Eutectics and insulation10 / 26

Phase point alone is not a selection criterion: ask for test conditions, cycling data and exact product match.

The product's outer carton, a washable divider or a suitable disposable board can serve as the separator; freeze sensitivity, moisture, airflow and lid closure decide the choice.

Verify the terms against a system diagram, then compare temperature records on the same route and load.

A hard surface, frost and an elapsed-time record do not show that the filling is solid. GEBHARDT's criterion: filling completely frozen, freezer at least 5 °C below the melting point, air gap between plates.

Ice packs stacked into a tight block freeze late in the middle. Layering them on a rack that keeps an air gap between packs works fine.

An intact reusable pack or eutectic plate is frozen again after thawing. Instant cold packs and packs that leak or crack do not go back into the freezer.

Ordinary ice melts at 0 °C and leaves free water in the box. A sealed pack keeps its filling inside the shell, and a eutectic plate can be chosen with a melting point between -3 and -21 °C.

Gel packs go above the product, with an insulating layer between pack and goods, and are held so they cannot move in the box. The layout is checked with a trial run for that box, the outside temperature and the transit time.

A frozen gel pack touching the product can freeze the contact point even while box air looks acceptable. The freezing limit, plate melting points and separator criteria are given below in numbers.

A gel pack laid flat in a single layer freezes through in 24-48 hours. A pack that is hard outside can still be soft in the middle; readiness is judged at the centre.

In 1718 ice cream was made with salted ice, and in 1724 Fahrenheit marked the zero of his thermometer with a salt and ice mixture. Today's eutectic plate uses the same physics in a sealed body.

A pack that stays soft may be unfrozen, or frozen but still flexible. The glycol content and the freezing time tell the two apart.

The word grows from Greek roots meaning to melt well, and it entered chemistry through Frederick Guthrie's 1884 paper. Below are the figures behind the definition, and how the melting point of a GEBHARDT plate sets its freezing temperature.

The gel pack temperature class, freezing time, the cooling capacity of a 500 g pack and how many packs a warm load needs.

Gel, water, eutectic plates and instant cold packs do not do the same job. Melting point, container fit and preparation flow decide the choice.

An ice pack is frozen at least 5 °C below the melting point of its filling. For a GEBHARDT plate that melts at -18 °C, that means -23 °C for 24 hours.