ConSciR (version 0.3.0)

calcLM: Calculate Life-time Multiplier for chemical degradation

Description

Function to calculate lifetime multiplier from temperature and relative humidity.

The `calcLM` function calculates the lifetime multiplier for chemical degradation of objects based on temperature and relative humidity conditions. This metric provides an estimate of an object’s expected lifetime relative to standard conditions (20°C and 50% RH); values >1 indicate conditions that prolong lifetime; values <1 indicate higher risk of chemical degradation.

Usage

calcLM(Temp, RH, EA = 100)

Value

Lifetime multiplier

Arguments

Temp

Temperature (Celsius)

RH

Relative Humidity (0-100%)

EA

Activation Energy (J/mol). 100 J/mol for cellulosic (paper) or 70 J/mol yellowing varnish

Details

Based on the experiments of the rate of decay of paper, films and dyes. Activation energy, Ea = 100 J/mol (degradation of cellulose - paper), 70 J/mol (yellowing of varnish - furniture, painting, sculpture).

Gas constant, R = 8.314 J/K.mol

$$LM=\left(\frac{50\%RH}{RH}\right)^{1.3}.e\left(\frac{E_a}{R}.\left(\frac{1}{T_K}-\frac{1}{293}\right)\right)$$

The lifetime multiplier gives an indication of the speed of natural decay of an object. It expresses an expected lifetime of an object compared to the expected lifetime of the same object at 20°C and 50% RH. This means that if the result = 1, the expected lifetime for your object is 'good'. The closer you go to 0, the less suited your environment is. The result is both expressed numerically and over time, which also gives an idea about the period over the year when the object suffers most. The data is based on experiments on paper, synthetic films and dyes.

References

Michalski, S., ‘Double the life for each five-degree drop, more than double the life for each halving of relative humidity’, in Preprints of the 13th IcOM-cc Triennial Meeting in rio de Janeiro (22–27 September 2002), ed. r. Vontobel, James & James, London (2002) Vol. I 66–72.

Martens Marco, 2012: Climate Risk Assessment in Museums (Thesis, Tue).

Examples

# Lifetime multiplier at 20°C (Temp) and 50% relative humidity (RH)
calcLM(20, 50)

calcLM(20, 50, EA = 70)


# mydata file
filepath <- data_file_path("mydata.xlsx")
mydata <- readxl::read_excel(filepath, sheet = "mydata", n_max = 5)

mydata |> dplyr::mutate(LifeTime = calcLM(Temp, RH))

mydata |>
  dplyr::mutate(LM = calcLM(Temp, RH)) |>
   dplyr::summarise(LM_avg = mean(LM, na.rm = TRUE))