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Feasibility of Using Composite Materials in Mobile Food Truck Tandoor Ovens - C116

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Case Studies - A7Development - A252Feasibility of Using Composite Materials in Mobile Food Truck Tandoor Ovens - C116
Feasibility of Using Composite Materials in Mobile Food Truck Tandoor Ovens
Case study
Document Type Case study
Document Identifier 116
Objective functions
MSTE workflow Development

Summary[edit | edit source]

This case study is a feasibility study which examines alternative materials for tandoor ovens in mobile food trucks, aiming to improve thermal insulation and reduce oven weight. The study explores composite materials such as perlite, vermiculite, and carbon fibers, which are evaluated for their low thermal conductivity and lightweight properties. The goal is to find a solution that maintains high heat within the oven while being durable and cost-effective for mobile food service applications. Key findings suggest that while these materials can enhance thermal efficiency, they also pose challenges in terms of structural strength and cost.

Introduction[edit | edit source]

Tandoor ovens are cooking utilities with long histories of development and use in various cultures around the world. They are integral in the preparation of some culinary dishes and are very relevant to the food industry today. Regardless of size, shape, or region of origin, all tandoor ovens have the same operating principles. The ovens are often made of clay, with some sort of insulating material, such as concrete or mud, on the outside. They are cylindrical in shape and often curve inward toward the top, much like a beehive or jug, to concentrate the heat within the chamber. An opening at the very top of the oven in present, to allow access and ventilation. The fire, which is built in the bottom of the chamber, heats both the walls of the oven and the air inside to upwards of 480 °C (900 °F). Before cooking, the fire is reduced to coals, so that the temperature remains consistent while food is cooked. Considering the high efficiency for burning little fuel and retaining a large portion of the heat, tandoors are quite beneficial. Once they are heated, they can keep their internal chamber temperature at consistently high values for many hours, using very little additional fuel. The modern, mobile food truck tandoor oven is investigated in this project. The main issues with the current mobile tandoor are:

  1. Loss of heat during naan baking, due to a large volume and high rate of food turnover to customers
  2. Consumption of propane throughout the day for maintaining constant temperature is quite expensive,
  3. The tandoor is heavy,
  4. Hard to clean the burners below the tandoor oven and
  5. Given the mobile nature of the oven, it is prone to experiencing impulse loads, which can easily cause fracture and mechanical failure of the brittle materials currently used.

Approach[edit | edit source]

The goal of this feasibility study is to explore and select alternative designs and materials (composite materials) for a mobile food truck tandoor oven, which has better thermal properties, such as high specific heat capacity and moderate thermal diffusivity, along with proper durability (not too brittle for transportation) and light weight. In the following sections, some of the composite materials used for thermal insulation purposes are investigated.

Composites Used for Thermal Insulation[edit | edit source]

Materials used for thermal insulation are characterized by a low thermal conductivity, see table below, which is mostly obtained by the use of air (a thermal insulator), as in the case of polymer foams (e.g., Styrofoam), glass fiber felts, and porous ceramics (e.g., perlite and vermiculite) [1]. Perlite is an amorphous volcanic glass that expands upon heating, due to the vaporization of the trapped water. Vermiculite is a natural clay mineral that expands upon heating. Foaming agents may be used in the fabrication of polymer and cement materials, in order to provide a large number of small air cells that are uniformly distributed. Silica fiber tiles are used as a high temperature thermal insulation for the Space Shuttles, which face very high temperatures during re-entry through the atmosphere. Multiple glass panes that are hermetically sealed (airtight), such that the environment inside the unit is isolated from that outside the unit, are commonly used for insulated glass windows.

Composite materials for thermal insulation are designed to obtain a low thermal conductivity, while the mechanical properties remain acceptable. They are mainly polymer-matrix and cement-matrix composites [1]. Either type of composite consists of a foamy or porous phase, which can be the matrix or the filler. However, such a phase is detrimental to the mechanical properties. For example, perlite and vermiculite are used as admixtures to decrease the thermal conductivity of concrete, although they decrease the strength of the concrete.

Material Thermal conductivity \((W/mK)\)
Diamond 2000
Boron nitride (cubic) 1700
Silver 429
Copper 401
Beryllium oxide (BeO) 325
Aluminum 250
Aluminum nitride 140-180
Molybdenum 138
Brass 109
Nickel 91
Iron 80
Cast iron 55
Carbon steel 54
Boron nitride (hexagonal) 33
Monel (Cu-Ni alloy) 26
Alumina 26
Zirconia (yttria stabilized) 2.2
Carbon 1.7
Fused silica 1.38
Window glass 0.96
Mica 0.71
Nylon 6 0.25
Paraffin wax 0.25
Machine oil 0.15
Straw insulation 0.09
Vermiculite 0.058
Paper 0.05
Rock wool insulation 0.044
Fiberglass 0.04
Styrofoam 0.033
Perlite (1 atm) 0.031
Air 0.024
Perlite (vacuum) 0.00137

Cement-Matrix Composites[edit | edit source]

In the case of a cement-matrix composite [2], methods of decreasing the thermal conductivity involve (i) the addition of a polymer (e.g., latex particles) admixture, since the thermal conductivity of a polymer is lower than that of cement, and (ii) the use of interfaces as thermal barriers. The table below lists the thermal conductivities of various cement pastes that utilize silica fume (fine particles), latex (a polymer), methylcellulose (molecules) and short carbon fibers as admixtures.

