METHOD FOR MONITORING THE THERMAL PERFORMANCE OF A TEMPERATURE-CONTROLLED TRANSPORT CONTAINER

Abstract

Method for monitoring thermal performance of temperature-controlled transport container. External temperature sensor is provided for measuring ambient temperature of container and internal temperature sensor is provided for measuring internal temperature. Ambient and internal temperature are measured and recorded while passing through first interior temperature range during first time period, and ambient and interior temperature are measured and recorded while passing through second interior temperature range during second time period. The phase change temperature is in first temperature range, and second temperature range is above or below the first temperature range. Thermal conductivity of the insulation layer is calculated based on temporal change of interior temperature relative to ambient temperature while passing through second temperature range, and subsequently enthalpy of phase change material is calculated based on temporal change of interior temperature relative to ambient temperature while passing through first temperature range and based on thermal conductivity of insulation layer.

Claims

1-7. (canceled)

8. A method for monitoring the thermal performance of a temperature-controlled transport container, the transport container including a container wall and an interior surrounded by the container wall, the container wall comprising a thermal insulation layer surrounding the interior on all sides and a latent heat storage layer, the latent heat storage layer including a phase change material having a phase change temperature, comprising: providing an external temperature sensor for measuring an ambient temperature of the transport container and an internal temperature sensor for measuring an interior temperature; measuring and recording a first ambient temperature and a first interior temperature during a first period of time in which the first interior temperature passes through a first temperature range, the phase change temperature being within the first temperature range; measuring and recording a second ambient temperature and a second interior temperature during a second period of time in which the second interior temperature passes through a second temperature range, the second temperature range being above or below the first temperature range; calculating a thermal conductivity of the insulation layer based on a first temporal change of the interior temperature relative to the ambient temperature while passing through the second temperature range; and calculating subsequently an enthalpy of the phase change material based on a second temporal change of the interior temperature relative to the ambient temperature while passing through the first temperature range and based on the thermal conductivity of the insulation layer.

9. The method according to claim 8, wherein a range in which a specific heat capacity of the phase change material is substantially constant is selected as the second temperature range.

10. The method according to claim 8, wherein the first temperature range extends from a temperature of 1-4 C. below the phase change temperature to a temperature of 1-4 C. above the phase change temperature.

11. The method according to claim 8, wherein the second temperature range is passed through with increasing interior temperature.

12. The method according to claim 8, wherein the calculation of the thermal conductivity of the insulation layer is carried out with the formula, ${}_{\mathrm{iso}}=\frac{\left(m_{PCM}.Math.c_{\mathrm{PCM}}+C_s\right).Math.\left[T_i\left(t_2\right)-T_i\left(t_1\right)\right].Math.d_{\mathrm{iso}}}{f.Math.A_{ref}.Math.{}_{t_1}^{t_2}\left[T_{\mathrm{amb}}\left(t\right)-T_i\left(t\right)\right].Math.\mathrm{dt}}$ with the following meanings: m.sub.PCM: Mass of phase change material [kg] C.sub.PCM: Specific heat capacity of the phase change material [J/kg.Math.K] C.sub.S: Heat capacity of the structural parts and of the insulation of the transport container [J/K] T.sub.i(t.sub.2): Internal temperature at the end of the second temperature range [K] T.sub.i(t.sub.1): Internal temperature at the beginning of the second temperature range [K] d.sub.iso: Wall thickness of the insulation layer [m] f: Correction factor for heat input A.sub.ref: Reference surface area A.sub.ref=A.sub.inside+0.3(A.sub.outsideA.sub.inside) [m.sup.2] T.sub.amb: Ambient temperature [K].

13. The method according to claim 12, wherein the calculation of the enthalpy of the phase change material is carried out with the formula $h_{\mathrm{PCM}}{.Math.}_{T_i\left(t_3\right).fwdarw.T_i\left(t_4\right)}=\frac{1}{m_{PCM}}.Math.\left[f.Math.A_{\mathrm{ref}}.Math.\frac{{}_{\mathrm{iso}}}{d_{\mathrm{iso}}}.Math.\underset{t_3}{\overset{t_4}{}}\left[T_{\mathrm{amb}}\left(t\right)-T_i\left(t\right)\right].Math.\mathrm{dt}-C_s.Math.\left[T_i\left(t_4\right)-T_i\left(t_3\right)\right]\right]$ with the following meanings: h.sub.PCM: Specific heat capacity of the phase change material T.sub.i(t.sub.4): Internal temperature at the end of the first temperature range [K] T.sub.i(t.sub.3): Internal temperature at the beginning of the first temperature range [K].

14. A system for monitoring the thermal performance of a temperature-controlled transport container, comprising a transport container with a container wall and an interior surrounded by the container wall, wherein the container wall comprises a thermal insulation layer surrounding the interior on all sides and a latent heat storage layer, wherein the latent heat storage layer includes a phase change material having a phase change temperature, and wherein the transport container comprises an external temperature sensor for measuring the ambient temperature of the transport container and an internal temperature sensor for measuring the interior temperature, and wherein the transport container comprises a measured value memory to which the measured values of the external temperature sensor and the internal temperature sensor are supplied, which are measured during a first time period in which the interior temperature passes through a first temperature range, and which are measured during a second time period in which the interior temperature passes through a second temperature range, wherein the phase change temperature is within the first temperature range and the second temperature range is above or below the first temperature range, and a computing unit for evaluating the measurement data, wherein the transport container and the computing unit each include a data transmission interface, via which the measured values are transmitted from the measured value memory of the transport container to the computing unit, and wherein the computing unit is configured to calculate a thermal conductivity of the insulation layer based on the temporal change of the interior temperature relative to the ambient temperature while passing through the second temperature range and subsequently to calculate an enthalpy of the phase change material based on the temporal change of the interior temperature relative to the ambient temperature while passing through the first temperature range and based on the thermal conductivity of the insulation layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The Figures show the following:

[0019] FIG. 1 shows a graph illustrating the relationship between specific heat capacity of a phase change material with respect to temperature; and

[0020] FIG. 2 illustrates a transport container suitable for carrying out the invention.

