062 0.062
124.0 0.062 0.061
129.9 0.061 0.061
134.9 0.060 0.060
139.8 0.060 0.059
144.8 0.059 0.059
149.7 0.059 0.059
154.7 0.059 0.058
159.7 0.058 0.057
164.7 0.058 0.056
69.9 0.069 0.069
74.9 0.068 0.068
169.7 0.056 0.056
174.7 0.056 0.055
179.7 0.057 0.055
184.8 0.055 0.055
189.7 0.056 0.054
194.6 0.055 0.053
Table 3. Calculated Volumetric Specific Heat of the Fresh and the Used Engine Oil.
T (°C) vCp (MJ/m3.K)
Fresh
vCp (MJ/m3.K)
Used
5.1 1.795 1.778
10.0 1.803 1.783
14.9 1.804 1.795
19.8 1.818 1.797
24.6 1.819 1.804
29.5 1.834 1.815
34.4 1.837 1.824
39.3 1.845 1.837
44.2 1.853 1.840
49.2 1.860 1.854
54.1 1.871 1.852
59.1 1.881 1.866
64.0 1.880 1.876
69.9 1.899 1.872
74.9 1.905 1.879
79.8 1.916 1.886
84.7 1.923 1.894
89.6 1.932 1.908
94.5 1.943 1.913
99.5 1.951 1.932
T (°C) vCp (MJ/m3.K)
Fresh
vCp (MJ/m3.K)
Used
104.4 1.959 1.940
109.3 1.968 1.947
114.2 1.989 1.959
119.1 1.993 1.965
124.0 1.997 1.981
129.9 2.002 1.988
134.9 2.030 1.999
139.8 2.022 2.019
144.8 2.040 2.027
149.7 2.035 2.040
154.7 2.046 2.048
159.7 2.069 2.082
164.7 2.071 2.089
169.7 2.107 2.090
174.7 2.109 2.128
179.7 2.109 2.130
184.8 2.148 2.149
189.7 2.138 2.163
194.6 2.173 2.186
Measured Thermal Conductivity of the Fresh and Used Engine Oil samples

Figure 2. Measured Thermal Conductivity of the Fresh and Used Engine Oil samples

Measured Thermal Diffusivity of the Fresh and Used Engine Oil samples

Figure 3. Measured Thermal Diffusivity of the Fresh and Used Engine Oil samples

Calculated Volumetric Specific Heat of the Fresh and Used Engine Oil samples

Figure 4. Calculated Volumetric Specific Heat of the Fresh and Used Engine Oil samples