Cement paste Thermal conductivity (W/mK) ± 0.02 Specific heat (J/gK) ± 0.001
Plain 0.52 0.703
+ latex (20% by mass of cement) 0.38 0.712
+ latex (25% by mass of cement) 0.32 0.723
+ latex (30% by mass of cement) 0.28 0.736
+ methylcellulose (0.4% by mass of cement) 0.42 0.732
+ methylcellulose (0.6% by mass of cement) 0.38 0.737
+ methylcellulose (0.8% by mass of cement) 0.362 0.742
+ silica fume 0.36 0.765
+ silica fume + methylcellulose\(^{a}\) 0.33 0.771
+ methylcellulose\(^{a}\) + fibers\(^{b}\) (0.5% by mass of cement) 0.44 0.761
+ methylcellulose\(^{a}\) + fibers\(^{b}\) (1.0% by mass of cement) 0.34 0.792
+ silica fume + methylcellulose\(^{a}\) + fibers\(^{b}\) (0.5% by mass of cement) 0.28 0.789

Carbon Fibers and Thermal Insulation[edit | edit source]

Although carbon fibers are thermally conducting, the addition of carbon fibers to cement lowers the thermal conductivity, thus allowing applications related to thermal insulation [3]. This effect of carbon fiber addition occurs due to the increase in air void content. The electrical conductivity of carbon fibers is higher than that of the cement matrix by about eight orders of magnitude, whereas the thermal conductivity of carbon fibers is higher than that of the cement matrix by only one or two orders of magnitude. As a result, the electrical conductivity increases upon carbon fiber addition in spite of the increase in air void content, but the thermal conductivity decreases upon fiber addition.

Expanded Perlite-Fumed Silica Composites[edit | edit source]

Currently, fumed silica (FS) is widely used as the core of vacuum insulation panels (VIPs) for longer service life required for building applications. It is relatively expensive and a major contributing factor to the current high cost of VIPs. Expanded perlite-fumed silica composites were experimentally investigated as an alternative lower cost material for VIP core, using expanded perlite as a cheaper substitute of fumed silica. Perlite has been used for different construction applications such as lightweight cement aggregate, insulation and ceiling tiles due to its low density (35–120 \(kg/m^{3}\)), porous nature, low thermal conductivity, ease of handling and non-flammability.

A study [4] investigated the thermo- physical properties of expanded perlite-fumed silica composites. The centre of panel thermal conductivity of the core board containing expanded perlite mass proportion of 60%, was measured as 53 \(mW/m K\) at atmospheric pressure and 28 \(mW/m K\) when expanded perlite content was reduced to 30%. The center of panel thermal conductivity with 30% expanded perlite content was measured as 7.6 \(mW/m K\) at 0.5 mbar pressure.

Porous Insulation Materials[edit | edit source]

A separate study [5] investigated the effective thermal conductivity (ETC) of porous insulation materials. This was determined based on the analysis of various heat transfer mechanisms such as conduction through the solid or the gas, gas convection in pores due to air movement, and radiation between the solid surfaces. Multilayer thermal insulation for low temperature applications was measured, by using a guarded hot plate apparatus, see figure below. The lowest thermal conductivity was achieved with an increase of additional layers in the insulation materials. The results indicated that significant correlations exist between ETC and the characteristics of the materials with decreasing temperature. The ETC decreases with reinforcement with aluminum foil at the same temperature or with temperature differences of 5 and 15 C. In addition, it was clearly observed that the ETC decreases sharply with decreased temperature. Consequently, reflective materials may reduce the ETC at low temperatures.

The structure of the ternary insulation materials reinforced with aluminum foil.

Porous Polymer Materials[edit | edit source]

Most porous polymer materials are thermally insulating. Recently, various types of polymer fibers, such as polyester and polypropylene, see table below [6], have been developed for thermal insulation. The thermal insulating performance of the porous polymer materials is strongly dependent upon the properties of the polymer fiber. Wu et al. 2007 found that the mechanisms of thermal energy transport within porous polymer materials, and found the effects of polymer fiber characteristics on the thermal energy transport investigated, in order to understand the thermal insulating performance of such materials. It was found that decreasing fiber radius would significantly reduce the total thermal energy flux through the porous polymer materials, whereas increasing fiber emissivity or decreasing the thermal conductivity would cause a just slight reduction of the total thermal energy flux.