DETAILED DESCRIPTION

[0021] The phase change of the latent heat storage is usually within the operating interval of the corresponding container. This results in a maximum in the distribution of the specific heat capacity of the phase change material in this temperature range. Outside this range, the specific heat capacity of the phase change material is almost constant and very well known (see FIG. 1). Therefore, this range is well suitable for calculating the thermal conductivity of insulation with equation (4).

[00004]$\begin{array}{cc}{}_{\mathrm{iso}}=\frac{\left(m_{PCM}.Math.c_{\mathrm{PCM}}+C_s\right).Math.\left[T_i\left(t_2\right)-T_i\left(t_1\right)\right].Math.d_{\mathrm{iso}}}{f.Math.A_{ref}.Math.{}_{t_1}^{t_2}\left[T_{\mathrm{amb}}\left(t\right)-T_i\left(t\right)\right].Math.\mathrm{dt}}& \left(4\right)\end{array}$

[0022] Since C.sub.PCM(T) is constant in the considered temperature range, the integral in equation (2) is simplified to C.sub.PCMT. An example: The typical operating temperature range of a transport container for the pharmaceutical industry is 2-8 C. A suitable phase change material should have a maximum of the specific heat capacity at about 5 C. A suitable temperature range for measuring the thermal conductivity according to equation (4) would therefore be, for example, 10-15 C. The measurement is automatically started at a temperature of 10 C. at time t.sub.1. As soon as the temperature inside the container has a value of 15 C., the measurement is stopped at time t.sub.2 and evaluated with equation (4).

[0023] With the help of the now known thermal conductivity of the insulation, the enthalpy of the latent heat storage can be calculated with equation (5). For this purpose, the desired temperature range must be passed through within the operating temperature interval of the container, so that a phase change occurs.

[00005]$\begin{array}{cc}{h}_{\mathrm{PCM}}{.Math.}_{T_i\left(t_3\right).fwdarw.T_i\left(t_4\right)}=\frac{1}{m_{PCM}}.Math.\left[f.Math.A_{\mathrm{ref}}.Math.\frac{{}_{\mathrm{iso}}}{d_{\mathrm{iso}}}.Math.\underset{t_3}{\overset{t_4}{}}\left[T_{\mathrm{amb}}\left(t\right)-T_i\left(t\right)\right].Math.\mathrm{dt}-C_s.Math.\left[T_i\left(t_4\right)-T_i\left(t_3\right)\right]\right]& \left(5\right)\end{array}$

[0024] In the example above, a temperature interval of 2-8 C. would be conceivable. The measurement is started at a temperature of 2 C. at time t.sub.3 and runs until a temperature of 8 C. has been reached (time t.sub.4).

TABLE-US-00001 Symbol Unit Description A.sub.ref [m.sup.2] Reference surface area A.sub.ref = A.sub.inside + 0.3 (A.sub.outside A.sub.inside) C.sub.PCM [J/kgK] Specific heat capacity of the phase change material C.sub.s [J/K] Heat capacity of the structural parts and insulation of the transport container d.sub.iso [m] Wall thickness of the insulation layer f [] Correction factor for heat input - From validation measurements h.sub.PCM [J/kg] Specific enthalpy of the phase change material .sub.iso [W/mK] Thermal conductivity of the insulation layer m.sub.PCM [kg Mass of the phase change material Q.sub.i [W] Energy input T.sub.amb [K] Ambient temperature T.sub.i [K] Temperature inside the transport container t [s] Time t.sub.1 [s] Starting time for measuring the thermal conductivity of the insulation t.sub.2 [s] End time for measuring the thermal conductivity of the insulation t.sub.3 [s] Starting time for measuring the enthalpy of the phase change material t.sub.4 [s] End time for measuring the enthalpy of the phase change material U [W] Change in the internal energy of the transport container

[0025] A transport container suitable for carrying out the invention is explained in more detail with reference to FIG. 2, which shows a sectional view of the transport container. The transport container comprises a cuboid wall 1, which encloses the interior of the transport container. A door is provided on a front side (not shown) of the transport container, via which the interior can be loaded and unloaded. The wall 1 comprises a thermal insulation layer 2 made of a material with a thermal conductivity of <0.02 W/(m.Math.K), preferably <0.012 W/(m.Math.K), such as vacuum insulated panels. A latent heat storage layer 3, which comprises a phase change material, is arranged on the side of the insulation layer 2 facing the interior. For measuring the interior temperature, an internal temperature sensor 4 is arranged on the side of the latent heat storage layer 3 facing the interior. For measuring the ambient temperature, an external temperature sensor 5 is arranged on the outside of the transport container. The measurement signals of the internal temperature sensor 4 and of the external temperature sensor 5 are supplied to a measured value memory (not shown) or to a computing unit, in which the thermal conductivity of the insulation layer and the enthalpy of the phase-change material are determined according to the invention.