Property Wool Polyester
Density (\(kg/m^{3}\)) 1310 1390
Thermal Conductivity (\(W/m K\)) 0.19 0.14
Volumetric Heat Capacity (\(kJ/m^{3}K\)) 1600 1300
Emissivity 0.78 0.62

Outcome[edit | edit source]

Selection of the top candidate among the different suitable composite materials for thermal insulation tasks, falls into a materials selection/design and multi-criteria decision-making problem. The criteria consist of the price of the composites, durability of the material and its thermal insulation characteristics. The chosen composite material must satisfy the limited budget of tandoor production, while making the tandoor lighter. Finally, finite element (FEM) analysis should be done on the selected material in order to monitor the product’s reaction to physical effects.

Related pages[edit | edit source]


  1. 1.0 1.1 [Ref] Chung, Deborah D.L. (2010). Composite Materials: Science and Applications. Springer London. doi:10.1007/978-1-84882-831-5. ISBN 978-1-84882-830-8.CS1 maint: uses authors parameter (link) CS1 maint: date and year (link)
  2. [Ref] Chung, D D L (2000). "Cement-matrix composites for smart structures". 9 (4). doi:10.1088/0964-1726/9/4/302. ISSN 0964-1726. Cite journal requires |journal= (help)CS1 maint: uses authors parameter (link)
  3. [Ref] Wu, Shang-Han et al. (2001). "Mechanical, thermal and morphological properties of glass fiber and carbon fiber reinforced polyamide-6 and polyamide-6/clay nanocomposites". 49 (6). doi:10.1016/S0167-577X(00)00394-3. ISSN 0167-577X. Cite journal requires |journal= (help)CS1 maint: extra punctuation (link) CS1 maint: uses authors parameter (link)
  4. [Ref] Alam, M. et al. (2014). "Experimental characterisation and evaluation of the thermo-physical properties of expanded perlite—Fumed silica composite for effective vacuum insulation panel (VIP) core". 69. doi:10.1016/j.enbuild.2013.11.027. ISSN 0378-7788. Cite journal requires |journal= (help)CS1 maint: extra punctuation (link) CS1 maint: uses authors parameter (link)
  5. [Ref] Tekce, H. Serkan et al. (2007). "Effect of Particle Shape on Thermal Conductivity of Copper Reinforced Polymer Composites". 26 (1). doi:10.1177/0731684407072522. ISSN 0731-6844. Cite journal requires |journal= (help)CS1 maint: extra punctuation (link) CS1 maint: uses authors parameter (link)
  6. [Ref] Wu, Huijun et al. (2007). "Thermal energy transport within porous polymer materials: Effects of fiber characteristics". 106 (1). doi:10.1002/app.26603. ISSN 0021-8995. Cite journal requires |journal= (help)CS1 maint: extra punctuation (link) CS1 maint: uses authors parameter (link)

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Welcome to the CKN Knowledge in Practice Centre (KPC). The KPC is a resource for learning and applying scientific knowledge to the practice of composites manufacturing. As you navigate around the KPC, refer back to the information on this right-hand pane as a resource for understanding the intricacies of composites processing and why the KPC is laid out in the way that it is. The following video explains the KPC approach:

Understanding Composites Processing

The Knowledge in Practice Centre (KPC) is centered around a structured method of thinking about composite material manufacturing. From the top down, the heirarchy consists of:

The way that the material, shape, tooling & consumables and equipment (abbreviated as MSTE) interact with each other during a process step is critical to the outcome of the manufacturing step, and ultimately critical to the quality of the finished part. The interactions between MSTE during a process step can be numerous and complex, but the Knowledge in Practice Centre aims to make you aware of these interactions, understand how one parameter affects another, and understand how to analyze the problem using a systems based approach. Using this approach, the factory can then be developed with a complete understanding and control of all interactions.

The relationship between material, shape, tooling & consumables and equipment during a process step

Interrelationship of Function, Shape, Material & Process

Design for manufacturing is critical to ensuring the producibility of a part. Trouble arises when it is considered too late or not at all in the design process. Conversely, process design (controlling the interactions between shape, material, tooling & consumables and equipment to achieve a desired outcome) must always consider the shape and material of the part. Ashby has developed and popularized the approach linking design (function) to the choice of material and shape, which influence the process selected and vice versa, as shown below:

The relationship between function, material, shape and process

Within the Knowledge in Practice Centre the same methodology is applied but the process is more fully defined by also explicitly calling out the equipment and tooling & consumables. Note that in common usage, a process which consists of many steps can be arbitrarily defined by just one step, e.g. "spray-up". Though convenient, this can be misleading.

The relationship between function, material, shape and process consisting of Equipment and Tooling and consumables


The KPC's Practice and Case Study volumes consist of three types of workflows:

  • Development - Analyzing the interactions between MSTE in the process steps to make decisions on processing parameters and understanding how the process steps and factory cells fit within the factory.
  • Troubleshooting - Guiding you to possible causes of processing issues affecting either cost, rate or quality and directing you to the most appropriate development workflow to improve the process
  • Optimization - An expansion on the development workflows where a larger number of options are considered to achieve the best mixture of cost, rate & quality for your application.